CA1292796C - Electronic motor control system for conveyance such as a wheelchair - Google Patents

Electronic motor control system for conveyance such as a wheelchair

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Publication number
CA1292796C
CA1292796C CA000550682A CA550682A CA1292796C CA 1292796 C CA1292796 C CA 1292796C CA 000550682 A CA000550682 A CA 000550682A CA 550682 A CA550682 A CA 550682A CA 1292796 C CA1292796 C CA 1292796C
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CA
Canada
Prior art keywords
motor
pulses
conveyance
modulating
driving voltage
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
CA000550682A
Other languages
French (fr)
Inventor
Lloyd L. Lautzenhiser
John L. Lautzenhiser
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Individual
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Individual
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Application filed by Individual filed Critical Individual
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Publication of CA1292796C publication Critical patent/CA1292796C/en
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Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61GTRANSPORT, PERSONAL CONVEYANCES, OR ACCOMMODATION SPECIALLY ADAPTED FOR PATIENTS OR DISABLED PERSONS; OPERATING TABLES OR CHAIRS; CHAIRS FOR DENTISTRY; FUNERAL DEVICES
    • A61G5/00Chairs or personal conveyances specially adapted for patients or disabled persons, e.g. wheelchairs
    • A61G5/04Chairs or personal conveyances specially adapted for patients or disabled persons, e.g. wheelchairs motor-driven
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61GTRANSPORT, PERSONAL CONVEYANCES, OR ACCOMMODATION SPECIALLY ADAPTED FOR PATIENTS OR DISABLED PERSONS; OPERATING TABLES OR CHAIRS; CHAIRS FOR DENTISTRY; FUNERAL DEVICES
    • A61G5/00Chairs or personal conveyances specially adapted for patients or disabled persons, e.g. wheelchairs
    • A61G5/10Parts, details or accessories
    • A61G5/1005Wheelchairs having brakes
    • A61G5/1032Wheelchairs having brakes engaging an element of the drive or transmission, e.g. drive belt, electrodynamic brake
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B60VEHICLES IN GENERAL
    • B60LPROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L50/00Electric propulsion with power supplied within the vehicle
    • B60L50/50Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells
    • B60L50/52Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells characterised by DC-motors
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B60VEHICLES IN GENERAL
    • B60LPROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L7/00Electrodynamic brake systems for vehicles in general
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B60VEHICLES IN GENERAL
    • B60LPROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L2200/00Type of vehicles
    • B60L2200/26Rail vehicles
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02TCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00Road transport of goods or passengers
    • Y02T10/60Other road transportation technologies with climate change mitigation effect
    • Y02T10/64Electric machine technologies in electromobility
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02TCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00Road transport of goods or passengers
    • Y02T10/60Other road transportation technologies with climate change mitigation effect
    • Y02T10/70Energy storage systems for electromobility, e.g. batteries

Abstract

Abstract of the Disclosure ELECTRONIC MOTOR CONTROL SYSTEM FOR CONVEYANCE
SUCH AS A WHEELCHAIR

A conveyance includes a power transmission that mechanically transmits power from an electric motor to a propulsion element, and that allows the propulsion element to drive the electric motor. The conveyance includes a parking mode in which the electric motor is made to operate as an electrically-loaded generator, and a manual-propelling mode in which the propulsion element is allowed to drive the electric motor. In a preferred embodiment, driving voltage pulses of a pulse-width-modulated driving voltage are supplied to the motor; and dynamic-braking pulses are interposed between respective ones of the driving voltage pulses while continuing to supply the driving voltage pulses to the electric motor.

Description

~Z~Z'~{36 ELECTRONIC MOTOR CONTROL SYSTEM FOR CO_VEYANCE
SUCH AS A WHEELCHAIR

Background of the Inventlon Field of the Invention 6 The present Invention relates to controls for electrlc or fluld actuators, and to conveyances propell ed by electric or fluld actuators.
More particularly, the present invention relates to dynamlcally braklng conveyances, and to controlling the turns of conveyances that are steered by separately controlling the speeds of the wheels.

I0 Descript?on of t}!e Related Art Conveyances of various types, for transporting people, for material handllng, and for propelling self-propelled machinery, have requirements for extremely high maneuverabili1;y.
One way to obtain extremely high maneuverability is to 15 separately and varlably control the speed and direction of rotatlon Or left and right wheels or other propulsion elements. When the wheels are movlng at the same speed, but in opposite dlrections, the conveysnce plvots In a flxed location, g1vlng the ulti1nate in maneuverabillty.
A propulslon system using electric or hydra~1lic motors can 20 provlde flexlbility of control, but preclslon Or control has been lacklng In prlor art desl~ns.
Further, achleving high maneuverability by separately controlllng the veloclty and direction of rotatlon of the wheels, or otl1er tractlon elements, may make a conveyance difficult to control, or even dangerous.
For Instance, It may be desirable to have the ablllty to make plvot turns wlth some conveyances, but It mlght be dangerous to attempt to make a plvotal turn at full speed.
But, If the rate of change Or speed of the individual wheels 19 llmlted, then the machlne may be sluggish in acceleration, and may be 30 dangerously filow In deceleration.
The problem o~ controllability is particularly acute In wheelchairs, and the discussion that follows centers on electrlcally-propelled wheelchalrs.

3~

~Z~71Jf~

Typlcally, separate D.C. electric motors have been connected to left and right wheels of a wheelchair by chains or belts, and by friction rollers that have separately engaged the rubber tires of the wheels.
D.C. motors provlde both directions of rotation by changing 6 polarity Or the drlving voltage, and produce rotational speeds that are dependent upon both the drlving voltage and the torque requlred of them .
Manually actuated controls have been used that separately and varlably supply electric power from a battery to left and right motors to 10 make changes in speed, and to make turns, includlng plvot turns.
One popular type of manual control includes a control lever that Is moved forward In accordance with a desired speed forward, that is moved rearward in accordance with a deslred speed in reverse, that is moved both forward and to one side to make a turn whlle moving 1~ forward, and that is moved directly to one side to make a plvot turn.
One probiem with prior art designs is that control of speed and directlon has been uncertain because of the lack of dynamic braking.
For instance, when the control lever has been positioned to make a left turn by reducing the electrical power to the left motor, Inertia of the 20 wheelchalr and occupant has driven the left motor through the drlve train that connects the left motor to the left wheel, and the wheelchair has not turned at the deslred radlus.
A second problem is that It has been necessary to engage and dlsengage the mechanical drive that connects the motors to their 26 respectlve wheels, ln order to manually propel electric wheelchairs. Thls has Increased deslgn complexlty and manufacturlng costs.
Commonly a drlvlng connectlon between the motors and the wheels has been accompllshed by uslng drive rollers that engage the tlres. Engap,ement and disengagement of this drivlng connection has 30 been accompilshed by movement of the motors and mechanical drlves, and by resultant movement of the drive rollers into, and away from, engagement with the tires, or by beit tighteners.
A thlrd problem Is that disengagement of the mechanical drive has left the wheelchair in a dangerous run away condltlon In sltuations 36 where someone has inadvertentiy forgotten to set the parking brake.
That Is, prlor art deslgns have provlded neither an automatic parking brake nor an automatic dynamlc brake that would restraln the wheelchalr from dangerous runaway condltions.

1.;Z~796 A fourth problem is that when a person with severe hand tremors has tried to control the positioning of the control lever, hls hand tremors have moved the control lever rapldly from one side to the other, givlng slgnals ror first one and then the other motor to rotate 6 faster, resultlng In rapid, and even dangerous, turns in one directlon and then the other.
A fifth problem has been a relatively poor overall efflciency of the drive trains that connect the electric motors to respective ones of the wheels, so that an unnecessarily large and heavy battery has been 1 0 required.
A sixth problem is that prior art deslgns have been heavy and unwleldy to t ransport. This has drastically reduced the mobility of handicapped persons, llmitlng employment posslbilities or llmiting their opportunltles to vlslt away from their homes or care facilitles.
However, If prior art deslgns of electrlcally propelled wheelchairs had used drive trains wlth better efficiencies, then the ablllty of the wheels to drive the motors through the more efficlent drlve tralns would have provided less dynamlc braklng, and controllablllty on turns would have been even poorer.
A seventh problem has been poor contact llfe In the relays that are used to reverse the potentials of the electrlc motors. Thls has resulted ln frequent repalrs and frequent perlods of the wheelchalr belng out of servlce.
There are thousands of Incapacitated people who would be able 25 l.o galn a greater degree of self-rellance, and some would be able to become a part Or the work force of their country, If they were able to control some type of self-propelled conveyance.
Thus, the present invention can help handlcapped people to galn a better sense of dlgnlty and self-worth, and can help many of them 30 become productlve members of soclety.

Sum_a y of the Inventlon The present Inventlon provldes a wheelchair, or conveyance, In which a left propulsion motor is continuously connected to a left propulslon element, or wheel, by a first power transmlsslon; and a rlght 36 propulslon motor is continuously connected to a right propulsion element, or wheel, by a second power transmisslon.

l.'Z~;27!:~

Electrlcal power to the motors is separately and varlably controlled In response to a manually-positioned control, slmllar to the type used wlth computer games.
The c ontrol lever is oriented with relation to the conveyance so 6 that movlng l he control lever forward results in maxlmum power in the forward direction being delivered to both the left and rlght motors.
In llke manner, maximum power in the rearward direction Is dellvered to bnth motors when the control lever is moved dlrectly rearward, power is dellvered to the left and rlght motors In opposite 10 directlons and plvotaJ turns are achleved when the control lever Is moved direct]y to one slde or the other, and varlous percentages of power in forward and reverse directions are provided when the control lever is positioned in varioua directions, and at various distances from the neutral posltlon.
16 Manual positionlng of the control lever separately and variably actuates the wiper arms of left-propulsion and right-propulsion potentiometers. Each Or the potentiometers provldes two variable resistances, one from the arm to one leg thereof, and another from the arm to the other leg t.hereof.
The following descrlptlon will describe operatlon for only one of the motor drives, slnce both sides functlon the same, and both clarlty and brevlty are best achleved In thls manner.
The right-propulsion potent.iometer cooperates wlth a slgnal supply voltaKe oi` elght volts that is applied across its legs and functions 26 as a voltage divider to provide a rlght-propulslon signal.
The r ighl;-propulsion signal is supplled as the input to two operatlonal amrlllflers. When the right-propulslon slgnal is more than four volts, one of the operational ampllfiers provldes a forward-rotation signal for con~.roillng tlle rlght propulsion motor; and when the rlght-30 propulslon slgrlal Is less than four volts, the other Or the operatlonalampllflers provldes a reverse-rotatlon signal for controlllng the same propulslon motor.
A forward-propulslon comparator receives the forward-rotation slgnal and cooperates wlth a first power transistor to actuate a forward-36 polarlty relay. In llke manner, a reverse-propulsion comparator receives the reverse-propulsion signal and cooperates with a second power translstor to actllate a reverse-polarity relay. The forward-polarity and l~?Z7~

reverse-polarity relays control the polarity of the drlving voltage that is supplied to the right-proplllsion motor.
But, the actual supplying of electrical power, and the varying of the electrical power that is supplied, Is controlled by separate means 6 whlch functions as follows.
The system uses two diodes to receive the forward-rotation signal and the reverse-rotation signal, and to develop a power-control signal. The power-control signal varles from zero to four volts when an attenuatlon control is ad)usted to allow maxlmum speed and power; and 10 the power-control signal is attenuated to lower maximum voltages when lower maximum acceleration, speed, and power are desired.
A sawtooth generator and the power control slgnal cooperate wlth a comparator to develop a pulse-width-modulated control signal whose pulse widths are proportional to the magnitude of the power-15 control signal.
The same sawtooth generator also cooperates wlth a comparator ln the left-propulsion clrcuitry to develop a pulse-wldth-modulated control circuit that cooperates with other components for driving the left-propulsion motor.
The pulse-wldth-modulated control slgnal cooperates with a translstor to provide a pulse and brake slgnal. The pulse and brake slgnal is pulse-width-modulated as is the pulse-wldth-modulated control slgnal, but Is ampllfled In power.
The pulse and brake slgnal controls two field-effect transistors.
25 The first field-effect translstor receives the pulse and brake signal and pulses a connectlon to ground, so that the supply voltage Is pulsed to the rlght-propulsion motor, thereby supplylng a pulse-width-modulated driving voltage to the right propulsion motor. The wldth Or the pulses determlnes the effectlve drlving voltage.
It should be remembered that the polarity nf the supply voltage that Is applied to the right propulslon motor has been determined by the forward-rotation and reverse-rotation relays, and the flrst field-effect transistor determines the width of the pulses of the supply voltage that are applled to the rlght propulslon motor.
The second field-effect transistor cooperates wlth the pulse and brake slgnal to short the motor winding of the right propulslon motor durlng at least a portlon of the Intervals that separate the voltage pulses of the pulse-wldt h-modulate(1 drlving voltage.

7~3~

This shorting of the motor windings during a portion of the lntervals between pulses of driving voltage causes the right propulsion motor to operate as an electrically loaded generator, and to provide dynamlc braklng.
6 llowever, if the motor windlng were shorted for even a small portlon of the tlme when pulses of the driving voltage were being applled to l.he motor wlnding, severe damage would be dolle to the clrcuit components. Thus, a delay circuit Is provided that prevents this occurrence.
The delay circult includes diodes, reslstors, and the parasitlc capacltance of the field-effect transistors, and provides a time-interval between the end of one pulse of the pulse-wldth-modulated driving voltage and shortlng of the motor wlnding.
The delay circuit also provides a tlme-lnterval between the 15 cessatlon of shortlng the motor winding and the start of the next pulse of the effective driving voltage.
The present Invention incllldes a differential-limitlng circuit for limiting the rate of change in the dlfference of power that is delivered to the left-propulslon and right-propulslon motors, while leaving the 20 change in the rates of power that can be dellvered substantially unaffected when the rates of change of power to both motors are generally equal.
In the preferred conflguration, a capacltor, whlch Is connected across the arms of the t wo potentlometers, limlts the rate of change In 26 the control voltages that are provided by the two potentlometers.
However, when the control lever is positioned to equally Increase or decrease the power to both motors, the voltages of the rlght and left propulsion signals change equally and the capacltor does not see a dlfference In differential voltage. Thus, the dlfferentlal llmltlng clrcult 30 does not affect acceleratlon or deceleratlon when changes In electrlcal power are substantially equal to both propulslon motors.
Limiting t;he rate of t.he difference in power delivered to the two motors provides a conveyance that can be controlled by people having severe hand t.remors because spurious signals produced by hand 36 tremorlng are time-averaged.
In additlon to dynamic hraking and differentlal change limitlng, the present inventiorl provides extende(i rela~ life, and provides dynamlc braking when no pulses of power are bein~ supplied to the motor.

7~36 The field-effect translstors cooperate wlth the relays to pulse the power after the relays are closed, and to cease delivering power before the relays open. thereb y avoiding arcinX across the relay contacts, and thereby resulting in greatly extended servlce life for the 6 relaYs~
In thelr unenerglzed state. the relays short the motor wlnding, thereby achlevlng power-off dynamlc braklng even when the battery Is removed from t;he conveyance.
In summary, the present invention provldes a conveyance, a 10 motor drive, and a control, in which: the power transmlssions continuously connect the motors to the wheels, thereby discontinuing the necessity of mechanlsms to connect and dlsconnect the power trains;
dynamic braklng is provided by shorting the motor windlng during a portion of the Intervals between power pulses, thereby provldlng superlor 16 control for turns and down-grade operation; dlfferentlal control llmlting provldes ease and accuracy of control, even for those with severe hand tremors, b,v llmit lng the rate of change In the differ ?nce of power that can be supplled to one motor wlth respect to the other motor; and power-off dynamlc braktng is achleved by shortlng the motor wlnding 20 when no power pulses are beln~ supplled to the motors.
In one embodlment, the present inventlon provl(3es extended relay llfe for reverslble electrlc motors by preventlng relay contacts from maklng or breaking contact under load.
In another embodlment, the present invention provldes a solld-26 state swltchlng device In whlch two electrlcal connections are alternatelymade and broken in response to the change in potentlal In a single conductor, and a delay Is provlded between the breaking of the one connection and the establlshing of the other connectlon.
Dlfferential control limiting Is appllcable to both electrlc and 30 fluld motors; dynamlc braking is applicable to any elect.ric motor that Is driven by voltage pulses whether wldth-modulated, amplltude-modulated, or unmodulated; power-off dynamlc braklng Is appllcable to varlous uses, particularly with permanent magnet motors; the clrcuitry for Increaslng relay llfe Is partlcularly appllcable to reverslble electrlc motors that are 35 drlven by pulsed drlvlng voltages; and the solid-state switchlng devlce is applicable to varlous uses, including reverslble electric motors.
In a flrst aspect of the Inventlon, a conveyance lncludes a propulslon element, an electric motor. PL power transmlsslon that drlvlngly connects the electrlc motor to the propulsJon element, a motor control means for supPIylng a drJving voltage to the motor, and means for selectively dlscontlnulng the supplying of the drivlng voltage to the electrlc motor, the Improvement which comprises: means~ includlng the 5 power transmlssion, for allowing the propulslon element to drlve the motor; parklng mode means for makJng the motor function as an electrically loaded generator w}len the propulsion element is driving the motor and the supplylng of the drivlng voltage Is discontinued; and means for selectively Inactivating the parking mode means.
In a second aspect of the Inventlon, a method speclally adapted for electrically propelllng, braking, and manually-propelllng a conveyance that Includes a propulsion element, an electric motor, and a power transmlsslon that drlvlngly connects the electric motor to the propulslon element, Includes the steps of supplylng a Arivlng voltage to the motor, 16 selectlvely Isolating the motor from the drlvlng voltage, allowing the propulsion element to drive the motor through the power transmlsslon, causlng the motor to functlon as an electrlcally loaded generator when the propulslon element drlves the mol:or, selectively inactlvatlng the causlng step, and manually propelllng the conveyance.

Brlef Descrlption of the Drawings FlGlJRE l ls a slde elevation of a conventlonal wheelchalr to whlch the electrlc motor drlve of the ~-resent Invention has been added;
FIGURE 2 Is a front elevation of the electrlc wheelchalr of FIGURE 1~ taken substantlally as shown by vlew line 2-2 of FIGURE 1;
26 FIGURE 3 ls a perspectlve v~ew of the drlve unlt of the electrlc wheelchalr of FIGURE 1, taken at a perspectlve angle that is both upward and rearward from that Or FIGURE l, and showlng a fJrst embodlment of a power transmission;
FIGURE 4 ls a top vlew of a second and preferred embodlment of 30 a power transmisslon for use wlth the present Inventlon, showlng some components ln cross-sectlon;
FICURE 6 is a schematic drawing of the source of electrlcal power, and the regulated voltages, for the s,vstems of FIGURES 9 and 10;
FIGURI;: 6 ls a schematic drawing of the sawtooth generator that 35 ls a part of pulse-wldth modulation of the drlving voltages for both motors;

7~6 FIGURE 7 shows the circuitry that limlts the difference In change In power that ls supplled to the left and rlght propulslon motors;
FIGURE 8A Illustrates the wave form of the pulse-wldth-modulated drlvlng voltage and shows the effective delay at the start of 6 each voltage pulse;
FIGURE 8B Illustrates the wave form of the dynamlc braklng pulses and shows the effectlve delay at the start of each pulse;
FIGURE 8C shows the wave forms Or FIGURES 8A and 8B
superlmposed;
FIGURES 9A and 9B combine to provlde a schematic drawlng of the motor and electronlcs for drlving the rlght wheel, and may be consldered as comblnlng to form FIGURE 9;
FIGURE 10 Is a schematic drawlng Or the motor and electronics for drlvlng the left wheel;
FIGURE 11 Is a schematic dlagram showlng a varlatlon Or the embodlment Or FIGURES 6-9 in which the electronic control, and the dlfferential control limlting thereof, is used to control hydraullc motors;
and FIGURE 12 Is a schematic drawing of the preferred embodlment Or 20 the present inventlon. showing a varlatlon Or the embodiment of FIGURES
9A and 9B, whereln fleld-effect transistors are used to control both the polarlty of the power and the appllcatlon of the pulses, thereby ellmlnatlng the need for mechanlcal relays.

Descrl~tlon Or the Preferred Embodime_ts Referrlng now to FIGURES 1-3, an electrlc wheelchair 10 Includes rlght and left wheels, or flrst and second propulalon elements, 12a and 1 2b, a frame 14, a seat bottom 16 and a seat back 18, castor wheels 1 9a and 1 9b, and footrests 20a and 20b. The wheelchair dlscussed thus far Is typlcal of the prlor art.
The electrlc wheelchalr 10 Includes drive unlts, 22a and 22b, which are generally mlrror images Or one another.
The drlve unlt 22a Includes a mountlng plate 24a, a flrst electrlc motor, or rlght electrlc motor, 26a of the permanent fleld-magnet type which Is mounted to the plate 24a and whlch Includes a motor shaft 35 28a that extends through the plate 24a, a drlve pulle,v 30a whlch Is mounted onto the motor shaft 28a, a statlonary splndle 32a whlch Is - attached to the plate 24a, a drlven pulle,v ~4a whlch Is rotatably Z7~6 mounted onto the spindle 32a, a drive roller 36a which is secured to the pulley 34a and whlch engages a tlre 38a of the wheel 12a, and belts 40a which enRage t;he pulleys 30a and 34a.
The plate 24a Is moved rearward to engage the drive roller 36a 6 wlth the tlre 38a for power propulsion, and is moved forward to dlsengage the drlve roller 36a for manual propulsion.
However, as will be described in con~unctloIl wlth FIGURE 4, In the present Inventlon, there Is no necesslty for dlsengaglng the drlving connectlon between the motors and the wheels.
A second electrlc motor, or left electric motor, 26b Is at a dlfferent helght than the right motor 26a; so that the motors, 26a and 26b, bypass each other when the wheelchair 10 Is folded wlth the wheels 12a and 12b proxlmal to one another.
The wheelchair 10 Include6 a control box 50 which is attached 15 near an armrest 52a. and which includes a control lever 54, an ON-OFF
switch 56, and a speed-power limiting control 58.
The control lever 54 controls two potentlometers, and the two potentiometers control rotational speeds of the motors, 26a and 26b.
Forward movement of the control lever 54 produces forward 20 propulslon, rearward movement produces rearward movement, forward and rlghtward movement produces forward propulslon wlth A right turn, and sideward movement produces a plvot turn wlth the wheels. 12a and 12b, turnlng In opposlte dlrectlons.
Referrlng now to FIGURE 6. a twelve volt battery, or source of 25 electrlcal power, 60 is connected to a voltage regulator 62 by the ON-OFF swltch 56 of FIGURE 1. The voltage regulator 62 provides outputs of one, four, and elght volts in 8 volt output conductors 64, 66, and 68, respect~vely. The switch 56 also controls supplylng Or twelve volts In a conductnr 70.
Referrlng now to FIGURES 9A, 9B, and 10, FIGURES 9A and 9B
comblne to provlde a clrcuitry that hereafter will be referred to as FIGURE 9. The clrcuitry of FIGIJRE 9 is for the rlght motor 26a. An Identlcal circult, as shown In FIGURE 10, controls the left motor 26b.
Operatlng voltages for FIGURES 9 and 10, are provided by the 35 clrcultry of FIGURE 5. A sawtooth generator 72 of FIGURE 6 provides asawtooth slgnal In a conductor ~4 for use wlth the circultrles of both FIGURES 9 and 10.

Il FIGURE 9 Includes a first potentiometer, or rlght motor potentlometer, 76a; and FlGURE 10 incJudes a second potentlometer, or left motor potentlomet,er 76b.
The potentiometers, 76a and 76b, may be a part of an X-Y
5 control that provides reslstances proportional to movement of a control lever from the intersection of X and Y axes, such as are commonly used to play video games, or the potentiometers, 7fia and 76b, may be controlled In any suitable manner.
Since the circultries of FIGURES 9 and 10 are Identlcal, only 10 FIGURE 9, whlch includes the circuitry which drives the rlght electrlc motor 26a, will be described.
Referring now to FIGURE 9, an electric motor drive, or right wheel drive, 90a includes the potentiometer 76a. The potentiometer 76a Includes an upper leg 92a that Is connected to the conductor 68 of 15 FIGURE 5 and receives a potential of eight volts therefrom, a lower leg 94a that Is connected to ground, as shown, and a wlper arm 96a.
Movement of the wiper arm 96a above a mldpolnt In the resistance of the potentiometer 76a produces a forward-rotation slgnal that Increases from four to elght volts in a conductor 98a as the wiper 20 arm 96a rnoves upwardly from the midpolnt In the reslstance; and movement of the wlper arm 96a below the mldpolnt In the reslstance of the potentlorneter 76a produces a reverse-rotatlon signal that varies from four volts down to zero as the wiper arm 96a moves downwardly from the mldpolnt;.
The forward-rotatlon signal in the conductor 98a Is supplled to an input reslstor lOOa and to an input resistor 102a. The input reslstor l OOa Is connected to the negative input termlnal of an operational amplifler 104a; and the input resistor 102a Is connected to the posltive Input terminal of an operatlonal amplifler 106a.
The posltlve input termlnal of the operatlonal amplifier 104a ls connected to four voits by an Input resistor 108a and to ground by a reslstor 11 Oa. The negative Input terminal Or the operatlonal ampllfler 106a Is connected to four volts by an input reslstor 112a; and the posltlve input terminal of the operational amplifier 106a is connected to 35 ground by a reslstor 114a.
The output of the operational amplifier 1O4A 1S a forward-rotatlon slgnQI; and the output of the operatloIlal ampllrier 106a Is a reverse-rotation signal.

7~36 The outputs of the operational ampllflers 104a and 106a are connected together by means of diodes 116a and 118a; and feedback resistors 120a and 122a are connected to a junction 124a that is intermedlate of the dlodes 116a and 118a, and to respective ones of the 5 negative lnput terminals of the operational ampliflers, 104a and 106a.
Contlnulng to refer to FIGURE 9, if the feedback resistor 120a were connected directly to the output terminal of the operational amplifier 104a, rather than between the diodes, 116a and 118a, then a decrease below four volts in the conductor 98a, as produced by the 10 wiper arm 96a moving downwardly from the midpolnt of the reslstance In the potentlometer 7fia, would produce a voltage that would vary from zero to four volts at the output terminal of the operatlonal ampllfier 104a.
I~owever, since the feedback resistor 120a is connected between 16 the diodes 116a and 118a, the voltage between the dlodes 116a and 118a varies from zero to four volts with movement of the wlper arm 96a from the midpoJnt of the potentiometer 76a downwardly toward zero volts; and the voltage at the output terminal of the operational amplifier 104a is higher by the voltage drop across the diode 116a, which is approximately 20 slx-tenths of a volt.
In like manner, with an increase in voltage in the conductor 98a from four volts to elght volts, as the wiper arm 96a is moved upwardly toward eight volts, the operational ampllfier 106a produces a volt;age that Increases from zero to four volts at the junction 124a, and that Is 25 approxlmately slx-tenths of a volt hlgher at the output of the operational ampllfier 106a.
The operatiollal ampllfiers 104a and 106a cooperate with the diodes 116a and 118a to form an absolute value circuit. That Is, whether the wiper arm 96a of the potentiometer 76a moves upwardly 30 above the midpoint of the resistance thereof, or moves downwardly below the mldpolnt of the resistance thereof, a power-control signal is produced at the Junct.ion 124a which increases as a function of the wlper arm 96a of the potentiometer 76a movlng away from the midpoint Or the reslstance thereof. The use of this power-control slgnal will be 35 descrlbed subsequently.
The circultry descrlbed thus far produces three control signals:
the operational amplifier 104a produces a forward-rotatlon signal in a conductor 126a; the operational amplifier l 06a produces a reverse-1~9;~:7~

rotatlon signal In a conductor 128a; and the diodes 116a and 118a cooperate with the forward-rotatlon slgnal In the conductor 126a and wlth the reverse-rotatlon signal Or the conductor 128a to provlde the power-control slgnal at the junction 124a.
The forward-rotatlon slgnal is supplled to the positive Input termlnal of a comparator 130a; and the reverse-rotatlon slgnal Is supplled to the positive input termlnal of a comparator 132a. Both of the comparators, 130a and 132a, are connected to the one volt source of FIGURE 5; so that both comparators, 130a and 132a, have a threshold Or 10 approxlmately one volt.
Continulng to refer to FIGURE 9, since the outputs of the operatlonal ampllflers, 104a and 106a have outputs that are approximately zero volts when the wlper arm 96a is at the mldpolnt of the reslstance of the potentlometer 76a, nelther will have sufflclent voltage to produce 16 an output from the respective one of the comparators, 130a or 132a.
When the signal voltage In the conductor 98a Is a few tenths of a volt below the four volt Input to the positlve Input resistors of the operational amplifler 104a, the output of the operatlonal ampllfler 104a wlll exceed the one volt threshold of the comparator 130a; and when the 20 slgnal voltage In the conductor 98a Is a few tenths of a volt above the four volt Input to the negative Input reslstors of the operational ampllfler 106a, the output of the operatlonal ampllfler 106a will exceed the one volt threshold of the comparator 132a.
Thus, It Is theoretlcally Imposslble for the comparators. 130a and 26 132a, to proliuce outputs slgnalllng both forward and reverse rotatlon of the electrlc motor 26a for any posltlon of the wlper arm 96a. Instead, the wlper arm 96a must be offset four-tenths of a volt on elther slde of the four volt mld-polnt to produce a signal that Inltlates rotatlon of the electrlc motor 26a In elther the forward or reverse dlrectlon.
The output termlnals of the comparators 130a and 132a are connected to the elght volt conductor 68 of FIGURE 5 by pull-up reslstors 134a and 136a respectlvely, and to forward-power translstor 138a and reverse-power translstor 140a, respectlvely.
The forward-power transistor 138a Is connected to ground, and 35 to twelve volts through a relay coll 142a Or a forward-power relay, or mechanlcal relay, 144a; and the reverse-power translstor 140a Is connected to ground, and to twelve volts through a relay coll 146a of a reverse-power relay, or mechanlcal relay, 148a.

7~6 The right electrlc motor 26a includes a motor windlng 150a which is connected to the relays, 144a and 148a, as shown; and the relays, 144a and 148a, are in their unenergized positions, as shown; so that the motor winding 150a ls shorted by the relays, 144a and 148a, and 5 by conduct.ors 152a.
Thus, when neither of the relay coils, 142a or 146a, is energized, the system shorts the motor winding 150a, thereby causlng the electric motor 2fia to function as an electrically loaded generator, and thereby provlding dynamic braking.
Thls condition of dynamic braking occurs in three dlfferent modes. It occurs when the manually selected positlon of the control lever 54 of FIGURES 1 and 2 is such that neither relay coil, 142a or 146a, ls energized; it occurs when the switch 56 of FIGURE 5 Is In the OFF posltion, as shown and it occurs when the battery 60 is removed 15 from the circuit.
l`hu~, the system pl ovldes power-off dynamlc braking as well as providing dynamlc braking during power-on conditions.
WheIl tlle comparator 130a provides an output, the transistor 138a energizes the relay coil 142a, and a relay contactor 164a is moved 20 to a contact 156a, thereby connecting an end 158a of the motor windlng 160a to a twelve volt conductor 160a.
In like manner, when the relay coil 146a Is energized, a relay contactor 162a is moved to a contact 164a, connectlng an end 166a of the motor wlnding 150a to tlle twelve volt conductor 160a.
Thus the re]ays 144a and 148a functlon to determine whlch of the ends, 168a or 166a, of the motor wlnding 150a ls connected to the twelve volt conductor 160a, function to determine the polarity of the power being ~;upplled to the electric motor 26a, and thereby determine the directlon 0r rotatlon of the electric motor 26a.
llowever, completion of tne circuitry to supply power to the electrlc motor 26a is dependent upon a field-effect transistor, or FET
168a. The functloning of the field-effect transistor 168a, and another field -effect transistor, or FE:T, 170a, will be descrlbed subsequently.
Continuing to refer to FIGURE g, it was shown previously that 35 a power-control signal is developed at the junctlon 124a, whereas direction-control slgnals are developed in the conductors 126a and 128a.
The power control signal of junction 124a is connected to a potentlometer ~ 72a which is mechanically connected to a potentiometer 79~

172b of FIGURE 10. The potentlometers 172a and 172b serve to attenuate the power-control signals of the junctlons 124a of FIGURE 9 and 124b of FIGURE 10, and thus to provlde the speed-power llmitlng control 58 Or FIGURE 1, whlch adjustably llmits the ma~lmum power 6 supplled to the electrlc motors 26a and 26b.
The attenuated power-control signal in a conductor 174a is supplied to the negative termlnal of a comparator 176a; and the positive terminal of the comparator 176a is connected to the sawtooth generator 72 by the conductor 74.
Referrlng now to FIGURE 6, the sawtooth generator 72 includes an operational amplifier 178, resistors 180, 182, 184, 186, and 188, a diode 190, and a capacitor 192. The sawtooth generator 72 Is a stàndard relaxation circult and a detailed description can be found in both electronlc t extbooks and handbooks. Thus, it Is sufflclent to note that a 16 sawtooth voltage is delivered to the conductor 74 that varies from A
minlmum of one volt to a maximum of three volts.
Referring again to FIC7UPE 9, the comparator 176a, together wlth a pull-up resistor 194a which is connected between the output Or the comparator 176a and the twelve volt conductor 160a, produces an 20 output in a conductor 196a whenever the input to the negatlve termlnal of the comparator 176a is greater than the sawtooth voltage whlch the sawtooth generator 72 supplles to the posltlve Input terminal of the comparator 176a vla the conductor 74.
The result is that a pulse-width-modulated control slgnal is 25 produced In the conductor 196a whose pulse widths are a function of the magnitude of the attenuat:ed power-control signal In the conductor 174a.
The conductor 196a is connected to a translstor 198a. The translstor 198a is connected to the twelve volt source In the conductor 160a by a conductor 200a and a pUIl-llp resistor 202a, and is connected 30 to ground~
The fleld-effect translstor 168a is an N channel enhancement mode MOSFET which turns on when its gate 204a Is Increased above ground potentlal; and the field-effect translstor 170a is a P channel enhancement mode MOSFET whlch turns on when Its gate 206a Is 35 decreased below its source potential.
When the Outpllt of the comparator 176a Is produclng a voltage pulse, the gate 204a of the FET ] 68a is above ground potential; and the FET 168a completes the circuitry of the electrlc motor 26a by 129Z7~6 connectlng one of the ends, 158a or 166a, of the motor windlng 160a to ground .
Of course, the one of the ends, 158a or 166a, that is connected to ground by the FET 168a depends upon the posltlons of the relay 6 contactors l54a and 162a of the relays 144a and 148a.
But when the comparator 176a is not produclng an output In the conductor 19fia, as is the condition between pulses Or the pulse-wldth-modulated control voltage, then the voltage In the conductor 196a Is approxlmately 0.7 volts and current flow In the pull-up resistor 202a, 10 and the voltage drop thereof, brings the voltage on the gate 206a of the FET I 70a down below the source voltage of the twelve volt conductor 160a.
Wlth the voltage on the gate 206a below the source voltage, the FET 1 70a conducts, connectlng the twelve volt conductor 160a to the 16 conductors 152a. Slnce one of the ends, 168a or 166a, of the motor wlndlng 150a Is ccnnected to the twelve volt conductor 160a by one of the relay contactors, 154a or 162a, the result Is that both ends, 168a and 166a, of the motor winding 160a are connected to the twelve volt conductor 160a; the motor windlng 150a Is shorted; the electric motor 20 26a functions as an electrlcally loaded generator; and the electrlc motor 26a provides dynamlc braklng.
Referring now to FIGURES 8A, 8B, 8C, and 9, the FET 168a pulses a connection to ground so that driving-voltage pulses, or power pulses, 207a of the supply voltage are applied to the electric motor 26a 26 that are an effective drlvlng voltage, or pulse-wldth-modulated drivlng voltage, or voltage pulses, 209a whose pulse widths 21 la are generally proportional to manual positioning of the control lever 54 and the potentiometer 76a.
The FET I 70a provldes dynamic braking pulses, or motor-30 loading pulses, 21~a whose pulse widths 215a are generally equal to no-power intervals, or no-voltage intervals, 217a between ad~acent ones of the power pulses 207a that are supplled by the FET 168a.
When the pulse widths 21 la of the drlvlng voltage 209a become wlder, the no-power Intervals 217a between pulses become smaller, and 36 the dynamic braking is reduced; and as the pulse wldths 211a of the drlvlng voltage 209a become narrower, the no-power Intervals 217a between the voltage pulses 209a become wider, and the dynamic braking is Increased.

Z~9~

Therefore, the dynamic braking has little effect on the efflclency of the drive when the electric motor 26a Is operatlng at, or near, maxlmum power. But the dynamlc braking ~s quite effective In provlding the deceleration that is needed to provlde controllability, 6 partlcularly the deceleratlon that is required to make turns with a conveyance which is propelled by two electrlc motors that separately and variably control left and right wheels.
Contlnulng to refer to FIGURE 9, It has been shown that both the FET 1 68a and the FET 1 70a are controlled by the voltage in the 10 conductor 196a. Remember that the FET I 68a applies power to the electric motor 26a, and the FET 170a shorts the motor windlng 150a; so it Is apparent that the FETS, I 68a and 170a, control functions that must not occur at the same tlme.
The present invention includes means for provldlng an effective 15 delay 219a In startlng each braking pulse 213a subsequent to the end of respective ones of the power pulses 207a.
Also, the present invention Includes means for providing an effectlve delay 221a in starting each power pulse 207a subsequent to the end of respective ones of the braking pulses 213a.
The means for providing the effectlve delays, 219a and 221a, Include a coupllng reslstor 208a, dlodes 210a and 212a, time-delay reslstors 214a and 216a, and parasitic capacltors, 218a and 220a, of the FETS, 168a and 170a, whlch are Indlcated by dash-lines.
The output of the translstor 198a Is delivered to the gate 204a 26 Or the FEl' 168a by means of the coupling resistor 208a and the time-delay resistor 214a. Now any transistor that has appreciable current-carrying capacity has some parasitic capacitance, as Indlcated by the parasitic capacitors 218a and 220a. So, an increase in voltage at the gate 204a, in response to an Increase in voltage in the conductor 200a 30 at the out,put of the transistor 198a, Is delayed by current flowing through the t,ime-delay resistor 214a to charge the parasitic capacltor 218a.
However, when the voltage falls at the output of the translstor 198a, the parasitic capacltor 218a is discharged rapldly through the dlode 35 210a which bypasses the tlme-delay resistor 214a.
Thus, the time-deiay resistor 214a, the parasltic capacitor 218a and the diode 210a cooperate to provide the effectlve delay 221a In the 7~

start of a pulse 207a of drivlng voltage 209a; and these same elements cooperate to promptly shut off the FET 168a.
In like manner, the output of the transistor 198a is delivered to the gate 206a of the FET 170a by means of the coupllng reslstor 208a 6 and the tlme-delay reslstor 216a.
When the output of the translstor 198a decreases, a decrease In the voltage at the gate 206a, below the supply voltage in the conductor 160a, Is del~yed by current flowing through the time-delay reslstor 216a as the parasitlc capacltor 220a of the FET 170a dlscharges.
However, when the voltage Increases at the output of the translstor 198a, the parasitlc capacitor 220a is charged rapidly through the dlode 212a which bypasses the time-delay resistor 216a.
Thus, the tlme-delay resistor 216a, the parasltlc capacitor 220a, and the dlode 212a cooperate to delay a decrease In voltage on the gate 15 206a, and to provlde the effective delay 219a in each dynamlc braklng pulse 213a subsequent to cessatlon of a power pulse 207a; and these same elements cooperate to promptly increase the voltage on the gate 206a, and promptly fihut of r the FET 170a.
So, means Is provlded for effectlvely delaylng the start Or 20 shorting the motor wlndlng 150a, and for delaying the start of the ne~t power pulse 207a, thereby preventlng the motor wlndlng 160a from belng shorted during the tlme that a pulse 207a of the drlving voltage 209a Is belng 6upplled to the motor wlnding IbOa.
Referring now to FIGURES 7, 9, and 10, the wlper arms 96a and 25 96b Or the potentlometers 76a and 76b are connected together by the conductors 98a and 98b, a time-averaglng capacltor 222, and a variable reslstor 224.
When the control lever 54 Is posltioned to make a sudden change In the positlon of one of the wiper arms, 96a or 96b, with 30 respect to former posltlons of the wlper arms, 96a and 96b, the capacltor 222 delays the change In voltage In the conductor 98a or 98b that Is connected to t he one of the wlper arms, 96a or 96b, that has been reposltioned abruptly.
Thus, the capacltor 222 time-averages changes In the differences 35 of the signRI supply voltages that are belng supplled by the potentlometers 76a and 76b; and the capacltor 222 functlons as a change llmltlng means 223 for limiting the rate of change ~n the dlfference In '7~t~

power that can be supplled to one motor, 26a or 26b, with respect to the other motor 26b or 26a.
The variable resistor 224 is an optlonal part of the change limlting means 223; but can be used to provide a means for selectlvely 5 varylng the r ate of change in the difference in power that can be supplied to one motor, 26a or 26b, with respect to the other motor, 26b or 26a. While It would be possible to vary the conductance, as represented by the capacltor 222, particularly by switching various capacitors in between the conductors, g8a and 98b, the variable reslstor 10 224 provides a means for infinitely varying the limiting of the rate of change In the signal supply voltages.
Referring now to FIGURE 11, a fluid motor drive 2~0a is slmilar to the electric motor drive 90a of FIGURE 9, is used to control a reversible fluid rnotor 232a, and achieves limiting of the rate of change 16 in the dlfference in the speed of the fluid motor 232a, and a similar fluid motor, not shown, slmilar to that which has been described for the electric mntors 26a and 26b.
The fluid motor drive 230a is used in cooperatlon with another fluid motor drive, not shown. Both of the fluid motor drlves, 230a and 20 the other fluid motor drive, are used with the sawtooth generator 72 of FIGURE 6, are connected thereto by the conductor 74, and cooperate wlth the sawtooth generator to separately provide, and to separately utilize, pulse-width-modulated control voltages.
In llke manner, the fluld motor drives, 230a, and a similar fluid 26 motor drive that is not shown, are connected together by the change llmltlng means 223 of FIGIJRE 7.
The fluld motor drive 230a Includes a dlrectional control valve 234a with a solenold coll 236a, the fluld motor 2~2a whlch is connected to the directional control valve 234a by motor condults 238a and 240a, a 30 fluid pump 242a whlch Is connected to a fluld reservolr 244a by an Inlet conduit 246a and to a proportional output valve 248a by an outlet condult 250a.
The fluld pump 242a and the fluid reservolr 244a provide a source of fluld power, the fluld power Is dellvered to the proportlonal 35 output valve 248a by the outlet condui t 250a, the proportional output valve 248a dellvers pressurlzed fluid to the directlonal control valve 234a by a 9uppl y condllit 2fi2a, the directional control valve 234a delivers the pressurlzed fluiA to the fluid motor 2:32a through one of the motor 1~.'3.:2 ~96 conduits 238a or 240a, the fluid motor 232a returns fluid to the dlrectional control valve 234a through the other of the motor conduits, 240a or 238a, the directional control valve 234a returns fluid to the proportlonal output valve 248a through a return conduit 254a, and the 6 proportional output valve 248a returns fluid to the fluid reservoir 244a through a reservolr conduit 256a.
Poslt;ioning the potentiometer 76a produces an output from the translstor 138a as descrlbed in conJunctlon with FIGURE 9.
The 1.ransistor 138a connects the solenold coil 236a between 10 twelve volts Rnd ground whenever the potentiometer 76a is positioned to develop a voltage in the conductor 98a that i8 less than four volts.
The directional control valve 234a is positioned to supply pressurized fluld to one Or the motor condults, 238a or 240a, when the solenoid coll 236a is energlzed, and ls positioned to supply pressurized 16 fluld to the other of the motor condults, 240a or 238a, when the solenold coil 236a is not energized. Therefore, only one comparator, 130a, ls needed, whereas two comparators, 130a and 132a, were used wlth the electric motor drlve 90a of FICURE 9.
The proportlonal OUtpl1t valve 248a includes a solenoid coll 268a 20 which controls the flow rate of pressurized fluid that ls delivered to the directlonal control valve 234a proportional to the effective drlvlng voltage that is applled across the solenold coll 258a. Or, alternately, the proportlonal output valve controls the flow of fluld comlng back from th0 fluld motor 232a.
As descrlbed in conJurlctlon wlth FIGURE 9, a pulse-wldth-modulated control slgnal ls developed at the output of the comparator 176a as the sawtooth output of the sawtooth generator 72 ls compared with the attenuated voltage out of the potentiometer 172a. Thls pulse-wldth-modul~ted controi slgnal cooperates wlth the FET 168a to provide 30 a pulse-width-modulated voltage as has been described in con~unction wlth FIGURF: 9; and this pulsed voltage is applled to the solenold coll 268a of the proportlonal output valve 248a to provide a fluid flow rate that is proportional to posltioning of the potentiometer 76a.
The fluid motor drive 230a lncludes a dlode 260a whlch is 36 connected across the solenoid coll 2~i8a of the proportlonal output valve 248a, and whlch prevents excessive voltages from being applled to the output of the FET ] 68a when ~;he magnetic field of the solenold coll 258a collapses. In like manner, a diode 262a ls placed across the '7~i solenoid coil 236a of the directional control valve 234a to prevent excessive voltages from heing applied to the output Or the transistor 138a when the magnetic field of the solenoid coll 236a collapses.
The electronlc circuitry of the embodiment of FIGURE 11 does 5 not include dynamic braking; so the circuitry of FIGURE 9 that Includes the FET 170a Is not needed. Consequently, time delays between pulses of drlving voltAge and pulses of braking voltage are not needed. So, only one FET, 168a, is required; and the time-delay resistor 214a and the diode 21Ua of FIGURE 9 are not needed. Thus, In FIGURE 11 the 10 coupllng resl~stor 208a Is connected directly to the gate 204a of the FET
168a.
Hydraulic circuits and components for achlevlng control of fluid motors, including thc direction of rotation, rotational speed, and dynamic braking are common to the art; so the hydraulic circuitry of FIGURE 11 16 Is representative of one of the many ways ln whlch the control of dlrectlon of rotation, speed of rotation, and l}mltatlon of the rate of change of two fluid motors can be achieved wlth the present inventlon.
Referrlng now to FIGURE 12, in the preferred embodiment of the present invention, an electric motor drive 268a Is provided whlch Is 20 slmllar to the electric motor drlve 90a of FIGURE 9, but whlch has the advantage Or ellmlnatlng the mechanlc~l relays, 144a and 148a, Or FIGURE 9.
The electric motor drive 268a cooperates with an Identical electrlc motor drive, not shown, with the sawtooth generator 72 of 25 FIGURE 6, and wlth the change llmltlng means 223 of FIGURE 7 for limltlng the rate Or change in the difference of power supplied to two electrlc motors, as descrlbed in conJunction with FIGURE 9.
The electric motor drive 268a of FIGURE 12 Includes the operatlonal amplifiers 104a and 106a of FIGURE 9. The operational 30 ampliflers 104a and lO6a are connected to the potentlometer 76a, to the four volt source, and to ground by Identically numbered and identically named parts as those of FIGURE 9. The embodlment of FIGURE 12 uses feedback resistors 270a and 272a to feed back the outputs of the ampllflers, 104a and 106a, to their respective Inputs.
When the control lever 54 of FIGURES 1 and 2 Is In its centered position, the wiper arm 96a of the potentiometer 76a Is at the midpoint of the reslstance, and the wiper arm 96a delivers four volts to the inpu~:s of both Or the operational amplifiers, 104a and 106a.

Since the ampllfiers, 104a and 106a, are differentlal amplifiers with four volts on both lnputs, the outputs of both ampliriers, 104a and 106a, are at ground potential when the wiper arm 96a supplles four volts to both operatlonal amplifiers, 104a and 106a.
6 As the wiper arm 9 ~a is moved downwardly, the output of the ampllfier 104a increases above ground potential; and as the wlper arm 96a ls moved upwardly, the output of the ampllfier 106a Increases above ground potentl~l. Notice that the amplifiers, 104a and 106a, cannot produce outputs slmultaneously.
If, for instance, the amplifier 104a Is producing an output, this output is compared to the sawtooth waveform of the sawtooth generator 72 by a comparator 274a and a pulse-width-modulated control signal is developed ln a conductor 276a by the comparator 274a and a pull-up reslstor 278a that is connected between the conductor 276a and the 16 twelve volt source.
The pulse-wldth-modulated control signal is delivered to a transistor 290a by the conductor 276a. The pulse-width-modulated control slgnal ls inverted and the level of the signal ls shifted by the translstor 290a and by a pull-up resistor 292a which ls connected 20 between the translstor 290a and the twelve volt source.
The output of the translstor 290a is connected to FETS 294a and 296a. The FET 294a Is an N channel enhancement mode MOSFET
whlch turns on when its gate 298a is increased above ground potential;
and the FET 296a Is a P charlnel enhancement mode MOSFET which 26 turns on when its gate 300a Is decreased below its source potentlal.
When the wlper arm 96a of the potentlometer 76a Is below the mld-point of the reslstance, and the voltage on the wlper arm 96a is less than four volts, the outr)ut of the comparator 274a is high durlng the pulse whlch ls developed by the comparator 274a, the output of the 30 translstor 290a ls low, the voltage to the gate 300a of the FET 296a Is below the source voltage, the FET 296a is on, and a terminal 301a of the motor 26a is connected to the twelve volt source by the FET 296a.
In like manner, the output of a comparator 302a Is connected to FETS 304a and 306a. THE FET 304a is an N channel enhancement mode 35 MOSFET which turns on when its gate 308a is lncreased above ground potentlal; and the FET ~06a ls a P c}~annel enhancement mode MOSFET
whlch turns on when its gate 310a is decreased below its source potentlal .

23 1;~9~ 6 Continulng the description of operation with the wlper arm 96a of the potentlometer 76a below the mid-polnt In Its reslstance, in thls conditlon, there Is no output from the comparator 302a, the output of a translstor 312a is hlgh, the voltage to the gate 310a Or the FET 306a Is 6 hlgh, the FF:T 306a is off, the gate 308a of the FET 304a is hlgh, the FET 304a is on, and the FET 304a connects a termlnal 314a of the electric motor 26a to ground.
Thus, in the conditlon described, the FETS 296a and 304a cooperate to determine the directlon of rotation of the electric motor 10 26a by maklng connectlons respectlvely to the termlnals 301a and 314a of the electric motor 26a; and the FET 29fia connects the electrlc motor to the twelve volt source with pulse widths that are proportlonal to the positioning of the wiper arm 96a below the mld-point Or the potentiometer 76a to provlde a pulse-wldth-modulated driving voltage.
Contlnuing to describe the operatlon of the FIGURI;: 12 embodiment, with a voltage on the wiper arm 96a that Is less than four volts, the comparator 274a is supplying pulses of voltage that are pulse-wldth-modulated. However, between voltage pulses of the comparator 274a, the output of the comparator 274a is low, the output of the 20 translstor 290a Is hlgh, the gate 300a of the FET 296a Is at source voltage, the FET 296a Is off, the gate 298a Or the FET 294a Is hlgh, the FET 294a Is on, and the FET 294a is connectlng the termlnal 301a of the electrlc motor 2fia to ground.
So, between voltage pulses of the comparator 274a, the termlnal 26 301a Or the electrlc motor 26a is connected to ground by the FET 294a and the termlnal 314a of the electric motor 26a Is connected to ground by the FET 304a.
Therefore, the clrcultry that has been descrlbed provides dynamlc braklng pulses 213a between pulses 207a of the pulse-width-30 modulated drivlng voltage 209a by shorting the electrlc motor 26a, andthereby causlng the electric motor 26a to functlon as an electrlcally loaded generator.
Operation of the circuitry with a voltage of more than four volts on the wiper arm 96a functions in like manner as has been 36 described for voltages of less than four volts on the wiper arm 96a, the difference being that the comparator 302a cooperates with the FETS
306a and 304a to provirle connections that determlne the dlrection of rotatlon of the ele(trlc motor 26a, that plllse the power, and that provide dynamlc braking, and the circuitry to ground Is completed by the FET 294a.
The output of the translstor 290a ls coupled to the FETS 294a and 296a by clrcultry that includes a coupling reslstor 316a; and the 6 output of the translstor 312a Is coupled to the FETS 304a and 306a by clrcuitry that includes a coupling resistor 318a.
An lncrease In voltage at the gate 298a of the FET 294a, and a delay in turning on the FET 294a, is achieved by a dlode 320a, a time-delay resistor 322a, and a parasitic capacitor 324a which is inherent in 10 the deslgn of the FET 294a, In the manner that has been described in conJunction with FIGURE 9.
Irl like manner, a decrease in voltage at the gate 300a of the FET 296a below the source voltage, and a delay In turning on the FET
296a, is achieved by a dlode 326a, a tlme-delay reslstor 328a, and a 15 parasitlc capacitor ,~30a which is inherent in the design of the FET 296a.
The constructlon thus described provides a tlme-lnterval between the cessation of one voltage pulse of the pulse-wldth-modulated drlving voltage and an adjacent one Or the dynamlc braklng pulses, and a tlme-lnterval between the end of one braking pulse and the start of the next 20 voltage pulse.
Thl s, It can be seen that the electrlc motor drlve of FIGURE 12 provldes the same advantages as the electrlc motor drive 90a of FIGURE
9, and also eliminates the necessity of using mechanlcal relays, such as the relays 144a and 148a.
Referrlng again to FIGURES 8A, 8B, and 8C, the power pulses 207a are al an amplltude of the source voltage, which preferably Is elther 12 or 24 volts. The frequency of the sawtooth which is generated by the sawtooth generator 72 preferably Is 125 hertz; so a perlod 331a of one complete cycle preferably Is 0.008 seconds.
In a typlcal deslgn ~;he effective delays, 219a and 221a, are approxlmately 200 microseconds; and the amplltude of the braklng pulses 213a Is about one volt.
The braklng pulse 213a ls applied for a portlon 233a of the no-power Interval 217a; and the portion 233a Is less t,han the no-power 35 Interval 217a by the effective delay 219a of the braklng pulse 213a.
Referring now to FIGURE 4, a conveyance, or electric wheelchair 360, is slmilar to the wheelchair 10 of ~IGURES 1 and 2, but Includes a drive unlt 362a for drivlng a right wheel, or propulsion 1~9~796 element 12a, and a simllar drlve unit, not shown, for driving the left wheel 12b of FIGURES 1 and 2.
The drive unlt 362a includes the electrlc motor 26a and a power transmlssion 364a. A similar power transmission, not shown, is used for 5 drlvlng the left wheel 12b of FIGURES 1 and 2.
The electric motor 26a of FIGURE 4 Is ldentical to the electric motor 26a of the other drawings, except a motor shaft 366a Is longer than shown In the other drawings. For simplicity, the number of the electric motor of FIGURE 4 has been kept the same as the electric 10 motors In the other drawings.
The power transmission 364a includes a flrst stage reduction 368a and a second stage reduction 370a. The first stage reduction Includes a drlve pulley 372 that is attached to the motor shaft 366a, a driven pulley 374, and a belt 376. The second stage Includes a drlv,e 15 gear 378 and a drlven gear 880.
l'he wheel 12a Is rotatably attached to a mountlng plate 382a of a wheelchair frame 384 by a shoulder bolt 386, a spaclng washer 387, and a nut 388.
An adapter p]ate 390a of the drive unit 362a Is attached to the 20 mountlng plate 382a of the wheelchair 360 by the shoulder bolt 386, the nut 388, and R bolt 392; nnd the motor 26a Is attsched to the adapter plate 390a by bolts 394.
Both the drlven pulley 374 and the drive gear 378 are fixedly secured to an Idler shaft 396. The idler shaft 396 Is rotatably mounted 25 to the adapter plate 390a. hy ball bearings 397, a houslng 398, bolts 400, and a retalnlng rlng 402.
The drlven gear 380 includes a hub 404 that abuts the wheel 12a, and that Is attached to the wheel 12a by bolts 406.
In a preferred design, the first stage reduction iB 6: 1; and the 30 second stage reduction is 8: 1.
Referring agaln to FIGURES 9, lO, and 12, the clrcultry shown thereln Includes manual-propulsion mode switches 408a and 408b. When the swltches 408a and 408b are in their open or disengaged posltlons, as shown, the motors 26a and 26b cannot be shorted and made to provlde 35 dynamlc braking.
Therefore, by openlng the switches 408a and 408b, the wheelchair 360 can be manually propelled without dynamic braklng occurring. I~owever, except when the swltches 408a and 408b are 2fi opened, dynamlc braking provides considerable safety from runaway condltlons, even though a parking brake, not shown, but typlcally Included on all wheelchalrs, has inadvertently been left unset.
Further, by provldlng dynamic braking, as descrlbed hereln, by 5 providing means for di~sengaging the dynamic braking, as descrlbed above, and by providing an efficient drive unit, such as the drive unit 362a, it is not necessary to provlde means for releasing the mechanlcal drive before manually-propelling the wheelchair.
There are two advantages: one is that the cost and complexity 10 of a release mechanlsm for the power transmission Is obvlated; and the other is that the dynamic braklng of the wheelchair is always effectlve to prevent runaway situat;ions, except when the manual-propulsion swltches are Intentionally opened.
In actual tests, with the swltches 408a and 408b open to 15 establlsh the manually-propelled mode, with a wheelchalr 360 that welghed 30.4 kllograms (67 pounds), and with an occupant that weighed 56.7 kllograms (125 pounds), lt required 3.63 kllograms (8 pounds) to manually-propel the wheeichair wlth the drlve unit 362a engaged at approxlmately 3.2 kilometers/hour (2 miles/hour), and 1.8 kilograms (4 20 pounds) to manually propel the wheelchalr 360 with the drlve unit dlsengaged .
It Is belleved that even thls modest force that is requlred to manually-propel the wheelchalr 360 can be reduced by further refinement of the design of the drive unit 362a.
26 In contrast, an electrlc wheelchalr Or a competitor, that weighs about 66.7 kilograms (125 pounds), wlth an occupant of 66.7 kilograms (125 pounds), requlred 10.0 kilograms (22 pounds) for manual propulsion.
Other competitlve designs of electrlc wheelchalrs require such hlgh forces to be manually propelled that it is virtually impossible to 30 manually propel them.
In the parklng mode, wlth the switches 408a and 408b closed, It required 10 kllograms (22 pounds) to manually propel the wheelchalr 360 wlth an occupant Or 56.7 kllograms (125 pounds) at 3.2 kilometers/hour (2 miles/hour).
36 Thus, the dynamic braklng, of the embodlment which has been described, provlded a deceleratlng force of about 6.3 kilograms (14 pounds) at 3.2 kilometers/hollr (2 miles/hour); and the dynamlc braklng is considerably greater at larger .speeds. Therefore, the dynamlc braklng 27 1'~ 796 of the present invent}on provldes considerable safety from dangerous run away conditions.
Referring again to FIGURES 1 and 2, the wheelchalr 10 includes hand-rlms 410a and 410b. The hand-rims 410a and 410b are also used wlth the wheelchair 360. Therefore, the hand-rims 410a and 410b serve as a manual self-propelllng means for use In a propulsion mode that lncludes openlng the fiwitches 408a and 408b.
For purpos2s Or understanding the appended clalms, a flrst electric embodiment of the invention includes a motor control 332a 10 whlch Includes all Or the components of the motor drlve 90a of FIGURE
9 except for the potentiometer 76a and the electrlc motor 26a, and includes the sawtoot h generator 72 of FIGURE 6.
A second electrlc embodlment includes a motor control 334a, includes the sawtoot;h generator 72 of FIGURE 6, and Includes all Or the 15 components of the motor drlve 268a of FIGURE 12 except for the potentlometer 76a and the electrlc motor 26a.
In the hydraulic embodlment, a motor control 336a includes the sawtooth generator 72 Or FIGURE 6, and Includes all of the components of the motor drlve 230a of FIGURE 11 except for the potentlometer 76a 20 and the fluid motor 232a.
While the motors 26a and 232a have been shown as rotary motors, it wlll be apparent that the present invention wlll provlde differentlal control llmlting for changes In llnear velocity of linear motors as well. Therefore, the word motor is to be construed In Its 25 broader sense of an actuator whlch Is elther rotary or llnear.
The hydraullc embodlment of FIGURE 11 Includes a source of fluld power 338a which includes the pump 242a and the reservolr 244a.
The motor control 332a of FIGURES 6 and 9 Includes both a power control, or driving voltage control, 340a and an electronlc control 30 342a. The power control 340a Includes the translstors 138a and 140a, the translstor 198a, the FET 168a, and the relays 144a and 148a.
The electronlc control 342a of FIGURES 6 and 9 includes the ampllflers 104a and 106a, the comparators 130a and 132a, the potentlometer 172a, the comparator 176a, and the sawtooth generator 72.
36 The motor control 334a of FIGURES 6 and 12 Includes both a power control, or drlvlng voltage control, 344a, and an electronlc control 346a.

In llke manner, the motor control 336a of FIGURES 6 and 11 Includes both a power control 348a and electronlc control 350a.
The power control 344a of FIGURE 12 Includes the translstors 290a and 312a and the FETS 296a and ~04a; and the power control 348a 6 o~ FIGURE 11 includes the transistor 138a, the transistor 140a, the FET
168a, the directional control valve 234a, and the proportional output valve 248a.
The manual control 7~, includes the potentiometers 76a and 76b, the control lever 54, and any mechanism that lnterconnects the control 10 lever 54 to the potentiometers 76a and 76b.
The embodiment of FIGURE 9 includes a motor loading means 354a which Includes the FET 170a, and the embodlment of FIGURE 12 includes a motor loading means 356a which includes the FET 294a.
The sawtooth generator 72 of FIGURE 6 cooperates with the 15 comparator 176a Or FIGURE 9 to provide a pulse-wldth modulator. In like manner, the sawtooth generator 72 cooperates with the comparator 274a of FIGURF, 12 to provide a pulse-wldth modulator.
The sawtooth generator 72 also cooperates with the comparator 274a to modulate the width 215a of the dynamic braking pulses 213a 20 because modulatlng the pulses 207a of the drlving voltage 209a Inversely modulates the width 216a of the dynamlc braking pulses.
In summary, the present invention provides apparatus and method for providlng a conveyance, a motor drlve, and a control, in whlch: dynamlc braklng Is provlded by shortlng the motor wlnding durlng 26 a portion Or the interval- between power pulses; differentlal control llmltlng ls provlded that assures ease and accuracy of manual control by llmltlng the rate Or change in the difrerence of power that can be supplied to one motor wlth respect to the other motor; power-off braklng is achleved by shorting the motor winding when no power pulses 30 are belng supplled to the motors; extended relay llfe ls achleved by transmlttlng power to the motors only when the relay contacts are closed; and a solld-state switching devlce ls provided that ls controlled by a slgnal in a single conductor and that provldes an effectlve delay in swltchlng.
Differentlal control llmiting is appllcable to both electric and fluld motors; dynamlc braking is applicable to any electric motor that can f~lrlction as an electrically loaded generator and that i6 driven by voltage pulses wlletiler width-modulated, amplltude-modulated, or ';'96 unmodulated; power-off braking is applicable to various uses, particularly wlth reverslng motors; and the circuitry for Increasing relay life is particularly applicable to reversible electrlc motors.
While speclfic apparatus and parameters have been disclosed In 6 the preceding description, it should be understood that these specifics have been given for the purpose of disclosing the principles Or the present invention and that many variations thereof will become apparent to those who are versed in the art. Therefore, the scope of the present invention is to be determined by the appended claims and the recitatlons 10 thereof.

_dustrial ApPlicability The present invention is appllcable to conveyances in whlch leM
and right traction elements are separately and varlably controlled by left and right electric or fluid motors, is applicable to conveyances in which 15 dynamlc braklng of electric motors Is needed, and is applicable to conveyances in which the operator has hand tremors.

Claims (23)

Claims The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A conveyance having a propulsion element, having an electric motor, having a power transmission that drivingly connects said electric motor to said propulsion element, having motor control means for supplying a driving voltage to said motor, and having means for selectively discontinuing said supplying of said driving voltage to said electric motor, the improvement which comprises:
means, comprising said power transmission, for allowing said propulsion element to drive said motor;
parking mode means for making said motor function as an electrically loaded generator when said propulsion element is driving said motor and said supplying of said driving voltage is discontinued; and means for selectively inactivating said parking mode means.
2. A conveyance as claimed in Claim 1 in which said driving voltage comprises a plurality of pulses.
3. A conveyance as claimed in Claim 1 in which said motor control means comprises a solid-state device and said motor control means includes means for making said solid-state device turn on more slowly than said solid-state device turns off.
4. A conveyance as claimed in Claim 1 in which said motor control means comprises first and second solid-state devices; and said motor control means includes means. comprising a resistor and a diode, for making one of said solid-state devices turn on more slowly than the other of said solid-state devices turns off.
6. A conveyance as claimed in Claim 1 in which said conveyance includes a second propulsion element and a second electric motor that is drivingly connected to said second propulsion element, and said conveyance further comprises:

means, comprising a second motor control that is operatively connected to said second motor, for supplying a driving voltage to said second motor;
means for separately and selectively modulating said driving voltages supplied to said motors; and means for limiting the rate of change in differences in modulating said driving voltage supplied to said motors while permitting larger changes in modulating said driving voltage when said changes in modulating are generally equal.
6. A conveyance as claimed in Claim 1 in which said driving voltage comprises a plurality of pulses;
said conveyance comprises means, being operatively connected to said motor, for applying a plurality of electrical dynamic braking pulses to said motor; and said motor control means comprises means for interspersing said dynamic braking pulses and said driving-voltage pulses.
7. A conveyance as claimed in Claim 6 in which said motor control means includes means for modulating one of said plurality of pulses.
8. A conveyance as claimed in Claim 6 in which said motor includes a motor winding having first and second ends; and said means for applying said dynamic braking pulses to said motor comprises means for providing an electrical flow path between said ends of said motor winding.
9. A conveyance as claimed in Claim 6 in which said motor includes a motor winding having first and second ends;
said means for applying said dynamic braking pulses to said motor comprises means for providing an electrical flow path between said ends of said motor winding;
said motor control means includes means for pulse-width modulating said driving-voltage pulses; and said motor control means includes means for inversely pulse-width modulating said dynamic braking pulses with respect to said driving-voltage pulses.
10. A conveyance as claimed in Claim 6 in which said motor control means comprises a first solid-state device;
said means for applying said dynamic braking pulses to said motor comprises a second solid-state device: and said motor control means includes means, comprising a resistor and a diode, for making one of said solid-state devices turn on more slowly in response to a change in the magnitude of a signal in one direction than the other of said solid-state devices turns off in response to a change in the magnitude of said signal in said one direction.
11. A conveyance as claimed in Claim 6 in which said motor control means includes means, comprising a resistor and a diode, for effectively providing an interval between one of said pulses of driving voltage and an adjacent one of said dynamic braking pulses.
12. A conveyance as claimed in Claim 6 in which said motor control means comprises a solid-state device having a parasitic capacitance; and said motor control means includes means, comprising a resistor, a diode, and said parasitic capacitance, for effectively providing an interval between one of said pulses of driving voltage and an adjacent one of said dynamic braking pulses.
13. A conveyance as claimed in Claim 6 in which said conveyance includes a second propulsion element and a second electric motor that is drivingly connected to said second propulsion element, and said conveyance comprises:
means, comprising a second motor control that is operatively connected to said second motor, for supplying pulses of a driving voltage to said second motor;
means for separately and selectively modulating said pulses of driving voltages supplied to said motors; and means for limiting the rate of change in differences in modulating said pulses of driving voltage supplied to said motors while permitting larger changes in modulating said pulses when said changes in modulating are generally equal.
14. A method specially adapted for electrically propelling braking, and manually-propelling a conveyance that includes a propulsion element, an electric motor, and a power transmission that drivingly connects said electric motor to said propulsion element, which method comprises the steps of:
a) supplying a driving voltage to said motor;
b) selectively isolating said motor from said driving voltage;
c) allowing said propulsion element to drive said motor through said power transmission;
d) causing said motor to function as an electrically loaded generator when said propulsion element drives said motor;
e) selectively inactivating said causing step; and f) manually propelling said conveyance.
15. A method as claimed in Claim 14 in which said conveyance includes a solid-state device; and said method further comprises the step of making said solid-state device turn on more slowly than said solid-state device turns off.
16. A conveyance as claimed in Claim 14 in which said method includes first and second solid-state devices; and said method further comprises the step of making one of said solid-state devices turn on more slowly in response to a change in magnitude of a signal in one direction than the other of said solid-state devices turns off in response to change of said signal in said one direction.
17. A method as claimed in Claim 14 in which said conveyance includes a second propulsion element and a second electric motor that is drivingly connected to said second propulsion element and that is supplied with a driving voltage, and said method further comprises the steps of:
a) selectively and separately modulating said driving voltages supplied to said motors;
b) limiting the rate of change in differences in modulating said driving voltage supplied to said motor; and c) permitting larger changes in modulating said driving voltage when said changes in modulating are generally equal.
18. A method as claimed in Claim 14 in which said supplying of said driving voltage comprises supplying a plurality or driving-voltage pulses, and said method further comprises the steps of:
a) applying a plurality of electrical dynamic braking pulses to said motor; and b) interspersing said dynamic braking pulses and said driving-voltage pulses.
19. A method as claimed in Claim 18 in which said method further comprises the step of modulating one of said plurality of pulses.
20. A method as claimed in Claim 18 in which said method further comprises the steps of:
a) pulse-width modulating said driving-voltage pulses; and b) inversely pulse-width modulating said dynamic braking pulses with respect to said modulating of said driving-voltage pulses.
21. A method as claimed in Claim 18 in which said conveyance includes first and second solid-state devices:
a) said method further comprises the step or providing an interval between said pulses; and b) said providing step comprises the step of making one of said solid-state devices turn on more slowly than said one solid-state device turns off.
22. A method as claimed in Claim 18 in which said method further comprises the step of providing an interval between one of said pulses of said driving voltage and an adjacent one of said dynamic braking pulses, and said providing step comprises:
a) restricting the rate of increase of a first signal;
b) allowing a greater rate of decrease of said first signal than said restricted rate of increase;
c) restricting the rate of decrease of a second signal; and d) allowing a greater rate of increase of said second signal than said restricted rate of decrease.
23. A method as claimed in Claim 18 in which said conveyance includes a second propulsion element and a second electric motor that is drivingly connected to said second propulsion element, and said method further comprises the steps of:
a) supplying pulses of a driving voltage to said second motor;
b) separately and selectively modulating said pulses of driving voltages supplied to said motors;
c) limiting the rate of change in differences in modulating said pulses of driving voltage supplied to said motors; and d) permitting larger changes in modulating said pulses when said changes in modulating are generally equal.
CA000550682A 1986-11-04 1987-10-30 Electronic motor control system for conveyance such as a wheelchair Expired - Lifetime CA1292796C (en)

Applications Claiming Priority (2)

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US06/927,273 1986-11-04
US06/927,273 US4906906A (en) 1986-11-04 1986-11-04 Conveyance with electronic control for left and right motors

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CA000550655A Expired - Lifetime CA1292795C (en) 1986-11-04 1987-10-30 Conveyance with electronic control for left and right motors

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EP (1) EP0328546A1 (en)
AU (1) AU8172587A (en)
CA (2) CA1292796C (en)
NZ (1) NZ222430A (en)
WO (1) WO1988003400A1 (en)

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Publication number Publication date
EP0328546A1 (en) 1989-08-23
US4906906A (en) 1990-03-06
WO1988003400A1 (en) 1988-05-19
CA1292795C (en) 1991-12-03
AU8172587A (en) 1988-06-01
US4978899A (en) 1990-12-18
NZ222430A (en) 1990-03-27

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