WO1994020325A1

WO1994020325A1 - Drive control device for a vehicle, in particular for a wheelchair, and vehicle provided with such a drive control device

Info

Publication number: WO1994020325A1
Application number: PCT/NL1994/000050
Authority: WO
Inventors: Arnoldus Marinus Johannes Van Der Vorst
Original assignee: Ligtvoet Products B.V.
Priority date: 1993-03-05
Filing date: 1994-03-01
Publication date: 1994-09-15
Also published as: NL9300400A; AU6221494A

Abstract

Drive control device for a vehicle, in particular for a wheelchair. The vehicle has two drive wheels which can each be driven by an electric motor, and at least one swivellable running wheel which can assume an angular position with respect to a reference axis of the vehicle. The drive control device comprises an operating unit and a control unit. The operating unit feeds two operating signals representing the desired speed and direction of the vehicle to the control unit. The control unit outputs an output signal to each electric motor. The drive control device furthermore comprises a sensor which feeds a wheel-position signal representing the angular position of a swivellable running wheel to the control unit. The control unit has a first control circuit which determines the output signals as a function of the first operating signal and the second operating signal and the wheel-position signal in such a way that the actual direction of the vehicle is adjusted to the desired direction. The drive control device furthermore comprises an electrical wheel steering device which can be linked to a swivellable running wheel of the vehicle.

Description

Drive control device for a vehicle, in particular for a wheelchair, and vehicle provided with such a drive control device.

The invention relates to a drive control device for a vehicle, in particular a wheelchair, in accordance with the preamble of claim 1. The invention also relates to a vehicle provided with such a drive control device. A drive control device for a vehicle of the type mentioned in the preamble is disclosed in US 4,549,624. This publication describes a drive control device which is used in a wheelchair. By operating the operating unit with the aid of a so-called "joystick", the wheelchair driver is able to set the wheelchair in motion and control it. For this purpose, the operating unit feeds the first operating signal and the second operating signal to the control unit.

In practise, situations regularly occur in which external causes are able to deflect a vehicle of the abovementioned type from its track intended by the vehicle driver. This occurs, inter alia, when travelling over a supporting surface which has different properties or a different profile at the position of one drive wheel than at the position of the other drive wheel, for example if one of the two drive wheels is driven over an elevation or the like. These external causes may result in an undesirable alteration of the direction of the vehicle, as a result of which the direction of the vehicle has to be corrected by the vehicle driver. In particular, in the case of a wheelchair whose directional stability is low as a consequence of the short distance between the drive wheels and the running wheels, this has the disadvantage that, when the wheelchair is used out of doors, small corrections are frequently required when steering the wheelchair. For many wheelchair drivers, this is very difficult to carry out.

To maintain the wheelchair on a straight line course (notwhitstanding the terrain may be uneven) the known drive control device comprises a sensor which is provided with means for determining a wheel-position signal representing the angle between a swivellable running wheel of the wheelchair and the reference axis, formed by the central longitudinal axis, of the wheelchair, and which is provided with means for feeding the wheel-position signal to the control unit. The control unit has a first control circuit which is provided with means for determining a wheel-position difference signal as a function of a reference signal and the wheel-position signal, which wheel-position difference signal represents the difference between the straight line course desired by the vehicle driver and the actual direction, associated with the respective angular position of the running wheel, of the wheelchair, and with means for determining the first output signal and second output signal of the control unit as a function of the first operating signal and the wheel- position difference signal in such a way that the actual direction of the vehicle is adjusted by the first control circuit to the desired direction and the wheel-position difference signal is minimized.

If the actual direction of the wheelchair alters as a consequence of an external cause, for example an unevenness in the supporting surface, this alteration will lead to an alteration, dependent thereon, of the angular position, with respect to the reference axis of the wheelchair, of the swivellable running wheel associated with the sensor and, therefore, to an alteration in the wheel-position signal. The first control circuit then causes mutually different values to be determined for the first output signal and the second output signal of the control unit in such a way that the drive wheels acquire a different speed of revolution and consequently alter the actual direction of the wheelchair, so that the actual direction again coincides with the straight line course direction desired by the vehicle driver. The vehicle driver does not therefore have to carry out any directional corrections himself.

The known drive control device described above is, in the case of a wheelchair, advantageous when driving out of doors, but does not provide a satisfactory drive control for manoeuvering the vehicle in more confined spaces.

The object of the present invention is therefore to eliminate the abovementioned disadvantage and to provide a drive control device for a vehicle which makes it possible to steer the vehicle in two different ways.

This object is achieved by providing a drive control device for a vehicle of the type mentioned in the preamble which is characterized in that the drive control device furthermore comprises an electrical wheel steering device which can be linked to at least one swivellable running wheel of the vehicle by interpositioning an engageable and disengageable clutch in such a way that the at least one swivellable running wheel is set to a controlled state by engaging the clutch, and the control unit has a second control circuit which comprises means for determining the first output signal and the second output signal of the control unit as a function of at least the first operating signal, means for determining a third output signal as a function of at least the second operating signal, and means for feeding the third output signal to the wheel steering device to set the angular position of the at least one swivellable running wheel, which is in the controlled state, with respect to the reference axis of the vehicle. On the one hand, the direc¬ tion of the vehicle can be altered by setting different speeds of revolution of the two drive wheels, the first control circuit being able to effect an automatic correc¬ tion of any external disturbances of the direction of the vehicle on the basis of the wheel-position signal. On the other hand, as a result of engaging the clutch between the wheel steering device and one or more swivellable running wheels, the position of said running wheels and consequently the direction of the vehicle can be altered. In the last-mentioned way, it is possible, for example, to alter the position of each swivellable running wheel coupled to the wheel steering device during a vehicle stoppage. As a result, the direction of the vehicle will alter immediately it drives off, which is desirable, in particular, in confined spaces.

Preferably, the second control circuit is provided with means for determining the first output signal and the second output signal of the control unit as a function of the first operating signal and the wheel-position signal in such a way that the speed of revolution of the first electric motor and the second electric motor are adjusted to the path to be traversed by the drive wheel coupled thereto. This achieves the result that a change in the direction of the vehicle desired by the vehicle driver is effected not only by swivelling each running wheel which is in the controlled state using the electrical wheel steering device but also by adjusting the speeds of revolution of the drive wheels. This adjustment is made in accordance with the path to be traversed by each drive wheel, which path can easily be determined on the basis of the angular position of a swivellable running wheel determined by the sensor. This results in a very favourable steering behaviour of the vehicle. Preferably, the drive control device is provided with means for activating the first control circuit if the at least one swivellable running wheel is in the freely swivellable state and for activating the second control circuit if the at least one swivellable running wheel is in the controlled state. This provides a vehicle which can be operated by the vehicle driver in the most desirable way in any practical situation.

It is furthermore advantageous if the drive control device is provided with means for activating the first control circuit if the value of the second operating signal approximately corresponds to the value representing the driving of the vehicle in a straight line. Although the drive control device described above can be advantageous in all directions of motion of the vehicle, it is sometimes undesirable when manoeuvring the vehicle, on the other hand, for the first control circuit to effect automatic corrections of the direction of the vehicle. In the case of a wheelchair, for example, it will often happen that attendant personnel move the wheelchair by hand in order to position the wheelchair with the person sitting in it. An automatic intervention of the control device is then undesirable.

The exclusive right requested also relates to a vehicle provided with a drive control device according to the invention.

The invention will be explained further below with reference to the description of a functional block diagram, shown in the drawing, of an exemplary embodiment of the drive control device according to the invention.

The drive control device comprises an operating unit 1 which is to be operated by a vehicle driver and which generates a first operating signal V representing the speed desired by the vehicle operator in the forward or reverse direction of the vehicle and a second operating signal R representing the direction desired by the vehicle driver to the left or right or straight on with respect to a reference axis of the vehicle, in this exemplary embodiment the central longitudinal axis of the vehicle. The operating unit 1 feeds both operating signals V and R to a control unit 2. The control unit 2 feeds, in turn, a first output signal Tl to a first electric motor 4 and a second output signal T2 to a second electric motor 5. In this exemplary embodiment, the first electric motor 4 is coupled to a left-hand drive wheel of the vehicle, while the second electric motor 5 is coupled to a right-hand drive wheel. The values of Tl and T2 determine the speed of revolution and the direction of rotation of the respective electric motor and consequently of the drive wheel coupled thereto. Furthermore, the drive control device comprises a sensor 7 which is coupled to a swivellable running wheel of the vehicle. The sensor 7 feeds a wheel-position signal S to the control unit 2. In this exemplary embodiment, the wheel-position signal S represents the angle, measured in one direction, between the actual angular position of the running wheel and the angular position of the running wheel when the vehicle is driven in a straight line in the forward direction.

The control unit 2 comprises a first control circuit 10 and a second control circuit 20, which will be explained further below.

The first control circuit 10 comprises a subtrac¬ tion circuit 11 which determines a wheel-position dif- ference signal R-S as a function of the first operating signal R and the wheel-position signal S. The wheel- position difference signal R-S therefore represents the difference between the direction desired by the vehicle driver and the actual direction of the vehicle associated with the angular position, determined by the sensor 7, of the running wheel coupled to the sensor. Furthermore, the first control circuit comprises a switch 12 which feeds either the wheel-position difference signal R-S or the second operating signal R out to a summing circuit 13 and a subtraction circuit 14. The position of the switch 12 is determined by a comparator 15. If the comparator 15 detects that the value of the second operating signal R approximately corresponds to the value which represents the driving of the vehicle in a straight line, the switch 12 feeds the wheel-position difference signal R-S to the summing and subtraction circuits 13, 14. The first operating signal V is also furthermore fed to the summing circuit 13 and the subtraction circuit 14, with the result that the summing circuit 13 feeds a signal L = V+K. (R-S) and the subtraction circuit 14 feeds a signal R = V+K. (R- S) to a switch unit 30 incorporated between the first control circuit 10 and the second control circuit 20, on the one hand, and the electric motors 4, 5, on the other. The gain factor K is at the same time a suitably chosen constant. The switch unit 30 can be operated by the vehicle driver from the operating unit 1.

The second control circuit 20 comprises a compara¬ tor 21 which converts the value of the first operating signal V into a logic signal V/A which represents whether the vehicle driver wishes to drive in the forward or in the reverse direction. A comparator 22 converts the value of the wheel-position signal S into a logic signal L/R which represents whether the running wheel is directed to the left or right with respect to the reference axis of the vehicle. The first operating signal V and the wheel- position signal S are fed to an absolute-value converter 23 and an absolute-value converter 24, respectively, which then feed a signal [V] and a signal [S] to an amplifier circuit 25. Here the signal [V] represents the magnitude of the desired speed and the signal [S] the smallest angle between the actual angular position of the running wheel coupled to the sensor and the angular position of said running wheel when the vehicle is driven forwards in a straight line. The amplifier circuit 25 feeds four signals to a direction-of-rotation selector 26, viz. [V], -[V], [V].K1, -[V].K1. Here the gain factor Kl is given by Kl = l-p.[S], where p is a constant which depends on some dimensions of the vehicle, such as the distance between the drive wheels and the distance between the drive wheels and the at least one swivellable running wheel. The factor p. [S] is less than 1. The direction-of-rotation selector 26 feeds two signals UL and UR to the switch unit 30. The values of UL and UR are determined by the direction-of- rotation selector on the basis of the logic signals V/A and L/R in accordance with the table below.

movement of vehicle reverse to the right/straight on reverse to the left/straight on

forward to the right/straight on

_.V_..K1 [V] forward to the left/straight on

The second control circuit 20 furthermore comprises converter 27 which converts the second operating signal R into a third output signal T3. The third output signal T3 is fed to a servomotor 40 having a servocircuit 41 which serves as wheel steering device for one or more running wheels, to be coupled thereto, of the vehicle. The coupling may be performed by engaging a clutch, for example an electromagnetic clutch (not shown) , located between the servomotor 40 and each running wheel to be coupled thereto. The clutch is preferably engaged simultaneously with the operation of the switch unit 30, with the result that, on activating the second control circuit 20, the clutch is also engaged.

The operation of the drive control device described above is as follows.

If the vehicle driver has activated the first control circuit 10 by operating the switch unit 30, it is the case for the output signals Tl and T2 of the control unit 2 that Tl = WL and T2 = R. As a result of operating the switch unit 30, the wheel steering device is also uncoupled, with the result that the at least one running wheel is in a freely swivellable state.

If the vehicle is driven in a straight line in the forward direction, the comparator 15 operates the switch 12 in such a way that the wheel-position difference signal R-S is fed to the summing and subtraction circuits 13 and 14. In the case where an external cause makes the actual direction of the vehicle deviate from the desired direction, viz. forward in a straight line, the summing circuit 13 and the subtraction circuit 14, respectively, determine the WL and WR signals so that WL = V + K. (R-S) and WR = V - K. (R-S) . As a result, the first drive motor 4 and the second drive motor 5 acquire a mutually different speed of revolution and the actual direction of the vehicle is again adjusted to the desired direction. The wheel- position difference signal R-S is minimized. The deviation from the desired direction does not therefore need to be corrected by the vehicle driver.

When driving in a direction other than the forward direction approximately in a straight line, the comparator 15 operates the switch 12 so that the second operating signal R is fed to the summing and subtraction circuits 13 and 14. The summing circuit 13 and the subtraction circuit 14 then feed a signal UR = V + K.R and UL = V - K.R, respectively, to the electric motors 4, 5. The operating signals V and R can be altered by operating the operating unit 1, as a result of which the speed and direction of the vehicle are set. A correction of external effects by the first control circuit does not then take place. If the vehicle driver has activated the second control circuit 20 by operating the switch unit 30, it is the case for the output signals Tl and T2 of the control unit that Tl = UL and T2 = UR. The clutch between the wheel steering device 40, 41 and each running wheel to be coupled thereto is also engaged by operating the switch unit 30, with the result that the at least one running wheel is in the controlled state. If the second control circuit 20 has been activated, the operation of the wheel steering device 40 is determined by the value of the third output signal T3.

For driving forwards in a straight line, it is the case for the signal [S] that [S] = 0. As a result, it is the case for the gain factor Kl that Kl = 1, as a result of which UL = [V] and UR = [V] .

For driving backwards in a straight line, it is the case for the signal [S] that [S] = 0. As a result, it is the case for the gain factor Kl that Kl = 1, as a result of which UL = -[V] and UR = -[V]. On making a turn to the right in the forward direction, it is the case that UL = [V] and UR = [V]. (l- p.[S]) . As a result, the left-hand drive wheel will have a higher speed of revolution than the left-hand drive wheel. This corresponds to the path to be traversed by the drive wheels concerned.

On making a turn to the left in the forward direction, it is the case that UL = [V] . (1-p. [S] ) and UR = [V] . As a result, the right-hand drive wheel will have a higher speed of revolution than the left-hand drive wheel. This corresponds to the path to be traversed by the drive wheels concerned.

On making a turn to the right in the backward direction, it is the case that UL = -[V] and UR = -[V].(l- p.[S]). As a result, the left-hand drive wheel will have a greater speed of revolution than the right-hand drive wheel. This corresponds to the path to be traversed by the drive wheels concerned.

On making a turn to the left in the reverse direction, it is the case that UL = -[V] . (1-p. [S] ) and UR = -[V]. As a result, the right-hand drive wheel will have a greater speed of revolution than the left-hand drive wheel. This corresponds to the path to be traversed by the drive wheels concerned. The drive control device described and in accor¬ dance with the invention can be constructed in many ways. Thus, the signals V, R and S can be analog and the control unit may be made up of analog electrical components, but one or more of said signals may also be fed in digital form to a control unit of the digital type. The output signals may also be produced in digital form.

Claims

1. Drive control device for a vehicle, in particular a wheelchair, which vehicle comprises two drive wheels which are situated on a common axis and which can be driven independently of one another by a first electric motor and a second electric motor, and at least one swivellable running wheel which has a freely swivellable state in which the running wheel can freely assume an angular position with respect to a reference axis of the vehicle, the drive control device comprising an operating unit which can be operated by the vehicle driver and a control unit, the operating unit being provided with means for feeding a first operating signal representing the speed desired by the vehicle driver in the forward and reverse direction of the vehicle and a second operating signal representing the direction desired by the vehicle driver to the left and to the right and straight on with respect to the reference axis of the vehicle to the control unit which is provided, in turn, with means for feeding a first output signal and a second output signal of the control unit to the first electric motor and the second electric motor, respectively, for setting the speed of revolution and the direction of rotation of the electric motor concerned, the drive control device furthermore comprising a sensor (7) which is provided with means for determining a wheel-position signal (S) representing the angle between a swivellable running wheel of the vehicle and the reference axis of the vehicle, and which is provided with means for feeding the wheel- position signal (S) to the control unit (2) , the control unit having a first control circuit (10) which is provided with means (11) for determining a wheel-position difference signal (R-S) as a function of the second operating signal (R) and the wheel-position signal (S) , which wheel-position difference signal represents the difference between the direction desired by the vehicle driver to the left and to the right and straight on and the actual direction, associated with the respective angular position of the running wheel, of the vehicle, and with means (13, 14) for determining the first output signal (Tl) and second output signal (T2) of the control unit as a function of the first operating signal (V) and the wheel-position difference signal (R-S) in such a way that the actual direction of the vehicle is adjusted by the first control circuit (10) to the desired direction and the wheel-position difference signal (R-S) is minimized, characterized in that the drive control device furthermore comprises an electrical wheel steering device (40, 41) which can be linked to at least one swivellable running wheel of the vehicle by interpositioning an engageable and disengageable clutch in such a way that the at least one swivellable running wheel is set to a controlled state by engaging the clutch, and in that the control unit (2) has a second control circuit (20) which comprises means for determining the first output signal (Tl) and the second output signal (T2) of the control unit (2) as a function of at least the first operating signal (V) , means (27) for determining a third output signal (T3) as a function of at least the second operating signal (R) , and means for feeding the third output signal to the wheel steering device (40, 41) to set the angular position of the at least one swivellable running wheel, which is in the controlled state, with respect to the reference axis of the vehicle.

2. Drive control device according to claim 1, characterized in that the second control circuit (20) is provided with means (21, 22, 23, 24, 25, 26) for deter¬ mining the first output signal (Tl) and the second output signal (T2) of the control unit as a function of the first operating signal (V) and the wheel-position signal (S) in such a way that the speed of revolution of the first electric motor (4) and the second electric motor (5) is adjusted to the path to be traversed by the drive wheel coupled thereto.

3. Drive control device according to claim 1 or 2, characterized in that the drive control device is provided with means (30) for activating the first control circuit (10) if the at least one swivellable running wheel is in the freely swivellable state and .for activating the second control circuit (20) if the at least one swivellable running wheel is in the controlled state.

4. Drive control device according to one or more of the preceding claims, characterized in that the drive control device is provided with means (15) for activating the first control circuit (10) if the value of the second operating signal (R) approximately corresponds to the value representing the driving of the vehicle in a straight line.

5. Vehicle, in particular a wheelchair, provided with a drive control device according to one or more of the preceding claims.