WO2009102228A2

WO2009102228A2 - Planar capacitive proximity sensor

Info

Publication number: WO2009102228A2
Application number: PCT/RS2009/000005
Authority: WO
Inventors: Boban Stojanovic
Original assignee: Boban Stojanovic
Priority date: 2008-02-14
Filing date: 2009-02-13
Publication date: 2009-08-20
Also published as: WO2009102228A3; RS20080063A

Abstract

Planar capacitive sensor consists of two electrodes, which are in the same plane, and most often, are carried out on a printed circuit board as two surfaces of a conductive material. In case there is no object of detection and since the distance between the electrodes is relatively long, capacitance that is made between the electrodes approximately equals zero. Because the electrodes are extremely thin less than 0.1mm and the area between them relatively large about 1cm, the capacitance which these electrodes make can be considered as 0. When there is no object the surface of the equivalent capacitor is somewhere near 1cm therefore C, proportionally 0.0001 times dialectic air constant plus parasitive capacitor made of two plates in the same plane which have isolator on one side (printed plate), and on the other thin varnish which coats conductor and the air. When the object is near electrodes of size about 1cm or less a capacitor is formed between the first electrode E1 and the object as well as between the object and the second electrode, E2. Total capacity between E1 and E2 is serial connection of these two capacitors. Since the surface between the electrodes and the object is now about 1 cm x 1 cm and the distance is 1 cm, capacity of the equivalent capacitor is proportional to 0.01 times dialectic air constant or some other isolator, in case electrodes are in an isolator. From the picture 1 it is seen that amplification of the capacity is about 100 times.

Description

HORIZONTAL CAPACITATTVE SENSOR

TECHNICAL FIELD

The subject of the invention, generally observed, is belonging to the field of basic electric elements, namely to horizontal capacitive sensor which is used in electronic circuit arrangements for the detection of conductors, electrolytes as well for the detection of bad insulators which have certain conductivity on small distances.

Under International Patent Classification (Int. Cl.⁸), the subject of the invention is classified by basic classification symbol HOlG 7/00 (2009.01) which relates to capacitors in which the capacitance is varied by non-mechanical means. Since the sensor according to the invention enable obtaining output voltages which may switch-on or switch-off devices connected to them, it may be classified by secondary classification symbol HOlH 21/86 (2009.01) which relates to tapping keys.

TECHNICAL PROBLEM

Technical problem which has to be resolved by subject invention consists in structure of sensor with corresponding electronic arrangement intended for the detection if extremely low capacitance, which will be distinguished by its simplicity, effectively and reliability, which is nearby enough consistent, with a low manufacturing price and extremely low consumption so that may find a large applications in the protection of home appliances, in manufacture of toys, etc. TECHNICAL BACKGROUND

Sensors are broadly used in the cases of general appliances, where nearby other usage are used as switches and tap keys. It is easy to be determined that there exist a large number of technical solutions for their realization, where are also used a different ways of their activation (by heat, mechanically, electromagnetically, by ionization, etc.). All sensors known to the author are technically rather complicated and as per a rule are used in devices which are manufactured in a considerable series therefore are reasonably expensive. Exactly these two elements were a reason to the author for his try to find a new sensor which will depreciate manufacture, but without loses in its reliability and effectively to detect changes necessary to be registered. In his earlier solution disclosed in the Serbian patent application P 2006-0439, published as WO 2008/010739 A2 24.01.2008, under title MUSIC FOR CHILDREN'S EDUCATIONAL POTTY, also is described a sensor activated by change of the capacitance between the electrodes, but in this invention were found some imperfections wherefore the author has decided on new, more current but much reliable structure, for which, after careful search through patent documentation he found that it is new, because the search, within the professional literature and within patent documentation funds, has revealed that there do not exist technical solution relevant to the subject invention.

SUMMARY OF INVENTION

The substance of the invention is a capacitive sensor consisting of two electrodes realized on the printed chip, which electrodes are overlaid by lacquer and bonded in the corresponding electric circuit consisting of six NOT inverters, resistors Rl and R2 and capacitor C2, which are mutually connected so that in case that there is no object near the sensor the output is a logic 0, respectively when we have an object near the sensor the output will be logic 1.

Novelty of this invention is represented by sensor so structured that in the interdependence of the distance between the object and the sensor are formed two serial condensers which therefore are changing the electrode capacitiveness Cx of sensor, causing excitation of an easy actuating oscillator which will oscillate with frequency proportional to 1/(Rl x Cx) and, in dependence of frequency in the corresponding electronic arrangement is formed an output voltage Vi which is used as a switch or as a tap key.

BRIEF DESCRIPTION OF DRAWINGS

For better understanding of the invention, as well for showing its practical embodiment, author refers, only for a way of an example, to the enclosed drawings related to the subject application, where: Fig. 1 represent the outlook of the subject sensor Fig. 2 represent the cross-sectional view of the sensor Fig. 3 represent the cross-sectional view for bed conductors Fig. 4 represent electric scheme of the subject sensor as tap key Fig.5 represent electric scheme of the subject sensor as meter Fig. 6 represent the flowchart of the subject sensor DISCLOSURE OF THE INVENTION

Horizontal capacitive sensor consists of two electrodes that flush and is most often , carried out on the printed plate as two surfaces of the conductor. In case there is no object of detection and since the distance between the electrodes is relatively long, the capacity consisted of the electrodes approximately equals zero. Because the electrodes are extremely thin, thinner than 0.1mm, and the distance between them relatively long, about lcm, the capacity made by the electrodes can be considered as zero, m case there is no object, the surface of the equivalent condenser is 0.1mm x 1 cm, and space between electrodes lcm, therefore C, proportionally 0.0001 times dielectric air constant plus parasitive condenser made of two plates that flush which on one side have isolator (printed plate) and on the other thin varnish that coats the conductor and the air Picture 1 and picture 2, When the object is near the electrodes of about lcm and less, it is formed between the first electrode El, the object condenser, also the body, and the other electrode

Total capacity between El and E2 is in line connection of two condensers. Since the area between the electrodes and the object is now lcm x lcm, and the distance is lcm, capacity of the equivalent condenser is proportional to 0.01 dielectric air constant or some other insulator in case electrodes are in an insulator.

Iti the Picture 1 you can see that the accretion of the capacity is a hundred times. The accretion can be higher if the distance between the object and the electrodes is smaller about lmm, then the accretion of the capacity is 1000 times.

Equivalent capacity Cx is somewhere IpF. That equivalent condenser is connected to the easily inducing oscillator which oscillates with a frequentation proportional to 1/(Rl x Cx) or 1/(SQR(LCx)). Depending on the frequency, the output voltage is log on 1 in the picture 4 when the sensor is used as a switch, Vi analogue voltage when the sensor is used as a meter. Depending on the configuration of the circuit, Horizontal capacitive sensor is consisted of a parasitive condenser Co which in case of oscillating oscillator (6) gives some f max frequency and when the capacity emerges gives some frequency which is in range NF filter or PLL and in that way gives proportional capacity.

In the picture 1 you can see the outlook of the sensor in space above which is placed an object. In the picture al is the width of the first electrode El, a3 the width of the second electrode E2, a2 distance between the electrodes, b the length of electrodes, c thickness of the carrying insulator. Horizontal capacitive sensor is described with: c- (thickness of the printed plate) about lmm, d- thickness of the electrode from the conductor ) copper on the printed plate 0.1mm, e-thin varnish which coats electrodes 0.1mm. the thickness of the conductor c and carrying insulator -d do not influence substantially on the operating of sensor. Object O can be conductor, electrolyte-liquid or bad isolator.

In picture 2 you can see cross-sectional cut of the sensor whereas the L is the distance between the object and electrodes, which is for the electrodes lcm or less.

In picture 3 you can see the cross-sectional cut of sensor for bad isolator whereas L is the distance between object and electrodes for conductors about 0.5 cm, and for bad isolators Im m and less(human body, wood, ceramics and the like) and (various salts as kitchen salt NaCl- which changes its conduction depending on moisture and the like). Sensor does not detect thin plastic, glass, air and low specific transparency materials with different dialectic constant from the air. Sensor detects thicker plastic depending on geometry and size.

Picture 4 shows electric scheme of the device as a tap key. El electrode Cx is connected to the input of NOTl inverter and Rl resistor. The output of the NOTl is connected to the input of the input NOT2 and Rc. The output of the NOT2 is connected to the input of NOT3 and the electrode E2 of the condenser Cx. The output of the NOT3is connected to the other end of the resistor Rl. NOT1,NOT2,NOT3 are also inverters and with the Rl and Cx make astabile multivibrator which oscillates with a period proportional 1/RlCx. Logic circuits of all CMOS series, which have enough amplification in transitional mode between logical levels, can be used as inverters. Resistor R2 and condenser C2 with inverter NOT4 make an integrator or NF filter. The output of the R2 is connected to the input of the NOT4 and the condenser C2. The other end of the condenser C2 is connected to the output of the inverter NOT4 and to the input of the Not5. NOT5 and N0T6 are inline connected and serve as an amplifier so that there is a logic 0 or logic 1 at the end of the circuit. When there is no object O, it's logic 0 at the input and when an object emerges Cx rises and oscillator starts to oscillate thereby if the period of oscillation is less than pass band of the integrator of NF filter of size range 1\RC at the end is logic 1. In case there is no capacity or it is too small, oscillator oscillates with a high frequency however; such signal does not pass through NF filter.

Picture 5 shows electric scheme of the device as a meter .Electrode Cx is connected to the input of the NOTl inverter and PLL input of phase-controlled loop. The output of the NOTl is connected to the N0T2 input and Rc. N0T2 output is connected to the N0T3 input and electrode e2 of the condenser Cx. The output of the NOT3 is connected to the other end of resistor Rl. N0Tl,N0T2, N0T3 are inverters and with Rl and Cx make astabile multivibrator which oscillates with a period proportional to 1/RlCx. Logical circuits of all CMOS series, which have enough amplification in transitional mode between logic levels, can be used as inverters. Central frequency of PLL loop f is set to be in rang of 1/RlCx therefore at the output of the PLL loop it would be from 0 to Vcc. Change in oscillation frequency of the astabile multivibrator caused by change in capacity Cx, changes the output voltage Vi at the output of PLL loop. INDUSTRIAL OR ANOTHER USE OF INVENTION

Industrial manufacture of the subject invention is entirely possible in electronic workshops based on technical documentation which the persons skilled in the art may easy to prepare using the specification and drawings disclosed in the subject application.

The invention is also suitable for mass production in series and tests made on prototypes have shown great rationality in using the subject sensor in home appliances, toys etc.

Boban STOJANOVIC

Claims

1. Horizontal capacitive sensor Cx (1) is characterized by the fact it consists of two plate shaped electrodes El and E2, which are not parallel but in the same plane that without the object 0(1) have minimal capacity, and with the object 0(2) give certain capacity which induces astabile multivibrator (4) which generates fixed (4) or univocal voltage Vi (5).

2. Horizontal capacitive sensor Cx (1) is characterized by the fact it detects object from the conductor (2) at distance at which the effective capacity Cx is sufficient to induce oscillator by which it makes in line condenser Cx (2) that induces osciUator(6)(4)(5) and gives certain voltage Vi.

3. Horizontal capacitive sensor is characterized bythe fact that it detects object O from isolator made of wood, plastic, ceramics, human body. (3) at distance at which the effective capacity Cx is sufficient to induce the oscillator by which it makes in line condenser Cx (2) which induces oscillator (6)(4)(5) and thereby it gives certain voltage Vi.

4. Horizontal capacitive sensor Cx (3) is characterized bythe fact it detects object and at the output it gives fixed voltage when used as a switch.

5. Horizontal capacitive sensor Cx (3) is characterized bythat it detects object and at the outlet it gives variable voltage in case a change of frequency is detected.