GB2291204A

GB2291204A - Object sensing apparatus

Info

Publication number: GB2291204A
Application number: GB9513852A
Authority: GB
Inventors: Kazunori Kawashima; Hajime Oda
Original assignee: Seikosha KK
Current assignee: Seikosha KK
Priority date: 1994-07-08
Filing date: 1995-07-07
Publication date: 1996-01-17
Also published as: JPH0821741A; DE19524884A1; FR2722287A1; GB9513852D0

Description

2291204 OBJECT SENSING APPARATUS The present invention relates to an

apparatus for sensing an object approaching or receding from the sensing apparatus. 5 More specifically, the present invention relates to an object sensing apparatus utilising the change in capacitance caused by movement of the object towards or away from the sensing apparatus. Japanese Utility Model Publication No. 63-36246 discloses such an object sensing apparatus.

In this known object sensing apparatus the detecting electrode is connected to a pulse delay circuit so that when an object approaches the detecting electrode, the delay time of the pulse is changed in response to variations in the capacitance between the detecting electrode and the ground. When the pulse delay time exceeds a reference delay time, the output signal is inverted.

The known object sensing apparatus has the merit that when the object approaches within a detection distance range of the sensing apparatus, the output signal maintains the inverted state. However this known object sensing apparatus has the disadvantage that its performance is greatly affected by changes in the ambient temperature or ambient humidity.

That is, when the temperature and humidity are changed, the detected distance varies. In the worst condition, even when no object is present, the output signal would be inverted or, even if the object approaches very close to the sensing apparatus, the output signal would not be inverted. Furthermore when the temperature suddenly changes, and condensation occurs, the output signal would be inverted.

The present invention seeks to overcome the above described problems, and to provide an object sensing apparatus capable of certainly sensing a close location of an object without any error operation even when temperature or humidity are changed and condensation occurs.

According to the present invention, there is provided an object sensing apparatus comprising a sensing circuit whose output is determined by the proximity of an object with respect to the object sensing apparatus; and output circuit means receiving the sensing circuit output and for cutputting a signal representing the sensing of an object when the rate of change of the output of the sensing circuit exceeds a predetermined rate.

For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 is a circuit block diagram showing a first embodiment of the present invention. 20 Fig. 2 is a sectional view indicating the structure of the capacitance converter of the present invention. Fig. 3 is a timing chart representing operations of the first embodiment of the present invention. 25 Fig. 4 is a circuit block diagram indicating a second embodiment of the present invention. Fig. 5 is a timing chart indicating operations of the second embodiment of the present invention. Fig. 6 is a circuit block diagram showing a third embodiment of the present invention.

Fig. 7 is a timing chart indicating operations of the third embodiment of the present invention.

The present invention will now be described in detail with reference to embodiments shown in the accompanying drawings.

In Fig. 1, there is represented a circuit diagram of a first embodiment of the present invention. In Fig. 1, symbols TRI to TR4 show transistors, symbols Cl to C9 represent capacitors, symbols Rl to R17 indicate resistors, symbols VRI and VR2 denote variable resistors, symbols Qi and Q2 show amplifiers such as operational amplifiers, and symbol D1 indicates a diode. Symbol +V is a power source, and symbol GND is the ground.

Reference numeral 4 shows a capacitance changing type converter (referred to as a "converter" hereinafter) in which a capacitor is constructed of a sensor electrode 5 made of a conductive member and a shield case 6 similarly made of a conductive member. To clarify the structure of the converter 4, an arrangement of an object sensing apparatus according to the present invention will now be explained with reference to Fig. 2.

Reference numeral 1 0 indicates a circuit board on which the circuit of Fig. is arranged. This circuit board is fixed within a metal box type shield case 6 This shield case 6 is electrically connected to a predetermined location on the circuit. The shield case 6 forms a capacitance between the sensor electrode 5 and itself, and has such a function that no external noise enters the sensor electrode and the circuit.

The sensor electrode 5 is fixed on the circuit board 1 0 with a predetermined spacim by way of a plurality of les 5b, and is also electrically connected to the circuit.

An edge portion 5 a of the sensor electrode 5 and an edge portion 6 a of the shield case 6 are arranged in such a manner that they are separated from each other by a suitable distance which is determined by considerinaobject detectable perfomE=.

Although the upper surface of the sensor electrode 5 is located on the same plane as the upper surface of the edge portion 6 a of the shield case 6 in FIC. 2, the present invention is not limited thereto.

Alternatively, a step may be provided between these upper surfaces, depending on the detectable performance. In some case, the shield case is not made in a box shape, but a metal plate may be simply located opposite to the sensor electrode 5 - The above-described shield case 6 is fixed on a case 8 made of plastic or other such material by way of a known method, and is sealed by a rear lid 9.

As shown by a dotted line of this drawing, a detection region AR, for detecting an object is normally narrowed as this detection region is separated from the sensor electrode.

nfexmca nr-en-1 1 dartes an tlp ewLlla--z drse cutp-lt I-S varied due to a change in capacitance when an obJect approaches or recedes from the converter 4. An output waveform (frequency and voltage) P1 (shown in Fig. 3) is d2t=red by tte resistanie values of the resistor RS and the variable resistor W1, ard also the capacitance value of the capacitor C2 Further, in this case, since the converter 4 is connected between the base of TR3 and the emitter thereof, if the capacitance of the converter 4 is varied when the object approaches to it, the output volta. e (P1) may be changed. It should be noted that although the shield case 6 of the converter 4 may be connected to the GNID, since the voltace between the base of the transistor and the emitter thereof is substantially constant, the converter 4 is connected between the base and the emitter, so that the capacitance of this converter 4 may be negligible under the normal condition. As a result, since only capacitance change caused by the approaching W C7 the object can be utilized, the detecting apparatus with high sensitivity can be arranged.

The transistor TR1 is such a transistor capable of improving temperature characteristics of an operation point for an ampliflier arranged by TR2, R2 and R4 The capacitor Cl is employed to stabilize the operation point of TR2 The output waveform, namely the detection sensitivity is controlled by using the VR1 Reference numeral 2 is an output discriminating circuit whose output is varied a=rdim to a relati-,ely fast in the output changes of the oscillater 1. The aztp d=mn=tu-S circuit 2 is fowed by the diode D1, the resistors R7 ard R8, tl-e capacitors C3 to C4, and the transistor TR4. Further, this discriminatin. circuit 2 is constructed of a peak value detecting circuit for holding a peak value of AC wave every substantially 1 time period, a high-pass filter constructed of the capacitor C5 and the resistors R9 and Rl 0, and an AC amplifier constructed of an amplifier Q1 the resistors Rl 1 to R1 4, and the capacitors C6 an5 C 7. The capacitor C7 is to eliminate relatively high frequency noise. The resistor Rl 3 is to speed up the charging operati acitor C 6 ion to a cap i when the po,-er source is turned ON, and to shorten the time duration until stable circuit operation is achieved.

Reference numeral 3 indicates an output circuit for converting the output waveform of the output discriminating circuit 2 into a pulse, which is arranged by a comparator constructed of an amplifier Q2, resistors R1 6 and R1 7, a variable resistor VR2 and a capacitor C9 and also a noise eliminating circuit constructed of a resistor R 1 5 and a capacitor C8 A threshold value Vth of the comparator may be controlled by the variable resistor ',-R2 Capacitor C9 is provided for stabilizir-5 the t'nlesbold value Vth.

Fig. 3 is a timing chart for indicating output voltage waveforms at the respective locaticris P1 to P6 (referred to as cutFit--, PI tc P6 of the cirmit of Fie., - 1. A time period T1 indicates an initial normal condition where no object to be detected is present. A time period T2 represents a time period during which the object approaches to the detection range of the converter 4 at a relative high speed, intercepts this detection range, and recedes from this detection range. A time period T3 indicates a time period during which ambient environments such as a temperature and humidity are gradually varied. A time period T4 shows a variation in the ambient environments which is slower than that of the time period T2, but faster than that of the time period T3. A time period T5 represents the normal condition after there is no ambient environment change.

Operations will now be described with reference to Fig. 1 to Fier. 3 Since there is no chan!ze in the condition at the time period T1, the oscillator 1 oscillates with a constant frequency and a constant amplitude, and then the output P1 is constant. The output P2 of the peak value detecting circuit arranged by the diode D1, the resistor R7, and the capacitor C3 becomes such a pulsatory current containing the high frequency components. However, the output P3 which has passed through a impedance convertin circuit and a smoothing circuit constructed of the capacitor C4 and 9 11Z the resistor R8 becomes a substantially constant DC voltage. The impedance converting circuit is employed so asnot to lower the voltage of the output P2 As a result, both of the output P4 of the high-pass filter and the output P5 of the AC amplifier also become constant DC voltages. Since the threshold value Vth of the comparator is set to be lower than the voltage of the output P5 under the normal condition, the output P6 of the comparator is the GN.D level.

In Fig. 2, considering now that an object 7 is transported in parallel with the sensor electrode 5 alone, the left direction, as viewed in this figure, to reach the detection recion AR (see solid line), and intercepts this detection region, and then is removed apart from this detection region (see waved line), such a condition is realized from the time period T1 of Fi g. 3 to the time period T2 Since the capacitance of the converter 4 is changed when the object approaches within the detecting range, the output P1 of the oscillator 1 is changed.

In response to this change, the output P3 is similarly changed. Since this change is relatively fast, the DC component is cut by the capacitor C5 for constituting the high-pass filter, so that it becomes such a differential waveform as shown in the output P4 The output P4 is further amplified by the AC amplifier to become the output P5 Only dL=ng the trm per=d vtw tw %cltag e>reed.- tte tutslold value 7th of the comparator (namely, time period during which it is lower than the threshold value Vth in Fica. 3), an output appears at the output P6.

The time period T3 illustrates the situaticn in Q-iich the cutat- P1 of ti-le oscillator 1 is gradually changed due to changes in the ambient environment Although the output P3 is a DC -,.,oltage variation, this is a slow variation and thus no output P4 is changed. As a result, the output P5 is also not changed, and no output appears at the output P6 The time period T4 represents the sit-iatien in,kdch a da in arbient environments slower than that of the time period T2 but faster than that of the time period T3 is produced. In this case, although the output P3 is also chancred, this change is slower than that of W the time period T2 Therefore, it is such a change -,x.,hich cannot be amplified by the high-pass filter and the AC amplifier. The output P5 does not exceed the threshold value Vth and no output appears at the output P6 During the time period T5, there is no change in the conditions similar to that of the time period T1, so that no output appears at the output P6.

It should be noted that it is possible to determine under which condition of the output is produced by properly setting the circuit constants of the oscillator 1 and the output discriminating. circuit 2 and also properly adjusting the threshold value Vth of the comparator in the output circuit 3 The output circuit is not limited to that shown in Fig. 1, but may be modified by employing a timer for outputting a pulse with a predetermined width.

In Fi pr. 4, i S a circuit block diagram of a second embodiment.

In Fi,_,. 4, reference numeral 4 1 is an oscillator arranged by resistors R4 Z1 CD to R4 5, a diode D4 1, a comparator Q4 1, and the converter 4 identical to that of the above-described embodiment. A duty ratio of an output pulse waveform is varied by a change in capacitance caused when an object is located close to the sensor electrode 5 of the converter 4, or located remote from this sensor electrode 5 In this circuit, the shield case 6 of the converter 4 is connected to the GNID.

Reference numeral 4 2 shows an output discriminating, circuit whose output is ne CU: j chanzed in resPcr-:-- t', mlat::i-e17i fast &-T-,ges iPI t: tP, -- (--f the oscillator 41.

The output discriminating circuit 4 2 is arranged by a smoothing circuit constructed of a resistor R4 6 and a capacitor C4 1, and an AC amplifier constructed of an amplifier Q4 2, resistors R4 7 to R5 1 and capacitors C4 2 to c4 3 The capacitor C4 3 is to eliminate relatively high frequency noise. The resistor R5 0 is to shorten the charging operation to the capacitor C4 2 when the power source is turned ON, and to shorten the ttm cliraticn uitil the circuit q:amtim is stabilimd.

Reference numeral 4 3 is a first output circuit constructed of a comparator, a timer, a waveform shaping circuit. The threshold value Vth2 of the comparator can be controlled by a variable resistor VR4 1 When the output voltage of the output discriminatin. circuit 4 2 is higher than the threshold value Vth2, a pulse is outputted C to an output terminal OUT1.

Similarly, reference numeral 4 4 is a second output circuit constructed of a comparator, a timer, and a waveform shaping circuit and so on. A threshold value Vth 3 of the comparator can be controlled by a variable resistor VR4 2 When the output voltage of the output discriminating circuit 4 2 is lower than the threshold value VtU W a pulse is outputted to an output terminal OUT2 Fig. 5 is a timing chart for indicating output voltage waveforms of the respective P4 1 to P4 6 in the circuit of Fig. 4 (referúed to as outputs P4 1 to P4 6 hereinafter). A time period T4 1 indicates such an inlitial normal condition that there is no detected object. A time period T4 2 shows a time period duning which an object approaches the detection rance of the converter 4 at a relatively high speed, intercepts this range, and recedes from this range. A time period T4 3 indicates a normal condition after there is no change in the ambient environments.

When the object comes close to the sensor electrode 5 (a point tA of F1g 5 the capacitance of the converter 4 is changed, and the duty ratio of the pulse of the output P4 1 from the oscillator 4 1 is reduced.. so that the voltage of the output P4 2 is reduced by the smoothing circuit. The output P4 3 is a differential Ywak-l= fcmed by the capacitor C42 from only the voltage changing c=-,t of ths cutput P42. output P43 is airplified by the =plifier. Finall,,,, the output P44 of the AC amplifier is increased higher than the normal voltage level, and then is returned to the oriainal value. At this time, when the voltage of the output P4 4 becomes hiaher than, or equal to the threshold value Vth2, an output P4 5 having a predetermined width can be obtained in the first output circuit.

Conversely, when the object recedes from the sensor electrode 5 (a point tB of Fig. 5), the capacitance of the converter 4 is varied, and the duty ratio of the pulse of the output P4 1 from the oscillator 4 1 is returned to the original duty ratio.

Accordingly, the voltage of the output P4 2 is returned to the original value, and becomes such a differential waveform P4 3 is fd=-:5= enly the ,Dltag-=, disinging =pxúnt of the ojdzut P42. S=lar to fw sitiatim in -Auch frr:t w3ect c- R=ad-ús the --er=, Toitacj-- P43 is aTplilled by the arplifier. tisn the aitp-t- P44 of t -zC aplifier d-jai such that the level of the output is lower than the nornal voltage level and then is returned to the oricrInal value. At this time, when the voltage of the output P4 4 becomes lower than the threshold value -Vth3, the output P4 6 having a predetermined width is obtained in the second output circuit. With respect to a slow change in ambient environments, similar to the first embodiment, since the circuit constant has been set in such a manner that the volta2e change of P4 4 is located between the threshold values Vth2 and Vth3, the outputs P4 5 and P4 6 are not chan2ed.

It should be noted that in F12. 4, it is possible to em, ploy a third output circuit (for example, a set!reset 'iilp-top circul"tE.) having an output P4 7 (OUT 3), which is set by the output P4 5 and reset by the output P4 6. Also, similar to the known object sensing apparatus, the signal may be maintained and outputted while the object is located near the sensor electrode.

It should be understood in the above-described embodiment that the outputs OUT1, OUT2, OUT3 may be solely employed, or arbitrarily combined with each other to constitute the actual apparatus.

Fig. 6 is a circuit block diagram of a third embodiment, and Fie'. 7 is a timing chart for showing voltage waveforms at a major portion. The same reference numerals shown in Fig. 4 will be employed as those for indicating the same elements in Fiol. 6 W In Fig. 6, reference numeral 6 4 is a first integrating circuit formed by a resistor 6 1 and a capacitor C6 1 Reference numeral 6 5 is a second integrating circuit constructed of a resistor R6 2 and a capacitor C6 2 - The integral constant of the second integrating circuit is selected to be larger than that of the first intearatine, circuit. In the embodiment, the resistance value of the resistor R6 1 is equal to that of the resistor R6 2, and the capacitance of the capacitor C6 2 is selected to be larger than that of the capacitor C6 1. A differential amplifier is arranged by an amplifier Q6 1, a resistor R6 3, and a capacitor C6 3. Thus, the output discriminating circuit 6 2 is constructed of the first and second integrating circuits 64, 65 and the differential arrplifier.

Now, when the object comes close to the sensor electrode 5 of the converter 4 (a point tA of Fig. 7), the capacitance of the converter 4 is changed, and the duty ratio of the pulse of the output P4 1 of the oscillator 4 1 is reduced. The output P 4 1 of the oscillator 4 1 is connected to the first and second integrating circuits The reduction of the duty ratio is converted the reduction of the voltage by the integrating circuits As shown in L, P of Fig. 7, the output P6 2 teccires the nnmal valw after tilre L, tl, whereas the output p6 3 b=w the =Tal value after tl-e tlm L\ t2.

il a state- cc= W-er= the WItaPe Of the = P63 's hic#= t= the vOltage of the waveform P6 2. Conversely, when the object is located remote from the sensor electrode (a point tB of Fig. 7), such a state is re,. in that the wltag-- of the v,-nl?ef= P6 3 is lower than the voltage of the waveform P6 2 The outputs of these two integrating circuits are substantially equal to each other, or a very small difference between them when the object is neither located close to er = rmetely f= the sensing electrcd--, and when the change caused by the environment variation is slow. Thus, there is a very small output variation in the differential amplifier. As a result, the output P6 4 of the differential amplifier is changed as P6 4 shown in Fig. 7 Similar to the second embodiment, when the object comes close to and rejedes f= the ser=, the cutp-t- can be dDtairúd f= each of the teiinirals OUT1 and OUT2.

It should be noted that the oscillator circuit is not limited to the above-explained oscillator, but may be realized by such a circuit to which the converter 4 can be connected and whose output is changed by the capacitance change. Also, the output discriminator may be substituted by such an output discriminator whose output is not changed when the output change of the oscillator is relatively slow, and whose output is largely changed when the output change of the oscillator is relatively quick.

Also, the output circuit may be substituted by such an output circuit capable of converting the output of the output dscriminating circuit into a pulse having a predetermined voltage, current, and width. Further, a circuit may be additionally provided for prohibiting the output while the power source is turned ON.

According to the arrangement of the present invention, only when an object approaches to, or recedes from the sensing range of the object sensing apparatus at a predetermined speed, and only when such a sudden chancre occurs in a state under which the object passes through the sensiner ran-c, the output appears at the output terminal. Even when a slow state chancre occurs, no output appears. Normally, a chancre in Z.) temperatures and humidity is slower than a chancre caused when the object comes close to the scrisin. ranee, so that it is possible to arrancre the object sensing apparatus capable of preventing the adverse influences caused by the temperarure/humidity variations.

Also, since the proper circuit constants are set, even when condensation occurs due to rapid temperature/humidity variations, it is possible to construct such an object sensing apparatus without any erroneous operation.

Furthermore, it is detectable whether the object approaches to, or recedes from the object sensing apparatus.

Claims

1. An object sensing apparatus comprising a sensing circuit whose output is determined by the proximity of an object with respect to the object sensing apparatus; and output circuit means receiving the sensing circuit output and for outputting a signal representing the sensing of an object when the rate of change of the output of the sensing circuit exceeds a predetermined rate.

2. An object sensing apparatus as claimed in claim 1 wherein the sensing circuit includes a capacitance changing type converter device.

3. An object sensing apparatus as claimed in claim 2 wherein the capacitance changing type converter device comprises a sensor electrode and a shield case.

4. An object sensing apparatus as claimed in one of claims 2 or 3 wherein the sensing circuit also includes an oscillator, the output of the oscillator being determined by the capacitance of the capacitance changing type converter device.

5. An object sensing apparatus as claimed in claim 4 wherein the duty ratio of the oscillator is varied subject to the output of the converter device.

6. An object sensing apparatus as claimed in one of claims 1-5, wherein the output circuit means further comprises an output discriminating circuit connected to the output of the sensing circuit, the discriminating circuit output being indicative of the rate at which the output of the sensing circuit changes, and wherein the output circuit means compares the output of the output discriminat-Lni cIrcuit with a threshold value.

7. An object sensing apparatus as claimed in claim 6 wherein the output discriminating circuit comprises a peak value circuit.

8. An object sensing apparatus as claimed in -is- claim 6 when dependent on one of claims 4 or 5 wherein the output discriminating circuit comprises a smoothing circuit to obtain a signal representative of the duty ratio of the oscillator.

9. An object sensing apparatus as claimed in claim 8 wherein the output discriminating circuit comprises first and second circuit means, the second circuit means having a longer time constant than the first, wherein the magnitude of the difference between the first and second circuit means is supplied as an indication of the rate of change.

10. An object sensing apparatus as claimed in claim 9 wherein the output discriminating circuit also comprises a differential amplifier connected to the outputs of the first and second circuit means.

11. An object sensing apparatus as claimed in one of claims 6-10 comprising a first and second comparator for comparing the output of the output discriminating circuit with a first and second threshold, respectively, wherein the outputs of the first and second comparators are connected to the set and reset inputs of a flip flop respectively, wherein the output of the flip flop indicates the presence or absence of an object near to the object sensing apparatus. 25

12. An object sensing apparatus comprising: an oscillator including a capacitance changing type converter device composed of a sensor electrode and a shield case, whose output is varied in response to a change in a capacitance, which is caused when an object approaches to the capacitance changing type converter, or recedes from the capacitance changing type converter; an output discriminating circuit whose output is not varied as to when an output changing ratio of said oscillator is lower than, or equal to a predetermined value, and whose output is varied as to when the output changing ratio exceeds said predetermined value; and an output circuit for converting the output from said output discriminating circuit into a predetermined out,Put. 5

13. An object sensing apparatus as claimed in claim 12, further comprising: a first output circuit for generating a predetermined output pulse when said object sensing apparatus senses that the object approaches to said object sensing apparatus; and a second output circuit for generating a predetermined output pulse when said object sensing apparatus senses that the object recedes from said object sensing apparatus.

is

14. An object sensing apparatus as claimed in claim 13, further comprising:

a third output circuit for generating such an output pulse that when said object sensing apparatus senses the approaching of said object, said output pulse is raised, and when said object sensing apparatus senses the receding of said object, said output pulse falls.

15. An object sensing device substantially as herein described with reference to Figs. 1-3, or 2, 4 and 5, or 2, 6 and 7 of the accompanying drawings.