WO1992008947A1 - Dispositif permettant de determiner la presence et/ou les caracteristiques d'un objet ou d'une substance - Google Patents

Dispositif permettant de determiner la presence et/ou les caracteristiques d'un objet ou d'une substance Download PDF

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Publication number
WO1992008947A1
WO1992008947A1 PCT/GB1991/002021 GB9102021W WO9208947A1 WO 1992008947 A1 WO1992008947 A1 WO 1992008947A1 GB 9102021 W GB9102021 W GB 9102021W WO 9208947 A1 WO9208947 A1 WO 9208947A1
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WO
WIPO (PCT)
Prior art keywords
sensors
sensor
capacitance
slave
members
Prior art date
Application number
PCT/GB1991/002021
Other languages
English (en)
Inventor
Thomas William Bach
Original Assignee
Moonstone Designs Limited
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from GB909024965A external-priority patent/GB9024965D0/en
Priority claimed from GB909024966A external-priority patent/GB9024966D0/en
Application filed by Moonstone Designs Limited filed Critical Moonstone Designs Limited
Priority to GB9309862A priority Critical patent/GB2265720B/en
Publication of WO1992008947A1 publication Critical patent/WO1992008947A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
    • G01B7/023—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring distance between sensor and object
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/28—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring contours or curvatures
    • G01B7/287—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring contours or curvatures using a plurality of fixed, simultaneously operating transducers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/34—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring roughness or irregularity of surfaces

Definitions

  • This invention relates to a device for determining the presence and/or characteristics of an object or a sub ⁇ stance.
  • a device for determining the presence and/or char ⁇ acteristics of an object or a substance said device com ⁇ prising capacitive means, the capacitance of which is changed due to the presence and/or characteristics of said object or substance, and a circuit arrangement for detect ⁇ ing said change in capacitance, characterised in that said capacitive means comprises one or more sensors and one or more slave members positioned relative to said sensor or sensors and arranged to be driven in a predetermined phase relationship with respect thereto, such that the change in capacitance detected by said circuit arrangement is influ ⁇ enced by electrostatic coupling between said one or more sensors and said one or more slave members.
  • the characteristics of the object can be determined by analysing the responses from the one or more sensors.
  • the sensor or sen ⁇ sors will be affected by the degree of electrostatic cou ⁇ pling between the one or more slave members and the one or more sensors.
  • Buffering means may be used to enhance the sensitivity of the device and to shield the sensors from unwanted external effects.
  • the invention thus makes use of capacitive means to cha ⁇ racterise an object or substance by use of one or more slave members, preferably in the form of specially shaped pads or plates, that drive the material of the object or substance capacitively and couple to a sensor which is also preferably a pad or plate.
  • slave members preferably in the form of specially shaped pads or plates
  • These shaped plates may form a physical matched filter. The short, medium and long range effects of these plates can be exploited.
  • the device in accordance with the invention, may be used to characterise an object of any material or of a substance such as a particular chemical.
  • the invention can be used to create a new effect which is the effective grounding out of this capacitive coupling effect by objects at a far dis ⁇ tance. This allows the presence of objects or substance to be sensed at an order of magnitude greater distance than previously possible and its characteristics determined dielectrically.
  • the or each sensor is suitably driven by an oscillator of the detection circuit, the sensor response being measured either by a change in frequency or by a change in amplitude of the output of the oscillator.
  • the oscillator circuit contains a Schmitt trigger.
  • the device may include means for storing the response of the or each sensor singly and when the or each slave member is addressed, thus building up a characteristic pattern of values. This stored information may be used in conjunction with pattern match ⁇ ing, algorithmic processing, or simple switching of sensors or slave members looking for effects above or below a threshold.
  • the frequency is affected by which sensor and which slave member is addressed.
  • the frequency output is typically an analogue reflection of the object characteristics.
  • Slave members may be driven in or out of phase with respect to the sensor with the same or a different waveform to the sensor, but generally a square wave.
  • the frequency of the oscillator is affected by coupling of the currently select ⁇ ed sensor to one or more slave members, either directly or via the object being sensed.
  • Measurement by change in amplitude is suitable for certain, particularly long range, applications.
  • a slave member which is inter ⁇ nally frequency locked by the use of, for example, a ceram ⁇ ic resonator.
  • the sensor is constructed to 'track' this frequency by the use of a Phase-locked loop (PLL) .
  • PLL Phase-locked loop
  • a device for determining the presence and/or characteristics of an object or a substance comprising capacitive means, the capacitance of which is changed due to the presence and/or characteristics of said object or substance, and a circuit arrangement for detecting said change in capacitance, characterised in that said circuit arrangement includes a fixed frequency oscil ⁇ lator, the amplitude output and/or phase of which is de ⁇ pendent on said change in capacitance.
  • a device for determining presence and/or charac ⁇ teristics of an object or a substance comprising capacitive means, the capacitance of which is changed due to the presence and/or characteristics of said object or substance, and a circuit arrangement for detecting said change in capacitance, characterised in that said capaci ⁇ tive means includes a plurality of sensors connected to the circuit arrangement via one or more multiplexers the power rails of which are connected to buffering means so as to inhibit internal capacitance to said rails.
  • the buffering means includes a voltage follower connected to the power rails via capaci ⁇ tors.
  • Unaddressed lines and sensors may be connected to the voltage follower by extra switches, thus eliminating the feed through capacitance effects in individual switches in the or each multiplexer and allowing long lines to the sensors on the same side of the PCB upon which the device is mounted.
  • the on/off ratio of these extra switches can be improved by novel means in the form of an additional impedance element from each sensor to the output of the voltage follower.
  • the back-plane may also be connected to the buffering means, so that not only is the sensitivity increased but also the device can be made very thin with connectors or electronics to one side. This allows a three dimensional or flexible design to be made.
  • the buffering means have good radio frequency rejection properties being so near the sensing pads.
  • the electronics driving the buffering means are band-pass in nature to increase this rejection and to cut down on spuri ⁇ ous emissions.
  • the output of the or each multiplexer is fed to the voltage follower which has its power supply rails driven by a later stage low output impedance voltage follower.
  • the voltage follower may include a dual-gate Mosfet and gate 2 of the Mosfet is suitably connected to a buffered point for optimal elimina ⁇ tion of the input capacitance.
  • the device preferably includes means for measuring the effective charge rate or loss tangent from the or each sensor, which is dependent on the object and which if any slave member is addressed. This can be measured indirectly by having this effect control the oscillator.
  • the internal characteristics and external dimensions of an object are determined by passing the object through a channel past the one or more sensors and slave members which are shaped to provide optimum identification of the object.
  • the sensors and slave members may be separated electrically by extra sections located between them on a PCB and in the wiring to the PCB. The extra sections are driven by the voltage follower.
  • the sensors and slave members may be etched onto one side of a double sided PCB, with one or more sensors and/or slave members being located opposite, typically detecting the thickness of the object.
  • the outer faces of the PCB(s) are connected to the voltage follower thus isolating the sens ⁇ ing system from external effects especially RFI.
  • One preferred embodiment comprises a single sensor and concentrically arranged buffer members and slave members.
  • the slave members are driven via a multiplexer.
  • the sensor may be circular and the buffer members and slave members may be shaped to form arcs of circles matching that of expected circular shaped objects. This arrangement can then determine the number of objects present as well as their diameter, surface area, surface roughness and thickness.
  • the sensor may be square or otherwise shaped and the buffer members and slave members may have corre ⁇ sponding corners and straight sides extending around two, three or all sides of the sensor.
  • the device may be arranged such that the characteristics of an object can be determined whilst the object is moving or rolling and/or while it is stationary.
  • the object is held stationary behind a solenoid controlled gate for recognition by the device and is released and redirected to a further solenoid gate or by 'pulsing' the first gate.
  • This embodiment is suitable when the objects to be measured are coins or tokens in a vending machine.
  • the total coin detect mechanism can be made only slightly thicker than the coin detected. All electronic components can be located off-board.
  • the circuitry is less expensive and less susceptible to temperature effects than non-capac- itive systems. Additionally, it works with coins of non metallic nature, and it can be cheaply upgraded to much higher degrees of discrimination by simply adding more or smaller slave members. This allows more highly specified items to be used i.e. value tokens or security/identifica ⁇ tion tokens to be used in once only or highly secure appli ⁇ cations.
  • the device in accordance with the present invention, may be used in many different applications. Examples of such applications are as follows:-
  • the term 'Slave' is intended to cover any mechanism for transmitting an electrostatic signal to a sensor.
  • Such devices are generally oscillating in a synchronous manner to the sensor in a predetermined phase relationship. They may be autonomous or directly controlled by an oscillator in the sensor.
  • 'capacitance' as used in this context is that property which is measured by the effective charge rate or loss tangent of a sensor. This is most generally the complex impedance of an object which is normally primarily determined by the object's dielectric characteristics.
  • a device or point which is 'buffered' is one which is connected, directly or indirectly, to the output of a voltage follower/buffer amplifier whose input is generally, directly or indirectly, connected to a sensor plate.
  • 'Buffering means' generally consist of one or more voltage followers connected to other components or plates.
  • Figure 3 shows schematically a circuit layout of the embodiment in Figures 1 and 2;
  • Figure 4 shows a schematic layout of the part of the cir ⁇ cuit shown in Figure 3;
  • Figure 5 shows a schematic layout of another embodiment in accordance with the present invention.
  • Figure 6 shows one application of the embodiment shown in Figure 5;
  • Figures 7a and 7b show diagrammatically the medium range effect of the present invention and the equivalent capaci ⁇ tive network, respectively;
  • Figures 8a and 8b show diagrammatically the long range effect of the present invention and the equivalent capaci ⁇ tive network, respectively;
  • Figure 9 shows the approximate long range detection effect lines of another embodiment, iso-potential lines being perpendicular to these detection effect lines;
  • Figures 10 and 11 show two possible arrangements of sensor arrays for use in three-dimensional surface or internal imaging;
  • Figure 12 shows a cross - section of field lines of a sensor array such as that in Fig. 10 or 11 when a curved object is nearby;
  • FIGS. 13 and 14 show schematically two alternative modi ⁇ fied circuit arrangements of a device in accordance with the invention
  • Figure 15 shows schematically a circuit arrangement in accordance with another embodiment
  • Figure 16 shows a plan view of an object being characte ⁇ rised by a sensor array
  • Figure 17 shows schematically another embodiment particu ⁇ larly for coin/token sensing
  • Figure 18 shows schematically a further embodiment wherein queuing of coins/tokens is permitted
  • Figure 19 shows schematically yet another embodiment for sensing of rolling coins/tokens
  • Figure 20 shows graphically a simplified statistical output of the embodiments shown in Figures 14, 15 and 16;
  • Figures 21 & 22 show schematically the physical layouts of two alternative embodiments suitable for chemical sensing;
  • Figure 23 shows a circuit arrangement of yet another embod ⁇ iment of the invention.
  • Figures 24 shows a technique for enhancing internal imag ⁇ ing.
  • a sensor plate 1 typically controlling the oscillation frequency of an oscillator 15 containing a CMOS Schmitt trigger 6 is buffered first by a low offset, low output impedance voltage 7 which drives a buffer plate 2 and a back shield plate 5.
  • Slave members in the form of special ⁇ ly shaped slave pads or plates 3a, 3b, 3c are switched to a point (F) in the circuit to cause the frequency of oscilla- tion to change, usually decreasing, by coupling through the air to the sensor plate 1.
  • a switch 8 may be included to cause the slave pads to be driven in phase (I), or out of phase (0) via an inverter 9, and the slave pads are selec ⁇ tively addressed via a multiplexer 10 controlled by micro ⁇ processor 14 and selective address and inhibit lines 16.
  • the voltage follower 7 is shown in detail in Figure 4.
  • the voltage follower is designed to have a negligible input capacitance by buffering the drain D of a dual gate Mosfet Ql and the power supply lines of the first stages, and for best use a dual-gate Mosfet is used with an Ft of several GHz.
  • the source of this Mosfet Q drives another high speed follower stage composed of an npn transistor T ⁇ and a pnp transistor T 2 with a current source C.
  • These circuits are designed for low capacitance at every internal node and the PCB is laid out so the buffer lines drive the smallest external capacitance to other lines on the board.
  • Figure 4 also shows an optional potential divider circuit 19 which provides a means to vary the fixed hysteresis level of the Schmitt trigger 6 thus decreasing the frequency and reduc ⁇ ing the effect of noise pulses.
  • the pads or plates 1, 2, 3a, 3b, 3c are etched on the same double sided PCB 4.
  • the object has an external capacitance to ground and as the circuit will have some connection to ground albeit only capacitive, this can affect the measure ⁇ ments.
  • the object is touching or almost touching the sensor/slave pad arrangement, the capacitance to ground will be small and can be made negligible by enclosing the object at this point in a box 18 whose walls consist of shield plates driven by the voltage follower. Plate 5 forms one wall of this box.
  • the box can then be lined with further slave pads (on the inside of the other walls) shaped to characterise the object spatially in three dimensions. Most usefully the thickness can be determined with a slave pad 17 opposite and parallel to the sensor. Extra sensors or slave pads can be added to the left of this sensor/slave pad arrange ⁇ ment to deal with the case of many objects on the same track.
  • a circular slave pad 17 ( Figure 2) located opposite the coin is turned on and driven in/out of phase. On going out of phase the frequency of oscillation decreases in proportion to the distance from the slave pad 17 to the top surface of the coin.
  • the slave pad which is measuring thickness is made physically smaller than any coin expected and smaller than the sensor plate 1. This is to allow an effect that is mainly due to thickness of the coin coupling the slave pad 17 to the sensor 1 rather than its diameter.
  • Figure 5 illustrates the layout of a device in accordance with another embodiment of the invention having a sensor arrangement 30 comprising four sensor pads pl-p4.
  • the pads pl-p4 are connected to multiplexers MUXl and MUX2 via lines 31 on the same layer of PCB.
  • the sensor pad to be ad ⁇ dressed is selected by data lines (dl,d2).
  • Both multiplex- ers have power supply lines (P) and (G) which are buffered by connection to the output of voltage follower 7 at buffer point (B) via capacitors Cl, C2.
  • the multiplexers are addressed by means of resistors (R1,R2) which are large enough to ensure that the protection diodes inherent in the multiplexers are not turned on and thyristor action does not commence.
  • the sensitivity is enhanced by elimination of feed-through capacitance (approximately 0.25 pF for each multiplexer switch) by connecting unused pads to the buffer point (B) .
  • This is effected by the group of switches (Swl - Sw4) whose power supply lines themselves are buffered. This prevents non-selected pads from affect ⁇ ing the frequency of oscillation when touched. If slave members are used, they are connected via inverter 9, to, for example point (F) in the circuit of Figure 5.
  • the device makes maximum use of buffer/follower techniques so that the multiplexer arrangement, having its power lines and unused input lines buffered, is transparent electrical ⁇ ly. This is accomplished by the buffering of the power lines to multiplexer MUXl which cancels the capacitance (approximately 4 pF) of each analogue input pin to the rails and the combined capacitance (i.e. approximate number of analogue switches multiplied by 4pF) at the common pin.
  • the unused input lines are connected to the buffer point (B) through multiplexer MUX2, the rails of which are also buffered for capacitance cancellation. This has the effect of cancelling the feedthrough capacitance of multiplexer MUXl.
  • the feedthrough capacitance of the switches SW1-SW4 is cancelled by having them addressed and pulled to the buffer by means of one of resistors 32.
  • the switches them ⁇ selves have buffered rails which cuts down on parasitic capacitance from the switches to the rails and allows the tracking of lines to or from the switches to be near the sensors.
  • the first stage of the oscillator 15 is designed to have an extremely low input capacitance so that any capacitive temperature effects at this point are made negligibly. This also allows smaller sensor pads to be used which means less noise is picked up. These very small pads still have high sensitivity due to a focussing effect and shielding from background capacitance caused by a common shield plate 33 also connected to the buffer point (B) and located behind all the pads and around each pad (pl- ⁇ 4).
  • the device is therefore sufficiently sensitive and stable that it can be used for multi-pad dielectric sensing of chemicals, for example in routine blood analysis. It is also so sensitive that single sided PCB technology can be used with resultant costs saving due to the lack of plated-through holes and the potential use of carbon film/membrane board techniques. This also can result in a much thinner design.
  • FIGs 6a and 6b illustrate one of many possible uses of the embodiment described in Figure 5 as a 'through-glass' keypad for public access information systems.
  • the whole device is mounted on the inside of a plate glass window 40.
  • the first 'layer' is typically legends and artwork on a sticker 43 visible through the glass indicating key posi ⁇ tioning and giving basic operating instructions. Bonded to the back of this is the main sensor PCB 30, which is double sided, consisting of the sensor pads (pl-p4 etc), layer 44 and the shield layer 33 as shown in Figure 5.
  • This is connected to a separate PCB 42 containing the electronics and providing a computer interface and connection 43 - typically keyboard emulation or RS232.
  • the electronics are sealed and protected in a cover 41 which is typically moulded ABS.
  • Substantially the same embodiment can be used as a 'through-book' sensor, or as a vandal resistant keypad for e.g. door entry systems on blocks of flats.
  • the main varia ⁇ tion is the material in front of the sensors, which can be anything conductive, but is paper in the first instance and typically a thick layer of polycarbonate in the second instance above.
  • the device is also sensitive to medium range and long range effects.
  • the effect of the slave on the sensor will be affected both by the capacitance from the object to sensor (Cs) and to slave pads (Cf) and also by the object's capacitance to ground (Cg) which causes a potential divider
  • This capacitance is of the same order of magnitude as the capacitance to the plates on the sensor board - i.e. Cg ⁇ Cs ⁇ Cf.
  • the capacitance to ground is so large that the object 35 is hardly driven at all by the capacitance Cs to the slave pad (F) and thus the object 35 is not relaying much of this effect to the sensor.
  • This can be exploited for greater range by making the slave pad to sensor distance much greater (of the order of ten times the sensor's greatest diameter).
  • the sensor's frequency is changed by only a few percent by action of the slave pad via the linkage capacitance (Cl). This change will be diminished significantly by the aforementioned capacitive potentiometer effect when an object is at a range of ap ⁇ proximately the sensor to slave pad distance.
  • phase inverter can be of any waveshape as long as it increases or decreases the frequency of the sensor.
  • the amplitude of the waveshape in the slave pad should be increased by using higher voltage supply rails until a suitable signal to noise ratio is observed, generally at least one percent change in frequency between the slave pad being active and inactive.
  • a suitable signal to noise ratio is observed, generally at least one percent change in frequency between the slave pad being active and inactive.
  • the slave pads are switched in and out of phase at a repetitive rate and correlation and synchronous demodula ⁇ tion methods are used to determine the presence and exact location of an object.
  • the distance at which this "far" field effect happens can also be changed by either provid ⁇ ing an earthed plane near the object or another plate driven by an out of phase signal with respect to the sensor with an adjustable amplitude.
  • This signal can be a square wave whose switching points are at the peaks of the trian ⁇ gle wave generated by the oscillator 15.
  • This effect can also be utilised in materials where, in ⁇ stead of air being the dielectric, a low dielectric medium is used and for the "object" a relatively high dielectric mass is located inside the material.
  • the high dielectric mass will be earthed if it is actually in the soil; or similarly if the mass on the further side has a large capacitive coupling to earth; or if an earthing plate is arranged on the back of the "object” to provide this; or if a "super earth” effect is generated by driving a slave plate on this back with a signal out of phase with the sensor. This signal can then be made greater or smaller which will move the long range effect toward or away from the sensor. This enables materials to be looked into and the internal characteristics determined further. This should be combined with known effects of placing slave pads at different distances from the sensor for internal throw ⁇ ing of the field.
  • Another embodiment uses the system for a collision avoid ⁇ ance device for automobiles. It uses two pads as in figure 9. This uses primarily the long and medium range effects described above. One of the two pads is used as a sensor, the other as a slave, which may be driven in or out of phase, with or without amplification. Possibly, the two pads can alternate as sensors and slaves to monitor any near field effects, which would differentially affect the pads according to object distance on both the X and Z axes.
  • Figs. 10 and 11 illustrate two examples, each comprising a plurality of multiplexed sensors S used without slaves wherein the subsequent image processing is made easier by arranging the sensors in symmetric grids.
  • Figure 12 illustrates the effect on the field surrounding each sensor in a matrix 50 caused by the approach through air of a curved object 35 with a high dielectric.
  • Figure 13 shows a circuit to improve the buffering of the multiplexer (MUXl, MUX2) power supply rails (P) (G), so that the substrate capacitance of the switch to the rails is reduced.
  • the ratio approaches 1:1 if the output impedance of the voltage follower is much smaller than any impedance being driven to an effective AC ground.
  • the variations in input capacitance causes a change in oscillator frequency the voltage follower must be capable of working at much higher frequencies than the oscillator. This also means that the output impedance of the voltage follower must be as low as possible to drive any stray capacitance.
  • voltage followers generally trade off accuracy of input:output ratio against low output impedance which means that a compromise has to be made.
  • a circuit configuration using a second voltage follower 86 is shown which avoids the need for this compromise.
  • the configuration allows a very high accuracy voltage follower 87 to be used in the first stage because it only has to drive a large impedance created by the second, lower accu ⁇ racy, voltage follower 86 which has a low output impedance.
  • This configuration is hereafter referred to as 'double buffering' .
  • the first stage voltage follower 87 might follow its input to an accuracy of one part in a thousand and the second stage 86 to one part in a hundred.
  • two resisters 84 and 85 in series are connected between 5V and the VDD pin.
  • the resistor 84 connected to 5V has its other pin driven by a capacitor 83 to the second stage voltage follower 86. This makes the resistor 85 to the VDD pin appear approximately one hundred times larger at the VDD pin.
  • the VDD pin is then driven by the first stage voltage follower 87 through a capacitor 82.
  • the first stage voltage follower 87 is thus not significantly degraded since it is driving a large impedance.
  • the same technique is applied to the Ov rail.
  • the second stage voltage follower 86 has a bipolar input it will generally have an output impedance dependent on its input impedance given by approximately 1/current gain. Thus if the second stage voltage follower 86 is driven by the output impedance of the first stage voltage follower 87, the second stage voltage follower's output impedance will be very small (1/current gain of first stage) so it also will not be seriously degraded by driving a resistor connected directly to the rails.
  • resistors 84 can be replaced with a constant current source or the inputs of power supplies which are made to follow and supply the rails of the multi ⁇ plexer can be double buffered.
  • the resistors 84 and 85 can be replaced with tuned circuits supplying the rails of the multiplexers. This is an effective way of cutting out input noise of a different frequency as it sees a large capacitance to the substrate in the multiplexers that is not buffered out.
  • the two voltage followers 87 and 86 can be either driven from the same input or one can drive the other as shown in the diagram.
  • This buffering technique can be extended to triple and higher orders of application to improve the buffer amplifiers in terms of follower action at higher frequen ⁇ cies and of reducing output impedance.
  • Figure 14 shows another method of improving the multiplexer action by reducing the effective co-capacitance C across each switch.
  • An additional impedance C2 approximately one thousandth of the value of said co-capacitance is added from each sensor pad pi to a voltage follower 7. This reduces unwanted feedthrough of capacitance from an unse ⁇ lected pad to the common via the co-capacitance C3.
  • an unselected sensor will add a capacitance Cl to the common whose value will be in series with the co- capacitance C3.
  • the co-capacitance C3 is approximately 0.2pF.
  • an almost 1:1 follower amplifier driving one pin of an additional capacitor C2 and the other pin connected to the sensor the equivalent capacitance of the unselected pad on the input of the voltage follower is
  • the additional impedance C2 forms a voltage divider with the impedance of a signal source driving a sensor pad, thus making the impedance of the 'off switch greater.
  • a tuned impedance at this point maximises the effect.
  • Figure 15 illustrates a technique whereby sensor plates pi can be used with individual back plates 90 which are switchable via a multiplexer MUX3 either to the voltage follower 7, making them into shield plates, or to signals in other phases via mux lines 92 thus making them into slaves. This can result in an imaging system capable of taking very complex readings but taking up minimal space.
  • the back plates are typically each driven by a second simple voltage follower 91.
  • the sensor plate pi will be significantly smaller than the back plate 90, thus allowing co-capacitance reduction by the method described in Fig. 14.
  • Figure 16 shows a rectangular array of sensors characteris ⁇ ing an object where the level of response from each sensor is displayed as a degree of shading.
  • a characteristic pattern such as this may represent: (i) the shape of an object (stronger response given by closer proximity at that point);
  • Figs. 17 to 19 are intended for use as coin/token sensors.
  • Fig. 17 uses only the short and medium range effects for sensing the diameter, surface area, roughness, and thickness of a coin or token. It also de ⁇ tects the presence of a following second coin near or touching the first coin.
  • This technique allows tokens to be used that are non-metallic. It consists of a partially enclosed buffered box with a "thickness" slave pad opposite the sensor on a parallel plate with the back sides of both plates buffered, as shown in Figure 2.
  • the arrangement of sensor and primary slaves is shown in Figure 17.
  • the arc-shaped slave pads 3a, 3b, 3c are ap ⁇ proximately the diameters of the various coins to be iden ⁇ tified. They are tracked with fine lines to a ribbon cable 11 in which every alternate wire is connected to the buffer point (B), which may also exist as fine tracks between the slave pads on the PCB.
  • a through-plated hole 20 leads to tracking on the buffer plane 5.
  • Slave pad 3d is a second coin detector. If a second coin is touching (or nearly touching) the first coin, its presence will be detected when slave pad 3d is switched on. When this happens a strong effect will be coupled to the second coin and on through the first coin to the sensor.
  • Slave pad 3e and its associated ground plate show the long range effect, but isolated to the region confined between the two parallel buffer plates formed from the backs of the plate containing the sensor and the opposing parallel plate containing the thickness slave pad (equivalent to the "buffered box" in Figure 2).
  • the slave pad 3e can be made to have an adjustable "superground” effect by driving it with a variable out of phase voltage.
  • the sensor pad and slave pads are made optimally in a particular shape such that on the side of mechanical coin stop 12 the minimum intersec ⁇ tion of the smallest and largest coin is used - i.e. an arc that fits the largest coin 34.
  • the shape of the sensor arc away from the stop is indirectly determined by the smallest coin that is to be identified as this will determine the arc of slave pad 3a.
  • a row of slave pads can be turned on. For example, if they are turned on in phase they will couple through coins sitting above them and through other coins, eventually to a coin above the sensor.
  • the slave pad determining coin thickness locates coins at a distance from the sensor with an analogue effect.
  • the frequency obtained when each slave pad is switched on in turn (in or out of phase) is measured, and may be stored.
  • the pattern of frequencies thus observed characte ⁇ rises a coin or other object.
  • the pattern may incorporate frequencies derived when slave pads to one side are switched on (a good measure of diameter) and/or those opposite (a good measure of thickness).
  • a comparison with previously stored values or limits can be made by algo ⁇ rithms ranging from complex pattern matching to simple thresholding (which determines which slave pads are over ⁇ lapped) . This comparison can then be used to make accept/reject decisions.
  • Identification without the "thickness" slave pad may be advantageous in that it allows identification to be performed simply by placing the coin/token onto a flat detector.
  • FIG. 20 shows graphically a simplified statistical output of the coin discriminator embodiment shown in figures 17, 18 and 19.
  • Each horizontal axis 51 in the diagram repre ⁇ sents the frequency measured at the sensor with a particu ⁇ lar slave turned on.
  • Each normal curve 52 represents the measured frequencies of a large number of samples of a particular type of coin with the same slave turned on.
  • Each type of coin can therefore be characterised as shown by the combination of frequency responses from all the slaves.
  • the 'accept window' i.e. allowable frequency deviation from the mean
  • FIG 21 there is shown an embodiment suitable for chemical dielectric measurement (of one or many containers).
  • This embodiment consists of a plurality of sensor devices 37, each comprising sensor pads (S), buffer areas (B), and slave pads (F) and being positioned optimally for the effect that it is desired to sense.
  • the chemical 38 to be tested may overlay one or more of the sensor devices 37. If multiple sensors, buffers or slave pads are in close proximity to the same container, differ ⁇ ences in density and dielectric can be measured in differ ⁇ ent places in the container.
  • Figure 22 shows another embodiment for chemical dielectric measurement, which has a cylindrical slave pad F forcing the field lines to cross most of the chemical 38 to be tested.
  • Other arrangements with different geometries of sensors, buffers and slaves attached to a container for containing the chemical to be tested may alternatively be utilised.
  • FIG 23 shows the circuit schematic for an amplitude- modulated version of sensor and slave arrangements de- scribed previously.
  • slave members (F) are being used they are connected, via a multiplexer if necessary, to a fixed frequency oscillator 68 and a voltage amplifier 69 via a resistive, capacitive, or inductive coupling 70.
  • the oscillator 68 may be locked by the use of a crystal, for instance.
  • the sensor (S) is connected (possibly via a multiplexer) to the voltage follower 7 as before, and then to an amplifier 62.
  • the amplified signal is then passed through a narrow band-pass filter 63 (e.g. 455 KHz ceramic) and amplified again by amplifier 64.
  • a narrow band-pass filter 63 e.g. 455 KHz ceramic
  • the signal is then rectified 65 by one of several means e.g. half wave, full wave, PLL quadrature demodulation or a multiplier driven by oscillator 68 and appropriate phase shift. Finally an op- amp 67 is used to give a high-gain output.
  • the slave (F) couples to the sensor (S) capacitively through the environment. If the arrangement is used as an array of multiplexed sensors without slaves then the oscillator 68 is connected directly to the sensor (S) via a resistive, capacitive, or inductive coupling 70 and a direct link 71.
  • Figure 24 shows a technique for enhancing internal imaging, particularly for impedance tomography, whether it be me ⁇ chanical or electrical impedance.
  • the description follows for mechanical impedance. If an object 73 is suspended in a medium 72 of similar, but not identical, dielectric constant a capacitive sensor array 74 will be unable to image the object if it is static. If, however, a modula ⁇ tion source 75, such as a loudspeaker, is used then the object 73 can be made to vibrate or resonate within the medium 72. The use of a correlation detector 76 will than allow the object to be picked out of the surrounding medium by virtue of its movement. The object and the medium must be significantly mechanically dissimilar, particularly in their rigidity, for this to work.
  • the senor, buffer and slave members may be any suitable shape accord ⁇ ing to the application in which the device is intended to be employed.
  • the sensor is square-shaped and the buffer and slave members have corresponding corners and straight sides.
  • the sensor is circu ⁇ lar and the buffer and slave pads are arcuate as described hereinabove. They may also be arranged in any suitable physical arrangements, such as in a plurality of shapes, for example parallel lines, in a zig-zag formation.
  • a device in accordance with the present invention may be used for detecting objects through water by use of slave members to set up a potential gradient in the water to the sensor, which is disturbed by the advent of an object to be detected.
  • the device may include a circular sensor and concentric buffer members and slave members driven in or out of phase with the sensor. The device is located inside the container with another sensor outside the container, thereby sensing the change in dielectric in vitro on one side of the inside sensor giving a gradient change from that sensor to the one located outside and thus positional information on density and composition of the chemical.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Geophysics And Detection Of Objects (AREA)

Abstract

Dispositif d'imagerie permettant de déterminer les caractéristiques intérieures et/ou les dimensions extérieures et/ou l'emplacement d'un objet au moyen d'un ou plusieurs capteurs (p1-p4) et d'un ou de plusieurs éléments asservis optionnels qui peuvent être entraînés en phase ou hors phase vers les capteurs et qui transmettent un effet aux capteurs de manière directe et par l'intermédiaire de l'objet devant être caractérisé. Les capteurs (p1-p4) font varier la fréquence ou l'amplitude d'un oscillateur (15) renfermant un amplificateur séparateur/régulateur (7) et un déclencheur Schmitt (6). Les éléments asservis sont entraînés de manière spécifique par un onduleur (9). Les lignes de capteurs sont munies d'un organe tampon au moyen de commutateurs à mémoire tampon (C1-C4). La connexion de lignes vers plusieurs capteurs ou plusieurs éléments asservis traverse des multiplexeurs (MUX1 par exemple) comprenant des pôles de l'alimentation munis d'un organe tampon (P,G), afin d'éliminer la capacitance interne pour l'alimentation en tension et les pôles de mise à la masse.
PCT/GB1991/002021 1990-11-16 1991-11-15 Dispositif permettant de determiner la presence et/ou les caracteristiques d'un objet ou d'une substance WO1992008947A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9309862A GB2265720B (en) 1990-11-16 1991-11-15 Device for determining the presence and/or characteristics of an object or a substance

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB9024965.7 1990-11-16
GB909024965A GB9024965D0 (en) 1990-11-16 1990-11-16 Improvements in or relating to proximity sensitive devices
GB909024966A GB9024966D0 (en) 1990-11-16 1990-11-16 Imaging devices
GB9024966.5 1990-11-16

Publications (1)

Publication Number Publication Date
WO1992008947A1 true WO1992008947A1 (fr) 1992-05-29

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AU (1) AU8866991A (fr)
GB (1) GB2265720B (fr)
WO (1) WO1992008947A1 (fr)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0556682A1 (fr) * 1992-02-10 1993-08-25 SYEL di FRANCHI A.- MARTOLINI A. & C. s.n.c. Appareil en forme de barre ayant des capteurs pour déterminer la forme et la proximité des objets de matériaux différents
WO1994015172A1 (fr) * 1992-12-28 1994-07-07 Microspace Mess- Und Sensortechnik Gmbh Procede et dispositif pour la mesure de la geometrie de surfaces de produits techniques
FR2738910A1 (fr) * 1995-09-15 1997-03-21 Superba Sa Capteur de mouvements dans l'espace, en particulier pour la mesure sans contact des caracteristiques d'un produit lineaire ou surfacique
US5802479A (en) * 1994-09-23 1998-09-01 Advanced Safety Concepts, Inc. Motor vehicle occupant sensing systems
US5844486A (en) * 1997-01-02 1998-12-01 Advanced Safety Concepts, Inc. Integral capacitive sensor array
DE19908974C2 (de) * 1998-03-03 2002-01-10 Gerhard Von Der Emde Verfahren und Vorrichtung zur Abstandsmessung
WO2010043936A1 (fr) * 2008-10-17 2010-04-22 Faurecia Bloc Avant Capteur de détection permettant de détecter un objet dans une zone de détection
RU2586269C2 (ru) * 2010-05-07 2016-06-10 Роберт Бош Гмбх Обнаружение скрытого диэлектрического объекта

Families Citing this family (1)

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Publication number Priority date Publication date Assignee Title
GB2293242B (en) * 1994-09-15 1998-11-18 Sony Uk Ltd Capacitive touch detection

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EP0004757A1 (fr) * 1978-03-31 1979-10-17 Gould Inc. Système de mesure capacitif sans contact
WO1988001747A1 (fr) * 1986-09-03 1988-03-10 Extrude Hone Corporation Reseau de capteurs a condensateurs pour la detection tactile et de proximite et leurs procedes d'utilisation
EP0425823A1 (fr) * 1989-09-29 1991-05-08 Antivision Systems Corp. Système électrostatique pour former des images

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DE2744785B2 (de) * 1977-10-05 1981-05-21 Robert 7995 Neukirch Buck Elektronischer Annäherungsschalter
US4814691A (en) * 1985-08-09 1989-03-21 Washington Research Foundation Fringe field capacitive sensor for measuring profile of a surface
GB2250822B (en) * 1989-05-17 1993-08-11 Moonstone Designs Ltd Proximity sensor

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Publication number Priority date Publication date Assignee Title
EP0004757A1 (fr) * 1978-03-31 1979-10-17 Gould Inc. Système de mesure capacitif sans contact
WO1988001747A1 (fr) * 1986-09-03 1988-03-10 Extrude Hone Corporation Reseau de capteurs a condensateurs pour la detection tactile et de proximite et leurs procedes d'utilisation
EP0425823A1 (fr) * 1989-09-29 1991-05-08 Antivision Systems Corp. Système électrostatique pour former des images

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0556682A1 (fr) * 1992-02-10 1993-08-25 SYEL di FRANCHI A.- MARTOLINI A. & C. s.n.c. Appareil en forme de barre ayant des capteurs pour déterminer la forme et la proximité des objets de matériaux différents
WO1994015172A1 (fr) * 1992-12-28 1994-07-07 Microspace Mess- Und Sensortechnik Gmbh Procede et dispositif pour la mesure de la geometrie de surfaces de produits techniques
US5802479A (en) * 1994-09-23 1998-09-01 Advanced Safety Concepts, Inc. Motor vehicle occupant sensing systems
US6014602A (en) * 1994-09-23 2000-01-11 Advanced Safety Concepts, Inc. Motor vehicle occupant sensing systems
FR2738910A1 (fr) * 1995-09-15 1997-03-21 Superba Sa Capteur de mouvements dans l'espace, en particulier pour la mesure sans contact des caracteristiques d'un produit lineaire ou surfacique
US5844486A (en) * 1997-01-02 1998-12-01 Advanced Safety Concepts, Inc. Integral capacitive sensor array
DE19908974C2 (de) * 1998-03-03 2002-01-10 Gerhard Von Der Emde Verfahren und Vorrichtung zur Abstandsmessung
WO2010043936A1 (fr) * 2008-10-17 2010-04-22 Faurecia Bloc Avant Capteur de détection permettant de détecter un objet dans une zone de détection
JP2012506042A (ja) * 2008-10-17 2012-03-08 フォルシア ブロック アバン 検出エリア内の物体を検出するセンサ装置
RU2489285C2 (ru) * 2008-10-17 2013-08-10 Форесья Блок Аван Сенсорное устройство для обнаружения объекта в зоне обнаружения
US8878550B2 (en) 2008-10-17 2014-11-04 Faurecia Bloc Avant Sensor device for detecting an object in a detection area
RU2586269C2 (ru) * 2010-05-07 2016-06-10 Роберт Бош Гмбх Обнаружение скрытого диэлектрического объекта

Also Published As

Publication number Publication date
GB2265720B (en) 1995-06-14
GB2265720A (en) 1993-10-06
GB9309862D0 (en) 1993-07-14
AU8866991A (en) 1992-06-11

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