United States Patent
`Edge et al.
`
`[19]
`
`[54] PROXIMITY SWITCHES
`[ 7 5]
`Inventors: Gordon Malcolm Edge; Peter
`William Lee, both of Cambridge,
`England
`
`[ 7 3] Assignee: Godwin Warren Engineering
`Limited, High Wycombe,
`Buckinghamshire, England
`Apr. 10, 1972
`
`[22] Filed:
`
`[21] Appl. No.: 242,629
`
`3, 761,736
`[ 11]
`[45] Sept. 25, 1973
`
`3,651,391
`3,588,875
`3,503,031
`3,492,440
`2,659,533
`3,643,041
`
`3/1972
`6/1971
`3/1970
`l/1970
`11/1953
`2/1972
`
`Vogelsberg .................... 200/DIG. I
`Gabor .......................... 200/5 A UX
`Nyhus et al... ................. 200/DIG. I
`Cerbone eta!. ............... 200/DIG. I
`Quinby eta!. ................. 200/DIG. I
`Jackson ........................ 200/5 A UX
`
`Primary Examiner-J. V. Truhe
`Assistant Examiner-William J. Smith
`Attorney-David Toren et al.
`
`[ 30]
`
`Foreign Application Priority Data
`May 12, 1971 Great Britain ................... 14,456/71
`
`[52] U.S. Cl ............. 307/116, 200/5 A, 200/DIG. 1,
`317/DIG. 2, 340/365
`Int. Cl •........................................... H01h 35/00
`[51]
`[58] Field of Search ............. 200/5 A, 52 R, DIG. I;
`307 /116; 317 /DIG. 2; 340/365 C
`
`[56]
`
`3,691,555
`
`References Cited
`UNITED STATES PATENTS
`9!1972 Looschen ....................... 200/DIG. I
`
`[57]
`
`ABSTRACT
`
`A proximity switch, the sensing portion of which is an
`insulated electrode whose capacitance can be changed,
`for example by bringing one's finger close to the elec(cid:173)
`trode, to operate the switch, wherein the charge in ca(cid:173)
`pacitance is coupled into a bridge circuit which has a
`delayed self-balancing action, so that rapid changes in
`capacitance will operate the switch but long term slow
`changes in the capacitance will fail to operate the
`switch.
`
`6 Claims, 2 Drawing Figures
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`MICROSOFT EXHIBIT 1011
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`

`

`PATENTED SEP2 51973
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`3~ 791 ~ 736
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`II
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`12
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`IS
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`FIG.I.
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`¢
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`FIG.2.
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`

`

`1
`PROXIMITY SWITCHES
`
`3,761,736
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`5
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`20
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`This invention relates to proximity switches intended
`for manual operation by human beings, or for opera(cid:173)
`tion by moving parts of machinery or by moving com(cid:173)
`ponents, parts or objects assembled by or operated on
`by machines, examples being machine tool tables, knit(cid:173)
`ting machine needles and bottles and other containers
`of various types.
`One serious problem encountered with switches of
`this type is the build-up of dirt, grease, etc., on the part
`of the switch intended to act as the sensor and this can
`lead to spurious spontaneous operation of the switch.
`This problem is considerably aggrevated when the
`switch is intended to be used outdoors due to the likely 15
`further effects of rain, snow, etc , to an extent that such
`switches have not normally been found to be usable in
`an outdoor environment.
`It is an object of the present invention to provide an
`improved proximity switch in which the above prob(cid:173)
`lems are effectively overcome.
`The present invention comprises a proximity switch,
`the sensing portion of which is an insulated electrode
`whose capacitance can be changed, for example by
`bringing one's finger close to the electrode, to operate
`the switch, wherein the change in capacitance is cou(cid:173)
`pled into a bridge circuit which has a delayed self(cid:173)
`balancing action, so that rapid changes in capacitance
`will operate the switch but long term slow changes in
`the capacitance will fail to operate the switch.
`The self balancing action will also compensate for
`permanent and temporary component value changes in
`the bridge circuitry due to the effects of temperature
`cycling or other effects.
`In the accompanying drawings:
`FIG. 1 is a diagrammatic front view of a panel of six
`proximity switches according to the present invention,
`and
`FIG. 2 shows a circuit a sociated. with one of the
`switches.
`As an example of one convenient method of putting
`the invention into use, FIG. 1 shows a panel of six
`switches, each of which consists of an electrode in the
`form of rectangular area 11 of electrically conductive
`material provided in the form of a thin layer by means
`of printed circuit techniques upon an insulating plate
`14. Each area 11 is surrounded by a gurad ring pro(cid:173)
`vided by a printed grid 15 connected to earth. This
`serves to prevent inadvertent operation of two adjacent
`switches simultaneously. Each area 11 is electrically 50
`connected by a lead, such as lead 13 to a circuit which
`will be described with reference to FIG. 2.
`Each area 11 has a central aperture 12 behind which
`suitable means (not shown) is provided to illuminate 55
`the aperture when the switch is operated.
`FIG. 2 shows a circuit in which P represents the ca(cid:173)
`pacitance between the area 11 and earth. The capaci(cid:173)
`tance P and the series combination of a reference ca(cid:173)
`pacitor C 1 and a voltage variable capacitor D 1
`conveniently in the form of a reversed biased silicon di(cid:173)
`ode, are connected into a bridge circuit comprising Rt.
`Rz, R3 and R4 •
`The bridge is made self-balancing in the following
`way.
`The bridge is energised by two input signals which
`are of identical frequency,. say IKH., but opposite in
`phase, q, and -q,. Two inputs from the bridge, one from
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`40
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`65
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`2
`Rz and one from R4, are summed by summing amplifier
`At whose output is fed to a phase sensitive detector
`PSD having as a phase reference signal R one of the
`two inputs q, whose phase may be adjusted by network
`tP2·
`A d.c. output from the detector PSD is amplified by
`amplifier A2 and fed back via delay circuit N.to control
`the variable capacitor 0 1 •
`The phasing of the feedback signal is such as to main-
`10 tain a null signal at the output of amplifier A 1 • Thus if
`the signal from either half of the bridge tends to domi(cid:173)
`nate, the d.c. control signal will act so as to bring the
`bridge back into balance with zero output from ampli-
`fier A 1.
`The delay circuit N is so chosen that the feedback
`circuit takes several seconds to respond to a change in
`the value of capacitance P.
`As a result, the circuit will respond to the sudden
`change in the value of P which occurs when a finger or
`hand is brought close to the area 11, but the circuit will
`not respond to, and will automatically compensate for,
`the majority of natural environment changes, such as
`rain, snow, grease, etc., which are relatively long term
`25 changes.
`The operative output from the switch may be taken
`in the form of a d.c. signal from the output of amplifier
`A., or in the form of an a.c. signal from the summed
`outputs from the bridge.
`30 The operative output may be used to provide conven(cid:173)
`tional on/off digited signal, or it may be used to provide
`an analogue signal proportional to proximity.
`Conveniently, the circuit may be provided in the
`form of an integrated circuit at the rear of insulating
`35 plate 14.
`It will be appreciated that the proximity switch de(cid:173)
`scribed above has. a number of advantages not only
`over conventional switches but also over known prox(cid:173)
`imity switches.
`It has the advantages of being insensitive to vibration,
`temperature or humidity or changes therein, of being
`robust and having no moving parts to suffer wear, and
`being proof against the build up or ingress of dust,
`swarf, coolant or other fluids, paint, steam, or other
`45 agents resulting from the local environment.
`We claim:
`1. An apparatus for responding to proximity of ob-
`jects by behaving as a switch, comprising a bridge cir(cid:173)
`cuit having two bridge arms, supply means for supply(cid:173)
`ing two alternating current signals, one to each of said
`arms, said two signals being of the same frequency but
`of opposite phase, sensing means including an insulated
`electrode connected to a first one of said bridge arms,
`said sensing means forming a capacitance with said in(cid:173)
`sulated electrode, a phase-sensitive detector connected
`to sum the outputs of the two bridge arms, a variable
`reference capacitor connected to a second one of said
`bridge arms, control means responsive to said phase-
`60 sensitive detector and coupled to said variable capaci(cid:173)
`tor for varying the capacitance of said variable capaci(cid:173)
`tor in response to long-term slow changes in the capaci(cid:173)
`tance of said sensing means so that the output of said
`detector remains balanced and for preventing rapid
`changes in the capacitance of said sensing means from
`balancing said bridge arms, said control means includ(cid:173)
`ing delay circuit means connected to the output of said
`phase-sensitive detector and having an output for con-
`
`

`

`3,761,736
`
`3
`trolling the capacitance of said variable reference ca(cid:173)
`pacitor with a delay.
`2. A switch as in claim 1, wherein said sensing means
`includes a grounded guard ring surrounding said elec(cid:173)
`trode.
`3. An apparatus as in claim 1, wherein said variable
`reference capacitor is connected to ground and said
`sensing means forms its capacitance with said electrode
`between said electrode and ground.
`4. A apparatus as claimed in claim 1, wherein said 10
`
`4
`reference capacitance includes a voltage variable ca(cid:173)
`pacitor.
`5. A apparatus as claimed in any one of claims 1,
`wherein a number of electrodes are provided on a sin(cid:173)
`S gle panel, each electrode being provided with a sepa(cid:173)
`rate bridge circuit.
`6. A apparatus as claimed in claim 5, wherein each
`electrode is surrounded by an grounded guard ring.
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