Hillllllllllillll||||||||i||llllllllllllllllllllllllllllllllllllllllllllll
`
`1180057961 83A
`
`United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,796,183
`
`Hourmand
`
`[45} Date of Patent:
`
`Aug. 18, 1998
`
`4,308,443
`4,323,829
`4,352,141
`4.360.737
`4,374,381
`4,476,463
`4,503,294
`4.731.548
`4,758,735
`4,831,279
`4,910,504
`4,939,382
`4,942,631
`5,012,124
`5,066,898
`5,087,825
`5,208,516
`5,233,231
`5,235,217
`5,386,219
`5,453,644
`5,572,205
`
`[54]
`
`[75]
`
`[73]
`
`[21]
`
`[22]
`
`[5 1]
`[52]
`
`[5 8]
`
`[56]
`
`CAPACITIVE RESPONSIVE ELECTRONIC
`SWITCHING CIRCUIT
`
`Inventor: Byron Hourmand. Hersey. Mich.
`
`Assignee: Nartron Corporation. Reed City.
`Mich.
`
`Appl. No.2 601,268
`Filed:
`
`Jan. 31, 1996
`
`Int. Cl.6 ..................................................... H0111 35/00
`US. Cl.
`.......................... 307/116: 361/131; 307/125;
`307/139
`Field of Search ..................................... 307/112. 113.
`307/116, 125, 139. 140. 157; 361/181
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`Adelson et a],
`.
`Vogelsberg ,
`Vogelsberg ,
`Bellis .
`Hurst .
`Larson .................................... 307/116
`Barkan et a].
`,
`Hurst et a].
`.
`Bellis .
`Alexander .
`Goa et al.
`.
`Moennig .
`Holz .
`Talmage et a1.
`Stone .
`Patrizio .
`Raupp .
`Senk .
`Wern .
`Deavenport et a].
`Conner .
`Gibson et a1.
`Waldron ,
`Chiang .
`Besson .
`Wern .
`Wern .
`McLaughlin .
`
`.
`
`.
`
`.
`
`12/1970
`2/1972
`3/1972
`5/1972
`3/1974
`4/1975
`8/1975
`10/1975
`11/1975
`6/1976
`10/1976
`4/1977
`6/1977
`1/1978
`7/1978
`10/1978
`5/1979
`6/1979
`7/1980
`7/1980
`7/1980
`9/1980
`12/1980
`1/1981
`3/1981
`4/1981
`9/1981
`9/1981
`
`3.549909
`3,641,410
`3,651 ,391
`3,666,988
`3,798,370
`3,879,618
`3,899,713
`3,91 1 ,215
`3,919,596
`3,965,465
`3,984,757
`4,016,453
`4,031,408
`4,071,689
`4,101,805
`4,119,864
`4,152,629
`4,159,473
`4,210,822
`4,211,959
`4,213,061
`4,220,815
`4,237,421
`4,246,533
`4,257,117
`4.264.831
`4,289,972
`4,289,980
`
`363/181
`
`.
`.
`
`.
`
`12/1981 Tucker et al.
`4/1982 Witney et a1.
`9/1982 Kent
`11/1982 Leopold.
`.
`2/1983 Ng et a],
`.
`10/1984 Ng et a].
`3/1985 Matsumaru ............................. 200/5 A
`3/1988 Ingraham.
`7/1988 Ingraham.
`5/1989 Ingraham.
`3/1990 Eriksson.
`7/1990 Gruodis.
`7/1990 Rosa ............................................ 4/623
`4/1991 Hollaway.
`11/1991 Miller et a1.
`2/1992 Ingraham.
`5/1993 Saidian.
`.
`8/1993 Wieth el al,
`8/1993 Kitten ..................................... 307/326
`l/l995 Greanias et a1.
`.
`9/1995 Yap et a1.
`.
`11/1996 Caldwell et a1.
`
`......................... 341/33
`
`Primary Examiner—William M. Shoop. Jr.
`Assistant Examiner—Jonathan Kaplan
`Anomey, Agent, or Finn—Price. Heneveld. Cooper. DeWitt
`& Litton
`
`[57]
`
`ABSTRACT
`
`A capacitive responsive electronic switching circuit com-
`prises an oscillator providing a periodic output signal having
`a frequency of 50 kHz or greater. an input touch terminal
`defining an area for an operator provide an input by prox-
`imity and touch. and a detector circuit coupled to the
`oscillator for receiving the periodic output signal from the
`oscillator. and coupled to the input touch terminal. The
`detector circuit being responsive to signals from the oscil—
`lator and the presence of an operator‘s body capacitance to
`ground coupled to the touch terminal when in proximity or
`touched by an operator to provide a control output signal.
`Preferably, the oscillator provides a periodic output signal
`having a frequency of 800 kHz or greater. An array of touch
`terminals may be provided in close proximity due to the
`reduction in crosstalk that may result from contaminants by
`utilizing an oscillator outputting a signal having a frequency
`of 50 kHz or greater.
`
`32 Claims, 13 Drawing Sheets
`
`2300
`
`
`
`FLOATING
`‘04
`
`A—(—
`GROUND
`Z
`~
`VOLTAGE — OSCILLATOR
`GENERATOR
`REGULATOR
`
`)
`
`101
`
`-—
`
`/
`
`102 ?
`
`
`
`106105
`
`1011
`
`103
`
`+Vcc
`
`600
`
`700
`
`\
`
`1
`LW, _LW
`MICRO-
`
`CONTROLLER
`[LOAD 1‘
`,. W WW
`T
`
`,W—Wl
`
`201
`
`
`460
`450
`
`W- r—-——4Lfi i/
`
`
`mi 400
`/
`‘
`TOUCH
`
`‘;
`CIRCUIT
`‘
`
`
`-
`MICRO- 1’7"
`
`CONTROLLER
`.2,
`‘1
`K2500
`
`301
`
`
`
`APPLE 1001
`
`APPLE 1001
`
`1
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 1 of 13
`
`5,796,183
`
`10
`
`20
`
`22
`
`24
`
`26
`
`T.
`
`Fig. 1
`
`
`
`2
`
`

`

`US. Patent
`
`Aug. 13, 1998
`
`Sheet 2 of 13
`
`5,796,183
`
`
`
`Fig. 8
`
`3
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 3 of 13
`
`5,796,] 83
`
`———-—ZGM|N
`
`FREQUENCY
`
`~~~~~zeMAx
`FREQUENCY
`
`
`
`1000
`
`1‘104
`
`1‘105
`
`1-105
`
`FREQUENCY
`
`Fig. 3A
`
`4
`
`

`

`US. Patent
`
`Aug. 18,1998
`
`Sheet 4 of 13
`
`5,796,183
`
`ozsomo
`
`comcom
`
`
`an,IImobfiaomm-.ECHfiuzumOiMO<HI_O>-
`moh<mmzmou"
`wowuu
`
`
`com
`
`FemAV.mwrw
`
`1030?
`
`.::om:u
`
`
`
`mmAJOmpzoommAJOmhzooo<04
`
`
`-05.:.95:2
`
`..coo.OQN
`
`oo>+
`
`
`
`Downo?I
`
`omvPmo?vromvno?..|Nov
`
`so
`
`5
`
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 5 of 13
`
`5,796,183
`
`
`
`6
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 6 of 13
`
`5,796,183
`
`S/N VS. BODY CAPACITANCE
`
`TEMPERATURE = 105‘C
`
`
`
`
`
`_
`F :9. 9
`
`-40 I... mam
`
`‘ I'M/[J I = "EdamI1
`
`430
`".‘ngvi/mm‘rma
`20 22° 330 550 1230
`CBODY (PF)
`'
`
`O
`
`3 ~20
`
`3 §
`
`SIN VS. BODY CAPACITANCE
`TEMPERATURE = 25°C
`
`
`
`
`”4-,:
`o 32::
`
` mm. ‘-
`g -20 "n
`2 -40 I...‘
`'
`m .60 1..
`
`\WATER=1M G
`
`20 22° 330 550 1230
`
`
`
`
`CBODY (PF)
`
`Fig. 10
`
`7
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 7 0f 13
`
`5,796,183
`
`oorcomcom
`
`mokfinwmmI«.9538
`
`02:.<0.E
`
`20—25—00
`
`mOqumeO
`
`610:2
`
`mmjomkzoo
`
`8
`
`
`
`
`
`

`

`US. Patent
`
`Aug. 18,1998
`
`Sheet 8 of 13
`
`5,796,183
`
`24v DC
`
`1100
`
`“04
`
`
`
`. :
`
`
`a
`“‘1‘!" RELAY
`
`
`g-a SWlTCH
`
`
`9
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 9 of 13
`
`5,796,183
`
`_
`
` nwvvwnmrvv_
`noovr"_
`rlljl111111NE:
`\xg_com?__
`
`__mmmrrsssssssssssssss.;llllllllllllllllllll....L
`”row?er..ll.__
`._
`
`POP
`
`OP_
`
`_
`
`10
`
`10
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 10 of 13
`
`5,796,183
`
`
`
`11
`
`11
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 11 of 13
`
`5,796,183
`
`
`
`12
`
`12
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 12 of 13
`
`5,796,183
`
`201
`74-1; -------------------f“--.
`:
`414
`I ‘ '
`|
`I
`
`2000
`
`401
`2002 1
`4 I - .
`2004
`i
`I.
`i
`J'
`
`|I
`
`b.
`
`410
`
`418
`
`CUSTOM IC
`_____________________
`
`400
`
`450
`
`2008
`
`:
`
`2006
`
`451-l
`.
`l
`_ I
`I}
`i ______
`
`i
`1
`
`Flg- 17
`
`106
`
`244
`
`FROM
`
`MICRO-
`_
`CONTROLLER ’
`¥___:_._____-_-_l
`600
`
`13
`
`13
`
`

`

`US. Patent
`
`Aug. 18, 1998
`
`Sheet 13 0f 13
`
`5,796,183
`
`
`
`A_‘ Fig. 20A
`
`2305
`
`2302
`
`1STSTEP
`
`2301
`
`Fig. 203 2304
`
`
`
`14
`
`14
`
`

`

`5.796.183
`
`2
`
`1
`CAPACITIVE RESPONSIVE ELECTRONIC
`SWITCHING CIRCUIT
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to an electrical circuit and
`particularly a capacitive responsive electronic switching
`circuit used to make possible a “zero force” manual elec-
`tronic switch.
`
`Manual switches are well known in the art existing in the
`familiar forms of the common toggle light switch. pull cord
`switches. push button switches. and keyboard switches
`among others. The majority of such switches employ a
`mechanical contact that “makes” and “breaks” the circuit to
`be switched as the switch is moved to a closed or an open
`condition.
`
`Switches that operate by a mechanical contact have a
`number of well known problems. First. mechanical move-
`ments of components within any mechanism make those
`components susceptible to wear. fatigue. and loosening. This
`is a progressive problem that occurs with use and leads to
`eventual failure when a sufficient amount of movement has
`occurred
`eak” between conductive
`Second. a sudden “’make or “
`contacts typically produces an electrical are as the contacts
`come into close proximity. This arcing action generates both
`radio frequency emissions and high frequency noise on the
`line that is switched.
`
`Third. the separation between contacts that occurs on each
`break. exposes the contact surfaces to corrosion and con—
`tamination. A particular problem occurs when the are asso-
`ciated with a “make” or “break” occurs in an oxidizing
`atmosphere. The heat of the arc in the presence of oxygen
`facilitates the formation of oxides on the contact surfaces.
`Once exposed. the contact surfaces of mechanical switches
`are also vulnerable to contaminants. Water borne contami—
`nants such as oils and salts can be a particular problem on
`the contact surfaces of switches. Arelated problem occurs in
`that the repeated arcing of mechanical contact can result in
`a migration of contact materials away from the area of the
`mechanical contact. Corrosion. contamination. and migra-
`tion operating independently or in combination often lead to
`eventual switch failure where the switch seizes in a closed
`or opened condition.
`An additional problem results from the mechanical force
`required in operating a mechanical switch. This problem
`occurs in systems where a human operator is required to
`repetitively operate a given switch or a number of switches.
`Such repetitive motions commonly occur in the operation of
`electronic keyboards such as those used with computers and
`in industrial switches such as used in forming and assembly
`equipment among other applications. A common type of
`industrial switch is the palm button seen in pressing and
`insertion equipment. For safety purposes. the operator must
`press the switch before an insertion or pressing can occur.
`This ensures that the operators hand(s) is(are) on the button
`(5) and not in the field of motion of the associated machinery.
`It also ensures that the mechanical motion occurs at a desired
`and controllable point in time. The difficulty arises from the
`motion and force required of the operator. In recent years. it
`has been noted that repeated human motions can result in
`debilitating and painful wear on joints and soft tissues
`yielding arthritis like symptoms. Such repetitive motion may
`result in swelling and cramping in muscle tissues associated
`with conditions such as Carpal Tunnel Syndrome. Equip-
`ment designers combat these Repetitive Motion or Cumu—
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`65
`
`lative Trauma Disorders by adopting ergonomic designs that
`more favorably control the range. angle. number. and force
`of motions required of an operator as well as the number of
`the operator’s muscle groups involved in the required
`motions. Prosthetics and tests are used as well to provide
`strain relief for the operator‘s muscles. joints. and tendons.
`In mechanical switches. the force required to actuate the
`switch may be minimized by reducing spring forces and
`frictional forces between moving parts. However. reducing
`such forces makes such switches more vulnerable to failure.
`
`For instance. weaker springs typically lower the pressure
`between contacts in a “make” condition. This lower contact
`pressure increases the resistance in the switch which can
`lead to fatal heating in the switch and/or loss of voltage
`applied to the switched load. Reducing frictional forces in
`the switch by increasing the use of lubricants is undesirable
`because the lubricants can migrate and contaminate the
`contact surfaces. A switch designer may also reduce friction
`by providing looser fits between moving parts. However.
`looser fits tend to increase wear and contribute to earlier
`switch failure. A designer can also reduce friction by using
`higher quality. higher cost. surface finishes on the parts.
`Thus. as apparent from the foregoing description. measures
`taken to reduce actuator force in mechanical switch parts
`generally reduce the reliability and performance of the
`switch and/or increase the cost of the switch.
`
`In applications such as computer keyboards or appliance
`controls. the electric load switched by a given switch can be
`quite low in terms of current and/or voltage. In such cases
`it is possible to use low force membrane switches such as
`described in US. Pat. No. 4.503.294. Such switches can
`relieve operator strain and are not as susceptible to arcing
`problems because they switch small loads. However. the
`flexible membrane remains susceptible to wear. corrosion.
`and contamination. Although such switches require very low
`actuation force. they are still mechanically based and thus
`suffer from the same problems as any other mechanical
`switch.
`
`A more recent innovation is the development of “zero
`force” touch switches. These switches have no moving parts
`and no contact surfaces that directly switch loads. Rather.
`these switches operate by detecting the operator’s touch and
`then use solid state electronics to switch the loads or activate
`mechanical relays or triacs to switch even larger loads.
`Approaches include optical proximity or motion detectors to
`detect the presence or motion of a body part such as in the
`automatic controls used in urinals in some public rest rooms
`or as disclosed in US. Pat. No. 4.942.631. Although these
`non—contact switches are by their very nature truly zao
`force. they are not practical where a multiplicity of switches
`are required in a small area such as a keyboard Among other
`problems. these non-contact switches sufier from the com—
`paratively high cost of electro-optics and from false detec-
`tions when the operator’s hand or other body part uninten-
`tionally comes close to the switch’s area of detection. Some
`optical touch keyboards have been proposed. but none have
`enjoyed commercial success due to performance and/or cost
`considerations.
`
`A further solution has been to detect the operator’s touch
`via the electrical conductivity of the operator’s skin. Such a
`system is described in US. Pat. No. 3.879.618. Problems
`with this system result from variations in the electrical
`conductivity of different operators due to variations in sweat.
`skin oils. or dryness. and from variable ambient conditions
`such as humidity. A further problem arises in that the touch
`surface of the switch that the operator touches mu st remain
`clean enough to provide an electrical conductivity path to
`
`15
`
`15
`
`

`

`5.796.183
`
`3
`the operator. Such surfaces can be susceptible to
`contamination. corrosion. and/or a wearing away of the
`conductive material. Also. these switches do not work if the
`operator is wearing a glove. Safety considerations also arise
`by virtue of the operators placing their body in electrical
`contact with the switch electronics A further problem arises
`in that such systems are vulnerable to contact with materials
`that are equally or more conductive than human skin. For
`instance. water condensation can provide a conductive path
`as good as that of an operator’s skin. resulting in a false
`activation.
`A common solution used to achieve a zero force touch
`
`switch has been to make use of the capacitance of the human
`operator. Such switches. which are hereinafter referred to as
`capacitive touch switches. utilize one of at
`least
`three
`different methodologies. The first method involves detecting
`RF or other high frequency noise that a human operator can
`capacitively couple to a touch terminal when the operator
`makes contact such as is disclosed in US. Pat. No. 5.066.
`898. One common source of noise is 60 Hz noise radiated
`from commercial power lines. A drawback of this approach
`is that radiated electrical noise can vary in intensity from
`locale to locale and thereby cause variations in switch
`sensitivity. In some cases. devices implemented using this
`first method. rely on conductive contact between the opera-
`tor and the touch terminal of the switch. As stated. such
`surfaces are subject to contamination. corrosion. and wear
`and will not work with gloved hands. An additional problem
`can arise in the presence of moisture when multiple switches
`are employed in a dense array such as a keyboard. In such
`instances. the operator may touch one touch terminal. but
`end up inadvertently activating others through the path of
`conduction caused by the moistm‘e contamination.
`A second method for implementing capacitive touch
`switches is to couple the capacitance of the operator into a
`variable oscillator circuit that outputs a signal having a
`frequency that varies with the capacitance seen at a touch
`terminal. An example of such a system is described in US.
`Pat. No. 5.235.217. Problems with such a system can arise
`where conductive contact with the operator is required and
`where the frequency change caused by a touch is close to the
`frequency changes that would result from unintentionally
`coming into contact with the touch terminal.
`Another method for implementing capacitive touch
`switches relies on the change in capacitive coupling between
`a touch terminal and ground. Systems utilizing such a
`method are described in U.S. Pat. No. 4.758.735 and US.
`Pat. No. 5.087.825. With this methodology the detection
`circuit consists of an oscillator (or AC line voltage
`derivative) providing a signal to a touch terminal whose
`voltage is then monitored by a detector. The touch terminal
`is driven in electrical series with other components that
`function in part as a charge pump. The touch of an operator
`then provides a capacitive short to ground via the operator's
`own body capacitance that lowers the amplitude of oscillator
`voltage seen at the touch terminal. A major advantage of this
`methodology is that the operator need not come in conduc-
`tive contact with the touch terminal but rather only in close
`proximity to it. Afurther advantage arises in that the system
`does not rely upon radiated emissions picked up by the
`operator’s body which can vary with locale. but relies
`instead upon the human body's capacitance. which can vary
`over an acceptable range of 20 pF to 300 pF.
`An additional consideration in using zero force switches
`resides in the difficulties that arise in trying to employ dense
`arrays of such switches. Touch switches that do not require
`physical contact with the operator but rather rely on the
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`4
`operator’s close proximity can result in unintended actua—
`tions as an operator’s hand or other body part passes in close
`proximity to the touch terminals. Above-mentioned US.
`Pat. No. 5.087.825 employs conductive guard rings around
`the conductive pad of each touch terminal in an effort to
`decouple adjacent touch pads and prevent multiple actua—
`tions where only a single one is desired. In conjunction with
`the guard rings. it is also possible to adjust the detection
`sensitivity by adjusting the threshold voltage to which the
`sensed voltage is compared. The sensitivity may be adjusted
`in this manner to a point where the operator’s body part. for
`instance. a finger. has to entirely overlap a touch terminal
`and come into contact with its dielectric facing plate before
`actuation occurs. Although these methods (guard rings and
`sensitivity adjustment) have gone a considerable way in
`allowing touch switches to be spaced in comparatively close
`proximity. a susceptibility to surface contamination remains
`as a problem. Skin oils. water. and other contaminants can
`form conductive films that overlay and capacitively couple
`adjacent or multiple touch pads. An operator making contact
`with the film can then couple multiple touch pads to his or
`her body capacitance and it’ s capacitive coupling to ground
`This can result in multiple actuations where only one is
`desired. Small touch terminals placed in close proximity by
`necessity require sensitive detection circuits that in some
`cases are preferably isolated from interference with the
`associated load switching circuits that they activate.
`As mentioned. in industrial controls. switches can be used
`to control actuation time and to ensure that the operator’s
`hand(s) or other body part(s) are out of the field of motion
`of associated machinery. A common type of switch used in
`this application is the palm button. The button is large
`enough so that the operator can rapidly bring his or her hand
`into contact with the button without having to lose the time
`that would be taken in acquiring and lining up a finger with
`a smaller switch. Zero force touch switches are also desir-
`
`able in this application as Repetitive Motion or Cumulative
`Trauma Disorders have been a problem with operator’s
`utilizing palm buttons—especially those palm buttons that
`must be actuated against a spring resistance. In this area
`capacitive touch switches have also been employed. US.
`Pat. No. 5.233.231 is an example of such an implementation.
`Due to the proximity of machinery with the potential to
`cause injury. false actuations are a particular liability in such
`applications. Capacitive touch switches that exhibit vulner-
`ability to radiated electromagnetic noise or that operate OE
`operator proximity have the potential to actuate when the
`operator’s hand(s) is not at the desired location on the palm
`button(s). In general. this is addressed by the use of redun-
`dancies. In US. Pat. No. 5.233.231. a separate detector is
`used to measure RF noise and disable the system to a safe
`state if excessive RF noise is present. Other systems such as
`UltraTouch vended by Pinnacle Systems. Inc. use redundant
`sensing methodologies. In UltraTouch. both optical and
`capacitive sensors are used and actuation occurs only when
`both sensor types detect the operator‘s hand at the desired
`location. These implementations have a number of disad-
`vantages. In the case of the RF noise detection system. the
`system is unusable in the presence of RF noise. This forces
`the user to employ a backup mechanical switch system or
`accept the loss of function when RF noise is present. The
`second system is less reliable and more expensive because
`it requires two sensor systems to accomplish the same task.
`i.e.. detect the operator. Such system may also suffer from
`problems inherent in any optical system. namely. suscepti—
`bility to blockages in the optical path and the need to achieve
`and maintain specific optical alignments. A further problem
`
`16
`
`16
`
`

`

`5.796.183
`
`5
`
`is that this system considerably constrains the angle and
`direction of motion that the operator must use in activating
`the switch.
`
`Currently. there are several zero force palm buttons in the
`market. These products utilize optical and/or capacitive
`coupling to activate a normally closed (NC) or a normally
`open (NO) relay. and thereby switching 110 V AC. 220 V
`AC. or 24 V DC to machine controllers. The UltraTouch by
`Pinnacle Systems Inc. uses two sensors (infrared &
`capacitive) with isolated circuits to activate a relay when a
`machine operator inserts his hand into a U-shaped sensor
`actuation tunnel. The company claims that by permitting the
`machine operator to activate the machine with no force or
`pressure and with the operator’s hand and wrist in the
`ergonomic neutral position (i.e. 0° wrist joint angle and
`100% hand power positions as shown in FIG. 1.0—1). hand.
`wrist. and arm stresses are minimized and contributing
`elements to Carpal Tunnel Syndrome are negated. After a
`machine cycle is initiated. the operator must maintain an
`initial posture until the cycle is completed. A typical cycle
`time lasts approximately one to two seconds and is repeated
`about 3000 times daily. This adds up to about one hour to
`one hour and a half per day while the operator is in the
`posture. While this module reduces stress on wrist and hand.
`it strains the muscles in the forearm. Also. because of limited
`space permitted for the operator to insert his hand. it stresses
`the operator mentally and reduces productivity by causing
`fatigue. Furthermore. the infrared emitters and detectors rely
`on a clean path between the transmitter and receiver and will
`not operate properly if contaminants block the beam of light.
`SUMMARY OF THE INVENTION
`
`The present invention overcomes the above problems by
`using the method of sensing body capacitance to ground in
`conjunction with redundant detection circuits. Additional
`improvements are offered in the construction of the touch
`terminal (palm button) itself and in the regime of body
`capacitance to ground detection which minimizes sensitivity
`to skin oils and other contaminants. The invention also
`allows the operator to utilize the system with or without
`gloves which is a particular advantage in the industrial
`setting.
`The specific touch detection method of the present inven-
`tion has similarities to the devices of U.S. Pat. No. 4.758.735
`and US. Pat. No. 5.087.825. However. significant improve-
`ments are offered in the means of detection and in the
`development of an overall system to employ the touch
`switches in a dense array and in an improved zero force palm
`button. The touch detection circuit of the present invention
`features operation at frequencies at or above 50 kHz and
`preferably at or above 800 kHz to minimize the effects of
`surface contamination from materials such a skin oils and
`
`water. It also offers improvements in detection sensitivity
`that allow close control of the degree of proximity (ideally
`very close proximity) that is required for actuation and to
`enable employment of a multiplicity of small sized touch
`terminals in a physically close array such as a keyboard. The
`circuitry of the present
`invention minimizes the force
`required in human operator motions and eliminates awkward
`angles and other constraints required in those motions. The
`outer surface of the touch switch typically consists of a
`continuous dielectric layer such as glass or polycarbonate
`with no mechanical or electrical feed-throughs. The surface
`can be shaped to have no recesses that would trap or hold
`organic material. As a result it is easily cleaned and kept
`clean and so is ideal for hygienic applications such as
`medical or food processing equipment.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`6
`In a first preferred embodiment the circuit offers enhanced
`detection sensitivity to allow reliable operation with small
`{finger size)
`touch pads. Susceptibility to variations in
`supply voltage and noise are minimized by use of a floating
`common and supply that follow the oscillator signal
`to
`power the detection circuit. The enhanced sensitivity allows
`the use of a 26V or lower amplitude oscillator signal applied
`to the touch terminal and detection circuit. This lower
`voltage (as compared to the device of US. Pat. No. 4.758.
`735) obviates the need for expensive UL listed higher
`voltage construction measures and testing to handle what
`would otherwise be large enough voltages to cause safety
`concerns. A further advantage of the present invention is
`seen in the manner in which the touch terminal detection
`circuit is interfaced to the touch terminals and to external
`control systems. A dedicated microprocessor referenced to
`the floating supply and floating common of the detection
`circuit maybe used to cost effectively multiplex a number of
`touch terminal detection circuits and multiplex the associ-
`ated touch terminal output signals over a two line optical bus
`to a dedicated microprocessor referenced to a fixed supply
`and ground. An additional advantage of the microprocessor
`is an expanded ability to detect faults. Le. a pad that is
`touched for an excessive amount of time that is known a
`
`priori to be an unlikely mode of operation or two or more
`pads touched at the same time or in an improper order.
`Additionally. the microprocessor can be used to distinguish
`desired multiple pad touches in simultaneous or sequential
`modes. i.e. two or more switches touched in a given order
`within a given amount of time. The microprocessor can be
`used to perform system diagnostics as well. The micropro-
`cessor also allows the use of visual indicators such as LEDs
`or annunciators such as a bell or tone generator to confirm
`the actuation of a given touch switch or switches. This is
`particularly useful in cases where a sequence of actuations
`is required before an action occurs. The feedback to the
`operator provided by a visual or audio indicator activated by
`the microprocessor in response to intermediate touches in a
`required sequence can minimize time lost and/or frustration
`on the part of the operator due to failed actuations from
`partial touches or wrong actuations from touching the wrong
`pad in a given required sequence or combination of touches.
`The second microprocessor may be used to communicate
`with the user’s control system. Additional features include a
`“sleep mode” to minimize power consumption during peri-
`ods of non-use or power brown outs. and redundant control
`circuits to facilitate “fail
`to safe” operation. Another
`improvement is oifered in a means to move much of the cost
`of the system into simplified custom integrated circuits that
`allow ease of sensitivity adjustment and assembly.
`In a second preferred embodiment. an improved palm
`button is featured. Through the use of a dielectric cover. a
`large metallic touch terminal can be used that difierentiates
`between the touch of a finger or partial touch and the full
`touch of a palm. In this way the system avoids false triggers
`due to inadvertent finger touches or brushing contact with
`the palm prior or after an intended touch. The second
`embodiment also features redundant control circuits to
`facilitate “fail to safe” operation.
`To achieve these and other advantages. and in accordance
`with the purpose of the invention as embodied and described
`herein. the capacitive responsive electronic switching circuit
`comprises an oscillator providing a periodic output signal
`having a frequency of 50 kHz or greater. an input touch
`terminal defining an area for an operator to provide an input
`by touch. and a detector circuit coupled to the oscillator for
`receiving the periodic output signal from the oscillator. and
`
`17
`
`17
`
`

`

`5.796.183
`
`7
`
`coupled to the input touch terminal. The detector circuit
`being responsive to signals from the oscillator and the
`presence of an operator‘s body capacitance to ground
`coupled to the touch terminal when touched by an operator
`to provide a control output signal. Preferably. the oscillator
`provides a periodic output signal having a frequency of 800
`kHz or greater.
`These and other features. objects. and advantages of the
`invention may be realized and obtained by means of the
`instrumentalities and combinations particularly pointed out
`in the written description and claims hereof. as well as by the
`appended drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is an electrical schematic of a testing circuit used
`to measure the impedance of the human body;
`FIG. 2 is an electrical schematic of a testing circuit used
`to measure the impedance of water;
`FIG. 3 is an electrical schematic of an equivalent circuit
`model for analyzing a human body in contact with glass
`covered with water;
`FIG. 4 is a block diagram of a capacitive responsive
`electronic switching circuit constructed in accordance with
`a first embodiment of the present invention;
`FIG. 5 is an electrical schematic of a preferred voltage
`regulator circuit for use in the capacitive responsive elec-
`tronic switching circuit shown in FIG. 4;
`FIG. 6 is an electrical schematic of a preferred oscillator
`circuit for use in the capacitive responsive electronic switch-
`ing circuit shown in FIG. 4:
`FIG. 7 is an electrical schematic of a preferred floating
`common generator circuit for use in the capacitive respon-
`sive electronic switching circuit shown in FIG. 4;
`FIG. 8 is an electrical schematic of a preferred touch
`circuit for use in the capacitive responsive electronic switch-
`ing circuit shown in FIG. 4;
`FIG. 9 is a three dimensional bar graph illustrating
`signal-to-noise ratio vs. body capacitance at T: 105° C.;
`FIG. 10 is a three dimensional bar graph illustrating
`signal-to-noise ratio vs. body capacitance at T=22° C.;
`FIG. 11 is a block diagram of a capacitive responsive
`electronic switching circuit constructed in accordance with
`a second embodiment of the present invention;
`FIG. 12 is a block diagram of a capacitive responsive
`electronic switching circuit constructed in accordance with
`a third embodiment of the present invention;
`FIG. 13 is an electrical schematic of a preferred voltage
`regulator. oscillator. and touch circuits for use in the capaci-
`tive responsive electronic switching circuit shown in FIG.
`12;
`FIG. 14 is an electrical schematic of preferred driver
`circuits for use in the capacitive responsive electronic
`switching circuit shown in FIG. 12;
`FIGS. lSA—C are top. side. and front views. respectively.
`of an example of a flat palm button constructed in accor—
`dance with the present invention;
`FIG. 16 is a cross-sectional view of an example of a
`dome—shaped palm button constructed in accordance with
`the present invention;
`FIG. 17 is an electrical schematic of a touch circuit of the
`present invention implemented in a custom integrated cir-
`cuit;
`FIG. 18 is an electrical schematic of an oscillator having
`a sleeper circuit for use in the capacitive responsive elec-
`tronic switching circuits of the present invention;
`
`8
`FIG. 19 is a pictorial View of a device having two palm
`buttons and an indicator light operated in accordance with
`the present invention: and
`FIGS. 20A-C are pictorial views of another embodiment
`of the device shown in FIG. 19.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`As apparent from the above summary. the touch circuit of
`present invention operates at a higher frequency than prior
`touch sensing circuits. A move to high frequency operation
`(>50 to 800 kHz) is not a benign choice relative to the lower
`frequency (60 to 1000 Hz) operation seen in existing art