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1. includes the steps of c enabling a device based upon the change in capacitance indicating that the hand is present and d disabling the device based upon the change in capaci tance indicating that the hand is not present 22 The method of claim 21 wherein the capacitance adjacent the electrode is adjacent a user manual contact area such that the switch is activated in said step b based upon the proximity of the user hand to the user manual contact area 23 The method of claim 22 wherein the capacitance adjacent the electrode is adjacent a user grip area such that the switch is activated in said step b based upon the proximity of the user hand to the user hand grip area Jun 24 2004 24 A vehicle horn switch comprising an electrode mounted on a vehicle steering wheel the electrode forming part of a capacitor a capacitance of the capacitor changing based upon a presence or absence of a user hand adjacent the electrode and a detection circuit measuring the capacitance of the capacitor and activating the horn based upon the mea sured capacitance 25 The vehicle horn switch of claim 24 wherein the detection circuit further includes a bridge circuit including the electrode the bridge circuit being balanced when no user hand is detected near the electrode the bridge circuit becoming unbalanced based upon the presence of the user hand near the electrode and a differential amplifier determining when the bridge2. Application Publication Jun 24 2004 Sheet 1 of 3 US 2004 0119484 A1 ELECTRODE DETECTOR CIRCUIT SWITCH 90 ELECTRODE DIFFERENTIAL RREF AMPLIFIER DETECTOR CIRCUIT SWITCH Patent Application Publication Jun 24 2004 Sheet 2 of 3 Output Voltage Vec Ye eo ee ee Cpa Capacitance 38 Function of hand exposure SWITCH n DETECTOR CIRCUIT US 2004 0119484 A1 Patent Application Publication Jun 24 2004 Sheet 3 of 3 US 2004 0119484 A1 Eie Apo occupied or on Oscillating signal Virtual Capacitor Cv Frequency W2 38 ijn LNE na et NER ENE zi Ground Fi i g 8 zu Ge an threshold off X threshold on OSCILLATOR FREQUENCY CAPACITANCE FUNCTION OF HAND EXPOSURE HAND APPROACHING Fig 9 US 2004 0119484 A1 CAPACITANCE BASED HUMAN TOUCH ACTIVATION AND SWITCHING DEVICE 0001 This application claims priority to U S Provisional Patent Application Serial No 60 430 892 filed Dec 4 2002 and U S Provisional Patent Application Serial No 60 404 018 filed Aug 16 2002 BACKGROUND OF THE INVENTION 0002 The present invention relates to a capacitance based human touch activation device especially for use in but not limited to automotive applications Many accesso ries inside a vehicle are activated by a switch Examples include interior lights headlights radio or other entertai
3. FIG 1 installed in a roof 70 of a vehicle near the dome light 72 In this case the detection circuit 27 is configured in a toggle mode for example by a toggle circuit in the threshold circuit 46 FIG 2 Each time the device is triggered the state of the dome light 72 is inverted The extra capacitance introduced into the capacitance Cv associated with electrode 34 will either activate or deactivate the dome light 72 depending on its initial state prior to the device being triggered 0025 FIGS 6 and 7 illustrate a third implementation of the capacitance based human touch activation and switching device 20 of the present invention for determining if an operator of a device 80 is maintaining proper hand contact to continue safe operation The electrode 34 is mounted in or adjacent a user contact area such as a user grip area or handle such as a joystick 74 as shown in FIG 6 handles 76 as shown in FIG 7 or other hand grip or control devices A second electrode 34a may optionally be used either to require both hands on the handlebars 76 or to require at least one hand on the handles 76 The switch 38 places the device 80 in a deactivated or disabled state until the operator s hand or hands are in position or signals an alarm indicating that the operator has released the joystick 74 or handles 76 The US 2004 0119484 A1 device 80 may be a power device such as a vehicle power tool machinery or other device where it would be desir
4. US 20040119484A1 a2 Patent Application Publication ao Pub No US 2004 0119484 Al as United States Basir et al 43 Pub Date Jun 24 2004 54 CAPACITANCE BASED HUMAN TOUCH ACTIVATION AND SWITCHING DEVICE 76 Inventors Otman A Basir Waterloo CA Vladimir Filippov Kitchener CA Jean Pierre Bhavnani Waterdown CA Emil Breza Beamsville CA Kristopher Desrochers Kitchener CA Fakhreddine Karray Waterloo CA Correspondence Address CARLSON GASKEY amp OLDS P C 400 WEST MAPLE ROAD SUITE 350 BIRMINGHAM MI 48009 US 21 Appl No 10 643 159 22 Filed Aug 18 2003 BRIDGE 90 REESE 54 REFERENCE WIRE 52 CIRCUIT 8 DIFFERENTIAL R REF AMPLIFIER Related U S Application Data 60 Provisional application No 60 430 892 filed on Dec 4 2002 Provisional application No 60 404 018 filed on Aug 16 2002 Publication Classification clit bored oce d GOIR 27 26 p USC s eel a e ans 324 680 57 ABSTRACT A capacitance based human touch activation and switching device includes an electrode adjacent a hand contact area The electrode is part of a capacitor and is connected to a detection device that monitors the capacitance When a user hand is near the electrode the capacitance increases Based upon the change in capacitance the device activates a switch such as a vehicle horn dome light or other vehicle accessory SWITCH AC Patent
5. able to disable the device if the use removes his hand from the user contact area such as releasing a handle 0026 In an alternate detection circuit 27a shown in FIG 8 capacitance is used indirectly as the means of presence detection The electrode 34 becomes a capacitor in an oscillator The frequency at which the oscillator functions is dependent on several parameters including the capacitance C When no hand is present the system will oscillate at a given frequency based on these parameters so long as they remain constant When a hand is present the C value increases If for example an RC oscillator is used an increase in capacitance C results in a decrease in oscillating frequency This phenomenon can be used to determine the presence of an occupant Other oscillator configurations may have an output in which an increase in capacitance results in an increase in frequency 0027 A control unit 46a is used to measure the oscilla tor s frequency and compare the incoming frequency to a set threshold frequency When no hand is present the oscillator operates at a fixed frequency based on the capacitance and its surroundings This known frequency is used to tune the control unit s 46a detection algorithm A threshold is set on the control unit that will serve to detect the presence of a hand when it is crossed When the operator places his hand near the electrode 34 the increase in capacitance causes the oscillator frequency to change
6. acitance e is the permittivity A is area of the plates and d is the distance between the plates The values of these variables determine the capacitance of the capacitor Therefore a change in one or more of these variables causes a change in capacitance The permittivity and the area of the plates are proportional to the capacitance while the distance between the plates is inversely proportional to the capaci tance This means that an increase in permittivity or area causes an increase in capacitance while a decrease in per mittivity or area causes a decrease in capacitance The opposite is true for the distance between the plates An increase in the distance between the plates causes a decrease in capacitance while a decrease in the distance between the plates causes an increase in capacitance The electrode 34 acts as one plate while the surrounding environment acts as the second plate 0019 One detection circuit 27 that could be used in the schematic of FIG 1 is shown in FIG 2 The detection circuit 27 includes a single differential amplifier 40 and an AC DC conversion circuit 42 to detect changes in the voltage current and phase of the waveform produced by the oscillator 44 A single threshold circuit 46 determines if these changes indicate the presence of an occupant Each of the two inputs to the differential amplifier 40 is connected to US 2004 0119484 A1 one of a pair of arms in a bridge circuit 48 One arm of the bridge ci
7. act area adjacent a user hand contact surface of a power device the switch deactivating the power device when no user hand is detected near the electrode 11 The user activated switch of claim 10 wherein the user hand contact surface is adjacent a user hand grip area 12 A method for determining a presence of a user hand including the steps of a measuring a change in permittivity of an area adjacent an electrode caused by the proximity of the user hand and b activating a switch based upon the change measured in said step a US 2004 0119484 A1 13 The method of claim 12 further including the steps of c measuring a rate of change in capacitance in said step a and d activating the switch in said step b based upon the rate of change measured in said step c 14 The method of claim 13 wherein a vehicle horn is activated based by the switch in said step d 15 The method of claim 12 wherein a vehicle accessory is activated by the switch in said step b 16 The method of claim 12 wherein a vehicle horn is activated based by the switch in said step b 17 The method of claim 12 wherein the switch is a manual user activated switch 18 The method of claim 17 wherein the switch activates a vehicle accessory 19 The method of claim 18 wherein the vehicle accessory is a vehicle light 20 The method of claim 18 wherein the vehicle accessory is a vehicle horn 21 The method of claim 12 wherein said step b further
8. and cross the set threshold When the control unit 46a detects the frequency has crossed the threshold it outputs a signal indicating the presence of a hand Adjusting the threshold and the surface are of the electrode can control the sensitivity of the device The threshold determines the amount of change that is necessary to trigger the system The threshold can be set to require contact with the electrode 34 or it may be set to values that only require the hand to be near the handlebar or joystick This threshold must be tuned based on the particular appli cation and the surrounding environment In addition since the system uses capacitance the surface area of the electrode plays a role in overall system s sensitivity The more surface area covered by the electrode the more sensitive the system will be 0028 Preferably the control unit 46a implements hys teresis with respect to the threshold frequency as is illus trated in the graph of FIG 9 to eliminate flickering of the output signal when the frequency is hovering around the threshold In the RC oscillator the operating frequency of the oscillator must cross threshold on in order for the invention to output an on signal c threshold off is the frequency that must be crossed prior to outputting an off signal These two thresholds can be tuned in the control unit 0029 The systems utilizing the detection circuit 27a of FIGS 8 and 9 can also function as a toggle
9. cir cuit is unbalanced and activating the horn switch based upon whether the bridge circuit is balanced 26 The vehicle horn switch of claim 24 wherein the capacitor is part of an oscillator oscillating at a first fre quency when no hand is present adjacent the electrode and at a second frequency different from the first frequency when the hand is adjacent the electrode the detection circuit activating the horn switch based upon the frequency of the oscillator 27 The vehicle horn switch of claim 24 wherein the capacitance of the capacitor is changed by a change in permittivity of a medium in the capacitor the permittivity being changed by the presence or absence of the hand adjacent the electrode
10. ction circuit 0010 FIG 3 illustrates the use of the activation and switching device in a vehicle steering wheel 0011 FIG 4 is a graph showing the operation of the activation and switching device of FIG 2 0012 FIG 5 illustrates the use of the activation and switching device of FIG 1 for controlling a vehicle dome light 0013 FIG 6 illustrates the use of the activation and switching device of FIG 1 in a joystick 0014 FIG 7 illustrates the use of the activation and switching device of FIG 1 in handlebars 0015 FIG 8 is the activation and switching device of FIG 1 showing a more detailed schematic of a second embodiment of the detection circuit 0016 FIG 9 is a graph showing the operation of the activation and switching device of FIG 8 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 0017 A capacitance based human touch activation and switching device 20 is shown schematically in FIG 1 Generally a detection circuit 27 measures capacitance Cv associated with an electrode 34 as it is changed by the presence or absence of a user hand near the electrode Based upon the capacitance or upon changes in the capacitance of the electrode 34 the detection circuit 27 activates switches on or switches off a switch 38 More particularly the detection circuit 27 measures or monitors the permittivity of an area adjacent the electrode 27 0018 The formula for a parallel capacitor is C eA d where C is cap
11. er contact area adjacent the electrode defining a permittivity of the capacitor and a detection circuit measuring a capacitance of the capaci tor and activating a switch based upon the measured capacitance 2 The user activated switch of claim 1 wherein the electrode is in a vehicle 3 The user activated switch of claim 2 wherein the electrode is on a vehicle steering wheel 4 The user activated switch of claim 2 wherein the switch is for activating a vehicle horn 5 The user activated switch of claim 1 further including a bridge circuit including the electrode the bridge circuit being balanced when no user hand is detected near the electrode the bridge circuit becoming unbalanced based upon the presence of a user hand near the electrode and a differential amplifier determining when the bridge cir cuit is unbalanced and activating the switch based upon whether the bridge circuit is balanced 6 The user activated switch of claim 5 further including an oscillator exciting the bridge circuit 7 The user activated switch of claim 1 wherein the switch is activated based upon a rate of change of the capacitance 8 The user activated switch of claim 1 wherein the electrode is mounted adjacent a user manual contact area 9 The user activated switch of claim 1 wherein the electrode is mounted adjacent a user hand grip area 10 The user activated switch of claim 1 wherein the electrode is mounted adjacent a user hand cont
12. n ment systems windshield wipers horn climate control power windows power locks and air conditioning Current technologies rely on contact based switches that can break or wear out causing devices to be stuck in either an ON or OFF state This can have adverse effects on the devices that are controlled by these switches A typical situation is when the mechanical switch controlling the horn fails in an always on state This can cause the driver of the vehicle and drivers of other vehicles in the vicinity to be distracted and can lead to traffic accidents The horn itself will eventually fail leading to a costly replacement 0003 Many of the switches in vehicles are also difficult to actuate under normal driving conditions For example actuating the dome light can be difficult while driving at night Tiny switches are hard to find by feel and often require the driver to look away from the road in order to find them 0004 In addition there are many devices such as vehicles or tools that require maintaining proper hand con tact during operation to ensure the safety of the operator Current systems may have only emergency deactivation switches attached elsewhere on the device or may have depression switches attached to handlebars or joysticks to allow activation of a device Depression switches require extra pressure to be applied to the handlebars or joystick by the operator and may become uncomfortable if operated for sustained peri
13. od of time SUMMARY OF THE INVENTION 0005 The invention is a touch sensitive switching device intended to replace mechanical switches A capacitive sensor is capable of sensing human touch through a layer of non conductive material This eliminates the need for a hole or opening to be cut into the console where the touch sensor is located This allows the user to actuate a device such as a light simply by touching a designated location containing asensing electrode Furthermore a capacitive based actuator does not affect the aesthetics of the interior of the vehicle 0006 Use of a capacitive sensor integrated into a handle or grip area of a device will eliminate the need for increased pressure during operation and will increase comfort of the operator The system can be designed to allow activation of the device only while the operator is holding the control Thus allowing for emergency deactivation and ensuring safety of the operator if the control is released BRIEF DESCRIPTION OF THE DRAWINGS 0007 Other advantages of the present invention can be understood by reference to the following detailed descrip tion when considered in connection with the accompanying drawings wherein Jun 24 2004 0008 FIG 1 is a high level schematic of a capacitance based human touch activation and switching device 0009 FIG 2 is the activation and switching device of FIG 1 showing a more detailed schematic of one embodi ment of the dete
14. rcuit 48 is used as a reference arm including Rref Cref and reference wire 52 The other arm of the bridge circuit 48 contains the electrode 34 and Rocc An oscillator 50 is connected to both arms Each arm of the bridge circuit 48 is essentially a low pass filter The reference arm of the bridge circuit 48 is tuned to have the same filter character istics as the arm that contains the electrode 34 The change in attenuation and phase of the waveform passing through the electrode arm of the bridge circuit 48 is measured with respect to the reference arm of the bridge circuit 48 Since both arms of the bridge circuit 48 are receiving the same waveform it does not matter if the amplitude varies slightly 0020 Noise rejection is accomplished by providing a second wire 52 that is connected to the reference arm of the bridge circuit 48 and twisted together with a wire 54 that connects the electrode 34 to the bridge circuit 48 Since both wires 52 54 pick up the same noise the noise is not amplified because it is common to both arms of the bridge circuit 48 and both inputs to the differential amplifier 40 All thresholds and signals in the device vary in proportion to the power supply voltage As such the device is tolerant to sudden changes in the supply voltage and will function over a wide range of supply voltages Wire 54 may also be a coaxial cable in order to avoid noise and interference problems 0021 The virtual capacitor Cv created b
15. switch the control unit 46a can be set to continuously output an on signal once the frequency threshold has been crossed The control unit 46a will continue outputting the on signal even if the frequency ceases to cross the threshold The control unit 46a will then toggle the output to signal off if the frequency crosses the threshold once again 0030 In addition the control unit 46a can monitor the rate of change of the oscillator s frequency This allows the control unit 46a to determine how quickly the frequency has Jun 24 2004 changed Using this method the control unit 46a can trigger an on signal if the rate of change is above a predetermined threshold This technique can be used in application to determine if the electrode 34 was stricken quickly or if the electrode 34 was only brushed by accident 0031 The detection circuit 27a and control unit 46a can be used in any of the configurations described with respect to FIGS 1 3 5 6 and 7 0032 In accordance with the provisions of the patent statutes and jurisprudence exemplary configurations described above are considered to represent a preferred embodiment of the invention However it should be noted that the invention can be practiced otherwise than as spe cifically illustrated and described without departing from its spirit or scope What is claimed is 1 A user activated switch comprising an electrode forming part of a capacitor a us
16. that determination the detection circuit 46 switches on or off depending upon the applica tion an accessory 58 As will be described below the accessory could be any vehicle accessory such as interior lights headlights radio or other entertainment systems windshield wiper horn power windows power locks and climate control 0022 FIG 3 illustrates the electrode 34 from FIGS 1 and 2 installed in a vehicle steering wheel 60 for activating an accessory 58 such as a vehicle horn The capacitance of the virtual capacitor Cv changes depending on the permit tivity of the medium between the electrode 34 and its Jun 24 2004 surroundings When the area in front of the steering wheel 60 is empty the medium adjacent the electrode 34 is air Water has a higher permittivity than air and the human body consists of approximately 65 water Hence putting a human body part between the electrode and its surroundings will increase the permittivity and in turn will increase the capacitance between the electrode 34 and its surroundings The result is the capacitance of the system Cv increases past the set threshold and activates the switch 38 In the event that the electrode 34 is moved to decrease or increase the distance between plates the relative change in the capacitance will be small compared to the action of the addition of capacitance of a human body part thus not accidentally triggering the system 0023 FIG 4 shows a plot of
17. the DC output of the differential amplifier 40 versus the value of the virtual capacitance Cv Areas A and B represent the regions of the graph that correspond to OFF and ON In the example where the switch is used to activate a vehicle horn Area A is the region of the graph that corresponds to OFF a balanced bridge no hand present and Area B is the region of the graph that corresponds to ON unbalanced bridge hand present Of course the ON and OFF states might be reversed for other applications The detection circuit 27 is tuned for a given environment as follows The position of the MINIMUM of the curve is set by the value of the components in the bridge circuit Rocc Rref and Cref These values are tuned so that the MINIMUM point on the curve occurs at the value of Cv that corresponds to no hand present Cbal The sensitivity of the device to changes in the virtual capacitance Cv is tuned by changing the gain of the differential amplifier and the predetermined threshold value Vthresh Vthresh must be situated between the MINI MUM of the curve and the saturation voltage of the differ ential amplifier less a diode drop Hysteresis may be imple mented by the threshold circuit 46 such that a higher threshold is required to switch the device from Area A to Area B while a lower threshold must be crossed to switch the device from Area B to Area A 0024 FIG 5 shows another implementation of the capacitive based actuation device 20 of
18. y electrode 34 is connected in series with the resistor Rocc to form one arm of the bridge circuit 48 These are connected in parallel with the resistor Rref and the capacitor Cref which form the reference arm of the bridge circuit 48 Each arm of the bridge circuit 48 is essentially a low pass filter The product RC determines the characteristic of each low pass filter When RC changes the phase and the amplitude of output of the filter changes The RC value for the reference low pass filter is chosen so the bridge circuit 48 is balanced when no hand is present near the electrode 34 When there is a hand present near the electrode 34 Cv increases and the RC value changes in only one arm of the bridge circuit 48 The outputs of the two low pass filters are no longer the same The unbalance in the bridge circuit 48 1s detected by amplifying the differences between the two signals The amplified signal is an AC signal representing the voltage difference between the two filters multiplied by the gain of the amplifier 40 The difference in phase shifts between the two filters is detected because the leading and lagging portions of each waveform overlap each other causing a voltage differences between theses signals The AC signal is then passed through the AC DC conversion circuit 42 to produce a DC signal that is then compared to a predetermined threshold in threshold detection circuit 46 to determine the presence or absence of a user hand Based upon
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