United States Patent [19J
`Klimo
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,634,941
`Jan.6, 1987
`
`[54] ELECTRIC WHEELCHAIR WITH
`IMPROVED CONTROL CIRCUIT
`Inventor: Robert G. Klimo, Parma, Ohio
`[75]
`Invacare Corporation, Elyria, Ohio
`[73] Assignee:
`[21] Appl. No.: 721,572
`Apr. 10, 1985
`[22] Filed:
`
`Related U.S. Application Data
`[60] Division of Ser. No. 351,990, Feb. 24, 1982, Pat. No.
`4,511,825, which is a continuation-in-part of Ser. No.
`254,443, Apr. 15, 1981, Pat. No. 4,387,325.
`Int. Cl.4 ............................................... GOSD 1/00
`[51]
`[52] U.S. Cl . .................................... 318/139; 318/587;
`320/2; 180/6.5; 180/907
`[58] Field of Search .................... 318/587, 139; 320/2;
`180/6.5, 907
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,629,633 12/1971 O'Callaghan ......................... 310/94
`3,683,253 8/1972 Rummel et al. .................... 318/331
`3,792,327 2/1974 Waldorf .............................. 318/139
`3,814,199 6/1974 Jones ................................... 318/587
`3,904,947 9/1975 Crews ............................. 318/139 X
`3,970,160 7/1976 Nowick ............................ 318/67 X
`4,059,786 11/1977 Jones et al. ........................... 318/17
`4,079,301 3/1978 Johnson .............................. 318/338
`4,151,450 4/1979 Fukuma et al. .
`4,157,123 6/1979 Rodaway ........................ 318/380 X
`4,166,238 8/1979 Binner ................................... 318/67
`4,291,260 9/1981 Nixon .................................. 318/331
`4,300,081 11/1981 Van Landingham .
`4,303,874 12/1981
`Iwai ..................................... 318/331
`4,375,631 3/1983 Goldberg ............................ 338/128
`4,415,049 11/1983 Wereb ............................. 318/331 X
`
`Primary Examiner-D. Dobeck
`Attorney, Agent, or Firm-Fay, Sharpe, Fagan, Minnich
`& McKee
`ABSTRACT
`[57]
`The electric wheelchair includes a battery pack (A), a
`right drive motor (B), a left drive motor (C), and a
`control circuit for controlling the amount of power
`supplied from the battery to the left and right control
`motors. A speed potentiometer (24) and a direction
`potentiometer (26) are connected with a joystick (22)
`for producing a selected vehicle speed signal and a
`selected vehicle direction signal, respectively. A right
`speed control circuit (E) and a left speed control circuit
`(F) receive the selected vehicle speed and direction
`signals and control the right and left motors in accor(cid:173)
`dance with them. Each speed control circuit includes a
`reference signal circuit (90) which receives the selected
`vehicle speed and direction signals and produces a ref(cid:173)
`erence signal whose magnitude varies with the speed
`selected for its motor. The voltage and current across
`the armature of the motor are detected as measures of
`the motors actual speed. A comparing circuit (92) com(cid:173)
`pares the actual speed as determined by the armature
`voltage and current with the selected speed as denoted
`by their reference signal. Specifically, it subtractively
`combines the armature voltage and the reference signal
`to produce a first difference signal. Further, it subtrac(cid:173)
`tively combines the first difference signal with the ar(cid:173)
`mature current signal to produce a speed error refer(cid:173)
`ence signal. The speed error reference signal controls a
`variable power regulator (94) which varies the amount
`of power supplied to the motor in a manner which tends
`to cause the actual and selected speeds to match.
`
`17 Claims, 11 Drawing Figures
`
`

`

`U.S. Patent Jan. 6, 1987
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`U.S. Patent Jan. 6, 1987
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`Sheet 6 of 6
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`1
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`4,634,941
`
`2
`Another exemplary prior art wheelchair control cir(cid:173)
`cuit is illustrated in U.S. Pat. No. 4,059,786, issued Nov.
`22, 1977 to Michael Lloyd Jones et al. In the Jones
`patent, the speed of the wheelchair is controlled by a
`5 joystick which operates a potentiometer providing a
`continuously variable analog voltage indicative of the
`selected speed. A pulse width modulator converts the
`modulus of the potentiometer voltage into a proportion(cid:173)
`ate amount of power for the driving motor. A reversing
`10 relay is provided for changing the polarity with which
`the power is provided to the motor for forward and
`reverse directions. Like the later Rodaway patent, the
`Jones et al. patent includes a dynamic braking resistor
`which is shunted across the motor to slow the wheel(cid:173)
`chair. The Jones circuit further has an armature voltage
`detector for enabling the forward/reverse relay to
`change states only when there is substantially no volt(cid:173)
`age across the armature, i.e., when the motor is station(cid:173)
`ary. An overload detector including a resistor in series
`with the power supply and the motor prevents an exces(cid:173)
`sive amount of power from being supplied to the motor
`regardless of the position of the joystick.
`One problem with the Jones control is that, like the
`Rodaway control, the amount of driving power sup(cid:173)
`plied to each motor depends only on the joystick posi(cid:173)
`tion. No accommodation is made for the actual speed of
`the chair. On uneven terrain, the speed and handling of
`the chair can become unpredictable and hard to control.
`The present invention contemplates a ne~ and im(cid:173)
`proved speed control circuit which overcomes the
`above-referenced problems and others. It provides a
`speed control circuit which accurately holds the se(cid:173)
`lected speed of a wheelchair even over uneven terrain.
`
`ELECTRIC WHEELCHAIR WITH IMPROVED
`CONTROL CIRCUIT
`
`This is a division of application Ser. No. 351,990, filed
`Feb. 24, 1982, now U.S. Pat. No. 4,511,825 which, in
`turn is a continuation-in-part of application Ser. No.
`254,443 filed Apr. 15, 1981, now U.S. Pat. No.
`4,387.325.
`
`20
`
`BACKGROUND OF THE INVENTION
`This application pertains to the art of electronic speed
`controls and more particularly to feedback speed con(cid:173)
`trols. The invention finds particular application in con(cid:173)
`trolling the speed of electric wheelchairs and will be 15
`described with particular reference thereto. It will be
`appreciated, however, that the invention has broader
`applications, such as controlling the speed of other
`motorized patient care devices, electric vehicles, ma-
`chine tool motors, and the like.
`Conventionally, electric wheelchairs are driven by a
`pair of permanent magnet, DC electric motors con(cid:173)
`nected with their driving wheels. A battery pack is
`mounted in the wheelchair for supplying electric power
`to the motors. A joystick, which is mounted with easy 25
`manual access to the operator, controls the amount and
`polarity of the power which is supplied from the battery
`to each of the drive motors. To move and accelerate the
`wheelchair, the control circuit supplies power to the
`motors. To slow the wheelchair, the control circuit 30
`stops supplying power to the motors. When a perma(cid:173)
`nent magnet DC motor coasts, it functions as a genera(cid:173)
`tor. Commonly, a resistor is connected across the coast(cid:173)
`ing motors to dissipate the generated electrical energy
`and slow the motors. This braking effect, which is com- 35
`manly denoted as dynamic braking, is increased as the
`size of the braking resistance is decreased.
`An exemplary prior art wheelchair speed control is
`illustrated in U.S. Pat. No. 4,157,123, issued June 5,
`1979 to Keith S. Rodaway. In the Rodaway patent, a 40
`manually operated joystick is surrounded by four on-off
`switches for independently applying power from the
`battery to the right and/or left wheel motors with either
`a forward or reverse polarity. The joystick can be
`tipped to actuate one of the switches for the right motor 45
`and/or one for the left motor. By operating the appro(cid:173)
`priate switches, the joystick can cause the chair to move
`forward, rearward, turn to the right, turn to the left, or
`pivot. When the joystick is not supplying power of
`either polarity to one or both of the motors, a power 50
`dissipating resistor is connected across that motor. To
`select the speed, a fast/slow switch is provided separate
`from the joystick.
`One of the problems with the Rodaway circuit is that
`the speed of the wheelchair is affected by several un- 55
`controlled factors. When the chair is proceeding down(cid:173)
`grade, it will move faster and, when it is moving up(cid:173)
`grade, it will move slower. Further, operating on-off
`switches rather than continuously variable switches,
`such as a potentiometer, with the joystick limits the 60
`selection of speed, handling, and performance. For
`example, there is a single turning radius for right and
`lefthand turns which, like the speed, varies if the chair
`is on a grade. Another problem is that the wheelchair
`can gain excessive speed on a downgrade, because the 65
`power to the motors and the connection of the braking
`resistor across the motors is controlled by the joystick
`position and not the actual speed.
`
`SUMMARY OF THE INVENTION
`In accordance with a first aspect of the present inven(cid:173)
`tion, there is provided a speed control circuit for an
`electric vehicle. The circuit includes a reference signal
`means for producing a reference signal whose magni(cid:173)
`tude varies with a selected motor speed. An oscillator
`produces an oscillating signal. A first pulse width mod(cid:173)
`ulator compares the magnitude of a signal received at its
`first input and a signal received at its second input. The
`first input is operatively connected with the reference
`signal means and the second input is operatively con(cid:173)
`nected with the oscillator. The first pulse width modu(cid:173)
`lator generates a first pulse train whose periodicity
`varies with the oscillating signal and whose pulse width
`varies with the reference and oscillating signal compari(cid:173)
`son. A second pulse width modulator compares the
`oscillating signal and the reference signal and generates
`a second pulse train whose pulses are generated alter(cid:173)
`nately with the pulses of the first pulse train. A first
`transistor means supplies voltage to an armature of an
`electric motor for driving the vehicle. The first transis(cid:173)
`tor means is gated periodically by the first pulse train. A
`second transistor means selectively connects the arma(cid:173)
`ture of the motor to ground. The second transistor
`means is gated by the second pulse train. In this manner,
`power supplied to the armature is limited to the voltage
`through the first transistor means and ground through
`the second transistor means and the speed is determined
`by the relative duration for which the first and second
`transistor means are gated. A unidirectional blocking
`means is operatively connected between the second
`pulse width modulator and the second transistor means
`for passing the second pulse train from the second pulse
`width modulator to the second transistor means and for
`
`

`

`4,634,941
`
`3
`blocking pulses from passing from the transistor means
`to the second pulse width modulator. In this manner,
`the second pulse width modulator is protected from
`transient noise.
`In accordance with a second aspect of the invention 5
`there is provided an electric vehicle. The vehicle in(cid:173)
`cludes at least one battery, at least one motor for driving
`the vehicle, a joystick for selecting the motor speed, and
`a control circuit. The control circuit includes a power
`relay having relay contacts. The control circuit further 10
`includes a motor speed control circuit which is opera(cid:173)
`tively connected with the battery, the motor, and the
`joystick for controlling the motor speed in accordance
`with the joystick selected speed. The motor speed con(cid:173)
`trol circuit passes electric power through the relay 15
`contacts to the motor. A low battery power sensing
`circuit senses whether the battery has become dis(cid:173)
`charged below a preselected to stored power level. The
`low battery sensor is operatively connected with the
`motor speed control circuit to cause the motor speed 20
`control circuit to stop supplying electric power to the
`motor through the relay contacts.
`In accordance with a third aspect of the present in(cid:173)
`vention, there is provided an electric vehicle including
`an electric power supply, left and right motors, a joy- 25
`stick, first and second combining means, and right and
`left motor speed control circuits. The joystick is con(cid:173)
`nected with a speed control means for producing a
`selected vehicle speed signal which varies with a se(cid:173)
`lected vehicle speed and is connected with a vehicle 30
`direction control means for producing a selected vehi(cid:173)
`cle direction signal which varies with a selected devia(cid:173)
`tion in vehicle direction from straight. The first combin(cid:173)
`ing means combines the selected vehicle speed signal
`and the selected vehicle direction signal to produce a 35
`right motor speed signal. The second combining means
`combines the selected vehicle speed signal and the se(cid:173)
`lected vehicle direction signal to produce a left motor
`speed signal. The right motor speed control circuit
`controls the right motor speed in accordance with the 40
`· · right motor speed signal. The left motor speed control
`circuit controls the left motor speed in accordance with
`the left motor speed signal.
`In accordance with a fourth aspect of the invention,
`there is provided an electric vehicle comprising at least 45
`one battery, a motor, a motor speed control circuit, an
`on-off switch means, and an off delay means. The motor
`speed control circuit includes a reference signal means
`for producing a reference signal which varies with a
`selected motor speed, a limiting circuit for limiting the 50
`rate of change of the reference signal, and a variable
`power regulator for regulating the amount of power
`supplied from the battery to the motor in accordance
`with the reference signal. The on-off switch means
`selectively passes electric power from the battery to at 55
`least the reference signal means, the limiting circuit, and
`the motor. The off delay means continues to provide
`electric power to the limiting circuit after the on-off
`switch means is turned off. In this manner, the reference
`signal is brought to zero speed in accordance with the 60
`limiting circuit rate of change decelerating the vehicle
`to a controlled stop.
`A primary advantage of the present invention is that
`it accurately controls the actual speed of the wheel(cid:173)
`chair. The circuit automatically compensates for the 65
`different power requirements of the motor -when the
`chair encounters uneven terrain and other speed affect(cid:173)
`ing conditions. The circuit provides automatic braking
`
`4
`when the actual speed of the chair exceeds the selected
`speed.
`Another advantage of the present invention is that
`the direction is changed and the speed is increased or
`decreased gradually and smoothly, even if the joystick
`is operated erraticly or suddenly. Sudden reversals,
`acceleration, and lurching are eliminated.
`Yet another advantage of the present invention is that
`low or discharged batteries are prohibited from causing
`erratic handling.
`Still other advantages will become apparent upon
`reading and understanding the following detailed de(cid:173)
`scription of the preferred embodiment.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The invention may take form in various parts and
`arrangements of parts. The drawings are for purposes of
`illustrating a preferred embodiment of the invention
`only and are not to be construed as limiting it.
`FIG. 1 is a diagrammatic illustration of an electric
`wheelchair in accordance with the present invention;
`FIG. 2 is a schematic diagram of the electrical circuit
`of the electric wheelchair of FIG. 1, highlighting the
`speed control circuits;
`FIG. 3 is a detailed circuit schematic of the joystick
`electronics of the circuit of FIG. 1;
`FIGS. 4A and 4B are detailed circuit schematics with
`exemplary component magnitudes of the right speed
`control circuit of FIG. 2;
`FIG. 5 is a top view of a joystick means in accor(cid:173)
`dance with the present invention;
`FIG. 6 is an inside view of the top of a joystick means
`housing in accordance with the present invention;
`FIG. 7 is a side elevational view of the joystick means
`housing of FIG. 5;
`FIG. 8 illustrates a joystick motion limiting mask in
`accordance with the present invention;
`FIG. 9 illustrates an alternate embodiment of a joy(cid:173)
`stick motion limiting mask in accordance with the pres(cid:173)
`ent invention; and,
`FIG. 10 illustrates another alternate embodiment of a
`joystick motion limiting mask in accordance with the
`present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`With reference to FIGS. 1 and 2, the electric wheel(cid:173)
`chair has a battery pack A which supplies power to
`right and left DC electric motors Band C, respectively.
`The speed and direction of the wheelchair is selected by
`positioning a speed and direction selector or joystick
`means D. Right and left speed control circuits E and F
`are physically mounted above the battery pack and are
`operatively connected with the battery, electric motors
`and the joystick means for controlling the speed and
`direction of the motors such that their actual speed
`strives to match the selected speed.
`With particular reference to FIG. 1, the wheelchair
`has a frame 10 to which right and left driving wheels 12
`and 14, respectively, are rotatably mounted. A shelf or
`other support means is positioned between the wheels
`for supporting the battery pack A. The right motor B is
`mounted on the frame and connected by a belt drive
`with the right driving wheel 12. The left motor C is
`mounted on the frame and is connected by a belt drive
`with the left driving wheel 14. Because the motors
`perform both braking and acceleration functions, clutch
`and mechanical brake mechanisms are not required.
`
`

`

`4,634,941
`
`5
`6
`Disposed above the battery pack is a housing 16 for
`the comparator output forces the square-wave oscilla-
`tor 44 to a non-oscillating state which causes an indica-
`receiving plug-in circuit boards on which the control
`tor lamp 46 to glow continuously. When the battery
`and other electrical circuits are disposed. Above the
`housing 16 and motors is an operator supporting seat 18.
`pack voltage drops below the reference voltage, the
`The joystick means D, which may be mounted at any 5 output of comparator 42 allows the gated oscillator 44
`convenient location, is most commonly mounted in
`to oscillate which causes the indicator lamp 46 to flash.
`Thus, the indicator circuit 40 indicates when the power
`conjunction with an arm support 20.
`The joystick means includes a control lever 22 which
`is on as well as when the batteries have become dis-
`is pivotally mounted for 360° of motion in the horizon-
`charged below a safe area. In the preferred embodi-
`tal plane. A speed control means 23 including a speed 10 ment, the fully charged battery pack has a 24 volt out-
`control potentiometer 24 is mounted to be controlled by
`put and the oscillator reference voltage is 22 volts.
`A low voltage lockout circuit 50 output is a safety
`fore and aft joystick movement and a direction control
`means 25 including a direction control potentiometer 26
`feature which disables the wheelchair when the battery
`is mounted to be controlled by side to side joystick
`pack voltage drops below a safe operating range. When
`movement. With this arrangement, pushing the joystick 15 the battery voltage drops sufficiently, it fails to bias
`straight forward or pulling it rearward causes the speed
`some of the electrical components to their normal, lin-
`control means 24 to produce a selected vehicle speed
`ear operating range. Thus, a partially discharged bat-
`signal hose amplitude varies in proportion to the se-
`tery can cause erratic operation of the control circuits.
`lected speed. In the preferred embodiment, the polarity
`In the preferred embodiment, the low voltage lockout
`of the selected vehicle speed signal denotes forward or 20 circuit disables the wheelchair when the battery pack is
`reverse movement. Moving the joystick to the side
`discharged below 18 volts. The low voltage lockout
`causes the direction control means 26 to produce a
`circuit includes a low battery power sensing circuit, in
`selected vehicle direction signal whose amplitude varies
`the preferred embodiment a low voltage sensing circuit
`in proportion to the selected deviation of the vehicle
`52 which compares the voltage from the battery pack
`direction from straight ahead or rearward. In the pre- 25 with a preselected lockout voltage. When the lockout
`ferred embodiment, the polarity of the selected vehicle
`voltage exceeds the battery pack voltage, the low volt-
`direction signal denotes left or right movement.
`age sensing circuit 52 produces a speed override signal
`By moving the joystick with various combinations of
`through diodes 54 and 54' to the right and left speed
`control circuits to stop the motors regardless of the
`fore and aft and side to side motion, the wheelchair can
`be turned at various speeds and with various radii of 30 joystick position. After a short delay imposed by capac-
`itor 55 or other delay means to allow time for the speed
`curvature or pivoted in one spot.
`With reference to FIG. 2, the battery pack A includes
`control circuits to terminate the flow of electric power
`to the motor, the low voltage sensing circuit 52 grounds
`one or more batteries with a relatively high ampere-
`hour rating. In the preferred embodiment, the battery
`the base of a transistor 56 to block current from flowing
`pack includes a pair of lead-acid automotive-type bat- 35 through a coil 58a of a power relay 58. This prevents
`the power relay 58 from being actuated or if actuated,
`teries connected in series to provide a voltage supply in
`the 22 to 30 volt range. A manual circuit breaker 30 is
`causes it to drop out. In this manner, normally· open
`contacts 58b are forced to their normally open state
`connected in series between the battery pack and the
`remaining electrical circuitry to protect it from electri-
`blocking power to the motors and normally closed
`cal malfunctions. The circuit breaker is positioned for 40 contacts 58c are forced to their normally closed states
`easy access to the user to allow easy and immediate
`grounding the motors.
`resetting after a malfunction has occurred. A manual
`A voltage regulator 60 provides a regulated positive
`power switch 32 selectively connects and disconnects
`12 volts DC and negative 12 volts DC for biasing the
`various circuit components. The positive 12 VDC bias
`the battery pack A with the remaining electrical cir-
`cuitry. More specifically, the manual switch 32 pro- 45 is produced with a conventional series regulator 62. The
`vides electric power to the speed and direction control
`negative 12 VDC bias is derived from the positive out-
`potentiometers through a voltage regulator 34. The
`put of the battery rather than the negative battery pack
`manual switch 32 also supplies power to an off delay
`output which is grounded. An oscillator 64 alternately
`circuit 36, which, in turn, supplies power to the remain-
`gates an NPN transistor 66 and a PNP transistor 68
`ing control circuitry. The off delay circuit rapidly gages 50 which alternately charges and discharges a capacitor
`70. A diode 72 allows the capacitor 70 to draw a second
`a transistor 38 conductive when the manual switch 32 is
`closed. When the manual switch is opened the off delay
`capacitor 74 to a negative potential when the capacitor
`70 is discharged by transistor 68, but blocks the charge
`circuit holds the transistor conductive for a preselected
`delay period, e.g. a few seconds, before gating it non-
`drawn to capacitor 70 from returning to the capacitor
`conductive. In this manner, opening the manual switch 55 74 as the transistor 66 charges the capacitor 70 through
`32 immediately removes power from the speed and
`a second diode 76. A conventional series regulator 78
`direction control potentiometers 24 and 26 causing the
`regulates the negative voltage drawn on the capacitor
`selected vehicle speed and direction signals to go to
`74 to the -12 VDC bias.
`zero. The other control circuitry continues to receive
`An oscillator 80, which is discussed in detail below,
`power during the delay period to bring the vehicle, if 60 provides an oscillating power reference signal for both
`moving, to a controlled stop.
`the right and left speed control circuits. In the preferred
`A power indicator circuit 40 indicates whether an
`embodiment, this oscillator signal is a triangular-wave
`in the range of 350 to 400 hertz with a six volt peak.
`appropriate voltage is being supplied to the circuitry
`from the battery pack. The indicator circuit includes a
`With continued reference to FIG. 2, the right speed
`comparator 42 and a gated, square wave oscillator 44. 65 control circuit E and the left speed control circuit F are
`The comparator 42 compares the magnitude of the
`substantially identical. To facilitate understanding of
`battery pack voltage with a reference voltage. When
`the invention, like parts in the left speed control circuit
`the battery voltage is greater than the reference voltage,
`F are marked with the same reference numeral as the
`
`

`

`4,634,941
`
`7
`corresponding part and the right speed control circuit E
`but followed by a prime ('). Only the right speed control
`circuit E is described in detail and it will be understood
`that, unless noted otherwise, this description applies
`equally to the left speed control circuit F.
`The speed control circuit includes a reference signal
`means 90 which receives the vehicle speed and direc(cid:173)
`tion signals from the joystick D and produces a refer(cid:173)
`ence signal whose magnitude varies with a correspond-
`ing right (left) motor selected speed. When the vehicle 10
`is moving straight forward the selected vehicle and
`motor speeds are the same. However, when the vehicle
`is turning one of the selected motor speeds is greater
`than the selected vehicle speed and the other is less than
`the selected vehicle speed. In this manner, the vehicle 15
`moves through a turn at substantially the selected vehi-
`cle speed. An actual and selected motor speed compar-
`ing means or circuit 92 compares selected and actual
`right motor speeds and produces a variance or speed
`error reference signal which varies with the difference 20
`between them. A variable power regulator 94 is con(cid:173)
`trolled by the difference or speed error reference signal
`from the speed comparing circuit 92 to regulate the
`amount of power to the drive motor in a manner which 25
`tends to cause the actual and selected motor speeds to
`match.
`With primary reference to FIG. 3 and secondary
`reference to FIG. 2, the manual switch 32 is a 3-way
`switch which includes an off, low speed range, and high 30
`speed range positions. In the low speed range position,
`the manual switch provides electric power to a low
`speed range adjustment potentiometer 100 of voltage
`regulator 34. In the high speed range position, the man(cid:173)
`ual switch provides power to a high speed range adjust- 35
`ment potentiometer 102. The inverting input of a unity
`gain amplifier 104 is connected with the high and low
`speed range adjustment potentiometer to provide bal(cid:173)
`anced positive and negative reference voltages to be
`·· applied to either side of the vehicle speed and direction 40
`control potentiometers 24 and 26. The direction control
`means 25 includes wiper or sliding contact 106 of the
`direction control potentiometer which is connected
`with an inverting amplifier 108 which inverts the poten(cid:173)
`tial from the direction potentiometer. A directional 45
`deadband selection means 110 such as an adjustable
`hysteresis amplifier, feeds back a portion of the output
`of amplifier 108 to its input. This obliterates relatively
`small signals from the wiper 106 to allow a limited
`amount of side to side movement of the joystick without 50
`producing a turning signal. The directional deadband
`means is adjustable to provide greater latitude for spas-
`tic or otherwise uncoordinated patients and a smaller
`deadband for highly coordinate patients. A joystick
`balance potentiometer 112 provides a ready correction 55
`for any mechanical imbalance in the mounting of the
`joystick assembly or the mechanical connection of the
`control lever with the potentiometer wiper 106. In nor(cid:173)
`mal usage, the joystick balance potentiometer 112 is
`adjusted such that the joystick control lever is vertical 60
`when it is in the center of the turning deadband. A
`directional sensitivity adjustment 114 adjusts the magni(cid:173)
`tude of the direction signal from the amplifier 108.
`Again, to accommodate patients with different degrees
`of coordination, the sensitivity adjustment 114 allows 65
`the control to be adjusted such that a relatively large or
`relatively small amount of joystick control lever motion
`is required to produce a given amount of turning.
`
`8
`A speed balance adjustment means 116 is connected
`with the vehicle speed potentiometer to assure that both
`the left and right motors respond the same to a given
`vehicle speed signal (Vs). The speed balance adjustment
`5 means 116 is adjusted until both the left and right mo(cid:173)
`tors rotate in the same direction with the same angular
`velocity for a given vehicular speed signal. A direction
`balance adjustment 118 provides an adjustment to in-
`sure that the left and right motors both respond the
`same to a given direction signal (V v). The direction
`balance adjustment 118 is adjusted until for a given
`direction signal, generally the maximum possible direc(cid:173)
`tion signal, both rotate with the same magnitude of
`angular velocity but in opposite directions. A first com(cid:173)
`bining means 120 additively combines the selected vehi(cid:173)
`cle speed signal with the selected vehicle direction sig-
`nal and inverts the sum to produce a selected right
`motor speed signal (-(Vs+ V v)). Analogously, a sec(cid:173)
`ond combining means 120' substractively combines the
`selected vehicle speed signal with the selected vehicle
`direction signal and inverts the difference to produce a
`selected left motor speed signal (-(Vs- V v)). It is to be
`appreciated that although convenient and preferred to
`use a change of polarity to designate the change from
`forward to reverse or between left and right turning, it
`is not required.
`With primary reference to FIG. 2 and secondary
`reference to FIGS. 4A and 4B, the selected right motor
`speed signal from the speed and direction signal com(cid:173)
`bining means is amplified by a first amplifier 122. The
`selected motor speed signal from the amplifier 122, in
`the preferred embodiment, has a positive polarity to
`indicate forward motion, negative polarity to indicate
`reverse motion, and magnitude to indicate the selected
`speed. A limiting circuit 124 limits the rate of change of
`the selected motor speed signal which limits the accel-
`eration and deceleration of the wheelchair. Specifically,
`the output of the limiting circuit is a reference signal
`which approaches its input exponentially. The limiting
`circuit input is connected with the amplifier 122. Op(cid:173)
`tionally, the acceleration and deceleration rate may be
`made selectable with selectably adjustabl