Electric wheelchair with improved control circuit

• US 4,634,941 A
• Filed: 04/10/1985
• Issued: 01/06/1987
• Est. Priority Date: 04/15/1981
• Status: Expired due to Fees

• Current Assignee: Invacare Corporation
• Original Assignee: Invacare Corporation
• Inventors: Klimo, Robert G.
• Primary Examiner(s): Dobeck, D.
• Application Number:
  US06/721,572
• Time in Patent Office: 636 Days
• Field of Search: 318/587, 318/139, 320/2, 180/6.5, 180/907
• US Class Current: 318/139
• CPC Class Codes: A61G 2203/14 Joysticks
• CPC Class Codes: A61G 5/045 Rear wheel drive
• CPC Class Codes: A61G 5/1032 engaging an element of the drive or transmission, e.g. drive belt, electrodynamic brake
• CPC Class Codes: A61G 5/1054 Large wheels, e.g. higher than the seat portion
• CPC Class Codes: B60L 50/52 characterised by DC-motors
• CPC Class Codes: H02P 5/68 controlling two or more dc dynamo-electric motors H02P5/46, H02P5/60 take precedence
• CPC Class Codes: H02P 7/2815 whereby the speed is regulated by measuring the motor speed and comparing it with a given physical value
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y10S 180/907 Motorized wheelchairs

Abstract

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 accordance with them. Each speed control circuit includes a reference signal circuit (90) which receives the selected vehicle speed and direction signals and produces a reference 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) compares 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 subtractively combines the first difference signal with the armature current signal to produce a speed error reference 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.

Claims

1. An electric vehicle for the physically impaired comprising:

(a) at least one battery;

(b) at least one motor for driving the vehicle;

(c) a speed selecting means for selecting the motor speed; and

,

(d) a control circuit including;

(i) a power relay having relay contacts;

(ii) a motor speed control circuit including reference signal means for producing a reference signal which varies with the selected motor speed, the reference signal means being operatively connected with the speed selecting means, motor speed detecting means for producing an actual motor speed signal which varies with the actual speed of the motor, the speed sensing means being operatively connected with the motor, speed comparing means for comparing the reference signal and the actual motor speed signal to produce a variance signal which varies with the variance between the selected and actual motor speeds; and

a variable power regulator operatively connected with the speed comparing means and the motor for regulating the electric power supplied to the motor, the power regulator being controlled by the comparing means to vary the power supplied in accordance with the variance signal;

(iii) a low battery power sensing circuit for sensing whether the battery has become discharged below a preselected stored power level, the low battery sensing circuit being operatively connected with the motor speed control circuit to cause the motor speed control circuit to stop supplying electric power to the motor through the relay contacts.

2. The electric vehicle as set forth in claim 1 wherein the low battery power sensing circuit senses battery voltage.

3. The electric vehicle as set forth in claim 1 wherein the low battery power sensing circuit is operatively connected with the power relay to open the power relay contact blocking power to the motor.

4. The electric vehicle as set forth in claim 3 wherein the control circuit further includes a delay means operatively connected with the low battery power sensing circuit and the power relay, whereby the delay provides time for the motor speed control circuit to stop supplying electric power to the motor through the relay contact before the relay contacts are opened whereby arcing across the relay contacts is inhibited.

5. The electric vehicle as set forth in claim 4 wherein the low battery power sensing circuit is operatively connected with the reference signal means for causing the reference signal to indicate zero selected speed, whereby the vehicle is brought to a controlled stop during the pre-power relay opening delay.

6. The electric vehicle as set forth in claim 5 wherein the low battery sensing circuit produces an overrride signal which overrides the reference signal.

7. The electric vehicle as set forth in claim 1 wherein the low battery sensing circuit is operatively connected with the speed comparing means to block the speed comparing means for receiving the reference signal.

8. An electric wheelchair comprising:

a battery;

at least one motor for driving at least one wheel of the wheelchair;

a joystick means for producing a reference signal which varies with a selected speed for the wheel to be driven;

a speed control circuit operatively connected with the battery, the motor, and the joystick for controlling the speed of the motor in accordance with the reference signal; and

a low voltage sensor for sensing battery voltage and producing an override signal in response to the battery voltage dropping below a predetermined voltage level, the low voltage sensor being operatively connected with the joystick means for overriding the reference signal with the override signal to cause the overriden reference signal to bring the wheelchair to a controlled stop

9. The electric wheelchair as set forth in claim 8 wherein the motor speed control circuit further includes a limiting circuit for limiting the 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;

and further including an on-off switch means for selectively passing electric power from the battery at least to the joystick means, the limiting circuit, and the motor; and

,

an off delay means for continuing to provide electric power to the limiting circuit after the on-off switch means is turned off such that the reference signal is brought to zero speed in accordance with the limiting circuit rate of change, whereby the wheelchair is decelerated to a controlled stop even after the on-off switch is turned off.

10. The electric wheelchair as set forth in claim 9 wherein the motor speed control circut further includes a motor speed detecting means for producing an actual motor speed signal which varies with the actual motor speed and a speed comparing means for comparing the reference signal and the actual motor speed signal, the variable power regulator being operatively connected with the speed comparing means to regulate the amount of electric power to the motor in accordance with the comparison between the reference signal and the actual speed signal.

11. The electric wheelchair as set forth in claim 8 wherein the motor speed control circuit further includes:

an oscillator for producing an oscillating signal;

a first pulse width modulator for comparing the magnitude of a signal received at its first input and a signal received at its second input, the first input being operatively connected with the joystick means and the second input being operatively connected with the oscillator, such that the first pulse width modulator generates a first pulse train whose periodicity varies with the oscillating signal and whose pulse width varies with the reference signal and oscillating signal comparison;

a second pulse width modulator for comparing the magnitude of a signal received at its first input and a signal received at its second input, its first input being operatively connected with the oscillator and its second input being operatively connected with the joystick means such that the second pulse width modulator generator a second pulse train whose periodicity is determined by the oscillating signal and whose pulse width varies with the oscillating signal and reference signal comparison, the pulses of the first and second pulse trains being generated alternately;

a pull-up transistor means for supplying a voltage to an armature of the motor for driving the wheelchair, the pull-up transistor means being gated periodically by the first pulse width modulator first pulse train;

a pull-down transistor means for connecting the armature of the motor to ground, the second transistor means being grated by the second pulse width modulator second pulse train, whereby the power supplied to the armature is limited to the voltage through the pull-up transistor means and ground and the speed is determined by the relative duration for which the pull-up transistor means and the pull-down transistor means are gated; and

,

a pulse width modulator protecting means operatively connected with at least one of the first and second pusle width modulators for protecting the pulse width modulator from transient noise.

12. The wheelchair as set forth in claim 11 wherein the pulse width modulator includes a transistor which is caused to assume a conductive and nonconductive state by the comparison of the oscillating signal and the reference signal.

13. The wheelchair as set forth in claim 12 wherein the pulse width modulator transistor is a V-moss field effect transistor.

14. The wheelchair as set forth in claim 13 wherein the pulse width modulator protecting means is a voltage clamp connected between a gate of the field effect transistor and one of the pull-up and pull-down transistors for clamping the voltage at the gate to a preselected range.

15. The wheelchair as set forth in claim 14 wherein the voltage clamp is a diode.

16. The wheelchair as set forth in claim 14 wherein the field effect transistor gate and source are connected such that the gate and source are both clamped to the preselected voltage range.

17. An electric wheelchair comprising:

a battery;

at least one motor for driving at least one wheel of the wheelchair;

a joystick means for producing a reference signal which varies in accordance with a selected speed for the wheel to be driven;

a limiting circuit for limiting the rate of change of the reference signal, the limiting circuit being operatively connected with the joystick means;

a variable power regulator operatively connected with the battery, the motor, and the joystick means for regulating the amount of power supplied from the battery to the motor in accordance with the reference signal;

an on-off switch means for selectively passing electric power from the battery to the joystick means, limiting circuit, and the motor;

a low battery sensing means for causing the on-off switch means to stop passing electric power from the battery to the joystick means, the limiting circuit, and the motor in response to sensing that the battery has become discharged below a preselected stored power level; and

,

an off delay means for continuing to provide electric power to at least the limiting circuit and the motor after the on-of switch means is turned off such that the vehicle is decelerated to zero speed in accordance with the limiting circuit rate of change, whereby the vehicle is decelerated to a controlled stop before power is turned off.