WHEEL CHAIRS

Abstract: An electrically powered wheel chair having two road wheels (1) each being drivable by an electric motor (10), each road wheel (1) including a hand wheel (24) with sensor means (27) for controlling the associated electric motor (10), the sensor means (27) responding to forces applied by the user of the chair to the hand wheel (24) relative to the road wheel (1) and thereby controlling movement of the chair by the motors (10).

Description: Wheel Chairs This invention concerns wheel chairs and more particularly electrically powered wheel chairs. Wheel chairs have long been known which have a pair of small front wheels on castors which allow the chairs to be steered and a pair large rear wheels with smaller hand wheels which allow the chairs to be driven by the occupant pushing the hand wheels. Steering can be effected by the occupant applying a different propelling forces to either side of the chairs using the hand wheels, and breaking can be effected by the occupant applying a frictional force to the hand wheels. For obvious reasons there have been proposals hitherto for driving wheel chairs using electric motors, one such proposal using a joy-stick control to effect control of both the speed and the direction of travel of the chairs, each rear wheel of the chair being driven by its own electric motor which is controlled by the joy-stick. However, some users of these chairs dislike the feeling that when they use them they are perceived to be more dependant than when they used the previously mentioned hand operated chairs. According to the present invention there is provided an electrically powered wheel chair having two road wheels each being drivable by an electric motor, each road wheel including a hand wheel with sensor means for controlling the associated electric motor, the sensor means responding to forces applied by the user of the chair to the hand wheel relative to the road wheel and thereby controlling movement of the chair by the motors . The drive from the electric motor to each road wheel is preferably effected through a clutch, for example a ball clutch, and actuation of the respective clutches is preferably effected by movement of the hand wheel relative to the associated road wheel . Wheel chairs according to the present invention preferably include sensor means for each wheel which provide control signals which serves to control the acceleration provided by the associated motor in response to the relative displacement of the hand wheel and the associated road wheel from a resting position. It is generally preferred that the chairs include tilt sensor means for sensing the angle of tilt of the chair relative to its orientation on a horizontal surface, thereby to control the acceleration provided by the respective motors. It is also preferable to include an accelerometer for sensing accelerations to which the chair is subjected, thereby to control the acceleration provided by the respective motors. Breaking of wheel chairs according to the present invention is preferably effected by displacement of the hand wheel relative to the road wheel in the sense opposite to that required to actuate the motors, and it is particularly preferred to effect regenerative breaking using the drive motors. In order to facilitate their movement when the motors are not operating, it is preferable to disengage the drive from the respective motors to their associated road wheels when electric current through the motors is zero. An embodiment of wheel chair in accordance with the present invention will now be described by way of example with reference to the accompanying diagrammatic drawings. Fig. 1 is a part cut away vertical section through one wheel of the chair along the line of its axle; and Fig. 2 shows part of the mechanism shown in Fig. 1. The wheel shown generally at 1 in Fig. 1 is formed from an inner disc 6 and an outer disc 7 which are joined along their respective outer peripheries and to a circumferential channel 8 into which is located a tyre 9. The wheel 1 is attached to an axle 2 of an otherwise conventional wheel chair (not shown) . A hub shown generally at 3 is mounted fast on the axle 2, the wheel 1 being rotatable on the hub 3 via respective inner and outer ball races 4 and 5. An electric motor indicated generally at 10 has its steel stator plate 11 mounted fast on the axle 2 and its steel flux plate 12 and magnets rotor 13 mounted on a rotor 14 which is rotatable on the axle 2 via a roller bearing 15. A printed circuit board 19 has a series of coils etched on it to form an electromagnet for driving the motor 10. The outer end portion of the rotor 14 is in the form of a gear 16 which is the start of a planetary gear system 17 which ends with a drive plate 18 which is free to rotate on a ball race 20 on the axle 2. Activation of the motor 10, by applying a suitable electric current to the printed circuit board 19, therefore causes the drive plate 18 to be rotated about the axle 2. A ball clutch 21 consisting of a ball 22 located in a hole through the outer wheel disc 7 is moveable from the outer position 22 in which the ball 22 does not contact the drive plate 18 to the inner position 22' shown in Fig. 1 in which the ball 22 is both within the hole in the disc 7 and also in a hemispherical recess in the plate 18, thereby causing the disc 7 to be rotated by the plate 18. The clutch 21 is operated by an actuator 23 which has a hemispherical recess into which the ball 22 is located when the clutch 21 is disengaged. Rotation of the actuator 23 relative to the disc 7 forces the ball 22 out of the recess in the actuator 23, through the hole in the disc 7 and thence into the recess in the drive plate 18, the ball 22 then taking up the position indicated at 22' . Drive from the motor 10 is then passed on to the wheel 1. The actuator 23 is connected to an external hand wheel 24 which is similar to that of a conventional wheel chair in that it can be used to propel the chair manually. However, instead of being connected directly to the wheel 1, the hand wheel 24 is mounted so that a certain amount of relative rotational movement can be effected between them. As can be seen from Fig. 1, the hand wheel 24 is connected to the actuator 23 by a pin 25, the latter extending through a slot 26 in the disc 7 where it engages a sensor device 27 within the wheel 1. The sensor device 27 consists of a pair of arms 28 and 29 which are pivotal about a pivot pin 30 located on the internal surface of the disc 7. The opposite ends of the arms 28 and 29 are biased towards each other by a spring 31, but, as can be seen from Fig. 2, they are prevented from closing fully by an arcuate land 32 above the slot 26. The pin 25 is therefore free to move in the slot 26 before engaging either of the arms 28 and 29, and during such movement the actuator 23 can be moved sufficiently to actuate the ball clutch 21. Further movement of the hand wheel 24, and therefore of the pin 25, will force the arms 28 and 29 apart against the action of the spring 31 because the arm 28 or 29 which is not engaged by the pin 25 is prevented from movement by the land 32. A series of similar scissors devices to that shown in Fig. 2 for the sensor device 27, but without the land 32, is spaced around the wheel to position the hand wheel 24 to be centered on the wheel axle and also to bring the pins 25 to a central position in the slot 26. In addition to the spring 31 urging the arms 28 and 29 together, when it is stretched it provides a signal to a microprocessor on a main control board 33 using a linear voltage displacement transformer (not shown) connected thereto. In addition, the arms of the sensor 27 to which the spring 31 is attached include magnets (not shown) which are positioned to activate reed switches when one or other arm of the sensor 27 is moved. The signals received by the microprocessor from the sensor 27 when the spring 31 is stretched is then be interpreted by the microprocessor as indicating the direction of movement of the hand wheel 24 relative to the wheel 1 itself and the amount of acceleration required by the user. The microprocessor causes electric current to be supplied to the printed circuit board 19 which starts the motor 10, the current applied, and therefore the acceleration produced, being subject to further control depending on other factors such as the angle of tilt of the chair itself and any accelerations to which the chair is currently being subjected. The clutch 21 will have been engaged by the actuator 23, and the current supplied to the motor 10, and therefore its speed, is then increased to increase the speed of the motor 10 until the displacing force on the ring 24 relative to the wheel 1 is reduced sufficiently that the spring 31 is no longer stretched. The microprocessor then maintains the speed of the motor 10 at the level it has reached. If braking of the chair is effected by the user gripping the ring 24, the pin 25 is then urged to the opposite end of the slot 26, and the resultant signal from the spring 31 is used by the microprocessor to reduce the current to the motor 10 so that the motor 10 slows down. This braking, which is preferably arranged to be regenerative, continues until the pin 25 no longer engages the arm 28, at which point the motor 10 will continue to run at a speed which maintains the new speed of the chair . If the chair is braked to a stop, the microprocessor will provide zero current to the motor, there will be no force from the actuator 23 to activate the clutch 21, and the ball 22 will be withdrawn from its engaged position 22' to its disengaged position as a result of magnetic attraction from a magnet 33 in the actuator 23. Although the mechanism shown in Fig. 1 shows only one ball clutch 21, seven other such clutches are provided for each wheel, all eight being actuated and functioning in a substantially similar manner to that described for the single illustrated clutch. The speed of the chair is monitored by the relative movement of a spoked disc 34 connected to the wheel disc 6 and the main control board 33 using magnetic sensing, the output being used to control the speed of the motor 10 as has previously been described. An inclinometer attached to the wheel chair itself, neither being shown, provides a signal to the microprocessor to control the degree of acceleration applied to the chair by the motor 10. Furthermore, an accelerometer (not shown) which is also attached to the chair also enables the acceleration of the chair to be limited for example for safety reasons. Thus the microprocessor can override or modify the information received from the two hand wheels 24 so that in a variety of instances the motor 10 does not provide as much acceleration to the chair as it might otherwise according to the amount of acceleration suggested by the movement of the hand wheels 24.

Claims: Claims 1. An electrically powered wheel chair having two road wheels each being drivable by an electric motor, each road wheel including a hand wheel with sensor means for controlling the associated electric motor, the sensor means responding to forces applied by the user of the chair to the hand wheel relative to the road wheel and thereby controlling movement of the chair by the motors. 2. A wheel chair according to claim 1, wherein the drive from the electric motor to each road wheel is effected through a clutch. 3. A wheel chair according to claim 2, wherein the clutches are each in the form of a ball clutch. 4. A wheel chair according to claim 2 or claim 3, wherein movement of the hand wheel relative to the associated road wheel actuates the associated clutch. 5. A wheel chair according to any of the preceding claims, wherein the sensor means for each wheel provides a control signal which serves to control the acceleration provided by the associated motor in response to the relative displacement of the hand wheel and the associated road wheel from a resting position. 6. A wheel chair according to any of the preceding claims, including tilt sensor means for sensing the angle of tilt of the chair relative to its orientation on a horizontal surface, thereby to control the acceleration provided by the respective motors . 7. A wheel chair according to any of the preceding claims, including an accelerometer for sensing accelerations to which the chair is subjected, thereby to control the acceleration provided by the respective motors. 8. A wheel chair according to any of the preceding claims, wherein displacement of the hand wheel relative to the road wheel in the sense opposite to that required to actuate the motors effects breaking of the chair. 9. A wheel chair according to claim 8, wherein the breaking is regenerative. 10. A wheel chair according to any of the preceding claims, wherein the drive from the respective motors to their associated road wheels is disengaged when electric current through the motors is zero. 11. An electric wheel chair substantially as herein described with reference to the accompanying drawings.

Inventors: MANASHE SAUL, MANASHE, SAUL
Applicants: MANASHE SAUL, MANASHE, SAUL
Application year: 1999
Main classification: A61G5
IPC codes: A61G5