GB2109321A - Invalid carriage - Google Patents

Abstract

A vehicle for a suitably supported handicapped person who may move around while in an upright position and without obstruction in front of him, the steering means of the vehicle being operable for turning about the position occupied by the user. The vehicle comprises a platform 1 supported on wheels 5a, 5b, 5 upon which the driver stands and is held secure by belt 2. Wheels 5a, 5b are mounted in a forward position for rotation about a common, horizontal axis. Wheel 5 is steerable by means of tiller 4 and is driven by the electrical motor 6. The object is to make it easier for a handicapped person to carry out activities including say work at a factory bench, kitchen worktop or the like (including ones which have cupboards underneath). <IMAGE>

Description

SPECIFICATION Vehicular aid This invention relates to a vehicular aid and in particular, but not exclusively to a vehicular aid for use by a paraplegic person having the use of their upper limbs only.

According to one aspect of this invention, there is provided a vehicular aid, which aid includes a platform member, location means to locate and hold a user in an upright, standing position on the platform member, a pair of ground-engaging wheels associated with a forward region of the platform and mounted for rotation about a common horizontal axis and positioned such that when a user is located on the platform, the vertical centre line of the body of the user intersects, or passes near, said common axis, and a driven, steerable, ground engaging wheel associated with a rearward portion of the platform member. In this way, when the aid follows a circular curve, the aid may itself rotate about a vertical axis substantially coincident with the centre body line of the driver.

Conveniently, said location means comprises a belt attached to a fixed structure of the vehicular aid and adapted to pass around a mid-body region of a user.

Preferably, steering means are provided to effect movement of the steerable, groundengaging wheel, said steering means including tiller means mounted on the vehicular aid for turning movement about a generally vertical axis, said tiller means preferably having a manually grippable portion positioned to be gripped by a user.

In another aspect, this invention provides a control circuit for use with the vehicular aid of this invention.

Further aspects of this invention will be apparent from the following exemplary description of a specific embodiment, reference being made to the accompanying drawings, in which: Figure 1 shows in side elevation a partsectional view of a vehicular aid in accordance with the invention.

Figure 2 is a plan view of the vehicular aid of Fig. 1.

Figures 3a, 3b and 3c are pictorial representations of a vehicular aid in accordance with the invention; and Figure 4 shows in diagrammatic form a control circuit adapted for use in a vehicular aid of this invention.

Referring to Figs. 1 to 4, the vehicular aid illustrated comprises a platform 1 upon which the driver stands with his body located and held secure in an upright standing position by means of a belt 2 attached to a fixed portion 3 of the aid, and adapted to pass around the mid body portion of the driver. The belt 2 may be adjusted in the vertical plane to accommodate different heights of driver.

Steering tillers 4, also mounted on fixed portion 3, are capable of turning movement about a vertical axis lying adjacent the longitudinal axis of the upper arm of a driver gripping the tiller to effect steering of the aid. The tiller means 3 are positioned either side of the aid and include grip portions positioned such that when the driver is standing on platform 1, with his forearms horizontal, his hands rest naturally on the grip positions. The tiller means 4 are adjustable vertically to suit different drivers.

The aid is provided with three wheels 5, 5a and 5b which support the platform at a small distance above the ground. Wheels 5a and 5b are mounted in a forward position on the aid for rotation about a common, horizontal axis.

Moreover, the wheels 5a and 5b are positioned so that when a driver is located in a standing position on the platform, his vertical centre line intersects, or passes near, the common axis of rotation of wheels 5a and 5b.

Of the three wheels only wheel 5 is steerable, steering movement of this wheel being effected by movement of tillers 4 via a cable drive, there being means to transform the movement of the tillers so that when they are moved to the right or to the left, the vehicular aid proceeds in that direction, driving power being supplied to wheel 5 in any conventional manner from a battery-powered electrical motor 8.

The motor 8, and wheels 5, 5a and 5b and some of the ancillary equipment are housed in cladding 1 0.

The grip portion of each tiller arm 4 is provided with a control switch 9, each operable by pressure exerted by the hand of the driver, one switch provides speed control, the other controls direction of movement-for- ward or backward.

These switches form part of an electrical and electronic control circuit which prevents inadvertent switching from putting a strain on the motor and associated circuitry such as changing into reverse while going forward or by load increasing when the movement of the vehicle is prevented by an obstacle.

The control "unit" associated with the control circuit also inhibits power by a key operated switch in conjunction with a safety harness switch ensures regulated power supply to the electronic circuits and provides accurate control of battery charging.

Several important features will be apparent from the above description. When wheel 5 is turned to effect steering of the aid, the aid as well as following a curved path, will rotate about the body centre line of the driver. When the wheel 5 is turned through 90 from its median position, the aid will simply rotate about the driver's centre-line. This greatly assists manoeuvrability of the device and renders it particularly suitable for use in confined spaces such as in the domestic home.

Moreover, the vehicular aid described is stable, has easy access and may easily and safely be controlled by a paraplegic person.

Furthermore the aid is designated to ensure the safety of the component parts of the aid by protecting them from accidental impact damage and from spillage of liquid onto motors or batteries.

In addition, it will be appreciated that the configuration of the device and its manoeuvrability allow a driver to gain access to work surfaces at standing level giving them improved independence from outside assistance.

Details of the circuits employed in the above embodiment, together with their method of employment now follow.

Proportional Control of Drive Motor A variable period 'square' wave signal of about 5 khz is used to drive a permanent magnet drive motor in a 'switching regulator' mode using the self inductance of the armature. The initial signal is driven from a thumb operated variable resistor in the control handle.

The basic oscillator is based on the type 555 integrated circuit. This is basically a comparator with an upper and lower threshold.

The output of the 555 pin 3 in addition to driving the power circuit and the relay control circuit (see later) is fed to the timing capacitor (c5) via the control potentiometer and two diodes. By connecting the output to the moving contact of the potentiometer the sum of the resistance in the timing circuit is kept constant and hence the frequency of operation.

The diodes ensure that the 'charge' and 'discharge' currents are isolated. The voltage across the timing capacitor (c 5) is fed to both the lower (pin 2) and the upper (pin 6) threshold inputs of the 555 I/C.

Assuming that the 'output' has just become positive, the timing capacitor will be charged via diode D 1, and the appropriate part of the potentiometer. When the voltage on the timing capacitor reaches the upper threshold the output (of the 555) will quickly return to within a fraction of a volt from zero. The timing capacitor will then discharge via diode D 2 and the other part of the potentiometer resistance.

Within practical limitations the circuit will therefore provide a linear relationship between the control 'button' and the on/period ratio of the 555 output.

The output of the 555 is used to drive the power circuit consisting of power transistors which are 'Darlington' connected.

This circuit provides voltage pulses which are an amplified version of the 555 output.

The current in the armature of the permanent magnet drive motor is maintained during 'off' periods by the energy stored in the armature and a 'catching diode' D 11, in the same manner as a conventional 'switching regulator'. The no load speed of the motor will be a function of the average voltage applied and the current a function of the load. This type of power control is more efficient that resistive control at speeds below the maximum.

An addition to the power circuit is resistance R 1 8 which provides a voltage proportional to the current in transistor TR 5 which is used in the following circuit.

Limitations of Drive Current A signal proportional to the power transistor current is compared with a reference voltage, and if greater used to limit the period of the 'on' output from the 555. This, due to the nature of the power circuit, will limit the current at this set value.

A voltage developed across the 0.05 ohm resistor in the emitter of the power transistor after simple filtering of inductive spikes via R 1 6 and C 4 is connected to one input of a comparitor. A type LM 339N has been selected for its ability to function at low input voltage. The other input of the comparitor is connected to a variable voltage controlled by RV1 It can be seen that if the voltage is set to say 0.5 volts then the comparitor will give a positive output if the voltage from the emitter exceeds 0.5 volts, equivalent to 10 amps.

When the output of the LM 339N is positive it 'fires' the thyristor D8. effectively reducing the drive to the power circuit to zero. Under proportional control, i.e. less than maximum speed, the signals involved will be variable period 'square waves' and the effect of the thyristor firing will be to limit the 'on' period to a value related to the set 'current limit'.

Since the drive signal returns to effective zero each 'cycle' the operation is continuous.

If the controller is fully depressed the drive signal would be a continuous positive voltage.

Under these conditions any excess current would 'fire' the thyristor which would stop the drive to the power transistor until the controller was released to the proportional band.

The setting of the reference voltage is primarily to safeguard the transitor from overload but will also limit the maximum current from the battery and to the drive motor, providing protection of these components also against overload.

It should be noted that the 'stall' current of the drive motor exceeds 50 amps.

The motor cannot take this current continupusly and it would be impractical to design the electronics to do so.

Soft Reversal of Drive Reversing ability is considered essential for the practical use of the wheel stand. A 'nor mal' reversing switch would enable the 'pilot' to change from full forward to full reverse.

This would put a great strain on the motor and associated electrical system (currents would be in excess of 100 amps!) In addition such violent retardation would put the 'pilot' at risk.

The solution adopted is to inhibit reverse until the wheel stand has been brought to rest, by incorporating appropriate delays in the relay drive circuits.

A pair of 2PCO Relays are connected such that when de-energised a resistor is connected across the motor terminals. This resistor provides regenerative braking, its value being a compromise between effective braking at low speeds and discomfort to the pilot.

The circuit is such that one of the two relays needs to be energised to determine direction. The coils of the relays are operated via three transistors. TR 3 which is turned on to make the system operative (see later), TR 1 controls RL1 and TR 2 controls RL2. A two position 'reversing switch' in the control handle selects one transistor or the other for the appropriate direction by applying + 1 2 volts to its emitter. In the steady state, the capacitor associated with the transistor, eg C9 with TR 1 is charged to about 6 volts with the base current provided by R 9. The other transistor TR2 is off, since there is no voltage applied. Capacitor C 10 is discharged by R 1 3 and D6 On charging the position of the switch, the capacitor C 9 associated with the energised relay is rapidly discharged and the relay is deenergised.The capacitor associated with the originally re-energised relay is now being charged via. R1 1. During this time neither relay is energised and the drive motor is in the 'braking' connection-bringing the wheel stand to a stop. After about 1 second the capacitor C10 is charged to about 6 volts such that the voltage drop of the zenner diode is exceeded thus enabling transistor TR 2 to be turned on. This in turn energises the relay and makes the appropriate contacts for the reverse direction.

To minimise the current drawn on the battery the reversing circuit is de-energised when the control signal for speed is close to zero.

The output of the 555 is recitified by D 7 and smoothed, R12 C 11 to provide a d.c.

signal to turn on transistor TR3 and therefore the complete reversing circuit. R 14 is provided to ensure that TR 3 is turned off when the 'control signal' is at its lowest value.

Safety Interlocks To prevent the wheel stand from being used without authorisation a key switch is provided in which the key can be removed in the 'on' and 'off' position.

In addition the speed control is inhibited by a switch on the retaining belt such that the wheel stand cannot be driven unless the retaining belt is fastened.

The switch to ensure only authorised operation controls the 1 2 volt supply to the control circuit only. It is connected in the supply side of the 1 2 volt regulator via a resistor R 1.

The resistor ensures that the dissipation in the 12 volt regulator type 7812 is minimised and limits the current in the advent of a short circuit at the switch or any part of the circuit on the load side of it.

The safety retaining belt switch is in the rewinding mechanism of the belt and is normally 'closed circuit' becoming open only when the belt is unwound the correct amount.

The switch is connected across the drive to the 2N3054 (TR 4) in the same circuit as the thyristor D 8. When the switch is closed clearly no signal can be provided to the Power Drive circuits.

12 Volt Regulated Supply for Control Elec tonics A well regulated supply to the control circuits is essential to prevent undesired interaction between the heavy current power circuits and the very small currents involved in the controls.

A 'series' regulator ensures that the current drain from the battery is minimised and the selection of an integrated circuit reduces the number of components and therefore reduces the cost and increases the reliability.

An integrated circuit series regulator type 7812 has been chosen since this has its own reference voltage and overload protection. A 10 ohm resistor R1 is connected in series to reduce dissipation and provide further short circuit protection. Capacitor C 1 and C 3 ensure that high frequency oscillations do not occur, and low inductance tantalum types have been selected as suitable.

The use of 'sealed-for-life' lead acid batteries for reasons of safety and minimum maintenance necessitates a close control of the charging conditions. It is unusual for the charging facilities in the working environment envisaged for the wheel stand to provide this control. An electron regulator is provided within the electronics control unit to give a constant voltage to the battery thus ensuring safe charging.

An integrated circuit series regulator is used to provide a constant 29 volts to charge the wheel stand battery. This unit type 78HGK can provide up to 5 amps and has inbuilt protection for overcurrent.

Resistor network R20 and R21 give the regulator an output of 29. 5 volts. This is reduced by the voltage drop across diode D 10 to 29 volts.

Diode D 9 and D 10 are inciuded to prevent damage to the circuits due to reverse polarity and to prevent reverse current via. the regulator to the charging socket, i.e. shorting this socket will not cause damage to the vehicle circuits.

The vehicle of figures 3a, b and c comprises three wheels 5, 5a and 5b, a tubular steel framework 30 (of which only part can be seen) and cladding 1 0. The wheels are positioned as in Figs. 1 and 2. The motor 8 and wheel 5 are mounted to a trunnion 32 which is rotatably mounted to steer the wheel. The motor, of which the axis is vertical, is coupled to the wheel via a right-angle step-down gear assembly 33. Coupling between the tiller arrangement, including the two tillers 4 extending round from the back of the user to the positions where they can be gripped, and the trunnion 32 is via a step-up gear arrangement (not shown) whereby a relatively small rotation of the tiller arrangement gives a large steering effect.The tiller arrangement consists of a shaft (not shown) extending inside the fixed steering column housing 3 and having a lug member 34 at its upper end, this lug member having the tillers 4 themselves fixed ZlrereZo irb adjuabls sXjushls Mss 8 fixed to the column J is a slotted braGKel 35 which supports the belt 2 and a back support member 36, the bracket being held in position by a hand-screw 37 extending through the slot in the bracket. When the screw is loosened, the height of the member 36 and belt 2 can be adjusted.

Instead of or in addition to switches 9, control switches can be provided in other convenient locations, for example at locations such as that of the switch 38 attached to the horizontal part of one of the tillers 4. A key switch 39 could also be provided.

As shown in Fig. 3c, it is preferred that the platform 1 and the free area above it should be sufficient for use by a person wearing a support frame 40 of the kind which provides forward movement in response to rocking motion of the wearer and which includes means for restraining the wearer's body at strategic points, e.g. the feet, just above the knees, and mid-body, and thereby supports him or her in an upright stance. Belt 2 should be able to accommodate such a frame or be properly usable by a person with sufficient power to stand without the frame 40. Accordingly, it is preferred that belt 2 by of adjustable length, for example in any of the ways well-known in the car industry.

Claims (4)

1. A vehicular aid, which aid includes a platform member, location means to locate and hold a user in an upright, standing position on the platform member, a pair of ground-engaging wheels associated with a forward region of the platform and mounted for rotation about a common horizontal axis and positioned such that when a user is located on the platform, the vertical centre line of the body of the user intersects, or passes near, said common axis, and a driven, steerable, ground engaging wheel associated with a rearward portion of the platform member.

2. A vehicular aid according to claim 1, wherein said location means comprises a belt attached to a fixed structure of the vehicular aid and adapted to pass around a mid-body region of the user.

3. A vehicular aid according to claim 1, including steering means in the form of a tiller mounted on the aid for movement about a vertical axis and having a manually grippable portion positioned for being gripped by a user.

4. A vehicular aid substantially hereinbefore described with reference to the accompanying drawings.