GB2358389A - Stairlift seat orientation controller - Google Patents

Abstract

A stairlift comprises a rail with sloping and level portions (11, 12 figure 1), a carriage (20 figure 1) movable up and down the rail with a seat 21 pivotally mounted on it. The chassis tilts as it moves along the rail and a motor 24 drives the seat to keep it level. The motor is controlled by level control circuitry 25, which has a gyroscope 30 to sense angular velocity of the chassis and a pendulum 31 to sense the angular position of the seat and to correct for gyroscopic drift. A set point signal unit 48 can be used to set the quiescent seat angle and optionally threshold circuitry can be included to prevent the motor from being driven until the drive signal exceeds a predetermined level. The level control circuitry can be switched off on straight sections.

Description

1 2358389 Stairlifts The present invention relates to stairlifts, and more

specifically to maintaining the seat of a stairlift level.

A stairlift is essentially a carriage which is supported on a track consisting of rail means which are attached to a staircase so that the carriage can be moved automatically up and down the staircase. The carriage consists of a seat mounted in a chassis. Such stairhfts are used primarily by old and/or disabled people who find it difficult or impossible to go up and down stairs unaided.

If the staircase is a simple straight run, it is possible for the seat to be fixed on the chassis. It is however desirable for the track to have level segments at the top and/or bottom, so that the user can get on and off comfortably and without coming too close to or onto the top or bottom of the stairs. Also., many staircases are not simple straight runs but have turns and/or landings where the gradient (and often also the direction) of the stairlift track has to change. The track has to follow these turns and changes of gradient, and the chassis will tilt as it ascends or descends the track. It is then necessary for the seat of the stairlift to be mounted on the chassis in such a way that the seat is kept level as the angle of the chassis changes.

It is possible to achieve this by purely mechanical techniques. However, these have their difficulties, and electrical/electronic servornechanisms have been proposed.

One such technique is described in WO 95/18763, Stannah Stairlifts. In this, a memory is used to store the desired angle between the chassis and the seat for different positions along the rail. As the carriage moves along the raid in use, so its position is 2 monitored. The carriage can be driven by a rack and pinion mechanism, with the tun of the driving pinion being counted to determine its position. As the chair passes thri ugh successive positions, so the seat angles for those positions are read firom the memojy an fed to the carnage to actuate a seat levelImg motor to maintain the seat level. A DID (proportional/integral/differential) control system may be used. The seat may cAy a pendulum for calibration; for this, the carriage is driven to each successive position i and stopped, and the angle of the pendulum recorded in the memory.

A further such technique is described in WO 98/37007, Bison Bede/DC Drives 1 this, an inclinometer is fixed to the seat, and its output is used to drive the seat lei e..ing motor. The inclinometer consists of an inertial mass mounted on a stiff arm with a s.. gauge and located on the axis of rotation of the seat on the carriage. A pendulum S so mounted on the seat, to sense substantially static inclinations.

q The general object of the present invention is to provide an improved techni fl r maintaining the seat of a stairlift carnage level.

According to the invention there is provided a stairlift carnage comprismig a c h ass having a seat rockably mounted thereon, level control circuitry fed by level sensing 1r s for sensing deviations of the seat firom the horizontal, and a seat levelling motor conAlled by the level control circuitry, wherein the level control circuitry includes angular vel cily sensing means mounted on the chassis. 1 As the chair moves up and down its track, the chassis will, as discussed abov,, tilt (le undergo angular rotation) with the changes of gradient of the track as discussed ilov. i In the present system, the velocity of the angular rotation of the chassis is sensed an 1. is d to drive the seat levelling motor to produce a substantially equal and opposite an,Rlar rotation of the seat, so keeping the seat level. The level sensing means on the seat we ised to sense and correct any inaccuracies in the angular velocity control. j i 3 The angular velocity sensing means preferably comprise a gyroscope which produces an output proportional to the angular velocity (rate of turn) of the chassis.

Preferably also the level sensing means comprise a pendulum for measuring static deviations of the seat. The seat mounting of the seat on the carriage can conveniently comprise a shaft to which the seat is attached and which is rotatably mounted on the carriage.

A velocity signal sensor such as a tachometer is preferably coupled to the seat levelling motor and feeding the level control circuitry. The position of the pendulum may be sensed by any convenient means, such as a rotary potentiometer or a shaft position encoder.

A stairlift embodying the invention will now be described, by way of example, with reference to the drawings, in which:

Fig. I is a diagrammatic view of the stairlift; and Fig. 2 is a block diagram of the level control circuitry.

Referring to Fig. 1, the stairlift consists of a track 10 and a carriage consisting of a chassis 20 mounted on the track and a seat 21 mounted on the chassis. The chassis 20 includes a main drive motor 22 for driving the carriage up and down the track 10, eg by a rack and pinion drive. The seat 21 is mounted on the chassis 20 via a pivot mounting 2-3) which is driven by a seat levelling motor 24. A control unit 25 carried on the carriage, and controls the motor 24.

The track or rail 10 typically follows a staircase, and is firmly attached to the staircase. If the staircase has bends in it the track will follow round those bends; if it has landings, it will follow horizontally across those landings; and it may also have horizontal 4 sections at one or both ends. Thus it will have sections of different gradients, as sh 1 or sections 11 and 12 in Fig. 1.

The carriage moves up and down track 10, to carTy the occupant of the seat 2 r p down stairs, being driven by any suitable means such as a motor 22 mounted on the 1 S is and engaging with the track 10. As the carriage moves up and down the track 10, it i v 1 t to different extents as the gradient of the track changes. The seat 21, however, mu t e maintained horizontal, to keep its occupant comfortable and prevent them from fall' i o The seat 21 is pivotally mounted oil the chassis 20 by a shaft 233, which is driven by se levelling motor 24. The angle of the seat 20 to the vertical is determined by th 1 control unit 25, which drives the motor 24 appr ately.

opn The drive from the levelling motor 24 to the shaft 23) is preferably non- reversi that the seat cannot drive the motor and so tilt as a result of loads placed on th e 1-5 Preferably also, however, a mechanical lock (not shown) is arranged to engage wi drive from the motor to the seat if the control system is switched off or otherwise be inoperative.

Fig. 2 shows the level control unit 25 in more detail. This includes a gyroscop 30 mounted on the chassis 20 and a pendulum unit 31 mounted on the seat 2 th remainder of the cirCUltry can obviously be located wherever convenient.

It is convenient to begin the description of the circuitry at the motor end. The to

24 is driven by a driver circuit 32. The motor drives the shaft 23, as noted above, an S drives a tachometer (tacho) unit 33, whose output is fed back to the negative input summing unit 34 which feeds the driver circuit 32. This summing unit is also fed velocity demand signal which will be described shortly. The feedback loo ou tacho unit 33 balances the actual velocity of the motor, as measured by the tac o unit, 1 the velocity demand signal, thus ensuring that the motor velocity matches the velocity demand signal.

The gyroscope unit 30, which is mounted on the chassis 20, generates an output signal which is proportional to its angular velocity. Thus if the chassis starts to tilt, the gyro signal will be proportional to its rate of tilt. This output signal is converted to digital form by an A/D converter 37 and passed through a linearizing circuit 40 to a summing unit 38, which feeds a D/A converter 39 which produces the velocity demand signal mentioned above. Thus if the chassis 20 is tilted, the rate of tilt will generate a corresponding velocity demand signal, which will drive the motor 24 to rotate the seat 21 with ail equal and opposite velocity.

The gyro unit 30, of course, measures the rate of tilt of the chassis 20 relative to an absolute or fixed frame of reference. As the carriage moves up and down the track 10, so the chassis will tilt as it moves past bends such as the bend between sections 11 and 12 (Fig. 1). The seat 21 will tend to tilt with the chassis, but any tilting of the chassis is detected by the gyro unit 30, and the level control unit 25 operates as just described to generate an equal and opposite tilt on the seat, so keeping the seat level.

Cheap and rugged gyro units suitable for present purposes are readily available.

However, such units, and the control system associated with them, may not be sufficiently accurate when used at the required operating speed, and are also liable to slow long-term drift. The pendulum unit 31, fixed to the seat 21, is therefore included, to give an absolute measure of the angular position of the seat. The control circuit combines this signal with that from the gyro in such a way as to maintain the required rapid response capability of the gyro, but with much increased accuracy. It is also able to maintain long- term horizontality.

Specifically, the pendulum unit may consist of an oil-damped penduhun coupled to a rotary potentiometer whose output is fed via an A/D converter 45 to a summing unit 46 which feeds the summing unit 38.

6 In practice, the pendulum and the gyroscope will both be operating tog f L r to maintain the seat horizontal. To understand the operation of the pendulum, howe I IS convenient to suppose for the ptu-poses of illustration that the carnage is stationary e seat has somehow been set at an angle to the horizontal by the gyro unit. The si in the pendulum unit will generate a velocity signal which will cause the motor 24 to U d so rotate the seat. As the seat rotates towards the horizontal, so the pendulum. outp al will decrease towards zero, and the rate at which the seat is rotating towards zero wi al o decrease until the system reaches stability when the seat is horizontal. SMce the 0 e is attached to the chassis, there will be no change in the output of the gyroscope s pendulum-controlled correction.

The sensitivity of the level control unit to the pendulum signal is set low, so e system does not react significantly to pendulum movements resulting from move e f the carnage. In other words, the time constant of the level control unit's respo changes in the pendulum output is long compared to the natural period of the pendul.

its response to carriage movement. The pendulum signal control circuit pre I I includes PI (proportional plus integral) control circuitry.

A set-point signal unit 48 feeds the summing -unit 46, and can be used to adj - s th seat angle for which the system is quiescent.

The output from the pendulum unit (or the summing unit 46) is preferably als e as shown at 47, to safety circuitry (not shown) which interrupts the main power suppl halts the carnage if the angle of the seat exceeds a predetermined limit. The oil dar 1], of the pendulum effectively smooths or low-pass filters its output signal, preventing it fl.

producing jediness when carriage is moving, and particularly when it is under a changes of movement. The effect of carnage movement on the safety circuit signal at 4 i therefore not excessive.

7 If desired, threshold circuitry can be included to prevent the motor 24 from being driven until the drive signal to it exceeds a predetermined level. This Will prevent hunting and reduce the power consumption.

Means can be provided for indicating when the carriage is on a straight section of rail. This can be achieved, for example, by a simple form of memory like that used in the Stannah Stairlifts system mentioned above, or by attaching indicator elements to the rail 10 and sensor means to the carriage. The entire level control unit 25 can then also be 10 switched off on such straight rail sections.

The A/D converters 37 and 45 may be formed by a single converter timeshared between the two sensors 30 and 3 1.

Claims (1)

1. Clams

   1 A stairlift carriage comprising a chassis having a seat rockably mounted th o level control circuitry including level sensing means for sensing deviations of the sea 2.011 the honzontg and a seat levelImg motor controlled by the level control circUltry, w A rei i the level control circuitry includes angular velocity sensing means mounted on the ch s s. i i i i 1 2 A stairlift according to claim 1 wherein the angular velocity sensing means cor.i) is, a gyroscope which produces an output proportional to the angular velocity (rate of tun ef the chassis.

   A stairlift according to any previous claim wherein the seat is mounted en th carriage by means of a shaft to which the seat is attached and which is rotatably mourll e 0 the carriage.

   4 A stairlift according to any previous claim wherein the level control cire includes a velocity signal sensor coupled to the seat levelling motor and providii feedback signal for the motor.

   A stairlift according to any previous claim wherein the level control cirit includes a set-point signal unit feeding a summing unit and effective to adjust the sea:t a: for which the system is quiescent.

   6 A stairlift according to any previous claim wherein the level sensing means fi ie comprise a pendulum for measuring static deviations of the seat.

   9 9 A stairlift according to claim 6 wherein the position of the pendulum is sensed by a shaft position encoder.

   A stairlift according to claim 6 wherein the position of the pendulum is sensed by a 5 rotary potentiometer.

   I I A stairlift according to any of claims 6 to 9 wherein the output from the pendulum is also fed to safety circuitry which halts the carriage if the angle of the seat exceeds a predetermined limit.

   12 A stairlift according to any previous claim wherein the level sensing means further comprise threshold circuitry to prevent the motor from being driven until the drive signal to it exceeds a predetermined level.

   13 A stairlift according to any previous claim including means for indicating when the carriage is on a straight section of rail.

   14 A stairlift according to claim 13 including a memory.

   15 A stairlift according to claim 13 including indicator elements attached to the rail and sensor means attached to the carriage.

   16 A stairlift substantially as herein described and illustrated.

   17 Any novel and inventIve feature or combination of features specifically disclosed herein within the meaning of Article 4H of the International Convention (Paris Convention).