CONTROL OF SEAT ORIENTATION FOR STAIR LIFT

Abstract: A control arrangement for controlling the orientation of the seat assembly of a stair lift with respect to the chassis of the stair lift as the chassis moves along an inclined elongate rail. The control arrangement includes means for causing relative movement between the seat assembly and the chassis, such as, for example an electric motor. These means are then further controlled by control means such as an electronic circuit to ensure that the seat assembly is maintained in a horizontal orientation with respect to the ground. In addition, a stair lift rail construction arrangement is also disclosed wherein transitional sections of rail between rail sections of different inclines are formed as arcs of a circle. This allows the control means to be simplified as the electric motor need only be run at a constant rate to maintain the seat orientation during the transitional sections.

Description: CONTROL OF SEAT ORIENTATION FOR STAIR LIFT The present invention relates to a stair lift and more particularly to a modified method of control of the lift. In addition, the present invention also relates to the modified construction of such a lift, .and in particular to the construction of the rail arrangement used in such lifts. Stair lifts, for transporting people who have difficulty negotiating staircases from one floor to another, have been used for several years in buildings where such people reside. These stair lifts generally comprise a rail arrangement which runs along a staircase in a similar manner to a bannister. They further comprise a chassis which runs .along the rails which in turn supports a load bearing means generally comprising a seat. When the stair lift is in operation and the chassis and seat arrangement are ninning along the rails, it is very important that the seat arrangement moves as smoothly as possible, and that it is kept in a horizontal orientation. This ensures that the person being transported, who wild frequently be frail and sensitive to sudden movements, is not injured. In many residential buildings, the stair lift will travel along a substantially straight inclined rail, or a curved rail of variable gradient from one level to another. No seat orientation mechanism will hence be necessary as the chassis can be fixed in a predetermined orientation to the seat means. However it is also common for staircases to comprise two or more flights, often of different gradients .and frequently with horizontal rail sections as corners are turned and level floor sections are negotiated. When stair lifts .are required to negotiate rails which vary in gradient, some mechanism is required for rotating the seat means relative to the chassis so that the seat means always remains horizontal as the chassis means rotates about a vertical axis when the rail gradient varies. Usually this is done mechanically using push or pull rods. It is also customary to tailor the rail or rails to the p.articul.ar site where the lift is installed. This makes re-siting a lift an expensive procedure. From one aspect the present invention provides a control arrangement for use in a stair lift wherein the .arrangement controls the orientation of the seat assembly of the lift relative to the chassis to ensure that the seat assembly remains substantially horizontal with respect to the ground. The orientation of the seat assembly with respect to the chassis can be controlled either in an open-loop or a closed loop manner. In the case of open- loop control a profile generator can be used to store the incline profile along the length of the rail of the stair lift, the profile then being used to set the seat assembly orientation at each point along the rail. Alternatively, in the case of closed-loop control, an inclinometer can be used to measure the incline experienced by the seat assembly and this measurement used to control the orientation in a dynamic manner. It will be further appreciated that a combination of open-loop and closed loop control can also be used for increased accuracy of seat assembly orientation. From another aspect, the present invention provides a rail for a stair lift comprising first and second straight sections of rail joined by a curved transition^ section, wherein the curved tr.ansitional section is in an arc of a circle. It will be appreciated that a transition from vertical motion to horizontal motion would require a tr.ansitional section extending through 90°. Any inclination less than vertical will require a smaller arc. The seat portion of the stair lift is driven by means of a gear arrangement engaging with a toothed rack with which the rail is provided. Preferably, the radius of the arc of the or each tr.ansition section .and the number of teeth are arranged such that there are an integral number of teeth on the transitional section no matter the length of the arc. It is currently preferred that each tooth occupies 2° of arc and so the transitional section can be any length but in 2° steps. The present invention proposes to utilise standardised parts. .An advantage of the use of a circular arc for the transitional section is that the control system can be simplified in the case that .an electronic control system is used in the control arrangement for levelling the seat of the lift. This 3 arises due to the fact that the levelling electric motor need only be driven at a constant speed in order to keep the seat level as the lift negotiates a transitional section. An advantage of the use of standardised parts of lengths an integral number of teeth is that a rail or rails can be constructed with the minimum of expense .and inconvenience. In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic sketch of a part of a rail system for a stair lift; Fig. 2 is an exploded view of the manner in which rail sections are joined together; Fig. 3 is a graph of motor speed v time for a levelling motor of a stair lift; Fig.4 is a diagrammatic view of a stair lift according to a modification of the present invention; and Fig. 5 is a control system for use with the embodiment shown in Fig. 4. A stair lift comprises .an assembly of an inclined rail fitted to a staircase, and a chair section pivotally mounted on a chassis section which engages with the rail. The chassis section is driven up the rail by a motor which turns a toothed wheel which in turn engages a toothed rack provided on the rail. Fig. 1 shows diagrammatically a portion of the rail 1 of a stair lift according to the present invention. By way of example, this rail 1 is formed from three sections, n.amely a horizontal strmght section 10, an inclined straight section 11 and a transitional section 12. Each straight section may be made from a plur.ality of straight sections of equal length. Each rail section has a uniform cross- section throughout its length and can be considered as being formed as two tubes 14, 15 joined by a vertical flange 16. In the present particular embodiment, the 4 upper tube 14 is provided with a respective toothed rack section 20,21,22, although it will be appreciated that the toothed rack section may be provided alternatively on the lower tube 15. The rail sections are joined together so that there is a seamless transition from one rail section to the next and in the case of the toothed rack this means that the ends of the rack sections form a continuous progression across the join. This places a constr.aint on the length of both the straight section 10 and 11 and also on the transitional section 12 as they must be integral multiples of the tooth pitch. It is .arr.anged that each tooth occupies 2°of .arc at the radius r. Each of the straight sections can be of the same length so that one long rail can be made up from a number of sections joined together. Equally it is possible to form transitional sections by joining together section shaped portions. When this is the case, all of the transitional sections joined together must have the same .arc radius r, but each may be a different length provided that the previous condition of an integral number of teeth is satisfied. Fig. 2 shows the rail section connection system between two sections, in this case two straight sections 10a and 10b. A u-shaped connecting link 17 has its legs 17a and 17b inserted through holes 16a and 16b in respective fl-anges 16 of the sections 10a and 10b. Nylon washers are fitted to protect the paint, and then a joint plate 18 is driven down over the ends of the legs of the connecting link 17. The joint plate 18 is an interference on the connecting link 17 so it clamps the rail sections together and it has a "return" on each of the chamfered sections to latch it in place. A vacuum formed cover 19 is fixed, with a quick fit and release rivet, to give a good aesthetic appearance. The join between a straight and a transitional section is made in the same way. As an alternative, the u-shaped link could be replaced by protrusions on the flanges shaped to receive the joint plate. The transitional section 12 is formed as an arc of a circle. The need to have the toothed rack section 22 ending in troughs of the rack means that there are discrete lengths of arc which can be formed. This in turn might mean that a horizontal section say on a half landing may be at a level slightly higher or lower than it might ideally be. However, the difference is very slight. A number of advantages accrue from the use of circular arcs for the transition section or sections 12. The first is that the rail becomes basically modular being made up of lengths of straight sections joined by arcuate transitional sections the only difference between two installations being the lengths of the sections. This means that lengths of rail sections can be re-used or cut to size on site or pre-formed. The second advantage is that when an electronic control system is used for levelling the seat of the stair lift, the control system can be simplified because the basic rate of change of seat angle with respect to the rail is constant along the arc of the tr.ansition.al section. This in turn means that the levelling motor need only be run up to a fixed predetermined speed which is a function of inter alia the radius of curvature of the arc. This is shown more clearly in Fig. 3 which is a graph of levelling motor speed with time. The ramp up and ramp down are of a predetermined slope and are initiated by means of indicators which indicate the start and finish of the transitional section. It is also necessary to know which direction to run the motor. This could be achieved by indicators or the processor arrangement forming part of the control system could store the fact of whether the transitional section is an inside our outside bend. It will be recognised that a detailed knowledge of a profile is not required; merely a description of the overall shape e.g. straight, inside bend, straight, outside bend, straight. With this knowledge together with indicators to mark the start/finish of end section and knowledge of the radius of the bends, a good basic control of seat orientation can be achieved. If desired, the control system can incorporate further control arrangements such as open or closed control loop systems. It is preferred to utilize a further closed loop control system incorporating further level sensors in order to improve the degree of control of seat inclination. Such an arrangement will now be described with reference to Figs 4 and 5. 6 Fig 4 shows a stair lift comprising a rail 1, a chassis assembly 27 and a seat arrangement 28 provided with an inclinometer comprising an inertial mass 44 attached to a stiff arm 40 of material provided with a strain gauge 42, wherein the centre of mass of the inertial mass is substantially located at the axis of rotation of the stair lift chassis. Using a stiff, bendable arm of material rigidly attached to, and not rotatable about a pivot instead of a free swinging pendulum, .and a strain gauge to monitor the strain on the arm, an inclinometer is generated which has a very high resonant frequency and quick resonance decay time. This inclinometer will be highly accurate as long as it remains in a substantially vertical orientation, as will be the case if it is attached to the seat arrangement. The arm is attached to the seat arrangement such that it hangs vertically from the seat arrangement 28 when the seat arrangement is in a horizontal orientation. The centre of mass of the mass 44 is located substantially at a point located on an extension of the axis A of the pivot, when the seat arrangement is in a horizontal orientation. The combination of the .arm of material 40, the strain gauge 42, and the mass 44 will hereinafter be referred to as an inclinometer. As is shown in Figure 5, the voltage V generated by the inclinometer is used as a control signal for a seat levelling motor 38; a clockwise rotation of the inclinometer generates a signal V to the motor to cause equal and opposite rotation of the seat arrangement 28 about the chassis arrangement 27 at a rate proportional to the value of the signal V. As the signal V is proportional to dθ/dt (the absolute rate of rotation of the seat arrangement), and the speed of the motor is proportional to the rate of rotation of the seat arrangement about the chassis means, calibration of the control signal allows the motor 3 8 to rotate the seat arrangement 28 at dθ/dt relative to the chassis arrangement and hence cancel any absolute rotation of the seat arrangement. If the stair lift is travelling along the rail 1 driven by motor 23 at one gradient and undergoes a change in gradient, the chassis .arrangement will begin to rotate at a rate ω as the leading one of two rollers 32 starts to rise or fall with 7 the change in gradient. This value ω will depend on the radius of curvature and speed of the stair lift at the point in question and the slope of the ramp in Fig. 3 will be a function of these factors. The seat arrangement 28, which is rigidly connected to the chassis arrangement 27 will also rotate at rate ω. This will cause a strain in the inclinometer generating an output voltage V from the inclinometer proportional to ω. This signal V controls the motor 38 which will rotate the seat arrangement at the same rate ~ in the opposite direction relative to the chassis arrangement. As a result, the seat maintains a generally horizontal attitude. When the seat arrangement undergoes angular acceleration at θ relative to the chassis arrangement, the mass 44 will accelerate at rθ. Inertia of the mass will mean that a significant component proportional to r is added to the strain on the inclinometer during this .angular acceleration. This str.ain on the inclinometer will generate a voltage V E which will be fed to the motor and cause an extra component of the angular acceleration of the seat arrangement which is unwanted. If r is large, this extra component of the signal V can be larger th.an the desired component due to .angular deviation, and in these situations significant undesirable resonance can be set up. The distance r between the centre of mass of mass 44 and the axis of rotation of the seat arrangement 28 and the chassis arrangement 27 is arranged to be substantially zero when the inclinometer is at rest and the seat arrangement is horizontal. In order to attain as low a value of r as possible, regardless of the rate and direction of the ch.ange of gradient, a substantially circular shape for mass 44 is advantageous as its accelerational properties will v.ary to a similar degree in whichever way it moves from a preferred position. Furthermore an annular shape has also been found to be advantageous. The output of the dynamic sensor actu ly comprises three components, one is due to the error caused by the seat being off-level, the second through inertia due to the rotational acceleration of the weight, .and the third through inertia due to the line.ar acceleration and deceleration of the stair lift. In practice, the third component sign.al due to the linear travel of the 8 lift is small and does not substantially affect the system perform.ance as the rate of change of linear speed is slow. The v.alue of the second component due to rotational acceleration is rninirnised by placing the center of mass of the weight at the point of rotation thus reducing the radius of rotation r to a minimum as described above. The remaining off-level error signal, which is proportional to the strain experienced by the strain gauge 42 is fed to the motor drive .and the phase is arranged so that the motor corrects the error until there comes a point at which the seat is level. Thus the control system is a closed loop. In this embodiment, the sensor is in the form of a piezoelectric strain gauge which generates a signal proportional to strain. The output of the strain gauge is temporarily stored as a charge on a capacitor the charge Q being a function of strain x K x e υCR . The charge will eventually be lost as the capacitor discharges through the inevitable resistance component. Thus the dynamic sensor on its own cannot provide long term positional information, typically a few minutes. In some cases, this is not important, but for a stair lift it is necessary to have a long-term levelling reference such that the lift has an absolute reference point to use when initially switched on. This problem is overcome by providing the stair lift with a pendulum arrangement 50 as well as the inclinometer. This pendulum .arrangement comprises a weight 51 on the end of a rigid arm 52 and can be located at any convenient position. As shown weight is positioned so that its centre of mass lies on the axis A and is provided with a potentiometer 52 or other means for providing a signal Y proportional to the angular deviation of the pendulum .arrangement. However as discussed earlier, pendulums in the size ranges allowable on a stair lift have reson.ant frequencies of the order of a few hertz. These are of the same order of magnitude as the angular accelerations of the stair lift, .and so, when the stair lift is in motion, significant sinusoidal unwanted components will be added to the signal Y. However, the signal gives an absolute position signal which is used as the long term levelling reference but is .also used for long term correction of errors caused by inaccuracies in the calibration of the inclinometer and small external effects such as draughts. The signal Y is preferably passed through a low pass filter 55 (Fig. 5) and the resultant signal added to a signal X from the inclinometer for supply to the tilt motor 38 speed control. The quick response of the inclinometer 42 is thus combined with the longer term accuracy of the pendulum 50 so that the seat arrangement travels over a smooth and horizontal path. It will be noted that the output of the inclinometer 42 is fed through the series combination of a low pass filter 56 and a high pass filter 57. This creates a pass band the volume of which is designed to pass seat error signals but cut off before the natural resonant frequency of the dynamic sensor assembly. In this embodiment, the low pass filter 56 suppresses signals above 15 Hz. Additionally, the high pass filter 57 suppresses signals at low frequency such as those due to drift caused by e.g. temperature change. In this embodiment these frequencies are below 0.15 Hz being of the order of 0.015 Hz. This also has the effect of leaving the pendulum 52 to compensate for these low frequency effects. The signals X and Y are added to the output of the profile generator (58) in order to control the horizontal orientation of the seat assembly as it goes through a tiansitional section. In some circumstances it may be possible to dispense with one or other of the sign-als X and Y in view of the fact that the main levelling control signal is derived from the output of the profile generator. In modifications of either of the above embodiments, resistive, semiconductor or light deflection strain gauges are used. Infra red, capacitative and ultra sonic means could be adopted to measure the .amount of deflection. It is thus possible that a single sensor could be used to replace the combination of the inclinometer .and pendulum. A further advantage of the inclinometer and pendulum aπangement disclosed above is that different levels of safety interlock can be provided to ensure that in the event of a malfunction, the seat cannot be rotated by more than a predetermined amount from the horizontal. It will be appreciated that the output of the inclinometer can be used to trigger a safety lock in the event that the output 10 from the inclinometer exceeds a preset value. The inclinometer provides a very fast output and consequently is suitable for providing a first level of safety. If this output signal is combined with a further output signal from the pendulum .arrangement which is slower acting, the combination of output signals from these two sensors could provide a second level of safety. Finally, by the addition of a static level switch such as a mercury tilt switch could inhibit the operation of the stair lift in the event of a gross fault. While a stair lift incorporating the sensor or sensors has been described, it will be appreciated that the sensors either separately or in combination can be used in other arrangements where the level of an object has to be controlled. Consequently the sensors either alone or in combination are to be considered as separate inventions.

Claims: 11 CLAIMS: 1. A control arrangement for controlling the orientation of a seat assembly (28) pivotally mounted on a chassis (27) moveable along an elongate inclined rail (1), the control arrangement comprising means (38) for causing relative movement between the assembly and the chassis, and control me.ans (56,57,58) for controlling the means for causing relative movement to operate at a fixed rate during the time wheen the chassis is moving through a transitional section (12) of the rail. 2. A control arrangement according to claim 1, wherein the control means comprises a profile generator (58) arranged to produce signals indicative of the profile of the rail. 3. A control arrangement according to claim 1 or 2 and comprising an inclinometer for producing an error signal for modifying the output of the control means to maintain the orientation of seat assembly. 4. A control arrangement according to claim 3 wherein the inclinometer comprises an inertial mass (44) fixed to one end of a substantially stiff arm (40), an opposite end of said arm being substantially rigidly attached to the seat assembly (28), said arm having a strain gauge (42) mounted thereon to monitor the strain on the arm, an output signal (V) of the strain gauge being a component of the error signal. 5. A control arrangement according to claim 4, wherein a centre of mass of the inertial mass is substantially located at an axis of relative movement between the assembly and the chassis. 6. A control arrangement according to claims 4 or 5, wherein the strain 12 gauge is a piezoelectric strain gauge. 7. A control arrangement according to any of the preceding claims and comprising a pendulum (51,52) for providing a signal indicative of the static orientation of the seat assembly (28). 8. A stair lift comprising an elongate rail (1) provided with a toothed rack (20,21,22) on which a chassis (27) is arranged to be mounted for movement along the length of the rail, said chassis having a seat assembly (28) pivotally mounted thereon, said rail being formed of individual straight sections (10, 11) joined by at least one transitional section (12) which is shaped as an arc of a circle, the length of each of the sections being an integral multiple of the rack tooth pitch, wherein said stair lift further includes a control arrangement for controlling the orientation of the seat assembly relative to the chassis, said control .arrangement comprising means for causing relative movement between the assembly and the chassis (38), and control means (56,57,58) for controlling the means for causing relative movement to operate at a fixed rate during the time when the chassis is moving through the tr.ansitional section (12) of the rail. 9. A control arrangement as substantially hereinbefore described with reference to the accompanying drawings. 10. A stair lift as substantially hereinbefore described with reference to the accompanying drawings.

Inventors: WHITEHOUSE DERRICK JOSEPH, WHITEHOUSE, DERRICK, JOSEPH
Applicants: BISON BEDE LIMITED, WHITEHOUSE DERRICK JOSEPH, WHITEHOUSE, DERRICK, JOSEPH
Application year: 1999
Main classification: B66B9
IPC codes: B66B9