GB2578136A

GB2578136A - Stairlift and method of operating a stairlift

Info

Publication number: GB2578136A
Application number: GB1816967.2A
Authority: GB
Inventors: Pugh Gavin
Original assignee: Stannah Stairlifts Ltd
Current assignee: Stannah Stairlifts Ltd
Priority date: 2018-10-18
Filing date: 2018-10-18
Publication date: 2020-04-22
Also published as: WO2020079395A3; GB201816967D0; WO2020079395A2

Abstract

A stairlift includes a stairlift rail 11, a carriage 15 mounted on the rail 11, a chair 20 pivotally mounted on the carriage 15, at least one motion sensor 30, 114, 27, a chair levelling motor 26 operable to pivot the chair 20 relative to the carriage 15 as the carriage 15 traverses the rail 11, memory and a control system. The control system is operable at step 414 to store a record (310/320 fig. 8) of an undesirable movement of the chair 20 such as chair levelling oscillations or overall chair angular lag from the upright position. The record (310/320 fig. 8) includes an indication of the position along the rail at which the undesirable movement occurred (336 fig. 8). The control system is also operable, during a subsequent traversal of the rail 11 by the carriage 15, to apply a remedy to attempt to prevent a reoccurrence of the undesirable movement of the chair at the position indicated in the record (310/320 fig. 8). The control system is further operable to determine at step 416 whether the undesirable movement of the chair reoccurred and, if it did reoccur, to reduce the speed of the carriage 15 during a subsequent traversal of the rail 11. Remedies may include using an anti-oscillation unit (122 fig. 4) to adjust or block the output from a low gain unit (116 fig. 4) forming part of a control signal (102 fig. 4) or to dynamically modify a primary signal (108 fig. 4) using a slow filter (124 fig. 4) receiving a signal from a gyroscopic gain unit (120 fig. 4) or to reduce the speed of the carriage 15 along the rail 11.

Description

STAIRLIFT AND METIIOD OF OPERATING A STAIRLIFT

FIELD

This invention relates to a stairlift and to a method of operating a stairlift.

BACKGROUND

Stairlifts typically comprise a rail following the contour of a staircase; a carriage mounted to move along the rail; and a chair mounted on the carriage, upon which the stairlift user sits during movement of the carriage along the rail. One of the requirements of any stairlift installation is that the chair remains substantially level at all times as the carriage moves along the rail.

Traditionally levelling has been achieved using mechanical arrangements, some of such arrangements involving variations in spacing between rail components. Now, however, electronic-based solutions are well established, one such approach being the subject of our European Patent 0 738 232. European Patent 0 738 232 describes and claims an electronic levelling arrangement in which data representing the correct chair position at points along the rail is stored in an electronic memory. This exercise is broadly referred to as rail mapping.

In operation, the position of the carriage along the rail is determined by comparing instantaneous data from, for example, an encoder attached to the carriage drive motor with data in memory indicating where, on the rail, the carriage will be for a given encoder reading.

In other words, an installer needs to map the rail thus increasing the time and complexity for installation. The appropriate control signal, also determined by data in memory can then be passed to the chair levelling mechanism to ensure that the chair is maintained in a level state.

An alternative approach to chair levelling is the reactive approach. This approach employs one or more sensors to sense when the chair is going off-level and to react by powering a seat levelling motor that operates in the opposite direction to restore the chair to level. In this approach it is known to combine signals from a gyroscope with signals from an accelerometer to effect levelling, the gyroscope providing a fast reaction to the chair rotating, but lacking accuracy, while the accelerometer reacts more slowly to changes of angle, but is more accurate.

One arrangement of this type is described in European Patent 2 216 284. This patent describes a levelling arrangement that employs an accelerometer and a gyroscope, both mounted on the chair. The signals from these are combined to provide a signal which is fed to a chair levelling motor.

A number of problems arise from mounting sensors on a chair. Firstly, since the chair is mounted at the end of a pivot arm, the noise is invariably high. Secondly, with both the gyroscope and the accelerometer being mounted on the chair, only small error signals are being processed (since in normal operation the angle of the chair does not deviate off-level to any great extent) and the signal-to-noise ratio is thus very low.

Thus a high level of filtering is required to extract the necessary control signals.

Further, whenever a signal is combined with noise, the signal must be averaged over a longer time period and so becomes slow thus giving rise to an angular lag.

A known approach is disclosed in United Kingdom Patent Application GB 2,358,389 and is described below in relation to Figures 1 to 3.

Figures 1 and 2 show a stairlift installation 10 that includes a rail 11 mounted in a stairway 12, the rail 11 including bends 13 around a substantially horizontal axis (transition bends') and typically bends 14 around a substantially vertical axis (inside/outside bends'). The rail 11 may also include bends that combine elements of both vertical and horizontal change, sometimes referred to as helical bends. A carriage 15 is mounted on the rail 11 for movement up and down the rail between an upper end 16 and a lower end 17.

Pivotally mounted on the carriage 15, by way of arm 18, is a chair 20. In the form shown the chair has a seating surface 21, a back 22, a pair of armrests 23 and a footrest 24. A levelling motor 26 is provided to alter the position of the chair 20 relative to the carriage 15 by pivoting the arm 18 about pivot axis 19.

A control system is described in detail below is provided to control the motor in such a way as to ensure the seating surface 21 remains substantially horizontal at all times, particularly when the carriage is passing over a transition bend in the rail.

Turning now to Figure 3, the primary levelling signal applied to the motor 26 is derived from a gyroscope 27 mounted in the carriage 5. The gyroscope is a Micro-ElectroMechanical Systems (MEMS) device in the form of a silicon-based sensor chip that provides a Serial Peripheral Interface (SPI) serial output indicative of the rate of rotation in a single plane although those skilled in the art will appreciate that the output may take other forms.

The gyroscope 27 may conveniently be mounted on the main drive circuit board in the carriage 15 so that it is rigidly coupled to the carriage chassis and so that the plane of rotation of the sensor is aligned with the direction of travel of the carriage along the rail.

To enhance the accuracy of the levelling system, the signal generated from the gyroscope 27 is added to a signal derived from an accelerometer 30 mounted on the chair.

The accelerometer 30 is may also be a MEMS-type device. The accelerometer is conveniently a 3-dimensional, or 3-axis,chip device mounted in such a manner that the plane made by two of the three axes is parallel to the direction of gravity and the axis of rotation 19 of the arm 18 so that trigonometric functions can be used to determine the angle of the chair relative to the direction of gravity. The trigonometric function can be ARCTAN2.

In the known levelling arrangement shown in Figure 3, a chair position signal is derived from the accelerometer 30 alone. However most of the signal that controls the motor 26 is derived from the rate of change of angle from the gyroscope 27. Upon an angular speed and position error signal being produced from the sensors 27 and 30, the gyroscope 27 is used to generate transitory injections of speed demand to the Speed PID Loop which, in turn, receives a feedback signal from encoder E mounted on the shaft of motor 26.

The gyroscope 27 directly measures angular speed and therefore feeds the Speed PID Loop that controls the angular speed of the chair. If the gain of the gyroscope is correctly set, in the Gain Match step, then levelling can be effected relatively well without significant input from the accelerometer 30.

If the carriage is subjected to a rapid change angle, then the gyroscope 27 measures the speed of movement and the inverse signal is added to the Speed PID input at the point just before the signals from the gyroscope and accelerometer are added. This moves the Speed PID loop input faster than the slow accelerometer 30 can measure. Over the long term the gyroscope 27 cannot track angular movement, and will slowly drift. In the absence of the accelerometer, this would lead to the seat surface 21 being off-level. However the heavily filtered signal from the accelerometer corrects the angle and thus avoids any long term angular drift.

The accelerometer signal is subjected to a control function in which a limit is applied to the chair rotation speed demand as this speed increases in proportion to the angular error. The function is Z-shapcd.

Figure 3 includes an automatic gain control for the gyroscope 27 via a 'slow integral'.

Accelerometer error, or deviation from zero, is used to adjust the degree to which the gyroscope feedback moves the chair. When a no error' or 'zero error' condition is established the integral will not change its value and the overall gyroscope feedback gain is thus fixed.

Figure 3 also illustrates gain control over the Z function. This allows for soft levelling when, for example, a passenger disembarking, causes the carriage to vary its angle relate to the rail and so causes the chair to be a few degrees off-level.

Known systems, such as described in relation to Figures 1 to 3, reduce the bandwidth 25 demand for accelerometer data. A significant demand for bandwidth remains, however, and is satisfied by a gyroscope.

It is to be noted that accelerometers (of the MEMS type) are inherently sensitive to mechanical noise, which can be filtered out at the cost of bandwidth (i.e. it will have low bandwidth). To achieve acceptable levels of control in any closed loop control system the primary feedback sensor needs high bandwidth. Therefore an accelerometer cannot be the primary sensor in a high performance system. Gyroscopes (of the MEMS type) are less sensitive to mechanical noise and only need a small amount of filtering. Gyroscopes are considered as high bandwidth sensors and can outperform accelerometers by about 20 times in this respect. A control system where a gyroscope is the primary feedback element will be inherently superior in dynamic performance than an accelerometer based system.

Unfortunately, gyroscopes slowly drift, and a secondary low bandwidth signal is needed to correct the control loop.

Further, mechanical play or 'slop' can occur in the movement of the carriage and/or chair. By way of example, this may occur as a result of an adverse tolerance stack-up in mounting or rail components, or wear-and-tear. This can cause oscillations in the control system that affect the levelling of the chair.

Levelling can be difficult to achieve in regions where the carriage changes level, angle and/or direction. In particular, when a carriage traverses a change in level and begins to travel in a horizontal direction, the change can affect the levelling of the chair.

For example, the release of mechanical energy stored in the interface can bias the level of the chair in one direction. Mechanical energy can be stored in the interface, including the springs, between the carriage (bogey arrangement) and the rail. When the carriage levels out released energy can bias the level of the chair in one direction.

SUMMARY

Aspects of the present disclosure are set out in the accompanying independent and dependent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as explicitly set out in the claims.

According to an aspect of the invention, there is provided a stairlift comprising: a stairlift rail, a carriage mounted on the rail for movement up and down the rail, a chair pivotally mounted on the carriage, at least one motion sensor, a chair levelling motor operable to pivot the chair relative to the carriage as the carriage traverses the rail for retaining the chair in an upright orientation, memory, and a control system operable: responsive to the at least one motion sensor detecting an undesirable movement of the chair while the carriage traverses the rail, to store in the memory a record corresponding to the undesirable movement of the chair, the record including an indication of the position along the rail at which the undesirable movement occurred; during a subsequent traversal of the rail by the carriage, to apply a remedy to attempt to prevent a reoccurrence of the undesirable movement of the chair at the position indicated in the record; and to determine whether the undesirable movement of the chair reoccurred during said subsequent traversal at the position indicated in the record.

According to another aspect of the invention, there is provided a method of operating a stairlift comprising a stairlift rail, a carriage mounted on the rail for movement up and down the rail, a chair pivotally mounted on the carriage, at least one motion sensor, a chair levelling motor operable to pivot the chair relative to the carriage as the carriage traverses the rail for retaining the chair in an upright orientation, and memory, the method comprising: the motion sensor detecting an undesirable movement of the chair while the carriage traverses the rail; the memory storing a record corresponding to the undesirable movement of the chair, the record including an indication of the position along the rail at which the undesirable movement occurred; and during a subsequent traversal of the rail by the carriage: applying a remedy to attempt to prevent a reoccurrence of the undesirable movement of the chair at the position indicated in the record; and determining whether the undesirable movement of the chair reoccurred during said subsequent traversal at the position indicated in the record.

By keeping a record of the position at which an undesirable movement of the chair takes place, and by determining whether the application of a certain remedy can prevent reoccurrence of the undesirable movement, the movement and stability of the carriage and/or chair during subsequent traversals of the rail may be optimised.

The control system may be further operable: responsive to determining that the undesirable movement of the chair reoccurred at the position indicated in the record, to apply, during a subsequent traversal of the rail by the carriage, an alternative remedy to attempt to prevent a further reoccurrence of the undesirable movement of the chair at the position indicated in the record; and to determine whether the undesirable movement of the chair reoccurred during said subsequent traversal at the position indicated in the record. In this way, more than one kind of remedy can be attempted. This can provide the stairlift with one or more additional options, in the event that a first attempted remedy fails to prevent reoccurrence of the undesirable movement.

The control system may be further operable: responsive to determining that the undesirable movement of the chair reoccurred at the position indicated in the record, to reduce the speed of the carriage during a subsequent traversal of the rail by the carriage; to determine whether the undesirable movement of the chair reoccurred during said subsequent traversal at the position indicated in the record; responsive to determining that the undesirable movement of the chair reoccurred at the position indicated in the record, to further reduce the speed of the carriage during a subsequent traversal of the rail by the carriage; and responsive to determining that the undesirable movement of the chair did not reoccur at the position indicated in the record, to control the carriage to traverse the rail at that reduced speed during subsequent traversals of the rail by the carriage. Accordingly, in the event that the attempted remedy or remedies fails to prevent reoccurrence of the undesirable movement, the stairlift can reduce the speed of the carriage until the undesirable movement no longer reoccurs. In this way, the stairlift can search for the optimum (maximum) speed of the carriage that avoids undesirable movements of the chair in the absence of a successful remedy.

The control system may be further operable: responsive to determining that, following the application of a remedy, the undesirable movement of the chair did not reoccur, to increase the speed of the carriage during a subsequent traversal of the rail by the carriage; to determine whether the undesirable movement of the chair reoccurred during said subsequent traversal at the increased speed of the carriage; responsive to determining that the undesirable movement of the chair did not reoccur at the increased speed of the carriage, to further increase the speed of the carriage during a subsequent traversal of the rail by the carriage; and responsive to determining that the undesirable movement of the chair reoccurred at the increased speed of the carriage, to control the carriage to traverse the rail, during subsequent traversals, at a highest speed at which the undesirable movement of the chair did not reoccur.

Accordingly, in the event that an attempted remedy is successful in preventing reoccurrence of the undesirable movement, the stairlift can increase the speed of the carriage until an undesirable movement of the chair is again detected. In this way, the stairlift can search for the optimum (maximum) speed of the carriage that avoids undesirable movements of the chair when the successful remedy is applied.

The optimum speed of the carriage may be a global speed, applied along the entire length of the rail. Typically however, it is envisaged that the optimum speed of the carriage may be specific to the position indicated in the record (or a region of the rail containing that 25 position).

The control system may be operable to store a set of said records, wherein each record corresponds to a respective undesirable movement of the chair while the carriage traverses the rail.

The stairlift may further include a weight sensor for measuring a weight of an occupant of the chair. The control system may be further operable, responsive to determining from the weight measured by the weight sensor that a user having a new weight is occupying the chair, to store a new set of records for the user. This can account for the differences in chair dynamics that can occur dependent upon the weight of the occupant of the chair. The user may be a new user who has not previously used the stairlift. It is also envisaged that the user may be a user who has previously used the stairlift but has experienced a change in weight.

The or each set of records may include: a first set of one or more records corresponding to undesirable movements of the chair as the carriage travels from a lower end of the rail to an upper end of the rail; and a second set of one or more records corresponding to undesirable movements of the chair as the carriage travels from the upper end of the rail to the lower end of the rail. The forces experienced by the carriage at a given position on the rail typically differ depending upon the direction of travel of the carriage. This may be accounted for by keeping a separate set of records for each direction of travel.

A remedy applied for the or each record may be applied only during traversal of the rail by the carriage in the same direction as the direction of travel in which the undesirable movement recorded in that record was detected. Again, this may account for the fact that the forces experienced by the carriage at a given position on the rail typically differ depending upon the direction of travel of the carriage. In particular, it is anticipated that undesirable movements of the chair at a given position may only occur while the carriage is travelling either from a lower end of the rail to an upper end of the rail, or vice versa.

The or each record may include at least one the following: one or more fields specifying a kind of undesirable movement of the chair; one or more fields specifying a kind of remedy; a field specifying a maximum speed of the carriage; and a speed search field. At least some or the fields may be implemented as flags. The control system may be operable to refer to the records as the carriage traverses the rail, in order to determine an appropriate speed for the carriage and/or the remedies to apply at different positions along the rail, and/or whether to attempt a different remedy and/or speed during a current traversal.

The stairlift may comprise: a gyroscope mounted on the carriage; an accelerometer mounted on the chair; and an accelerometer mounted on the carriage, and wherein the control system is further operable to: derive a primary signal from the gyroscope mounted on the carriage for levelling the chair; adjust the primary signal using a secondary signal derived from the accelerometer mounted on the chair, said adjusted signal used to control said chair levelling motor; and modify the primary and/or secondary signal, prior to adjustment, using a tertiary signal derived from the accelerometer mounted on the carriage for stabilising chair movement as the carriage moves through a zone on the rail in which the carriage changes level and/or direction; wherein a modified primary and/or secondary signal is used to control said chair levelling motor as it passes through, enters or leaves the zone.

Various kinds of undesirable movement of the chair are envisaged.

An undesirable movement of the chair may comprise an oscillation of the chair.

In one embodiment, the control system may be operable to apply a remedy to attempt to prevent a reoccurrence of the oscillation of the chair at the position indicated in the record by: monitoring the tertiary signal to determine whether the carriage is passing through, entering or leaving the zone in which the carriage changes level and/or direction; detecting a level of activity of the signal from the accelerometer mounted on said chair that provides the secondary signal; and adjusting the signal from the accelerometer mounted on said chair if the level of activity from said accelerometer exceeds a threshold when the carriage is entering or leaving the zone.

Adjusting the signal from the accelerometer mounted on the chair, for providing the secondary signal, may include temporarily deactivating the secondary signal if the level of activity exceeds a threshold when the carriage is entering or leaving the zone.

In one embodiment, the control system may be operable to apply a remedy to attempt to prevent a reoccurrence of the oscillation of the chair at the position indicated in the record by: monitoring the tertiary signal to determine whether the carriage is entering or leaving a zone in which the carriage changes level and/or direction; and adjusting the signal from the gyroscope mounted on said carriage, for providing the primary signal, for levelling the chair, if the carriage is entering or leaving the zone, Adjusting the signal from the gyroscope mounted on the carriage, for providing the primary signal, may include filtering the signal from a gyroscope to adjust the primary signal to improve the stability of the chair level.

An undesirable movement of the chair may include a lag in the levelling of the chair by the levelling motor as the carriage navigates a bend in the rail.

In one embodiment, the control system may he operable to apply a remedy to attempt to prevent a reoccurrence of the levelling lag of the chair at the position indicated in the record by increasing a levelling speed of the levelling motor.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will he described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs relate to like elements and in winch: Figure 1 shows an isometric view of a known stairlift installation to which a known levelling method and system are applied; Figure 2 shows an enlarged diagrammatic view of the stairlift carriage shown in Figure 1; Figure 3 shows a block-diagram of a known control system used in the levelling implemented to manage the stairlift shown in Figures 1 and 2; Figure 4 shows an improvement to the control system of Figure 3; Figure 5 schematically shows a stairlift having a rail including a number of bends, and indicates a number of locations where oscillations and/or angular lags may be detected as a carriage and chair of the stairli ft traverses the rail according to an embodiment of this invention; Figure 6 shows a method according to an embodiment of this invention; Figure 7 shows a method according to another embodiment of this invention; Figure 8 shows an example of a record that may be stored in a memory of the stairlift according to an embodiment of this invention; and Figure 9 shows an array of records of the kind shown in Figure 8.

DETAILED DESCRIPTION

Embodiments of this disclosure are described in the following with reference to the accompanying drawings.

Figure 4 shows an improved control system used in the levelling implemented to manage the stairlift shown in Figures 1 and 2.

Figure 4 illustrates an arrangement of modules for a control system 100 forming part of a stairlift 10, such as, by way of example, the stairlift shown in Figures 1 and 2. The system includes the encoder E and motor 26.

A control signal 102 is filtered to provide a speed signal to the motor 26, which is passed in to a speed proportional-integral-derivative (PID) loop 104 that feeds a conversion unit 106 that converts the output from the PID loop to a pulse-width-modulated signal for driving the motor. The encoder E on the motor provides feedback to the PID loop 104. Alternative motor drive and control systems can utilise the control signal.

The control signal 102 is, preferably, a summation of (i) a primary signal 108, derived from a gyroscope 27 mounted on a carriage 15 for levelling the chair, and (ii) a secondary signal 110 derived from a chair accelerometer 30, mounted on a chair 20. The secondary signal is added to the primary signal to adjust the control signal.

A tertiary signal 112 derived from a carriage accelerometer 114 is utilised to dynamically modify the primary and/or secondary signal such that the control signal 102 provides for a stabilised chair movement as the carriage moves through a zone in which the carriage changes level and/or direction. It is anticipated that the carriage travels along a path defined by a rail however a path can be defined as the route the carriage takes in traversing stairs.

The secondary signal 110 is derived from the output from the chair accelerometer 30, which is connected to a low gain unit 116 that functions to transform the chair accelerometer signal and provide a smooth output using, for example, a sigmoid-shaped response function. In other words, the unit 116 is a sigmoid curve accelerometer correction unit that uses a gentler conversion to correct smaller off-level angles of the chair. The unit 116 reduces over-correction and inhibits oscillations in the control system that may be felt by a user in the chair.

The output from the low gain unit 116 is utilised by an adaptive gain adjusting unit 118 to adjust the gyroscopic gain unit 120. The output from the gyroscope 27 is filtered and gain adjusted to correspond to the rotation required by the motor 26. In known systems this is corrected and a fixed gain is assigned to the gyroscope output.

However, a standard gyroscope 27 has an imperfect, and often asymmetric, output.

The adaptive gain adjusting unit 118, however, is used to more accurately correct the gain of the gyroscope by adjusting the gain, over time, using the errors in the chair accelerometer 30 signal. More specifically, the output from the low gain unit 116 enables a lower sigmoid curve gain to set the gain in the gyroscopic gain unit 120. By revising the gain through learning in the adaptive gain adjusting unit 1 1 8 the gyroscopic gain unit 120 can provide a primary signal 108. Note that the adaptive gain adjusting unit 118 is disabled to prevent changing the gain when the carriage is stationary, and/or experiencing a spot or concentrated load, or there are low gyroscopic levels of movement.

To dynamically modify the secondary signal 110, an anti-oscillation unit 122 can also receive the tertiary signal 112 and determines whether the carriage is entering or leaving a zone in which the carriage changes level and/or direction. If the output from the chair accelerometer 30 signal indicates instability as a result of the change in level or direction then the anti-oscillation unit 122 can adjust, or even block, the output from the low gain unit 116 becoming the secondary signal 110 and being added to the primary signal 108 to provide the control signal 102.

In other words, if the carriage 15 changes level and, for example, passes through a zone in which it travels over a bend before levelling out to a horizontal portion of rail, then the energy or tension in the chairlift that is stored between the chair and the rail, will be released and balance out. As the chair levels itself mechanically the adjustment can bias the chair to one side or another when not horizontal. The chair may bounce or rock from side to side about a vertical position. This condition is detectable by the level of activity of the secondary signal and if the tertiary signal indicates that the chair is in a 'zone' then the secondary signal is, preferably, deactivated for a period of time while the level of the chair and its movement settles. Deactivation can occur when the chair has moved through a zero-degree (vertical) position twice. In this way the noisy signal is limited or switched off to avoid feeding irregular or erratic noise in to the system. The secondary signal can be deactivated for a period of 1 second, two seconds or until sigmoid signal from the low gain unit 116 reaches a threshold level of stability in the zone.

To dynamically modify the primary signal 108, a slow filter 124 receives a signal from the gyroscopic gain unit 120 and further adjusts, by dampening or otherwise softening, the signal derived from the gyroscope. The slow filter is activated to do so when the tertiary signal 112 indicates that the carriage is entering or leaving a zone in which the carriage changes level and/or direction. Adjusting the signal derived from the gyroscope to produce the primary signal includes applying a filter to the primary signal, for example at a rate of between 5 degrees/s2 and 10 degrees/s2, and preferably at 7.5 degrees/s2. In or around the zone the slow filter inhibits oscillations caused by the carriage levelling out or rocking at, for example, horizontal sections or rail. The slow filter lowers the sensitivity of the stability feedback and, therefore, is deactivated outside the zone.

According to embodiments of this invention, a stairlift may be provided with functionality for recording and attempting to remedy the occurrence of undesirable movements of the chair during operation of the stairlift. An example of such undesirable movements are the oscillations already mentioned above. Another example of such undesirable movements is the lag that can occur between a change in direction of the carriage as it traverses the rail and the operation of the chair levelling motor to adjust the orientation of the chair relative to the carriage to retain the chair in an upright orientation. By identifying and recording the positions on the rail at which these undesirable movements of the chair occur, and by trialing one or more remedies to attempt to prevent reoccurrences of the undesirable movements, the movement and stability of the carriage and/or chair during subsequent traversals of the rail may be optimised.

Figure 5 schematically shows a stairlift. The stairlift may be a stairlift having similar features to those described above in relation to Figures 1 to 4, to which the further improvements to be described herein below have been added.

The stairlift includes a rail 11. As can be seen in Figure 5, the rail 11 may include a number of bends. These bends are provided to navigate the turns and changes in elevation in a stairway. Accordingly, the bends may effect a change in direction and/or a change in ascent/decent angle in the rail 11. It is envisaged that undesirable movements of the chair 20 of the stairlift tend to take place in the vicinity of the bends in the rail 11.

As noted previously, the stairlift also includes a carriage 15. The carriage 15 is mounted on the rail 11 for movement up and down the rail. The carriage 15 may be provided with means such as an electric motor, for moving the carriage 15 along the rail I I. As noted previously, the stairlift further includes a chair 20. The chair 20 is pivotally mounted on the carriage 15 via an arm 18. The chair may include features such as the seating surface 21, a back 22, pair of armrests 23 and footrest 24 described above. Furthermore, as described above, a chair levelling motor 26 is provided to alter the position of the chair 20 relative to the carriage 15 by pivoting the arm 18 about pivot axis 19. Accordingly, the chair levelling motor 26 may be operable (under the control of the control system of the stairlift) to pivot the chair 20 relative to the carriage 15 as the carriage 15 traverses the rail 11 for retaining the chair 20 in an upright orientation. The stairlift may include two incremental encoders. One of these encoders may be provided on the main carriage motor and can be used to measure the speed of the carriage and carriage rail position. Another encoder may be provided on the levelling motor 26. This encoder may be used to used to measure the speed associated with the levelling of the chair 20.

The stairlift also includes at least one motion sensor. The or each motion sensor may, for instance, be a linear accelerometer or a gyroscope. The or each motion sensor may, for instance, be mounted on the chair 20, the arm 18 or the carriage 15. In the present embodiment (Figure 5), the at east one motion sensor includes the three sensors described above. The stairlift in this embodiment includes an accelerometer 30 mounted on the chair 20, and a carriage accelerometer 114 and a gyroscope 27 mounted on the carriage 15. In use, these sensors and the control system of the stairlift may operate in the way already described above in relation to Figures 1 to 4. Further functionality of the stairlift in accordance with embodiments of this invention will be described herein below.

The stairlift also includes memory. The memory may be provided as part of the control system, or may be provided separately from the control system. The memory may be random access memory (RAM). The memory is operable to store data including one or more records relating to the operation of the stairlift. These records may be accessed and updated by the control system during operation of the stairlift, for optimising the movement of the stairlift for preventing undesirable movements of the chair 20.

The control system may, for instance, comprise a microcontroller storing instructions for controlling the operation of the stairlift. The control typically may include one or more I/O ports for connecting it to the various features of the stairlift, such as the motors, sensors and any user interface features. As described herein, the control system of the stairlift includes functionality for optimising the movement of the carriage 15 and the chair 20 during operation of the stairlift, for reducing undesirable movements of the chair 20 while moving the carriage along the rail 11 at a reasonable speed. An embodiment of one such method is schematically illustrated in the flow diagram of Figure 6.

The method of Figure 6 starts at step 410. Step 410 may, for instance, represent the initiation of the movement of the carriage 15 from one end of the rail 11 to other end of the rail 11. At step 412, during movement of the carriage 15 on the rail, the control system monitors the signals it receives from the at least one motion sensor) to determine whether an undesirable movement of the chair 20 has occurred. By way of example, these undesirable movements may be categorized as chair levelling oscillations or overall chair angular lag from the upright position. Both of these kinds of undesirable movements may, for instance, be measured by the accelerometer 30 mounted on the chair 20.

If the at least one motion sensor detects an undesirable movement of the chair 20 while the carriage 15 traverses the rail 11, the method continues to step 414. In step 414, the control system stores a record in the memory. The record corresponds to the undesirable movement of the chair 20. The record includes an indication of the position along the rail 11 at which the undesirable movement of the chair 20 occurred. The record may also indicate the type of undesirable movement that was detected.

During a subsequent traversal of the rail 11 by the carriage 15, the control system is operable to apply a remedy to attempt to prevent a reoccurrence of the undesirable movement of the chair 20 at the position indicated in the record saved in the memory. A variety of different remedies are envisaged. For instance, in the case that the undesirable movement associated with the record is an oscillation of the kind described in relation to Figure 4, the remedy applied may be to use an anti-oscillation unit 122 to adjust, or even block, the output from a low gain unit 116 becoming the secondary signal 110 and being added to the primary signal 108 to provide the control signal 102 as explained previously. In another example, again in which the undesirable movement associated with the record is an oscillation of the kind described in relation to Figure 4, the remedy applied may be to dynamically modify the primary signal 108, by a slow filter 124 receiving a signal from the gyroscopic gain unit 120 and further adjusting, by dampening or otherwise softening, the signal derived from the gyroscope as described previously. In a further example, the undesirable movement may comprise the lag that can occur between a change in direction of the carriage as it traverses the rail and the operation of the chair levelling motor to adjust the orientation of the chair relative to the carriage to retain the chair in an upright orientation. In such cases, the applied remedy may involve generating transitory injections of speed demand to the Speed PID Loop which, in turn, receives a feedback signal from encoder E mounted on the shaft of motor 26 as explained previously. In another example, an applied remedy may be to reduce the speed of the carriage 15 as it traverses the rail 11. This change in speed may, for instance, he applied locally, to the position on the rail 11 indicated in the record saved in the memory.

In step 416, during a subsequent traversal of the rail 11 by the carriage 15, the control system is operable to determine whether, with the aforementioned remedy applied, the undesirable movement of the chair 20 reoccurred at the position indicated in the record. This may be achieved by once again monitoring the output(s) of the at least one motion sensor.

If the control system determines, in step 416, that the undesirable movement of the chair 20 did not reoccur at the position indicated in the record, then the method may conclude. The control system may optionally update the record to indicate that the remedy applied was successful in preventing the able movement of the chair 20 The control system may consult the record during any subsequent traversals of the rail 11 so as to be able to determine the remedy to apply at the position along the rail indicated in the record.

In some embodiments, if the control system determines, in step 416, that the undesirable movement of the chair 20 did not reoccur at the position indicated in the record, the method may optionally proceed to step 418. In this branch of the flow diagram of Figure 6, the control system searches for an optimal (increased) speed of the carriage 15 as it traverses the rail 1 1, in accordance with the remedy determined in steps 412, 414 and 416. At step 418, the control system may set a speed search flag stored in the record to "UP" or such like. This indicates to the control system, during subsequent travels of the rail 11 by the carriage 15, that an increased optimal speed for the carriage is being sought. In a subsequent traversal of the rail 11 by the carriage 15, the control system, noting the contents of the speed search flag, may increase the speed of the carriage 15. This increase in speed may be a global increase, but it is envisaged that the increase may be applied specifically in the vicinity of the undesirable movement stored in the record (e.g. 20cm along the rail, either side of the recorded position). The increase in speed may be applied as a predetermined increment (e.g. +0.005m/s).

Next, during further subsequent traversal of the rail 11 by the carriage 15, the control system again monitors (step 420) the output(s) of the one or more sensors to determine whether the increase in speed has resulted in a reoccurrence of the undesirable movement of the chair 20, which had been remedied in steps 414 and 416. If, in step 420 it is determined that the increase in speed did not result in a reoccurrence of the undesirable movement of the chair 20, then the method may proceed to step 422, in which the speed of the carriage 15 may again be increased (e.g. again using the aforementioned increment) during a further subsequent traversal of the rail 11 by the carriage 15. This loop 420, 422 may recur a number of times until at some stage, the increase in speed results in the detection in step 420 of a reoccurrence of the undesirable movement of the chair 20. At this point, the method may proceed to step 424 in which the control system may reduce the speed of the carriage 15 for future traversals of the rail 11 to the highest speed at which no reoccurrence of the undesirable movement of the chair was detected. This may typically correspond to the speed at which the reoccurrence of the undesirable movement of the chair 20 was detected, minus one speed increment. This "maximum" speed may be stored in the record for the control system to refer to during future operation of the stairlift. The control system may also change the speed search flag to "SPEED FOUND" or such like, to indicate that the optimal speed has been determined (whereby the control loop of steps 418, 420, 422, 424 need not be repeated). In this way, the maximum speed that does not result in the aforementioned undesirable movement of the chair 20 may be adopted, whereby the operation of the stairlift may be optimised. The method may then end at step 434.

Returning to step 416, if it is detected that the applied remedy did not prevent a reoccurrence of the undesirable movement of the chair 20 detected in step 412, then the method may optionally proceed to step 426. In this branch of the flow diagram of Figure 6, the control system searches for an optimal (reduced) speed of the carriage as it traverses the rail 11, in view of the fact that the applied remedy did not prevent the reoccurrence of the undesirable movement of the chair 20. At step 426, the control system may set a speed search flag stored in the record to "DOWN" or such like. This indicates to the control system, during subsequent travels of the rail 11 by the carriage 15, that a reduced optimal speed for the carriage 15 is being sought. in a subsequent traversal of the rail 11 by the carriage 15, the control system, noting the contents of the speed search flag, may reduce the speed of the carriage 15. This reduction in speed may be a global reduction, but it is envisaged that the reduction may be applied specifically in the vicinity of the undesirable movement stored in the record (e.g. 20cm along the rail, either side of the recorded position).

The reduction in speed may be applied as a predetermined increment (-0.005m/s).

Next, during further subsequent traversal of the rail 11 by the carriage 15, the control system again monitors (step 428) the output(s) of the one or more sensors to determine whether the reduction in speed has prevented a reoccurrence of the undesirable movement of the chair 20. If, in step 428 it is determined that the reduction in speed did not prevent a reoccurrence of the undesirable movement of the chair 20, then the method may proceed to step 430, in which the speed of the carriage 15 may again be reduced (e.g. again using the aforementioned increment) during a further subsequent traversal of the rail 11 by the carriage 15. This loop 428, 430 may recur a number of times until, at some stage, the reduction in speed results in the detection in step 428 that undesirable movement of the chair 20 did not reoccur. At this point, the method may proceed to step 432 in which the control system may store the determined "maximum" speed in the record for reference during future operation of the stairlift. '1 he control system may also change the speed search flag to "SPEED FOUND" or such like, to indicate that the optimal speed has been determined (whereby the control loop of steps 426, 428, 430, 432 need not be repeated). In this way, the maximum speed that does not result in the aforementioned undesirable movement of the chair 20 may be adopted, whereby the operation of the stairlift may be optimised. The method may then end at step 434.

It is envisaged that in some embodiments, more than one remedy may be attempted. An example of this is shown in Figure 7. The methodology shown in Figure 7 is similar to that described in relation to Figure 6 and only the significant differences will be described below.

In the method of Figure 7, a first remedy is attempted in step 416 as explained in relation to Figure 6. Again, if it is determined at step 416 that the remedy was successful in preventing a reoccurrence of the undesirable movement of the chair 20, then the method of Figure 7 branches off to steps 418, 420, 422 and 424, in which the speed of the carriage is increased until a maximum speed is found at which the undesirable movement of the chair 20 does not reoccur while the successful reedy is employed. On the other hand, if in step 416 it is determined that the remedy was not successful in preventing a reoccurrence of the undesirable movement of the chair 20, then instead of entering the branch 26, 428, 430, 432 in which the speed of the carriage is incrementally reduced, the method first proceeds to step 436. In step 436, an alternative remedy is applied. This may for instance involve the control system setting an alternative remedy flag in the remedy for indicating to the control system that the alternative remedy should be attempted on a subsequent traversal of the rail 11 by the carriage 15.

In step 438, during a subsequent traversal of the rail 11 by the carriage 15, the control system is operable to determine whether, with the aforementioned alternative remedy applied, the undesirable movement of the chair 20 reoccurred at the position indicated in the record. As before may be achieved by once again monitoring the output(s) of the at least one motion sensor.

If the control system determines, in step 438. that the undesirable movement of the chair 20 did not reoccur at the position indicated in the record, then the method may conclude. The control system may optionally update the record to indicate that the remedy applied was successful in preventing the able movement of the chair 20. The control system may consult the record during any subsequent traversals of the rail 11 so as to be able to determine the remedy to apply at the position along the rail indicated in the record.

In some embodiments, if the control system determines, in step 438, that the undesirable movement of the chair 20 did not reoccur at the position indicated in the record, the method may optionally proceed to step 418. Thereafter, the method may proceed substantially as described in relation to Figure 6, with the exception that in the branch 418, 420, 422, 424 the control system incrementally increases the speed of the carriage 15 to find a maximum speed of the carriage 15 to prevent the undesirable movement of the chair 20 while the alternative remedy of steps 436 and 438 is applied, instead of the initial remedy of step and 416.

Returning to step 438, if it is detected that the alternative applied remedy did not prevent a reoccurrence of the undesirable movement of the chair 20, then the method may optionally proceed to step 426. Thereafter, the method may proceed substantially as described in relation to Figure 6.

It is envisaged that more than one alternative remedy may be attempted. It will be appreciated that the method of Figure 7 may he modified to accommodate these further alternative remedies, in the event that the remedy of step 416 and the remedy of step 38 both fail to prevent a reoccurrence of the undesirable movement of the chair 20.

It is envisaged that the branch 426, 428, 430, 432 of Figures 6 and 7 may be applied while an attempted remedy (e.g. one of the unsuccessful remedies of steps 416 and 438) is still in place. It is, for instance, envisaged that the unsuccessful remedy or remedies may yet be successful at a reduced carriage speed. Alternatively, the control system may dispense with the unsuccessful remedies in subsequent traversals of the rail 11 by the carriage 15, and simply attempt to find a reduced speed that prevents a reoccurrence of the undesirable movement of the chair 20 absent any specific remedy.

Figure 8 shows an example of a record 310/320 that may be stored in the memory of the stairlift by the control system in accordance with an embodiment of this invention. In this embodiment, the record 310/320 includes a plurality of fields 332, 334, 336, 338, 340, 342, 344, 346. The record 310/320 may include a header, which identifies the record in the event that a plurality of different records are stored.

One or more fields in the record 310/320 may specify the kind of undesirable movement of the chair 20 that has been detected. For instance, in the present embodiment, field 332 specifies whether oscillations of the kind explained previously were detected, while field 332 specifies whether an angular lag of the kind explained previously was detected. Fields such as fields 332, 334 may be referred to by the control system during subsequent traversals of the rail 11 by the carriage 15, so that the control system can, for example, compare a detected undesirable movement of the chair 20 with the kind of undesirable movement of the chair 20 stored in the record 310/320 for verifying whether an undesirable movement of the chair 20 has reoccurred. Fields such as fields 332, 334 may comprise a "true/false" flag, which may be set to "true" in the event that the kind of undesirable movement of the chair 20 associated with that field is detected. It is envisaged that any number of further fields such as fields 332, 334 could be used to specify a variety of different undesirable movements of the chair 20. It is also envisaged that a value contained in the field(s) may itself specify the kind of undesirable movement of the chair 20 that has been detected. In this way, a single field could be used to specify different kinds of undesirable movement of the chair 20, such that multiple fields containing "true/false" flags as shown in Figure 8 may not be needed.

One of the fields of the record 310/320 (e.g. the field 336 in the embodiment of Figure 8) may specify the position on the rail 11 at which the undesirable movement of the chair 20 was detected. This field may be referred to by the control system during subsequent traversals of the rail 11 by the carriage 15, so that the control system can apply a remedy of the kind described above and/or adjust the speed of the carriage 15 at the appropriate location on the rail 11. Field 336 may for instance store a numerical value corresponding to a distance (e.g. an encoder value) along the rail 11 from either end of the rail 11, for recording the position.

One of the fields of the record 310/320 (e.g. the field 338 in the embodiment of Figure 8) may specify the maximum allowed speed of the carriage 15 on the rail 11 in the vicinity of the position on the rail 11 associated with the record 310/320. This field may be referred to by the control system during subsequent traversals of the rail 11 by the carriage 15, so that the control system can set/adj ust the speed of the carriage 15 appropriately. This maximum speed may be the speed determined in the branch 418, 420, 422, 424 or the branch 426, 428, 430, 432 of Figures 6 and 7. Note that this field may also be used to store the incremented speed of the carriage 15 while the speed search methodology of branch 418, 420, 422, 424 or branch 426, 428, 430, 432 is being carried out.

One of the fields of the record 310/320 (e.g. the field 340 in the embodiment of Figure 8) may contain the speed search flag discussed above in relation to the branch 418, 420, 422, 424 and the branch 426, 428, 430, 432 of Figures 6 and 7. This field may be referred to by the control system during subsequent traversals of the rail 11 by the carriage 15, so that the control system can determine that it is presently in, and can continue to implement, the branch 418, 420, 422, 424 or the branch 426, 428, 430, 432. This field may be set to "UP" or "DOWN" as described previously, and may also be set to a null value (e.g. "FALSE") in the event that the speed search methodology of the branch 418, 420, 422, 424 and the branch 426, 428, 430, 432 is not in progress. In an alternative approach, separate "search faster" and "search slower" fields, each field containing a "true/false" flag, could he used.

One or more fields in the record 310/320 may specify a kind of remedy. In the present embodiment: * the field 342 specifies the use of an anti-oscillation unit 122 to adjust, or even block, the output from a low gain unit 116 becoming the secondary signal 110 and being added to the primary signal 108 to provide the control signal 102 as explained previously; * the field 344 specifies the dynamic modification of the primary signal 108, by a slow filter 124 receiving a signal from the gyroscopic gain unit 120 and further adjusting, by dampening or otherwise softening, the signal derived from the gyroscope as explained previously; and * the field 346 specifies the generation of transitory injections of speed demand to the Speed PID Loop which, in turn, receives a feedback signal from encoder E mounted on the shaft of motor 26, as explained previously.

Fields such as fields 342, 344, 346 may comprise a "true/false" flag, which may be set to "true" in the event that the remedy associated with that field is to be applied/attempted in a subsequent traversal of the rail 11 by the carriage 15. Fields such as fields 342, 344, 346 may be referred to by the control system during subsequent traversals of the rail 11 by the carriage 15, so that the control system can apply the appropriate remedy. It is envisaged that any number of further fields such as fields 342, 344, 346 could be used to specify a variety of different remedies. It is also envisaged that a value contained in the field(s) may itself specify the kind of remedy to be applied. In this way, a single field could be used to specify different kinds of remedy, such that multiple fields containing "true/false" flags as shown in Figure 8 may not be needed.

It is envisaged that more than one undesirable movement of the chair 20 may be detected while the carriage 15 traverses the rail 11. The control system may store a respective record for each detected undesirable movement of the chair 20. These records may be stored in an array 300 of the kind shown schematically in Figure 9.

In the embodiment of Figure 9, the array 300 includes a first set of N records 3101, 3102, 3103, 3104... 310N, which correspond to the positions in which undesirable movements of the chair 20 have been detected while the carriage 15 traverses the rail 11 in a first direction (e.g. from a lower end of the rail 11 to an upper end of the rail 11) and a second set of M records 3201, 3202, 3203, ... 320m, which correspond to the positions in which undesirable movements of the chair 20 have been detected while the carriage 15 traverses the rail 11 in a second direction (e.g. from an upper end of the rail 11 to a lower end of the rail 11). The forces experienced by the carriage 15 at a given position on the rail 11 may typically differ depending upon the direction of travel of the carriage. This may be accounted for by keeping a separate set of records 310/320 for each direction of travel. In particular, a remedy applied for the or each record 310/320 may be applied only during traversal of the rail 11 by the carriage 15 in the same direction as the direction of travel in which the undesirable movement recorded in that record 310/320 was detected. In some embodiments, the record 310/320 may include a field specifying the direction of travel.

In some embodiments, the stairlift may be provided with a weight sensor. The weight sensor may be located in the chair 20. Chair dynamics tend to change with the weight of the individual using the chair. Because of this, different passengers having different weights may give rise to a different set of undesirable movements of the chair 20. When the control system determines, using an output of the weight sensor, that an individual having a weight that has not yet been optimised for is occupying the chair 20, this may trigger the creation of a new array of records (e.g. of the kind described in relation to Figures 8 and 9). The control system may subsequently select the appropriate array of records to use according to e weight measured by the weight sensor. This approach can provide a personalised optimisation of the operation of the stairlift for each person using the stairlift. This approach can also provide for a re-optimisation of the operation of the stairlift in the event of change in weight (e.g. beyond a predetermined tolerance) of an existing user.

It will be appreciated that the use of the records described herein may allow for significant levels of optimisation of the operation of the stairlift. The control system may use the records and the methods described in Figures 6 and 7 to prevent one or more instances of different kinds of undesirable movements of the chair 20 as the carriage 15 moves along the rail 11 and may also optimise the speed of the carriage 15. Once optimised using the methods described herein, in normal operation the control system may compare the position of the carriage 15 against the position(s) indicated in the record(s) and, ahead of time, apply the appropriate remedies and speed adjustments for preventing undesirable movements of the chair 20. The ability to apply measures ahead of time instead of reactively has advantages in terms of smoothness of operation and stability.

Accordingly, there has been described a stairlift and a method of operating the same.

The stairlift includes a stairlift rail, a carriage mounted on the rail, a chair pivotally mounted on the carriage, at least one motion sensor, a chair levelling motor operable to pivot the chair relative to the carriage as the carriage traverses the rail, memory, and a control system. The control system is operable to store a record of an undesirable movement of the chair The record includes an indication of the position along the rail at which the undesirable movement occurred. The control system is also operable, during a subsequent traversal of the rail by the carriage, to apply a remedy to attempt to prevent a reoccurrence of the undesirable movement of the chair at the position indicated in the record. The control system is further operable to determine whether the undesirable movement of the chair reoccurred.

Although particular embodiments of this disclosure have been described, it will be appreciated that many modifications/additions and/or substitutions may be made within the scope of the claims.

Claims

CLAIMS1. A stairlift comprising: a stairlift rail, a carriage mounted on the rail for movement up and down the rail, a chair pivotally mounted on the carriage, at least one motion sensor, a chair levelling motor operable to pivot the chair relative to the carriage as the carriage traverses the rail for retaining the chair in an upright orientation, memory, and a control system operable: responsive to the at least one motion sensor detecting an undesirable movement of the chair while the carriage traverses the rail, to store in the memory a record corresponding to the undesirable movement of the chair, the record including an indication of the position along the rail at which the undesirable movement occurred; during a subsequent traversal of the rail by the carriage, to apply a remedy to attempt to prevent a reoccurrence of the undesirable movement of the chair at the position indicated in the record; and to determine whether the undesirable movement of the chair reoccurred during said subsequent traversal at the position indicated in the record.
2. The stairlift of claim 1, wherein the control system is further operable: responsive to determining that the undesirable movement of the chair reoccurred at the position indicated in the record, to apply, during a subsequent traversal of the rail by the carriage, an alternative remedy to attempt to prevent a further reoccurrence of the undesirable movement of the chair at the position indicated in the record; and to determine whether the undesirable movement of the chair reoccurred during said subsequent traversal at the position indicated in the record.
3. The stairlift of claim I or claim 2, wherein the control system is further operable: responsive to determining that the undesirable movement of the chair reoccurred at the position indicated in the record, to reduce the speed of the carriage during a subsequent traversal of the rail by the carriage; to determine whether the undesirable movement of the chair reoccurred during said subsequent traversal at the position indicated in the record; responsive to determining that the undesirable movement of the chair reoccurred at the position indicated in the record, to further reduce the speed of the carriage during a subsequent traversal of the rail by the carriage; and responsive to determining that the undesirable movement of the chair did not reoccur at the position indicated in the record, to control the carriage to traverse the rail at that reduced speed during subsequent traversals of the rail by the carriage.
4. The stairlift of any preceding claim, wherein the control system is further operable: responsive to determining that, following the application of a remedy, the undesirable movement of the chair did not reoccur, to increase the speed of the carriage during a subsequent traversal of the rail by the carriage; to determine whether the undesirable movement of the chair reoccurred during said subsequent traversal at the increased speed of the carriage; responsive to determining that the undesirable movement of the chair did not reoccur at the increased speed of the carriage, to further increase the speed of the carriage during a subsequent traversal of the rail by the carriage; and responsive to determining that the undesirable movement of the chair reoccurred at the increased speed of the carriage, to control the carriage to traverse the rail, during subsequent traversals, at a highest speed at which the undesirable movement of the chair did not reoccur.
5. The stairlift of any preceding claim, wherein the control system is operable to store a set of said records, and wherein each record corresponds to a respective undesirable movement of the chair while the carriage traverses the rail.
6. The stairlift of claim 5, further comprising a weight sensor for measuring a weight of an occupant of the chair, wherein the control system is further operable, responsive to determining from the weight measured by the weight sensor that a user having a new weight is occupying the chair, to store a new set of said records for the user.
7. The stairlift of claim 5 or claim 6, wherein the set of records includes: a first set of one or more records corresponding to undesirable movements of the chair as the carriage travels from a lower end of the rail to an upper end of the rail; and a second set of one or more records corresponding to undesirable movements of the chair as the carriage travels from the upper end of the rail to the lower end of the rail.
8. The stairlift of any preceding claim, wherein a remedy applied for the or each record is applied only during traversal of the rail by the carriage in the same direction as the direction of travel in which the undesirable movement recorded in that record was detected.
9. The stairlift of any preceding claim, wherein the or each record includes at least one the following: one or more fields specifying a kind of undesirable movement of the chair; one or more fields specifying a kind of remedy; a field specifying a maximum speed of the carriage; anda speed search field.
10. The stairlift of any preceding claim, wherein the stairlift comprises: a gyroscope mounted on the carriage; an accelerometer mounted on the chair; and an accelerometer mounted on the carriage, and wherein the control system is further operable to: derive a primary signal from the gyroscope mounted on the carriage for levelling the chair; adjust the primary signal using a secondary signal derived from the accelerometer mounted on the chair, said adjusted signal used to control said chair levelling motor; and modify the primary and/or secondary signal, prior to adjustment, using a tertiary signal derived from the accelerometer mounted on the carriage for stabilising chair movement as the carriage moves through a zone on the rail in which the carriage changes level and/or direction; wherein a modified primary and/or secondary signal is used to control said chair levelling motor as it passes through, enters or leaves the zone.
11. The stairlift of any preceding claim, wherein an undesirable movement of the chair comprises an oscillation of the chair.
12. The stairlift of claim 11 when dependent on claim 10, wherein the control system is operable to apply a remedy to attempt to prevent a reoccurrence of the oscillation of the chair at the position indicated in the record by: monitoring the tertiary signal to determine whether the carriage is passing through, entering or leaving the zone in which the carriage changes level and/or direction; detecting a level of activity of the signal from the accelerometer mounted on said chair that provides the secondary signal; and adjusting the signal from the accelerometer mounted on said chair if the level of activity from said accelerometer exceeds a threshold when the carriage is entering or leaving the zone.
13. The stairlift of claim 12, wherein adjusting the signal from the accelerometer mounted on the chair, for providing the secondary signal, includes temporarily deactivating the secondary signal if the level of activity exceeds a threshold when the carriage is entering or leaving the zone.
14. The stairlift of claim 11 when dependent on claim 10, wherein the control system is operable to apply a remedy to attempt to prevent a reoccurrence of the oscillation of the chair at the position indicated in the record by: monitoring the tertiary signal to determine whether the carriage is entering or leaving a zone in which the carriage changes level and/or direction; and adjusting the signal from the gyroscope mounted on said carriage, for providing the primary signal, for levelling the chair, if the carriage is entering or leaving the zone.
15. The stairlift of claim 14, wherein adjusting the signal from the gyroscope mounted on the carriage, for providing the primary signal, includes filtering the signal from a gyroscope to adjust the primary signal to improve the stability of the chair level.
16. The stairlift of any preceding claim, wherein an undesirable movement of the chair comprises a lag in the levelling of the chair by the levelling motor as the carriage navigates a bend in the rail, and wherein the control system is operable to apply a remedy to attempt to prevent a reoccurrence of the undesirable movement of the chair at the position indicated in the record by increasing a levelling speed of the levelling motor.
17. A method of operating a stairlift comprising a stairlift rail, a carriage mounted on the rail for movement up and down the rail, a chair pivotally mounted on the carriage, at least one motion sensor, a chair levelling motor operable to pivot the chair relative to the carriage as the carriage traverses the rail for retaining the chair in an upright orientation, and memory, the method comprising: the motion sensor detecting an undesirable movement of the chair while the carriage traverses the rail; the memory storing a record corresponding to the undesirable movement of the chair, the record including an indication of the position along the rail at which the undesirable movement occurred; and during a subsequent traversal of the rail by the carriage: applying a remedy to attempt to prevent a reoccurrence of the undesirable movement of the chair at the position indicated in the record; and determining whether the undesirable movement of the chair reoccurred during said subsequent traversal at the position indicated in the record.