GB2391539A

GB2391539A - Stairlift levelling and speed control

Info

Publication number: GB2391539A
Application number: GB0317617A
Authority: GB
Inventors: Dominic Delacourt Williams; Leonard Smith
Original assignee: Stannah Stairlifts Ltd
Current assignee: Stannah Stairlifts Ltd
Priority date: 2002-08-10
Filing date: 2003-07-28
Publication date: 2004-02-11
Anticipated expiration: 2023-07-28
Also published as: GB2391539B; GB0218653D0; GB0317617D0

Abstract

The invention provides means for levelling a stairlift chair 13 electronically, whilst ensuring that the optimum speed of the carriage 12 along rail 16 is maintained. This is effected by relating the speed of chair levelling motor 18 to the speed of the main drive motor 15.

Description

239 1 539

IMPROVEMENTS IN OR RELATING TO STAIRLIFTS

Title of the invention

This invention relates to stairlifts and, in particular, to a method of and apparatus for, levelling a chair forming part of a stairlift carriage.

Background to the Invention

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 be kept substantially level at all positions of the carriage along the rail.

Levelling is not an issue in stairlift installations in which the rail remains at a constant angle with respect to the horizontal. However, in those installations in which the rail passes over landings, and around bends in the staircase, means must be provided to vary the angular of the chair with respect to the carriage. Traditionally levelling has been achieved using mechanical arrangements, some including a levelling bar and linkage arrangement to rotate the chair on the carriage, and others involving variations in spacing between rail components which rotate the entire carriage.

More recently, electronic based solutions have been proposed, and some such solutions are now being incorporated in stairlifts on the market. In our European Patent 0 738232 we describe and claim an electronic levelling

arrangement in which the profile of the rail is stored in an electronic memory, together with data establishing the settings necessary to maintain the chair level at all points along the profile. This exercise is typically referred to as rail mapping and He combination of data is then used to drive a separate chair levelling motor.

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. The appropriate signal, also determined by data in memory, can then be passed to the chair levelling motor to ensure that chair level is maintained.

Other proposals have used an electronic level sensor to sense the level of the carriage and to set the position of the chair accordingly, the level sensor being used in conjunction with a pendulum or the like to ensure the system does not become overly sensitive, particularly about the level position.

The various forms of levelling are all capable of establishing level per se, but often the levclling function must be combined with significant reductions in forward speed of the carriage to ensure the chair does not go 'off-level' to a significant degree as the carriage negotiates a transition bend. This can significantly reduce the overall efficiency of the installation.

It is an object of the present invention to provide a method of and/or apparatus for, levelling a stairliR chair mounted on a stairlift carriage which takes at least some of the benefits of known electronic based levelling systems whilst addressing at least some of the drawbacks or concerns thereof; or which will at least provide a novel, useful alternative.

Summary of the Invention

Accordingly, in one aspect, the invention provides a stairlift installation including: a rail having at least one transition bend therein; a carriage mounted on said rail for movement there along, said carriage including a carriage drive motor operable to drive said carriage along said rail; a chair mounted on said carriage; chair drive means operable to vary the position of said chair with respect to said rail; and control means including an electronic memory, said control means being operable to control said chair drive means in a manner so as to maintain said chair substantially horizontal at various positions of said carriage on said rail, said stairlift installation being characterised in that said control means is further operable to relate the speed of said carriage drive motor to the speed of said chair drive means as said carriage traverses said at least one transition bend. Preferably said control means includes a level sensor operable to sense the level of said chair.

Alternatively said control means includes data representing the desired level position of said chair with respect to said carriage, at various positions of said carriage on said rail.

Preferably said installation further includes position establishing means operable to read data representing the instantaneous position of said carriage and compare this with data in said electronic memory to determine the position of said carriage on said rail.

Preferably said positioning establishing means includes an encoder combined with said carriage drive motor.

Preferably said control means has variable sensitivity. More preferably the sensitivity of said control means is varied in response to the position of said carriage along said rail.

In a second aspect the invention provides a method of controlling the levelling of a chair attached to a stairlift carriage, as said carriage moves along a rail, said method including; determining the presence of a transition bend on said rail; monitoring data representing the position of said chair with respect to said carnage; I5 adjusting the position of said chair with respect to said carriage to maintain said chair substantially level as said carriage traverses said transition bend; said method being characterized in that the speed of said carriage along said rail, whilst traversing said transition bend, is varied and related to the rate of levelling of said chair.

s Preferably the positions of all changes of profile in said rail are determined.

These changes may be characterized electronically according to their positions along the rail from a datum; and data representing these changes of profile stored in an electronic memory.

Preferably said method includes monitoring the position of said carriage along said rail and comparing the monitored position with that stored in said memory to allocate a predetermined speed to said carriage.

Preferably the position of said chair with respect to said carriage is monitored using a level sensor attached to said chair.

Alternatively data representing the required angular position of said chair at various positions of said carriage on said rail, is entered in said memory.

Preferably said method further includes operating chair drive means to effect relative movement between said chair and said carriage.

Preferably said method includes reducing the speed of said carriage as said carriage traverses a transition bend.

Many variations in the way the present invention can be performed will present themselves to those skilled in the art. The description which follows is

intended as an illustration only of one means of performing the invention and the lack of description of variants or equivalents should not be regarded as

limiting. Wherever possible, a description of a specific element should be

deemed to include any and all equivalents thereof whether in existence now or in the future. The scope of the invention should be limited by the appended claims alone.

Brief Description of the Drawings

One embodiment of the invention will now be described with reference to the drawings in which: Fig 1: shows a schematic front elevation of a stairlift carriage incorporating the invention on a level section of rail; Fig 2: shows a profile of a further section of stairlift rail including two different types of transition bend; Fig 3: shows details of a level sensor incorporated in a stairlift chair; Fig 4: shows a block diagram of the main operating elements of a stairlift installation according to the invention; Fig 5: shows a flow diagram of the primary levelling functions; and Fig 6: shows a flow diagram of the speed control elements of the stairlift carriage. Detailed Description of Working Embodiment

The present invention provides a system of levelling the chair of a stairlift installation generally designated 10 in Fig 1. As can be seen the installation 10 includes a rail l 1, a carriage 12 mounted for rolling movement along the rail 1 1, and a chair 13 mounted on the carriage 12. In accordance with conventional practice the chairl3 is pivotally mounted on the carriage at 14

and chair drive means are provided to rotate the chair about the pivot 14 in order to maintain the chair level as the carriage is moving over sections of rail that are other than level.

In the embodiment shown in Fig 1, the carriage is powered along the rail 11 by a main drive motor (not shown) rotating drive pinion 15, the drive pinion 15 engaging rack 16 extending along the under-surface of the rail 11. The chair drive means includes a further motor (not shown) mounted in the carriage 12, and arranged to drive levelling pinion 18, the pinion 18 engaging an annular quadrant l 9 fixed to the chair and being centred around the pivot 14. The quadrant 19 has gear teeth formed on the periphery thereof, to engage with the teeth of pinion 18.

The chair drive means responds to a control means which will be described in greater detail below. In one form, this control means includes a level sensor 20 mounted on the chair, the sensor being shown in greater detail in Fig 3.

Suitable forms of sensor for use herein include a tilt sensor or an accelerometer chip. The sensor 20 is advantageously mounted on a pcb mounted beneath the main seating surface of chair 13 so that the pcb is horizontal when the carriage is traversing a horizontal section of rail as shown in Fig 1. The particular level sensor 20 described herein gives an analogue feedback with horizontal being indicated by an intermediate reading between the outer limits of the sensor output. Thus the sensor not only gives an indication of whether the chair is off-level, it also indicates if the chair is tilting in a clockwise or anti-clockwise direction.

Alternatively, the control means may incorporate a form of level control substantially as described in our European Patent 0738232 and thus, rather than using a sensor to derive information on chair position, the desired chair position, as a function of carriage position on the rail, is held in memory in the

form of electronic data.

The present invention is not just concerned with level per se, but also with the rate at which levelling is effected, the overall objective being to ensure optimum speed of the carriage along the rail is maintained whilst levelling is effected smoothly and without imparting concern to the stairlift user. With these requirements in mind, optimum speeds are pre-set empirically for each part of the rail and, within each transition bend, the rate of levelling is also monitored to ensure that the speed of the carriage is not too great or to slow to an extent which leads the chair to go off-level to an unacceptable degree. For example, if the speed of levelling appears to be too slow for a given carriage speed, the carriage is slowed.

Given the need to identify where, on the rail, the carriage is at any given time, the rail profile is preferably 'mapped' i.e. the co-ordinates of the various changes of profile are determined and stored in an electronic memory. This technique is substantially as described in our European Patent 0 738232.

Turning now to Fig 4, in its broadest embodiment, input signals representing position and chair level are fed into a form of logic or control means which, conveniently, comprises a microprocessor 25 having an electronic memory.

The microprocessor is programmed with the rail 'map' together with the optimum speed for each section of the 'map'. The microprocessor is also programmed with data representing the off-level limits beyond which the chair should not be allowed to pass, and a levelling speed which should not be exceeded. These inputs and predetermined factors are processed into output drive signals to the carriage drive motor and to the chair drive motor. Motor speeds can be monitored and controlled using encoders (not shown).

Referring now to Fig 2, it should be appreciated that there may be essentially two different forms of transition bend, the two forms being shown in Fig 2 and being described as a type 1 transition and a type 2 transition respectively. In the normal course of events, the carriage is slowed while traversing transition bends. It will also be appreciated that, in order to achieve overall speed efficiency and consistency, the speeds of the carriage over the different types of transition bend should be varied to differing extents.

Thus, as the carriage traverses a type I transition, it will be slowed less than when it is traversing a type 2 transition.

The actual carriage speed changes applied while traversing transition bends do not form part of the invention and may be set by the system specifier. By way of example only, the carriage may be slowed in the order of 5% when traversing a type l transition and slowed in the order of 10 to 15% from the normal straight line speed when traversing a type 2 transition.

Because of the variations in load, power, and angle, the chair drive motor may not be able to vary the seat angle with sufficient speed on a tight transition to maintain level within acceptable tolerances. In this event, the carriage speed is reduced by the microprocessor 25 to assist the levelling system. This additional speed feedback is achieved by supplying the carriage speed control function with both level error and level drive rate feedback, allowing the carriage drive control function to modify the speed accordingly.

As an additional safety feature, a tilt switch (not shown) is positioned on the chair and operates to cut power to both the carriage drive motor and the chair levelling motor in the event the chair tilts more than 5 either side of horizontal. This tilt switch acts with the backup of the level sensor 20 to provide a fail safe system.

A broad description of elements of the logic process will now be described

with reference to Figs 5 and 6. The description is based on the use of a level

sensor however it will be appreciated, by those skilled in the art, that level information could equally be derived from data stored in memory, and which represents the desired chair position at various positions of the carriage on the rail As shown in Fig 5, the control means begins with a determination of whether a call is present; in effect whether a prompt is present causing the carriage 12 to move along the rail 11.

Obviously if there is no such call present, nothing further happens. If there is a call present, then the logic first determines where, on the rail, the carriage is and, therefrom, determines an appropriate speed in a manner as will be described below with reference to Fig 6. The logic further monitors the output from level sensor 20 and is preferably programmed to ignore minor variations, beneath a 'null' level, of output as occurs when the carriage is travelling along a horizontal section of rail. Without this variable sensitivity function, the chair might undergo numerous minor changes in attitude whilst moving along a horizontal section of rail. This is not only unnecessary but also upsets the smoothness of ride. Obviously when the level sensor output is below the null' value, no output signal is applied to the chair levelling motor.

Feedback from the sensor 20 controls the chair levelling motor via a Proportional Integral Differential (PID) control system. Thus, when the sensor output exceeds the 'null' value, the microprocessor calculates a control output to be applied to the chair levelling drive or H-Bridge. This control output, in the form of a PWM output, is then applied to the levelling drive motor.

Turning now to Fig 6, carriage speed is also determined by operation of the logic system or control means. A first determination is whether the carriage is passing through a transition. This will generally be established by comparing carriage drive motor encoder reading with the rail map programmed into the microprocessor 25.

If the carriage is not passing through a transition then a predetermined straight line speed will be set by the microprocessor and the levelling system will also be set to its low resolution mode as described above. If, however, the chair is traversing a transition, then the level sensing is set in its high resolution mode and the microprocessor also interrogates the map to determine if the transition is of the type 1 type or the type 2 type. Whichever one is determined to be present, the carriage speed is set accordingly.

It will thus be appreciated that the present invention provides a chair levelling system for a stairlift which, at least in the case of the detailed embodiment described herein, combines electronic rail mapping techniques with level determining means to provide a system which ensures smooth chair levelling whilst maintaining optimum carriage speed.

Claims

Claims

1) A stairlift installation including: a rail having at least one transition bend therein; a carriage mounted on said rail for movement there along, said carriage including a carriage drive motor operable to drive said carriage along said rail; a chair mounted on said carriage; chair drive means operable to vary the position of said chair with respect to said carriage; and control means including an electronic memory, said control means being operable to control said chair drive means in a manner so as to maintain said chair substantially horizontal at various positions of said carriage on said rail, said stairlift installation being characterized in that said control means is further operable to vary the speed of said carriage drive motor and to relate the speed of said carriage drive motor to the speed of said chair drive means as said carriage traverses said at least one transition bend.

2) A stairlift as claimed in claim 1 wherein said control means includes a level sensor operable to sense the level of said chair.

3) A stairlift as claimed in claim 1 wherein said control means includes data representing the desired level position of said chair with respect to said carriage, at various positions of said carriage on said rail.

4) A stairlift as claimed in any one of the preceding claims further including position establishing means operable to read data representing the instantaneous position of said carriage and compare this with data in said electronic memory to determine the position of said carriage on said rail.

5) A stairlift as claimed in claim 3 or claim 4 wherein said position establishing means includes an encoder combined with said carriage drive motor.

6) A stairlift as claimed in any one of claims I to 5 wherein said control means has variable sensitivity.

7) A stairlift as claimed in claim 6 wherein the sensitivity of said control means is varied in response to the position of said carriage along said rail.

8) A method of controlling the levelling of a chair attached to a stairlift carriage, as said carriage moves along a rail, said method including; determining the presence of a transition bend on said rail; monitoring data representing the position of said chair with respect to . said carriage; adjusting the position of said chair with respect to said carriage to maintain said chair substantially level as said carriage traverses said transition bend; said method being characterized in that the speed of said carriage along said rail, whilst traversing said transition bend, is varied and related to the rate of levelling of said chair.

9) A method as claimed in claim 8 wherein the positions of all changes of profile in said rail are determined.

10) A method as claimed in claim 9 wherein said changes are characterized electronically according to their positions along the rail from a datum; and data representing these changes of profile stored in an electronic memory. 11) A method as claimed in claim 10 including monitoring the position of said carriage along said rail and comparing the monitored position with that stored in said memory to allocate a predetermined speed to said carriage. 12) A method as claimed in any one of claims 8 to 11 wherein the position of said chair with respect to said carriage is monitored using a level sensor attached to said chair.

13) A method as claimed in any one of claims 8 to 11 wherein the position of said chair with respect to said carriage is monitored by referring to data in an electronic memory representing the desired angle of said chair with respect to said carriage at various positions of said carriage along said rail. I 14) A method as claimed in any one of claims 8 to 13 further including chair drive means to effect relative movement between said chair and said carriage.

15) A method as claimed in any one of claims 8 to 14 including reducing the speed of said carriage as said carriage traverses a transition bend.