GB2542488B

GB2542488B - Improvements in or relating to stairlifts

Info

Publication number: GB2542488B
Application number: GB1613528.7A
Authority: GB
Inventors: Smith Leonard; Neil Russell Stannah Alan
Original assignee: Stannah Stairlifts Ltd
Current assignee: Stannah Stairlifts Ltd
Priority date: 2012-12-14
Filing date: 2012-12-14
Publication date: 2019-11-13
Anticipated expiration: 2032-12-14
Also published as: GB2510810B; GB2542488A; GB2510810A; GB201222612D0

Description

IMPROVEMENTS IN OR RELATING TO STAIRLIFTS

Field of the Invention

This invention relates to stairlifts and, in particular, to a method of and/or means for, reducing the energy consumption of a stairlift.

Background to the Invention

Energy consumption is of international concern and the energy consumption of all apparatus is now assessed as a matter of course. It is of particular benefit if energy can be recovered during use of a particular piece of apparatus.

This may apply to stairlifts.

It will be appreciated that a stairlift is a safety-critical apparatus used by persons having a physical impairment and, in many cases, a degree of mental impairment. It is therefore essential that any attempt to recover energy from use of the stairlift does not compromise operational safety or demand noticeable changes in the way in which the stairlift is operated.

It is an object of this invention to provide a method of, and means for, providing a stairlift installation which will go at least some way in addressing the aforementioned problem or opportunity; or which will at least provide a novel and useful choice.

Summary of the Invention

Accordingly in one aspect the invention provides a method of controlling a battery charger for a stairlift powered from one or more batteries, said stairlift having a carriage mounted on a rail for movement between an upper end and a lower end of said rail, said method including assessing the state of charge of said one or more batteries and controlling said charger to ensure that said one or more batteries are not fully charged when said carriage is at the upper end of said rail.

Preferably said method includes monitoring the voltage of said one or more batteries, and only switching on said charger when said voltage falls below a threshold.

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.

Brief Description of the Drawings

One operating embodiment of the invention will now be described with reference to the accompanying drawings in which:

Figure 1: shows a diagram of a stairlift to which the invention is applied;

Figure 2: shows a schematic view of a circuit for implementing the invention; and

Figure 3: shows a logic diagram applicable to the invention.

Detailed Description of Working Embodiment

Referring to Figure 1, a stairlift 10 is shown including a stairlift carriage 11 mounted on a rail 12 for movement between an upper end 13 and a lower end 14 of the rail.

The carriage 11 includes a motor 15 and gearbox 16, the motor 15 being driven from one or more batteries 17. A pinion 18 is mounted on the output shaft of the gearbox to engage a toothed rack 19 extending along the rail and thus provide the means for driving the carriage along the rail. Included within the motor/gearbox combination is an electro-mechanical brake (EMB), shown schematically at 20, to serve as a holding brake.

In the form shown the motor 15 and EMB 20 are under the control of electronic control unit (ECU) 21. The ECU also includes a facility to effect braking of the stairlift as the carriage 11 descends the rail 12. This facility is referred to herein as dynamic braking and will be described in greater detail below. It will be appreciated by those skilled in the art that the ECU also monitors and controls other aspects of the stairlift’s operation but, since these are not relevant to the present invention, they will not be described in further detail herein.

Conventionally the batteries 17 are charged from a charger 22 via charge points located at the ends of the rail 12, or via a busbar extending along the rail. Typically two 12 volt batteries are provided, wired in series.

Referring now to Figure 2, a diagram is shown of one possible embodiment of regeneration circuit according to the invention. The overall objective of the circuit is to harness energy dissipated when the carriage 11 is descending the rail 12 whilst preventing over-charging of the batteries which might lead to damage and, possibly, danger to the user. We are aware that when the battery voltage exceeds 30 volts, permanent damage to the batteries may result. Thus the charge voltage of the batteries must be monitored and controlled while energy is being harvested or recovered.

To achieve energy recovery during descent the motor 15 is used as a generator on the descent and, for this, it is necessary to connect the motor directly to the batteries 17. This also has a braking effect on the motor. One aspect of this invention lies in the nature of the connection that alternatively applies charge to the batteries or dissipates the energy by dynamic braking thus preventing the charge voltage to the batteries from rising to a level that could damage the batteries.

By monitoring the voltage of the batteries, the ECU can switch between energy recovery and dynamic braking to ensure optimum energy is recovered without causing damage to the batteries. By way of example, the motor 15 could be switched to dynamic braking when the battery voltage reaches 29 volts.

It is convenient to dissipate excess energy not required for charging by dynamic braking i.e. by applying a direct short across the motor. As can be seen in Figure 2, this can be achieved using a field effect transistor (FET), the ‘Braking FET’, or similar switching device across the motor terminals. Switching is controlled by the ECU upon the ECU determining that the voltage to the batteries 17 exceeds a predetermined maximum. The FET can be controlled using a pulse width modulated (PWM) signal from the ECU so that the amount of dynamic braking is varied to control the maximum voltage across the battery terminals.

In order to maintain the possibility of battery charging during partial dynamic braking, the brake and drive devices should be driven in anti-phase i.e. when the brake device is on, the drive device is off, and vice versa.

Whilst the system described above enables control of the charge applied to the battery, in order to recover energy from the descending carriage it is necessary to ensure that the batteries 17 have the capacity to absorb the charge. Thus an aspect of the invention involves controlling the operation of the charger 22 in response to measured voltages of the batteries 17.

As described above, typical stairlift installations include charging points at the ends of the rail. This generally ensures that the batteries are fully charged at the beginning of a journey whether that be up or down the rail. According to another aspect of this invention, the ECU monitors the battery voltage and applies control over the mains charger using a Battery Charger Control facility (Figure 2) to ensure that charge from the mains charger is terminated before the batteries are fully charged, when the carriage is at at position other than the lower end of the rail, thus providing capacity for charge to be absorbed from regeneration.

It will be appreciated that regeneration only occurs during descent of the carriage down the rail and that considerably more energy than that recovered will be required to power the carriage up the rail. It is therefore sensible to programme the ECU to ensure that the batteries are fully charged at the bottom of the rail, in preparation for an upward journey.

By monitoring the battery voltage and/or charge current it is possible to determine a point at which the mains charger should be switched off in order to leave capacity in the batteries for the energy harvested during the following descent of the carriage. Once this point is reached, if the carriage is not at the bottom of the rail, the mains charger input is switched off. A logical method for determining whether or not mains charging is required is shown in Figure 3. This logic is based on the premise that the batteries should be fully charged at the bottom of the rail. If the carriage is stopped at a position above the bottom of the rail then the stopped position should be considered when determining the optimum charge level. This position can be determined, for example, using the rail mapping method described in our European Patent 0 738 232. If the positon is near the bottom of the rail then the amount of energy that can be recovered is low and thus energy from the batteries would be required if the next movement is in the upward direction. The optimum charge level would therefore be higher than if the carriage were at the top of the rail.

As can be seen in Figure 3, at any given positon where the carriage is stopped on the rail the state of charge (SoC) is estimated and compared with a predetermined measure to determine if charge needs to be applied from the mains charger. If the estimated SoC is greater than that required then a control loop is activated to cause the comparison to be repeated until such time as the carriage next moves.

If a directional call is received causing the carriage to move, or if the mains charger is turned off, the sequence illustrated in Figure 3 terminates until the carriage next stops at some intermediate point on the rail.

It will thus be appreciated that the invention, at least in the case of the working embodiment herein described, provides a novel and effective means of applying charge to the batteries in a stairlift from energy recovered during descent of the carriage. The precise amount of energy harnessed will depend on many factors including the angle of the rail, the weight of the carriage and user, and the efficiency of the motor and gearbox.

Claims

1. A method of controlling a battery charger for a stairlift powered from one or more batteries, said stairlift having a carriage mounted on a rail for movement bertween an upper end and a lower end of said rail, said method including assessing the state of charge of said one or more batteries and controlling said charger to ensure that said one or more batteries are not fully charged when said carriage is at the upper end of said rail.

2. A method as claimed in claim 1 including monitoring the voltage of said one or more batteries, and only switching on said charger when said voltage falls below a threshold.