GB2216681A - A control device, especially for a wheelchair - Google Patents

Description

1 0 c 1 is so nI n 4 16 6 8 1 Ortopedia GmbH Kiel, Federal Republic of

Germany A control device, especially for a wheelchair The present invention relates to a control device, especially for a wheelchair, in which a command variable can be supplied from an operating unit to a first input of a comparator the output (side) of which transmits, through a correcting unit and a positioning element, a manipulated variable to a control path for providing a control variable which is detected by a measuring or detection unit and supplied to a second input of the comparator.

The major part of the present, commercially available wheelchairs with electric drive means include an electronic system which is designed in accordance with the non-feedback or open-loop control and not the feedback or closed-loop control principle. This electronic system will be explained below with reference to Figure 1.

A command variable 2 input by a user, e.g. a wheelchair driver, through an operating unit 1 of the wheelchair, namely, for example, the velocity. at which the wheelchair is desired to travel, is supplied through a control circuit 3 to a positioning element 5 which provides a manipulated variable 6. This manipulated variable 6 influences the energy or power flow, namely, for example, the torque transmitted 1 so to the drive wheels of the wheelchair, thereby to set a predetermined control variable 8 at the output of a control path 7.

In this instance, the electronic system does not perform automatic followup in such a form that the energy or power provided is properly conformed to the energy or power demand. In other words, no comparison is made between the command v'ariable 2 and the control variable 8.

This means that the user himself must pay attention that the output value demanded by him, i.e. the speed of travel, for example, is obtained in fact. In order to provide for this, the user must, in case of need, readjust the command variable 2 by a corresponding variation thereof, in such a manner that the output value is kept constant as far as possible.

Now, in view of the fact that the time behaviour of the command value 2 is most frequently subject to requirements extremely different from the requirements imposed on the time behaviour of the control circuit 3 and the positioning element 5, it is mostly possible to impart to the wheelchair acceptable travel characteristics only within a relatively narrow range of consideration. Accordingly, in many situations of travel either it is expected too much of the user for effecting the necessary variations of the command variable 2, or it is even not possible at all to specifically set the desired output value with corresponding disturbance variables 9 acting upon the control path 7, because of the control concept chosen.

In order to overcome these problems, wheelchairs -p 1 4L 1 1 so have been provided with electric drive means in which the non-feedback control principle has been replaced by the feddback control priniple.

As is known, the significant difference between feedbatk control and nonfeedback control resides in the fact that in a feedback control an electronic system or an apparatus based on a different physical principle performs automatic control (monitoring) of the output value (or variable), and this may be effected in accordance with the principle explaindd below with reference to Figure 2.

Preferably, a control variable 10 analogous to the output value, for example, instead of the velocity of the whelchair, the speed of rotation which is directly proportional to this velocity, is evA]uatdd or processed by measurement tethniques. A thus obtained actual value 12 is supplied to a comparator unit 13 from an actual value receiver 11, and substracted in the comparator unit from the command variable 2 input through the operating unit 1, i.e. from the set value. A resulting control difference 14 is supplied to a correcting unit 15 which ififluences or driVes-the positioning element 5 which, in turn, meters by the ifiAnipulted variable 6 thereof the energy or 06wer flow, theeby to 6btain the contol variable 10 on the output side of a control path 16.

A control loop of such a construction provides, without any action by the user, for the fact that the drive means of the wheelchair keeps as small as possible the control difference 14 when disturbance variables 9 occur. This means that the actual value 12 is made to 1 approach the command variable 2 as far as possible. Here, no variation of the command variable 2 is necessary.

Thus, dimensional requirements with respect to the command variable 2 regarding the time behaviour can be set separately, without causing conflicts with regard to the dimensioning of the controller. Rather, the controller may, and should,be optimized regardless of the behaviour (Characteristic) of the command variable 2. A limit to the application of the wheelchair is defined merely by higher conditions, such as the available power, for example.

Accordingly, compared to the non-feedback control electronic system according to'Figure 1, a (feedback or closed-loop) controller electronic system according to Figure 2 is of considerable advantage to a user: the vehicle is fully controllable for the user even if disturbances 9 occur.

Now, it has been found that with controller electronic systems of the type according to Figure 2, specifically when adopted for a wheelchair, problems may be caused by the actual value transmitter 11, i.e. the measuring or detection unit for detecting the control variable 10. If this assembly does not operate or malfunctions, the comparator unit 13 is not supplied with the real, true actual value 12, but rather with a faulty, deceptive (erroneous) actual value 12. Such a situation, however, immediately results in unmatched and possibly even extremely wrong reactions for the drive means, namely in excessive power supply, for example. In the case of malfunction and failure of the actual value transmitter 11, the resulting control variable jo therefore cannot' c IM v 1 be mastered, and this results in a situation which is further aggrevated considerably by the unexpected In such an by complete o n 1 y.

occurence of this wrong control variablE instance, controllability can be ensurec deactivation of the electronic svstem For this reason, existing control electronic systems include monitoring elements which monitor the actual value detection in the. transmitter by plausibility criteria: If an error or a defect is recognized, the electronic system is blocked (deactivated). In the case of a wheelchair, however, this means that travel by means of the drive electronic system i. s no more possible. In such an instance, an escorting person is normally required to wheel the wheelchair, mostly alone with the user thereof, by physical strength.

control or actual value It is therefore the object of the present invention to provide a control device which ensures relatively comfortable (vehicle) handling characteristics of the wheelchair even in the case of failure or mlfunction of the actual value transmitter.

in a control device according to the preamble of patent claim 1, according to the invention this object is solved in that the measuring or detection unit has connected thereto a monitoring elemeht; the correcting unit has connected subsequently thereto a selector switch the input (side) of which is adapted to be switched between the output of the operating unit' and thd outpOt of the correctin bhit, and the outpOt of which is connected to the input of the positioning element; and the monitoring element is adapted to signal specific malfunctions or defects and/or operate the selector sqitch in response to a malfunction or defect.

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1 1 f) - 1 so / a Accordingly, in the case of malfunction in the detection unit or in the actual value transmitter, respectively, in the control device according to the invntion it is done without the driving comfort inherent to the control, if the wheelchair can be driven at least to some degree by making use of the available power. In such an instance, a possibly present escorting person is required at most to provide assistance in order to ensure pu.rposeful locomotion.

However, the above operational conditions must be regarded particularly advantageous compared to complete deactivation of the wheelchair. In principle, this advantage is obtained in that the electronic system is downgraded from the feedback control concept to the non-feedback control concept.

Below, an embodiment of the invention is explained greater detail with reference to Figures, Wherein:

Figure 1 is a block diagram for explaining the nonfeedback control in a wheelchair; Figure 2 is a block diagram for explaining the feedback control in a wheelchair; and Figure 3 is a block diagram for explaining the control device according to the invention.

Figure 3 in which corresponding components are identified by the same reference-numerals as in Figures 1 and 2, illustrates a monitoring element 17 which can signal, as required, malfunctions or defects occuring in the actual value transmitter 11, and7or operate a C 1 1 i.

1 so selector switch 18. If a malfunction or defect occurs in the actual value transmitter 11, this selector switch 18 connects the output of the operating unit 1 to the input of the positioning ele'ment 5, whereby the command variable 2 is fed directly to the positioning element 5. Upon elimination of the malfunction or defect, the selector switch 18 is capable of automatically switching back to the position shown in Figure 3, such that the output of the correcting unit 15 is conne cted again to the input of the positioning element 5.

If necessary, however, the selector swi have a self-locking function so as not to.switch back to control when the malfunction or defect has been removed, but possibly only after an acknowledgement of such malfunction or defect removal.

tch 18 may automatically A contact-type switch, i.e. a relay, for example, or a contactless switche.g. an analog switch, may be used for the selector switch 18.

Accordingly, it is essential to the present invention that in the case of a malfundtion or error in the actual value transmitter 11 the command variable 2 may be supplied directly to the positioning element 5 while bypassing the comparator unit 13 and the correcting unit 15. thereby to eliminate the defective actual value 12, while the wheelchair is still provided with a control electronic system of the type explained above in conjunction with Figure 1.

In wheelchairs and generally in vehicles having more than one drive unit, and especially in vehicles which rely upon the difference between the speeds of rotation of a right-hand and a left-hand drive unit for directional 1 1 so 3 control, in'the case of failure of an actual value transmitter for a drive unit, change-over from feedback control to non-feedbac control should nevertheless be effected in both electronic systemsy i.e. in the electronic system for the right-hand drl;-ve unit and in that for the left-hand drive unit, because it is extremely difficult to preset the command variables for both electronic systems in such a manner that the speeds of rotation of both driving sides correspond to each other in a meaningful manner,-if the one side is to be controlled with e.g. feedback, -her side is to be controlled without while the ot feedback.

The invention is not limited to a wheelchair, but also applicable to (feedback or closed-loop) controlled systems in general. Also, the invention can be realized not only by electric-means, but, for example, also by fluidics, mechanical means and/or pneumatic means.

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Claims (4)

C 1 a i m s

1. A control device in whidh a.command variable (2) can be supplied from an operating un'it'(1) to a first input of a comparator (13) the output (side) of which transmits, through a correcting unit (15) and a positioning element (5), a manipulated variable (6) to a control path (16) for-providing a control variable (10) which is detected by a measuring or detection unit (11) and supplied to a second input of the comparator (13), characterized in that the measuring or detection unit (11) has connected thereto a monitoring element (17); the correcting unit rlql has connected subsequently thereto a selector switch (18) the input (side) of which is adapted to be switched between the output of the operating unit (1) and the output of the correcting unit, and the output of which is connected to the input of the positioning element (5); and -'the monitoring element is adapted to signal specifid malfunctions or defects and/or operate the selector swith in response to a malfunction or defect.

2. A control device according to claim 1, characterized in that the selector switch comprises an analog switch withoUt or with a self-locking function, which, when the malfunction or defect is removed, re-connects the correcting unit (15) to the positioning element (5)-automatically or after an a cknowledgement (of the rem6val6f the niaTfuhCtion or defect).'

3. A wheelchair comprising a control device according to claim -in- 1 20, so 1 or 2 for the independent driving of each drive wheel of the wheelchair.

4. A lchair according to claim 3, characterized in that when a malfunction or defett has been recognizedin the measuring or detection unit (11), at least one of the drive wheels is downgraded from feedback or closed-loop control to non-feedbatk or open loop control.

Publimb d 1989 atThe Patent O:Mr-e, State House, 88171 High Holborn, IjondonWC1R 4TP. Further copies maybe obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BRS 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1/87