WO2005030008A1

WO2005030008A1 - Apparatus with fabric sensor

Info

Publication number: WO2005030008A1
Application number: PCT/GB2004/004079
Authority: WO
Inventors: David Lee Sandbach; John Burkitt; Andrew Newman; Kevin Flory
Original assignee: Eleksen Limited
Priority date: 2003-09-25
Filing date: 2004-09-24
Publication date: 2005-04-07
Also published as: WO2005031557A1

Abstract

Apparatus comprising a first member and a second member in which relative movement occurs between said first member and said second member in response to operation of an actuator; wherein a fabric sensor is attached to said first member, having a first conductive plane and a second conductive plane, in which an electrical characteristic of said sensor changes when said first conductive plane and said second conductive plane are brought together at a position of interaction; and a control circuit is configured to detect said change in said electrical characteristic and to modify the operation of said actuator in response to said detection.

Description

Apparatus with Fabric Sensor

Background of the Invention 1. Field of the Invention The present invention relates to apparatus having a first member and a second member in which relative movement occurs between said first member and said second member in response to operation of an actuator and the fabric sensor attached to the first member.

2. Description of the Related Art A fabric sensor is shown in US 6,501 ,465 in which, by the provision of two conducting layers separated by an insulating layer, it is possible to determine the level of pressure applied to a sensor by taking a measurement of current. An enhanced fabric sensor is shown in US 6,452,479, in which additional conductive and insulating layers are provided so as to facilitate flexing and folding of the sensor while preventing false triggering.

Brief Summary of the Invention According to the present invention, there is provided apparatus comprising a first member and a second member in which relative movement occurs between said first member and said second member in response to operation of an actuator; wherein a fabric sensor is attached to said first member, having a first conductive plane and a second conductive plane, in which an electrical characteristic of said sensor changes when said first conductive plane and said second conductive plane are brought together at a position of interaction; and a control circuit is configured to detect said change in said electrical characteristic and to modify the operation of said actuator in response to said detection. In a preferred embodiment, the first member having the sensor attached thereto is forced to move by the actuator but, alternatively, it is possible for the second member to be forced by the actuator. According to a second aspect of the present invention, there is provided an orthopaedic chair, comprising an actuator to effect relative movement between a first member and a second member of said chair to assist an occupant to reach a standing position from a seated position; a fabric sensor attached to said first member, having a first conductive plane and a second conductive plane, wherein an electrical characteristic of said sensor changes when said first conductive plane and said second conductive plane are brought together at a position of interaction; and a control circuit configured to detect said change in said electrical characteristic and to modify the operation of said actuator in response to said detection. In a preferred embodiment, the operation of the actuator when returning to a seated configuration is modified in response to a mechanical interaction taking place. Thus, in the preferred embodiment, the sensor is configured to detect objects that may have been placed under the chair when the chair was in a raised condition, having assisted an occupant to reach a standing position. Brief Description of the Several Views of the Drawings Figure 1 shows an orthopedic chair making use of the present invention; Figure 2 shows the orthopedic chair of Figure 1 in an alternative configuration; Figure 3 illustrates the first preferred embodiment of the invention; Figure 4 illustrates a second preferred embodiment of the invention; Figure 5 illustrates three strip sensors connected in series; Figure 6 shows a strip sensor with an inactive area; Figure 7 shows the strip sensor of Figure 6 in a folded configuration; Figure 8 illustrates a three-layer detector system; Figure 9 illustrates a five-layer detector system; Figure 10 illustrates a detector system using spacer fabric; Figure 11 shows an example of a strip sensor; Figure 12 illustrates a strip sensor being used as a flap switch; Figure 13 shows use of a sensor with an absorbing foam; Figure 14 shows a sensor with absorbing foam in an alternative configuration; Figure 15 shows a sensor covered with fabric; Figure 16 illustrates a bed frame having sensors applied thereto; Figure 17 details a portion of the bed frame shown in Figure 16; and Figure 18 shows an adjustable table having sensors applied thereto.

Written Description of the Best Mode for Carrying Out the Invention Many forms of apparatus are known in which relative movement occurs between a first member and a second member in response to the operation of an actuator. In many situations of this type, relatively large force may be required in order to effect movement, therefore there is a danger that damage, or even personal injury, may occur if an object or a limb etc is placed in the path between the moving objects. The provision of detection mechanisms is made difficult because many positions may exist where object interference may occur. The present invention provides for a fabric sensor to be attached to a first member, having a first conductive plane and a second conductive plane, in which an electrical characteristic of the sensor changes when the first conductive plane and the second conductive plane are brought together in a position of interaction. It has been found that sensors of this type provide an attractive solution in many apparatus of the aforesaid type. In particular, the sensor is relatively inexpensive but at the same time can be applied over relatively large areas and surfaces of the apparatus so as to provide detection of objects or limbs causing object interference at many locations. In accordance with the invention, a control circuit is configured to detect the change in the electrical characteristic (such as a change in impedance) and to modify the operation of the actuator in response to the detection. A preferred embodiment is disclosed below in the form of an orthopaedic chair, but it should be appreciated that similar techniques may be used in other applications, and a suggestion of further applications is provided with respect to Figures 16 to 18.

Figure 1 An orthopaedic chair is shown in Figure 1 having a seating area 101, a back rest 102, arms 103 and a foot rest 104. In response to the operation of manual controls, it is possible for an occupant to raise and lower footrest 104 between a rest position and an elevated position. When returning to its rest position, it is possible for objects or limbs to be trapped between the footrest 104 and the main body of the chair, identified as 105. In accordance with the preferred embodiment, a fabric sensor is attached such that pressure will be applied to said sensor if an interfering object is present between rest 104 and the chair body 105. In addition to providing the actuation illustrated in Figure 1, the chair also includes an actuator to assist a user moving between a seated position and a standing position, as illustrated in Figure 2.

Figure 2 In Figure 2, the main body of the chair is identified as 201 and a base section is identified as 202. An actuator operates so as to move the body of the chair 201 relative to the base of the chair 202. In this way, the seat 101 is brought into an inclined orientation so as to assist an occupant in terms of moving from a seated position to a standing position. For the purposes of illustration, an interfering object in the form of a wine glass 203 has been placed under the chair when in its raised condition such that, upon returning the chair to its standard condition, the body of the chair would come into contact with the interfering object which, in this example, would lead to the glass 203 being broken. Examples are also known of children becoming trapped below a chair of the type shown in Figure 2, such that serious injury may occur when the chair is lowered to its standard condition. Consequently, in accordance with the present invention, a fabric strip sensor is attached to the body of the chair such that, in the example shown in Figure 2, a portion of the sensor would come into contact with glass 203, resulting in a characteristic of the sensor changing and such a change being detected by a control circuit. Thus, many areas of the chair where movement occurs which could result in object interference are covered in fabric strip sensors, preferably configured such that conducting planes are brought together when object interference causes an interaction to take place. In this example, the base 202 remains static and an actuator causes the body of the chair 201 to rotate relative to the base 202. The present preferred embodiment, in the form of a fabric strip sensor, facilitates the attachment of the strip either to the moving member (the chair 201 in this example) or to the static member (the base 202 in this example). These possibilities are detailed further with respect to Figures 3 and 4. It can also be appreciated that fabric strip sensors may be applied at other positions where interactions may take place. Thus, a fabric sensor may be attached to the back edge 204 of the chair so as to detect conditions where the back of the chair 204 is being forced against a wall, for example.

Figure 3 The apparatus provides for a first member and a second member in which relative movement occurs between the first member and the second member. The fabric strip sensor may be considered as being attached to the first member. In the example shown in Figure 3, it is the first member that undergoes movement in response to the actuator. Thus, a chair frame or body 301 (considered as a first member) moves relatively to a static base section 302. The fabric sensor strip 303 is attached to the moving chair body and under normal operation, the chair body will come to rest before a mechanical interaction takes place, resulting in the sensor being activated. However, if an object is placed between the chair body 301 and the base 302, such an object will interfere with the sensor 303 and this interference condition will be detected. In a first embodiment, detection results in the actuator being de- energised such that no further movement of the chair in the downwards direction occurs. However, in a preferred embodiment, detection results not only in the actuator being de-energised but, prior to this, the actuator is reversed so as to return the chair away from the interfering object before de-energisation occurs.

Figure 4 The example shown in Figure 4 is similar, in that a chair body 401 is provided that moves relative to a static base 402. However, on this occasion, a fabric strip sensor 403 is attached to the static base 402. Thus, in this example, the static base may be considered as a first member having a fabric sensor attached thereto, whereas the moving chair body may be considered as a second member. As previously described, strip sensors or similar devices may be provided at many locations throughout the chair. Further possibilities include sensors within the seat area to provide a detection of occupancy. Thus, under these conditions, if a seat is not occupied all actuators may be disabled. Similar sensors may also be included in chair arms 103 so as to provide mechanisms for controlling the actuators in response to manual interaction. In a preferred embodiment, a plurality of fabric sensors are connected in series, as illustrated in Figure 5.

Figure 5 In this example, three strip sensors 501, 502 and 503 are connected in series. For the purposes of illustration, sensor 501 is positioned to detect object interference with respect to footrest 104. Similarly, sensor 502 is positioned to detect object interference with respect to the raising and lowering of the chair as described with respect to Figure 2. Similarly, sensor 503 may be positioned in the backrest to detect contact with a wall. Electrically, the sensors are connected in series, and an interaction occurring with respect to any of the sensors results in a noticeable reduction in sensor impedance. Thus, such a reduction in impedance is detected and used to modify operation. At a first end, the chain of fabric detectors is connected to an interface circuit 504, primarily configured to energise the detectors and to produce an output signal to a control circuit 505 upon detecting a lowering of transmission impedance as a result of object interference. At the remote end of the sensor chain, there is provided a bridging resistor 506 providing a degree of conduction between conducting planes within the sensor system. In this way, when the sensors are energised, a degree of current will be allowed to flow (via resistor 506) which is in turn used to monitor the fact that the sensors are energised and are operational. Thus in normal

steaUy state condit ^rAa relatively low current flows, as provided by the termination resistor 506, but in response to a mechanical interaction impedance is reduced significantly and a substantially higher current flows, thereby allowing the mechanical interaction to be detected. A control sensor 507 is provided, positioned under a cover at the armrest 103, allowing manual operation to be detected resulting in movement of a selected actuator. Two-dimensional positioning is required in order to identify the location of individual buttons. A further detector is provided within the seat area 101 so as to provide an occupancy detector 508. The occupancy detector preferably deploys the technology described with respect to Figure 10 such that an

• output signal is generated, in response to an occupant being sat in the chair. Thus, at the control circuit 505, the logical way in which the signals are processed is effectively reversed to the effect that actuation is prevented when the occupancy sensor is not activated, representing a state to the effect that no one is sat in the chair and it is therefore undesirable for actuators to be operated. Control system 505 receives power from an appropriate power supply 509. In response to input commands received via the control device 507, control circuit 505 applies power to actuator motors 510 and 511. Thus, actuator motor 510 may result in movement of the footrest 104. Similarly, actuation of motor 511 results in the rising mechanism illustrated with respect to Figure 2 being activated. However, should an object interference be detected by any of sensors 501, 502 or 503, the movement of motor 510 or motor 511 is prevented. Furthermore, in a preferred embodiment, any motor that was moving is then reversed slightly in order to ease off any object interference situation that may have been detected.

Figure 6 It is advantageous if relatively large strip sensors can be deployed, but problems may occur in that the sensors, in order to be long, are required to negotiate bends and cover irregularities. In order to facilitate such situations, it is possible for sensors to be provided with inactive zones, as illustrated in Figure 6. In the example of a fabric strip sensor shown in Figure 6, the sensor has a first active zone 601 and a second active zone. 602. Between the first active zone 601 and the second active zone 602, there is provided an inactive zone 603. As illustrated in Figure 6, it is possible for the inactive zone 603 to negotiate an irregularity without the risk of introducing false triggering. Inactive regions may be provided by masking the conductive planes at the position of the inactive region. In this way, with the mask present, it is not possible for the conductive planes to be brought into contact and thereby activate the detector. Alternatively, inactive regions may be provided by including regions where the conducting planes are not present. Adjacent conducting planes are then connected together in series by the inclusion of conducting wires or similar conducting items.

Figure 7 The inclusion of an inactive region, such as region 603, also allows the fabric strip detector to be folded, as illustrated in Figure 7. In a preferred embodiment, the strip sensor is configured with a linear active region 701 at a central location with non-active regions 702 and 703 running along either side. Non-active regions 702 and 703 facilitate the connection of the fabric sensor to mechanical devices, such as chairs, by simple processes such as stapling. , The construction of the fabric sensor itself may take many forms. In a first preferred embodiment, and as described with respect to Figure 8, the detector is substantially a three-layer configuration, substantially as described in US 6,501 ,465. Alternatively, and as described with respect to Figure 9, the detector may adopt a substantially five-layer configuration, as described with reference to US 6,452,479. Alternatively, and as described with respect to Figure 10, spacer fabric may be deployed, as described in the applicant's copending international patent application referenced by attorneys as 2040-P149-WO.

Figure 8 A three-layer sensor is illustrated in Figure 8 consisting of a first conductive layer 801 a second insulating layer 802 and a third conducting layer 803. When a mechanical interaction occurs, illustrated by arrow 804, it is possible for the conductive layers to be forced through holes in the insulating layer 802 thereby allowing conduction between the conducting layers. A known attribute of three-layer detectors is that conduction between the layers, and hence triggering, tends to occur when the assembly is folded. Thus, in situations where it is necessary to express a degree of folding in order to position the detector, the three-layer system provides a less-than-ideal solution. However, in alternative configurations the sensor is secured along only one edge (in cantilever fashion) and an interaction is detected by a flapping operation being performed with respect to the sensor. Thus, detection occurs when a folding operation takes place, and therefore the three-layer system may provide a preferred configuration for such applications.

Figure 9 In situations where it is desirable to introduce folding, it is preferable to provide a fabric sensor which is resilient to the folding process. This may be achieved using a five-layer system as illustrated in Figure 9. The system of Figure 9 is also provided with a first conducting layer 901 and a second conducting layer 902. These conducting layers 901 and

902 provide substantially similar functionality to the outer conducting layers 801 and 803 of the three-layer system. However, a third layer 903 is an insulating layer, a fourth central layer 904 is a further conducting layer and a fifth layer 905 is a further insulating layer. When a mechanical interaction takes place, as illustrated by arrow

906, conduction occurs through both insulating layer 903 and insulating layer 905. However, the five-layer system is resilient to false triggering caused by folding because the folding process will only tend to allow conduction on the internal bend. Thus, for example, if the ends of the system shown in Figure 9 are folded upward, conduction would tend to occur between layers 901 and 904 but not between layers 904 and 902.

Figure 10 An alternative approach to providing sophisticated fabrications involving many layers is to make use of spacer fabric, where it is possible to provide two conducting planes operated by insulating spacer threads in a unified knitting operation. A fabric of this type is illustrated in Figure 10. The spacer fabric produced by a unified knitting operation includes a first planar portion 1001 and a second planar portion 1002 separated by individual spacer threads 1003. In order to make use of a configuration of this type, both conducting and non-conducting yarns are employed during the knitting process. In this way, it is possible to knit the configuration such that planes 1001 and 1002 include conducting threads and are thereby rendered conductive. However, for the production of the spacer portions 1003 non-conducting yarn is used thereby providing an insulating region. The spacer fabric has a physical property such that it is possible for a certain degree of force to be applied without bringing the conducting planes into contact. However, when a threshold is reached the spacer threads tend to collapse resulting in conduction taking place. In this way it is possible for a bias force to be applied to the planes, thereby making them particularly suitable in applications where the sensor is covered and said cover continually applies a force to the sensor, as detailed with respect to Figure 15. In order for the sensor to be activated, it is necessary for additional force to be applied which, in the present embodiment, may take the form of an object interference. Sensors of this type are suitable for many applications within the embodiment but are particularly suitable for providing the basis for the occupancy sensor, if provided. Sensors of this type may also be used to provide control panels, such as located at the arm of the chair 103. However, when deployed in this way, it is necessary to identify the position of a mechanical interaction in two dimensions. In order to achieve this it is necessary for conducting fibres of one plane to run in a different direction to the conducting fibres of the opposing plane. The knitted construction of the spacer fabric does not facilitate this, and therefore when two-dimensionality is required it is possible to add a second sheet 1004 with conducting planes running in an opposite direction. Thus, in the spacer fabric conducting threads may run in the direction indicated by arrow 1005, whereas in the second sheet 1004 the conducting threads run in the direction illustrated by arrow 1006.

Figure 11 In a preferred embodiment, the detector takes form of a strip thereby presenting a preferred configuration for many typical applications. An example of a strip _. sensor is shown in Figure 11. The sensor includes a thin rectangular active region 1101, possibly constructed in accordance with a technology of the type illustrated in Figure 8, Figure 9 or Figure 10. Furthermore, and as previously described, to facilitate attachment of the sensor to mechanical members a first edge extension 1102 is provided along with a second edge extension 1103. In some applications, only one of these edge extension portions may be provided, such as when the device is operating as a flap switch as described with respect to Figure 12. In addition to the edge extensions 1102 and 1103, the preferred embodiment also includes a first end extension 1104 and a second end extension 1105. The end extensions are terminated with appropriate mechanical connecting devices such as press-studs 1106. In this way, it is possible to use the press-studs 1106 to facilitate daisy chaining of detectors, as shown in Figure 5, and to facilitate the connection to electrical connectors. Furthermore, it should also be appreciated that electrical conductors are provided along the length of the end extensions 1104 and 1105 so as to provide electrical connection to the active region 1101. Figure 12 A flap switch configuration is illustrated in Figure 12. The sensor is provided with an active region 1201 and an edge extension 1202, allowing the sensor to be attached to a mechanical member 1203. An edge extension may be provided on the opposite side or, alternatively no edge extension is provided. An interfering object is illustrated at 1204. In this example, the interfering object 1204 causes the sensor to fold or flap as movement occurs. This folding results in a triggering of the sensor and, as previously described, the three-layer

, system as illustrated in Figure 8 may provide a preferred technology for this particular application.

Figure 13 In many applications for sensors embodying the present invention, objects causing an interference may be fragile, susceptible to damage or may represent bodily parts. In each of these examples it is undesirable for high levels of force to be applied to the interfering object before the mechanism takes effect in modifying the operations of the actuator. In order to allow for a degree of absorption before triggering occurs, it is possible to provide additional material, such as a foam 1301 in contact with a sensor. Thus, in the example shown Figure 13, the foam 1301 is applied on top of an active sensor region 1302 and the assembly is secured via edge extensions 1303 and 1304.

Figure 14 An alternative configuration providing absorbing foam is illustrated in Figure 14. In the previous example, the foam was applied on top of the sensor. In the example shown in Figure 14, foam 1401 is located between a supporting base section 1402 and the detector itself 1403. Again, the whole assembly may be secured by applying staples or similar devices through the edge extensions 1404 and 1405.

Figure 15 In many applications, devices, such as orthopaedic chairs, are covered with a fabric, which may be merely decorative or, alternatively, may be provided in order to protect the chair from abrasion, leak or spillage. The fabric sensors of the present preferred embodiment allow for the body of the sensor to be placed under the cover such that it is not obtrusive to a user and is again protected by the mechanical attributes of the cover itself. An example of such an orientation is illustrated in Figure 15. A cross- section of chair back 204 is illustrated at Figure 15. The chair back 204 is protected by a cover 1501. An active detector region 1502 is present beneath the cover having edge extensions 1503 and 1504 thereby allowing the sensor to be secured to the chair back so as to prevent movement from a preferred location. As previously stated, sensor technology of the type described with respect to Figure 10 deploying spacer fabrics is particularly attractive for applications of this type, given that the outer cover 1501 will tend to apply a bias force to the active region 1502 of the sensor. Alternative applications for the apparatus are described with reference to Figures 16 to 18.

Figure 16 A bed frame is illustrated in Figure 16 constructed primarily from wood and configured so as to support a mattress when in use. The bed frame has a first hinge 1601 , second hinge 1602 and a third hinge 1603. The first hinge 1601 facilitates upward movement of a backrest section 1604. Similarly, hinge 1603 when co-operating with hinge 1602 allows support for a patient's legs with the hinge 1603 being elevated in an upward direction. The movement of the bed frame tends to take place when the bed frame is in use, and therefore actuators are required to effect movement. As portions of the bed frame are lowered, they are received within support members 1605 and it is possible for an object interference to occur, as shown in Figure 17, when the lowering takes place. Thus, a further situation arises in which movement occurs between a first member (1603) and a second member 1605. In a first embodiment, a fabric strip sensor is applied to the moving portion, as illustrated at 1606. However, in an alternative embodiment, a strip sensor may be applied to the stationary portion as illustrated at 1616.

Figure 17 Strip sensor 1616 is shown in greater detail in Figure 17. The nature of sensor 1616 is such as to provide the flap configuration as described with reference to Figure 1≥ In this example, an operator's hand is found between the two moving members and it is clear to see that serious injury could occur when situations of this type arise. In the present preferred embodiment, the inclusion of the hand between the moving members may in itself cause flap sensor 1616 to be activated, resulting in the actuator motor being reversed and then de- energised. Alternatively, if the hand in itself actuates strip sensor 1616, an activation will occur as the moving member is lowered, thereby forcing the hand into contact with the strip sensor. 1616 and again resulting in a deactiyation of the actuator.

Figure 18 An alternative application for the preferred embodiment is illustrated in Figure 18. In this example a table includes extendible leg supports 1801 ,

1802. These are configured so as to allow adjustment of the height of the table by effecting movement .of the table top in the direction of arrow 1803. Situations may arise where people are sat at the table thereby placing their legs underneath the tabletop. It is possible that, when intending to raise the table, an alternative selection is made resulting in the table being lowered. Under these circumstances, it could be possible for people using the table to be injured or at least placed in a degree of discomfort due to their legs being squashed beneath the downward motion of the table. Situations of this type may create further problems if the table is being used with, for example, wheelchair-bound disabled users. To prevent injury of the aforesaid type, the table has fabric strip sensors 1804 located on the underside of each of its edges. Thus when the table is being lowered, any object interference will result in one of sensors 1804 being triggered which in turn will result in a deactivation of the driving mechanism.

Claims

1. Apparatus comprising a first member and a second member in which relative movement occurs between said first member and said second member in response to operation of an actuator; wherein a fabric sensor is attached to said first member, having a first conductive plane_ and a second conductive plane, in which an electrical characteristic of said sensor changes when said first conductive plane and said second conductive plane are brought together at a position of interaction; and a control circuit is configured to detect said change in said electrical characteristic and to modify the operation of said actuator in response to said detection.

2. Apparatus according to claim 1 , wherein said first member, having said sensor attached thereto, is forced to move by said actuator.

3. Apparatus according to claim 1 , wherein said second member is forced to move by said actuator.

4. Apparatus according to claim 1 , wherein the first conductive plane and the second conductive plane are separate sheets and are separated by a third separate insulating sheet.

5. Apparatus according to claim 1 , wherein the first conductive plane and the second conductive plane are separated by a third insulating sheet, a fourth conductive sheet and a fifth insulating sheet.

6. Apparatus according to claim 1 , wherein said first conductive plane and said second conductive plane are fabricated together with insulating spacer threads to define a spacer fabric.

7. Apparatus according to claim 6, wherein an additional conducting plane is attached to said spacer fabric to facilitate two dimensional positioning.

8. Apparatus according to claim 1 , wherein said electrical characteristic is impedance and said control circuit detects a change in said impedance.

9. Apparatus according to claim 8, wherein a reduction in impedance is detected when an interaction occurs.

10. Apparatus according to claim 1 , wherein said apparatus comprises a chair, a bed or a table.

11. Apparatus according to claim 10, wherein said apparatus comprises a chair and said movable member is part of said chair, configured such that said movement is arranged to assist a person to stand up from being seated in said chair or to raise a leg support.

12. Apparatus according to claim 1 , wherein said modification to the actuator results in the actuator being stopped, reversed by a predetermined amount and then stopped again.

13. Apparatus according to claim 1 , wherein said sensor is configured as a linear strip sensor and said strip sensor is attached along the length of said first mechanical member.

14. Apparatus according to claim 1 , wherein said sensor is attached to a leading edge of said member.

15. Apparatus according to claim 1 , wherein a high impedance contact is provided at an end of the sensor between two conductive layers to provide an indication of system failure.

16. Apparatus according to claim 1 , wherein a compliant element is placed over the sensor, such that said compliant member experiances a degree of compression prior to said control circuit making said detection.

17. Apparatus according to claim 16, wherein said compliant element is placed under the sensor.

18. Apparatus according to claim 1, wherein insulation is provided within areas of the sensor rendering said areas inactive.

19. An orthopaedic chair, comprising an actuator to effect relative movement between a first member and a second member of said chair to assist an occupant to reach a standing position from a seated position; and a fabric sensor attached to said first member, having a first conductive plane and a second conductive plane, wherein an electrical characteristic of said sensor changes when said first conductive plane and said second conductive plane are brought together at a position of interaction; a control circuit configured to detect said change in said electrical characteristic and to modify the operation of said actuator in response to said detection.

20. A chair according to claim 19, wherein operation of said actuator when returning to a seated configuration is modified in response to a mechanical interaction taking place.