DE102009046408A1 - Force sensor for use in bed for determining weight change of sick person during monitoring of rotation of person, has force-sensitive sensor element elevatedly arranged at side of plate, where force to be detected is exerted at another side - Google Patents

Abstract

The sensor (1) has a force-sensitive sensor element (3) i.e. force-dependent resistor, elevatedly arranged at a side of a deformation-resistant plate (2), where force to be detected is exerted at another side of the plate according to the use of the sensor. The former side of the plate is divided into different sections, and the sensor element is attached to one of the sections. The force exerted at the latter side of the plate is determined by a measuring result of the sensor element, where the measuring result is outputted by a Bluetoothconnection. An independent claim is also included for a method for operating an arrangement of a couch device and a force sensor.

Description

The present invention relates to a force sensor and an arrangement comprising such a force sensor.

Force sensors are well known in the art. In some applications, it may be necessary for a force sensor, with which, for example, a weight force is measured, to be made very flat or thin.

From the European patent publication EP 0 696 782 A1 an optical force sensor is known in which a light waveguide extends in a very flat formed contact mat, which is mechanically deformed by loading the contact mat. Due to this mechanical deformation, light energy of a light beam coupled into the optical waveguide passes from low-order light modes to higher-order light modes. This mode transition can be exploited to determine the force applied to the contact mat.

A disadvantage of such a force sensor is that the force to be measured must be exerted over a relatively large area on the contact mat, so that damage to the optical waveguide is prevented.

It is consequently not possible to use such a force sensor in applications in which the force to be measured is transmitted over a small area.

The object of the present invention is to provide a flat force sensor which can be used independently of the size of the surface over which the force to be measured is transmitted.

This object is achieved with a force sensor according to the invention, wherein the force sensor comprises a deformation-resistant plate with a first use, on which the force to be detected is to be exerted, and a second side, on which at least one force-sensitive sensor element is raised.

An advantage of such a force sensor is that it is made relatively thin and a force that is transmitted over a relatively small area, can be measured.

Further preferably, the second side of the first plate can be divided into different sections in terms of area and a force-sensitive sensor element can be assigned to each section, whereby the force exerted on the first side can be detected via the individual measurement results of the sensor elements.

By way of such an embodiment of the force sensor according to the invention, it can be achieved that various types of sensors can be used as force-sensitive sensor elements, wherein the measurement result of the force sensor according to the invention can be calculated via the individual measurement results of the sensor elements.

Preferably, the second side has a rectangular surface and, when dividing the rectangular area into nine uniform sections, one sensor element is associated with each of an outer corner section and a center section.

Preferably, the second side has a rectangular surface and, when dividing the rectangular area into twelve uniform sections, one sensor element is associated with each of an outer corner section and one of each of two center sections.

Further preferably, the second side has a rectangular surface and, when dividing the surface into uniform sections, in each case a sensor element is arranged in three outer corner sections.

By such arrangements of the sensor elements on the second side of the first plate, a force exerted on the first side force can be determined and calculated regardless of the position of the force.

Preferably, in such a subdivision, a force-dependent resistor is used as the sensor element.

Further preferably, the sensor element may be configured such that it has a flexible contact mat in which an optical waveguide extends, wherein a force exerted on the first side of the first plate force is detectable via a change in the transmission or mode change of a current in the optical waveguide light ,

An advantage of such a force sensor is that damage to the optical waveguide is prevented by the first plate when a force is exerted on the sensor element over a relatively small area.

Further preferably, the force sensor according to the invention may comprise a second plate which is arranged such that the at least one sensor element is located between the first and second plate.

By providing a second plate, the sensor elements are protected from damage, at the same time the thickness of the force sensor according to the invention increases only slightly.

Preferably, the first and / or second plate is dimensioned to have a thickness that is much smaller than the circumference of the first and / or second plate. In addition, the first and / or second plate is formed of a material with high torsional rigidity and / or bending stiffness.

As a result, the force sensor can be kept very thin in layered construction.

Preferably, the first and / or the second plate of the force sensor according to the invention are formed from aluminum.

Further preferably, the force sensor comprises a communication unit for outputting the measurement result or an output signal of the sensor element.

Furthermore, the force sensor preferably also includes an evaluation unit for determining a measurement result.

Advantageously, an entire measuring system can thereby be constructed with one or more force sensors according to the invention, wherein the individual force sensors can be arranged at different locations.

Further preferably, the evaluation unit and the communication unit are arranged between the first and the second plate.

This makes it possible to build the measuring system, at the same time do not change the dimensions of the force sensor according to the invention.

Further preferably, the communication unit is set up to output the measurement result or the output signal of the sensor element via a radio link.

This allows an easy and quick setup of a measuring system even under extreme conditions.

Further preferably, the communication unit of the force sensor according to the invention is adapted to output the measurement result or the output signal of the sensor element via a wireless connection, Bluetooth ^® connection or a WPAN connection or a cellular connection.

The advantage here is that a measuring system can be easily adapted to specific application requirements and situations.

Further preferably, in the force sensor according to the invention, a watertight enveloping element is provided, which encloses the individual elements of the force sensor according to the invention.

As a result, the force sensor according to the invention is protected against harmful effects, such as moisture.

In an advantageous arrangement of the force sensor according to the invention this is arranged together with a reclining device, such as a bed, such that the force sensor is located under a support member or the mattress of the reclining device.

Preferably, in each case one force sensor is arranged under several or all supporting elements of the lying device.

In a method according to the invention for operating such an arrangement, a weight force change and / or a displacement of the load point of the lying device can be detected via the force sensor (s) and a specific process can be carried out as a function of the detected change in weight force.

In this way, advantageously, a person in need of care or a sick person can be monitored, so that critical situations can be detected.

In an advantageous embodiment of the method according to the invention, for example, a time measurement can be started after the detection of a change in weight force and a warning message issued if no further change in weight force is detected after a certain time has elapsed, which is detected via the time measurement.

In particular, such a time measurement can be started when a reduction in the weight of the reclining device is detected by the detection of a change in weight force.

In this way, it can be determined, for example, that a person in need of assistance has left the lying device and does not find his way back to it after a certain time.

Further preferably, such a time measurement can be started depending on the time of day.

This makes it possible to draw different conclusions from the measurement results as a function of the time of day.

According to a further preferred embodiment of the method according to the invention, the detected weight force changes are logged together with a time of day and / or a date.

This advantageously makes it possible to estimate certain causes of changes in weight.

With reference to the accompanying drawings, preferred embodiments of the force sensor according to the invention and the arrangement thereof together with a reclining device will be described below.

1a shows schematically the force sensor according to the invention in section;

1b shows schematically the force sensor according to the invention in a plan view;

1c schematically shows the configuration of a first and second plate, which can be used in the force sensor according to the invention;

2a schematically shows a sensor element which can be used in the force sensor according to the invention, in section;

2 B schematically shows an alternative sensor element which can be used in the force sensor according to the invention, in section;

2c schematically shows a third sensor element which can be used in the force sensor according to the invention, in a plan view;

3a shows a further sensor element which can be used in the force sensor according to the invention, in section;

3b - 3d show individual components of in 3a shown sensor element

4a and 4b schematically show preferred arrangement positions of individual sensor elements on the underside of the first plate of the force sensor according to the invention; and

5 shows a block diagram of an exemplary evaluation of the measurement result, which has been detected in a preferred arrangement of the force sensor according to the invention.

In 1 schematically a force sensor according to the invention is shown, wherein 1b a schematic plan view and 1a a schematic sectional view represents. The sectional view in 1a shows a view along the in 1b shown section line AA.

With reference to 1a has the force sensor according to the invention 1 a first layer 2 (hereinafter referred to as the first plate) on a sensor element 3 is arranged. The first plate 2 is made of a material with high rigidity, such as aluminum, an aluminum alloy, steel or plastic with the required mechanical properties. The first plate 2 and the sensor element 3 are preferably together on a second plate 4 arranged. The first and second plates can be made the same material. The respective plates 2 . 4 can also have the same or similar dimensions in the in 1a and 1b have shown x, y, z directions. The plates 2 . 4 are preferably dimensioned such that their thickness is much smaller than their circumference (sum of the dimensions of in 1b shown pages 8th . 9 ). In other words, the plates are very thin. Preferred dimensions of the plates 2 and 4 amount (x, y and z direction) 200 mm × 200 mm × 7 mm. Besides, the plates can 2 . 4 in the xy plane have a round, rectangular, square or oval shape or any shape.

In 1c is a schematic sectional view of the first plate 2 shown. The second plate 4 can be identical. The plate 2 points in the in 1c shown training on three sections. The plate 2 is preferably formed for reasons of weight of aluminum or an aluminum alloy and constructed in a layered construction. The plate 2 has a first aluminum layer 21 and a second aluminum layer 23 on, between which is a corrugated third aluminum layer 22 located. The third aluminum layer 22 is to form a strong and warp resistant structure in the 1c periodically wavy shown x-direction. Depending on the size of the weight G to be measured, the periodic formation of the third aluminum layer 23 be varied so that the plate 2 in different thicknesses (z-direction in 1c ) can be formed.

In a further preferred construction, the third aluminum layer 22 formed with a honeycomb structure lying in the xy plane.

To form a solid structure, the plates can 2 . 4 and the sensor element 3 connected by different connection methods. Preferred compounds are, for example, adhesive compounds or compression compounds, ie generally material and / or non-positive connections. However, it must be ensured that these compounds have a relative movement of the plates 2 . 4 allow each other. This relative movement is for transmitting the force to be measured to the sensor element 3 necessary.

Furthermore, the force sensor according to the invention comprises an enveloping element 5 such as a rubber cover that protects against moisture or other harmful effects.

According to the invention, the force sensor according to the invention is arranged such that a force G to be measured is applied to the first plate 2 is exercised. Ie. a force to be measured is applied to a first side 21 (hereinafter referred to as upper side) of the first plate 2 of the force sensor, whereas its second side 22 (hereinafter referred to as the underside) of the sensor element 3 is facing.

This in 1a shown sensor element is between the plates 2 . 4 and thus arranged on the underside of the first plate. In this embodiment, the sensor element has the same dimensions in the xy plane as the plates 2 . 4 , The force sensor according to the invention is, as will become apparent hereinafter, but not limited thereto.

With reference to 1b the force sensor continues to point either in the first plate 2 or the second plate 4 an access 6 in the interior of the force sensor. About such access 6 For example, a battery compartment or generally the electronics of the force sensor, such as a communication unit, may be achieved. Access 6 may be configured such that the plates 2 . 4 with the sensor element 3 first out of the shell 5 need to be taken to allow access 6 is reachable. On the other hand, the shell 5 according to the access 6 have a closable opening over which the access 6 is achievable without the shell 5 to remove beforehand.

The communication unit can be equipped with a control unit 7 , which can be provided depending on the measuring arrangement at a certain location, are connected.

The connection can be either a cable or radio connection. Preferred radio links are z. As W-LAN, Bluethooth ^® - or WPAN connections. A preferred cable connection, z. As a LAN connection, may be configured such that each sensor is individually connected to the control unit. A further preferred cable connection can be configured such that the sensors are interconnected and only one of the sensors is connected directly to the control unit via a cable.

Preferably, the control unit 7 designed such that several force sensors can communicate with her via the connections shown above. In this way, it is possible to quickly and easily construct a measuring arrangement comprising a plurality of force sensors. The control unit and the force sensors can be interconnected, for example, in a master-slave hierarchy (control unit = master, force sensor = slave).

The control unit may preferably evaluate or process the sensor signal obtained via the communication unit.

Alternatively, however, an evaluation unit, which is preferably arranged within the force sensor, an output signal of the sensor element 3 capture and / or evaluate and output this to the communication unit.

Preferably, the control unit 7 be an element of a force sensor. In this case, one of the force sensors assumes the master function and the remaining force sensors assume the slave function.

In the control unit 7 For example, a processor and at least one memory on which a program is stored may be provided, whereby various processing of the output signal (s) is possible.

Furthermore, the control unit may be configured such that a message via a cable or radio link 11 can be issued. Preferred compounds are, for. B. W-LAN, Bluethooth ^® - or WPAN, or cellular connections. As a result, a remote-controlled measuring arrangement can be set up.

2a - 2c show different embodiments of a sensor element. In these alternative embodiments, the sensor element is designed as an optical force sensor, in which an optical waveguide 31 in a deformable under force mat 32 runs. At least in the area where the optical fiber 31 runs, the area can be 35 the mat 32 be structured such that when a load on the mat 32 (Force G) of the optical fibers 31 is mechanically deformed depending on the structuring. At the in 2a shown sensor element 3 is the structuring of the mat 32 periodically formed. One period length is I _p .

For detecting the force G exerted on such a sensor element is at a first end 33 of the optical fiber 31 Light in the optical fiber 31 coupled and on its second end proved. With a load on the mat 32 indirectly over the first plate 2 and a concomitant deformation of the optical waveguide 31 goes light energy of the in the optical fiber 31 coupled light from low order modes to higher order modes. The degree of transition to light energy allows a conclusion to be drawn on the force exerted on the force sensor.

A light-emitting element for coupling light into the optical waveguide 31 and a photodetector for detecting the coupled light are respectively at one end of the optical waveguide 31 provided, which may be arranged in the evaluation unit.

2 B schematically shows a further alternative of the sensor element 3 , This sensor element 3 is identical to the one in 2a shown that the area where the optical fiber 31 runs, is structured. It is different that not only the surface facing the optical waveguide 35 the mat 32 , but also the other surface facing the optical waveguide 36 the mat 32 is structured. In the 2 B shown structuring of the optical waveguide facing surfaces of the mat 32 are periodically formed in phase. As a result, a stronger mechanical deformation of the optical waveguide under load of the force sensor indirectly via the first plate 2 generated, whereby the sensor element is more sensitive to changes in the force.

2c shows a schematic view of another alternative of an optical sensor element. In 2c is in particular the course of the optical waveguide 31 inside the mat 32 shown. The optical fiber 31 is so inside the mat 32 arranged that the course in certain places 37 crosses. In this alternative of the optical sensor element 3 are the the optical fiber 31 facing surfaces 35 . 36 the mat 32 unstructured. A deformation of the optical waveguide occurs when the mat is loaded 32 at the respective crossing points, whereby the mode change described above occurs.

The light coupling of the light into the optical waveguide 31 at one end 33 and the proof of light at its second end 34 be with all alternatives in 2a - 2c are shown performed in the same way.

In general, in the sensor elements shown above, the course of the optical waveguide can be selected depending on the application. If a higher sensitivity is required, the routing of the optical fiber is denser, ie, for example, the number of crossing points in the in 2c , shown sensor element higher.

In the force sensor according to the invention, which has one of the sensor elements described above, the measurable forces are in a range up to 20 kN.

3a shows another alternative sensor element 3 that can be used in the force sensor according to the invention. This sensor element is a force-dependent resistor. This one is in 3a shown in section, where this is a carrier film 38 with a semiconductive polymer layer, an adhesive layer 39 and an electrode foil 310 includes. These three elements are as in 3a shown, arranged such that the adhesive layer 39 , which serves as a spacer, on the electrode foil 310 and the carrier film 38 on the adhesive layer 39 is arranged.

This creates the in 3a shown layer sequence, due to the adhesive layer 39 between the electrode foil and the carrier foil 38 a gap arises.

The electrodes are by means of a Silberleitpaste on the electrode foil 310 imprinted, where, as in 3d shown, individual electrode fingers of the electrodes 312 . 311 are arranged alternately. Depending on the carrier film 38 force applied, the electrodes are contacted via the semiconducting polymer layer, which increases the resistance between the in 3d shown electrodes 311 . 312 can be measured, reduced. The pressure measuring range of in 3a The sensor element shown covers three decades from 0.1 N / cm ² to 100 N / cm ² .

In the force sensor according to the invention are preferably more with reference to 3a - 3d explained sensor elements used.

4a and 4b schematically show two preferred arrangements of several sensor elements between the in 1 shown plates 2 . 4 ,

With reference to 4a becomes the plate 2 divided into different sections, which arise from each one of the pages 8th . 9 the rectangular shaped first plate 2 Divided into three sections. This results in a division of the bottom of the first plate 2 in nine even areas. With reference to each side, one sensor element is preferably assigned to the outer sections (corner sections). Further, in the portion corresponding to the central portion with respect to each divided side, a sensor element is arranged.

In 4b is another preferred arrangement of in 3a - 3d explained sensor element 3 shown. This preferred arrangement differs from that in 4a shown in the way that the page 8th the first plate 2 is divided into four sections. The rectangular area of the plates 2 . 4 is thus divided into twelve equal sections. One sensor element each is associated with the corner portions and the middle portions lying between the corner portions with respect to each side.

Both in the in 4a as well as in 4b As shown arrangement, the measurement results are merged in the evaluation unit or control unit and a resulting on the first plate 2 applied force calculated.

In a further preferred arrangement of a plurality of sensor elements, the underside of the first plate, as in 4a and 4b , shown, each having three corner sections associated with a sensor element.

Generally, the number of sensor elements and their distances from each other are determined depending on the use of the force sensor.

In this force sensor according to the invention forces can be measured in a range of about 10 N to about 20 kN.

In the above description it has been described that the plates 2 . 4 have a high bending and / or torsional rigidity. By this is meant that the plates 2 . 4 are dimensioned such that no plastic deformation of the plate occurs in the region of the force to be measured.

Hereinafter, a preferred arrangement using at least one above-described force sensor and a method of operating such an arrangement will be described.

Preferably, a force sensor according to the invention is used in arrangement together with a reclining device, such as a bed.

In both domestic and home care, collecting data related to the behavior of a person in need in their bed can be very helpful.

Due to the very thin design of the force sensor according to the invention, this example, easily under a support element of the reclining device, d. H. be placed under the foot of a bed, or the mattress. In each case, a force sensor is preferably arranged either under the feet at the end of the bed (foot end) or at the bed head (head end).

The dimensions of the force sensor according to the invention can in the XY plane, the in 1 is shown to be dimensioned so that a single force sensor can be placed under both feet of the bed at the foot or head end.

Due to the thin design of the force sensor according to the invention, the arrangement of the same under the feet leads to no serious change in the inclination of the bed surface on which a person lies.

In addition, a change in this surface can be prevented by placing an inventive force sensor under all feet of the bed.

As explained above, a plurality of force sensors according to the invention may be connected to the control unit preferably in the form of a master-slave hierarchy. Each individual force sensor is connected to the control unit via the communication unit.

It can be seen that with the force sensor according to the invention in nursing homes, hospitals and in home care quickly and easily an arrangement can be created over which helpful data can be obtained.

Certain operations may be controlled by a program executed in the control unit. Depending on the measurement results output by the force sensors, certain operations are started or terminated.

The block diagram 5 schematically shows a performed in dependence of the detected weight force change operation.

When a force sensor determines a force change ΔG, it outputs this result to the control unit via the communication unit.

When it is judged in the control unit in a comparison S1 with a target value that the output measurement result is equal to or not equal to this, various switching outputs S2, S3 are made.

On the basis of these switching outputs S2, S3, a specific process is started or terminated.

The mentioned set value may for example indicate a weight force applied to the plate of the Force sensor acts when a person is in the bed.

If the comparison shows that the total force acting on the force sensor (s) is greater than the setpoint, it means that a person is in the bed. Here, if a pending switching output S3 is made that the total weight is less than the target value, it is determined that no person is in the bed.

Based on this, the control unit can start a certain process. For example, starting from the determination that no person is in the bed, a time measurement can be started over which the time elapsed since the weight force change is determined. If, after a certain period of time, no further change in the weight force, which indicates that the person with good comparable or the same weight has returned to bed, is detected, the control unit issues a warning message about the radio connection 11 out. Such a warning may have the content that the person in need has left the bed and is unlikely to be able to return to the bed. Reason for this can be a fall of the person. On the other hand, if it is determined within the specified time that the person has returned to bed, no warning message will be issued. As can be seen, critical situations can be easily and easily detected with such remote monitoring, which is why z. As nurses in nursing homes or home care can be relieved.

Furthermore, for example, the acquired measurement data can be recorded together with a time of day and / or the date. Based on this, then the time measurement can be adjusted accordingly. During the daytime, leaving the person's bed can have a variety of different reasons. For example, the person may leave the bed to wash himself in the bathroom or to follow a doctor's leave the bed. Experience has shown that this requires more time than a bowel movement at night, which is why the above warning message is issued only after a longer period of time. In addition, the data provided with the time of day and / or the date can be used to a certain period of time, such. B. leaving the bed in a day to calculate.

Preferably, the control can also be carried out as a function of personal data. For example, it may be set beforehand in the control unit that the person is suffering from dementia. Based on this information, the control unit immediately issues a warning message when it is determined that the person has left the bed because of the likelihood that they will not find their way back to bed. The nursing staff can then respond immediately.

It can also be determined via several force sensors whether a person has turned in the bed or not. For such determination, the control unit determines that the weight acting on individual force sensors has shifted from one force sensor to another. From this it can be concluded that the person lying in the bed has turned. For example, after detecting a person's turn in the bed, a time measurement may also be started to determine that the person in the bed is rotating at regular intervals. From this it can be concluded, for example, that the person is still alive or moves sufficiently to avoid pressure points on the body. In addition, it can be estimated via the above-mentioned logging of the progressions of the weight force change, whether certain activities (eg, washing, massage, etc.) were performed on the person.

Furthermore, several possible activities can be estimated by providing different setpoints. For example, a set point indicating that the headboard of the bed has been set up may be stored. If a force measurement using the target value shows that the headboard has been set up, it can be used to close a possible food intake (breakfast, lunch or dinner).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0696782 A1 [0003]

Claims (24)

A force sensor comprising a first deformation-resistant plate when the intended use of the force sensor has a first side, on which the force to be detected is to be exerted, and a second side, on which at least one force-sensitive sensor element is arranged raised. The force sensor according to claim 1, wherein the second side of the first plate is divided into different sections and at least one section is associated with a force-sensitive sensor element, whereby the force exerted on the first side of the first plate can be detected via the measurement results of the sensor elements. A force sensor according to claim 1, wherein the second side has a rectangular area and, when the rectangular area is divided into nine uniform portions, one outer corner portion and one center portion each have a sensor element associated therewith. A force sensor according to claim 1, wherein the second side has a rectangular area and, when dividing the rectangular area into nine equal sections, three outer corner sections are each assigned a sensor element. A force sensor according to claim 1, wherein the second side has a rectangular area and, when dividing the rectangular area into twelve uniform portions, one outer corner portion and two center portions are each assigned a sensor element. Force sensor according to one of the preceding claims, wherein the sensor element is a force-dependent resistor. Force sensor according to one of the preceding claims, wherein the sensor element comprises a contact mat, in which an optical waveguide extends, and the force exerted on the first side force is detectable via a change in the transmission or mode change of a running light in the optical waveguide. A force sensor according to any one of the preceding claims, wherein the force sensor comprises a second plate arranged such that the at least one sensor element is located between the first and second plates. A force sensor according to any one of the preceding claims, wherein the first and / or second plate has a thickness which is much smaller than the circumference of the first and / or second plate and the first and / or second plate is formed of a material having high rigidity , Force sensor according to one of the preceding claims, wherein the force sensor has an evaluation unit for determining a measurement result and a communication unit for outputting the measurement result. A force sensor according to claim 10, wherein the evaluation unit and the communication unit are disposed between the first and second plates. A force sensor according to claim 10 or 11, wherein the communication unit is arranged to output the measurement result via a radio link. A force sensor according to claim 10 or 11, wherein the communication unit is arranged to output the measurement result via a Wi- ^Fi connection, Bluetooth® connection, or WPAN connection. A force sensor according to any one of the preceding claims, wherein the force sensor comprises a watertight sheath member including at least the first plate and the at least one sensor element. Force sensor according to one of the preceding claims, wherein the first and / or the second plate are formed from the following materials: aluminum, aluminum alloy, steel, structured aluminum. Force sensor according to one of the preceding claims, wherein the first and / or the second plate of two aluminum layers, between which a periodic corrugated aluminum layer is formed. Arrangement of a reclining device and a force sensor according to one of claims 1 to 16, wherein at least one force sensor is arranged under a support element of the reclining device. Arrangement according to claim 17, wherein in each case a force sensor is arranged under a plurality or each support element of the lying device. Arrangement according to claim 17 or 18, wherein the arrangement further comprises a control unit, to which the at least one force sensor is connected via the communication unit. Method for operating an arrangement according to claim 17, 18 or 19, the method comprising the following steps: (a) detecting a weight force change of the reclining device via the force sensor; (b) Issuing detected weight force change via the communication unit; (c) performing a particular operation in response to the detected weight force change. A method according to claim 20, wherein in step (c) a time measurement is started after the detection of a weight force change and a warning message is issued if no further change in weight force is detected after a certain time has elapsed, which is detected via the time measurement. Method according to FIG. 20, wherein in method step (c) the time measurement is started when it is detected in method step (a) that the weight force of the reclining device is reduced. Method according to 20, wherein in step (c) the time measurement is started if, in method step (a), the change in weight force is detected at a certain time of day. Method according to one of claims 20 to 23, wherein in step (c) the detected weight changes are logged together with a time of day and / or a date.

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