OPERATING METHODS FOR A LINEAR ACTUATOR AND FURNITURE WITH A LINEAR ACTUATOR

Description

[0001] The invention relates to a method for detecting a displacement position of an output element relative to a base element in a linear drive.

[0002] Electric motor-driven furniture drives designed as linear drives are used, for example, in beds, armchairs, or other furniture to adjust, in particular pivot, support surfaces or similar movable furniture parts. For this purpose, the furniture usually has one or more movement fittings to which the linear drive is coupled. When the linear drive is actuated, an output element moves linearly relative to a base element. Linear means that the movement of the output element relative to the base element occurs along a straight line. Such drives are also referred to as linear actuators, and the relative movement of the output element relative to the base element is referred to as a linear movement or simply a stroke.

[0003] The lifting movement is converted by the furniture fitting into a swivel movement or a combined swivel and lifting movement. For example, in beds, the backrest and / or footrests can be swiveled. In recliners, especially so-called relaxation or TV chairs, the backrest, a seat, and even a footrest can often be swiveled and / or extended.

[0004] A basic requirement that linear actuators for these applications must generally meet is that one or both end positions can be detected in order to shut down the actuator in these end positions. To detect the end positions, limit switches are often used in the linear actuator, which are actuated by the moving output element.

[0005] The linear actuators can be operated, for example, via a hand control connected to a control unit. For more convenient operation of the furniture, it can also be provided that programmed positions can be conveniently recalled via individual operating commands, such as the press of a button, which the furniture then assumes.

[0006] For this purpose, the linear drive must not only detect end positions, but also have information about its current set position. For this, at least the following two basic principles are known: With so-called absolute position detection, the current position of the output element relative to the base element, i.e. the current displacement position, can be detected at any time by a position sensor. For example, a potentiometric position sensor can be used that returns a resistance value that is proportional to the set position. The position sensor can be formed by a linear potentiometer with a tap that moves with the output element, or by a rotary potentiometer whose rotational position changes proportionally to the position of the output element via a corresponding gear.

[0007] The advantage of such absolute position detection is that the position information is available at any time, especially immediately after the furniture is put into operation.

[0008] Alternatively, so-called incremental position sensors are known, which determine a position by summing differential position change signals. For example, the revolutions of a linear actuator's drive motor can be detected, and starting from a known position, a position change due to the motor rotation can be taken into account. The motor rotation itself can be determined, for example, via a Hall sensor attached to its axis or by evaluating commutation signals from the motor. This type of position detection requires that at least one reference position of the motor is known and that the position change signals are detected correctly at all times.Since it cannot be guaranteed that any motor movement (even externally caused) will be detected, especially when the control unit of the linear drive is not powered, a reference run is usually required after a power interruption to the furniture, during which, for example, a limit switch is approached, which then defines the reference position.

[0009] However, such reference runs cannot be easily performed in all applications for furniture with electric motor drives. For example, this is not the case with nursing beds in hospitals or care facilities, which must be moved to other rooms while partially occupied by patients, temporarily interrupting the power supply to the control unit and the linear drive. In principle, it would be possible to provide uninterruptible power supplies, at least for the position detection system, for this period, thus eliminating the need for a subsequent reference run. However, this increases manufacturing costs and requires more maintenance, as the reliable function of the uninterruptible power supply must be ensured, for example, by regularly replacing a used rechargeable battery.

[0010] Therefore, absolute position sensors are preferable to incremental position sensors for high operational reliability. However, absolute position sensors based on potentiometers complicate the design of linear actuators and are themselves prone to failure, as the sliding contact of the potentiometer tends to develop contact problems with increasing operating time.

[0011] From the publication DE 20 2004 002 924 U1, a piece of furniture with an electric motor-driven furniture drive is known, in which inclination switches are arranged on movable furniture parts. The drives are stopped when the inclination switches detect that specified inclinations of the movable furniture part are exceeded or undershot. In this way, limit switches on the linear drive can be dispensed with. Absolute position detection for intermediate positions is not possible with the arrangement shown. Furthermore, the inclination switches, which must be mounted separately on the movable furniture parts, increase the effort required for installing the linear drives. The additional cables must also be correctly mounted and routed on the movable furniture parts to prevent them from becoming trapped by the movement fitting. The document EP 2 737 829 A discloses a known method for detecting a displacement position of an output element relative to a base element.

[0012] It is an object of the present invention to describe a method for its operation, with which the position of the linear drive can be detected at any time, without a potentiometric sensor and without additional effort during installation of the linear drive in the furniture. Furthermore, a piece of furniture with a linear drive with these advantages is to be created.

[0013] This problem is solved by a position detection method and a piece of furniture with a linear drive having the features of the respective independent claim. Advantageous embodiments and further developments are the subject of the dependent claims.

[0014] A method according to the invention for determining a displacement position in such a linear drive comprises the following steps: Several value pairs of displacement positions and inclination angles of the linear drive are determined when installed in a piece of furniture, and these value pairs are stored in a memory unit assigned to the linear drive. During operation of the linear drive in the piece of furniture, a current value of the inclination angle is then determined, and a current value for the displacement position is determined based on the stored value pairs and the determined inclination angle.

[0015] Unlike a pivot drive, a linear drive does not initially have any components whose inclination fundamentally changes upon actuation. However, the invention is based on the recognition that linear drives, due to their use in and coupling with a movement fitting in furniture, often also change their own orientation relative to the vertical upon actuation. This change can then be detected by the inclination sensor and converted into a value for the displacement position of the output element relative to the base element. As a rule, with conventional movement fittings and installation situations for linear drives, there is a monotonic functional dependency between the inclination angle and the displacement position, so that the displacement position can be clearly determined from a measured inclination angle. The inclination sensor thus acts as an absolute position sensor.

[0016] An inclination sensor operates reliably and without failure-prone mechanical components. An evaluation unit for determining the current value of the displacement position can be located in the linear drive or in a control device for the linear drive coupled to it.

[0017] Because the linear actuator itself incorporates the inclination sensor, a sensor signal can be evaluated within the linear actuator itself or can be routed via a (pre-existing) connection cable of the linear actuator for remote evaluation, for example, in a control unit of the linear actuator. This eliminates the need for additional wiring during installation.

[0018] The value pairs can be determined in a learning phase in the furniture or can be calculated theoretically in advance from the geometry and kinematics of the movement fitting and the installation situation of the linear drive. Interpolation can be carried out between measured value pairs during operation in order to determine the current displacement position with an angular or path resolution that is higher than that of the value pairs. The value pairs can also be stored in the form of a functional equation or a functional equation can be approximately determined from stored value pairs, with the help of which the actual conversion can be carried out particularly easily, quickly and with little computational effort. As an alternative to teaching the value pairs or the functional relationship between inclination and displacement position, it can also be provided to calculate these in advance based on a (known) geometry of the furniture or a furniture fitting to which the linear drive is coupled. Linear drive orThe control device can then be set up and ready for use before it is installed in the furniture.

[0019] The inclination sensor can be located in or on the linear drive. When mounted on the linear drive, the inclination sensor is also advantageously suitable for retrofitting a linear drive with an absolute position sensor. The inclination sensor can be mounted, for example, on a standpipe of the linear drive using a mounting clamp. If the inclination sensor is integrated into the linear drive, it can advantageously be located in a gear housing of the linear drive.

[0020] In a preferred embodiment of the electromotive linear drive, the inclination sensor is a MEMS system, i.e. a Micro-Electro-Mechanical System. This is characterized by its small design and low manufacturing costs. In principle, one-dimensional detection of the inclination is sufficient for use in or on the linear drive, i.e. measuring the inclination when pivoting around a predetermined axis. However, with a permanent installation in the linear drive, it may not yet be clear about which axis the pivoting takes place during operation. With retrofitting, this is usually known, but due to available positions, it cannot always be guaranteed that the attached inclination sensor will pivot precisely around its measuring axis during operation. It can therefore be advantageous to use a sensor that measures inclination around 2 or 3 axes and can flexibly detect inclinations around different axes during operation.

[0021] A piece of furniture according to the invention with an electric motor-driven furniture drive comprises at least one such linear drive and a control device configured to carry out a method described above. This results in the advantages stated in connection with the linear drive and the method.

[0022] The invention is explained in more detail below using exemplary embodiments and figures. The figures show: Fig. 1 shows an embodiment of a piece of furniture with an electric motor-driven furniture drive with linear drives and in an isometric view; Fig. 2, 3 each show a sectional side view of the piece of furniture from Figure 1in different positions of its movable furniture parts; Fig. 4 shows a schematic diagram of a relationship between the pivot angle and stroke of a linear drive installed in a piece of furniture; Fig. 5 shows a first embodiment of a linear drive for use in a piece of furniture; and Fig. 6 shows a second embodiment of a linear drive for use in a piece of furniture.

[0023] Figure 1 shows a bed 1 as an example of furniture with an electric motor-driven furniture drive. The bed 1 has a frame 2, which carries a plate-shaped support element on which upholstery, e.g., a mattress, can be placed. In alternative embodiments, the support element can also be designed as a slatted frame.

[0024] In the example shown, the support element is constructed in four parts, with one part being rigidly connected to the frame 2 and three parts being pivotably mounted relative to the frame 2 and / or relative to each other. For this purpose, a movement fitting with fitting parts 3, 4 is provided. In the example shown, the fitting part 3 is fixedly mounted to the frame 2 using the non-movable part of the support element. The fitting parts 4 are movable relative to this fitting part 3 and guide or support movable furniture parts 5, which here correspond to a back part and two leg parts of the support element.

[0025] In the present example, two linear drives 6 are provided to move the movable furniture parts 5, of which Figure 1only one is visible for adjusting the head section. In the linear drives 6, an output element moves linearly relative to a base element. The linear drives 6 are connected to the base element and the output element with a fitting part 3, 4.

[0026] Due to the geometry of the movement fitting, a linear movement of the output element relative to the base element leads to a pivoting of the movable fitting part 4 or the movable furniture part 5.

[0027] A control device 7 is also provided, which in the present example is attached to the frame 2 and is connected to the linear drives 6 via cables not shown here. The control device 7 is further coupled to an operating unit, via which the linear drives 6 are actuated. The operating unit can be coupled to the control device 7 via a wired or wireless connection. Wireless transmission can be optical, e.g., via infrared light, or radio. The latter also includes transmission via a WLAN network or a Bluetooth connection.

[0028] In the example shown, the control device 7 is configured to control both linear drives 6 of the bed 1. In alternative embodiments, the control device 7 can be integrated into one of the linear drives 6, which then represents a type of higher-level drive that also controls the other drive. It is also conceivable for both (or possibly several existing) linear drives to have their own integrated control devices that respond to control instructions from an operating unit independently of one another or in a coordinated manner.

[0029] The electric motor furniture drive can be supplied with power via a power supply unit integrated into the control device 7 or via an external power supply unit connected to the control device 7 via a low-voltage cable.

[0030] According to the application, the linear drives 6 are characterized in that an inclination sensor 10 is integrated into the linear drive 6 or, as in the example shown, is mounted on the linear drive 6. The inclination sensor 10 detects an inclination of the linear drive 6 relative to the vertical defined by gravity. Due to the coupling of the linear drive 6 to the fittings 3, 4, actuation of the linear drive 6 is associated not only with a pivoting of the movable furniture part 5, but also with a pivoting of the linear drive 6 and thus of the inclination sensor 10 relative to the vertical.

[0031] Under the assumption, valid in many applications, that a functional relationship between the inclination detected by the inclination sensor 10 and a displacement position of the linear drive 6, i.e., a relative position of the output element relative to the base element, is monotonous, a measured inclination can be unambiguously converted into a displacement position, hereinafter also referred to as stroke. In this way, a measured inclination value can be converted into position information at any time, similar to an absolute position sensor.

[0032] In the Figures 2 and 3 The bed 1 is shown in a sectional side view with different positions of the movable furniture parts 5. These views also show the second linear drive 6, which adjusts the leg parts of the support element.

[0033] For the linear drive 6, which adjusts the head section, the Figure 2an angle of inclination α and a stroke d are shown. The angle of inclination α is shown here relative to a horizontal line. This is purely an example. The inclination sensor 10 itself measures relative to the vertical, whereby the output value depends on the precise installation position of the actual sensor in the inclination sensor 10 as well as on the mounting orientation of the inclination sensor 10 on or in the linear drive 6. It is understood that a value measured by the inclination sensor 10 can be easily related to the angle of inclination α used here for illustration using geometric relationships. Likewise, the definition of the stroke d as a measure of the position of the output element relative to the base element is purely an example. All that is important is that the stroke d is a measure of the linear movement of the linear drive 6, whereas the angle of inclination α characterizes its orientation within the furniture.

[0034] Fig. 4shows in a schematic diagram the relationship between the measured inclination angle α and the resulting stroke d in a curve 20. The inclination angle α is shown in ° (degrees) and the stroke in mm (millimeters).

[0035] In the present case, a linear relationship is evident over a large angular range, which only becomes steeper at larger angles. Such a curve 20 can be stored in an evaluation unit in the linear drive 6 or the control device 7 and used to convert the inclination angle α measured by the inclination sensor 10 into the stroke d. The curve is preferably stored in a non-volatile memory, for example, a flash memory, so that it is immediately available even after an interruption of the operating current.

[0036] Curve 20 can either be calculated in advance based on the (known) geometry of the fitting and the installation situation of the linear drive 6 in the fitting and stored before delivery of the linear drive 6 or the control device 7. Alternatively, a type of learning phase can be provided in which certain angular positions of the movable furniture part 5 are manually approached, e.g., using a gauge, and the corresponding inclination angles α are measured and stored. Curve 20 can then be interpolated and stored based on the measured values from the control device 7 or the linear drive 6.

[0037] Depending on the fitting and installation situation, curve 20 may look more complicated than in the example of the Fig. 4 . As long as the curve is strictly monotonous, i.e., it has no local maxima or minima, it is nevertheless possible to clearly assign a stroke d to a measured inclination angle α.

[0038] In certain cases, a position determination can even be performed when a local maximum or minimum is present. The magnitude and / or sign of the first derivative of curve 20 are used for this purpose. As soon as the linear drive has started, a change in the inclination angle α can be detected based on the known direction of travel and, if applicable, speed. This makes it possible, for example, to determine on which side (toward smaller or larger inclination angles α) of the maximum or minimum the position of the output element of the linear drive 6 is located. This then allows the correct position to be clearly determined.

[0039] In the Figures 5 and 6Two linear drives 6 are shown in isometric views, each equipped with an inclination sensor 10. In terms of basic construction, both are identical, differing only in the mounting type and position of the inclination sensor 10. Both can be used in the previously shown embodiments of the bed 1 according to the Fig. 1 to 3 be used.

[0040] The linear drives 6 each have a gear housing 61 with a dome, beneath which an electric motor 62 is located. A speed reduction gear with at least one gear stage, for example a worm gear, is connected downstream of the electric motor 62. This gear acts on a threaded spindle gear with a threaded spindle, which generates a linear movement from the rotary movement of the motor. The threaded spindle is arranged in a standpipe 63 protruding from the housing 61, which also serves as a guide for a lifting tube 66. A fork head as a fastening element 67 is attached to the free end of the lifting tube 66. A comparable fork head as a fastening element 64 is located at the opposite end of the gear housing 61. Furthermore, an outlet for a connecting cable 65 is formed on the gear housing 61.

[0041] The linear actuator 6 is mounted in the furniture with the two fastening elements 64, 67. The lifting tube 66 with the fastening element 67 form the aforementioned output element of the linear actuator 6; all other components are assigned to the base element.

[0042] The inclination sensor 10 is in the embodiment of the Fig. 5 in a housing 11 using a mounting element 12, here a type of fastening clamp, attached to the standpipe 63. In this embodiment, the inclination sensor 10 can also be easily retrofitted to existing linear drives as a retrofit element.

[0043] In the embodiment of the Fig. 6 the inclination sensor 10 is integrated in the gear housing 11 of the linear drive 6.

[0044] In both cases, the inclination sensor can be designed, for example, as a single- or multi-axis acceleration sensor based on MEMS (Micro-Electro-Mechanical System). List of reference symbols

[0045] 1Bed 2Frame 3, 4Fitting part 5Movable furniture part 6Linear drive 61Gear housing 62Motor 63Standpipe 64Fastening element (fork head) 65Connecting cable 66Lifting tube 67Fastening element (fork head) 7Control device 10Inclination sensor 11Housing 12Mounting clamp 20Curve dSliding position (stroke) αInclination angle

Claims

1. Method for ascertaining a displacement position (d) of an output element relative to a base element in a linear drive (6) for a furniture item having a movable furniture part, wherein the linear drive (6) includes a base element and an output element which is displaceable linearly with respect to the base element, and a measuring device for ascertaining a position of the output element with respect to the base element, comprising the following steps: - determining several value pairs of displacement positions (d) and tilt angles (α) of the linear drive (6) in a state installed in a furniture item; - storing the value pairs in a memory unit associated to the linear drive (6); - determining a current value of the tilt angle (α) during operation of the linear drive (6) in the furniture item; - determining a current value for the displacement position (d) based on the stored value pairs.

2. Method according to claim 1, in which interpolation is performed between measured value pairs to determine the current displacement position (d).

3. Method according to claim 1 or 2, in which the value pairs are stored in the form of a function equation or in which a function equation is determined by approximation from stored value pairs.

4. Method according to one of the claims 1 to 3, in which the value pairs are determined in a learning phase in the furniture item.

5. Method according to one of the claims 1 to 3, in which the value pairs are calculated based on a geometry of the furniture item or a furniture fitting to which the linear drive (6) is coupled.

6. Method according to one of the claims 1 to 5, in which an evaluation unit for determining the current value of the displacement position (d) is arranged in the linear drive (6) or in a control device (7) for the linear drive (6) coupled thereto.

7. Method according to one of the claims 1 to 6, in which the tilt sensor (10) is mounted on the linear drive (6).

8. Method according to claim 7, in which the tilt sensor (10) is mounted on a standpipe of the linear drive (6) by a mounting clamp (12).

9. Method according to one of the claims 1 to 6, in which the tilt sensor (10) is integrated in the linear drive (6).

10. Method according to claim 9, in which the tilt sensor (10) is arranged in a gearbox housing (61) of the linear drive (6).

11. Method according to one of the claims 1 to 10, in which the tilt sensor (10) is a MEMS system.

12. Method according to one of the claims 1 to 11, in which the tilt sensor (10) is suitable for measuring a tilt relative to at least 2, preferably 3 axes.

13. Furniture item with an electromotive furniture drive, comprising at least one linear drive (6), wherein the linear drive (6) includes a base element and an output element which is displaceable linearly with respect to the base element, and a measuring device for ascertaining a position of the output element with respect to the base element and comprising a control device (7) which is designed to carry out a method according to one of the claims 8 to 13.