Patent Application
20240206634
The invention relates to an electromotive linear drive for a furniture item having a movable furniture part, with the linear drive having a base element and an output element which is displaceable linearly with respect to the base element, and to a measuring device for ascertaining a position of the output element with respect to the base element. The invention further relates to a method for ascertaining a displacement position of an output element relative to a base element in such a linear drive.
Electromotive furniture drives designed as linear drives are used, for example, in beds, armchairs or other furniture items in order to adjust, in particular to swivel, support surfaces or similar movable furniture parts. For this purpose, the furniture item usually has one or more motion 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 hereby that the movement of the output element relative to the base element is along a straight line. Such drives are also referred to as lift drives and the relative movement of the output element with respect to the base element is referred to as lifting movement or simply lift.
The lifting movement is converted by the furniture fitting into a swivel movement or a combined swivel and lift movement. In the case of beds, for example, back and/or foot sections can be swiveled. In the case of recliners, especially so-called relax or TV recliners, the backrest, a seat and also a footrest can often be swiveled and/or extended.
A basic requirement that linear drives must meet for these applications is usually that one or both end positions are detected in order to switch off the drive in these end positions. To detect the end positions, limit switches are often used in the linear drive, which are actuated by the moving output element.
For operation, the linear drives can be moved forward or moved backward, e.g. via a manual operation that is connected to a control device. For more convenient operation of the furniture item, it is also possible to retrieve programmed positions in a user-friendly manner via individual operating commands, for example a keystroke, which are then assumed by the furniture item.
For this purpose, it is necessary that the linear drive not only detects end positions, but also has information about its current setting position. At least the following two basic principles are known for this purpose: In the case of 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 by a position sensor at any time. For example, a potentiometric position sensor can be used which feeds back a resistance value proportional to the set position. The position sensor can be formed by a linear potentiometer, which has a pick-off that is moved with the output element, or also by a rotary potentiometer, the rotational position of which changes proportionally with the position of the output element via a corresponding gear mechanism.
This type of absolute position detection is advantageous because the position information is available at any time, especially also immediately after the furniture item has been put into operation.
As an alternative, so-called incremental position sensors are known which determine a position by summing up differential position change signals. For example, the revolutions of a drive motor of the linear drive can be ascertained and, starting from a known position, a change in position due to the motor revolution can be taken into account. The motor revolution 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 a reference position of the motor is known and that the position change signals are correctly ascertained at all times. Since it cannot be guaranteed, especially when the control unit of the linear drive is not powered, that any motor movement (including one that is caused externally) is detected, a reference run is normally necessary after a power interruption of the furniture item, during which reference run a limit switch is approached for example, which then defines the reference position.
However, such reference runs cannot be carried out without problems in all areas of application for furniture items with electromotive furniture drives, e.g. not for hospital beds that have to be moved to other rooms in hospitals or care facilities and sometimes are occupied by patients, so that the power supply of the control unit and the linear drive is temporarily interrupted. In principle, it would be possible to provide uninterruptible power supplies at least for the position detection system for this time period in order to be able to eliminate a subsequent reference run. However, this increases manufacturing costs and is more maintenance-intensive, since the reliable function of the uninterruptible power supply must be ensured, e.g., by regularly replacing a used rechargeable battery.
For this reason, absolute position sensors are preferable to incremental position sensors in terms of high operational reliability. Absolute position sensors based on potentiometers, however, complicate the structure of the linear drives and, in turn, are prone to fail, since the sliding contact of the potentiometer tends to develop contact problems with increasing operating time.
A furniture item with an electromotive furniture drive is known from the DE 202004002924 U1 publication, in which tilt switches are arranged on movable furniture parts. The drives are stopped when the tilt switches detect that the tilt of the movable furniture part exceeds or falls below a predefined value. In this way, the need for limit switches on the linear drive is eliminated. Absolute position detection for intermediate positions is not possible with the arrangement shown. In addition, the tilt switches that have to be mounted separately on the movable furniture parts increase the complexity in installing the linear drives. The additional cables must also be correctly mounted and routed on the movable furniture parts to prevent them from being jammed by the motion fitting.
It is an object of the present invention to describe a linear drive for a furniture item and a method for its operation, with which the position of the linear drive can be ascertained at any time, without a potentiometric sensor and without additional effort when mounting the linear drive in the furniture item. Furthermore, a furniture item with a linear drive having these advantages is to be created.
This object is attained by a linear drive, a position detection method and a furniture item with such a linear drive having the features of the respective independent claim. Advantageous configurations and refinements are the subject matter of the dependent claims.
A linear drive of the type mentioned above is characterized according to the invention in that it includes a tilt sensor as a measuring device.
A method according to the invention for determining a displacement position in such a linear drive has the following steps: A plurality of value pairs of displacement positions and tilt angles of the linear drive are determined in a state installed in a furniture item and these value pairs are stored in a memory unit associated with the linear drive. During operation of the linear drive in the furniture item, a current value of the tilt angle is then determined and on the basis of the stored value pairs and the determined tilt angle a current value for the displacement position is determined.
Unlike a swivel drive, a linear drive does not initially have any components whose tilt fundamentally changes when actuated. However, the invention is based on the realization that linear drives often change their own orientation relative to the vertical when actuated due to their use in and coupling with a motion fitting in the furniture item, which can then be ascertained by the tilt sensor and converted into a value for the displacement position of the output element relative to the base element. Normally, there is a monotonic functional dependency between the tilt angle and the displacement position in conventional motion fittings and installation situations of linear drives, so that the displacement position can be unambiguously inferred from a measured tilt angle. The tilt sensor thus acts as an absolute position sensor.
A tilt sensor operates reliably and without mechanical components that are prone to fail. An evaluation unit for determining the current value of the displacement position can be arranged in the linear drive or in a control device for the linear drive coupled to it.
Since the linear drive itself includes the tilt sensor, a sensor signal can be evaluated in the linear drive itself or can be routed via a (anyway existing) connection cable of the linear drive for remote evaluation, e.g. in a control device of the linear drive. This thus eliminates the need for additional wiring during installation.
The value pairs can be determined in a learning phase in the furniture item or can also be determined theoretically in advance from the geometry and kinematics of the motion fitting and the installation situation of the linear drive. Interpolation can be performed between measured value pairs during operation to determine the current displacement position with an angular or travel resolution that is higher than that of the value pairs. The value pairs can also be stored in the form of a function equation or a function equation can be determined approximately from stored value pairs, with the help of which the actual conversion can be performed particularly easily, rapidly and with little computational effort. As an alternative to learning the value pairs or the functional relationship between tilt and displacement position, provision may also be made for their calculation in advance on the basis of a (known) geometry of the furniture item or a furniture fitting to which the linear drive is coupled. Linear drive and control unit can then be set up ready for operation before installation in the furniture item.
The tilt sensor can be arranged in or on the linear drive. When mounted on the linear drive, the tilt sensor is also advantageously suitable for retrofitting a linear drive with an absolute position sensor. The tilt sensor can, for example, be mounted on a standpipe of the linear drive via a mounting clamp. When being integrated into the linear drive, the tilt sensor can advantageously be arranged in a gearbox housing of the linear drive.
In a preferred configuration of the electromotive linear drive, the tilt sensor is a MEMS system, i.e. a Micro-Electro-Mechanical System. This is characterized by a small structure and low manufacturing costs. In principle, a one-dimensional detection of the tilt is sufficient for the application in or on the linear drive, i.e. a measurement of the tilt when pivoting about a predefined axis. When a fixed installation in the linear drive is involved, it may, however, not yet unambiguously be clear about which axis is pivoted during operation. When a subsequent installation is involved, this is usually known, but due to the available positions, it cannot always be guaranteed that the installed tilt sensor will also be pivoted precisely about its measuring axis during operation. It may therefore be advantageous to use a sensor that measures the tilt around 2 or 3 axes and can also flexibly measure tilts around different axes during operation.
A furniture item according to the invention with an electromotive furniture drive includes at least one such linear drive and a control device which is designed to carry out a method described above. The advantages indicated in connection with the linear drive or the method are realized.
The invention will be explained in more detail hereinafter with reference to exemplary embodiments with the aid of figures. The figures show:
In the example shown, the support element is designed in four parts, with one part being firmly connected to the frame 2 and three parts which are mounted such as to swivel relative to the frame and/or to each other. For this purpose, provision is made for a motion fitting with fitting parts 3, 4. In the example illustrated, the fitting part 3 is mounted stationary on the frame 2 with the aid of the non-movable part of the support element. In relation to this fitting part 3, the fitting parts 4 are mobile and guide or carry movable furniture parts 5, which correspond here to a back part and two leg parts of the support element.
In the present example, two linear drives 6 are provided for moving the movable furniture parts 5, only one of which is visible in
Due to the geometry of the motion fitting, a linear movement of the output element relative to the base element causes the movable fitting part 4 or the movable furniture part 5 to swivel.
Provision is further made for a control device 7, which in the present example is attached to the frame 2 and is connected to the linear drives 6 via cables not illustrated here. The control device 7 is further coupled to an operating unit via which actuation of the linear drives 6 is controlled. The operating unit can be coupled to the control device 7 via a wired or wireless connection. A wireless transmission can be implemented optically, e.g. via infrared light, also via radio. The latter also includes transmission via a WLAN network or a Bluetooth connection.
In the illustrated example, the control device 7 is configured to control both linear drives 6 of the bed 1. In alternative designs, the control device 7 can be integrated in one of the linear drives 6, which then represents a type of higher-level drive that also controls the further drive. It is also conceivable that both (or possibly also several existing) linear drives have their own integrated control devices, which react independently of one another or in coordination with one another to control instructions from an operating unit.
A power supply of the electromotive furniture drive can be provided via a power supply unit integrated in the control device 7 or via an external power supply unit connected to the control device 7 via a low-voltage cable.
According to the application, the linear drives 6 are characterized in that a tilt sensor 10 is integrated in each linear drive 6 or, as in the example illustrated, is mounted on the linear drive 6. The tilt sensor 10 ascertains a tilt of the linear drive 6 relative to the vertical defined by the earth's gravity. Due to the coupling of the linear drive 6 with the fitting parts 3, 4, an actuation of the linear drive 6 is not only connected with a pivoting of the movable furniture part 5, but also with a pivoting of the linear drive 6 and thus of the tilt sensor 10 relative to the vertical.
Assuming in many applications that a functional relationship between the tilt ascertained by the tilt sensor 10 and a displacement position of the linear drive 6, i.e. a relative position of the output element with respect to the base element, is monotonic, a measured tilt can be unambiguously converted into a displacement position, hereinafter also referred to as lift. In this way, a measured tilt value can be converted into position information at any time and thus in the manner of an absolute position sensor.
A tilt angle α and a lift d are shown in
In the present case, a linear relationship is shown over a great angular range, which only becomes steeper at greater 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 tilt angle α measured by the tilt sensor 10 into the lift d. The curve 20 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.
The curve 20 can either be calculated in advance on the basis of the (known) geometry of the fitting and the installation situation of the linear drive 6 in the fitting and stored prior to delivery of the linear drive 6 or the control device 7. As an alternative, provision may be made for a kind of learning phase in which certain angular positions of the movable furniture part 5 are approached manually, e.g. with the aid of a gauge, and the corresponding tilt angles α are measured and stored. The curve 20 can then be interpolated and stored by the control device 7 or the linear drive 6 on the basis of the measured values.
Depending on the fitting and installation situation, the curve 20 may look more complicated than in the example of
In certain cases, the position can even be determined in the presence of a local maximum or minimum. In this case, the magnitude and/or the sign of the 1st derivative of the curve 20 are used. As soon as the linear drive has started up, a change in the tilt angle α can be detected on the basis of the known direction of travel and, optionally, speed, so that it becomes possible to e.g. determine on which side (towards smaller or greater tilt angles α) of the maximum or minimum the position of the output element of the linear drive 6 is located. This then also allows the correct position to be determined unambiguously.
The linear drives 6 each have a gearbox housing 61 with a dome under which an electric motor 62 is located. Downstream of the electric motor 62 is a speed reduction gear train with at least one gear stage, for example a worm gear unit. This acts on a threaded spindle gear unit with threaded spindle, which generates a linear motion from the rotary motion of the motor. The threaded spindle is arranged in a standpipe 63 projecting from the housing 61 and also serving as a guide for a lifting tube 66. A clevis as a fastening element 67 is attached to the free end of the lifting tube 66. A comparable clevis as fastening element 64 is located at the opposite end of the gearbox housing 61. Furthermore, an outlet for a connection cable 65 is also formed on the gearbox housing 61.
In the furniture item, the linear drive 6 is mounted with the two fastening elements 64, 67. The lifting tube 66 with the fastening element 67 form the aforementioned output element of the linear drive 6; all other components are associated to the base element.
In the exemplary embodiment of
In the exemplary embodiment of
In both cases, the tilt sensor can be designed as a single-axis or multi-axis acceleration sensor based on MEMS (Micro-Electro-Mechanical System).
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 112 749.1 | May 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/054461 | 5/13/2022 | WO |
