ELECTROMOTORIC FURNITURE DRIVE

Description

[0001] The invention relates to an electromotive furniture drive with at least one motorized adjustment drive for the motorized adjustment of at least one furniture component, at least one control unit which is connected to a motor control of the at least one adjustment drive, and at least one operating unit for operating the at least one adjustment drive, wherein the control unit is designed, depending on the operating situation of the electromotive furniture drive, to control, to stop and / or to temporarily reverse a direction of rotation of at least one motor of the at least one adjustment drive, wherein the at least one motor is designed as a brushed DC motor.

[0002] In practice, such furniture drives are used, for example, in work tables or functional furniture such as armchairs or sofas. Beds, hoists, and patient lifts are also potential applications for such furniture drives. Operational situations can arise in the form of overloading or imminent danger to people or objects, for example, due to entrapment, if people or objects are located in a danger zone and the operator fails to recognize the potential hazard.

[0003] State-of-the-art furniture drives with a control unit are known that intervene in the adjustment process depending on the operating situation. Often, an increase in motor current or a decrease in motor voltage is detected, and the operating situation, for example, in the form of a pinch, is derived from this. In such a pinch situation, the motor assigned to the adjustment function is then at least switched off, possibly even redirected for a short time.

[0004] To detect an increase in motor current, the prior art uses corresponding sensors or shunts, as disclosed, for example, in document DE 44 44 762 A1. Alternatively, the prior art, for example, in document DE 10 2016 109 524 A1, describes vibration and acceleration sensors or piezo sensors that are mechanically coupled to the adjustment drive or to a movable furniture component and detect a hard obstacle during the adjustment process. Such sensors have proven effective, but their use requires considerable additional assembly and material expenditure, since a circuit board with appropriate components and external wiring is required in the respective adjustment drive for connection to the control unit.Another alternative is known from the publication WO 2019 / 145440 A1, a voice-controlled anti-pinch device in which furniture drives are switched off when certain keywords indicating an emergency or danger are recognized.

[0005] Detection with additional sensors is more reliable than evaluating the level of the motor current, but it complicates the design and assembly of the electric furniture drive.

[0006] The object of the present invention is to provide an arrangement which is improved compared to the evaluation of the level of the motor current and yet is easy to assemble.

[0007] This object is achieved by an electric motor furniture drive having the features of claim 1.

[0008] It is provided that the control unit is designed to evaluate the frequency of a generated back EMF signal of the at least one motor. Since the motor of the adjustment drive is designed as a DC motor with brushes, it generates a back EMF (electromotive force) signal from which its rotational speed can be derived. According to the invention, this signal is used to detect a drop in rotational speed, which indicates a collision or pinching.

[0009] This back EMF signal reflects the motor speed more reliably than evaluating the motor current. However, the back EMF signal can be easily obtained from a motor current measurement, eliminating the need for additional sensors that would complicate the design of the electric furniture drive.

[0010] The evaluated signals are present at the motor's terminals, as they are generated by the motor itself. Since the motor's connecting cable is designed as a two-wire cable, standardized motors can be used, and at the same time, signal lines parallel to the motor cables can be omitted. This saves assembly effort and material resources. The motor itself is designed as a brushed DC motor with permanent magnet excitation. The typical operating voltage is below 40 volts.

[0011] The back EMF is generated directly dependent on the motor's speed. This occurs as an alternating or rising voltage signal with a specific frequency and can be evaluated by the control unit. The control unit is designed to evaluate the frequency of this alternating or rising voltage signal.

[0012] According to the invention, the control unit is designed to carry out a target-actual comparison and to carry out a switching operation when the frequency of the signal falls below a predetermined threshold and / or when an absolute value of the change in frequency per unit of time exceeds a predetermined threshold.

[0013] In an advantageous embodiment, the target-actual comparison can also be event-related. Furthermore, the threshold value can be configured as a variable threshold value within predetermined limits.

[0014] If the frequency falls below a previously defined and predetermined threshold, for example, this can be interpreted as an overload of the adjustment drive, resulting in the shutdown of the respective motor. The predetermined threshold can be permanently programmed, based on events, such as the supply voltage, or selected based on the situation. For example, a starting situation can be distinguished from a continuing driving situation.

[0015] Alternatively or additionally, the control unit evaluates the frequency mentioned above over time. If the evaluated frequency changes by a predetermined value within a predetermined period of time, this can be interpreted as a jamming event. The respective motor is then shut down and / or, in one variant, can also be operated in the opposite direction for a short period.

[0016] The control unit is coupled to a motor controller or integrated with it. The motor controller includes mechanical or electromechanical switches for switching the respective motor on and off. Relays, for example, are used to switch the motor current. Alternatively, electronic switches in the form of semiconductor switches can be provided to switch the motor current. The latter can be discrete or present as a compact component in the form of a so-called motor driver. MOSFETs (metal-oxide semiconductor field-effect transistors) are preferably used as semiconductor switches. These are characterized by low voltage losses in the switched-on state, which reduces losses and the associated heat generation in the motor controller.In addition, the switching path (source-drain path) of a MOSFET exhibits the behavior of an ohmic resistor when switched on, which allows the switching path itself to be used as a shunt to measure the motor current. Alternatively, the motor current can be measured using an external current measuring sensor, such as an external shunt or a Hall sensor. This type of current measurement is also suitable if the motor controller uses switches other than the MOSFETs mentioned. Such other switches could include relays, possibly in combination with manually switching buttons.

[0017] When using a motor driver, i.e., an integrated component that includes the motor control function, this can itself evaluate and process the aforementioned alternating or pulsating signals generated by the motor's back EMF. Furthermore, the evaluation and processing can be performed in such a way that an electrical signal corresponding to the motor's speed is available at a signal output of the motor driver. This signal can be in the form of a variable frequency or a variable voltage.

[0018] Furthermore, the control unit is preferably equipped with a microcontroller running an executable program. The program is designed to record the threshold value(s) mentioned above, perform the target-actual comparison mentioned above, and at least switch off the respective motor in an event-driven manner.

[0019] A collision or entrapment event is characterized by the fact that the motor speed decreases by more than a previously defined threshold within a predetermined period of time. According to the invention, this is detected based on the frequency of the back EMF signal, which is proportional to the motor speed. To determine the frequency of the back EMF signal in a robust and interference-resistant manner, averaging is advantageously performed over a current frequency value. The averaging is preferably performed as a moving average over a time window of a specified width.

[0020] The invention is explained in more detail below using exemplary embodiments and figures. The figures show: Fig. 1-3 each show a schematic representation of an electric motor furniture drive in a block diagram.

[0021] In Fig. 1A first exemplary embodiment of an electric motor-driven furniture drive is shown schematically. The illustration is in the form of a block diagram, without reference to a piece of furniture in which the furniture drive is installed. Within the furniture, the furniture drive serves to adjust at least one furniture component. The furniture can be, for example, a seating or reclining piece of furniture.

[0022] The furniture drive has a control unit 10, which is coupled to at least one operating unit 20. Two different operating units 20 are shown as examples: a wired operating unit 21, which is connected to the control unit 10 via a connecting cable 22, and a wireless operating unit 23, which is connected to the control unit 10 via a radio link. The radio link is controlled by a radio signal 24 in the Fig. 1 symbolized.

[0023] Depending on the design of the control unit 10, it may be provided that only the wired control unit 21 or only the wireless control unit 23 can be used. In alternative designs, the wired or wireless control unit 21, 23 can be used either at will, or both in parallel. The wireless control unit 23 can be manufactured specifically for this purpose. Alternatively, it may also be provided to use a mobile device, for example, a smartphone, with appropriate software as the wireless control unit 23.

[0024] The control unit 10 has a supply voltage connection 11 through which it is supplied with operating current. Furthermore, a connection 12 for the wired control unit 21 and / or a receiver 13 for the radio signal 24 of the wireless control unit 23 may be provided.

[0025] In addition, the control unit 10 is connected via control lines 14 to a motor controller 30, which controls a motor 40. The motor 40 is the motor of an adjustment drive for adjusting the aforementioned furniture component relative to a base frame of the furniture or relative to another, possibly also adjustable, furniture component. A brushed DC motor is used as the motor 40.

[0026] Several adjustment drives can be used within a piece of furniture, wherein the control unit 10 is preferably used jointly for all existing adjustment drives, whereas a motor control 30 is provided for each adjustment drive.

[0027] The motor controller 30 has a supply voltage connection 31 which, like the supply voltage connection 11 of the control unit 10, is connected to a power supply for supplying the furniture drive. This power supply is not shown here. It can be designed as a single unit with one or both of the described units, i.e., the control unit 10 and / or the motor controller 30. Alternatively, it is conceivable to design the power supply separately and couple it to the motor controller 30 or the control unit 10. The power supply preferably outputs a very low DC voltage, for example, in the range of approximately 24-32 volts, at its outputs, which is supplied to the control unit 10 and the motor controller 30 as the supply voltage.

[0028] Switching elements 33 are arranged in the motor control 30, which enable the motor 40 to be switched on and off, as well as to select the direction. The switching elements 33 are Fig. 1Semiconductor switches, in this case MOSFETs (metal-oxide semiconductor field-effect transistors), are provided. These are arranged in the manner of an H-bridge, which allows reversing the direction of rotation of the motor 40. The switching elements 33 can be controlled with pulse width modulation to influence the motor speed or torque, thus allowing, for example, a smooth start of the motor 40.

[0029] During operation of the electric furniture drive, a user's inputs on one of the control units 20 are evaluated by the control unit 10 and converted into control signals on the control lines 14, which actuate the motor controller 30 according to the user's input. Within the motor controller 30, the current consumed by the motor 30 is measured. Information reflecting the measured motor current is fed from the motor controller 30 back to the control unit 10 via a current measuring line 15. This can be in the form of an analog signal or in the form of digital data.

[0030] As explained in more detail below, the signals or data from the current measuring line 15 are evaluated within the control unit 10 to detect a collision and / or entrapment. As a result of a detected collision or entrapment, the motor controller 30 can be controlled by the control unit 10 such that the motor 40 stops its movement or briefly changes its direction of rotation and then stops in order to resolve a potential entrapment.

[0031] In the embodiment of the Fig. 1 In a system in which MOSFETs are used as switching elements 33, a voltage drop across the switching elements 33 can be evaluated as a measure of the motor current. Alternatively, it is also conceivable that an additional current measuring sensor is present, for example, a Hall sensor or a shunt, via which the motor current is determined.

[0032] Fig. 2 shows in the same way as Fig. 1an alternative design of an electric motor-driven furniture drive. Regarding the basic structure, reference is made to the embodiment of the Fig. 1 The differences to this first embodiment are shown below.

[0033] Unlike the example of the Fig. 1 are in the engine control 30 according to Fig. 2 as switching elements 33 relays with corresponding switching contacts instead of the MOSFETs of the Fig. 1 Except for the possibility of pulse-width modulated control of the motor 40, the function of the relays as switching elements 33 is analogous to that of the H-bridge with the MOSFETs in the first embodiment. Fig. 2 A rest position of both relays is shown, which is assumed when no operation is performed on one of the control units 20. In this rest position, the motor 40 is short-circuited, which brakes it regeneratively.

[0034] To measure the current of the motor 40, a separate current measuring sensor 34 is provided, which is arranged in series with the motor 40. As already mentioned in connection with Fig. 1 , in which this type of current measurement was mentioned as an alternative, the current measuring sensor 34 can be a shunt or a Hall sensor.

[0035] Fig. 3 Finally, a third possible embodiment of an electric motor furniture drive is shown.

[0036] In contrast to the previously described embodiments, the motor control 30 and an operating unit 20 are integrated here, in that switching elements 33 that switch the motor current are manually operated pushbutton switches, which thus directly form the switches of the operating unit 20. Upon manual actuation of one of the two switching elements 33, the motor is switched on in a different direction of rotation.

[0037] Again, a current measuring sensor 34 is provided to perform a current measurement and to provide the measured motor current via the current measuring line 15 to the control unit 10 for evaluation.

[0038] In this exemplary embodiment, the control unit 10 accordingly has no connection options for a separate operating unit 20. In order to be able to stop the motor 40 in the event of a detected collision or pinching, a higher-level switching element 35 is provided in the motor control unit 30, which can interrupt the supply voltage for the electric motor 40. The higher-level switching element 35 is designed here, for example, as a relay with a normally closed contact.

[0039] In all three illustrated embodiments, the control unit 10 monitors the signal or data at current measuring terminal 15 during operation of the electric motor 40 in order to detect a collision and / or pinching. If the motor is a brushed DC motor, an alternating signal resulting from the motor's commutation is superimposed on a DC component as the motor rotates. This alternating signal is also referred to as a back EMF (electromotive force) signal. The frequency of the back EMF signal is proportional to the motor's speed.

[0040] According to the application, the frequency of this signal, and thus a frequency proportional to the motor speed, is used to detect a collision or entrapment. For this purpose, a limit frequency can be specified as a threshold value, below which a collision or entrapment may be suspected. Furthermore, a rate of change of the frequency can be observed. If the frequency changes during operation at a rate whose value exceeds another specified threshold value, this also indicates a collision or entrapment.

[0041] In a further development, it can be provided that the threshold value for the frequency is not fixed, but is determined in one or more learning runs. For this purpose, the adjustment drive is operated over the entire travel range in a learning phase and the frequency of the back EMF signal is measured. A minimum frequency value can then be recorded which is exceeded during the entire learning phase, i.e. at every position within the entire travel range of the adjustment drive. A tolerance component, for example 20%, is deducted from this minimum frequency value, which is reached under normal conditions, i.e. without a collision or in the event of pinching, to determine the threshold value. If this threshold value is undershot during operation, this indicates a collision or pinching.

[0042] The threshold value can be the same across the entire travel path of the electric furniture drive, regardless of whether it is fixed or detected during a learning run. However, this threshold value can also be defined in sections along the travel path. For this purpose, the travel path can be divided into at least two, or possibly several or many sections, each of which has its own threshold value specified or determined during a learning phase. This takes into account the fact that certain movement sections of the travel path are exposed to different levels of load due to the lever kinematics of a furniture fitting moved by the electric furniture drive, which results in a different rotational speed of the motor and therefore a different frequency of the back EMF even during normal operation, i.e. without a collision or pinching.This configuration requires knowledge of the current position of the adjustment drive. This can also be detected using the back EMF, for example, based on a limit switch actuation by counting pulses of the back EMF signal. The number of counted pulses is then a measure of the current position of the adjustment drive, which can then be used to retrieve the position-dependent threshold value or determine it during a learning phase. List of reference symbols

[0043] 10Control unit 11Supply voltage connection 12Hand switch connection 13Receiver 14Control cable 15Current measuring connection 20Control unit (hand switch) 21Wired control unit 22Connection cable 23Wireless control unit 24Radio signal 30Motor control 31Supply voltage connection 32Motor connection 33Switching element 34Current measuring sensor 35Higher-level switching element 40Engine

Claims

1. Electromotive furniture drive having at least one motorized adjustment drive for motorized adjustment of at least one furniture component, at least one control unit (10) which is connected to a motor controller (30) of the at least one adjustment drive, and at least one operating unit (20) for operating the at least one adjustment drive, the control unit (10) being designed, as a function of the operating situation of the electromotive furniture drive, for actuating, for stopping and / or for temporarily reversing at least one motor (40) of the at least one adjusting drive via the motor control (30), the at least one motor (40) being designed as a brush-loaded DC motor, characterized in that the control unit (10) is designed to evaluate a frequency of a counter-EMF signal generated by the at least one motor (40) and to detect and signal a collision and / or a jamming case as a function of the evaluated signal, wherein the collision and / or the jamming case are detected when the determined frequency of the signal falls below a predetermined threshold value and / or when an absolute value of a change in frequency exceeds a further predetermined threshold value.

2. Electromotive furniture drive according to claim 1, in which the control unit (10) is designed to switch off the at least one motor (40) and / or reverse its direction of rotation after detection of the collision and / or the jamming case.

3. Electromotive furniture drive according to claim 1 or 2, in which the threshold value and / or the further threshold value are fixedly predetermined.

4. Electromotive furniture drive according to claim 1 or 2, in which the threshold value and / or the further threshold value are determined in a learning phase in which the at least one adjusting drive is moved without collision and / or a jamming case.

5. Electromotive furniture drive according to any one of claims 1 to 4, wherein the threshold value and / or the further threshold value is constant over the entire travel distance of the at least one adjustment drive.

6. Electromotive furniture drive according to any one of claims 1 to 4, wherein the threshold value and / or the further threshold value is different in different sections of the travel path of the at least one adjustment drive.

7. Electromotive furniture drive according to any one of claims 1 to 6, wherein the threshold value and / or the further threshold value are varied according to the situation.

8. Electromotive furniture drive of any one of claims 1 to 7, wherein the counter-EMF signal is obtained based on a measurement of an operating current of the at least one motor (40).

9. Electromotive furniture drive of claim 8, wherein a current measurement sensor (34) is provided in the form of a shunt or a Hall sensor.

10. Electromotive furniture drive according to any one of claims 1 to 9, wherein the motor controller (30) comprises MOSFET transistors as switching elements.

11. Electromotive furniture drive of claims 9 and 10, wherein a drain-source switching path of one of the MOSFET transistors is used as a current measurement sensor (34).