Spring-return actuator comprising a DC motor having a detent-torque restraint for latching and releasing an actuating element of the actuator into and out of an actuating position

Abstract

The invention relates to a spring-return actuator (SA) comprising an electric motor (MO) and a downstream gearbox (G), wherein a permanent-magnetic detent-torque restraint is effective between the stator (ST) and the rotor (RO) of the electric motor. The latter is dimensioned in such a way that, owing to the effective detent-torque restraint, an output-side actuating element (Z) remains in the actuating position in a current-free state after it has been moved from a rest position (RP) into an actuating position (BP) and after the motor-side torque has subsequently been removed by a motor control unit (MS). The motor control unit is designed, in the event of a fault or triggering situation, to actuate the electric motor with a torque pulse in the direction of rotation back towards the rest position in order to release the electric motor from the current-free actuating position of the actuating element. The actuator comprises a device (DG, H) for detecting a rotational position of the electric motor. If a change is detected in the rotational position in a direction of rotation back towards the rest position, the electric motor is actuated in order to apply a torque in the opposite direction of rotation so as to move the actuating element back into the (current-free) actuating position.

Description

[0001] Description

[0002] Spring-return actuator with a DC motor with cogging torque damping for locking and unlocking an actuating element of the actuator into and out of an operating position.

[0003] The present invention relates to an actuator for actuating a connected load, in particular a (fire protection) damper or a valve, comprising an electric motor with a stator and a rotor, a downstream gearbox, and an output-side actuating element, in particular with an actuating terminal for connecting the load. A permanent magnet detent torque interlock is effective between the stator and rotor. The electric motor is designed to move the actuating element between a rest position and an actuating position, in particular to move the actuating element from a (safe) rest position to an actuating position. The actuator includes a power supply unit for the electrical supply of the actuator and a motor control unit for the electrical control of the electric motor to apply a torque with a predefinable direction of rotation.Furthermore, the actuator includes a return mechanism, in particular a return spring, to automatically return the actuator to its rest position in the event of a fault or trip, especially a power failure, by means of a return torque acting on the actuator via the return unit. The cogging torque of the electric motor is designed such that, after the actuator moves from its rest position to its actuated position and after the motor control unit releases the motor torque, the actuator remains de-energized in the actuated position due to the effective cogging torque of the electric motor. The actuator also includes an energy storage device, in particular a capacitor.The motor control unit is designed to drive the electric motor in the event of a fault or triggering event by means of the electrical energy stored in the energy storage device with a torque pulse in the direction of rotation back to the rest position to release the electric motor from the de-energized actuation position of the actuator.

[0004] US Patent 6,100,655 A describes an electrically driven actuator for a positioning device, such as a flap, valve, elevator, or similar device. The actuator comprises a gearbox, an electric motor connected to a power source to drive the gearbox, and a positioning device connected to the gearbox that moves from a retracted safety position to an extended position when the motor is operating normally. In the event of a power failure, an auxiliary power source (a capacitor) supplies current to the motor to overcome the magnetic and frictional resistances of the motor and gearbox. This allows a spring to move the positioning device from the extended position to the retracted safety position.The capacitor is connected to the motor's electrical circuit in such a way that it is charged during normal operation of the motor and, in the event of a power failure, provides an opposing impulse to the motor, causing the actuator to return to the safety position.

[0005] From DE 102021 209 914 B3, an actuator is known which comprises an electric motor, a downstream reduction gearbox, and an output-side actuating element with an actuating connection. The electric motor has a stator and, as an external rotor, a rotor cup rotating around an axis of rotation of the electric motor. The rotor cup is magnetically detented in the direction of rotation. The actuator includes a contactless magnetic detent lock, which can be electrically switched on and off by means of an electromagnet, for holding or releasing the rotor cup. The electromagnet further comprises a coil arrangement which encloses a magnetic coil core with two pole shoes for the possible formation of two magnetic poles. The electromagnet is designed and arranged relative to the rotor cup such that the two pole shoes are opposite each other on the outer side of the rotor cup, each forming an air gap.The rotor cup has armatures arranged circumferentially around the axis of rotation of the electric motor on its outer surface in such a way that at least one of the armatures can magnetically lock with the two pole shoes of the electromagnet to potentially provide cogging torque protection. To hold the rotor cup in a rotor holding position, a first short current pulse can be impressed into the coil assembly by means of a circuit arrangement of the actuator, so that a residual magnetic field remains in the coil core to provide the magnetic cogging torque protection. To release the rotor cup in a rotor freewheeling position, a second short current pulse can be impressed into the coil assembly by means of the circuit arrangement, so that the residual magnetic field remaining in the coil core is subsequently substantially dissipated, thus dissolving the magnetic cogging torque protection.

[0006] From DE 102021 210 332 A1, an actuator is known which comprises a drive element, in particular an electric motor, a downstream gearbox, and an output-side actuating element. The drive element is designed to drive the actuating element around an actuating axis between a rest position and an actuating position. The actuator further comprises a return spring to automatically return the actuating element to its rest position in the event of a fault or triggering. The drive element can be coupled to a preload spring to apply a preload torque to the drive element that opposes the return torque of the return spring. The preload spring is wound up when the actuator is coupled and when it is moved to its rest position.The actuator has a coupling device designed to couple the preload spring to the drive element or to a first gear directly downstream of it from an engagement position shortly before reaching the rest position.

[0007] Actuators are frequently used, for example, to drive a damper, such as a fire damper, or a valve, particularly for heating, ventilation, or air conditioning a building. The damper or valve is typically moved by the actuator's actuating element or even at least partially formed by it. The actuator is often designed to move the actuating element from a first position to a second position. Both positions usually also represent mechanical end stops. The first position can also be called the rest position, in which the actuator returns the actuating element to its original position when the electric motor is de-energized, particularly by means of a pre-tensioned return spring. The second position can be called the actuating position. Instead of a return spring, the return mechanism may, for example, include a pneumatic accumulator.These types of fail-safe actuators are also known as spring-return actuators.

[0008] Starting from the aforementioned prior art, it is an object of the present invention to provide an improved actuator.

[0009] Another objective of the invention is to provide a more reliably operating actuator.

[0010] The object of the invention is achieved by the features of the main claim. Advantageous embodiments of the actuator according to the invention are specified in the dependent claims.

[0011] According to the invention, the actuator comprises a device connected to the motor control unit for directly or indirectly detecting the rotational position of the electric motor. The motor control unit is configured to monitor the rotational position of the electric motor in the de-energized actuation position for an impermissibly large change in one direction of rotation back to the rest position. Furthermore, the motor control unit is configured, in the event of a detected impermissibly large change in rotational position, to drive the electric motor to apply a torque in the opposite direction of rotation in order to move the actuator back to the actuation position. This advantageously prevents an unintentional return of the actuator to its safe rest position, i.e., a false triggering. This can be caused by a mechanical impact on the actuator, such as...Vibrations during construction work, or an external torque acting on the connected load, such as a gust of wind on a fan flap connected to the actuator.

[0012] In this context, "without current" means that no significant current is applied to the windings of the electric motor by means of the motor control unit, apart from a possible test current to monitor the operational capability of the electric motor.

[0013] In particular, the motor control unit is designed to leave the windings of the electric motor unenergized or not energized in the de-energized operating position.

[0014] Direct detection of the rotational position of the electric motor, i.e. the relative rotational position of the rotor to the stator, can be achieved, for example, by means of a rotary encoder, a light barrier, a potentiometer or by means of one or more magnetic field sensors.

[0015] An indirect detection of the rotational position of the electric motor can alternatively be achieved by assigning the rotational position of the actuating element or by assigning the rotational position of a gear wheel arranged between the actuating element and the electric motor, in each case corresponding to the transmission ratio relevant on the transmission side.

[0016] An excessively large change in rotational position can occur, for example, when a predetermined angle of rotation is exceeded, by which the rotor twists relative to the stator of the electric motor. This angle can, for example, be in a range of 10° to 720°, preferably in a range of 30° to 90°.

[0017] According to one embodiment, the motor control unit is designed to reduce the motor-side torque when the actuator has reached the actuating position again, so that the actuator can remain de-energized in the actuating position.

[0018] According to another embodiment, the actuator has a motion sensor connected to the motor control unit for detecting linear and / or rotary movements of the actuator. The motor control unit is configured to monitor the linear and / or rotary movements of the actuator in the de-energized operating position for impermissibly high movement values. Furthermore, the motor control unit is configured to control the electric motor in the event of an impermissibly high movement value, in order to apply a holding torque in a direction of rotation opposite to the direction of rotation returning to the rest position. Preferably, the motion sensor is an acceleration sensor configured to detect linear and / or rotary accelerations.In this case, the motor control unit is configured to monitor the linear and / or rotational accelerations of the actuator in the de-energized operating position for impermissibly high acceleration values. Specifically, the motion or acceleration sensor is arranged on the housing or a mounting plate of the actuator, i.e., it is fixed to the housing or mounting plate. This allows the motion or acceleration sensor to accurately detect external movements or accelerations acting on the actuator. Preferably, the motion or acceleration sensor is mounted on a circuit board of the actuator, which in turn is fixed to the housing or mounting plate of the actuator.

[0019] The advantage here lies in the fact that the electric motor is preemptively subjected to a torque, anticipating a possible disengagement and thus the unintentional return of the actuator from the de-energized actuation position to its rest position. This torque counteracts the potential disengagement of the electric motor. The motor control unit can be configured to apply this counter-torque to the electric motor within a fraction of a second, particularly in less than 100 milliseconds, preferably in less than 25 milliseconds. Specifically, the electric motor is actuated so quickly that, due to its inertia and moment of inertia, it is mechanically incapable of disengaging on its own. Such an actuator therefore operates with exceptional reliability.

[0020] According to one embodiment, the holding torque is dimensioned to a torque value in the range of 0.3 to 0.9 times the torque value required by the electric motor to drive the actuator back into the actuated position. This advantageously keeps the rotor of the electric motor fixed in its current rotational position, acting like a magnetic clamp, without an external torque or shock causing the electric motor to disengage.

[0021] If the motion sensor is an accelerometer, the motor control unit can be configured to individually monitor each of the measured linear and / or rotational accelerations for an impermissibly high acceleration value. If one or at least two of the detected accelerations exceed their respective impermissibly high acceleration values, the motor control unit can then control the electric motor to apply a holding torque in a direction of rotation opposite to the direction of rotation returning to the rest position. The accelerometer is preferably a MEMS accelerometer. Such an accelerometer can be configured, for example, to detect one, but also two or three translational measurement axes and / or rotation axes arranged orthogonally to each other.Such cost-effective MEMS accelerometers, each with three measuring and rotation axes, can be found in every newer smartphone.

[0022] According to another embodiment, the cogging torque of the electric motor for magnetic cogging torque control is in the range of 1.2 to 3 times, and in particular 1.5 to 2 times, the torque value of the restoring torque. The latter acts in the actuated position of the actuator via the actuating element and further via the gearbox back onto the DC motor. The actuating element is, for example, a gear segment. This dimensioning rule advantageously ensures that, for operational load torque surges that could reach the electric motor via the actuator's actuating terminal, there is no unintentional disengagement of the electric motor.

[0023] According to another embodiment, the motor control unit is configured to detect a power outage and, in such a case, to briefly apply a torque to the electric motor, rotating it back to its rest position using the electrical energy still stored in the energy storage device. "Briefly" preferably refers to a period of less than one second. To detect the power outage, the motor control unit can, for example, include an analog-to-digital converter (ADC) to detect the electrical supply voltage provided by the power supply unit. If a predetermined minimum voltage value is undershot, the motor control unit can then briefly activate the electric motor, effectively giving it a "push."

[0024] In one embodiment of the actuator, the electric motor is a DC motor, in particular a brushless, permanent magnet DC motor. Such DC motors are also referred to as BLDC motors.

[0025] In a preferred embodiment, the rotor of the DC motor comprises a plurality of permanent magnet poles, such as four or six, arranged circumferentially around the rotor or motor axis. The device for directly detecting the rotational position of the electric motor includes at least one magnetic field sensor located in the rotor region, i.e., in the area of ​​the rotor with the permanent magnet poles located there. The magnetic field sensor particularly includes at least one Hall sensor or at least one digital Hall sensor with switching hysteresis for detecting the rotational position of the rotor. A minimum rotation angle and the direction of rotation of the rotor can be unambiguously determined by a suitable arrangement of the at least one magnetic field sensor positioned circumferentially around the rotor or motor axis. In the case of a 6-pole DC motor, for example, a minimum rotation angle of 30° can be determined using two Hall sensors.In the case of a 4-pole DC motor, this angle is 45°. When using a digital Hall sensor with switching hysteresis, this value doubles, enabling unambiguous detection of the direction of rotation.

[0026] The motor control unit can be configured, for example, to return the electric motor to its rest position after one, or only after two, three, or four changes in the same direction of rotation, in order to apply a torque in the opposite direction of rotation and move the actuator back to its operating position. For this purpose, the motor control unit is equipped to measure and evaluate the electrical signals from the two Hall sensors or from the digital Hall sensor with switching hysteresis.

[0027] According to another embodiment, the DC motor comprises, as its rotor, a rotor cup rotating coaxially around the stator, i.e., radially externally, with a plurality of permanent magnet poles arranged circumferentially around the motor axis. The DC motor has a cogging torque plate connected to the stator with a plurality of pole shoes for generating an additional magnetic cogging torque that brings the rotating rotor cup into a detent position. The pole shoes are arranged and designed such that, in the detent position, they form a magnetic short circuit between two adjacent permanent magnet poles of the rotating rotor cup, thus providing the total cogging torque inhibition effective between the rotor and stator with a predetermined cogging torque value.Such a detent torque plate is advantageous if the electric motor's own detent torque value is too low to reliably lock in the actuating position of the actuator.

[0028] To set a required cogging torque value, the cogging torque plate can have a different sheet thickness and / or a different permeability coefficient p. r exhibit.

[0029] In another embodiment, the return mechanism includes a return spring. The return torque is composed of a return spring torque originating from the return spring itself and, optionally, a load torque acting on the actuator via the connected load. The load can increase or decrease the magnitude of the return spring torque. With a suitable load arrangement, the load torque acting on the actuator can be virtually zero. The return mechanism can, for example, include a coiled constant-force spring. The constant-force spring acts on the actuator in such a way that a substantially constant return spring torque acts on the actuator. This ensures that the electric motor remains in the "sliding friction phase," i.e., in the unlocked state, particularly reliably when returning to its rest position.

[0030] Alternatively, the return mechanism can include a return spring, in particular a coil spring, a spiral spring, or a helical spring. The return spring has a spring characteristic with a substantially constant spring stiffness. In particular, the return spring, as in the case of a coil spring, has a flat spring characteristic. The return spring can also have a substantially progressive spring characteristic.

[0031] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can be essential to the invention individually or in any combination. Elements with the same function and mode of operation are designated with the same reference numerals in Figures 1 to 3.

[0032] They show schematically:

[0033] FIG 1 shows the functional structure of an actuator according to the invention with power supply unit, motor control unit, DC motor and with a gearbox for driving an exemplary flap,

[0034] FIG 2 shows a gear train of an exemplary actuator according to the invention in an actuating position with a DC motor with magnetic cogging torque damping, with a reduction gear and with a return spring acting directly on an actuating element of the actuator, and

[0035] FIG 3 shows, by way of example, the course of a restoring torque in a gear train of an actuator plotted over a number of motor revolutions.

[0036] FIG 1 shows the functional structure of an actuator SA according to the invention, comprising a power supply unit SV, a motor control unit ST, a DC motor MO, and a gearbox G for driving an exemplary damper K by means of a drive shaft W. Reference numeral A denotes an actuating shaft of the actuator SA, and reference numeral Z denotes an actuating element, typically a toothed segment of the actuator SA. The damper K is connected to an actuating port AN of the actuator SA for adjusting a gaseous volume flow, such as for adjusting an air flow for heating, ventilating, or air conditioning a building. Alternatively, a valve for adjusting a liquid volume flow, such as for adjusting a water volume flow, can be connected to the actuating port AN.

[0037] In the example shown in FIG. 1, the power supply unit SV already includes an electrical energy storage device C in the form of a capacitor. The capacitor C can be, for example, an electrolytic capacitor or a so-called ultracapacitor. The motor control unit MS is configured to drive the electric motor MO in the event of a fault or tripping event by means of a torque pulse in the direction of rotation back to the rest position, thus releasing the electric motor MO from the de-energized actuation position BP of the actuator Z, using the electrical energy stored in the energy storage device C. Alternatively or additionally, the energy storage device C can be a battery. The reference symbols L denote a supply voltage input and GND a reference potential. MA denotes a motor shaft or a rotor shaft of the electric motor MO.

[0038] FIG 2 shows a gear train of an exemplary actuator SA according to the invention in an actuating position BP with a DC motor MO with magnetic cogging torque damping, with a reduction gear G and with a return spring RF acting directly on an actuating element ZG of the actuator SA. The latter is provided to automatically return the actuating element Z to the rest position RP in the event of a fault or tripping event, in particular in the event of a power failure, by means of a return torque MRM acting on the actuating element Z via the return unit RF. The cogging torque damping of the electric motor MO is dimensioned accordingly.has a predetermined detent torque value such that the actuator Z shown, after the motor-side procedure of the actuator Z from the rest position RP to the actuating position BP shown and after subsequent retraction of the motor-side torque by the motor control unit MS, remains de-energized in the actuating position BP due to the effective detent torque inhibition.

[0039] In this example, the electric motor MO is a 6-pole DC motor with a coaxially mounted external rotor RO in the form of a rotor cup or rotor bell. The north poles N and S, respectively, are designated as permanent magnet poles. These are arranged circumferentially around the motor axis MA. Furthermore, two magnetic field sensors H1 and H2, in this case two Hall sensors, are arranged circumferentially around the motor axis MA, so that they are axially opposite the rotor cup. The two Hall sensors H1 and H2 are typically mounted on a circuit board of the actuator SA and connected to a motor control unit MS. In this example, the circumferentially offset arrangement of the two Hall sensors H1 and H2 enables the determination of a minimum rotation angle of 30° while simultaneously allowing the determination of the direction of rotation of the rotor RO.According to the invention, the motor control unit MS is configured to monitor the rotational position of the electric motor in the de-energized actuation position for an impermissibly large change in one direction of rotation back towards the rest position. Furthermore, the motor control unit is configured, in such a case, to control the electric motor to apply a torque in the opposite direction of rotation in order to move the actuating element back to the (de-energized) actuation position.

[0040] Alternatively, instead of the magnetic field sensors H, a rotary encoder DG can be arranged directly on the output-side actuator Z. With a sufficiently high resolution of the rotary encoder DG, the current rotational position of the electric motor MO can be determined via the gear ratio of the gearbox G.

[0041] BG is a motion or acceleration sensor that is fixedly arranged in the actuator SA, preferably on a circuit carrier of the actuator SA, to detect mechanical effects such as shocks on the actuator SA.

[0042] FIG. 3 shows an example of the curve of a restoring torque MRM in a gear train of an actuator SA plotted against a number of motor revolutions U. M denotes the ordinate corresponding to the number of motor revolutions U. MG denotes a torque applied by the mounted gear train.

[0043] To move an actuator element from a rest position RP to an actuated position BP, a number of revolutions UR of the DC motor are required, starting from a rotational speed Uo of a DC motor in the relaxed state of the gear train, until actuating movements SBS are again observed at the actuator element after the gear train is fully compressed. This occurs when the torque MG applied by the compressed gear train exceeds a required closing torque MS of a return spring acting on the actuator element. Conversely, no actuating movements SBN are observed during the actuator's rotational range between the relaxed and compressed gear train.

[0044] The right-hand side of FIG. 3 shows the curve of the restoring torque MRF of a coil spring used as a return spring for an actuator. The characteristic curve, typical of a coil spring, is relatively flat, meaning that the spring stiffness of the coil spring increases only moderately with winding, in accordance with Hooke's Law. Thus, in the actuated position BP of the actuator, the coil spring exhibits its maximum torque value MX at a corresponding rotational speed UB. The coil spring acts either directly on the actuating element or on one of the directly upstream gears.

[0045] In summary, the invention relates to a spring-return actuator SA in which a permanent magnet cogging torque interlock is effective between the stator ST and rotor RO of an electric motor MO. The actuator SA includes a reset device RF to automatically return an actuating element Z of the electric motor MO from an actuating position BP to a rest position RP in the event of a fault or trip. The cogging torque interlock of the electric motor is dimensioned or set such that, after the actuating element Z has moved from the rest position RP to the actuating position BP and after the motor-side torque has been subsequently released by the motor control unit MS, the actuating element Z remains de-energized in the actuating position BP due to the effective cogging torque interlock.The motor control unit MS is configured to actuate the electric motor MO with a torque pulse in the direction of rotation back to the rest position RP in the event of a fault or trip, thus releasing the electric motor MO from the de-energized actuation position BP of the actuator Z. The actuator includes a device DG, H for detecting the rotational position of the electric motor MO. In the event of a detected change in the rotational position back to the rest position RP, the electric motor MO is actuated to apply a torque in the opposite direction of rotation in order to move the actuator Z back to the (de-energized) actuation position BP.

[0046] Reference symbol list

[0047] A positioning axis, rotation axis

[0048] AN Stellanschluss

[0049] BP Actuation Position

[0050] C buffer storage, capacitor

[0051] G gearbox, reduction gearbox

[0052] GND reference potential, ground

[0053] K flap, fire damper

[0054] L Supply voltage

[0055] MG gearbox clamping torque

[0056] MO electric motor, DC motor, BLDC

[0057] MRF restoring torque

[0058] MS closing torque

[0059] MX maximum restoring torque

[0060] MZ engine gear

[0061] RF reset device, return spring

[0062] RP Resting position

[0063] SA actuator

[0064] SBN area without visible positioning movements

[0065] SBS area of ​​visible positioning movements

[0066] MS engine control unit

[0067] SV power supply unit

[0068] U revolution, engine revolution

[0069] Uo revolutions per minute in relaxed state

[0070] UB Rotational speed in actuation position

[0071] UR revolutions per minute in rest position

[0072] W drive shaft

[0073] Z1 first gear wheel

[0074] Z2 second gear

[0075] Z3 third gear

[0076] ZS Actuating element, tooth segment

Claims

Patent claims 1. Actuator (SA) for actuating a connected load (L), comprising an electric motor (MO) with a stator (ST) and a rotor (RO), a downstream gearbox (G) and an output-side actuating element (Z), wherein a permanent magnetic detent is effective between the stator (ST) and the rotor (RO), wherein the electric motor (MO) is provided for moving the actuating element (Z) between a rest position (RP) and an actuating position (BP), wherein the actuator (SA) comprises a power supply unit (SV) for supplying electrical power to the actuator (SA) and a motor control unit (MS) for electrically controlling the electric motor (MO) to apply a torque with a predefinable direction of rotation, wherein the actuator (SA) comprises a return device (RF), in particular a return spring, to ensure that in the event of a fault or trip, in particular in the event of a power supply failure,the actuating element (Z) is automatically returned to the rest position (RP) by means of a restoring torque (MRM) acting on the actuating element (Z) via the restoring unit (RF), wherein the cogging torque damping of the electric motor (MO) is dimensioned such that the actuating element (Z) remains de-energized in the actuating position (BP) after the motor-side movement of the actuating element (Z) from the rest position (BP) to the actuating position (RP, BP) and after subsequent reversal of the motor-side torque by the motor control unit (MS) due to the effective cogging torque damping of the electric motor (MO), wherein the actuator (SA) has an energy storage device (C), in particular a capacitor, wherein the motor control unit (MS) is configured toIn the event of a fault or trip, the electric motor (MO) is driven by the electrical energy stored in the energy storage device (C) with a torque pulse in the direction of rotation back to the rest position (RP) to release the electric motor (MO) from the de-energized actuating position (BP) of the actuating element (Z), wherein the actuator (SA) comprises a device (DG, H) connected to the motor control unit (MS) for directly or indirectly detecting a rotational position of the electric motor (MO), wherein the motor control unit (MS) is configured to monitor the rotational position of the electric motor (MO) in the de-energized actuating position (BP) for an impermissibly large change in one direction of rotation back to the rest position (RP), and wherein the motor control unit (MS) is configured, in the event of a detected impermissibly large change in rotational position, to drive the electric motor (MO) to apply a torque with the opposite direction of rotation.to move the actuating element (Z) back into the actuating position (BP).

2. Actuator (SA) according to claim 1, wherein the motor control unit (MS) is configured to reduce the motor-side torque when the actuating element (Z) has returned to the actuating position (BP).

3. Actuator (SA) according to claim 1 or 2, comprising a motion sensor (BS) connected to the motor control unit (MS), in particular an acceleration sensor (BS), for detecting linear and / or rotary movements of the actuator (SA), wherein the motor control unit (MS) is configured to monitor the linear and / or rotary movements of the actuator (SA) in the de-energized actuation position (BP) for an impermissibly high movement value, and wherein the motor control unit (MS) is further configured to control the electric motor (MO) in the event of an impermissibly high movement value to apply a holding torque in a direction of rotation opposite to the direction of rotation back to the rest position.

4. Actuator (SA) according to claim 3, wherein the holding torque is dimensioned to a torque value in a range of 0.3 to 0.9 times the torque value required by the electric motor (MO) to drive the actuating element (Z) back into the actuating position (BP).

5. Actuator according to one of the preceding claims, wherein a predetermined value for the magnetic cogging torque of the electric motor (MO) is in the range of 1.2 to 3 times, in particular 1.5 to 2 times, the torque value of the restoring torque (MRM), wherein the restoring torque (MRM) acts in the actuating position (BP) of the actuator (SA) via the actuating element (ZS) and further via the gearbox (G) back onto the electric motor (MO).

6. Actuator according to one of the preceding claims, wherein the motor control unit (MS) is configured to detect the loss of power supply and, in the detected case, to control the electric motor (MO) by means of the electrical energy still stored in the energy storage unit (C) to briefly apply a torque with the direction of rotation back to the rest position (RP).

7. Actuator (SA) according to one of the preceding claims, wherein the electric motor (MO) is a DC motor, in particular a brushless permanent magnet DC motor BLDC.

8. Actuator (SA) according to claim 7, wherein the rotor (RO) of the DC motor (MO) has a plurality of distributed circumferentially to the rotor or motor axis (MA). comprising arranged permanent magnetic poles (N, S), and wherein the device (H) provided for direct detection of the rotational position of the electric motor (MO) comprises at least one magnetic field sensor (H; H1, H2) arranged in the area of ​​the rotor (RO), in particular at least one Hall sensor or at least one digital Hall sensor with switching hysteresis, for detecting a rotational position of the rotor (RO).

9. Actuator according to claim 7 or 8, wherein the DC motor (MO) comprises as rotor (RO) a rotor cup rotating coaxially around the stator (ST) with a plurality of permanent magnetic poles (N, S) arranged circumferentially to the rotor or motor axis (MA), wherein the DC motor (MO) has a detent torque plate connected to the stator (ST) with a plurality of pole shoes for generating an additional magnetic detent torque bringing the rotating rotor cup into a detent position, and wherein the pole shoes are arranged and designed such that, in the detent position, they form a magnetic short circuit between two adjacent permanent magnetic poles (N, S) of the rotating rotor cup to provide the total detent torque inhibition effective between the rotor (RO) and stator (ST) with a predetermined detent torque value.

10. Actuator according to one of the preceding claims, wherein the return device (RF) comprises a return spring and wherein the return torque (MRM) is composed of a return spring torque (MRF) originating from the return spring (RF) and a load torque acting on the actuating element (ZS) via the connected load (L).

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