Locking the electric motor of a linear actuator against rotation

Abstract

The present invention relates to an improved linear actuator for electric motors. In particular, the invention focuses on an improved technical solution for braking or locking a rotary electric motor by using an electromechanical locking mechanism. The mechanism uses a solenoid displaceable by solenoid action and having a non-rotating locking element arranged to engage a rotating locking element. In particular, a solution has been found that allows for the effective unidirectional or bidirectional locking of the motor against rotation, while still allowing for a surprisingly small solenoid with significantly reduced stroke length requirements.

Description

[Technical Field]

[0001] The present invention relates to a linear actuator with an improved electric motor. In particular, the present invention focuses on an improved technical solution to braking or locking of an electric motor. Throughout this specification, the term "motor" refers to an electric motor.

[0002] Linear actuators and electric motors are useful for providing mechanical power to machines to lift or otherwise move loads. To make the movement of such elevators irreversible, particularly when power to the motor is switched off, a lock or brake is desirable to prevent external forces on the machine from rotating the motor. In elevators, such a lock or brake allows the machine to hold the load in place after the motor is electrically switched off. [Background technology]

[0003] In some applications, it is common to rely on frictional restraint of the elevator and / or motor to achieve a sufficient degree of braking or locking. The motor's rotary mechanical power is often transformed and transmitted through gearing, which inevitably introduces friction and thereby aids load-holding behavior. Certain gears, such as worm gears, can be specially designed to achieve high friction. Motors equipped with such gearing are sometimes referred to as "self-locking." Another means of achieving braking is to incorporate a wrap spring clutch on the rotating shaft of the machine. An example is disclosed in U.S. Patent No. 9,369,026. When properly installed, a wrap spring clutch can exert a higher friction force when the shaft rotates in one direction than in the other.

[0004] The braking effect can be further made possible by equipping the motor with a specially designed motor that exhibits a so-called detent torque or cogging torque due to magnetic interaction between the stator and rotor of the motor, even when the motor is switched off.

[0005] The above solutions have the drawback of not providing a sufficiently secure and reliable lock. A further drawback is that the braking effect remains during machine and motor operation, resulting in wasted energy in overcoming friction and / or cogging torque. Relying on friction is not always satisfactory because the braking effect depends, for example, on lubrication, manufacturing tolerances, and wear. A further drawback of relying on friction is when, for example, a fault condition occurs and too much torque is applied to the rotating shaft of the machine or motor. In such a situation, the rotating shaft or motor may rotate unintentionally, causing an unreliable lock.

[0006] A lock against rotation of an electric motor can also be implemented (as a supplement or alternative to any of the above solutions) by using a ring-shaped disk for the lock. Examples are disclosed, for example, in U.S. Patent Application Publication No. 2008 / 0251329 and European Patent Application No. 1320176. A ring-shaped disk attached to a shaft or other rotating element can be selectively moved from a position where it disengages from an opposing, fixedly arranged ring-shaped disk to a locking or braking position where it engages and frictionally interferes with the fixed ring-shaped disk. One or the other disk can be moved axially by an external force. The external force can be of any known type. In some applications, electromagnetic force is preferred to activate such a motor lock, for example, by using a solenoid mechanism. The mechanism is arranged with a spring return. The solenoid allows movement of the locking portion in a direction parallel to the motor shaft axis. The solenoid is shaped as a ring through which the motor shaft passes. Known solenoid designs are centrally located on the motor shaft. This requires large and heavy coil windings.

[0007] These solutions also suffer from the disadvantage of being unnecessarily bulky. Relying on friction between the surfaces of two ring-shaped discs is also a drawback, since friction characteristics are known to depend on external factors and cannot be adequately controlled during the motor's lifetime. As mentioned above, a further drawback of relying on friction occurs when very large torques are applied to the motor shaft. In such situations, the friction between the surfaces of the two ring-shaped discs is overcome, causing unreliable locking. Unacceptable noise is associated with relatively large rings bending back and forth when starting and stopping the motor. Costs arise due to the fact that strict manufacturing tolerances must be adhered to in order for the motor lock to be reliable. Especially for motors that only need to be locked in one direction, these motor lock designs appear more robust and often have more features than are required for the intended application. Furthermore, for motor locks that lock in both directions, it would be advantageous to propose a less bulky design.

[0008] Another known motor locking mechanism includes a solenoid-actuated pin configured to selectively engage or disengage a gear. An example is disclosed in U.S. Patent Application Publication No. 2010 / 0319477. The gear further functions as a working part of a mechanism for reducing the rotational speed of the motor output shaft. The gear forms part of the gear mechanism and is located close to the motor. This arrangement has the disadvantage of unreliable engagement with the lock. It also requires a large solenoid mechanism with a long stroke, resulting in a bulky and expensive design. Another disadvantage is that if the motor shaft is subjected to a very large torque, the solenoid mechanism may be damaged, causing the mechanism to malfunction.

[0009] Yet another solenoid-actuable motor lock design is known in which a pin is driven radially relative to the motor shaft into a longitudinal groove in the shaft, an example of which is disclosed in U.S. Patent Application Publication No. 2017 / 0170708. A further drawback of such a design is that the motor shaft is weakened. This poses a further disadvantage if the motor shaft is to be subjected to very large torques, as the weaker motor shaft may break.

[0010] In the case of the pin-based gear locks and solutions using a rotating and fixed ring, electromagnetically actuated locks are necessarily equally effective for rotation in both directions. This can be seen as a drawback in the event of a lock malfunction. If the lock cannot be released, motor rotation in any direction is impossible, making recovery from a fault situation more difficult.

[0011] One important application of motor braking or motor locking is in linear actuators, particularly spindle-and-nut-driven linear actuators. These linear actuators often include a drive motor with additional gearing beyond the spindle and nut itself. Such devices are increasingly being used in furniture, for example, where they are used to adjust the furniture to a user-selectable setting and maintain that setting while the electric motor is switched off. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] U.S. Patent No. 9,369,026 [Patent Document 2] US Patent Application Publication No. 2008 / 0251329 [Patent Document 3] European Patent No. 1320176 [Patent Document 4] US Patent Application Publication No. 2010 / 0319477 [Patent Document 4] US Patent Application Publication No. 2017 / 0170708 Summary of the Invention [Problem to be solved by the invention]

[0013] The above-mentioned problems, drawbacks, and disadvantages of known electromagnetically actuated motor locks have been at least partially resolved by a motor locking mechanism including an electromechanical transducer, as presented below. In particular, a solution has been found that allows for an effective one-way lock against rotation, using a surprisingly small electromechanical solenoid with significantly reduced stroke length requirements. While embodiments are shown using an electromechanical solenoid that moves the non-rotating locking portion in a direction parallel to the motor shaft axis, other embodiments have an electromechanical solenoid that moves the non-rotating locking portion in a direction perpendicular to the motor shaft axis. However, bidirectional locking is also demonstrated when two small electromechanical solenoids with the same reduced stroke length are used. [Means for solving the problem]

[0014] A motor equipped with a locking mechanism according to the present invention can act on a rotary locking element, such as a dedicated locking disk or a dedicated locking sleeve. Cam elements are configured on the locking disk or the locking sleeve. Each cam has a non-engageable side opposite an engageable side. In some embodiments, the non-engageable side is an inclined side, and the engageable side is a steep side. The steep side is typically approximately perpendicular to the surface of the locking disk or the locking sleeve. Such a cam design ensures high strength of the cam against shear. The cam is durable and allows the rotary locking element to be designed to be lighter and smaller than is possible with conventional cams.

[0015] The motor lock mechanism of the present invention focuses, among other things, on locking against rotation in only one direction, thus creating design flexibility and reducing costs. This creates a lightweight, reliable one-way motor lock that keeps the motor operable in one direction, even in fault conditions where the motor shaft is jammed and the lock preventing the motor from rotating in the other direction may not be easily released, thereby allowing recovery from the fault condition by reversing the direction of rotation. Even in bidirectional embodiments, if a fault condition locks one solenoid mechanism, it is possible to release the lock by reversing the direction of rotation, as long as the other solenoid mechanism is not locked or is not affected by the fault and can be operated by it.

[0016] The rotation locking element may be attached to the shaft of the motor, for example, at its output end or rear end. In this specification, output end and front end are used interchangeably, as are rear end and back end.

[0017] The mass of the element moved during locking and unlocking is significantly smaller than in other known designs, thus making any disturbance noise negligible.In the motor lock according to the invention, the small stroke of a small solenoid may be amplified by a leaf spring biased pivot arm, which carries a non-rotating locking element at its distal end.

[0018] The electromechanical solenoid comprises a coil. One end of the coil presents itself as the solenoid base, which is preferably used to secure the solenoid directly or indirectly to the motor housing. On the top surface opposite the coil, a non-rotating locking element is displaceable by solenoid action and positioned to engage with a rotating locking element. When locking occurs under load, the two locking elements come into contact, exerting a lateral force on the pivot arm, which in turn exerts a lateral force on the solenoid. The force attacks the pivot arm, which is supported only by the bent portion or hinge of the leaf spring, since it must be able to pivot back and forth between the extended and retracted positions. In some embodiments, it is preferable to support the solenoid at a point near its top, opposite the non-rotating locking element, thereby stabilizing the solenoid against tilting forces. In a preferred embodiment, a support at the top of the solenoid supports the portion of the pivot arm around which the leaf spring is bent or hinged. The support is fixed directly or indirectly to the motor housing.

[0019] In an embodiment, the motor locking mechanism comprises a torque limiting clutch disposed between the motor shaft and the rotation locking element, which inherently anticipates and prevents damage to the locking mechanism, i.e., the rotation locking element, in the event of excessive torque being applied to the motor shaft.

[0020] In its basic form, the rotation locking element is not intended to be subjected to any excessive torque overload. However, it can be seen that such torque overloads can occur in certain circumstances, such as in fault situations. One such fault situation occurs when the locking mechanism is activated while the electric motor is running. Another overload fault can occur when excessive torque is applied to the motor shaft when the electric motor is already stopped and locked via the locking mechanism. Most importantly, the overload situation can be characterized as a sudden impact acting on the rotation locking element.

[0021] The small size and light weight of the components means that the motor lock can be damaged, particularly the cam of the rotary locking element itself, the entire structure of the rotary locking element, or the non-rotary locking element.

[0022] This problem is solved by the motor lock mechanism of the present invention by placing a torque limiting clutch between the motor shaft and the rotation locking element, thereby essentially predicting and avoiding said damage.

[0023] The torque limiting clutch can be implemented in several different locations relative to the two elements: the motor shaft and the rotation locking element. Between the inner surface of the cup-shaped or hollow end of the rotation locking element and the outside of the motor shaft, thereby establishing a clutch integrated with the rotation locking element. Between the inside of the cup-shaped or hollow distal end of the motor shaft and the outside of the rotation locking element Establishing a clutch between the proximal and distal portions of the motor shaft, thereby at a distance from the rotation locking element.

[0024] It is further noted that the rotational locking element on which the torque limiting clutch acts may be either a disk type or a sleeve type as described above.

[0025] Several clutch principles can be applied: Piezoelectric crystal electromechanical clutch Dog clutch Torque limiter Centrifugal clutch ·Circlip-lock ring principle Single coil spring Multi-wound coil spring

[0026] When considering coil spring principle clutches, which are typically provided in a spiral, it should be noted that several materials and dimensions of the wire are possible. Furthermore, the wire can have a cross section of any suitable shape, such as circular, rectangular, trapezoidal, elliptical, etc.

[0027] The coil spring torque limiting clutch may include a first end of the coil wire secured to either the motor shaft or a rotation locking element, and a second end of the coil wire remaining free. Alternatively, the second end of the coil wire may be secured to the same element to which the first end is secured.

[0028] For purposes of this disclosure, the term torque limiting clutch is defined as any active or passive mechanism that functions to limit the torque acting on a rotational locking element to a certain maximum predetermined value. Embodiments of a torque limiting clutch include, but are not limited to, any and all combinations of the features described above.

[0029] The presence of these and other features distinguishes the present motor lock mechanism from other known electromagnetically actuated motor locks.

[0030] The present invention can be further summarized by observing the following embodiments:

[0031] The linear actuator includes an electric motor, a spindle driven by the reversible motor, and a spindle nut attached to the spindle and fixed against rotation, the spindle nut arranged to move between two end positions. The electric motor includes a stator attached to a motor housing and a rotor including a motor shaft, the motor adapted to be electrically controlled to selectively rotate the rotor in one of two opposing angular directions. The electric motor further includes an electromechanical locking mechanism including an electromechanical transducer fixedly attached to the motor housing and including a non-rotating locking element, the electromechanical transducer adapted to be electrically controlled to selectively shift the non-rotating locking element between an extended position and a retracted position, and a rotational locking element attached to the motor shaft and including at least one cam protruding in a direction toward the transducer, the at least one cam having a non-engageable side opposite an engageable side. The non-rotating locking element protrudes in a direction toward the rotational locking element and is arranged to interfere with and lock with the at least one cam by selectively engaging the engageable side of the at least one cam. The electromechanical transducer is configured to control engagement by maintaining the anti-rotation locking element out of engagement with the engageable side of the at least one cam when the electromechanical transducer is energized, and the electromechanical transducer further comprises a spring element arranged to maintain the anti-rotation locking element in engagement with the engageable side of the at least one cam when the electromechanical transducer is not energized, whereby the electromechanical locking mechanism is configured to lock the motor shaft against rotation in one rotational direction, thereby unidirectionally locking the motor.

[0032] In a linear actuator embodiment, the electromechanical transducer is an electromechanical solenoid comprising a coil and a non-rotating locking element. However, other types of electromechanical transducers can be used as well. Examples include piezoelectric actuators or microactuators.

[0033] When the motor is locked and under load, a compressive load retention force is transferred from the rotary locking element to the non-rotating locking element. The pivot arm can form an angle with the surface of the rotary locking element at the side supporting the engageable cam side. This angle can be less than 30 degrees, or less than 15 degrees, or less than 12 degrees, or less than 9 degrees, or can be greater than 3 degrees or greater than 6 degrees, for example.

[0034] In a linear actuator embodiment, the electromechanical solenoid includes a pivot arm, the distal end of which constitutes a non-rotating locking element, the pivot arm further including an armature configured to be actuated by current in the coil, and the spring element including a leaf spring configured to bias the pivot arm toward the rotating element. It should be noted that due to the gear ratio of the linear actuator, i.e., the gear ratio caused by the spindle and the transmission or reduction gear, the high forces applied to a linear actuator, for example, in a height-adjustable table, are reduced to significantly lower forces on the actuator's motor shaft. Therefore, even when the actuator is heavily loaded, it can be locked using a locking mechanism with a small electromechanical solenoid that uses a leaf spring as the spring element.

[0035] In linear actuator embodiments, the electromechanical solenoid is implemented by a micro-signal relay, in which case the contact sets of the relay can be omitted, left unused, or used to provide a feedback signal indicating whether the locking mechanism is locked or not.

[0036] In linear actuator embodiments, the electromechanical transducer further comprises a support member fixedly mounted to the housing and configured to support the electromechanical solenoid against tilt and shear forces, which further helps ensure that a small electromechanical solenoid using a leaf spring as the spring element is sufficient to lock the actuator even under large loads.

[0037] In an embodiment of the linear actuator, the longitudinal axis of the motor shaft is offset from the longitudinal axis of the solenoid coil.

[0038] In an embodiment of the linear actuator, the longitudinal axis of the motor shaft and the longitudinal axis of the solenoid coil are parallel but not coincident.

[0039] In an embodiment of the linear actuator, the rotary locking element is shaped as a locking disk, and at least one cam is positioned on an essentially flat side of the disk that would otherwise face the solenoid;

[0040] In this case, the disc is positioned adjacent the solenoid to allow the non-rotating locking member to engage the engageable side of the at least one cam.

[0041] In an embodiment of the linear actuator, the longitudinal axis of the motor shaft and the longitudinal axis of the solenoid coil are perpendicular.

[0042] In an embodiment of the linear actuator, the rotary locking element is configured as a locking sleeve, with at least one cam disposed on an essentially circular curved surface of the sleeve facing the solenoid, and the sleeve positioned proximate the solenoid to allow the non-rotary locking member to interact with an engageable side surface of the at least one cam.

[0043] In the linear actuator embodiment, the locking mechanism is located at the output end of the motor shaft.

[0044] In the linear actuator embodiment, the locking mechanism is located at the rear end of the motor shaft of the motor.

[0045] In an embodiment of the linear actuator, the motor includes a torque limiting clutch disposed between the rotation locking element and the motor shaft. The torque limiting clutch may be a coil spring having multiple windings, the windings tightly grippingly connected to the motor shaft, and the free end of the coil spring mounted in a slot in the rotation locking element.

[0046] In an embodiment, the motor comprises a rotating member that facilitates detection of rotation, such as a ring magnet for a Hall sensor or an optical disk for an optical sensor, the rotating member being fixedly disposed on the motor shaft, and at least one rotation sensor, i.e., a Hall sensor or an optical sensor, being fixed directly or indirectly to the housing.

[0047] In an embodiment of the linear actuator, the at least one rotation sensor is mechanically and electrically connected to a printed circuit board, the printed circuit board being fixedly mounted relative to the motor housing.

[0048] In linear actuator embodiments, the printed circuit board also carries an electromechanical transducer and provides electrical connections.

[0049] In an embodiment, the motor includes a controller adapted to receive signals from at least one rotation sensor, the controller including a processor, the controller configured to perform position, speed, and directional control of the motor. Further, the controller can switch the anti-rotation locking element between its extended position and its retracted position by switching on or off current to a coil of the solenoid.

[0050] In an embodiment, the electromechanical locking mechanism comprises a rotary locking element comprising two sets of oppositely disposed cams and two electromechanical transducers, each electromechanical transducer arranged such that its non-rotary locking element selectively engages with an engageable side of each of the two oppositely disposed sets of cams.

[0051] In another embodiment, the exterior of the motor housing presents a flat geometric shape, preferably with two parallel planes on each side, said planes being connected by an arcuate surface.

[0052] The present invention further comprises an actuator system comprising the linear actuator described above, a control box comprising at least a power source and a driver circuit configured to drive the electric motor of the linear actuator, and a cable connecting the linear actuator to the driver circuit in the control box.

[0053] In an actuator system including a linear actuator mechanism having a spindle and a nut driven by an electric motor according to any of the above embodiments, the actuator mechanism is adapted for use with an expected load pattern in which the load is typically unidirectional, such that rotation of the motor shaft in a direction against the expected load requires significantly more power than rotation in the opposite direction, i.e., with the expected load. An example of this can be a height-adjustable table with a heavy load placed on top of the table, and the actuator mechanism is configured to raise and lower the table, respectively. In this case, raising the table requires significantly more power than lowering the table when the motor is operating with the expected load, since the motor can be considered to be operating with the expected load. In such a situation, the unidirectionality of the locking mechanism ensures that the locking mechanism is configured to lock the motor shaft against rotation in the direction in which the table is lowered, i.e., the motor is operating with the expected load (locking direction). Correspondingly, the locking mechanism does not lock in the opposite direction (unlocking direction), and the motor is operating with the expected load by raising the table. The present invention also relates to such height-adjustable tables.

[0054] In an embodiment of the invention, the motor comprises a controller and an angular position sensor, the controller having data acquisition and processing capabilities and configured to use the sensor signals to determine the angular position, angular velocity, total number of rotations, etc. of the motor shaft.

[0055] In combination with the controller's other tasks, it can be configured to control the timing and on / off switching of the solenoid that drives the anti-rotation locking element. During an operational phase in which the motor is moving in either direction, the controller can be configured to take action to facilitate the desired motor locking operation when instructed to stop the motor while holding the load. The instruction to stop can be given, for example, by a user pressing a button or by signaling from an external control system.

[0056] According to the present invention, a specific control scheme can be employed for setting and releasing the motor lock.

[0057] To set the lock, the following can be applied: While the motor is operating to move the load, and when external intervention, for example from a user or an external control system, commands the controller to stop the motor, the controller is configured to: After stopping the motor rotation, the controller can be configured to check the angular position sensor signal for a short predetermined time interval, i.e., the motor is stopped but still on; and if during said time interval the controller satisfies that no rotation is occurring, the controller is configured to switch off power to the motor, controller, and solenoid.

[0058] This displaces the non-rotating locking element of the motor lock, thus bringing its locking edge into contact with the rotating locking element in the form of a locking disc or locking sleeve, and the sharp protrusion of the locking edge captures the cam with its engageable side, thus effectively locking the motor against rotation in the locking direction, after which the motor can be switched off.

[0059] When unlocking, the appropriate control is determined according to the direction of rotation that is to occur after unlocking, where the control differs depending on whether the desired direction of movement after unlocking is in the locked or unlocked direction.

[0060] If the intended direction is the unlocked direction, the control is configured to simply turn on the controller, solenoid, and motor.

[0061] If the intended direction is the locking direction, the controller is configured to switch the solenoid on but not yet start rotating the motor in the locking direction. As a next step, the controller can be configured to operate the motor to gradually operate in the unlocking direction, resulting in successful release of the lock.

[0062] The rotation in the unlocking direction only needs to be sufficient to ensure that the non-rotating locking element can disengage from the cam of the rotating locking element. For example, the number of cams on the locking disk or locking sleeve can determine the minimum rotation by the motor in the unlocking direction. Thus, if the number of cams is n, the minimum rotation performed by the controller can be 1 / n of 360 degrees.

[0063] This action ensures that the sharp protrusion on the distal end of the leaf spring moves from its pressing position against the engageable side of the cam. Following this initial increment, the controller is configured to rotate the motor in the locking direction after verifying that the lock has been released.

[0064] Therefore, the following method for operating an actuator mechanism also serves to summarize the invention:

[0065] In an embodiment, the following applies to a method for operating an actuator comprising an electric motor according to one of the above embodiments, the method being operable to stop and lock the motor while operating the actuator mechanism, the method comprising the steps of: Uses an actuator mechanism to move the load, While the motor is operating to move the load, providing a signal to the controller indicating that the motor is to stop; Use electrical controls to stop the rotation of the electric motor, Continuously checking the angular position sensor signal for a predetermined time interval; Keeps the motor stopped but still electrically switched on, During said time interval, the controller may determine that no rotation is occurring and switches off power to the motor, solenoids, and motor control system.

[0066] In an embodiment, the following applies to a method for operating an actuator comprising an electric motor according to one of the above embodiments, the method being operable to unlock and start the motor and then operate the actuator mechanism in the locking direction. The method comprises the following steps: While power to the motor, motor control system, and solenoid is switched off, a signal is provided to the actuator to initiate movement in the locking direction, for example, by a user pressing a button or by a signal from an external control system. Switch on the power to the controller. The solenoid switches on but the motor still does not start to rotate. · To unlock by having the controller increase the motor by at least one revolution in the unlock direction, gradually operate the actuator mechanism in the unlock direction, thereby confirming that the locking mechanism has been released. Following this first increment, the controller will rotate the motor in the locked direction.

[0067] These and other features and advantages of the present invention will become apparent from the following detailed description of the invention. [Brief explanation of the drawings]

[0068] [Figure 1a] 1 shows a schematic example of a linear actuator. [Figure 1b] 1 shows an example of an actuator system in which a linear actuator is controlled by a control box. [Figure 2a] 1 is a partial exploded view of a first embodiment of a motor in a linear actuator according to the present invention. FIG. [Figure 2b] FIG. 10 is a perspective view of a second embodiment of a motor in a linear actuator according to the present invention. [Figure 3] FIG. 10 is a perspective view of a rotation locking element. [Figure 4a] FIG. 1 is a perspective view of an electromechanical solenoid. [Figure 4b-4c] 1 shows further details of an electromechanical solenoid. [Figure 5] FIG. 10 is a side view of the locking mechanism when engaged. [Figure 6a] 1 shows a side view of a first embodiment of a motor according to the present invention. [Figure 6b] 1 shows a perspective view of a first embodiment of a motor according to the present invention. [Figure 7a] 1 shows a side view of a second embodiment of a motor according to the present invention. [Figure 7b] FIG. 2 shows a perspective view of a second embodiment of a motor according to the present invention. [Figure 8a] 10 shows a side view of a third embodiment of a motor according to the present invention based on the first embodiment. [Figure 8b] 1 shows a perspective view of a third embodiment of a motor according to the present invention based on the first embodiment; [Figure 9a] 4 shows a side view of a fourth embodiment of a motor according to the invention based on the second embodiment; [Figure 9b] 10 shows a perspective view of a fourth embodiment of a motor according to the invention based on the second embodiment; FIG. [Figure 10-13] 5 shows a fifth embodiment of an electric motor having a locking mechanism according to the first embodiment with a torque limiting clutch. [Figure 14-18] 10 shows a sixth embodiment of an electric motor having a locking mechanism according to the second embodiment with a torque limiting clutch. [Figure 19-22] 7 shows a seventh embodiment of an electric motor having a locking mechanism according to the second and sixth embodiments. [Figure 23] 1 shows a perspective view of the rear end of a motor according to a first embodiment of the present invention, shown with the motor housing removed; FIG. [Figure 24] 1 shows a height-adjustable table with a linear actuator, the table being loaded by a weight placed on it. DETAILED DESCRIPTION OF THE INVENTION

[0069] 1-9 show embodiments of a motor having a worm gear mechanism. This is for illustrative purposes only. The present invention is not limited to a motor driving any particular device.

[0070] FIG. 1a shows a schematic diagram of an example linear actuator 1. The linear actuator 1 includes an electric motor 10, a transmission or reduction gear 3, typically with several stages, a spindle 4 with a screw thread 5, a spindle nut 6 that engages the screw thread 5, and a tubular actuating element 7. A mounting bracket 8 is located at the end of the actuating element 7 for attaching the linear actuator 1 to, for example, a carrier element. The spindle nut 6 is fixed against rotation, either directly or indirectly. In some linear actuators, the spindle nut is connected directly to, for example, the carrier element, without the use of an actuating element. When the spindle 4 is rotated by the motor 10, the spindle nut 6 moves along the spindle 4, thus converting the rotation into linear motion of the spindle nut 6 and / or the actuating element 7 between two end positions. Furthermore, the linear actuator 1 includes an electromechanical locking mechanism 40 located on the motor 10. This locking mechanism is described in more detail below. Note that in some motor types, the electric motor 10 can drive the spindle 4 directly, thereby avoiding the need for a transmission 3. Electric motor 10 is typically a reversible electric DC motor, although other types of electric motors may be used.

[0071] Typically, linear actuators are used in actuator systems controlled by a control box. An example of such an actuator system 9 is shown in Figure 1b. Via cable 12, linear actuator 1 is connected to a control box 13, which includes at least a power supply 14, a controller 15, and a driver circuit 16 for linear actuator 1. Driver circuit 16, and therefore electric motor 10 of actuator 1, are controlled by control signals from controller 15. Controller 15 typically includes a microcomputer. Control box 13 is typically installed in the equipment in which linear actuator 1 is used. This equipment can represent any one of several different applications, such as trucks, agricultural machinery, industrial automation equipment, hospital and nursing beds, leisure beds and chairs, tables, or other furniture with adjustable height, and several other similar applications. Power supply 14 is typically connected to a commercial AC power grid by a power cable 17. Furthermore, control box 13 can be connected to a remote control 18, which allows the operation of linear actuator 1 to be controlled by a person in the vicinity of the actuator. The connection between the remote control 18 and the control box 13 may be a wired connection as shown in FIG. 1b, but wireless communication systems such as radio or infrared links can also be used. The control box can also be configured to control an actuator system having multiple linear actuators. The control box then includes a driver circuit for each linear actuator. Each driver circuit, and therefore the electric motors of the actuators, are individually controlled by control signals from the controller, meaning that some or all of the actuator motors may operate simultaneously.

[0072] FIG. 2a is a partial exploded view showing a first embodiment of a motor 10 having a locking mechanism 40 in a linear actuator according to the present invention.

[0073] The electric motor 10 includes an electromechanical locking mechanism 40. The motor 10 includes a stator and a rotor (not shown). The stator is attached to a motor housing 20. The motor housing 20 includes an elongated housing component, the exterior of which exhibits, for example, a flat geometric shape, with two parallel planes 26 connected on each side by arcuate surfaces 24, 25. A motor 10 having such a flat geometric shape may be desirable in space-constrained applications, such as linear actuators. The motor housing 20 further includes a rear housing portion 22 and an end cover 23.

[0074] The rotor comprises a motor shaft 31, which at one end is provided with a protruding portion at its front end adapted to serve as an output end (not shown), which in the example of Figure 2a is connected to drive the worm of the worm gear mechanism 11. At its rear end 32, the motor shaft 31 is supported by a bearing 34.

[0075] The motor 10 is adapted to be electrically controlled to selectively switch between clockwise and counterclockwise rotation.

[0076] The locking mechanism 40 comprises an electromechanical solenoid 41 fixedly mounted to the motor housings 20, 22, 23. The electromechanical solenoid 41 is an electromechanical transducer comprising a coil 42 and a pivot arm 43. In the following, the electromechanical solenoid will also be referred to simply as a solenoid. It should be noted that other types of electromechanical transducers can also be used instead of the electromechanical solenoid 41.

[0077] The locking mechanism 40 further comprises a rotary locking element 45 , shown in this embodiment as a disk-shaped locking element attached directly or indirectly to the motor shaft 31 .

[0078] The locking mechanism 40 further comprises a non-rotating locking element 44, and FIG. 2a shows that the rotating locking element 45 and the non-rotating locking element 44 are configured to engage, the engagement being selectively controllable by a solenoid 41.

[0079] Motor shaft 31 has a longitudinal axis 33. Solenoid 41 has a coil 42, and solenoid coil 42 has a longitudinal axis 53. The embodiment of motor 10 in Figure 2a shows motor shaft longitudinal axis 33 parallel to, but not coincident with, coil longitudinal axis 53, such that the two axes are offset from one another.

[0080] The rotary locking element 45 has a longitudinal axis 48. As shown in Figure 2a, the longitudinal axis 33 of the motor shaft 31 and the longitudinal axis 48 of the rotary locking element 45 are coincident. The rotary locking element 45 co-rotates with the motor shaft 31, and their rotational movement is identical.

[0081] 2a further shows motor 10 with rotary locking element 45 comprising at least one cam 47 (three cams are shown) projecting in a direction towards solenoid 41 and a non-rotary locking element 44 on pivot arm 43 projecting in a direction towards rotary locking element 45. Non-rotary locking element 44 is arranged to enter a locked position when engaged with at least one cam 47, which is enabled when the current to the coil of solenoid 41 is switched off.

[0082] The rotation locking element 45 comprises a surface 49 facing the pivot arm 43 .

[0083] 2a further shows that the base of the solenoid 41 is fixed to a printed circuit board 50, which is fixed to the rear housing portion 22. On its upper surface opposite the coil, the anti-rotation locking element 44 is supported by a support member 27, thereby stabilizing the solenoid 41 against tilting and shear forces. The support member 27 is positioned to support the pivot arm 43 at its hinged end. The support member 27 is formed as an integral part of the end cover 23.

[0084] In the embodiment of the electric motor 10 of the linear actuator according to the present invention shown in FIG. 2a, it can be seen that the motor 10 includes a rotating member 51 that facilitates detection of rotation. The rotating member 51 is disposed on the motor shaft 31 and co-rotates therewith. The rotating member 51 can have various configurations, such as a ring magnet for a Hall sensor or an optical disk for an optical sensor. The electric motor 10 further includes at least one rotation sensor 52, such as a Hall sensor or an optical sensor, that is fixed directly or indirectly to the housing. FIG. 2a shows two Hall sensors that may be preferred in some applications.

[0085] At least one rotation sensor 52 is mechanically and electrically connected to a printed circuit board 50, which is fixed directly or indirectly to the housings 20, 22, 23, said printed circuit board 50 also carrying the solenoid 41 and providing it with an electrical connection. Nevertheless, this is not the only option: it is equally feasible for the rotation sensor 52 and the solenoid 41 to be mounted and connected independently.

[0086] 2b shows a second embodiment of the invention in which the rotating locking element of the locking mechanism 60 is shaped as a locking sleeve 63, with at least one cam 61 (four cams are shown) disposed on an otherwise essentially circular curved surface 62 of the sleeve facing a solenoid 64. The locking sleeve 63 is disposed proximate to the solenoid 64 to allow a non-rotating locking element 65 to interact with an engageable side surface 66 of the at least one cam 61.

[0087] This second embodiment further comprises an end cover which is not shown in Figure 2b.

[0088] The motor shaft 31 has a longitudinal axis. The solenoid 64 has a coil, and the solenoid coil has a longitudinal axis. The electric motor 10 in the embodiment of Figure 2 shows the motor shaft longitudinal axis orthogonal to the coil longitudinal axis, so that the two axes are offset from one another.

[0089] Referring to the first embodiment of Figure 2a, Figure 3 shows a rotary locking element 45 shaped as a locking disc, with at least one cam 47 (three cams are shown) positioned on an essentially flat side of the disc facing the solenoid 41. The locking disc 45 is positioned adjacent to the solenoid 41 to allow the non-rotating locking member 44 to interact with the steep side of the cam 47.

[0090] FIG. 3 shows that each cam 47 has a non-engageable side 75 (shown here as a sloped side) opposed to an engageable side 76 (shown here as a steep side), the steep side being approximately perpendicular to the surface of the rotational locking element 45. The engageable side may also have other configurations that allow it to lock with the non-rotational locking member 44. Note that the non-engageable side 75 is non-engageable because it faces away from the non-rotational locking member 44. It does not need to be sloped; it would be equally non-engageable. As explained below, it is the placement and angularity of the pivot arm that allows the non-engageable side 75 to disengage. FIG. 3 shows that the rotational locking element is designed for small size and mass, yet high strength, compared to conventional cams. This strength is achieved by designing the non-engageable side 75 with a large footprint.

[0091] The electric motor 10 is unidirectionally lockable against rotation using the locking mechanism 40, and is locked in only one direction of rotation, either clockwise or counterclockwise. This is achieved by adapting the topographical configuration of the ring-shaped region 46 located on the surface of the rotational locking element 45 so that the topography of the ring-shaped region 46 locks into engagement with the non-rotational locking element 44 only when rotation in one of the directions is attempted.

[0092] The rotation locking element 45 comprises a rotation axis 48 shown in FIG. 2a.

[0093] The locking mechanism 40 of the first embodiment comprises an electromechanical solenoid 41 fixedly mounted relative to the motor housings 20, 22, 23, as shown in Figure 4a, the solenoid 41 comprising a coil 42, a yoke 72 which may be formed as an angle bracket, and a movable armature 74 in the form of a pivot arm 43. Further details of an example electromechanical solenoid 41 are shown in Figures 4b and 4c.

[0094] The armature 74 is formed from a magnetic material. The pivot arm 43 carries the anti-rotation locking element 44 formed at its distal end. The armature 74 is hinged to the yoke 72 and held in place by a leaf spring 73 attached to the yoke 72 and bent approximately 90 degrees, so that when the electromechanical solenoid 41 is not energized, the pivot arm 43, and therefore the anti-rotation locking element 44, are maintained in their extended position. This situation is shown in Figure 4b. When current is passed through the coil 42, a magnetic field is generated that actuates the armature 74 by attracting it toward the coil 42 with a magnetic force that exceeds the force provided by the leaf spring 73. This means that the pivot arm 43, and therefore the anti-rotation locking element 44, is brought to its retracted position. This situation is shown in Figure 4c. When the current through the coil is switched off again, the pivot arm 43 is returned to its extended position by the force provided by the leaf spring 73.

[0095] It should be noted that due to the gear ratio of the linear actuator, i.e., the gear ratio caused by the spindle 4 and the transmission or reduction gear 3, the high forces applied to the linear actuator, for example in a height-adjustable table, are reduced to significantly lower forces on the motor shaft of the actuator. Therefore, even if the actuator is heavily loaded, it can be locked using a locking mechanism with a small electromechanical solenoid as shown in Figures 4a and 4b, using a leaf spring 73 as the spring element.

[0096] Thus, in an embodiment, the electromechanical solenoid can be implemented by a microsignal relay. In that case, a set of relay contacts can be omitted, left unused, or used to provide a feedback signal indicating whether the locking mechanism is locked. An example of such a feedback signal is energizing a coil when an attempt is made to unlock the locking mechanism after it has been locked. However, the non-rotating locking element may be pressed against the engageable side of the cam and therefore difficult to disengage. In that case, the relay contacts indicate that the non-rotating locking element is still in its extended position despite the coil being energized, and the motor can be controlled to incrementally rotate in the unlocking direction to unlock before the intended rotation in the locking direction can begin. As another example, it can be noted that when the coil is de-energized and the non-rotating locking element is therefore in its extended, locked position, the relay contacts can connect (i.e., short) the motor terminals. This increases the cogging torque of the motor, thereby at least reducing the resulting speed of the motor in the locking direction, for example, if there is a mechanical defect in the rotating locking element.

[0097] The solenoid 41 is adapted to be electrically controlled to selectively switch the non-rotating locking element 44 between an extended position and a retracted position, as indicated by dotted line 35. When the electromechanical solenoid 41, 64 is not energized, the spring element or leaf spring 73 holds the pivot arm 43, and thus the non-rotating locking element 44, in its extended position and engaged with the rotating locking elements 45, 63. Thus, when no current flows through the windings of the coil 42, the non-rotating locking element assumes its extended position.

[0098] Magnetizing the coil 42 with an electric current causes the leaf spring 73 and pivot arm 43 to resiliently bend toward the coil 42, thereby moving the armature 74 closer to the coil 42, thereby placing the anti-rotation locking element 44 in its retracted position.

[0099] Figure 5 shows the principle of engagement between the rotary locking element 45 (here shown as a disk) and the non-rotary locking element 44 in a first embodiment of the invention, in which the current to the solenoid is switched off and the pivot arm 43 is in its extended position.

[0100] FIG. 5 further shows that the anti-rotation locking element 44 is the distal end of the armature 74 .

[0101] The armature 74 of the pivot arm 43 is supported against tilting and shear forces by a support member 27 (see FIG. 2 a ) rigidly attached to the housings 20 , 22 , 23 at points 78 .

[0102] In Figure 5, 77 indicates the point of engagement between the rotation locking element 45 and the non-rotating element 44. As can be seen, if an external load acts to rotate the disc 45 in a direction that would move the point 77 to the right, this is effectively prevented by the engagement between the pivot arm 43 and the engageable side 76 of the cam 47.

[0103] However, as can be seen in the figure, if an external load tries to rotate the rotary locking element or disc 45 in a direction that moves point 77 to the left, this is possible even when pivot arm 43 is in its extended position. The flexibility of pivot arm 43 will cause pivot arm 43, and therefore non-rotating locking element 44, to slide past the cam, assuming said external load is large enough.

[0104] 5 further shows that in its extended position, the armature 74 of the pivot arm 43 abuts the engageable side 76 of the cam 47 (see FIG. 3), and the armature 74 forms an angle 79 with the underside of the rotational locking element 45. The locking and load-holding force is transmitted as a compressive force within the armature 74 of the pivot arm 43, which is then transmitted in large part to the support member 27 (see FIG. 2a).

[0105] Similarly, in the second embodiment according to Figure 2b, the cam 62 lies on a curved surface and the tangent at the location of the engageable side 61 of the cam also forms an angle with the armature 74 of the pivot arm when arranged in an arrangement similar to that shown in Figure 5. In Figure 2b it is clear that when the rotary locking element 63 is shaped as a sleeve and the longitudinal axis of the solenoid coil is perpendicular to the longitudinal axis of the motor shaft 31, the locking and load holding force is also transmitted as a compressive force in the armature of the pivot arm.

[0106] Generally, the load holding force in the embodiments shown in Figures 2b and 5 is the force transmitted from the rotating locking element to the non-rotating locking element.

[0107] A feature of the present invention is that angle 79 is, for example, less than 30 degrees, or less than 15 degrees, or less than 12 degrees, or less than 9 degrees, but is, for example, greater than 3 degrees, or greater than 6 degrees. Keeping angle 79 low has the advantage of allowing the solenoid to be positioned close to rotation locking element 45, which allows for the construction of a compact motor lock. Positioning the motor lock at such a low angle 79 further ensures unidirectional locking action.

[0108] Figures 6 to 9 show four configurations of the electromechanical locking mechanism according to the present invention, which differ due to the choice of rotation locking element and the choice of which end of the motor it is located at. Figures 6a and 6b show a first embodiment of the electromechanical locking mechanism located at the rear end 71 with a disk element. Figures 7a and 7b show a second embodiment of the electromechanical locking mechanism located at the rear end 71 with a sleeve element. Figures 8a and 8b show a third embodiment of the electromechanical locking mechanism based on the first embodiment located at the output end 70 with a disk element. Figures 9a and 9b show a fourth embodiment of the electromechanical locking mechanism based on the second embodiment located at the output end 70 with a sleeve element.

[0109] In another embodiment of the electromechanical locking mechanism according to the present invention, the motor includes a torque limiting clutch disposed between the motor shaft and the rotation locking element.

[0110] Additional embodiments will now be described: In general, it is not intended that any overloads in terms of excessive torque occur on the rotation locking elements 45, 63. It is understood that in certain circumstances, such as fault situations, such torque overload cases may nevertheless occur. One such fault situation occurs when the locking mechanism 40, 60 is activated while the electric motor 10 is running. Another overload fault may be when excessive torque is applied to the motor shaft 31 in a situation where the electric motor 10 is already stopped and locked via the locking mechanism 40, 60. Most importantly, the overload situation can be characterized as a sudden impact acting on the rotation locking elements 45, 63.

[0111] Due to the characteristics of the small and lightweight components, there is a risk of damage to the locking mechanism 40, 60. In particular, there is a risk of damaging the cam of the rotary locking element 45, 63 itself, of damaging the entire structure of the rotary locking element 45, 63, or of damaging the non-rotary locking element 44.

[0112] 10 to 13 show a fifth embodiment based on the electromechanical locking mechanism of the first or fourth embodiments, in which the locking mechanism 40, 60 comprises a torque limiting clutch in the form of a coil spring having multiple windings 36 arranged between the motor shaft 31 and the rotary locking element 45. To simplify the description of the invention, the worm gear mechanism 11 and the motor housings 22, 23 are not shown.

[0113] In this fifth embodiment, the locking mechanism 40, 60 operates as described in the first embodiment. A torque-limiting clutch in the form of a coil spring 36 is disposed between the inner surface of the cup-shaped or hollow end 38 of the rotary locking element 45, 63 and the outside of the motor shaft 31, thereby establishing an integral clutch with the rotary locking element 45, 63. The free end 37 of the coil spring 36 rests within a slot 39 in the rotary locking element 45, 63. The coil spring 36 has its windings connected, e.g., tightly gripping, to the motor shaft 31 so that the rotary locking element 45, 63 rotates with the motor shaft 31 when the non-rotating locking element 44 is in the retracted position. As can be seen in FIG. 12 , the rotary locking element 45, 63 surrounds a portion of the motor shaft 31 but can rotate relative to it, thereby only making a driving connection via the coil spring 36.

[0114] In normal operation, the coil spring 36 does not slide on the motor shaft 31. The grip of the coil spring is adjusted to be strong enough to prevent such sliding from occurring. The friction between the coil spring 36 and the motor shaft 31 is great enough to avoid any sliding in normal operation.

[0115] Only in the event of a fault condition can too much torque be applied to the rotation locking element 45, 63, causing slippage between the coil spring 36 and the motor shaft 31. The torque limiting clutch thereby inherently anticipates and prevents damage to the locking mechanism 40, 60.

[0116] When anti-rotation locking element 44 is in the extended position, rotation locking elements 45, 63 are held in a non-rotational position, i.e., prevented from rotating. The same applies to motor shaft 31, which is held against rotation via rotation locking elements 45, 63, thereby unidirectionally locking electric motor 10 in either a clockwise or counterclockwise direction.

[0117] 14 to 18 show a sixth embodiment based on the electromechanical locking mechanism of the second or third embodiment, where the locking mechanism 40, 60 comprises a torque limiting clutch in the form of a coil spring 67 arranged between the motor shaft 31 and a rotary locking element 63. The locking mechanism 40, 60 can be covered by a housing 28 as shown in FIG.

[0118] In this sixth embodiment, the locking mechanisms 40, 60 operate as described in the first and second embodiments. A torque-limiting clutch in the form of a coil spring 67 is disposed between the inner surface of the cup-shaped or hollow end 68 of the rotary locking element 63 and the outside of the motor shaft 31, thereby establishing an integral clutch with the rotary locking element 63. A free end 69 of the coil spring 67 rests within the slot 39 of the rotary locking element 63. The coil spring 67 has its windings connected, e.g., by a tight grip, to the motor shaft 31 so that the rotary locking element 63 rotates with the motor shaft 31 when the non-rotating locking element 65 is in the retracted position. As can be seen in FIG. 18, the rotary locking element 63 surrounds a portion of the motor shaft 31 but can rotate relative to it, thereby only making a driving connection via the coil spring 63.

[0119] When anti-rotation locking element 65 is in the extended position as seen in Figure 17, rotation locking element 63 is held in a non-rotational position, i.e., held against rotation. The same applies to motor shaft 31, which is held against rotation via rotation locking element 63, thereby unidirectionally locking electric motor 10 in either a clockwise or counterclockwise direction.

[0120] This sixth embodiment of the electric motor 10 is able to predict and avoid damage to the locking mechanisms 40, 60 in the event of excessive force being applied to the motor shaft 31, in a manner similar to that described in the fifth embodiment.

[0121] 19 to 22 show a seventh embodiment based on the electromechanical locking mechanism of the second and sixth embodiments. In this seventh embodiment, the electromechanical locking mechanism is bidirectional. For ease of illustration, only the motor shaft 31 of the electric motor and the electromechanical locking mechanism 90 are shown.

[0122] The locking mechanism 90 has a rotary locking element 91 embodied as a locking sleeve with two rows of cams arranged in opposite directions. This means that one row of cams has an engageable side facing the clockwise rotation direction, and the other row faces the counterclockwise rotation direction. Each row of cams has four cams. The locking mechanism 90 also has two solenoids 92, 93, both mounted on the same printed circuit board 94, but on opposite sides. Each of the two solenoids 92, 93 has a non-rotating locking element 95, 96 connected to it. The non-rotating locking elements 95, 96 are positioned to engage with engageable sides 97, 98 of cams 99, 100, as in the previous embodiment. Figures 21 and 22 show both the engageable sides 97, 98 and the non-engageable sides 101, 102 of the cams 99, 100 belonging to one of the cam rows. The respective planes of the engageable sides 97, 98 face each other, but are not in the same plane. The engageable sides 97, 98 of the two rows of cams are positioned relative to the non-rotating locking elements 95, 96 of their respective solenoids so that the angular position of one of the non-rotating locking elements 91, where it engages with the engageable sides 101, 102 of its corresponding row of cams, is different from the corresponding position of the other non-rotating locking element. This is to avoid both non-rotating locking elements being loaded simultaneously. Positioning the cams in this way ensures that at least one of the rotation directions can always be reversed to release.

[0123] The locking mechanism 90 also comprises a coil spring 103 in a cup-shaped or hollow end 104 of the rotary locking element 91. The coil spring 103 has two rotationally displaceable free ends 104, 105 disposed in slots in the rotary locking element 91.

[0124] When the anti-rotation locking elements 95, 96 are in the extended position, thereby engaging the engageable sides 97, 98 of the cams 99, 100, the rotation locking element 91 is held in a non-rotational position, i.e., held against rotation. The same applies to the motor shaft 31, which is held against rotation via the rotation locking element 91, thereby bidirectionally locking the electric motor 10 in both clockwise and counterclockwise directions.

[0125] In principle, the locking mechanism 90 locks the electric motor 10 in only one direction, as the load on the motor shaft can be either clockwise or counterclockwise. Depending on the situation, the load on the motor shaft 31 can shift, for example, from clockwise to counterclockwise. In such a situation, the locking mechanism 90 can still lock the electric motor.

[0126] An electric motor having a locking mechanism 90 may also experience the failure condition described above in which an overload is applied to the non-rotating locking element 91. In such a condition, the windings of the coil spring 103 will slide against the motor shaft 31, as described above, and exert a frictional force as the motor shaft 31 rotates. Again, this essentially anticipates and prevents said damage to the locking mechanism 90.

[0127] 23 shows that an electric motor 80 comprises a controller 81 adapted to receive signals 82 from at least one rotation sensor 83, the controller comprising a processor 84, the controller being capable of performing position, speed and direction control of the electric motor. Furthermore, the controller is capable of switching on or off a locking mechanism 85 by switching on or off current to a coil 86.

[0128] 24 shows a table with an actuator mechanism 90 driven by an electric motor 10. The actuator mechanism is adapted to raise and lower the table, where rotating the motor shaft against an expected load (thereby raising the table) requires significantly more power than rotating in the opposite direction (lowering the table) with the expected load. In the case of locking mechanism embodiments 1 to 6, the unidirectionality of the locking mechanism 40, 60 is evident in that it is adapted to lock against rotation in the direction in which the weight pushes the table downward.

[0129] Specifically, FIG. 24 illustrates one possible embodiment of an actuator mechanism 110, in which a linear actuator operating according to the nut-and-spindle principle includes a motor 10 driving the actuator. A load 111 is shown in the form of a weight to be raised or lowered. The actuator's loading pattern is configured to controllably raise or lower the weight by converting motor rotation into motion that extends or retracts the length of the linear actuator, in a known manner. In this case, when the motor 10 rotates against the load, the weight moves upward. When the motor rotates with the load, the weight moves downward. As a result, moving the weight upward requires significantly more power than moving the weight downward. The locking mechanisms 40, 60 of the motor 10 are unidirectional in that the motor lock only acts in a direction that prevents the actuator mechanism 90 from moving downward when the motor is switched off and locked.

[0130] A fault condition can occur if the current to the locking mechanism is unintentionally interrupted. If such an interruption occurs while the table is descending, the solenoid loses its magnetization, causing the non-rotating locking element to suddenly contact the rotating locking element. Rotation of the rotating locking element immediately stops. Due to the inertia of the table, the impact can be large enough to damage the locking mechanism. For example, if either the non-rotating or rotating locking element breaks, the table could continue to descend uncontrollably at an increased speed. The presence of the torque-limiting clutch 36, when properly adjusted, creates slippage between the clutch 36 and the motor shaft 31. This prevents damage to the locking mechanism. Instead, the table continues to descend, but at a significantly reduced speed, or it can actually brake or stop the table in a fault condition.

Claims

1. A linear actuator (1), an electric motor (10); a spindle (4) driven by said electric motor (10); a spindle nut (6) attached to the spindle (4) and fixed against rotation, the spindle nut (6) being arranged to move between two end positions; the electric motor (10) comprising a stator mounted in a motor housing (20) and a rotor having a motor shaft (31), the electric motor (10) adapted to be electrically controlled to selectively rotate the rotor in one of two opposing angular directions; The electric motor further comprises an electromechanical locking mechanism (40, 60), the electromechanical locking mechanism (40, 60) comprising: an electromechanical transducer (41, 64) fixedly mounted relative to the motor housing (20) and comprising a non-rotating locking element (44), the electromechanical transducer (41, 64) adapted to be electrically controlled to selectively shift the non-rotating locking element (44) between an extended position and a retracted position; a rotation locking element (45, 63) attached to the motor shaft (31) and comprising at least one cam (47, 61) projecting in a direction towards the transducer (41, 64), the at least one cam (47, 61) comprising a non-engageable side opposite an engageable side; the non-rotating locking element (44) is configured to selectively engage the engageable side of the at least one cam (47, 61) to project in a direction toward the rotating locking element (45, 63) and interfere with and lock with the at least one cam (47, 61); the electromechanical transducer (41, 64) is configured to control the engagement by keeping the anti-rotation locking element (44) out of engagement with the engageable side of the at least one cam (47, 61) when the electromechanical transducer (41, 64) is energized, and the electromechanical transducer (41, 64) further comprises a spring element configured to keep the anti-rotation locking element (44) in engagement with the engageable side of the at least one cam (47, 61) when the electromechanical transducer (41, 64) is not energized; whereby the electromechanical locking mechanism (40, 60) is configured to lock the motor shaft (31) against rotation in one direction of rotation, thereby unidirectionally locking the motor (10); the electromechanical transducer (41, 64) is an electromechanical solenoid comprising a solenoid coil (42, 86) and the anti-rotation locking element (44); 1. A linear actuator comprising: the electromechanical solenoid comprising a pivot arm (43), a distal end of which constitutes the non-rotation locking element (44), the pivot arm further comprising an armature (74) configured to be actuated by a current in the coil (42, 86), and the spring element comprising a leaf spring (73) configured to bias the pivot arm (43) in a direction toward the rotation locking element (45, 63).

2. 10. The linear actuator of claim 1, wherein the electromechanical solenoid is implemented by a microminiature signal relay.

3. 3. The linear actuator according to claim 1 or 2, characterized in that the electromechanical transducer (41, 64) further comprises a support member (27) fixedly attached to the motor housing (20) and configured to support the electromechanical solenoid against tilting and shear forces.

4. A linear actuator according to any one of claims 1 to 3, characterized in that the rotary locking element (45) is shaped as a locking disc.

5. 5. The linear actuator of claim 4, wherein the longitudinal axis (33) of the motor shaft (31) and the longitudinal axis (48) of the solenoid coil (42) are parallel but not coincident.

6. A linear actuator according to any one of claims 1 to 3, characterized in that the rotational locking element (45, 63) is shaped as a locking sleeve.

7. 7. The linear actuator according to claim 6, wherein the longitudinal axis (33) of the motor shaft (31) and the longitudinal axis of the solenoid coil (42) are perpendicular to each other.

8. A linear actuator according to any one of claims 1 to 7, characterized in that the motor comprises a torque limiting clutch arranged between the rotation locking element (45, 63, 91) and the motor shaft (31).

9. 9. The linear actuator of claim 8, wherein the torque limiting clutch is a coil spring having multiple windings (36, 67) wrapped tightly around the motor shaft (31), the free end (37, 69) of the coil spring being attached to a slot (39) in the rotation locking element (45, 63).

10. 10. The linear actuator according to claim 1, further comprising a rotating member facilitating detection of rotation, said rotating member being fixedly arranged on the motor shaft, and at least one rotation sensor, said rotation sensor being fixed directly or indirectly to the motor housing.

11. 11. The linear actuator of claim 10, wherein the motor includes a printed circuit board fixedly mounted to the motor housing, and the at least one rotation sensor is mechanically and electrically connected to the printed circuit board.

12. 12. A linear actuator according to claim 11, characterized in that the printed circuit board also carries the electromechanical transducer (41, 64) and provides electrical connections.

13. 13. The linear actuator of any one of claims 10 to 12, further comprising a controller adapted to receive signals from the at least one rotation sensor, the controller comprising a processor, the controller configured to perform position, speed, and directional control of the motor, the controller further configured to switch the anti-rotation locking element between its extended position and its retracted position by switching on or off current to the solenoid coil.

14. The electromechanical locking mechanism a rotational locking element (91) comprising two sets of cams arranged in opposite directions; - two electromechanical transducers (92, 93), each arranged so that its anti-rotation locking elements selectively engage with respective engageable sides of two sets of oppositely arranged cams.

15. A linear actuator (1), an electric motor (10); a spindle (4) driven by said electric motor (10); a spindle nut (6) attached to the spindle (4) and fixed against rotation, the spindle nut (6) being arranged to move between two end positions; the electric motor (10) comprising a stator mounted in a motor housing (20) and a rotor having a motor shaft (31), the electric motor (10) adapted to be electrically controlled to selectively rotate the rotor in one of two opposing angular directions; The electric motor further comprises an electromechanical locking mechanism (40, 60), the electromechanical locking mechanism (40, 60) comprising: an electromechanical transducer (41, 64) fixedly mounted relative to the motor housing (20) and comprising a non-rotating locking element (44), the electromechanical transducer (41, 64) adapted to be electrically controlled to selectively shift the non-rotating locking element (44) between an extended position and a retracted position; a rotation locking element (45, 63) attached to the motor shaft (31) and comprising at least one cam (47, 61) projecting in a direction towards the transducer (41, 64), the at least one cam (47, 61) comprising a non-engageable side opposite an engageable side; the non-rotating locking element (44) is configured to selectively engage the engageable side of the at least one cam (47, 61) to project in a direction toward the rotating locking element (45, 63) and interfere with and lock with the at least one cam (47, 61); the electromechanical transducer (41, 64) is configured to control the engagement by keeping the anti-rotation locking element (44) out of engagement with the engageable side of the at least one cam (47, 61) when the electromechanical transducer (41, 64) is energized, and the electromechanical transducer (41, 64) further comprises a spring element configured to keep the anti-rotation locking element (44) in engagement with the engageable side of the at least one cam (47, 61) when the electromechanical transducer (41, 64) is not energized; whereby the electromechanical locking mechanism (40, 60) is configured to lock the motor shaft (31) against rotation in one direction of rotation, thereby unidirectionally locking the motor (10); the motor includes a torque limiting clutch disposed between the rotation locking element (45, 63, 91) and the motor shaft (31); 1. A linear actuator, characterized in that the torque limiting clutch is a coil spring having multiple windings (36, 67) wrapped tightly around the motor shaft (31), and a free end (37, 69) of the coil spring is attached to a slot (39) of the rotation locking element (45, 63).

16. An actuator system (9), comprising: A linear actuator (1) according to any one of claims 1 to 15, a control box (13) comprising at least a power supply (14) and a driver circuit (16) configured to drive the electric motor (10) of the linear actuator (1); a cable (12) connecting said linear actuator (1) to said driver circuit (16) in said control box (13).

17. A height-adjustable table comprising an actuator system (9) according to claim 16.

Images