LINEAR DRIVE SYSTEM

Abstract

A linear drive system having an actuator (10), which can be moved in a translatory manner by means of an electric drive (12) and which is coupled to a mechanical energy storage (16) in the form of a spring (32) such that in the event of a loss of energy at the electric drive (12) or in an emergency operation the actuator (10) travels to a predeterminable position and in so doing exerts an actuating force, characterized in that one free end of the spring (32) is supported at the free end of the spindle housing (20) and the other free end of the spring (32) is supported at a closing part (36) of the actuator (10) or at the actuator (10) itself and is tensioned in every travel position of the actuator (10).

Claims

1. A linear drive system having an actuator (10), which can be moved in a translatory manner by means of an electric drive (12) and which is coupled to a mechanical energy storage (16) in the form of a spring (32) such that, in the event of a loss of energy at the electric drive (12) or in an emergency operation, the actuator (10) travels to a predeterminable position and in so doing exerts an actuating force, wherein the electric drive (12) can be used to control a spindle drive (18) moving the actuator (10) in a translatory manner, wherein said spindle drive (18) has a threaded spindle (22) rotatably guided in a spindle housing (20), wherein said threaded spindle (22) interacts with the actuator (10) for the latter's motion via an adjustment nut (24) in engagement with the threaded spindle (22), wherein said adjustment nut (24) is non-rotatable but can be moved in a translatory manner in the spindle housing (20), and wherein said actuator (10) has a cylindrical tube (30) which, in each of its travel positions, is partially guided in the spindle housing (20) via the adjustment nut (24) and the free end (31) of which projects out of the spindle housing (20), characterized in that one free end of the spring (32) is supported at the free end of the spindle housing (20) and the other free end of the spring (32) is supported at a closing part (36) of the actuator (10) or at the actuator (10) itself and is tensioned in every travel position of the actuator (10).

2. The linear drive system according to claim 1, characterized in that the closing part (36) is projectingly arranged on the free end (31) of the actuator (10).

3. The linear drive system according to claim 1 or 2, characterized in that the actuator (10) has a cylindrical tube (30), which is partially guided in the spindle housing (20) via the adjustment nut (24) in each of its travel positions.

4. The linear drive system according to claim 1, characterized in that in emergency operation the actuator (10) preferably extends or retracts to a maximum and the spring (32) thereby acts permanently on the actuator (10) in a pushing or pulling manner, and in that in normal operation the spindle drive (18) uses the electric drive (12) to apply a pulling or pushing force to the actuator (10) relative to the stationary spindle housing (20).

5. The linear drive system according to claim 1, characterized in that in emergency operation the spring (32) pulls or pushes the actuator (10) into its predetermined position, resulting in a passive rotation of the threaded spindle (22) and the rotor of the electric actuator (12) coupled thereto.

6. The linear drive system according to claim 1, characterized in that the electric drive (12) is operatively connected to the threaded spindle (22) via a transmission or a belt drive (38).

7. The linear drive system according to claim 1, characterized in that the longitudinal axis (40) of the electric drive (12) is parallel to the longitudinal axis (26) of the spindle drive (18).

8. The linear drive system according to claim 1, characterized in that the electric actuator (12) and the spindle actuator (18) are interconnected via a connecting console (56), and in that the actuator (10) acts on a force transducer, such as a valve or a fitting, at least in emergency operation.

Description

[0016] Below, the solution according to the invention is explained in more detail based on an exemplary embodiment according to the drawing. In the figures, in principle and not to scale,

[0017] FIG. 1 shows a perspective view on the linear drive system according to the invention; and

[0018] FIG. 2 shows the linear drive system according to FIG. 1 partly in view, partly in longitudinal section.

[0019] Because of their easy integrability and freedom from maintenance, electric cylinders are often used to implement linear motions. In these cylinders, a screw drive is used to convert a rotary motion of the drive shaft of an electric drive into a linear motion of an actuator. Such electric cylinders are known from the prior art, for instance from DE 20 2014 104 735 U1.

[0020] FIG. 1 shows a linear drive system according to the invention with an actuator 10, which can be moved in a translatory manner by means of an electric drive 12 in the form of an electric motor 14. The actuator 10 is coupled to a mechanical energy storage device 16 in such a way that in the event of a loss of energy at the electric actuator 12, i.e., in an emergency mode, the actuator 10 travels to a predeterminable position and in so doing exerts an actuating force. For this purpose, the electric drive 12 can be used to control a spindle drive 18 moving the actuator 10 in a translatory manner.

[0021] The spindle drive 18 has a threaded spindle 22 rotatably guided in a spindle housing 20, wherein said spindle 22 interacts via an adjustment nut 24 in engagement therewith with the actuator 10 for the latter's motion in the direction of a longitudinal axis 26 of the threaded spindle 22. The adjustment nut 24 is guided in the spindle housing 20 so as to be non-rotatable about the longitudinal axis 26, but movable in a translatory manner along the longitudinal axis 26. To do so, the spindle housing 20 is hollow and has a non-rotationally symmetric, in particular a rectangular, preferably square, internal cross-section, in particular having rounded edges. The outer cross-section of the adjustment nut 24 largely matches the inner cross-section of the spindle housing 20 such that the adjustment nut 24 is guided non-rotatably in the spindle housing 20. The threaded spindle 22 is formed as a cylindrical rod having threads on its outer periphery which engage with threads on the inner periphery of the adjustment nut 24. The actuator 10 has a cylindrical tube 30 that is guided via the adjustment nut 24 in a non-rotatable manner. In each of its travel positions, the cylindrical tube 30 is partially disposed inside the spindle housing 20 and partially its free end 31 protrudes from the spindle housing 20, the free end 33 of which is flush with the free end 35 of the threaded spindle 22.

[0022] The mechanical energy storage 16 is formed as a spiral compression spring 32, the one free end of which rests against the free end face 34 of the spindle housing 20 and the other free end of which rests against an end part 36, which arranged transversely to the longitudinal axis 26 of the actuator 10, closes the free end 31 of the actuator 10 and is formed as a circular disc 37, the radius of which is larger than the radius of the cylinder tube 30 of the actuator 10. At least during normal operation, the compression spring 32 is tensioned in every travel position of the actuator 10. A disc spring or a disc spring assembly (both not shown) can also be used instead of the coil spring 32 shown in the Figures.

[0023] In normal operation, in which the electric drive 12 is supplied with sufficient electric current, the spindle drive 18 works against the compression spring 32 when retracting into the spindle housing 20 and, under the action of the electric drive 12, applies in relation to the stationary spindle housing 20 a pulling force to the actuator 10 or is supported by the compression spring 32 when extending from the spindle housing 20, thus applying in relation to the stationary spindle housing 20 a pulling force to the actuator 10 under the action of the electric drive 12, wherein the absolute value of said pulling force is smaller. In normal operation, the compression spring 32 is permanently tensioned in every travel position of the actuator 10.

[0024] In emergency operation, on the other hand, in which the electric actuator 12 experiences a power failure, the electric drive 12 no longer acts on the actuator 10, so that the actuator 10 extends from the spindle housing 20 by means of the pressurized disc 37 under the action of the spring force of the relaxing compression spring 32. The spindle drive 18 can be used to retract or extend the electric linear drive to the maximum in an “extended” normal mode until all coils of the compression spring 32 are in full contact or until the adjustment nut 24 hits the end stop at the free end 33 of the spindle housing 20. In the solution according to the invention, however, the maximum free inward and outward motions of the actuator 10 of the spindle drive 18 are selected in such a way that the compression spring 32 retains its inherent tension to such an extent that the emergency actuation of a force transducer (not shown), such as a valve, which is connected to or can be actuated by the system, is ensured.

[0025] In an exemplary embodiment not shown in the figures, the spring 32 can also be formed as a tension spring, one free end of which is firmly connected to the spindle housing 20 and the other free end of which is firmly connected to the end part 36 of the actuator 10. In normal operation, the spindle drive 18 is then supported in the opposite direction, as described above for the compression spring 32, by the tension spring when retracting into the spindle housing 20 and works against the spring's tension force when extending out of the spindle housing 20. In every travel position of the actuator 10 in normal operation, the tension spring is also permanently kept under inherent stress. In emergency operation, the effect of the electric actuator 12 on the actuator 10 ceases again, such that the actuator 10 moves into the spindle housing 20 under the force of the tension spring. It goes without saying that in this case the force transducer has to have a different “fail-safe” design than in the case with the compression spring 32, where the valve is pressed into its fluid-locking position in an emergency.

[0026] While the compression spring 32 pushes the actuator 10 or the tension spring pulls the actuator 10 into its predetermined actuating position for the force transducer, the rotor of the electric drive 12, which is de-energized in an emergency, is passively driven by a rotation of the threaded spindle 22 in the way of a generator, but this does not inhibit the motion of the actuator 10.

[0027] The electric drive 12 is in operative connection with the threaded spindle 22 via a belt drive 38, wherein the further longitudinal axis 40 of the electric drive 12 is arranged in parallel to the longitudinal axis 26 of the spindle drive 18. Instead of a belt drive 38 having a drive belt 42, which is wrapped around two friction pulleys 44 (driving and driven pulleys) or as a toothed belt 46, which is wrapped around two toothed pulleys 48, a gear drive having meshing toothed wheels (not shown) can also be used, omitting the belt 42.

[0028] The rotor or output shaft 50 of the electric motor 14 extends in parallel to the threaded spindle 22 and its drive shaft 52, which is guided at the ends in bearing points 54 of the usual construction. However, the motor 14 and the threaded spindle 22 can also be arranged in a U- or L-shape relative to each other. All transmission components for the drive shaft 52, including the latter, are guided in a console 56, closed off from the outside, which can be set up on the floor or a machine part by means of a foot part 58 in a pivotable manner.

[0029] Preferably, it is provided that in emergency operation the actuator 10 acts on a force transducer not shown in the figures, such as a valve or a fitting, wherein said force transducer is brought into a predeterminable position within a predeterminable time and, if necessary, is held in this position by an end stop. For this purpose, the actuator 10 can be firmly connected to the force transducer, if necessary.

[0030] Preferably, a frequency converter (not shown in the figures) is provided and operatively connected to the electric drive 12 and open-loop or closed-loop controls the torque and/or the rotation speed of the electric drive 12. The drive 12 is formed as a synchronous or asynchronous electric motor 14, which can be controlled via an inverter. In addition, a controller (not shown in the figures) is provided to control the frequency converter.

[0031] In a position controlling system, the input end of the controller for determining the position of an adjusting part of the force transducer can be electrically connected to an encoder or displacement measuring system that detects the travel distance of the adjusting part and/or the actuator 10. It is also conceivable that the controller is connected to a sensor for detecting the position and/or a sensor for detecting the rotation speed and/or the rotation angle of the electric motor 14. Alternatively, the position and/or the rotation speed of the motor can also be estimated with the aid of a stored motor model. Depending on the position and/or the rotation speed of the motor 14 in addition to the thread pitch of the threaded spindle 22, the controller can control the travel position of the adjustment part and the actuator 10 of the linear drive accordingly via the associated controlling system and thus also without a displacement encoder.

[0032] In a force controlling system, the input side of the controller may be connected to a load cell or torque measuring bolt for determining the force exerted by the actuator 10. Alternatively, the torque of the motor 14 can be estimated with the aid of the motor model. Depending on the torque and the thread pitch of the threaded spindle 22, the force can be determined and the force exerted by the actuator 10 is used to control the linear drive.

[0033] The frequency converter preferably has so-called insulated gate bipolar transistors (IGBTs) which are designed to be self-blocking, i.e. in a non-controlled state, for instance in the event of a power failure, they are open in the sense of a “fail-safe” solution, which helps to ensure that there is no undesirable braking effect of the linear motion due to an electric motor 14 in generator operation, so that the travel position of the actuator 10, which can be specified in emergency operation, can be approached unhampered.