DEVICE

Field of the Invention

The present invention relates to electromechanical linear actuators, in particular to an electromechanical drive unit. Preferably the invention can be used for drive units to provide high-speed motion of an output rod.

Background Art

An important object in designing high-speed electromechanical linear actuators is to provide reliable stop of its output rod at extreme positions without mechanical damage to the drive unit and without jamming.

Use of electromechanical drive units comprising damping devices and based on a roller screw pair for transforming rotary motion into linear motion and controlling machinery and mechanisms connected thereto is known in the art.

RU2009138441 discloses an electromechanical drive unit comprising a damping device. Said electromechanical drive unit can be used for moving the cutoff valve in a turbine set control system.

The above electromechanical drive unit utilizes a roller screw pair, and the drive unit further comprises an electric motor with the stator thereof enclosing a hollow rotor having a base end and a working end. The working member of said drive unit is a retractable rod comprising a lumen and mounted coaxially with the rotor in such manner that the rotor lumen receives one end of the retractable rod, said end having a barrel shape and comprising a bottom end and a working end. The rod is mounted in such manner that it is prevented from axial rotation. The roller screw pair in the above electromechanical drive unit is formed by a threaded sleeve, rollers and a screw. The threaded sleeve comprises an inner thread, is provided within the barrel and is fixedly connected thereto. The rollers comprise an outer thread and are provided within the threaded sleeve around the circumference thereof in such way that the rollers' axes are parallel to the rotor axis. The screw comprises an outer thread, a support end and a drive unit end. The screw is provided within the threaded sleeve coaxially with the rotor in such manner that the screw thread interacts with the roller threads; the rotor is fixedly connected to the support end of the screw. The drive end of the screw is received in the lumen of the retractable rod.

Travel of the retractable rod travel to fully extended and fully retracted positions is limited by elastic members, such as two disc spring packs mounted at the opposite ends of the barrel. Furthermore, disc spring packs act as a damping device for damping retractable rod bumps, as said packs damp the kinetic energy of moving parts of the electromechanical drive unit when the retractable rod reaches extreme positions, i.e. the fully extended position and the fully retracted position.

The first disc spring pack is provided at the bottom end of the barrel, such that the springs extend around the base of the retractable rod. The second disc spring pack is placed parallel to the first pack on a flange annularly covering the opposite (i.e. working) end of the barrel. Springs of the second pack extend around the screw.

Outward extension of the retractable rod is limited by the end of the body housing the electric motor, with the first disc spring pack abutting said body when the retractable rod is in fully extended position. When the retractable rod approaches fully extended position, the first disc spring pack is displaced linearly, contacts the end of stationary body from the inside and is pressed against said body. As a result, the retractable rod is forced to stop in extended position with concurrent damping of the resulting bumps.

The reverse travel of the retractable rod, when said rod is displaced into the body, is internally limited by the end of the rotating rotor, with the second disc spring pack abutting said rotor when the retractable rod is fully retracted. When the retractable rod approaches fully retracted position, the second disc spring pack is displaced linearly, contacts the end of rotating rotor from the inside and is pressed said rotor. As a result, the retractable rod is forced to stop.

In practical use of the electromechanical drive unit disclosed in RU2009138441, however, insufficient damping in extreme positions of the retractable rod moving at high speed was discovered, leading to unwanted bumps of the retractable rod upon reaching extreme positions.

Patent application EA201200702 discloses an electromechanical drive unit considered to be prior art for the present invention. Said electromechanical drive unit overcomes the disadvantages of the drive unit of RU2009138441. In contrast to the drive unit of RU2009138441, one of the elastic limiting members in the electromechanical drive unit of the prior art is fixedly mounted on the inside of the base end of the rotor, adapted to rotate along with the rotor and adapted to contact the working end of the barrel, while another elastic limiting member is fixedly mounted on the outside of the bottom end of the threaded sleeve barrel and adapted to contact the working end of the rotor from the inside. The damping device of the above electromechanical drive unit comprises two disc spring packs, wherein one of said packs is rotated during drive unit operation, and the other pack is not rotated. The non- rotating disc spring pack is adapted to move in a reciprocal manner along with the retractable rod, while the rotating disc spring pack is adapted to rotate along with the rotor.

As the rod being retracted approaches fully retracted position, in which the rod is fully retracted, a gradually developing interaction between the rotating disc spring pack and the non-rotating rod, particularly with the working end of the barrel formed integrally with the rod, occurs. Damping effect is obtained due to gradually increasing frictional torque between the springs of the rotating pack and the working end of the barrel developed as a result of the interaction therebetween.

When the retractable rod approaches fully extended position, in which the rod is fully extended, the non-rotating disc spring pack is displaced linearly, contacts the rotating working end of the rotor from the inside and is pressed against said rotor. The gradually developing interaction between the non-rotating disc spring pack and the working end of the rotating rotor leads to a gradual increase in frictional torque defining the damping effect.

Braking system of the above electromechanical drive unit is highly efficient in use, however, the retractable rod thereof tends to lock in extreme positions while moving at high speed, which prevents the rotor from starting rotation when driven by torque generated by the electric motor, thus requiring additional operations for releasing the drive unit from the locked state. Therefore, it is an object of the present invention to eliminate rotor rotation locking in braked state.

Summary of the Invention

The object is achieved by a linear electromechanical drive unit with a new structure of damping devices.

In particular, the object is achieved by an electromechanical drive unit comprising an electric motor comprising a hollow rotor and a stator disposed around the rotor, a shaft mounted coaxially with the rotor and restricted from rotation around the axis thereof, wherein the rotor rotation is transformed into reciprocal movement of the shaft, and one end of the shaft is received in the rotor; an elastic limiting member adapted to restrict shaft travel, wherein in the present electromechanical drive unit, the elastic limiting member is rotatably mounted on said one end of the shaft and adapted to rotate at a restricted angle with respect to the shaft.

In contrast to the prior art drive unit, in the present device, the elastic limiting member forming a damping device is mounted at one end of the shaft, said end received in the rotor and adapted for restricting rotation with respect to the shaft. This results in decreasing torque needed to be generated by the electric motor to start rotation of the rotor, thus eliminating additional operations for releasing the drive unit from the locked state.

In another embodiment, the elastic limiting member of the electromechanical drive unit is a disc spring.

In yet another embodiment, the elastic limiting member of the electromechanical drive unit is a multi-blade disc spring. In yet another embodiment, the electromechanical drive unit further comprises a threaded sleeve having inner thread and adapted to rotate along with the rotor, and rollers having outer thread provided within the threaded sleeve around the circumference thereof in such manner that axes of the rollers are parallel to the rotor axis, and the thread of the rollers engages the inner thread of the sleeve, wherein the shaft comprises outer thread engaging the thread of the rollers.

In yet another embodiment, the electromechanical drive unit further comprises a retractable rod mounted coaxially with the rotor and fixedly connected with the shaft.

The object is also achieved by an elastic limiting member for an electromechanical drive unit, said member having a disc shape, adapted to be mounted on the drive shaft, and comprising peripheral cutouts formed along the periphery of the elastic member, an opening positioned in the center of the elastic member, and at least one limiting cutout positioned at the edge of the opening and adapted to engage at least one corresponding protrusion, thus limiting rotation of the elastic member with respect to the shaft.

Brief Description of the Drawings

Following is the detailed description of specific embodiments of the present invention with reference to accompanying drawings, wherein :

Fig. 1 shows a schematic illustration of the electromechanical drive unit;

Fig. 2 shows a schematic cross-sectional view along the line A-A of the electromechanical drive unit of Fig. 1;

Fig. 3 shows a schematic cross-sectional view along the line 5-B of the electromechanical drive unit of Fig. 1; Fig. 4 shows one of the possible embodiments of elastic member attachment according to the present invention.

Description of the Invention

According to one embodiment shown in Fig. 1, the electromechanical drive unit comprises an electric motor 17 comprising a hollow rotor 3 and a stator 7 arranged around the rotor, a threaded sleeve 1, rollers 6 and a shaft formed by a screw 2, wherein sleeve 1, rollers 6 and the screw 2 form a roller screw pair. The threaded sleeve 1 has inner thread, the sleeve being fixedly connected to the hollow rotor 3 and rotatably mounted in the drive body 12 by ball bearings. The rollers 6 have outer thread and are arranged within the threaded sleeve 1 around the circumference thereof in such way that the rollers' axes are parallel to axis of the rotor 3. The screw 2 has outer thread, and further has a support end and a drive end. The support end is the upper end in Fig. 1, while the drive end is the lower end in Fig. 1. The elastic member 5 is mounted at the support end of the screw 2 and adapted for restricted rotation with respect to the screw 2. The support end of the screw 2 is received into the rotor 3 in such manner that the elastic member 5 can be displaced within the hollow rotor 3 and is adapted to engage the inner surface of the rotor in extreme positions. The screw 2 is at least partially arranged within the threaded sleeve 1 coaxially with the rotor 3 in such manner that thread of the screw engages thread of the rollers 6.

In this embodiment, the elastic member 5 is an elastic limiting member having a disc (i.e. short cylinder) shape and is preferably made of metal. The elastic member 5 comprises peripheral cutouts formed along the periphery of the elastic member, an opening formed in the center of the elastic member, and at least one limiting cutout formed at the edge of the opening. The peripheral cutouts in the elastic member 5 are used to equally distribute pressure. The limiting cutout is used for engaging at least one corresponding protrusion to restrict rotation of the elastic member with respect to the shaft. The elastic member configuration (i.e., thickness, diameter, cutout pattern) is selected in a known way to provide maximum flexibility (maximum travel), at which metal stress values are not exceeded, while at the same time providing required operational properties of the elastic member. Furthermore, in order to provide optimal characteristics, thickness of the elastic member can vary.

Fig. 4 shows one of the embodiments of the elastic member 5 attachment. The elastic member 5 is sleeved on the screw 2, and then pressed by means of a ring comprising two limiting protrusions. In other embodiments, a smaller or larger number of limiting protrusions can be used. Then the ring is fixed with respect to the screw 2 in such manner that the attachment of the elastic limited member is prevented from rotation by the screw 18. The elastic member is adapted to rotate around the screw. When the elastic member 5 is rotated, limiting cutouts thereof interact with the limiting protrusions of the ring, thus limiting rotation of the elastic member 5 around the screw 2.

According to this embodiment, the working or actuating driving member is the retractable rod 4 mounted coaxially with the rotor 3. The retractable rod 4 is prevented from rotation about the longitudinal axis thereof by means of an anti-rotation device comprising a rocker 10 mounted on the retractable rod 4 extending generally perpendicular thereto and fixedly connected thereto. Two ends of the rocker 10 comprise grooves (Fig. 2) engaged with the corresponding protrusions on the body 11. The drive end of the screw 2 is fixedly connected to the retractable rod 4 or can be formed integrally therewith. The outer end of the retractable rod 4, which forms the actuating member of the electromechanical drive unit, is moveably connected to the controlled object. The controlled object can be, e.g. a steam distribution valve, a damper valve, a lever, a hatch, etc.

Multiple sets of pole magnets 9 are attached to the rotor 3 coaxially with respect to each other and enclosed by sets of pole coils of the stator 7, respectively, arranged coaxially and adjacent with respect to each other.

The electromechanical drive unit further comprises a feedback sensor 14 mounted on the cylindrical sleeve 19 of the rotor 3 and covered by a cap 15 on the outside. The feedback sensor can be formed by, e.g. a rotor angular position sensor (for determining motion parameters), a retractable rod linear position sensor, etc.

In operation, rotation of the hollow rotor 3 of the electric motor 17 causes rotation of the sleeve 1, the inner thread thereof engaging with the thread of enclosed rollers 6 and causing them to rotate about their axes. The thread of the rollers 6 further engages the outer thread of the screw 2. The rotation of rollers 6 causes linear motion of the screw 2 fixedly connected to the retractable rod 4 and driving the controlled object to move progressively.

Travel of the retractable rod 4 to fully extended and fully retracted positions is limited by the elastic member 5 mounted at the support end of the screw 2 and adapted for limited rotation with respect to said screw 2. The screw 2 is fixedly connected to the retractable rod 4. When the retractable rod reaches its extreme positions, the elastic element starts pressing against the inner surface of the rotor 3 and, due to forces of friction, starts rotating with the rotor, and due to rotation limiting, upon rotating to a determined angle, the elastic element stops rotating and at least one of the outer surfaces of the elastic element prevents the rotor from rotating by means of forces of friction, and subsequently, the mechanism stops. Angle of rotation is determined by the elastic member travel required to obtain the necessary axial force and/or by the transfer function of the screw mechanism. The longer distance has to travel the elastic member to develop the necessary axial force, the wider has to be the angle for free rotation of the elastic member. The lower is the transfer function, the wider has to be the angle for free rotation of the elastic member. The angle of rotation is preferably 5° or more, as a narrower angle is insufficient for the electric motor to generate torque so as to reliably start rotation of the rotor. Most preferably, the rotation angle is in the range of 5° to 30°.

When it is necessary to start rotation in the opposite direction from the locked position, the torque for starting rotation in the opposite direction is several times less than the braking torque due to the fact that the elastic member has a certain angular degree of freedom with respect to the screw, and due to the fact that the contact radius between the elastic member and the screw (i.e., the distance between the axis of rotation and the point of contact between the elastic member and the screw) is much smaller than the contact radius between the elastic member and the rotor (i.e. the distance between the axis of rotation and the point of contact between the elastic member and the rotor). Therefore, the elastic member 5 allows to decrease torque needed to be generated by the electric motor to start rotation of the rotor, thus eliminating additional operations for releasing the drive unit from the locked state. Although the present invention is described herein with respect to a specific embodiment, various changes and modifications may be made without departing from the spirit and scope of the present invention, as defined in the appended claims.

Reference Numerals in the Figures

1. Threaded sleeve

2. Screw

3. Electric motor rotor

4. Retractable rod

5. Elastic limiting member

6. Rollers

7. Stator

8. Bearing unit for fixating the threaded sleeve

9. Pole magnets

10. Anti-rotation device rocker

11. Electromechanical drive body

12. Bearing unit body

13. Electric motor body

14. Feedback sensor

15. Feedback sensor covering cap

16. Mounting flange

17. Electric motor

18. Elastic limiting member attachment screw

19. Cylindrical sleeve