WO2012161650A1

WO2012161650A1 - Actuator

Info

Publication number: WO2012161650A1
Application number: PCT/SE2012/050558
Authority: WO
Inventors: Krister Kumlin
Original assignee: Reac AB
Current assignee: Reac AB
Priority date: 2011-05-25
Filing date: 2012-05-24
Publication date: 2012-11-29
Anticipated expiration: 2013-11-25
Also published as: SE535816C2; SE1150484A1

Abstract

An actuator comprising a motor (1) which comprises a rotatable drive shaft (2), a first spindle (3) which is rotatably arranged to be driven directly or indirectly by the drive shaft (2) of the motor, and a piston rod (4) which is arranged to perform a linear translational movement in an axial direction relative to the first spindle between a first end position and a second end position while the first spindle is rotating. The actuator is characterized in that it furthermore comprises a rotatable second spindle (5) which the drive shaft of the motor is arranged to directly or indirectly drive, wherein the second spindle is arranged to drive the rotation of the first spindle via a carrier (6, 7, 40).

Description

Actuator

The present invention relates to an actuator comprising:

a motor which comprises a rotatable drive shaft, - a first spindle which is rotatably arranged,

a piston rod which is arranged to perform a linear translational movement in an axial direction relative to the first spindle between a first end position and a second end position while the first spindle is rotating, and

a rotatable second spindle which the drive shaft of the motor is arranged to directly or indirectly drive, wherein the second spindle is arranged to drive the rotation of the first spindle via a carrier.

US 7,066,041 B2 discloses a previously known actuator. The disclosed actuator comprises a motor, a worm gear having a worm and a worm wheel, a spindle, a spindle nut, and a piston rod. The motor is arranged to rotatably drive the worm, which in its turn drives the worm wheel. The worm wheel is fixedly arranged on the rearward portion of the spindle to cause the spindle to rotate. The spindle nut is arranged to perform a translational movement along the spindle during rotation of the

spindle, and the piston rod is connected to the spindle nut to perform an axial translational movement. A well- known problem with this type of actuators is that the worm gear and/or motor of the actuator may run the risk of being damaged if the piston rod is subjected to radial and/or transverse forces .

US 2005/0103138 Al discloses an actuator for partially solving the above-mentioned problem. The actuator has a rotatable screw which is driven by a driving assembly.

A spring- loaded safety nut, which takes over the load if the load on the main driving nut becomes too great, is arranged on the rotating screw. However, this design is rather complicated and there is risk that the spring will snag on the nut and not function as it is intended to do. EP 0 577 541 Al discloses an actuator having a rotating spindle, which is driven by a motor via a gear drive. The spindle can be disconnected from the gear drive in that one gear is spring- loaded. This solution is rather complicated and expensive, and also here there is an apparent risk that the disconnecting function will break down .

US 3,682,283 discloses an actuator comprising a motor shaft which, via a splined coupling, drives a first spindle in the form of a screw to rotate. The screw, in its turn, drives a piston rod to perform a linear

translational movement relative to the first spindle between a first end position and a second end position. In the event that the piston rod is subjected to radial and/or transverse forces, the drives and/or motor of the actuator may run the risk of being damaged. Also the splined coupling runs the risk of being damaged.

EP 0 811 461 Al discloses an actuator, in which a motor shaft drives the feed screw of the actuator via a

separate coupling member. The coupling member is designed with axial recesses which are connected to the ends of the motor shaft and the feed screw, respectively. Also this actuator runs the risk of being damaged if its piston rod is subjected to radial and/or transverse forces .

The present invention seeks to provide an actuator whose piston rod can be subjected to radial and/or transverse forces, and which is not afflicted with the problems and disadvantages mentioned above . The actuator according to the invention is characterized in that that the carrier is elongated and comprises a first end portion and a second end portion, wherein the first end portion is arranged in an axial cavity of the first spindle and wherein the second end portion is arranged in an axial cavity of the second spindle, that the carrier has a radial and axial play in at least one of the cavities, and that the carrier acts as a torsion spring, which makes the second spindle mechanically isolated from the first spindle.

Figure 1 shows an actuator of a preferred embodiment of the invention, where a carrier is arranged between a rotatable first spindle and a rotatable second spindle and where the piston rod of the actuator is retracted to an inner end position.

Figure 2 shows the actuator of Figure 1, where the piston rod is extended to an outer end position.

Figure 3 shows a cross-section of the actuator, where a preferred profile of the carrier can be seen.

Figures 1-2 show an actuator comprising a motor 1, which comprises a rotatable drive shaft 2 and a motor housing 8.

The actuator furthermore comprises a gear drive in the form of a bevel gear 9, 10 comprising a first gear wheel 9 which is arranged on, or inside, the drive shaft 2 of the motor, and a second gear wheel 10 which is

perpendicularly arranged relative to the first gear wheel 9. The, second gear wheel 10 cooperates with the first gear wheel 9 such that the rotation of the first gear wheel 9 drives the second gear wheel 10 to rotate. The bevel gear 9, 10 is surrounded by a bearing housing 13. Furthermore, the actuator comprises a forward, elongated, rotatable first spindle 3 which extends between a

forward, first end 14 and a rearward, second end 15. The first spindle 3 is delimited externally by a lateral surface which is provided with a thread 11 along the entire extension thereof. A bearing 27 is arranged between the lateral surface of the first spindle 3 and the bearing housing 13 at a predetermined distance near the rearward, second end 15 of the first spindle 3. At its rearward, second end 15, the first spindle 3 exhibits an axial cavity 16 which is delimited by an inner

delimiting surface 17.

The actuator furthermore comprises an elongated, sleeve- shaped piston rod 4 which extends between a forward, first end 18 and a rearward, second end 19. The piston rod 4 exhibits an axial cavity 20 which is delimited by a substantially circularly cylindrical, inner delimiting surface 12 of the piston rod 4. The piston rod 4

comprises an internal thread 21 which is arranged along a longitudinal portion of said delimiting surface 12 near the second end 19 of the piston rod 4. The thread 21 of the piston rod is arranged to cooperate with the external thread 11 of the first spindle 3 in such a way that the rotation of the first spindle 3 drives the piston rod 4 to move in a linear translational movement relative to the first spindle 3 between a first, inner end position, which is shown in Figure 1, and a second, outer end position, which is shown in Figure 2. The inner end position and the outer end position define a length of stroke of the piston rod 4. The outer lateral surface 37 of the, piston rod 4 is smooth.

A forward, first fixing element 22 is arranged at the forward, first end 18 of the piston rod 4. The fixing element 22 exhibits a through hole 23 which is intended to be used for attaching the first fixing element 22 to a first, not shown, structural element, wherein the actuator is intended to actuate the first structural element relative to a second, not shown, structural element. The attachment of the piston rod 4 to the first structural element prevents a rotation of the piston rod 4 about its own axis when the first spindle 3 rotates. The actuator also comprises a rearward, second fixing element 35 which is arranged at the bearing housing 13. The rearward, second fixing element 35 exhibits a through hole 36 which is intended for attaching the second fixing element 35 to the previously mentioned second structural element .

The actuator also comprises a piston tube 24 which extends between a free, forward, first end 25 and a rearward, second end 26. At its rearward, second end 26, the piston tube 24 is fixedly connected to the bearing housing 13. In the axial direction, the piston tube 24 has a length such that it surrounds the forward, first end 14 of the first spindle 3 with its forward, first end 25. An end plate 28 is arranged at the free, forward, first end 21 of the piston tube 21. The end plate 28 exhibits a circular hole for the piston rod 4. A seal is arranged in the circular hole for sealing against the smooth^' lateral surface 37 of the piston rod 4.

Furthermore, the actuator comprises a rearward,

elongated, rotatable second spindle 5 which extends between a forward, first end 29 and a rearward, second end 30, wherein the second spindle 5 exhibits an outer delimiting surface 33 between the two ends 29, 30. The rotational axis of the second spindle 5 is in line with the rotational axis of the first spindle 3 and

perpendicular to the rotational axis of the drive shaft 2. The second gear wheel 10 is fixedly arranged on the outer delimiting surface 33 so that the drive shaft 2 of the motor, when rotating, drives the rotation of the second spindle 5. The second spindle 5 is journalled by- means of a bearing 34 which is arranged between the outer delimiting surface 33 and the bearing housing 13. The rotational axis of the second spindle 5 is arranged in line with the rotational axis of the first spindle 3. At its forward, first end 29, the second spindle 5 exhibits an axial cavity 31 which is delimited by an inner delimiting surface 32. The rearward, second end 15 of the first spindle 3 is facing the forward, first end 29 of the second spindle 5, which ends 15, 29 are arranged at a predetermined distance from each other. Finally, the actuator comprises a separate, elongated carrier 6 which is arranged to transfer the rotation of the second spindle 5 to the first spindle 3, i.e. that the second spindle 5 drives the first spindle 3 to rotate via the carrier 6. As mentioned previously, the rotation of the second spindle 5 is driven by the drive shaft 2 of the motor via the bevel gear 9, 10. The carrier 6 comprises a forward, first end portion 38 and a rearward, second end portion 39. The forward, first end portion 38 is arranged in the axial cavity 16 of the first spindle 3, and the rearward, second end portion 39 of the carrier 6 is arranged in the axial cavity 31 of the second spindle 5. The carrier 6 is arranged in the two cavities 16, 31 such that the carrier 6 has a radial and axial play in the two cavities 16, 31. The cavities 16, 31 and the end portions 38, 39 of the carrier 6 each exhibit a non-circular profile, which enables the carrier 6, when rotating, to cooperate with the delimiting surfaces 17, 32 of the cavities so that the carrier 6 transfers the rotation of the second spindle 5 to the first spindle 3. The dimensions of the carrier 6 and the insertion length thereof into the respective axial cavity 16, 31. will of course depend on the fields of application of the actuator and the capacity of the actuator. In a preferred exemplary embodiment, the carrier has a length between its ends of 40-70 mm, preferably 50-60 mm, and a cross-sectional dimension of 3-9 mm, preferably 4-8 mm. The insertion length of the carrier 6 into the respective axial cavity 16, 31 is then about 10-30 mm. The axial play can, for example, be 2-5 mm, and the radial play is about 0.1-0.5 mm. The carrier is made of a material that is resilient, which means that the elongated carrier 6 also acts as a torsion spring. The design according to the invention with an actuator comprising a carrier 6 and a second spindle 5 as above provides a number of advantages relative to the prior art. Because of the fact that the carrier 6 has a radial and axial play in the cavities, the second spindle 5 will not be affected if the first spindle 3 is subjected to radial and/or transverse movements. Since the carrier 6 acts as a torsion spring in that the material of the carrier is resilient, the carrier will be twisted

slightly, to then return, if the piston rod reaches an end position or contacts an external, fixed obstacle. This further contributes to mechanically isolating the rearward, second spindle 5 from the forward, first spindle 3. The radial and axial plays, together with the torsion spring' action of the carrier, means that the bevel gear, motor shaft, motor drive etc. are mechanically protected from this type of stresses, and that they do not run the risk of being damaged in the same way as the prior art. In addition to protecting the rearward, second spindle 5 mechanically, the carrier 6 contributes to making the actuator quieter during operation than a conventional actuator. This is especially true in connection with starting and stopping of the actuator, since this can be done more advantageously thanks to the torsion spring action of the carrier. Figure 3 shows a cross -section of the actuator, showing a suitable profile of the carrier 6 and the cavities 16, 31. In the shown example, the cross section of the carrier is constituted by a round rod having two

bevelled, longitudinal sides, which sides are opposite to each other. It is appreciated, however, that other non- circular profiles of carriers 6 and axial cavities 16, 31 are possible, such as e.g. rectangular profiles. In the foregoing, the invention has been described based on a number of specific embodiments. It is appreciated, however, that other embodiments and variants are possible within the scope of the following claims. For instance, it is not necessary that the second spindle is driven by the drive shaft of the motor via a bevel gear. Naturally, other types of drives, such as e.g. worm gears and gear drives or other transmissions from the motor to the second spindle, are possible. Furthermore, the drive shaft could drive the spindle directly, i.e. without using a gear box between the drive shaft and the second spindle. In such an embodiment, the drive shaft is arranged linearly with respect to the second spindle. Furthermore, the translational movement of the piston rod relative to the first spindle, while the first spindle is rotating, can be configured in alternative ways. For instance, the first spindle can instead exhibit an axial cavity with an internal thread and the piston rod then comprises an external thread, wherein the external thread of the piston rod is arranged to cooperate with the internal thread of the first spindle. Such an actuator is disclosed in SE 533597 C2.

Claims

C L A I M S

An actuator comprising:

a motor (1) which comprises a rotatable drive shaft (2) ,

a first spindle (3) which is rotatably arranged, a piston rod (4) which is arranged to perform a linear translational movement in an axial

direction relative to the first spindle (3) between a first end position and a second end position while the first spindle (3) is rotating, and

a rotatable second spindle (5) which the drive shaft (2) of the motor is arranged to directly or indirectly drive, wherein the second spindle (5) is arranged to drive the rotation of the first spindle (3) via a carrier (6) , characterized in that the carrier (6) is elongated and comprises a first end portion (38) and a second end portion (39) , wherein the first end portion (38) is arranged in an axial cavity (16) of the first spindle (3) and wherein the second end portion (39) is arranged in an axial cavity (31) of the second spindle (5) , that the carrier (6) has a radial and axial play in at least one of the cavities (16, 31), and that the carrier (6) acts as a torsion spring, which makes the second spindle (5) mechanically isolated from the first spindle (3) .

2. The actuator according to claim 1, characterized in that the rotational axis of the second spindle (5) is linearly arranged with respect to the rotational axis of the first spindle (3) .

3. The actuator according to any one of the claims 1-2, characterized in that the actuator comprises a bevel gear (9, 10) which comprises a first gear wheel (9) and a second gear wheel (10) , wherein the first gear wheel (9) is fitted to the drive shaft (2) of the motor and wherein the second gear wheel (10) is fitted to the second spindle (5) .

4. The actuator according to any one of the claims 1-3, characterized in that the carrier (6) has a length of 30- 70 mm, preferably 50-60 mm.

5. The actuator according to any one of the claims 1-4, characterized in that the carrier (6) has a cross- sectional dimension of 3-9 mm, preferably 4-8 mm.

6. The actuator according to any one of the claims 1- characterized in that the carrier (6) has an insertion length into the axial cavities (16, 31) of 10-30 mm.

7. The actuator according to any one of the claims 1-6, characterized in that the axial play is 1-5 mm.

8. The actuator according to any one of the claims 1-7, characterized in that the radial play is 0.1-0.5 mm.

9. The actuator according to claim 1, characterized in that the drive shaft (2) of the motor is arranged in line with the second spindle (5) .