JP2014025515A - Linear motion actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear motion actuator capable of compatibly achieving high efficiency and self-locking performance and being miniaturized.SOLUTION: A linear motion actuator includes: a driving source 1; an eccentric shaft 11 which is rotationally driven by the driving source 1 and rotates eccentrically; a drive gear 14 rotatably supported on the eccentric shaft 11; a fixed gear 15 which is fixed to a housing 5 and includes an internal gear engaged with a small diameter gear 14b of the drive gear 14; an output shaft 4 which is rotatably supported on the housing 5 and includes an internal gear 4a engaged with a large diameter gear 14a of the drive gear 14; a screw shaft 6 connected to the output shaft 4; and a nut 7 assembled to the screw shaft 6 via a rollable ball. When the driving source 1 eccentrically rotates the eccentric shaft 11, the drive gear 14 revolves while rotating around itself, the output shaft 4 is reduced in speed and rotates, and the nut 7 performs a linear motion in an axial direction.

Description

  The present invention relates to a linear actuator that linearly moves a nut or screw shaft of a rolling element screw device.

  In the ball screw, a ball rolling groove of a screw shaft and a load ball rolling groove of a nut are opposed to each other, and a ball as a rolling element is interposed between them so as to allow rolling motion. Since the ball rolls between the screw shaft and the nut, it has a feature that a higher efficiency can be obtained compared to the slide screw.

  As a linear motion actuator using a ball screw, Patent Literature 1 discloses a linear motion actuator that converts the rotational force of an electric motor into a linear motion of a nut via a planetary gear mechanism. The rotational movement of the rotor of the motor is decelerated by the planetary gear mechanism. A screw shaft is coupled to the planetary shaft carrier of the planetary gear mechanism. When the screw shaft rotates, the nut of the ball screw moves linearly.

JP 2006-112520 A

  Incidentally, the ball screw has a feature that both the positive efficiency for converting the rotational motion into the linear motion and the reverse efficiency for converting the linear motion into the rotational motion are both high. For this reason, there is an advantage that the nut can be linearly moved by a small motor, but there is a problem that the screw shaft is rotated by the reverse input of the force, that is, the axial force acting on the nut. In order to prevent the screw shaft from rotating, it is necessary to supply a current to the motor so that the motor has a holding force.

  In order to prevent the nut from moving even if current is not supplied to the motor against the reverse input of the force, the speed reduction mechanism that decelerates the rotational movement of the motor is self-locking, that is, it is held against the reverse input of the force. It is necessary to have sex. However, the linear motion actuator described in Patent Document 1 using a planetary gear mechanism as a speed reduction mechanism has a problem that it cannot have a self-locking property because the speed reduction ratio cannot be increased. In order to provide the self-locking property, it is necessary to make the planetary gear mechanism multistage, and this increases the size of the linear motion actuator. Even when a spur gear is used instead of the planetary gear, an unlimited multi-stage is required, and the linear actuator is enlarged.

  When a mysterious planetary gear is used, the reduction ratio can be increased, but there is a problem that the efficiency is as low as about 40% because it does not mesh unless the dislocation is increased. When Harmonic Drive (registered trademark) and a cycloid gear are used, there is a problem that the structure is complicated and very expensive, and the efficiency is as low as about 50%. When these speed reduction mechanisms are used in the rotating part, it is possible to provide a self-locking property, but there is a problem that efficiency is sacrificed.

  Accordingly, an object of the present invention is to provide a linear motion actuator that can achieve both high efficiency and self-locking property and can be miniaturized.

  In order to solve the above problems, the present invention provides a drive source, an eccentric shaft that is rotationally driven by the drive source and rotates while being eccentric, a drive gear that is rotatably supported by the eccentric shaft, and a housing that is fixed A fixed gear having an internal gear meshing with one end portion in the axial direction of the drive gear, an output shaft having an internal gear rotatably supported by the housing and meshing with the other end portion in the axial direction of the drive gear; One of a screw shaft and a nut of a rolling element screw device coupled to the output shaft, and the other of the screw shaft and the nut assembled to the one via a large number of rolling elements, When the drive source rotates while rotating the eccentric shaft, the drive gear revolves while rotating, the output shaft rotates at a reduced speed, and other than the screw shaft and the nut of the rolling element screw device There is a linear actuator for linear movement in the axial direction.

  According to the present invention, the reduction ratio of the output shaft is determined by the difference between the number of teeth of the internal gear of the fixed gear and the number of teeth of the internal gear of the output shaft, and / or the number of teeth at one end of the drive gear and the other end of the drive gear. Since it is determined according to the difference in the number of teeth of the part, a large reduction ratio can be obtained by reducing the difference in the number of teeth. For this reason, the linear motion actuator can be provided with a self-locking property. That is, even if an axial force is reversely input to the other of the screw shaft and the nut of the rolling element screw device, the other of the screw shaft and the nut can be prevented from moving in the axial direction. Further, each gear can be meshed with a small shift or no shift, and since the number of via gears is small, it is efficient and the linear actuator can be downsized.

1 is a perspective view (including a sectional view) of a linear motion actuator according to a first embodiment of the present invention. 1 is an exploded perspective view of a linear motion actuator according to a first embodiment of the present invention. Sectional drawing of the linear motion actuator of 1st embodiment of this invention Sectional view showing the position of the center of gravity of the eccentric shaft

  Hereinafter, a linear actuator according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a perspective view of a linear actuator according to this embodiment. The linear motion actuator includes an electric motor 1 as a drive source, a speed reduction mechanism 2 that decelerates rotation of the output shaft 1a (see FIG. 2) of the electric motor 1, and a rolling element in which the screw shaft 6 is rotationally driven by the speed reduction mechanism 2. A ball screw 3 as a screw device. When the electric motor 1 rotates, the rotation of the output shaft 1 a is decelerated and transmitted to the output shaft 4 of the speed reduction mechanism 2. When the output shaft 4 of the speed reduction mechanism 2 rotates, the screw shaft 6 of the ball screw 3 rotates together with the output shaft 4, and the nut 7 of the ball screw 3 moves linearly in the axial direction. The linear actuator of this embodiment is self-locking, that is, when the axial force is reversely input to the nut 7, the nut 7 is prevented from moving in the axial direction without supplying current to the electric motor 1. It has the feature that it can.

  As shown in the exploded perspective view of FIG. 2, the housing 5 is formed by coupling a cylindrical first housing 5a and a cylindrical second housing 5b. The speed reduction mechanism 2 is accommodated in the first housing 5a, and the ball screw 3 is accommodated in the second housing 5b. A flange 5a1 is formed at one end of the first housing 5a. A flange 5b1 is also formed at one end of the second housing 5b. The first housing 5a and the second housing 5b are coupled in the axial direction by a fastening member 8 such as a bolt. A screw hole into which the fastening member 8 is screwed is formed in the flange 5a1 of the first housing 5a. A through hole through which the fastening member 8 is passed is formed in the flange 5b1 of the second housing 5b.

  The electric motor 1 is coupled to one end of the housing 5. A spline groove is formed on the outer peripheral surface of the output shaft 1 a of the electric motor 1. One end of the eccentric shaft 11 is fitted to the output shaft 1a of the electric motor 1 so as to rotate together with the output shaft 1a. A hole into which the output shaft 1 a is fitted is formed at one end of the eccentric shaft 11. Spline protrusions that fit into the spline grooves of the output shaft 1a are formed on the inner peripheral surface of the hole.

  The eccentric shaft 11 rotates around the center of gravity of the eccentric shaft 11, the large-diameter portion 11 c and the small-diameter portion 11 b having the same center line as the center line 11 a as the center of rotation, the eccentric shaft body 11 d eccentric from the center line 11 a And a counterweight 11e that approaches the center line 11a. The large diameter portion 11 c and the small diameter portion 11 b of the eccentric shaft 11 are provided at both ends of the eccentric shaft 11 in the axial direction. The large-diameter portion 11c of the eccentric shaft 11 is supported by the housing 5 via a bearing 12 as a bearing so as to be rotatable around the center line 11a. The small diameter portion 11b of the eccentric shaft 11 is rotatably supported by the output shaft 4 via a bearing 13 as a bearing. A drive gear 14 is rotatably supported on the eccentric shaft main body 11d of the eccentric shaft 11.

  FIG. 4 shows a sectional view of the eccentric shaft 11. The eccentric shaft body 11d rotates while being eccentric about the center line 11a. The center of gravity G1 of the eccentric shaft main body 11d is eccentric from the center line 11a. The center of gravity G2 of the counterweight 11e formed in a disc shape is on the opposite side to the center of gravity G1 of the eccentric shaft main body 11d across the center line 11a. By providing the counterweight 11e, the center of gravity of the eccentric shaft 11 and the drive gear 14 can be arranged on the center line 11a.

  As shown in FIG. 2, the drive gear 14 includes a large-diameter gear 14a and a small-diameter gear 14b having an outer diameter smaller than that of the large-diameter gear 14a. The large diameter gear 14 a meshes with the internal gear 4 a of the output shaft 4. The small diameter gear 14 b meshes with the internal gear of the fixed gear 15 fixed to the housing 5. The difference between the number of teeth of the large diameter gear 14a and the number of teeth of the small diameter gear 14b is set to 1, for example. The outer diameter of the large diameter gear 14a and the outer diameter of the small diameter gear 14b are different, and the module of the large diameter gear 14a and the module of the small diameter gear 14b are different. The difference between the number of teeth of the large-diameter gear 14a and the number of teeth of the small-diameter gear 14b is, for example, 1, the large-diameter gear 14a and the small-diameter gear 14b have a common center line, and are shifted to the large-diameter gear 14a and the small-diameter gear 14b. The module is selected so that it will not be charged. If a gear is dislocated, the slip ratio increases and the efficiency decreases, so it is desirable not to displace. The large gear 14a, the small gear 14b of the drive gear 14, the internal gear of the fixed gear 15, and the internal gear 4a of the output shaft 4 are all formed in an involute tooth profile. By not shifting the gear and by forming the gear into an involute tooth profile, it is possible to simplify the processing and assembly of the gear. A through hole is formed in the drive gear 14. A bush 14c is fitted in the through hole.

  The small-diameter gear 14 b of the drive gear 14 meshes with the internal gear of the fixed gear 15. The fixed gear 15 is fixed to the housing 5 using a fixing means such as adhesion or press fitting. The module of the internal gear of the fixed gear 15 is equal to the module of the small diameter gear 14b of the drive gear 14. The number of teeth of the internal gear of the fixed gear 15 is larger than the number of teeth of the small-diameter gear 14b, and the inner diameter of the fixed gear 15 is larger than the outer diameter of the small-diameter gear 14b. Therefore, a clearance δ1 (see FIG. 3) is vacant between the fixed gear 15 and the small-diameter gear 14b of the drive gear 14. The small diameter gear 14 b of the drive gear 14 revolves while rotating inside the fixed gear 15.

  The large-diameter gear 14 a of the drive gear 14 meshes with the internal gear 4 a of the output shaft 4. The module of the internal gear 4 a of the output shaft 4 is equal to the module of the large-diameter gear 14 a of the drive gear 14. The number of teeth of the internal gear 4a of the output shaft 4 is larger than the number of teeth of the large diameter gear 14a, and the inner diameter of the internal gear 4a of the output shaft 4 is larger than the outer diameter of the large diameter gear 14a. For this reason, a clearance δ2 (see FIG. 3) is provided between the internal gear 4a of the output shaft 4 and the large-diameter gear 14a of the drive gear 14. The large-diameter gear 14 a of the drive gear 14 revolves while rotating inside the internal gear 4 a of the output shaft 4.

  The principle of deceleration of the speed reduction mechanism of this embodiment is as follows. As described above, the small diameter gear 14 b of the drive gear 14 revolves while rotating inside the fixed gear 15. The large-diameter gear 14 a of the drive gear 14 revolves while rotating inside the internal gear 4 a of the output shaft 4. The difference between the number of teeth of the large diameter gear 14a and the number of teeth of the small diameter gear 14b is set to 1, for example. The number of teeth of the fixed gear 15 is equal to the number of teeth of the internal gear 4 a of the output shaft 4.

  Assuming that the output shaft 4 does not rotate, the circumferential position of the small-diameter gear 14b and the circumferential position of the large-diameter gear 14a shift as the drive gear 14 rotates and revolves. However, the small-diameter gear 14b and the large-diameter gear 14a share the center line, and the circumferential position does not shift. The output shaft 4 rotates in order to absorb the circumferential displacement. The reduction ratio of the output shaft 4 depends on the difference between the number of teeth of the fixed gear 15 and the number of teeth of the internal gear 4a of the output shaft 4, and / or the difference between the number of teeth of the large diameter gear 14a and the number of teeth of the small diameter gear 14b. Will be decided accordingly. By reducing the difference in the number of teeth, a large reduction ratio (the number of rotations of the output shaft 4 / the number of rotations of the eccentric shaft 11 ≦ 1/30) can be realized.

  An internal gear 4a, a bearing support portion 4b, and a screw shaft fitting portion 4c are formed on the inner peripheral surface of the cylindrical output shaft 4. A bearing 13 is incorporated in the bearing support portion 4b. A small diameter portion 11b of the eccentric shaft 11 is rotatably supported by the bearing 13. One end 6c of the screw shaft 6 is fitted into the screw shaft fitting portion 4c of the output shaft 4 (see FIG. 3). A screw hole 4 d for connecting the screw shaft 6 is formed at one end of the output shaft 4 in the axial direction. A large number of through holes 6 b are formed in the flange 6 a coupled to the screw shaft 6. The flange 6a of the screw shaft 6 is coupled to the output shaft 4 using a number of fastening members 18 such as bolts.

  The output shaft 4 is rotatably supported by the housing 5 via an angular bearing 16 as a bearing. The angular bearings 16 are arranged outside the output shaft 4 and inside the housing 5, and two angular bearings 16 are provided in this embodiment. A lock nut 17 screwed to the output shaft 4 fixes the angular bearing 16 to the housing 5 (see FIG. 3). The angular bearing 16 rotatably supports the output shaft 4 and receives an axial force acting on the screw shaft 6 coupled to the output shaft 4. That is, the angular bearing 16 has both a function of holding the rotation of the output shaft 4 and a function of holding the rotation of the screw shaft 6. As shown in FIG. 3, at least a part of the angular bearing 16 and at least a part of a portion R where the internal gear 4 a of the output shaft 4 and the large-diameter gear 14 a of the drive gear 14 mesh with each other overlap in the axial direction. In FIG. 3, the meshing range is indicated by S.

  As shown in FIG. 2, the screw shaft 6 of the ball screw 3 is coupled to the output shaft 4. A flange 6 a is coupled to one end of the screw shaft 6. The screw shaft 6 is coupled to the output shaft 4 via a flange 6a. On the outer peripheral surface of the screw shaft 6, a spiral ball rolling groove 6d in which the ball rolls is formed.

  A cylindrical nut 7 is assembled to the screw shaft 6 via a number of balls as rolling elements. A load ball rolling groove facing the ball rolling groove 6 d of the screw shaft 6 is formed on the inner peripheral surface of the nut 7. A large number of balls are interposed between the ball rolling groove 6 d of the screw shaft 6 and the loaded ball rolling groove of the nut 7 so as to be capable of rolling motion. The nut 7 is provided with a deflector (not shown) that connects one end of the load ball rolling groove and the other end of the load ball rolling groove immediately before the winding so that a large number of balls can circulate. The nut 7 is formed with a deflector fitting hole 7a for mounting the deflector. A large number of spline protrusions 7 b extending in the axial direction are formed on the outer peripheral surface of the end portion of the nut 7 at equal intervals in the circumferential direction.

  A spline ring 21 is coupled to the inner peripheral surface of the housing 5. A large number of spline grooves 21 a extending in the axial direction are formed on the inner peripheral surface of the spline ring 21 at equal intervals in the circumferential direction. The spline protrusion 7 b on the outer peripheral surface of the nut 7 is fitted into the spline groove 21 a on the inner peripheral surface of the spline ring 21. This restricts the nut 7 from rotating around the axis while allowing the nut 7 to move in the axial direction. The housing 5 is provided with a sliding bush 22 for guiding the nut 7 to move in the axial direction.

  The operation of the linear actuator of this embodiment is as follows. First, the electric motor 1 rotates the eccentric shaft 11 around the center line 11a. When the eccentric shaft 11 rotates around the center line 11a, the drive gear 14 rotates while being eccentric. As the drive gear 14 rotates and revolves, the output shaft 4 is decelerated and rotated as described above. Since the screw shaft 6 of the ball screw 3 is coupled to the output shaft 4, the screw shaft 6 rotates as the output shaft 4 rotates. Since the nut 7 is assembled to the screw shaft 6 via a large number of balls, the nut 7 moves linearly as the screw shaft 6 rotates.

  The linear actuator according to the present embodiment has the following effects. Since the shift of each gear of the speed reduction mechanism 2 is small (or the shift of each gear is zero) and the number of via gears is small, the efficiency of the speed reduction mechanism 2 can be improved to 90% or more, for example.

  Even if an axial reverse input acts on the nut 7, the speed reduction ratio of the speed reduction mechanism 2 is high, so that self-locking can be provided. If the self-locking property cannot be provided, it is necessary to keep the current flowing through the electric motor 1 in order to hold the nut 7 at a certain position. By providing the self-locking property, it is not necessary to pass a current for holding the electric motor 1. Ultimately, the cogging torque of the electric motor 1 and the frictional force of the speed reduction mechanism 2 become the self-locking holding force.

  The angular bearing 16 combines the function of holding the rotation of the output shaft 4 and the function of holding the rotation of the screw shaft 6. For this reason, size reduction of a linear motion actuator can be achieved.

  Since the internal gear 4a of the output shaft 4 and the large-diameter gear 14a of the drive gear 14 are provided with a pressure angle, when a torque acts on the drive gear 14, a reaction force corresponding to the pressure angle acts on the output shaft 4. . Since at least a part of the angular bearing 16 and at least a part of the portion R where the output shaft 4 and the drive gear 14 mesh with each other overlap in the axial direction (see FIG. 3), the reaction force acting on the output shaft 4 is affected by the angular bearing. 16 can receive. For this reason, the output shaft 4 rotates smoothly.

  Since the eccentric shaft 11 is provided with a counterweight 11e that brings the center of gravity of the eccentric shaft 11 and the drive gear 14 closer to the center line 11a that is the center of rotation, the eccentric shaft 11 can be rotated at high speed.

  As described above, since the drive gear 14 has a pressure angle, when torque acts on the drive gear 14, a reaction force corresponding to the pressure angle of the drive gear 14 acts on the eccentric shaft 11. By supporting both ends of the eccentric shaft 11 via bearings 12 and 13, it is possible to withstand a reaction force acting on the eccentric shaft 11.

  Since one end 6c of the screw shaft 6 is fitted inside the hollow output shaft 4 (see FIG. 3), the screw shaft 6 is positioned so that the center line of the output shaft 4 coincides with the center line of the screw shaft 6. Can do.

  By forming the spline groove 21 a in the spline ring 21 fixed to the housing 5 and forming the spline protrusion 7 b in the nut 7, the nut 7 can be prevented from rotating.

  By providing the housing 5 with the sliding bush 22 for guiding the nut 7 to move in the axial direction, the sliding bush 22 can receive a moment load acting on the nut 7.

  The present invention is not limited to the embodiment described above, and can be embodied in various embodiments without departing from the scope of the present invention.

  For example, in the above-described embodiment, the housing is provided with a non-rotating portion (spline ring) that prevents the nut from rotating. However, when the mating component to which the nut is attached has a function of preventing rotation, the anti-rotating portion is omitted. You can also

  In the above embodiment, the screw shaft of the ball screw is coupled to the output shaft of the speed reduction mechanism. However, a nut of the ball screw may be coupled to the output shaft of the speed reduction mechanism so that the screw shaft moves linearly.

  In the above embodiment, the drive gear is provided with a large-diameter gear and a small-diameter gear. However, the large-diameter gear and the small-diameter gear may have the same outer diameter and the same original gear. In this case, however, it is necessary to shift the drive gear.

  In the above embodiment, the lead of the ball rolling groove of the screw shaft and the lead of the load ball rolling groove of the nut are smaller than the diameter of the screw shaft, but may be larger leads than the diameter of the screw shaft. When a large lead is used, the stroke speed of the nut can be increased even if the rotational speed of the screw shaft is reduced.

  Since the linear actuator of the present invention can achieve both high efficiency and self-locking performance, it can be used for automobile transmissions such as automobile transmissions, parking brakes, machine tool actuators such as injection molding machines and press machines, and heavy objects. It can be used for lifting jacks.

DESCRIPTION OF SYMBOLS 1 ... Electric motor (drive source), 4 ... Output shaft, 4a ... Internal gear of output shaft, 5 ... Housing, 6 ... Screw shaft, 7 ... Nut, 7b ... Spline protrusion, 11 ... Eccentric shaft, 11a ... Eccentric shaft Center line, 11d ... eccentric shaft body, 11e ... counter weight, 14 ... drive gear, 14a ... large diameter gear (the other end of the drive gear), 14b ... small diameter gear (one end of the drive gear), 15 ... fixed gear, 16 ... Angular bearing (bearing), 21a ... Spline groove, 22 ... Bush

Claims (8)

A driving source;
An eccentric shaft that is rotationally driven by the drive source and rotates eccentrically;
A drive gear rotatably supported on the eccentric shaft;
A fixed gear having an internal gear fixed to the housing and meshing with one axial end of the drive gear;
An output shaft having an internal gear rotatably supported by the housing and meshing with the other axial end of the drive gear;
Any one of a screw shaft and a nut of a rolling element screw device coupled to the output shaft;
The screw shaft and the other of the nut, which are assembled to either one of the rolling elements via a large number of rolling elements,
When the drive source rotates with the eccentric shaft eccentric, the drive gear revolves while rotating, the output shaft rotates at a reduced speed, and the other of the screw shaft and the nut of the rolling element screw device Linear actuator that linearly moves in the axial direction.   The housing is provided with a bearing that rotatably supports the output shaft and that can receive an axial force acting on either the screw shaft or the nut coupled to the output shaft. The linear actuator according to claim 1, wherein the actuator is a linear actuator.   The at least part of the bearing and at least a part of a portion where the internal gear of the output shaft and the other end of the drive gear mesh with each other overlap in the axial direction. Linear actuator.   The eccentric shaft is eccentric from a center line that is the center of rotation of the eccentric shaft, and an eccentric shaft main body on which the drive gear is rotatably supported, and the center of gravity of the eccentric shaft and the drive gear are brought close to the center line. The linear motion actuator according to claim 1, further comprising a counterweight. One end portion of the eccentric shaft in the axial direction is supported by the housing through a bearing so as to be rotatable around the center line,
The linear actuator according to claim 4, wherein the other end portion of the eccentric shaft in the axial direction is rotatably supported around the center line through a bearing inside the output shaft. The screw shaft is coupled to the output shaft,
6. The linear actuator according to claim 1, wherein one end of the screw shaft in the axial direction is fitted inside the output shaft formed to be hollow. The screw shaft is coupled to the output shaft,
Spline grooves or spline protrusions extending in the axial direction are formed on the inner peripheral surface of the housing,
The linear actuator according to claim 1, wherein a spline protrusion or a spline groove that fits into the spline groove or the spline protrusion is formed on an outer peripheral surface of the nut.   The linear actuator according to claim 7, wherein the housing is provided with a sliding bush for guiding the nut to move in an axial direction.

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