JP2020070885A - Ball screw device - Google Patents

Abstract

To provide a ball screw device capable of promptly and properly adjusting a preload according to a situation.SOLUTION: A ball screw device 11 includes: a screw shaft 13 formed with a spiral screw groove 21 on an outer peripheral surface, a first nut 15A and a second nut 15B that have spiral screw grooves 23 on an inner peripheral surfaces, are externally fitted with the screw shaft 13, and are aligned in an axial direction; and a plurality of balls 17 rollably disposed in rolling paths formed between the screw groove 21 of the screw shaft 13 and the respective screw grooves 23 of the first nut 15A and the second nut 15B. The ball screw device 11 is equipped with a driving portion 19 relatively generating rotation force around the shaft to apply a preload to the first nut 15A and the second nut 15B by being powered.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ball screw device.

  In a ball screw device used for a machine tool or the like, a preload is applied to the ball screw in order to secure rigidity and improve positioning accuracy during cutting. Since the preload acts as a resistance to the rotation of the screw shaft and the nut, it causes heat generation of the ball screw when the high-speed feed or the amount of movement is large. Therefore, a ball screw device that can adjust the preload during processing and during movement has been proposed.

  As a ball screw device that can adjust the preload, the load applied to each nut by changing the size of the spacer of the two nuts by an actuator such as a piezoelectric element provided between the two nuts that are divided in the axial direction. And a mechanism for changing the preload applied to the ball (for example, see Patent Document 1).

  Further, there is known an electric actuator in which an electric motor is incorporated on the outer peripheral side of a nut of a ball screw, and the nut is rotated by the electric motor to linearly move the screw shaft (for example, refer to Patent Document 2).

JP-A-2-221747 JP, 2017-155762, A

  By the way, in the ball screw device described in Patent Document 1 in which the size of the spacer between the two nuts is changed by an actuator such as a piezoelectric element, it is difficult to minutely and quickly adjust the applied preload. there were. Further, if the contact portion between the ball and the thread groove is worn, it may be difficult to properly adjust the preload.

  The electric actuator described in Patent Literature 2 linearly moves the screw shaft by applying a rotational force to the nut by an electric motor, and cannot adjust the preload by varying it.

  The present invention has been made in view of the above matters, and an object thereof is to provide a ball screw device capable of quickly and appropriately adjusting a preload according to a situation.

The present invention has the following configurations.
A screw shaft with a spiral thread groove formed on the outer peripheral surface,
Having a spiral thread groove on the inner peripheral surface, a first nut and a second nut externally fitted to the screw shaft and arranged in the axial direction,
A plurality of rolling elements arranged to be rollable in a rolling path formed between the thread groove of the screw shaft and the respective thread grooves of the first nut and the second nut,
A ball screw device comprising:
A ball screw device provided with a drive unit which, when supplied with electric power, causes the first nut and the second nut to relatively generate a rotational force around an axis to apply a preload.

  The ball screw device of the present invention can adjust the preload quickly and appropriately according to the situation.

It is the side view which carried out sectional view of a part of ball screw device concerning the embodiment of the present invention. It is an enlarged view of the A section in FIG. It is a side view which shows a part of peripheral surface of a ball screw device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional side view of a part of a ball screw device 11 according to an embodiment of the present invention. FIG. 2 is an enlarged view of part A in FIG.

  As shown in FIGS. 1 and 2, the ball screw device 11 according to the present embodiment includes a screw shaft 13, a first nut 15A and a second nut 15B, a ball (rolling element) 17, and a drive unit 19. Prepare mainly.

  A spiral thread groove 21 is formed on the outer peripheral surface of the screw shaft 13. The first nut 15A and the second nut 15B are externally fitted on the screw shaft 13 and arranged in the axial direction. An annular flange 20 is formed at the end of the first nut 15A. The first nut 15A and the second nut 15B are each formed with a spiral thread groove 23 facing the thread groove 21 of the screw shaft 13 on the inner peripheral surface thereof. As a result, rolling paths are formed between the screw shaft 13 and the first nut 15A and the second nut 15B by the opposed screw grooves 21 and 23. The ball 17 is made of a steel ball and is rollably arranged in a rolling path formed by the screw grooves 21 and 23.

  A ball return passage (not shown) is formed in the first nut 15A and the second nut 15B along the axial direction. Both ends of the ball return passages of the first nut 15A and the second nut 15B are communicated with the thread groove 23, respectively. As a result, the balls 17 rolling in the rolling path move up to one end of each rolling path of the first nut 15A and the second nut 15B, and then are scooped up by the end deflector (not shown) to move in the ball returning path. It is sent to the other end side and returned to the rolling path. As described above, the first nut 15A and the second nut 15B of the ball screw device 11 each have an independent end deflector type circulation path, and a plurality of rolling elements in the rolling path while circulating the circulation path. The screw shaft 13 and the first nut 15A and the second nut 15B move relative to each other via the ball 17.

  The first nut 15A has a cylindrical portion 31 formed in a cylindrical shape at the end portion on the second nut 15B side. The tubular portion 31 is provided so as to project from the outer edge portion of the end surface 33 of the first nut 15A toward the second nut 15B side. The second nut 15B has a small diameter portion 35 on the first nut 15A side. By forming the small diameter portion 35, a step portion 37 is formed at the end portion of the second nut 15B.

  The small diameter portion 35 of the second nut 15B is inserted and arranged in the tubular portion 31 of the first nut 15A. The accommodation chamber 41 is formed between the first nut 15A and the second nut 15B by the end surface 33 and the tubular portion 31 of the first nut 15A, and the small diameter portion 35 and the step portion 37 of the second nut 15B. It is formed over the circumferential direction.

  The drive unit 19 is provided in the accommodation chamber 41. The drive unit 19 includes a stator 51 and a rotor 53. The stator 51 is fixed by shrink fitting on the inner peripheral side of the tubular portion 31 of the first nut 15A. The rotor 53 is provided on the outer peripheral side of the small diameter portion 35 of the second nut 15B. The stator 51 and the rotor 53 are arranged at the same position in the axial direction, and are overlapped with each other with a slight radial gap. In the drive unit 19, for example, the rotor 53 is composed of a magnet, and a coil (not shown) wound around the stator 51 is supplied with power from the power supply device, whereby a rotational force is generated in the rotor 53.

  A power supply wire (not shown) connected to the coil of the stator 51 is drawn out, for example, between the first nut 15A and the second nut 15B. An electric wire insertion hole (not shown) may be formed in the first nut 15A, and an electric wire for power supply may be passed through the electric wire insertion hole and pulled out from the end portion of the first nut 15A where the flange 21 is formed. The drive unit 19 may have a structure in which the stator 51 is formed of a magnet, and a rotational force is generated in the rotor 53 by supplying power to a coil wound around the rotor 53. In this case, the power supply wire connected to the coil of the rotor 53 may be drawn out, for example, between the first nut 15A and the second nut 15B, or may be passed through the wire insertion hole formed in the second nut 15B. You may pull out from the edge part of the 2nd nut 15B.

  A seal member 61 circumferentially seals between the end portion 31a of the tubular portion 31 of the first nut 15A and the step portion 37 of the second nut 15B. Further, a gap between the end surface 33 of the first nut 15A and the end surface 35a of the small diameter portion 35 of the second nut 15B is circumferentially sealed by a seal member 63. That is, the accommodation chamber 41 in which the drive unit 19 is accommodated is sealed at the outer peripheral side and the inner peripheral side so that foreign matter such as oil and dust does not enter from the outside. Further, on the end surface 33 of the first nut 15A, an elastic member 65 is provided in the circumferential direction on the outer peripheral side of the sealing portion by the sealing member 63. A part of the elastic member 65 projects toward the second nut 15B side and is elastically deformed by being pressed by the end surface 35a of the small diameter portion 35 of the second nut 15B. Thereby, a repulsive force is applied between the first nut 15A and the second nut 15B in a direction in which they are separated from each other. Therefore, the second nut 15B is applied to the first nut 15A with a rotational force directed in one direction (direction of arrow B in FIG. 1) determined by the spiral direction of the rolling path.

FIG. 3 is a side view showing a part of the peripheral surface of the ball screw device 11.
As shown in FIG. 3, the second nut 15B has a key groove 71 formed on the peripheral surface on the first nut 15A side. A key 73 protruding to the second nut 15B side is fixed to the first nut 15A. The key 73 is arranged in the key groove 71 formed in the second nut 15B. The key groove 71 has a width dimension slightly larger than the width dimension of the key 73. By disposing the key 73 in the key groove 71, the second nut 15B is prevented from rotating in a slightly rotatable state with respect to the first nut 15A.

Next, the preload in the ball screw device 11 will be described.
(steady state)
In the ball screw device 11 having the above structure, the second nut 15B to which the elastic force of the elastic member 65 is applied has a rotational force directed in one direction (the arrow B direction in FIGS. 1 and 3) with respect to the first nut 15A. Granted. Therefore, the key 73 abuts on one edge 71 a of the key groove 71, and a clearance Cr is formed between the key 73 and the other edge 71 b of the key groove 71. In this state, the elastic force of the elastic member 65 is applied to the first nut 15A and the second nut 15B as a reaction force that separates them from each other in the axial direction, and a necessary minimum preload is applied. As a result, the balls 17 in the rolling path are brought into contact with each other at one point of the thread groove 21 of the screw shaft 13 and one point of the thread groove 23 of the first nut 15A and the second nut 15B.

(When preload is applied)
In the ball screw device 11 in the steady state, power is supplied from the power supply device to the coil of the stator 51 of the drive unit 19. Then, in the second nut 15B having the small diameter portion 35 provided with the rotor 53, a rotational force in the other direction (direction of arrow C in FIGS. 1 and 3) is generated with respect to the first nut 15A. As a result, the second nut 15B is screwed into the screw shaft 13 and is displaced in the direction of approaching the first nut 15A against the elastic force of the elastic member 65. Then, the end portion 31a of the tubular portion 31 of the first nut 15A and the step portion 37 of the second nut 15B come into contact with each other, and the end surface 33 of the first nut 15A and the end surface 35a of the small diameter portion 35 of the second nut 15B. Come into contact. At this time, the key 73 moves in the key groove 71 and comes into contact with the other edge portion 71b of the key groove 71. Thereby, the rotation of the second nut 15B with respect to the first nut 15A is restricted, and the rotational force of the second nut 15B with respect to the first nut 15A is a reaction force along the axial direction of the first nut 15A and the second nut 15B. Granted. Therefore, a large preload is applied to the first nut 15A and the second nut 15B. At this time, the preload applied to the ball screw device 11 is easily adjusted by adjusting the amount of power supplied from the power supply device to the drive unit 19.

(When releasing preload)
In the ball screw device 11 that is supplied with electric power to the drive unit 19 and is preloaded, the electric power supply from the power supply device to the coil of the stator 51 of the drive unit 19 is stopped. Then, the rotational force generated in the rotor 53 disappears and the application of the large preload applied to the first nut 15A and the second nut 15B is released. Then, the second nut 15B is rotated in one direction (the arrow B direction in FIGS. 1 and 3) with respect to the first nut 15A by the elastic force of the elastic member 65, and the key 73 causes one edge of the key groove 71. 71a is contacted and stopped. As a result, the first nut 15A and the second nut 15B are in a steady state in which the elastic force of the elastic member 65 is applied as a reaction force that separates them from each other in the axial direction and a required minimum preload is applied.

  By the way, in a machine tool having a ball screw device in a moving mechanism portion, a preload is always applied to a ball of the ball screw device in order to secure rigidity during machining and improve positioning accuracy. However, this preload becomes a resistance against high-speed feed in the moving mechanism section and when the moving amount is large, it becomes a heat source and deteriorates mechanical accuracy. Therefore, it is desired to adjust to an appropriate preload according to the situation such as movement or processing.

  According to the ball screw device 11 according to the present embodiment, the preload applied to the first nut 15A and the second nut 15B is appropriately and quickly adjusted according to the situation by supplying the drive unit 19 with an appropriate amount of electric power. can do. As a result, it is possible to efficiently generate an appropriate preload while suppressing heat generation due to excessive preload and extending the life. That is, if this ball screw device 11 is used in a machine tool, the preload is reduced to reduce resistance and suppress heat generation during high-speed movement of the movement mechanism section and when the movement amount is large, and high precision is required. It is possible to increase the preload at the time of processing to increase the rigidity and the positioning accuracy. Further, even when the preload decreases due to wear of the balls 17 and the like, by adjusting the amount of electric power supplied to the drive unit 19, it is possible to apply an appropriate preload, and it is possible to prolong the life. ..

  The drive unit 19 is composed of a stator 51 provided on the first nut 15A and a rotor 53 provided on the second nut 15B, and the rotor 53 applies a rotational force to the stator 51 by supplying power. It is possible to easily generate an appropriate preload on the first nut 15A and the second nut 15B.

  In addition, the elastic member 65 is provided which applies a preload by axially repulsing the first nut 15A and the second nut 15B in a steady state where no preload is applied by the drive unit 19. Therefore, even in the steady state, an appropriate preload can be surely applied and stable positioning can be performed.

  In the above embodiment, the first nut 15A is provided with the stator 51 and the second nut 15B is provided with the rotor 53. However, the first nut 15A is provided with the small diameter portion to provide the rotor 53, and the second nut 15B is provided. The stator 51 may be provided by forming a tubular portion.

  Further, the circulation system for circulating the balls 17 is not limited to the end deflector system, and various circulation systems such as a tube system for returning the balls 17 through a tube can be applied. Further, the rolling element is not limited to the ball 17, and may be a structure using a top as the rolling element.

  Further, in the above-described embodiment, the case where the motor including the stator 51 and the rotor 53 is provided as the drive unit 19 has been illustrated, but the drive unit 19 is relative to the first nut 15A and the second nut 15B. The motor is not limited to the motor including the stator 51 and the rotor 53 as long as it can generate a rotational force. For example, the drive unit 19 may be an actuator such as a solenoid.

  As described above, the present invention is not limited to the above-described embodiments, and those skilled in the art can make changes and applications based on the combination of the configurations of the embodiments with each other, the description of the specification, and the well-known technology. This is also the scope of the present invention and is included in the scope of protection required.

As described above, the following items are disclosed in this specification.
(1) A screw shaft having a spiral thread groove formed on the outer peripheral surface,
Having a spiral thread groove on the inner peripheral surface, a first nut and a second nut externally fitted to the screw shaft and arranged in the axial direction,
A plurality of rolling elements arranged to be rollable in a rolling path formed between the thread groove of the screw shaft and the respective thread grooves of the first nut and the second nut,
A ball screw device comprising:
A ball screw device provided with a drive unit which, when supplied with electric power, causes the first nut and the second nut to relatively generate a rotational force around an axis to apply a preload.
According to the ball screw device having this configuration, by supplying power to the drive unit, it is possible to rapidly generate a preload on the first nut and the second nut by relatively generating a rotational force about the axis. Then, by adjusting the amount of electric power supplied to the drive unit, the preload applied to the first nut and the second nut can be appropriately adjusted according to the situation. As a result, it is possible to efficiently generate an appropriate preload while suppressing heat generation due to excessive preload and extending the life. In other words, if this ball screw device is used in a machine tool, during high-speed movement of the movement mechanism section and when the movement amount is large, the preload is reduced to reduce resistance and suppress heat generation, and high precision machining is required. At the same time, the preload can be increased to increase the rigidity and the positioning accuracy. Further, even when the preload decreases due to wear of the rolling elements and the like, by adjusting the amount of electric power supplied to the drive unit, it is possible to apply an appropriate preload, and it is possible to prolong the service life.

(2) The drive unit includes a stator provided on one of the first nut and the second nut, and a rotor provided on the other of the first nut and the second nut, and is supplied with power. The ball screw device according to (1), in which the rotor causes a rotational force to the stator.
According to the ball screw device having this configuration, a rotational force is generated between the stator and the rotor that form the drive unit, so that an appropriate preload can be easily applied to the first nut and the second nut. ..

(3) In a state where a preload is not applied by the drive unit, an elastic member is provided that repulsively repels the first nut and the second nut in the axial direction to apply a preload (1) or (2). Ball screw device.
According to the ball screw device of this configuration, the elastic member repels the first nut and the second nut in the axial direction in the state where the preload is not applied by the drive unit, thereby reliably applying an appropriate preload. , Can be positioned stably.

11 Ball Screw Device 13 Screw Shaft 15A First Nut 15B Second Nut 17 Ball (Rolling Element)
19 Drive part 21,23 Screw groove 51 Stator 53 Rotor 65 Elastic member

Claims (3)

A screw shaft with a spiral thread groove formed on the outer peripheral surface,
Having a spiral thread groove on the inner peripheral surface, a first nut and a second nut externally fitted to the screw shaft and arranged in the axial direction,
A plurality of rolling elements arranged to be rollable in a rolling path formed between the thread groove of the screw shaft and the respective thread grooves of the first nut and the second nut,
A ball screw device comprising:
A ball screw device provided with a drive unit which, when supplied with electric power, causes the first nut and the second nut to relatively generate a rotational force around an axis to apply a preload. The drive unit is composed of a stator provided on one of the first nut and the second nut, and a rotor provided on the other of the first nut and the second nut, and is supplied with power to achieve the above. The ball screw device according to claim 1, wherein the rotor generates a rotational force with respect to the stator. The ball screw according to claim 1 or 2, further comprising an elastic member that applies a preload by axially repulsing the first nut and the second nut when a preload is not applied by the drive unit. apparatus.

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