JP2016054618A - Electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric actuator deterioration of which due to fretting can be suppressed.SOLUTION: Since an electric actuator 1 includes lubricant J filling a case C housing a motion conversion unit 2 having a rotary member 3 and a direct-acting member 4 and an output cylinder 5 coupled with the direct-acting member 4, and an elastic member 6 housed in the case C, the rotary member 3 and direct-acting member 4 are immersed in the lubricant J, lubrication of both members is carried out at all times, even if the output cylinder 5 enters the case C or exits therefrom, the output cylinder 5 can move smoothly by volume change of the elastic member 6, fretting never occurs even when telescoping with a fine amplitude, and thereby deterioration of the electric actuator 1 can be prevented.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electric actuator.

  Conventionally, as an electric actuator, for example, a screw shaft, a ball nut screwed to the screw shaft, a motor connected to the screw shaft, a cylinder that accommodates the ball nut so as to be axially movable, and a ball nut When the screw shaft is rotationally driven by a motor, a ball nut that is prevented from rotating with respect to the cylinder can be driven in the axial direction (for example, Patent Document 1). reference).

  The inside of the ball nut used in such an electric actuator is filled with grease, so that the axial movement of the screw shaft with respect to the ball nut can be smoothly performed (see, for example, Patent Document 2).

JP 9-327149 A JP 2011-144831 A

  However, when a vibration test is performed using a conventional electric actuator to apply a small amplitude vibration at a high frequency to the specimen, the grease does not reach the entire circumference of the screw groove of the screw shaft, Or the ball nut of the ball nut and the screw groove of the screw shaft cannot be lubricated well, causing surface damage due to friction called fretting, which accelerates the deterioration of the electric actuator. There is a problem.

  Therefore, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric actuator that can suppress deterioration due to fretting.

  The electric actuator according to the present invention includes the lubricating oil filled in the case and the output cylinder in which the motion conversion unit is accommodated and the elastic member accommodated in the case. It is possible to smoothly move the output cylinder due to the change in volume of the elastic member even if the output cylinder is moved in and out of the case.

  In addition, gas is not enclosed in the case, and the change in displacement of the output cylinder is absorbed by the volume change of the elastic member, so that the oil level is rippled in the case by the expansion and contraction operation of the electric actuator. It wo n’t happen. As described above, according to the electric actuator of the present invention, since the entrainment of the gas of the lubricating oil is prevented, the rotation member and the linear motion member do not come into contact with the motion conversion portion, so that the oil film breakage at the contact portion between both of them It does not occur and is prevented from causing poor lubrication.

  Further, in the problem solving means of claim 2, since the intermediate member is provided and the elastic member is accommodated between the case main body, the elastic member moves within the case and interferes with the output tube, thereby preventing the output tube from moving. There is nothing. In addition, since the intermediate cylinder functions as a detent for the linear motion member, the detent itself is always immersed in the lubricating oil, and a smooth expansion and contraction operation of the output cylinder is guaranteed.

  Further, in the problem solving means of claim 3, the case includes a case body and a holder for rotatably holding the rotating member, and the holder is provided with an inlet for lubricating oil. Lubricating oil is injected from the vicinity of the ball bearing that supports the rotating member. Therefore, the ball bearing is not filled with lubricating oil and does not cause poor lubrication.

  Further, in the problem solving means of claim 4, since the screw shaft is used as the rotating member and the ball nut is used as the direct acting member, the ball nut is not required to be connected as compared with the case where the ball nut is connected to the motor. Therefore, the electric actuator becomes lighter and the cost is reduced.

  According to the electric actuator of the present invention, even when the elastic member expands and contracts with a small amplitude, the rotating member and the linear member in the motion conversion unit are always lubricated by the lubricating oil, so that fretting does not occur and the electric actuator is deteriorated. Can be prevented.

It is a longitudinal cross-sectional view of the electric actuator in embodiment of this invention.

  The present invention will be described below based on the embodiments shown in the drawings. As shown in FIG. 1, the electric actuator 1 according to the embodiment includes a motion conversion unit 2 having a screw shaft 3 as a rotating member and a ball nut 4 as a linear motion member screwed to the screw shaft 3. A motor C that is connected to the screw shaft 3 and rotationally drives the screw shaft 3, an output cylinder 5 that is mounted on the ball nut 4, and a motion conversion unit 2, and a case C in which the output cylinder 5 is movably inserted. And an elastic member 6 accommodated in the case C and a lubricating oil J filled in the case C and the output cylinder 5. The electric actuator 1 in this embodiment can move the ball nut 4 in the axial direction on the screw shaft 3 by rotating the screw shaft 3 by driving the motor M, and through the output cylinder 5. A thrust for moving the ball nut 4 can be applied to an external device (not shown).

  Hereinafter, each part of the electric actuator 1 will be described in detail. The motion conversion unit 2 includes a rotating member and a linear motion member that exhibits a linear motion by the rotation of the rotating member. In this embodiment, the rotational member is the screw shaft 3, and the linear motion member is the screw. A feed screw mechanism is formed as a ball nut 4 screwed onto the shaft 3.

  As shown in FIG. 1, the screw shaft 3 is formed in a cylindrical or columnar shape, and a screw portion 3 a in which a spiral screw groove 3 b is formed on the outer periphery thereof, and a shaft extending from the screw portion 3 a to the motor side. Part 3c. Although not shown in detail, the ball nut 4 has a cylindrical shape, and has a spiral ball path facing the screw groove 3b of the screw shaft 3, and a ball path that is accommodated in the ball path and travels through the screw groove 3b. And a large number of balls. When the ball nut 4 is prevented from rotating and the screw shaft 3 is rotated, the ball can travel in the screw groove 3b to smoothly move the ball nut 4 in the axial direction.

  Next, as shown in FIG. 1, the motor M includes a motor body 7 that houses a stator and a rotor (not shown), and an output shaft 8 that is coupled to the rotor, and the output shaft 8 is coupled. 9 is connected to the left end of the screw shaft 3 in FIG. When the output shaft 8 is rotationally driven by supplying current to the motor M, the screw shaft 3 connected to the output shaft 8 is also rotationally driven, and the ball nut 4 can be linearly reciprocated in the axial direction.

  The ball nut 4 is connected to the output cylinder 5 via a nut holder 10. The nut holder 10 has a cylindrical shape, and includes a key 10a provided on the outer periphery along the axial direction, and a wear ring 10b attached on the outer periphery along the circumferential direction. A ball nut 4 is housed and fixed on the inner periphery of the nut holder 10 on the left side in FIG. Further, the left end in FIG. 1 of the output cylinder 5 is screwed to the inner periphery of the nut holder 10 and the right end in FIG. 1, whereby the ball nut 4 and the output cylinder 5 are connected.

  A bracket 11 is attached to the right end of the output cylinder 5 in FIG. 1 to enable connection to an external device or a specimen. An annular slider 12 is slidably inserted into the output cylinder 5. The slider 12 is provided with a seal ring 12a slidably in contact with the inner periphery of the output cylinder 5 on the outer periphery, and provided on the inner periphery on the right side in FIG. 1 which is the ball bearing 12b and the ball bearing 12b on the side opposite to the ball nut. And a seal ring 12c. A screw shaft 3 is inserted into the output cylinder 5, and the right end in FIG. 1 of the screw shaft 3 is rotatably supported by a ball bearing 12 b of the slider 12. The seal between the output tube 5 and the screw shaft 3 is sealed by the seal rings 12a and 12c of the slider 12. Even if the output shaft 5 moves linearly in the left-right direction in FIG. The left side in FIG. 1 which is the ball nut 4 side of the slider 12 is maintained in a sealed state.

  The case C has a cylindrical case body 13, an annular end cap 14 fitted to the right end in FIG. 1 that is the side opposite to the motor of the case body 13, and a left end in FIG. 1 that is the motor side of the case body 13. An annular holder 15 to be fitted is provided.

  The end cap 14 includes a slide bearing 14a that is slidably in contact with the outer periphery of the output cylinder 5 provided on the inner periphery, and a seal ring 14b that is provided on the right side in FIG. 1 and closes the right end in FIG. 1 of the case body 13 while pivotally supporting the output cylinder 5 in a slidable manner. Thereby, the end cap 14 seals the right end of the case C while guiding the reciprocation of the output cylinder 5 in the linear direction in the case C.

  The holder 15 includes ball bearings 15a and 15b mounted on the inner periphery, a seal ring 15c provided on the motor side of the ball bearings 15a and 15b, an injection port 15d that opens from the outer periphery and communicates with the inside, and an injection port 15d. And a plug 15e for closing. The holder 15 is connected to the motor M via a cylindrical connecting member 17, and the motor M and the case C are integrated.

  The case main body 13 has a cylindrical shape, is attached to the outer periphery of the end cap 14 and the holder 15, and is integrated with the end cap 14 and the holder 15. Seal rings 14c and 15f are interposed between the case main body 13 and the end cap 14, and between the case main body 13 and the holder 15, and between the case main body 13 and the end cap 14, and the case. The space between the main body 13 and the holder 15 is sealed.

  The screw shaft 3 is inserted into the holder 15, and the left end of the screw shaft 3 in FIG. 1 protrudes outward from the holder 15. The screw shaft 3 is rotatably supported by ball bearings 15a and 15b. Therefore, both ends of the screw shaft 3 are rotatably supported by the ball bearings 15 a and 15 b provided on the holder 15 and the ball bearing 12 b provided on the slider 12, so that the screw shaft 3 can exhibit a rotational motion without being shaken. So that it is considered. Two ball bearings 15a and 15b are provided on the holder 15 side, but if one is sufficient, either one can be eliminated.

  The ball bearings 15 a and 15 b are sandwiched from the outside by a flange 3 d provided at the boundary between the shaft portion 3 c and the screw portion 3 a of the screw shaft 3 and an annular collar 18 fitted to the outer periphery of the screw shaft 3. Has been. Then, by tightening the collar 18 toward the flange 3d with the nut 19 screwed to the shaft portion 3c, the screw shaft 3 can be attached to the ball bearings 15a and 15b without any play in the axial direction.

  Further, between the collar 18 and the inner ring of the ball bearing 15a, an O-ring 20 that is in close contact with the outer periphery of the screw shaft 3 is interposed, and the outer periphery of the screw shaft 3 is sealed. The seal ring 15 c is in sliding contact with the outer periphery of the collar 18 and seals the outer periphery of the collar 18.

  In the case of this embodiment, an intermediate cylinder 16 is accommodated in the case C and fixed to the holder 15 and the end cap 14. Specifically, the intermediate cylinder 16 is fixed by inserting and fixing the left end in FIG. 1, which is the motor side end, to the inner periphery of the holder 15, and the right end in FIG. The left end is fitted and fixed to a step 14c provided with a small diameter. Further, the intermediate cylinder 16 is provided with a hole 16a, and an annular gap between the case body 13 and the intermediate cylinder 16 communicates with the inside of the intermediate cylinder 16. Furthermore, a groove 16b is provided on the inner periphery of the intermediate cylinder 16 along the axial direction. A key 10a provided on the outer periphery of the nut holder 10 is inserted into the groove 16b so that it can run, and the intermediate cylinder 16 functions as a detent. The ball nut 4 held by the nut holder 10 linearly reciprocates in the axial direction. Movement is allowed but rotation in the circumferential direction is restricted. The intermediate cylinder 16 may be provided with a slit instead of the groove 16b, and the key 10a may be inserted into the slit, or the key may be provided in the intermediate cylinder 16 so that the groove in which the key travels is formed in the nut holder 10. You may make it provide.

  Thus, since the ball nut 4 is prevented from rotating, when the motor M is driven and the screw shaft 3 is rotationally driven, a linear reciprocating motion is caused in the left-right direction in FIG. 1, and the output cylinder 5 enters and exits the case C. Thus, an external device or sample attached to the bracket 11 can be vibrated.

  The case C and the output cylinder 5 are filled with lubricating oil J. In this embodiment, since the elastic member 6 is accommodated between the case body 13 and the intermediate cylinder 16, more specifically, the lubricating oil J is in the case C and the output cylinder 5 is placed in the case. The space S formed between C and the output cylinder 5 is filled.

  The lubricating oil J can be filled through the inlet 15d provided in the holder 15. By providing the inlet 15d in the holder 15 in this way, the lubricating oil J can be lubricated from the vicinity of the ball bearings 15a and 15b. Oil J can be injected into the case C, and the ball bearings 15a and 15b can be sufficiently immersed in the oil. In the present embodiment, the nut holder 10 that connects the ball nut 4 and the output cylinder 5 is provided with a through hole 10c that allows the inside of the output cylinder 5 and the space S to communicate with each other. In the case of this embodiment, the space S is partitioned by the nut holder 10 into a motor side chamber r1 on the motor side and an antimotor side chamber r2 on the counter motor side, but the through hole 10c communicates both chambers r1 and r2. In addition, both chambers r1 and r2 are communicated with the output cylinder 5. Even if the through hole 10c is not provided, since there is a gap between the ball nut 4 and the screw shaft 3, it is possible to inject the lubricating oil J into the output cylinder 5, but the through hole 10c is provided in this way. Thus, the lubricating oil J injected from the injection port 15d can be quickly filled into the output cylinder 5 as well.

  Further, the right end in FIG. 1 of the case C is sealed by a seal ring 14b that is in sliding contact with the outer periphery of the output cylinder 5, and the left end in FIG. 1 of the case C is sealed by an O-ring 20 and a seal ring 15c. Further, the space between the output cylinder 5 and the screw shaft 3 is sealed by the seal rings 12 a and 12 c of the slider 12 provided in the output cylinder 5. In the electric actuator 1 of the present embodiment, the sliding portion is sealed in this way, so that the leakage of the lubricating oil J from the case C and the output cylinder 5 is prevented. As described above, the ball bearings 12b, 15a, 15b, the wear ring 10b, and the sliding bearing 14a are placed in the case C and sealed inwardly by the seal rings 12a, 12c, 14b, 15c, 15f and the O-ring 20. Since all the sliding portions of the rotation preventing portion formed by the key 10a and the groove 16b are immersed in the lubricating oil J, the sliding portions can be smoothly slid.

  The elastic member 6 is annular and is accommodated in an annular gap between the case main body 13 of the case C and the intermediate cylinder 16. As described above, the elastic member 6 is positioned by the intermediate cylinder 16 so as not to be displaced in the case C. The elastic member 6 changes its volume according to the pressure when the pressure is applied. When the output cylinder 5 is driven and moves in the case C, the displacement volume that the output cylinder 5 pushes in the case C changes, and the pressure in the output cylinder 5 and the case C fluctuates. This pressure fluctuation also acts on the elastic member 6 accommodated in the annular gap through the hole 16a provided in the intermediate cylinder 16, and the volume of the elastic member 6 changes. Due to the volume change of the elastic member 6, it is possible to absorb the change in the displacement volume in the case C of the output cylinder 5 due to the movement of the output cylinder 5 described above.

  Therefore, if the elastic member 6 can absorb the displacement volume of the output cylinder 5 when the output cylinder 5 enters and exits the case C with respect to the pressure fluctuation caused by the output cylinder 5 entering and exiting the case C. Good. However, in order to reduce the damping action of the movement of the output shaft 5 caused by filling the lubricating oil J in the case C and the output cylinder 5, the lower the volume elastic modulus of the elastic member 6 is better. The material of the elastic member 6 is not limited as long as it is not deteriorated by the lubricating oil J, but considering the reduction of the damping action described above, for example, urethane rubber may be used for the elastic member 6.

  When the output cylinder 5 is driven, the lubricating oil J moves back and forth in the output cylinder 5, the motor side chamber r1 and the counter motor side chamber r2 in accordance with the amount and direction of movement of the output cylinder 5. By providing the hole 10c, the lubricating oil J can be moved smoothly. Therefore, it is possible to suppress the occurrence of differential pressure in the pressure in the output cylinder 5, the motor side chamber r1, and the counter motor side chamber r2, and effectively suppress the generation of damping force that hinders the movement of the output cylinder 5. Can do.

  The electric actuator 1 of the present invention is configured as described above, and the operation thereof will be described. As described above, when the motor M in the electric actuator 1 is driven to rotate the screw shaft 3, the ball nut 4 that is prevented from rotating by the intermediate cylinder 16 fixed to the case C is left and right in FIG. It can be moved in the axial direction. As a result, the output cylinder 5 connected to the ball nut 4 moves in and out of the case C, so that the electric actuator 1 can expand and contract, and an external device or sample (not shown) connected to the output cylinder 5 is vibrated. Can do.

  As the output cylinder 5 moves in and out of the case C, the displacement volume of the output cylinder 5 in the case C changes. This change is absorbed by the volume change of the elastic member 6. Thus, even if the lubricating oil J is filled in the case C and the output cylinder 5, the displacement volume of the output cylinder 5 in the case C is absorbed by the volume change of the change elastic member 6. Can be extended and contracted smoothly.

  And since the electric actuator 1 of this invention is equipped with the lubricating oil J with which the case C and the output cylinder 5 are filled, and the elastic member 6 accommodated in the case C, the screw groove 3b of the screw shaft 3 and The balls of the ball nut 4 are immersed in the lubricating oil J. In this way, the screw shaft 3 and the ball nut 4 are always lubricated, and even if the output cylinder 5 enters and exits in the case C, the output cylinder 5 can move smoothly due to the volume change of the elastic member 6. Therefore, according to the electric actuator 1 of the present invention, the screw shaft 3 as the rotating member and the ball nut 4 as the linear member in the motion converting unit 2 are always kept in contact with the lubricating oil J even when extending and contracting with a small amplitude. Since it is lubricated, fretting does not occur and deterioration of the electric actuator 1 can be prevented.

  In addition, gas is not sealed in the case C, and the change in displacement volume of the output cylinder 5 is absorbed by the volume change of the elastic member 6, so that the oil level in the case C is waved by the expansion / contraction operation of the electric actuator 1. There will be no gas standing up. As described above, according to the electric actuator 1 of the present invention, the entrainment of the gas of the lubricating oil J is prevented. Oil film breakage does not occur, and poor lubrication is prevented.

  In the electric actuator 1 of the present embodiment, since the intermediate member 16 is provided and the elastic member 6 is accommodated between the case main body 13 and the elastic member 6 moves in the case C, it interferes with the output tube 5. Thus, the movement of the output cylinder 5 is not hindered. Further, since the intermediate cylinder 16 functions as a detent for the ball nut 4 as the linear motion member, the key 10a and the groove 16b constituting the detent are immersed in the lubricating oil J and lubricated, so that the smoothness is ensured. The expansion and contraction operation of the output cylinder 5 is guaranteed. The intermediate cylinder 16 functions as a rotation stopper for the rotating member and a positioning of the elastic member 6. However, the rotation stopper of the rotating member may be implemented by other than the intermediate cylinder 16, and the positioning of the elastic member 6 may be different. It is also possible to carry out by the configuration of However, the use of the intermediate cylinder 16 is advantageous in that it can satisfy both functions of detent of the rotating member and positioning of the elastic member 6.

  In the case of this embodiment, the motion conversion unit 2 uses the screw shaft 3 as a rotating member and the ball nut 4 as a direct acting member. Conversely, the ball nut 4 serves as a rotating member and the screw shaft 3 serves as a direct acting member. It is also possible. When the ball nut 4 is used as a rotating member, a connecting part for connecting the output shaft 8 of the motor M to the ball nut 4 is required, but this connecting part must allow the threaded shaft 3 to be inserted in a cylindrical shape. It needs to be. Thus, in addition to the need for a connecting part for connecting the ball nut 4 to the output shaft 8 of the motor M, it is better to keep the ball nut 4 away from the motor M as much as possible from the viewpoint of securing the stroke. The length of becomes longer. On the other hand, when the screw shaft 3 is a rotating member as in the electric actuator 1 of the present embodiment, a connecting part for connecting the ball nut 4 to the output shaft 8 is not necessary, and therefore the ball nut 4 is rotated. Compared with the case of using a member, the electric actuator 1 becomes lighter and costs are also reduced.

  In addition, although the motion conversion part 2 is comprised with the screw shaft 3 and the ball nut 4 in the place mentioned above, although not shown in figure, it may be comprised with the nut which does not use a screw shaft and a ball | bowl. It is also possible to configure the rack as a member in which the member is a pinion and the linear motion member is engaged with the pinion. In this case, as the structure of the case C, the motion converting portion 2 is accommodated in the case C, and the portion where the rotating member and the linear motion member in the motion converting portion 2 come into contact with each other is always immersed in the lubricating oil J. A structure that can be used.

  In addition, as described above, the through hole 10c is provided to suppress the generation of damping force when the output cylinder 5 is moved, so that the output cylinder 5 can be moved smoothly. Instead of providing such a through hole 10c, it is necessary to communicate the output cylinder 5 and the space S. However, a groove is provided in the inner periphery of the intermediate cylinder 16 to communicate the motor side chamber r1 and the counter motor side chamber r2. Alternatively, a passage for communicating the motor side chamber r1 and the counter motor side chamber r2 may be provided. In addition, the valve which adjusts the flow-path resistance of the above-mentioned through-hole 10a and the above-mentioned through-hole 10a can also be provided. Further, when the passage is provided instead of providing the through hole 10a, a valve for adjusting the flow resistance of the passage can be provided. In the case of providing the valve in this way, it is possible to increase the flow resistance of the through hole 10a in an emergency or the like to generate a damping force to attenuate the expansion / contraction operation of the electric actuator 1. Furthermore, instead of providing the through-hole 10c, a groove along the axial direction is provided on the inner periphery of the intermediate cylinder 16 of the electric actuator 1 so that the motor-side chamber r1 and the counter-motor-side chamber r2 that are partitioned by the nut holder 10 are communicated. In this case, the cross-sectional area of the groove can be made smaller than that of the central portion by reducing the depth of the groove at both ends of the intermediate cylinder 16 or by reducing the width of the groove. In this case, when the nut holder 10 reaches a section where the cross-sectional area of the groove becomes small, a cushioning function that suppresses the movement of the output cylinder 5 at the stroke end by generating a damping force with respect to the movement of the output cylinder 5. May be exhibited.

  Although the ball nut 4 is connected to the output cylinder 5 using the nut holder 10, the nut holder 10 can be omitted by directly connecting the ball nut 4 to the output cylinder 5.

  This is the end of the description of the embodiment of the present invention, but the scope of the present invention is of course not limited to the details shown or described.

DESCRIPTION OF SYMBOLS 1 ... Electric actuator, 2 ... Motion conversion part, 3 ... Screw shaft (rotating member), 4 ... Ball nut (linear motion member), 5 ... Output cylinder, 6 ... Elasticity Member, C ... Case, J ... Lubricating oil, M ... Motor, 13 ... Case body 14 ... End cap, 15 ... Holder, 15a, 15b ... Ball bearing, 15d ... Inlet

Claims (4)

A motion converter having a rotating member and a linear motion member that exhibits linear motion by rotation of the rotating member;
A motor coupled to the rotating member;
An output cylinder coupled to the linear motion member;
A case in which the output cylinder is movably inserted while accommodating the motion conversion unit;
An elastic member housed in the case;
An electric actuator comprising: a lubricating oil filled in the case and the output cylinder. An intermediate cylinder that is disposed between the case and the output cylinder and stops the rotation member in the circumferential direction;
The electric actuator according to claim 1, wherein the elastic member is cylindrical and is accommodated between the intermediate cylinder and the case. The case is
A case body that is cylindrical and accommodates the output cylinder;
A holder provided on the motor side end of the case body to rotatably hold the rotating member;
An annular end cap provided at the end of the case body on the side opposite to the motor and slidably supporting the output cylinder
The electric actuator according to claim 1, wherein an injection port for injecting the lubricating oil into the holder is provided. The rotating member is a screw shaft,
The linear motion member is a ball nut screwed onto the screw shaft;
The electric actuator according to any one of claims 1 to 3, wherein the screw shaft is connected to the motor.

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