Electric Linear Actuator

Abstract

To improve responsiveness of an electric linear actuator.SOLUTION: An electric linear actuator according to an embodiment of the present invention comprises an outer cylinder, an electric motor attached to the outer cylinder, a ball screw for converting rotational motion outputted by the electric motor into rectilinear motion in a predetermined direction, and a ball spline for transmitting only the rectilinear motion in the predetermined direction. The ball screw comprises a screw shaft connected to a shaft of the electric motor, and a first nut attached to the outer cylinder, and fitted to the screw shaft. The ball spline comprises a spline shaft connected to the first nut, and a second nut attached to the outer cylinder, and fitted to the spline shaft.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electric linear actuator. [Background technology]

[0002] Parallel mechanisms, which connect multiple links in parallel, are known as mechanisms for realizing industrial manipulators and multi-axis vibration test devices. In some parallel mechanisms, a linear actuator that outputs linear motion is used as the driving device.

[0003] A vibration testing device using a parallel mechanism is described in Patent Document 1. In the parallel mechanism described in Patent Document 1, a hydraulic cylinder with excellent response (e.g., having a speed response frequency of 100 Hz or more) is used as an actuator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-121961 A Summary of the Invention [Problem to be solved by the invention]

[0005] Hydraulic actuators require a hydraulic supply system including an oil tank and a hydraulic pump, which requires high costs for installation and maintenance. Hydraulic systems also have other problems, such as environmental pollution due to oil leakage, the risk of hydraulic oil catching fire, and low energy efficiency.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide an electric linear actuator with excellent responsiveness. [Means for solving the problem]

[0007] According to one embodiment of the present invention, there is provided an electric linear actuator comprising an outer cylinder, an electric motor attached to the outer cylinder, a ball screw that converts the rotational motion output by the electric motor into linear motion in a predetermined direction, and a ball spline that transmits only the linear motion in the predetermined direction, wherein the ball screw comprises a screw shaft connected to a shaft of the electric motor and a first nut that engages with the screw shaft, and the ball spline comprises a spline shaft connected to the first nut and a second nut attached to the outer cylinder that engages with the spline shaft.

[0008] In the above-mentioned electric linear actuator, a bearing may be provided for rotatably supporting a shaft that transmits rotational motion, the outer cylinder may have a cylindrical base portion, a bracket on the load side of the motor may be fixed to one end of the base portion, and the bearing may be fixed to the other end of the base portion.

[0009] The above electric linear actuator may further include a coupling that connects the shaft of the electric motor and the screw shaft, and the screw shaft may be supported by a bearing.

[0010] In the above electric linear actuator, a hole capable of accommodating one end of the threaded shaft and extending in a predetermined direction may be formed on one end side of the spline shaft connected to the first nut.

[0011] In the above electric linear actuator, the outer cylinder may have a plurality of cylinder portions that are aligned in a predetermined direction and connected to each other.

[0012] In the above-mentioned electric linear actuator, the multiple cylindrical portions may include an electric motor accommodating portion that accommodates the electric motor, a base portion, a ball screw accommodating portion that accommodates the ball screw, and a ball spline accommodating portion that accommodates the ball spline, and the electric motor accommodating portion, the base portion, the ball screw accommodating portion, and the ball spline accommodating portion may be arranged in this order in a predetermined direction and connected together.

[0013] In the above electric linear actuator, the outer cylinder may have a cover portion that closes one opening of the motor housing portion, and a connecting portion that connects the cover portion to a bracket on the anti-load side of the motor.

[0014] In the above electric linear actuator, the brackets on the load side and the anti-load side of the motor may be fixed to the outer cylinder.

[0015] In the above electric linear actuator, the electric motor has a rated output of 3 kW or more and a moment of inertia of the rotating part of 0.01 kg m 2 The following configuration may also be used. Effect of the Invention

[0016] According to one embodiment of the present invention, an electric linear actuator with excellent responsiveness is provided. [Brief description of the drawings]

[0017] [Figure 1] 1 is an external view of an electric linear actuator according to an embodiment of the present invention; [Diagram 2] 1 is a diagram showing the internal structure of an electric linear actuator according to an embodiment of the present invention; [Diagram 3] 1 is a diagram showing the internal structure of an electric linear actuator according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, identical or corresponding components are given the same or corresponding reference numerals, and duplicated descriptions are omitted. In addition, when multiple items with the same reference numerals are displayed in each drawing, the reference numerals are not necessarily given to all of the multiple displays, and the reference numerals are appropriately omitted for some of the multiple displays.

[0019] The electric linear actuator 1 according to the embodiment of the present invention described below is an electric actuator capable of outputting reciprocating linear motion. The electric linear actuator 1 according to the present embodiment is a general-purpose actuator, but is suitable as a drive source for parallel mechanisms such as a Stewart platform used as a mechanism for robot manipulators, machine tools, multi-axis vibration test devices, flight simulators, etc.

[0020] Fig. 1 is an external view of an electric linear actuator 1 according to one embodiment of the present invention. Fig. 2 and Fig. 3 are views showing the internal structure of the electric linear actuator 1.

[0021] As shown in Fig. 2, the electric linear actuator 1 has a fixed part 1F and a movable part 1M that can move back and forth in the length direction relative to the fixed part 1F (i.e., reciprocating linear motion), and expands and contracts as the movable part 1M moves back and forth. Fig. 2 shows the electric linear actuator 1 in a contracted state, and Fig. 3 shows the electric linear actuator 1 in an extended state.

[0022] 2 and 3, the direction from left to right is defined as the Z-axis direction, the direction from bottom to top as the X-axis direction, and the direction perpendicular to the paper from back to front as the Y-axis direction. The Z-axis direction is the direction in which the movable part 1M moves back and forth, with the positive Z-axis direction being called the forward or forward direction and the negative Z-axis direction being called the backward or backward direction. The Z-axis direction in which the movable part 1M moves back and forth is called the operating direction of the electric linear actuator 1.

[0023] As shown in FIG. 3, the electric linear actuator 1 includes an outer tube 10, a motor 20 (electric motor) having a main body 21 (stator) attached to the outer tube 10, a knuckle joint 70 (hinge) attached to the outer tube 10, a bearing 40 that rotatably supports a shaft (in this embodiment, a screw shaft 51 described later) that transmits the power of the motor 20, a ball screw 50 that converts the rotational motion output from the motor 20 into linear motion, a coupling 30 that connects the shaft 22 of the motor 20 and the screw shaft 51, and a ball spline 60 and a spherical joint 80 that transmit the linear motion output from the ball screw 50.

[0024] The outer cylinder 10 has a first cylindrical portion 11 (motor housing portion) that houses the motor 20, a second cylindrical portion 12 (base portion) to which the motor 20 and the bearing 40 are attached, a third cylindrical portion 13 (ball screw housing portion) that houses the ball screw 50, a fourth cylindrical portion 14 (ball spline housing portion) that houses the nut 62 of the ball spline 60, a lid portion 15 that closes the opening at the rear end of the first cylindrical portion 11, and a cylindrical connecting portion 16 that connects the motor 20 and the lid portion 15. More specifically, the first cylindrical portion 11 houses the main body 21 (and a part of the shaft 22) of the motor 20, and the third cylindrical portion 13 houses the nut 52 (and a part of the screw shaft 51) of the ball screw 50. A flange 621 formed on one end of the nut 62 of the ball spline 60 is disposed outside the fourth cylindrical portion 14.

[0025] The multiple cylindrical portions of the outer tube 10 (first cylindrical portion 11, second cylindrical portion 12, third cylindrical portion 13, and fourth cylindrical portion 14) are arranged in a row in this order concentrically (i.e., with their center lines aligned) and are connected together by welding, bolting, etc.

[0026] The second cylindrical portion 12 has an outer flange 121 formed on the outer periphery of the rear end portion (left end portion in FIG. 3), an outer flange 122 formed on the outer periphery of the front end portion (right end portion in FIG. 3), and an inner flange 123 formed on the inner periphery of the front end portion. The front end of the first cylindrical portion 11 is joined to the outer flange 121, and the rear end of the third cylindrical portion 13 is joined to the outer flange 122.

[0027] A flange portion 231 of the bracket 23 on the load side of the motor 20 is fixed to the rear end of the second cylindrical portion 12. Also, a flange 41 of the bearing 40 is fixed to the inner flange 123 of the second cylindrical portion 12. In this manner, by configuring the motor 20 and the bearing 40 to be attached to a common member (the second cylindrical portion 12), centering of the motor 20 and the bearing 40 is facilitated.

[0028] An outer flange 141 is formed on the outer periphery of the rear end of the fourth cylindrical portion 14, and the front end of the third cylindrical portion 13 is joined to the outer flange 141. In addition, the rear end of the first cylindrical portion 11 is joined to the edge of the lid portion 15.

[0029] The rear end of the connecting part 16 is joined to the center of the inner surface of the lid part 15. A bracket 24 on the anti-load side of the motor 20 is attached to the front end of the connecting part 16. The bracket 24 may be fixed directly to the lid part 15 without using the connecting part 16. The outer cylinder 10 of this embodiment is formed to be larger than the size of the motor 20 so that the motor 20 can be replaced with one with a larger capacity. The outer cylinder 10 of this embodiment is configured to be able to mount motors 20 of a certain range of sizes by changing the size of the connecting part 16 and the position of the mounting hole according to the size of the motor 20.

[0030] The shaft 22 of the motor 20 is rotatably supported by bearings (not shown) attached to the bracket 23 and the bracket 24, respectively. Usually, the motor 20 is fixed only to the bracket 23 on the load side and is supported in a cantilever manner. In this case, the support rigidity on the anti-load side of the shaft 22 of the motor 20 is relatively low. Therefore, when a large load is applied to the shaft 22, a precession motion of the shaft 22 occurs with the bearing attached to the bracket 23 on the load side as a fulcrum. This causes distortion in the power transmission shaft including the shaft 22, and the driving performance and driving control accuracy of the electric linear actuator 1 decrease.

[0031] In this embodiment, the bracket 24 on the opposite side of the motor 20 to the outer cylinder 10 is also fixed to the outer cylinder 10. in By fixing the shaft 22, the supporting rigidity of the anti-load side of the motor 20 is improved, and the deterioration of performance due to the precession of the shaft 22 is suppressed.

[0032] The motor 20 of this embodiment has a moment of inertia of the rotating part of 0.01 kg m 2 Less than or equal to 0.008 kg m 2It is a high-output, ultra-low inertia AC servo motor with a rated output of 3 kW to 60 kW (more practically, 7 kW to 37 kW) with the output suppressed to a maximum of 100 Hz (or less). By using such an ultra-low inertia motor, the electric linear actuator 1 of this embodiment is capable of linear reciprocating drive at a frequency exceeding 100 Hz, for example, and can be used in applications requiring high responsiveness, such as vibration testing equipment.

[0033] The motor 20 is an AC servo motor, but various motors that can control the drive amount (rotation angle), such as a DC servo motor or a stepping motor, may also be used as the motor 20.

[0034] In the second cylindrical portion 12, the shaft 22 of the motor 20 and the screw shaft 51 of the ball screw 50 are connected by a coupling 30. For example, a fixed shaft coupling is used for the coupling 30. By using a fixed shaft coupling, it is possible to improve responsiveness. The coupling 30 in this embodiment is a cylindrical shaft coupling, but a flange-type fixed shaft coupling may also be used.

[0035] The ball screw 50 includes a screw shaft 51 and a nut 52 that fits onto the screw shaft 51. The nut 52 reciprocates along the screw shaft 51 in the Z-axis direction in response to the rotation of the screw shaft 51.

[0036] The ball spline 60 includes a spline shaft 61 and two nuts 62 that fit with the spline shaft 61 .

[0037] A fixing flange 621 is formed on one axial end of the nut 62. The two nuts 62 are fitted into the hollow portion of the fourth cylindrical portion 14 of the outer cylinder 10 from both axial ends, and fixed to the fourth cylindrical portion 14 at the flanges 621. The spline shaft 61 is prevented from rotating with respect to the nuts 62 (i.e., with respect to the outer cylinder 10 to which the nuts 62 are attached), and only linear movement in the Z-axis direction is permitted.

[0038] The rear end of the spline shaft 61 is connected to the front end of the nut 52 of the ball screw 50. This prevents the nut 52 from rotating around the Z axis relative to the outer cylinder 10, and only allows linear movement in the Z axis direction.

[0039] A hole 61a extending in the Z-axis direction is formed concentrically in the rear part of the spline shaft 61. The hole 61a has an outer diameter larger than that of the screw shaft 51 of the ball screw 50, and accommodates the front part of the screw shaft 51 in the contracted state as shown in FIG.

[0040] As described above, in the electric linear actuator 1 of this embodiment, the fixed part 1F is provided with the knuckle joint 70, and the movable part 1M is provided with the spherical joint 80 so that the electric linear actuator 1 is suitable for use as a rectilinear joint of a parallel mechanism such as a Stewart platform. For example, when the electric linear actuator 1 is used as a rectilinear joint of a Stewart platform, the mounting part 71 of the knuckle joint 70 is attached to the base side, and the mounting part 81 of the spherical joint 80 is attached to the output link side.

[0041] It should be noted that the knuckle joint 70 and the spherical joint 80 are not essential components, and for example, the outer cylinder 10 may be directly attached to one of the two objects to which relative movement is imparted by the electric linear actuator 1, and the spline shaft 61 may be directly attached to the other object.

[0042] The above is a description of exemplary embodiments of the present invention. The embodiments of the present invention are not limited to those described above, and are within the scope of the technical idea of ​​the present invention. Inside For example, the present invention also includes an appropriate combination of the embodiments and the like explicitly shown in the specification or obvious embodiments and the like.

[0043] In the above embodiment, the bearing 40 supports the screw shaft 51, but the bearing 40 may support the shaft 22 of the motor 20. Also, an intermediate shaft may be provided between the shaft 22 and the screw shaft 51, and the bearing 40 may support the intermediate shaft.

[0044] The ball screw 50 may be replaced by another type of lead screw.

[0045] A universal joint may be used instead of the spherical joint 80. Also, a knuckle joint 70 Alternatively, a spherical joint or a universal joint may be used. [Explanation of symbols]

[0046] 1 Electric Linear Actuator 10 Outer cylinder 20 Motor 30 Coupling 40 Bearings 50 Ball screw (feed screw mechanism) 60 Ball spline 70 Knuckle joint (hinge) 80 Universal joint / spherical joint

Claims

1. An outer cylinder, An electric motor attached to the outer cylinder; a ball screw for converting a rotational motion output by the electric motor into a linear motion in a predetermined direction; a ball spline that transmits only linear motion in the predetermined direction; Equipped with The ball screw is A screw shaft connected to a shaft of the electric motor; A first nut that fits onto the screw shaft, The ball spline is a spline shaft connected to the first nut; a second nut attached to the outer cylinder and fitted with the spline shaft, The outer cylinder is a cover portion that closes an opening on one end side of the outer cylinder in the predetermined direction; a connecting portion that is disposed in a space between the cover portion and the electric motor in the predetermined direction and connects the cover portion and a bracket on the opposite load side of the electric motor, Electric linear actuator.

2. Brackets on the load side and the non-load side of the motor are fixed to the outer cylinder.

2. The electric linear actuator of claim 1.

3. An outer cylinder, An electric motor attached to the outer cylinder; a ball screw for converting a rotational motion output by the electric motor into a linear motion in a predetermined direction; a ball spline that transmits only linear motion in the predetermined direction; Equipped with The ball screw is A screw shaft connected to a shaft of the electric motor; A first nut that fits onto the screw shaft, The ball spline is a spline shaft connected to the first nut; a second nut attached to the outer cylinder and fitted with the spline shaft, Brackets on the load side and the non-load side of the motor are fixed to the outer cylinder. Electric linear actuator.

4. The outer cylinder is a cover portion that closes an opening on one end side of the outer cylinder in the predetermined direction; a connecting portion that is disposed in a space between the cover portion and the electric motor in the predetermined direction and connects the cover portion and a bracket on the opposite load side of the electric motor, 4. The electric linear actuator according to claim 3.

5. A hole extending in the predetermined direction capable of accommodating one end of the screw shaft is formed on one end side of the spline shaft that is connected to the first nut. The electric linear actuator according to any one of claims 1 to 4.

6. a bearing for rotatably supporting a shaft for transmitting the rotational motion; The outer cylinder has a cylindrical base portion, A bracket on a load side of the motor is fixed to one end of the base portion, The bearing is fixed to the other end of the base portion. The electric linear actuator according to any one of claims 1 to 5.

7. A coupling is provided to connect the shaft of the electric motor and the screw shaft, The screw shaft is supported by the bearing.

7. The electric linear actuator according to claim 6.

8. the outer cylinder has a plurality of cylinder portions arranged and connected in the predetermined direction, The plurality of cylindrical portions are a motor housing portion that houses the motor; The base portion; a ball screw receiving portion that receives the ball screw; a ball spline receiving portion that receives the ball spline, the electric motor accommodating portion, the base portion, the ball screw accommodating portion, and the ball spline accommodating portion are arranged in the stated order in the predetermined direction and connected to each other; The electric linear actuator according to claim 6 or 7.

9. The electric motor has a rated output of 3 kW or more and a moment of inertia of a rotating part of 0.01 kg m ２ is as follows: It is possible to perform linear reciprocating drive at a repetition frequency exceeding 100 Hz. The electric linear actuator according to any one of claims 1 to 8.

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