Control device for electric actuator, electric actuator system, control method for electric actuator, and program
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-01-28
- Publication Date
- 2026-08-13
Smart Images
Figure JP2026002767_13082026_PF_FP_ABST
Abstract
Description
Control Device for Electric Actuator, Electric Actuator System, Control Method for Electric Actuator, and Program
[0001] The present disclosure relates to a control device for an electric actuator, an electric actuator system, a control method for an electric actuator, and a program.
[0002] Japanese Patent Application Laid-Open No. 2004-64951 discloses a DC brushless motor control device. According to Japanese Patent Application Laid-Open No. 2004-064951, the position of the rotor of a DC brushless motor is detected by a Hall element.
[0003] Recently, better technologies have been desired for the control of an electric actuator having a cylinder device and a motor.
[0004] A first aspect of the present disclosure is a control device for an electric actuator having a driving device including a mover that moves linearly or rotationally and a motor that moves the mover, the motor including a rotor that drives the mover and a magnetic sensor that outputs a signal corresponding to the rotational position of the rotor, a determination unit that determines whether the mover has reached a braking start position set in advance before the end of the movement range of the mover based on the signal, and a braking control unit that controls the motor to reduce the movement speed of the mover when the determination unit determines that the mover has reached the braking start position.
[0005] A second aspect of the present disclosure is an electric actuator system having the control device for an electric actuator according to the first aspect of the present disclosure and the electric actuator.
[0006] A third aspect of the present disclosure is a control method for an electric actuator having a drive device equipped with a linearly moving or rotating movable element and a motor for moving the movable element, wherein the motor includes a rotor for driving the movable element and a magnetic sensor that outputs a signal corresponding to the rotational position of the rotor, and the control method for an electric actuator includes a determination step of determining, based on the signal, whether the movable element has reached a preset braking start position located in front of the end of the movable element's range of motion, and a braking control step of controlling the motor to reduce the moving speed of the movable element when the determination step determines that the movable element has reached the braking start position.
[0007] A fourth aspect of this disclosure is a program for causing a computer to execute a control method for an electric actuator according to a third aspect of this disclosure.
[0008] This disclosure provides a better electric actuator control device, electric actuator system, electric actuator control method, and program.
[0009] The above-mentioned objectives, features, and advantages will be readily apparent from the following description of the embodiments, which will be illustrated with reference to the attached drawings.
[0010] Figure 1 is a perspective view of an electric actuator system according to the first embodiment. Figure 2 is a diagram illustrating the schematic configuration of a drive device (cylinder device) provided in the electric actuator system. Figure 3 is a diagram illustrating the schematic configuration of a motor provided in the electric actuator system. Figure 4 is a block diagram illustrating the schematic configuration of a control device provided in the electric actuator system. Figure 5 is a graph schematically illustrating the change in the movement speed of a movable element provided in the drive device. Figure 6 is a flowchart of the control method of the electric actuator according to the first embodiment. Figure 7 is a diagram illustrating the schematic configuration of an electric actuator (rotary table) according to the second embodiment. Figure 8 is a cross-sectional view of the rotary table.
[0011] An electric actuator comprises a motor and a drive unit. The drive unit is, for example, a cylinder unit, a rotating unit, etc. The drive unit is equipped with a movable element driven by the motor. The movable element is, for example, a nut provided in a cylinder unit. This nut may be provided on the piston of the cylinder unit. The nut is screwed onto a lead screw. As the lead screw rotates due to the motor, the nut moves in the axial direction of the lead screw. The position and speed of the movable element can be controlled based on the rotational position of the motor's rotor. This rotational position is detected by an optical encoder, which is an optical sensor provided in the motor.
[0012] Regarding such electric actuators, the following problems can be cited, for example. Electric actuators such as electric stoppers are often installed indoors in logistics facilities and the like. Foreign matter such as dust floating in the room may enter the motor and adhere to the optical encoder, potentially adversely affecting the function of the optical encoder. As disclosed in Japanese Patent Application Publication No. 2004-64951, detecting the rotational position without using an optical encoder by using a magnetic sensor such as a Hall element is a possible solution. However, the accuracy of rotational position detection by magnetic sensors is generally inferior to that of optical encoders. Therefore, when detecting the rotational position of the rotor of a motor that drives a movable element using a magnetic sensor, it is difficult to accurately control the position and speed of the movable element. As a result, there is a risk that the movable element and the edge of its range of motion (for example, the inner wall of the case) may collide relatively strongly.
[0013] Based on the preliminary explanation above, embodiments will be described below. In the following description, the term "program" (computer program, computer software) is also referred to as a "computer program product." A computer program product is not limited to programs stored on a storage medium, but also includes programs transmitted, distributed, or downloaded via networks such as the Internet.
[0014] (First Embodiment) Figure 1 is a perspective view of the electric actuator system 10 according to the first embodiment.
[0015] The electric actuator system 10 comprises an electric actuator 12 and a control device 14 for the electric actuator 12. The electric actuator 12 has a drive device 100 and a motor 200. In this embodiment, the case in which the electric actuator 12 is an electric stopper 12A will be described. The electric actuator system 10 may further include a housing 16 that can cover at least a part of the electric actuator 12 and the control device 14.
[0016] Figure 2 is a diagram illustrating the schematic configuration of the drive device 100 (cylinder device 100A) provided in the electric actuator system 10.
[0017] The drive device 100 is, for example, a cylinder device 100A. The cylinder device 100A is an electric cylinder that can be driven by a motor 200. The cylinder device 100A comprises a case 102, a piston 104, and a lead screw 108A. The piston 104 is fitted with a nut 106A.
[0018] The case 102 is a component (cylinder case, cylinder tube) that houses the piston 104. The nut 106A is a movable element 106 provided on the piston 104. The lead screw 108A is a transmission member 108 that transmits the rotation of the motor 200's shaft 206 (described later). The lead screw 108A is supported, for example, by a bearing portion 111 provided on the case 102.
[0019] The nut 106A is screwed onto the lead screw 108A. The nut 106A moves (linearly) within the case 102 together with the piston 104 in response to the motor 200 being driven.
[0020] The direction of movement DX of the nut 106A is shown in Figure 2. The direction of movement DX of the nut 106A coincides with the axial direction of the lead screw 108A. The direction of movement DX encompasses a first direction DX1 and a second direction DX2. The second direction DX2 is the opposite direction to the first direction DX1.
[0021] The piston 104 is connected to a stopper member 18 (see also Figure 1), which is provided, for example, on an electric stopper 12A. This allows the stopper member 18 to reciprocate together with the piston 104. The stopper member 18 can be inserted into or removed from the transport path of transported goods, for example, in a logistics facility. The stopper member 18 can restrict the transport of the transported goods by interfering with them.
[0022] The cylinder device 100A further comprises a plurality of movement restricting parts 110 (1101, 1102). The plurality of movement restricting parts 110 define the ends PE (PE1, PE2) of the movement range of the movable element 106 within the case 102. In this embodiment, the movable element 106, which is the nut 106A, and the piston 104 can move together. In such a case, the movement range of the movable element 106 can be substantially defined as the movement range of the piston 104.
[0023] For example, the first movement restricting part 1101 among the multiple movement restricting parts 110 defines the first end PE1. The first end PE1 is the end PE of the movement range of the piston 104 in the first direction DX1. The piston 104 comes into contact with the first movement restricting part 1101 by reaching the first end PE1. The first end PE1 (first movement restricting part 1101) defines, for example, the top dead center position of the piston 104.
[0024] In contrast, the second movement restricting section 1102 among the multiple movement restricting sections 110 defines the second end PE2. The second end PE2 is the end PE of the movement range of the piston 104 in the second direction DX2. The piston 104 comes into contact with the second movement restricting section 1102 by reaching the second end PE2. The second end PE2 (second movement restricting section 1102) defines, for example, the bottom dead center position of the piston 104.
[0025] Each of the multiple movement restricting sections 110 is, for example, a part of the inner wall of the case 102, but is not limited to this. At least one of the multiple movement restricting sections 110 may be a separate component from the case 102 that is disposed inside the case 102.
[0026] The movement restricting section 110 may have a cushioning member 112 disposed at the end PE. Each of the multiple movement restricting sections 110 may have a cushioning member 112. That is, the cylinder device 100A may have multiple cushioning members 112 (1121, 1122). For example, the first movement restricting section 1101 may have the first cushioning member 1121 among the multiple cushioning members 112. On the other hand, for example, the second movement restricting section 1102 may have the second cushioning member 1122 among the multiple cushioning members 112.
[0027] Figure 3 is a diagram illustrating the schematic configuration of the motor 200 provided in the electric actuator system 10.
[0028] The motor 200 is a drive source (electric motor) that drives the drive unit 100. The motor 200 comprises a stator 202, a rotor 204, a shaft 206, and a magnetic sensor 208. The motor 200 may further comprise a housing 210 that can cover at least a portion of the stator 202, rotor 204, shaft 206, and magnetic sensor 208. The stator 202 comprises a coil 212. The rotor 204 contains a magnet (permanent magnet). The magnetic sensor 208 has, for example, a Hall element 208e. The magnetic sensor 208 may have a plurality of Hall elements 208e. The magnetic sensor 208 may also be a magnetic encoder.
[0029] The rotor 204 rotates when current is supplied to the coil 212. The magnetic sensor 208 outputs a signal corresponding to the rotational position of the rotor 204. More specifically, the magnetic sensor 208 outputs a signal indicating the magnetism that changes as the rotor 204, which contains magnets, rotates. This signal is input to the control device 14.
[0030] The shaft 206 can rotate integrally with the rotor 204, thereby rotating the lead screw 108A. This causes the piston 104 (nut 106A) to move inside the case 102. The direction of movement DX of the piston 104 can change in accordance with the change in the rotation direction of the shaft 206.
[0031] Motor 200 is preferably a brushless DC motor (DC: direct current). The reason for this will be explained later.
[0032] Figure 4 is a block diagram illustrating the schematic configuration of the control device 14 provided in the electric actuator system 10.
[0033] The control device 14 is an electronic device (computer) that controls the electric actuator 12. The control device 14 may be a relatively small computer such as a microcontroller. The control device 14 may be installed on the motor 200. In that case, for example, the control device 14 may be installed on the motor 200 together with a motor driver (not shown). As shown in Figure 4, the control device 14 includes a storage unit 20 and an arithmetic unit 22.
[0034] The storage unit 20 includes one or more memories. For example, one or more non-volatile memories are included in the storage unit 20. The storage unit 20 stores a control program. The control program is a program that causes the control device 14 to control the electric actuator 12. One or more volatile memories may be further included in the storage unit 20.
[0035] The arithmetic unit 22 includes a processing circuit. The processing circuit is a circuit capable of performing arithmetic processing. This processing circuit may have one or more processors. For example, the processing circuit may have a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), etc. The processing circuit may also have discrete devices.
[0036] The calculation unit 22 includes an acquisition unit 24, a determination unit 26, and an actuator control unit 28. The acquisition unit 24, the determination unit 26, and the actuator control unit 28 are realized by the processing circuit described above. For example, the acquisition unit 24, the determination unit 26, and the actuator control unit 28 are realized by the execution of a control program stored in the storage unit 20 by the processor of the calculation unit 22. The discrete devices described above may realize at least a part of the acquisition unit 24, the determination unit 26, and the actuator control unit 28.
[0037] The acquisition unit 24 acquires the signal output from the magnetic sensor 208.
[0038] The determination unit 26 determines whether the piston 104 (nut 106A) has reached the braking start position PB, which will be described later, based on the signal acquired by the acquisition unit 24. Since the rotational position of the rotor 204 of the motor 200 and the piston position, which is the position of the piston 104, are correlated, the piston position can be estimated based on the signal from the magnetic sensor 208. Therefore, the determination unit 26 can determine whether the piston 104 has reached the braking start position PB based on the signal from the magnetic sensor 208.
[0039] The braking start position PB is a predetermined position within the movement range of the movable element 106. The braking start position PB is a predetermined position just before the end PE of the movement range of the movable element 106. For example, a first braking start position PB1 and a second braking start position PB2 are shown in Figure 2.
[0040] The first braking start position PB1 is a braking start position PB set in front of the first end PE1. The first braking start position PB1 is located in the second direction DX2 relative to the first end PE1. When the moving element 106 (piston 104) is moving toward the first direction DX1 (first end PE1), the determination unit 26 determines whether the piston 104 has reached the first braking start position PB1 based on the signal acquired by the acquisition unit 24.
[0041] The second braking start position PB2 is a braking start position PB set in front of the second end PE2. The second braking start position PB2 is located in the first direction DX1 relative to the second end PE2. When the moving element 106 (piston 104) is moving toward the second direction DX2 (second end PE2), the determination unit 26 determines whether the piston 104 has reached the second braking start position PB2 based on the signal acquired by the acquisition unit 24.
[0042] The distance between the first braking start position PB1 and the first end PE1, and the distance between the second braking start position PB2 and the second end PE2, may be equal or different.
[0043] The first braking start position PB1 and the second braking start position PB2 may overlap. In this case, a substantially single braking start position PB that also serves as the first braking start position PB1 and the second braking start position PB2 can be set. This single braking start position PB is, for example, the midpoint position within the movement range of the mover 106 (piston 104), but is not limited thereto.
[0044] The actuator control unit 28 controls the motor 200 to move the piston 104. More specifically, the actuator control unit 28 executes a process for instructing the above-described motor driver. The motor driver drives the motor 200 based on the instruction from the actuator control unit 28.
[0045] The actuator control unit 28 may control the motor 200 based on a control command input from an external device (not shown) of the control device 14. The external device may include, for example, an input device that can be operated by a person to give a movement instruction to the mover 106 (piston 104). In this case, the actuator control unit 28 may control the motor 200 according to a control signal output from the input device. An operation unit (not shown) having the input device may be provided in the electric actuator system 10. Further, for example, a monitoring device (monitoring system) that monitors the inside of a logistics facility or the like where the electric actuator 12 is installed may input a control signal to the actuator control unit 28 (control device 14).
[0046] FIG. 5 is a graph schematically illustrating the transition of the moving speed V of the mover 106 provided in the drive device 100. The transition of the moving speed V during the period in which the mover 106 moves from one of the first end PE1 and the second end PE2 to the other of the first end PE1 and the second end PE2 is illustrated in FIG. 5.
[0047] The actuator control unit 28 controls the motor 200 so that the piston 104 can move at a first speed V1 which is a predetermined speed. The first speed V1 is the target speed of the mover 106 during the period from when the mover 106 (piston 104) in a stationary state starts to move until it is determined by the determination unit 26 that it has reached the braking start position PB. In this case, the actuator control unit 28 accelerates the stationary piston 104 to the first speed V1 and then maintains the moving speed V of the mover 106 at the first speed V1. The period from the time point t0 to the time point t1 shown in FIG. 5 is the period from when the mover 106 in a stationary state starts to move until it is determined by the determination unit 26 that it has reached the braking start position PB.
[0048] The actuator control unit 28 includes a braking control unit 30. The braking control unit 30 executes braking control when it is determined by the determination unit 26 that the mover 106 (piston 104) has reached the braking start position PB. The braking control is control for reducing the moving speed V of the mover 106. That is, when it is determined by the determination unit 26 that the mover 106 has reached the braking start position PB, the braking control unit 30 controls the motor 200 to reduce the moving speed V. As a result, after the time point t1 when it is determined by the determination unit 26 that the mover 106 has reached the braking start position PB, the mover 106 moves at a speed lower than the above-described first speed V1.
[0049] Braking control may include a process to gradually reduce the amount of current supplied to the motor 200. This allows the braking control unit 30 to gradually reduce the moving speed V of the moving element 106 (piston 104). In this case, the braking control unit 30 may reduce the moving speed V of the moving element 106 with a target of a second speed V2. The second speed V2 is the lower limit of the moving speed V in braking control. The second speed V2 is lower than the first speed V1. Braking control may include control to maintain the moving speed V at the second speed V2 until the moving element 106 reaches the end PE of the moving range, if the moving speed V is reduced to the second speed V2 before the moving element 106 reaches the end PE. For example, during the period from time t2 to time t3 in Figure 5, the moving speed V is maintained at the second speed V2. More specifically, the control that can be performed by the braking control unit 30 during the period from time t2 to time t3 in Figure 5 includes acceleration control and deceleration control. In this case, acceleration control is a control to increase the moving speed V when the moving speed V falls below the second speed V2. Conversely, deceleration control is a control to decrease the moving speed V when the moving speed V exceeds the second speed V2.
[0050] By performing braking control, the movable element 106 (piston 104) can reach the end PE of the movement range at a speed lower than the first speed V1. Time t3 in Figure 5 is the time when the movable element 106 reaches the end PE of the movement range. As mentioned above, the movement restricting unit 110 may also have a cushioning member 112.
[0051] The actuator control unit 28 further includes a positioning control unit 34. The positioning control unit 34 performs positioning control when the movable element 106 (piston 104) reaches the end PE. The positioning control unit 34 can determine whether the movable element 106 has reached the end PE, for example, based on whether the moving speed V after the start of braking control has become zero (see also time t3 in Figure 5). Positioning control is a control that supplies a current to the motor 200 that is smaller than the current supplied to the motor 200 before the movable element 106 reached the end PE, thereby bringing the movable element 106 to a stop at the end PE.
[0052] Figure 6 is a flowchart of the control method for the electric actuator 12 according to the first embodiment.
[0053] The control device 14 is capable of executing the control method shown in Figure 6. This control method is realized, for example, by the arithmetic unit 22 (processor) provided in the control device 14 executing a program (control program) stored in the memory unit 20. As shown in Figure 6, this control method includes a drive control step S1, an acquisition step S2, a determination step S3, a braking control step S4, and a positioning control step S5.
[0054] In the drive control step S1, the actuator control unit 28 controls the motor 200 to move the movable element 106. The drive control step S1 may be started in response to a control signal being input to the control device 14 by, for example, the input device, monitoring device, etc. The target speed of the movable element 106 in the drive control step S1 is the first speed V1 described above.
[0055] In acquisition step S2, the acquisition unit 24 acquires the signal output from the magnetic sensor 208. Next, in determination step S3, the determination unit 26 determines whether or not the moving element 106 has reached the braking start position PB, based on the signal acquired in acquisition step S2.
[0056] If it is determined in the determination step S3 that the movable element 106 has not reached the braking start position PB, the control device 14 continues the flow from the drive control step S1 to the determination step S3. If it is determined in the determination step S3 that the movable element 106 has reached the braking start position PB, the control device 14 proceeds to the braking control step S4.
[0057] In braking control step S4, the braking control unit 30 performs braking control. As a result, the piston 104 reaches the end PE of the movement range at a movement speed V lower than the first speed V1.
[0058] In positioning control step S5, the positioning control unit 34 performs positioning control. As a result, the movable element 106 comes to rest at the end PE.
[0059] According to the first embodiment, the control device 14, the electric actuator system 10, the control method, and the program provide the effects described below, for example.
[0060] The control device 14 includes a determination unit 26. The determination unit 26 determines whether the moving element 106 has reached the braking start position PB based on the signal from the magnetic sensor 208 provided on the motor 200. Since the position of the moving element 106 is estimated based on the signal from the magnetic sensor 208, an optical encoder is not required.
[0061] The control device 14 includes a braking control unit 30. The braking control unit 30 executes braking control when the determination unit 26 determines that the movable element 106 has reached the braking start position PB. As a result, the movement speed V of the movable element 106 is suppressed to some extent before the movable element 106 reaches the end PE of the movement range. Consequently, the impact caused by contact between the movable element 106 and the end PE of the movement range of the movable element 106 is mitigated.
[0062] By mitigating the impact, the risk of damage or deformation to the drive unit 100, for example, can be reduced. Furthermore, by mitigating the impact, irregular rotation (such as reverse rotation) of the shaft 206, which is mechanically connected to the movable element 106, can be suppressed. As a result, unnecessary regenerative current from the motor 200 can be suppressed, for example.
[0063] The braking control unit 30 does not perform braking control until the determination unit 26 determines that the movable element 106 has reached a predetermined braking start position PB located just before the end PE. As a result, the movable element 106 can move at a relatively high speed until it approaches the end PE to a certain extent. Therefore, the electric actuator system 10 is useful for applications that require the movable element 106 to move at a relatively high speed.
[0064] If the moving speed V of the moving element 106 is suppressed before the moving element 106 reaches the edge PE of the range of motion, the above-mentioned impact can be mitigated to some extent. For this reason, the braking control according to this embodiment can be realized if the approximate position of the moving element 106 can be determined. Therefore, according to this embodiment, even if the magnetic sensor 208 is used to detect the rotational position of the rotor 204, a sufficient impact mitigation effect can be achieved.
[0065] The braking control unit 30 may gradually reduce the movement speed V of the moving element 106 by performing braking control. As a result, after the determination unit 26 determines that the braking start position PB has been reached, the moving element 106 can continue to move while reducing its movement speed V. The lower the movement speed V of the moving element 106, the greater the impact can be mitigated.
[0066] The positioning control unit 34 may stop the movable element 106 at the end PE by executing positioning control when the movable element 106 reaches the end PE. This suppresses irregular movement of the movable element 106 between the time the movable element 106 reaches one end PE (for example, the second end PE2) and the time the movable element 106 starts moving to the other end PE (for example, the first end PE1).
[0067] The drive unit 100 preferably includes a cushioning member 112. The cushioning member 112 is disposed at the end PE of the range of movement of the movable element 106. The cushioning member 112 disposed at the end PE comes into contact with the movable element 106 as it moves toward the end PE. In this case, the cushioning member 112 can further mitigate the aforementioned impact.
[0068] The control device 14 is preferably provided on the motor 200. By integrating the motor 200 and the control device 14, the electric actuator system 10 can be made more compact.
[0069] The motor 200 is preferably a brushless DC motor. Typically, a brushless DC motor is equipped with a rotor 204 formed by permanent magnets and a magnetic sensor 208 (Hall element 208e) for controlling the rotation of the rotor 204. Therefore, many common brushless DC motors can be used as the motor 200 according to this embodiment. This eliminates the need to customize the motor 200, for example, in order to specifically install the magnetic sensor 208. Furthermore, since there is no need to procure the motor 200 according to this embodiment as a custom-made product, the manufacturing cost, procurement cost, etc. of the electric actuator 12 can be reduced.
[0070] (Second Embodiment) The second embodiment is described below, but any description that overlaps with the first embodiment will be omitted as appropriate. The reference numerals used for drawing reference in the first embodiment will be used in the following description unless otherwise specified. The second embodiment differs from the first embodiment in that the movable element 106 is rotatable.
[0071] Figure 7 is a diagram illustrating the schematic configuration of the electric actuator 12 (rotary table 12B) according to the second embodiment. Figure 8 is a cross-sectional view of the rotary table 12B. The cross-section taken along line VIII-VIII in Figure 7 is shown in Figure 8.
[0072] The rotary table 12B includes a rotating device 100B which is a drive device 100 and a motor 200. The rotating device 100B includes a worm wheel 106B which is a rotatable moving element 106 and one or more movement restricting units 110.
[0073] The worm wheel 106B is rotatable around the rotation axis (rotation axis line) LR in accordance with the rotation of the rotor 204 of the motor 200. The rotation direction DR of the worm wheel 106B in this case is shown in Figure 7. The rotation direction DR includes a first rotation direction DR1 and a second rotation direction DR2. The second rotation direction DR2 is the opposite direction to the first rotation direction DR1.
[0074] A transmission member 108 may be interposed between the worm wheel 106B and the shaft 206. In this case, the transmission member 108 may have, for example, a worm 108Ba, but may also have a belt 108Bb, a pulley 108Bc, etc. as appropriate.
[0075] The worm 108Ba may be supported by one or more bearing portions 111 appropriately provided in the case (housing) 102 of the rotating device 100B. The worm wheel 106B may also be supported by one or more bearing portions 113 separate from the bearing portions 111 that support the worm 108Ba.
[0076] The worm wheel 106B may be connected to a table member 31 (Figure 8) provided on the rotary table 12B. The table member 31 rotates in response to the rotation of the worm wheel 106B.
[0077] The movement restricting unit 110 defines the movement range of the worm wheel 106B. In this embodiment, the rotational direction DR described above is specified as the movement direction of the worm wheel 106B, which is the movable element 106. Furthermore, the rotational range of the worm wheel 106B in the rotational direction DR is specified as the movement range of the worm wheel 106B.
[0078] The worm wheel 106B may be provided with a contact portion 32 that can come into contact with the movement restricting portion 110 while the worm wheel 106B is rotating. This contact portion 32 is, for example, a projection that protrudes in a direction intersecting the rotation direction DR (the tangential direction of the rotation direction DR). The contact portion 32 may also be provided on other members that rotate integrally with the worm wheel 106B.
[0079] The contact portion 32 may be, for example, a part of a screw (bolt) disposed on the worm wheel 106B. For example, the contact portion 32 may be formed by the head 32H of a screw disposed on the body of the worm wheel 106B. In contrast, the movement restricting portion 110 may be another screw (bolt) disposed on the case 102 of the rotating device 100B.
[0080] The position where the movement restricting portion 110 and the contact portion 32 come into contact (the rotational position of the worm wheel 106B) is identified as the end PE of the movement range of the worm wheel 106B. The first end PE1 is the end PE in the first rotational direction DR1. The second end PE2 is the end PE in the second rotational direction DR2. The rotary table 12B may also be provided with a first movement restricting portion 1101 defining the first end PE1 and a second movement restricting portion 1102 defining the second end PE2 (see also the first embodiment).
[0081] In this embodiment, the braking start position PB (first braking start position PB1, second braking start position PB2) is predetermined based on the specified range of movement and the end PE of the range of movement as described above. For example, a predetermined rotation position in front of the first end PE1 (towards the second rotation direction DR2) is determined as the first braking start position PB1. Similarly, a predetermined rotation position in front of the second end PE2 (towards the first rotation direction DR1) is determined as the second braking start position PB2.
[0082] The control device 14 can perform braking control based on the braking start position PB determined in this way. In this case, the determination unit 26 of the control device 14 can estimate the position (rotational position) of the worm wheel 106B based on the signal from the magnetic sensor 208. If it is determined that the worm wheel 106B has reached the braking start position PB, the braking control unit 30 of the control device 14 controls the motor 200 to reduce the rotational speed (moving speed V) of the worm wheel 106B. In addition, the positioning control unit 34 of the control device 14 performs positioning control when the moving element 106 (worm wheel 106B) reaches the end PE. As a result, the positioning control unit 34 brings the rotational position of the moving element 106 to a stationary position at the end PE.
[0083] In this embodiment as well, the control device 14 can execute the control method shown in Figure 6 (drive control step S1 to positioning control step S5). Note that the explanation of Figure 6 is omitted in this embodiment (see the first embodiment).
[0084] The control device 14, electric actuator system 10, control method, and program according to the second embodiment can achieve the same effects as the first embodiment, as will be described below.
[0085] In other words, the determination unit 26 determines whether the moving element 106 has reached the braking start position PB based on the signal from the magnetic sensor 208 provided on the motor 200. Since the position of the moving element 106 is estimated based on the signal from the magnetic sensor 208, an optical encoder is not required.
[0086] The braking control unit 30 executes braking control when the determination unit 26 determines that the movable element 106 has reached the braking start position PB. As a result, the movement speed V of the movable element 106 is suppressed to some extent before the movable element 106 reaches the end PE of the movement range. Consequently, the impact caused by contact between the movable element 106 and the end PE of the movement range of the movable element 106 is mitigated.
[0087] By mitigating the impact, the risk of damage or deformation to the drive unit 100, for example, can be reduced. Furthermore, by mitigating the impact, irregular rotation (such as reverse rotation) of the shaft 206, which is mechanically connected to the movable element 106, can be suppressed. As a result, unnecessary regenerative current from the motor 200 can be suppressed, for example.
[0088] The braking control unit 30 does not perform braking control until the determination unit 26 determines that the movable element 106 has reached a predetermined braking start position PB located just before the end PE. As a result, the movable element 106 can move at a relatively high speed until it approaches the end PE to a certain extent. Therefore, the electric actuator system 10 is useful for applications that require the movable element 106 to move at a relatively high speed.
[0089] If the moving speed V of the moving element 106 is suppressed before the moving element 106 reaches the edge PE of the range of motion, the above-mentioned impact can be mitigated to some extent. For this reason, the braking control according to this embodiment can be realized if the approximate position of the moving element 106 can be determined. Therefore, according to this embodiment, even if the magnetic sensor 208 is used to detect the rotational position of the rotor 204, a sufficient impact mitigation effect can be achieved.
[0090] The braking control unit 30 may gradually reduce the movement speed V of the moving element 106 by performing braking control. As a result, after the determination unit 26 determines that the braking start position PB has been reached, the moving element 106 can continue to move while reducing its movement speed V. The lower the movement speed V of the moving element 106, the greater the impact can be mitigated.
[0091] The positioning control unit 34 may stop the movable element 106 at the end PE by executing positioning control when the movable element 106 reaches the end PE. This suppresses irregular movement of the movable element 106 between the time the movable element 106 reaches one end PE (for example, the second end PE2) and the time the movable element 106 starts moving to the other end PE (for example, the first end PE1).
[0092] The cushioning member 112 is positioned at the end PE of the range of movement of the movable element 106. The cushioning member 112 positioned at the end PE comes into contact with the movable element 106 as it moves toward the end PE. In this case, the cushioning member 112 can further mitigate the aforementioned impact.
[0093] The control device 14 is preferably provided on the motor 200. By integrating the motor 200 and the control device 14, the electric actuator system 10 can be made more compact.
[0094] The motor 200 is preferably a brushless DC motor. This eliminates the need to customize the motor 200 in order to, for example, install a magnetic sensor 208. Furthermore, since there is no need to procure the motor 200 according to this embodiment as a custom-made product, the manufacturing cost, procurement cost, etc. of the electric actuator 12 can be reduced.
[0095] The first or second embodiment may be modified as described below. In the following description, any descriptions that overlap with the first or second embodiment will be omitted as appropriate.
[0096] (Modification 1) The form of the electric actuator 12 is not limited to an electric stopper 12A, a rotary table 12B, etc. The electric actuator 12 can be any type of actuator having a motor 200 and a movable element 106 (drive device 100) driven by the motor 200. For example, the electric actuator 12 may be an electric gripper, an electric slider, an electric clamp, etc.
[0097] (Modification 2) The first embodiment and the second embodiment may be combined as appropriate, insofar as they do not contradict each other.
[0098] The following additional information is disclosed regarding the embodiments and modifications described above.
[0099] (Note 1) The control device (14) according to the present disclosure is a control device for an electric actuator (12) having a drive device (100) equipped with a linearly moving or rotating movable element (106) and a motor (200) for moving the movable element, wherein the motor includes a rotor (204) for driving the movable element and a magnetic sensor (208) that outputs a signal corresponding to the rotational position of the rotor, and the control device comprises a determination unit (26) that determines, based on the signal, whether the movable element has reached a braking start position (PB) which is set in front of the end (PE) of the movable element's range of motion, and a braking control unit (30) that controls the motor to reduce the moving speed (V) of the movable element when the determination unit determines that the movable element has reached the braking start position. This mitigates the impact caused by contact between the movable element and the end of the movable element's range of motion.
[0100] (Note 2) The control device for the electric actuator described in Note 1 may also be a control device for the electric actuator in which, when the determination unit determines that the moving element has reached the braking start position, the braking control unit gradually reduces the moving speed.
[0101] (Note 3) The control device for the electric actuator described in Note 1 or 2 may further include a positioning control unit (34) that, when the movable element reaches the end, stops the movable element at the end with a current smaller than the current before the movable element reached the end. This suppresses irregular movement of the movable element after it reaches the end of the range of motion.
[0102] (Note 4) The electric actuator system (10) relating to this disclosure is an electric actuator system comprising an electric actuator control device described in any one of Notes 1 to 3 and the electric actuator.
[0103] (Note 5) The electric actuator system described in Note 4 may be an electric actuator system in which the drive device is provided with a cushioning member (112) disposed at the end. This further reduces the impact caused by contact between the movable element and the end of the movable element's range of motion.
[0104] (Note 6) An electric actuator system as described in Note 4 or 5 may also be an electric actuator system in which the motor is equipped with the control device. This may promote the miniaturization of the electric actuator system.
[0105] (Note 7) An electric actuator system described in any one of Notes 4 to 6 may also be an electric actuator system in which the motor is a brushless DC motor. This eliminates the need to customize the motor in order to install a magnetic sensor.
[0106] (Note 8) The control method relating to the present disclosure is a control method for an electric actuator (12) having a drive device (100) equipped with a linearly moving or rotating movable element (106) and a motor (200) for moving the movable element, wherein the motor includes a rotor (204) for driving the movable element and a magnetic sensor (208) that outputs a signal corresponding to the rotational position of the rotor, and the control method for an electric actuator includes a determination step (S3) for determining whether the movable element has reached a braking start position (PB) that is set in advance of the end (PE) of the movable element's range of movement based on the signal, and a braking control step (S4) for controlling the motor to reduce the moving speed (V) of the movable element when it is determined in the determination step that the movable element has reached the braking start position.
[0107] (Note 9) The program relating to this disclosure is a program for causing a computer to execute the control method of the electric actuator described in Note 8.
[0108] While this disclosure has been described in detail, it is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the gist of this disclosure or from the intent of this disclosure derived from the claims and their equivalents. These embodiments can also be implemented in combination. For example, the order of operations and processes in the embodiments described above are given as examples only and are not limited thereto. The same applies when numerical values or mathematical formulas are used in the description of the embodiments above.
Claims
1. A control device (14) for an electric actuator (12) having a drive device (100) equipped with a linearly moving or rotating movable element (106) and a motor (200) for moving the movable element, wherein the motor includes a rotor (204) for driving the movable element and a magnetic sensor (208) that outputs a signal corresponding to the rotational position of the rotor, a determination unit (26) that determines, based on the signal, whether the movable element has reached a braking start position (PB) that is set in front of the end (PE) of the movable element's range of motion, and a braking control unit (30) that controls the motor to reduce the moving speed (V) of the movable element when the determination unit determines that the movable element has reached the braking start position, the control device for an electric actuator.
2. A control device for an electric actuator according to claim 1, wherein when the determination unit determines that the moving element has reached the braking start position, the braking control unit gradually reduces the moving speed.
3. A control device for an electric actuator according to claim 1, further comprising a positioning control unit (34) that, when the movable element reaches the end, brings the movable element to rest at the end with a current smaller than the current before the movable element reached the end.
4. An electric actuator system (10) comprising: a control device for an electric actuator according to any one of claims 1 to 3; and the electric actuator.
5. An electric actuator system according to claim 4, wherein the drive device comprises a buffer member (112) disposed at the end.
6. An electric actuator system according to claim 4, wherein the motor is equipped with the control device.
7. An electric actuator system according to claim 4, wherein the motor is a brushless DC motor.
8. A control method for an electric actuator (12) having a drive device (100) equipped with a linearly moving or rotating movable element (106) and a motor (200) for moving the movable element, wherein the motor includes a rotor (204) for driving the movable element and a magnetic sensor (208) that outputs a signal corresponding to the rotational position of the rotor, and the control method for an electric actuator includes: a determination step (S3) for determining whether the movable element has reached a braking start position (PB) that is set in advance of the end (PE) of the movable element's range of motion based on the signal; and a braking control step (S4) for controlling the motor to reduce the moving speed (V) of the movable element when it is determined in the determination step that the movable element has reached the braking start position.
9. A program for causing a computer to execute the control method of an electric actuator according to claim 8.