Actuator and magnetic pole position estimation method

Abstract

To provide a technique capable of grasping a position of a magnetic pole of a rotor in a direct-acting motor without moving a shaft in an actuator.SOLUTION: An actuator comprises: a direct-acting motor which moves a shaft in an axial direction by moving a rotor relatively to a stator; a brake device which brakes the movement of the shaft in the axial direction; and a force sensor which detects a direction of a force acting on the rotor in the axial direction of the shaft. In the actuator, estimation means estimates a position of a magnetic pole of the rotor based on the direction of the force detected by the force sensor when the direct-acting motor is electrified in a state where the movement of the shaft in the axial direction is stopped by the brake device.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an actuator for performing pick and place. [Background technology]

[0002] Conventionally, there is known an actuator that performs a series of operations (pick and place) such as picking up a workpiece with a shaft and then placing the picked-up workpiece in a predetermined position with the shaft. In such an actuator that performs pick and place, the tip of a hollow shaft is pressed against the workpiece, and a negative pressure is created inside the shaft, thereby attracting the workpiece to the tip of the shaft and picking it up.

[0003] Furthermore, Patent Document 1 discloses a technology for estimating the magnetic pole position of a mover of a linear motor in a linear actuator. The technology disclosed in Patent Document 1 estimates the section in which the mover is located based on the direction in which the mover moves during successive first and second pulse energizations. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6191086 Summary of the Invention [Problem to be solved by the invention]

[0005] In an actuator that picks and places a workpiece by moving a shaft axially, it is necessary to know the position of the mover in the linear motor that moves the shaft in order to control the axial position of the shaft. However, in a linear motor, it is sometimes impossible to detect the absolute position of the mover. Therefore, when current begins to be applied to the actuator (when current begins to be applied to the linear motor), the actuator may be excited once to generate a moving magnetic field to move the mover in order to know the magnetic pole position of the mover in the linear motor.

[0006] However, if the linear motor is energized without knowing the magnetic pole position of the mover, a moving magnetic field will be generated without knowing whether the shaft will move upward or downward. As a result, there is a risk of problems occurring, such as the shaft coming into contact with a workpiece being prepared for pickup as the shaft moves, as a result of exciting the motor in order to determine the magnetic pole position of the mover.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a technology that makes it possible to grasp the magnetic pole position of a mover in a linear motor in an actuator without moving the shaft. [Means for solving the problem]

[0008] An actuator according to a first aspect of the present invention comprises: An actuator that picks up a workpiece by sucking it onto the tip of a shaft, a linear motor having a stator and a mover, the shaft being connected to the mover, and the mover moving relative to the stator to move the shaft in its axial direction; a brake device that brakes the axial movement of the shaft; a force sensor that detects the direction of a force acting on the mover in the axial direction of the shaft; an estimation means for estimating a magnetic pole position of the mover based on a direction of force detected by the force sensor when the linear motor is energized with axial movement of the shaft stopped by the brake device; and Equipped with.

[0009] A location estimation method according to a second aspect of the present invention includes: An actuator that picks up a workpiece by sucking it onto the tip of a shaft, a linear motor having a stator and a mover, the shaft being connected to the mover, and the mover moving relative to the stator to move the shaft in its axial direction; a brake device that brakes the axial movement of the shaft; a force sensor that detects the direction of a force acting on the mover in the axial direction of the shaft; A position estimation method for estimating a magnetic pole position of a mover in an actuator comprising: The magnetic pole position of the mover is estimated based on the direction of force detected by the force sensor when the linear motor is energized with the axial movement of the shaft stopped by the brake device. [Effects of the Invention]

[0010] According to the present invention, in an actuator, the magnetic pole position of a mover in a linear motor can be detected without moving the shaft. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is an external view of an actuator according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating the internal structure of the actuator according to the embodiment. [Figure 3] 1 is a cross-sectional view showing a schematic configuration of a shaft housing and a tip end portion of a shaft according to an embodiment. [Figure 4]10A and 10B are conceptual diagrams for explaining a method for estimating the magnetic pole position of a mover in a linear motor according to an embodiment. [Figure 5] 4 is a flowchart showing a process flow for estimating the magnetic pole position of a mover in a linear motor according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] The actuator according to the present invention picks up a workpiece by attracting the workpiece to the tip of a shaft, and includes a linear motor, a brake device, a force sensor, and an estimation means.

[0013] A linear motor is a motor that moves a shaft in its axial direction. A linear motor has a stator and a mover. A shaft is connected to the mover. When the mover moves relative to the stator, the shaft moves together with the mover. A brake device is a device that brakes the axial movement of the shaft. In an actuator, the brake device can stop the axial movement of the shaft.

[0014] The force sensor detects the direction of the force acting on the mover in the axial direction of the shaft. In other words, in the actuator, it can detect whether a force is acting on the mover in the upward direction, Alternatively, the force sensor detects whether a downward force is acting. Note that the force sensor may be configured to include a strain gauge, for example.

[0015] When starting to energize the linear motor, the controller estimates the magnetic pole position of the mover in the linear motor with the axial movement of the shaft stopped by the brake device. Specifically, the controller energizes the linear motor with the axial movement of the shaft stopped by the brake device. At this time, the current is energized to the linear motor so that the mover is attracted to a predetermined target position by a moving magnetic field generated in the linear motor. However, because the axial movement of the shaft is stopped by the brake device, the mover connected to the shaft does not actually move even if a moving magnetic field is generated in the linear motor.

[0016] However, a force acts on the mover in the axial direction of the shaft. In other words, if the linear motor is energized when the mover is positioned above a predetermined target position, a downward force acts on the mover due to the moving magnetic field. On the other hand, if the linear motor is energized and excited when the mover is positioned below the predetermined target position, an upward force acts on the mover due to the moving magnetic field.

[0017] Therefore, in the present invention, the estimation means estimates the magnetic pole position of the mover based on the direction of the force detected by the force sensor. That is, if a downward force is acting on the mover, the estimation means estimates that the mover is located above a predetermined target position when current is applied to the linear motor. Also, if an upward force is acting on the mover, the estimation means estimates that the mover is located below a predetermined target position when current is applied to the linear motor.

[0018] Therefore, according to the present invention, in the actuator, the magnetic pole position of the mover in the linear motor can be detected without moving the shaft.

[0019] Specific embodiments of the present disclosure will be described below with reference to the drawings. The dimensions, materials, shapes, and relative positions of the components described in the present embodiments are not intended to limit the technical scope of the present disclosure unless otherwise specified.

[0020] <Embodiment> FIG. 1 is an external view of an actuator 1 according to this embodiment. The actuator 1 has a housing 2 having an approximately rectangular parallelepiped outer shape, and a lid 200 is attached to the housing 2. FIG. 2 is a schematic diagram showing the internal structure of the actuator 1 according to this embodiment. A portion of a shaft 10 is accommodated inside the housing 2. The tip portion 10A of the shaft 10 is formed to be hollow. The shaft 10 and the housing 2 may be made of, for example, metal (e.g., aluminum), or resin. In the following description, an XYZ Cartesian coordinate system is set, and the position of each component will be described with reference to this XYZ Cartesian coordinate system. The Z-axis direction is the long side direction of the largest surface of the housing 2, which is the direction of the central axis 100 of the shaft 10. The X-axis direction is the short side direction of the largest surface of the housing 2. The Y-axis direction is the direction perpendicular to the largest surface of the housing 2. The Z-axis direction is also the vertical direction. In the following description, the upper side in the Z-axis direction in FIG. 2 will be referred to as the upper side of the actuator 1, and the lower side in the Z-axis direction in FIG. 2 will be referred to as the lower side of the actuator 1. 2 is the right side of the actuator 1, and the left side of the X-axis direction in FIG. 2 is the left side of the actuator 1. Furthermore, the front side of the Y-axis direction in FIG. 2 is the front side of the actuator 1, and the back side of the Y-axis direction in FIG. 2 is the back side of the actuator 1. The dimension of the housing 2 in the Z-axis direction is longer than the dimension in the X-axis direction, and the dimension in the X-axis direction is longer than the dimension in the Y-axis direction. The housing 2 has an opening at a location corresponding to one face (the face on the front side in FIG. 2) perpendicular to the Y-axis direction, and this opening is closed by a lid 200. The lid 200 is fixed to the housing 2 by screws, for example.

[0021] The housing 2 accommodates a rotary motor 20, a linear motor 30, an air control mechanism 60, and a brake device 90. The rotary motor 20 rotates a shaft 10 around its central axis 100. The linear motor 30 linearly moves the shaft 10 relative to the housing 2 in a direction along the central axis 100 (i.e., the Z-axis direction). A shaft housing 50, through which the shaft 10 is inserted, is attached to a lower end surface 202 of the housing 2 in the Z-axis direction. A recess 202B is formed in the housing 2 so as to recess from the lower end surface 202 toward the inside of the housing 2, and a portion of the shaft housing 50 is inserted into this recess 202B. A through-hole 2A is formed in the upper end portion of the recess 202B in the Z-axis direction, and the shaft 10 is inserted through this through-hole 2A and the shaft housing 50. A lower tip portion 10A of the shaft 10 in the Z-axis direction protrudes outward from the shaft housing 50. The shaft 10 is provided at the center of the housing 2 in the X-axis direction and the center of the Y-axis direction. In other words, the shaft 10 is provided so that a central axis 100 of the shaft 10 overlaps with a central axis that passes through the center of the housing 2 in the X-axis direction and the center of the Y-axis direction and extends in the Z-axis direction. The shaft 10 is linearly moved in the Z-axis direction by the linear motor 30, and rotated around the central axis 100 by the rotary motor 20.

[0022] The base end 10B side of the shaft 10, which is the end opposite to the tip end 10A (the end on the upper side in the Z-axis direction), is accommodated in the housing 2 and is connected to the output shaft 21 of the rotary motor 20. The rotary motor 20 rotatably supports the shaft 10. The central axis of the output shaft 21 of the rotary motor 20 coincides with the central axis 100 of the shaft 10. In addition to the output shaft 21, the rotary motor 20 has a stator 22, a rotor 23 that rotates inside the stator 22, and a rotary encoder 24 that detects the rotation angle of the output shaft 21. As the rotor 23 rotates relative to the stator 22, the output shaft 21 and the shaft 10 also rotate in conjunction with the stator 22.

[0023] The linear motor 30 includes a stator 31 fixed to the housing 2 and a mover 32 that moves in the Z-axis direction relative to the stator 31. The linear motor 30 is, for example, a linear motor. The stator 31 is provided with a plurality of coils 31A, and the mover 32 is provided with a plurality of permanent magnets 32A. The coils 31A are arranged at a predetermined pitch in the Z-axis direction, and a plurality of sets of three coils 31A for U, V, and W phases are provided. In this embodiment, three-phase armature currents are passed through the U, V, and W phase coils 31A to excite them and generate a moving magnetic field, thereby linearly moving the mover 32 relative to the stator 31. The linear motor 30 is provided with a linear encoder 38 that detects the relative position of the mover 32 with respect to the stator 31. The linear encoder 38 is an incremental encoder. Alternatively, a permanent magnet may be provided in the stator 31, and a plurality of coils may be provided in the mover 32.

[0024] The mover 32 of the linear motor 30 and the stator 22 of the rotary motor 20 are connected via a linear table 33. The linear table 33 is movable in accordance with the movement of the mover 32 of the linear motor 30. As a result, the shaft 10 is connected to the mover 32 of the linear motor 30 via the rotary motor 20 and the linear table 33, and the shaft 10 moves in the Z-axis direction in accordance with the movement of the mover 32 of the linear motor 30. The movement of the linear table 33 is guided in the Z-axis direction by a linear guide device 34. The linear guide device 34 has a rail 34A fixed to the housing 2 and a slider block 34B attached to the rail 34A. The rail 34A extends in the Z-axis direction, and the slider block 34B is movable in the Z-axis direction along the rail 34A.

[0025] The linear motion table 33 is fixed to the slider block 34B. 4B. The linear motion table 33 is connected to the mover 32 of the linear motion motor 30 via two connecting arms 35. The two connecting arms 35 connect both ends of the mover 32 in the Z axis direction to both ends of the linear motion table 33 in the Z axis direction. The linear motion table 33 is connected to the stator 22 of the rotary motor 20 via two connecting arms 36, closer to the center than both ends. Because the linear motion table 33 and the stator 22 of the rotary motor 20 are connected to the stator 22 of the rotary motor 20 via the two connecting arms 36, the stator 22 of the rotary motor 20 and the shaft 10 also move as the linear motion table 33 moves. The connecting arms 36 have a square cross section. A strain gauge 37 is fixed to the surface of each connecting arm 36 facing upward in the Z axis direction. Although the two strain gauges 37 in this embodiment are provided on the surfaces of the connecting arms 36 facing upward in the Z-axis direction, they may alternatively be provided on the surfaces of the connecting arms 36 facing downward in the Z-axis direction. Also, the strain gauge 37 may be provided on only one of the two connecting arms 36.

[0026] The brake device 90 is a device for braking the movement of the shaft 10 in the Z-axis direction. When the brake is ON, the brake device 90 is pressed against the stator 22 of the rotary motor 20. This brakes the movement of the stator 22 of the rotary motor 20 in the Z-axis direction, and therefore the movement of the shaft 10 in the Z-axis direction. Furthermore, the movement of the mover 32 of the linear motor 30, which is connected to the shaft 10 via the stator 22 of the rotary motor 20, the connecting arm 36, the linear table 33, and the connecting arm 35, in the Z-axis direction is also braked. Therefore, by stopping the movement of the stator 22 of the rotary motor 20 and the shaft 10 in the Z-axis direction with the brake device 90, the movement of the mover 32 of the linear motor 30 in the Z-axis direction can also be stopped. Furthermore, when the brake is OFF, the brake device 90 is separated from the stator 22 of the rotary motor 20. This allows the stator 22 of the rotary motor 20 to move in the Z-axis direction. Accordingly, the shaft 10 and the mover 32 of the linear motor 30 can also move in the Z-axis direction.

[0027] The air control mechanism 60 is a mechanism for generating positive and negative pressure at the tip 10A of the shaft 10. That is, when picking up the workpiece W, the air control mechanism 60 sucks in air from inside the shaft 10 to generate negative pressure at the tip 10A of the shaft 10. This causes the workpiece W to be attracted to the tip 10A of the shaft 10. In addition, by sending air into the shaft 10, positive pressure is generated at the tip 10A of the shaft 10. This allows the workpiece W to be easily detached from the tip 10A of the shaft 10.

[0028] The air control mechanism 60 has a positive pressure passage 61A (see dashed line) through which positive pressure air flows, a negative pressure passage 61B (see dashed line) through which negative pressure air flows, and a shared passage 61C (see dashed line) shared by positive pressure air and negative pressure air. One end of the positive pressure passage 61A is connected to a positive pressure connector 62A provided on the upper end surface 201 of the housing 2 in the Z-axis direction, and the other end of the positive pressure passage 61A is connected to a positive pressure solenoid valve (hereinafter referred to as a positive pressure solenoid valve 63A). The positive pressure solenoid valve 63A is opened and closed by a controller 7, which will be described later. One end of the positive pressure passage 61A is formed by a tube 610, and the other end is formed by a hole opened in a block 600. The positive pressure connector 62A penetrates the upper end surface 201 of the housing 2 in the Z axis direction, and a tube connected to a pump or the like that discharges air is connected to the positive pressure connector 62A from the outside.

[0029] One end of the negative pressure passage 61B is connected to a negative pressure connector 62B provided on the upper end surface 201 of the housing 2 in the Z-axis direction, and the other end of the negative pressure passage 61B is connected to a negative pressure solenoid valve (hereinafter referred to as a negative pressure solenoid valve 63B). The negative pressure solenoid valve 63B is opened and closed by the controller 7, which will be described later. One end of the negative pressure passage 61B is formed by a tube 620, and the other end is formed by a hole opened in the block 600. The negative pressure connector 62B penetrates the upper end surface 201 of the housing 2 in the Z-axis direction, and the negative pressure connector 6 A tube connected to a pump or the like that sucks air is connected to 2B from the outside.

[0030] The shared passage 61C is formed by a hole opened in the block 600. One end of the shared passage 61C branches into two and is connected to the positive pressure solenoid valve 63A and the negative pressure solenoid valve 63B, and the other end of the shared passage 61C is connected to an air flow passage 202A, which is a through-hole formed in the housing 2. The air flow passage 202A communicates with the shaft housing 50. By opening the negative pressure solenoid valve 63B and closing the positive pressure solenoid valve 63A, the negative pressure passage 61B and the shared passage 61C are connected, generating negative pressure in the shared passage 61C. This causes air to be sucked from inside the shaft housing 50 via the air flow passage 202A. On the other hand, by opening the positive pressure solenoid valve 63A and closing the negative pressure solenoid valve 63B, the positive pressure passage 61A and the shared passage 61C are connected, generating positive pressure in the shared passage 61C. This causes air to be supplied into the shaft housing 50 via the air flow passage 202A. The common passage 61C is provided with a pressure sensor 64 that detects the pressure of the air in the common passage 61C and a flow rate sensor 65 that detects the flow rate of the air in the common passage 61C.

[0031] A connector 41, including power supply wires and signal wires, is connected to the top end surface 201 of the housing 2 in the Z-axis direction. The housing 2 also includes a controller 7. The power and signal wires leading from the connector 41 into the housing 2 are connected to the controller 7. The controller 7 includes a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), and erasable programmable read-only memory (EPROM), all of which are interconnected by a bus. The CPU loads and executes various tables stored in the EPROM into the RAM's work area. The CPU executes programs to control the rotary motor 20, linear motor 30, brake device 90, positive pressure solenoid valve 63A, negative pressure solenoid valve 63B, and other components. This allows the CPU to achieve functions consistent with a specific purpose. Output signals from the pressure sensor 64, flow rate sensor 65, strain gauge 37, rotary encoder 24, and linear encoder 38 are input to the controller 7.

[0032] FIG. 3 is a cross-sectional view showing the schematic configuration of the shaft housing 50 and the tip portion 10A of the shaft 10. The shaft housing 50 includes a housing main body 51, two rings 52, a filter 53, and a filter stopper 54. The housing main body 51 is formed with a through-hole 51A through which the shaft 10 is inserted. The through-hole 51A penetrates the housing main body 51 in the Z-axis direction, and the upper end of the through-hole 51A in the Z-axis direction communicates with a through-hole 2A formed in the housing 2. The diameter of the through-hole 51A is larger than the outer diameter of the shaft 10. Therefore, a gap is provided between the inner surface of the through-hole 51A and the outer surface of the shaft 10. Enlarged-diameter portions 51B with enlarged diameters are provided at both ends of the through-hole 51A. A ring 52 is fitted into each of the two enlarged-diameter portions 51B. The ring 52 is formed in a cylindrical shape, and the inner diameter of the ring 52 is slightly larger than the outer diameter of the shaft 10. Therefore, a gap is also formed between the inner surface of ring 52 and the outer surface of shaft 10. Therefore, shaft 10 can move in the Z-axis direction inside ring 52, and shaft 10 can rotate around central axis 100 inside ring 52. However, the gap formed between the inner surface of ring 52 and the outer surface of shaft 10 is smaller than the gap formed between the inner surface of through hole 51A excluding expanded diameter portion 51B and the outer surface of shaft 10. The ring 52 on the upper side in the Z-axis direction is referred to as first ring 52A, and the ring 52 on the lower side in the Z-axis direction is referred to as second ring 52B. When there is no need to distinguish between first ring 52A and second ring 52B, they are simply referred to as ring 52. The ring 52 can be made of a material such as metal or resin.

[0033] A protruding portion 511 is formed in the center of the housing main body 51 in the Z-axis direction, protruding in both the left and right directions in the X-axis direction. The protruding portion 511 is formed with a mounting surface 511A, which is a surface parallel to the bottom end surface 202 of the housing 2 and comes into contact with the bottom end surface 202 when the shaft housing 50 is attached to the bottom end surface 202 of the housing 2. The mounting surface 511A is The surface is perpendicular to the central axis 100. When the shaft housing 50 is attached to the housing 2, a portion 512 of the shaft housing 50 that is above the attachment surface 511A in the Z-axis direction is formed to fit into a recess 202B formed in the housing 2.

[0034] As described above, a gap is provided between the inner surface of the through hole 51A and the outer surface of the shaft 10. As a result, an internal space 500 is formed inside the housing main body 51, which is a space surrounded by the inner surface of the through hole 51A, the outer surface of the shaft 10, the lower end surface of the first ring 52A, and the upper end surface of the second ring 52B. The shaft housing 50 also has a control passage 501 formed therein, which serves as an air passage connecting the opening of the air flow passage 202A formed in the lower end surface 202 of the housing 2 with the internal space 500. The control passage 501 includes a first passage 501A extending in the X-axis direction, a second passage 501B extending in the Z-axis direction, and a filter section 501C, which is a space connecting the first passage 501A and the second passage 501B and in which the filter 53 is disposed. One end of the first passage 501A is connected to the internal space 500, and the other end is connected to the filter section 501C. One end of the second passage 501B opens to the mounting surface 511A and is positioned so as to be connected to the opening of the air flow passage 202A.

[0035] The other end of the second passage 501B is connected to the filter unit 501C. A cylindrical filter 53 is provided in the filter unit 501C. The filter unit 501C is formed to have a cylindrical space extending in the X-axis direction so that its central axis coincides with that of the first passage 501A. The inner diameter of the filter unit 501C and the outer diameter of the filter 53 are approximately equal. The filter 53 is inserted into the filter unit 501C in the X-axis direction. After the filter 53 is inserted into the filter unit 501C, the end of the filter unit 501C that serves as the insertion port for the filter 53 is closed by a filter stopper 54. The other end of the second passage 501B is connected to the filter unit 501C from the outer peripheral surface side of the filter 53. The other end of the first passage 501A is connected to the center side of the filter 53. Therefore, air circulating between the first passage 501A and the second passage 501B passes through the filter 53. Therefore, for example, even if foreign matter is sucked into the internal space 500 together with air when a negative pressure is generated in the tip portion 10A, the foreign matter is captured by the filter 53. A groove 501D is formed at one end of the second passage 501B to hold a sealing agent.

[0036] Near both ends in the X-axis direction of the overhanging portion 511, two bolt holes 51G are formed through which bolts are inserted when the shaft housing 50 is fixed to the housing 2. The bolt holes 51G penetrate the overhanging portion 511 in the Z-axis direction and open to the mounting surface 511A.

[0037] A hollow portion 11 is formed on the tip end 10A side of the shaft 10 so that the shaft 10 is hollow. One end of the hollow portion 11 is open at the tip end 10A. A communication hole 12 is formed at the other end of the hollow portion 11, connecting the internal space 500 and the hollow portion 11 in the X-axis direction. The communication hole 12 is formed so that the internal space 500 and the hollow portion 11 are in communication throughout the entire stroke range when the shaft 10 is moved in the Z-axis direction by the linear motor 30. Therefore, the tip end 10A of the shaft 10 and the air control mechanism 60 are in communication via the hollow portion 11, the communication hole 12, the internal space 500, the control passage 501, and the air flow passage 202A. The communication hole 12 may be formed in the Y-axis direction in addition to the X-axis direction.

[0038] With this configuration, when the linear motor 30 is driven to move the shaft 10 in the Z-axis direction, the communication hole 12 always communicates between the internal space 500 and the hollow portion 11, regardless of the position of the shaft 10 in the Z-axis direction. Also, when the rotary motor 20 is driven to rotate the shaft 10 around the central axis 100, the communication hole 12 always communicates between the internal space 500 and the hollow portion 11, regardless of the angle of rotation of the shaft 10 around the central axis 100. Therefore, Regardless of the state of the shaft 10, the hollow portion 11 is always in communication with the air control mechanism 60 because communication between the hollow portion 11 and the internal space 500 is maintained. Therefore, regardless of the position of the shaft 10, when the positive pressure solenoid valve 63A is closed and the negative pressure solenoid valve 63B is opened in the air control mechanism 60, air in the hollow portion 11 is sucked through the air flow passage 202A, the control passage 501, the internal space 500, and the communication hole 12. As a result, negative pressure can be generated in the hollow portion 11. In other words, negative pressure can be generated at the tip end 10A of the shaft 10, so that the workpiece W can be attracted to the tip end 10A of the shaft 10. As described above, a gap is also formed between the inner surface of the ring 52 and the outer surface of the shaft 10. However, this gap is smaller than the gap forming the internal space 500 (i.e., the gap formed between the inner surface of the through-hole 51A and the outer surface of the shaft 10). Therefore, by closing the positive pressure solenoid valve 63A and opening the negative pressure solenoid valve 63B in the air control mechanism 60, even if air is sucked from the internal space 500, the flow rate of air flowing through the gap between the inner surface of the ring 52 and the outer surface of the shaft 10 can be suppressed. This makes it possible to generate a negative pressure at the tip end 10A of the shaft 10 that allows the workpiece W to be picked up. On the other hand, regardless of the position of the shaft 10, by opening the positive pressure solenoid valve 63A and closing the negative pressure solenoid valve 63B in the air control mechanism 60, it is possible to generate a positive pressure in the hollow portion 11. In other words, since a positive pressure can be generated at the tip end 10A of the shaft 10, the workpiece W can be quickly detached from the tip end 10A of the shaft 10.

[0039] (Magnetic pole position estimation) As described above, in the actuator 1, the shaft 10 moves in the Z-axis direction as the mover 32 of the linear motor 30 moves relative to the stator 31. Therefore, in order to pick and place a workpiece by moving the shaft 10 in the Z-axis direction, it is necessary to know the magnetic pole position of the mover 32 of the linear motor 30. However, if the mover 32 is moved to estimate the magnetic pole position of the mover 32 when current begins to be applied to the linear motor 30, as in the conventional method, there is a risk that the shaft 10 will come into contact with a workpiece that was prepared for pickup when the shaft 10 moves downward as the mover 32 moves.

[0040] Furthermore, multiple actuators 1 may be installed so as to be stacked in the Y-axis direction. In this case, if the movers 32 of the linear motors 30 in each of the multiple actuators 1 are excited while the magnetic pole positions of the movers 32 are unknown, it is possible that the movers 32 in each actuator 1 will move in different directions. As a result, in two adjacent actuators 1, one shaft 10 may move upward and the other shaft 10 may move downward. In such a case, depending on the size, shape, and rotational position of the tip ends of the shafts 10, there is a risk that the tip ends of the shafts 10 of the two adjacent actuators 1 will interfere with each other.

[0041] Therefore, in this embodiment, the magnetic pole position of the mover 32 in the linear motor 30 is estimated without moving the shaft 10. Hereinafter, a method for estimating the magnetic pole position of the mover 32 in the linear motor 30 according to this embodiment will be described with reference to Fig. 4. Fig. 4 is an image diagram for explaining a method for estimating the magnetic pole position of the mover 32 in the linear motor 30 according to this embodiment.

[0042] 4(a), (b), and (c) show an example of the state of the mover 32 when the linear motor 30 is energized and excited with the movement of the mover 32 in the Z-axis direction stopped by the brake device 90. In FIG. 4, 0 rad to 2π rad in the stator 31 indicates the movement range of the mover 32 in the Z-axis direction in the linear motor 30. In other words, in the linear motor 30, the mover 32 is located at any position within the range of magnetic pole positions between 0 rad and 2π rad. Note that in FIG. 4, the movement range of the mover 32 in the Z-axis direction is The position of the upper end of the movable element 32 in the Z-axis direction is set to 0 rad, and the position of the lower end of the movable element 32 in the Z-axis direction is set to 2π rad. For convenience, only a portion of the position of the movable element 32 is shown in FIG.

[0043] 4, the white arrow indicates the direction of the force acting on the mover 32 when the linear motor 30 is energized and excited with the movement of the mover 32 in the Z-axis direction stopped by the brake device 90. Here, when the linear motor 30 is energized and excited with the movement of the mover 32 in the Z-axis direction stopped, strain is generated in the connecting arm 36. The direction of the strain in the connecting arm 36 at this time correlates with the direction of the force acting on the mover 32. Therefore, the direction of the force acting on the mover 32 can be determined based on the detection value of the strain gauge 37 provided on the connecting arm 36.

[0044] In this embodiment, the controller 7 energizes the linear motor 30 while stopping the movement of the shaft 10 and the mover 32 of the linear motor 30 in the Z-axis direction by the brake device 90. At this time, the controller 7 first energizes the linear motor 30 with the position of π rad set as the first target position of the mover 32. That is, the linear motor 30 is energized so that the moving magnetic field generated in the linear motor 30 attracts the mover 32 to the position of π rad. However, even when the linear motor 30 is energized in this manner, the mover 32, whose movement in the Z-axis direction is stopped by the brake device 90, does not actually move. Therefore, the shaft 10 does not move either. Note that even when the movement of the mover 32 in the Z-axis direction is braked by the brake device 90, the mover 32 may move very slightly (for example, by a few μm) in the Z-axis direction due to the moving magnetic field immediately after energizing the linear motor 30. However, if the distance traveled by the mover 32 at this time is extremely small, it can be said that this is equivalent to a state in which the movement of the mover 32 has stopped.

[0045] However, a force in the Z-axis direction generated by the excitation acts on the mover 32, i.e., a force that tries to attract the mover 32 to the position of π rad. Therefore, for example, as shown in FIG. 4(a), if the mover 32 is located in the section from 0 rad to π rad, a downward force acts on the mover 32. On the other hand, if the mover 32 is located in the section from π rad to 2π rad, an upward force acts on the mover 32. Therefore, the controller 7 determines the direction of the force acting on the mover 32 in the Z-axis direction based on the detection value of the strain gauge 37. Furthermore, the controller 7 estimates the section of the magnetic pole position in which the mover 32 exists (hereinafter, sometimes referred to as the "existence section") based on the direction of the force acting on the mover 32. Specifically, the controller 7 estimates whether the mover 32 is located in the section from 0 to π rad or the section from π rad to 2π rad. In the following, the process performed to estimate whether the movable element 32 is located in the interval from 0 to π rad or the interval from π rad to 2π rad may be referred to as the first estimation process.

[0046] Next, the controller 7 energizes the linear motor 30, setting the center position of the existence section estimated by the first estimation process as the second target position. That is, the linear motor 30 is energized so that the moving magnetic field generated in the linear motor 30 attracts the mover 32 to the center position of the existence section. As a result, a force acts on the mover 32, trying to attract the mover 32 to the center position of the existence section. Therefore, if the mover 32 is located in a section above the center of the existence section, a downward force acts on the mover 32. On the other hand, if the mover 32 is located in a section below the center of the existence section, an upward force acts on the mover 32.

[0047] For example, in the case of FIG. 4(b), the section from 0 rad to π rad is estimated as the existence section in the first estimation process, so the position of π / 2 rad becomes the second target position. Therefore, a force acts on the mover 32 to attract it to the position of π / 2 rad. Therefore, as shown in FIG. 4(b), if the mover 32 is located in the section from 0 rad to π / 2 rad, a downward force acts on the mover 32. On the other hand, if the mover 32 is located in the section from π / 2 rad to π rad, an upward force acts on the mover 32. Therefore, similar to the first estimation process, the controller 7 determines the direction of the force acting on the mover 32 in the Z-axis direction based on the detection value of the strain gauge 37. Furthermore, the controller 7 estimates the existence section based on the direction of the force acting on the mover 32. Specifically, the controller 7 estimates whether the mover 32 is located in a section above the center of the existence section estimated in the first estimation process (for example, the section from 0 rad to π / 2 rad in FIG. 4(b)) or a section below the center (for example, the section from π / 2 rad to π rad in FIG. 4(b)). In the following, the process performed to estimate whether the movable element 32 is located in the section above the center or in the section below the center of the existence section estimated by the previous estimation process may be referred to as the second estimation process.

[0048] Next, the controller 7 executes the second estimation process. At this time, the controller 7 energizes the linear motor 30, setting the center position of the existence interval estimated by the first second estimation process as the second target position. As a result, a force acts on the mover 32, attracting the mover 32 to the center position of the existence interval estimated by the first second estimation process. For example, in the case of FIG. 4(c), the interval from 0 rad to π / 2 rad is estimated as the existence interval in the first second estimation process, so the position of π / 4 rad becomes the second target position in the second second estimation process. Therefore, a force acts on the mover 32, attracting the mover 32 to the position of π / 4 rad. Therefore, as shown in FIG. 4(c), if the mover 32 is located in the interval from π / 4 rad to π / 2 rad, an upward force acts on the mover 32. On the other hand, if the mover 32 is located in the interval from 0 rad to π / 4 rad, a downward force acts on the mover 32. Therefore, similarly to the first estimation process and the first second estimation process, the controller 7 determines the direction of the force acting on the mover 32 in the Z-axis direction based on the detection value of the strain gauge 37. Furthermore, the controller 7 estimates the existence interval based on the direction of the force acting on the mover 32. Specifically, the controller 7 estimates whether the mover 32 is located in an interval above the center (for example, the interval from 0 rad to π / 4 rad in FIG. 4(c)) or in an interval below the center (for example, the interval from π / 4 rad to π / 2 rad in FIG. 4(c)) of the existence interval estimated in the first second estimation process.

[0049] Then, the controller 7 repeatedly executes the second estimation process as described above a predetermined number of times while updating the second target position. At this time, the existence section is narrowed down each time the second estimation process is executed. Therefore, by repeatedly executing the second estimation process a predetermined number of times, the magnetic pole position of the mover 32 can be estimated with high accuracy. In this embodiment, the controller 7 corresponds to the "estimation means" according to the present invention.

[0050] (Estimation process flow) Next, a process flow for estimating the magnetic pole position of the mover 32 in the linear motor 30 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart showing a process flow for estimating the magnetic pole position of the mover 32 in the linear motor 30 according to this embodiment. This flow is executed by the controller 7.

[0051] In this flow, first, in S101, the brake device 90 is turned ON. This stops the movement of the mover 32 in the Z-axis direction. Next, in S102, the linear motor 30 is energized with the position of π rad as the first target position of the mover 32. Next, in S103, based on the detection value of the strain gauge 37, the force acting on the mover 32 in the Z-axis direction is applied. The direction of the force acting on the mover 32 is determined. Next, in S104, the existence interval is estimated based on the direction of the force acting on the mover 32. That is, it is estimated whether the mover 32 is located in the interval from 0 to π rad or in the interval from π rad to 2π rad. The series of processes from S102 to S104 in this flow corresponds to the first estimation process.

[0052] Next, in S105, the linear motor 30 is energized with the center position of the existence section estimated in S104 as a second target position. Next, in S106, the direction of the force acting on the mover 32 in the Z-axis direction is determined based on the detection value of the strain gauge 37. Next, in S107, the existence section is estimated based on the direction of the force acting on the mover 32. That is, it is estimated whether the mover 32 is located in a section above the center or a section below the center in the existence section estimated in the first estimation process. A series of processes from S105 to S107 in this flow corresponds to the second estimation process.

[0053] Next, in S108, it is determined whether the second estimation process has been performed a predetermined number of times. Here, the predetermined number of times is a number that is set in advance depending on the required estimation accuracy of the magnetic pole position of the mover 32. If a negative determination is made in S108, that is, if the number of times the second estimation process has been performed has not reached the predetermined number, the second estimation process is performed again. Specifically, a series of processes from S105 to S107 are performed again. In this case, in S105, the center position of the existence section estimated in the previous second estimation process is set as the second target position in the current second estimation process, and current is applied to the linear motor 30. Furthermore, in S107, it is estimated whether the mover 32 is located in a section above the center or a section below the center of the existence section estimated in the previous second estimation process.

[0054] On the other hand, if the determination in S108 is affirmative, the process proceeds to S109. In S109, the second estimation process is repeated a predetermined number of times, and the finally estimated existence section is determined as the magnetic pole position of the mover 32.

[0055] When the magnetic pole position (estimated position) of the mover 32 is determined by the flow of the estimation process shown in FIG. 5, the controller 7 executes a process for final positioning of the mover 32. In this positioning process, the brake device 90 is turned off, and current is applied to the linear motor 30 with the magnetic pole position determined by the estimation process as the target position. As a result, even if the actual position of the mover 32 is slightly deviated from the magnetic pole position determined by the estimation process, the actual position of the mover 32 can be aligned with the magnetic pole position determined by the estimation process. However, in the flow of the estimation process shown in FIG. 5, by repeatedly executing the second estimation process a sufficient number of times, the deviation between the actual position of the mover 32 and the magnetic pole position determined by the estimation process can also be made sufficiently small. In this case, it is not necessary to execute a process for positioning after executing the estimation process.

[0056] As described above, according to the method for estimating the magnetic pole position of the mover 32 in the linear motor 30 of this embodiment, it is possible to estimate the magnetic pole position of the mover 32 in the actuator 1 without moving the shaft 10. Therefore, it is possible to avoid various problems that arise when the shaft 10 is moved in order to determine the magnetic pole position of the mover 32, as in the conventional method.

[0057] In the above embodiment, the first target position in the first estimation process is set to a position of π rad, but the first target position is not limited to a position of π rad. In other words, the first target position in the first estimation process can be set to any position of n rad between 0 rad and 2π rad.

[0058] In the above embodiment, in the first estimation process and the second estimation process, The detection value of the strain gauge 37 was used to determine the direction of the force acting on the mover 32 in the Z-axis direction. However, the direction of the force acting on the mover 32 in the Z-axis direction may be detected using another sensor such as a load cell.

[0059] Furthermore, in the above embodiment, the detection value of the strain gauge 37 can be used for purposes other than detecting the direction of the force acting on the mover 32 in the Z-axis direction. That is, when the shaft 10 picks up a workpiece, the strain gauge 37 may be used to detect that the tip end 10A of the shaft 10 has come into contact with the workpiece. Furthermore, the detection value of the strain gauge 37 may be used to detect that the workpiece has come into contact with the ground when the shaft 10 places the workpiece. When the tip end 10A of the shaft 10 comes into contact with the workpiece when the workpiece is picked up, and when the workpiece has come into contact with the ground when the workpiece is placed, strain is generated in the connecting arm 36 due to the force applied to the shaft 10. The strain at this time is detected by the strain gauge 37. Therefore, it is possible to detect, based on the detection value of the strain gauge 37, that the tip end 10A of the shaft 10 has come into contact with the workpiece when the workpiece is picked up, and that the workpiece has come into contact with the ground when the workpiece is placed. [Explanation of symbols]

[0060] 1···actuator, 2···housing, 10···shaft, 10A··tip portion, 11··hollow portion, 20··rotary motor, 22···stator, 23··rotor, 30··linear motor, 31···stator, 32···moving portion, 36···connecting arm, 37···strain gauge, 50··shaft housing, 60··air control mechanism, 90··brake device, 500··internal space, 501··control passage

Claims

1. An actuator that picks up a workpiece by sucking it onto the tip of a shaft, a linear motor having a stator and a mover, the shaft being connected to the mover, and the mover moving relative to the stator to move the shaft in its axial direction; a brake device that brakes the axial movement of the shaft; a force sensor that detects the direction of a force acting on the mover in the axial direction of the shaft; an estimation means for estimating a magnetic pole position of the mover based on a direction of force detected by the force sensor when the linear motor is energized with axial movement of the shaft stopped by the brake device; and An actuator comprising:

2. The estimation means a first estimation process and a second estimation process are executed in a state in which the axial movement of the shaft is stopped by the brake device, thereby estimating a magnetic pole position of the mover; the first estimation process is a process of estimating whether the mover is located in a section from n-πrad to nrad or a section from nrad to n+πrad, based on a direction of force detected by the force sensor when current is applied to the linear motor with a position of nrad in a magnetic pole position range from 0 to 2πrad as a first target position of the mover, The second estimation process is a process of estimating whether the mover is located in a section above the center of the estimated section or in a section below the center of the estimated section, based on a direction of force detected by the force sensor when the linear motor is energized with the center position of the section in which the mover is estimated to be located set as a second target position of the mover after the first estimation process is executed. The actuator of claim 1 .

3. the estimation means estimates the magnetic pole position of the mover by repeatedly executing the second estimation process a predetermined number of times while updating the second target position. The actuator according to claim 2 .

4. the force sensor includes a strain gauge; the strain gauge is provided on a connecting member that connects the mover and the shaft of the linear motor and detects strain in the connecting member; An actuator according to any one of claims 1 to 3.

5. An actuator that picks up a workpiece by sucking it onto the tip of a shaft, a linear motor having a stator and a mover, the shaft being connected to the mover, and the mover moving relative to the stator to move the shaft in its axial direction; a brake device that brakes the axial movement of the shaft; a force sensor that detects the direction of a force acting on the mover in the axial direction of the shaft; A position estimation method for estimating a magnetic pole position of a mover in an actuator comprising: The linear motion motor is operated with the brake device stopping the axial movement of the shaft. a magnetic pole position of the mover based on a direction of force detected by the force sensor when a current is applied to the mover.

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