Actuator

Abstract

The present invention includes: a shaft 10 including a hollow part 11 on a tip 10A side; a rotation part 20 that rotates the shaft 10 around an axis; a pressure supply part 50 into which the shaft 10 is rotatably inserted and which supplies positive pressure or negative pressure to the hollow part of the shaft 10; a connection member 36 that transmits force for moving the shaft 10, the rotation part 20, and the pressure supply part 50 in the axis 100 direction of the shaft 10; a sensor 37 that is disposed on the connection member 36 and that detects force applied to the shaft 10; and a first flow passage 62 that is a part of a gas flow passage 60 through which gas flows, that is connected to the pressure supply part 50, and that moves in the axis 100 direction of the shaft 10 together with the shaft 10, the rotation part 20, and the pressure supply part 50.

Description

Actuator

[0001] The present invention relates to an actuator.

[0002] By creating a negative pressure inside the hollow shaft while pressing the hollow shaft against the workpiece, the workpiece can be attracted to the shaft and picked up. Here, when the workpiece is attracted to the shaft, if there is a gap between the workpiece and the shaft, the workpiece may collide forcefully with the shaft and the workpiece may be damaged, or the workpiece may not be attracted. On the other hand, if the pressing load on the workpiece is too large, the workpiece may be damaged. Therefore, it is desired to press the shaft against the workpiece with an appropriate load. Also, when the speed of the shaft is high when the shaft contacts the workpiece, there is a risk that the workpiece may be damaged due to the shaft colliding with the workpiece, so it is desired to mitigate this impact. Conventionally, a force sensor has been attached to a member connecting the mover of a linear motor and the support portion of the shaft to detect the force applied to the shaft (see, for example, Patent Document 1).

[0003] Japanese Unexamined Patent Application Publication No. 2020-020678

[0004] In order to supply negative pressure to the shaft, if the shaft slides in the fixed portion, friction may occur and the detected value of the force sensor may change. For this reason, the detected value of the force sensor may not indicate the actual load generated between the shaft and the workpiece. Then, when the shaft is moved based on the detected value of the force sensor, the actual load generated between the shaft and the workpiece may not match the required value. Although it is conceivable to obtain in advance the influence of the frictional force, the frictional force changes due to aging changes of the shaft and the like, temperature, humidity, etc.

[0005] The present invention has been made in view of the various circumstances as described above, and its object is to more accurately detect the load applied to the shaft and the workpiece.

[0006] One aspect of the present invention is an actuator comprising: a shaft having a hollow portion at its tip; a rotating portion for rotating the shaft about an axis; a pressure supply portion through which the shaft is rotatably inserted and which supplies positive or negative pressure to the hollow portion of the shaft; a connecting member for transmitting a force to move the shaft, the rotating portion, and the pressure supply portion in the axial direction of the shaft; a sensor disposed on the connecting member for detecting a force applied to the shaft; and a first flow path which is part of a gas flow path, a gas passage through which gas flows, and is connected to the pressure supply portion, and moves in the axial direction of the shaft together with the shaft, the rotating portion, and the pressure supply portion.

[0007] According to the present invention, the load applied to the shaft and workpiece can be detected with greater accuracy.

[0008] This is a schematic diagram of the actuator according to the embodiment. This is a schematic diagram of the actuator in the state where the shaft according to the embodiment is located at the lowest position in the Z-axis direction.

[0009] In one embodiment of the present invention, the actuator comprises a shaft, a rotating part, and a pressure supply unit, which move in the axial direction of the shaft due to a force transmitted from a connecting member. The shaft is moved when picking up, pressing, or placing a workpiece. The shaft is also rotatable around its axis by the rotating part. The pressure supply unit supplies positive or negative pressure, such as air, to the hollow part at the tip of the shaft. When the shaft moves in the axial direction, the shaft, the rotating part, and the pressure supply unit move simultaneously.

[0010] When the shaft moves and comes into contact with the workpiece, a load is generated between the shaft and the workpiece. When this force is transmitted to the connecting member, strain occurs in the connecting member. This strain is correlated with the load generated between the shaft and the workpiece. Therefore, by detecting this strain with a sensor, the load applied to the shaft and the workpiece can be detected.

[0011] Conventionally, the pressure supply unit slid relative to the shaft, which affected the sensor's detection value. In contrast, the pressure supply unit according to this disclosure moves together with the shaft when the shaft moves axially, so no axial frictional force is generated between the shaft and the pressure supply unit. Therefore, it is possible to suppress the effect on the sensor's detection value. Furthermore, by circulating gas through the gas flow path, positive or negative pressure can be generated in the hollow part of the shaft via the pressure supply unit. However, since the first flow path, which is part of this gas flow path, also moves together with the shaft and the pressure supply unit, it is possible to suppress the repulsive force of the first flow path from affecting the sensor's detection value.

[0012] Furthermore, the system may further include a drive unit that moves the shaft, the rotating part, and the pressure supply part in the axial direction of the shaft via the connecting member. The drive unit may be, for example, a linear motor. Such a drive unit allows the shaft to be moved in the axial direction.

[0013] Furthermore, the first flow path may be fixed to the pressure supply unit and to a first part that moves with the shaft and is located on the drive unit side of the sensor. The first part is located on the drive unit side of the sensor in the force transmission path. By fixing the first flow path to the first part that moves with the shaft in this way, it is possible to suppress the generation of a repulsive force from the first flow path when the shaft moves. This makes it possible to suppress the first flow path from affecting the sensor's detected value.

[0014] Furthermore, the gas flow path includes a second flow path connected to the first flow path, and the second flow path is fixed to the first part and a second part that does not move with the shaft, and may deform in accordance with the movement of the shaft. The second part is, for example, a housing or a member fixed to the housing, and even if the shaft moves relative to the housing, the second part does not move with the shaft. Deformation includes, for example, positional deformation and elastic deformation. Even if the second flow path deforms and a repulsive force is generated, since the first flow path is fixed to the pressure supply unit and the first part, the repulsive force generated in the second flow path can be prevented from affecting the sensor's detected value.

[0015] Furthermore, the drive unit is configured to include a linear motor having a stator and a movable element that moves in the axial direction of the shaft relative to the stator, and the first part may be located between the movable element and the sensor. By positioning the first part on the movable element side of the sensor, the detection of the repulsive force of the gas flow path by the sensor can be suppressed.

[0016] Furthermore, the gas flow path may include a third flow path that is adjacent to the drive unit, parallel to the axial direction of the shaft, and positioned on the opposite side of the shaft from the view of the drive unit. By positioning the third flow path adjacent to the drive unit, heat generated in the drive unit can be removed. Therefore, cooling inside the actuator can be promoted. In addition, by positioning the third flow path on the opposite side of the shaft, obstruction of the shaft's movement can be suppressed.

[0017] Embodiments for carrying out the present invention will be described below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment are not intended to limit the scope of this invention to those.

[0018] <Embodiment> Figure 1 is a schematic diagram of the actuator 1 according to this embodiment. The actuator 1 has a housing 2 that forms its outer casing. A lid is attached to the housing 2, but Figure 1 shows the state with the lid removed. A part of the shaft 10 is housed inside the housing 2. The tip 10A side of the shaft 10 is formed to be hollow. The shaft 10 and housing 2 can be made of materials such as metal (e.g., aluminum), but resin can also be used. In the following description, an XYZ Cartesian coordinate system will be set up, and the position of each component will be described with reference to this XYZ Cartesian coordinate system. The direction of the central axis 100 of the shaft 10, which is the long side direction of the largest surface of the housing 2, will be defined as the Z-axis direction, the direction of the short side direction of the largest surface of the housing 2 will be defined as the X-axis direction, and the direction perpendicular to the largest surface of the housing 2 will be defined as the Y-axis direction. The Z-axis direction is also the vertical direction. In the following, the upper side in the Z-axis direction in Figure 1 will be defined as the upper side of the actuator 1, and the lower side in the Z-axis direction in Figure 1 will be defined as the lower side of the actuator 1. Furthermore, the right side in the X-axis direction in Figure 1 is considered the right side of actuator 1, and the left side in the X-axis direction in Figure 1 is considered the left side of actuator 1. Also, the front side in the Y-axis direction in Figure 1 is considered the front side of actuator 1, and the back side in the Y-axis direction in Figure 1 is considered the back side of actuator 1. The housing 2 has a dimension in the Z-axis direction that is longer than the dimension in the X-axis direction, and a dimension in the X-axis direction that is longer than the dimension in the Y-axis direction. The housing 2 has an opening in one place that is perpendicular to the Y-axis direction (the front side in Figure 1), and in the operating state, this opening is closed by a cover. Note that Figure 1 shows the state in which the shaft 10 is located at the uppermost position in the Z-axis direction.

[0019] The housing 2 houses a rotary motor 20 that rotates the shaft 10 around its central axis 100, a linear motor 30 that moves the shaft 10 in a direction along its central axis 100 (i.e., the Z-axis direction) relative to the housing 2, and a pressure supply unit 50 that supplies positive or negative pressure to the shaft 10. A through hole 2021 is formed in the Z-axis direction of the lower end surface 202 of the housing 2, through which the pressure supply unit 50 passes. The lower tip 10A of the shaft 10 in the Z-axis direction protrudes downward from the pressure supply unit 50 in the Z-axis direction. The shaft 10 is located approximately at the center of the housing 2 in the Y-axis direction. The shaft 10 moves in the Z-axis direction by the linear motor 30 and rotates around the central axis 100 by the rotary motor 20.

[0020] The base end 10B of the shaft 10, which is the end opposite to the tip 10A (the upper end in the Z-axis direction), is housed in the housing 2 and connected to the output shaft 21 of the rotary motor 20. This 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 includes 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. The stator 22 is fixed to the motor housing 39. Note that the rotary motor 20 is an example of a rotating part.

[0021] The linear motor 30 has a stator 31 fixed to the housing 2 and a movable element 32 that moves in the Z-axis direction relative to the stator 31. The stator 31 is provided with a plurality of coils, and the movable element 32 is provided with a plurality of permanent magnets. The coils are arranged at a predetermined pitch in the Z-axis direction, and a plurality of sets of three coils, U, V, and W phases, are provided. In this embodiment, a moving magnetic field that moves linearly is generated by passing a three-phase armature current through these U, V, and W phase coils, causing the movable element 32 to move linearly relative to the stator 31. The linear motor 30 is provided with a linear encoder 38 that detects the relative position of the movable element 32 with respect to the stator 31. Alternatively, the stator 31 can be provided with permanent magnets and the movable element 32 can be provided with a plurality of coils. Note that the linear motor 30 is an example of a drive unit.

[0022] The movable element 32 of the linear motor 30 and the stator 22 of the rotary motor 20 are connected via a linear guide device 34. The linear guide device 34 is movable in conjunction with the movement of the movable element 32 of the linear motor 30. The linear guide device 34 has a rail 341 fixed to the housing 2 and two slider blocks 342 assembled on the rail 341. The rail 341 extends in the Z-axis direction, and the slider blocks 342 are configured to move along the rail 341 in the Z-axis direction. The slider block 342 located on the upper side in the Z-axis direction is called the upper slider block 3421, and the slider block 342 located on the lower side in the Z-axis direction is called the lower slider block 3422. When the two slider blocks 342 are not distinguished, they are simply referred to as slider blocks 342.

[0023] One end of the upper connecting member 351 is connected to the upper end of the upper slider block 3421. The other end of the upper connecting member 351 is connected to the upper end of the movable element 32 of the linear motor 30. One end of the lower connecting member 352 is connected to the lower end of the lower slider block 3422. The other end of the lower connecting member 352 is connected to the lower end of the movable element 32 of the linear motor 30. Because the slider block 342 and the movable element 32 of the linear motor 30 are connected via the upper connecting member 351 and the lower connecting member 352, the slider block 342 moves in conjunction with the movement of the movable element 32 of the linear motor 30.

[0024] One end of the upper arm 361 is connected to the lower end of the upper slider block 3421. The other end of the upper arm 361 is connected to the motor housing 39. One end of the lower arm 362 is connected to the upper end of the lower slider block 3422. The other end of the lower arm 362 is connected to the motor housing 39. When the upper arm 361 and the lower arm 362 are not distinguished, they are referred to as the connecting arm 36. Because the slider block 342 and the stator 22 of the rotary motor 20 are connected via the connecting arm 36 and the motor housing 39, the stator 22 of the rotary motor 20 moves along with the movement of the slider block 342.

[0025] The connecting arm 36 has a square cross-section and is positioned in the X-axis direction. A strain gauge 37 is fixed to the upper surface of the connecting arm 36 facing upward in the Z-axis direction. The strain gauge 37 fixed to the upper arm 361 is called the upper strain gauge 371, and the strain gauge 37 fixed to the lower arm 362 is called the lower strain gauge 372. When the upper strain gauge 371 and the lower strain gauge 372 are not distinguished, they are simply referred to as strain gauge 37. In this embodiment, the two strain gauges 37 are each provided on the upper surface of the connecting arm 36 facing upward in the Z-axis direction, but they may instead be each provided on the lower surface of the connecting arm 36 facing downward in the Z-axis direction. The connecting arm 36 is an example of a connecting member. The strain gauge 37 is an example of a sensor.

[0026] The actuator 1 further includes an air passage 60. The air passage 60 is a passage through which air flows that generates positive and negative pressure at the tip 10A of the shaft 10. That is, when picking up a workpiece W, negative pressure can be generated at the tip 10A of the shaft 10 by drawing air from inside the shaft 10 through the air passage 60. This causes the workpiece W to be attracted to the tip 10A of the shaft 10. Also, positive pressure can be generated at the tip 10A of the shaft 10 by sending air into the shaft 10 through the air passage 60. This allows the workpiece W to be easily detached from the tip 10A of the shaft 10. Note that other gases may be used, not just air, as long as they can generate positive or negative pressure at the tip 10A of the shaft 10.

[0027] The air passage 60 includes a first connector 61, a first tube 62, a second connector 63, a second tube 64, a third connector 65, a third tube 66, a fourth connector 67, and an external connector 68. One end of the first connector 61 is fixed to the through hole 501 of the pressure supply unit 50, for example, by a screw structure. One end of the first tube 62 is connected to the other end of the first connector 61. The other end of the first tube 62 is connected to one end of the second connector 63. The second connector 63 is fixed to the lower end surface of the lower connecting member 352. In the example shown in Figure 1, the first tube 62 extends upward in the Z-axis direction from the first connector 61, then bends 90 degrees to the left in the X-axis direction and is connected to the second connector 63. However, the shapes of the first connector 61, the first tube 62, and the second connector 63 are not limited to these. The first tube 62 can be configured to move together with the pressure supply unit 50. Note that the air passage 60 is an example of a gas passage. The first tube 62 is an example of a first passage. The second tube 64 is an example of a second flow path. The third tube 66 is an example of a third flow path. The lower connecting member 352 is an example of a first part.

[0028] Furthermore, one end of the second tube 64 is connected to the other end of the second connector 63. The other end of the second tube 64 is connected to one end of the third connector 65. The second tube 64 extends downward in the Z-axis direction from the second connector 63, rotates 180 degrees to the left in the X-axis direction, and then connects to the third connector 65 from the lower Z-axis direction. The second tube 64 is an elastically deformable tube. The second tube 64 may be formed from, for example, a synthetic resin.

[0029] The third connector 65 is fixed to the housing 2. Note that this housing 2 is an example of the second part. One end of the third tube 66 is connected to the other end of the third connector 65. The third tube 66 is provided adjacent to the linear motor 30, parallel to the movable element 32 of the linear motor 30. Also, the third tube 66 is positioned on the opposite side from the shaft 10 when viewed from the linear motor 30. The other end of the third tube 66 is connected to one end of the fourth connector 67. The other end of the fourth connector 67 is connected to an external connector 68 provided on the upper end surface 201 of the housing 2 in the Z-axis direction. The external connector 68 penetrates the upper end surface 201 of the housing 2 in the Z-axis direction. A tube connected to a pump for discharging and sucking air is connected to the external connector 68 from the outside. An air vent connector 69 is provided next to the external connector 68. The air vent connector 69 penetrates the upper end surface 201 of the housing 2 in the Z-axis direction, and communicates the inside and outside of the housing 2. The air vent connector 69 is connected to a suction pump via a tube, and the pump sucks air out of the housing 2 through the air vent connector 69, thereby cooling the housing 2.

[0030] The first tube 62 and the third tube 66 may be the same type of tube as the second tube 64, or they may be different types of tubes. The third tube 66 may also be made of a metal with high thermal conductivity to facilitate heat dissipation from the stator 31 of the linear motor 30. In this case, the heat generated by the linear motor 30 can be supplied to the air inside the third tube 66, and this heat can be discharged to the outside along with the air. Furthermore, since the third tube 66 is located on the opposite side of the shaft 10 from the linear motor 30, it does not interfere with the operation of the components that move the shaft 10 in the Z-axis direction.

[0031] Here, Figure 2 is a schematic configuration diagram of the actuator 1 in the state in which the shaft 10 according to the embodiment is located at the lowest position in the Z-axis direction. The second connector 63, to which one end of the second tube 64 is connected, is fixed to the lower connecting member 352. Therefore, when the linear motor 30 is operated to move the lower connecting member 352 downwards in the Z-axis direction, the second connector 63 moves downwards in the Z-axis direction together with the lower connecting member 352. On the other hand, the third connector 65, to which the other end of the second tube 64 is connected, is fixed to the housing 2 and does not move in the Z-axis direction even when the linear motor 30 is operated. Therefore, one end of the second tube 64 moves in the Z-axis direction, while the other end does not. When the linear motor 30 is operated, the second tube 64 elastically deforms, maintaining the connection between the second connector 63 and the third connector 65 and the second tube 64. In this embodiment, an example in which the second tube 64 elastically deforms has been described, but it is not limited to this and may deform in other ways.

[0032] On the upper end surface 201 of the housing 2 in the Z-axis direction, there is a connector 41 for connecting a signal line to a pneumatic unit that controls the pressure of the air passage 60, and a connector 42 for connecting signal lines to an external controller and wires for supplying power. A base plate 7 is fixed to the housing 2. The wires drawn into the housing 2 from connectors 41 and 42 are connected to the base plate 7. The output signals of the strain gauge 37, rotary encoder 24, and linear encoder 38 are input to the base plate 7. The strain gauge 37, rotary motor 20, and linear motor 30 are connected to the base plate 7 via a flexible cable 71. One end of the flexible cable 71 is fixed to the base plate 7, and the other end is fixed to the upper slider block 3421. Therefore, as the upper slider block 3421 moves in the Z-axis direction, the flexible cable 71 elastically deforms, maintaining the connection state of the flexible cable 71.

[0033] The pressure supply unit 50 has a cylindrical section 51 and two collars 52. The upper end of the cylindrical section 51 is formed in a flange shape and is fixed to the lower end of the motor housing 39. A through hole 511 is formed in the cylindrical section 51 through which the shaft 10 is inserted. The through hole 511 penetrates the cylindrical section 51 in the Z-axis direction. The diameter of the through hole 511 is larger than the outer diameter of the shaft 10. Therefore, a gap is provided between the inner surface of the through hole 511 and the outer surface of the shaft 10. Enlarged diameter sections 512 are provided at both ends of the through hole 511, where the diameter of the hole is enlarged. Collars 52 are fitted into each of the two enlarged diameter sections 512. The collars 52 are formed in a cylindrical shape, and the inner diameter of the collars 52 is slightly larger than the outer diameter of the shaft 10. The collar 52 on the upper side in the Z-axis direction is called the first collar 521, and the collar 52 on the lower side in the Z-axis direction is called the second collar 522. When the first collar 521 and the second collar 522 are not distinguished, they are simply referred to as collar 52. The material of collar 52 can be, for example, metal or resin. The inner diameter of collar 52 and the outer diameter of shaft 10 are adjusted so that shaft 10 can rotate around the central axis 100 inside collar 52. In addition, the gap between collar 52 and shaft 10 is formed to suppress airflow as much as possible. For this reason, shaft 10, through hole 511, and collar 52 are formed such that the gap between the inner surface of collar 52 and the outer surface of shaft 10 is smaller than the gap between the inner surface of through hole 511 near the center of cylindrical portion 51 and the outer surface of shaft 10.

[0034] As described above, a gap is provided between the inner surface of the through hole 511 and the outer surface of the shaft 10. As a result, an internal space 500 is formed inside the cylindrical portion 51, which is a space enclosed by the inner surface of the through hole 511, the outer surface of the shaft 10, the lower end surface of the first collar 521, and the upper end surface of the second collar 522. In addition, the pressure supply portion 50 has a through hole 501 that connects the first connector 61 and the internal space 500, serving as an air passage.

[0035] A hollow section 11 is formed at the tip 10A of the shaft 10, such that the shaft 10 is hollow. One end of the hollow section 11 is open at the tip 10A. At the other end of the hollow section 11, a communication hole 12 is formed that connects the internal space 500 and the hollow section 11 in the X-axis direction. Therefore, the tip 10A of the shaft 10 and the first connector 61 are in communication via the hollow section 11, the communication hole 12, the internal space 500, and the through hole 501. Note that the communication hole 12 may also be formed in the Y-axis direction in addition to the X-axis direction.

[0036] With this configuration, when the linear motor 30 is driven to move the shaft 10 in the Z-axis direction, the pressure supply unit 50 also moves along with it, so the communication hole 12 is always in communication with the internal space 500 and the hollow portion 11. Also, when the rotary motor 20 is driven to rotate the shaft 10 around the central axis 100, the communication hole 12 is always in communication with 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, no matter what state the shaft 10 is in, the communication between the hollow portion 11 and the internal space 500 is maintained, so it can be said that the hollow portion 11 is always connected to the first connector 61.

[0037] Therefore, regardless of the position of the shaft 10, when air is drawn in from the external connector 68, air in the hollow section 11 is drawn in through the air passage 60, the through hole 501, the internal space 500, and the communication hole 12. As a result, negative pressure can be generated in the hollow section 11. That is, negative pressure can be generated at the tip 10A of the shaft 10, so that the workpiece W can be attracted to the tip 10A of the shaft 10. As mentioned above, a gap is also formed between the inner surface of the collar 52 and the outer surface of the shaft 10. However, this gap is smaller than the gap that forms the internal space 500 (i.e., the gap formed between the inner surface of the through hole 511 and the outer surface of the shaft 10). Therefore, even if air in the internal space 500 is drawn in from the air passage 60, the flow of air between the inner surface of the collar 52 and the outer surface of the shaft 10 can be suppressed. This makes it possible to generate negative pressure at the tip 10A of the shaft 10 that is sufficient to pick up the workpiece W. Furthermore, regardless of the position of the shaft 10, supplying positive pressure to the external connector 68 can generate positive pressure in the hollow portion 11. That is, positive pressure can be generated at the tip 10A of the shaft 10, allowing the workpiece W to be quickly detached from the tip 10A of the shaft 10.

[0038] (Pick and Place Operation) The pick and place operation of a workpiece W using actuator 1 will be described below. Pick and place is performed in response to a signal from an external controller. When picking up the workpiece W, positive and negative pressure are not supplied to the external connector 68 until the shaft 10 makes contact with the workpiece W. In this case, the pressure at the tip 10A of the shaft 10 is atmospheric pressure. Then, the linear motor 30 moves the shaft 10 downward in the Z-axis direction. When the shaft 10 makes contact with the workpiece W, the linear motor 30 is stopped. After stopping the linear motor 30, negative pressure is supplied to the external connector 68 to generate negative pressure at the tip 10A of the shaft 10, attracting the workpiece W to the tip 10A of the shaft 10. After that, the linear motor 30 moves the shaft 10 upward in the Z-axis direction. At this time, the rotary motor 20 rotates the shaft 10 as needed. In this way, the workpiece W can be picked up.

[0039] Next, when placing the workpiece W, the linear motor 30 moves the shaft 10, which is in contact with the tip 10A of the workpiece W, downward in the Z-axis direction. When the workpiece W touches the ground, the linear motor 30 is stopped, thereby stopping the movement of the shaft 10. Furthermore, positive pressure is generated at the tip 10A of the shaft 10 by supplying positive pressure to the external connector 68. Subsequently, the linear motor 30 moves the shaft 10 upward in the Z-axis direction, causing the tip 10A of the shaft 10 to separate from the workpiece W.

[0040] Here, when the workpiece W is picked up, the contact of the tip 10A of the shaft 10 with the workpiece W can be detected using the strain gauge 37. Similarly, when the workpiece W is placed, the contact with the ground can be detected. When the tip 10A of the shaft 10 contacts the workpiece W and pushes the workpiece W, a load is generated between the shaft 10 and the workpiece W. That is, the shaft 10 receives a force from the workpiece W as a reaction to the force applied by the shaft 10 to the workpiece W. This force received by the shaft 10 from the workpiece W acts in a direction that generates strain on the connecting arm 36. This force causes strain in the connecting arm 36. This strain is detected by the strain gauge 37. The strain detected by the strain gauge 37 is correlated with the force that the shaft 10 receives from the workpiece W. Therefore, based on the detected value of the strain gauge 37, the force that the shaft 10 receives from the workpiece W, i.e., the load generated between the shaft 10 and the workpiece W, can be detected. The relationship between strain gauge readings and load can be determined in advance through experiments or simulations.

[0041] In this way, the load generated between the shaft 10 and the workpiece W can be detected based on the detected value of the strain gauge 37. For example, it may be determined that the tip 10A of the shaft 10 has come into contact with the workpiece W at the moment the load is generated, or, taking into account the effects of errors, it may be determined that the tip 10A of the shaft 10 has come into contact with the workpiece W when the detected load is greater than or equal to a predetermined load. The predetermined load is the threshold value at which it is determined that the shaft 10 has come into contact with the workpiece W. The predetermined load may also be set to a load that allows for more reliable pickup of the workpiece W while suppressing damage to the workpiece W. Furthermore, the predetermined load can be changed depending on the type of workpiece W.

[0042] Since the change in resistance due to strain in the strain gauge 37 is extremely small, a Wheatstone bridge circuit is used to extract it as a voltage change. In actuator 1, the output of the bridge circuit related to the upper strain gauge 371 and the output of the bridge circuit related to the lower strain gauge 372 are connected in parallel. By connecting the outputs of both bridge circuits in parallel in this way, a voltage change that is free from the effects of temperature is obtained.

[0043] In the conventional actuator 1, the pressure supply unit 50, which is positioned around the shaft 10, was not fixed to the motor housing 39 but to the housing 2. The entire air passage 60 was also fixed to the housing 2. Therefore, when the shaft 10 was moved in the Z-axis direction by the linear motor 30, the shaft 10 moved relative to the pressure supply unit 50. At this time, sliding resistance sometimes occurred between the shaft 10 and the collar 52. This sliding resistance affected the detected value of the strain gauge 37. Therefore, when the shaft 10 was moving in the Z-axis direction, it was difficult to accurately detect the load generated between the shaft 10 and the workpiece W.

[0044] On the other hand, in the actuator 1 according to this embodiment, the pressure supply unit 50 is fixed to the motor housing 39. Also, the first tube 62 is fixed to the pressure supply unit 50 via the first connector 61 and to the lower connecting member 352 via the second connector 63. Therefore, when the linear motor 30 moves the shaft 10 in the Z-axis direction, the pressure supply unit 50 also moves together, so the sliding resistance described above does not occur. Also, since the first tube 62 moves together with the pressure supply unit 50, the detection of the repulsive force of the air passage 60 by the strain gauge 37 can be suppressed. The second tube 64 deforms in accordance with the second connector 63 when the linear motor 30 is operating, so a repulsive force is generated. However, since the second tube 64 is fixed to the lower connecting member 352 at the second connector 63, the influence of its repulsive force on the detected value of the strain gauge 37 is small. Therefore, compared to conventional actuators, since no sliding resistance is generated in the shaft 10, the load applied to the shaft 10 can be detected more accurately.

[0045] Also, since an appropriate force can be applied to the workpiece W, the pickup of the workpiece W can be executed more reliably. For example, when picking up the workpiece W, by generating a negative pressure in the hollow portion 11 while pressing the workpiece W against the tip portion 10A of the shaft 10, it is possible to more reliably pick up the workpiece W and suppress the workpiece W from colliding with the shaft 10 forcefully and being damaged when the workpiece W is sucked. On the other hand, if the load for pressing the workpiece W is too large, the workpiece W may be damaged. Therefore, by detecting the load applied to the workpiece W and applying an appropriate load to the workpiece W, it is possible to suppress the damage of the workpiece W and more reliably pick up the workpiece W. Also, at the time of placement, it may be required to apply an appropriate load to the workpiece W. For example, when adhering the workpiece W to another member using an adhesive, it is necessary to apply a load according to the characteristics of the adhesion. Also at this time, by appropriately controlling the load applied to the workpiece W, more reliable adhesion becomes possible.

[0046] <Other Embodiments> In the first embodiment, the strain gauge 37 is provided on the connecting arm 36, but instead, the strain gauge 37 can also be provided on the motor housing 39.

[0047] Also, in this embodiment, two strain gauges 37 are provided, but instead, only either the upper strain gauge 371 or the lower strain gauge 372 may be provided. In this case, the detected value of the strain gauge may be corrected according to the temperature using a well-known technique. Even when one strain gauge 37 is provided, the output of the strain gauge 37 becomes a value corresponding to the load generated between the shaft 10 and the workpiece W. Therefore, based on the output of the strain gauge 37, the load generated between the shaft 10 and the workpiece W can be detected.

[0048] 1...Actuator, 2...Housing, 10...Shaft, 10A...Tip, 11...Hollow section, 20...Rotating motor, 22...Stator, 23...Rotor, 30...Linear motor, 31...Stator, 32...Motor, 36...Connecting arm, 37...Strain gauge, 39...Motor housing, 50...Pressure supply section, 60...Air passage, 62...First tube

Claims

1. An actuator comprising: a shaft having a hollow portion at its tip; a rotating portion for rotating the shaft about its axis; a pressure supply portion through which the shaft is rotatably inserted and which supplies positive or negative pressure to the hollow portion of the shaft; a connecting member for transmitting a force to move the shaft, the rotating portion, and the pressure supply portion in the axial direction of the shaft; a sensor disposed on the connecting member for detecting the force applied to the shaft; and a first flow path which is part of a gas flow path, a passage through which gas flows, and is connected to the pressure supply portion, and moves in the axial direction of the shaft together with the shaft, the rotating portion, and the pressure supply portion.

2. The actuator according to claim 1, further comprising a drive unit for moving the shaft, the rotating part, and the pressure supply part in the axial direction of the shaft via the connecting member.

3. The actuator according to claim 2, wherein the first flow path is fixed to the pressure supply unit and to a first portion which moves together with the shaft and is located on the drive unit side of the sensor.

4. The actuator according to claim 3, wherein the gas flow path includes a second flow path connected to the first flow path, and the second flow path is fixed to the first portion and a second portion that does not move with the shaft, and deforms in accordance with the movement of the shaft.

5. The actuator according to claim 3, wherein the drive unit comprises a linear motor having a stator and a movable element that moves in the axial direction of the shaft relative to the stator, and the first portion is located between the movable element and the sensor.

6. The actuator according to claim 2, wherein the gas flow path includes a third flow path adjacent to the drive unit, arranged parallel to the axial direction of the shaft, and arranged on the opposite side from the shaft when viewed from the drive unit.

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