Patent Publication Number: US-2021162609-A1

Title: Actuator

Description:
TECHNICAL FIELD 
     The present invention relates to an actuator. 
     BACKGROUND ART 
     A workpiece can be sucked to a hollow shaft and picked up by providing a negative pressure to an interior of the shaft while the shaft is pressed against the workpiece. Here, if there is a space between the workpiece and the shaft when the workpiece is sucked to the shaft, the workpiece might strongly collide with the shaft and be damaged, or the workpiece could not be sucked. On the other hand, if a load to press the workpiece is excessively large, the workpiece might be damaged. Therefore, it is desirable to press the shaft against the workpiece with an appropriate load. Furthermore, if a speed of the shaft is high when the shaft comes in contact with the workpiece, the workpiece might be damaged due to the collision of the shaft with the workpiece. Therefore, it is desirable to reduce this impact. Heretofore, a chuck member has been provided to a tip of a shaft body via a cushioning member such as a spring (e.g., see Patent Literature 1). Specifically, the spring contracts to reduce the impact, when the chuck member comes in contact with the workpiece. Afterward, when the shaft further moves toward the workpiece, the workpiece is pressed with a load corresponding to a spring constant. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] Japanese Patent Laid-Open No. 2009-164347 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     An appropriate load may vary with a workpiece. In a case where such a cushioning member as described above is provided, however, the load applied to the workpiece is determined in accordance with a spring constant. It is therefore difficult to change the load applied to the workpiece in accordance with the workpiece. If the load applied to the workpiece is adjusted with this configuration, for example, it is necessary to replace the cushioning member. Furthermore, if the cushioning member is provided as described above, the load applied to the workpiece tends to vary. Therefore, it is difficult to use the member in the workpiece for which it is necessary to accurately adjust the load. Here, if the load applied to a shaft and the workpiece can be detected, the shaft can be controlled in accordance with the detected load. 
     An object of the present invention, which has been made in view of various actual situations described above, is to provide an actuator in which a load applied to a shaft and a workpiece is controlled. 
     Solution to Problem 
     One of aspects of the present invention is an actuator comprising a shaft, a support part that rotatably supports the shaft, a linear motion motor including a stator and a mover, movement of the mover in parallel with a central axis of the shaft relative to the stator of the linear motion motor causing the support part and the shaft to move in a direction of the central axis of the shaft, a connecting member that is at least a part of a member connecting the mover of the linear motion motor and the support part, a strain gauge provided in the connecting member to detect strain of the connecting member, and a control device that controls the linear motion motor, based on the strain detected by the strain gauge. 
     Advantageous Effects of Invention 
     According to the present invention, in an actuator, a load applied to a shaft and a workpiece can be controlled. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an appearance view of an actuator according to an embodiment. 
         FIG. 2  is a schematic configuration view illustrating an inner structure of the actuator according to the embodiment. 
         FIG. 3  is a cross-sectional view illustrating a schematic configuration including a shaft housing and a tip of a shaft according to the embodiment. 
         FIG. 4  is a view illustrating a schematic configuration in a case where a strain gauge is provided in a bearing that supports an output shaft of a rotating motor according to the embodiment. 
         FIG. 5  is a view illustrating a schematic configuration in the case where the strain gauge is provided in the bearing that supports the output shaft of the rotating motor according to the embodiment. 
         FIG. 6  is a flowchart illustrating flow of pickup processing according to a first embodiment. 
         FIG. 7  is a flowchart illustrating flow of place processing according to the first embodiment. 
         FIG. 8  is a flowchart illustrating flow of pickup processing according to a second embodiment. 
         FIG. 9  is a flowchart illustrating flow of place processing according to the second embodiment. 
         FIG. 10  is a flowchart illustrating flow of pickup processing according to a third embodiment. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     In a load detector according to one of aspects of the present invention, a support part and a shaft are moved in a moving direction of a mover by a linear motion motor. The moving direction of the mover of the linear motion motor is parallel to a central axis direction of the shaft, and the linear motion motor is therefore driven to move the shaft in the central axis direction. An example of the linear motion motor is a linear motor. Furthermore, examples of the support part include a rotating motor that rotates the shaft, or a bearing provided between a stator of the rotating motor and an output shaft of the rotating motor. The mover of the linear motion motor is connected to the support part via a connecting member. Note that a plurality of connecting members may be present. Furthermore, the mover of the linear motion motor may be integrated with the connecting member, or the support part may be integrated with the connecting member. The support part rotatably supports the shaft regardless of the driving of the linear motion motor. Consequently, moving the shaft in the central axis direction by the linear motion motor, and rotating the shaft about a central axis can be performed individually. 
     If the shaft comes in contact with a workpiece by the driving of the linear motion motor, a load is generated between the shaft and the workpiece. 
     Consequently, a force in a direction to move the shaft toward the workpiece acts on one end side (a linear motion motor side) of the connecting member, and a force in a direction to move the shaft away from the workpiece acts on the other end side (a support part side) of the connecting member, thereby generating strain in the connecting member. This strain has correlation with the load generated between the shaft and the workpiece. Therefore, detection of this strain by a strain gauge allows detection of the load applied to the shaft and the workpiece. Based on the load detected in this manner, the linear motion motor is controlled, so that appropriate load can be applied to the workpiece. It is therefore possible to more securely pick up the workpiece, while inhibiting damage on the workpiece. 
     Furthermore, the control device may detect a load applied to the shaft based on the strain detected by the strain gauge while the shaft is being moved by the linear motion motor, and may stop the linear motion motor in a case where the detected load is equal to or larger than a threshold. Note that the threshold is a load by which it is determined that the shaft comes in contact with the workpiece during the pickup of the workpiece. Furthermore, the threshold may be set as a load with which it is possible to more securely pick up the workpiece while inhibiting the damage on the workpiece during the pickup of the workpiece. Additionally, the threshold is, for example, a load by which it is determined that the workpiece is grounded or it is determined that the workpiece comes in contact with another member, during placing of the workpiece. In addition, the threshold may be set as a load with which it is possible to more securely press the workpiece against the other member while inhibiting the damage on the workpiece during the placing of the workpiece. The threshold can be changed in accordance with a type of workpiece. The linear motion motor is stopped in a case where the detected load is equal to or larger than the threshold, so that the shaft can be immediately stopped when the shaft comes in contact with the workpiece, or the shaft can be immediately stopped when the workpiece is grounded or comes in contact with the other member. Furthermore, it is possible to apply an appropriate load to the workpiece during the pickup or during the placing. 
     Additionally, the control device may detect a load applied to the shaft based on the strain detected by the strain gauge while the shaft is being moved by the linear motion motor, may set a speed at which the shaft is moved by the linear motion motor to a lower speed, in a case where the detected load is equal to or larger than a threshold than in a case where the load is less than the threshold, and may stop the linear motion motor, in a case where the detected load is equal to or larger than a second threshold indicating a load larger than the threshold. Note that the threshold is the load by which it is determined that the shaft comes in contact with the workpiece during the pickup of the workpiece. 
     Furthermore, the threshold is, for example, the load by which it is determined that the workpiece is grounded or it is determined that the workpiece comes in contact with the other member, during the placing of the workpiece. Furthermore, the second threshold may be set as the load with which it is possible to more securely pick up the workpiece while inhibiting the damage on the workpiece during the pickup of the workpiece. Alternatively, the second threshold may be set as the load with which it is possible to more securely press the workpiece against the other member while inhibiting the damage on the workpiece during the placing of the workpiece. The threshold and the second threshold can be changed in accordance with the type of workpiece. Thus, the speed of the shaft is initially set to be high, and then the speed of the shaft is decreased after the shaft comes in contact with the workpiece during the pickup of the workpiece, or after the workpiece is grounded during the placing of the workpiece. Further load is applied to the workpiece while decreasing the speed of the shaft, and hence it is possible to more securely pick up the workpiece. Additionally, for example, in a case where the workpiece is bonded to the other member during the placing of the workpiece, the workpiece can be more appropriately bonded by applying the appropriate load. Furthermore, in a case where the load is less than the threshold, the shaft rapidly moves, and hence tact time can be shortened. 
     In addition, the shaft may include a hollow part formed on a tip side of the shaft such that an interior of the shaft is hollow, the actuator may further include a supply part that supplies a negative pressure to the hollow part, and the control device may supply the negative pressure from the supply part to the hollow part, after the linear motion motor is stopped, when a workpiece is to be picked up. Thus, the appropriate load is applied to the workpiece and then the negative pressure is supplied to the hollow part. Consequently, the damage on the workpiece due to the collision of the workpiece with the shaft can be inhibited. Furthermore, a space can be inhibited from being generated between the workpiece and the shaft, by pressing the shaft against the workpiece. Consequently, it is possible to more securely pick up the workpiece. 
     Furthermore, the shaft may include a hollow part formed on a tip side of the shaft such that an interior of the shaft is hollow, the actuator may further include a supply part that supplies a negative pressure to the hollow part, a flow sensor provided in a middle of an air passage to detect a flow rate of the air flowing through the air passage, the air passage being a passage through which air sucked from the hollow part when supplying the negative pressure to the hollow part flows, and a pressure sensor provided in a middle of the air passage, to detect a pressure in the air passage, and the control device may control the linear motion motor, based on, in addition to the strain detected by the strain gauge, the flow rate detected by the flow sensor and/or the pressure detected by the pressure sensor. 
     It can be detected that the shaft is in contact with the workpiece, based on the strain detected by the strain gauge. However, if the pressure in the hollow part is not sufficiently low even when the shaft is in contact with the workpiece, the workpiece might not be picked up, and the workpiece might drop halfway. Here, it can be determined whether or not the pressure in the hollow part sufficiently decreases, based on at least one of values of the flow rate detected by the flow sensor and the pressure detected by the pressure sensor. Consequently, it can be determined whether or not the workpiece is sucked to the shaft. That is, after the negative pressure is supplied to the hollow part, air flows through the air passage until the pressure in the hollow part sufficiently decreases. It is detected by the flow sensor that the air flows through this passage. Therefore, it can be determined, based on a detected value of the flow sensor, whether or not the pressure in the hollow part sufficiently decreases. Furthermore, the pressure in the air passage is also high (the negative pressure is small) until the pressure in the hollow part sufficiently decreases. Consequently, it can be determined, based on the detected value of the pressure sensor, whether or not the pressure in the hollow part sufficiently decreases. Therefore, the linear motion motor is controlled based on, in addition to the strain detected by the strain gauge, the flow rate detected by the flow sensor and/or the pressure detected by the pressure sensor. Consequently, it is possible to more securely pick up the workpiece. 
     The control device may supply the negative pressure from the supply part to the hollow part, when a workpiece is to be picked up, and may move the shaft upward in the central axis direction by the linear motion motor, when the flow rate detected by the flow sensor decreases down to a predetermined flow rate or less, and/or when the pressure detected by the pressure sensor decreases down to a predetermined pressure or less. 
     The flow of air through the air passage slows down as the pressure in the hollow part decreases (the negative pressure increases). Furthermore, the pressure of air in the air passage decreases as the pressure in the hollow part decreases. Therefore, it can be determined that the pressure in the hollow part sufficiently decreases, when the flow rate detected by the flow sensor decreases down to the predetermined flow rate or less and/or when the pressure detected by the pressure sensor decreases down to the predetermined pressure or less. Thereafter, the shaft is moved upward in the central axis direction, so that it is possible to more securely pick up the workpiece. Note that the predetermined flow rate is a flow rate at which the pressure in the hollow part decreases down to the pressure at which the workpiece can be picked up, and the predetermined pressure is a pressure to which the pressure in the hollow part decreases and at which the workpiece can be picked up. 
     Furthermore, the connecting member may include a first member and a second member that are provided in a shifted manner in a direction of the central axis of the shaft, and the strain gauge may be provided on each of surfaces that are provided on the first member and the second member, respectively, the surfaces facing in the same direction and being parallel to each other and orthogonal to the central axis of the shaft. 
     Here, the linear motion motor operates to generate heat. Furthermore, another device provided in the actuator may generate heat. Such heat may thermally expand the linear motion motor, the support part, and the connecting member. In this case, even if any load is not applied from the workpiece to the shaft, strain may be generated in the first member and the second member. For example, if there is a difference in temperature between a member to which the first member and the second member are connected on one end side and a member to which the members are connected on the other end side, a difference may be made in expansion amount. Note that hereinafter, the member to which the first member and the second member are connected on the one end side will be illustrated as a member having a large thermal expansion amount (a high expansion member), and the member to which the members are connected on the other end side will be illustrated as a member having a small thermal expansion amount (a low expansion member). In a case where the first member and the second member are connected to the high expansion member and the low expansion member in this manner, a distance between the first member and the second member may be larger on a high expansion member side than on a low expansion member side. Furthermore, forces in opposite directions are applied to the first member and the second member, respectively, in a direction to separate the first member and the second member on the high expansion member side. Consequently, strain in a contracting direction is generated in one of the surfaces that are provided on the first member and second member, respectively, face in the same direction and are parallel to each other and orthogonal to the central axis of the shaft, and strain in an expanding direction is generated on the other surface. In consequence, one of the strain gauge provided in the first member and the strain gauge provided in the second member has an output corresponding to the strain in the contracting direction, and the other strain gauge has an output corresponding to the strain in the expanding direction. At this time, the forces having the same magnitude are applied to the first member and the second member in the opposite directions, respectively, and hence the output of the one strain gauge and the output of the other strain gauge are different in positive or negative sign and have about the same absolute amount. Thus, the outputs of both the strain gauges are connected in parallel, so that influences of thermal expansion cancel each other. Consequently, it is not necessary to separately perform correction in accordance with a temperature. That is, the load applied only to the shaft and workpiece can be simply and accurately detected. 
     Hereinafter, modes for carrying out the present invention will be described with reference to the drawings. However, a dimension, material, shape, relative arrangement and the like of a component described in this embodiment do not restrict the scope of the invention unless otherwise described. Furthermore, the following embodiments can be combined as much as possible. 
     First Embodiment 
       FIG. 1  is an appearance view of an actuator  1  according to the present embodiment. The actuator  1  includes a housing  2  having a substantially rectangular parallelepiped outer shape, and a lid  200  is attached to the housing  2 .  FIG. 2  is a schematic configuration view illustrating an inner structure of the actuator  1  according to the present embodiment. A part of a shaft  10  is housed within the housing  2 . The shaft  10  is formed to be hollow on a tip  10 A side. In a material of the shaft  10  and the housing  2 , for example, a metal (e.g., aluminum) may be used, or a resin or the like may be used. Note that in the following description, an XYZ orthogonal coordinate system will be set, and positions of respective members will be described with reference to this XYZ orthogonal coordinate system. A long side direction of the largest surface of the housing  2 , i.e., a direction of a central axis  100  of the shaft  10  is a Z-axis direction, a short side direction of the largest surface of the housing  2  is an X-axis direction, and a direction that is orthogonal to the largest surface of the housing  2  is a Y-axis direction. The Z-axis direction is also a perpendicular direction. Note that hereinafter, an upper side in the Z-axis direction in  FIG. 2  is an upper side of the actuator  1 , and a lower side in the Z-axis direction in  FIG. 2  is a lower side of the actuator  1 . Furthermore, a right side in the X-axis direction in  FIG. 2  is a right side of the actuator  1 , and a left side in the X-axis direction in  FIG. 2  is a left side of the actuator  1 . Additionally, a front side in the Y-axis direction in  FIG. 2  is a front side of the actuator  1 , and a back side in the Y-axis direction in  FIG. 2  is a back side of the actuator  1 . The housing  2  is formed such that a dimension in the Z-axis direction is larger than a dimension in the X-axis direction, and a dimension in the X-axis direction is larger than a dimension in the Y-axis direction. In the housing  2 , a region corresponding to one surface (a front surface in  FIG. 2 ) orthogonal to the Y-axis direction is open, and this opening is closed with the lid  200 . The lid  200  is fixed to the housing  2  with, for example, screws. 
     The housing  2  houses therein a rotating motor  20  that rotates the shaft  10  about the central axis  100 , a linear motion motor  30  that moves the shaft  10  relatively straight in a direction along the central axis  100  (i.e., the Z-axis direction) relative to the housing  2 , and an air control mechanism  60 . Furthermore, a shaft housing  50  into which the shaft  10  is inserted is attached to a lower end face  202  of the housing  2  in the Z-axis direction. In the housing  2 , a recess  202 B is formed to be recessed from the lower end face  202  toward an interior of the housing  2 , and a part of the shaft housing  50  is inserted into the recess  202 B. A through hole  2 A in the Z-axis direction is formed in an upper end of the recess  202 B in the Z-axis direction, and the shaft  10  is inserted into the through hole  2 A and the shaft housing  50 . The tip  10 A of the shaft  10  on the lower side in the Z-axis direction protrudes outward from the shaft housing  50 . The shaft  10  is provided at a center of the housing  2  in the X-axis direction and a center of the housing in the Y-axis direction. That is, the shaft  10  is provided such that a central axis extending in the Z-axis direction through the center of the housing  2  in the X-axis direction and the center of the housing in the Y-axis direction is superimposed on the central axis  100  of the shaft  10 . The shaft  10  is moved straight in the Z-axis direction by the linear motion motor  30 , and is rotated about the central axis  100  by the rotating motor  20 . 
     A base end  10 B side of the shaft  10  that is an end on a side opposite to the tip  10 A (an upper end in the Z-axis direction) is housed in the housing  2 , and connected to an output shaft  21  of the rotating motor  20 . The rotating motor  20  rotatably supports the shaft  10 . A central axis of the output shaft  21  of the rotating motor  20  coincides with the central axis  100  of the shaft  10 . The rotating motor  20  includes, in addition to the output shaft  21 , a stator  22 , a rotor  23  that rotates in the stator  22 , and a rotary encoder  24  that detects a rotation angle of the output shaft  21 . The rotor  23  rotates relative to the stator  22 , and the output shaft  21  and the shaft  10  also rotate in conjunction with the stator  22 . 
     The linear motion motor  30  includes a stator  31  fixed to the housing  2 , and a mover  32  that relatively moves in the Z-axis direction relative to the stator  31 . The linear motion motor  30  is, for example, a linear motor. The stator  31  is provided with a plurality of coils  31 A, and the mover  32  is provided with a plurality of permanent magnets  32 A. The coils  31 A are arranged at a predetermined pitch in the Z-axis direction, and a plurality of sets of three coils  31 A of U, V, and W-phases are provided. In the present embodiment, a three-phase armature current is applied to the coils  31 A of the U, V, and W-phases to generate a straight moving magnetic field, and the mover  32  is straight moved relative to the stator  31 . The linear motion motor  30  is provided with a linear encoder  38  that detects a relative position of the mover  32  to the stator  31 . Note that in place of the above configuration, the stator  31  may be provided with a permanent magnet, and the mover  32  may be provided with a plurality of coils. 
     The mover  32  of the linear motion motor  30  is coupled to the stator  22  of the rotating motor  20  via a linear motion table  33 . The linear motion table  33  is movable with movement of the mover  32  of the linear motion motor  30 . The movement of the linear motion table  33  is guided in the Z-axis direction by a linear motion guide device  34 . The linear motion guide device  34  includes a rail  34 A fixed to the housing  2 , and a slider block  34 B attached to the rail  34 A. The rail  34 A is configured to extend in the Z-axis direction, and the slider block  34 B is configured to be movable along the rail  34 A in the Z-axis direction. 
     The linear motion table  33  is fixed to the slider block  34 B, and is movable together with the slider block  34 B in the Z-axis direction. The linear motion table  33  is coupled to the mover  32  of the linear motion motor  30  via two coupling arms  35 . The two coupling arms  35  couple opposite ends of the mover  32  in the Z-axis direction to opposite ends of the linear motion table  33  in the Z-axis direction. Furthermore, the linear motion table  33  is coupled, on a central side of the opposite ends, to the stator  22  of the rotating motor  20  via two coupling arms  36 . Note that the coupling arm  36  on the upper side in the Z-axis direction will be referred to as a first arm  36 A, and the coupling arm  36  on the lower side in the Z-axis direction will be referred to as a second arm  36 B. Furthermore, the first arm  36 A and the second arm  36 B will be referred to simply as the coupling arms  36  when the arms are not distinguished. For the stator  22  of the rotating motor  20 , since the linear motion table  33  is coupled to the stator  22  of the rotating motor  20  via the coupling arms  36 , the stator  22  of the rotating motor  20  also moves with the movement of the linear motion table  33 . The coupling arm  36  has a quadrangular cross section. A strain gauge  37  is fixed to a surface of each coupling arm  36  which faces upward in the Z-axis direction. Note that the strain gauge  37  fixed to the first arm  36 A will be referred to as a first strain gauge  37 A, and the strain gauge  37  fixed to the second arm  36 B will be referred to as a second strain gauge  37 B. The first strain gauge  37 A and the second strain gauge  37 B will be referred to simply as the strain gauges  37  when the gauges are not distinguished. Note that two strain gauges  37  of the present embodiment are provided on surfaces of the coupling arms  36  which face upward in the Z-axis direction, respectively. In place of the surfaces, the gauges may be provided on surfaces of the coupling arm  36  that face downward in the Z-axis direction. 
     The air control mechanism  60  is a mechanism to generate a positive pressure or a negative pressure at the tip  10 A of the shaft  10 . That is, the air control mechanism  60  sucks air in the shaft  10  during pickup of a workpiece W, to generate the negative pressure at the tip  10 A of the shaft  10 . Consequently, the workpiece W is sucked to the tip  10 A of the shaft  10 . Furthermore, air is supplied into the shaft  10 , to generate the positive pressure at the tip  10 A of the shaft  10 . Thus, the workpiece W is easily removed from the tip  10 A of the shaft  10 . 
     The air control mechanism  60  includes a positive pressure passage  61 A (see a dashed chain line) through which positive pressure air flows, a negative pressure passage  61 B (see a double-dashed chain line) through which negative pressure air flows, and a shared passage  61 C (see a broken line) shared by the positive pressure air and the negative pressure air. The positive pressure passage  61 A has one end connected to a positive pressure connector  62 A provided on an upper end face  201  of the housing  2  in the Z-axis direction, and the positive pressure passage  61 A has the other end connected to a solenoid valve for positive pressure (hereinafter, referred to as a positive pressure solenoid valve  63 A). The positive pressure solenoid valve  63 A is opened and closed by an after-mentioned controller  7 . Note that the positive pressure passage  61 A has one end portion constituted of a tube  610 , and the other end portion constituted of a hole made in a block  600 . The positive pressure connector  62 A extends through the upper end face  201  of the housing  2  in the Z-axis direction, and the positive pressure connector  62 A is connected to an external tube linked to an air discharging pump or the like. 
     The negative pressure passage  61 B has one end connected to a negative pressure connector  62 B provided on the upper end face  201  of the housing  2  in the Z-axis direction, and the negative pressure passage  61 B has the other end connected to a solenoid valve for negative pressure (hereinafter, referred to as a negative pressure solenoid valve  63 B). The negative pressure solenoid valve  63 B is opened and closed by the after-mentioned controller  7 . Note that the negative pressure passage  61 B has one end portion constituted of a tube  620 , and the other end portion constituted of a hole made in the block  600 . The negative pressure connector  62 B extends through the upper end face  201  of the housing  2  in the Z-axis direction, and the negative pressure connector  62 B is connected to an external tube linked to an air sucking pump or the like. 
     The shared passage  61 C is constituted of a hole made in the block  600 . The shared passage  61 C has one end branching into two to be connected to the positive pressure solenoid valve  63 A and the negative pressure solenoid valve  63 B, and the shared passage  61 C has the other end connected to an air flow passage  202 A that is a through hole formed in the housing  2 . The air flow passage  202 A communicates with the shaft housing  50 . The negative pressure solenoid valve  63 B is opened and the positive pressure solenoid valve  63 A is closed, to communicate between the negative pressure passage  61 B and the shared passage  61 C, thereby generating the negative pressure in the shared passage  61 C. Then, air is sucked from the shaft housing  50  through the air flow passage  202 A. On the other hand, the positive pressure solenoid valve  63 A is opened and the negative pressure solenoid valve  63 B is closed, to communicate between the positive pressure passage  61 A and the shared passage  61 C, thereby generating the positive pressure in the shared passage  61 C. Then, air is supplied into the shaft housing  50  through the air flow passage  202 A. The shared passage  61 C is provided with a pressure sensor  64  that detects a pressure of air in the shared passage  61 C and a flow sensor  65  that detects a flow rate of air in the shared passage  61 C. 
     Note that in the actuator  1  illustrated in  FIG. 2 , the positive pressure passage  61 A and the negative pressure passage  61 B have a part constituted of a tube, and the other part constituted of a hole made in the block  600 . The present invention is not limited to this embodiment, and all the passages may be constituted of tubes, or all the passages may be constituted of holes made in the block  600 . This also applies to the shared passage  61 C, and the passage may be entirely constituted of a tube, or may be constituted by combined use of the tube. Note that a material of the tube  610  and the tube  620  may be a material such as a resin having flexibility, or may be a material such as a metal that does not have any flexibility. Furthermore, an atmospheric pressure may be supplied, instead of supplying the positive pressure to the shaft housing  50  by use of the positive pressure passage  61 A. 
     Additionally, on the upper end face  201  of the housing  2  in the Z-axis direction, provided are a connector (hereinafter, referred to as an inlet connector  91 A) that is an inlet of air for cooling the rotating motor  20  and a connector (hereinafter, referred to as an outlet connector  91 B) that is an outlet of air from the housing  2 . The inlet connector  91 A and the outlet connector  91 B extend through the upper end face  201  of the housing  2  so that air can flow through. A tube linked to an air discharge pump or the like is connected to the inlet connector  91 A from outside the housing  2 , and a tube that discharges air flowing out of the housing  2  is connected to the outlet connector  91 B from outside the housing  2 . The interior of the housing  2  is provided with a metal pipe (hereinafter, referred to as a cooling pipe  92 ) through which air for cooling the rotating motor  20  flows, and the cooling pipe  92  has one end connected to the inlet connector  91 A. The cooling pipe  92  is formed to extend from the inlet connector  91 A in the Z-axis direction to a vicinity of the lower end face  202  of the housing  2 , and to curve in the vicinity of the lower end face  202  such that the pipe, at the other end, faces the rotating motor  20 . Thus, air is supplied from the lower side in the Z-axis direction into the housing  2 , thereby allowing efficient cooling. Furthermore, the cooling pipe  92  extends through the stator  31 , to take heat from the coils  31 A of the linear motion motor  30 . The coils  31 A are arranged around the cooling pipe  92 , to take more heat from the coils  31 A provided in the stator  31 . 
     The upper end face  201  of the housing  2  in the Z-axis direction is connected to a connector  41  including a power supplying wire and a signal line. Furthermore, the housing  2  is provided with the controller  7 . The wire or signal line pulled from the connector  41  into the housing  2  is connected to the controller  7 . The controller  7  is provided with a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and an erasable programmable ROM (EPROM), which are connected to one another via a bus. In the EPROM, various programs, various tables and others are stored. The program stored in the EPROM is loaded and executed in a work area of the RAM by the CPU, and through the execution of this program, the rotating motor  20 , the linear motion motor  30 , the positive pressure solenoid valve  63 A, the negative pressure solenoid valve  63 B and others are controlled. Thus, the CPU achieves a function that meets a predetermined purpose. Furthermore, output signals of the pressure sensor  64 , the flow sensor  65 , the strain gauge  37 , the rotary encoder  24  and the linear encoder  38  are input into the controller  7 . Note that the controller  7  does not have to entirely control the rotating motor  20 , the linear motion motor  30 , the positive pressure solenoid valve  63 A, the negative pressure solenoid valve  63 B and others, and another control equipment connected to the connector  41  may control some of these components. Alternatively, the program may be supplied from external control equipment to the controller  7  via the connector  41 . 
       FIG. 3  is a cross-sectional view illustrating a schematic configuration including the shaft housing  50  and the tip  10 A of the shaft  10 . The shaft housing  50  includes a housing body  51 , two rings  52 , a filter  53 , and a filter stop  54 . In the housing body  51 , a through hole  51 A is formed into which the shaft  10  is inserted. The through hole  51 A extends through the housing body  51  in the Z-axis direction, and an upper end of the through hole  51 A in the Z-axis direction communicates with the through hole  2 A formed in the housing  2 . A diameter of the through hole  51 A is larger than an outer diameter of the shaft  10 . Consequently, a space is provided between an inner surface of the through hole  51 A and an outer surface of the shaft  10 . In opposite ends of the through hole  51 A, enlarged parts  51 B each having a hole diameter enlarged are provided. The rings  52  are fitted in two enlarged parts  51 B, respectively. Each ring  52  is formed in a cylindrical shape, and an inner diameter of the ring  52  is slightly larger than the outer diameter of the shaft  10 . Therefore, the shaft  10  is movable in the Z-axis direction in the ring  52 . Consequently, a space is also formed between an inner surface of the ring  52  and the outer surface of the shaft  10 . Therefore, the shaft  10  is movable in the Z-axis direction in the ring  52 , and the shaft  10  is rotatable about the central axis  100  in the ring  52 . However, the space formed between the inner surface of the ring  52  and the outer surface of the shaft  10  is smaller than the space formed between the inner surface of the through hole  51 A excluding the enlarged parts  51 B and the outer surface of the shaft  10 . Note that the ring  52  on the upper side in the Z-axis direction will be referred to as a first ring  52 A, and the ring  52  on the lower side in the Z-axis direction will be referred to as a second ring  52 B. The first ring  52 A and the second ring  52 B will be referred to simply as the rings  52  when the rings are not distinguished. In a material of the ring  52 , for example, a metal or a resin may be used. 
     A protrusion  511  protruding in opposite right and left directions in the X-axis direction is formed in a central part of the housing body  51  in the Z-axis direction. In the protrusion  511 , a mounting surface  511 A is formed which is a surface parallel to the lower end face  202  of the housing  2 , the surface coming in contact with the lower end face  202 , when the shaft housing  50  is mounted to the lower end face  202  of the housing  2 . The mounting surface  511 A is a surface orthogonal to the central axis  100 . Furthermore, a part  512  that is a part of the shaft housing  50  on the upper side of the mounting surface  511 A in the Z-axis direction is formed to fit in the recess  202 B formed in the housing  2 , when the shaft housing  50  is mounted to the housing  2 . 
     The space is provided between the inner surface of the through hole  51 A and the outer surface of the shaft  10  as described above. As a result, in the housing body  51 , an inner space  500  is formed which is a space surrounded with the inner surface of the through hole  51 A, the outer surface of the shaft  10 , a lower end face of the first ring  52 A, and an upper end face of the second ring  52 B. Furthermore, in the shaft housing  50 , a control passage  501  is formed which communicates between an opening of the air flow passage  202 A formed in the lower end face  202  of the housing  2  and the inner space  500  to form an air passage. The control passage  501  includes a first passage  501 A extending in the X-axis direction, a second passage  501 B extending in the Z-axis direction, and a filter part  501 C that is a space where the first passage  501 A and the second passage  501 B are connected and the filter  53  is disposed. The first passage  501 A has one end connected to the inner space  500 , and the other end connected to the filter part  501 C. The second passage  501 B has one end opened in the mounting surface  511 A and aligned to be connected to the opening of the air flow passage  202 A. 
     Furthermore, the second passage  501 B has the other end connected to the filter part  501 C. In the filter part  501 C, the filter  53  formed in a cylindrical shape is provided. The filter part  501 C is formed in a columnar space extending in the X-axis direction such that a central axis coincides with that of the first passage  501 A. An inner diameter of the filter part  501 C is substantially equal to an outer diameter of the filter  53 . The filter  53  is inserted into the filter part  501 C in the X-axis direction. After the filter  53  is inserted into the filter part  501 C, an end of the filter part  501 C which is an insertion port of the filter  53  is closed with the filter stop  54 . The other end of the second passage  501 B is connected to the filter part  501 C from a side of an outer circumferential surface of the filter  53 . Furthermore, the other end of the first passage  501 A communicates with a central side of the filter  53 . Therefore, air flowing through a space between the first passage  501 A and the second passage  501 B flows through the filter  53 . Therefore, foreign matter is captured by the filter  53 , even if the foreign matter is sucked together with air into the inner space  500 , for example, when the negative pressure is generated at the tip  10 A. In the one end of the second passage  501 B, a groove  501 D is formed to hold sealant. 
     In vicinities of opposite ends of the protrusion  511  in the X-axis direction, two bolt holes  51 G are formed into which bolts are inserted, when the shaft housing  50  is fixed to the housing  2  by use of the bolts. The bolt holes  51 G extend through the protrusion  511  in the Z-axis direction and opens in the mounting surface  511 A. 
     A hollow part  11  is formed on the tip  10 A side of the shaft  10  such that the shaft  10  is hollow. The hollow part  11  has one end opened at the tip  10 A. Furthermore, at the other end of the hollow part  11 , a communication hole  12  that communicates between the inner space  500  and the hollow part  11  in the X-axis direction is formed. The communication hole  12  is formed to communicate between the inner space  500  and the hollow part  11 , in an entire range of a stroke when the shaft  10  is moved in the Z-axis direction by the linear motion motor  30 . Therefore, the tip  10 A of the shaft  10  communicates with the air control mechanism  60  through the hollow part  11 , the communication hole  12 , the inner space  500 , the control passage  501 , and the air flow passage  202 A. Note that the communication hole  12  may be formed in the Y-axis direction in addition to the X-axis direction. 
     According to this configuration, the communication hole  12  always communicates between the inner space  500  and the hollow part  11 , even if the shaft  10  is at any position in the Z-axis direction when the linear motion motor  30  is driven to move the shaft  10  in the Z-axis direction. Furthermore, the communication hole  12  always communicates between the inner space  500  and the hollow part  11 , even if a rotation angle of the shaft  10  is any angle about the central axis  100  when the rotating motor  20  is driven to rotate the shaft  10  about the central axis  100 . Therefore, a communication state between the hollow part  11  and the inner space  500  is maintained even if the shaft  10  is in any state, and hence the hollow part  11  always communicates with the air control mechanism  60 . For that reason, air in the hollow part  11  is sucked through the air flow passage  202 A, the control passage  501 , the inner space  500 , and the communication hole  12 , if the positive pressure solenoid valve  63 A is closed and the negative pressure solenoid valve  63 B is opened in the air control mechanism  60 , regardless of the position of the shaft  10 . As a result, the negative pressure can be generated in the hollow part  11 . That is, the negative pressure can be generated at the tip  10 A of the shaft  10 , and hence the workpiece W can be sucked to the tip  10 A of the shaft  10 . Note that the space is also formed between the inner surface of the ring  52  and the outer surface of the shaft  10  as described above. However, this space is smaller than a space that forms the inner space  500  (i.e., the space formed between the inner surface of the through hole  51 A and the outer surface of the shaft  10 ). Thus, in the air control mechanism  60 , the positive pressure solenoid valve  63 A is closed and the negative pressure solenoid valve  63 B is opened, so that a flow rate of air flowing through the space between the inner surface of the ring  52  and the outer surface of the shaft  10  can be suppressed, even if air is sucked from the inner space  500 . Consequently, the negative pressure at which the workpiece W can be picked up can be generated at the tip  10 A of the shaft  10 . On the other hand, the positive pressure can be generated in the hollow part  11 , if the positive pressure solenoid valve  63 A is opened and the negative pressure solenoid valve  63 B is closed in the air control mechanism  60 , regardless of the position of the shaft  10 . That is, since the positive pressure can be generated at the tip  10 A of the shaft  10 , the workpiece W can be quickly removed from the tip  10 A of the shaft  10 . 
     (Pick and Place Operation) 
     Description will be made as to pick and place of the workpiece W by use of actuator  1 . The controller  7  executes a predetermined program to perform the pick and place. During the pickup of the workpiece W, the positive pressure solenoid valve  63 A and the negative pressure solenoid valve  63 B are both in a closed state, until the shaft  10  comes in contact with the workpiece W. In this case, the pressure of the tip  10 A of the shaft  10  is the atmospheric pressure. Then, the linear motion motor  30  moves the shaft  10  downward in the Z-axis direction. Upon contact of the shaft  10  with the workpiece W, the linear motion motor  30  is stopped. After the linear motion motor  30  is stopped, the negative pressure solenoid valve  63 B is opened to generate the negative pressure at the tip  10 A of the shaft  10 , thereby sucking the workpiece W to the tip  10 A of the shaft  10 . Afterward, the linear motion motor  30  moves the shaft  10  upward in the Z-axis direction. At this time, the shaft  10  is rotated by the rotating motor  20  as required. 
     Thus, the workpiece W can be picked up. 
     Next, during the placing of the workpiece W, the shaft  10  in a state where the workpiece W is sucked to the tip  10 A is moved downward in the Z-axis direction by the linear motion motor  30 . If the workpiece W is grounded, the linear motion motor  30  is stopped, to stop the movement of the shaft  10 . Furthermore, the negative pressure solenoid valve  63 B is closed and the positive pressure solenoid valve  63 A is opened, to generate the positive pressure in the tip  10 A of the shaft  10 . Afterward, the linear motion motor  30  moves the shaft  10  upward in the Z-axis direction, and the tip  10 A of the shaft  10  accordingly leaves the workpiece W. 
     Here, during the pickup of the workpiece W, it is detected, using the strain gauge  37 , that the tip  10 A of the shaft  10  comes in contact with the workpiece W. Hereinafter, this method will be described. Note that it is similarly detected that the workpiece W is grounded during the placing of the workpiece W. If the tip  10 A of the shaft  10  comes in contact with the workpiece W and the tip  10 A 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 due to reaction when the shaft  10  applies the force to the workpiece W. The force received from the workpiece W by the shaft  10  acts in a direction to generate strain relative to the coupling arm  36 . That is, the strain is generated in the coupling arm  36  at this time. This strain is detected by the strain gauge  37 . Then, the strain detected by the strain gauge  37  has correlation with the force received from the workpiece W by the shaft  10 . Consequently, the force received from the workpiece W by the shaft  10 , that is, the load generated between the shaft  10  and the workpiece W can be detected based on a detected value of the strain gauge  37 . A relation between the detected value of the strain gauge and the load can be obtained beforehand by experiment, simulation or the like. 
     Thus, since 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, upon the generation of the load, that the tip  10 A of the shaft  10  comes in contact with the workpiece W, or it may be determined, in consideration of influence of error or the like, that the tip  10 A of the shaft  10  comes in contact with the workpiece W in a case where a detected load is equal to or larger than a predetermined load. Note that the predetermined load is the load by which it is determined that the shaft  10  comes in contact with the workpiece W. Furthermore, the predetermined load may be set as the load with which it is possible to more securely pick up the workpiece W while inhibiting damage on the workpiece W. 
     Additionally, the predetermined load can be changed in accordance with a type of workpiece W. 
     Here, change in resistance of the strain gauge  37  due to the strain is extremely small, and hence the change is taken as change in voltage by use of a Wheatstone bridge circuit. In the actuator  1 , an output of a bridge circuit associated with the first strain gauge  37 A and an output of a bridge circuit associated with the second strain gauge  37 B are connected in parallel. Thus, the outputs of both the bridge circuits are connected in parallel, and accordingly the change in voltage is obtained, from which influence of temperature is eliminated as follows. 
     Here, assuming that there is not any strain of the coupling arm  36  due to the influence of temperature, the loads detected by the first strain gauge  37 A and the second strain gauge  37 B, respectively, are about the same. However, for example, in a case where operation frequency of the linear motion motor  30  is high and operation frequency of the rotating motor  20  is low, a temperature on a linear motion motor  30  side is higher than a temperature on a rotating motor  20  side. 
     Therefore, an expansion amount in the Z-axis direction of the linear motion table  33  is larger than an expansion amount in the Z-axis direction of the rotating motor  20 , between the first arm  36 A and the second arm  36 B. Consequently, the first arm  36 A is not parallel to the second arm  36 B, and a distance between the first arm  36 A and the second arm  36 B is larger on the linear motion motor  30  side than on the rotating motor  20  side. At this time, the first strain gauge  37 A contracts, and the second strain gauge  37 B expands. In this case, the output of the first strain gauge  37 A apparently indicates the generation of the load, and the output of the second strain gauge  37 B apparently indicates generation of a negative load. At this time, a force generated due to a difference between the expansion amount in the Z-axis direction of the linear motion table  33  and the expansion amount in the Z-axis direction of the rotating motor  20  is equally applied to the first arm  36 A and the second arm  36 B in opposite directions, and hence the output of the first strain gauge  37 A and the output of the second strain gauge  37 B have an equal absolute value and are different in positive or negative sign. For that reason, if the outputs of both the strain gauges are connected in parallel, the outputs due to the influence of temperature can cancel each other, and hence it is not necessary to separately perform correction in accordance with the temperature. Therefore, the load can be simply and accurately detected. Thus, the outputs of both the bridge circuits are connected in parallel, so that the change in voltage from which the influence of temperature is eliminated can be obtained, and this change in voltage has a value corresponding to the load generated between the shaft  10  and the workpiece W. 
     Note that in the present embodiment, two strain gauges  37  are provided, and instead of this, only one of the first strain gauge  37 A or the second strain gauge  37 B may be provided. In this case, the detected value of the strain gauge is corrected in accordance with the temperature by use of known technology. Even in a case where one strain gauge  37  is provided, the output of the strain gauge  37  has a value corresponding to the load generated between the shaft  10  and the workpiece W. Consequently, the load generated between the shaft  10  and the workpiece W can be detected based on the output of the strain gauge  37 . 
     Thus, the strain gauges  37  are provided in the coupling arms  36 , and hence it can be detected that the shaft  10  comes in contact with the workpiece W. 
     Heretofore, it has been difficult to detect the force applied to the workpiece W. To solve this problem, an impact absorbing spring or a highly flexible member (e.g., a rubber) is attached to the tip  10 A of the shaft  10 . In this case, it is difficult to accurately adjust the force to be applied to the workpiece W. Furthermore, a speed at which the shaft  10  is brought close to the workpiece W may be decreased to reduce the impact generated when the shaft  10  abuts on the workpiece W. In this case, tact time lengthens. On the other hand, according to the actuator  1  of the present embodiment, it can be correctly detected by the strain gauge  37  that the shaft  10  comes in contact with the workpiece W, and hence the force to be applied to the workpiece W can be more accurately adjusted without decreasing the speed of the shaft  10 . 
     Furthermore, an appropriate force can be applied to the workpiece W, and hence it is possible to more securely pick up the workpiece W. For example, when the workpiece W is picked up, the negative pressure is generated in the hollow part  11  in a state where the workpiece W is pressed against the tip  10 A of the shaft  10 . Consequently, it is possible to more securely pick up the workpiece W, and it is possible to inhibit the workpiece W from strongly colliding with the shaft  10  and being damaged when the workpiece W is sucked. On the other hand, if the load to press the workpiece W is excessively large, the workpiece W might be damaged. To solve this problem, an appropriate load is applied to the workpiece W while detecting the force to be applied to the workpiece W, so that it is possible to more securely pick up the workpiece W while inhibiting the damage on the workpiece W. Furthermore, also during the placing, it may be required to apply the appropriate load to the workpiece W. For example, it is necessary to apply a load in accordance with characteristics of bonding, in a case where the workpiece W is bonded to another member by use of adhesive. Also, at this time, appropriate control of the force to be applied to the workpiece W allows more secure bonding. 
     (Another Aspect 1 of Strain Gauge  37 ) 
     In the actuator  1 , the strain gauge  37  is provided in the coupling arm  36 . Alternatively, the strain gauge  37  may be provided in another member as long as the member generates strain in accordance with a load, when the load is generated between the shaft  10  and the workpiece W. 
       FIG. 4  and  FIG. 5  are views illustrating a schematic configuration in a case where strain gauges  37  are provided in two bearings  25  supporting the output shaft  21  of the rotating motor  20 , respectively.  FIG. 4  is a view around a bearing  25 A provided on the upper side in the Z-axis direction, and  FIG. 5  is a view around a bearing  25 B provided on the lower side in the Z-axis direction. Note that both the bearings will be referred to simply as bearings  25  when both the bearings are not distinguished. The bearings  25  are provided on the upper side (see  FIG. 4 ) and the lower side (see  FIG. 5 ), in the Z-axis direction, of the rotor  23  in the output shaft  21 , respectively. 
     First, description will be made as to the strain gauge  37  provided on the upper side of the rotor  23  in the Z-axis direction with reference to  FIG. 4 . The bearing  25 A has an inner circumferential surface fitted in an outer circumferential surface of the output shaft  21 , and has an outer circumferential surface fitted in an inner circumferential surface of a fixing part  220 A formed in the stator  22 . The fixing part  220 A includes an upper protrusion  221 A protruding toward a central axis  100  side to come in contact with the bearing  25 A on the upper side in the Z-axis direction. The first strain gauge  37 A is provided on an upper surface of the upper protrusion  221 A in the Z-axis direction. 
     Next, description will be made as to the strain gauge  37  provided on the lower side of the rotor  23  in the Z-axis direction with reference to  FIG. 5 . The bearing  25 B has an inner circumferential surface fitted in the outer circumferential surface of the output shaft  21 , and has an outer circumferential surface fitted in an inner circumferential surface of a fixing part  220 B formed in the stator  22 . The fixing part  220 B includes a lower protrusion  221 B protruding toward the central axis  100  side to come in contact with the bearing  25 B on the upper side in the Z-axis direction. The second strain gauge  37 B is provided on an upper surface of the lower protrusion  221 B in the Z-axis direction. 
     Therefore, the first strain gauge  37 A and the second strain gauge  37 B are provided on the surfaces that face in the same direction and are parallel to each other and orthogonal to the central axis  100  of the shaft  10 , respectively. According to this configuration, strain is generated in the upper protrusion  221 A and the lower protrusion  221 B due to the load generated between the shaft  10  and the workpiece W. This strain has correlation with the load generated between the shaft  10  and the workpiece W, and hence the detection of the strain by the strain gauge  37  allows detection of the load generated between the shaft  10  and the workpiece W. Furthermore, the first strain gauge  37 A and the second strain gauge  37 B detect strains in opposite directions due to the influence of temperature. That is, forces having the same magnitude are applied to the upper protrusion  221 A and the lower protrusion  221 B in opposite directions, in a case where there is a difference between an expansion amount of the stator  22  between the upper protrusion  221 A and the lower protrusion  221 B and an expansion amount of the output shaft  21 . At this time, the output of the first strain gauge  37 A and the output of the second strain gauge  37 B have an equal absolute value and are different in positive or negative sign. Therefore, the outputs of both the strain gauges are connected in parallel, so that the outputs due to influence of temperature can cancel each other. 
     Consequently, it is not necessary to separately perform correction in accordance with the temperature. In consequence, the load applied to the shaft  10  and the workpiece W can be easily and accurately detected. 
     (Another Aspect 2 of Strain Gauge  37 ) 
     In the actuator  1 , the strain gauge  37  is provided in the coupling arm  36 . Alternatively, the strain gauge  37  may be provided in the coupling arm  35 . That is, the strain gauges  37  may be provided on surfaces of two coupling arms  35  which face upward in the Z-axis direction. Alternatively, the strain gauges  37  may be provided on surfaces of two coupling arms  35  which face downward in the Z-axis direction. Strain is generated in both an upward facing surface and a downward facing surface of the coupling arm  36  in the Z-axis direction in accordance with a magnitude of load generated between the shaft  10  and the workpiece W. Therefore, detection of this strain allows detection of the load. Furthermore, two coupling arms  35  are arranged in a shifted manner in the Z-axis direction, and include central axes parallel to each other, respectively, the respective central axes being orthogonal to the central axis  100  of the shaft  10 . For that reason, outputs of two strain gauges are connected in parallel as described above, even in a case where strain is generated in the coupling arms  35  due to thermal expansion. Consequently, influence of the strain due to the thermal expansion can be canceled. In consequence, the load applied to the shaft  10  and the workpiece W can be easily and accurately detected. 
     (Pick and Place Control) 
     Next, specific control of pick and place will be described. The controller  7  executes the predetermined program, to perform this pick and place. Note that in the present embodiment, the output of the strain gauge  37  is replaced with the load, and the linear motion motor  30  is controlled based on this load. Instead of this, the linear motion motor  30  may be directly controlled based on the output of the strain gauge  37 . First, pickup processing will be described.  FIG. 6  is a flowchart illustrating flow of the pickup processing. The present flowchart is executed by the controller  7  every predetermined time. This predetermined time is set in accordance with tact time. In an initial state, the shaft  10  is at a sufficient distance from the workpiece W. 
     In step S 101 , the positive pressure solenoid valve  63 A and the negative pressure solenoid valve  63 B are both closed. That is, the pressure at the tip  10 A of the shaft  10  is set to the atmospheric pressure. In step S 102 , the shaft  10  is lowered. That is, the linear motion motor  30  is driven to move the shaft  10  downward in the Z-axis direction. In step S 103 , the load applied to the shaft  10  is detected based on the output of the strain gauge  37 . In step S 104 , it is determined whether or not the load applied to the shaft  10  is equal to or larger than the predetermined load. The predetermined load herein is the load by which it is determined that the shaft  10  comes in contact with the workpiece W. Note that the predetermined load may be set as the load with which it is possible to more securely pick up the workpiece W while inhibiting the damage on the workpiece W. If affirmative determination is made in the step S 104 , the processing advances to step S 105 , and if negative determination is made, the processing returns to the step S 103 . Therefore, the linear motion motor  30  moves the shaft  10  downward in the Z-axis direction until the load applied to the shaft  10  reaches the predetermined load or more. 
     In the step S 105 , the linear motion motor  30  is stopped. Note that even if the linear motion motor  30  is stopped, energization to the linear motion motor  30  is feedback controlled such that the predetermined load is continuously applied to the shaft  10 . 
     In step S 106 , the negative pressure solenoid valve  63 B is opened. Note that a closed valve state of the positive pressure solenoid valve  63 A is maintained. Consequently, the negative pressure is generated at the tip  10 A of the shaft  10 , to suck the workpiece W to the tip  10 A of the shaft  10 . In step S 107 , the shaft  10  is raised. At this time, the linear motion motor  30  moves the shaft  10  by a predetermined distance upward in the Z-axis direction. At this time, the shaft  10  may be rotated by the rotating motor  20  as required. Thus, the workpiece W can be picked up. 
     Next, place processing will be described.  FIG. 7  is a flowchart illustrating flow of the place processing. The place processing is executed by the controller  7 , after the pickup processing illustrated in  FIG. 6 . At start of the place processing, the workpiece W is sucked to the tip of the shaft  10 . That is, the positive pressure solenoid valve  63 A is closed, and the negative pressure solenoid valve  63 B is opened. In step S 201 , the shaft  10  is lowered. That is, the linear motion motor  30  is driven to move the shaft  10  downward in the Z-axis direction. In step S 202 , the load applied to the shaft  10  is detected based on the output of the strain gauge  37 . In step S 203 , it is determined whether or not the load applied to the shaft  10  is equal to or larger than a second predetermined load. Note that the second predetermined load is the load by which it is determined that the workpiece W is grounded, or the load by which it is determined that the workpiece W comes in contact with another member. The second predetermined load may be the same as or different from the predetermined load in the step S 104 . If affirmative determination is made in the step S 203 , the processing advances to step S 204 , and if negative determination is made, the processing returns to the step S 202 . 
     Therefore, the linear motion motor  30  moves the shaft  10  downward in the Z-axis direction until the load applied to the shaft  10  reaches the second predetermined load or more. 
     In the step S 204 , the linear motion motor  30  is stopped. Note that even if the linear motion motor  30  is stopped, the energization to the linear motion motor  30  is feedback controlled such that the second predetermined load is continuously applied to the shaft  10 . 
     In step S 205 , the positive pressure solenoid valve  63 A is opened, and the negative pressure solenoid valve  63 B is closed. Consequently, the positive pressure is generated at the tip  10 A of the shaft  10 , to remove the workpiece W from the shaft  10 . In step S 206 , the shaft  10  is raised. That is, the linear motion motor  30  moves the shaft  10  by a predetermined distance upward in the Z-axis direction. At this time, the shaft  10  may be rotated by the rotating motor  20  as required. Thus, the workpiece W can be placed. 
     As described above, according to the actuator  1  of the present embodiment, the load applied to the shaft  10  can be detected based on the output of the strain gauge  37 . Then, the linear motion motor  30  is controlled based on the detected load, so that appropriate load can be applied to the workpiece W. Therefore, it is possible to more securely pick up the workpiece W while inhibiting damage on the workpiece W. 
     Second Embodiment 
     Here, if a linear motion motor  30  is stopped at a moment when a shaft  10  comes in contact with a workpiece W in pickup processing, a tip  10 A of the shaft  10  does not come in contact sufficiently closely with the workpiece W, and a space may be generated between a part of the tip  10 A of the shaft  10  and the workpiece W. If a negative pressure is generated in the tip  10 A in this state, the workpiece W moves toward the tip  10 A, and the workpiece W collides with the tip  10 A in a region where there is the space between the tip  10 A and the workpiece W. Due to this collision, the workpiece W might be damaged. Furthermore, if there is a space between a part of the tip  10 A of the shaft  10  and the workpiece W, air flows into an inner space  500  from outside the shaft  10 . Consequently, a pressure in the inner space  500  does not sufficiently decrease, and the workpiece W may not be picked up. Therefore, it is desirable that the whole tip  10 A of the shaft  10  is in contact closely with the workpiece W. For that reason, it is considered that during the pickup processing, the shaft  10  is pressed against the workpiece W until a certain degree of load is applied to the workpiece W. 
     However, if a moving speed of the shaft  10  is excessively high in the pickup processing and the linear motion motor  30  is to be stopped, the linear motion motor  30  may not be immediately stopped due to a factor such as response delay. In this case, more load than necessary is applied to the workpiece W, and the workpiece W might be damaged. On the other hand, if the moving speed of the shaft  10  is decreased, tact time may increase. 
     To solve the program, in the present embodiment, the shaft  10  is moved at a comparatively high speed until the shaft  10  comes in contact with the workpiece W. After the shaft  10  comes in contact with the workpiece W, the shaft  10  is moved at a comparatively low speed until appropriate load is applied to the workpiece W. Consequently, the shaft  10  is more securely brought into contact closely with the workpiece W while inhibiting the damage on the workpiece W. 
     This pickup processing will be described.  FIG. 8  is a flowchart illustrating flow of pickup processing. The present flowchart is executed by a controller  7  every predetermined time. This predetermined time is set in accordance with the tact time. Note that a step in which the same processing as the pickup processing illustrated in  FIG. 6  is performed is denoted with the same reference numeral or symbol and description is omitted. 
     In the flowchart illustrated in  FIG. 8 , if processing of step S 103  ends, the processing advances to step S 301 . In the step S 301 , it is determined whether or not load applied to the shaft  10  is equal to or larger than a third predetermined load. The third predetermined load is a load by which it is determined that the shaft  10  comes in contact with the workpiece W. In the present step S 301 , it is determined whether or not the shaft  10  comes in contact with the workpiece W. If affirmative determination is made in the step S 301 , the processing advances to step S 302 , and if negative determination is made, the processing returns to the step S 103 . 
     Therefore, the linear motion motor  30  moves the shaft  10  downward in a Z-axis direction at a comparatively high speed until the load applied to the shaft  10  reaches the third predetermined load or more. In the step S 302 , the moving speed of the shaft  10  is decreased. That is, the speed at which the linear motion motor  30  moves the shaft  10  downward in the Z-axis direction is decreased. At this time, the moving speed decreases below the moving speed of the shaft  10  set in step S 102 . 
     In step S 303 , the load applied to the shaft  10  is detected based on an output of a strain gauge  37 . In step S 304 , it is determined whether or not the load applied to the shaft  10  is equal to or larger than a fourth predetermined load. The fourth predetermined load is a load with which it is possible to more securely pick up the workpiece W while inhibiting the damage on the workpiece W. If affirmative determination is made in the step S 304 , the processing advances to step S 105 , and if negative determination is made, the processing returns to the step S 303 . Therefore, the linear motion motor  30  moves the shaft  10  downward in the Z-axis direction at a low speed until the load applied to the shaft  10  reaches the fourth predetermined load or more. Thus, it is possible to more securely pick up the workpiece W while inhibiting the damage on the workpiece W. 
     Similar control is possible also in place processing.  FIG. 9  is a flowchart illustrating flow of place processing. The place processing is executed by the controller  7  after the pickup processing illustrated in  FIG. 6  or  FIG. 8 . Note that a step in which the same processing as the place processing illustrated in  FIG. 7  is performed is denoted with the same reference numeral or symbol and description is omitted. 
     In the flowchart illustrated in  FIG. 9 , if processing of step S 202  ends, the processing advances to step S 401 . In the step S 401 , it is determined whether or not the load applied to the shaft  10  is equal to or larger than a fifth predetermined load. Note that the fifth predetermined load is a load by which it is determined that the workpiece W is grounded, or a load by which it is determined that the workpiece W comes in contact with another member. If affirmative determination is made in the step S 401 , the processing advances to step S 402 , and if negative determination is made, the processing returns to the step S 202 . 
     Therefore, the linear motion motor  30  moves the shaft  10  downward in the Z-axis direction at a comparatively high speed until the load applied to the shaft  10  reaches the fifth predetermined load or more. 
     In the step S 402 , the moving speed of the shaft  10  is decreased. That is, the speed at which the linear motion motor  30  moves the shaft  10  downward in the Z-axis direction is decreased. At this time, the moving speed decreases below the moving speed of the shaft  10  set in step S 201 . In step S 403 , the load applied to the shaft  10  is detected based on the output of the strain gauge  37 . In step S 404 , it is determined whether or not the load applied to the shaft  10  is equal to or larger than a sixth predetermined load. The sixth predetermined load is a load with which the workpiece W can be appropriately pressed against another member. If affirmative determination is made in the step S 404 , the processing advances to step S 204 , and if negative determination is made, the processing returns to the step S 403 . 
     Therefore, the linear motion motor  30  moves the shaft  10  downward in the Z-axis direction at a low speed until the load applied to the shaft  10  reaches the sixth predetermined load or more. Thus, the workpiece W can be more securely pressed against an object while inhibiting the damage on the workpiece W. 
     As described above, according to an actuator  1  of the present embodiment, the speed of the shaft  10  is first set to be high. After the shaft  10  comes in contact with the workpiece W during pickup of the workpiece W, or after the workpiece W is grounded during placing of the workpiece W, the speed of the shaft  10  is decreased. The speed of the shaft  10  is decreased, while load applied to the workpiece W is further increased. Therefore, it is possible to more securely pick up the workpiece W. Furthermore, for example, appropriate load is applied in a case where the workpiece W is bonded to the other member during placing of the workpiece W. Consequently, the workpiece W can be more appropriately bonded. Additionally, the shaft  10  moves at a high speed until the shaft  10  comes in contact with the workpiece W, and hence tact time can be shortened. 
     Third Embodiment 
     In the above embodiment, after the linear motion motor  30  is stopped, the negative pressure solenoid valve  63 B is opened. Consequently, the negative pressure is generated in the tip  10 A of the shaft  10 , to suck the workpiece W to the tip  10 A of the shaft  10 . However, it is not determined whether or not the workpiece W is actually sucked to the tip  10 A of the shaft  10 . 
     Therefore, there might be failure in pickup of the workpiece W. To solve the problem, in the present embodiment, it is determined whether or not pressure in a hollow part  11  sufficiently decreases, before the shaft  10  is moved upward in a Z-axis direction to pick up the workpiece W. If the pressure in the hollow part  11  is sufficiently low, it can be determined that the workpiece W is sucked to the tip  10 A of the shaft  10 , and that it is possible to pick up the workpiece W. Then, if the pressure in the hollow part  11  sufficiently decreases, the linear motion motor  30  moves the shaft  10  upward in the Z-axis direction. 
     It is determined whether or not the pressure in the hollow part  11  sufficiently decreases, by using a detected value of at least one of a pressure sensor  64  and a flow sensor  65 . After the shaft  10  comes in contact with the workpiece W, a positive pressure solenoid valve  63 A is closed, and a negative pressure solenoid valve  63 B is opened. Then, a negative pressure is generated in a shared passage  61 C. The tip  10 A of the shaft  10  communicates with the shared passage  61 C through the hollow part  11 , a communication hole  12 , an inner space  500 , a control passage  501 , and an air flow passage  202 A. Therefore, if the negative pressure is generated in the shared passage  61 , air flows from the tip  10 A of the shaft  10  toward the shared passage  61  through the hollow part  11 , the communication hole  12 , the inner space  500 , the control passage  501  and the air flow passage  202 A. At this time, a pressure detected by the pressure sensor  64  has correlation with the pressure in the hollow part  11 . That is, the lower the pressure detected by the pressure sensor  64  is, the lower the pressure in the hollow part  11  becomes. Therefore, the pressure in the tip  10 A of the shaft  10  is low. 
     Furthermore, at this time, a flow rate detected by the flow sensor  65  has correlation with the pressure in the hollow part  11 . That is, the smaller the flow rate detected by the flow sensor  65  is, the lower the pressure in the hollow part  11  is. Therefore, the pressure in the tip  10 A of the shaft  10  is low. 
     To solve the problem, in the present embodiment, at least one of a case where the pressure detected by the pressure sensor  64  decreases down to a predetermined pressure or less, and a case where the flow rate detected by the flow sensor  65  decreases down to a predetermined flow rate or less, it is determined that the pressure in the hollow part  11  sufficiently decreases, and the linear motion motor  30  moves the shaft  10  upward in the Z-axis direction. Note that the predetermined flow rate is a flow rate at which the pressure in the hollow part  11  decreases to a pressure with which the workpiece W can be picked up, and the predetermined pressure is a pressure to which the pressure in the hollow part  11  decreases and at which the workpiece can be picked up. The predetermined flow rate and the predetermined pressure are obtained beforehand by experiment, simulation or the like. 
     This pickup processing will be described.  FIG. 10  is a flowchart illustrating flow of pickup processing. The present flowchart is executed by a controller  7  every predetermined time. This predetermined time is set in accordance with tact time. Note that a step in which the same processing as the pickup processing illustrated in  FIG. 6  is performed is denoted with the same reference numeral or symbol and description is omitted. 
     In the flowchart illustrated in  FIG. 8 , if the processing of the step S 106  ends, the processing advances to step S 501 . In the step S 501 , the pressure sensor  64  detects the pressure, and the flow sensor  65  detects the flow rate. Note that in the present flowchart, in the next step S 502 , it is determined whether or not the pressure in the hollow part  11  sufficiently decreases, by using both the detected value of the pressure sensor  64  and the detected value of the flow sensor  65 , and therefore, in the step S 501 , both the pressure and the flow rate are detected. However, in the step S 501 , one of the pressure and the flow rate may be detected, in a case where it is determined whether or not the pressure in the hollow part  11  sufficiently decreases, by using one of the detected value of the pressure sensor  64  and the detected value of the flow sensor  65 . 
     Next, in the step S 502 , it is determined whether or not the pressure detected by the pressure sensor  64  is the predetermined pressure or less, and whether or not the flow rate detected by the flow sensor  65  is the predetermined flow rate or less. If affirmative determination is made in the step S 502 , the processing advances to step S 107 , and if negative determination is made, the processing returns to the step S 501 . Therefore, the linear motion motor  30  is stopped until the pressure detected by the pressure sensor  64  reaches the predetermined pressure or less and until the flow rate detected by the flow sensor  65  reaches the predetermined flow rate or less. Note that in the step S 502 , it may be determined one of whether or not the pressure detected by the pressure sensor  64  is equal to or smaller than the predetermined pressure or whether or not the flow rate detected by the flow sensor  65  is equal to or smaller than the predetermined flow rate. 
     As described above, according to an actuator  1  of the present embodiment, it is determined whether or not the pressure in the hollow part  11  sufficiently decreases, based on the pressure detected by the pressure sensor  64  and/or the flow rate detected by the flow sensor  65 . Thereafter, the shaft  10  is moved upward in the Z-axis direction, and hence it is possible to more securely pick up the workpiece W. 
     DESCRIPTION OF THE REFERENCE NUMERALS AND SYMBOLS 
     
         
           1  actuator 
           2  housing 
           10  shaft 
           10 A tip 
           11  hollow part 
           20  rotating motor 
           22  stator 
           23  rotor 
           30  linear motion motor 
           31  stator 
           32  mover 
           36  coupling arm 
           37  strain gauge 
           50  shaft housing 
           60  air control mechanism