JP2010093904A - Moving body drive unit - Google Patents

Abstract

A moving body driving apparatus capable of preventing the moving body from vibrating during backlash compensation.
When a driving force of a motor exceeds a reference value, a moving body drive device starts detection of a rotation angle by a rotary encoder.
[Selection] Figure 4

Description

  The present invention relates to a moving body driving apparatus that moves a moving body such as a sample stage.

  Conventionally, a moving body drive device that moves a moving body such as a sample stage has been described (for example, Patent Document 1). A conventional moving body drive apparatus includes an actuator, a moving body, and a transmission unit that transmits driving of the actuator to the moving body. The actuator is, for example, a motor, and the transmission means is, for example, a universal joint.

  This transmission means has mechanical backlash and finite torsional rigidity. For this reason, backlash occurs when the moving body is moved from a stopped state or when the moving direction of the moving body is changed. Backlash means that the moving body does not move even when the actuator is driven. The reason why the moving body does not move is that even if the actuator is driven, the driving is used to eliminate the play of the transmission means or to twist the transmission means.

  Semi-closed loop control is known as a control method for moving a moving body to a target position. Semi-closed loop control is a method for detecting a driving amount of an actuator (for example, a rotation angle of a motor), and a target driving amount (for example, a target angle) set according to the detected driving amount and a target position of a moving body. Based on the above, the driving of the actuator is controlled. In the semi-closed loop control, the actuator is driven until the detected drive amount matches the target drive amount.

  Backlash is particularly a problem when performing semi-closed loop control. This is because when the actuator starts to drive, if detection of the driving amount of the actuator is started, the moving amount of the moving body becomes insufficient by the amount of backlash. Therefore, it is necessary to compensate for backlash. Backlash compensation refers to eliminating backlash before starting detection of drive amount.

Conventionally, the backlash is compensated by driving the actuator in a pulse manner before starting the detection of the drive amount.
JP-A-5-66834

  By the way, the amount of backlash varies depending on the structure of the transmission means and the position of the moving body, but conventionally, the compensation amount (the amount of pulse driving) has been made constant. For this reason, conventionally, the compensation amount is too small to be sufficiently compensated, or the compensation amount is too large and the moving body may vibrate during backlash compensation.

  The invention according to the present application has been made in order to solve the above-described problems, and an object of the invention is to prevent backlash compensation from being insufficiently compensated, and to prevent the moving body from vibrating during backlash compensation. It is an object of the present invention to provide a movable body drive device.

  The invention according to the present application includes an actuator, a transmission unit that transmits the actuator drive to a moving body, a setting unit that sets a target drive amount of the actuator, a detection unit that detects the drive amount of the actuator, and a predetermined speed. On the other hand, when the driving force necessary for driving the actuator at a predetermined speed exceeds a predetermined reference value, the detection means starts detecting the driving amount of the actuator and the detected driving Control means for driving the actuator until the amount matches the target drive amount.

  In the invention according to the present application, when the driving force necessary for driving the actuator at a predetermined speed exceeds a predetermined reference value, the detection unit starts detecting the driving amount of the actuator. It is possible to start detection of the driving amount of the actuator after driving by the backlash and after the spring element of the transmission means bends. Therefore, the invention according to the present application can perform backlash compensation. Furthermore, since the actuator according to the present application continuously drives the actuator without driving it in a pulsed manner, the moving body can be prevented from vibrating during backlash compensation.

(First embodiment)
Next, a first embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing an outline of a moving body driving apparatus 1 according to the first embodiment. The moving body drive device 1 includes a motor 2, a transmission unit 3, and a moving body 6. The motor 2 is originally an actuator that rotates the rotating shaft, but here it is assumed to move to the left and right. The transmission means 3 includes a spring element 4 and a backlash element 5, and transmits the drive of the motor 2 to the moving body 6. The moving body 6 includes a stage 7 and rolling elements 8 provided on the stage 7. When the rolling element 8 rolls on the base 9, the stage 7 moves. First, backlash and after drift will be described with reference to FIG.

  When no force is applied to the transmission means 3 and the moving body 6 is stationary, if the motor 2 starts moving to the right side, backlash occurs. That is, the motor 2 first moves to the right by the backlash element 5 of the transmission means 3. Thereby, the loose element 5 of the transmission means 3 is eliminated. At this time, since the driving force of the motor 2 is not transmitted to the moving body 6, the moving body 6 remains stationary. When the motor 2 further moves to the right side, the spring element 4 of the transmission means 3 is contracted, while the driving force of the motor 2 is transmitted to the moving body 6 via the spring element 4. However, since the static frictional force between the rolling element 8 and the base 9 acts, the moving body 6 remains stationary.

  The motor 2 continues to move while increasing its driving force. When the driving force exceeds the maximum static frictional force between the rolling element 8 and the base 9, the moving body 6 starts moving. Thereafter, the moving body 6 moves in a state where the driving force of the motor 2 and the frictional force between the rolling element 8 and the base 9 are balanced.

  Therefore, backlash occurs, that is, a phenomenon in which the moving body 6 does not move even when the motor 2 is driven. The driving force required for the motor 2 to move by the backlash element 5 of the transmission means 3 is much smaller than the driving force required for the motor 2 to contract the spring element 4 of the transmission means 3.

  Thereafter, when the motor 2 is stopped, the moving body 6 is also stopped. In this state, the spring element 4 of the transmission means 3 stores a force that balances the driving force of the motor 2. Conventionally, since no processing was performed on the force accumulated in the spring element 4 of the transmission means 3, the force accumulated in the spring element 4 of the transmission means 3 was gradually released. For this reason, the spring element 4 may move the moving body 6 by the force accumulated in the spring element 4. This is an after drift, that is, a phenomenon in which the moving body 6 gradually moves after stopping.

  Note that backlash also occurs when the motor 2 is immediately moved in the opposite direction (here, leftward) after the motor 2 is stopped. That is, when the motor 2 starts to move to the left, the spring element 4 extends in accordance with the movement of the motor 2 and the force accumulated in the spring element 4 is gradually released. At this time, since the static frictional force between the rolling element 8 and the base 9 acts, the moving body 6 remains stationary. When the force accumulated in the spring element 4 is completely released, the motor 2 moves to the left by the backlash element 5 of the transmission means 3. Thereby, the loose element 5 of the transmission means 3 is eliminated.

  When the motor 2 further moves to the left side, the spring element 4 of the transmission means 3 extends, while the driving force of the motor 2 is transmitted to the moving body 6 via the spring element 4. However, since the static frictional force between the rolling element 8 and the base 9 acts, the moving body 6 remains stationary.

  The motor 2 continues to move while increasing its driving force. When the driving force exceeds the maximum static frictional force between the rolling element 8 and the base 9, the moving body 6 starts moving. Thereafter, the moving body 6 moves in a state where the driving force of the motor 2 and the frictional force between the rolling element 8 and the base 9 are balanced. Therefore, backlash occurs.

  The mobile body drive device 1 compensates for backlash and suppresses the occurrence of after drift. Specifically, it will be described later.

  Next, a specific configuration of the moving body driving device 1 will be described. FIG. 2 is a schematic diagram illustrating a mechanical configuration of the moving body driving apparatus 1, and FIG. 3 is a block diagram illustrating an electrical configuration of the moving body driving apparatus 1. In FIG. 2, three-dimensional coordinates are defined. In FIG. 2, the left-right direction is the X axis, the direction perpendicular to the paper is the Y axis, and the up-down direction is the Z axis.

  The moving body driving device 1 is a part of the components of the scanning electron microscope 100. The motor 2 includes a rotating shaft 2a and rotates the rotating shaft 2a. The moving body drive device 1 includes a universal joint 3a, spur gears 3b and 3c, a bearing 3d, a feed screw 3e, and a feed nut 3f as the transmission means 3. The universal joint 3a transmits the rotation of the rotating shaft 2a to the spur gear 3b. The spur gear 3b meshes with the spur gear 3c and transmits the rotation to the spur gear 3c. The spur gear 3c has a ring shape and is rotatably fixed to a predetermined position inside the scanning electron microscope 100 by a bearing 3d. The feed screw 3e is inserted into the hollow portion of the spur gear 3c and rotates integrally with the spur gear 3c. The feed nut 3f meshes with the feed screw 3e, and moves to the left and right when the feed screw 3e rotates.

  The torsional rigidity of each component of the transmission means 3 becomes the spring element 4 of the transmission means 3. Elements such as the gap between the parts constituting the universal joint 3a, the gap between the teeth of the spur gear 3b and the teeth of the spur gear 3c, and the gap between the thread of the feed screw 3e and the thread of the feed nut 3f The backlash element 5 is obtained. A force having the same magnitude as the driving force of the motor 2 is transmitted to the X stage 7a.

  The movable body drive device 1 includes an X stage 7 a, a Y stage 7 b, a Z stage 7 c, an R stage 7 d, and a T stage 7 e as the stage 7. In addition, although the rolling element 8 is provided for every stage, it abbreviate | omits in FIG. The following description will focus on the movement of the X stage 7a, but the same processing can be performed for other stages.

  The X stage 7a is provided on the feed nut 3f and moves in the X-axis direction together with the feed nut 3f. The rolling element of the X stage 7 a rolls on the base 9. The Y stage 7b moves in the Y-axis direction, and the Z stage 7c moves in the Z-axis direction. The R stage 7d rotates with the straight line 71 as a rotation axis, and the T stage 7e rotates with the straight line 72 as a rotation axis. A sample 11 to be observed by the scanning electron microscope 100 is placed on the R stage 7d.

  The rotary encoder 10 detects the rotation angle of the motor 2 and outputs it to the controller 12. The input unit 13 is a keyboard or the like, and is used for inputting a target position of each stage by an operator. The input unit 13 outputs the target position input by the operator to the controller 12. The controller 12 sets the target angle of the motor 2 based on the target position input by the operator, and rotates the rotating shaft 2a of the motor 2 until the rotation angle detected by the rotary encoder 10 matches the target angle. Furthermore, the controller 12 adjusts the driving force of the motor 2, that is, the force (torque) for rotating the rotating shaft 2a by adjusting the power supplied to the motor 2.

  Next, the procedure of the process by the mobile body drive device 1 will be described based on the flowchart shown in FIG. 4 and the graph shown in FIG. The horizontal axis in FIG. 5 is the rotation angle of the rotation shaft 2a (that is, the rotation angle of the motor 2), and the rotation direction when the X stage 7a moves in the X axis positive direction is the positive direction. The vertical axis is the driving force of the motor 2, specifically, the torque necessary for the rotating shaft 2a of the motor 2 to rotate at a predetermined speed. The origin indicates a state in which the motor 2 is stopped and no driving force is applied to the motor 2. Here, a case where the motor 2 is rotated in the positive direction from the origin will be described as an example.

  In step S1, the operator inputs a target position for each stage. In step S2, the controller 12 sets the target angle of the motor 2 based on the target position of the X stage 7a input by the operator. In step S3, the controller 12 starts rotation of the motor 2 (that is, rotation of the rotating shaft 2a). Thereafter, the controller 12 rotates the motor 2 at a predetermined speed. As shown in FIG. 5, the rotation of the motor 2 is used to eliminate the backlash element 5 of the transmission means 3 until the rotation angle reaches θ1. The predetermined speed is such that the rotation angle of the motor 2 changes from 0 to θ1 (that is, the motor 2 rotates the backlash element 5 minutes of the transmission means 3) so as not to impair the operational feeling of the scanning electron microscope 100. It takes a speed that takes 0.1 to 0.3 seconds. When the rotation angle of the motor 2 exceeds θ1, the rotation of the motor 2 is used to deflect the spring element 4 of the transmission means 3. Therefore, as the rotation angle of the motor 2 increases (that is, the deflection of the transmission means 3 increases), the driving force required to rotate the motor 2 at a predetermined speed increases. On the other hand, after the rotation angle of the motor 2 exceeds θ1, the driving force of the motor 2 is transmitted to the X stage 7a. This driving force generates the maximum static frictional force between the rolling element of the X stage 7a and the pedestal 9. The X stage 7a remains stationary until it exceeds.

  In step S4, the controller 12 determines a condition that the driving force of the motor 2 has exceeded a predetermined reference value T. If this condition is satisfied, the process proceeds to step S5. If this condition is not satisfied, Return to step S4. Specifically, the controller 12 determines a condition that the power supplied to the motor 2 has reached a value corresponding to the reference value T. If this condition is satisfied, the controller 12 proceeds to step S5. If is not satisfied, the process returns to step S4. As shown in FIG. 5, when the rotation angle of the motor 2 exceeds θ2, the driving force of the motor 2 exceeds the reference value T.

  In step S <b> 5, the controller 12 requests the rotary encoder 10 to detect the rotation angle of the motor 2, and in response, the rotary encoder 10 starts detecting the rotation angle of the motor 2. The rotary encoder 10 outputs the detection result to the controller 12. Therefore, since the moving body drive device 1 starts detecting the rotation angle after the motor 2 rotates by the backlash element 5 of the transmission means 3 and the spring element 4 of the transmission means 3 bends, the backlash compensation is performed. It can be performed.

  As shown in FIG. 5, when the rotation angle of the motor 2 exceeds θ3, the driving force exceeds the maximum static frictional force, and the X stage 7a starts moving. Thereafter, since the frictional force between the rolling element of the X stage 7a and the pedestal 9 decreases, the driving force of the motor 2 also decreases. The motor 2 maintains its rotation in a state where the driving force of the motor 2 and the frictional force (that is, the frictional force between the rolling element of the X stage 7a and the pedestal 9) are balanced.

  In step S6, the controller 12 determines a condition that the detected rotation angle matches the target angle. If this condition is satisfied, the process proceeds to step S7. If this condition is not satisfied, step S6 is performed. Return to.

  In step S <b> 7, the controller 12 stops the rotation of the motor 2. Here, since the rotary encoder 10 starts detecting the rotation angle before the X stage 7a starts to move, a deviation occurs between the target position and the stop position of the X stage 7a. For example, when the target angle is θ6, as shown in FIG. 5, the motor 2 is ideally stopped when the rotation angle becomes θ5 (= θ3 + θ6). However, in this case, the motor 2 stops when the rotation angle reaches θ4 (θ2 + θ6). Therefore, the target position and the stop position of the X stage 7a are shifted by a distance corresponding to θ7 (= θ3−θ2). Therefore, the operator may set the target position by shifting the target position by a distance corresponding to θ7.

  In step S <b> 8, the controller 12 releases the force accumulated in the transmission unit 3 (that is, the force accumulated in the spring element 4 of the transmission unit 3). That is, as described above, immediately after the motor 2 is stopped, the spring element 4 of the transmission means 3 stores a force that balances the driving force of the motor 2. If no treatment is applied to this force, after-drift may occur. Therefore, the controller 12 releases the force accumulated in the spring element 4 of the transmission means 3. Specifically, the controller 12 reduces the power supplied to the motor 2 to a predetermined value. Thereby, the driving force of the motor 2 is released. When the driving force of the motor 2 is released, the spring element 4 of the transmission means 3 rotates the motor 2 in the opposite direction while releasing the force. Therefore, since the force accumulated in the spring element 4 is released, the occurrence of after drift is suppressed. Specifically, the possibility of occurrence of after drift is reduced as compared with the conventional case, and even if after drift occurs, the movement amount of the X stage 7a is reduced as compared with the conventional case.

  The spring element 4 may move the X stage 7a when releasing the force. Therefore, the operator may set the target position in anticipation of the amount of movement of the X stage 7a. Note that the movement of the X stage 7a by the process of step S8 is different from after-drift. The after drift is that the X stage 7a gradually moves after the stop, but this movement occurs immediately after the X stage 7a stops. Further, the after-drift causes a problem that the X stage 7a moves during observation by the scanning electron microscope 100. However, since the movement by the process of step S8 occurs immediately after the X stage 7a stops, such a problem occurs. Does not occur.

  The controller 12 may release the force accumulated in the spring element 4 of the transmission means 3 by rotating the motor 2 in the opposite direction (here, the negative direction) after the motor 2 is stopped. Thereafter, the controller 12 ends the process.

  As described above, the mobile body drive device 1 according to the first embodiment starts detecting the rotation angle of the motor 2 when the driving force of the motor 2 exceeds a predetermined reference value, and the detected rotation angle. Rotate the motor 2 until is equal to the target angle. Therefore, the mobile body drive device 1 can perform backlash compensation. Furthermore, since the moving body drive apparatus 1 does not rotate the motor 2 continuously as in the prior art, but it rotates continuously, it can prevent the moving body from vibrating during backlash compensation.

  Furthermore, since the moving body drive device 1 releases the force accumulated in the spring element 4 of the transmission means 3 when the detected rotation angle coincides with the target angle, the occurrence of after drift can be suppressed. .

  Specifically, the moving body driving device 1 reduces the driving force of the motor 2 or rotates the motor 2 in the opposite direction to release the force accumulated in the spring element 4 of the transmission means 3.

(Second Embodiment)
Next, a second embodiment will be described. The moving body drive device 1 according to the second embodiment is described mainly with reference to this portion because the processing in step S4 in FIG. 4 is different from that described above.

  In step S4, the controller 12 determines a condition that the driving force of the motor 2 has started to decrease. If this condition is satisfied, the process proceeds to step S5. If this condition is not satisfied, the process proceeds to step S4. Return. That is, the moving body drive device 1 according to this modification starts detecting the rotation angle when the X stage 7a actually starts moving. Therefore, the mobile body drive device 1 can perform backlash compensation more accurately than in the first embodiment. Furthermore, the magnitude of the maximum static frictional force, that is, the amount of backlash, varies depending on the position of the X stage 7a and the like. In the first embodiment, since the reference value T is constant, if the reference value T is larger than the maximum static frictional force, there is a problem that the X stage 7a starts to move without detecting the rotation angle. To do. On the other hand, if the reference value T is too smaller than the maximum static frictional force, there arises a problem that the unreached distance, that is, the difference between the target position and the stop position of the X stage 7a becomes too large. When the reference value T is smaller than the maximum static friction force, depending on the target angle, the rotation angle detected by the rotary encoder 10 matches the target angle before the driving force of the motor 2 reaches the maximum static friction force, There is a possibility that the motor 2 stops. However, the moving body drive device 1 according to the second embodiment is capable of adjusting the rotation angle when the X stage 7a actually starts moving, regardless of the magnitude of the maximum static frictional force. Detection can begin. Therefore, the moving body drive device 1 can accurately perform backlash compensation regardless of the magnitude of the maximum static frictional force.

  Note that the driving force of the motor 2 may not simply increase (that is, when the driving force of the motor 2 is less than the maximum static frictional force between the rolling element of the X stage 7a and the base 9), Therefore, detection by the rotary encoder 10 may be started when the driving force of the motor 2 exceeds the reference value T and the driving force of the motor 2 starts to decrease.

  Each of the above embodiments is merely an example of the present invention, and it is needless to say that the embodiments can be appropriately changed without departing from the gist of the present invention.

It is a schematic diagram which shows the outline | summary of the moving body drive device which concerns on 1st Embodiment. It is a schematic diagram which shows the mechanical structure of a moving body drive device. It is a block diagram which shows the electric constitution of a moving body drive device. It is a flowchart which shows the procedure of the process by a mobile body drive device. It is a graph which shows the relationship between the rotation angle of a motor, and the driving force of a motor.

Explanation of symbols

1: moving body drive device 2: motor 3: transmission means 4: spring element 5: loose element 6: moving body 7: stage 8: rolling element 9: base

Claims (5)

An actuator,
A transmission means for transmitting the drive of the actuator to the moving body;
Setting means for setting a target drive amount of the actuator;
Detecting means for detecting the driving amount of the actuator;
While the actuator is continuously driven at a predetermined speed, when the driving force necessary for driving the actuator at a predetermined speed exceeds a predetermined reference value, the detection means is configured to determine the drive amount of the actuator. Control means for starting detection and driving the actuator until the detected drive amount coincides with the target drive amount.   2. The moving body drive apparatus according to claim 1, wherein the control means releases the force accumulated in the transmission means when the detected drive amount coincides with the target drive amount.   3. The moving body driving apparatus according to claim 2, wherein the control means releases the force accumulated in the transmission means by reducing the driving force of the actuator.   3. The moving body drive apparatus according to claim 2, wherein the control means releases the force accumulated in the transmission means by driving the actuator in the opposite direction. An actuator,
A transmission means for transmitting the drive of the actuator to the moving body;
Setting means for setting a target drive amount of the actuator;
Detecting means for detecting the driving amount of the actuator;
While the actuator is continuously driven at a predetermined speed, the detection means starts detecting the drive amount of the actuator when the driving force necessary to drive the actuator at a predetermined speed starts to decrease. And a control means for driving the actuator until the detected drive amount coincides with the target drive amount.

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