JP4692046B2 - Control method and apparatus for tailstock - Google Patents

Description

  The present invention relates to a method and apparatus for controlling a servomotor-driven tailstock for a machine tool.

  A conventional servomotor-driven tailstock control device for machine tools is configured to keep the current value of the servomotor constant, and the output torque of the motor becomes the direct pressing torque via the feed mechanism. (For example, refer to Patent Document 1).

  The conventional servomotor-driven tailstock for machine tools is configured to use an elastic member for the tailstock, and operates so as to generate a constant pressing force by the elastic force of the elastic member ( For example, see Patent Document 2).

  Furthermore, the conventional servomotor-driven tailstock control device for machine tools is configured to monitor the positional deviation of the tailstock-driven servomotor, and operates so that the positional deviation is constant. (For example, refer to Patent Document 3).

Japanese Unexamined Patent Publication No. 2000-153431 (pages 5-6, FIG. 3) Japanese Patent No. 4-63603 (pages 4-5, FIG. 2) Japanese Patent No. 6-55310 (pages 4-5, FIG. 2)

  In the conventional servomotor-driven tailstock control device for machine tools as described above, the proper pressing torque during machining on the tailstock is small due to the low rigidity of the workpiece, etc. If the force is not negligible, excessive tailstock torque is applied to the workpiece because the tailstock does not move backward due to the static frictional force of the tailstock even if the workpiece expands due to processing heat, etc. There was a problem that deformation of the workpiece occurred.

  In addition, in a servomotor-driven tailstock for machine tools using an elastic material, if the amount of elastic deformation is small with respect to slight thermal expansion of the work piece, the above-described drawbacks can be avoided, but the mechanism becomes complicated. There was a disadvantage of being expensive.

  The present invention has been made in order to solve such a problem. Even when the appropriate tailstock torque is lower than the static frictional force of the tailstock, an appropriate tailstock torque can be maintained. It is an object of the present invention to provide a pedestal control method and apparatus.

  Another object of the present invention is to provide a tailstock control method and apparatus capable of easily measuring and storing the static friction force of a servomotor-driven tailstock for machine tools.

  According to the control method of the tailstock according to the present invention, when the tailstock is in contact with the workpiece and is stationary, the pressing torque of the tailstock against the workpiece is the tailstock pressing target torque minus the tailstock. The servo motor is controlled so that the stand static friction torque is obtained.

  The tailstock control method according to the present invention controls the servo motor so that the tailstock moves with the tailstock pressing target torque when the tailstock moves.

  Further, the control method of the tailstock according to the present invention is such that after the predetermined time has elapsed after the tailstock abuts on the workpiece and the tailstock is pressed against the workpiece, the tailstock is pressed against the workpiece. The servo motor is controlled so that the target torque is equal to the tailstock static friction torque.

  Also, the control method of the tailstock according to the present invention is to monitor the stationary state of the tailstock while gradually increasing the supply current to the servomotor in the stationary state of the tailstock, and at the time when the tailstock starts to move. A current value corresponding to the output torque of the servo motor is stored as a current value corresponding to the tailstock static friction torque.

  The tailstock control device according to the present invention includes a friction current memory for storing a servomotor current value when the servomotor generates a torque equivalent to the static friction of the tailstock, and the servomotor presses the workpiece. A command current memory for storing the current value of the servomotor when generating the tailstock pressing target torque, a movement monitoring means for monitoring the stationary state of the tailstock, and the movement monitoring means to allow the tailstock to be processed. When the signal indicating that the tailstock is stationary is output, the servo motor current values stored in the friction current memory and the command current memory are read out, and using these current values, Control means for controlling the servo motor so that the pressing torque of the tailstock against the workpiece is equal to the tailstock pressing target torque minus the tailstock static friction torque.

  The tailstock control apparatus according to the present invention is such that when the control means outputs a signal indicating that the tailstock is moving from the movement monitoring means, the tailstock is The servo motor is controlled to move with the target pressing target torque.

  Further, in the control device for the tailstock according to the present invention, the movement monitoring means is a signal indicating that the tailstock is stationary after a lapse of a predetermined time after the tailstock comes into contact with the workpiece and is stationary. To the control means, and based on this signal, the control means is such that the pressing torque of the tailstock to the workpiece becomes the tailstock pressing target torque-the tailstock stationary friction torque. It controls the servo motor.

  Further, in the tailstock control device according to the present invention, the control means gradually increases the supply current to the servomotor when the tailstock is stationary, and the output torque of the servomotor when the tailstock starts to move. Is stored in the friction current memory as a current value corresponding to the tailstock static friction torque.

  According to this invention, even when the proper pressing torque at the time of processing in the tailstock is small and the static frictional force of the tailstock is not negligible, the workpiece thermally expands when the tailstock is stationary. In this case, the tailstock always moves backward to prevent the workpiece from being deformed. In addition, once the tailstock starts to move backward, the frictional force decreases and the tailstock pressing torque is insufficient, but at this time it is detected that the tailstock is not stopped, and the tailstock again presses with the target torque, An appropriate workpiece pressing torque can be secured again.

  Further, according to the present invention, the tailstock torque can be maintained until the frictional force increases after the tailstock stops, and as a result, the tailstock can be pressed against the workpiece with an appropriate torque.

  Further, according to the present invention, no special device for measuring the torque of the servo motor corresponding to the static friction force is required.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to FIGS. The first embodiment is an example where the control device for the tailstock is configured by a numerical control device.
FIG. 1 is a block diagram showing an overall configuration when a control device for a tailstock is constituted by a numerical control device. In FIG. 1, 1 is a workpiece attached to a machine tool, and 2 is a workpiece 1 pressed. Tailstock 3 is a ball screw drive mechanism for moving the tailstock 2 back and forth, 4 is a servo motor for rotating a ball screw attached to the ball screw mechanism 3, and 5 is a position for detecting the rotational angle position of the servo motor 4. An encoder 6 is connected to the servo motor 4 via a power line, and a numerical control device 7 is connected to the position encoder 5 via a signal line. A numerical control device 7 is built in the numerical control device 6 and controls the current value supplied to the servo motor 4. A command device 8 is built in the numerical control device 6 and is a current limiting device that calculates the maximum value of the current value supplied to the servo motor 4 and outputs it to the current command device 7. To.

  Further, 9 is built in the numerical controller 6, a current storage device connected to the current limiting device 8, 10 is connected to the current storage device 9, and the servo motor 4 generates torque equivalent to static friction of the tailstock 2. A friction current memory 11 for storing the servo motor current value when the servo motor 4 is connected is connected to the current storage device 9, and the servo motor 4 generates a proper torque for pressing the workpiece 1 (a tailstock pressing target torque). A command current memory 12 for storing a motor current value is connected to the position encoder 5 by a signal line, determines a stationary state of the tailstock 2, and outputs a tailstock stationary signal to the current limiting device 8. The movement monitoring device 13 is a timer provided in the movement monitoring device 12.

In the numerical control device configured as described above, the movement monitoring device 12 detects the stationary state of the tailstock 2 by the change in the position input by the position encoder 5, and when the tailstock 2 is moving, A signal indicating that the tailstock 2 is moving is output to the current limiting device 8, and a signal indicating that the tailstock 2 is stationary after a certain time has elapsed after the tailstock 2 has stopped moving. Output to the current limiting device 8. The detailed operation of the movement monitoring device 12 will be described later with reference to FIG.
In addition, the current limiting device 8 determines the servo motor current value (servo motor 4 is read from the friction current memory 10 and the command current memory 11 through the current storage device 9 depending on whether the tailstock 2 is stationary or moving. Current limit value using servo motor current value when generating torque equivalent to static friction of tailstock 2 and servo motor current value when servo motor 4 generates appropriate torque for pressing work piece 1) It operates to calculate Further, the current limiting device 8 updates the friction current memory 10 through the current storage device 9 while gradually increasing the current value, so that the minimum current value when the tailstock 2 starts moving from the stationary state is set to the friction current memory 10. To remember.

FIG. 2 is a flowchart showing the detailed processing contents of the current limiting device 8 in the numerical controller according to Embodiment 1 of the present invention.
This numerical control device is configured to move the tailstock 2 from the state where the tailstock 2 is not pressing the workpiece 1, that is, the state where the tailstock 2 is stationary and away from the workpiece 1. When the workpiece 1 is moved in the direction of the workpiece 1 and the workpiece 1 is pressed, power is first supplied to the servo motor 4 and the current is gradually increased. The current limiting device 8 is a servo motor. When the current supply to 4 starts (until the tailstock 2 starts to move), the following operation is performed.

  That is, when the current supply to the servo motor 4 is started, the movement monitoring device 12 recognizes from the output signal of the encoder 5 that the tailstock 2 is in a stationary state, and transmits the state to the current limiting device 8. The apparatus 8 recognizes that the tailstock 2 is stationary in step 1 and moves to step 2. Since the tailstock 2 is not pressing the workpiece 1 at the start of current supply, it is recognized in step 2 that it is not being pressed, and the process proceeds to step 3, and the process proceeds to step 3. Is the first time, the content of the friction current memory 10 is cleared (step 4). This is to prevent this because there is a case where a current value equivalent to an illegal static friction is stored. In this state, since the current supplied to the servo motor 4 is gradually increased, this current value is added in increments of the current value and stored in the friction current memory 10 (step 5).

At this time, the current value supplied to the servo motor 4 is the same as the current value stored in the friction current memory 10 (step 7). When the tailstock 2 starts to move, an output signal indicating that the tailstock 2 is in an operating state is output from the movement monitoring device 12. For this reason, in step 1, the current limiting device 8 recognizes that the tailstock 2 is not stationary in step 1 and shifts to step 8 to stop the operation of step 3 to step 5. The current value corresponding to the static friction torque of the tailstock 2 is finally stored. The operations of Step 3 to Step 5 are performed by moving the tailstock 2 toward the workpiece 1 from the state in which the tailstock 2 is stationary and away from the workpiece 1. This is performed every time the pressing operation is performed.
The current limiting device 8 operates as described above when the current supply to the servo motor 4 is started (until the tailstock 2 starts to move).

  When the tailstock 2 starts to move, the movement monitoring device 12 recognizes the state from the output signal of the encoder 5 and informs the current limiting device 8 of that fact. As a result, the current limiting device 8 recognizes that the tailstock 2 has started to move in step 1 and stores a command current memory that stores a servo motor current value when the servo motor 4 generates an appropriate torque for pressing the workpiece 1. 11, the current value is read and output to the current command device 7 (step 8).

  After a while, since the tailstock 2 comes into contact with the workpiece 1 and stops moving, the movement monitoring device 12 recognizes the state from the output signal of the encoder 5 and informs the current limiting device 8 of this. As a result, the current limiting device 8 recognizes that the tailstock 2 is stopped during pressing (steps 1 and 2), and proceeds to step 9. In Step 9, when the command value (current value read from the command current memory 11) is smaller than the friction force (current value read from the friction current memory 10) (when the difference is a negative value), the process proceeds to Step 10. After the command direction is reversed, the process proceeds to step 11. When the command value (current value read from the command current memory 11) is equal to or larger than the friction force (current value read from the friction current memory 10) (when the difference is a positive value), the command direction is reversed. Instead, the process proceeds to step 11. In step 11, the current value read from the command current memory 11−the current value read from the friction current memory 10 is calculated, and the state where the tailstock 2 presses the workpiece 1 is continued with this current value.

  That is, if the command value (current value read from the command current memory 11) <friction force (current value read from the friction current memory 10), the current value read from the command current memory 11−read from the friction current memory 10. The tailstock 2 is controlled in the counter-pressing direction against the workpiece 1 by the current value |, and the command value (current value read from the command current memory 11) ≧ friction force (current value read from the friction current memory 10) ), The tailstock 2 is controlled in the pressing direction with respect to the workpiece 1 by the amount of current value read from the command current memory 11−current value read from the friction current memory 10.

Further, when the workpiece 1 is thermally expanded in the state of step 11, the tailstock 2 has the current value of the calculated current value read from the command current memory 11 −current value read from the friction current memory 10. Since the workpiece 1 is pressed, the tailstock 2 is easily retracted to prevent the workpiece 1 from being deformed. Further, when the tailstock 2 starts to move backward, the frictional force decreases and the tailstock pressing torque becomes insufficient. At this time, in order to detect that the movement monitoring device 12 is not stopped, the operation of step 8 (servo motor 4 starts the operation of reading out the current value from the command current memory 11 storing the servo motor current value when the proper torque for pressing the workpiece 1 against the workpiece 1 is stored, and then outputting it to the current command device 7, and then the tailstock Since 2 stops moving and returns to the state of step 11 again, an appropriate workpiece pressing torque can be quickly secured again.
As described above, the current limiting device 8 operates.

FIG. 3 is a flowchart showing detailed processing contents in the movement monitoring apparatus 12 in the numerical control apparatus according to the first embodiment of the present invention.
In the movement monitoring device 12, when electric power is supplied to the numerical control device, it is confirmed whether or not there is a change in the position information from the position encoder 5 attached to the servo motor 4 that drives the tailstock 2 (step). 20) If there is no change, the timer 13 operates and starts counting (step 21). Then, it is determined whether or not the count value of the timer 13 has exceeded a predetermined value set in advance (step 22). The stationary signal is turned on (step 23). The tailstock stationary signal is turned off until the count value of the timer 13 exceeds a predetermined value set in advance (step 25). If there is a change in the position information from the position encoder 5 in step 20, the count value of the timer 13 is cleared (step 24), and the process proceeds to step 25. This signal state is transmitted to the current limiting device 8.

In addition, the operation of the route of Step 20, Step 21, and Step 25 is performed in Step 1 of FIG. 2 for a while even when the tailstock 2 presses the workpiece 1 and stops. It is determined that the tailstock 2 is still operating, and the operation of step 8 (from the command current memory 11 that stores the servomotor current value when the servomotor 4 generates an appropriate torque for pressing the workpiece 1, This is because the tailstock torque is maintained until the frictional force is increased after the tailstock 2 is stopped by continuing the reading of the current value and outputting it to the current command device 7).
Further, the operation of the route from step 20 to step 23 is performed by the operation of step 8 after the operation of increasing the friction force after the tailstock 2 is stopped by the operation of step 8. This is to make the transition.

  As described above, according to the first embodiment, when the workpiece 1 is pressed with a predetermined pressing pressure and the tailstock 2 is stopped, the tailstock is pressed against the workpiece. The torque is the tailstock pressing target torque minus the tailstock static friction torque. When the tailstock 2 is moved, the tailstock 2 is controlled to move with the tailstock pressing target torque. Even if the proper pressing torque at the time of machining in 2 is small and the static frictional force of the tailstock 2 is not negligible, if the work is thermally expanded when the tailstock is stationary, the tailstock 2 The workpiece 1 is always retracted and deformation of the workpiece 1 can be prevented. Further, once the tailstock 2 starts to move backward, the frictional force decreases and the tailstock pressing torque becomes insufficient. At this time, it is detected that the tailstock 2 is not stopped, and the tailstock 2 presses again with the pressing target torque. Therefore, an appropriate workpiece pressing torque can be secured again.

  Further, after the tailstock 2 comes into contact with the workpiece 1 and stops, after a predetermined time has elapsed, the pressing torque of the tailstock 2 against the workpiece 1 is set as the tailstock pressing target torque-the tailstock static friction. Since the torque is set, the tailstock torque can be maintained until the frictional force increases after the tailstock stops, so that the tailstock can be pressed against the workpiece with an appropriate torque.

  Further, the movement of the tailstock 2 is monitored while the output torque of the servomotor 4 is gradually increased in the stationary state of the tailstock, and the output torque of the servomotor 4 at the time when the tailstock 2 starts to move is measured. Since it is stored as a static friction torque, a special device for measuring the torque of the servo motor 4 corresponding to the static friction force is not required, and a servo corresponding to the static friction force using a general machine tool position control configuration. The torque of the motor 4 can be measured.

  The control method and apparatus for the tailstock according to the present invention are suitable for use as a machine tool control device for processing a workpiece while pressing the workpiece with the tailstock.

It is a block diagram which shows the whole structure of the numerical control apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows detailed operation | movement of the current limiting apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows detailed operation | movement of the movement monitoring apparatus which concerns on Embodiment 1 of this invention.

Explanation of symbols

1 Workpiece, 2 Tailstock, 3 Ball screw drive mechanism, 4 Servo motor, 5 Position encoder, 6 Numerical control device, 7 Current command device, 8 Current limit device, 9 Current storage device, 10 Friction current memory, 11 Command Current memory, 12 movement monitoring device, 13 timer.

Claims (8)

  In the tailstock control method in which the tailstock is driven by a servo motor and presses the workpiece with a predetermined pressing pressure, when the tailstock is in contact with the workpiece and is stationary, the tailstock is processed. A tailstock control method, wherein the servomotor is controlled so that a pressing torque against an object is a tailstock pressing target torque-a tailstock static friction torque.   2. The method for controlling a tailstock according to claim 1, wherein when the tailstock is moved, the servo motor is controlled so that the tailstock moves with a tailstock pressing target torque.   After the tailstock comes into contact with the workpiece and stops, after a predetermined time has elapsed, the pressing torque of the tailstock to the workpiece becomes the tailstock pressing target torque-the tailstock stationary friction torque. 3. A method for controlling a tailstock according to claim 1 or 2, wherein the servomotor is controlled.   While the tailstock is stationary, the supply current to the servo motor is gradually increased while the stationary state of the tailstock is monitored, and the current value corresponding to the output torque of the servomotor when the tailstock starts moving is calculated. The method for controlling a tailstock according to any one of claims 1 to 3, wherein the current value is stored as a current value corresponding to the base static friction torque. Servo motor current value when the servo motor generates torque equivalent to static friction of the tailstock in the tailstock control device that drives the tailstock by the servomotor and presses the workpiece with a predetermined pressing pressure. A friction current memory for storing a torque, a command current memory for storing a servo motor current value when generating a tailstock pressing target torque against which the servomotor presses a workpiece, and monitoring a stationary state of the tailstock When the movement monitoring means and a signal indicating that the tailstock is in contact with the workpiece and the tailstock is stationary are output from the movement monitoring means, the movement monitoring means stores the friction current memory and the command current memory. The current value of each servomotor is read, and using this current value, the pressing torque of the tailstock to the workpiece becomes the tailstock pressing target torque-the tailstock static friction torque. Cormorant said controller tailstock comprising a control means for controlling the servomotor.   When the control means outputs a signal indicating that the tailstock is moving from the movement monitoring means, the control means controls the servo motor so that the tailstock moves with the tailstock pressing target torque. The control device for a tailstock according to claim 5, wherein the control device is controlled.   The movement monitoring means outputs a signal indicating that the tailstock is stationary after a lapse of a predetermined time after the tailstock comes into contact with the workpiece and is stationary. The servomotor is controlled based on the signal so that the pressing torque of the tailstock to the workpiece becomes a tailstock pressing target torque-a tailstock static friction torque. The tailstock control device according to claim 6.   The control means gradually increases the current supplied to the servomotor in a stationary state of the tailstock, and sets the current value corresponding to the output torque of the servomotor when the tailstock starts to move to the tailstock stationary friction torque. 8. The tailstock control device according to claim 5, wherein the current value is stored in the friction current memory as a corresponding current value.

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