JP2016193469A - Abutment detection method of machine tool and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technical means which can further surely and quickly detect the abutment of a workpiece detection implement and a workpiece, and a collision or interference with a tool and the workpiece without being influenced by an increase of the output torque of a motor at a normal operation.SOLUTION: At the detection of a measurement point p of a workpiece w and the collision detection of a tool 4, thresholds (detection levels) of abnormal loads of a feed motor 5 of a spindle head 3b and feed motors 6, 7 of a bite holder 11 are set at values of increase amounts per unit time of a physical amount related to the output torque of the motors, and a detected change amount per unit time of the physical amount is compared with the thresholds, thus enabling the detection at torque smaller than large output torque which is generated at the acceleration of the bite holder and the heavy cutting of a workpiece.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and an apparatus for detecting that a tool or work detection tool mounted on a tool post is in contact with a work or a spindle chuck.

  To confirm that the workpiece is loaded in the correct posture on the machine tool, to measure the material dimensions and the position of the tip of the material, and to check whether the workpiece has been processed correctly, the machine tool The position and dimensions of the workpiece are measured in the machine. In NC machine tools, since the controller recognizes the position of the tool post, a tool is mounted when a workpiece detection tool of a predetermined size is mounted at a predetermined position of the tool post and the workpiece detection tool comes into contact with the workpiece. By reading the position of the table, the position and dimensions of the workpiece can be measured.

  That is, the turret mounted with the workpiece detector is moved toward the workpiece, the turret is stopped when the workpiece detector comes into contact with the workpiece, and the position of the turret at that time is read. The position is measured, and the workpiece dimension is measured by the difference from the reference position of the loaded workpiece to the contact position.

  In addition, when machining a large number of workpieces according to the machining program, a test that executes the machining program step by step to prevent the tool from colliding with the workpiece or the chuck holding the workpiece during machining due to a program error. Processing is performed. During this test machining, if the tool collides with a workpiece or chuck, a serious accident such as tool breakage will occur unless the tool post is stopped immediately. Therefore, it is necessary to immediately stop the movement of the tool post when the tool collides, and for this purpose, it is necessary to detect contact between the tool and the workpiece or chuck.

  When the workpiece detector or tool comes into contact with the workpiece, the feed resistance of the tool post increases. Since the tool post is moved by the feed motor in each axial direction, the output torque of the feed motor increases. Therefore, the torque of the feed motor is monitored during the feed movement of the tool post, and when the torque reaches a preset threshold, it is judged that it is in contact or collision and the tool post is immediately stopped. Yes.

  Since the motor torque has a correlation with the current value flowing through the motor, a change in the output torque can be detected by detecting the motor current. If the motor is a servo motor or a motor having a control system similar to the servo motor (for example, some spindle motors), as described in Patent Documents 1 and 2, a position command (from a controller to a servo amplifier) The movement state of the tool rest can be monitored using a position deviation that is a difference signal between the feed movement command) and a position feedback signal indicating the value of the actual tool rest moving.

  In other words, when the tool post moves according to the command from the controller, the tool post moves according to the position command output one after another from the controller, so the position deviation that is the difference signal between the position command and the position feedback signal is zero. Maintain a nearly constant value close to. On the other hand, when the workpiece detector comes into contact with the workpiece, or when an unexpected collision between the tool and the workpiece or chuck occurs, the movement of the tool rest is hindered, and the tool rest cannot move according to the position command. Since fewer position feedback signals are returned, the position deviation increases.

  Therefore, a threshold value for position deviation is set in the controller, and the contact determination condition is that the position deviation has reached the threshold value. The control using the position deviation as the stable condition can detect the contact of the workpiece detection tool or the tool more quickly and accurately than the control using the current value as the stable condition.

JP-A-5-245740 Japanese Patent No. 4271272

  As the machine tool becomes multifunctional, the weight of the tool post increases. For example, in turret turrets that can be fitted with many tools and composite turrets that can be fitted with large-diameter rotating tools, the weight of the turrets increases due to the size of the turret and the size of the tool drive motor. . When the weight of the tool post increases, the torque of the feed motor necessary for the movement, particularly the torque of the feed motor at the start of the movement, increases, and accordingly, the movement of the tool post with respect to the position command is delayed, and the position deviation is increased. Increase.

  The threshold value for detecting the contact of the workpiece detection tool or tool needs to be set higher than the maximum value generated during normal operation. When the turret's moving speed is increased in order to increase the weight of the turret or to improve productivity and operating rate, especially when the moving speed of the turret is increased during rapid feed, a large inertial force is applied at the start of movement to feed the turret. Since the output torque of the motor increases, the threshold for contact detection must be increased.

  However, when this threshold value is increased, the stress acting on the workpiece detection tool or tool increases when the workpiece detection tool or tool abuts. For this reason, repeated large stresses cause fatigue failure of the workpiece detection tool, or breakage of a small tool due to collision.

  Therefore, the present invention is more sensitive to contact between the work detection tool and the work and unscheduled contact (collision or interference) between the tool and the work without being affected by an increase in the output torque of the motor during normal operation. It is an object to provide technical means capable of reliably and promptly detecting.

  In the present invention, an output amount of a motor or a physical quantity related to the output torque per unit time (hereinafter referred to as “torque increase rate”) is compared with a threshold value set in the controller 31 to obtain a workpiece. This problem is solved by detecting the contact between the detection tool 8 and the workpiece w and the collision between the tool 4 and the workpiece w or the chuck 2 (2a, 2b).

  That is, in detecting the measurement point p of the workpiece w and the collision of the tool 4, the abnormal load thresholds (detection levels) of the feed motor 5 of the headstock 3b and the feed motors 6 and 7 of the tool post 11 are set to these motors. And the amount of change per unit time of the physical quantity related to the detected output torque of the motor or the output torque (hereinafter referred to as “torque change rate”) is compared with a threshold value. By doing so, it is possible to detect with a torque lower than the large output torque generated when the tool post is accelerated or when the workpiece is heavily cut.

  The contact detection device for a machine tool according to the present invention is a contact detection device for a machine tool that detects contact between the tool 4 or the workpiece detector 8 and the workpiece w or the spindle chuck 2, and is a motor 5 to be controlled. , 6, 7, 9, a differentiator 33 to a difference detector 24 for calculating or detecting a torque change rate, a setting device 35 for setting a threshold value of a torque increase rate of the motor, a differentiator 33 and a difference detector And a comparator 34 for comparing the torque change rate output from 24 with the threshold value. The comparator 34 abuts when the output of the differentiator 33 or the difference detector 24 reaches the threshold value. The signal i is output.

  That is, in the present invention, the torque increase rate of the spindle head feed motor 5 and the tool feed motors 6 and 7 is used as a threshold value as a threshold value for determining the contact between the tool 4 or the workpiece detector 8 and the workpiece w. It is to do.

  In the NC machine tool, the headstock feed motor 5 and the tool feed motors 6 and 7 are servo motors. The threshold value of the torque increase rate in this case is the amount of change per unit time of the difference signal (position deviation) c between the position command a given to the feed motor and the position feedback signal b returned from the motor. By using a threshold value or a difference signal (speed deviation) f between a speed command d given to these feed motors and a speed feedback signal e returned from the motor as a threshold value, a special device (hardware ) Can be detected accurately.

  The threshold value (detection level) for detecting contact between the workpiece detector 8 and the workpiece w is not the load torque value of the motors 5, 6, 7, 9 but the torque increase rate. The contact detection can be performed with a lower torque, and the impact force acting on the workpiece detector 8 and the workpiece w at the time of contact can be reduced.

  Moreover, it is also possible to use the torque increase rate of the motors 5, 6, 7, and 9 as the detection level of the collision detection of the tool 4, and to stop the movement of the tool post 11 at the time of collision detection and collision detection by constant monitoring. Thus, damage at the time of a machine collision can be reduced.

Block diagram of the first embodiment of the present invention. Illustration of collision between tool and workpiece The block diagram of the principal part of 2nd Example

  Hereinafter, an embodiment of the present invention will be described by taking a two-spindle opposed lathe shown in FIG. 1 as an example. The two-spindle opposed lathe shown in the figure includes a left main spindle 1a and a right main spindle 1b that face each other on the same main spindle axis s. A left chuck 2a and a right chuck 2b are mounted on the ends of the left main shaft 1a and the right main shaft 1b facing each other. The left main spindle 1a is pivotally supported by a left main spindle 3a fixed to a bed (not shown). The right spindle 1b is pivotally supported by a right spindle base 3b that is movably mounted on a guide in the spindle axis direction (Z-axis direction) provided on the bed. The right spindle stock 3b is screwed to a spindle feed screw 15 in the Z-axis direction that is rotated forward and backward by the spindle feed motor 5.

  A tool post 11 is arranged on the side of the spindle axis s. A two-spindle opposed lathe is usually equipped with a plurality of tool rests, but the figure shows only one of them. The tool post 11 includes a turret 12. The turret 12 includes a plurality of tool mounting stations as mounting positions of the tool 4 necessary for processing. In the example shown in the figure, the work detection tool 8 is mounted at one place of the tool mounting station of the tool post 11.

  The tool post 11 is mounted via a saddle (Z-axis direction feed base) 13. The saddle 13 is screwed into a Z-axis feed screw 17 that is driven to rotate forward and backward by a Z-axis feed motor 7 mounted on the bed. The tool post 11 is screwed into an X-axis feed screw 16 that is driven to rotate forward and backward by an X-axis feed motor 6 mounted on the saddle 13. The left main spindle 1a and the right main spindle 1b are rotationally driven by a left main spindle motor 9a and a right main spindle motor 9b mounted on the respective spindle heads. The spindle motors 9a and 9b can be switched between a low-speed rotation that is phase-controlled (rotation angle control) and a high-speed rotation that is not phase-controlled (rotation during turning).

  The spindle head feed motor 5, the Z-axis feed motor 7, and the X-axis feed motor 6 are servo motors controlled via a servo amplifier 21. Although only the control system of the Z-axis feed motor 7 is shown in the figure, the spindle head feed motor 5 and the X-axis feed motor 6 also have a similar control system.

  The servo amplifier 21 includes difference detectors 23 and 24, a compensation circuit 25, a power amplifier 26, and a differentiator 27. The difference detector 23 gives the compensation circuit 25 a difference signal (position deviation) c between the position command a given from the NC device 31 and the position feedback signal b given from the pulse encoder 14 attached to the Z-axis feed motor 7. ing. The compensation circuit 25 calculates a speed command d based on the position deviation c and supplies it to the difference detector 24. The difference detector 24 supplies the power amplifier 26 with a difference signal (speed deviation) f between the speed feedback signal e obtained by differentiating the speed command d given from the compensation circuit 25 and the position feedback signal b by the differentiator 27. Giving. The current output from the power amplifier 26 is limited by the set value of the maximum current setting device 28. The NC device 31 increases or decreases this set value at a necessary timing.

  The NC device 31 includes a differentiator 33, a comparator 34, and a threshold setting device 35. The position deviation c output from the difference detector 23 is differentiated by the differentiator 33, that is, converted into an increase / decrease rate of the position deviation c (positional change rate per unit time) g, and given to the comparator 34. It has been. On the other hand, the determination value h of the torque increase rate of the Z-axis feed motor 7 is set in the threshold setting device 35 and given to the comparator 34. The comparator 34 outputs the control output i when the increase / decrease rate g of the position deviation c reaches the determination value h. When the control output i is output, the NC device 31 stops the Z-axis feed motor 7 and coordinates of the tool post 11 (when the controlled object is a spindle feed motor or spindle motor, the coordinates of the spindle stock and the spindle ) Is read and stored in the memory.

  Next, the dimension measuring operation of the workpiece w gripped by the left chuck 2a in the two-spindle opposed lathe having the above configuration will be described. The work detection tool 8 is mounted at one place of the tool mounting station of the turret 12, and the tip of the work detection tool 8 is set in the closest position to the measurement position p of the work w by the indexing operation of the turret 12 and the movement of the tool post 11. Position it at the measurement start position. The measurement position is set to a position that is as close to the measurement point p as possible and outside the range of dimensional variation of the workpiece w.

  Next, with the maximum current setter 28 limiting the torque of the Z-axis feed motor 7 (or X-axis feed motor 6 when measuring the dimension in the X-axis direction), the tool rest 11 is moved toward the workpiece w at a low speed. To do. When the tool post 11 is moved, target positions are successively set in the position counter 32 of the NC device 31. In the normal state in which the tool post 11 moves accordingly, the position deviation c, which is a difference signal between the position command a and the position feedback signal b, maintains a substantially constant value.

  When the workpiece detector 8 comes into contact with the workpiece w in this state, the Z-axis feed motor 7 is forcibly stopped by an increase in load torque applied to the Z-axis feed motor 7. Then, while the count value of the position counter 32 continues to change, the position feedback signal b cannot follow this, so the position deviation c increases rapidly. When the degree of increase (increase rate) reaches the threshold set in the setting device 35, the comparator 34 outputs a control output i, stops the Z-axis feed motor 7, and stores the coordinates of the tool post 11 in memory. To remember.

  Since the distance between the reference position of the turret (position recognized by the NC device) and the tip of the work detection tool and the position of the left chuck are known, the workpiece dimensions can be calculated from the recorded coordinates of the turret.

  The above description is an example of measuring the position and dimensions of the workpiece w with the workpiece detector 8 mounted on the tool post 11, but the spindle chuck feed motor 5 is gripped by the right chuck 2b by performing the same control. The tip of the workpiece can be detected. For example, when the workpiece is transferred from the left chuck 2a to the right chuck 2b, it can be detected that the tip of the workpiece w gripped by the left chuck 2a is in contact with the reference surface of the right chuck 2b. It is possible to detect that the workpiece has been reliably inserted into 2b and to detect the position of the workpiece tip and the workpiece length from the position of the tool post 11 at that time.

  Next, collision detection during workpiece machining will be described with reference to FIG. FIG. 2 shows a state where a workpiece w having a level difference r is turned by a cutting tool 4 mounted on the turret 12. When the machining program sends the cutting tool 4 in the Z-axis minus direction (direction approaching the step) and the processing end position is on the minus side from the position of the step r, the cutting tool 4 collides with the step r during the processing. When the tool collides, the tool post is forcibly stopped although the feed command a is successively given to the Z-axis feed motor 7, so that the position deviation c increases. When the degree of increase (increase rate) reaches the threshold set in the setting device 35, the comparator 34 outputs the control output i and stops the Z-axis feed motor 7. It can be prevented from becoming a defective product. The higher the hardness and rigidity of the object to be collided, the more rapidly the increase rate of the position deviation c when the object collides. Therefore, the turret is stopped earlier than the conventional means for detecting the collision by the value of the position deviation c. It is possible to prevent damage to tools and workpieces more reliably.

  In the example of FIG. 1, the amount of change per unit time of the output torque of the tool feed motor 7 is obtained by differentiating the position deviation c obtained from the servo amplifier 21 by the differentiator 33. The difference detector 24 of the servo amplifier 21 generates a difference signal (speed deviation) f between the speed command d given from the compensation circuit 25 and the speed feedback signal e obtained by differentiating the position feedback signal b by the differentiator 27. Detected. Therefore, it is also possible to perform control in which the detection value f is directly supplied to the comparator 34 and compared with the determination value h to output the control output i.

  As described above, the torque fluctuation of the Z-axis feed motor 7 is monitored by utilizing the change of the position deviation c and the speed deviation f according to the torque fluctuation of the servo motor, and the increase rate of the load torque exceeds the determination level. An example of detecting this is shown. The load torque of the motor can also be detected by the value of current flowing through the motor. FIG. 3 shows an example in that case. That is, the output current of the power amplifier 26 detected by the ammeter 36 is converted into a current increase / decrease rate by the differentiator 33, and compared with the judgment value set in the threshold value setter 35 by the comparator 34, thereby increasing the current. In this example, the control output i is output when the rate reaches the determination value.

  As described above, the present invention can also be implemented by detecting the current value flowing through the motor. However, the method using the position deviation and the speed deviation described above can detect torque fluctuations more accurately. More suitable for the implementation of the invention.

  The same control as described above can be applied to the spindle head feed motor 5 and the spindle motors 9a and 9b. As described above, when the workpiece w is transferred from the left chuck 2a to the right chuck 2b, when the right spindle stock 3b approaches the workpiece w, the rate of increase in the load torque of the spindle feed motor 5 is increased in the same manner as described above. By monitoring, it is possible to quickly detect that the workpiece w has been inserted into the right chuck 2b and stop the approaching operation of the right chuck 2b. Further, by performing the same control on the spindle motor, for example, detection of a tool collision during contouring processing performed by rotating the spindle at a low speed, or the workpiece detector 8 mounted on the tool post approaches the peripheral surface of the workpiece w. Then, by rotating the workpiece w at a low speed, it is possible to measure the phase of the protrusion provided on the peripheral surface.

2 (2a, 2b) Chuck 3 (3a, 3b) Spindle table 4 Tool 5 Spindle feed motor 6 X-axis feed motor 7 Z-axis feed motor 8 Work detector 9 Spindle motor 23 Detector 11 Tool post 31 Controller 33 Differential 34 Comparator 35 Threshold setting device a Position command b Position feedback signal c Difference signal (position deviation)
f Difference signal (speed deviation)
i Control output (contact signal)
p Measurement point w Work

Claims (4)

  In a contact detection device for a machine tool that detects contact between a tool or workpiece detection tool and a workpiece, a torque change rate that is a change amount per unit time of a physical quantity related to an output torque of a motor to be controlled is calculated or calculated. A detector for detecting, a setter for setting a threshold value of a torque increase rate that is the rate of change on the increasing side, and a comparator for comparing the torque change rate output from the detector with the threshold value And the comparator outputs a contact signal when the output of the detector reaches a threshold value.   In a contact detection method for a machine tool that detects contact between a tool or workpiece detector and a workpiece, the amount of increase in the output torque of the tool feed motor per unit time is used as a threshold for determining contact. A method for detecting contact between a tool of a machine tool or a workpiece detector and a workpiece, which is a threshold value.   The contact detection method according to claim 2, wherein the tool feed motor is a servo motor, and the threshold value per unit time of a difference signal between a position command given to the motor and a position feedback signal given from the motor. The contact detection method according to claim 2, wherein the contact detection method is a threshold value for the increase amount.   3. The contact detection method according to claim 2, wherein the tool feed motor is a servo motor. The threshold value is a threshold value for a difference signal between a speed command given to the motor and a speed feedback signal returned from the motor. The contact detection method according to claim 2, wherein

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