JP2009083074A - Control device for machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for a machine tool capable of performing a control to suppress interference between a pair of servo motors and efficiently performing highly accurate machining without adjusting torsional rigidity for each kind of workpiece. <P>SOLUTION: This control device is provided with a non-interference correction device 10 to suppress mutual interference of the pair of servo motors 7a and 7b. The non-inference correction device 10 is provided with a difference value of each of position feed back values FB1 and FB2 detected from the pair of servo motors 7a and 7b, a torsion rigidity estimation block for estimating torsion rigidity of the workpiece based on a torque command value for measuring torsion rigidity imparted to the pair of servo motors 7a and 7b to generate torsion in the workpiece, a difference value of each of speed feedback values FB3 and FB4 detected from the servo motors 7a and 7b, and a torque command value correction block for estimating a torque command correction value to correct a torque command value of the servo motors 7a and 7b based on the torsion rigidity estimated by the torsion rigidity estimation block. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a machine tool control apparatus that controls a pair of tandem electric motors that rotationally drive a work held by both ends from both sides.

  When a long workpiece such as a camshaft or crankshaft is driven to rotate in a cantilevered state, the workpiece may be twisted due to torque fluctuation or processing load during acceleration / deceleration, and high-precision rotation control cannot be performed. There's a problem. For this reason, the long work is held in a both-sided state and is rotationally driven. A method of driving a long workpiece in a both-end holding state includes a method of rotationally driving the other end of the work while one end of the work is rotatably supported by a tailstock or the like, and a pair of tandem structures. There is a method of rotating and driving a work supported from both sides using an electric motor. The latter method is a method of rotating a workpiece while synchronizing a pair of electric motors, and is often employed when processing a long workpiece with high accuracy.

  However, even when a long workpiece is rotationally driven using a pair of electric motors, (a) when the rotation centers of the pair of electric motors are deviated, (b) torsion occurs due to the offset load or deflection of the workpieces. (C) When the load applied to the pair of motors is unbalanced due to the unbalanced load of the workpiece, (d) When the workpiece is bent or twisted due to machining disturbance, the torque of the pair of motors interferes. That is, the rotational driving force of the pair of electric motors may fluctuate and the workpiece may vibrate.

  In the case of (d) above, increasing the servo rigidity and increasing the speed gain is effective in obtaining high rotational accuracy. In particular, learning control is most effective for periodically repeated disturbances. However, when vibration occurs due to the difference in rotational driving force between the pair of electric motors, the vibration is amplified, so that the speed gain cannot be increased or learning control cannot be performed.

As an example of a control device that controls a plurality of electric motors that rotationally drive a work held by both ends, those disclosed in Patent Document 1 and Patent Document 2 are known.
Paragraph No. [0013] of Patent Document 1 states that “when one drive system is driven by a plurality of servo motors, a plurality of servo motors are related to one main servo motor and another sub servo motor, and position control is performed. Is performed on the main servo motor side, and speed control and current control are performed for each servo motor. The sub servo motor speed command is the position error between the main servo motor side and the sub servo motor side. The position correction is performed on the servo circuit side to improve the responsiveness, and the speed control on the slave servo motor side is performed using the speed command obtained by the position correction. In addition, it is possible to perform highly accurate synchronous control by performing current control. "

  Paragraph [0012] of Patent Document 2 states that “the vibration damping control device can be configured in a plurality of forms. The first form of the vibration damping control device is the difference between the speed feedback amounts of the two motors. The first calculation means for integrating and multiplying the speed feedback deviation by a constant and the second calculation means for multiplying the speed feedback deviation by a constant, and adding the outputs of the first calculation means and the second calculation means The first calculation means obtains a position deviation by integrating the speed deviation between the two motors (drive shafts), and this position deviation is used as a spring constant of the machine to be controlled. The mechanical system spring compensation is performed by multiplying the first constant corresponding to the second constant, and the second computing means is a second deviation corresponding to the friction coefficient of the machine to be controlled and the speed deviation between the two motors (drive shafts). Multiply by the constant of By, it has been described as performing the friction compensation of the mechanical system. "

Japanese Patent Laid-Open No. 11-305839 JP 2001-85826 A

  However, the control described in Patent Document 1 that performs so-called tandem learning is effective when vibration having periodicity is generated between a plurality of servo motors, but vibration having non-periodicity during machining of a workpiece or the like. In this case, the mutual interference between the plurality of servo motors is not sufficiently suppressed. In addition, the control described in Patent Document 2 that performs tandem vibration suppression is a control that suppresses interference between a pair of servo motors, but the torsional rigidity is adjusted for each type of work held at both ends. There is a problem that adjustment is required and adjustment takes time.

  It is an object of the present invention to provide a machine tool control device that can automatically adjust the torsional rigidity of a workpiece and perform control to suppress interference between a pair of servo motors, and thereby perform highly accurate machining efficiently. Objective.

  In order to achieve the above object, the machine tool control device according to claim 1 is a machine tool control device that controls a pair of tandem electric motors that rotationally drive a work held by both ends from both sides. A non-interference corrector for suppressing mutual interference between the pair of electric motors, the non-interference corrector so that the difference between the position feedback values respectively detected from the pair of electric motors and the workpiece is twisted; A first circuit element that estimates the torsional rigidity of the workpiece based on a torque command value for measuring the torsional rigidity given to the pair of electric motors, and speed feedback values detected from the pair of electric motors, respectively. And a torque for correcting torque command values of the pair of electric motors based on the torsional rigidity estimated by the first circuit element. A second circuit element for estimating the command correction value, characterized by comprising a.

  The invention according to claim 2 is the machine tool control device according to claim 1, wherein the first circuit element is used for measuring torsional rigidity with respect to the pair of electric motors so that the work is twisted. A torsion torque command unit that provides the torque command value, a difference value between the torque command value given to the pair of electric motors by the torsion torque command unit and a position feedback value detected from each of the pair of electric motors And a torsional stiffness estimating means for estimating a torsional stiffness value of the workpiece from the torsional angle of the workpiece calculated based on the speed of the workpiece, wherein the second circuit element is a speed feedback detected from the pair of electric motors, respectively. After integrating the difference value between the values, the first arithmetic unit that calculates the spring compensation component of the machine tool by multiplying the torsional stiffness value, and the pair of electric motors Re respectively by a constant multiple of the difference value of the detected velocity feedback value, and a second arithmetic unit for calculating a friction compensation component of the machine tool, characterized by comprising.

  The invention of claim 3 is the machine tool control device according to claim 1 or 2, wherein the machine tool control is configured to control a pair of tandem electric motors that rotationally drive a work held by both ends from both sides. The apparatus further includes a speed gain adjuster for automatically adjusting a speed gain in order to suppress fluctuations in rotational driving force of the pair of electric motors, and the speed gain adjuster is a predetermined torque command value for the pair of electric motors. From the torque command section that gives a sinusoidal measurement torque command value of the frequency, the measurement torque command value, and the speed feedback value of the pair of motors detected when the measurement torque command is given An adaptive control unit that estimates the inertia of the workpiece and automatically adjusts the speed gain.

  According to a fourth aspect of the present invention, there is provided the machine tool control device according to any one of the first to third aspects, wherein the machine tool simultaneously controls a pair of electric motors that rotationally drive a work held by both ends. In the machine control device, a learning controller that calculates a position correction value for reducing a position deviation that is a difference between the position command value and the position feedback value in order to suppress fluctuations in the rotational driving force of the pair of electric motors. It is provided with.

  As described above, according to the first and second aspects of the present invention, since the first circuit element for estimating the torsional rigidity of the workpiece is provided, the torsional rigidity of the workpiece is obtained in the two-inertia model having the torsional rigidity as a variable. Can be automatically adjusted, and control for suppressing interference between the pair of servo motors can be performed. In addition, since the second circuit element for estimating the torque command correction value for correcting the torque command value of the pair of electric motors is provided, not only the case where vibration having periodicity occurs but also vibration having non-periodicity Even when this occurs, the mutual interference generated between the pair of servo motors can be sufficiently suppressed, and high-precision machining can be performed. Therefore, high-precision machining can be performed efficiently.

  According to the invention of claim 3, it is possible to calculate the optimum speed gain from the feedback value by adding a measurement disturbance to the torque command of the pair of electric motors. Thereby, the speed gain of a pair of electric motor can be made equivalent, and a speed gain can be automatically adjusted according to the load added to a pair of electric motor which drives a workpiece | work. For this reason, the mutual interference between a pair of electric motors by the twist of a workpiece | work at the time of acceleration / deceleration can be prevented.

  According to the invention of claim 4, when the workpiece rigidity is low by applying the learning control independently to the control of the pair of electric motors that drive the workpiece from both sides, particularly for the disturbance that is periodically repeated. Even when the machining disturbance is large, highly accurate rotation control can be performed.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic block diagram for explaining a first embodiment of a machine tool control device (hereinafter referred to as “control device”) according to the present invention. The control device 1 of the present embodiment is not particularly limited in application, but may be applied to a cylindrical grinding machine that finishes the crankpin 3 of the crankshaft 2 that is a long workpiece shown in FIG. it can. The cylindrical grinding machine is normally used, and a pair of servo motors 7a and 7b (electric motors) having a base table, a grinding wheel base 4 having a grinding wheel 5, and a crankshaft 2 supported at both ends are rotationally driven from both sides. ) And auxiliary equipment. The first servo motor 7a and the second servo motor 7b are configured to be synchronously controlled and non-interference controlled by the control device 1. Non-interference control is performed by the non-interference corrector 10, thereby suppressing mutual interference between the first servo motor 7 a and the second servo motor 7 b.

  As shown in FIG. 1, the control device 1 includes position control units 11a and 11b, speed control units 12a and 12b, current control units 13a and 13b, and amplifiers that control the first servo motor 7a and the second servo motor 7b. (Current amplifiers) 14a and 14b are provided. The first servo motor 7a and the second servo motor 7b include position detectors 15a and 15b for detecting position feedback values FB1 and FB2, respectively, and speed detectors (not shown) for detecting speed feedback values FB3 and FB4, respectively. )).

  The position controllers 11a and 11b process a position deviation amount that is a difference between the position command given from the host controller and the position feedback values FB1 and FB2 detected by the position detectors 15a and 15b, and the speed controller A speed command value is output to 12a and 12b. The speed control units 12a and 12b process a speed deviation amount which is a difference between the speed command value given from the position control units 11a and 11b and the speed feedback values FB3 and FB4 detected by the speed detector, and perform current control. A current command value is output to the units 13a and 13b.

  Current control units 13a and 13b are current deviation amounts which are differences between current command values given from speed control units 12a and 12b and current feedback values FB5 and FB6 from sensors (not shown) that detect motor currents. To output voltage command values to the amplifiers 14a and 14b. The amplifiers 14a and 14b receive voltage command values from the current control units 13a and 13b, respectively, generate drive currents for driving the servo motors 7a and 7b, and rotationally drive the servo motors 7a and 7b.

  As illustrated in FIG. 3, the non-interference corrector 10 includes a torsional rigidity estimation block (first circuit element) 17, a torque command value correction block (second circuit element) 18, and processing by a torsional rigidity estimation block 17. And a switch 19 for switching processing by the torque command value correction block 18. The switch 19 switches between processing for calculating (estimating) torsional rigidity and processing for calculating a torque correction value for each type of workpiece.

  The torsional rigidity estimation block 17 is applied to the pair of servomotors 7a and 7b so that the difference between the position feedback values FB1 and FB2 detected from the pair of servomotors 7a and 7b and the crankshaft 2 are twisted. Based on the given torque command value for measuring torsional rigidity, the torsional rigidity of the crankshaft 2 is estimated. The torque command value correction block 18 is based on the difference between the speed feedback values FB3 and FB4 feedback values detected from the pair of servomotors 7a and 7b, respectively, and the torsional rigidity estimated by the torsional rigidity estimation block 18. The torque command correction value for correcting the torque command value of the servo motors 7a and 7b is estimated.

  The non-interference corrector 10 will be described in more detail. The torsional rigidity estimation block 17 provides torque that gives a torque command value for measuring torsional rigidity to the pair of servomotors 7a and 7b so that the crankshaft 2 is twisted. The command unit 21, the torque command value given to the pair of servo motors 7a, 7b by the torque command unit 21, and the difference value between the position feedback values FB1, FB2 detected from the pair of servo motors 7a, 7b, respectively And a torsional rigidity estimating unit 20 for estimating a torsional rigidity value of the crankshaft 2 from the torsion angle of the crankshaft 2 calculated based on the above.

  The torque command value correction block 18 integrates the difference value of the speed feedback values FB3 and FB4 detected from the pair of servo motors 7a and 7b by the integrator 22, and then the torsional rigidity estimation unit 20 by the constant multiplier 23. Multiplied by the torsional rigidity value K1 estimated in step 1, the spring compensation calculation unit (first calculation unit) 25 for calculating the spring compensation component of the cylindrical grinding machine, and the speed feedback values FB3 detected from the pair of servo motors 7a and 7b, respectively. , FB4 is multiplied by a constant multiplier 24 to calculate a friction compensation component of the cylindrical grinding machine, a friction compensation calculation unit (second calculation unit) 26, a spring compensation component, and a friction compensation component. And a phase lag compensation unit 27 for calculating a phase lag compensation component. The torque command value correction block 18 estimates a torque command correction value that compensates for mutual interference between the pair of servo motors 7a and 7b, and adds or subtracts this torque command correction value to or from the current command value of one servo motor. The current command value is corrected by subtracting or adding to the current command value of the other servo motor. That is, the two servomotors 7a and 7b are added with the signs of the torque command correction values reversed. This is because the torque command correction value is calculated based on the deviation between the speed feedback values FB3 and FB4.

  In the spring compensation calculation unit 25, the integrator 22 obtains a position deviation by integrating the speed deviation between the two servo motors 7a and 7b, and the constant multiplier 23 calculates the position deviation to the spring constant of the machine to be controlled. The spring compensation of the mechanical system is performed by multiplying the torsional rigidity value K1 estimated to be equivalent to. The friction compensation calculation unit 26 includes a constant multiplier 24 that multiplies the difference between the speed feedback values FB3 and FB4 by a constant. The constant multiplier 24 performs friction compensation of the mechanical system by multiplying the speed deviation between the two servo motors 7a and 7b by a constant K2 corresponding to the friction coefficient of the machine. Note that the first constant K1 and the second constant K2 correspond to the gain of the calculation means.

The phase advance compensation unit 27 uses the added value of the outputs of the spring compensation calculation unit 25 and the friction compensation calculation unit 26 as a torque command correction value, and compensates the delay by advancing the phase of the torque command correction value. The phase advance compensation unit 27 compensates for a control system delay (current loop delay) and a detection system delay (sampling delay), thereby enabling highly accurate control.
The phase advance compensation unit 27 can apply a phase advance compensation element having a transfer function G (s) characteristic represented by the following equation.
G (s) = (1 + Ts) / (1 + αTs) (1)
Note that s represents a differential operator of Laplace transform, and there is a relationship represented by the following formulas (2) and (3) between the variable T and α.
Maximum phase advance frequency w = 1 / (T · α ^1/2 ) (2)
Maximum phase lead Φ = arctan ((α-1) / (2.α ^1/2 ) (3)
Here, the unit of w is rad / sec, and the unit of Φ is deg. The advance amount by the phase advance compensation means 2d can be changed using T and α as parameter values.

  In addition, the spring compensation calculation unit 25 and the friction compensation calculation unit 26 can be configured to be used independently or a configuration in which both the calculation units 25 and 26 are added. Further, the phase advance compensation unit 27 may be configured to be added to the combination of the spring compensation calculation unit 25 or the friction compensation calculation unit 26 or may be configured not to be added.

  Next, a second embodiment of the control device according to the present invention will be described. As shown in FIG. 4, the control device 30 of the present embodiment includes a speed gain adjuster 31 instead of the non-interference corrector 10 of the first embodiment. As shown in FIG. 5, the speed gain adjuster 31 includes a torque command unit 32 that gives a sinusoidal measurement torque command value having a predetermined frequency as a torque command value of the pair of servomotors 7 a and 7 b, and the crankshaft 2. And adaptive control units 33a and 33b that estimate the inertia and automatically adjust the speed gain. The inertia estimation is calculated based on the measurement torque command value and the speed feedback values of the pair of servomotors 7a and 7b detected when the measurement torque command is given.

Adjustment of the speed gain by the method of the present embodiment is performed as follows.
First, after the crankshaft 2 is attached to the cylindrical grinder, the position control is turned off (shut off), and a sinusoidal measurement torque having a specific frequency is added to each torque command. From the speed feedback value and the measured torque at this time, an optimum speed gain is calculated using the steepest descent method so that a predetermined response (speed band) can be obtained. Since the responsiveness is inversely proportional to the magnitude of the load inertia, it is necessary to readjust the speed gain in order to obtain a predetermined responsiveness. In the speed gain adjusting method of this embodiment, the change in the load inertia is changed. By estimating the minutes in advance, the change in inertia can be reflected in the speed gain.

The algorithm of the speed gain adjustment method using the steepest descent method is shown below.
(1) Estimation error calculation Estimated error Ve (n) = F (n) −2 × F (n−1) −F (n−2) −Md (n) × Δ (measured torque command) n
However, the frequency of the sine wave of the measured torque is the speed band.
(2) From the estimation error, control target Md = Kt × T / J2 estimation control target Md (n) = Md (n−1) + Ka × Ve (n) × Δ (measured torque command) n
However, Ka is an adaptive gain.
(3) Adjustable load inertia ratio of speed proportional gain k2 and speed integral gain k1 J2 / J1 = (Kt × T / J1) / Md
Proportional gain after adjustment = k2 x J2 / J1, integral gain after adjustment = k1 x J2 / J1
Here, initial load inertia: J1, estimated load inertia: J2, torque constant: Kt, sampling: T, speed feedback: F.

  In this way, by automatically adjusting the speed gains of the pair of servomotors 7a and 7b to be equivalent, mutual interference between the pair of servomotors 7a and 7b due to the torsion of the workpiece during acceleration / deceleration is prevented. And the occurrence of vibration can be suppressed.

  Next, a third embodiment of the control device according to the present invention will be described. As shown in FIG. 6, unlike the control device 1 of the first embodiment, the control device 40 of the present embodiment creates correction data for correcting the position command values for the pair of servo motors 7a and 7b. Learning controllers 41a and 41b are provided.

  The learning controllers 41a and 41b compensate for a filter means (not shown) for limiting the band, a memory means (not shown) for storing correction data, and phase lag and gain reduction of each servo motor 7a and 7b. And a dynamic characteristic compensation element (not shown). The memory means has a memory area corresponding to the sampling number, and stores a large number of correction data in the memory area corresponding to each sampling time.

  The old correction data stored in the memory means is read every predetermined sampling time (every process), and after being subjected to filter processing, is stored as new correction data updated in the memory means. ing. On the other hand, the old correction data read from the memory means is added to the position command value after compensation for phase delay and gain reduction. In the same manner, correction of the position deviation is repeatedly performed, so that highly accurate machining is brought about.

  As described above, the control device 40 according to the present embodiment applies the learning control independently to the pair of servo motors 7a and 7b, so that even when the workpiece rigidity is low or the machining disturbance is large, high accuracy is achieved. Rotation control can be performed.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, it can deform | transform and implement variously. For example, non-interference control is performed in the first embodiment, speed gain is automatically adjusted in the second embodiment, and learning control is performed in the third embodiment. It is also possible to perform control combining at least two of automatic gain adjustment and learning control.

It is a schematic block diagram for demonstrating 1st Embodiment of the control apparatus for machine tools which concerns on this invention. It is explanatory drawing for demonstrating the grinding state of a crankshaft. FIG. 2 is a detailed view of a non-interference controller of the machine tool control device shown in FIG. 1. It is a schematic block diagram for demonstrating 2nd Embodiment of the control apparatus for machine tools which concerns on this invention. FIG. 5 is a detailed view of a speed gain adjuster of the machine tool control device shown in FIG. 4. It is a schematic block diagram for demonstrating 3rd Embodiment of the control apparatus for machine tools which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control apparatus 7a, 7b Servo motor 10 Non-interference corrector 17 Torsional rigidity estimation block 18 Torque specification value correction block 31 Gain adjuster 41a, 41b Learning controller

Claims (4)

In a machine tool control device that controls a pair of electric motors of a tandem structure that rotationally drives a workpiece held by both ends from both sides,
A non-interference corrector for suppressing mutual interference between the pair of electric motors;
The non-interference corrector
The workpiece based on a difference value between position feedback values detected from the pair of electric motors and a torque command value for measuring torsional rigidity given to the pair of electric motors so that the workpiece is twisted. A first circuit element for estimating the torsional stiffness of
A torque command for correcting a torque command value of the pair of electric motors based on a difference value between speed feedback values detected from the pair of electric motors and the torsional rigidity estimated by the first circuit element. A second circuit element for estimating a correction value;
Machine tool control device. The first circuit element is:
A torsion torque command unit that gives the torque command value for measuring torsional rigidity to the pair of electric motors so that the workpiece is twisted;
From the torque command value given to the pair of electric motors by the torsion torque command unit, and the torsion angle of the workpiece calculated based on the difference value between the position feedback values respectively detected from the pair of electric motors A torsional rigidity estimating means for estimating a torsional rigidity value of the workpiece,
The second circuit element is:
A first arithmetic unit that integrates the differential value of the speed feedback values detected from the pair of electric motors, and then multiplies the torsional stiffness value to calculate a spring compensation component of the machine tool;
2. The second calculation unit which calculates a friction compensation component of the machine tool by multiplying a difference value between speed feedback values respectively detected from the pair of electric motors by a constant, and comprising: Machine tool control device. In order to suppress fluctuations in the rotational driving force of the pair of electric motors, a speed gain adjuster that automatically adjusts the speed gain is provided.
The speed gain adjuster, as a torque command value of the pair of electric motors, a torque command unit for giving a sinusoidal measurement torque command value of a predetermined frequency;
Adaptive control for automatically adjusting the speed gain by estimating the inertia of the workpiece from the torque command value for measurement and the speed feedback value of the pair of motors detected when the torque command for measurement is given. And
The machine tool control device according to claim 1, wherein: In a machine tool control device that simultaneously controls a pair of electric motors that rotationally drive a work held by both ends from both sides,
In order to suppress fluctuations in the rotational driving force of the pair of electric motors, a learning controller is provided that calculates a position correction value for reducing a position deviation that is a difference between the position command value and the position feedback value. The machine tool control device according to any one of claims 1 to 3.

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