JPH0628839B2 - Machine tool rotation speed controller - Google Patents

Description

The present invention relates to a rotational speed control device for a machine tool. In particular, the present invention relates to the one in which the accuracy of controlling the rotational speed of the spindle is improved in order to process the lead portion and the like formed on the cylinder of the VTR.

[Prior art]

Conventionally, the control of the rotation speed of a drive shaft of a machine tool, for example, a main shaft, detects the rotation speed of the drive shaft with a speed generator, negatively feeds back the detected voltage to a speed command voltage obtained by DA converting a speed command value, The speed of the servo motor is controlled based on the amplified voltage of the error. However, the above speed control system is excellent in speed response, but due to the offset of the DA converter, the offset or drift of the DC amplifier provided in the servo motor drive device, the non-linearity of the speed generator, etc. There was a drawback that there was an error in.

The lead of the cylinder of the VTR is inclined with respect to the axis, and this inclination needs to be processed with high precision in processing the video signal. Therefore, when cutting this lead with a numerically controlled machine tool, the feed motion of the tool and the rotary motion of the spindle must be perfectly synchronized. Therefore, the rotation speed of the spindle needs to be accurately controlled to a predetermined command speed. However, in the conventional machine tool, due to the above-mentioned drawbacks, there is a problem in accurately performing the oblique step processing on the cylindrical surface like the lead of the cylinder of the VTR.

[Problems to be Solved by the Invention]

The present invention has been made to improve the above drawbacks, and an object thereof is to control the rotational speed of a drive shaft of a machine tool with high accuracy.

[Means for solving problems]

FIG. 1 is a block diagram showing the concept of the present invention.

The present invention includes a DA converter 31 for DA converting a commanded speed,
A speed generator 35 that detects the rotation speed of a servo motor that rotationally drives the drive shaft 80, and an error between the command speed DA-converted by the DA converter 31 and the detection speed detected by the speed generator 35 is amplified. Error amplifier 33 and a drive circuit 32 for controlling the rotation of the servomotor by the cylinder of the error amplifier 33.
A pulse generator 51 that outputs a pulse signal having a frequency corresponding to the rotation speed of the drive shaft 80; and a pulse signal output from the pulse generator 51 is counted for a predetermined time to detect the rotation speed of the drive shaft 80. Speed detecting device 70, error detecting means 10a for returning an error between the rotational speed of the drive shaft 80 detected by the speed detecting device 70 and the command speed to before the machining of the workpiece, and before the machining of the workpiece. In addition, the rotation speed control device for a machine tool includes a speed correction unit 10b that corrects a command speed used when machining a workpiece according to the error obtained by the error detection unit 10a.

INDUSTRIAL APPLICABILITY The present invention is used for pre-control of the rotation speed, for example, when the drive shaft is controlled so as to have a predetermined rotation speed before the processing of the work and the processing is performed after the predetermined rotation speed is obtained. .

[Action]

According to the present invention, a normal speed control system including an error amplifier 33, a drive circuit 32, and a speed generator 35 corrects a command speed as a target value of the control system. An integral type speed detection loop is provided for measuring the rotation speed for a fixed time to obtain the rotation speed. This integral type velocity detection loop is composed of a pulse generator 51, a velocity detection device 70, an error detector 10a and a velocity correction means 10b.

That is, by counting the output of the pulse generator 51 for a predetermined time, an integrated value of the rotation speed of the drive shaft is obtained. This rotation speed is the DC offset or drift in the normal speed control system or the speed generator 35. The rotation speed deviates from the command speed due to non-linearity or the like. That is, the speed control system is D
The rotation speed when a command speed is given to an actual system affected by C offset or the like is shown.

Therefore, by detecting the error between the rotation speed from the speed detection device 70 and the command speed from the DA converter 31 before machining the workpiece, and correcting the command speed used during machining according to the error, DC It will specify the correct command speed for the actual speed control system considering the offset etc.
It becomes possible to drive the drive shaft at an ideal rotation speed.

〔Example〕

Hereinafter, the present invention will be described in more detail based on specific examples.

The main shaft 81 is a drive shaft that is a target of speed control, and is a main shaft of a machine tool. The main shaft 81 has a chuck 82,
The processed object 85 is held. The work piece 85 is a cylinder of a VTR and has an inclined lead 851. 86 is a cutting tool. The drive device 30 rotates the main shaft 81 D
C servo motor 34 and drive circuit 32 for driving it
And an error amplifier 33 that amplifies the error between the target value and the measured value.
A DA converter 31 for DA converting the command speed, and a speed generator 35 for detecting the rotation speed of the DC servo motor.
It consists of and.

As the displacement detector 50, a pulse generator 51 that outputs a pulse according to the rotational displacement is used.

The speed detection device 70 includes an addition counter 72 that counts output pulses of the pulse generator 51, and an addition counter 72.
, A subtraction counter 74 for determining the addition time, a timing control circuit 75 for giving a timing signal, and a gate circuit 7.
It consists of 1, 73.

An initial value is set to the subtraction counter 74 by the control device 10, and the pulse signal from the timing control circuit 75 driven by the start signal from the control device 10 is input through the gate circuit 73 and subtracted one by one to set the time. measure.
When the subtraction counter 74 becomes zero, the timing control circuit 75
Then, a signal is output to the gate circuit 71 and the gate circuit 71 is turned off. The addition counter 72 is reset by the timing control circuit 75 and counts the output pulse from the pulse generator 51 via the gate circuit 71. When a predetermined time has elapsed, the timing control circuit 75 outputs an interrupt signal to the control device 10. The control device 10 can read the value of the addition counter 72 and know the rotation speed of the spindle.

The control device 10 includes a CPU 14, a memory 15, a command speed setting device 16, and interfaces 17, 18, and 19. The control device 10 receives a command signal from the numerical control device 90, and when a command is given, executes a predetermined program and holds the spindle at a predetermined rotation speed with high accuracy. FIG. 3 is a flowchart showing the processing of the CPU.
The numerical control device 90 outputs a speed command signal, and the CPU 1
4 drives the drive device 30 to rotate the main shaft. When the command code M24 is transmitted from the numerical control device 90 to the CPU 14, the CPU 14 executes a program for performing the correction control of the rotational speed of the spindle, which is the object of the present invention. CPU
In step 100, 14 outputs the measurement time data to the subtraction counter 74 in order to detect the rotation speed of the spindle. In step 102, the CPU 14 outputs a start signal to the timing control circuit 75 to drive the speed detecting device 70. The operation of the speed detection device 70 is as described above. In step 104, it is detected that the interrupt signal from the timing control circuit 75, which means the end of measurement, is input, and the process proceeds to step 106. In step 106,
The actual rotation speed Sr at that time is read from the addition counter 72, and a tracking error Δ with the command speed Sc is obtained. Further, the command speed Sc is corrected using the tracking error Δ to obtain a new corrected command speed Sa. Next, in step 108, the correction command speed Sa is output to the DA converter 31 of the drive device 30, and D
The speed of the C servo motor 34 is corrected and controlled. As a result, the rotation speed of the main spindle specifies the command speed for the actual speed control system in consideration of the DC offset and the like. Next, at step 110, the speed correction end signal MFIN is transmitted to the numerical controller 90, and a series of speed correction processing is performed.

In this way, the spindle is held at the desired command speed Sc with high precision before machining. After this, the cutting tool 86 is moved,
Processing is performed. The speed control of the spindle during this machining is controlled by the drive device 30 so as to be a constant speed Sc based on the correction command speed Sa.

Next, at the end of machining, as shown in FIG. 4, the numerical control device 90 transmits a speed correction cancellation command code M25, and C
In step 200, the PU 14 sets the command speed to the initial command speed Sc and cancels the speed correction. Then step 20
In step 2, the MFIN signal indicating the end of the process is output to the numerical controller 90.

In the above-described embodiment, the speed correction is realized by one-time processing of steps 102 to 108, but by repeating this processing a plurality of times until the tracking error Δ becomes zero in step 106, the speed correction with higher accuracy is achieved. Can be done.

〔The invention's effect〕

The device of the present invention is provided with an ordinary speed control system having high responsiveness, and an integral type speed detection loop for correcting the command speed based on the rotation speed obtained by counting the number of rotations for a certain period of time. Since the error is detected before machining and the command speed used during machining is corrected, the command speed is corrected to the command speed considering the influence of the DC offset or drift in the normal speed control system, The rotation speed of the drive shaft can be accurately controlled to perform high-precision machining.

Further, since the command speed to the normal speed control system having high responsiveness is input while being corrected, the convergence operation of the speed control system is also performed in a short time, and machining can be performed in a short time.

[Brief description of drawings]

FIG. 1 is a block diagram showing the concept of the present invention, FIG. 2 is a block diagram showing the configuration of a rotation speed control device according to a specific embodiment of the present invention, and FIG.
FIG. 4 and FIG. 4 are flowcharts showing the processing of the computer used in the apparatus. 81 ... Spindle 85 ... Workpiece 86 ... Cutting tool 34 ... DC servo motor 51 ... Pulse generator 35 ... Speed generator

Claims (1)

[Claims] 1. A rotation speed control device for a machine tool, wherein a drive shaft of a machine tool is rotationally controlled by a servo motor at a commanded rotation speed, and a DA converter for converting a command speed into a DA converter and a rotation speed of the servo motor. A speed generator for detecting, an error amplifier for amplifying an error between the command speed DA-converted by the DA converter and the detected speed detected by the speed generator, and rotation control of the servomotor by the output of the error amplifier. A drive circuit, a pulse generator that outputs a pulse signal having a frequency according to the rotational speed of the drive shaft, and a speed that detects the rotational speed of the drive shaft by counting a pulse signal output from the pulse generator for a predetermined time. A detection means, and the rotation speed of the drive shaft detected by the speed detection means and the command speed An error detecting means for obtaining the difference before machining the workpiece and a speed correcting means for correcting the command speed used during machining of the workpiece according to the error obtained by the error detecting means before machining the workpiece. A rotation speed control device for a machine tool having