JPS62224519A - Rigid tapping control system - Google Patents

Abstract

PURPOSE:To enable a high precision tapping process and complex machining by providing a spindle motor position control means and a control changeover means in a machine tool using a digital spindle motor. CONSTITUTION:In a tapping process, control is changed over to feed back control according to the changeover instruction 'CS' of changeover means 7 and 8. And depending upon a specified pitch amount, speed instructions 'VS' and 'VZ' are inputted to a position control means 4 and the position control part 12a of a servo circuit 12 as distribution pulses 'PS' and 'PZ' via an interpolation circuit 3a. Also, the position control means 4 makes speed control for a spindle motor 1 via a digital circuit 5 and a power circuit 6 on a difference from a feedback pulse 'FS' from a pulse coder 'PC1'. Also, the servo circuit 12 controls a servo motor 2 similarly on the basis of a feedback pulse 'FZ' for the synchronization thereof and the tapping process to a specified pitch. In the case of complex machining, the changeover means 7 and 8 cut feedback pulses and a numerical control part 3 makes speed control.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tapping control system for a multi-machine machine tool that is capable of high-precision tapping and heavy cutting.

Conventional technology Various tools such as tapping tools and cutters are replaceably mounted on a tool holder, and the tool connected to the drive shaft via the tool holder is rotated by a spindle motor, and at the same time, a shaft feed motor is applied to the workpiece. A multi-machine type machine tool that performs various types of machining by relatively moving the machine is known.

However, the main shaft motor is not normally subjected to position control, but only speed control. Therefore, in the case of tapping processing, since the rotational position of the spindle, that is, the rotational position of the tool, and the axial position of the tool are related to each other, it is necessary to establish some kind of correlation.

Therefore, in order to perform high-viscosity thread cutting and gear cutting, a technique is conventionally known in which the rotation of a tool and the feed of the tool relative to a workpiece are driven in synchronization. for example,
The spindle motor for tool rotation is rotated at a predetermined command speed, and the rotation of the tool feed motor is controlled in accordance with a pulse train generated from a pulse coder attached to the rotation motor, so that both motors rotate in synchronization with each other. .

However, this type of synchronous control gives a speed command to each motor, in other words, uses a speed control loop as a control loop, and has a weak restoring force against speed fluctuations, and the rotational speed of the rotating motor changes with load fluctuations. This has the drawback that the rotational speed of the rotation motor tends to change easily, and as a result, the synchronization of both motors becomes inaccurate and machining accuracy deteriorates.

Furthermore, it is possible to control the rotation of a rotation drive machine that relatively rotates a workpiece and a processing tool based on the feed slip caused by a feed drive machine that moves the workpiece and a screw tool relative to each other. No. 60-155319.

However, this machine is dedicated to thread machining, and although it is capable of high-precision thread machining, it cannot perform any machining other than thread machining.

It uses a servo motor that cannot rotate at high speeds without using a spindle motor for the main shaft motor, and even if it is modified to be able to attach various processing tools, it cannot actually perform heavy cutting processes that place a large load on the processing tools. do not have.

Problems to be Solved by the Invention The present invention solves the above-mentioned problems in a multi-machine machine tool in which various tools are replaceably mounted.
It is an object of the present invention to provide a control system that allows heavy cutting such as milling to be performed in this type of machine tool, as well as high-precision tapping.

Means for Solving the Problems The present invention provides a control method for a machine tool using a digital spindle motor controlled by a digital control circuit as the main spindle motor. A position control means for feedback controlling the position of the spindle motor based on a feedback signal from an output pulse coder and outputting a speed command to the digital circuit, and a switching means for switching from oven control to feedback control are provided. , the switching means is switched to the feedback control position, and the control circuit of the spindle motor and the servo circuit of the servo motor for moving the tool in the axial direction are linearly interpolated and pulse distributed by an interpolation circuit according to the pitch amount of the screw to be machined. However, the above problem was solved by driving the spindle motor and servo motor in synchronization.

Function: When performing heavy cutting with the above machine tool, the above switching means is switched to the oven control side, a speed command is given to the above digital control circuit, the above spindle motor is driven at high speed and large torque, and the same operation as normal is performed. Perform heavy cutting work. on the other hand,
During tapping processing, the switching means is switched so that the position of the spindle motor is also feedback-controlled, and the interpolation circuit connects the control circuit of the spindle motor and the servo circuit of the servo motor that feeds the tool in the axial direction to the screw to be machined. By outputting linearly interpolated pulses according to the pitch of the tap and driving the spindle motor and servo motor in synchronization, tapping is performed by driving the rotation of the tap and feeding in the axial direction in synchronization.

Embodiment FIG. 1 shows a control block diagram of a multi-faceted machine tool to which a control method according to an embodiment of the present invention is applied, and the machine tool operates in various machining modes including tapping mode and heavy cutting mode. 1 is an AC digital spindle motor as a spindle motor for rotating the tool, and 2 is an AC servo motor for tool feeding. The feed motor 2
The machine is designed to drive the workpiece in the processing direction. The spindle motor 1 is capable of rotating at high speed in order to overcome the large load during heavy cutting, such as milling, and the tool holder is equipped with a plurality of tools, such as a tapping tool and a milling cutter (both not shown). For example, it is installed so as to be replaceable by an automatic tool changer, and is also designed to non-extendably hold a tapping tool for tapping.

3 is a numerical control unit, 3a is an interpolation circuit provided in the numerical control unit 3, PCl is a pulse width modulator that generates a feedback pulse FS every time the spindle motor 1 rotates by a predetermined angle, and 4 is generated from the interpolation circuit 3a. It is a position control means that outputs the difference between the distribution pulse Ps and the feedback pulse l"s from the pulse width modulation PC1 as a speed command value, and is composed of an error register. 7 and 8 are switching commands from the numerical control section 3. When performing feedback control of the spindle motor 1 during tapping processing, etc. using the switching means C8, the switching means 7 sends the output of the position control means 4 to the digital control circuit 5, and the switching means 8 sends the feedback pulse l'' s is input to the position control means 4, and when feedback control is not performed, the switching means 7 inputs the speed command SV from the numerical control section 3 to the spindle motor 1 to the digital control circuit 5. Switch to

Further, the switching means 7 cuts off input of the feedback pulse Fs to the position control means 4. The digital control circuit 5 has a speed control section 5a, a current control section 5b, and a PWM (pulse width modulation) control section 5c. PC1
The current controller 5b receives this torque command and controls the spindle motor 1 based on the current drive current from the current detectors 9 and 10. A command current to each phase is outputted, pulse width modulation is performed in the PWM III m section 5C, and the power circuit 6 is driven to drive the spindle motor 1 at the command speed.

This digital control circuit 5 is already known (for example, Japanese Patent Application No. 60-36051), and a comparison between the case of driving with this digital control circuit 5 and the case of driving a spindle motor using the conventional method is shown in Fig. 2. As shown in (A), in the conventional driving method, there is a considerable delay in the spindle motor following the speed command S■;
As shown in (b), the spindle motor controlled by the digital control circuit 5 follows accurately with almost no delay.

On the other hand, as is conventionally known, the servo circuit 12 detects the difference between the distribution pulse Pz from the interpolation circuit 3a and the feedback pulse Fz from the pulse width modulation PC2 with an error register in the position control section 12a, and registers the difference in this error register. The output is converted into an analog signal speed command by a D/A converter and outputted, and the difference from the actual speed from the F/V converter 12c is amplified by the speed control section 12b and a torque command is output, which controls the current. The section 12a outputs a drive current command to each phase according to the torque command from the speed control section 12b and the actual drive current value from the current detector 14.15 that detects the drive current of the servo motor 2, and outputs a drive current command to each phase. Upon receiving the current command, the PWM I control section 12e performs pulse width modulation, drives the power circuit 13, and drives the AC servo motor 2. Note that 11.16 is a three-phase power supply.

The operation of the control section of the multi-machine machine tool configured as described above will be explained.

When the tapping command is decoded from the machining program, the tapping tool is attached to the tool holder by an automatic tool changer (not shown), and the switching means 7.8 is switched to the feedback control position by the switching command C8, and the tapping tool is switched to the feedback control position specified in the machining program. Speed commands vs, vz to the spindle motor 1 and servo motor according to the pitch amount are input to the interpolation circuit 3a, and the interpolation circuit 3a outputs linearly interpolated distribution pulses PS, PZ, and the position control means 4 and The signal is input to the position control section 12a of the servo circuit 12.

In other words, if P is the pitch, which is the distance between threads to be machined, in machining a single thread, the tap advances by iP in the axial direction while the spindle motor 1 of the main shaft rotates once (while the tap rotates once). Therefore, for each revolution of spindle motor 1, servo motor 2
Pulse distribution PS and PZ will be performed so as to advance by P in the axial direction.

In the position control means 4, the distribution pulse PS and the pulse coder PC
The difference from the feedback pulse Fs from 1 is output as a speed command to the digital circuit 5, and the digital circuit 5 performs speed control to drive the spindle motor 1 at the command speed via the power circuit 6. 12 also performs position control and speed control based on the distribution pulse PZ and the feedback pulse FZ from the pulse coder PC2, and drives the servo motor 2 via the power circuit 13.

As a result, the spindle motor 1 and the servo motor 2 are synchronized to perform tapping at the commanded pitch.

On the other hand, when a heavy cutting command, such as a milling command, is input from the Canadian program, after the milling tool is mounted on the tool holder, the numerical control unit 3 issues a switching command C.
8 is output, the switching means 7.8 is switched, the input of the feedback pulse FS from the pulse coder PC1 to the position control circuit 4 is stopped, and the switching means 7 causes the speed command S from the numerical control section 3 to be transferred to the digital control circuit. 5. As a result, the spindle motor 1 receives the speed command SV
Rotation is started at a speed corresponding to the speed, that is, at a high speed, and heavy cutting processing such as milling is performed.

Effects of the Invention As described above, according to the present invention, in the tapping mode, the interpolation circuit that performs linear interpolation based on the pitch command value read from the cutting program is connected to the digital spindle motor as the spindle motor for rotating the tool and the tool feed. Since the motor is rotated in synchronization with the motor, tapping can be performed accurately without using a 70-ting boulder as a tool holder. In addition, in the -blade cutting mode, the position control loop for the spindle motor is canceled and the spindle motor is rotated at high speed, so in the tapping mode, precise rigid tapping can be performed, and in the heavy cutting mode, it can overcome the load and ensure reliability. Heavy cutting can be performed. In particular, by using a digitally controlled digital spindle motor for the spindle motor, the spindle follows commands without delay, and also enables large torque and high-speed rotation, making it possible to perform tapping and heavy cutting.

[Brief explanation of drawings]

FIG. 1 is a control block diagram of an embodiment of the present invention, and FIG. 2 (
A) is a diagram showing the characteristics of a conventional spindle motor, and FIG. 2(B) is a diagram showing the characteristics of a digital spindle motor. 1...AC digital spindle motor, 2...AC
Servo motor, 3... Numerical control unit, 3a... Interpolation circuit, 4... Position control means, 5... Digital control circuit, 7.8... Switching means, 12... Servo circuit.

Claims (1)

[Claims] In a machine tool control system using a digital spindle motor controlled by a digital control circuit as the main spindle motor, the control circuit of the digital spindle motor is controlled based on a feedback signal from a pulse coder that is output in accordance with the rotation of the spindle motor. A position control means for feedback controlling the position of the spindle motor and outputting a speed command to the digital circuit, and a switching means for switching from open control to feedback control, and during tapping processing, the switching means is switched to the feedback control position, and the above-mentioned The control circuit of the spindle motor and the servo circuit of the servo motor that moves the tool in the axial direction are linearly interpolated by an interpolation circuit according to the pitch of the screw to be machined, and pulses are distributed to drive the spindle motor and servo motor in synchronization. Rigid tapping control method.