JPS63103686A - Controlling method foe spindle - Google Patents

Abstract

PURPOSE:To synchronize motors with each other and accelerate them with maximum power, by shifting the acceleration starting time points of a spindle motor and a Z-axis motor from each other, and by setting the acceleration or deceleration characteristic of the spindle motor to be a straight-line-formed characteristic up to a constant speed. CONSTITUTION:A spindle motor 13 driven by speed signal directed through a numerical controller 16, and a Z-axis motor 22 driving a table 1 on which processed substance is mounted, are arranged. The starting time lag of the spindle motor 13 and the Z-axis motor 22 is set, and the motors are synchronized with each other. By controlling acceleration or deceleration between the rotation al frequency 0 and the maximum-torque-obtainable rotational frequency of the spindle motor 13, with a straight-line-formed characteristic, the spindle motor 13 is accelerated with maximum power.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a spindle control method that reduces acceleration and deceleration operation time.

(Prior art) Machining centers that can perform milling using contour control, drilling and tapping using various fixed cycles have been developed and are now being used in many factories.

Tapping operation using this machining center involves attaching the tap directly to the spindle, then operating the Z-axis feed motor to bring the tip of the tap close to the entrance of the hole drilled in the workpiece material, and rotating the spindle while rotating the Z-axis. The feed motor continues to operate to cut the tap into the hole to cut a thread on the inner surface of the hole. When the thread has been cut to a predetermined length, the spindle is rotated in the opposite direction, and the Z-axis feed motor is also rotated in the reverse direction to remove the tap, thereby performing so-called rigid tapping.

When performing tapping processing, as shown in Figure 2,
The speed at which the table 1 pushes up the workpiece 2 during tapping operation and lowers the workpiece 2 when cutting is completed, that is, the feed rate in the Z-axis direction, is f m [mm/m E
nl , the rotational speed of the main shaft, that is, the rotational speed of the tap 3, is Ns [rpm], and the pitch of the screw 4 is P, then between these, t m = N s 11 p

- If the relationship (1) is always obtained, the tap 3 will push forward into the hole 5 while cutting the thread without expanding or contracting.
Even when the tap 3 is reversed, it is similarly pulled out without expanding or contracting. When performing the tapping operation,
First, from the depth dt and pitch P of the tap, calculate the number of rotations N for tap 3 from the time it starts cutting until it ends [N
= (dt/P)], and the total cutting length is calculated by the following formula.

π X d By the way, the cutting speed when tapping a normal stop hole is 8 m/min or less, and the cutting speed when the material to be cut is a light metal and the tap is made of carbide is 25 m/min or less. Then, the cutting time T is obtained from the following equation (3) using this cutting speed.

T = sentence / V e ... (3
), substitute equation (2) into the statement of equation (3), and get N/T=N
Substituting equation (3) into T of s, NS is obtained by the following equation.

Ns= [Ve/ (π・d)] −(4) After obtaining the rotational speed Ns of the tap in this way, (1)
According to the formula, the tapping operation is performed by synchronizing the feed rate fm in the Z-axis direction with the rotational speed Ns.

FIG. 3 is a block diagram of the spindle control device of the present invention for relating the feed rate fm in the Z-axis direction and the rotational speed Ns by the above equation (1) when performing a tapping operation. An output shaft 14 of the motor 13 is connected via a coupling device 11 to a main shaft (spindle) 10 having a tap 3 attached to its tip, and the position of the tap 3 is detected by a position coder 12. In addition, the table 1 is driven by an AC motor 2 for driving the table.
2 and is driven in the Z-axis direction at a feed rate fm.

The NC control device 16 outputs a speed command signal for the AC spindle motor and a synchronization command signal for the AC spindle motor and table drive motor 22, which will be described later. When the switching device 18 connects the contact to the ■ side, the switching device 18 sets the position control mode for the AC spindle motor,
When the contact is connected to the VC side, the speed control mode is set.

The spindle servo circuit is composed of a digital circuit and vector-controls the AC spindle motor. A signal from a pulse coder 23 attached to the table driving AC motor 22 is fed back to the Z-axis position control circuit 20 and the Z-axis servo circuit 21.

Next, the operation of this control device will be explained.

When the contact of the switching device 18 is connected to the ■ side to set the spindle position control mode, the NC device 216 operates according to the program written on the paper tape 15 and sends a position control command to the spindle position control circuit 17.

A detection signal from a position coder 12 that detects the position of the spindle 10 is input to the spindle position control circuit 17, and a deviation signal between the two is provided to a spindle servo circuit 19. The AC spindle motor 13 is digitally controlled by an output signal from a spindle servo circuit 19. on the other hand,
The output signal from the NC control device 16 is sent to the Z-axis position control circuit 20, and the Z-axis position control circuit 20 includes a pulse coder 23 that detects the position of the AC motor 22 for driving the table.
The output signal from the NC control device 16 is compared with the command signal from the NC control device 16, and an error signal is applied to the Z-axis servo circuit 21. The table driving AC motor 22 is connected to the Z-axis servo circuit 2
It is digitally controlled by the output signal from 1.

Note that the AC spindle motor and the table driving AC motor are vector-controlled by a digital servo circuit, so that highly accurate control can be performed.

(Problems to be Solved by the Invention) In such tapping processing, the torque-rotational speed characteristic of the spindle motor is as shown in FIG. 4. In the figure, the horizontal axis represents the rotational speed N, and the vertical axis represents the torque T, where Nb is the rotational speed at which the maximum torque Tm is obtained.

In tapping processing, the spindle has inertia added to it, so it moves slower than the Z-axis. Therefore, in order to control acceleration with maximum power and achieve a rapid stop during deceleration, the spindle is moved as shown in Figure 5. Acceleration and deceleration characteristics are given to the spindle servo circuit as speed commands from the NC control device. Here, the rotation speed Nb at which the maximum torque Tm is obtained
During the acceleration period from time O to tl, the acceleration is linear, and thereafter the speed increase up to the maximum rotation speed is performed according to the characteristic of an exponential function.When decelerating, the characteristic of an exponential function is performed from the maximum rotation speed to the rotation speed Nb. The speed is linearly reduced from time t2 when the rotational speed Nb is obtained to time t5 when the rotational speed reaches zero.

By the way, when controlling the spindle motor and the Z-axis motor in conjunction with the acceleration/deceleration characteristics as shown in FIG. 1(a), the time t. When the spindle motor is driven with the characteristics shown in Fig. 5 so that acceleration starts at time tc, the speed increases to the maximum rotation speed Nm, deceleration starts at time tc, and the rotation speed reaches zero at time te, the shaded area A and B do not match, and the spindle motor and Z
There was a problem that synchronous control with the shaft motor could not be performed.

Therefore, the present invention aims to solve the problems of the prior art and provides a spindle control method that accelerates the spindle motor with maximum power while synchronizing the spindle motor and the Z-axis motor. be.

(Means for solving the problem) The spindle control method of the present invention includes a spindle motor driven by a speed signal commanded from a numerical control device;
In a spindle control method that includes a Z-axis motor that drives a table on which a workpiece is placed and drives both motors in synchronization, the spindle motor has a rotational speed (N b) at which maximum torque is obtained. The acceleration/deceleration between the speed and the speed zero is controlled by a linear characteristic, and the acceleration/deceleration between the rotational speed N and the maximum rotational speed is controlled by an exponential characteristic. This method is characterized by performing synchronization by delaying the time point.

(Function) In the present invention, when controlling the spindle motor and the Z-axis motor synchronously, the spindle motor has a linear characteristic between the rotation speed (Nt) at which the maximum torque is obtained and the speed of zero. Furthermore, between the rotational speed N and the maximum rotational speed, acceleration and deceleration are performed with an exponential characteristic, and since the acceleration start point of the spindle motor and Z-axis motor is delayed, both motors can be synchronized. Spindle motors can accelerate at maximum power and reduce operating time.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. First, an overview of the CNC two-axis simultaneous control device used in the present invention will be explained. FIG. 3 is a schematic block diagram of such a control device.

This control system includes a host computer A that sets position parameters and speed parameters for two-wheel servo motors M on the X-axis and Y-axis, and a positioning control algorithm (a) and a deviation counter algorithm (b). CPUB, servo amplifier, pulse width modulation (PW
Next, the operation of this system, which has a servo driver block C consisting of a driver and a servo driver block C as a main component, will be explained. Host computer A has X-axis, Y-axis
The amount of movement of each load on each axis is set, and the CPU decomposes each of the X-axis and Y-axis into speed patterns using a positioning control algorithm. The weighting function of the pulses decomposed into the speed pattern is sent to the deviation counter in parallel (or serially) every cycle time Tsec, and is compared with the contents of the movement amount counter to which the pulse encoder output is input.
Forms the deviation counter output. This deviation counter output is sent to the servo driver block C, and for each TSeC, the servo side repeats the operation according to the contents of the counter, that is, according to the set speed (acceleration/deceleration) pattern, and when the target value is reached. Stop operation.

In the figure, DA is a DA converter that converts a digital signal into an analog value, CT is a current transformer that detects the current of the servo motor, and the detected current forms a minor loop of current control. TG is a speed detector, and PC is a pulse encoder, each of which detects a speed signal and a position signal.

The rigid tapping process according to the present invention performs two-axis control of the main axis (spindle) and two axes using a CNC two-axis simultaneous control device as shown in FIG. It is based on doing.

(1) In a machining center, the maximum rotational speed (No Wa
Find x).

(2) The value obtained by dividing the maximum rotation speed by a predetermined constant is calculated as the highest position gain that can be obtained for that main axis. 1
/5ec).

(3) Set the position gain of the two axes to the same value as the position gain of the main axis.

(4) In order to determine the time constants of the main shaft and the two axes, calculate the shortest time that can be accelerated and decelerated with the inertia of the main shaft from the maximum rotational speed used. In this example, T act4
= 113 rasec, a margin is taken from this value and Ta=150 tasec is set as the actual time constant.

(5) Accelerate and decelerate the servo motor using this time constant.

In the present invention, the spindle motor is controlled by the characteristics set as described above, and is shown in FIG.
In a), the startup time of the spindle motor and the two-axis drive motor is delayed from the conventional ta to tb, and the diagonal line A
Control is performed so that the area of B (the area surrounded by the time from ta to td and the rotational speed O to Nm) and B are equal.

That is, the acceleration of the spindle motor from rotational speed O to Nb increases linearly from time tb to tc, and increases exponentially from rotational speed Nb to maximum rotational speed Nm from time tC to td. During deceleration, between times te and tf from the maximum rotational speed Nm to the rotational speed Nb,
Controlled by exponential characteristics. Further, between times tf and tg from one rotational speed Nb to one rotational speed, control is performed using a linear characteristic.

The acceleration/deceleration control of the spindle motor during tapping processing has the characteristics shown in Fig. 1(b), and is expressed as a solid line.
Since the response is faster than the response during other normal machining, where the response is as shown by the broken line, the characteristics are set so that the excitation is strengthened in advance by an external signal so that there is no delay in excitation.

Although one embodiment of the present invention has been described above, various different embodiments can be easily constructed without departing from the spirit of the present invention. The present invention is not limited to the embodiments.

(Effects of the Invention) As described above, according to the present invention, the spindle motor and the two-axis motor are accelerated by delaying their acceleration start points, and the acceleration and deceleration characteristics of the spindle motor are controlled in a straight line up to a constant speed. Since both the linear characteristic and the exponential characteristic are used, the spindle motor can be accelerated with maximum power while synchronizing the spindle motor and the two-axis motor.

[Brief explanation of the drawing]

Figures 1 (&) and (b) are characteristic diagrams of the present invention, Figure 2 is an explanatory diagram of tapping processing, Figure 3 is a circuit diagram, Figures 4 and 5 are characteristic diagrams of the spindle motor, and Figure 6 is a characteristic diagram of the spindle motor. The figure is a schematic block diagram of a CNC simultaneous two-axis control device. DESCRIPTION OF SYMBOLS 1...Table, 2...Workpiece, 3...Tap, 4...Screw, 10...Main shaft, 13...Spindle motor, 22...Table drive motor. Patent applicant: Fanuc Co., Ltd. Representative: Patent attorney Minoru Tsuji Figure 1 (b) Figure 2

Claims (1)

[Claims] Equipped with a spindle motor driven by a speed signal commanded by a numerical control (NC) device and a Z-axis motor that drives the table on which the workpiece is placed, both motors are driven in synchronization. In the spindle control method,
The spindle motor has a rotational speed (N
b) The acceleration/deceleration between Nb and the speed zero is controlled by a linear characteristic, and the acceleration/deceleration between the rotation speed Nb and the maximum rotation speed is controlled by an exponential characteristic, and the acceleration of both motors is controlled by an exponential characteristic. A spindle control method characterized by performing synchronization by delaying the start point.