JPS6374551A - Control method for machining speed of machine tool - Google Patents

Abstract

PURPOSE:To set a position deviation automatically decreasing to an assigned amount or less, by automatically calculating a speed and a period, in which the theoretical position deviation, generated in a connecting part with the block halfway or the next block, is decreased to a preset position deviation amount or less, and performing machining prior to the assigned machining speed. CONSTITUTION:From a microcomputer 1, a speed condition arithmetic part 2 accepts the information of this time block and the next time block, while a pulse distributor 3 accepts a moving amount of this time block and its speed. And the speed condition arithmetic part 2, to which a permissible position deviation amount is previously given, calculates a speed limit and its distance in a certain section after a block start to be transmitted to the pulse distributor 3, performing a speed control. Accordingly, if only the permissible position deviation amount is previously set in the speed condition arithmetic part 2, a speed reduction process is performed so as to suppress an error decreasing to a fixed amount or loss automatically prior to the assigned machining speed, and a machining shape can be ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a machining speed control method for a machine tool configured with two or more axes.

[Conventional technology]

The servo system of a machine tool usually has an acceleration/deceleration pattern in speed to avoid shock to the machine when giving a movement command, and the servo system has a so-called exponential function type or linear type (trapezoidal type) increase/decrease curve. use When converting a series of blocks described by an additive ezrogram into mechanical operations one after another, in order to smooth the connections between blocks, the start point of pulse distribution for the next block should be the point at which the pulse distribution of the previous block is completed. is normal. A special function is an exact stop function that advances the next block after the previous block has completely reached the target point, but especially in the case of an exponential function type, the time from the completion of pulse distribution to the in-position is long. Therefore, it is only used when you want to increase accuracy even at the expense of cycle time. If the next block is started while the previous block is not completely finished, the phenomena of so-called uncut parts and over-cut will become noticeable if the directions of both blocks change drastically.

Furthermore, since there are various delay elements in the servo system, there is a follow-up delay that cannot be eliminated even if feedback control is performed, and this causes a positional deviation with respect to the command trajectory.

For example, in Figure 1, if you instruct the machine to move from point A to point B at a speed of ■, and then from point B to point 0 at a speed of V, the actual path the machine follows will be as shown by the dashed line. The shaded area is the position deviation. The line segment connecting points B and P becomes the maximum amount of deviation, and this amount is determined by the angle θ and the speed v
1, ■2, etc. are known to be affected. Further, as shown in FIG. 2, in the case of circular interpolation, there is a constant positional deviation ε except near the starting point or the ending point E, and this amount is influenced by the radius and speed.

[Problem that the invention seeks to solve]

In other words, in the conventional method, there is always a positional deviation due to accumulated pulses at the block joints or a positional deviation due to delay elements of the servo system, and in order to move the machine accurately according to the command trajectory, the operator has to make appropriate adjustments based on the operator's judgment. Methods such as reducing the speed, setting a low speed in the machining program, and issuing an exact stop command have been used, but all of them have problems such as lengthening cycle time or not being able to quantitatively guarantee errors.

The present invention has been made in view of the above points, and an object of the present invention is to provide a machining speed control method for a machine tool that can automatically reduce the positional deviation to a specified amount or less.

[Child actor to solve problems]

Set the allowable positional deviation amount in advance, and before executing the block information, check the speed and speed at which the theoretical positional deviation that occurs in the middle of the block or at the connection with the next block can be reduced to below the set positional deviation amount. The period during which this speed is continued is automatically calculated, and machining is performed using a calculated speed that guarantees trajectory accuracy, giving priority to the machining speed specified in the machining program.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 3 and 4. In FIG. 3, 1 is a microcomputer that is the core of the Nc device, 2 is a speed condition calculation section, 3 is a pulse distributor, 4 is a deviation counter, 5 is a digital-to-analog (D/A) converter, and 6 is a Servo amplifier, 7 is a drive motor, 8 is a speed detector, 9 is a position detector, 20 is block information that is the source information for calculating the theoretical position deviation,
21 is position/speed information, 22 is a command pulse, 23 is a deviation signal, 24 is a speed command signal, 25 is a motor, drive signal,
26 is a speed feedback signal, and 27 is a position feedback signal (pulse).

Although FIG. 3 shows an example of one axis of the servo system, in reality there are only 10 microcomputer sections other than the number of axes of the machine.

A method of implementing the present invention with the above configuration will be explained. From the microcomputer 1, the speed condition calculation section 2
The current block and next block information are received, and the pulse distributor 3 also receives the movement amount and speed of the current block. The pulse distributor 3 uses a predetermined acceleration/deceleration pattern (
A dense command pulse train signal 22 is generated according to a time constant (exponential function type, linear type, etc.) and is applied to the deviation counter 4. The deviation counter 4 counts up or down the command pulse train and the position feedback pulse train, and passes the position deviation amount (droop amount) 23 to the D/A converter 5. The deviation amount converted into an analog amount, that is, the speed command signal 24, is transmitted to the servo amplifier 6, where it is amplified and becomes the motor drive signal 2.
5 causes the motor 7 to operate. The rotational speed of the motor is detected by the speed detector 8 as a speed feedback signal, which is fed back to the servo amplifier 6 and controlled to a specified speed. Similarly, a position feedback signal 27 from the position detector 9 is fed back to the deviation counter 4 to form a position control loop.

Here, the speed condition calculating section 2 operates as follows. Generally, the positional deviation amount (line segment BP) ε1 shown in FIG. 1 and the steady error ε2 shown in FIG. 2 can be determined as follows.

1, = / (θ, ”r, Vt, T+,
Tt )−・−−・−・(1)ε! =/(R,V,T
,,T, ) ・・・・・・・・・・・・・・・・・・
(2) Here, R is the radius of the circle, T8 is the acceleration/deceleration time constant, and T2 is the time constant of the mechanical system including the motor. The values of each of these parameters change for each machine or for each block command, but if ε and ε2 are given in advance as allowable position deviation amounts, then 3 or V in equation (2) can be found. (1) It is not necessary; the speed can be limited only in a certain section after the block start, and then the speed can be adjusted to the original designated speed V (the speed limit distance mentioned above can also be calculated).

In this way, the “limit speed,
J and the "speed limit distance" are transmitted to the pulse distributor 3, and speed control is performed as shown in fbl in FIG. By the way, in Figure 4 (al indicates the speed command of the block connecting part in the conventional method, whereas (bl) moves at a limited speed to keep the positional deviation within the desired range for a certain limited distance. It is shown that.

In the case shown in FIG. 2, speed control is performed to maintain the speed limit throughout the entire section of one block. Therefore, the pulse distributor 3 distributes pulses according to the above-mentioned limiting conditions from the speed condition calculating section 2, and otherwise performs pulse distribution as known in the art. do.

〔Effect of the invention〕

According to the present invention, if only the allowable positional deviation amount is set in advance, speed reduction processing is automatically performed to give priority to the specified machining speed and keep the error below a certain amount.
This method can be used without sacrificing cycle time like an exact stop, or without specifying an unnecessarily low speed over the entire block in the machining program information and causing the same bad results (guaranteeing the machining shape). It will be possible.

Therefore, according to the present invention, it is possible to provide a machining speed control method for a machine tool that obtains a machine trajectory that faithfully follows a specified trajectory within an allowable range, and provides excellent effects.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a trajectory error that occurs at a connecting part of blocks in the conventional method, FIG. 2 is an explanatory diagram showing a trajectory error in a circular interpolation block, and FIG. 3 is a block diagram showing an embodiment of the present invention. FIG. 4 is a diagram illustrating a speed reduction method. In the figure, 1... Microcomputer, 2... Speed condition calculation section, 3... Pulse distributor, 4... Deviation counter, 5... D/A converter, 6... Servo amplifier ,7
... Cervical motor, 8... Speed detector, 9... Position detector.

Claims (1)

[Claims] The permissible positional deviation for the commanded trajectory is set in advance, and the speed command value specified in the machining program is adjusted so that the positional deviation in the middle of one block or the positional deviation at the joint of blocks does not exceed the permissible range. A machining speed control method for a machine tool, characterized in that an optimum machining speed is automatically determined as a priority, and machining is performed at that speed.