JPS6012165B2 - Reverse control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a backward control method for reversing the direction of relative motion between an electrode and a workpiece in an electrical discharge machine, and particularly to a backward control method when the electrode comes into contact with the workpiece.

Electric discharge machines that use wires as discharge electrodes are capable of machining complex shapes with high precision, and are superior in that they produce no noise during machining. Incidentally, an electric discharge machine applies a high voltage between a wire and a workpiece to generate an electric discharge between them, and moves either the wire or the workpiece to obtain a desired shape by destruction of the wire and the workpiece. Once a short circuit occurs, processing can no longer be performed.

Therefore, once a short circuit occurs, it becomes necessary to retreat the electrode or workpiece.

In this case, since a high voltage is always applied to the machining electrode, if the machining electrode or the workpiece is retreated following a trajectory different from the trajectory during machining, cutting will be performed even during the retreat, resulting in a decrease in machining accuracy. For this reason, it is necessary for the backward control to move backward by following the trajectory during machining. When a short circuit occurs between an electrode and a workpiece, the present invention promptly releases the short circuit state by retracting the machining electrode or workpiece along the trajectory during machining, and achieves highly accurate electric discharge machining. In the present invention, this purpose is given as command information in the numerical control device of the electric discharge machine that controls the relative motion between the machining electrode and the workpiece machined by the machining electrode. A means for dividing or approximating the command shape into a large number of minute straight lines, distributing pulses for the relative movement based on the numerical data of each axis component of each minute straight line, and storing numerical data of each axis component of the minute straight lines. Let it be remembered,
If a short circuit occurs between the machining electrode and the workpiece, pulse distribution is performed again based on the numerical data of each axis component of the minute straight line stored in the storage means, and relative movement between the machining electrode and the workpiece is performed. This is achieved by reversing the direction. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram of a numerical control device according to the present invention, FIG. 2 is a diagram for explaining pulse distribution, and FIG. 3 is a diagram for explaining backward control.

In FIG. 1, 1 is a tape perforated with command information, 2 is a tape reader, 3 is a processing unit (CPU), and 4 and 4' are known pulse distributors, such as DDA (Digital Digital
merentiaI AM1yzer Interpo
ra's r) Okema device, 5 is a memory that stores the X and Y axis components of minute straight lines, 6 is a monitor that detects short circuits between the workpiece and the electrode, 7 and 7' are ×, and Y servo motors such as pulse motors. -It's evening.

When the processing information is read from the tape reader 2, the CPU 3 decodes and calculates the information according to a control program given in advance, and converts the command straight line or command arc into minute segments as shown in Fig. 2 a and b. At the same time, the axis components Δx and Δy of each segment are calculated.

The minutely divided segment components Δx and Δy are transferred to known DDA interpolators 4 and 4', respectively, where they generate a pulse train for driving the motor. CPU
2 transfers the segments Δx and Δy to the DDA 4, 4' and at the same time transfers them to the memory 5 for storage.

When all the pulses of the number relative to the segment components △×, △y are transferred from the DDA 4, 4' to the motors 7, 7', the CPU 3 transfers the new segment components △×, △y to the ODA.
4, 4' and memory 5.

Thereafter, the same operation is repeated, and when a number of pulses corresponding to all segments of one block have been transferred to the motor, the tape reader reads the next block and supplies it to the CPU.

The CPU and DDA execute this block using the same process as the first block. Note that the memory 5 only has a certain capacity, so when the axial components Δx and Δy of segments obtained sequentially are stored, the memory 5 becomes full. In this case, the oldest segment is erased, and a new segment component is stored there. The monitor 6 reports the occurrence of a short circuit.

When the CPU 3 is notified of the occurrence of a short circuit by the monitor 6, the CPU 3 calculates the Fuji components △×, △ of the segment stored in the memory 5.
y is taken out in the opposite order to the order in which it was stored, reversed the sign, and transferred to the DDA 4, 4'.

The DDA 4, 4' distributes pulses based on the transferred values and applies the obtained pulses to the outside of the machining machine so as to rotate the machine in the opposite direction to that during machining.

The above process continues until the short circuit is removed.

When the short circuit is released and the forward movement starts again, "all segment components taken out from the memory 5 during the backward movement △×
, Δy are again transferred to DDA 4, 4' with forward-dimensional codes. When all the pulses corresponding to the axial components of all the segments taken out during the backward movement are sent to the motor from the DDA 4, 4', the work of taking out the segment components from the memory 5 is completed and normal control returns. The reverse control in the present invention is DDA4,4
All the pulses of the number corresponding to the segment components transferred to
, 4' is issued and a signal indicating a short circuit is generated from the monitor.

Further, the memory 5 controls the stop of the backward movement depending on whether the short circuit is released when all the pulses corresponding to one segment output from the DDA are sent to the motor.
Therefore, even if a short circuit occurs or is released in the middle of a segment, the forward and reverse start and stop controls are executed only on a segment-by-segment basis.

However, since the length Q of the segment is set to Q = ノ△之〆〆 = 5 mm, cutting errors do not pose a problem.

It continues to move backward, and when the short circuit is removed, it moves forward again, but at this time, discharge begins at the same time as it moves forward. Since short-circuit monitoring is performed on a segment-by-segment basis, due to the principle of DDA, strictly speaking, when reversing, the vehicle does not return on the same trajectory as when moving forward. That is, as shown in FIG. 3, the pulse pattern for segment AB will appear for BA during retraction. However, one pulse corresponds to one French movement length of the electrode or workpiece, which is very small compared to the gap and does not pose a problem in terms of accuracy.

As described above in detail with reference to the drawings, according to the present invention, even if a short circuit occurs between the electrode and the workpiece, the electrode or the workpiece can be quickly retreated along the machining trajectory with a simple configuration. Short circuits can be canceled and highly accurate electrical discharge machining can be achieved.

Further, according to the present invention, as a method of memorizing the path of relative motion between the processing electrode and the workpiece, there is a method of memorizing each axis component △×, △Y of a minute straight line segment given to the pulse distributor. , the advantage is that the storage capacity of the storage element (memory) is small compared to the conventional method of storing the pattern of the output pulse train from the pulse distributor. Furthermore, electric discharge machines have a function that constantly monitors the state of the discharge gap between the machining electrode and the workpiece, and interrupts the relative feed operation between the machining electrode and the workpiece when the gap is about to short-circuit. It is generally installed in conjunction with a retraction control function, and in such electrical discharge machines, the pulse distributor has a The distribution pulse train for each axis is interrupted, and therefore, in the secondary method of storing the distribution pulse train, the pulse train is stored even during such interruptions (actually, there are no pulses, so the absence of pulses is stored). Therefore, if a short circuit occurs after feeding resumes, and the contents of the memory are used to perform a certain amount of backward movement, it will take the same amount of time as it took to move forward (including the time it took to stop feeding due to the risk of short circuit). However, according to the present invention, each axis component numerical data of the minute straight line given to the pulse distributor during forward movement is
, .DELTA.Y are also used during the backward control, which has the advantage of completely eliminating the above-mentioned situation in which the feeding interruption time during the forward movement lengthens the time required for the backward movement.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the present invention, FIG. 2 is a diagram explaining pulse distribution, and FIG. 3 shows trajectories during backward and forward movement. In the figure, 3 is a processing device, 4 and 4' are DDAs, 5 is a memory,
6 is a monitor. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 A command shape given as command information in a numerical control device of an electrical discharge machine that controls relative motion between a machining electrode and a workpiece machined by this machining electrode is divided into a large number of minute straight line groups, or approximated, and each A pulse for the relative movement is distributed based on numerical data of each axis component of the minute straight line, and the numerical data of each axis component of the minute straight line is stored in a storage means, so that a short circuit occurs between the machining electrode and the workpiece. If such a case occurs, the pulse distribution is performed again based on the numerical data of each axis component of the minute straight line stored in the storage means, and the relative movement direction between the machining electrode and the workpiece is reversed. .