JPH0144455B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical discharge machining control device, particularly for processing a workpiece by moving the machining electrode in a multidimensional manner while forming a predetermined discharge machining gap between the machining electrode and the workpiece. The present invention relates to an electrical discharge machining control device that controls the electrical discharge machining gap using a positioning control system.

This type of electric discharge machining control device performs optimal machining by maintaining the electric discharge machining gap between the machining electrode and the workpiece at a predetermined value, so it responds quickly to changes in the discharge state and performs machining. It is required to optimize the discharge gap, and hydraulic cylinders, pulse motors, DC servo motors, etc. are used as servo actuators for moving the machining electrode, and in particular sampling, logical operations, etc. are used to precisely control the machining gap. Attempts have been made to use a servo system (for example, controlled by a microprocessor, minicomputer, etc.) having a hold function.

A conventional control device is configured as shown in FIG. 1 when performing XY simultaneous two-axis interpolation control. That is, the machining electrode 12 is opposed to the workpiece 10 across the electrical discharge machining gap, and the electrode 1
2 is detachably attached to a table 19 that is connected via nuts 18X and 18Y to ball screws 16X and 16Y that are directly connected to the rotating shafts of DC servo motors 14X and 14Y, and the workpiece is rotated according to the rotation of the motors 14X and 14Y. It is driven forward and backward relative to the object 10.

A power source 20 is connected between the workpiece 10 and the processing electrode 12.
A controlled pulsed voltage is applied from
The workpiece 10 is machined by generating electric discharge in the discharge machining gap.

At this time, the voltage actually applied between the electrodes changes depending on the discharge state. Since this discharge state changes depending on the machining distance, that is, the electric discharge machining distance, the machining voltage can be used as a signal for controlling the positioning of the electric discharge machining distance.
Here, since the electrode-to-electrode voltage is in the form of a pulse, it is converted into a signal that continuously outputs an average value by a suitable well-known means such as a smoothing circuit. Then, this electrode-to-electrode voltage is compared with the reference voltage V _R in the comparator circuit 21, and the difference voltage is
After V _g is supplied to an analog-to-digital converter 22 and digitized, it is supplied to a control device 24 that has sampling, logical operation, and hold functions, and is sampled at regular intervals by an input latch circuit 26 in the device. After that, the logic operation circuit 28
The table position command value is converted into a table position command value which is vector distributed in the X and Y axis directions according to the voltage between the electrodes, and is held by the output latch circuit 30 until the next command value is output as a hold signal. here,
The distribution into the X and Y axis direction vectors is performed by the logic operation circuit 28 using a distribution axial direction pulse signal for each feeding direction vector of the transfer device, which is generated in the pulse distribution generation circuit in response to a machining command.

The output of the latch circuit 30 is supplied to a binary rate multiplier 32 that converts parallel digital outputs at fixed time intervals into serial digital outputs, and is converted into serial pulse signals X _p and Y _p , which are then sent to an error counter that constitutes a position servo system. 34X and 34Y, and these counters 34
The X and Y directions detected by the X and Y axis direction displacement detectors 42X and 42Y, respectively, are
A detection pulse signal representing the amount of shaft displacement is fed back, and this detection pulse signal is calculated from the serial pulse signals X _p and Y _p , and a count output (position error value) representing the difference is sent to digital/analog converters 36X and 36Y. The signals are supplied to the same circuit, converted into analog signals, and output as position correction signals V _X and V _Y.

These position _correction signals _V
8X and 38Y, DC servo motor 14X and 1
The output voltage of the tachometer generators 40X and 40Y is connected to the amplifiers 38X and 38 via a resistor _R2 .
A speed command signal is supplied to the servo system with the speed fed back to Y via the resistor _R1 , and the servo motors 14X and 14Y are rotationally driven to rotate the ball screws 16X and 16Y, and the table 19 to which the electrode 12 is fixed. The X-axis and Y-axis displacements of the table are detected by the displacement detectors 42, respectively.
X and 42Y are detected and these are detected by error counter 3.
The servo motors 14X and 14Y continue to rotate until the displacement of the table 19 becomes equal to the position command as a result of feedback from the servo motors 4X and 34Y, thereby controlling the electric discharge machining interval to a constant value.

The above control method is used for positioning control by well-known numerical control, and since it is so-called follow-up control, the position servo gain is generally selected to be about 20 Hz.

Next, the operating X-axis servo system of the conventional device described above will be explained. When the interpole difference voltage V _g changes as shown in FIG. 2A, the controller 24 converts it into a position command signal based on this voltage V _g . Then, the multiplier 32X outputs a step pulse signal +X _p or -X _p as shown in FIG. 2B.

If the motor 14X is driven without any delay time occurring in the _stepping pulse signal Yes, but
In reality, since there is a delay time in the control system, a processing time in the control device, etc., the processing electrode 12 is operated as shown by the dotted line 46 in FIG. 2C. Also, the rotational speed of the servo motor 14X is shown in Fig. 2D when viewed from the output voltage V _M of the tachogenerator 40X.
Characteristics of the system based only on the general speed loop (V _M1 as shown in the dashed line) with respect to the voltage between poles V _g shown in the dotted line shown in
The V _M2 shown by the solid line has the disadvantage that the response is extremely reduced compared to that of the Y-axis servo system. This means that in the position servo system, the position command is replaced with a pulse train and the output is a ramp, so even if the speed servo system is a step input, the output must be in the form of a ramp, so this should be avoided. It was impossible.

In addition, in electrical discharge machining, control is performed to follow the state of the electrical discharge machining gap, so a response frequency of at least 50 Hz or higher is required for stable machining, but the conventional device shown in Figure 1 does not perform static precision electrode positioning or servo control. Even if the system can be optimized, when evaluated as a servo system in actual machining, its frequency response is inferior to a simple electrode feed control system with only a speed servo system, that is, a control system without the control device 24. There was a fatal flaw.

In addition, in order to improve the responsiveness of the conventional device, a third
The control device shown in the figure can be considered.

In FIG. 3, parts corresponding to those in FIG.
In the configuration shown in the figure, the differential voltage V _{g is}
Amplifiers 38X and 3 through C _Y and resistors R ₃ and R ₃
It has the same configuration as that in FIG. 1, except that the differential signals _{X S} and Y _S of the differential voltage V _g are added and superimposed on the position correction signals V X and V _Y.

According to this configuration, the voltages _{X S} and Y _S obtained through the capacitors _C Therefore, a voltage is generated only when a change occurs in the discharge machining gap and the discharge state changes. In other words, since the value obtained by integrating the differential voltage V _g, which is the control input for the speed system, is the amount of positional displacement,
The voltage V _S affects the displacement only when the speed changes, and the voltages X _S and Y _S do not pass through a circuit with an accumulation function such as a counter, so they themselves do not affect the displacement of the position. It simply affects the start or transition of motion in the speed servo system.

The operation of the device shown in FIG. 3 will be explained using the X-axis servo system as an example with reference to FIG. 4. Assuming that the differential voltage V _g is obtained as shown in FIG. Pulse +X _p is obtained, is supplied to error counter 34X, and is added and counted.
A digital output representing the count contents is converted into an analog signal by a digital-to-analog converter 36X, and a position correction signal _VX is obtained as shown in FIG. 4C. This position signal _VX is supplied to the drive amplifier 38X via a resistor _R1 , and the amplified signal is supplied to the servo motor 14X to move the processing electrode 12. In this state, a displacement detection pulse signal is output from the displacement detector 42X in accordance with the direction of movement of the processing electrode 12, and this is supplied to the error counter 34X, so that its content approaches zero.

On the other hand, when the differential voltage V _g is obtained, it is supplied to the capacitor C _X , so that a differential output signal X _S is obtained as shown in FIG. 4B, and is supplied to the drive amplifier 38X via the resistor R ₃ . Therefore this amplifier 38X
The position correction signal V _X and the differential output signal X _S are added on the input side of
V ₀ is obtained, and an analog signal corresponding to the differential voltage V _g is obtained. By amplifying the composite signal V ₀ and supplying it to the servo motor 14X, a differential voltage V _g is generated from the tachogenerator 40X as shown in FIG. 4E.
A speed voltage output V _M can be obtained that is similar to , and similar results can be obtained for the Y-axis servo system.

However, according to this configuration, good results can be obtained when the X-axis and Y-axis correction signals V _X and V _Y are approximately equal, but as shown in FIG. For example, when the ratio is 1:3, the differential output signals X _S and Y _S have the same value as shown in FIG. 5B. 40
The waveforms of the speed voltage output V _MX and V _MY of Y are the 5th waveforms, respectively.
As shown in Figures C and D, an X-axis servo system with a small amount of displacement will over-compensate, while a Y-axis servo system with a large amount of displacement will over-compensate, making it impossible to achieve the desired purpose. It is something that you have.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to distribute differential output signals according to the distribution ratio of each control axis, and to appropriately issue position correction commands for each direction of movement. By doing so,
It is an object of the present invention to provide a novel electrical discharge machining control device that can increase response speed and accurately perform position control.

The present invention provides a transfer device that forms a predetermined machining gap between a machining electrode and a workpiece and moves them relative to each other in a multidimensional manner, and a transfer device that applies a predetermined voltage between the machining electrode and the workpiece. A circuit that compares the voltage actually applied between the pressurizing electrode and the workpiece with a reference voltage by generating electric discharge between the applied power source, the machining electrode, and the workpiece, and outputs a differential voltage. a pulse distribution generation circuit that generates a distribution axial direction pulse signal according to a feed direction vector for each moving axis direction of the transfer device; and a pulse distribution generation circuit that samples the differential voltage at regular intervals to obtain a position command value of the transfer device. A control device that calculates, holds, and outputs calculations and distribution based on the distribution axis direction pulse signal; pliers, a displacement detector that resolves the displacement corresponding to the position of the processing electrode for each movement axis direction of the transfer device and generates each axial direction pulse signal according to each direction; An error counter that receives and compares step pulse signals and counts errors; a digital-to-analog converter that converts the count contents of this error counter into an analog signal; and amplifies this analog signal and sends it to the transfer device. an amplifier circuit for supplying the voltage, a differentiation circuit for differentiating the differential voltage, and a gain correction provided in the control device for outputting a correction coefficient for each movement axis direction of the transfer device based on the distribution ratio of the distribution axis direction pulse signal. a circuit that multiplies the differential output obtained by the differential circuit by the correction coefficient obtained by the gain correction circuit, and superimposes the signal for each movement axis direction of the transfer device with the analog signal; It is characterized by consisting of.

A preferred embodiment of the present invention will now be described with reference to FIG.

In FIG. 7, parts corresponding to those in FIGS. 1 and 3 are given the same reference numerals, and detailed explanations thereof are omitted _.
and C _Y and the comparison circuit 21 are disconnected, and the differential voltage V _g
is supplied to multiplying digital-to-analog converters 50X and 50Y, while converters 50X and 50Y
Correcting coefficient _{outputs k}
The multiplication output of converters 50X and 50Y is a capacitor.
3rd except that it is supplied to C _X and C _Y
It has the same configuration as the figure. In _this case, the ratio of the correction coefficient outputs _k You can get it here. It is output so that it is equal to the ratio of parallel data on the X-axis and Y-axis and coincides with the direction in which the electric discharge machining gap between the workpiece 10 and the machining electrode 12 on the X-axis and Y-axis both decreases or expands. In addition, the multiplier type digital-to-analog converters 50X _and 50Y have outputs k X V _g and k Y V _g obtained by multiplying the input voltage V _g by the correction coefficient outputs _{k X} and k _Y.
For example, AD7520 manufactured by Analog Devices, Inc. in the United States can be applied, and the frequency used is
It is over 1MHz, so there is no risk of delay.

The above is an example of the configuration of the present invention. According to the configuration including such a gain correction circuit, the differential voltage V _g is
Since these are supplied to Y and multiplied by correction coefficient outputs k _X and k _Y according to the ratio of the interpolation of the
_A correction _output signal adjusted _according to the peak values of the position correction signals V _X and V _Y of V _g is obtained, and this is superimposed on the position correction signals _V Therefore, the speed output voltage obtained from tachogenerators 40X and 40Y
V _MX and V _MY are always equal to the differential voltage V _g as shown in Figure 4E.
The delay corresponding to this is extremely small.

As described above, according to the present invention, the correction output obtained by correcting the inter-electrode voltage in accordance with the actual feed direction vector of the control axis is superimposed on each axial position correction signal of the positioning control system. Each axial position correction signal is obtained with extremely little delay with respect to the inter-electrode voltage, and has the great feature of being able to perform optimal position tracking control with high responsiveness and high positioning accuracy.

Further, in the above example, the case where the processing electrode moves in two dimensions has been described, but it goes without saying that the present invention can also be applied to cases where the processing electrode moves in three dimensions in the X, Y, and Z directions.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing a conventional electric discharge machining control device, Fig. 2 is a signal waveform diagram for explaining its operation, Fig. 3 is a system diagram showing the electric discharge machining control device which is the basis of the present invention, and Fig. 4 is a system diagram showing a conventional electric discharge machining control device. 5 and 5 are signal waveform diagrams for explaining the same, FIG. 6 is a diagram showing the feed direction vectors of the X-axis and Y-axis, and FIG. 7 is a system diagram showing an example of the electrical discharge machining control device according to the present invention. be. The same members in each figure are given the same reference numerals, 10 is the workpiece, 12 is the processing electrode, 14X and 14Y are the DC servo motors, 24 is the control device, 32 is the multiplier, 34X and 34Y are the error counters, and 36X
and 36Y is a digital-to-analog converter, 40
X and 40Y are tachogenerators, C _X and C _Y are capacitors, and 50X and 50Y are multiplying digital-to-analog converters.

Claims (1)

[Claims] 1. A predetermined machining interval between the machining electrode and the workpiece
a transfer device that forms and relatively moves these along at least two orthogonal movement axes; a power supply that applies a predetermined voltage between the processing electrode and the workpiece; and a power source that applies a predetermined voltage between the processing electrode and the workpiece. A circuit that compares the voltage actually applied between the machining electrode and the workpiece due to the generation of electric discharge between the two and a reference voltage and outputs a differential voltage, and a feed direction for each axis of movement of the transfer device. a pulse distribution generation circuit that generates a distributed axial direction pulse signal according to the vector; and a pulse distribution generation circuit that samples the above-mentioned differential voltage at fixed time intervals, calculates and distributes the position command value of the above-mentioned transfer device using the above-mentioned distributed axial direction pulse signal, and holds it. a control device that outputs a displacement corresponding to the position of the processing electrode; a multiplier that receives the output of the control device and outputs a step pulse signal that controls the movement of the transfer device in each movement axis direction; A displacement detector separates the movement of the transfer device into each moving axis direction and generates each axial direction pulse signal according to each direction, and the each axial direction pulse signal and the above step pulse signal are inputted and compared, and the error is detected. an error counter that counts the error counter, a digital-to-analog converter that converts the count contents of the error counter into an analog signal, an amplifier circuit that amplifies the analog signal and supplies it to the transfer device, and differentiates the differential voltage. a differentiation circuit; a gain correction circuit provided in the control device and outputting a correction coefficient for each movement axis direction of the transfer device according to the distribution ratio of the distribution axial pulse signal; a circuit that multiplies the differential output obtained by the differential circuit by the correction coefficient obtained by the differential circuit, and superimposes a signal for each movement axis direction of the transfer device on the analog signal. .