JPS6040342B2 - numerical control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for automatically correcting backlash of a feed drive shaft in a numerically controlled machine tool.

Numerical control machine tools are now widely used in general due to their various advantages. In addition, because it is highly versatile, it has a higher operating rate than conventional machines. Therefore, the positioning operation of the driven body in the feed drive system requires a large number of repetitions, resulting in a decrease in accuracy. In other words, when a machine is operated for a long time due to wear of the feed drive shaft, for example, play may occur between the feed drive shaft and the nut that engages with the drive shaft, causing damage to the workpiece driven by the feed drive shaft. As the driving body repeatedly moves forward and backward, it becomes difficult to position the driving body while maintaining dimensional accuracy according to a predetermined feed command. Therefore, an error occurs between the command value and the actual value during the positioning process of the driven object. If this error is within the tolerance, there is no problem, but if it exceeds the tolerance, it will seriously affect the machining accuracy. This can lead to the occurrence of defective products. For this reason, in order to maintain the precision of the machine, various improvements have been made in terms of surface treatment, etc. by increasing the precision of the machine parts and adding hardness to the parts, but the precision of the initial state is completely maintained. It's difficult to do. In addition, efforts for precision in machines are not limited to the feed drive system, and there are various factors such as wear on sliding surfaces and play in couplings, but past empirical studies have shown that the accuracy of the feed drive system is decreasing. shows the most depressing results. Therefore, keeping the deterioration in accuracy of the feed drive system, that is, the error value due to backlash in particular, to a minimum will lead to improved accuracy. Therefore, in numerically controlled machine tools,
Using a measuring device such as a dial indicator, the actual amount of movement is periodically checked against the command value, and based on the measurement results, the difference between the command value and the actual value is input to the numerical control device as a correction value. However, a method has been adopted in which the amount of movement of the machine is adjusted to the command value. In addition, in lathes and the like, a method is also used in which a workpiece is automatically measured and the results are automatically sent to a numerical control system for automatic correction. However, measurement requires time and skill above a certain level, and it cannot be carried out frequently due to the technical difficulty of measurement. In the former case, errors occur in measurement control due to human movements, and accurate and stable dimensional control cannot be performed. The latter also had some drawbacks, such as the equipment being expensive. The present invention solves the above-mentioned conventional drawbacks,
To provide a simple and low-cost correction method that automatically calculates the amount of backlash and automatically inputs it as a correction value to a numerical control device to maintain high precision of a machine.

That is, the current value of the servo motor of the feed drive system changes during the period from an unstable state to a normal driving state if there is a backlash when starting, and it takes time to stabilize to a constant value.

The purpose of the present invention is to convert the time it takes for the variable current value to stabilize into a travel distance and input this value as a correction value to the numerical control device.Also, the amount of backlash to be corrected is automatically calculated. Since it can be interpreted as a numerical value, it is easy to manage counts, and therefore it is possible to accurately judge the timing of readjustment such as overhaul of the machine.

Next, embodiments of the present invention will be described in detail with reference to the drawings. 1st
The figure is a block diagram in which the present invention is applied to a machining center. An overview of the present invention will be explained according to this block diagram. Based on commands from the numerical control device 1, the servo motors for each feed axis, that is, the servo motor 2 for the X axis, the servo motor 3 for Y axis, the servo motor 4 for Z axis, and the servo motor 5 for additional axes, control each command value. There will be an uproar depending on the situation. The drive current state of the servo motors 2, 3, 4, and 5 for each axis is detected by current detection circuits 6, 798, and 9 corresponding to each servo motor outer motor. The characteristics of this current state are shown in FIG. A indicates current, and t indicates elapsed time. That is, the current rises as time t elapses from the starting state when the axis movement direction is changed, and becomes constant at a certain point of time to reach a stable state. In the figure, the arrows indicate the elapsed time in the range where backlash occurs, and the current value at this time is Ao. This current value Ao is set below a stable steady current value as a current value that is assumed to cause backlash. When there is backlash, there is no load, and the current value between the two is unstable until a certain load is applied.

Also, considering the number of input pulses to the corresponding axis, it is the same machine. In the current detection circuit, a processable voltage, that is, an isolated measurement voltage, is extracted from the drive current of the servo circuit.

A DC-DC converter or the like is used as the current detector. The current value switched by the switching circuit 10' or the circuit for switching the current of the servo motor of each feed axis, that is, the isolated measured voltage value, is sent to the processing circuit one bag at a time. The preprocessing circuit 11 determines the current value of each switched feed axis servomotor and the isolated measured voltage value, and converts the time in an unstable state due to backlash into a driven distance. For example, the unit movement distance is 0.
It is set as 0.06 seconds per 01 rib. As mentioned above, time t
The value obtained by converting o to the moving distance is the rate of change in current value, which varies depending on each machine, so check the characteristics of each machine with the actual machine and make accurate corrections by setting based on that data. is possible. The processing circuit 11 is provided with an alarm circuit 12, which issues an alarm signal when the correction value exceeds a limit value. Further, the correction value is sent from the processing circuit 11 to the numerical control device as a feedback signal 13. Next, the above-mentioned contents will be explained in detail with reference to FIG. First, regarding the symbols in the figure, CT is processing information such as command tape, CC is a control circuit that takes in processing information, T is a circuit between buckets that receives driving body movement command information from the control circuit, and ER is the movement command position. An error register that calculates and stores the difference from the actual movement position from the feed pulse (distribution pulse) and feedback pulse, DA is a digital-to-analog converter that converts a digital amount to an analog amount, and the AM circle is from the above-mentioned PA converter. MX is an X-axis feed servo motor that rotates with DC current from the multiplier, ENC is a pulse encoder that generates feedback pulses by the rotation of the servo motor,
RX is a resistor, DET is a current detector that extracts the current value of the servo motor MX as a voltage value, AD is an analog-to-digital converter that converts the analog voltage value of the current detector DET into a digital value, and RXA is the first one tried. CMPX is a register that stores the voltage value of the AD converter corresponding to the steady current value of the servo motor when the backlash is eliminated (hereinafter referred to as the steady current register), and CMPX is the current detector used for the second and subsequent attempts. A comparator that compares the detected value of DET with the value of the steady current register RXA and outputs a signal when they match. GX is a measurement command TBX from the control circuit CC.
CXB is a counter that counts the feed pulses from the gate circuit, and DBX is a counter CXB.
RXB is a backlash correction register that stores the correction data, RXL is a backlash limit register, and CMPA compares the value of the counter with the value of the backlash limit register and determines that the value of the counter is the limit. ALM, a comparator that outputs a signal when the register value is exceeded.
indicates an alarm which is issued by the output signal of the comparator CMPA. The control circuit CC gives a feed command to the Kusuma circuit INT based on the feed command data given from the command tape CT to perform pulse distribution. The distribution pulse spans each axis, but
Since the signal input/output relationship is common to each type, only the x-axis will be described in detail here. The distribution pulse PX is input to the servo circuit to drive the feed axis.

The x-axis distribution pulse PX is sent to the error register ER,
Furthermore, digital to analog converter DA, multiplier AMP
The servo motor Mx is rotated to drive the feed shaft.
The current value of the servo motor MK is converted and taken out as a voltage value by the current detector DET. The extracted voltage value is digitized by an analog-to-digital converter AD. The digital amount corresponding to the current value when the axis movement starts at a constant speed and the servo motor current reaches a steady value is stored in the register RXA as a value indicating the steady current value. This register is hereinafter referred to as a steady current register RXA. Next, perform an axial movement in the opposite direction to return the machine to the original position. Start moving again at the same speed. At this time, measurement command TBX is sent out at the same time. When the measurement command TBX is issued, the gate GX opens and starts comparing the servo motor current and the steady current value with the register RXA. When the servo motor current reaches a certain percentage (for example, 70%), a signal is sent to the comparator from MPX. It is sent out and gate GX is closed. At this time, a pulse corresponding to the time from when the measurement command TBX is sent until the signal from the comparator CMPX rises, that is, from the time the gate opens until it closes, enters the counter CXB. In this example, since the time is determined by pulses, a gate CX and a counter CXB are provided to convert the delay time due to backlash into a moving distance. The distribution pulse PX is sent from the Tachibana circuit INT to the servo circuit, and at the same time, the measurement command TBX causes the comparator CMPX to open.
The counter CXB counts the feed pulses until the gate GX is closed by the signal. A signal value corresponding to the number of pulses, that is, the amount of backlash is used as a feedback signal in the X-axis backlash register R.
Administered to XB. If correction is necessary, the administered backlash amount is sent to the control circuit CC and correction of the x-axis is performed via the x-ball servo circuit. On the other hand, the comparator CMPA compares the counted number of distributed pulses, that is, the amount equivalent to backlash, with the X-axis backlash limit value and the limit value of the resistor RXL.If this limit value is exceeded, an alarm occurs. It is designed to output a signal ALM. Said alarm signal is for example sent to a control circuit CC to stop the operation of the machine. As mentioned above, the above configuration has a Y axis,
The same holds true for the Z-axis and other additional axes.

The effects of the present invention are as follows.

1. Find the distance from the maximum backlash state of the drive system until the backlash disappears in terms of the time it takes for the changing current value of the servo motor to stabilize, and use this backlash correction amount to correct the position of the machine tool drive system. do the
Furthermore, since corrections can be repeated during automatic operation, there is no need for man-hour-consuming measurement work or input work that is prone to errors, as is the case with secondary controls.

2 The amount of backlash to be corrected can be automatically detected as a numerical value, so if you set this limit value to a value suitable for overhaul, etc., you can automatically know the optimal time for overhaul. can.

Also, if the machine is bumped for some reason during processing, the degree of damage to the machine can be known by checking the amount of backlash at multiple arbitrary positions. As described above, the present invention is not limited to the configurations shown in the embodiments, and modifications are expected without departing from the technical idea of the present invention as described in the claims.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the basic configuration of the present invention, Figure 2 is a block diagram showing the basic configuration of the present invention.
The figure is a current characteristic diagram of a servo motor, and FIG. 3 is a block diagram showing an embodiment of the present invention. In the figure, 1...a numerical control device;
2...x-axis servo motor, 1 1...processing circuit, C
〇...Control circuit, DET... Current detector, AD...analog-digital converter,
CMPX…Comparator. Younger brother 1 figure 2 figure 3

Claims (1)

[Scope of Claims] 1. In a numerical control device having numerical control means and servo drive means for numerically controlling a feed drive system, a detection means for detecting a current value of a servo motor that operates the drive system;
A memory means for setting the load current value of the servo motor when the drive system is no longer bumpy, and counting pulses when the drive system is operated in a direction in which the buckle is reduced from the maximum drive system buckle. It comprises a counting means, and a comparison means which compares the values of the storage means and the detection means and issues an instruction to the counting means to stop counting when the value of the detection means reaches the value of the storage means, and the comparison means outputs a count stop command to the counting means, and a backlash correction of the counting means is performed. A numerical control device characterized in that data is taken into the control means and a backlash correction is applied to the drive system. 2. In a numerical control device that has a numerical control means for numerically controlling a feed drive system and a servo drive means, there is no detection means for detecting the current value of a servo motor that operates the drive system, and there is no bump in the drive system. a first storage means for setting the load current value of the servo motor at the time; a counting means for counting pulses when the drive system is operated in a direction in which the buck crash is decreased from a maximum buck crash state; a first comparison means that compares the values of the first storage means and the detection means and issues an instruction to the counting means to stop counting when the value of the detection means reaches the value of the storage means; and sets a tolerance value for backlash. The second storage means compares the value of the counting means with the value of the second storage means and generates an alarm when the value of the counting means exceeds the value of the second storage means. Characteristic numerical control device.