JPS6351820B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a driving device for a machine such as a table of a machine tool.

Conventionally, the table of a machine tool is driven by a servo motor 1 driving a table 3 via gears 5, 6 and a ball screw 2, as shown in FIG. According to the drive of the servo motor 1, the upper part is slid in the direction of the arrow shown in the figure. The servo motor 1 is controlled by a speed control device 7 that inputs a speed command VS calculated by a calculation device such as a CPU, and the speed signal VF from a speed detector 8 connected to the servo motor 1 is The speed of the servo motor 1 is controlled in accordance with the input speed command VS, which is fed back to the control device 7, so that the workpiece mounted on the table 3 is processed.

In such a configuration, the table 3, which is a driven object, is slid on the bed 4 in the direction of the arrow shown in the figure in accordance with the speed command VS, but the sliding resistance of the table 3 in this case is, for example, The characteristics are as shown in Figure 2. That is, a indicates static frictional resistance and b indicates dynamic frictional resistance, and when the table 3 starts moving, the operating point moves from state A of static frictional resistance a to state B of dynamic frictional resistance b in FIG. , in this case, the sliding resistance becomes smaller as it moves, resulting in negative resistance. In some cases, intermittent movements, the so-called states-slip phenomenon, are observed. Normally, lubricating oil is applied to the sliding surfaces of table 3 and bed 4 to reduce sliding resistance, but as the moving speed of table 3 increases, the viscous resistance of the lubricating oil increases, resulting in state D in Figure 2. This results in a large sliding resistance.

In addition, the table 3
When precisely controlling the movement of , the movement MD of the drive shaft of servo motor 1 and the amount of movement TM of table 3
When driven at low speed, this shows a hysteresis characteristic as shown by the solid line in FIG. The reason for such a hysteresis characteristic is the existence of machine lost motion caused by the backlash of the machine and the deflection that occurs due to the finite rigidity of the machine. Normally, in machines that require precise position control, it is possible to minimize the deflection of the mechanical drive system, but there is a cost limit to reducing the deflection of the machine. When positioning the machine at low speed, the deflection of the machine is proportional to the static frictional resistance a of the sliding surface shown in FIG. However, if the moving speed of the table 3 is in the range of the dynamic frictional resistance b, the deflection of the machine will be proportional to the dynamic frictional resistance b. Therefore, when controlling the position of a machine using a normal NC device, certain lost motion corrections are performed depending on the direction of movement. Conventionally, such lost motion correction has been performed, but since the sliding resistance changes depending on the moving speed, the amount of deflection of the machine also changes depending on the moving speed, so it is not possible to completely correct the lost motion of the machine. Can not do it.

As described above, since the conventional mechanical drive device cannot completely correct lost motion of the machine, accuracy problems occur in contour control and the like. That is, due to the hysteresis phenomenon that changes depending on the feed speed of the mechanical drive system, there are drawbacks such as the occurrence of convex portions at quadrant switching positions during contour control such as circular arcs. Furthermore, if the position of the table 3 is directly detected using an inductor or the like and position feedback is performed, precise position control becomes possible, but this becomes expensive and disadvantageous in terms of cost.

This invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a mechanical drive device that maintains constant lost motion by forcibly applying micro-vibration to a machine such as a table. It is said that

This invention will be explained below.

This invention relates to a machine drive device for a machine tool, etc., and when the machine is driven by an actuator,
A small alternating current signal is added to the machine's target signal to give the machine a slight vibration.

That is, FIG. 4 shows an example of the device of the present invention, in which a table control condition CD for instructing the table movement speed of the table 3, movement, stop of the table 3, etc. is inputted to the judgment circuit 10. detects from the input table control condition CD when the table 3 starts driving, when it stops moving, and when the movement speed becomes less than the set value, and outputs the detection signal as the decision signal DS,
The decision signal DS is input to the micro-vibration generation circuit 11,
The micro-vibration generating circuit 11 is designed to generate a triangular-wave micro AC signal SV only during the time when the decision signal DS is input. Then, the minute alternating current signal SV output from the minute vibration generation circuit 11 is added to the speed command VS in an adder 12, and the added signal VSA is inputted as a speed command to the speed control device 7 as described above. ing. For example, speed command
When VS is at the signal level as shown in FIG. 5A, and when the micro-vibration generation time based on the judgment of the judgment circuit 10 is from time t0 to t1, from time t2 to t3, and from time t4 to t5, The micro-vibration generating circuit 11 outputs a triangular-wave minute alternating current signal SV as shown in FIG. 5B, and the adder 12 adds this minute alternating-current signal SV to the speed command VS. Therefore, the addition result VSA of the adder 12 has a signal level as shown in FIG.
will be driven. As a result, the servo motor 1 causes the servo 3 to vibrate minutely during the speed change time of moving the table 3, and when stopping and starting. Due to such forced micro-vibration of the table 3, the static friction shown by the solid line in FIG. 2 changes to dynamic friction, so that the sliding property changes to the one shown by the broken line in the same figure. Although the above has been explained qualitatively, it will be explained more specifically. When the servo motor is moving only in one direction, lost motion of the machine is not a problem, so P5 and P in Figure 3
1. As shown in P6, the incremental position accuracy is good. However, when the moving direction of the servo motor is reversed, a lost motion L1 approximately proportional to the sliding resistance occurs as shown at P1, P6, and P2 in FIG. 3, resulting in a position error. Furthermore, since this lost motion L1 is approximately proportional to the sliding resistance shown in FIG. 2, its magnitude changes depending on the moving speed. However, since the device of the present invention applies slight vibrations, the sliding resistance shown in FIG. 2 decreases from a to b even when the moving speed is slow.
The hysteresis characteristics shown in Figure 3 also change from the solid line characteristics to the broken line characteristics, and the lost motion is P3 and P3.
It decreases to L2, which is expressed as the difference from 4. If the magnitude of the microvibration at this time is L3, the table 3 which is the controlled object will pass further inward by L3 than the broken line characteristic in the hysteresis characteristic shown in Fig. 3, so the lost motion of the table 3 will be substantially reduced. Therefore, it will be significantly reduced from L1 to L4 expressed by the following equation (1).

L4=L2-2×L3...(1) Note that the AC minute signal SV generated by the minute vibration generation circuit 11 can obtain the same effect as long as it is the same as the dimension of the command value. The waveform may be an alternating current signal such as a sine wave or a rectangular wave.

As described above, according to the machine drive device of the present invention, the hysteresis phenomenon of the machine, which conventionally changes depending on the feed rate, is simply and quantitatively reduced. Position control is possible, and more accurate position control is possible in contour control, etc.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an example of a conventional mechanical drive system, Fig. 2 is a characteristic diagram of the sliding resistance of the machine, Fig. 3 is a diagram showing the hysteresis phenomenon of a general mechanical drive system, and Fig. 4 is a diagram showing the hysteresis phenomenon of a general mechanical drive system. A configuration diagram showing an example of this invention device,
FIGS. 5A to 5C are waveform diagrams for explaining the operation. 1... Servo motor, 2... Ball screw, 3...
...Table, 4...Bed, 7...Speed control device, 10...Judgment circuit, 11...Micro-vibration generating circuit.

Claims (1)

[Claims] 1. In a machine drive device consisting of a servo motor that drives a machine and a control means that controls the servo motor to control the position or speed of the machine, a minute alternating current signal is generated to give minute vibrations to the servo motor. and an adder for adding a minute alternating current signal from the signal generating means to a speed command signal for the machine inputted from the outside and outputting the result to the control means. Device.