JPS61122722A - Servo amplifier for accurate positioning - Google Patents

Abstract

PURPOSE:To improve the gain at a high frequency range and the phase characteristic of a servo system by inserting phase advancement compensating amplifiers between the positional deviation value of an objective position inputted from a numeral control device and a current position and a speed adding point and between the speed adding point and a current adding point. CONSTITUTION:The 1st phase advancement compensating amplifier circuit 13 having advancing phase compensating and amplifying functions is inserted between a D/A converter 9 for converting a phase deviation value into an analog value and the speed adding point 8 and the 2nd phase advancement compensating amplifier circuit 12 is inserted between the adding points 7 and 8 instead of a delay phase compensating amplifier circuit. Each of the circuits 12, 13 consists of a resistor, a capacitor and an operational amplifier. Respective constants are determined so that the maximum angle (40-60 deg.C) of the phase advancement is set up to 150-200Hz, and the gain is adjusted by a resistor R4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a servo amplifier for driving a servo motor for moving a positioning table of a precision machine tool with submicron accuracy using a numerical controller.

BACKGROUND OF THE INVENTION A block diagram of a servo system of a conventional machine tool is shown in FIG. 1 is a DC servo motor that drives a table such as a processing table of a machine tool. 2 is a tachometer generator, and 3 is a high-precision position detector that outputs pulses of changes in position, each of which is mechanically coupled to the DC servo motor 1. 4 is a current detector that outputs a voltage proportional to the current value of the DC servo motor, and 6 is a power amplifier circuit that has linear characteristics with respect to the input amplitude and frequency, and the input voltage and output current are determined by current feedback. becomes a proportional relationship. 6 is a delay phase compensation amplifier circuit with delay phase compensation and amplification functions to increase the gain in the low frequency range, 7 and 8 are addition points, and 9 is a digital-to-analog conversion circuit (hereinafter abbreviated as DA conversion circuit). be. A position deviation counter 10 receives target position command data 11 from the numerical control device and up or down pulses from the pulse generator 3, and outputs the difference between the current position and the target position as a digital value. Therefore, the output ΔP of the DA converter 1o
is the positional deviation amount. The GA and ψA curves in FIG. 3 show typical gain and phase frequency characteristics when the positioning table of the machine tool is driven by this servo amplifier. The frequency characteristics were measured when the feedback voltage of the tacho generator was used as the output when the positional deviation amount ΔP was used as the input.

The fo and fl portions represent the inertia and mechanical resonance point of the positioning table.

Problems to be Solved by the Invention In order to obtain a positioning accuracy of 1 to 2 μm with the above configuration, the rigidity of the mechanical system must first be improved and the power amplifier circuit 5 and the D-A converter 10 The purpose can be achieved by optimally adjusting the phase characteristics and gain of the gain and phase lag compensation amplifier circuit 6. However, as a precision machine tool,
When trying to obtain a positioning accuracy of 61 to 0.2 μm,
Since the gain of the position loop is 10 times that of the conventional one, if delay phase compensation is performed, there will be no phase margin near the resonance point f0, and the positioning table will oscillate. Therefore, in precision machine tools, the structure is devised to increase the frequency 10 of this resonance point in order to improve rigidity and reduce weight, but it is difficult to increase the frequency to 200 or more due to the size of the workpiece. .

On the other hand, precision machine tools generally have a rotating spindle that rotates at high speed, and the tool is applied to the workpiece to be machined while moving the positioning table. The surface of the workpiece has irregularities and material irregularities, and during processing, these are transmitted to the positioning table as small reaction force irregularities.

Therefore, even if the gain of the servo system can be sufficiently large in the DC state, if it is small in the high range of 100 to 2001 or more, it will result in uneven machining on the machined surface of the workpiece. This effect is particularly noticeable when the processing speed is increased.

In view of the above-mentioned problems, the present invention provides a servo amplifier for precision positioning of a servo motor that drives a positioning table that requires a machining shape accuracy of 0.1 to 1 μm, particularly in a precision machining machine tool.

ζ In-law + Means for Solving In order to solve the above problems, in the present invention, there is a A first leading phase compensation amplifier circuit 12 having a leading phase compensation and amplification function is inserted, and the lagging phase compensation amplifier circuit 6 is replaced with a second leading phase compensation amplifier circuit 13 between addition points 7 and 8. This particularly improves the characteristics of the processing machine.

As a result of doing the above, the band of the entire servo system becomes wider, and the reaction torque of the DC motor that counters the small unevenness of reaction force caused by the surface condition of the workpiece increases, thereby reducing the unevenness of feeding the workpiece. Furthermore, the phase compensation makes the phase margin wider than before, so the gain of the servo amplifier from direct current to low frequencies can be made larger than before, and as a result, positioning accuracy is improved.

Embodiment FIG. 1 is a block diagram of a servo system of a precision processing machine according to an embodiment, and the portion surrounded by a chain line is a block diagram of an embodiment of a servo amplifier for precision positioning according to the present invention. 1 is a DC servo motor that drives the positioning table, 2 is a tacho generator, 3 is a position detector, 4 is a current detector, 7 is a current feedback addition point 1.8 is a speed feedback addition point, 1o is a D-A conversion 10 is a position deviation counter, 1
1 represents a target position command of the numerical control device, and during machining, this target command is changed at regular intervals. The position detector 3 is a laser length measuring device with a resolution of 0.01 μm.

5 is a power amplifier circuit whose input and output have a linear relationship and drives the DC servo motor 1. 12 and 13 are phase lead compensation amplifier circuits equipped with phase lead compensation and amplification functions.

The transfer function of each amplifier circuit is shown in the figure.

FIG. 2 shows an embodiment of the phase lead compensation amplifier circuit 12, 13, which is composed of a resistor, a capacitor, and an operational amplifier (integrated circuit). The maximum angle of phase advance (40 to 6
Each constant is determined so that 0°) is between 150 and 200 degrees, and the gain is adjusted with R4.

The curves GB and ψB in FIG. 3 represent the frequency characteristics of gain and phase when the positioning table of the precision machine tool is driven by the servo amplifier of the present invention. Similar to the conventional example, the output ΔP of the DA converter 10 was varied in a sine wave pattern, and the feedback voltage of the tacho generator was measured. Since two phase lead compensation amplifier circuits are included, compared to the conventional example,
Gain is improved at frequencies above 1501-lx. Therefore, it is possible to counter the uneven reaction force of the workpiece that occurs during machining, and improve the shape accuracy of the workpiece. The phase characteristics have also been improved, eliminating the resonance phenomenon caused by inertia and direct current
Since the gain of the servo system can be increased at low frequencies,
．． It is possible to stably achieve a positioning accuracy of 1 μm.

In the explanation so far, the drive motor 1 for the positioning table has been considered as a DC servo motor, but a brushless servo motor may be used, and a power amplification circuit for the brushless servo motor may be used for the drive motor 5.

Effects of the Invention As described above, according to the present invention, in servo amplification of machine tools, etc., the deviation output of the position between the target position and the current position from the numerical control device is calculated between the speed addition point and the speed addition point. By inserting a phase lead compensation amplifier having a phase lead compensation and amplification function between the servo system and the current addition point, the high frequency gain and phase characteristics of the servo system can be improved. By using the servo amplifier of the present invention, a machine tool that processes workpieces with submicron precision can be realized.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the servo system of a precision processing machine in an embodiment of the present invention, Fig. 2 is a circuit diagram of a lead phase compensation circuit used in the embodiment of the present invention, and Fig. 3 is a block diagram of a servo system of a precision processing machine according to an embodiment of the present invention. FIG. 4 is a characteristic diagram of the servo system showing the relationship between the positional deviation amount and the tachogenerator feedback amount. FIG. 4 is a block diagram of the servo system of a conventional machine tool. 5... Power amplifier circuit, 7, 8... Addition point, 9... D-A converter, 1o...
Position deviation counter, 12.13... Phase lead compensation amplifier circuit. Figure 1 Mother-in-law Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] It has a position deviation counter that outputs the deviation between the target position and the current position, a digital-to-analog converter that converts the output of this position deviation counter into an analog value, and a current feedback loop for driving the servo motor. a power amplifier circuit, and a summing point that feeds back the output from the tacho generator that detects the speed of the servo motor;
Precision device characterized by comprising: the digital-to-analog converter, a summing point, and two leading phase amplifier circuits having the same characteristics and having a leading phase characteristic and an amplification function, which are inserted between the summing point and the power amplifier circuit. Servo amplifier for positioning.