JPS605789A - Ac servo motor - Google Patents

Abstract

PURPOSE:To stably and reliably start a motor by outputting a stepped analog phase signal until an arithmetic unit outputs an initial reference position signal at the starting time. CONSTITUTION:U, V, W phase signals having 120 deg. phase difference of an electric angle are outputted to an encoder RE, an arithmetic unit mu. CON calculates steps in a starting mode range on the basis of the signals until an initial reference position signal is at least outputted, and outputs a stepped analog phase signals U', V', W' to a D/A converter. Thus, the rotor position can be discriminated in the range of 120 deg. at the maximum of an electric angle from the starting time, and the adaptive coil current can be supplied.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an AC system that reads out sine wave data stored in a ROM in synchronization with the rotational position of a rotor using a digital arithmetic unit, and controls the current of a triad armature coil using a sine wave phase signal.
Regarding servo motors.

In an AC servo motor in which the current pattern of an armature coil is controlled by a phase signal obtained by a digital calculator of this type, a phase signal is necessary for starting the motor. Therefore, it is conceivable to use an absolute rotary encoder or resolver that detects the absolute position of the rotor.

However, the former is very expensive, and the latter requires complicated peripheral equipment.

The present invention has been made in view of the above circumstances, and provides an AC servo motor that is based on an inexpensive incremental rotary encoder and can be stably started by obtaining a phase signal at the time of starting. The purpose is to

In order to achieve this objective, the present invention provides an encoder with an electrical angle of 1
200 interval U, V, W phase signals are output during the start mode until the encoder outputs at least the first reference position signal.

The phase signal is obtained by the W-phase signal. In other words, the rotor position and rotation direction are detected by the output of the incremental encoder, and the R
In an AC servo motor that reads data from the OM using a digital arithmetic unit and converts this data into an analog phase signal using a D/A converter to control the current of the triad armature coil, the encoder has an electrical angle of 120°. Interval U, ■.

While outputting the W-phase signal, the arithmetic unit outputs the signal to the D/A converter based on the U-, V-, and W-phase signals at least until the encoder signal indicating the initial reference position at startup is output. It was configured to output a step-like analog phase signal. The present invention will be described in detail below based on the illustrated embodiments.

FIG. 1 is an overall view of one embodiment, and FIG. 2 shows its phase signal generating section. SM is, for example, a permanent magnet synchronous AC motor having a four-pole permanent magnet rotor, and RE is a rotary encoder.

In Figures 3 and 4, numeral 10 is a disk, and this disk 10 is 3
It is connected directly or through a joint to the rotor of a phase synchronous motor and rotates together with the rotor. A large number of slits (shaded areas in FIG. 1) are formed in this disk 10 as position markers. A large number of slits 12 as first position markers are formed at equal intervals on the outermost circumferential side, and first sensors 14a, 14b are connected to the slits 12 with a phase difference of 90 degrees.
and light emitting elements 15a and 15b are opposed to each other (FIG. 2), and these sensors 4a and 14b detect the light passing through the slit 12 and output a continuous pulse train of A phase and B phase shown in FIG. The rotational speed, rotational direction, and rotational amount of the rotor are detected by these A and B4fl pulse trains.

One slit 16 as a second position marker is formed within one circumference on the inner peripheral side of the slit 12, and a second sensor 18 and a light emitting element 19 are opposed to this. This sensor 18
detects the reference position of the disk 10 from the light transmitted through the slit 16 and outputs one Z-phase pulse (index signal) as shown in FIG. 2 per round. By adding or subtracting the A or B phase pulse based on this Z phase pulse, the absolute position of the disk 10 can be calculated.

However, until this Z-phase pulse is output at the time of starting, the reference position is unknown, so the position of the rotor cannot be determined. This rotor position information at the time of startup is obtained by the slit 20 as a third position indicator and the three sensors 22 (22a, 22b, 2
2c) and the light emitting element 23 facing these (only 23b is shown, see FIG. 2).

The slits 20 are formed alternately so as to equally divide the circumference with an angular variation of 360° divided by the number of poles of the motor.

This embodiment is used for a four-pole motor, and the slits 20 are alternately provided at 90° intervals. The three sensors 22 (, 22a, 22b, 22c) are sensor 2
They are placed every 120 degrees in electrical angle on the left and right with 2b as the center. In this example, the motor has 4 poles, so the actual angle is 60.
They are spaced at ° intervals. Therefore, three sensors 22a,
22BL 22C outputs rectangular waves whose phases are shifted by 120 degrees in electrical angle, as shown by U phase, ■ phase, and W phase in FIG.

The output of the encoder RE is an analog phase signal U, V generated by the rotor in a phase signal generating section P.

Converted to W.

The A and B phase signals are waveform-shaped by a pulse generator PG, and the rotation direction is determined. Here, the waveform-shaped A-phase signal is input as a clock pulse CL to an up/down counter U/D-C, and a forward/reverse signal U/D indicating the rotation direction is input to an up/down flip-flop U/D-C.
The rotation direction is memorized by FF. Counter U/D-C integrates clock pulses CL during forward rotation, and subtracts clock pulses CL during reverse rotation. Note that the Z phase signal (indicating the reference position) is U/D/C.
is input to reset the counter U/D-C.

The digital arithmetic unit (microcomputer) μCON is in the starting mode until the first Z-phase signal at startup is output (logic 1), and once the Z-phase signal is output, it is in the steady mode and outputs the digital phase signal. Output U(D) and W(D). This mode is determined based on the output of the flip-flop F/F which stores the Z-phase signal (logic 1) once it is output.

First, the steady mode will be explained. The mode is 2 phase signal is 0 or 1
(Step 100 in FIG. 6). At this time, the 8-bit output of counter U/D-C (starting from the Z-phase signal position) is read into μCON (6th
In step 102 in the figure, tt-coN adds the counter output value to the start address (corresponding to the Z-phase signal position) of the sine wave data (SIN table) in the ROM (not shown) that stores the sine wave data. Find the address of the sine wave data corresponding to the counter output (step 104 in the figure) and read out its contents (step 106). This becomes the U-phase digital phase signal U(D) with the Z-phase signal as the base point. . This signal is converted into an analog phase signal U by the D/A converter D/A(U) (step 108).

Therefore, its waveform becomes a sine wave shown in FIG. 4U.

As for the W phase, since the phase is 240° ahead of the U phase, the take of the address obtained by adding 240° to the U phase address is read (steps 110 and 112), and the converter D/A
(W) to convert it into an analog phase signal W (step 11
4).

The signals U and W obtained as above are multiplied by the current amplitude command signal i which is proportional to the difference between the speed reference vi and the speed feed pack signal vo (multiplier 30a
, 30b), this product becomes the current command values a and c for the U and W phases, and from the difference between these, the current command value for the V phase is determined, and the current value of the armature coil (not shown) of each phase is determined from these and the current command values of the armature coils (not shown) of each phase. Feedback signal i.

The pulse width modulation circuit (PWM) of each phase selectively controls on/off each transistor of the transistor bridge B based on the difference between the two and the armature coil current.

In the starting mode until the Z-phase signal is output during starting (
(Step 100→Y in FIG. 6), μCON performs calculations for each step within the starting mode range in FIG.
output to the converter.

(2) is determined by inverting the sum of the two as in the normal mode. Analog phase signals U', v'.

Since W has a step shape, the current in the armature coil of each phase also has a step shape.

In the above embodiment, the reference position of the rotor is determined by the Z-phase signal, but if it is detected based on the rise and fall of the waveforms of the U, V, and W-phase signals, only a maximum of 120 degrees in electrical angle can be set to the starting mode. , after that you can switch to steady mode,
Since the starting mode period is shortened compared to the previous embodiment, starting performance is improved.

Note that the sine wave data in the ROM is not in a strict sense, but is data with a waveform that approximates a sine wave, and there is no major disadvantage if it is data, and it goes without saying that such data is included in the present invention.

Further, within the range of the waveform width (180 degrees in electrical angle) of the U, V, and W phase signals, another slit or optical sensor is provided to detect a predetermined angle at the center of the waveform width (180 degrees in electrical angle) to detect the analog phase signal U.

If v' and w' are changed in a stepwise manner, rotational irregularities at the time of starting will be reduced and the rotation will be even smoother.

As described above, the present invention provides an encoder with an electrical angle of 120°.
The arithmetic unit outputs U, V, and W phase signals with phase differences, and at the time of startup, the computing unit generates a step-like (rectangular wave, Now outputs an analog phase signal (step wave). Therefore, the rotor position can be changed to a maximum of 1 in electrical angle from the time of starting.
It can be determined within a range of 20 degrees, and by supplying an appropriate coil current, the motor can be started stably and reliably. Furthermore, since only a small amount of processing is required on the conventional incremental rotary encoder, it is not expensive.

[Brief explanation of the drawing]

Fig. 1 is an overall diagram of an embodiment of the present invention, Fig. 2 is a block diagram of its phase signal generation section, Fig. 3 is a partially sectional plan view of the encoder, and Fig. 4 is a cross section taken along the line ■-■. 5 is a diagram of output waveforms of each part, and FIG. 6 is an operation flowchart of the arithmetic unit. RE...Encoder, M...AC motor, μmC0N
...Digital calculator, Z...Reference position signal. Patent applicant Shibaura Seisakusho Co., Ltd. Agent Patent attorney Yama 1) Written by Ml Figure 3 I-1 Draft procedural amendment (voluntary) 8 July 20, 1985 Commissioner of the Patent Office Kazuo Wakasugi 1 Indication of the case Showa 1958 Patent Application No. 109373 2 Title of the invention AC servo motor 3 Relationship with the supplementary case Patent applicant representative Ryo Watanabe 4, agent 8 Contents of amendment Contents of amendment (1) Description No. In the fourth line of page 8, the phrase ``From these differences'' is corrected to ``From the value obtained by scaling the sign of these sums.'' (2) On page 9, lines 2-3 and page 10, line 2 of the same book. The phrase “maximum 120°min” has been corrected to “maximum 60°min.” (hereinafter)

Claims (1)

[Claims] An RO that detects the rotor position and rotation direction using the output of an incremental encoder and stores sine wave data.
In an AC servo motor that reads data from M by a digital arithmetic unit and converts this data into an analog phase signal by a D/A converter to control the current of a triad machine coil, the encoder has an electrical angle of 120°. Interval U, V. While outputting the W-phase signal, the arithmetic unit operates the D/A on the basis of the U, V, and W-phase signals for at least 5 minutes until the encoder signal indicating the initial reference position at startup is output.
An AC servo motor characterized in that a converter outputs a substantially step-like analog phase signal.