JPS63277485A - Excessive speed control system for servomotor - Google Patents

Abstract

PURPOSE:To detect the condition of excessive speed correctly, by a method wherein the condition of excessive speed, in which the speed of a servomotor has become higher than a set limit speed, is detected by the speed signal of a servo control loop. CONSTITUTION:An excessive speed control system for a servomotor is constituted of a detecting unit 11, detecting the driving speed of the servomotor 4, an excessive speed detecting unit 13, a servo control unit 14 and a driving unit 15 while the servomotor 4 is driven in accordance with the control output DVS of the servo control unit 14 and the servomotor 4 is short-circuited when the servo control unit 14 has received an excessive speed detecting signal BS. The excessive speed detecting unit 13 is constituted of an excessive speed deciding circuit 13a and a latch circuit 13b while the detecting unit 13 changes a speed signal VS from the speed detecting unit 11 into an absolute value and compares it with a limit speed signal V0. When ¦VS¦>=V0, the detecting unit 13 outputs an excessive speed output to latch the running of the servomotor and generates the excessive speed detecting signal BS.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Prior art (Fig. 4) Problems to be solved by the invention Means for solving the problems (Fig. 1) Working examples (a) ) Explanation of the configuration of one embodiment (FIGS. 2 and 3) (b) Explanation of the operation of one embodiment (C) Explanation of other embodiments Effects of the invention [Summary] Detecting runaway of a servo motor In the servo motor runaway control method, which controls the servo motor to stop by short-circuiting the servo motor, the speed of the servo motor is monitored to detect runaway, and the servo motor drive unit stops the servo motor in response to the runaway detection. By short-circuiting, stop control in the event of runaway is performed accurately and easily.

[Industrial application field]

The present invention relates to a runaway control method for a servo motor, which detects runaway in a servo motor such as a voice coil motor, and controls the runaway to stop. The present invention relates to a runaway control method for a servo motor.

For example, in a magnetic disk drive, a voice coil motor is used as a positioner for a magnetic head, and performs a seek operation on a magnetic disk.

In a device that uses a servo motor as a drive source, such as a voice coil motor, if a failure occurs in the circuit system that controls the motor, the motor may run out of control. If the motor runs out of control, the movable part may collide with the fixed part and destroy a part of the device, so it is desired to detect runaway at an early stage and control the motor to stop it.

[Conventional technology]

FIG. 4 is an explanatory diagram of the prior art.

As shown in FIG. 4(A), the drive mechanism 8 of the magnetic disk device includes a magnetic disk 5 rotated by a spindle shaft 7, and a positioner 1 that supports a magnetic helad 3 at the tip of an arm 2. .

The positioner 1 has rollers 1a and 1b at its lower part, is movable, and uses a voice coil motor 4 to position the magnetic head 3 in the radial direction of the magnetic disk 5.

The voice coil motor 4 includes a fixed magnetic circuit 4b,
This is a linear servo motor composed of a voice coil 4a provided in a positioner 1.

A protrusion 1c is provided at the bottom of the positioner 1, while a pair of mechanical stoppers 6a and 6b made of springs or the like are provided on the drive mechanism 8.

Therefore, the positioner l has a pair of mechanical stops 6a,
The range between 6b and 6b is the operating range, and constitutes a mechanical stopping mechanism when the voice coil motor 4 runs out of control.

If only such a mechanical runaway stop means is used, when runaway occurs, the positioner 1, which is a movable part, will stop at the fixed part (spring) 6a.
, 6b), the impact is large, so a method is used to detect runaway and electrically apply the brakes.

For example, in Japanese Patent Application Publication No. 57-56149, there is shown in Fig. 4 (B
), a pair of runaway detection coils 9a and 9b are provided, the occurrence of runaway is detected by the voltage induced in the coils 9a and 9b, the voice coil 4a is short-circuited, and braking is applied using a back electromotive force. It is shown.

Therefore, as shown in FIG. 4(C), the voice coil 4a
A voice coil 4 is connected to a circuit connecting the power amplifier 10 and the voice coil 4.
a pair of thyristors (electronic switching elements) 12a in parallel with a;
12b is provided, the runaway detection coils 9a and 9b are connected to the thyristor 12aS and 12b, and the voltage induced in the coils 9a and 9b turns on the thyristor 12a or 12b to short-circuit the voice coil 4a. ) to generate braking force.

[Problem that the invention seeks to solve]

However, in the conventional method, the excitation coil (voice coil) 4a of the servo motor (voice coil motor) 4
It is necessary to separately provide runaway detection coils 9a and 9b, which poses the problem of complicating the shape of the motor coils.
This is unfavorable in terms of performance and cost of the servo motor.

Also, the characteristics of the coils 9a and 9b change due to temperature changes. Therefore, even if the coils 9a and 9b are set to induce a voltage sufficient to turn on the sirisk at a speed exceeding a certain speed limit, the characteristics may not be accurate due to the change in characteristics. There was a problem in that the short-circuit operation was not performed at speeds above the speed limit, and as a result, stop control in the event of runaway was not performed in a timely manner.

SUMMARY OF THE INVENTION An object of the present invention is to provide a servo motor runaway control method that can accurately detect the occurrence of runaway and perform electrical stop control without changing the servo motor.

[Means for solving problems]

FIG. 1 is a diagram explaining the principle of the present invention.

In the figure, the same parts as those shown in FIG. 4 are indicated by the same symbols, 11 is a speed detection section,
13 is a runaway detection section which monitors the detected speed Vs of the speed detection section 11 and detects the detected speed Vs.
Runaway detection signal B is detected when s exceeds the scheduled speed.
14 is a servo control unit that performs servo control according to the difference between the target speed and the detected speed Vs;
15 is a drive section, and the control output DV of the servo control section 14
The servo motor 4 is driven in response to S, and the servo motor 4 is short-circuited in response to receiving the runaway detection signal BS.

[Effect]

In the present invention, a runaway state in which the speed of the servo motor 4 exceeds a set limit speed is detected by the speed signal of the servo control loop, and when runaway is detected, the drive section 15 is operated to short-circuit the servo motor 4. .

Thereby, there is no need to change the servo motor, and runaway conditions can be accurately detected and the servo motor can be short-circuited.

〔Example〕

(al) Explanation of the configuration of one embodiment FIG. 2 is a configuration diagram of one embodiment of the present invention, taking control of a voice coil motor of a magnetic disk device as an example.

In the figure, the same parts as those shown in FIGS. 1 and 4 are indicated by the same symbols, lla is a servo signal demodulation circuit, and one side of the magnetic disk 7 is used as a servo disk.
one that writes a servo signal, demodulates the servo signal SvS read by the magnetic head 3, and outputs a position signal ps;
llb is a speed signal generation circuit, which differentiates the position signal ps and calculates the voice coil current 1t/I2 of the drive unit 15.
13 to create a speed signal Vs (voltage) in conjunction with
a is a runaway determination circuit, which converts the speed signal Vs into an absolute value,
13b is a latch circuit that latches the runaway output of the runaway determination circuit 13a and issues a runaway detection signal BS; 14b is a target speed generation circuit that generates a target speed Vc in response to an instruction from a higher level device (not shown); a servo control circuit 14b that performs servo control according to the difference between the target speed VC and the detected speed Vs;
, a control output (drive signal) DVS is generated.

Figure 3 shows the drive section (power amplifier section) in Figure 2.
FIG. 5 is a configuration diagram of No. 5.

In the figure, 15a is the original power amplifier, with H-type connection (
It constitutes a power amplifier (balanced connection). That is,
A pair of motor drive switching transistors Q3
, Q4 are connected in series with current control transistors Q5 and Q4.
6 is connected, a motor coil (VCM coil) 4a is connected to the connection point, and further transistors Q3, Q4, Q
5. Drive transistors Q1 and Q are connected to the base of Q6.
2 is provided. Note that D1 to D4 are protection diodes, R1, R2, R3, R4, R5, and R6 are bias resistors, and R3I and R52 are current detection resistors.

In order to short-circuit the voice coil 4a with the runaway detection signal BS, a first short-circuiting transistor Q7 forcibly turns on the transistors Q3 and Q4 in response to the runaway detection signal BS, and transistors Q1, Q2, and Q5 are connected to the power amplifier section 15a. ,
A second shorting transistor Q8 is provided to forcibly turn off Q6.

In addition, D6, D7, D8, D9 are protection diodes, R8 is an output resistance, vl, v2, v3 are potential sources, and Vl>
V2, Vl>V3 is set.

(bl　Explanation of operation of one embodiment Next, the operation of the configurations shown in FIGS. 2 and 3 will be explained.

Upon receiving a seek command from a higher-level host, the target speed generation circuit 14a of the servo control unit 14 generates a target speed Vc, and the servo control circuit 14b generates control outputs DVS (DVI, DV2).
) is emitted.

In the power amplifier section of FIG. 3, upon receiving the control output DVI, the transistor Q1 turns on, thereby turning on the transistor Q3 and operating the transistor Q5. Since transistors Q5 and Q6 serve as a current control stage,
In accordance with the control output DVI, a current flows through the route of potential source v1, diode D5 and resistor R7, transistor Q3, voice coil 4a, transistor Q5, current detection resistor R51, and potential source v2. It is driven by current flowing from right to left.

Conversely, upon receiving the control output DV2, the transistor Q2 turns on, which turns on the transistor Q4 and operates the transistor Q6. Therefore, a current corresponding to the control output DV2 flows through the route of the potential source ■l, the diode D5, the transistor Q4, the voice coil 4a, the transistor Q6, the current detection resistor R52, and the potential source v2, and the voice coil 4a has a It is driven by current flowing from left to right.

On the other hand, the voice coil 4a is driven to move the positioner l, and the magnetic head 3 traverses the servo disk 7 and reads the servo signal. The read servo signal SVS is demodulated into a position signal ps by a servo signal demodulation circuit 11a, and a speed signal Vs indicating the actual speed of the voice coil motor 4 is created by a speed signal creation circuit 11b.

The speed signal Vs is input to the servo control circuit 14b, and the servo control circuit 14b performs servo control based on the difference from the target speed Vc, changes the drive signal DVS (DVI/DV2), and controls the voice coil 4a of the power amplifier section 15. The speed of the voice coil motor 4 is controlled to the target speed Vc by changing the current flowing through the voice coil motor 4.

Therefore, servo control of the DC motor is performed.

On the other hand, when the vehicle runs out of control, the speed of the voice coil motor 4 exceeds the speed limit.

The runaway detection unit 13 monitors the speed signal Vs, converts the speed signal Vs into an absolute value in the runaway determination circuit 13a, and determines the speed limit Vo.
Compare with. When the runaway determination circuit 13a determines that 1Vsl≧Vo, it determines that the runaway has occurred, sets the latch circuit 13b, and generates the runaway detection signal BS. Runaway detection signal BS
is input to the power amplifier section 15 and is transmitted to the upper level as a seek failure signal SKI, and the higher level recognizes the seek failure.

In the power amplifier section 15, the runaway detection signal BS is input to the bases of the short-circuiting transistors Q7 and Q8 to turn them on. When the short-circuiting transistor Q7 is turned on, the base potential of the switching transistors Q3 and Q4 is set to V3 via the output resistor R8 and the protection diodes D6 and D7, and these are forcibly turned on.

Furthermore, when the short-circuit transistor Q8 is turned on, the drive transistors Ql,
The base of Q2 is set to the potential v2 to forcibly turn off these transistors, thereby also forcibly turning off current control transistors Q5 and Q6.

Therefore, both ends of the voice coil 4a are connected and short-circuited through the route of the protection (flyback) diode D2, the transistor Q3, or the protection diode Di,) and the transistor Q4.

Therefore, the current due to the back electromotive force induced in the voice coil 4a flows from the coil 4a to the diode DI to the transistor Q.
4-Coil 4a or Coil 4a-Diode D2-) Transistor Q3-Coil 4a flows through the route, and the current in the opposite direction to the drive current generates a braking force and performs control to stop runaway.

On the other hand, after receiving the sequin complete signal SKI, the higher-order device clears the launch circuit 13b and turns off the runaway detection signal BS after a certain period of time has elapsed.

This power amplifier section 15 is the original power amplifier section 15a.
By adding short-circuiting transistors Q7 and Q8 to the power amplifier section 15a, the short-circuiting function can be provided with a relatively small number of additional parts.

(C) Description of other embodiments In the above embodiments, the explanation was given using a magnetic disk device as an example, but it can be applied to other well-known devices having moving parts and motors, and a servo motor can also be used as a linear voice coil motor. However, it can be applied to other well-known servo motors.

Further, the speed detection section is not limited to one using a servo signal, but may also be one based on an output from a low reencoder or the like.

Although the present invention has been described above using examples, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As described above, according to the present invention, there is an effect that stop control in the event of runaway can be performed without changing the servo motor, and accurate and simple implementation is possible.

Further, since runaway is detected using the speed signal of the existing servo control loop, runaway can be detected accurately and inexpensively, and runaway control can be easily performed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is a configuration diagram of an embodiment of the present invention, FIG. 3 is a configuration diagram of the drive section in the configuration shown in FIG. 2, and FIG. 4 is an explanatory diagram of the prior art. . In the figure, 4--Voice coil motor (servo motor), 11--Speed detection section, 13--Runaway detection section, 14--Servo control section, 15-- Drive section.

Claims (1)

[Claims] A speed detection unit (11) detects the speed of the servo motor (4).
), a servo control unit (14) that performs servo control according to the difference between the target speed and the detected speed, and a speed detection unit (11) that monitors the detected speed, and when the detected speed exceeds the scheduled speed. a runaway detection unit (13) that detects this and generates a runaway detection signal;
), and a drive section () that drives the servo motor (4) according to the control output of the servo control section (14) and short-circuits the servo motor (4) in response to receiving the runaway detection signal. 15) A runaway control method for a servo motor, comprising: