JPH0226300A - position control device - Google Patents

Abstract

PURPOSE:To improve the positioning accuracy of an apparatus to the stop accuracy of a stepping motor itself and below, by increasing or decreasing a current command according to a position error. CONSTITUTION:A signal read by a reproducing head 5 is amplified by a regenerative amplifier 7, outputted as a position signal 10 by a servo signal generator 9, and compared with a reference position signal 12 and operated by a comparator 11 to generate a positional-error signal 13. Said positional-error signal 13 increases or decreases a control voltage Vc 27 via charge and discharge circuits. Said control voltage Vc is added to a B-phase control signal VBC via changeover device 30 and addition amplifier 31. Such action varies the magnitude of torque generated in the B-phase of a stepping motor, controls a resultant force of torques by A- and B-phase coils, rotates a rotor minutely, and moves a recording and reproducing head by a minute amount.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a position control device that enables precise positioning of a magnetic disk device or the like using an electromagnetic drive device.

2. Description of the Related Art Conventionally, stepping motors have been widely used for precise positioning control of a positioning mechanism for a recording/reproducing head of a magnetic disk drive. In a magnetic disk drive, it is necessary to accurately position the head on a data track written on a signal recording medium. Therefore, the relative position of the head and data track is determined from a specific signal written on the recording medium. Control is performed to move the head by a minute amount so as to reduce the positional error.

A conventional position control device will be described below with reference to the drawings. FIG. 5 is a block diagram of a head position control section of a magnetic disk device using a stepper motor, and the same parts as in FIG. 1 showing the embodiment are given the same reference numerals.

The recording/reproducing head 5 reads the signal written on the recording medium 6, and the signal is amplified and detected by the reproducing amplifier 7. The reproduced signal 8 is sent to a servo signal generator 9 as a position signal 10 A-
The signal is quantized through the D converter 45 and taken into the CPU 33.

An example of this position signal is shown in FIG. A signal proportional to the width of the overlap between the servo patterns S1 and S2 written on the recording medium and the recording/reproducing head is reproduced, and by holding the peak value, the relative position of the recording/reproducing head and the data track can be determined. A signal 10 shown is obtained.

The CPO 33 calculates a relative position error from the captured position signal, and uses the calculated value to refer to the ROM 32 in which the current values to be passed through the two phases of the stepper motor are written in advance. Then, by outputting a current command value that brings the relative position error close to zero from the data in the ROM to the D-A converters 34 and 35, the A-phase coil/L/1 and B-phase coil/L of the stepper motor are output.
/2 to move the recording/reproducing head by a minute amount.

Next, the current flowing through the stepper motor and the stop position of the rotor 4 will be explained.

FIG. 7 is a conceptual diagram of a stepper motor torque generation mechanism. IA = Io cos (b) 1B = Io sin (b) When the current flowing through the A-phase coil 1 and B-phase coil v2 is tossed, the electric angle a is changed by the A-phase coil and the B-phase coil. The torque generated at each position is TA = -kt4A]in (a) TB = kt4BHsxn(H-a) =]ct4B
9 cos a However, kt: can be written as torque coefficient, so the composite torque Tl! is Ts+ = TA+TB=kt-Io(-s 1ria
lcos(bl+cosf&l・s 1n(bl)=
kt-Io・5in(a-b). If a = b, then T at the electrical angle a
s"O indicates that the simulator is positioned. For example, if current is applied only to the B phase coil, it will stop at the position Pl,
When current is applied only to the human-phase coil, it stops at position P3, and A
When equal currents are passed through the phase coil and B-phase coil, they stop at position P2. Therefore, by writing in advance the current to flow through the in-phase coil and B-phase coil in the ROM in accordance with the position to be stopped, and changing the current according to the position error,
It is possible to minutely control the stop position of the motor and accurately position the recording/reproducing head, which is linked to the motor, on the target data track.

As described above, even with the above-mentioned conventional position control device using a stepper motor, positioning can be performed by controlling the current flowing through the motor based on the relative position error between the recording/reproducing head and the data track.

Problems to be Solved by the Invention However, the conventional position control device described above has a problem in that the stop position of the stepper motor does not accurately correspond to the current flowing through the coil /l/ of each phase. The torque coefficient of the motor does not take a constant value due to the influence of the stop position of the stepper motor and the magnetic hysteresis of the magnetic material that makes up the motor, so even if the same current is passed through each phase of the coil, the stop position will not be constant. The position changed and accurate positioning was not possible. FIG. 8 shows an example of changes in the stop position when currents corresponding to the SIN wave and the CO5 wave are passed through the A-phase coil/V and B-phase coils of the step motor as described above. If kt is constant, it should be a straight line passing through the origin of the diagram according to the electrical angle for all mechanical angles, but for a certain measurement P4, even if the current electrical angle of the step motor is the same, the stopping position changes. However, this change appears as a different locus at another measurement point P5.

As described above, the conventional position control device has a problem in that the positioning accuracy cannot be improved beyond the stopping accuracy of the stepper motor itself.

SUMMARY OF THE INVENTION In order to solve the above problems, it is an object of the present invention to provide an excellent position control device that can improve positioning accuracy to a level lower than the stopping accuracy of the stepper motor itself.

Means for Solving the Problems In order to achieve the above object, the present invention is comprised of a drive device that generates electromagnetic force, a support means, a position detection means, a position command means, a comparison means, a current control means, a current drive means, By increasing or decreasing the magnitude of the current flowing through the electromagnetic drive device until the magnitude of the device error signal constituted by the comparison means falls within an allowable range, it is possible to stop the electromagnetic drive device at the target position.

For production The present invention has the following effects due to the above configuration.

That is, when the position of the movable part of the electromagnetic drive device deviates from the target position by more than an allowable amount, the current flowing through at least one coil of the electromagnetic drive device can be increased or decreased to reduce the position error. As a result, even if the current-to-torque conversion coefficient kt of the electromagnetic drive device does not take a constant value, it is possible to increase or decrease the flowing current in accordance with the position error, thereby achieving accurate positioning.

Embodiment FIG. 1 shows the configuration of an embodiment of the present invention. The configuration and operation of this embodiment will be described below with reference to the drawings.

The stepper motor is a driving device using electromagnetic force, and includes a member A consisting of an A-phase coil lv1, a B-phase coil lv2, and a stator 3, and a member B, which is a rotor 4. FIG. 2 shows an example of this stepper motor.

The recording and reproducing head 5 and the rotor are connected by means such as a steel plate and the rotor, and the recording and reproducing head 5 linearly moves over the recording medium 6 by an amount proportional to the rotation angle of the rotor to record and reproduce data. The read signal is amplified by a regenerative amplifier 7, outputted as a position signal 10 by a servo signal generator 9, and then sent to a comparator 1.
1, it is compared with the reference position signal 12 and the position error signal 13 is calculated.
occurs.

The reference position signal is a signal corresponding to the position of the target data track, and is generated from the CPU 33 via the DA converter 36.

The position error signal is outputted by the permissible upper limit comparator 14 and the permissible lower limit comparator 15 to Vref 16 and V, which respectively indicate the permissible error width.
It is compared with ref (-) 17 and generates a discharge signal 18 and a charge signal 19, which turn on and off gate (E) 20 and gate (21). Discharger 22 and charger 2
3 is a control voltage V which causes a current 25 to flow through the resistor element 24 and is generated in the capacitor 26 when the gate is turned OFF.
Increase or decrease c27.

The correspondence between the position error signal and the change in the control voltage will be explained with reference to FIG. If the position error signal is larger than Vzef (2), the gate ◯ is ONL, the charge on the capacitor is reduced by the discharger, and the control voltage is lowered. On the other hand, the position error signal is Vref
(If it is smaller than El, the gate ■ turns ON and the control voltage is increased by the charger. In this way, the position error signal becomes Vref■
The control voltage increases or decreases until it reaches between Vref and Vref e, and the position error signal and the control voltage are not in a proportional relationship.

Next, this control voltage is input to the buffer amplifier 28, and this signal and the signal from the inverting amplifier 29 are transferred to the CP by a switch 30.
It is switched by the switching signal 39 from U33, and added to the B phase instruction signal VB38 from the CPU by the adding amplifier 31.
It is input to the B-phase current driver 42 as a phase control signal VBC40. On the other hand, the CPU inputs the human phase instruction signal VA37 from the D-A converter 34 to the A-phase current drive device 41.

This controls the A-phase motor current IA43 and the B-phase motor current xB44, and changes the stop position of the step motor. Note that the CPU generates command values for VA and vB by referring to the ROM 32 in accordance with the target position.

The operation of driving the stepper motor with such a configuration and accurately positioning the recording/reproducing head will be explained. The position signal read by the recording/reproducing head is converted into a position error signal, and the relative positional error between the actual recording/reproducing head and the recording medium is proportional to this position error signal. Furthermore, as shown in Fig. 3, the control voltage VC is set so that the magnitude of the position error signal is Vr.
It increases or decreases until it becomes between ef and Vrefθ.

FIG. 4 shows the correspondence between the control voltage VC, the B-phase instruction voltage VB, the B-phase control signal VBC, and the B-phase motor current IB.

vB output from the CPU gives a bias value for the current flowing through the B-phase coil, and IB changes to a straight line 11 by increasing or decreasing vc.
It is controlled as shown in . On the other hand, 12 is the increase/decrease in vc and I
This is a case where the increase or decrease of B is reversed, and this is selected by a switch according to a command from the CPU according to the mechanical angle. Through such an operation, the magnitude of the torque generated in the B phase of the system chipper motor is changed, the resultant force of the torque by the A phase coil and the B phase coil is controlled, the rotor is rotated minutely, and the recording/reproducing head is moved a minute amount. I can do it. Therefore, VC increases or decreases until the magnitude of the position error signal falls within an acceptable range, and IB increases, decreases, or reverses accordingly, and the rotor of the stepper motor rotates even if the torque coefficient varies in value. It can be seen that the recording/reproducing head is moved closer to the data track and operates so that the positional error is reduced.

As described above, according to this embodiment, even if the stepper motor has variations in the top coefficient, the position can be accurately controlled by increasing or decreasing the current until the positioning error falls within the allowable range.

In this embodiment, a two-phase stepper motor is used as the electromagnetic drive device, but other types of electromagnetic drive devices that perform positioning by controlling the torque of each phase of the motor may be used.

Further, although the position error signal is obtained from the reproduced signal, it can be constructed similarly using a position encoder or the like.

Effects of the Invention As is clear from the above embodiments, the present invention is advantageous in that, in an electromagnetic drive device such as a stepper motor, the current value to be applied can be adjusted to a certain position even if the conversion coefficient from current to torque of each phase does not take a constant value. It has the effect that it increases or decreases according to the error and allows accurate positioning.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a position control device according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing an example of a drive device that generates electromagnetic force, and FIG. 3 is a diagram showing changes in a position error signal and a control signal. Figure 4 is a diagram showing the correspondence between the control voltage configuration and motor current, Figure 5 is a schematic block diagram showing an example of a conventional position control device, and Figure 6 is a diagram showing the relationship between the recording/reproducing head and the servo pattern. Figure 7 is a diagram showing the correspondence between position and position signal; Figure 7 is a diagram showing the correspondence between the current of each phase of the motor and torque; Figure 8 is a diagram showing an example of the current of each phase of the stepper motor and the stop position. . 1...AN coil, 2...B phase coil, 3...
...Stator, 4...Rotor, 5...
Recording/playback head, 6... Recording medium, 7...
・Regenerative amplifier, 9... Servo signal generator, 11
... Comparison calculator, 14 ... Allowable upper limit comparator, 15 ... Allowable lower limit comparator, 28 ......
Buffer amplifier, 29...Inverting amplifier, 30.
...Switcher, 31...Summing amplifier, 32...
...ROM. 33...CPU, 34-36...D/
A converter, 41...A phase current drive device, 42.
...B phase current drive device. Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (5)

[Claims] (1) A drive device that generates electromagnetic force, consisting of a member A that includes a soft magnetic material and a plurality of coils, and a member B that includes a soft magnetic material or magnet that faces the member A with a certain gap therebetween. a supporting means for maintaining a gap between the member A and the member B and allowing relative movement; a position detecting means for recognizing the position of the member A or the member B; and a position detecting means for detecting the position of the member A or the member B.
a position command means for providing a desired position, a comparison means for comparing a position signal generated from the position detection means with a position command signal indicating the desired position, and a position error signal outputted from the comparison means having an allowable magnitude. current control means for increasing or decreasing a command value of the magnitude of the current flowing through at least one of the plurality of coils of the member A until the current command value reaches a range within which the current is supplied to the coil based on the command value of the current; A position control device comprising current drive means. (2) The current control means controls the current flowing into and out of the capacitor based on the position error signal output from the comparison means, changes the magnitude of the voltage generated in the capacitor, and changes the magnitude of the current flowing through member A. The position control device according to claim 1, characterized in that it is configured to control. (3) The comparison means and the current control means are composed of a memory means for storing programs and data created to realize processing contents, and an arithmetic processing section that performs processing according to the programs and data, and from this comparison means, It is characterized in that it is configured to increase or decrease the command value of the magnitude of the current flowing through at least one of the plurality of coils of member A until the magnitude of the output position error signal falls within an allowable range. A position control device according to claim 1. (4) The current control means causes current to flow through at least two of the plurality of coils of member A, increases or decreases the magnitude of the current flowing through at least one coil, and controls the resultant force of the torque generated by each coil. The position control device according to claim 1, characterized in that it is configured as follows. (5) At least one of member A and member B has magnetic pole pieces carved at a constant pitch, and is configured to face each other with a constant gap between them. The position control device described.