JPH04271023A - Servo circuit - Google Patents

Abstract

PURPOSE:To prevent a head form colliding against a megneto-optical disk. CONSTITUTION:An arithmetic circuit 2 supplies an action signal to 8 control circuit 3 in response to the difference between the target value received from a target value setting circuit 1 and the detection signal received from a detecting circuit 6. An operating circuit 4 turns the operating signal received from the circuit 3 into an operating signal and supplies this signal to an actuator 5 via a switch 12. The actuator 5 drives a heed (not shown in the diagram) to keep a prescribed distance from a megneto-optical disk. Then the circuit 6 detects the distance between the head and the disk and supplies this detection signal to the circuit 2. An abnormality detecting circuit 16 detects the abnormality based on the outputs of both window comparators 14 and 15 and then turns off the switch 12.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo circuit suitable for use, for example, in maintaining the distance between a head and a disk at a predetermined value in a magneto-optical disk device.

0002

2. Description of the Related Art In a magneto-optical disk drive, the distance between a head and a magneto-optical disk is set to a predetermined distance (for example, 1
00 μm). A servo circuit is provided to maintain the distance between the head and the magneto-optical disk.

FIG. 6 shows the basic configuration of this servo circuit. As shown in the figure, the target value setting circuit 1 outputs an electrical signal corresponding to a predetermined target value (100 μm in this example). The calculation circuit 2 calculates the difference between the target value input from the target value setting circuit 1 and the detection signal input from the detection circuit 6, and generates an operation signal. This operation signal is input to a control circuit 3 inserted as necessary, and subjected to processing such as phase compensation. The operation signal output from the control circuit 3 is input to the operation circuit 4, which includes, for example, a driver, and is converted into an operation signal. The actuator 5 is driven by this operation signal. The actuator 5 adjusts the position of the head (none of which is shown) with respect to the magneto-optical disk so that the head is located at a position corresponding to the operation signal. The detection circuit 6 detects the actual distance between the head and the magneto-optical disk, and supplies a signal corresponding to the detection result to the arithmetic circuit 2. In this way, the actuator 5 drives the head so that it is always positioned at a predetermined distance from the magneto-optical disk.

0004

[Problem to be solved by the invention] The conventional servo circuit is
In this way, the detection circuit 6 detects the distance between the head and the magneto-optical disk, and the servo is applied so that the distance matches the target value set by the target value setting circuit 1. However, for example, if the arithmetic circuit 2, control circuit 3, operation circuit 4, or actuator 5 breaks down, the correct servo operation will not be performed, and the head will collide with the magneto-optical disk, causing the head to be damaged due to the heat and shock caused by the collision. Otherwise, one or both of the disks could be damaged.

The present invention has been made in view of this situation, and is intended to prevent damage to the servo target even if the components of the servo circuit fail.

[0006]

[Means for Solving the Problems] The servo circuit of the present invention has the following features:
A setting means for setting a predetermined target value, an operating means for performing a predetermined operation, a detecting means for detecting the operating state of the operating means, and an operating signal from the detection result by the detecting means and the target value set by the setting means. In a servo circuit, the servo circuit includes a calculation means for calculating the operation signal, and an operation means for generating an operation signal in response to an operation signal outputted by the calculation means and operating the operation means, the servo circuit and protection means for stopping the operation of the device.

[0007]

[Operation] In the servo circuit configured as described above, the operating signal input to the operating means and the operating signal output from the operating means are monitored, and the operation of the servo circuit is stopped in accordance with the states of both signals. Therefore, even if a failure occurs in the means constituting the servo circuit, damage to the object targeted by the servo can be prevented.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the configuration of an embodiment of a servo circuit according to the present invention. Components corresponding to those in FIG. Since it is repetitive, it will be omitted as appropriate. In the servo circuit in the embodiment shown in FIG.
, a protection circuit 11 is added to a servo circuit consisting of a detection circuit 6. In this embodiment, the protection circuit 11 includes a switch 1 inserted between the operating circuit 4 and the actuator 5.
2, a phase compensation circuit 13 that performs phase compensation so that the operation signal output from the arithmetic circuit 2 has the same phase as the operation signal output from the operation circuit 4; A window comparator 14 compares the operation signal outputted by the operation circuit 4 with a predetermined reference value, and detects an abnormality in the servo circuit from the outputs of the window comparators 14 and 15. Then, switch 1 is turned on in response to the detection result.
and an abnormality detection circuit 16 that controls 2.

The calculation circuit 2 calculates the difference between the target value input from the target value setting circuit 1 and the detection signal input from the detection circuit 6, and generates an operation signal corresponding to the difference. This operation signal is input to the control circuit 3, compensated for a predetermined phase, and then supplied to the operation circuit 4, where it is converted into an operation signal. This operation signal is supplied to the actuator 5 via the switch 12, and the actuator 5 drives a head (not shown) in response to this operation signal. The detection circuit 6 detects the distance between the head and the magneto-optical disk, and outputs the detection result to the arithmetic circuit 2. This closed loop operation controls the distance between the head and the magneto-optical disk so that it matches the target value set by the target value setting circuit 1.

The window comparator 14 compares the operating signal whose phase has been compensated by the phase compensation circuit 13 with a predetermined reference value, and outputs a signal corresponding to the comparison result. For example, it is 1 when the input signal is larger than a predetermined positive reference value (+ref1), and - when it is smaller than a negative reference value (-ref1).
1. Outputs a detection signal of 0 when the value is between the negative reference value and the positive reference value (Figure 2). Similarly, window comparator 15
The operation signal output from the operation circuit 4 is a predetermined positive reference value (
1 when larger than +ref2), negative reference value (-ref
2) Outputs a detection signal of -1 when it is smaller than the negative reference value and 0 when it is between the negative reference value and the positive reference value (FIG. 3). The abnormality detection circuit 16 determines the presence or absence of an abnormality based on the outputs of the window comparators 14 and 15.

If the control circuit 3 and the operation circuit 4 do not convert the polarity of the operation signal into an operation signal, the abnormality detection circuit 16 detects the servo circuit when the product of the outputs of the window comparators 14 and 15 is 0 or positive. is determined to be operating normally. And window comparators 14 and 1
If the product of the outputs of 5 becomes negative, it is detected that there is an abnormality. That is, the output of the window comparator 14 is 1.
If the output of the window comparator 15 also becomes 1 when this is the case, the output is increasing in accordance with the input, and therefore it is operating normally. Similarly, if the output of the window comparator 15 is -1 when the output of the window comparator 14 is -1, it means that the system is operating normally. However, window comparator 1
When the output of the window comparator 15 is -1 even though the output of the window comparator 4 is 1, or when the output of the window comparator 14 is -1 and the output of the window comparator 15 is 1, the input increases or Since the output is decreasing or increasing despite the decrease, it is determined that the servo circuit is not operating normally. Therefore, the abnormality detection circuit 16 determines that there is an abnormality in such a case, and opens the switch 12. As a result, the operation signal output from the operation circuit 4 is no longer supplied to the actuator 5, and the operation of the servo circuit is stopped. As a result, even if the distance between the head and the magneto-optical disk is less than 100 μm, for example, the head is driven even closer to the magneto-optical disk and is prevented from colliding with the disk.

Note that it is theoretically possible to use normal comparators as the window comparators 14 and 15. However, by using a window comparator, the section between the positive and negative reference values can be set as a dead zone, and it is possible to prevent the protection circuit 11 from operating due to noise or the like. Therefore, it is preferable to use a window comparator as in the embodiment.

FIG. 5 shows a more specific configuration of the embodiment shown in FIG. In this embodiment, the control circuit 3 and the phase compensation circuit 13 are omitted, and the FET 29 as the switch 12 is used as the coil 30 as the actuator 5.
It is connected to the rear of the . The window comparator 14 is made up of comparators 22 and 23, and the window comparator 15 is made up of comparators 24 and 25. The abnormality detection circuit 16 is an AND gate 26
27 and a Noah gate 28. The inverting input terminal of the comparator 22 has a positive reference voltage +r
ef1 is supplied, and a negative reference voltage -ref1 is supplied to the non-inverting input terminal of the comparator 23. Further, the inverting input terminal of the comparator 24 is supplied with a positive reference voltage +ref2, and the non-inverting input terminal of the comparator 25 is supplied with a negative reference voltage -ref2. Furthermore, the operation circuit 4 includes a driver 21 consisting of an inverting amplifier.
It is made up of.

When the operating signal input to the driver 21 (gap error signal between the head and the magneto-optical disk) is greater than the positive reference voltage +ref1, the output of the comparator 22 becomes 1, and when it is smaller than the reference voltage +ref1, the output becomes 0.
become. Further, the output of the comparator 23 becomes 1 when the operating signal is smaller than the negative reference voltage -ref1, and becomes 0 when it is larger (FIG. 2). Further, when the operation signal output from the driver 21 is larger than the positive reference voltage +ref2, the output of the comparator 24 becomes 1, and when it is smaller, it becomes 0. The output of the comparator 25 becomes 1 when the operation signal is smaller than the negative reference voltage -ref2, and 0 when it is larger.
(Figure 3). Now, the driver 2 as the operation circuit 4
1 is constituted by an inverting amplifier, so in normal operation, when its input is positive, its output is negative, and when its input is negative, its output is positive. Therefore, if the output of the comparator 22 is 1 (the output of the comparator 23 is 0) and the output of the comparator 24 is 0 (the output of the comparator 25 is 1), the operating state is normal. At this time, since one input of the AND gate 26 to which the outputs of the comparators 22 and 24 are supplied is 1 and the other is 0, its output is 0. Also, an AND gate 27 to which the outputs of the comparators 23 and 25 are supplied
Since one input is 1 and the other is 0, its output is 0. Therefore, the output of the NOR gate 28 becomes 1, and the FE
T29 is turned on. As a result, the operation signal output from the driver 21 flows through the coil 30 and the FET 29.

Further, if the output of the comparator 22 is 0 (the output of the comparator 23 is 1) and the output of the comparator 24 is 1 (the output of the comparator 25 is 0), the operating state is normal. At this time, the inputs of the AND gate 26 and the AND gate 27 are both 1 and the other is 0, so the output is 0, and the output of the NOR gate 28 is 1.
becomes. Further, when the outputs of the comparators 22 to 25 are all 0 (in the range of ±ref1 and ±ref2), this is also a normal operating state. At this time, the outputs of AND gates 26 and 27 are 0, and the output of NOR gate 28 is 1 (FIG. 4).

On the other hand, when the output of the comparator 22 is 1, if the output of the comparator 24 is also 1, the output is also large when the input is large, which is an abnormal operating state. At this time, both inputs of the AND gate 26 become 1, so its output also becomes 1, and the NOR gate 28
The output of becomes 0. Therefore, FET 29 is turned off and coil 30 is no longer supplied with an operating signal. Similarly, if the output of comparator 23 is 1, comparator 25
If the output is 1, it is an abnormal operating state. At that time, both inputs of the AND gate 27 become 1, so its output becomes 1, and the output of the NOR gate 28 becomes 0. Therefore, FET 29 is turned off (FIG. 4).

[0017] It is also conceivable that the above-described protective operation may be performed by, for example, comparing the level of the operation signal supplied to the actuator with a predetermined reference level. However, since the operation signal supplied to the actuator does not necessarily correspond to the distance between the head as the target object and the magneto-optical disk, it is difficult to perform an accurate protection operation. In contrast, in the case of the present invention, since an abnormality is detected from the states of both the operation signal and the operation signal, it is possible to perform a more accurate protection operation.

In the above description, the present invention has been applied to a servo circuit for always holding the head of a magneto-optical disk at a predetermined position with respect to a magneto-optical disk. It can also be applied to ordinary focus servo circuits, tracking servo circuits, radial servo circuits, etc.

[0019]

As described above, according to the servo circuit of the present invention, the operation signal and the operation signal are monitored, an abnormality in the servo circuit is determined based on the state of both signals, and the operation of the servo circuit is stopped when there is an abnormality. This prevents, for example, the head as a servo object from colliding with the disk.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of a servo circuit of the present invention.

FIG. 2 is a diagram illustrating the operation of a comparator in the embodiments of FIGS. 1 and 5;

FIG. 3 is a diagram illustrating the operation of a comparator in the embodiments of FIGS. 1 and 5. FIG.

FIG. 4 is a diagram illustrating the operation of a comparator in the embodiment of FIG. 5;

FIG. 5 is a diagram showing a more specific configuration in the embodiment of FIG. 1;

FIG. 6 is a diagram showing the configuration of an example of a conventional servo circuit.

[Explanation of symbols]

1 Target value setting circuit 2 Arithmetic circuit 3 Control circuit 4 Operation circuit 5 Actuator 6 Detection circuit 11 Protection circuit 12 Switch 13 Phase compensation circuit 14, 15 Window comparator 16 Abnormality detection circuit

Claims (1)

[Claims] [Claim 1] Setting means for setting a predetermined target value;
an operating means for performing a predetermined operation; a detecting means for detecting the operating state of the operating means; a calculating means for calculating an operating signal from a detection result by the detecting means and a target value set by the setting means; A servo circuit that generates an operation signal in response to an operation signal output by a calculation means and includes operation means for operating the operation means, and stops the operation of the servo circuit in response to the operation signal and the operation signal. A servo circuit characterized by comprising a protection means to prevent