JP2882078B2 - Servo circuit - Google Patents

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 in, for example, maintaining a distance between a head and a disk at a predetermined value in a magneto-optical disk drive.

[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 a basic configuration of this servo circuit. As shown in the figure, the target value setting circuit 1 outputs an electric signal corresponding to a predetermined target value (100 μm in this example). The arithmetic 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 to generate an operation signal.
This operation signal is input to the control circuit 3 inserted as needed, and is subjected to processing such as phase compensation. The operation signal output from the control circuit 3 is input to an operation circuit 4 including, 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 (both not shown) with respect to the magneto-optical disk so that the head (both not shown) 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 manner, the head is driven by the actuator 5 so as to be always positioned at a predetermined distance from the magneto-optical disk.

[0004]

The conventional servo circuit is
As described above, the distance between the head and the magneto-optical disk is detected by the detection circuit 6, and servo is applied so that the distance matches the target value set by the target value setting circuit 1. However, for example, when the arithmetic circuit 2, the control circuit 3, the operation circuit 4, the actuator 5, or the like fails, a correct servo operation is not performed, and the head collides with the magneto-optical disk, and the head and the head are hit by heat and impact at the time of the collision Alternatively, one or both of the disks may be damaged.

The present invention has been made in view of such a situation, and it is an object of the present invention to prevent a servo object from being damaged even if a component of a servo circuit fails.

[0006]

The servo circuit according to the present invention comprises:
To keep the distance between the disk and the head at a certain distance
Setting means for setting the target value of the
Operating means and the distance between the head and the disk.
Output means, the detection result by the detection means, and the setting means
An operation signal corresponding to the error from the set target value
And an operation signal output by the operation means.
Operation signals specified regardless of the operating state of the operating means.
Operation to generate and operate the operating means based on the operation signal
Means and the operation signal to be in the same phase as the operation signal
Phase compensating means for phase compensating, and output from the phase compensating means.
First comparing means for comparing the obtained operation signal with a predetermined reference value
And second comparing means for comparing the operation signal with a predetermined reference value
And the comparison result of the first comparison means and the comparison result of the second comparison means
Compare the results, and according to the comparison result,
Operation of the operating means to prevent collision with
Protective means to stop supply by cutting off supply
It is characterized by the following.

[0007]

In the servo circuit having the above structure, the operation signal input to the operation means and the operation signal output from the operation means are monitored, and the operation of the servo circuit is stopped according to the state of both signals. Therefore, even if a failure occurs in the means constituting the servo circuit, it is possible to prevent an object to be servo-served from being damaged.

[0008]

FIG. 1 is a block diagram showing a configuration of an embodiment of a servo circuit according to the present invention. Components corresponding to those in FIG. 6 are denoted by the same reference numerals, and the description thereof will be omitted. It will be omitted as appropriate because it will be repeated. In the servo circuit in the embodiment shown in FIG. 1, a protection circuit 11 is added to a servo circuit including a target value setting circuit 1, an arithmetic circuit 2, a control circuit 3, an operation circuit 4, an actuator 5, and a detection circuit 6. In the case of this embodiment, the protection circuit 11 includes a switch 12 inserted between the operation circuit 4 and the actuator 5 and an operation signal output from the arithmetic circuit 2.
A phase compensating circuit 13 for compensating the phase so as to have the same phase as the operation signal output therefrom; a window comparator 14 for comparing the output of the phase compensating circuit 13 with a predetermined reference value and outputting the comparison result; A window comparator 15 for comparing the operation signal output from the circuit 4 with a predetermined reference value
And an abnormality detection circuit 16 that detects an abnormality of the servo circuit from the outputs of the window comparators 14 and 15 and controls the switch 12 according to the detection result.

The arithmetic 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, and after being compensated to a predetermined phase, supplied to the operation circuit 4 and 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) according to the 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. By the operation in the closed loop, the distance between the head and the magneto-optical disk is controlled so as to match the target value set by the target value setting circuit 1.

The window comparator 14 compares the operation signal phase-compensated by the phase compensation circuit 13 with a predetermined reference value, and outputs a signal corresponding to the comparison result. For example, 1 when the input signal is larger than a predetermined positive reference value (+ ref1), and when the input signal is smaller than a negative reference value (-ref1).
A detection signal of 0 is output when the value is between a negative reference value and a positive reference value (FIG. 2). Similarly, the window comparator 15
Is 1 when the operation signal output from the operation circuit 4 is larger than a predetermined positive reference value (+ ref2),
f2) A detection signal of -1 is output when the value is smaller than 0 and a detection signal of 0 is output 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 from the outputs of the window comparators 14 and 15.

If the control circuit 3 and the operation circuit 4 do not convert the operation signal into an operation signal by converting its polarity, the abnormality detection circuit 16 will operate 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. Then, the window comparators 14 and 1
If the product of the outputs of the outputs 5 is 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 becomes 1 at this time, the output is increased in response to the input, so that the window comparator 15 operates 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 operation is normal. However, window comparator 1
When the output of the window comparator 15 is -1 even though the output of 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 not 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 so as to be closer to the magneto-optical disk, and collision is finally prevented.

The window comparators 14 and 15 can theoretically be ordinary comparators. However, by using a window comparator, a section between the positive and negative reference values can be set as a dead zone, and the protection circuit 11 can be prevented 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 replaced by the coil 30 as the actuator 5.
Is connected to the subsequent stage. The window comparator 14 is constituted by comparators 22 and 23, and the window comparator 15 is constituted by comparators 24 and 25. The abnormality detection circuit 16 includes an AND gate 26
, 27 and a NOR 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 a non-inverting input terminal of the comparator 23. 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. Further, the operation circuit 4 includes a driver 21 formed of an inverting amplifier.

When the operation signal (gap error signal between the head and the magneto-optical disk) inputted to the driver 21 is larger than the positive reference voltage + ref1, the output of the comparator 22 becomes 1, and when it is smaller than the reference voltage + ref1, it becomes 0.
become. The output of the comparator 23 becomes 1 when the operation signal is smaller than the negative reference voltage −ref1, and becomes 0 when it is larger (FIG. 2). When the operation signal output from the driver 21 is higher than the positive reference voltage + ref2, the output of the comparator 24 becomes 1;
become. The output of the comparator 25 becomes 1 when the operation signal is smaller than the negative reference voltage −ref2, and becomes 0 when it is larger (FIG. 3). Now, since the driver 21 as the operation circuit 4 is constituted by an inverting amplifier, its output becomes negative when its input is positive, and its output is positive when its input is negative, when operating normally. Become. Therefore,
When 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), it is in a normal operation state. At this time, one of the inputs of the AND gate 26 to which the outputs of the comparators 22 and 24 are supplied is 1 and the other is 0, so that the output is 0. The AND gate 2 to which the outputs of the comparators 23 and 25 are supplied.
One of the inputs of 7 is 1 and the other is 0, so the output is 0
Becomes Therefore, the output of the NOR gate 28 becomes 1, and F
ET29 is turned on. Thus, the operation signal output from the driver 21 flows through the coil 30 and the FET 29.

When 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 operation is normal. At this time, one of the inputs of the AND gate 26 and the AND gate 27 is 1 and the other is 0, so the output is 0, and the output of the NOR gate 28 is 1
Becomes When the outputs of the comparators 22 to 25 are all 0 (when the output is within the range of ± ref1 and ± ref2), this is also a normal operation state. Also at this time, the outputs of the AND gates 26 and 27 become 0, and the output of the NOR gate 28 becomes 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, if the input is large, the output is large, which is an abnormal operation state. At this time, since both inputs of the AND gate 26 become 1, the output thereof also becomes 1, and the NOR gate 28
Becomes 0. Therefore, the FET 29 is turned off, and no operation signal is supplied to the coil 30. Similarly, when the output of the comparator 23 is 1, the comparator 25
Is an abnormal operation state. At that time, since both inputs of the AND gate 27 become 1, the output thereof becomes 1, and the output of the NOR gate 28 becomes 0. Therefore, the FET 29 is turned off (FIG. 4).

The above-described protection operation may be executed, for example, by comparing the level of an operation signal supplied to the actuator with a predetermined reference level. However, since the operation signal supplied to the actuator does not always correspond to the distance between the head as the object and the magneto-optical disk, an accurate protection operation is difficult. On the other hand, in the case of the present invention, the abnormality is detected from both the state of the operation signal and the state of the operation signal, so that a more accurate protection operation can be performed.

In the above description, the case where the present invention is applied to a servo circuit for always holding a head of a magneto-optical disk device at a predetermined position with respect to a magneto-optical disk has been described. It can be applied to a normal focus servo circuit, tracking servo circuit, radial servo circuit, and the like.

[0019]

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

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining the operation of the comparator in the embodiment of FIGS. 1 and 5;

FIG. 3 is a diagram for explaining the operation of the comparator in the embodiment shown in FIGS. 1 and 5;

FIG. 4 is a diagram for explaining the operation of the comparator in the embodiment of FIG.

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

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 target value setting circuit 2 operation 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)

(57) [Claims] A distance between a disk and a head is set to a predetermined value.
Setting means for setting a target value for the distance; Operating means for operating the head; Detection for detecting a distance between the head and the disk
Means, The detection result by the detection means and the setting result by the setting means
From the set target value, the operation signal corresponding to the error is calculated.
Calculating means for calculating; The operation means is obtained from the operation signal output by the operation means.
Generates the specified operation signal regardless of the operation state of
An operating hand for operating the operating means based on the operating signal
Steps and So that the operation signal has the same phase as the operation signal
Phase compensation means for phase compensation, The operation signal output from the phase compensation means is
First comparing means for comparing with a reference value; Second comparing means for comparing the operation signal with a predetermined reference value
When, The comparison result of the first comparison unit and the comparison result of the second comparison unit
Compare the comparison result, and according to the comparison result,
Movement of the operating means so that the head does not collide with the head.
Operation is stopped by shutting off the supply of the operation signal.
Protection measures and A servo circuit comprising: