JPH0762942B2 - Off-track detection method - Google Patents

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to a disk device that reads position information written concentrically on a disk with a head, reproduces a position signal with an automatic gain amplifier and a peak hold circuit, and positions a magnetic head group on a target track. , Especially to off-track detection schemes.

[Prior art]

Conventionally, this type of off-track detection system, as shown in FIG. 2, detects one position signal of two position signals with a phase difference of 90 degrees and detects a positive potential side comparator 21 and a negative potential side. Each of them is input to the comparator 22, and an off-track generation signal is output when the detection level of either one is exceeded. In this conventional off-track detection method, since the level of the position signal is detected, the automatic gain control circuit operates even if one of the peak hold circuits becomes defective. Although the position information is off-track, the position signal is normally reproduced and the off-track state is not detected.

[Object of the Invention]

Therefore, an object of the present invention is to provide an off-track detection method that can normally detect off-track even if one peak-hold function in the peak-hold circuit becomes defective. According to the present invention, the position information written on the disk is read by the magnetic head to reproduce the dipulse signal,
Peak hold the peak part in a predetermined order,
The four types of peak hold signals are subtracted in a certain combination of two types, the two types of position signals that are 90 degrees out of phase with each other are reproduced, and the addition signal obtained by adding the four types of peak hold signals is used as the AGC signal. Then, the off-track detection method is characterized in that the peak hold signals are added by the low-pass filter in the same combination as when the position signal is reproduced, and the off-track is detected by comparing the output signal of the low-pass filter with a certain potential. To be Embodiment Next, the present invention will be described in detail with reference to the drawings showing an embodiment of the present invention. Referring to FIG. 1, in one embodiment of the present invention, the magnetic head 1 reads the position information of the disk 2, and the read signal (die pulse) is sent to the automatic gain amplifier 3. The automatic gain amplifier 3 generates a dipulse 4 having a constant amplitude and inputs it to the peak hold circuit 5. The four separated synchronization signals of the synchronization circuit 6 are input to the peak hold circuit 5, and the peak hold circuit 5 generates four peak hold signals A to D. The four peak hold signals A to D are
The signals are added by the AGC control signal generation circuit 7 and input to the automatic gain amplifier 3 as the AGC control signal 8. The four peak hold signals A to D are further subtracted by a combination determined by two, and a position signal reproducing circuit 9 and
Input to 10 to generate a one-phase position signal 11 and a two-phase position signal 12 with a 90-degree phase shift, respectively. Further, the four peak hold signals A to D are input to the low-pass filters 13 and 14 which add in the same combination as the above, and each generate an off-track detection signal. Each off-track detection signal is input to the comparators 15 and 16. One of the peak hold circuits is generated by adding the peak hold signal with the low pass filter in the same combination as the position signal is reproduced to generate the off-track detection signal, and comparing the signal with the reference voltage by the comparator. If the peak hold operation becomes abnormal and the amplitude of B of the peak hold signal becomes low, the amplitude of the other peak hold signals A, C, D becomes high due to the AGC operation, and off-track is not detected as far as the position signal sees. . However, the level of the peak hold signal (A + C) is higher than the normal value and the level of the peak hold signal (B + D) is low due to the combination, so that there is an effect that the off-track can be detected. Effect of the Invention As described above, in the present invention, even if one peak hold operation in the peak hold circuit is defective, off-track can be detected.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional off-track detection circuit. Explanation of the sign of the main part. 1 ... Magnetic head 2 ... Disk 5 ... Peak hold circuit 9,10 ... Position signal reproduction circuit 13,14 ... Low pass filter 15,16 ... Comparator

Claims (1)

[Claims] 1. A magnetic head reads position information written on a disk, reproduces a dipulse signal, peak-holds a peak portion thereof in a predetermined order, and outputs four kinds of peak-hold signals of two kinds each. Subtract in a certain combination, reproduce two types of position signals that are 90 degrees out of phase with each other, and use the added signal obtained by adding the four types of peak hold signals as the AGC signal. An off-track detection method characterized by adding a peak hold signal with a low-pass filter and comparing the output signal of the low-pass filter with a certain potential to detect off-track.