JPS61177606A - Magnetic disc device - Google Patents

Abstract

PURPOSE:To make degaussing in a wide band possible by starting slowly a motor, which rotates and drives a magnetic disc, with a slow start circuit and supplying an AC signal having a prescribed frequency to the magnetic head as a degaussing signal while the motor is started slowly. CONSTITUTION:In a magnetic disc device 21, a slow start circuit 22 is provided between a servo circuit 20a and a motor driving circuit 20, and a degaussing circuit 23 is provided which supplies the AC signal having the prescribed frequency to a magnetic head 6 at the motor start time. The slow start circuit 22 is so constituted that a low-pass filter circuit 25 or a signal line 26 is selected alternatively by a pair of changeover switches 24a and 24b which are provided in signal input and output terminals and are interlocked with each other, and the slow start is performed if changeover switches 24a and 24b are switched to the side of the low pass filter circuit 25. The degaussing circuit 23 is connected to the magnetic head 6 in series to a recording amplifying circuit 12 by switching of a degaussing switch 27 connecting a mixing circuit 11 and the recording amplifying circuit 12, and the degaussing switch 27 is switched while interlocking with changeover switches 24a and 24b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic disk device in which magnetic disk t+4 is demagnetized when starting up.

[Conventional technology]

Electronic still camera devices record one field's worth of video information on an annular track of a magnetic disk that rotates at a constant speed, making it easy to record and play back still images.

It can also be used to record data. In the conventional magnetic disk device 1 shown in FIG. 3, a magnetic disk 2 is moved by a motor 3.
The magnetic head 6 is rotated by the recording circuit 4, and the image information supplied from the recording circuit 4 is supplied to the magnetic head 6 via the changeover switch 5, thereby recording video information for the field. The recording circuit 4 uses a comb filter circuit 7 to separate a luminance signal and a chrominance signal from the video signal to be recorded, and decodes the chrominance signal in a decoding circuit 8, and then sends the chrominance signal to an FM modulation circuit 9.10. After performing FM modulation at center frequencies of 7 MHz and 1.2 MHz, and mixing the outputs of both FM modulation circuits 9 and 1° in a mixing circuit 11, the recording amplifier circuit 12
The circuit is configured to amplify the signal.

The changeover switch 5 selectively connects either the recording circuit 4 or the reproducing circuit 13 to the magnetic head 6, and switches to the reproducing circuit 13 side during reproduction. This reproducing circuit 13 separates a luminance signal and a chrominance signal from a signal reproduced by the magnetic head 6 by a high frequency wave circuit 15 and a low frequency F wave circuit 16 connected to a reproduction amplifier circuit 14, and separates the luminance signal and color signal from the reproduced signal from the magnetic head 6, respectively.
The circuit configuration is such that the signal is demodulated by M demodulation circuits 17 and 18, and then converted into a signal of a predetermined television system by a common encoding circuit 19 and output.

The motor 3 that rotationally drives the magnetic disk 2 is configured to rotate at a constant speed by a motor drive circuit 20, and the motor drive circuit 20 is a servo that operates based on a rotation detection signal from a rotation sensor 3a provided in the motor 3. circuit 20aK
More controlled.

[The problem that the invention attempts to solve]

The above-mentioned conventional magnetic disk device 1 erases previously recorded video information by overlapping and records data on a high coercive force magnetic disk 2 using a magnetic head 6 with a narrow gap width. Because of this, low-frequency signal components disappear<<, the S/N ratio of color signals with low modulation center frequencies decreases, and image quality tends to deteriorate<<.Also, when data is recorded instead of video information, There were problems such as a high error rate and decreased reliability.

[Means for solving problems]

This invention solves the above problems.

A magnetic disk device that records still images via a magnetic head on an annular track on a magnetic disk that is rotated at a constant speed by a motor that is started when recording a signal, the motor being started at a slow speed when the motor is started. A slow start circuit that prolongs the time required to reach constant speed rotation, and a degaussing circuit that supplies an alternating current signal of a predetermined frequency to the magnetic head as a degaussing signal when the slow start circuit is activated. The purpose of this article is to remember that.

[Effect]

In this invention, a motor that rotationally drives a magnetic disk is slowly started by a slow speed starting circuit, and during this time, an alternating current signal of a predetermined frequency is supplied to the magnetic head as a degaussing signal, and before the magnetic disk reaches constant speed rotation. Then, wideband demagnetization is performed from low to high frequencies.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 and 2. 1 and 2 are a schematic circuit diagram and a signal waveform diagram of each part of the circuit, respectively, showing an embodiment of the magnetic disk device of the present invention. In FIG. 1, the same components as in FIG. 83 are given the same reference numerals.

In FIG. 1, the magnetic disk device 21 includes a servo circuit 20a
A slow start circuit 22 is provided between the motor drive circuit 20 and the motor drive circuit 20, and a degaussing circuit 23 is provided for supplying an alternating current signal of a constant frequency to the magnetic head 6 when starting the motor. The slow startup circuit 22 is connected such that one of the low-frequency F-wave circuit 25 and the signal line 26 is selected by a pair of fast-moving switching switches 24a and 24b provided at the input and output ends of the signal. As a result, there is a changeover switch 24a.

24b is switched to the low frequency F wave circuit 25 side,
A slow start is performed.

The degaussing circuit 23 is connected to the recording amplifier circuit 12 Kilf column and the magnetic head 6 by switching the degaussing switch 27 that connects the mixing circuit 11 and the recording amplifier circuit 12. , 24
It can be switched in conjunction with b.

If a new video signal is to be recorded on the already recorded magnetic disk 2, the degaussing switch 27 is switched to the degaussing circuit 23 side as shown in FIG. , 24bt-switch to the low frequency F wave circuit 25 side. Due to this.

The servo signal that is the output of the servo circuit 20a is supplied to the motor drive circuit 20 via the low-frequency F-wave circuit 25. Therefore, the servo signal supplied to the motor drive circuit 20 is delayed by the low-frequency F wave circuit 25, and the motor 3 is
Compared to the normal startup shown by the dotted line in FIG. 4, the engine is started slowly as shown by the solid line.

On the other hand, as the degaussing switch 27 closes, the degaussing circuit 23
The AC signal for demagnetization shown in FIG. 2 is supplied to the magnetic head 6 via the changeover switch 5. In this case, since the magnetic disk 2 is started slowly, its rotational speed gradually increases, and therefore the frequency of the AC signal applied to the magnetic disk 2 decreases as time passes after starting.

Therefore, the AC signal applied to the magnetic disk 2 until the motor 3 reaches a constant speed rotation state and the degaussing switch 27 is opened has a wide band from low to high frequencies, as shown in Fig. 2G)). As a result, any frequency components of the previous signal recorded on the track on which the signal is to be recorded are effectively erased.

Note that when the motor 3 slows down to a constant speed rotation state, the degaussing switch 27 is switched to the mixing circuit 11 side.

At the same time, the changeover switches 24a and 24b are turned on and off from the signal line 26.
Switch to the side. Thereby, the motor drive circuit 20 is directly controlled by the servo circuit 20&. In this state, a recording signal is supplied from the recording circuit 4 to the magnetic head 6 and recorded on the magnetic disk 2, but since the previously recorded signal has been completely erased, the SN ratio is This ensures that high-quality signal recordings are made.

In this manner, the magnetic disk device 21 operates the motor 3 that drives the magnetic disk 2 11,116 times using the slow start circuit 2.
2, the magnetic head 6 is started at a slow speed, during which an AC signal of a predetermined frequency is supplied as a demagnetizing signal from the degaussing circuit 23 to the magnetic head 6, so that the magnetic disk 2 reaches a constant speed rotation state necessary for recording still images. In the meantime, the magnetic head 6
As the relative speed of the magnetic disk 2 increases, the degaussing signal supplied to the magnetic disk 2 via the magnetic head 6.

Since the number of friends for the magnetic disk 2 is reduced to a low wavenumber,
With a degaussing signal having a fixed frequency, it is possible to demagnetize a wide range from low to high frequencies, making it suitable for electronic still cameras and the like that record high-density signals with a narrow track pitch.

〔Effect of the invention〕

As explained above, according to the present invention, the motor that rotationally drives the magnetic disk is slowly started (by the slow start circuit), and during this time an alternating current signal of a predetermined frequency is supplied to the magnetic head as the 4a signal. Because of this structure, as the relative speed between the magnetic head and the magnetic disk increases until the magnetic disk reaches the constant speed rotation required for recording still images, the demagnetization supplied to the magnetic disk via the magnetic head increases. Since the frequency of the signal relative to the magnetic disk is lowered, a degaussing signal with a fixed frequency is used.

It has excellent effects such as being able to demagnetize a wide range from low to high frequencies, and being suitable for electronic still cameras and the like that perform high-density signal recording with a narrow track pitch.

[Brief explanation of drawings]

81.2 is a schematic circuit configuration diagram and a signal waveform diagram of each part of the circuit, respectively, showing an embodiment of the magnetic disk device of the present invention, and FIG. 3 is a schematic circuit configuration diagram showing an example of a conventional magnetic disk device. It is. 21...Magnetic disk device, 2...Magnetic disk. 3...Motor, 6...Magnetic head, 22...Slow speed starting circuit, 23...Degaussing switch.

Claims (1)

[Claims] A magnetic disk device that records still images via a magnetic head on an annular track on a magnetic disk that is rotated at a constant speed by a motor that is started when recording a signal, wherein the motor is started at a slow speed when the motor is started. , a slow-speed starting circuit that prolongs the time required to reach constant speed rotation, and a degaussing circuit that supplies an alternating current signal of a predetermined frequency to the magnetic head as a demagnetizing signal when the slow-speed starting circuit is activated. A magnetic disk device.