JPH04349202A - Magnetic field control system - Google Patents

Abstract

PURPOSE:To prevent an excess current and to shorten a time for setting the magnetic field by detecting a current flowing into a coil at the control system of the external magnetic field generation of a rewritable optical disk driving device. CONSTITUTION:The current of a magnet coil 4 which determines a generated magnetic field is detected by a detection circuit 10, by a comparator 11 having histerisis voltage v an initial control circuit 6 and a normal control circuit 7 are switched via a switch 8 and a magnet coil driving circuit 9 is controlled. Thus, the time for setting the magnetic field between slice levels vs and vs' of the comparator 11 is shortened and a current becomes acceptable value below a current for the vs.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to recording and erasing in a rewritable optical disk drive, and more particularly to a generated magnetic field control method suitable for shortening the rise time of a bias magnetic field and stabilizing the drive current during recording and erasing. .

0002

[Prior Art] A conventional device is disclosed in Japanese Patent Application Laid-Open No. 57-133503.
As described in the publication, the magnetic field applied to the recording medium was kept constant by changing the electromagnetic coil current according to changes in the relative position between the electromagnetic coil and the recording film surface.

0003

SUMMARY OF THE INVENTION The above-mentioned prior art does not take into account the suppression of the peak value of the drive current and the shortening of the settling time when a magnetic field is applied, and there is a problem in performing stable recording and erasing.

An object of the present invention is to provide a control system that suppresses the peak value of the current flowing through the magnet coil and shortens the settling time.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the control system of the magnet coil is made into two systems, and the external The intensity of the generated magnetic field is controlled.

[0006]

[Operation] The rise time of the generated magnetic field when entering the recording or erasing mode is determined by the resistance and inductance of the coil and the applied voltage. Therefore, the rise time of the magnetic field fluctuates as the characteristics of the coil change depending on the ambient temperature and the like.

On the other hand, in order to speed up the rise time and reduce the power consumption of the drive circuit during steady state, a method is generally used in which the power supply voltage of the drive circuit is switched between the rise time and the steady state. In a control system that applies a larger voltage than during steady state during this rise, a stable rise of the magnetic field can be obtained by controlling the time of the initial applied voltage so as to detect the current flowing through the coil and adjust the magnetic field strength.

[0008]

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

A control system for a magnet coil during recording/erasing of an optical disk device for recording, reproducing, or erasing information can be configured as shown in FIG. A rewritable optical disk 1, which is a medium, has an information recording film, and is controlled and rotated at a constant or variable speed by a spindle motor 3. Recording, reproducing, and recording information on rewritable optical discs
In erasing, a light beam emitted from an optical system 5 including a light source and an optical lens is focused on the recording surface 2, and information is recorded or erased by causing physical deformation or physical change of the recording surface. . In other words, as the light beam focuses on the recording surface, the temperature of that area rises, and at the same time,
By applying a magnetic field from the magnet coil 4,
The direction of magnetization of that portion is oriented in the same direction as the externally applied magnetic field. This records and erases information. Furthermore, the recorded information is reproduced by detecting the polarized light component of the reflected light or transmitted light from this recording surface.

Commands for recording and erasing information are issued by the logic control circuit 12, and are sent to the initial control circuit 6 and steady-state control circuit 7 of the magnet coil. These control circuit output signals 13 and 14 pass through the switch 8, and one of the signals is transmitted to the magnet coil drive circuit 9, which causes current to flow through the magnet coil 4 and generate an external magnetic field necessary for recording and erasing. That is, at the initial stage when the switch 8 causes current to flow through the coil or when the magnetic field is reversed, the control signal 13 from the initial control circuit 6 controls the drive circuit 9, and in the steady state, the steady state control circuit 6
A control signal 14 from the drive circuit 9 controls the drive circuit 9. but,
When these two control systems are switched for a certain period of time T1, overshoot occurs as shown in Figure 2(a) due to variations in characteristics due to coil variations and temperature changes, and the range of the external magnetic field that can be recorded and erased is exceeded. If the establishment time becomes longer than T2 in the figure or an excessive current flows through the coil, there is a risk that the allowable current of the magnet coil control system will be exceeded. Here, the detection circuit 10 detects the current that determines the magnetic field generated by the magnet coil,
It is converted into a voltage vx, compared by a comparator having a hysteresis voltage Δv, and the switch 8 is driven so as to select the output 13 of the initial control circuit 6 and the output 14 of the steady control circuit 7 using this output. If the slice levels vs and vs' of the hysteresis comparator are set to a level that allows recording and erasing, or within that range,
As shown in FIG. 2(b), the time required to control the magnetic field to allow recording and erasing is shortened to T3. In addition, overshoot can be reduced, and power consumption and the peak value of current in the magnet control system can be suppressed. Furthermore, by adjusting the hysteresis voltage Δv of the comparator, it is possible to adjust the accuracy of the generated magnetic field, and also to monitor the magnetic field strength during recording and erasing, ensuring stable recording and erasing against power supply fluctuations and temperature fluctuations. It has the effect of making it possible.

[0011]

According to the present invention, the current flowing through the coil that determines the strength of the generated external magnetic field is detected and the drive circuit is controlled. Therefore, an excessive current is not required and the settling time of the external magnetic field is It has the effect of making it shorter.

[0012] Also, the setting range and accuracy of the external magnetic field are recorded and
It can be set according to the erasable range, so power fluctuations and
This has the effect of stably recording and erasing against temperature fluctuations, etc.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a diagram showing temporal changes in magnet coil drive current.

[Explanation of symbols]

1...optical disc, 2...Recording film surface, 4...Magnetic coil, 5...Optical system, 6...Initial control circuit, 7...steady control circuit, 8...Switch, 9... Magnet coil drive circuit, 10...Current detection circuit, 11... Comparison circuit.

Claims (1)

[Claims] Claim 1: A rewritable optical recording and reproducing device, comprising:
A first control comprising a coil for generating a bias magnetic field during recording/erasing, a drive circuit for driving the coil, and means for detecting the intensity of the generated magnetic field, and controlling the drive circuit when the drive circuit starts up. and a second control means for controlling the drive circuit in a steady state, and the detection means switches between the first control means and the second control means.