JPH0450655B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a rotation control device for an optical disk, and more particularly to a rotation control device at the start of rotation of an optical disk.

Prior Art During the recording mode of a recordable and reproducible optical disk, the driving current of a semiconductor laser is turned on and off according to pulses corresponding to recorded data, for example, and this causes a laser beam emitted intermittently from the semiconductor laser to be turned on and off. Accordingly, the recording data is recorded. On the other hand, in the playback mode, the previously recorded signal is played back using a laser beam with a constant power that is controlled to an energy level that does not cause changes in the optical properties of the recording film of the optical disk due to the focused light spot. .

Therefore, the laser power in the playback mode is lower than that in the record mode, and the laser power must be kept at a constant value to prevent the laser power from becoming excessive and causing erroneous recording or falsifying previously recorded information. On the other hand, in the recording mode, the laser power is too low and recording with poor S/N due to the influence of noise etc. is prevented, and the laser power is too high and resolution with adjacent pit information deteriorates. It is necessary to control the laser power within an optimal range to avoid this.

In such an optical disk recording/reproducing apparatus, the focus servo can be pulled in most easily when the optical disk is not rotating. For this reason, from the viewpoint of ease of retraction of the focus servo, if the focus servo is turned on at the same time as the optical disk starts rotating, the optical disk will not start rotating immediately due to inertia, and the light beam spot will be placed at approximately the same location. It will be irradiated for a long period of time, and in the case of sensitive optical discs, even in the playback mode with low laser power as mentioned above, the temperature of the irradiated area will rise before it starts rotating, causing the recorded information to be lost. There were problems such as damage. Further, if the optical disk does not rotate for some reason, the optical disk will obviously be damaged.

For this reason, the focus servo was turned on after the conventional optical disk reached a predetermined steady rotation speed (for example, 1800 rpm).

Problems to be Solved by the Invention However, when the optical disk rotates steadily, the disturbance frequency to the focus servo circuit becomes high due to the effects of surface runout, etc., making it difficult to pull in the focus servo.

Therefore, the present invention is an optical system that solves the above problems by first starting the rotation of the optical disc at a predetermined low speed, turning on the focus servo in that state, and then increasing the rotation speed to a steady rotation speed. The purpose of the present invention is to provide a disk rotation control device.

Means for Solving the Problems The optical disk rotation control device according to the present invention includes means for starting the rotation of the optical disk to a first rotation speed lower than the steady rotation speed, and means for outputting a focus servo signal at a second rotational speed on the way to the rotational speed;
It consists of a means for increasing the rotational speed of the optical disk to a steady rotational speed by switching the drive voltage of the motor for rotating the optical disk at the time when the focus lock signal is supplied from the focus servo.

Function: The focus servo is turned on at a second rotation speed on the way to the first rotation speed, which is lower than the steady rotation speed. That is, the focus servo is turned on at the second rotational speed at which the frequency of disturbances such as surface runout of the optical disk is sufficiently low. Thereafter, the rotational speed of the optical disk is controlled to a predetermined steady rotational speed by a focus lock signal obtained from the focus servo.

Embodiment FIG. 1 shows a circuit diagram of an embodiment of the device of the present invention. In the figure, an optical disk 1 is rotated by a DC motor 2, and its number of rotations (rotational speed) is detected by a head 3 and a rotation detector 4. Note that the rotation speed detection means is a frequency generator (FG) of a known configuration that generates a rotation detection signal with a frequency corresponding to the rotation speed of the motor shaft of the DC motor 2.
Alternatively, it may be a device that optically reads circuit control signals of a certain period recorded in advance on, for example, a circular track outside the program area of an optical disk. In either case, as shown in FIG. 2, the rotation detector 4 smoothes a rotation detection pulse having a frequency corresponding to the rotation speed of the optical disk 1 and the DC motor 2, and outputs a voltage proportional to the rotation speed.

Now, when a disk start (rotation start) switch (not shown) is turned on, a low level signal is input to terminal 5. Note that the terminal 5 is maintained at a low level until the motor is stopped. At this time, the focus servo is not yet locked, so no focus lock signal is received at the terminal 6, which is at a high level. Therefore, when the disk start switch is turned on, terminal 5 is
The output signal of the NOR circuit 7 to which both the signals 1 and 6 are supplied is at a low level, and the switch _SW1 , which is switching-controlled by this signal, is connected to the terminal L side. Furthermore, the polarity of the low level input signal at the terminal 5 is inverted by the inverter 8 and applied to the switch circuit _SW2 , which is then switched and connected to the terminal H side. Further, the low level input signal of the terminal 5 is supplied to one input terminal of the two-input NAND circuit 9. Therefore, the output signal of the NAND circuit 9 is at a high level regardless of the signal from the comparator 13, which will be described later, that is supplied to the other input terminal.

The high level output signal of NAND circuit 9 is PNP
Applied to the base of transistor Tr ₁ , turning it off. The collector of transistor Tr ₁ is a resistor
The base of NPN transistor Tr ₂ via R ₃ and R ₄ ,
Since it is connected to the emitter, the transistor
Due to the above-mentioned turning off of Tr ₁ , the transistor Tr ₂ is also turned off. The collector of the transistor Tr ₂ is connected to the non-inverting input terminal of the inverting amplifier 10, but by turning off the transistor Tr ₂ , the non-inverting input terminal of the inverting amplifier 10 is grounded only through the resistor R ₅ . .

On the other hand, the switch circuit _SW1 is connected to the terminal L as described above.
Since the power supply voltage is resistively divided by resistors _R1 and _R2 , a predetermined voltage _V0 is supplied to the inverting input terminal of the inverting amplifier 10 through the resistor _R6 and the switch circuit _SW1 . After being inverted and amplified, the signal is applied to one terminal of the DC motor 2 through the resistor R ₇ , the operational amplifier 11 forming a voltage follower, and the switch circuit SW ₂ connected to the terminal H side. Since the other terminal of the DC motor 2 is connected to a negative power supply voltage (for example, -15V) via the switch circuit _SW2 , the DC motor 2 is started by applying the inverted amplified voltage of _V0 . As a result, immediately after the disk starts, the number of rotations (rotational speed) of the optical disk 1 and the DC motor 2 increase so that they rotate at the first number of rotations determined by the DC voltage V ₀ . Here, the above DC voltage V ₀ drives the DC motor 2 and the optical disk 1 at a constant rotation speed of 1800 rpm.
The rotation speed is set to about 400 to 500 rpm, which is lower than that of the engine.

When the rotational speed of the optical disk 1 reaches a predetermined second rotational speed while increasing to the above-mentioned 400 to 500 rpm, the output rotation detection voltage of the rotation detector 4 becomes a voltage value V ₁ (V ₁ < V ₀ ). The comparator 12 compares the levels of the reference voltage _V1 and this rotation detection voltage, and the rotation detection voltage is the reference voltage _V1.
When the signal becomes larger, a high-level focus-on signal is supplied to a focus servo circuit (not shown) via the terminal 14. As a result, when the focus servo circuit is turned on, the pick-up 15 is vibrated at a predetermined frequency in a direction perpendicular to the surface of the optical disc 1, and as a result, the amount of reflected light changes (maximum at the position of the focused point). , the output signal changes accordingly. The focus servo circuit detects when this output signal exceeds a predetermined level and when the focus error signal reaches a level near the in-focus point, and uses this detection output to operate a flip-flop, thereby adjusting the focus. The servo loop is configured to be a closed loop. The output signal of this flip-flop is applied as a low level focus lock signal to one input terminal of the NOR circuit 7 via the terminal 6 in FIG.

As a result, both of the two input signals of the NOR circuit 7 become low level, so that the output signal of the NOR circuit 7 becomes high level, and the switch circuit _SW1 is switched and connected to the terminal H side. On the other hand, the originally constant cycle signal obtained by picking up the recorded information on the optical disc 1 by the pick-up 15 is discriminated and separated by the speed detector 16, and is converted into a signal with a frequency corresponding to the rotational speed of the optical disc 1 by the speed control circuit 17. , where it undergoes frequency-to-voltage conversion. As mentioned above, since the switch circuit SW ₁ is switched to the terminal H side when the focus lock signal is input, the output speed error signal of the speed control circuit 17 is sent to the inverting amplifier 10 through the resistor R ₆ and the switch circuit SW ₁ , respectively. The DC motor 2 is further supplied to the DC motor 2 through the resistor R ₇ , the operational amplifier 11 and the switch circuit SW ₂ , and its rotation is controlled to be, for example, 1800 rpm.

Here, the input signal frequency (rotational speed) vs. output voltage characteristic of the speed control circuit 17 is selected as shown in FIG. The output voltage increases from a predetermined value, and this is passed through the inverting amplifier 10 and the resistor _R7 to the operational amplifier 11.
As a result, the negative output voltage from the operational amplifier 11 increases in the negative direction, and the potential difference between both terminals of the DC motor 2 becomes small, reducing the rotational speed.
On the other hand, when the rotational speed of the optical disk 1 and the DC motor 2 decreases below the predetermined value of 1800 rpm, the negative output voltage of the operational amplifier 11 increases in the positive direction, contrary to the above, so that the rotational speed of the DC motor 2 increases. In this way, the rotational speed (rotational speed) of the DC motor 2 and the optical disk 1 is maintained at a steady rotational speed of 1800 rpm.

The signal used by the speed detector 16 to detect the speed is, for example, a playback horizontal synchronization signal in the playback video signal of the optical disk 1 in the playback mode, and an information track of the optical disk 1 is formed in the record mode. There is a playback signal of a guide track (for example, a pre-pit in Japanese Patent Application No. 141696/1986 proposed by the present applicant) in which signals of a fixed period are recorded in advance on both sides of the position.

When using the playback horizontal synchronization signal, the switch circuit SW1 cannot be distinguished from the playback video signal unless the optical disc 1 reaches _a constant rotation speed.
Immediately after being switched to the terminal H side, the output error signal of the speed control circuit 17 outputs a signal that causes the DC motor 2 to rotate at the highest speed. As a result, the rotation speed of the DC motor 2 quickly rises to around the predetermined steady rotation speed of 1800 rpm.

In addition, in FIG. 1, the comparator 13 uses the rotation detection voltage from the rotation detector 4 and the reference voltage V ₂ (V ₂ <V ₁ ).
When the rotation detection voltage becomes a value smaller than _V2 , a high level signal is output. At this time, when a high level stop signal is input to terminal 5, the output signal of NAND circuit 9 becomes low level, transistors Tr ₁ and Tr ₂ are turned on, and the output voltage of inverting amplifier 10 increases. The voltage increases in the negative direction and becomes approximately equal to the negative power supply voltage, and the potential difference between both terminals of the DC motor 2 becomes approximately zero, so the DC motor 2 stops rotating.

It goes without saying that the present invention can also be applied to rotation control of a CLV type optical disk. In this case, the steady rotation speed is not constant at 1800 rpm,
It is clear that the rotation speed is gradually decreased from 1800 rpm in response to the movement of the pickup 15 toward the outer circumference.

Effects of the Invention As described above, according to the present invention, the focus servo is turned on at a rotation speed slower than the steady rotation speed, so that the optical disk can be operated without damaging the optical disk.
It has features such as being able to quickly bring the focus servo into a locked state.

[Brief explanation of drawings]

FIG. 1 is a circuit system diagram showing one embodiment of the apparatus of the present invention, and FIGS. 2 and 3 are diagrams showing the characteristics of each main part of the circuit system shown in FIG. 1, respectively. 1... Optical disk, 2... DC motor, 4...
Rotation detector, 5...Start signal input terminal, 6...
...Focus lock signal input terminal, 10...Inverting amplifier, 12, 13...Comparator, 14...
Focus-on signal output terminal, 15...Pickup, 16...Speed detector, 17...Speed control circuit, _SW1 , _SW2 ...Switch circuit.

Claims (1)

[Claims] 1 means for starting the rotation of the optical disk so that the rotational speed of the optical disk reaches a first rotational speed lower than the steady rotational speed when the optical disk starts rotating; means for outputting a focus servo on signal that turns on the focus servo at a rotational speed of A rotation control device for an optical disk, comprising means for increasing the rotational speed of the optical disk to the steady rotational speed by switching the drive voltage.