JP2562869B2 - Braking device for disk-shaped recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking method for an apparatus for reading a digital signal from a disc on which a digital signal is recorded, and more particularly to a stop braking of the disc.

[Prior Art] A conventional device of this type is also disclosed in Japanese Patent Laid-Open No. 58-208970. This relates to a disc rotation control device for a compact disc player, and more particularly to stop control of a disc on which digital signals are recorded at a constant recording density. Then, a digital signal having a maximum inversion interval (the maximum interval between two adjacent inversion portions of signal levels) Tmax of 5.5T (where T is a bit cell period of input data) is recorded on the disc. The case is explained. When the disc rotates and the reproducing device is in the normal reproducing state, the maximum reversal interval of the reproduction signal is the same as that at the time of recording, and when the reproduction is completed, the motor which is the rotation driving means of the disc generates the braking torque. As described above, the voltage opposite to that in the normal reproduction state is applied. As a result, the rotation speed of the disk decreases due to the braking torque, and the maximum inversion interval of the reproduction signal also increases accordingly. Since the reproduction signal cannot be obtained when the disc is stopped, the disc will be stably stopped if the application of the reverse voltage is stopped when the maximum inversion interval becomes sufficiently long.

[Problems to be Solved by the Invention] The above-mentioned conventional device is described on the assumption that the signal reading means can stably reproduce the signal recorded on the disc regardless of the number of revolutions of the disc. . However, the control means of the signal reading means obtained from the disc, when the rotation of the disc decreases, the reversal interval of the reproduction signal which is the recorded information also becomes long, and further, the signal contains a low frequency component strongly. Since this low frequency component is superimposed on the control signal as a nozzle, stable signal reading cannot be performed. Further, since the signal obtained from the disc is weak, it is usually amplified by an AC coupling circuit. For this reason, when the inversion interval becomes long, waveform distortion occurs and the measurement of the maximum inversion interval becomes unstable.

Therefore, in the above-mentioned conventional device, in order to prevent reverse rotation, the application of the braking voltage must be released without waiting for the rotation of the disk to sufficiently decrease, and therefore, from the time of this release until the rotation is stopped. As the time becomes longer, the timing of stopping the rotation of the disk becomes uncertain.

By the way, the disc reproducing apparatus employs a mechanism that allows the user to stop the rotation of the disc at any time by operating a stop button. Especially when the eject button is operated to eject the disc during playback, it is necessary to remove the disc after stopping the rotation of the disc, and the disc was not completely stopped. In some cases, the disc may be scratched by rubbing against a guide mechanism for guiding the disc.
In order to prevent such a situation, the disc reproducing apparatus is required to accurately stop the rotation of the disc in a short time. However, the above-mentioned JP-A-58-208970
As described in the publication, if the timing of stopping the rotation of the disc is uncertain, such a request cannot be met and the disc may be damaged.

Further, Japanese Patent Application Laid-Open No. 57-46687 discloses a stop control of a DC motor used for sending out a form, but this aims at stopping the DC motor at a target angle. For this reason, the time from the start of braking to the passage of the time detection point (θ) is compared with a reference value, and extension control of the braking time with respect to the predetermined braking time is performed based on the difference. As described above, in this control method, since the target is to stop at the target angle, it is necessary to provide a time detection point (θ) that is a reference angle, and a code plate or the like is attached to the rotating shaft of the DC motor. It has to be attached, and it is not required to stop in a short time, and it is not always possible to stop in a short time (the stop time varies depending on not only the load but also the timing of the stop command). However, this control method cannot be applied to the braking control of the above-mentioned demanded disc reproducing apparatus.

The present invention has been made to solve the above-mentioned problems, and a disc braking method capable of accurately and accurately stopping the rotation of a disc in a short time, whenever an instruction to stop the rotation of the disc is issued. Is provided.

[Means for Solving the Problems] A braking method for a disc according to the present invention is a braking method for a device for reading a digital signal from a disc on which a digital signal is recorded, in which the digital signal read from the disc is bit-synchronized with the signal. Generating a bit-synchronized clock signal, detecting the rotational speed of the disk based on the bit-synchronous clock signal and a reference clock signal having a preset frequency, and driving a braking means for applying a braking force to the disk. To start braking the disc and the rotation speed of the disc at the start of braking
Dividing V ₀ by a preset value a, the reference rotation speed
A step of obtaining V _a (: the predetermined value a is set so that the signal is read out from the disc within a speed range);
The step of measuring the braking time T ₁ until the rotational speed V _{0 of the} disk reaches the reference rotational speed V _a , and the remaining braking time T ₂ is calculated based on the braking time T ₁ , and the braking time T ₂ The step of further driving the braking means for a period of time to give a braking force to stop the disk.

[Operation] According to the present invention, a bit synchronization clock signal bit-synchronized with the digital signal read from the disc is generated, and the disc is rotated based on the bit synchronization clock signal and a reference clock signal having a preset frequency. Detect speed. Then, the reference rotational speed V _a is obtained by dividing the rotational speed V ₀ of the disk at the start of braking by the predetermined value a. At this time, this reference rotation speed V _a
The predetermined value a is determined so that it falls within the speed range in which the signal is read from the disk. Then, the dynamic characteristics of the braking system are grasped by measuring the braking time T ₁ until the rotational speed V ₀ of the disc at the start of braking reaches the rotational speed V _a, and the remaining braking time is determined by the braking time T _1. Time T ₂ can be calculated by However, a = V ₀ / V _{a is} obtained, and the braking means is further driven for the braking time T ₂ to apply a braking force to the disk to stop the disk.

[Embodiment] A disk reproducing apparatus to which a braking method according to an embodiment of the present invention is applied will be described below with reference to the block diagram of FIG. In the figure, 1 is a disc on which a digital signal is recorded, 2 is a pickup for reading a recording signal from the disc 1 by making laser light incident on the disc 1 and converting the reflected light into an electric signal, 3 is a pickup 2 PLL (phase locked loop) circuit that generates a clock signal (PLCK) bit-synchronized with the reproduced digital signal from
4 is a signal processing circuit that receives a signal (PLCK) and a reproduced digital signal from the pickup 2 and performs signal processing, and 5 is a reference signal RFCK from the clock generation circuit 6 (this frequency is 7.
Counter for starting counting of the signal (PLCK) in synchronism with 35 kHz), 7 for a comparator, 8 for a servo circuit for controlling the rotation of the disk 1 in the normal reproduction state, 9 for a servo circuit 8
Is a braking control circuit, 11 is an amplifier, and 12 is a motor that gives a rotational force to the disk 1. Here, the comparator 7 compares the count output value of the counter 5 with a reference value (here, 294),
When the count value becomes the reference value or less, the output signal rises from the low level L to the high level H.

Further, the brake control circuit 10, the brake voltage from the contacts 92 movable piece 91 of the servo circuit 8 side at time t ₁ of the switching circuit 9 (-Vcc)
After switching to the contact 94 on the side, the output of the comparator 7
The state of the contact is maintained for the subsequent period T _{2 with} respect to the period T ₁ until rising at t ₂ , and the movable piece 91 is switched to the contact 93 on the ground side at the subsequent time t ₃ . The movable piece 91 is in contact with the contact 92 on the servo circuit 8 side so that the motor 12 is controlled by the output of the servo circuit 8 during normal reproduction.

Next, according to the timing chart of FIG. 2 showing the operation state from the time of the normal reproduction to the stop of the rotation of the disk 1,
The operation of the apparatus shown in FIG. 1 will be described.

In the normal reproduction state, the disk 1 is rotating stably by the servo circuit 8, and the digital signal recorded on the disk 1 from the pickup 2 has a normal bit rate fcho = 4.3218 × 10 ⁶ (bit / Second). At this time, the PLL circuit 3 outputs a bit clock signal (PLCK) synchronized with this. Therefore, the frequency (fplcko) of the output signal (PLCK) is equal to the regular bit rate (fcho).

Next, when the braking control circuit 10 receives a stop instruction from an external device (not shown), it starts the operation of stopping the rotation of the disk 1 from time t ₁ when the stop instruction is input. That is, the braking control circuit 10 outputs a switching command to the switching circuit 9, and the switching circuit 9 moves the movable piece 91 from the contact 92 to the contact on the braking voltage (-Vcc) side based on the command from the braking control circuit 10. Switch to 94. This allows the motor 12 to have an amplifier
A braking voltage (-Vcc) that rotates in the opposite direction to the normal playback state is applied via 11, and the braking voltage (-Vcc), contact 9
4,91 (switching circuit 9), amplifier 11 and motor 12 function as the braking means of the present invention.

The counter 5 in the normal reproduction state counts the signal (PLCK) in synchronization with the reference signal (RFCK) from the clock generation circuit 6 as described above. That is, the counter 5 counts the signal (PLCK) and outputs the reference signal (RFCK) at a constant cycle and is reset, so that the count value is calculated. Becomes

Next, the motor 12 applies the braking voltage (-Vcc) to the torque in the stopping direction to the disk 1, and the rotation of the disk 1 is reduced. At the same time, the bit rate (fch) of the reproduced digital signal obtained from the pickup 2 also decreases. Since the signal (PLCK) outputs a clock signal synchronized with the reproduced digital signal, its frequency (fplck) is the same as the bit rate (fch), which depends on the rotation decrease of the disc 1 as shown in FIG. Decrease. Therefore, the count value of the counter 5 is also the value 588 in the normal reproduction state.
It decreases sequentially from. After the braking voltage (−Vcc) is applied to the motor 12 at time t ₁ , the count value is 294 at time t _2.
Then, the comparator 7 detects the coincidence between the count value of the counter 5 and the reference value (= 294), and its output rises and changes from the low level L to the high level H.

On the other hand, the braking control circuit 10 starts the time measurement after the movable piece 91 of the switching circuit 9 is brought into contact with the contact point 94 on the voltage (−Vcc) side (time t ₁ ), and the output from the comparator 7 changes from L to L. The time measurement is interrupted once at the time when it changes to the H level (time t ₂ ). The period from this time t ₁ to t ₂ is T ₁ . This time
The fact that the count value of the counter 5 reaches 294 at t ₂ means that the number of revolutions of the disc 1 has become half of that in the normal reproduction state because the value in the normal reproduction state is 588. .

Next, the reverse torque generated when the braking voltage (-Vcc) is applied to the motor 12 is set to -Tb Newton-m (however, the load symbol indicates braking). Here, if the number of revolutions of the disc 1 and the motor 12 in the normal reproduction state is N ₀ and the rotational moment is I (kg.sec ² ), their momentums are represented by (N ₀ × I). This momentum is the reverse torque (-T
b), and after the period T ₁ , the rotation speed of the disk 1 becomes N _a (= N _0/2 ). _{That, I × (N 0/2} ) = N 0 · I-Tb · T 1 I × (N 0/2) = Tb · T 1 I × (N 0/2) = Tb · T 2 ... [2] The following formula is obtained. From the formula [2], when the count value of the counter 5 reaches 294, that is, from the time t _{2 when} the rotation speed of the disk 1 reaches N _a (= N _0/2 ), the reverse torque (-
It can be seen that if Tb) is applied to the disk 1 for a period T ₂ (provided that the decrease in the rotation speed is a linear function with respect to time T ₁ = T ₂ ), the momentum becomes zero and the rotation stops.

When the count value of the counter 5 reaches 294 (= N _0/2 ),
The output of the comparator 7 becomes the high level H as described above, and the output signal of the comparator 7 causes the disc 1 to be transferred to the pickup 2.
Stop playing and reading. Therefore, the reproduction signal cannot be obtained, and the operation of the PLL circuit 3 becomes unstable. Therefore, the brake control circuit 10 after becoming the output the time t ₂ of the comparator 7 from the low level L to high level H, the switching circuit so as to apply a braking voltage (-Vcc) further between the motor 12 of the period T ₂ Control 9 Thus the disc 1 is given a braking momentum comprising (-Tb · T _1), the disk 1 stops rotating at time t _3. At this time t ₃ , the control circuit 10 moves the movable piece 91 of the switching circuit 9 from the contact 94 on the braking voltage (−Vcc) side to the contact 9 on the ground side.
Switch to 3 and make contact. As a result, the voltage application to the motor 12 is stopped, and the reverse torque application to the disk 1 is stopped.

As described above, according to this embodiment, it is possible to obtain a device that can stably stop by predicting the time until the stop based on the rotation change until the reproduction state becomes unstable.

It should be noted that in the above-described embodiment, the number of rotations changes from N ₀ to N _a (=
The period T ₁ up to N _0/2 ) was measured, but if the period until N ₀ / a (where a> 1) is T _{1 then} I · (N ₀ / a) = N ₀ · _{I-Tb · T 1 Tb ·} T 1 = N 0 · I · (a-1) / a (N 0 / a) · I = Tb · {T 1 / (a-1)} (N 0 / a) _{· I = Tb · T 2 ...} [3] , provided that _{T 2 = T 1 / (a} -1).

Then, the rotation is stopped by braking for T ₂ (= T ₁ / (a-1)) after the rotation speed reaches N _a (= N ₀ / a). In addition, in the case of friction, if the torque due to this friction is (Ts) and (Tb + Ts) is replaced with (Tb) in [3], the same effect as in [2] or [3] can be obtained. can get.

By the way, the total braking time (=
T ₁ + T ₂ ) is specified by the state at the start of braking, does not vary with the length of the first braking time T ₁ , and
Examples of the state include the rotational speed of the disk, the moment of inertia, friction, and the braking force (motor characteristics, braking voltage). Although in the embodiment of Figure 1 has been described for the case of constant does not change the rotational speed of the disk (this case may be obtained only once the rotational speed N _a criterion) is,
When the rotation speed of the disk changes, the reference rotation speed N _a is calculated and set by dividing the rotation speed N ₀ at the start of braking by a predetermined value a each time braking is applied.

Next, the range in which the rotation speed N _a (= N ₀ / a) is set,
That is, the range of the predetermined value a (= N ₀ / N _a ) is examined.

Regarding the restriction on the upper limit of a, when the value of a becomes large, the braking time T ₁ also becomes large, but during that time, the signal must be stably read from the disk. For this purpose, the condition that the frequency band of the servo circuit (not shown) of the pickup 2 <low frequency component of the read signal must be satisfied. In a servo circuit of a normal disc reproducing apparatus, it is not easily affected by the read signal in an ideal state, but generally, the frequency component of the read signal (the EFM signal which is the information itself) is mixed in the servo circuit as noise. To do. During normal reproduction, since the EFM signal has almost no spectrum (energy) below 10 KHz, the servo circuit is not affected by the read signal. However, since the spectrum of the EMF signal also moves to the low frequency side in proportion to the decrease in the rotation speed of the disk, the servo circuit may become unstable if the above conditions are not satisfied, and Cannot be read.

For example, if you look at the case where the frequency band of the servo circuit is 1.5 KHz and the low frequency component of the signal is 10 KHz, the disk rotation speed can measure T ₁ up to 1.5 / 10 of normal playback, The upper limit of a is about 7 (N _a = N _0/7 ).

As for limitation of the lower limit of the above a, the a is the braking time T1 becomes small small, low detection accuracy of T ₁ is stopping accuracy (speed during rpm / normal playback operation when the brake release) Therefore, the lower limit value of a is appropriately determined in relation to the stopping accuracy.

In the above embodiment, part of the function of the electric circuit may be performed by software processing.

As described above, according to the present invention, a bit synchronization clock signal bit-synchronized with a digital signal read from a disk is generated, and the bit synchronization clock signal and a reference clock signal having a preset frequency are generated. detecting the rotational speed of the disk based on the bets and the rotational speed V ₀ which disk at the start of braking is divided by the predetermined value a determined rotational speed V _a of the reference, the rotational speed V ₀ which at the start of braking Rotation speed V _a
The braking time T ₁ is measured, the remaining braking time T ₂ is calculated from the braking time T ₁ , and the braking means is further driven for the braking time T ₂ to apply the braking force to the disk to Therefore, even if the reproduction signal becomes unstable due to the decrease in the rotation of the disk, the rotation can be stopped stably. Therefore, the rotation can be surely stopped by _one braking control (= T ₁ + T ₂ ), and as a result, the time required for the stop is short.

Further, according to the present invention, the remaining braking time T ₂ is obtained based on the rotation speed obtained from the reproduction signal of the disc, so that the rotation of the disc can be stopped in a short time no matter when the stop instruction is issued. it can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a reproducing apparatus to which a braking method according to an embodiment of the present invention is applied, and FIG. 2 is a timing chart of each section showing the operating state of FIG. In the figure, 1 is a disk, 2 is a pickup, 3 is a PLL circuit, 5 is a counter, 7 is a comparator, 9 is a switching circuit, 10 is a braking control circuit, and 12 is a motor. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A braking method for a device for reading out a digital signal from a disc-shaped recording medium (hereinafter referred to as a disc) on which a digital signal is recorded, which is a bit synchronization bit-synchronized with the digital signal read from the disc. Generate a clock signal,
A step of detecting the rotational speed of the disk based on the bit synchronization clock signal and a reference clock signal of a preset frequency; and a braking means for applying a braking force to the disk to drive the disk. The step of starting, the step of dividing the rotational speed V _{0 of the} disk at the start of braking by a preset predetermined value _a to obtain _a reference rotational speed V _a , and the rotational speed V _{0 of the} disk is the rotational speed Measuring the braking time T ₁ until reaching V _a , determining the remaining braking time T ₂ based on the braking time T _1, and further driving the braking means for the braking time T ₂ A step of applying power to stop the disk, the method of braking the disk.