JPH0527185B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a recording medium in which tracks are formed concentrically or spirally on a signal surface with respect to the center of rotation, and the number of revolutions is increased at the inner circumference of the tracks. This invention relates to a spindle servo mechanism with a constant linear velocity, which controls rotation so that the linear velocity of a track being written or read becomes constant by decreasing the speed at the outer periphery.

BACKGROUND TECHNOLOGY AND PROBLEMS For example, in an optical compact disk player, a constant linear velocity method (CLV=Constant Linear
The optical system picks up the recorded information by sending the optical system pickup in the radial direction of the compact disc from the inner circumferential side to the outer circumferential side of the track formed on the signal surface of the compact disk serving as the recording medium. Reproduction is performed by reading the .

Now, considering the transfer function G ₀ (x) from the torque generated by the spindle motor to the linear velocity of the track being read, which is a constant linear velocity of the compact disc, based on FIG. 1, it is as follows.

First, when a compact disk D having a moment of inertia J is rotated by a spindle motor M generating a generated torque T, and if the angular velocity of the compact disk D is ω, then the following differential equation holds true.

T=J・dω/dt+R・ω ...(1) (∵R; viscous resistance of mechanical system) If both sides are Laplace transformed and the initial value is set to zero,
The transfer function G ₁ (x) from the generated torque T of the spindle motor M to the angular velocity ω of the compact disk D is G ₁ (x)=1/J·S+R.

By the way, if the rotational radius position r of the compact disk D on the track being read at a constant linear velocity; the linear velocity is v _e , then v _e =r・ω, and when substituted into the above equation (1), T= It becomes J・1/r・dv _e /dt+R/r・v _e .

Therefore, the transfer function G ₀ (x) is expressed as G ₀ (x)=1/J·S+R×r, and is proportional to the rotation radius position r.

However, since the track formed on the signal surface of the compact disc has a diameter of approximately 50 mm at its inner circumference and approximately 120 mm at its outer circumference, the transfer function from the inner circumference side to the outer circumference side of the track G ₀ (x) The gain difference is a large value of 20log120/50≒7.6db.

Therefore, even if you set the required gain on the inner track, the gain will be 7.6db on the outer track.
As shown in the Bode diagram of FIG. 2, there is no phase margin or gain margin, and servo stability cannot be obtained. Furthermore, if the gain is set at the outer circumference of the track, the servo's quick response cannot be obtained at the inner circumference of the track. That is, there is a problem in that the required response characteristics cannot be obtained over the inner and outer peripheries of the track, and linear velocity unevenness increases in response to disturbances from the compact disk such as eccentricity or warping.

Purpose of the Invention The present invention was invented in view of the above-mentioned problems, and its purpose is to change the gain of the servo transfer function according to the rotational radius position of the truck to record data. To provide a spindle servo mechanism with a constant linear velocity, which can obtain required response characteristics over the inner and outer peripheries of a track formed on a medium, and which reduces linear velocity unevenness due to disturbances such as eccentricity or warpage from a recording medium. be.

Summary of the Invention The spindle servo mechanism with a constant linear velocity according to the present invention controls the rotation of a recording medium in which a track is formed concentrically or spirally on a signal surface with respect to the center of rotation at a constant linear velocity. The spindle servo mechanism is characterized in that the transfer function of the servo is compensated according to the rotational radius position of the track so that a desired response characteristic can be obtained over the inner and outer circumferences of the track. .

As a result, the required response characteristics of servo stability and quick response can be obtained across the inner and outer peripheries of the track formed on the recording medium, and linear velocity unevenness due to disturbances such as eccentricity or warping from the recording medium is reduced. .

Embodiment Next, a specific embodiment in which the spindle servo mechanism with constant linear velocity according to the present invention is applied to an optical compact disc player will be described with reference to the drawings.

FIG. 3 is a block circuit diagram when a compensation method by gain adjustment is used to obtain the required response characteristics.

On the signal surface of a disk-shaped compact disk D, which is an example of a recording medium rotated by a spindle motor M, tracks are formed concentrically or spirally with respect to the center of rotation. Note that the track is composed of a row of pits modulated by audio information serving as recorded information.

Thus, the signal output of the audio information sequentially read by the optical pickup P, which is sent in the radial direction of the compact disc D from the inner circumferential side to the outer circumferential side of the tracks formed on the compact disc D, is outputted by the clock. The signal is applied to the extraction circuit section 1. The extracted clock is then converted to PLL (Phase
Locked Loop) circuit section 2 and LPF (Low Pass)
(filter) circuit section 3 to the error detection circuit section 4. The error detection circuit section 4 compares it with a predetermined clock reference signal to form an error signal S _E of an analog voltage signal that is the basis of a control operation.

This error signal S _E is given to the multiplication circuit section 5 and is used as a rotation radius information signal of an analog voltage signal, which will be described later.
Multiplied by S _r . The multiplied signal is then applied to the drive circuit unit 6 through the first switch circuit unit (SW ₁ ), and is applied to the spindle motor M after being amplified. Thus, the rotation of the spindle motor M is controlled so that the linear velocity of the track being read by the optical system pickup P is constant. Note that the first switch circuit section _SW1 is driven and controlled by the motor drive command signal S _M ,
It becomes “ON” state with motor drive command signal S _M.

The transfer function of the above closed-loop control system servo is
Rotation radius information signal S _r given to the multiplication circuit section 5
is so-called "1" when is at the inner circumference of the track, and is set so that the necessary gain can be obtained at the inner circumference of the track.

On the other hand, a rotating disk 8 having slits 7 formed radially and circumferentially is fixed to the spindle motor M. A light-emitting element 9A such as an LED and a light-receiving element 9B such as a phototransistor are disposed facing each other with the rotating disk 8 in between. A rotation speed detection mechanism is constituted by the rotating disk 8, the light emitting element 9A, the light receiving element 9B, and the like.

Thus, the spindle motor M rotates, the compact disk D is rotated, and the rotating disk 8 is also rotated. Light emitted from the light emitting element 9A intermittently through the slit 7 is received by the light receiving element 9B, and a pulse is generated.

However, this pulse is generated by the slits 7 formed in the rotating disk 8 at equal intervals in the circumferential direction, and since the compact disk D rotates integrally with the spindle motor M, the frequency of the generated pulse is
Then, the following formula holds true.

n=K・ω...(A) (∵K: constant, ω: angular velocity of compact disk D) Also, the radius of rotation position r and linear velocity _{v e} of compact disk D in the reading track where the linear velocity is constant Since v _e =r·ω, the relationship with ve = r·n/k can be obtained by substituting the above equation (A).

Therefore, the rotational radius position r is as follows: r=1/n·K· _ve , and since the constant K and the linear velocity v _e are constant, it is inversely proportional to the frequency n of the generated pulse.

By the way, the generated torque T of the spindle motor M
The transfer function G ₀ (x) from the linear velocity v _e of the track being read by the optical system pickup P is G ₀ (x)=1/J・S+R×r (∵J; inertia of the compact disk D moment, R; viscous resistance of mechanical system). Therefore, since the gain of the transfer function G ₀ (x) is proportional to the rotation radius position r, if the frequency n of the generated pulse is multiplied by the transfer function G ₀ (x), the closed loop control The gain of the system remains constant. Note that the transfer function of the entire closed-loop control system is the product of the transfer function G ₀ (x) multiplied by a constant.

Thus, the pulse is given to the counter circuit section 11 after being waveform-shaped by the waveform shaping circuit section 10 . This counter circuit section 11 is configured to be reset by a timer circuit section 12 at fixed time intervals _t1 . Then, the counter circuit section 1
The number of pulses counted in 1 is a certain period of time after reset.
Every t ₂ (t ₁ ), the data is latched by the shift register circuit 13 based on a transfer command from the timer circuit 12.

The count value corresponding to the frequency n of the latched generated pulse is given to the D/A converter 14, where it is converted into a rotation radius information signal Sr of an analog voltage signal and is sent to the second switch circuit (SW ₂ ). It is applied to one input terminal a. This rotation radius information signal S _r
is inversely proportional to the rotation radius position r of the track being read as described above, and the frequency n of the generated pulse is
is proportional to. Therefore, when the track being read is on the inner periphery, it is assumed to be "1", but on the outer periphery it is a value below the decimal point in inverse proportion to the rotation radius position r.

The other input terminal b of the second switch circuit SW ₂ is supplied with a constant voltage E which is so-called "1" and corresponds to the rotation radius information signal S _r at the inner circumference of the truck.
has been added. The second switch circuit section _SW2 is supplied with a motor drive command signal _SM through the delay circuit section 15 to perform drive control.

Therefore, the delayed motor drive command signal S _M
A constant voltage E is applied to the multiplier circuit unit 5 through the input terminal b until it is applied to the second switch circuit unit _SW2 . This is because the linear velocity of the track being read does not reach a constant level immediately after the spindle motor M starts rotating, and the rotation radius information signal S _r does not correspond to the rotation radius position r. Note that even in a state where there is no motor drive command signal S _M , a constant voltage E is applied to the multiplier circuit section 5, but the motor drive command signal
Until S _M is applied and driven, the first switch circuit section SW ₁ is kept in the "OFF" state and the closed loop control system is open, so no trouble occurs.

Then, around the time when the spindle motor M starts up, the second switch circuit section _SW2 is drive-controlled by the delayed motor drive command signal S _M , and the rotation radius information signal S _r is sent to the multiplication circuit through the input terminal a. Part 5 is given.

As described above, in accordance with the rotational radius position r on the compact disk D of the track being read, the multiplication circuit section 5 receives rotational radius information proportional to the frequency n of the generated pulse, which is inversely proportional to the rotational radius position r. A signal S _r is provided and multiplied by an error signal S _E . Therefore, the transfer function of the closed loop control system servo, which is proportional to the rotation radius position r, is multiplied by the rotation radius information signal S _r , which is inversely proportional to the rotation radius position r, so that the gain becomes constant. Therefore, stability and quick response can be achieved over the inner and outer peripheries of the track, and the desired response characteristics can be obtained.

Note that a frequency generator may be used as the rotation speed detection mechanism.

Next, a modification using a potentiometer which can directly obtain the rotational radius position r on the compact disk D of the track being read in place of the rotational speed detection mechanism will be described with reference to FIG. In addition,
The same reference numerals as in the above embodiment indicate the same content,
Duplicate explanations will be omitted.

Optical system pick-up P is compact disk D
As the potentiometer 16 is fed in the radial direction, the slider 16a of the potentiometer 16 is moved. As a result, the rotation radius information signal S _r ', which is an analog voltage signal, is obtained directly from the potentiometer 16 and is proportional to the rotation radius position r of the track, which is read by the optical pickup P. This rotational radius information signal S _r ' is directly given to the division circuit 5', unlike the previous embodiment, and is used to divide the error signal S _E from the error detection circuit 4.

Therefore, the transfer function of the closed loop control system that is proportional to the rotational radius position r is divided by the rotational radius information signal S _r ' that is proportional to the rotational radius position r,
The gain remains constant.

In the above, in order to obtain the required response characteristics of the closed-loop control system servo based on the rotational radius information signals S _r and S _r ′, a compensation method using gain adjustment with a constant gain was used. Alternatively, series compensation by phase adjustment may be used to obtain an appropriate phase margin using a series compensation circuit using a lead/lag circuit. Furthermore, both compensation by gain adjustment and series compensation may be used.

Effects of the Invention The present invention has the following advantages.

The servo transfer function, which is proportional to the rotational radius position on the recording medium of the track formed in a concentric or spiral shape, is recorded by compensating the gain or phase, or both, according to the rotational radius position. The required response characteristics of servo stability and quick response can be obtained over the inner and outer circumferences of the tracks formed on the medium. Therefore, linear velocity unevenness due to disturbances such as eccentricity or warpage from the recording medium is reduced.

[Brief explanation of the drawing]

1 and 2 are a schematic diagram and a Bode diagram of a mechanical system for explaining the background art and its problems, respectively. FIG. 3 is a block circuit diagram of a spindle servo mechanism with a constant linear velocity according to the present invention, and FIG. Figure 4 is the second
FIG. 3 is a block circuit diagram of a modified example corresponding to that shown in FIG. In addition, in the symbols used in the drawings, D: compact disk, M: spindle motor.

Claims (1)

[Scope of Claims] 1. A rotational radius position detection means for detecting a rotational radius position during recording/reproduction of an optical pickup for recording/reproducing an optical disk; and a rotational radius information signal corresponding to the rotational radius position. a comparator that compares the clock signal obtained by the optical pickup with a reference clock signal and outputs an error signal; and a comparator that computes the rotation radius information signal and the error signal. means, and uses the calculation result from the calculation means to keep the gain of the transfer function constant and to rotate a spindle motor that rotationally drives the optical disk at a constant linear velocity. Spindle servo mechanism with constant speed.