JP2757357B2 - Servo circuit for rotating recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo circuit for a rotary recording medium, and more particularly to a servo circuit of a pickup for reading or recording information from a disk. [Summary of the Invention] The present invention relates to a tracking servo circuit or a focus servo circuit required for reading information recorded on a rotary recording medium such as an optical disk. And a second transmission element having a high transmission gain with respect to the eccentricity error component of the rotary recording medium, wherein the first transmission element is an analog circuit. And the second transmission element is constituted by a digital circuit. [Prior art] As a rotary recording medium, a magnetic disk, an optical disk, or the like has been put to practical use. And a servo system with small residual deviation are required. Conventionally, therefore, a servo system for an optical disc is designed to obtain a high loop gain and stability. For example, the response of an actuator (two-axis mechanism) that irradiates a laser beam is improved,
In order to compensate for phase rotation due to the following characteristics, a complicated phase compensation circuit is used to design a servo characteristic with high gain in a wide band as much as possible. However, generally, in a servo circuit, widening the servo band and increasing the overall loop gain not only cause a loss of stability as is known in control theory, but also cause unnecessary heat loss. This causes a problem that the temperature of the actuator increases and the power consumption increases. Therefore, the present applicant has proposed a servo method (Japanese Patent Application No. 61-129125) for reducing the above problem. The outline of this servo system is to provide a circuit having a high transmission gain with respect to the rotational eccentric error component of the optical disk as a first transmission element, and to compensate for a mechanical transmission characteristic of an actuator as a second transmission element. By using a circuit that can generate a feedback circuit selectively with respect to the servo error signal,
Further, a servo device with a small residual deviation is constituted. [Problems to be Solved by the Invention] However, for example, a tracking error signal due to the eccentricity of the disk includes a harmonic component in addition to a component of a basic frequency f ₀ proportional to the rotation cycle of the disk, In addition, in the CLV method (Constant Velocity Angulan), the rotation cycle changes between the inner and outer sides of the disk. It was extremely difficult to construct. That is, when a servo system having a high loop gain is formed for _n eccentric frequency components f ₁ ... F _i ... F _n , as shown in FIG. ₁ , A
_2, A _3-state variable filter comprising, A ₄ (a state variable filter) and the n parallel-connected sets the resonance frequency of each state variable filter f ₁ ... f _i ... f _n, respectively. Then, a clock signal FG proportional to the rotation cycle output from a drive motor of the rotating disk or the like is divided by a frequency dividing circuit D.
₍₁₎ ... D _(i) ... 1 / n (n = _1.2) via D _(n)
... N) and supply them to the switched capacitors CS ₍₁₎ ... CS _(i) ... CS _(n) that determine the band pass frequency f _(n) of each state variable filter so that each frequency becomes ωd ₁ , ωd ₂ , ωd ₃ ... Constitute a transmission circuit in which the gain becomes infinite. Therefore, the circuit configuration becomes complicated, and it is difficult to realize such adjustment and configuration of the transmission circuit even though the frequency to be handled is low. Means for Solving the Problems The present invention has been made in view of the above problems, and a servo circuit responding to a servo error signal based on an eccentric component having a relatively low frequency in a servo circuit for a rotary recording medium. The loop is formed by a digital circuit, and the servo system circuit for the actuator, which responds to a relatively high frequency and the transfer characteristics are fixed by the mechanical characteristics of the actuator, is formed by an analog circuit. [Operation] Since the servo system for the eccentric component is constituted by a digital circuit, even when the type of disk and its rotation cycle change, it is easy to make the transmission characteristics variable in accordance with the eccentric error signal. In addition, the compensation system of the servo system for the actuator can be made constant by the mechanical transmission characteristics of the actuator, so that it can be easily realized by an analog circuit even if the frequency handled is relatively high. Embodiment FIG. 1 shows a servo circuit for a rotary recording medium according to an embodiment of the present invention. A portion 10 surrounded by a dashed line is a first circuit for a servo target value constituted by a digital circuit. The compensating circuit 20 is also a second compensating circuit for mechanical transmission characteristics of an actuator constituted by an analog circuit. The first compensation circuit 10 includes an adder circuit 11 and an A / D converter 12 that samples a servo error signal and converts the sampled signal into a digital signal.
And a shift register 13, a D / A converter driven by a clock signal FG proportional to the rotation cycle of a spindle motor or the like
14, and a coefficient circuit 15. _{Reference numeral} 16 denotes a comparator that compares the disk control target value _Xreff with the control amount x of the actuator and outputs a tracking error signal TE, 17 denotes a low-pass filter, and 18 denotes a coefficient circuit. The second compensating circuit 20 includes an operational amplifier 21 for compensating a phase shift in a low frequency band to compensate for a mechanical response characteristic of the actuator, and two-stage operational amplifiers 22 and 23 for compensating a phase advance in a high frequency band. The phase compensation is provided so that the servo characteristics are stabilized within a predetermined servo band by the response characteristics of the transmission element 30 of the actuator. A tracking servo circuit according to an embodiment of the present invention includes:
The tracking error signal TE output from the comparator 16 is
The signal is distributed to a first compensation circuit 10 formed of a digital circuit and a second compensation circuit 20 formed of an analog circuit. Adder 11, A / D converter 12, shift register 13, D / A converter 1
The closed loop consisting of 4 is given a delay amount by the clock signal FG so as to make a round with the rotation period L of the disk.
Therefore, its transfer function G _(s) is As shown in FIG. 2 (a), the rotational angular velocity ω of the disk is Thus, a comb-type band-pass filter having a peak point and having a lower peak point on the high frequency side is constructed. Therefore, the first compensation circuit 10 becomes a transmission element having a high transmission gain with respect to an eccentric error component and a harmonic component of the eccentric error with the rotation period L of the disk as the fundamental wave ω _0, and the servo loop makes the disk Control with a small steady-state error can be performed with respect to the tracking error based on the eccentricity. The coefficient circuit 15 sets the transfer gain K ₀ to 1 or less, is to set the attenuation of the peak point. Also, a second compensation circuit 20 composed of operational amplifiers 21, 22, and 23
Is generally the transfer function of the second order system The phase compensation of the transmission element 30 of the actuator shown in FIG.
As shown in (1), the actuator is set so as to mainly exhibit an effective response characteristic to a disturbance component. Therefore, this circuit is uniquely set by the mechanical transmission characteristic of the actuator, and can be easily formed by an analog circuit including a high-frequency component. The coefficient circuits 18 and 24 appropriately set the ratio of the servo gain to the eccentric component and the ratio of the servo gain to the disturbance component, and supply the ratio to the actuator via the adder 19, so that the servo characteristics of the entire servo circuit are improved. To decide. In the above, the tracking servo has been described as an example. However, in a servo circuit for a rotary recording medium, most of the target value is regarded as an eccentric component, and thus such a servo circuit is also useful for focus servo, spindle servo and the like. [Effects of the Invention] As described above, the servo circuit for a rotary recording medium of the present invention converts a servo error signal into a digital signal, supplies the digital signal to a shift register, and A servo system capable of setting a high loop gain for an eccentric component with respect to a rotary recording medium is constituted by a digital circuit having means for driving corresponding to the rotation cycle of the actuator. Since the servo circuit is configured, there is an effect that a steady-state error can be suppressed with respect to eccentricity and a servo circuit having high responsiveness to disturbance can be constructed. Further, there is an advantage that the design and adjustment of such a servo circuit becomes easy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a servo circuit for a rotary recording medium according to the present invention, and FIGS.
FIG. 3 is a data diagram showing the frequency response characteristics of the compensating circuit and the second compensating circuit. FIG. 3 is a circuit diagram showing a part of the prior art of the present invention. In the drawing, reference numeral 10 denotes a first compensation circuit formed of a digital circuit, reference numeral 20 denotes a second compensation circuit formed of an analog circuit, reference _numeral 30 denotes a transmission element of an actuator, _Xreff denotes a control target value, and x denotes a control amount.

Claims (1)

(57) [Claims] An actuator that records information on a rotating recording medium, or reads information, and a servo circuit that performs target value tracking control of the actuator based on a servo error signal output when recording or reading the information, The servo error signal is converted into a digital signal, the data is supplied to a shift register, the shift register is operated by a clock signal corresponding to the rotation cycle of the rotary recording medium, and the feedback amount is set to 1 or less. A first compensation circuit comprising a digital circuit having a comb-shaped filter characteristic that provides a higher peak gain as the frequency becomes lower than the eccentric frequency of the rotary recording medium. Phase in a given frequency band to compensate for the mechanical response characteristics of And a second compensating circuit comprising an analog circuit for compensating the servo. The output of the first compensating circuit is supplied to the actuator together with the output of the second compensating circuit via a low-pass filter. A servo circuit for a rotating recording medium, which forms a loop.