JPS6339978B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for electrically damping pickup actuator resonance in a reproducing apparatus that optically reads and reproduces information from an information recording carrier, such as an optical digital audio disc reproducing apparatus or an optical video disc reproducing apparatus. In this specification, the term "pickup actuator" is used to refer to a focus actuator, a tracking actuator, or a tangential actuator. In order to optically read information from a rotationally driven information recording carrier in an optical digital audio disc playback device, etc., as shown in FIG.
A light beam from a He--Ne laser light source is projected onto the signal recording surface of the information recording carrier 5 via the polarizing beam splitter 1, tangential mirror 2, tracking mirror 3, and objective lens 4, and is reflected by the signal recording surface. The projected beam is reflected by the film, the reflected beam is projected onto the photoelectric conversion element 6, and the information recorded on the information recording carrier 5 is electrically converted from the output of the photoelectric conversion element 6 and detected. However, in order to read the recorded information on the information recording carrier 5, it is necessary to connect the optical spot of the projection beam to the signal recording surface of the information recording carrier 5. Therefore, the convergence state of the projected beam on the signal recording surface is determined by using the reflected beam itself, and a relative displacement signal (hereinafter referred to as a focus error signal) between the objective lens 4 and the information recording carrier 5 is obtained from the output of the photoelectric conversion element 6. detect,
The voltage is applied to the focus servo amplifier, and the objective lens 4 is driven by the focus actuator, thereby controlling the relative position between the objective lens 4 and the information recording carrier 5 to be constant. In addition, in order to make the light spot of the projection beam narrowed down by the objective lens 4 follow a track consisting of a row of pits on the information recording carrier 5, a relative displacement signal (hereinafter referred to as A tracking error signal) is detected from the output of the photoelectric conversion element 6 and applied to the tracking servo amplifier, and the tracking actuator rotates the tracking mirror 3.
The light spot is moved in the normal direction of the track and controlled so that it follows the track. In addition, in order to move the optical spot at a constant speed on the track in relation to the rotational speed of the information recording carrier 5, a time axis fluctuation error (jitter component) (hereinafter referred to as jitter component) is generated.
The tangential error signal (referred to as tangential error signal) is detected and applied to the tangential servo amplifier, and the tangential actuator rotates the tangential mirror 2 to move the optical spot in the tangential direction of the track. The light spot is controlled so that it follows the track at a constant relative speed. However, the hocus actuator mentioned above,
Conventionally, when driving a tracking actuator and a tangential actuator (hereinafter also referred to as a pick-up actuator), the back electromotive force generated in the actuator is extracted and
It is controlled by applying speed feedback to the servo amplifier.
However, because the back electromotive voltage is relatively small due to the structure of the actuator, the signal-to-noise ratio is poor and there are cases where the signal is not suitable as a speed feedback signal. Furthermore, since each actuator described above has temperature dependence, the sharpness Q of the mechanical resonance at the corner frequency in the amplitude-frequency characteristic changes greatly depending on the temperature, and the servo circuit for driving the pick-up actuator changes. The drawback was that the stability changed depending on the temperature. The present invention has been made in view of the above, and an object of the present invention is to provide a method for electrically damping pickup actuator resonance, which eliminates the above-mentioned drawbacks by electrically damping the mechanical resonance of a pickup actuator. It is something. This object is achieved according to the invention by detecting the velocity component signal of the moving part of the pick-up actuator and feeding it back negatively to the servo amplifier of the pick-up actuator. The method of the present invention will be explained below using examples. FIG. 2 is an explanatory diagram showing the configuration of the focus actuator. Hocus actuator A is yoke fixing member 1
An objective lens holder 12 that holds an objective lens 4 is supported by a spring plate 11 on the 0, and a coil 13 is wound around the objective lens holder 12. On the other hand, the coil 13 is connected to the magnet 14 and the yoke 1.
The objective lens holder 12 is disposed in the magnetic circuit formed by the coil 13 and
is driven, and the relative position of the objective lens 4 with respect to the information recording carrier 5 is controlled via the objective lens holder 12. The focus actuator A shown in FIG. 2 is now connected to an amplifier 16 and a feedback resistor 17 as shown in FIG.
The _equation of motion _of actuator A when driven with a _constant current by a servo amplifier _consisting of In equation (1), m is objective lens 4 and coil 1
3, B is the magnetic flux density in the gap of the yoke 15, N is the total number of turns of the coil 13, D is the diameter of the coil 13, e _ff is the electromagnetic conversion rate, i is the drive current, k _s is the spring constant of the spring plate 11, γ is the attenuation constant of the spring plate 11, and x is the displacement of the objective lens. Further, the electric circuit of actuator A can be considered to be a series circuit of a resistance R, an inductance L, and a back electromotive force, as shown in FIG. Therefore, the circuit equation of the electric circuit shown in FIG. 4 is expressed as Ldi/dt+R ₁ =E-BNπDe _ff dx/dt (2). In equation (2), E is the voltage applied to the electric circuit shown in _FIG . On the other hand, FIG. 5 is an explanatory diagram showing the configuration of a tracking actuator and a tangential actuator. The tangential actuator and the trunking actuator are supported by a support member 19 made of an elastic body, and a reflecting mirror 20 forming the tangential mirror 2 or the tracking mirror 3 is provided at both ends of the reflecting mirror 20. It consists of a movable part consisting of fixed magnets 21 and 22 of mutually opposite polarity, and a coil 24 that applies electromagnetic force to the magnets 21 and 22 to rotate the reflecting mirror 20, and is essentially a focus actuator. It has a moving magnet structure similar to Yueta A. Therefore, its equation of motion is also the same as equation (1) above. In this case, m is the mass M of the entire movable part of the magnet 21 on one side.
Or, it is the equivalent mass when it is considered that it is concentrated at the center of gravity of 22. Moreover, the magnetic flux density B is
It is the sum of the magnetic flux density B' of magnets 21 and 2.
When the two magnetic flux densities B' are equal, B=2B'.
Further, the spring constant K _s is the stayness of the elastic body constituting the support member 19 , and the damping constant γ of the spring is the damping constant of the elastic body constituting the support member 19 . Further, the electrical equivalent circuit is the same as that shown in FIG. 4, and the equation of the electrical circuit is also the same as equation (2). Further, the present invention is not limited to the structure of the actuator shown in FIGS. 2 and 5, but the same applies to actuators driven by the electromagnetic force between a coil and a magnet. Now, when formula (1) is Laplace transformed, as ² X (s) = dI (s) - cX (s) - bsX (s) ... (3). Here a=m, b=γ, c= _ks , d=
I set it as BNπDe _ff . Therefore, X(s)/I(s)=d/as ² +bs+c...(4) G(s)=X(s)/I(s)=A/s ² +2δω _o s+
ω _o ² ...(5). here

【formula】

It is. Therefore, from equation (5), the transfer characteristic of displacement with respect to the actuator current becomes as shown in Figure 6a, and the phase rotation becomes as shown in Figure 6b.The sharpness of the mechanical resonance at the corner frequency is Q. (=1/2δ) is determined by the mass m, the spring constant k _s , and the spring damping constant γ, and the gain at the corner angular frequency ω _o is also determined by the mass m,
It is determined by the spring constant k _s and the damping constant γ of the spring.
Furthermore, when the Q value is large, the phase delay also becomes faster with respect to an increase in frequency. Generally, when performing follow-up control using a servo system, the braking constant δ is normally selected to be approximately 0.6 to 0.8, but the above-mentioned focus actuator, tracking actuator, and tangential actuator In order to achieve a damping constant δ = 0.6 to 0.8, the mass m, spring constant _ks , and spring damping constant γ must be appropriately selected, and it is extremely difficult to realistically obtain such a material. be. Moreover, even if a material that can obtain a damping constant δ = 0.6 to 0.8 is obtained, if its temperature dependence is high, the sharpness Q of the resonance at the corner frequency ω _o will change depending on the temperature. Affects system stability. However, in the method of the present invention, as described above, the displacement signal X of the actuator is differentiated to obtain a velocity component signal, and the velocity component signal is negatively fed back to the servo amplifier of the actuator. Therefore, a block diagram of a servo system when the method of the present invention is applied is as shown in FIG. The transfer function of the actuator is A/(s ² +2δω _o s + ω _o ² ) as shown in equation (5), and by differentiating the actuator displacement signal X and feeding back the velocity component negatively to the actuator's servo amplifier, Transfer function of displacement X to current input I
G'(s) is calculated as follows: G'(s) = A/S ² +2δω _o s+ω _o ² /1+(A/S ² +2δω _o s)
+ωn ² )α _s =A/s ² +2δ′ω _o s+ω _o ² ...(6). Here, δ′ is δ+Aα/2ω _o , and by multiplying the speed feedback, the braking constant δ′ becomes + more than the braking constant δ before multiplying the speed feedback.
It becomes larger by Aα/(2ω _o ), and the sharpness Q of the resonance of the actuator becomes smaller. Further, the braking constant δ' is determined by the speed feedback amount α, and can be freely changed by changing the speed feedback amount α. Next, FIG. 8 shows a specific example of a circuit in an embodiment of the method of the present invention in which mechanical resonance is electrically damped by applying velocity feedback as described above. That is, as in the conventional case, a focus error signal, a tracking error signal, or a tangential error signal detected from the output signal of the photoelectric conversion element 6 is applied through the input resistor 26 to the inverting input terminal of the amplifier 16 that drives the coil 13 with a constant current. The coil 13 is configured to be driven. Note that the resistors 17 and 18 are resistors for negative feedback of the amplifier 16. Further, the error signal is applied to a differentiating circuit consisting of a capacitor 27 and a resistor 28 for differentiation, and this differentiated output is applied to a non-inverting input terminal of an amplifier 29. The output of the amplifier 29 is passed through a resistor 30 to the amplifier 16. The configuration is such that it is applied to the inverting input terminal. Note that resistance 31
The variable resistor 32 is for negative feedback of the amplifier 29, and by changing the resistance value of the variable resistor 32, it is possible to set the speed feedback amount α for differentiating the error signal and negative feedback to the input terminal of the actuator. . Now, the resistance values of the resistors 17, 18, 26, 28, 31 and the variable resistor 32 are R ₁₇ , R ₁₈ , R ₂₆ , R ₂₈ ,
When R ₃₁ and R ₃₂ , R ₂₆ = R ₃₀ = R _s , R ₁₈ =
It is assumed that R _f , R ₁₇ = R _p , R ₂₈ = R, R ₃₁ = R ₁ , R ₃₂ = R ₂ , and R ₅ = R _f >> R _p = R. In Fig. 8, the current I(s) flowing through the coil 13
The _{transfer function} of the ^actuator _{displacement X ( s )} ^for / _Rs・1/ _Rp =1/
It becomes R _p . Here, V _p is the voltage drop across the resistor 17. Therefore, H(s)=X(s)/V _IN =I(s)・X(s)/V _IN
I(s) = 1/R _p・A/s ² +2δω _o s+ω _o ² ...(7) P(s)=V ₂ /X(s)=R/R+1/SC(1+R ₂ /
R ₁ ) = SCR / 1 + SCR (1 + R ₂ / R ₁ ) = αS / 1 + SCR ... (8) where α = [(1 + R ₂ / R ₁ )CR], V ₂ is the voltage at the output terminal of the amplifier 29 . Therefore, the block diagram of the servo system when using the servo amplifier shown in FIG. 8 becomes as shown in FIG. =
V ₂ /X(s)αs up to 5kHz, which is equivalent to the block diagram shown in Fig. 7, and the resistance value of the variable resistor 32
The damping coefficient δ′ can be changed by R ₂ . Further, as shown in FIG. 10, a DC negative feedback circuit 33 may be further provided in the servo amplifier of the block diagram shown in FIG. 9 to apply negative DC feedback with a feedback amount β. In addition, in FIG. 10, numeral 34 indicates a compensation circuit for improving stability when negative direct current feedback with feedback amount β is applied. Furthermore, in the specific circuit shown in FIG. 8, an example has been described in which the error signal obtained from the output signal of the photoelectric conversion element 6 is differentiated by the capacitor 27 and the resistor 28 to obtain a velocity component signal. Alternatively, the same effect can be obtained by directly detecting the moving speed of a movable object such as the reflecting mirror 20 using a speed detecting means such as a photointerrupter, applying speed feedback, and electrically damping the resonance. As explained above, according to the present invention, the speed component signal of the moving part of the pick-up actuator is detected, and the speed component signal is applied negative feedback to the input terminal of the servo amplifier for driving the pick-up actuator. Even if the sharpness Q of resonance varies greatly with temperature due to the temperature dependence of the actuator, this can be suppressed. In addition, since the velocity component signal of the moving part of the pick-up actuator can be detected from the output of a conventional photoelectric conversion element for detecting optical information, it is possible to easily damp the mechanical resonance of the pick-up actuator electrically. This can be done with configuration. In addition, in order to detect the speed component from an error signal with sufficient S/N and apply speed feedback, which is necessary for servo control, the back electromotive voltage of the drive coil of the pick-up actuator is extracted as in the past. Compared to a method in which velocity feedback is applied by using the method, velocity feedback can be applied sufficiently.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the optical system of a reproducing device that optically reads and reproduces information from an information recording carrier, Fig. 2 is an explanatory diagram showing the configuration of a focus actuator, and Fig. 3 is an explanatory diagram of the focus actuator. Fig. 4 is a circuit diagram showing an equivalent electric circuit of a focus actuator, Fig. 5 is an explanatory diagram showing the configuration of a tracking actuator and a tangential actuator, and Fig. 6 is a block diagram of a servo amplifier. a
and b are a frequency-amplitude characteristic diagram and a frequency-phase characteristic diagram when a pickup actuator is driven by the drive circuit shown in FIG. 3, and FIG. 7 is a block diagram of an embodiment in which the method of the present invention is applied. , FIG. 8 is a specific circuit diagram of an embodiment in which the method of the present invention is applied, FIG. 9 is a block diagram of the specific circuit diagram shown in FIG. 8, and FIG. A block diagram when direct current negative feedback is applied to the circuit shown in the block diagram, 1... polarizing beam splitter, 2... tangential mirror, 3... tracking mirror, 4... objective lens, 5... information recording carrier, 6... photoelectric conversion element,
11...Spring plate, 12...Objective lens holder,
13, 24... Coil, 14, 21, 22... Magnet,
15...Yoke, 19...Support member, 20...Reflector,
16, 29... Amplifier, 27, 28... Capacitor and resistor that constitute a differential circuit.

Claims (1)

[Claims] 1. Detects an error signal from the output of a photoelectric conversion element that receives the reflected light of the light projected onto the information recording surface of the information recording carrier being rotated and converts it into an electrical signal, and uses the error signal as input to generate a pick-up actuator. In an information reproducing apparatus equipped with a servo amplifier for driving an actuator, a velocity component signal corresponding to a moving speed of a driven body of the pick-up actuator is obtained by differentiating the error signal,
A method for electrically damping pickup actuator resonance, characterized in that the speed component signal is negatively fed back to the servo amplifier to electrically damp mechanical resonance of the pickup actuator.