JPH0445916B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a positioning device for an optical disk device, and particularly to a positioning device suitable for positioning a light spot with submicron precision.

[Background of the invention]

Currently, information is recorded by irradiating a metal film deposited on a rotating disk with laser light, narrowing it down to a spot of about 1 μm, and then modulating the irradiation power to thermally make holes in the metal film. death,
An information processing device called a digital optical disk has been proposed, which focuses and irradiates a metal film with a weak laser beam during reproduction, and reads information by using changes in the amount of light reflected from the information hole (referred to as a hit).
This kind of proposal is given in Electronics magazine, Nov.23,
1978, P75 “Ten Billion Bits Fit onto Tow
For example, a typical configuration of this type of system is as shown in Fig. 1. In other words, a digital optical disk 3 having a sanderch structure with a diameter of 30 cm is connected to a rotating shaft 4. It is rotated in the direction of the arrow by a rotating motor at the center.The optical head 2, which consists of a laser light source and an optical system, is mounted on a swing arm actuator 1 used for magnetic disks, and
driven in the radial direction. Information is recorded/reproduced in the structure shown in the partially enlarged view of the disk shown in FIG.

That is, guide grooves 13 are formed on a glass or plastic substrate 11 using UV resin 14 or the like.
A concave cross-sectional structure with a certain width and depth is created. A metal film 10 is deposited thereon. The focusing spot of the optical head is guided along this guide groove 13, and a pit 12 is formed by the above-mentioned means. Also during resetting, a light spot is irradiated along the guide groove 13 and the amount of reflected light is read. Furthermore, a signal for controlling the light spot is also detected from the amount of reflected light.

There are two main types of signals that control this light spot: a focus shift detection signal that detects a shift in focus due to vertical vibration of the disk, and a track shift detection signal that detects a shift between the center of the light spot and the center of the guide groove. be. All of these signals use the amount of light reflected from the metal film among the amounts of reflected light.

This optical disk has a track hitch of 1.6μm,
In this case, one side of a disk with a diameter of 300φ will have approximately 50,000 tracks, and the data stored per track will be approximately 4,000 bytes.

Conventionally, in this type of optical disk device, an actuator as shown in FIGS. 3a and 3b has often been used as an optical head positioning device. That is, FIG. 3a shows a swing arm type actuator, which is equipped with an optical head 2 at its tip. This actuator body 1 has a magnetic circuit 7 centered around a shaft 8.
The coil 6 intersects with the disk in the radial direction 2.
Swings to 0. On the other hand, FIG. 3b shows a direct-acting actuator, which is equipped with an optical head 2 and an indicator wheel 9. As shown in FIG. This actuator body 1 has a magnetic circuit 7
The coil 6 intersects with the disk in the radial direction 2.
Driven to 0. However, these actuators have a drawback that they have so-called mechanical resonance due to the mechanical rigidity between the drive coil 6 and the optical head 2, which makes it difficult to perform highly accurate positioning. FIG. 4 is a block diagram showing a control system of a positioning device using these actuators. When the relative displacement between the _{disk position} Represented by the constant K _SNS .
The output of this detector 200 is input to the actuator 100 via the compensation circuit 300.
Letting the transfer functions of 00 and actuator 100 be G _C and _CM , respectively, the one-round transfer function can be expressed by the following equation.

G _OS = K _soS G _C G _M ...(1) Figure 5 shows an outline of this Bode diagram. The gain is _GO in the low range and approximately -40dB/in the midrange.
dec, and becomes 0 dB at the cutoff frequency f _C ,
ΔG _SOB increases at mechanical resonance frequency f _SOB . If you increase the low-frequency gain G _O to improve positioning accuracy, or increase the cutoff frequency f _C to improve quick response, the mechanical resonance frequency
If the gain margin G _MSOB in f _SOB becomes small or becomes negative, the control system becomes unstable. Therefore, the actuator is usually designed so that the mechanical resonance frequency f _SOB is 5 to 10 times higher than the cutoff frequency f _C . However, there is a limit to increasing the stiffness of the actuator, and the mechanical resonance frequency
It is very difficult to increase f _SOB to 2 to 3 KHz or higher. Therefore, with conventional positioning devices, the positioning accuracy is approximately 1 μm or less, and the cutoff frequency f _C is
It is extremely difficult to increase the frequency to about 1KHz or higher. For this reason, conventional positioning devices cannot be applied to high-speed, high-precision optical disk devices that require a positioning accuracy of 0.1 μm or less and a cutoff frequency f _C of 2 KHz or more.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems and provide a positioning device that can perform high-speed and highly accurate positioning.

[Summary of the invention]

The present invention provides a second actuator that performs high-speed and high-precision positioning on a first actuator that is capable of large displacement and performs positioning of low frequency components, and provides a track error signal and a second actuator for both.
A controllable and observable control system is configured by feeding back the deflection signal of the first actuator via a compensation circuit, and for the first actuator, a compensation circuit having low-pass filter characteristics is provided at the front stage of the drive circuit. This reduces the influence of mechanical resonance of the first actuator and provides high-speed, high-precision positioning characteristics.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 6 shows the overall configuration, in which the first actuator 3 is supported by wheels 35 and driven by a coil 32 that intersects with the magnetic circuit 31.
0 has a magnetic circuit 33 and a coil 34 that intersects with it.
A second actuator comprising a deflection mirror 43 driven by the deflection mirror 43 is mounted thereon. The deflection mirror 43 is supported by a spring 36. An optical head is mounted on the first actuator 30, and the light emitted from the laser diode 41 passes through an optical system 42, is reflected by a deflection mirror 43, and is focused on a light spot 4 on the surface of the disk 3 by a diaphragm lens 44.
form 5. The reflected light from the disk passes through a focusing lens 44 and a deflection mirror 43, is separated by an optical system 42, and enters a track deviation detector 46. That is, the position of the optical spot 45 is roughly determined by the first actuator 30 and narrowly positioned by the deflection mirror 43 of the second actuator, and the relative displacement between the guide groove and the optical spot is determined by using the output of the detector 46 via the head amplifier 51. Track error signal
e Detected as _SNS . first actuator 3
0, there is no mechanical resonance with small attenuation in the band below about 500 Hz, and the frequency characteristics of the deflection angle of the deflection mirror 43 with respect to the current flowing in the drive coil 34 of the second actuator are Other than the natural frequency determined by the moment of inertia of the moving part and the rigidity of the support spring 36,
For example, it is assumed that there is no mechanical resonance below about 10 KHz. These vibration characteristics are sometimes not of high performance use. Further, a signal proportional to the rotation angle of the deflection mirror 43 is a displacement signal e _DF of the second actuator.
is output as An example of means for detecting this signal _eDF is shown in FIG. That is, light from a light emitting body 47 such as an LED is projected as a light spot using an optical system 48 onto a deflection mirror 43 that is driven by a coil 34 that intersects with a magnetic circuit 33 and supported by a support spring 36, and the light is reflected. The light is received by a detector 49 and detected as a displacement signal _eDF via an amplifier 52. When the deflection mirror 43 rotates, the balance of the amount of light incident on the light receiving elements 49-1 and 49-2 of the detector 49 changes according to the rotation angle, and if the output of each element is input to the differential amplifier 52, its output e _DF has a value almost proportional to the rotation angle of Mira 43.
In FIG. 6, the track error signal e _SNB and the deflection signal e _DF of the second actuator are represented by the compensation circuit 6.
The drive coil 34 of the second actuator is driven with current through the power amplifier 91 and the power amplifier 91, and the drive coil 32 of the first actuator is driven with current through the compensation circuit 70, the low-pass filter 80, and the power amplifier 92. Here, the low-pass filter 80 functions to prevent the influence of mechanical resonance of the first actuator 30 from reaching the entire system.

Before explaining the characteristics of the compensation circuits 60 and 70, the control system will be modeled to clarify the configuration of the entire system. FIG. 8 shows a model of the first and second actuators, where the first actuator 30 is a pure inertial system of mass M _C driven by the driving force F, and the second actuator 12
0 has a mass m _F driven by the increment of driving torque τ from the equilibrium point, a moment of inertia I _F , and is acted on by a rotational spring constant K _F and a rotational viscous friction coefficient C _F 2
It can be expressed as a mechanical model of a vibration system with degrees of freedom. The respective displacements and rotation angles from the equilibrium point are X and θ. Further, it is assumed that the distance L _G between the fulcrum of the second actuator 120 and the point of emphasis is negligibly small. Here, if the focal length of the diaphragm lens 44 is _lFC , the amount of movement of the light spot on the disk surface due to the rotation angle θ of the second actuator 120 is _2lFCθ , and the displacement of the light spot from the equilibrium point is _SP can be expressed by the following formula.

X _{SP =} The state equation can be described as follows as a system in which the input signal and the input signal of the low-pass filter 80 are input.

X・＝AX＋BU ……(3) Y＝CX ……(4) However, X＝Θ X F Θ〓 X〓 F〓 Y＝X _SP Θ C=l _FC 01 0 0 0 1 0 0 0 0 U=e _F e _Cwhere Θ: Angle of deviation from the equilibrium point of the second actuator X: Deviation of the first actuator from the equilibrium point F: _Driving force _{applied to the} first actuator C _M : Viscous friction coefficient of the second actuator M _C : Mass of the first actuator K _T : Torque constant of the second actuator K _PF : Current sensitivity of the power amplifier of the second actuator K _F : Current sensitivity of the second actuator Thrust constant K _PC : Current sensitivity of the power amplifier of the actuator shown in Equation 1 w: Angular natural frequency ξ of the low-pass filter 80: Tamping coefficient of the low-pass filter 80 e _F : Power amplifier input of the second actuator e _C : Input of the low-pass filter Equation The system represented by (3) and (4) is a controllable and observable coefficient with 2 inputs and 2 outputs, and all variables of the state variable Using regulator 1200
The poles of the system can be set to arbitrary values.

FIG. 10 shows an example of the configuration of a control system in which the deflection of the optical spot, _XSP , is controlled, and the deflection angle Θ of the second actuator 120 is subjected to minor feedback. e _SNS is the output of the track error detection device 200 (consisting of a detector 46 and an amplifier 51), which detects the displacement of the guide groove of the disk in a minute range.
The displacement of X _DSK and the optical spot is proportional to the relative displacement of X _SP . This error signal _SNS is multiplied by K _AF by an amplifier 61, and from this signal, the second phase compensation circuit 6 receives the displacement signal E _DF of the second actuator 120.
3 is subtracted, and this is used as the input e _F of the current drive amplifier 91 of the second actuator via the first phase compensation circuit 62. On the other hand, the error signal e _SNS
is input to the third phase compensation circuit 71, and from the output thereof, the output of the fifth phase compensation circuit 73, which inputs the deviation signal _eDF , is subtracted, and this is sent via the fourth phase compensation circuit 72. 2 installed in front of the current drive amplifier 92 (amplification factor S _PC ) of the first actuator.
Let it be the input e _C of the next low-pass filter 80.

First to fifth phase compensation circuits 62, 63, 71,
The transfer characteristics of 72 and 73 are G _CF , G _VF ,
Let GG _CB , G _CC , G _VC be the control signals e _F and E _C
can be expressed by the following formula.

e _F = (K _AF e _SNS −G _VF e _DF ) G _CF …(5) e _C = (G _CB e _SNS −G _VC e _DF ) G _CC …(6) Phase compensation circuit 62, 63, 71 ,72,73,
The above-mentioned observer design requires the characteristics of a high-order transfer function of 4th order or higher, but this is difficult to realize in terms of the S/N ratio, so we approximated this and obtained the following characteristics as a transfer function. It is possible to have one.

G _CF =K _CF α _CF (T _DCF S+1)/α _CF T _DCF S+1 ...(7) G _VF =K _VF T _VF S/T _VF S+1 α _VF (T _DVF S+1)/α _VF
T _DVF S+1 ...(8) G _CB =K _CB T _ICB S+1/β _CB T _ICB S+1 α _CB (T _DCB S+1)/α _CB T _DCB S+1 ...(9) G _CC =K _CC α _CC (T _DCC S+1)/α _CC T _DCC S+1...(10) G _VC =K _DC +K _VC T _VF S/T _VF S+1 α _VC (T _DVC S+1)/α _VC T _DVC S+1...(11) The above transfer function is It is constructed by parallel and series connections of the following transfer functions.

G _D =K _D α(T _D S+1)/αT _D S+1...(12) G _I =K _I T _I S+1/βT _I S+1...(13) G _V K _V T _V S/T _V S+1... (14) G _P = K _P ...(15) In general, G _D in equation (12) is called a phase lead element, which is a compensation element that advances the phase in the intermediate frequency band, and is
G _I in (13) is called a phase delay element, and is a compensation element that increases the gain in the low frequency range. Further, G _V in Equation (14) is a type of phase advance element, and is particularly called a pseudo-differential element, which is a compensation element that advances the phase in the operating band of the system. In equation (15), G _P is a proportional element.

Therefore, Equations (7) to (11) are determined by the combination of these elements; G _CF in Equation (7) is G _D in Equation (12), that is, the phase lead element, and G _VF in Equation (8) is Equation (14). ) is the series connection of G _V in equation (12), that is, the phase lead element, and G _CB in equation (9 ₎ is the series connection of G _I in equation (13) and G _D in equation (12), that is, the phase delay and The phase lead element, G _CC in equation (10) is a phase lead element similar to G _CF in equation (7), and G _VC in equation (11) is the same as G _V in equation (14) and G CF in equation (12).
It can be said that it is a phase advance element in which G _D connected in series and G _P of equation (15) are paralleled. That is, G _CF : Phase lead element (G _D ) G _VF : Phase lead element (G _V ×G _D ) G _CB : Phase lag and phase lead element (G _I ×G _D ) G _CC : Phase lead element (G _D ) G _VC : Phase lead element (G _P +G _V ×G _D ) A specific example of the configuration of an electric circuit that realizes the transfer characteristics of equations (12) to (15) is shown in FIG. Figure 11a corresponds to equation (12), K _D = -R ₁₄ /R ₁₃ ... (16) T _D = C ₁ R ₁₁ ... (17) α = R ₁ /R ₁₁ + R ₁ ...(18) R ₁ = R ₁₂ R ₁₃ /R ₁₂ +R ₁₃ ...(19) Figure 11b corresponds to equation (13), K _I = -R ₂ R ₂₄ /R ₂₁ R ₂₃ ... (20) T _I = C ₂ R ₂₂ ... (21) β = R ₂ + R ₂₂ /R ₂₂ ... (22) R ₂ = R ₂₁ R ₂₃ /R ₂₁ + R ₂₃ ... (23) Figure 11c corresponds to equation (14), K _V = −R ₃₄ /R ₃₃ ... (24) T _V = C ₃ R ₃₂ R ₃₃ /R ₃₂ + R ₃₃ ... (25) Figure 11d corresponds to equation (15) ), and K _P = −R ₄₄ /R ₄₃ .

However, since the polarity of these circuits is reversed at the input and output, insert an inverter as necessary.
It is necessary to ensure that negative feedback is applied. The explanation will be omitted here. Furthermore, the transfer characteristic G _LP of the low-pass filter 80 can be expressed as G _LP =w ² /S ² +2ξwS+w ² (26), and a specific configuration example of an electric circuit to realize this characteristic is shown in Fig. 12. Shown below. The following relationship holds between equation (26) and the constants of the circuit shown in FIG.

W=1/√ _{51 52 51 52} ξ=C ₅₂ (R ₅₁ +R ₅₂ )/2√ _{51 52 51 52} [Effects of the Invention] According to the present invention, the first actuator machine that performs positioning with a large deviation Since the influence of mechanical resonance can be reduced, the optical spot can be positioned in the guide groove on the disk at high speed and with high precision due to the characteristic having a band equal to or higher than the mechanical resonance frequency.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of an optical disk device, Figure 2 is an enlarged view of the disk surface, Figure 3 is a diagram showing the actuator configuration a and b, Figure 4 is a block diagram showing a conventional control system, and Figure 5 is a diagram showing the configuration of actuators. 6 is a diagram showing a schematic configuration of an embodiment of the present invention, FIG. 7 is a diagram showing an example configuration of a deflection mirror deflection detection device, and FIG. 8 is a diagram showing an example of the configuration of an actuator. Dynamic model diagram, Figure 9 is a schematic configuration diagram of the control system, Figure 10 is a block diagram showing the control system of the device in Figure 6, and Figure 11 is a schematic diagram of the control system.
Figures a to d are diagrams showing specific examples of the circuit configuration of the compensation circuit, and FIG. 12 is a diagram showing an example of the circuit configuration of the low-pass filter. Explanation of symbols, 2... Optical head, 3... Disk, 30... First actuator, 43... Deflection mirror, 60, 70... Compensation circuit, 80... Low pass filter, 91, 92... Drive circuit .

Claims (1)

[Claims] 1. A first actuator, a second actuator mounted on the first actuator, and a displacement proportional to the relative displacement between the combined displacement of the first and second actuators and the target displacement. and a second signal detecting means for generating a second signal proportional to the relative displacement of the second actuator with respect to the first actuator.
a signal detection means, first and second phase compensation means receiving the first and second signals as input, and a low-pass filter, and the output of the first phase compensation means is passed through the low-pass filter. A positioning device characterized in that the output of the second phase compensation means is applied to the drive circuit of the first actuator via the drive circuit of the first actuator, and the output of the second phase compensation means is applied to the second actuator. 2 The first phase compensation means inputs a phase delay and phase lead circuit which receives the first signal as an input, a phase lead circuit which receives the second signal as an input, and the difference between the outputs of both circuits. The second phase compensation means has a phase lead circuit which receives the second signal as input, and a phase lead circuit which receives the difference between the output of the phase lead circuit and the first signal as input. The positioning device according to claim 1, further comprising a lead circuit.