JPS59152572A - Optical disk reproducing device - Google Patents

Abstract

PURPOSE:To increase the low-band gain of a carriage servo to improve a disturbance eliminating capacity, by adopting a direct drive system as the drive transmitting system of a carriage and providing means which detect tracking and carriage error respectively. CONSTITUTION:In the current-displacement conversion frequency characteristic of a carriage motor 14, the phase characteristic is -180 deg. independently of frequency as shown in Fig. (a), and a servo band can be set freely by phase advancing compensation. When this servo band is set near a low-band resonance frequency f0 of an actuator 16 in Fig. (b), the overall open loop characteristic of both servos becomes as shown in figures, and the low-band gain is increased in comparison with a conventional case. At this time, the low-band resonance frequency of the actuator 16 is set to a value several - several tens times as high as eccentric components. The part indicated by oblique lines in the figure is the increment of the gain. Thus, a high open loop gain is attained, especially, in the low band, and the response to disturbance is improved, and the following-up capacity for eccentricity is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical disc reproducing device, and more specifically, a slider servo (carriage servo) and a tracking servo.
This increases the low-frequency gain of the servo's overall open-loop characteristics.

A carriage mechanism installed in a conventional optical disc playback device is configured as shown in FIG. 1, for example. In the figure, reference numeral 1 denotes an optical disk, 2 a track on the optical disk 1, 3 a gear body that moves in the radial direction of the optical disk 10, and a 4-carriage motor.

Mounted on the carriage body 3 are an objective lens 5, an actuator 6 for moving and operating the objective lens 5, and a tracking drive magnetic circuit 1.

Further, a detector 8 for detecting a misalignment between the track 2 and the objective lens 5 is provided inside the carriage body 3.

FIG. 2 shows the circuit of the servo system of the carriage mechanism. According to the fourth article, two systems are provided in conjunction: a tracking servo that moves the objective lens 5 with respect to the carriage body 3, and a carriage servo that moves the entire carriage. Due to the amount of deviation of the lens 5, that is, the tracking error, the actuator 6 is moved by 1d to reduce the deviation between the track 2 and the objective lens 5 by 4tf. actuator 6
When current flows through the motor, it is detected and the carriage motor 4
is driven, and the carriage body 3 is moved in the radial direction of the disk 10 through the meshing of the pinion 9 and the rack 10, causing the objective lens 5 to follow the track 2.

FIG. 3 shows the open loop characteristics of the servo. The shaded area indicates the increase in gain due to the addition of carriage servo.

According to the above-mentioned carriage mechanism, there is a time delay element in the carriage servo loop, which is the meshing of the binion 9 and the rack 10, and the gain of the carriage servo is limited, so the rotation frequency of the optical disk is 3. ~911z, but it is difficult to control up to this band. As shown in FIG. 3, since the eccentric frequency response is performed only by the tracking servo, the burden on the actuator 6 is heavy.

The present invention has been made in view of the above circumstances, and uses a direct drive system as the drive transmission system for the carriage instead of the meshing system with the rack ζ-binion, and also provides means for detecting tracking errors and carriage errors. The object of the present invention is to provide an optical disc reproducing device in which the low-frequency gain of the carrier servo is increased and the disturbance rejection ability is improved.

An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 4a to 4c show an example of an optical disc reproducing apparatus according to the present invention. In the figure, reference numeral 11 is an optical disc, 12 is a track on the optical disc 11, and 13 is an optical disc 1.
10 is a carriage body that moves in the radial direction, and 14 is a carriage motor.

In this embodiment, a flat type DC motor is used as the carriage motor 14, and the drive coil 14a constituting the motor 14 is disposed on the carriage body 13, and the yarn 18 facing the carriage body 13 is provided with a magnet). 14
b is placed.

The spindle 140 of the carriage motor 14 is connected to the chassis 1.
8, and the carriage body 13 is provided with a bearing 14d for this spindle 14C''.

Therefore, when the carriage motor 14 is driven, 1! without going through the rack or pinion. The contact carriage main body 13 is driven and the spindle 14of.

The center moves from the inner circumference of the optical disc 11 to the outer circumference.

Mounted on the carriage body 13 are an objective lens 15 and an optical system including a two-axis actuator 16 that drives the objective lens 15 in the focus direction and the trunk direction. Although the two-axis actuator 16 is not shown in detail,
It is constructed using leaf springs.

In the figure, 17 is a spindle motor that rotates the optical disk 11, and is installed on the chassis 18.

The detection means for tracking error H and carriage error E (see FIG. 5) is constructed as shown in FIG. 6.

In the figure, 21 is a laser light source, 22 is a lens, 23 is a beam splitter, 24 is a 1/4 wavelength plate, 25a, 25b
is a set of photoelectric conversion elements 26a.

26bl-1, amplifier, 27a, 27buO-pa/(
7 Ilter (LPF), 28 is differential 77b, 29a, 29
b is bypass 7 il p (HPF'), 30 &, 30
b is a full-wave rectifier, 3 i & , 31 b, l are low-pass filters (LPF), and 32 is a differential amplifier.

The irradiated light beam from the laser light source 21 passes through the lens 22, the beam splitter 23.1/4 wavelength plate 24, and then reaches the objective lens 1.
5 and enters the optical disk 11. Then, the reflected light (or transmitted light) from the optical disk 11 is separated by the beam splitter 23 and irradiated onto each light receiving surface of the set of photoelectric conversion elements 251LI25b.

As shown in FIG. 7, the photoelectric conversion elements 252L and 25b are installed so that their light-receiving surfaces are divided by a tree dividing m 2 s c, and the dividing line 25Cii trunk 1
Parallel to the tangent direction of 2 (indicated by arrow Y) iL
element 25a with respect to S and the optical axis of the reflected light of the light spot.
, 25b are symmetrical.

When the center of the light spot (the center of the objective lens 15) deviates from the track center in the direction perpendicular to the track, the intensity distribution of the light incident on the photoelectric conversion elements 252L and 25b becomes asymmetrical in accordance with this deviation (as indicated by the dotted line in FIG. 7). reference).

Photoelectric conversion element z5a, 25bo output ^1, A.

passes through amplifiers 2B2L and 2sb to LPF27a and 27
b, and the low frequency components B1 and B are extracted.

These low frequency components B, , B, are applied to the differential amplifier 28. On the other hand, HPF 29a, 29b outputs A, , A
The high frequency components of ,D, are extracted.

These high frequency components, D, are full wave rectifiers 30λ, 30b
After full-wave rectification, the output becomes E, , , and then the low-frequency components are extracted by LPF 31 h and 3 l b and the envelope component F, ! , and is applied to the differential amplifier 32.

The differential amplifier 28 obtains the difference component C between the low frequency components B, , B2, and the differential amplifier 32 obtains the envelope components F, B2.
, F, is obtained.

These difference components a, G1-1: Differential amplifier 3
3. It is input to the adder 34, and the differential amplifier 33 obtains the difference component H (tracking error No. 1h) between the components C and G. An error signal (carriage error signal) is obtained.

The two-axis actuator 14' is driven by this truck m@H, and the carriage motor 14 is driven by the carriage error mechanism.

The above-mentioned adder 34, compensation circuit 36, drive amplifier 38, and carriage servo means for the carriage motor 14 are configured, and the differential amplifier 33 and the compensation circuit 35
The drive amplifier 31 and the actuator 16 constitute a tracking servo means.

Figures 8 (a) to (1) are diagrams of each part II + b of the circuit block shown in Figure 6. In the case of type 1Lc) e, the center of the reflected light flux from the disk is shifted to the photodetector 25 & ,2
5b is displaced from the dividing line 25c. That is, in the state shown by the dotted line in FIG. 1, the tracking servo loop is in an oven state, and the optical spot is working to soften the recording track by stopping the disk bleeding. This shows the amount of water used. to in the diagram
is the time when the light spot coincides with the center of one track, t
-0°t-I+ indicates the time when the original spot coincides with the center of one track and the trunks adjacent to the inner and outer peripheries, respectively, and ゎ(1'1IIIi is the signal level).

FIGS. 8(a) and 8(b) show -1 set of photoelectric conversion elements 25 &
, Z 5 b.The output A1 of the detector 25a, which has a smaller irradiation area, has a higher frequency (RF ) component, envelope component, and DC component are all large and have a substantially proportional relationship. In addition, both coefficients A,
The phase relationship of the envelope components of , A2 is shown in Figures (&) and (b
), they have a phase difference of δ from each other. The phase difference is determined by each photodetector 9a with respect to the optical axis of the reflected light from the disk.

This is due to the fact that the center of the light receiving surface of 9b is symmetrically shifted.

FIG. 8(C) shows the waveforms of signals B, B2 from which only the low-frequency components of signals 1 and A2 have been completely extracted, and are approximated by the following equation.

j(ωt+δ) B,=to, (o +Ll ・・・・・・・・・
(1) j (ωt-δ) B, = 2 (θ 1 L) ・・・・・・・・・(
2) In particular, K, , are proportional constants that change due to disturbances, L is the ratio of the direct current component to the father current component, δ is the phase difference mentioned above, and ω is the operating time of one track interval for one period. This is the angular frequency when . Figure (α) is the inner signal B'13
The waveform showing the difference in Bt is 7JLt5, which is the same as the conventional tracking error No. 18. As shown in the figure, the tracking servo cannot be locked because a DC offset force exists. This DC offset component shows the influence of the disturbance, and is canceled out by the following signal.

FIG. 8 (8) and (f) each detector 251L l 25
The high frequency (RF) component of the output of b, that is, the waveform of i self-recorded information a No. 8 component 1), D, HPF29a, 29
The DC component is removed by b, resulting in an envelope that is symmetrical with respect to the zero level. Figures (g) and (h) are RF waveforms D
Signals x, , g obtained by full-wave rectification of HHD s.

(1) is this waveform K IHI! : t
are divided by the LPFs 31a and 31b to obtain envelope detection signals F, , F,. The waveform of F,,F, is approximated by the following equation.

"s = Kt (e""+a)+1) --(3
) Ft = K 1 (-61(*t-δ)-1)
-・-・-(4) Figure 8 (j) is the waveform of the difference component O of the signal 'l+F*, G=F, -F, =(-K a e'δ y,,
, a-Jδ)・e101+ to 1-, ......
... (5). Comparing the waveforms in Fig. 8 (d") and (j), the DC offsets at each time are both accurate and in phase, but the anti-seismic AC components are both in anti-phase relationship. Therefore, both signals The DC offset component can be removed by mixing Bl-B! and G at an appropriate ratio and taking the difference component. Therefore, the signal obtained by multiplying the B HB i signal by an appropriate gain (α) is shown in Figure (k ) in the differential amplifier 28, the amplifier.

The output C of 28 is: C=α(B,-13,) == (K, , ejδ-!', e-Jδ>
, αe Jc't = (x r x t )
αL ...... (6). Therefore, (
From equations 5) and (6), (KI −Kt )”(J −
By selecting a value of α that satisfies the formula αL...(y), H-G-C with DC offset removed.
A difference signal can be obtained as shown in Figure (1). H and α are expressed as follows.

H: (K, −ejδ10, −e−”) (α+1
)・el“1・・・・・・・・・・・・・・・・・・
・・・・・・・・・(8)α=1/L・・・・・・・
・・・・・・・・・・・・・・・・・・(9)(8)
As is clear from Eq., the tracking error (darbo)
As shown in FIG. 8(1), the signal H becomes a good trunking error signal with no DC offset due to disturbance removed and no deviation from the j target value.

In this way, according to this embodiment, the DC component due to the disturbance is read in the same phase as the difference in the low frequency component and the difference in the high frequency envelope component of a pair of photodetectors, and the tracking error component is also read in the same phase. Utilizing the fact that the current-changing component is included in the opposite phase, malfunction of the tracking servo due to disturbance can be prevented by simply performing electrical processing.

9(LL) shows the current-displacement conversion frequency characteristic of the carriage motor 14, and FIG. 9(b) shows the current-displacement conversion frequency characteristic of the actuator 16.

As is clear from Fig. 9 (l), the phase characteristic is -180° regardless of the frequency, and if phase lead compensation is performed, the servo range can be set to sunrise. When set near the low-frequency resonant frequency fo, the overall open-loop characteristics of both servos become as shown in Figure 10, and the low-frequency gain increases compared to the conventional case shown in Figure 3.In this case The low resonant frequency of the actuator 16 is set to be several times to several tens of times as large as the eccentric component.The shaded area in FIG. 10 is the increase in gain.

In the above embodiment, a rotary type carriage motor 14 is used, but a ν near motor may also be used.

Furthermore, the current flowing through the actuator 16 may be used to obtain the carriage error signal.

As explained above, according to the present invention, a direct drive type is used as the carriage drive means (carriage motor), and a tracking encoder detecting means for detecting the displacement between the reading means (objective lens) and the track center. and a carriage error detection means for detecting the displacement of the reading means with respect to the carriage body, and a control band of a carriage servo means for controlling the carriage drive means according to a carriage error signal from the carriage error detection means, The tracking drive means (actuator)'s low-frequency resonant frequency is maintained close to that of the tracking drive means (actuator).

Therefore, the oven loop gain can be particularly high in the low range, the response to disturbances is good, and the ability to follow eccentricity is improved. Further, by setting the low-frequency resonance frequency of the tracking drive means high and making the carriage respond to that range, the movable range of the tracking drive means can be kept small, and the design of the tracking drive means can be facilitated.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of a conventional device, FIG. 2 is a circuit diagram of its servo mechanism, FIG. 3 is a comprehensive open loop characteristic diagram thereof, and FIGS. 4a to 4C show an embodiment of the present invention. Figure a is a plan view, Figure 0 is a partially cutaway side view, Figure 0 is a front view, Figure 5 is an explanatory diagram of tracking error and carriage error, Figure 6 is a block diagram, and Figure 7 is photoelectric conversion. An explanatory diagram showing the relationship between the element and the light spot, FIG. 8 2L-1 is the sixth
The operation waveform diagram of each part of the block in the figure, Figure 9a is the current-displacement conversion frequency characteristic diagram of the carriage driving means, the same figure is the current-displacement conversion frequency characteristic diagram of the tracking and driving means, and Figure 10 is the overall open loop. It is a characteristic diagram. 11... Disc, 12... Trunk, 13... Carriage body, 14...
Carriage drive means (carriage motor) 15...
...Reading means (objective lens), 16...Tracking drive means (actuator), 25a, 25b.
...Photoelectric conversion element, 261L, 26 b・-
...Amplifier, 2γa, 27 b r31 a
, 31b-=-LPF, 29a, 29b-
---HPF, 28, 32.33... Group differential amplifier, 34... Adder, 36.35... Compensation circuit, 3γ. 38...Drive amplifier.

Claims (1)

[Claims] (1) A tracking error signal from a reading means for reproducing the track signal of the disk, a tracking drive means for driving the reading means, and a tracking error detection means for detecting the displacement between the reading means and the center of the track. tracking servo means for controlling the tracking drive means to correct displacement; a gear ridge body that is equipped with the reading means and the tracking drive means and moves in the radial direction of the disk to track the trunk signal; and the gear ridge body. and a carriage error signal from a carriage error detection means for detecting the displacement of the reading means with respect to the gear body body to control the gear carriage drive station 1 means to correct the displacement. 1. An optical disk reproducing apparatus, comprising: a carriage servo means, and a control band of the carriage servo means is provided around a low resonant frequency of the tracking drive means. ,-) A patent claim characterized in that the range resonance frequency of the tracking drive means is set to several times to several tens of times the eccentricity component, and the control band of the carriage support means is set to a frequency that almost matches the low-range resonance frequency. The optical disc playback device according to item 1.