JPS62150530A - Focus controller - Google Patents

Abstract

PURPOSE:To attain the high efficient drive of a focus actuator part by providing a power supply switching means switching the 1st voltage level into the 2nd voltage level higher than the 1st voltage level with a focus search of an objective lens is requested. CONSTITUTION:An L level control signal is fed from an operation control circuit (not shown in figure) incorporating a microcomputer or the like is fed to a control terminal 23 in the focus servo state and an H level control signal is fed in the focus servo state. Thus, a power voltage V1 is impressed to a BTL drive circuit 18 in the focus servo state, the peak value of a pulse width modulation signal is suppressed lower, the focus actuator part is driven with a large duty ratio and efficient state. Further, a power voltage V2 is fed to the circuit 18 in the focus search state to increase the peak of the pulse width modulation signal and the gain to drive the focus actuator part. Thus, the focus actuator part is driven with a high efficiency and low power consumption is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical disc playback device such as a compact disc player, and particularly relates to an improvement of a focus control device thereof.

[Technical Background of the Invention] As is well known, in the field of sound W equipment, in order to record and reproduce data with as high density and high fidelity as possible, information signals are converted into digitized data and recorded on discs, for example. Digital recording and reproducing systems that record on a recording medium such as a magnetic tape or the like and reproduce the recorded information have become widespread. Of these, compact discs, which use discs as recording media, are currently the mainstream, with bit strings corresponding to digitized data formed on a 12 cm diameter disc and read optically. .

On the other hand, a compact disc player that plays the above-mentioned compact disc moves an optical pickup containing a semiconductor laser, a charge conversion element, etc. in a linear tracking manner from the inner circumference of the disc toward the outer circumference. Compact disc at constant linear velocity (CL
The data recorded on the compact disc can be read by rotating it using the V) method.

Here, the optical pickup is configured to read IC data recorded on the disk by focusing a laser beam emitted from the semiconductor laser onto a pit row of the disk using an objective lens.

In this case, the objective lens is set at the initial position when the disc is stopped, and when the disc is requested to be played back, it is forced to move at high speed from the initial position to the vicinity of the in-focus position. A search is performed.

This focus search is performed by supplying a focus search voltage signal to a focus actuator section for moving the objective lens in the focus direction.

When the objective lens reaches the vicinity of the in-focus position through this focus search, the focus servo is applied to the objective lens in order to prevent the following types of objective lenses from shifting from the in-focus position, that is, to prevent focus deviation. I am trying to apply it.

This focus servo generates a focus error signal corresponding to the focus shift of the objective lens based on the data read by the optical pickup, and transmits the voltage signal generated based on this focus error signal to the focus actuator section. This is done by supplying the

Incidentally, in recent years, compact disc players have become smaller and lighter, and there has been a push to introduce them as portable devices for so-called outdoor use. In such a case, a battery is naturally used as a power source, so it will be a major challenge in the future to design a compact disc player that consumes less power and can operate at low voltage.

Therefore, PWM (Pulse Width Modulation) is currently used because it has a high conversion efficiency from electrical energy to kinetic energy.
Techniques have been utilized to generate a voltage signal to be applied to the focus actuator section.

FIG. 4 shows a conventional compact disc player using such PWM technology.

That is, 11 in the figure is a disk, and the disk motor 12
It is designed to be rotationally driven by.

An optical pickup 13 is installed at the bottom of the disk 11 in the figure so as to be movable in the radial direction of the disk 11. And this optical pickup 13
is moved in the radial direction of the disk 11 by the rotational force of a pickup feed motor (not shown).

Here, when the disc 11 is being played back, a signal obtained from the optical pickup 13 is supplied to the geocus error signal generation circuit 14, thereby causing a focus shift of an objective lens (not shown) provided in the optical pickup 13. A focus error signal FE corresponding to is generated.

This focus error signal FE is then supplied to a PWM conversion circuit 16 via a phase compensation circuit 15. The PWM conversion circuit 16 generates a pulse width modulation signal by comparing the levels of the signal output from the phase compensation circuit 15 and the reference triangular wave signal output from the triangular wave generation circuit 17.

In that case, the pulse width modulated signal is transmitted to the BTL drive circuit 18.
is supplied to This BTL drive circuit 18 has a power supply terminal 1
The peak value level of the pulse width modulation signal is amplified up to the power supply voltage applied to the power source 9, and is supplied to a focus actuator section (not shown) provided in the optical pickup 13 for moving the objective lens in the focus direction. The focus servo is operated in five colors so that the objective lens is held at the in-focus position.

By the way, in a compact disc player equipped with the focus servo means as described above, when moving the optical pickup 13 in the focus direction during focus search, the above-mentioned method is used in order to quickly bring the objective brick near the in-focus position. It is necessary to increase the gain for driving the focus actuator section. That is, the gain for driving the focus actuator section is switched between the focus servo state in the normal playback state and the focus search state.

[Problems with the Background Art] However, in the conventional compact disc player using the PWM technology as described above, the efficiency when driving the load (focus actuator section) with a pulse width modulation signal, that is, the conversion from electrical energy to kinetic energy is low. The following problems arise in terms of conversion efficiency.

First, the electric power W when driving a load with a pulse width modulation signal is W=E2/R, where R is the load resistance and E is the effective voltage of the pulse width modulation signal.

Here, as shown in FIG. 5, if one period of the pulse width modulation signal is the king and the instantaneous voltage is e, the effective voltage E is as follows.

In addition, by Fourier series transformation of the instantaneous voltage e, each sine wave (harmonic) component en (n=1.2, 3
．． ), and if the maximum voltage of the sine wave component en is E maxn en −EIlaXn−5ill(nωt+θn), then the effective voltage E is゜).

Here, when the pulse width modulation signal shown in FIG. 5 is transformed into a Fourier series, with its peak value as V and its on time as τ, the following results. Then, by substituting ω-2π/T and refining it, we get the following. From this, the effective voltage E can be found as follows.

By the way, the pulse width modulation signal has its DC component Eo
(-τV/T) is the only effective voltage that is substantially converted into kinetic energy, and the others become harmonic components and become invalid, so the ratio of the DC component Ee+ included in the effective voltage E (Ea/E ), the conversion efficiency can be found. Also, as is clear from the above equation, the effective voltage E is
τ/T, that is, the on time τ and period T of the pulse width modulation signal
(hereinafter referred to as duty ratio), it can be seen that the conversion efficiency depends on the duty ratio.

FIG. 6 shows the peak value 1V'r carrier frequency 44
．． FIG. 3 is a characteristic diagram showing changes in conversion efficiency when a 1 kHz pulse width modulation signal is supplied to a pure resistor R and its duty ratio is changed. In this case, the cycle T of the pulse width modulation signal is kept constant, and the duty ratio is varied by changing the on time τ.

The characteristic shown by the solid line in the figure shows the actual change in conversion efficiency obtained by dividing the actually measured DC component level Eo by the actually measured effective voltage E. In addition, the characteristic shown by the dotted line in the figure is that the level Ea of the actually measured DC component can be calculated as 1 using the above formula.
Effective voltage E obtained by calculating the total up to the 00th harmonic
It shows the change in theoretical conversion efficiency divided by .

Therefore, as can be seen from FIG. 6, it is theoretically and experimentally clear that as the duty ratio becomes smaller, that is, as the on-time τ becomes shorter, the conversion efficiency becomes significantly lower.

This means that when trying to obtain the same effective voltage va from two types of pulse width modulation signals with different peak values as shown in FIGS. 7 and 8, the voltage shown in FIG. It is shown that the pulse width modulated signal has higher conversion efficiency than that shown in FIG.

Therefore, in the focus servo state, the pulse width modulation signal supplied to the focus actuator section should have a long on time and a low peak value to obtain an effective voltage that can achieve a low focus servo gain.
This is advantageous in terms of efficiency.

However, as mentioned above, the pulse width modulation signal supplied to the focus actuator section can be changed by changing its duty ratio during focus search.
It is also required that an effective voltage high enough to increase the gain for driving the focus actuator section can be obtained. For this purpose, the peak value of the pulse width modulation signal must be set high.

□ Here, change the pulse width to supply f to the one-stage actuator section! The peak value of the l signal is determined by the f source voltage applied to the BTL drive circuit 18.

Therefore, if the power supply voltage is set high considering focus search, it is effective to shorten the on time of the pulse width modulation signal during focus servo, reduce the duty ratio, and achieve a low focus servo gain. However, as mentioned above, the conversion efficiency becomes extremely poor and the power consumption increases.

[Object of the Invention] This invention has been made in consideration of the above circumstances, and is an extremely favorable method that can drive the focus actuator section with high efficiency in both the focus search state and the focus servo state, and can reduce power consumption. The purpose of the present invention is to provide a focus control m device.

[Summary of the Invention] That is, a focus control device according to the present invention generates a focus error signal corresponding to a focus shift of an objective lens provided in an optical pickup based on data read from a disk via an optical pickup. a focus error signal generation means for converting the focus error signal to a pulse width modulation signal; In a focus control device, the power supply voltage supplied to the drive means is set to a disk power supply switching to set the first withstand voltage level when regeneration is requested and to set the second voltage level higher than the first voltage level when focus search of the objective lens is requested; Get the means! By doing so, the focus actuator section can be driven with high efficiency in the focus search state and the focus servo state, respectively, and power consumption can be reduced.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 4 are indicated by the same symbols, and only the different parts will be explained here. That is, 20 and 21 in FIG. 1 are power supply terminals, respectively. Among these, a low-level power supply voltage v1 is applied to the power supply terminal 20, and a high-level voltage 2 higher than the power supply voltage V1 is applied to the power supply terminal 21. These terminals 20 and 21 are
@1 of the changeover switch 22 and the second fixed contact 22a,
22b, respectively.

Here, the changeover switch 22 has a common contact 22c.
is connected to the power input terminal of the BTL drive circuit 18. The changeover switch 22 has its common contact 2
2c, the movable contact piece 22d is in constant contact with the first and second fixed contacts 2:! a, 22bk: Switching is performed by selectively connecting. In this case, the changeover switch 22 is controlled so that the movable contact piece 22d is connected to the first and second fixed contacts 22a, depending on whether the control signal supplied to the l terminal 23 is an L level or an H level.
22b.

Here, in order to control the operation of the compact disc player, an arithmetic control circuit (not shown) having a built-in microcomputer or the like is connected to the sub-leg terminal 23 at an L level in the playback state of the disc 11, that is, in the focus servo state. A control signal of H level is supplied in the focus search state.

Therefore, in the negative servo state, the power supply voltage v1 is applied to the BTL drive circuit 18, and the peak value of the pulse width modulation signal supplied to the focus actuator section is kept low, increasing the duty ratio. Thus, the focus actuator section can be driven in an efficient manner. In addition, in the focus search state, the power supply voltage V2 is applied to the BTL drive circuit 18, so that the peak value of the pulse width modulation signal supplied to the focus actuator section can be increased, and the focus actuator section is driven. It is possible to increase the gain.

Therefore, according to the configuration of the above embodiment, B
Since the power supply voltage applied to the TL drive circuit 18 is changed to change the peak value of the pulse width modulation signal supplied to the focus actuator section, the focus actuator can be operated efficiently in both the focus surge state and the focus servo state. 3. Here, FIG. 2 shows the configuration of the BTL drive circuit 18. That is, this is a pair of input terminals 24
．． By supplying the pulse width modulation signal outputted from the PWM conversion circuit 16 to 25 in reverse phase and turning on and off the switches 26, 27 and 28, 29 in an opposite relationship to each other, the negative resistance R( In this case, the power supply voltage applied to the power input terminal 30 is supplied to the focus actuator section (focus actuator section) at a duty ratio corresponding to the pulse width modulation signal.

For example, if the power supply voltage ■1 is applied to the power supply input terminal 30, the load resistance R is supplied with a pulse width variation: A signal with a peak value V1 as shown by the solid line in FIG. It turns out. Further, if the power supply voltage V2 is applied to the power supply input terminal 30, the load resistance R has a third
As shown by the dotted line in the figure, a pulse width modulated signal with a peak value of V2 is supplied.

In this case, as is clear from FIG. 3, even if the wave 15 value of the pulse width modulation signal changes, the duty ratio does not change, so when the power supply voltage is switched to 2, the B
It is possible to expand the dynamic range of the TL drive circuit 18 and increase the gain, which is more effective in increasing the gain for driving the focus actuator section.

It should be noted that the present invention is not limited to the above-mentioned example of the actual cage, and can be implemented with various modifications within a range that does not give the gist of the invention.

[Effects of the Invention] Therefore, as described in detail above, according to the present invention, the focus actuator section can be driven with high efficiency in both the force surge state and the focus servo state, and extremely low power consumption can be achieved. A good focus control device can be provided.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram showing an embodiment of a focus control device according to the present invention, FIG. 2 is a circuit diagram showing the configuration of a BTL drive circuit of the same embodiment, and FIG. 3 shows the operation of the same embodiment. FIG. 4 is a block configuration diagram showing a conventional focus control means, FIG. 5 is a waveform diagram for explaining a pulse width modulation signal, and FIG. 6 is a duty ratio of a pulse width modulation signal. Characteristic curve diagram showing the relationship between and efficiency, No. 7
8 and 8 are waveform diagrams for explaining the conventional problems, respectively. 11... Disc, 12... Disc motor, 13
... Optical pickup, 14... Focus error signal generation circuit, 15... Phase compensation circuit, 16...
PWM conversion circuit, 17... Triangular wave generation circuit, 18...
・BTL parking circuit, 19...power terminal, 20.21・
...Power terminal, 22...Selector switch, 23...Control terminal, 24.25...Input terminal, 26-29...
Switch, 30...Power input terminal. Patent attorney representing the applicant! Takehiko ToeFigure 2Figure 3Figure 7Figure 8

Claims (1)

[Claims] A focus error signal generation means for generating a focus error signal corresponding to a focus shift of an objective lens provided in the optical pickup based on data read from the disk via the optical pickup, and an output from the focus error signal generation means. pulse width modulation means for converting the focused error signal into a pulse width modulation signal; In a focus control device, the power supply voltage supplied to the drive means is set to a first voltage level in a state where playback of the disc is requested. and a power supply switching means for switching to a second voltage level higher than the first voltage level when focus search of the objective lens is requested. Control device.