SU1767526A1 - Device for displacement control of optical head relative to data disk carrier - Google Patents

Abstract

Use: in tracking systems of the information track by the read beam, for example, in laser CD players. SUMMARY OF THE INVENTION: The device comprises a track tracking signal forming unit 1, a reference voltage source 2, a comparator 3, a driver stage 4, an optical head movement actuator 5, an optical carrier rotation period sensor 7, a pulse driver 8, a delay element 9, an integrator 10 , adder 11, coincidence circuit 12, key 13. 1-11-2-10-3-12-4-5-6-1, 7-8-9-13-10, 10-13-8-12, 2 -11, 2 Il.

Description

The invention relates to techniques for recording / reading information on optical discs and can be used in tracking systems of the information track by a reading beam, for example, in laser CD players.

A device for controlling the movement of an optical head is known, comprising a position sensor for an optical head relative to a disk information carrier, including an optical Scale mounted in an optical head body, a processing unit for a signal read from a disk, a scale corrector register, the input of which is connected to the outputs of the optical head position sensor and the processing unit the signal read from the disk, the comparator and the drive moving the optical head [1].

In this device, the movement of the optical head is controlled by comparing the signals read by the head from the disk with the signals of the optical scale.

However, the known device is cumbersome, since it contains an optical scale mounted in the body of the optical head. The accuracy of its operation is affected by the eccentricity of the disk storage medium and other interference.

Of the known technical solution closest to the invention is a device for controlling the movement of the optical head relative to the disk information medium, comprising a track tracking signal generating unit, a voltage reference, a comparator and. a master cascade, the output of which is connected to the optical drive displacement drive, as well as a filter circuit with a time constant of 2-3 s, a D-trigger, central and additional processors [2].

In this device, the movement control of the optical head occurs as a result of the analysis of the track tracking error signal read from the disk information medium. The rate of development of the arising tracking errors is determined mainly by the time constant of the filter circuit, i.e. cannot be less than 2-3 s, and the accuracy of the development is determined by the quality of the signal tracking error track. This signal consists of the components of the three different frequency ranges: 1) the high-frequency component and _B h, due to fluctuations in scanning beam near the center of the track when the tracking ATS for track, the optical disk defects, mechanical vibrations, noises, these components generally range from hundreds of hertz and higher: 2) the low-frequency component and _N h caused by the radial beats of the disk, i.e. its eccentricity: the frequency range of this component is determined by the speed of rotation of the disk and is 3.3-8.3 Hz; 3) the ultra-low-frequency component Up, due to the slow radial movement of the reading beam when reading information in normal mode; the frequency range of this component is from 1 Hz and below. Thus, only one component of the read signal Up carries useful information, the other two components introduce errors, false alarms, i.e. reduce the accuracy of controlling the movement of the optical head relative to the disk storage medium.

The aim of the invention is to increase the speed and accuracy of management by eliminating the influence of the eccentricity of the disk medium. In addition, • the influence of oscillations of the read beam near the center of the track during the operation of the ATS tracking the track, as well as the influence of optical defects of the disk, mechanical vibrations and other noise were eliminated.

This goal is achieved in that the device for controlling the movement of the optical head relative to the disk information medium, comprising a track tracking signal generating unit, a reference voltage source, a comparator and a driver stage whose output is connected to the optical head movement drive, a disk medium rotation period sensor with a shaper is introduced pulse and delay element, at least one integrator with an adder, a coincidence circuit and a key, while the outputs of the signal conditioning block are tracked The signals behind the track and the reference voltage source are connected to the integrator input with an adder, the output of which is connected to the comparator input, the output of the latter is connected to the first input of the coincidence circuit, the second input of which is connected to the output of the pulse shaper, and the output is connected to the input of the driver stage, the integrator output is connected with an input through a key, the control circuit of which is connected through a delay element to the pulse shaper.

Figure 1 shows the structural diagram of a device for controlling the movement of the optical head with one integrator and adder; figure 2 is the same with two integrators.

The device comprises a track tracking signal generating unit 1, a reference voltage source 2, a comparator and a driving stage 4, the output of which is connected to the optical drive 6 displacement drive 5, a disk carrier rotation period sensor 7, a pulse shaper 8 and a delay element 9, an integrator 10 , adder 11, match pattern 12 and key 13. In this case, the outputs of the track tracking signal generation unit 1 and the reference voltage source 2 are connected to the input of the adder 11, the output of which is connected to the input of the integrator 10 (as indicated in ph d.1), the output of the integrator 10 is connected to the input of the comparator 3, the output of which is connected to the first input 14 of the matching circuit 12, the second input 15 of which is connected to the output of the pulse shaper 8! and the output 16 of the circuit 12 is connected to the input of the master stage 4, the output 17 of the integrator 10 is connected to its input 18 through the key 13, the control input of which 19 switches the keys through the delay element 9 to the pulse shaper 8,

Figure 2 shows a variant of the described circuit, in which less high-quality microcircuits can be used to build the integrator (for example, with an increased value of the temperature drift and a lower gain). In this case, two integrators 20 and 21 are used (on two operational amplifiers in one case). The input of the integrator 20 is connected to the output of the track tracking signal generating unit 1, the input of the integrator 21 is connected to the output of the reference voltage source 2, the outputs of the integrators 20 and 21 are connected to the input of the adder 22, the output of which is connected to the input of the comparator 3.

As in the circuit of FIG. 1, in this circuit the outputs of the integrators are connected to their inputs through a key 13 (in the circuit of FIG. 2, a two-pin key is used). With such a connection scheme, the error accumulating during the integration time will be approximately the same at the outputs of both integrators and when the output signals of the integrators (with opposite signs) are applied to the inputs of the voltage adder, the errors of the integrators will be mutually compensated.

The device for controlling the movement of the optical head operates as follows.

During the rotation of the disk information carrier, the signal read by the optical head 6 is supplied to the track tracking error signal generating unit 1, while the disk rotation period sensor 7 generates a signal whose repetition period T is equal to the disk rotation period. Shaper 8 generates a short pulse from the sensor signal (with a repetition period T), which is fed to the input 15 of the coincidence circuit 12.

In this case, the voltage from the output of unit 1 is added to the reference voltage from the source 2 of the reference voltage in the adder 11 and supplied to the integrator 10, which integrates the total voltage of the unit 1 and source 2 during one period of disk rotation. This happens as follows; upon receipt of a control pulse at the input 19 of the key 13, the latter briefly closes the output 17 of the integrator 10 with its input 18 and thereby resets the integrator output voltage (discharges the integrating capacitor, not shown in Fig.). The integrator is reset every period T.

The output signal of the integrator (with the integration time equal to one period T of disk rotation) will be t + t

Uhht ~ f (UcnrH + Uon) 'dt, t where ΐ is the current time;

Isign - voltage at the output of track tracking signal generation unit 1 Ucnm = Ubm + Uh4 ⁺ Up!

Uon is the voltage at the output of the reference voltage source 2;

and _In h is the high-frequency component due to oscillations of the reading beam near the center of the track during operation of the ATS tracking the track, optical defects of the disk, mechanical vibrations and noise:

and _N h is the low-frequency component due to radial beats of the disk, i.e. eccentricity;

Up - ultra-low-frequency component due to slow radial movements of the reading beam when reading information in normal mode.

Substituting its components in UcnrH, we have t + t

Uhht - f (U _B 4 + Uhm + Up + Uon) 'dt t

or t + t t + t

Uhht ~ f U _B n dt + f Uhm 'dt + tt (1) t + tt + t + f Updt + JU _on ' dt.

t t

Since the integrator time constant and the integration time significantly exceed the periods of the high-frequency range frequencies, the integrator 10 plays the role of a good smoothing filter for them; therefore, the signal at the integrator output due to this component will be equal to zero.

The component and _Nh due to the eccentricity of the disk) has a shape that quite accurately corresponds to a sinusoid (it is known from mathematical physics that if a circle rotates in its plane around an axis that does not coincide with its center, then the intersection point of this circle with a fixed radius passing through the center of rotation will move in time according to a sinusoidal law).

It is also known that the integral of a sinusoid for a time equal to its period is zero t + t t + t / sin ω t · dt = - cos ωΐ j = 0, tt _;

7Γ where ω = -γ— (see Bronstein I.N. Handbook of mathematics for engineers and students of technical colleges, M 1959, p. 333, 387).

Therefore, the second term in the expression (1) will also be equal to zero.

The Up component changes so slowly that during a single period of disk rotation it can be considered, to a first approximation, constant.

When integrating the voltage Up with a real electronic integrator, the time constant τ of which is much longer than the integration time (i.e., the rotation period of the disk T), the voltage at the integrator output will be t + t t + t _t f Up · dt = Upi I = U _P V

those. the output voltage of the integrator grows linearly in time and reaches its maximum value

Up Hu. (2) towards the end of the integration time.

Similarly, the result of integrating the constant reference voltage Uon will be

Uon y

The integration time T equal to the disk rotation period is set due to the fact that the output voltage of the integrator 10 is reset to zero by short pulses from the former through the delay element 9 through each period T.

The output voltage of the integrator 10 and _And nt is supplied to the comparator 3, which, if the voltage Umhh 0, sends a command through the circuit 12 to the driver stage 4, which gives a normalized pulse to the drive motor 5 of the optical head 6. The latter makes a small jump towards the edge of the disk , and the positioner lens (continuing to track the information track) moves the same distance relative to the head in the opposite direction.

As information is read from the disk, the positioner moves smoothly to the edge of the disk (over the period T by 1.6 μm). Accordingly, the ultra-low-frequency component Up increases.

At the end of each period T, a voltage proportional to the Up value appears at the output of the integrator 10.

In fact, this device allows you to receive information about the average over the period of displacement of the positioner from the neutral position at short intervals (equal to the period of rotation of the disk).

The duration of the period T is a variable value: it increases when the reading spot moves from the center of the disk to its edge (since the disk rotation speed slows down from about 8 to 3 r / s and, in addition, can vary by several percent depending on the particular player disk (since the linear speed of track deployment for different disks can vary from 1.2 to 1.4 m / s.) Therefore, in accordance with formula (2), the voltage at the output of the integrator 10 will also depend not only on the value of Up, but also from period value and T. In order to eliminate this dependency, the reference voltage inputted to the map.

. Indeed, if at the end of the period T the output voltage of the integrator is zero, i.e.

Up y - NEP y - 0, then the current value of Up is equal to the set value of the reference voltage, regardless of the magnitude of the period of rotation of the disk. Therefore, when setting up the device, it is necessary to set Uon equal in magnitude (but with opposite sign) to the voltage corresponding to the deviation of the lens (not shown in Fig.) From the equilibrium position, at which a pulse should be applied to the drive motor 5 of the optical head 6.

When the voltage at the output of the integrator 10 exceeds zero, the comparator sends a signal through the matching circuit 12 to the master stage 4 and, therefore, to the drive 5 of the optical head.

The delay element 9, for example a one-shot, is introduced into the circuit so that the reset of the integrator 10 is carried out immediately after the signal of the comparator 3 is supplied to the driving stage 4.

Claims (1)

Claim A device for controlling the movement of the optical head relative to the disk storage medium, comprising a track tracking signal generating unit, a reference voltage source, a comparator, and a driver stage whose output is connected to the optical movement drive 10