RU2035772C1 - Automatic radiation focusing device - Google Patents

Abstract

FIELD: automatic control. SUBSTANCE: movable slip member displaces in axial direction within fixed member under action of focusing drive accoirding to signals arriving from control unit. Interference pattern is formed across photodetectors of photodetector unit; photodetectors are grouped and connected in phase opposition. Control unit performs digital control of focusing drive. EFFECT: improved design. 12 dwg

Description

 The invention relates to automation and the accumulation of information by optical means, in particular to a technique for recording and reproducing information, and can be used in audio and video players and other means for providing optical recording and reproduction of information.

A device is known that contains an actuator, an auxiliary laser, the beam of which through a system of mirrors at an angle hits the micro lens and focuses on the metal surface of the disk blank film, then, reflected, returns through the lens to a photodetector with two paired sensitive elements. If the sensitive surface of the information carrier coincides with the focal plane of the micro-lens, then the light flux is directed by the lens precisely to the interface of the photosensitive elements. In this case, the photocurrents of the two LEDs are equal, and the reverse unit generates zero voltage. If the surface of the sensitive layer is shifted relative to the focal plane of the micro lens, the light flux will exit the micro lens at a certain angle, depending on the size and sign of the defocus. The radiation focusing point on the surface of the photodiodes is shifted relative to the interface. A voltage will appear at the output of the unit, the sign of which is uniquely associated with the direction of defocus. Connecting the actuating element of the movement of the micro-lens to the output of the unit allows you to close the automatic control circuit [1]
A micro lens moves in time with the beats of the workpiece, ensuring the combination of the photocanal plane of the micro lens with the surface of the photosensitive layer of the disk with an accuracy of no worse than 0.5 μm in the frequency band of the beats 0-100 Hz. A visual inspection microscope with a magnification of 600 ^x is used to aim at the initial frame and control the accuracy of focusing.

 In autofocus systems with an auxiliary laser, the beam of which is directed at an angle to the optical axis of the micro-lens, use different wavelengths of the working source and auxiliary to reduce crosstalk. This makes it necessary to use optical filters, which complicates the calculation and implementation of the optical system.

The closest in technical essence is a device for automatically focusing radiation on a medium in an information recording-reproduction system, comprising a generator, a focusing executive element, a switch and a series-connected digital-to-analog converter (DAC) and a low-pass filter, as well as a two-loop control unit, one circuit of which consists of a series-connected photodetector unit and a differential amplifier connected by an output to the signal input of the switch, the output to It is connected to the input of the focusing actuator, as well as series-connected summing resistive unit and matching amplifiers, through which the output of the switch is connected to the inputs of the focusing actuator, and series-connected pulse synchronization unit and optocoupler isolation unit, while the pulse synchronization unit consists of series-connected logic circuit OR and counter, the inputs of the synchronization block are the inputs of the logic circuit OR, and the output is the counter output, the switch you full in the form of a double multiplexer, with the synchronizing input of which the output of the optocoupler isolation unit is connected, and the output of the low-pass filter with another signal input, the other circuit of the control unit is made four-channel, each of the channels of which includes a carrier angular position sensor, two RS-flip-flops, a reversible counter of three states, a comparator and a digital synthesized pulse generator, the output of which is connected to the input of the comparator, the other input of which is connected to the output of the reversible counter, and the output is in the reset house of the first RS-trigger, the synchronizing inputs of the RS-triggers are connected to the output of the carrier angular position sensor, the output of the first RS-trigger is connected to the counting input of the reverse counter, the information inputs of which are connected to the outputs of another RS-trigger, the generator output is connected to the clock inputs of the reversing counters of all channels, the outputs of the reversible counters of all channels are connected to the DAC inputs, the outputs of the sensors of the angular position of the carrier of all channels are connected to the inputs of the logic circuit OR block synchronization pulses owls, and the output of the angular position sensor of each subsequent channel carrier is connected to the reset inputs of the RS-trigger another up-down counter and the three states of the previous channel [2]
The photodetector unit is an optical system containing a laser, a beam splitter, a micro lens, a limb, the reflection plane of which is placed in the focal plane of the micro lens, a slit aperture, and a photodetector.

 The system uses an auxiliary laser. Its beam is spatially separated from the beam of the technological laser, and an auxiliary projection system is used for autofocusing.

 The disadvantage of this system is the limited technological capabilities, since it seems difficult to implement spatial multi-layer recording with an automatic transition from one layer to another.

 The purpose of the invention is improving the accuracy of focusing and simplifying the design of the electronic part of the device.

 To achieve the goal in a device for automatically focusing radiation, containing a gas-lubricated bearing with movable and fixed sliding elements, a focusing sensor with a beam splitter, a lens and an information carrier with information tracks, and also a photodetector installed in series with the optical axis of the laser radiation source the ability to project onto it through a beam splitter the information tracks of the information carrier, the outputs of the photodetector unit are connected to the inputs a control lok, the output of which is connected to the focusing drive, the control unit consisting of two amplifiers, an analog-to-digital converter, a generator, a switch, a synchronization circuit, a resistive block, and a focus positioner, a mirror and an additional lens mounted between the beam splitter and the focus sensor are introduced photodetector unit, and in the control unit, the averaging circuit made in the form of an adder on an operational amplifier, the generator is made controllable, the photodetector unit, an additional lens, a beam splitter, a mirror and a lens are mounted inside the movable sliding element of the gas-lubricated bearing, the mirror is optically connected to the lens, as well as to the photodetector block through a beam splitter and an additional lens, the movable element is placed inside the laser radiation source that can be moved along the optical axis, the focusing drive is placed on a fixed element and magnetically connected with a movable bearing element on gas lubrication, photodetectors of the photodetector unit are combined in two groups, in each of which photodetectors are installed in parallel on the projection edges of the corresponding information tracks, the groups are placed with parallel displacement relative to each other and are connected in antiphase, the amplifiers of the control unit are installed in parallel and their inputs are connected to the inputs of the control unit, and the outputs to the inputs of the adder connected by the output to the input analog-to-digital Converter, the first input of the synchronization circuit and the input of the resistive block, the outputs of which are connected to the first group input of the synchronization circuit and, the synchronization input and the second group input of which are connected to the corresponding inputs of the analog-to-digital converter, the outputs of the synchronization circuit are connected to the inputs of the controlled generator, the output of which through the switch is connected to the output of the control unit, while the synchronization circuit is made of N RS triggers with combined R - inputs whose outputs are connected to the control inputs of N 2-by-1 multiplexers, connected by outputs to the corresponding outputs of the synchronization circuit, the signal buses of the multiplexers are connected to group inputs of the synchronization circuit, the combined R inputs of the RS flip-flops with the synchronization input, the S-inputs of the RS flip-flops with the second group inputs of the synchronization circuit, and the outputs of the focus position switch are connected to the group inputs of the analog-to-digital converter of the control unit.

 In FIG. 1 shows a device in section, General view; in FIG. 2 same, cross section; in FIG. 3 design of the nozzle of the outflow of gas lubricant in the body of the fixed element; in FIG. 4 is a block diagram of a control unit; in FIG. 5 structure of repeating blocks in a synchronization circuit; in FIG. 6 optical diagram of the device; in FIG. 7, 8 simplified kinetic constructions to prove changes in the optical path difference and split beams with axial displacement of the moving sliding element; in FIG. 9 is a fragment of a flowchart explaining its operation; in FIG. 10 a matrix of photodetectors in the focus of a micro lens on the surface of the sensitive layer, forming an interferogram; in FIG. 11 diagrams of photoconversion signals; in FIG. 11A signal from the first row of sensing elements; in FIG. 11B signal from the second row; in FIG. 11C signal at the output of the adder; in FIG. 12 structure of the averaging circuit of the photoconversion signal.

 The device comprises (Fig. 1) projection system lenses 1 and 2, fixed 3 and movable 4 gas lubricated sliding elements interacting with the possibility of axial movement by an actuator 5 (focusing drive), a focus position sensor F of the beam working component 7, a beam splitter surface 8, reflector 9, information carrier 10, photodetector unit 11 and control unit 12.

 The bypass channels 13 for supplying gas lubricant to the nozzles 14 (Fig. 2, 3) are mounted in the fixed element 3, and the end spherical surface 15 (Fig. 1) of the fixed element with the center of the sphere at the focal point F interacts with the base 16 by means of adjusting screws 17.

 The split beam components are indicated (Fig. 1, 6): 18 beam incident at an angle β to the normal to the surface of the information carrier 10 and providing a varying optical path difference of the split rays during end beats on Δ L of the surface of the information carrier 10; 19 a beam reflected from the surface of the information medium 10, the reflector 9 and the transmitted beam splitter 8 in the orthogonal plane to the beam 7; 20 beam of a constant optical path obtained by dividing beam 7 on a light carrier 8; 20 'beam with changes in optical travel.

The energy values of the rays 6, 7, 18-21 and the reflected components are indicated (Fig. 6):
W ₂ 'working beam 6;
W incoming beam 7;
W ₂ ″ a normally reflected component from the surface of the information medium 10;
W ₃ 'reflected component from the beam splitter 8;
W ₄ 'reflected component from the reflector 9;
W ₄ '' reflected component with offset Δ l on the surface of the information carrier;
W ₅ ″ the reflected component from the reflector 9 in the orthogonal plane;
W ₅ ″ component passed the beam splitter 8;
W ₁ 'component with a constant optical path l ₃ reflected from the beam splitter 8.

The control unit 12 includes a generator 21 (Fig. 4) of a controlled pulse frequency, a photodetector 11, the photodetectors of which are grouped into groups 22. The photodetectors in each group are shifted by the π phase of the light wave of the radiation source, and each group of parallel photodetectors is connected to amplifiers 23 in antiphase, analog-to-digital Converter (ADC) 24, the synchronization circuit 25 of the generator 21 connected to the switch 26 of the actuator 5 (focus drive), the focus position switch 27, the adder 28. Synchronization circuit 25 connected by the first input to the output of the adder 28, combined with the input of the ADC 24, connected by the output to the second (and bus) R-input of the synchronization circuit 25, the first group (S ₁ .S _i ) -input of this circuit is connected to the outputs of the block 29 of 3I elements ( coincidences) (Fig. 9), the second group input of the circuit 25 is connected to the outputs of the block 30 of resistors of a discretely changing nominal value.

ADC 24 (Fig. 4) includes a block 31 of threshold elements 31 _{(1 ... n)} , blocks 32, 33 of D-flip-flops, a block of 34 inverters, a logical element n AND-OR 35, and a block 29 of elements 3I (matches) .

 The threshold elements of block 31 are made with discrete response thresholds and are connected channel by channel to the information inputs of the first block 32 of D-flip-flops, as well as to the inputs of block 34 of inverters, which are connected to the information inputs of the second block 33 of D-flip-flops.

Blocks 32, 33 and inverter block 34 are connected channel-by-channel through the corresponding triggers of block 33 to coincidence elements in the AND-OR logic element n 35, adjacent threshold elements of block 31 are connected to two coincidence inputs of each element 3 AND in block 29 (Fig. 9), and the third input of each element 3I is the information input of the ADC 24 (Fig. 4, 9), which are connected to the inputs of the setter 27 of the focus position. The synchronization circuit 25 includes structures of RS-flip-flops 36 _{(1 ... i)} (Figs. 4, 5, 9) connected by R-inputs, and the outputs of the triggers are connected to the control inputs of the multiplexers 37 _{(1 ... i)} , the outputs of the latter are the outputs of block 25, and their first inputs are combined at all multiplexers and are the first input of block 25, and the second are group inputs of block 25, which is connected to the group outputs of block 30 of resistors (Fig. 4).

The focus position switch 27 includes a buffer register 38 connected to the control S _i inputs of the 1-by-1 multiplexer 39. Beam 7 (W) of a monochromatic source (Figs. 1, 6) is split on a beam splitter 8 into components W ₁ 'and a working beam 6 (W ₂ ') in orthogonal planes. The reflected component W ₂ ″ from the plane of the information carrier 10 having end beats with displacements Δ h along the optical axis of the lens 1 is reflected from the beam splitter 8 in the orthogonal plane and is reflected from the reflector 9 (W ₄ ′) in the form of the component W ₃ ′ with the direction falling at an angle β to the normal to the plane of the information medium 10. Having passed the lens 1 and reflected from the plane of the medium 10 with an offset Δ l from the optical axis of the lens (due to the inclination at an angle β), the component W ₄ '' is reflected from the reflector 9 (W ₅ '' ) in the orthogonal plane and as a component W ₅ '''passes the beam splitter 8, connecting through the lens 2 with the component W ₁ ' in its focal plane, creates an interferogram in accordance with the optical difference of the rays along the shoulders (l ₃ + l ₂ ) and h.

 Changes in the optical difference in the path of the rays due to a change in one of the arms cause a shift in the bands of the interferogram, which is recorded by the photodetector unit 11. Of the constructions in FIG. 7 and 8, we give evidence that changes in the optical difference in the path of the rays when the movable element is displaced along the optical axis of the lens 1 by Δ h do occur.

Changing the shoulder l ₁ (Fig. 6) by Δ l when moving the movable element 4 by Δ h gives:
Δ l Δ h (1)
We denote the beam path W ₄ '(Fig. 6, 7) at an angle β with the C-segment, and the double stroke (taking into account the beam W ₄ '') 2 C.

Having examined the increment ratio in FIG. 8:
Δ h Δ C ˙cosβ (2) or by substituting the coefficients:
К cos β h К ˙Δ С, and taking into account (2) Δ h 2К ˙Δ С
Given (1) Δ l 2k кΔ C.

From (3) Δ С Δ l / 2К (3)
Let us conditionally accept: Δ l unit increment:
Δ l 1, then Δ С 1 / 2к (4)
From (4) it can be seen that, at a unit increment Δ h 1, the change in the course of one of the split rays
Δ l 1, (5) and the change in the course of another split beam
Δ C ≠ 1 (comparable in (4)) Therefore, the optical difference in the path of the rays during the movements of the movable element 4 (Fig. 1) takes place.

 These changes cause a shift in the interferogram and are analyzed in block 12 (Fig. 4), and the resulting discrepancies are processed by the actuator 5. During shifts in the tracking mode of changes Δ h of the surface of the carrier 10, the position of the invariance of the optical path difference of the rays is restored by a digital code, and as a result focus F can monitor not only the surface of the information medium 10, but also be at a certain depth from this surface with a reduction in the constancy of depth in dynamics. This allows for multilayer recording with surface translucency and to significantly increase the recording density by the number of layers. Positioning accuracy is determined by the capabilities of the regulatory system.

 In a static state, self-centering of the movable element 4 is carried out on air lubrication. The consumption of air lubrication is relatively small and is ensured by the design of the nozzles (Fig. 3) with a discharge hole with a diameter of about 0.06 mm.

 The movable element 4 (Fig. 1) is suspended with the possibility of axial movements by electromagnetic forces of interaction with the actuator 5 (focusing drive), and the fixed element 3 is fixed on the base 16 on the surface 15 with adjusting screws.

The photodetectors of the photodetector unit 11 are grouped with an offset of the light source of the radiation source (Fig. 4) by the π phase (Fig. 4) into groups 22 (Fig. 10), which are parallelized in groups and combined through two channels through amplifiers 23 to the inputs of the adder 28 made on an operational amplifier. When interacting with interferogram bands, such a scheme gives an increase in the steepness of the output signal of the adder when averaging over the leading and trailing edges of the pulses. Let the i-bus be excited at the focus positioner 27 (Fig. 4) by supplying a code to the information S _i- inputs of the multiplexer 39 "1 by n". With plus mismatch, the signal W _i at the output of the adder 28 increases due to the displacement of the bands of the interferogram. As W _i increases, the threshold elements (31 ₁ .31 _n ) sequentially trigger.

At the moment of triggering of the threshold element, for example, 31 _n-1 , preparation is made for the triggering of the D-trigger 32 _n , which occurs when the threshold element 31 _{n is} triggered by a positive differential across the C input. A logical “0” is formed at the output of the inverter 34 _n (when forming a logical “1” at its input), and this prepares the D-trigger 33 _n for operation, which will occur when there is a positive difference at the C-input of the D-trigger 33 _n , that is when the threshold element 31 _n returns to the initial state "0".

Before this happens, the presence of a logical "1" at the outputs of the threshold elements 3 _1n-1 and 31 _n (shaded in Fig. 4) and a given excitation of the logical "1" information bus a _{i of the} setpoint 27 will trigger element 3I in block 29 coincidence elements, which causes the S-response of the trigger 36i in the synchronization circuit 25 (Fig. 4, 5). The resulting trigger state through the multiplexer 37i and 2-by-1 commutes the bus with the corresponding resistor 30i, and the output signal of the synchronization circuit acts on the generator 21 of the controlled pulse frequency so that the pulse repetition rate decreases depending on the value of the resistor 30i connected to its input. As a result of the shift of the strip, the signal W _i at the output of the adder decreases and this leads to the return of the threshold element 31n to the initial “0” state.

This transition (1 _ → 0) causes a signal drop (0 _ → 1) at the output of the inverter 34 _n , which ensures the triggering of the D-trigger 33 _n , since the logic “1” is at its D-input. As a result, the coincidence is provided at the inputs of the coincidence element of the AND-OR logic element n and this element is triggered, forming a short pulse and this pulse carries out an R-reset of all D-flip-flops of the ADC circuit 24. In addition, the trigger 36i in the synchronization block 25 is returned to the original a state that causes a direct transmission of a larger amplitude signal W _i to its output directly on the adjacent input bus of the multiplexer 37i. This increases the frequency of the oscillator 21 and causes the band offset to be opposite to the previous one. Then the process is repeated, and the interaction force of the actuator 5 is fixed with an error associated with the discrete thresholds of the threshold elements and the accepted values of the resistors in block 30. The intensity of operation of the focusing actuator 5 depends on the values of the code signal recorded in the buffer register 38 of the positioner 27 focus, where F _{i is the} position recording code signal.

 In a dynamic state, the surface of the information medium 10 is monitored. The design of the projection systems, the adopted optical design, and the structure of the control unit make it possible to change the focus position using a digital code signal over a wide range. In addition, this makes it possible to eliminate the auxiliary laser and simplify the design by using, instead of the auxiliary laser, a split beam entering the system. A number of new qualities of the device appear.

Claims (1)

 DEVICE FOR AUTOMATIC FOCUSING OF RADIATION, comprising a gas-lubricated bearing with movable and fixed sliding elements, a focusing sensor with a beam splitter, a lens and an information carrier with information tracks, as well as a photodetector installed with the possibility of projection onto it, sequentially mounted on the optical axis of the laser radiation source through the beam splitter of the information tracks of the information carrier, the outputs of the photodetector unit are connected to the inputs of the control unit, for which it is connected to the focusing drive, the control unit consisting of two amplifiers, an analog-to-digital converter, a generator, a switch, a synchronization circuit, a resistive unit and a focus position adjuster, characterized in that, in order to increase the focusing accuracy and simplify the design of the electronic part of the device , a mirror and an additional lens mounted between the beam splitter and the photodetector block are introduced into the focusing sensor, and the averaging circuit made in the form of an adder for operation is introduced into the control unit This amplifier, the generator is controllable, the photodetector unit, an additional lens, a beam splitter, a mirror and a lens are mounted inside the movable sliding element of the gas-lubricated bearing, the mirror is optically connected to the lens and also with the photodetector block through a beam splitter and an additional lens, the movable element is placed inside the fixed with the ability to move along the optical axis of the laser radiation source, the focusing drive is placed on a fixed element and magnetically connected to the movable element gas lubricated bearing volume, photodetectors of the photodetector unit are combined in two groups, in each of which photodetectors are mounted parallel to the projection edges of the respective information tracks, the groups are placed with parallel displacement one from the other and are connected in antiphase, the control unit amplifiers are installed in parallel and their inputs are connected to the inputs of the control unit, and the outputs to the inputs of the adder, connected by the output to the input of the analog-to-digital converter, the first input of the synchronization circuit and input the house of the resistive block, the outputs of which are connected to the first group input of the synchronization circuit, the synchronization input and the second group input of which are connected to the corresponding inputs of the analog-to-digital converter, the outputs of the synchronization circuit are connected to the inputs of the controlled generator, the output of which through the switch is connected to the output of the control unit, when This synchronization circuit is made of N RS-flip-flops with combined R-inputs, the outputs of which are connected to the control inputs of N 2-on-1 multiplexers, connected outputs to the corresponding outputs of the synchronization circuit, the signal buses of the multiplexers are connected to the first and first group inputs of the synchronization circuit, the combined R inputs of RS triggers with the synchronization input, the S inputs of RS triggers with the second group inputs of the synchronization circuit, and the outputs of the focus position switch are connected with group inputs of the analog-to-digital converter of the control unit.

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