MXPA96006103A

MXPA96006103A - Apparatus and method for control of enfo

Info

Publication number: MXPA96006103A
Application number: MXPA/A/1996/006103A
Authority: MX
Inventors: Ceshkovsky Ludwig
Original assignee: Discovision Associates
Priority date: 1995-12-06
Filing date: 1996-12-04
Publication date: 1997-08-01

Abstract

The present invention relates to an apparatus for controlling a focal point of a convergent beam of light that is directed on a focal plane, a focal plane located within an optical medium having first and second information layers, characterized in that it comprises: an optical feedback which responds to light coming back from the focal point, the optical feedback has a first and second optical feedback outputs, a signal control generator to produce a first control signal and a second control signal, the control signal generator implemented for moving the focal plane from a first information layer to the second information layer, a first multiple coupling to the first optical feedback output and the first control signal, the first multiplier having a first multiplier output, a second multiplier coupling to the second optical feedback output and the second control signal, the second multiplier that has a second multiplier output, a circuit to combine the first multiplier output and the second multiplier output generates a focus of the error signal representative of the location of the focal point with respect to the focal plane, a servo error of focus responds to the signal of focus error, and an actuator drives response to the servo focus error to effect movement of the focal point with the foc plane

Description

APPARATUS AND METHOD FOR FOCUS CONTROL DESCRIPTION OF THE INVENTION This invention relates to the control of an energy beam. More particularly, this invention relates to the controlled movement of a focal point of a light beam to selected positions in a multi-layer optical information medium. Digital optical media such as optical discs and optical tapes are now commonly used for mass storage of information, for example audio and video signals encoded by compressed MPEG. The information storage capacity of the disks and tapes can be improved by stratifying a plurality of layers containing information on a substrate. To read an optical medium of multiple layers, a focal point of light is selectively placed on the layers, and this is diverted from one layer to another, according to the format in which the medium has been written. The deviation of the focal point is generally accompanied by arrangements that require mechanical movement of the optical parts in relation to the medium. This requires a large separation of layers to ensure differentiation of the individual layers REF: 23147 by an optomechanical link and is associated with servo circuits. Acquisition of focus is conventionally carried out by various servo arrangements that initially operate in an open circuit mode. The feedback loop of the servo approach includes a switch that is initially open, during which the servo-focusing time is driven by an oscillating waveform, such as a sawtooth waveform, which causes the objective lens to shift moving away from the optical medium, and a beam of light passing through the objective lens is in focus and out of focus in the middle. At the same point, when the beam is close to the desired focal position, the sawtooth shape is removed and the switch closed, thereby closing the feedback loop. The description of achi, U.S. Patent No. 5,379,282, and proposes the use of detectors that detect a maximum and a minimum of light returns from the optical medium, and a maximum and a minimum of a focus error signal. These maximum and minimum signals are processed by a servomechanism, which drives a focusing actuator. Subsequently, a servo-focusing operation is executed to fix the light focus to a desired level.

In Millar et al., U.S. Patent No. 4,607,157, it is proposed to intensively remove the point of light from an optical disk after the acquisition of focus has been obtained and while the servomechanism is operating in the closed circuit mode. The resulting variation in the back-reading signal is used by a synchronous detection circuit to extract the magnitude and polarity information of the focus deviation. This is supplied back to the servo-focusing signal to nullify the lack of focus effect, and to reset the focus setting. A conventional focus control circuit 10 is illustrated in FIG. 1, in which an astigmatic optical extractor 12 comprises a matrix of four photoelectric transducers 12a-12d arranged to detect a light beam returning from an optical information medium through of an objective lens (not shown). It will be understood that in the present the objective lens is a component of a known optomechanical link 28 between the focus control circuit 10 and the optical extractor 12. The signals of diagonally opposed paired transducers (par 12a, 12d and par 12b, 12c) are combined in lines 13a, 13b, respectively, and amplified respectively by operational amplifiers 14a, 14b. The paired signals on the lines 13a, 13b vary independently as the focal point of the objective lens travels over the information layer of an optical medium, and these signals are sensitive to the focus deviation of the objective lens from the information layer. The outputs of the operational amplifiers 14a, 14b activate a differential amplifier 16, which outputs a focus error signal on the line 32. The focus error signal on the line 32 is representative of the difference between the signals on the lines 13a, 13b. In closed circuit operation, the focus error signal on line 32 is coupled with conventional phase compensation and gain circuits, mentioned herein as servocircuits 18. Servocircuits are described, for example, in Ceshkovsky et al. , U.S. Patent No. 4,332,022. The focus error signal on line 32 is an input to the servo circuits and causes a modification in their behavior, according to the circuit design. The output of the servo switches 18 is added with the output of the focus acquisition control circuits 20 in the add-on circuit 22. The output of the addiver circuit 22 is amplified in an activating amplifier 24, and coupled to a focusing actuator, represented as an actuator coil 26. The optomechanical link 28 between the actuator coil 26 and the optical extractor 12 is indicated by a dashed line .

Initially, the switch 30 is opened by a control means (not shown) so that the focus error signal on the line 32 decouples from the servo switches 18, but remains coupled to the focus acquisition control circuits 20. means of the line 34. In this circumstance, the focus actuator coil 26 is driven by an oscillating waveform added over the add-on connection 22, and in the optomechanical link 28 it moves the objective lens (not shown) generally towards and away from it. the surface of the optical medium. The output of the optical extractor 20 varies as the focal point of the objective lens approaches an information layer of the optical medium. When the lens is approximately focused on the information layer, the switch 30 is closed, and the servo switches 18 start the closed circuit operation. When a light beam is perfectly focused on an information layer of an optical medium, the light intensity of the paired photodetector elements 12a, 12d, and 12b, 12c of the optical extractor 12 is the same. The signals on the lines 13a, 13b and the signals developed by the operational amplifiers 14a, 14b are also equal, and the output of the differential amplifier 16 is nominally zero. As the focal point of the objective lens deviates away from the information layer, the intensity of light measured by the pairs of photodetector elements varies, so that the signals on lines 13a and 13b become different, and the differential amplifier 16 generates a focus error signal on line 32 that has a voltage level either greater than zero, or less than zero, based on the direction in which the focal point of the objective lens is moved from the layer of information. A typical waveform graph of a focus error signal according to the circuit of Fig. 1 is shown as a waveform 50 in Fig. 3, where Fl and F2 indicate the points of two layers presenting information in a multi-layer optical medium. When the focal point of the objective lens moves away from the information layer of the optical medium, for example, on the left side of the focus error form 50, the focus error signal has a baseline value. As the focus point of the objective lens approaches the first information layer Fl, in a direction indicated by the arrow A, the differential amplifier 16 begins to develop a positive signal which is approximately sinusoidal, and the which rns to the baseline value when the focal point of the objective lens actually traverses the first information layer Fl at point 52. As long as the objective lens continues to travel beyond the first layer, the amplifier 16 difference and produces a signal which is less than the value of the baseline. When the objective lens is far enough away from the first information layer Fl, the focus error signal again rns to the baseline. The above sequence is repeated to the extent that the focal point of the objective lens transits to a second information layer F2, and a zero crossing is presented at point 54. With the approaches indicated above, it is necessary to rn to the mode of open circuit operation when it is desired to shift the focus from a first information layer to a second information layer, and to close the circuit again in order to fix the focus on the second layer. Otherwise, the servo circuit will initially impede movement to the second information layer and will eventually be overcome, after which the focus will move in an uncontrolled manner. It is a principal object of the present invention to provide an improved apparatus and method for focusing control in a multi-layer optical information medium that allows controlling the circuit to remain closed while the focus deviates from one layer to another. It is another object of the invention to provide accurate and reliable control of a power beam in an apparatus that reads or writes a multi-layer information medium in which the separation between layers is very small. These and other objects of the present invention are achieved with an apparatus for controlling a focal point of a focused beam of light which is directed to an optical multi-layered medium. The apparatus has an optical extractor which has a plurality of outputs and is sensitive to light returning from the medium. A control signal generator generates the first and second control signals. A first multiplier multiplies a first output of the optical extractor and the first control signal, and a second multiplier multiplies a second output of the optical extractor and the second control signal. The multipliers provide input to a difference amplifier which produces a focus error signal. A servomechanism responsive to the focus error signal controls an actuator exciter to carry out the movement of the focal point to and from the medium. Preferably, the first and second control signals comprise smooth continuous waveform deviations from one another at a predetermined phase angle, optimally, 90 degrees. Most preferably, the smooth continuous waveforms are substantially sinusoidal.

In one aspect of the invention, the control signal generator, the first multiplier, the second multiplier, the circuit and the focusing error servomechanism are constituted in a digital signal processor. The invention provides a method for controlling a beam of radiant energy that is directed to a medium having a plurality of information regions. The medium has a characteristic that varies according to a deviation of the information regions. A beam of radiant energy is directed over the medium and interacts with the medium. The energy that results from the interaction between the medium and the beam is determined, and the determined energy is representative of the characteristic. A first and second signals sensitive to the detected energy are generated, preferably in quadrature, and modified in a predetermined manner. A servomechanism is coupled to the first modified signal and to the second modified signal, where the servomechanism operates in closed circuit mode. The servomechanism is attached to a beam adjustment means, with which it cooperates to vary the beam optimization with respect to a first information region of the medium, for an optimization thereof with respect to a second information region of the medium. In one aspect of the invention, the first signal is generated independently of the second signal.

In another aspect of the invention, the first and second signals have continuous waveforms uniformly or regularly deviated from each other by a predetermined phase angle, preferably approximately 90 degrees. The uniform or regular continuous waveforms are preferably substantially sinusoidal. For a better understanding of these and other objects of the present invention, reference is made to the detailed description of the invention, by way of example, which will be read together with the following drawings, in which: Figure 1 is a partially schematic block diagram of a focus control circuit according to the prior art; Figure 2 is a partially schematic block diagram of a focus control circuit according to a preferred embodiment of the invention; Figure 3 is a waveform representing a focus error signal produced by a focus control circuit plotted with respect to the position of the focal point; Figures 4 and 5 show a plurality of waveforms that occur during the focusing deviation operation executed by the focus control circuit shown in Figure 2; Figure 6 is a partially schematic block diagram according to a first alternative embodiment of the invention; and Figure 7 is a partially schematic block diagram according to a second alternative embodiment of the invention. Now, returning to Figure 2, a focus control circuit according to a preferred embodiment of the invention is shown, in which parts identical to those of Figure 1 are given like reference numbers. The arrangement of the optical extractor 12 and the operational amplifiers 14a, 14b are the same as those previously described, except that now the outputs of the operational amplifiers 14a, 14b, are each coupled to the inverted input of the operational amplifiers 40a and 40b, respectively. The non-inverted inputs of the operational amplifiers 40a and 40b are connected to a voltage Vm. The voltage V ^ can be set as a reference voltage or it can be derived from a characteristic of the optical medium. The output signals on the lines 47a, 47b of the operational amplifiers 40a, 40b (which represent the focus error components of the output of the optical extractor 12) are connected, respectively, to the multiplying circuits 44a, 44b, which, preferably, they are analogous multipliers. The multiplying circuits 44a, 44b are also coupled, respectively, to the control signals on the lines 49a, 49b of a control signal generator 42. The multiplier circuits 44a, 44b activate another differential amplifier 46, which outputs a focus error signal on the line 48. The focus error signal on the line 48 represents the difference between the outputs on the lines 43a, 43b of the multiplying circuits 44a, 44b, and propagates towards the switch 30, towards the servocircuits 18. The switch 30, the servocircuits 18, focus acquisition control circuit 20, the adding circuit 22, the activating amplifier 24, the coil The actuator and the optomechanical link between the operation of the focus actuator and the operation of the optical extractor 12 are indicated by the discontinuous line 28 and are identical to the arrangement described with reference to FIG. 1. In operation, when the error signal of The focus on line 48 is not a baseline, it is interpreted considering that a deviation of focus is present. The servo circuit 18 responds to that circumstance by varying the current flow through the actuator coil 26 in a manner that carries out a movement of the objective lens so as to nullify the focus deviation. The response of the optical extractor 12 changes accordingly, and the focus error signal is reset to its baseline level. This, as is well known to those skilled in the art, is a fundamental aspect of the operation of a servomechanism control circuit. It has been found that the apparent position of the focal plane of the first information layer, evaluated by the servo circuits 18, can be continuously shifted towards the second information layer, and that the servocircuits 18 will accurately track the movement of a "ghost" focal plane. "from one layer of real information to another, while maintaining the closed circuit operation. Now, a focusing deviation operation will be described with reference to Figures 2, 3 and 4. According to the invention, when it is desired to shift the focus of the objective lens from a first information layer Fl of the optical medium to a second layer of information F2 in a closed circuit mode of servoactive operation, a phantom focal plane is generated by multiplying the two control signals activated on lines 49a, 49b with the output signals on lines 47a, 47b to produce two error components of modified approaches on lines 43a, 43b. The phantom focal plane is diverted to the second information layer F2 by independently varying the voltages of the two control signals on the lines 49a, 49b in a previously defined manner. The two focus error components modified on the lines 43a, 43b are compared with each other by a differential amplifier 46 to generate a focus error signal on the line 48 that is supplied to the servocircuits 18. The error signal on the line 48 has the effect of attempting to cause the servo switches 18 to move the objective lens to follow the phantom focal plane of deflection in a continuous manner. Therefore, this reaction causes the focal point of the objective lens to deviate from the first information layer Fl to the second information layer F2. When the focal point of the objective lens effectively separates from the first information layer Fl, the influence on the focus error signal on line 48 is removed by returning the control signals on lines 49a, 49b to a nominal value of +1. Subsequently, the servo switches 18 continue to focus on the second information layer F2. During focus deviation operation, the control signal generator 42 develops control signals that vary in time over lines 49a, 49b that vary in voltage levels from -1 to +1, which is explained with reference to Figure 4. The range from -1 to +1 volts is used for descriptive purposes only, but it should be considered that many real voltage ranges can be used. For purposes of this explanation, the assumption is established that the focus has been acquired on a first information layer, and that the magnitudes of the output signals on lines 47a and 47b are equal. The control signals on lines 49a and 49b are represented by waveforms 60a, 60b, respectively, and have initial values of +1. Accordingly, the output multiplier on the lines 43a, 43b are initially equal, and are also equal to the output signals on the lines 47a and 47b, respectively. The focus error signal on line 48 is initially a baseline with a value of zero. An ideal time plot for the focus error signal on line 48 is shown by waveform 62. The signals on lines 47a and 47b are represented by ideal waveforms 68a and 68b, respectively. The signals on lines 43a, 43b are represented by ideal waveforms 69a and 69b, respectively. 1 The focusing deviation operation begins at the time indicated by the reference number 64. When the control signal generator 42 receives a motion control signal on the line 29, and an address control signal on the line 31, which indicates that the focus must be diverted to the second information layer F2, the control signal on the line 49a starts a sinusoidal transition from a value of +1 to a value of -1 at the time point 64. When the signal control on line 49a has reached a zero volt potential at a subsequent time 66, the control signal on line 49b begins a sinusoidal transition in the same manner, so that waveform 60b delays or deforms the shape of 60th wave It will be apparent from inspection of the waveforms 60a, 60b, that the interval between the moments 64 and 74, the control signals on the lines 49a and 49b is never, simultaneously, at zero volts. The outputs of multiplier circuits 44a, 44b, differ during this interval, and the focus error signal on line 48 (waveform 62) begins to increase as a result of differential amplification by amplifier 46. In practice, the focus error signal on line 48 has high frequency components, which are not shown in waveform 62, and is also affected by the outputs on lines 13a, 13b of optical extraction link 12. Between time points 64 and 74 there is a net increase in waveform 62 from its baseline value. In practice, the outputs on the lines 13a, 13b depend on the characteristics of the particular optical medium that is read. The objective lens attempts to follow the apparent focal plane in response to the focus error signal on line 48 (waveform 62) and begins to lose focus with respect to the information layer Fl. As the reflectance of an optical medium differs between the information layer F2 and the regions that have no information in the medium, the astigmatic outputs amplified in the lines 47a, 47b (Figure 2) of the optical extractor link 12 diverge (waveforms 68a , 68b). The waveforms 69a, 69b, which respectively represent the products of the signals on the line 47a, 47b and the control signals on the lines 49a, 49b, also diverge. By treating the intervals defined by the time points 64, 74 as a 360 degree cycle, the angular deviation in phase, between the wave forms 60a, 60b is optimally 90 degrees, which coincides with the deviation phase of the signals on lines 13a, 13b. Although the invention has been implemented with a relatively wide range of phase deviations, if the angular phase deviation between the waveforms 60a, 60b is greatly reduced, the differential amplifier 46 will detect input values approaching zero. , and the system will become unstable. On the other hand, if the angular phase deviation is increased too much above a preferred value, the waveform 62 will acquire increasing sinusoidal characteristics, sometimes it will perform zero crossings, and the system will not operate again effectively. The phase deviations of the signals on the lines 49a, 49b (waveforms 60a, 60b) must be adjusted to match the phase deviation of the outputs of the optical extractor 12 for optimal operation. As explained above, during the focusing deviation operation, the servo circuits 18 receive an intensionally incorrect representation of the position of the information layer Fl. and they attempt to compensate by means of the actuator coil 26 so that the objective lens moves in a direction of the second information layer F2. After the control signals on the lines 49a, 49b have returned, both to the values of +1, the servos 18 continue in closed circuit operation to maintain a fixed focus on the second information layer F2. The focus error signal on line 48 has returned to its baseline value. The interval defined by times 64, 74 is selected according to the response of the servomechanism system, in the characteristics of the optomechanical link between the servocircuits 18 and the optical extractor 12. Sinusoidal control waveforms are preferred because they are symmetric, uniform or regular and continuous , and therefore avoid abrupt movements of the actuator. However, other waveforms can be used that produce a transition from a level of +1 to -1, for example, triangular waves. It is important that during the focusing deviation operation, the control signals on the lines 49a, 49b are never zero simultaneously, in order to avoid a condition in which the servocircuits 18 detect a value of zero, and become unstable. It is unnecessary to adjust the duration of the sinusoidal control signals on lines 49a, 49b to correspond to the travel time of the optomechanical link 28. In the case where the focal point is between the information layers, for example in the region 53 (Figure 3) when both control signals on the lines 49a, 49b return to the baseline, the servo switches 18 continue to move the objective lens until a higher voltage level of the focus error signal is detected on line 48, in region 55. The servo switches 18 will subsequently continue to focus the focal point of the objective lens on the information layer F2. To divert the focus from the first information layer Fl to a third information layer (not shown) which is placed in the opposite direction to the second information layer F2, it is not necessary that the waveform described by the control signal 49b is forward instead of delaying the waveform described by the control signal 49a. This is illustrated in Figure 5, in which the control signals on the lines 49a and 49b are represented by the waveform 70a, 70b, respectively and have initial values of +1. When the focusing deviation operation is started at the moment 64, the control signal 49a starts a sinusoidal transition from a value of +1 to a value of -1. In like manner, the control signal 49a starts a sinusoidal transition at the subsequent time 66, so that the waveform 70a delays the waveform 70b. The focus error signal on the line 48 now describes the waveform 72, and is folded down below its baseline value during the interval defined by the moments 64, 74. The response of the servocircuits 18 is to activate the drive coil 26 and therefore move the objective lens in a direction towards the third information layer.

It should be noted that through the focusing deviation operation, the position of the phantom focal plane corresponds to an error signal that is within the operating range of the closed-circuit focusing of the servocircuits 18. The above explanation is provided with reference to an astigmatic optical extractor 12 as a non-limiting example. The invention can be practiced with other types of optical extractors, so that the output can be separated or resolved into at least two components, for example, a well-known blade edge detector, or the concentric ring detector. described in Elliott, U.S. Patent No. 4,152,586. The control signal generator 42 is any conventional signal generator capable of producing two sinusoidal signals in phase or other signal outputs that vary in time, in a defined range of amplitudes, preferably from -1 to +1 volts. . The control signal generator 42 can be a digital signal processor or even an analogous device. It must be responsive to an address control signal on line 31 and a motion control signal on line 29 from another control means, for example, a microprocessor (not shown) which generates search commands in accordance with the requirements of an information reading application, and the format of the particular optical medium. A search command is initiated by providing the motion control signal on the line 29. The optical extractor link 28 then operates in an address specified by the address control signal on line 31. In another operating mode, when it is not desired to divert the focus from one information layer to another, the control signals on lines 49a, 49b are maintained at +1 volts. The outputs of the multiplying circuits 44a, 44b on the lines 43a, 43b are the same as the signals on the lines 47a, 47b, and the circuit operates in the same way as the circuit illustrated in Figure 1. As can be seen from In the above discussion, the invention provides an apparatus for controlling the focal point of a focused light beam that is directed to a multilayer optical medium. The apparatus has an optical extractor 12 responsive to light that returns from the medium and has a first and second outputs 13a, 13b and a control signal generator 42 to produce a first and second control signals 49a, 49b. A first multiplier 44a is coupled to the first output 13a of the optical extractor 12, and to the first control signal on the line 49a. A second multiplier 44b is coupled to the second output 13b of the optical extractor 12 and to the second control signal on the line 49b. A circuit is coupled to the output of the first multiplier 44a and the output of the second multiplier 44b, and a focus error signal is generated on the line 48. A focus error servomechanism 18 is responsive to the focus error signal and , an actuator actuator, presented by the actuator coil 26, is sensitive to the servo switches 18 to carry out a movement of the focal point toward and away from the medium. Preferably, the optical extractor 12 is an astigmatic optical extractor, but it can be a blade edge detector or a concentric ring detector. The first output 13a is optimally in a quadrature relationship with the second output 13b. Preferably, the first and second control signals on the lines 49a, 49b constitute deviations in the form of a continuous wave, uniform or regular with each other by a predetermined phase angle, and, optimally, are substantially sinusoidal waveforms separated by a phase angle of approximately 90 degrees. A first alternative embodiment of the invention will now be described with reference to Figure 6, in which the identical parts with those of the previous embodiments are indicated by the same reference numerals. As explained in the aboveIt is a feature of the invention that the output of the optical extraction link 12 includes a plurality of components, and that these components are modified in a predetermined manner. In Figure 6, the multipliers multiplying the output signals on the lines 47a, 47b of the operational amplifiers 40a, 40b and the control signals on the lines 49a, 49b have been replaced by variable resistance elements 77a, 77b. The control signals on the lines 49a, 49b now control the variable resistance elements' 77a, 77b to independently modify the output signals on the lines 47a, 47b according to a predetermined pattern, preferably waveforms 60a, 60b (Figure 4) and 70a, 70b (figure 5). A resistor 78 is placed across the amplifier 46, so that the signal on the line 43a is connected to an input of the amplifier 46 which represents the output of a voltage divider comprising a variable resistor 77a and a resistor 78. Similarly , a resistor 79 is connected to the other input of the amplifier 46 and is grounded, so that the signal on the line 43b represents the output of a voltage divider comprising a variable resistor 77b and a resistor 79. In other respects , this modality is identical to the previous modality. The invention provides a method for manufacturing an apparatus for controlling a beam of radiant energy that is directed to an optical medium, which has a plurality of focal planes and an optical characteristic that varies according to the deviation of the focal planes. A source is provided to emit a focused beam of radiant energy. The beam has a focal point in the middle and comes back from it. A sensor responsive to the return beam is provided, wherein the sensor has an output responsive to the focus deviation from a first focal plane of the medium. The output of the sensor is divided into a plurality of components, preferably in quadrature. A first control means for modifying a first component of the sensor output is provided, and a second control means for modifying a second component of the sensor output is provided. A servomechanism is coupled to the first control means and to the second control means, wherein the servomechanism operates in a closed circuit mode. An optomechanical link is attached to the servomechanism to vary the focal point. In operation, the first control means and the second control means are operative, and the focal point moves from a first focal plane of the medium to a second focal plane of the medium, and the servomechanism fixes the focus on the second focal plane. In figure 7 a second alternative embodiment of the invention is shown, in which the identical parts with those of the previous embodiments are indicated with the same reference numerals. In this embodiment, the control signal generator, the multipliers, the electronic circuits for producing a focus error signal, the focus acquisition circuits and the servo circuits are all realized as a digital signal processor 200. The digital signal processor 200 includes a signal control section 242, a focus acquisition section 220, and a servomechanism section 218. The operational amplifiers 14a, 14b are coupled to analog to digital converters 80a, 80b respectively, and the signals that leave the analog-to-digital converters are independently modified in the control signal section 242, by using a predetermined pattern as the previous mode. An error signal is supplied by the control signal section 242 to the servomechanism section 218. The output of the servomechanism section 218 is converted back to an analogous signal and suitably conditioned in a digital-to-analog conversion section 222 . The output of the digital signal processor 200 is amplified in the activation amplifier 24 and then handled as described in the first embodiment. The focus acquisition section cooperates with the section 218 of the sevomechanism that initially acquires approaches on an information layer of the optical medium that is read. The invention can also be implemented in applications where the sensor measures the optical characteristics in addition to the intensity of the beam, so that the sensor produces an output having two components, preferably in a quadrature relationship. For example, it can be used in arrays or arrangements in which the sensor detects diffraction patterns produced by an information layer of a multi-layer medium, or which uses interferometry to direct an interrogation beam. In such arrangements, more than one beam can be directed into the middle. In general, the invention provides a method for controlling a beam of radiant energy that is directed to a medium having a plurality of information regions, and the medium has a feature that varies according to the deviation of the information regions. A beam of radiant energy is directed to the medium and interacts with the medium. The energy that results from the interaction between the medium and the beam is detected, and the energy detected is representative of the characteristic. First and second signals sensitive to the detected energy are generated, preferably in quadrature, and modified in a predetermined manner. A servomechanism is coupled to the first modified signal and to the second modified signal, in which the servomechanism operates in closed circuit mode. The servomechanism is linked to a beam adjusting means, with which it cooperates to vary a beam optimization with respect to a first information region of the medium, towards the optimization thereof with respect to a second information region of the medium. The first signal can be generated independently of the second signal, and preferably has continuous and uniform waveform deviations or regular with each other by a predetermined phase angle, which is optimally about 90 degrees. The regular or uniform continuous waveforms are preferably substantially sinusoidal. The embodiments described herein use light beams as an example; however, the application of the invention is not limited to light. The invention can be carried out in applications using other radiant energies that interact with a multi-segment medium, in which the variant energies are required to optimally adjust and interact with different regions of the medium through the use of a circuit feedback servoactive. Such energies include, but are not limited to, radiation in the infrared, ultraviolet or microwave spectra.

For example, a chrominance variation can be measured in optical media of multiple colors in which the color varies with a deviation of the information layers. The invention can also be implemented in applications in which the light beam incident on the sensor is transmitted through means, instead of being scattered back or reflected. The radiation that reaches the sensor does not need to be the same radiation as the radiation that goes to the medium. For example, in a particular application, the energy received by the sensor may be a secondary emission of materials in the optical media, or in the information layer thereof which is excited by a primary beam and which possesses photochemical properties. Not only is it necessary for the first beam to interact with a medium to produce a signal that reaches the sensor, and for the sensor to produce an output that has more than one component, such as two quadrature outputs. Although this invention has been explained with reference to the structure described herein, it is not restricted to the details that are set forth, and this application is considered to encompass any modification and change that may be found within the scope of the following claims.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims

REGVINDICATIONS

1. A method for controlling a beam of radiant energy which is directed to impinge on a medium, which has a plurality of information regions and which has characteristics that vary according to the deviation of the information regions, the method is characterized in that it comprises the stages of: directing a beam of radiant energy to the medium; detect the energy that results from the interaction between the medium and the beam, where the energy detected is representative of the characteristic; generating first and second signals responsive to the detected energy; modifying the first signal in a first predetermined manner; modifying the second signal in a second predetermined manner; coupling a servomechanism to the first modified signal and to the second modified signal, wherein the servomechanism operates in a closed circuit mode; linking the servomechanism to a means of adjusting the beam; wherein the servomechanism cooperates with the means of adjusting the beam to vary the optimization of the beam with respect to the first region of information of the medium towards the optimization thereof with respect to a second region of information of the medium.

2. The method according to claim 1, characterized in that the first signal is in quadrature relation with respect to the second signal ..

3. The method according to any of claims 1 to 2, characterized in that the first signal is generated independently of the second signal.

4. The method according to any of claims 1 to 3, characterized in that the first and second signals have continuous waveform deviations in a uniform or regular manner, each other, by a predetermined phase angle.

5. An apparatus for controlling the focal point of a focused beam of light that is directed to a multilayer optical medium, comprising: an optical extractor responsive to light that returns from the medium and has a first and second outputs; a circuit for generating a focus error signal; a focus error servomechanism sensitive to the focus error signal; and a driving exciter responsive to the focusing error servomechanism to carry out the movement of the focal point to and from the medium; the apparatus is characterized in that the circuit for generating the focusing error signal comprises: a control signal generator for producing a first and second control signals; a first multiplier coupled to the first output of the optical extractor and to the first control signal; and a second multiplier coupled to the second output of the optical extractor and to the second control signal.

6. The apparatus according to claim 5, characterized in that the first output is in quadrature relation with respect to the second output.

7. The apparatus according to claim 5 or 6, characterized in that the first and second control signals have uniform or regular continuous waveforms offset from each other at a predetermined phase angle.