MXPA01011127A - Focus control device, recording medium and optical disk reproducing device - Google Patents

Abstract

A focusing control device for use in an optical disk playback apparatus, comprising:an object lens which condenses a light beam on an optical disk having a plurality of signal recording layers;focusing drive means for moving said object lens in a direction orthogonal to the recording layers of the optical disk;photodetection means for detecting light reflected from said optical disk;focus error signal generation means for generating a focus error signal which corresponds to defocusing of said object lens relative to a specified one of said recording layers of said optical disk, on the basis of a detection signal of said photodetection means;peak detection means for detecting peaks of the focus error signal;reference value calculation means for calculating reference values of said focus error signal in accordance with detection signals of said peak detection means;comparison signal generation means for comparing said focus error signal with its reference values, and generating comparison signals based on results of the comparisons;and control means for accepting a request for moving a focusing position of said object lens, and generating and outputting signals which control said focusing drive means, on the basis of the detection signals of said peak detection means and the comparison signals.

Description

APPARATUS FOR FOCUS CONTROL, RECORD MEDIA AND OPTICAL DISC PLAYER DEVICE TECHNICAL FIELD The present invention relates to a reproduction apparatus for a multi-layer recording optical disk. More particularly, it relates to the layer jumping control technology e where an object lens moves in its focus direction in order to to perform a servo focusing operation for any desired registration layer.

PREVIOUS TECHNIQUES In recent years, an optical disc called "DVD" has been put into practical use as a means of recording large storage capacity. The DVD has at most two recording layers per side, and the data can be recorded on both sides of it. The function of controlling the movement of an object lens in the focus direction thereof ("layer jump function") is required of a reproduction apparatus for said optical multi-layer recording disk so that, when the reproduction of a record layer (simply referred to as "layer" below) has been requested in a state where a servo focusing operation is proceeding for the other layer under reproduction, a servo focusing operation can be performed for the desired layer . A multi-layer recording optical disc reproducing apparatus in the prior art embodies the above function by processing as shown below. Figure 12 is a flow chart of a layer skipping process in the case where, during reproduction of the lower layer of an optical disk including the two recording layers of the lower layer (layer closest to the lens of object, and called "layer 0") and an upper layer (called "layer 1"), the reproduction of the upper layer has been requested. Figure 13 is a timing chart showing the relationship between a focus error signal, control signals, etc. on this occasion Referring to Figure 13, the comparator splice levels FcH and FcL are reference voltages with which the focus error signal is compared and whose values are adjusted at the embarkation of the reproduction apparatus in advance. The FcH signal assumes a Hi (high) output for a period of time during which the voltage of the focus error signal exceeds the comparator splice level FcH (the voltage goes to Hi), while assuming a Lo output ( low) during any other period of time. On the other hand, the FcL signal assumes the Hi output during a period of time in which the voltage of the casting error signal exceeds the comparator splice level FcL (the voltage goes to Lo), while assuming the output Lo during any other period of time. A coil portion is disposed around an object lens that condenses a laser beam in the recording layer of the optical disk, and are supported by a spring so that it can be raised and lowered. When a jolting voltage is applied to the coil, a force is exerted in the direction of bringing the object lens close to the optical disk. In contrast, when a brake voltage is applied, a force is exerted in the direction of bringing the object lens away from the optical disk. When the reproduction of the layer 1 is requested during the reproduction of layer 0, that is, in a state where a servo focusing operation is procedure for layer 0, the reproduction apparatus disconnects a servo approach (S401), after whereof the jitter voltage is applied in the direction in which the object lens ascends (ie, in which the object lens approaches the optical disk) (S402, time a in Figure 13). It then supervises a course from the elevation of the FcL impulse (time b in Figure 13) to the fall thereof (time c in Figure 13) (S403). When the impulse drop FcL is detected, the application of the jitter voltage (S404) ends. Then, begins to monitor the boost of the FcH pulse (time d in Figure 13) (S405). Upon detecting the pulse lift FcH (time d in Figure 13), apply the brake voltage in the direction in which the object lens descends (S406). Next, start monitoring the fall of the FcH pulse (S407). Upon detecting the fall of the pulse FcH (time e in Figure 13), it stops the application of the brake voltage (S408). Subsequently, it connects the servo approach (S409), in order to start the reproduction of layer 1. Incidentally, the control processing in a tracking direction and omits here.

EXPOSITION OF THE INVENTION In the process indicated above, the comparator splice levels FcH and FcL have a previously established constant value. Therefore, the layer skip function can not deal with the discrepancy in the error levels of individual optical discs or reproduction apparatuses, or changes in the characteristics of the reproduction apparatus attributed to environmental conditions such as temperature. In addition, since the comparator splice levels need to be confined within the peak levels of the focus error signal securely in any reproduction state, they can not be set to very large values. Therefore, in the case of the occurrence of a castling error phenomenon called "deviated light" where a small ridge other than the essential ridges of the casting error signal appears in the vicinity of the reference level of the same , the layer jump could end in failure due to the wrong recognition of a peak point, depending on the values of the comparator splice levels. An object of the invention is to provide a high stability layer jumping technique which can deal with discrepancy in the error levels of individual optical discs or reproduction apparatuses, and changes in characteristics of the reproduction apparatus attributed to environmental conditions such as temperature. In order to achieve the above object, a focus control device according to the invention is characterized in that it comprises an object lens that condenses a light beam into an optical disk constructed of a plurality of signal recording layers; a focusing drive element for moving the object lens in a direction orthogonal to the recording layers of the optical disk; a photodetection element for detecting light reflected from the optical disc; a focusing error signal generation element for generating a casting error signal corresponding to the out of focus of the object lens relative to any of the recording layers of the optical disc, based on a detection signal of the photodetection element; a peak detection element for detecting the crests of the focus error signal; a calculation element and reference value for calculating the reference values of the focus error signal in accordance with detection signals the peak detecting element; a comparison signal generation element for comparing the focus error signal with its reference values, and generating comparison signals based on the results of the comparisons; and an element e control to accept a request to move a focus position of the object lens, and generate and output signals to control the focus drive element, based on the detection signals of the detection element and Crest and comparison signals.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram showing the focus control mechanism of a multilayer recording optical disc reproduction system; Figure 2 is a sectional view for explaining the structure of a multi-layer optical recording disc. Figure 3 is a diagram to explain an example of the structure of an optical collection; Figure 4 is a sectional view for explaining the driving mechanism of a two-axis actuator in a focusing direction; Figure 5 is a waveform diagram of a focus error signal measured in a case where an object lens has been moved from a remote position of a two-layer recording optical disc to a position near this disc optical; Figure 6 is a flow chart for explaining the processing of the focus control mechanism; Figure 7 is a flow chart showing a peak level detection process; Figure 8 is a flow chart to explain a layer skip process; Figure 9 is a crop survey chart showing the relationship between a focus error signal, control signals, etc .; . Figure 10 is a timing graph showing the relationship between the focus error signal, the control signals, etc .; Figure 11 is schematic views for explaining the influence of gravitation as it depends on whether a reproduction apparatus is of the horizontal type or of the vertical type; Figure 12 is a flow chart of a layer skipping process in a prior art scheme; and Figure 13 is a timing chart showing the relationship between a focus error signal, control signals, etc. in the prior art scheme.

BEST MODE FOR CARRYING OUT THE INVENTION One aspect of the operation of the invention will be described with reference to the drawings. Figure 1 is a block diagram showing the focus control mechanism of a multilayer register optical disc reproduction system. With the multi-layer recording optical disc playback system, an optical disc 11 having a multi-layer recording structure, for example, DVD is driven to rotate at a predetermined speed by a spindle motor 12. A laser beam is projected from an optical collector 13 and condensed in the recording layer of the optical disk 11 by an object lens 13a. The reflected light from the recording layer is read by the optical collector 13. Part of the optical signal read is converted into an electrical signal, which is admitted to a focus error generation circuit 14. The focus error generation circuit 14 generates a focus error signal from the converted electrical signal. Here, the focusing error signal can be generated, for example, in such a way that the quad-photodetection elements are arranged in the light-receiving portion of the optical collector 13, and that the difference between the outputs of the upper-photodetection elements , lower, right and left is amplified in accordance with a method of astigmatism. In addition, the signal read by the optical collector 13 is converted into an electrical signal (RF signal), which is admitted to a reproduction circuit 50. The playback circuit 50 reproduces the audio data, video data, etc., on the basis of the digital signal recorded in the recording layer of the optical disc 11.

The focus error signal generated by the focus error generation circuit 14 is admitted to a peak detection circuit 15, a FcH comparator 17, a FcL comparator 18 and a switch 20. FcH comparator 17 output to an FcH signal in a case where the focus error signal has exceeded a FcH comparator splice level. The FcL comparator 18 outputs an FcL signal in a case where the focus error signal has exceeded a FcL comparator splice level. The FcH and FcL comparator splice levels are reference voltages that are established by a comparator splice level setting circuit 16 in advance of the reproduction of disk 11, and an adjustment method for it will be explained below. . The FcH signal and the FcL signal respectively outputs from the comparators 17 and 18 are both admitted to a layer jump control circuit 19. During a peak level detection process preceding the production of optical disk, the peak detection circuit 15 detects the peak point of the focus error signal and measures the peak voltage thereof, which is given to it. output to the comparator level setting circuit 16. During optical disc playback, the circuit 15 detects the peak point of the focus error signal and outputs a detection signal to the layer jump control circuit 19 The splice level adjustment circuit 16 of compared ! - adjusts the comparator splice levels for each optical disc playback operation, The comparator splice levels are set as the two levels on Hi (high) and Lo (low) sides in accordance with the signal peak voltage of focus error in the peak level detection process, and are respectively compared with the focus error signal in comparators 17 and 18 during optical disc reproduction. The layer skip control circuit 19 performs control of a layer skip process in the case where, in a state in which a servo focusing operation is proceeding for a certain record layer, the reproduction of another registration layer is being requested during the reproduction of the optical disk 11. More specifically, when the reproduction of the other recording layer has been requested, the layer skip control circuit 19 operates the switch 20 to disconnect a servo approach. Next, the circuit 19 outputs a signal to drive the object lens 13a, to an addition circuit 22, while monitoring the signals of the comparators 17, 18 and the signal of the peak detection circuit 15. When the layer skipping process has completed in due course, circuit 19 operates switch 10 to connect the servo approach. In addition, the circuit 19 has the function of measuring a period of time for which the signal is output, and the function of controlling the period of time during which the signal is output. A servo focus control circuit 21 is constituted by a shunt adjustment circuit, a gain adjustment circuit, a phase compensation circuit, an amplification circuit, etc., and executes a servo focusing process in which A control signal to be applied to a focus drive coil is generated so that the allowed focus error signal can assume its reference level. That is, the servo focus control circuit 21 executes a process in which the focused position of the laser beam is maintained following a signal recording surface against so-called "surface oscillations" etc. of the optical disk 11 during the rotation thereof. CONNECTION / DISCONNECTION of the input from the focus error signal to the servo focus control circuit 21 is controlled by turning the switch 20 on and off. The addition circuit 22 adds the objective lens drive signals 13a delivered from the circuit 21 of servo focus control and the layer jump control circuit 19, and outputs the resulting signal to a focus control drive circuit 23. The focus control drive circuit 23 generates a voltage to drive the object body 13a as it corresponds to the admitted control signal, and feeds the voltage to a two-axis actuator 24. Incidentally, the above processes of individual circuits can be very embodied by software. The two-axis actuator 24 drives the object lens 13a of the optical collector 13 to move in two directions; the focusing direction of the object lens 13a and the radial direction of the optical disk 11. In this embodiment, the optical multi-layer recording disk 11 is constructed as a two-layer structure having two recording layers as shown in Figure 2. In the present, the layer near the object lens 13a in the mode of reproduction will be denominated the "layer 0", and the remote layer of the same the "layer 1". In the figure, the recording layer indicated by a solid line is layer 0, while the recording layer indicated by a broken line is layer 1.

The outer dimensions of the optical multi-layer recording disk 11 are, for example, a diameter of 120 mm and a thickness of 1.2 mm which are the same as those of a CD-ROM. The DVD, however, has a structure in which two discs, each being 0.6 mm thick, are pasted together. Each side of the DVD has at most two layers of recording, and the data can be recorded on both sides of it. The storage capacities of the DVD are 4.7 Gbytes in the case of registration in a layer on one side, 8.5 Gbytes in the case of registration in the two layers on one side, 9.4 Gbytes in the case of registration on each of each of Both sides, and 17 Gbytes in the case of registration in the two layers of each of both sides, The track pitch of the DVD is 0.74 micrometers, and the wavelength of a laser that reads data used for the playback system is 650 nm Incidentally, as a matter of course that the layer skip control according to the invention is applicable, not only to the optical disk of the two-layer structure, but also to an optical disk having a layer structure of at least three layers. The data is read from the optical disk 11 by the optical collector 13. As shown in Figure 3 by way of example, the optical collector 13 is constituted by the object lens 13a, a collimating lens 13b, a polarization prism 13c, a semiconductor laser oscillator 13d, a cylindrical lens 13e and a 13 f photodetection element. A laser beam emitted from the semiconductor laser oscillator 13d propagates rectilinearly through the polarization prism 13c and passes through the collimating lens 13b. Next, the collimated laser beam is condensed in any recording layer of the optical disc 11 by the object lens 13a. The light reflected from the optical disc 11 retrograded through the object lens 13a, and passes through the lens 13b of collimation. Next, the collimated beam of light is bent orthogonally by the prism, 13c of polarization, and the bent beam of light falls on the photodetection element 13f through the cylindrical lens 13e. Figure 4 is a sectional view showing a mechanism in which the object lens 13a is driven in a focusing direction by the two-axis actuator 24. The object lens 13a is supported by the object lens support springs 24c through an object lens accessory 13g so that it is movable vertically and horizontally. A focusing coil 24a is disposed around the object lens 13a, and a magnet 24b is further disposed outside the focusing coil 24a. When the focusing coil 24a is supplied with a control signal, the object lens 13a receives a driving force in its focusing direction as indicated by a double-headed arrow, - Figure 5 is a waveform diagram of the focus error signal in the case where the object lens 13a has moved from a position remote from the optical disc 11 and recording two layers, to a position near this optical disc 11. Referring to the figure, a "layer 0" focus point indicated by an arrow is the focus position of the bottom layer (layer 0), and a "layer 1" focus point is the focus position of the layer. upper layer (layer 1). Here, the focus error levels of the "layer 0" focus point and "layer 1" focus point change depending on the optical characteristics, and do not always match. An upward direction and a downward direction will be set as a Hi (high) address and a Lo (low) address with respect to the 0 (zero) voltage of the focus error signal. When the object lens 13a begins to move from the remote position of the optical disk 11, the focus error signal forms a peak in the Hi direction once, and reaches the focus point of the layer 0 in the vicinity of the level of reference reached. Then, the focus error signal forms a ridge in the Lo direction, and passes through the reference level again and forms a ridge in the Hi direction. In addition, the focus error signal reaches the focus point of layer 1 in the vicinity of the subsequently reached reference level. When the object lens 13a moves to a position closer to the optical disk 11 still, the focus error signal forms a crest in the Lo direction again. The processing operation of the focus control mechanism constructed as explained above will be described with reference to the flow chart shown in Figure 6. First, the processing is initiated (S101) in a case such that the optical disk 11 is has charged, or where a power source has been connected in a charged state, then, the peak detection circuit 15 detects the peak levels (S102). In this way, the processing is executed each optical disc, whereby the process of layer jump is allowed to deal with the discrepancy in the characteristics of the optical discs, changes in the environmental conditions of the reproduction system, etc. Here, the peak level detection process (S102) will be described referring to the waveform diagram of Figure 5 again and to a flow chart shown in Figure 7. First, the object lens 13a fits a remote position of optical disk 11 (descending search, S201). Subsequently, the laser emission is connected (S202). In addition, the object lens 13a is gradually moved to a position near the optical disk 11 (upward search, S203), and the change of the focus error signal is monitored. On this occasion, the focus error signal illustrates ^ a waveform shown in Figure 5 as explained above. The crest points to be detected are the two points of the ridge point Lo and the ridge point Hi indicated by the arrows. The reason for this is that, in a case where a servo approach operation is procedure for either layer 0 and layer 1 and where the focus is to be moved to the other layer in this state, a scale in the that the object lens 13a moves is limited between the "layer 0" focus point and the "layer 1" focus point indicated in Figure 5. Consequently, the peak of the Hi side first detected is omitted in the detection of peak level, and the voltage of the focus error signal relative to the reference level thereof at the peak point Lo is first detected as the peak of the side Lo (S204) is adjusted as the peak level Lo ScL (S205). In addition, the voltage of the focus error signal relative to the reference level thereof at the crest point Hi detected in second place as the crest of the Hi side (S20S) is adjusted as a Hi ScH crest level (S207). ). Next, the object lens 13a is restored to its original position (S208), in order to finish the peak level detection process (S102). When peak levels ScH and ScL have been acquired by peak level detection (S102), comparator splice niel fit circuit 16 adjusts the FcY purchaser splice level and splice level of comparator FcL being the reference voltages of the focus error level, based on the values of the peak levels ScH and ScL by means of a method explained below (S103). More specifically, the comparator splice level FcH is adjusted to a value obtained by multiplying the peak level ScH by a predetermined coefficient, and the splice level of the comparator FcL to a value obtained by multiplying the peak level ScL by a predetermined coefficient ß. Here, the values of the coefficients a, ß are positive values less than 1, for example, 0.2 or 0.5, and specified values are adjusted as specific numerical values in accordance with the characteristics of the optical disc playback apparatus in advance. Incidentally, each of the coefficients a, ß can also be adjusted to values that differ between the case of moving layer 0 to layer 1 and in case of moving layer 1 to layer 0. Therefore, in this way , the comparator splice levels are adjusted every operation of inserting the disc, each connection operation of the power source and each operation of start of reproduction in a stopped state, the values of them can deal with the discrepancy in the levels of individual discs and changes in environmental conditions. Especially, even when a small peak deviation has appeared in the vicinity of the reference level of the deviated light component of an optical system, no influence is exerted by previously adjusting the values of the coefficients a, β in order to confine the deviation peak within the comparator splice levels. As a result, the stability of the layer jump becomes very good. When the comparator splice levels e have been adjusted, a reproduction instruction is provided by the reproduction system operator is accepted (S104). and a reproduction process (S105) is started. Next, the layer skipping process according to the invention will be described with reference to the drawings taking a case where the reproduction of layer 1 has been requested while a servo focusing operation is proceeding for layer 0, as an example of an operation in the reproduction process (S105). Figure 8 is a flow graph to explain the process on this occasion. In addition, Figures 9 and 10 are timing graphs in the case of the layer jump from layer 0 to layer 1. In each of Figures 9 and 10, the lower stage represents time. A time a corresponds to the initiation of the application of a jitter voltage, a time j the termination of the application of the jolting voltage, a time d the beginning of the application of a brake voltage, a time e the completion of the application of a brake voltage, and a time p_ the detection of a ridge Hi. Figure 9 illustrates a case where the time e_ of the brake voltage application termination is after the time p_ of the peak detection Hi, while Figure 10 illustrates a case where the time e of the application termination Brake voltage is before the r time of the peak detection i. When the reproduction of the layer 1 is requested during the reproduction of the layer 0, that is, in a state where a servo focusing operation is procedure for the layer 0, the layer jumping control circuit 19 changes to the switch 20 to disconnect a servo approach (S301). Subsequently, the layer skip control circuit 19 sends a signal to generate the jitter voltage in the direction in which the object lens 13a ascends (i.e., in which the object lens 13a approaches the optical disk 11). ), to the focus drive circuit 23 through the addition circuit 22 (S302, time a in Figure 9, time a in Figure 10), and start the measurement of a shake time period (S303) . Next, it begins to monitor the elevation of the FcL signal (S304) through the peak detection circuit 15. Upon detecting the boost of the pulse FcL (time b in Figure 9, time jb in Figure 10), the layer jump control circuit 19 terminates the application of the jitter voltage (S305), and ends the measurement of the shaking time (S306). Since the average shaking time period serves as the reference for a brake time period, it is retained by the layer jump control circuit 19. In this way, according to the invention, the application of the jolting voltage is terminated in accordance with the lift of the pulse FcL, so that the period of time of application of the jolting voltage can be shortened. This means that a period of time from the time of the termination of the application of the jitter voltage to the time of the initiation of application of the brake voltage can be adjusted for a prolonged period. Therefore, the two-axis actuator 24 is allowed to initiate braking when it has become stable, and the ability of the two-axis actuator 24 to converge is improved. Incidentally, the jitter voltage desirably must be higher. The reason for this is that, when the jitter voltage is higher, the application time period is still further shortened, so that the ability to converge is further improved. When the ability to converge is higher, the layer jump can be faster, and playback that is a greater number of times faster can be performed. Additionally, due to the superior ability to converge, it is allowed to release the differences of the characteristics attributed to a different effective gravitation direction involved between the horizontal type of the reproduction apparatus (in which the rotating surface of the disk is placed horizontally) and the vertical type of the same (in which the rotating surface of the disk is placed vertical). Figures 11 (a) and (b) are schematic views for explaining the presence or absence of gravitational influence in the case where the reproduction apparatus 50 is of the horizontal or vertical type. In the case where the reproduction apparatus 50 is installed horizontally as shown in Figure 11 (a), the gravitation acts on the object lens 13a in parallel with the focusing direction of this object lens, and so both, the apparatus 50 is influenced by gravitation. In contrast, in the case where the reproduction apparatus 50 is vertically installed as shown in Figure 11 (b), the gravitation acts on the object lens 13a perpendicularly to the focusing direction of this object lens, and by therefore, the apparatus 50 is not influenced by gravitation. When the convergence capability of the two-axis actuator 24 becomes higher, a period of time for which the horizontal type is influenced by gravitation can be shortened. Therefore, it is possible to release the differences in characteristics between the vertical type and the horizontal type attributed to the influence of gravitation. Subsequently, the layer jump control circuit 19 begins to monitor the elevation of the FcH signal (S307) through the peak detection circuit 15. Upon detecting the rise of the FcH (time d in Figure 10), the layer skip control circuit 19 sends a signal to generate the braking voltage in the direction in which the object lens 13a descends (i.e. , in which the object lens 13a moves away from the optical disk 11), to the focus driving circuit 23 through the addition circuit 22 (S308), and initiates the measurement of a braking time period (S309). The braking signal is kept sent until the braking time period is equal to a value obtained in such a way that the shaking time period measured before it is multiplied by a coefficient? (S311). Here, the coefficient? it is one for adjusting the time delay of the control circuit 19 in terms of the adjustment of the braking time period relative to the shaking time period, and is adjusted to the numerical value of, for example, 0.8 or 0.9.

Incidentally, the coefficient? it can also be adjusted to values that are different between the case of the jump from layer 0 to layer 1 and in the case of the jump from layer 1 to layer 0. When the braking time period has been equal to the value obtained multiplying the shaking time period by the coefficient? (time a.

Figure 9, time e in Figure 10), the layer jump control circuit 19 terminates the application of the braking voltage (S312). Incidentally, the braking time period can be adjusted well to a value obtained by subtracting the delay of circuit time 19 e control from the measured shaking time period, instead of the value obtained by multiplying the shaking time period by the coefficient? Since the braking time period corresponding to the shaking time period is adjusted in this manner, the convergence capacity of the two-axis actuator 24 can be made higher. Meanwhile, the peak detection circuit 15 is monitoring the peak Hi of the focus error signal (S310) The layer jump control circuit 19 judges whether the peak point Hi (time JD in Figure 9, time £ in Figure 10) has already detected or not at the time of the braking voltage application termination (time e in Figure 9, time e in Figure 10), Here, in a case where the point of Hi crest has been detected, the servo approach is connected (S314), and layer 1 playback is initiated. On the other hand, in a case where the peak point Hi has not yet been detected at the time of the brake voltage application termination, the detection of the peak point Hi is expected (S313), and the servo approach is connects (S314) so as to start the reproduction of layer 1 after the peak point Hi (time .p in Figure 9, time in Figure 10 J has been detected.) This processing is based on the fact that a Stable servo focusing operation is performed by connecting the servo approach after the Hi-point has been passed. More specifically, when the servo approach is connected immediately after the braking voltage application termination, an interval between the crest point Hi is left out of a focus traction scale, and therefore, the focus may not be attracted. In contrast, in accordance with the processing, the servo approach is connected after the peak point Hi without failure, so that the focus It can be attracted safely In a case where layer 0 playback has been requested during a servo focusing operation for layer 1, merely the application directions of the jitter voltage and the braking voltage and the upstream directions and descending of the focus error signal are reversed, and the basic processing contents can be executed substantially by the same algorithm as in the case where the layer 1 reproduction was requested during the servo focusing operation for the layer 0. After the layer jump processes as explained above have been repeated, the reproduction of the optical disk 11 is terminated (S106). As described hitherto, according to the invention, it is possible to perform a high stability layer jump dealing with the discrepancy in the error levels of individual discs or reproduction apparatuses, and changes in the characteristics of the reproduction apparatus attributed to environmental conditions such as temperature.

Claims (9)

1. - A focus control device for use in an optical disc reproducing apparatus, comprising: an object lens that condenses a light beam into an optical disk having a plurality of signal recording layers; a focusing drive element for moving the object lens in a direction orthogonal to the recording layers of the optical disk; a photodetection element for detecting light reflected from the optical disc; a focus error signal generating element for generating a focus error signal corresponding to the focusing output of the object lens relative to a specified one of the recording layers of the optical disk, based on a signal detection of the photodetection element; a peak detection element for detecting peaks of the focus error signal, a reference value calculation element for calculating reference values of the focus error signal in accordance with detection signals of the peak detection element. a comparison signal generation element for comparing the focus error signal with its reference values, and generating comparison signals based on the results of the comparisons; and a control element for accepting a request for moving a focus position of the object lens, and generating output signals to be controlled to the focusing drive element, based on the detection signals of the peak detecting element and the comparison signals.

2. A focus control device according to claim 1, wherein the signals to be controlled to the focusing drive element are a signal that moves the object lens, and a signal that brakes the object lens.

3. A focus control device according to claim 2, wherein: when the request to move the focus of the object lens is accepted, the signal to move the object lens receives an output; and when it is perceived from the comparison signal that the focus error signal has exceeded its reference value, the output of the signal to move the object lens is terminated.

4. A focus control device in accordance with the claim. 3, which also comprises. an element for measuring a first period of time for which the signal to move the object lens receives output, and an element for calculating a second period of time for which the signal for braking the object lens receives output, on the basis of of the measured time period; wherein, when it is perceived from the comparison signal that the focus error signal has exceeded its reference value, after the termination of the signal output to move the object lens, the signal to brake the object lens receives output; and after the second period of time has elapsed, the output of the signal to stop the object lens is terminated.

5. A focus control device according to claim 4, further comprising: a servo focusing element for controlling the focusing drive element on the basis of the focusing error signal, to thereby adjust the object lens so that the focus position of the object can match the specified registration layer of the optical disc; wherein, when the request to move the focus of the object lens is accepted, the servo focusing element is disconnected; in a case where the peak detection element has already detected the peak of the focus error signal at a time point of the termination of the signal output to brake the object lens, the servo focusing element is connect; and in a case where the peak detection element has not yet detected the peak of the focus error signal, the servo focusing element is switched on after the peak detecting element has detected the peak of the signal of focus error.

6. A focus control device according to any of claims 1 to 5, wherein. the reference value calculation element for calculating the reference values of the focus error signal calculates the reference values before the optical disc reproduction; and the reference values of the focus error signal are calculated on the basis of the higher error values of the focus error signal in both polarities, in each of the states from a state where the focus of the lens of object matches the lowermost record layer of the optical disk, to a state where it accepts with the highermost record layer.

7. A program that can be run by an entertainment apparatus comprising: an object lens that condenses a beam of light on an optical disk constructed of a plurality of signal recording layers; a focusing drive element for moving the object lens in a direction orthogonal to the recording layers of the optical disk; a photodetection element for detecting light reflected from the optical disc; and a focus error signal generating element for generating a focus error signal corresponds to the focusing output of the object lens relative to a specified one of the recording layers of the optical disk, based on a detection signal of the photodetection element; wherein the program causes the entertainment apparatus to execute: a peak detection process for detecting crests of the focus error signal; a process for calculating the reference value for calculating the reference values of the focus error signal in accordance with the detection signals of the peak detection process; a comparison signal generation process for comparing the focus error signal with its reference values, and generating comparison signals based on the results of the comparisons; and a process for accepting a request to move a focus position of the object lens, and generating and outputting signals to control the focus drive element, based on the detection signals of the peak detection element and the comparison signals.

8. A recording medium readable by entertainment apparatus in which a program according to claim 7 is stored.

9. An optical disc reproducing apparatus comprising a focus control device in accordance with any of the claims 1 to 6.