Track access device and tracking control device

Abstract: A data recording/reproducing device has a pickup for recording/reproducing information on disk which has tracks formed on recording area and ROM area. A track access device for moving the pickup from a starting track at which the pickup is presently located to a target track includes moving arrangement for moving pickup in a direction crossing tracks, a tracking error signal generator for generating an analog signal representing the crossing of the tracks by the pickup, and position detector for detecting the position of the pickup in either one of the recording and ROM areas. Also, for processing the tracking error signal, an amplifier, an offset adder and hysteresis comparator are provided each of which operate differently between when the pickup is located in the recording area and when it is located in the ROM area.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data recording/reproducing device and, more particularly, to a track access device for accessing a desired track on a recording medium, such as disc, having a large number of tracks, and also to a tracking controlling device. 2. Description of the Prior Art An optical recording and reproducing device is known which utilizes a recording medium with a number of tracks formed thereon. The optical recording and reproducing device is arranged to condense light beams generated from a light source with a condensing lens and irradiate the same onto an information recording medium having tracks so as to record and reproduce signals. The information recording medium, such as a disk, is made by forming a film of material capable of optically recording and reproducing on the surface of a substrate having concentric circular tracks of uneven structure by the vapor deposition method, etc. As the light source, for example, a semiconductor laser diode is used. The reproduction of signals is performed by setting the light beam at a relatively weak predetermined light intensity and by reading out the intensity of the reflected light from the disk. The recording of signals is conducted by modulating the amount of light beam into an intensity thereof in accordance with each signal to be recorded. In such an optical recording and reproducing device, a focusing control is provided for controlling the condensing of light beams onto the recording material film approximately in a predetermined condensed state at all times. Furthermore, a tracking control is provided so that light beams are located on a predetermined track at all times. In the optical recording and reproducing device, in order to allow the light beam to access a track on the disk at random, a track access control is effected. The track access control is effected by making the tracking control non-operative, moving the light beam radially on the disk towards the target track, and again actuating the tracking control when the light beam has reached the target track. The preceding technology regarding the track access is disclosed, for example, in US-A-4,106,058 or 4,332,022. One of the important factors in the track access control is the velocity of the light beam when it crosses the tracks, that is, the tracking pull-in velocity. The control band of the tracking control is limited, and normally in the range of several KHz. Therefore, when the tracking pull-in velocity is too fast, the tracking control into the target track fails. On the contrary, when the tracking pull-in velocity is too slow, it takes time to access the target track. Therefore, the velocity control for controlling the velocity of the light beam is effected when moving the light beam radially on the disk in the track accessing process. The object of the velocity control is to control accurately the track pull-in velocity so as to achieve stable pull in of the tracking control into the target track. The track access is effected by moving the light beam radially in the disk so that the pull-in velocity of the light beam is set to a predetermined reference velocity determined correspondingly to the current position of the light beam along the radial direction of the disk. The light beam moving velocity necessary to effect the velocity control is detected by the period of the track crossing signal arising when the light beam crosses tracks. For the track access operation, the current position of the light beam is obtained by counting the number of track crossing signals from the starting track from which the track access operation starts. In Fig. 2, the tracking error signal and the track crossing signal taking place when the light beam crosses a track in the radial direction of the disk are shown. Particularly, in Fig. 2, diagram a shows the state where the light beam crosses tracks on the disk and waveform b shows the tracking error signal. On the disk, pregrooves of uneven structure having optical depth of approximately λ/8 (λ is a wavelength of the light beam) are formed at a predetermined pitch. A band between adjacent pregrooves is a track where information is recorded. A disk of such a structure is called an on-land disk. In an on-land disk, the tracking error signal can be taken out by a push-pull method as shown in Fig. 2, diagrams a and b. Since the push-pull method is described in detail, for example, in JP-A-59-9085 or in FR-7529707, 1975, the explanation thereof is omitted. In Fig. 2, waveform c is a digital signal obtained by digitalizing the tracking error signal with the use of a hysteresis circuit, and waveform d is the edge detection signal obtained by detecting the leading edge of the tracking error signal. Each pulse in the edge detection signal occurs when the light beam crosses the center of each track, and therefore, it represents the track crossing signal. Therefore, the edge detection signal shown in Fig. 2 waveform d is hereinafter referred to as a track crossing signal. Therefore, the count obtained by counting the track crossing signals from the starting of the track access represent the current position of the light beam. Such a position detection of the track accessing according to this method is referred to as the groove count method. Also, since tracks are arranged approximately at the same pitch P in the radial direction of the disk, the light beam velocity V is obtained by V = P/T, in which T is a period of one cycle of the track crossing signal. The velocity detection according to this method is referred to the period measurement type detection method. In Fig. 2 waveform e, pulses having a period t are shown which represent leading and trailing edges of the pulse shown in waveform c. Thus, the velocity of the light beam can be given V = P/2t. There are two methods for writing information onto the disk: one is to change the amount of light beam in accordance with the information to be recorded; and the other is to form pits during the manufacture of the disk along the track, as realized in compact disks. The latter method has an advantage that many copies can be made at a low cost by the mastering replication technology used in the compact disk, and is suitable for disks storing softwares such as encyclopedias, dictionaries, atlases, operation systems. In Fig. 3 a disk is shown which has an outer recording area RD for recording data by modulating the amount of light beam in accordance with the information, and an inner ROM area RM in which information is recorded in advance by the formation of number of pits. Also, in Fig. 3, a fragmentary enlarged view is depicted, particularly showing the boundary portion between the recording area RD and the ROM area RM. As apparent from Fig. 3, the tracks in the recording area RD have plain surface, and the tracks in the recording area RM have uneven surface. In Fig. 4, signals are shown which are obtained during the light beam crossing the tracks in the radial direction of the disk in the recording area RD and also in the ROM area RM. Specifically, waveform a shows the tracking error signal, and waveform b shows the binary signal obtained by digitalizing the tracking error signal using a hysteresis circuit. Waveform c shows the track crossing signal obtained by detecting the leading edges of the binary signal, and waveform d shows pulses obtained by detecting the leading and trailing edges of the binary signal. In Fig. 4, the abscissa represents time and narrow pulses are shown by arrows. When the period S 2 of the sinusoidal noise signal imposed on the tracking error signal in ROM area RM is compared with the period S 1 of the tracking error signal in the recording area RD, a relationship S 1 >> S 2 is obtained. The short period S2 of the noise signal in the ROM area is caused by the deterioration of S/N ratio in the tracking error signal which is erroneously modulated by the presence of pits. The amplitude of the tracking error signal in the ROM area is decreased because of the presence of the pits, and the offset of amount V 2 is produced because of the non-uniformity of the pit shape. Accordingly, at time regions K 1 and K 2 , pulsating noise signal with an extremely shortened period is generated during the procedure when the track error signal is changed to the binary signal. Furthermore in the time region K 3 , since the amplitude of the signal is extremely reduced, the hysteresis circuit fails to detect the low amplitude tracking error signal, and therefore, no pulse will be present in the binary signal in the region K3. Thus, the pulse spacing period is lengthened. Since the velocity of the light beam is detected from the period of the track crossing signal, an erroneous detection of the light beam velocity takes place. As a result, an abnormal velocity variation takes place and the track pull in of the tracking control may fail. Furthermore, the position of the light beam is detected erroneously, and the track detection may be ended at a position other than the target track. As a result, it becomes necessary to again conduct the track access in order to correctly reach the target track, resulting in a defect that the track access time becomes longer. In order to further shorten the time required for the track access, it is necessary to move the light beam at a high velocity. In Fig. 5, the tracking error signal and the track crossing signal are shown obtained by the prior art track access device when the light beam is moved at a high velocity so that the period S 1 of the tracking error signal becomes nearly equal to the period S 2 of the signal recorded in ROM area. In Fig. 5, waveform a shows the tracking error signal at such a condition, waveform b shows the binary signal obtained by digitalizing the tracking error signal using a hysteresis circuit, and waveform c shows the track crossing signal obtained by detecting the rising edges of the binary signal. Furthermore, waveform d shows the signal obtained by detecting the rising and falling edges of the signal of waveform b. The period S 2 of the signal recorded in the ROM area and the period S 1 of the tracking error signal become nearly equal to each other. EP-A-232 134 defining the closest prior art from which the invention proceeds discloses a device for reading/writing an optical disc having ROM areas comprising pits and RAM areas without pits which device comprises means for moving optical pick-up means in a direction crossing the tracks, means for generating a tracking error signal, means for generating a track crossing signal in a search mode when the tracking servo loop is opened, position detecting means for determining by counting based on the track crossing signal and a starting track number the current position of the optical pick-up means, and means for determining whether the pickup means is located in either one of the RAM or ROM areas and for controlling the gain in the focus and tracking servo in dependence thereon. From EP-A-242 215, there is known a similar device wherein the tracking servo amplifier and the carriage servo which is also active in the search mode are controlled. In the prior art, the tracking error signal is more disturbed when crossing a ROM area with pits than when crossing a RAM area. So, the tracking error signal may not be properly formed in the ROM area. Also, since there are occurrence of offset and the decrease of amplitude of the tracking error signal are observed greatly in the ROM area as compared with the recording area, the offset in the tracking control and the decrease in loop gain take place. Therefore, in the final stage of the track access when the light beam reaches the target track and actuates the tracking control, the pull in of the tracking control into the target track has often failed. SUMMARY OF THE INVENTION An essential object of the present invention is to provide a track access device which can access to the target track stably at a high velocity even in a disk having a ROM area. In order to accomplish the above-mentioned object, according to the present invention, there is provided a track access device in a data recording/reproducing device having a pickup means for recording/reproducing information in tracks formed on a recording medium which includes a first area having tracks formed by a plane surface and a second area having tracks formed by an uneven surface, for moving said pickup means from a starting track at which the pickup means is presently located to a target track, comprising means for moving said pickup means in a direction crossing said tracks, means for generating an analog signal representing the crossing of said tracks by said pickup means, and position detecting means for detecting the position of said pickup means in either one of said first and second areas, characterized by amplifier means for amplifying said analog signal at a first amplification ratio, when said position detecting means detects that said pickup means is in said first area, and at a second amplification ratio being greater than said first amplification ratio, when said pickup means is detected as being in said second area, and binary circuit means having a hysteresis comparator for changing said analog signal to a digital signal with a first hysteresis amount, when said position detecting means detects that said pickup means is in said first area, and with a second hysteresis amount being greater than said first hysteresis amount, when said pickup means is detected as being in said second area. Further advantageous embodiments are defined in the sub-claims. By the above-mentioned arrangement, since the amplification ratio of the tracking error signal in the ROM area can be increased, the amplitude of the tracking error signal becomes approximately equal to that in the recording area. Therefore, the pulse formation failure in the output signal of the binary circuit due to the effect of pits in the ROM area can be prevented. Furthermore, since the loop gain of the tracking control system in the ROM area can be made approximately equal to that in the recording area, it is possible to perform stably the pull-in operation into the tracking control. Furthermore, since the hysteresis amount of the binary circuit can be increased in the ROM area, the occurrence of pulse noise signal in the output of the binary circuit due to the presence of pits in ROM area can be prevented. Moreover, in a preferred embodiment of the invention, since the offset taking place in the tracking error signal can be canceled by switching the offset adder circuit to add offset amount to the tracking error signal in ROM area, the pulse formation failure in the output signal of the binary circuit due to the effect of pits in the ROM area can be prevented. Similarly, the pull in to the tracking control can be made stably. Moreover, in a further preferred embodiment of the invention, since in the ROM area, the reference velocity can be reduced and the moving velocity of the light beam can be reduced, the misforming of the tracking error signal due to the effect of pits arising from a too fast velocity of the moving light beam can be prevented. By the above-mentioned arrangement, even in a disk having a recording area and a ROM area, an abnormal velocity change of the moving light beam by an erroneous velocity detection of the moving light beam due to the pits in ROM area, and the track access time increase due to erroneous position detection of the light beam can be prevented. Also, the failure of pull in of the tracking control in the target track can be prevented so that the track access of the desired track can be made rapidly and stably. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing a preferred embodiment of the track access device according to the present invention; Fig. 2 is a graph showing the tracking error signal and the track crossing signal when the light beams crosses tracks; Fig. 3 is a diagrammatic view showing the constitution of a disk having a recording area and a ROM area; Fig. 4 is a graph showing the tracking error signal and the track crossing signal obtained by the prior art circuit when the light beam moves to cross tracks in the recording area and the ROM area; Fig. 5 is a graph showing the tracking error signal and the track crossing signal obtained by the prior art circuit when the light beam moves to cross tracks in the recording area and the ROM area at a high velocity; Fig. 6 is graph showing the relationship between the count value of the counter and the reference velocity; and Fig. 7 is a graph showing the tracking error signal and the track crossing signal obtained by the circuit of Fig. 1 when the light beam moves to cross tracks in the recording area and the ROM area. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1, a block diagram of a track access device according to an preferred embodiment of the present invention is shown and is equipped in a data recording/reproducing device. A disk 6 having a recording area RD and ROM area RM, such as the one described above in connection with shown in Fig. 3, is mounted on a disk holder (not shown) which is rotated by a motor 5. A pickup arrangement for reading/writing information on the disk is formed by a light source arrangement which irradiating light beam on the disk. The light source arrangement includes a carrier 3, on which there are mounted a condensing lens 1 and a reflection mirror 2. The carrier 3 is driven approximately in the radial direction of a disk 6 by a voice coil motor 4 driven by a drive circuit 17. A light source such as a semiconductor laser 7 generates a laser which passes through a collimator lens 8 for collimating the light beam. The light beam having passed through the collimator lens 8 passes through a prism beam splitter 9 and through a ¼λ plate 10 (λ is the wavelength of the laser beam) and irradiated onto the reflection mirror 2 mounted on the carrier 3. The light beam reflected by the reflection mirror 2 is condensed by the condensing lens 1 and is irradiated onto the disk 6. The light beam reflected by the disk 6 returns back through the condensing lens 1 and reflected by the reflection mirror 2. The light beam reflected by the reflection mirror 2 passes through the ¼ λ plate 10 and reflected by the prism beam splitter 9 and impinges on a light receiving surface formed by a divided photo detector 11 having two photosensitive segments. A line dividing the photo detector 11 extends in alignment with the extending direction of the track on the light receiving surface. Both outputs from the divided photo detector 11 are applied to a differential amplifier 12 and also to an adder 40 so as to calculate the difference and the sum. The output of the differential amplifier 12 is applied to a numerator input terminal of an AGC circuit 41, and the output of the adder 40 is applied to a denominator input of AGC circuit 41. The AGC circuit 41 is arranged to output a quotient obtained by dividing an input signal from the numerator input terminal by an input signal from the denominator input terminal. As apparent to those skilled in the art, an output signal of the AGC circuit 41 is a tracking error signal, such as shown in Fig. 7 waveform a. The purpose for performing the dividing operation in the AGC circuit 41 is to prevent the amplitude variation of the tracking error signal due to the variation in the light emitting power of the light source 7. The tracking error signal is inputted to the voice motor coil 4 through an offset adding circuit 50, a gain switch circuit 42, a phase compensation circuit 14, a switch 15, an adder 16 and a drive circuit 17 to constitute a tracking control. Offset adding circuit 50 switches, in accordance with the offset switch signal from a microcomputer 26, between a non-adding state in which the tracking error signal from AGC 41 is directly passed to gain switch circuit 42, and an adding state in which the tracking error signal from AGC 41 is added with -V 2 to counterbalance the undesirable offset amount in the tracking error signal produced during the tracking control in the ROM area RM. Gain switch circuit 42 switches between a low amplification state in which the tracking error signal is amplified by a standard or low amplification ratio and a high amplification state in which the tracking error signal is amplified by a high amplification ratio, in accordance with the gain switch signal from the microcomputer 26. Phase compensation circuit 14 is provided to control the stability of the tracking control, and switch 15 is provided to switch between the operation and non-operation of the tracking control. The tracking error signal produced from gain switch circuit 42 is also applied to an edge detection circuit 49 through a binary circuit 43. Binary circuit 43 produces a binary signal, such as shown in Fig. 7 waveform d, based on the output signal of the gain switch circuit 42. Binary circuit 43 includes a hysteresis comparator 46 having an operation amplifier 45 and a switch 45, a level conversion circuit 47 and an invertor 48. The signal produced from gain switch circuit 42 is in binary formed by the use of hysteresis comparator 46. The level of the binary signal is converted to a preferable level for being processed in the logic circuit by the level conversion circuit 47, and the level converted signal is inverted in polarity by invertor 48. Hysteresis comparator 46 is so arranged that the hysteresis amount can be changed in two levels by the on and off of the switch 45 controlled by microcomputer 26. When switch 45 is on, the hysteresis amount is decreased, and when it is off, the hysteresis amount is increased. The output of the binary circuit 43 is applied to edge detection circuit 49 which detects the leading edge of the binary signal and supplies the track crossing signal, such as shown in Fig. 7, waveform e, to a timer 20 and also to a counter 25. Timer 20 measures the period of the track crossing signal from edge detection circuit 49 and produces the measured time DT in a binary form. The signal representing the measured time DT is applied to a velocity calculation circuit 21 which calculates the velocity DV of the track crossing light beam by the following equation: DV = P/DT wherein P is a track pitch. The velocity DV of the track crossing light beam is sampled every time the light beam crosses a track. Therefore, the velocity calculation circuit 21 is arranged to hold the sampled velocity DV at least till the next sampling. The velocity DV produced from velocity calculation circuit 21 is converted into an analog signal in a D/A converter 22 and is in turn applied to one input of a differential amplifier 23. The output signal of the differential amplifier 23 is applied to the voice coil motor 4 through a switch 24, an adder 16 and the drive circuit 17 for the velocity control. Switch 24 is provided to switch between the operation and non-operation of the velocity control. The track crossing signal from edge detection circuit 49 is also applied to a down-counter 25 which counts down each time the beam crosses a track. When the track access operation is requested, microcomputer 26 presets the down-counter 25 with a number representing the number of tacks between the present track at which the beam is impinging and a target track. The counted value of counter 25 is applied to a reference velocity generator 27 having a memory such as ROM for storing a table or a graph such as shown in Fig. 6 for producing an appropriate track crossing reference velocity RV relatively to the distance to the target track. After having been advance to a position within a predetermined distance from the target track, the track crossing reference velocity RV becomes small, as the distance to the target track becomes short. As will be described in detail later, the reference velocity generator 27 is capable of generating two different reference velocities RV 1 and RV 2 which are for the recording area RD and rom area RM, respectively. The reference velocity RV from reference velocity generator 27 is converted to an analog value by a D/A convertor 28, and is applied to another input of differential amplifier 23 so as to control the drive circuit 17 to drive the carrier 3 at a velocity equal to the reference velocity RV. The counted-down value of counter 25 is also applied to access detection circuits 29 and 30 which are formed for example by digital comparators. Access detection circuit 29 compares the counted-down value from counter 25 with a predetermined reference value, such as zero, and produces a high level signal to microcomputer 26 if the counted-down value is greater than zero indicating that the light beam is still located away from the target track, and a low level signal if the counted value is equal to zero indicating that the light beam has accessed to the target track. Similarly, access detection circuit 30 compares the counted-down value from counter 25 with a set reference value representing the number of tacks between the target track and a boundary track which is located at the end of ROM area RM and is adjacent to the recording area RD. The reference value is set by the microcomputer 26. Access detection circuit 30 produces a high level signal to microcomputer 26 if the counted-down value is greater than the set reference value indicating that the light beam is still located away from the boundary track, and a low level signal if the counted value is equal to the set reference value indicating that the light beam has accessed to the boundary track. The output of the velocity calculation circuit 21 is also applied to the microcomputer 26 so that microcomputer 26 can calculate the current velocity of the track crossing light beam. The control signals for the switches 15 and 24 are produced from the microcomputer 26 so that the operations thereof can be controlled by the microcomputer 26. Next, the operation of the track access device of Fig. 1 is explained. For the simplicity of the explanation, it is assumed that the light beam is moved from the recording area to the ROM area for the track access operation. Before the track access operation, switch 15 is on and switch 24 is off so that the tracking control is being carried out. Thus, the light beam follows along a track in the recording area. Furthermore, at this time, the offset switch signal applied to offset adding circuit 50 from microcomputer 26 is a low level signal. Thus, the offset adding circuit 50 adds zero offset amount to the tracking error signal. Accordingly, the offset adding circuit 50 adds no offset, and therefore, the tracking error signal obtained from the recording area is as shown in Fig. 7, waveform b, producing no offset. Moreover, at this time, the gain switch signal applied to the gain switch circuit 42 from the microcomputer 26 is a low level signal. Thus, the gain switch circuit 42 is set to have a lower amplification ratio (standard amplification ratio). Furthermore, at this time, the reference velocity signal applied to the reference velocity generator 27 from the microcomputer 26 is set at a high level RV 1 . Also, the control signal applied to switch 45 in the binary circuit 43 from the microcomputer 26 is set at low level to turn switch 45 on. As a result, the hysteresis amount of the hysteresis converter 46 is set at a smaller level. In order to start the track access operation, the address of the target track and the address of the boundary track are inputted to microcomputer 26. Although not shown in Fig. 1, microcomputer 26 is coupled with a track address reader which reads the address of the track at which the light beam is presently located. Therefore, the microcomputer 26 is further inputted with the address of a starting track from which the track access operation starts. With the use of these information, the microcomputer 26 presets the track difference between the track access starting track and the target track into counter 25. Furthermore, microcomputer 26 inputs the difference in address between the target track and the boundary track into the access detection circuit 30 as a reference value. Then, by the instruction signal from microcomputer 26, switch 15 turns off and switch 24 turns on to move the light beam toward the target track thereby starting the track access operation. During the track access operation, counter 25 counts down by one each time the track crossing signal produced from the edge detection circuit 49 is inputted. Therefore, the counted value of counter 25 during the track access represents the distance between the current position of the light beam and the target track. The reference velocity generator 27 storing a table or graph of Fig. 6 receives the counted value from counter 25 and produces a reference velocity RV 1 corresponding to the counted value. Therefore, during the track access operation, the reference velocity corresponding to the current position of the light beam is applied to D/A converter 28. Thus, the track access operation is carried out quickly and smoothly, such that reference velocity becomes small as the distance to the target track becomes short. Furthermore, as described above, the reference velocity generator 27 can produce one of the two different reference velocities RV 1 and RV 2 in accordance with the instructions obtained from microcomputer 26. The first reference velocity RV 1 is for the recording area RD and is produced when the instruction signal from the microcomputer 26 is of high level, and the second reference velocity RV 2 is for the ROM area and is produced when the instruction signal from microcomputer 26 is of low level. During the light beam moving in the recording area RD and when the counted value of counter 25 is still larger than a predetermined value, the reference velocity RV 1 is set at a constant velocity V maxh which is at a limit not to receive an adverse effect due to the restriction on the dynamic range of the velocity control. Furthermore, during the light beam moving in the ROM area RM and when the counted value of counter 25 is larger than a predetermined value, the reference velocity RV 2 is set at a constant reference velocity V maxl which is at a limit not to receive an adverse effect due to the deterioration of the tracking error signal by pits. The output signal of the reference velocity generator 27 is converted to an analog form by D/A converter 28 and is applied to the differential amplifier 23 to provide a reference velocity signal for the velocity control. As a result, by the velocity control, the light beam moves at a velocity approximately equal to the reference velocity. Therefore, as the light beam moves towards the target track, the counted value of counter 25 decreases, and the moving velocity of the light beam decreases accordingly as the light beam approaches the target track. During the track access, the counted value of the counter 25 is compared in the access detection circuits 29 and 30 with respective reference values. The access detection circuit 30 produces a low level signal to microcomputer 26 when the counted value of the counter 25 become equal to the value set by the microcomputer 26 representing a distance between the starting track and the boundary track, and during other times a high level signal. Thus, when the light beam has passed the recording area RD and enters the ROM area RM, the output of the access detection circuit 30 produces a low level. When the output of the access detection circuit 30 produces a low level signal, microcomputer 26 immediately switches the offset switch signal applied to offset adding circuit 50 to a high level signal, the gain switch signal applied to gain switch circuit 42 to a high level signal, the control signal to switch 45 to a high level signal, and the instruction signal to reference velocity generator 27 to a low level signal. Accordingly, when the offset switch signal becomes high, the offset adding circuit 50 starts to add the offset amount -V 2 to tracking error signal. As a result, the offset generated by the entering of the light beam into ROM area is counterbalanced. When the gain switch signal becomes high, gain switch circuit 42 is switched to the high amplification ratio for amplifying the tracking error signal in greater degree than the amplification of the tracking error signal effected during the light beam moving in the recording area. The ratio of the high amplification ratio to the low amplification ratio is so set as to become equal to the reciprocal of the ratio of the tracking error signal amplitude obtained in the recording area to that obtained in the ROM area in order to generally compensate the signal amplitude reduction in the ROM area. Therefore, by the offset adding circuit 50 and gain switch circuit 42, the offset and amplitude of the tracking error signal inputted to the binary circuit 43 during the track access and the track controlling in the ROM area become approximately equal to those observed in the recording area. Thus, it is possible to prevent binary circuit 43 from failing to produce an output signal in response to each crossing of the track due to the effect of pits in ROM area. Furthermore, when the control signal from the microcomputer 26 becomes high, switch 45 is turned off. As a result, the hysteresis amount of the hysteresis comparator 48 becomes larger and the occurrence of the pulse noise signal generated by the existence of pits in ROM area can be prevented. The reference velocity generator 27 outputs a reference velocity RV 2 with reduced maximum value for ROM area as shown by the dotted line in Fig. 6 in accordance with the instruction signal from the microcomputer 26. As a result, the light beam moves in ROM area at a velocity lower than in the recording area. Therefore, the misformation of a pulse in the tracking error signal due to the effect of pits caused by a too high moving velocity of the light beam can be prevented. Then, when the light beam reaches the target track in ROM area, counter 25 has counted down to zero and therefore, access detection circuit 29 produces a low level signal to microcomputer 26. Thereupon, microcomputer 26 immediately turns off the switch 24 and turns on the switch so as to restart the tracking control. At this time, since the offset adding circuit 50 and the gain switch circuit 42 are still maintained in adding state and high amplification state, respectively, the offset and loop gain of the tracking control system are made approximately equal to those in the recording area. Therefore, the failure in the proper tracking control caused by the occurrence of offset and decrease of loop gain of the tracking control system does not take place, and the smooth tracking control pull in is made and the track access is ended. By the above-mentioned arrangement, even in a disk having a recording area and a ROM area, an abnormal velocity variation of the light beam by the erroneous velocity detection due to the pits in ROM area can be prevented. Furthermore, the increase in the access time by the erroneous detection of the light beam position due to the pits in ROM area can be also prevented. Moreover, the failure in the pull-in of the tracking control into the target track due to the offset and amplitude variation of the tracking error signal in ROM area can be prevented. As a result, even in a disk having both recording area and ROM area, the track access to a target track can be effected stably and rapidly. In the above description, the track access is explained as effected from the recording area to ROM area, but the track access in the opposite direction, i.e., from ROM area to the recording area, can also be carried out stably and rapidly with the arrangement according to the present invention as explained below. Before the track access operation from the ROM area to the recording area, the offset switch signal from the microcomputer 26 to the offset adding circuit 50 is of a high level, and thus, the offset adding circuit 50 adds an offset of -V 2 . Furthermore, the gain switch signal to the gain switch circuit 41 is of a high level and thus, the gain switch circuit 41 is switched to the high amplification state. Moreover, the instruction signal from the microcomputer 26 to the reference velocity generator 27 is set at a low level and thus, the reference velocity generator 27 outputs a reference velocity RV 2 for ROM area as shown by the dotted line in Fig. 6. The control signal from microcomputer 26 to switch 45 in the binary circuit 43 is set at a high level and thus, switch 45 is off. As a result, a large hysteresis amount is set in the hysteresis comparator 46. Also, microcomputer 26 input the difference in address between the present track and the target track in the access detection circuit 29 and between the target track and the boundary track in the access detection circuit 30. After the start of the track access operation and when the light beam has passed the ROM area and reached the recording area, the output of the access detection circuit 30 becomes low so that microcomputer 26 immediately produces a low level offset switch signal to offset adding circuit 50, a low level gain switch signal to gain switch circuit 42, a low level control signal to switch 45, and a high level instruction signal to reference velocity generator 27. As a result, offset adding circuit 50 sets zero offset, since there is no offset being observed in the tracking error signal. Furthermore, gain switch circuit 42 is set in the low amplification state. Therefore, the offset and amplitude of the signal applied to the binary circuit 43 in the recording area become approximately equal to those observed in ROM area. Also, switch 45 is turned on and thus, the small hysteresis amount is set in the hysteresis comparator 46. Furthermore, since the reference velocity generator 27 produces the reference velocity RV 1 having an increased maximum value shown by the solid line in Fig. 6, time required for the track access can be shortened. Then, when the light beam reaches the target track in the recording area, the access detection circuit 29 produces a low level signal. Thereupon, microcomputer 26 turns off switch 24 and turns on switch 15 to terminate the track access operation and restart the tracking control. Since the offset adding circuit 50 and the gain switch circuit 42 are, as described above, in the states to match with the offset and amplitude of the tracking error signal in the recording area, the offset and loop gain of the tracking control system are approximately equal to those in ROM area. Accordingly, the failure in the pull-in to the tracking control arising from the occurrence of offset and decrease in gain of the tracking control system does not take place, and the transition to the tracking control can be effected stably. Although the above description is directed to a case using a disk having one recording area and one ROM area, it is possible to use the track access device of the present invention with the use of a disk having a plurality of recording areas and a plurality of ROM areas by adding one or more access detection circuits similar to the access detection circuit 30 which can set from microcomputer 26 a reference value representing the number of tracks between the target track and the boundary track, and yet obtaining a similar effect. Furthermore, the above description is directed to a case using an on-land disk wherein a band area enclosed by adjacent pregrooves is a track where information recording is effected. However, a similar effect can be obtained on an in-groove disk wherein pits are formed by the existence or non-existence of pregrooves and information recording is effected on pregrooves. Furthermore, in the above described embodiment, the edge detection circuit 49 is arranged to detect the light beam crossing at the mid point of a track, such as shown in Fig. 2 waveform d. However, it is clear that a similar effect can be obtained even when it is arranged to detect the light beam crossing the middle point of a track and the middle point between tracks, such as shown in Fig. 2 waveform e. In this case, the velocity calculation circuit 21 calculates the velocity DV of the light beam from the measurement value of timer 20 by the following equation: DV = P/(DT*2), where P is a distance between tracks, and DT is a measurement value of timer 20. Furthermore, before the track access operation, two times the track difference between the starting track and the target track is preset at the counter 25 by the microcomputer 26. Furthermore, on the access detection circuit 30, two times the track difference between the target track and the boundary track is set before the track access operation.

Claims: A track access device in a data recording/reproducing device having a pickup means (1-3) for recording/reproducing information in tracks formed on a recording medium which includes a first area (RD) having tracks formed by a plane surface and a second area (RM) having tracks formed by an uneven surface, for moving said pickup means (1-3) from a starting track at which the pickup means (1-3) is presently located to a target track, comprising: means (4, 17) for moving said pickup means (1-3) in a direction crossing said tracks; means (41) for generating an analog signal (Fig. 7a) representing the crossing of said tracks by said pickup means (1-3); and position detecting means (25, 29, 30) for detecting the position of said pickup means (1-3) in either one of said first and second areas (RD, RM); characterized by amplifier means (42) for amplifying said analog signal at a first amplification ratio, when said position detecting means (25, 29, 30) detects that said pickup means (1-3) is in said first area (RD), and at a second amplification ratio being greater than said first amplification ratio, when said pickup means (1-3) is detected as being in said second area (RM); and binary circuit means (43) having a hysteresis comparator (44) for changing said analog signal to a digital signal with a first hysteresis amount, when said position detecting means (25, 29, 30) detects that said pickup means (1-3) is in said first area (RD), and with a second hysteresis amount being greater than said first hysteresis amount, when said pickup means (1-3) is detected as being in said second area (RM). A track access device as claimed in Claim 1, wherein said position detecting means (25, 29, 30) comprises: counter means (25) for counting the number of tracks crossed by said moving means (4, 17); first setting means (30) for setting a boundary track data indicative of the location of a boundary track located adjacent the boundary between said first and second areas (RD, RM); and first access detecting means (30) for detecting the access of said pickup means (1-3) to said boundary track as said counter (25) counts tracks until in commensurate with said boundary track data. A track access device as claimed in Claim 2, wherein said position detecting means (25, 29, 30) further comprises: second setting means (29) for setting a target track data indicative of the location of said target track; and second access detecting means (29) for detecting the access of said pickup means (1-3) to said target track as said counter (25) counts tracks until in commensurate with said target track data. A track access device as claimed in anyone of the preceding claims, further comprising: reference velocity setting means (21) for setting reference velocity of said pickup means (1-3), said reference velocity including a first reference velocity (RV 1 ) which is set when said position detecting means (25, 29, 30) detects that said pickup means (1-3) is in said first area (RD), and a second reference velocity (RV 2 ) which is set when said pickup means (1-3) is detected as being in said second area (RM). A track access device as claimed in Claim 4, wherein each of said first and second reference velocities varies to be small as the pickup means (1-3) moves towards said target track. A track access device as claimed in Claim 4, wherein said first reference velocity (RV 1 ) is greater than said second reference velocity (RV 2 ). A track access device as claimed in anyone of the preceding claims, further comprising: offset adding means (50) for adding a predetermined amount to said analog signal when said position detecting means (25, 29, 30) detects that said pickup means (1-3) is in said second area (RM) to counterbalance an offset amount observed in said analog signal.

Inventors: MORIYA MITSURO, YAMAGUCHI HIROYUKI, MORIYA, MITSURO, YAMAGUCHI, HIROYUKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: G11B7
IPC codes: G11B21, G11B7