METHODS OF ACCESSING AN OPTICAL RECORDING TRACK

Abstract: Lens (20) is accelerated on a coarse tracking carriage (2) while enabling a lens position servo, which moves the carriage to return the lens to a neutral position on the carriage; after the beam spot (BS) becomes fast enough, the carriage is accelerated and decelerated until the beam spot arrives near a destination track; then the lens is decelerated on the carriage to stop on the destination track while not stopping at each track to cross. A second method is: the carriage is first accelerated while the fine tracking servo (3) is enabled to trace a start track; after the carriage becomes fast enough, the fine tracking servo is disabled, thus the beam spot is moved by a lens lock force which returns the lens to the neutral position on the carriage; the carriage is further accelerated and decelerated, next the lens is decelerated, respectively by the same ways as in the first method.

Description: DESCRIPTION TITLE OF THE INVENTION METHODS OF ACCESSING AN OPTICAL RECORDING TRACK TECHNICAL FIELD This invention relates to a method of track accessing in an optical recording apparatus and, in particular, to a novel technique for a beam spot to quickly cross the plural tracks while the number of tracks the beam spot has crossed is accurately checked. BACKGROUND ART An optical recording disk system is hereinafter described as an example of prior art optical recording systems. In an optical recording disk system, as shown in FIG. 1A, data is written in a recording track on a recording medium, a disk 1, by a beam spot focused thereon and the data is read out from a reflected light therefrom. The system employed there is constituted as follows: The optical recording disk 1 is rotating around its axle driven by a motor la. An optical head 2 coarsely travels along a radial direction of the disk, driven by a motor, which is not shown in the figure, driven by a carriage controller 5. The optical head 2 is constituted so that a light emitted from a semiconductor laser 24, as a light source, is introduced via a lens 25 and a polaroid beam splitter 23 into an object lens 20; the light is focused by the object lens 20 as a beam spot BS so as to project onto the optical disk 1; and a light reflected from the optical disk 1 is input via the object lens 20 by the polaroid beam splitter 23 into a 4-division light receiver 26. Thus, the optical head 2 may be referred to as a carriage 2. In such an optical recording disk, tracks are formed with a pitch of several micron meters, for example 1.6 um, in great numbers along a radial direction of the optical disk 1; accordingly, even a little eccentricity, typically 100 um peak to peak, may cause a large track-displacement for a narrow single track, and an undulation of the optical disk 1 causes a displacement of a focusing point of the beam spot as well; therefore, it is necessary for the beam spot to be less than 1 μm to follow these displaced and/or undulated track. For this purpose, there are provided a focus-actuator (focus coil) 22 for moving the object lens 20 on the optical head 2 along the axial direction of the lens so as to change the location of the focusing point, and a track-actuator (tracking coil) 21 for moving the object lens 20 (i.e. along left and right directions in the figure) so as to change the location of the beam spot along the orthogonal (i.e. radial) direction of the tracks. Corresponding to this, there are also provided a focus servo controller 4 for generating a focusing error signal FES from the light signal of the light receiver 26 to drive the focus actuator 22, and a fine tracking servo controller 3 for generating a. tracking error signal TES from the light signal of the light receiver 26 to drive the track actuator 21. Principle of the fine tracking control is, as shown in FIG. IB and 1C, to utilize a diffraction phenomena of the beam spot BS caused by a coaxial or spiral guide groove (track) 10 provided in advance on the optical disk 1. In other words, a fact that distribution of the amount of the reflected light into the light receiver 26 is varied by the light diffraction at the track 10 depending on the relative position of the beam spot BS to the track 10, is utilized in order to acquire the beam spot's position error from the track 10. For example, when a push-pull method having a four-division light receiver which consist of four photo diodes 26a, 26b, 26c, and 26d is employed as well known, the reflected light distributions at the light receiver 26 are such that: for the case where the location of the beam spot P, is deviating toward left hand side of the track 10 as shown in FIG. 1C the distribution is as shown in FIG. ID; for the case where the beam spot P, is not deviating from the track 10 (i.e. on track) the distribution is as shown in FIG. IE; and for the case where the location of the beam spot P 2 is deviating toward right hand side of the figure from the track 10 the distribution is as shown in FIG. IF. Therefore, { (a+b)-(c+d) } obtained in the fine tracking servo controller 3 from the outputs a ~ d of the photo diodes 26a ~ 26d forms a tracking error signal TES shown in FIG. 1G, which then drives the tracking actuator 21, accordingly drives the object lens 20 toward left and right directions. Thus, the beam spot can be controlled to trace the track 10 regardless of the eccentricity and undulation of the optical disk 1. For the beam spot to cross many of the tracks to access a particular track (referred to hereinafter as track jumping), there have been employed two basic methods. The first one of the methods is to move the beam spot by moving the optical head (a carriage) 2, on which there are installed the lens 20 or a galvano mirror (not shown in the figure) thereon, along the orthogonal directions of the tracks for a long stroke, such as 120 mm. The second method is to move the beam spot by means of a fine tracking mechanism, which is originally provided for the beam spot to trace a track by moving the lens 20 or the mirror (representatively referred to hereinafter as lens) on a carriage along orthogonal directions of the tracks in order to compensate an eccentric movement of the track, while the carriage is fixed or following the lens by a lens position servo control (details of which will be described later) , for the case the number of track jumping is less than one hundred, for example. These two methods are used generally in combination. Number of tracks the beam spot is crossing is acquired by counting zero cross transitions in a zero cross signal TZCS which is generated from a tracking error signal which is originally provided for the fine tracking servo control of the lens. On the other hand, the optical disk, i.e. the tracks, rotates undesirably eccentrically as mentioned, for example as much as 100 um peak to peak, having a frequency of 30 Hz for 1800 revolutions per minutes, for example. The amount 100 u corresponds to about 60 tracks having a pitch of 1.6 um. Accordingly, in the first method a wrong zero cross signal is generated when the radial speed of the eccentric track exceeds the beam spot's radial speed, resulting in an error in the counting of the number of track crossing. Therefore, an ID (identification) number recorded in each track has to be read out after the track jumping is finished, and then according to the read out track ID number, the beam spot location must be adjusted by moving the lens to reach the destination track. Consequently, the track jumping takes a long time. In the second method, the counting of the crossed tracks is correct if the track crossing is done track by track. In this track-by-track jump method, a track actuator 21 drives the object lens 20 to move the beam spot BS from a present track 10a to a destination track lOd. And, as shown in FIGs. 2A and 2B a single-track jumping is repeated, i.e. a sequence that an acceleration current i is applied to the track actuator for an acceleration and next a deceleration current -ia is applied for a deceleration to stop, is carried out for each track. In each single track jumping, the beam spot BS can not trace the track quickly and stably after the single track jump is carried out as its natural characteristics; accordingly, a settling period is necessarily provided until the beam spot captures the track by the fine servo (i.e. until the tracking error signal TES becomes almost to zero) . It takes a relatively long period, such as 2.5 ms, for the beam spot to cross to an adjacent track and to stop at the centre of the track. Accordingly, the period required for jumping a great number of tracks becomes the multiplication of the 2.5 ms by the track numbers to be jumped. Such a long period can not satisfy the recent trend of fast accessing of the optical disk. DISCLOSURE OF THE INVENTION It is a general object of the invention to provide methods of a fast track jumping over a long distance, without stopping at each track, while the number of tracks the beam spot has crossed is accurately counted. A track jumping of the present invention is carried out by the steps of: accelerating a fine tracking device on a carriage while enabling a position servo which moves the carriage so that the fine tracking device returns to its neutral position on the carriage, until the beam spot becomes faster than a radial speed of the eccentric tracks; further accelerating the carriage; decelerating the carriage until the beam spot speed becomes slow enough for the fine tracking device to seek a destination track; counting a number of zero crossings, which indicate that said beam spot crosses to adjacent track, in the tracking error signal since the track jumping is initiated; and accelerating/decelerating the fine tracking device according to a difference of the counted number of crossed tracks and an instructed number of track jumping to reach a destination track. Another method of the track jumping is carried out by the steps of: accelerating a carriage having a fine tracking device thereon while enabling the fine tracking servo to keep a start track at which the beam spot has been located when the track jumping is instructed, until the carriage speed becomes higher than a predetermined level; disabling the fine tracking servo and enabling a lock, by which the fine tracking device returns to a neutral position on the carriage, accordingly the beam spot is accelerated; further accelerating the carriage until the beam spot reaches a preprogrammed track; decelerating the carriage until the beam spot speed becomes slow enough for the fine tracking device to seek the destination track; counting a number of zero crossings, which indicate that the beam spot crosses to adjacent track, in the tracking error signal since the track jumping is initiated; and accelerating/decelerating the fine tracking device on the carriage according to a difference of the counted number of crossed tracks and instructed number of track jumping so as to reach a destination track. Still another method of track jumping using a fine tracking device, applicable to above described two methods is carried out by the steps of: measuring each time interval of zero crossings, which indicate that the beam spot crosses to adjacent track, in the tracking error signal, while.the beam spot is moving; obtaining a time difference between the time interval between the zero crossings and a predetermined time interval; and accelerating or decelerating the fine tracking device on the carriage according to the time difference, so as to make the time interval of said zero crossings essentially equal to the predetermined time interval, i.e. so that the beam spot is at a predetermined speed, without stopping the beam spot at each track to cross. According to the methods of the present invention, the track the beam spot has crossed is always accurately counted, while the beam spot is moving fast without stopping at each track; therefore, a quick and accurate track jumping is accomplished. The above-mentioned features and advantages * of the present invention, together with other objects and advantages, which will become apparent, will be more fully described hereinafter, with reference being made to the accompanying drawings which form a part hereof, wherein like numerals refer to like parts throughout. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A schematically illustrates servo mechanisms in an optical recording disk apparatus. FIGs. IB through 1G explain a principle of a fine tracking servo control. FIGs. 2 explain a prior art track-by-track jumping method. FIG. 3 shows a block diagram of an optical disk apparatus used for the methods of the present invention. FIG. 4A schematically illustrates an optical head (carriage) used for the optical disk where the methods of the present invention are applied to. FIGs»4B and 4C schematically illustrate a structure for a lens lock and a lens position servo. FIG. 5 shows a block diagram of electrical circuits of the optical disk apparatus where the methods of the present invention are embodied. FIG. 6 shows detailed circuits of a head circuit of the block diagram of FIG. 5. FIG. 7 shows detailed circuits of a TES generating circuit, a total-signal generating circuit, an AGC circuit, a zero-cross detector circuit and an off-track detector circuit of the block diagram of FIG. 5. FIG ' . 8 shows detailed circuits of a phase compensation circuit, a return signal generating circuit, a lock-on switch, a driver circuit and a power amplifier of the block diagram of FIG. 5. FIG. 9 explains a principle of a track access method of the present invention. FIG. 10 shows a flow chart of a preferred embodiment of the present invention of FIG. 9. FIG. 11 shows a timing chart of a preferred embodiment of the present invention of FIGs. 9 and 10. FIG. 12 shows a flow chart of a second preferred embodiment of the present invention of FIG. 9. FIGs. 13 explain a track-by-track speed control method of the the present invention. FIGs. 14 show a flow chart of the track-by-track speed control method of the the present invention of of FIG. 13. FIGs. 15 show timing charts of the track-by-track speed control method of the present invention of FIGs. 13 and 14. BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention are hereinafter described referring cases where a fine tracking device consists of a lens. First of all, an optical head, which is a carriage having the lens thereon, is explained. In FIG. 4A, a light generated in a semiconductor laser 24 is made a parallel light beam by a collimator lens 25a; the cross-section of the light beam is corrected to be a true round ' by a true-round correction prism 25b; the light beam is projected into a polarization beam splitter 23; further projected into an object lens 20 via a 1/4 wavelength plate 25c; and focused as a beam spot BS on an optical disk 1 (FIG. 1A) . A reflected light from the beam spot on the optical disk 1 is projected into the polarization beam splitter 23 via the object lens 20, the 1/4 wavelength plate 25c; and then projected into a four division light receiver 26 via a focusing lens 27. The object lens 20 is installed on an end of main body 28 of an actuator rotatable around an axle 28a, and a slit 28b is provided on the other end of the main, body 28. The main body 28 is provided with a coil holder 28c; the coil holder 28c is provided with a focus coil 22 therearound; and with a spiral tracking coil 21 on its side; and a magnet 28d is provided surrounding the coil 28c. Therefore, when a current is applied into the focus coil 22, the actuator 28 having the object lens 20 thereon moves along the lens's axis, i.e. up or down in the X direction on the figure, thus is able to vary its focusing point; and when a current is applied into the actuator coil (the tracking coil) 21, the actuator 28 rotates around the axle 28a in d. direction, thus is able to vary its position in a direction orthogonal to the tracks, i.e the radial direction of the tracks. For the slit 28b on another end of the actuator 28, there is provided a position sensor 29 on the carriage 2 (the lens head 2 is referred to hereinafter as carriage 2) . The position sensor 29 is located so that a light emitter 29e and four-division light receiver 29 are facing and aligned each other via the slit 28b as shown in FIGs. 4B and 4C. The slit 28b is provided with a window W, through which the light beam from the light emitter 29e is received by the four photo diodes 29a _ 29d of the light receiver 29. So, as shown in FIG. 4B, the received light distribution upon the photo diodes 29a _ 29d varies depending on the amount of the displacements along the β( and X directions of the actuator 28. Therefore, a lens position signal LPS indicating the lens's displacement on the carriage 2 in the track's radial direction and a focus position signal for the focus direction FPS are acquired from the outputs A, B, C and D of each of the four photo diodes 29a ~ 29d in a similar way to those of focusing and tracking servos, as follows: LPS = (A+C) - (B+D) FPS = (A+B) - (C+D) These lens position signals LPS and FPS exhibit an S shape form for the displacements X and βf from each essentially centre position, which is referred to hereinafter as a neutral position, of the stroke and rotation of the lens on the carriage. Each signal becomes zero at each neutral position, as shown in FIG. 4B. Thus, an electrical spring force returning the lens toward each I neutral position can be generated from these signals. This function is referred to as a lens lock and a focus lock, and its original purposes are to prevent the lens from floating when the carriage is traveling and to prevent the lens from shifting too much from the centre of the coverage of the fine tracking servo. The lens position signal LPS may also be negatively fed back to the carriage controller 6 to move the carriage so that the lens returns to its neutral position on the carriage. This may be referred to as a double servo control, a lens position servo control or simply a position servo control. Purpose of this position servo control is also to prevent the range of the fine servo control from exceeding the allowable range of the lens on the carriage. • Next, referring to the circuit diagram in FIG. 5, details of the the present invention is hereinafter explained. An operation controller, which is composed of a micro processor (referred to hereinafter as MPU) 7, which receives a track jump instruction from an upper processor (not shown in the figure) and stores an instructed number of tracks to jump D; and then transmits instructions to the tracking servo controller 3, the focus controller and the carriage controller 5 by running a program installed in MPU 7 in advance. MPU 7 also receives a track zero-cross signal TZCS from the zero cross detector 34a and an off-track signal TOS from an off-track detector 34b so that the beam spot location is controlled by the use of a lens forwarding signal FWR, a lens reversing signal RVS, and a lock-on signal LKS. A head circuit 6, as shown in FIG. 6, includes an RF-composing circuit 60 for composing an RF signal RFS from the outputs a ~ d of the four-division light detector 26, an amplifier 61 for amplifying the outputs a _ d of the four photo diodess 26a ~ 26d so as to output servo outputs SVa _ SVd, an LP-generating circuit 62 for generating the lens position signal LPS from the outputs A _ D of the four photo diodes 29a ~ 29d of the position sensor 29, the four-division light detector 26 and a constant voltage power source 63 for the position sensor 29. In the head circuit 6, as shown in FIG. 6, the constant voltage power source 63 is composed of a zenor diode ZD, a condenser C, and a resistor R, is connected to four photo diodes 26a ~ 26d of the four-division light receivers 26 as well as to the four photo diodes 29a ~ 29d of the position sensor 29, and supplies a power source voltage V thereto. The LP-generating circuit 62 composed of a differential amplifier performs a differential amplification, i.e. (A+C) - (B+D) , of the outputs A - D of the photo diodes 29a __. 29d so as to generate the lens position signal LPS; the RF-generating circuit 60 is composed of a high-pass filter, and adds the outputs of the four photo diodes 26a _ 26d via differentiator condensers C, so as to be output to an operational amplifier 60. Furthermore, the amplifier 61 is composed of amplifiers 61a ~ 61d connected respectively to the photo diodes 26a ~ 26d and outputs servo outputs SVa ~ SVd. Returning back to FIG. 5, a TES (tracking error signal) generating circuit 30 generates the tracking error signal TES from the servo outputs SVa _ SVd of the amplifier 61 (61a - 61d) . A total-signal generating circuit 31 adds the servo outputs SVa ~ SVd so as to generate a total-signal DSC which indicates a total reflection level. An AGC (Automatic Gain Control) circuit 32 divides the tracking error signal TES by the total-signal (total reflection ' level) to perform the AGC in reference to the total reflection level, so that a variation of the projecting light intensity or the reflection coefficient is compensated. In a phase compensation circuit 33 the tracking error signal TES is differentiated and then added with a proportional component of the tracking error signal TES so as to advance the - 15 - phase . A zero-cross detector 34a detects a zero-cross transition of the tracking error signal TES so as to output the track zero-cross signal TZCS to MPU 7. An off-track detector 34b detects that the tracking error signal TES becomes larger than a predetermined level Vo in a positive direction or lower than a predetermined level -Vo in a negative direction, i.e. becoming an off-track state, and then outputs an off-track signal TOS to MPU 7. A servo switch 35 closes a servo loop when the servo signal SVS is output from the MPU 7, as well as opens the servo loop when the servo signal is disabled. A return signal generating circuit 36 generates, from the lens position signal LPS acquired from the LP-generating circuit 62, a return signal RPS which generates a return force on the actuator 28 toward the neutral position on the carriage as shown in FIG. 4B. A lock-on switch 37 is closed by the lock-on signal LKS from MPU 7 so as to introduce the return signal RPS to the servo loop, and opens by the disabling of the same so as to cut the introduction of the return signal to the servo loop. A driver circuit 38 generates a forward acceleration signal +V corresponding to the lens forwarding signal FWR and a backward deceleration signal -V corresponding to the lens reversing signal RVS, as well as for outputting a sum of the outputs from the servo switch 35 and the lock-on switch 37. A power amplifier 39 amplifies an output of the driver circuit 38 so as to deliver a track driving current TDV to the track actuator coil 21. Details of the tracking servo controller 3 are shown in FIG. 7 and FIG. 8. As shown in FIG. 7, the TES generating circuit 30 includes an adder amplifier 300 for adding the servo outputs SVa and SVb via input resistors r, and r 2 respectively, an adder amplifier 301 for adding the servo outputs SVc and SVd via input resistors r 3 and r. respectively, and an adder amplifier 302 for reducing the output -(SVa+SVb) of the adder amplifier 301 from the output -(SVc+SVd) of the adder amplifier 300, and then the differential amplifier 302 outputs the tracking error signal TES {= (SVa+SVb) - (SVc+SVd) } . The total-signal generating circuit 31 includes an adder amplifier 310 for adding each servo output SVa __. SVd via input resistors r 5 _ r gr and outputs the total-reflection level signal DCS (= SVa + SVb + SVc + SVd) . The AGC circuit 32 includes an operational amplifier 302 for receiving the tracking error signal TES, a first FET (Field Effect Transistor) 321 for dividing and controlling the input to the first operational amplifier 320 according to the output of the operational amplifier 320, a second operational amplifier 322 for receiving the total-reflection level signal DCS for controlling FET 321, and a second FET 323 for voltage-dividing the input to the second operational amplifier 322, thus, the first FET 321 is controlled by the total-reflection level signal DCS, which is an output of the operational amplifier 322, so as to control the gain of the operational amplifier 320, then an AGC-controlled tracking error signal TES/DCS is acquired from the output of the operational amplifier 320. The second FET 323 is provided in order to compensate the non-linearity of the first FET 321 so as to accomplish a linear characteristics. The zero-cross detector 34a is composed of a comparator 340 for comparing the zero-cross potential with the tracking error signal TES from the AGC circuit 32, so as to output the track zero-cross signal TZCS. The off-track detecting circuit 34b includes a first comparator 341 for comparing the tracking error signal TES with the predetermined level Vo and then outputting a "High" level output when TES > Vo, and a second comparator 342 for comparing the tracking error signal TES with the predetermined level (-Vo) and then outputting a "High" level output when TES < -Vo, and outputs a sum of the outputs from both the comparators 341 and 342 as the off-track signal TOS. The phase compensating circuit 33, in which a differentiation circuit composed of a resistor r and a condenser C and a proportion circuit formed of a y y resistor R are connected to an operational amplifier 330, y outputs to the servo switch 35 a signal of a sum of the differentiation of the track error signal TES of the AGC circuit 32 and its proportion, i.e. a signal TCS which is a tracking error signal added with a phase-advancing component. The return signal generating circuit 36 includes an operational amplifier 360 for amplifying the lens position signal LPS from the LP-generating circuit 62 and a phase compensating circuit 361 for phase-compensating the output of the operational amplifier 360, and outputs the return signal RPS. The lock-on switch 37 includes a first switch 370, which is closed when the lock-on signal LKS is output, for adding the return signal RPS to the signal TCS of the servo switch 35; an inverter circuit 371 for inverting the lock-on signal LKS; and a second switch 372 which becomes closed when the inverted lock-on signal LKS is output, i.e. the lock-on signal is disabled. The driver circuit 38 includes an adder amplifier 380; a first switch 381 which is enabled by the lens forwarding signal FWR. to deliver the forward driving signal +V to the adder amplifier 380; and a second switch' 282 which is enabled by the lens reversing signal RVS to deliver the backward driving signal -V to the adder amplifier 380, and outputs driving signals (voltages) +V, -V and a sum of the control signals TCS, RPS from the adder amplifier 380. In the summation of the signals TCS and RPS, the signal RPS is set weaker than the signal TCS. The power amplifier 39 amplifies the output of the driving circuit 38 by serial two-stage amplifiers 390 and 391 so as to apply a positive or negative track driving current TDV into the tracking actuator coil 21. Operation of the above-described embodiment is hereinafter explained. First of all, the concept of the track access of the present invention is described with FIG. 9. In the above-described embodiment the lens is moved as the fine tracking means on the carriage 2; therefore, the track access by moving the fine tracking device, i.e. the lens 20 in this embodiment, on the carriage is referred to hereinafter as a lens seek. A track seek carried out by moving the carriage 2 is referred to hereinafter as a carriage seek. At first, the carriage 2 is stationary to the disk. The range (a) in FIG. 9 is for a lens seek acceleration, in which the beam spot, i.e. lens 20, is accelerated on the carriage from a start track, on which the beam spot is projected when the track jumping is instructed, driven by the fine tracking controller 3, until the speed of the beam spot exceeds the maximum radial speed Vec of the eccentric tracks. During this range (a), the fine tracking servo control is disabled, and the lens position servo is kept enabled. Therefore, the carriage follows the beam spot by the function of the lens position servo so that the lens returns to the neutral position on the carriage. Then, the lens position signal which was once increased becomes close to zero. Now the speed of the beam spot by the lens seek is adequately faster than the radial speed of the eccentric tracks varying typically at 30 Hz. Accordingly, the number of the tracks the beam spot has crossed can be accurately counted from the track zero-cross signal TZCS. The range (b) is a range of the carriage seek where the beam spot acceleration is carried out by further accelerating the carriage until the beam spot reaches almost half of the number of tracks to jump. The range (c) is a range of the carriage seek where a beam spot deceleration is carried out by decelerating the carriage until the beam spot speed becomes slower than a limit speed Vis, below which the lens seek deceleration is surely possible, but faster than the radial speed Vec of the eccentric tracks. During the ranges (b) and (c) , the beam spot speed is faster than the radial speed Vec of the eccentric tracks; therefore, the number of the crossed tracks can be accurately counted. The range (d) is for deceleration of the beam spot by the lens seek, in which the beam spot, i.e. lens 20 is decelerated on the carriage driven reverse-ward by the fine tracking controller 3, so that the beam spot reaches a destination track. During the range (D) , the crossed number of the tracks can be accurately counted because the beam spot speed is faster than the radial speed of the eccentric tracks. Operation of the circuits where the present invention is embodied is described hereinafter in detail referring to a block diagram in FIG.. 5, a flow chart in FIG. 10 and a timing chart in FIG. 11. The beam spot has been tracing a start track by the fine tracking servo control and the position servo control, and then is instructed to jump toward the inner direction of the disk; therefore, the inner direction is referred to hereinafter as a forward direction, and the outer direction as the reverse direction. In FIG. 10, in the step (1) the fine tracking servo is disabled; the lens position servo is kept enabled; and a lens seek acceleration denoted with the range (a) is initiated by disabling the lens reversing signal RVS, which moves the beam spot reverse-ward, i.e. outer-ward, and enabling the lens forwarding signal FWR, which moves the beam spot inner-ward, to be input to the lens driving circuit 38 so that the lens 20 is accelerated on the carriage 2 toward the inner direction. Owing to the lens position servo, the carriage 2 automatically moves to follow the beam spot. Amount of acceleration/deceleration may be controlled by the duration of the signal FWR or RVS, according to the beam spot speed measured from the interval of track zero-cross signal TZCS. In the lens seek, the beam spot speed easily becomes faster than the radial speed of the eccentric tracks because the lens system movable on the carriage is originally designed to be light enough to move fast for the fine tracking control. There is a track-by-track speed control method, as one of the preferable methods of the lens seek. In this method, the beam spot speed crossing each track is watched and controlled, i.e. accelerated or decelerated, by the measurement of the interval of track zero-cross signal TZCS, so that the beam spot travels at an essentially constant speed without stopping at each track. Details of this method will be described later. At the end of the step (1), i.e. at the end of the range (a) of FIG. 9, the lens position signal is approximately zero, i.e. the lens 20 is approximately at the neutral position on the carriage 2. In the step (2) , the beam spot speed is discriminated whether the beam spot speed is adequately higher than the radial speed of the eccentric tracks. This discrimination is carried out by MPU 7 by judging whether the beam spot speed exceeds the maximum radial speed Vec of the the eccentric tracks according to the time interval of the track zero-cross signal TZCS while the beam spot crosses a single track. If the judge is YES, the step (3) is executed, but if the judge is NO, the step (2) is repeated. In step (3) , the carriage seek denoted with the range (b) is initiated by the disabling of the lens position servo control and by applying a signal INR, which accelerate the carriage toward the inner direction, to the carriage tracking control circuit 52. During this step, the lens position servo control is disabled by disabling the lens position servo switch signal PSS, and the lens lock is enabled by outputting the lens lock signal LKS. In step (4) , which is carried out concurrently with the step (4) , the carriage seek is discontinued by enabling the lens lock. In the step (5), it is discriminated whether the beam spot has reached, by the carriage seek of the range (b) , a track where the carriage deceleration is to be started. The track where the carriage deceleration is to be started is typically chosen at approximately half of or a little less than the number of tracks to jump usually for the case where the acceleration speed or the deceleration speed, i.e. the acceleration or deceleration, is of the same degree. Accordingly, when the natures or the conditions, such as friction, etc., are different, the optimum location of the track where the carriage is to be decelerated becomes different from the half of the track jump number. Therefore, the track where the carriage deceleration is to begin may be calculated by a program installed in MPU 7 in advance. If the discrimination is NO, the step (5) is repeated. In the step (6) , when the discrimination in the step (5) is YES, the carriage 2 is decelerated, shown in the range (c) of the carriage seek, by disabling the signal INR and applying the signal OUT, which decelerates the carriage toward the outer direction, to the carriage tracking controller 2. In the step (7) , it is discriminated whether the beam spot speed has reached a predetermined speed which is slower than the limit speed Vis but faster than the maximum radial speed Vec of the eccentric tracks. If the discrimination is NO, the step (7) is repeated. In the step (8) , when the discrimination in the step (7) is YES, the carriage seek deceleration is discontinued by disabling the signal OUT. In the step (9) , the lens seek deceleration is started, as shown in the range (d) , by the disabling of the lens lock signal LKS and outputting the lens position servo signal PSS. During this lens seek, the beam spot is decelerated by applying the lens reversing signal RVS to the lens driving circuit 38 so that the lens moves on the carriage toward the reverse direction of the track jumping. i.e. outward. Because of the lens position servo, the carriage is automatically decelerated to follow the beam spot according to the lens position signal generated by this lens seek. During the lens seek, the number of the tracks the beam spot has crossed is accurately counted from the track zero-cross signal TZCS. If the beam spot speed at the beginning of this lens seek deceleration is slow enough for the lens to be able to stop at a destination track, the beam spot is kept moving at the constant speed until the beam spot reaches a predetermined track, typically one track prior to the destination track. In the strict sense of word, it is until a half track prior to the destination as explained later about a deceleration period tc in FIG. 15. And then, the lens is decelerated as mentioned above by the lens reversing signal RVS to stop at the destination track. If the beam spot speed at the beginning of this lens seek is not slow enough for the lens to be able to surely stop at a destination track, the beam spot is decelerated by decelerating the lens by the lens reversing signal RVS gradually or step by step until the beam spot speed becomes slow enough for the lens to stop at a destination track. The track-by-track speed control can be preferably employed to the lens seek of the range (d) as well. Though in the description of this preferred embodiment the lens position servo is enabled in the step (9) , this is not an absolute requirement to achieve this lens seek deceleration for the range (d) , because the carriage can be stopped by other means, for example by the signal OUT, than this lens position servo. Though in the description of this preferred embodiment the lens lock is disabled in the steps (1) and (9) , disabling the lens lock is not an absolute condition for the respective steps to achieve the operation of the invention. This is because the lens lock as well as the lens position servo is designed weaker than the lens seek signal; accordingly, the lens lock or the lens position servo may be continuously kept enabled from the start through all the steps, including a case where a spring or a rubber damper is employed as the lens lock means,, then there is no way to disable the lens lock. A second preferred embodiment of"the present invention is hereinafter described, referring to a flow chart in FIG. 12. The beam spot has been tracing a start track by the fine tracking servo control and the position servo control; and then is instructed to jump toward the inner direction of the disk. In the step (1), when the track jump is instructed, the carriage is accelerated by the output of the signal INR of the instructed direction and by the disabling of the lens position servo and the lens lock while the fine tracking servo is kept enabled for the beam spot to keep the start track, at which the track jump is initiated. Accordingly, the lens position signal is increased. In the step (2), it is discriminated whether the lens position signal, which now corresponds to the amount of the carriage's travel, indicates adequately - 26 - larger than a predetermined amount of the radial displacement of the eccentric tracks. This predetermined amount is chosen much larger than the maximum radial displacement of the eccentric tracks. When the carriage has traveled this predetermined amount, the carriage speed is already larger than the maximum radial speed Vec of the eccentric tracks. If the discrimination is NO, the step (2) is repeated. In the step (3), when the discrimination in the step (2) is YES, the fine tracking servo is disabled and the lens lock is enabled. Accordingly, the lens lock force returns the lens to the neutral position on the carriage, causing the beam spot to move. At this time, the beam spot speed is high enough to accurately count the number of tracks the beam spot has crossed, eliminating the effect of the eccentric track rotation. In the step (4) , the carriage acceleration is continued while the lens lock is enabled. In the step (5) , it is discriminated whether the beam spot has reached a track where the carriage deceleration is to be started. The track where the carriage decelerated is to be started is typically chosen at approximately half of the number of tracks to jump usually for the case where the acceleration speed or the deceleration speed, i.e. the acceleration or deceleration, is of the same degree. Accordingly, when the natures or the conditions, such as friction, etc. of the apparatus, are different, the optimum location ofthe track where the carriage deceleration is to be started becomes different from the half of the track jump number. Therefore, the track where the carriage deceleration is to begin may be calculated by a program installed in the MPU 7 in advance. If the discrimination is NO, the step (5) is repeated. In the step (6) , when the discrimination in the step (5) is YES, the carriage 2 is decelerated by the disabling of the signal INR and by the output of the signal OUT to the carriage tracking controller 2, in a same way of the step (6) for the range (c) of the carriage seek of the first preferred embodiment. In the step (7) , the beam spot speed is discriminated in the same way as the step (7) of the first preferred embodiment. If the discrimination is NO, the step (7) is repeated. In the step (8), ' when the discrimination in the step (7) is YES, the carriage seek is discontinued by the disabling of the signal OUT. And, the lens seek deceleration is started in the same way as the range (d) of the previous embodiment, by the disabling of the lens lock signal LKS and preferably by enabling the lens position servo. During this lens seek deceleration, the beam spot is decelerated by applying the lens reversing signal RVS to the lens driving circuit 38 so that the lens moves on the carriage toward the reverse direction of the track jumping, i.e. outward in this case. Because of the lens position servo, the carriage is automatically decelerated to follow the beam spot according to the lens position signal generated by this lens seek. During the lens seek deceleration, the number of the tracks the beam spot has crossed is accurately counted from the track zero-cross signal TZCS. If the beam spot speed at the beginning of this lens seek is slow enough for the lens to be able to stop at a destination track, the beam spot is kept moving at the constant speed until the beam spot reaches a predetermined track, typically one track prior to the destination track; and then, the lens is decelerated to stop at the destination track. If the beam spot speed at the beginning of this lens seek deceleration is not slow enough for the lens to be able to surely stop at a destination track, the beam spot is decelerated by decelerating the lens gradually or step by step until the beam spot speed becomes slow enough for the lens to to stop at a destination track. The track-by-track speed control can be preferably employed to this lens seek as well. Though in the description of the second preferred embodiment the lens position servo and the lens lock are disabled in the step (1) , and the lens lock is enabled in the step (3) , whether the lens position servo or the lens lock is enabled or disabled is not an absolute condition, but preferable, for the respective step to achieve the operation of the invention. This is because the lens position servo as well as the lens lock is designed weaker than the fine tracking servo, accordingly, they may be continuously kept enabled from the start through all the steps, including a case where a spring or a rubber damper is employed as the lens lock means and there is no way to disable the lens lock. A preferred embodiment of the track-by-track speed control method preferably referred to as a method of the lens seek in the above-described two embodiments is hereinafter explained, referring to a principle diagram in FIG. 13, a circuit block diagram in FIG. 5, a flow chart in FIGs. 14 and a timing chart in FIG. 15, where a case of a cycle of an acceleration from a start track, a constant speed travel over a plurality of tracks and an arrival at a destination track is described as an example. This method is used while the carriage is stationarily fixed or following the beam spot by means of the lens position servo control. The circuit constitution for this method is essentially same as that used for the above-described two embodiments in FIG. 5. MPU 7 further includes a timer 7a and in the memory 7b there are stored: a predetermined acceleration period ta; a target period tb for a single track crossing corresponding to a target speed; a predetermined deceleration period tc; a number D of tracks to jump; a number D Q of tracks for which the target speed is switched; an acceleration/ deceleration control pulse time t for the track-by-track speed control; a processing time tp; a high speed target time tbh which corresponds to a high target speed; a low speed target time tbl which corresponds to a low target speed. FIG. 13A shows a relation of the track number the beam spot is located and the time lapse on the X axis, and the beam spot speed, tracking error signal TES, track zero-cross signal TZCS and acceleration/ deceleration signal on the Y axis. When the MPU 7 is instructed from an upper processor to start the track access, if the number of track jumping instructed "n" is larger than (D Q + 2) , a target speed is set at a high target speed Vh up to the (n - D Q - 2) th track which is near the destination track as shown in FIG. 13A; and after the (n - D Q - 2) th track the target speed is set at a low target speed VI, where D Q is a number chosen for the beam spot to easily stop at the destination track from the low target speed while crossing D Q tracks, allowing enough margin considering the inertia, etc., of the movable part of the lens system. The number D Q is referred to hereinafter as a speed switching track number. Amount of the high target speed Vh is chosen an available highest speed at which the lens control is possible, in order to enhance the high speed capability. Amount of the low target speed VI is chosen a speed from which the beam spot can stop at the destination track while crossing a single track, for example, approximately 200 us per track. When the instructed track jump number n is " less than (D + 2) , the target speed is set at only VI as shown in FIG. 13 B. Dotted lines in FIGs. 13 show an actual speed Vr of the beam spot when the beam spot is controlled by the target speeds. Referring to a flow chart in FIGs. 14, the operation is hereinafter explained. It is assumed now that the servo-on signal SVS from MPU 7 is enabling the servo switch 35, and the disabled lock-on signal LKS is disabling the lock switch 37, until the track jump instruction is received. In other words, it is assumed that the fine tracking servo loop is closed so that the track actuator 21 is servo-controlled by the control signal TCS from the tracking error signal TES, accordingly the beam spot is tracing the track 10a. In the step (1), at this state, a track jump procedure shown in FIG. 14 starts when a track jump instruction as well as its track jump number D is given from the upper processor to MPU 7. In this embodiment, the track jump is instructed toward the inner direction. At first, MPU 7 reduces t2] from the given track jump number D (= n) , and stores it in the memory 7b. The reduction of this [2] is because an acceleration is made during the travel toward the second track (10b of FIG. 15 and a deceleration is made for stopping at the destination, D-th track; therefore, these two times of track crossings are reduced from D and a track-by-track speed control is carried out (D - 2) times for the residual tracks. Next, MPU 7 compares the track number D (= n - 2) with the speed switching track number D Q ; then, if D > D Q , this is the case of FIG. 13A, where the target speed tb is set with the high target speed Vbh; and the acceleration period ta is set with tah for the acceleration up to the speed Vh. If D < D Q , this is the case of FIG. 13B, where the target speed tb is set with the low target speed Vbl; and the acceleration period ta is set with tal for the acceleration up to the speed VI. Next, MPU 7 disables the servo signal SVS to disable the servo switch 35, so as to open the servo loop of the tracking error signal TES. Thus, the servo control of the tracking error signal TES is inhibitted. This is necessary to smoothly control the travel of the beam spot as instructed by MPU 7, and to acquire an accurate actual speed from the track error signal TES. Next, MPU 7 checks which the track jump is directed to, i.e. toward the outer direction or inner direction along the radius of the optical disk 1, and then, if the direction is toward the outer, a procedure for the outer direction is executed. The procedure for the track jump toward the outer side are almost the same as the track jump process toward the inner side shown in the step (2) and the followings. In the step (2) , MPU 7 enables the lens forwarding signal FWR for the acceleration period ta so as to apply the acceleration voltage +V for the period ta. That is, after outputting the lens forwarding signal FWR, MPU 7 sets the timer 7a with a complement of the acceleration period ta in the memory 7b, and then starts the timer 7a. The timer 7a being set with the complement of the acceleration period ta counts the clock pulses, and generates a count-up signal when the period ta is counted. When the timer 7a generates the count-up signal, MPU 7 terminates the timer 7a so as to disable the lens forwarding signal FWR. Therefore, the first switch 381 of the driver circuit 38 is enabled for the period ta; the acceleration voltage +V is - 33 - applied to the adder amplifier 480 for the period ta; an acceleration current is applied as the track driving current TDV from the power amplifier 39 to the track actuator 21 for the period ta; accordingly, the object lens 20 (i.e. the beam spot) is accelerated up to the high target speed Vh. In the step (3) , MPU 7 observes the track zero-cross signal TZCS and detects a timing when the track zero-cross signal TZCS changes from "0" state to "1" state, i.e. a rise transition of the track zero-cross signal TZCS, and then starts measuring an interval of the track zero-cross signals TZCS. That is to say, MPU 7 reads out the target period tb (tbh or tbl) corresponding to the target speed Vh or * VI respectively, from the memory 7b; sets a complement of the target period tb in the timer 7b; and then starts the timer 7b. In the step (4) , MPU 7 observes the track zero-cross signal TZCS and detects the rise transition, i.e. from "0" state to "l" state, of the track zero-cross signal TZCS ; and then stops the timer 7a so as to terminate measuring the interval of the track zero-cross signals TZCS. The timer 7a being set with the complement of the target period tb generates a count-up signal when the period tb is counted. Therefore, if the time interval T between a rise transition, at which the timer 7a is started, and the next rise transition, at which the timer is terminated, is T > tb (i.e. the actual speed is equal to or slower than the target speed) , the timer 7a has been already counted up when the timer 7a is terminated. On the contrary, if T < tb (i.e. the actual speed is faster than the target speed), the timer 7a is not counted up yet when the timer 7a is terminated. In the step (5), MPU 7, therefore, checks whether the timer 7a is counted up. On finding a count-up, which means the actual speed is equal to or slower than the target speed, the lens acceleration is performed. The timer 7a continues to count until the timer 7a terminates even after counting up; therefore, MPU 7 reads out a count-over amount t and calculates therefrom a control pulse period t. Then, MPU 7 outputs the lens forwarding signal FWR for the lens acceleration; sets a complement of the control pulse period t in the timer 7a; and initiates the timer 7a. On counting the control pulse period t, the timer 7a counts up; therefore, MPU 7 terminates the timer 7a on counting-up of the timer 7a so as to disable the lens forwarding signal FWR. Thus, the first switch 381 of the driver circuit 38 is enabled for the period t; the acceleration voltage +V is applied to the adder amplifier 480; the acceleration current as the track driving current TDV is applied from the power amplifier 39 to the track actuator 21 for the period t; accordingly, the lens 20 is accelerated. If the actual speed is equal to the target speed, then [ t = 0, accordingly t = 0; therefore, the first switch 381 is enabled only for a moment. In the step (6) , on the other hand, when the timer 7a has not counted up yet, MPU 7 discriminates that the actual speed is faster than the target speed, and decelerates the lens. For this purpose, MPU 7 reads out the counted number n of the timer 7a. The count-up number N of the timer 7a is known in advance; therefore, the difference (tb - T) = βt between the target period tb and the interval (period T) of the rise transitions of the track zero-cross signals TZCS is acquired from (N - n) , so as to calculate the control pulse period t. Then, MPU 7 enables the lens reversing signal RVS for lens deceleration; sets a complement of the control pulse period t in the timer 7a; and then initiates the timer 7a. On counting up of the timer 7a, MPU 7 stops the timer 7a and disable the lens reversing signal RVS. Therefore, the second switch 382 of the driver circuit 38 is enabled for the period t; the deceleration voltage -V is applied to the adder amplifier 480; the deceleration current as the track driving current TDV is applied from the power amplifier 39 to the track actuator 21 for the period t; thus the lens 20 is decelerated. In the step (7) , as a rise transition of the track zero-cross signal TZCS has been detected in step (4) , MPU 7 renews the track jump number D in the memory 7b to (D - 1) after the step (5) or the step (6) . And, MPU 7 checks whether D is [0] or not. Next, MPU 7 discriminates whether the renewed track jump number D is less than the speed switching track number „ or not. That is, if the remaining track jump number D is less than the speed switching track number D Q (i.e. D ^ D Q ) r and excluding the case where the target speed is set with the low target speed VI already, the target speed tb is renewed with the low target speed VI. If not, (i.e. D > D Q ) , the target speed is kept to remain with the high target speed Vh. Next, MPU 7 discriminates whether D = 0 or not. If D ≠ 0 is true, it means that the beam spot has not arrived at the track prior next to the target track yet. If D ≠ 0 is not true (i.e. D = 0) , the beam spot has arrived at the track prior next to the target track. In the step (8) , if D ≠ 0 is true, the measurement of the interval of the track zero-cross signals and the above-described track-by-track speed control is carried out again. For this purpose, MPU 7 sets the -target period tb in the timer 7a; initiates the timer 7a; and returns to the step (4) . At this time, since the timing when the rise transition was detected in the step (4) it has elapsed over the control pulse period t and the process period tp needed for the processes in the steps (5) or (6) (7) . Therefore, the target period tb in the timer 7a is set with (tb - t - tp) . In the step (9) , thus repeating the track-by-track speed controls, the beam spot arrives at the track prior next to the destination track, and then it is discriminated that D = 0. Now, MPU 7 instructs the deceleration of the lens to stop. That is, observing the track zero-cross signal TZCS, MPU 7 discriminates whether a fall transition, i.e. from "1" to "0", of the track zero-cross signal TZCS, takes place indicating a timing to begin the lens deceleration. The fall transition in the track zero-cross signal TZCS indicates that the the beam spot crosses to an adjacent track. On detecting the fall transition of the track zero-cross signal TZCS, MPU 7 outputs the lens reversing signal RVS so as to start the lens deceleration; sets a complement of the predetermined deceleration period tb in the timer 7a; and then initiates the timer 7a. When the timer 7a counts up, i.e. the period tc is counted, MPU 7 disables the lens reversing signal RVS and outputs the servo-on signal SVS, then the track jumping is terminated after a predetermined adjusting period has elapsed. That is to say, the second switch 382 of the driving circuit 38 is enabled for the period tc; the deceleration voltage -Vc is applied to the adder amplifier 480 for the period tc; a deceleration current as a track driving current TDV is applied from the power amplifier 39 to the track actuator 21 for the period tc; and accordingly the lens, i.e. the beam spot, is decelerated to stop. Then, the servo switch 35 is enabled to close the servo loop of the tracking error signal TES; the track driving current TDV according to the control signal TCS of the phase compensation circuit 33 is applied from the power amplifier 39 to the track actuator 21; accordingly, the fine tracking servo control is started. When this servo switch 35 is enabled, the beam spot is located on the destination track and its speed is zero; therefore, the track servo control can be smoothly started. Though in the description of the preferred embodiment of the track-by-track speed control the lens lock is kept disabled, the track-by-track speed control can be also ■ achieved while the lens lock is kept enabled. This is ' because the lens lock is weaker than the signal of the lens seek. For a case where the lens lock is mechanically made with a spring or a rubber damper, there is no way to disable the lens lock. Details of the timing chart of FIGs. 15 is hereinafter described. FIGs. 15 show waveforms when a track-jumping carried out from track 10a to the fifth-next track lOf. At first, disabling the fine tracking servo; outputting the lens forwarding signal FWR; the acceleration current is applied for the period tah so that the beam spot reaches the target speed Vh. Next, a time interval T, between the second and third rise transitions of the track zero-cross signal TZCS is measured by enabling the timer 7a so that the actual speed is obtained, and then is compared with the target period tbh which corresponds to the target speed Vh. If tbh > T, , it means the actual speed is faster than the target speed Vh according to the step (6) ; therefore, the lens reversing signal RVS is output for the period t which corresponds to the speed difference (tb - T,) ; accordingly, a deceleration current is applied to the actuator coil 21 for the period t so as to retard the actual speed to , the target speed Vh. Next, it is attempted to measure the interval between the third and fourth rise transitions of the track zero-cross signal TZCS; however, the measurement of the interval after the the third rise transition of the track zero-cross signal TZCS is impossible because the track-by-track speed control (the steps (5), (6) and (7)) is being carried out after the third rise transition of the track zero-cross signal TZCS as mentioned above. Therefore, after entering the track-by-track speed control, the timer 7a is enabled; the interval till the fourth rise transition is measured; and the target period tb is set (tb - t - tp) in order to meet this interval. In this example, this interval 2 is equal to the target period tb (= tb - t -tp) ; therefore, an acceleration/deceleration is not actually carried out according to the step (5) . In a similar way, the track-by-track speed control is carried out between the fourth and fifth rise transitions. In this case the interval T 3 is larger than (tb - t -tp) , i.e. the actual speed is slower than the target speed Vh; therefore, an acceleration is carried out for the period t. Thus, when the beam spot controlled at the high target speed Vh arrives at the (n - 4) th track (lOn - 4) , the target speed is switched to the low target speed VI, because the beam spot is now close to the destination track. Further in a similar way, at the (n - 3) th and (n - 2) th rise transitions of the track zero-cross signal TZCS the track-by-track speed control is carried out at the low target speed VI. deceleration current is applied for a period tc in synchronization with the n-th fall transition of the track zero-cross signal TZCS so as to decelerate the lens (i.e. the beam spot) to stop. Immediately after this, the fine tracking servo control is enabled. The track jump number D is also renewed by the rise transition of the track zero-cross signal TZCS. Track jumping toward the outer direction is almost the same as those mentioned above in the steps (2) to (9) for the inner-ward jump, because the difference is only in that the direction is reversed. That is, all the procedures are carried out in the same way as those for the jump toward the inner direction except: the lens forwarding signal FWR via the forward switch 381 is replaced by the lens reversing signal RVS via the reverse switch 382 in step (2) and (5) ; and the lens reversing signal RVS via the reverse switch 382 is replaced by the lens forwarding signal FWR via the forward switch 381 in the steps (6) and (9); the detection of the rise transitions of the track zero-cross signal TZCS in the steps (3) and (4) are replaced by the detection of the fall transitions; and the discrimination of TZCS = 0 in step (9) is replaced by the discrimination of TZCS = 1. As described above, the beam spot BS, after being initiated the acceleration, is controlled at the high target speed Vh, thus the beam spot travels at the possible highest speed; and decelerated to a low target speed VI, which is easy for the beam spot to surely stop, in the vicinity of the destination track, then the beam spot is surely positioned at the destination track, while the long distance quick track jump is achieved without stopping at each track. For the case where a great number of tracks, for example a thousand tracks, are to be jumped, a prior art jumping requires 40 ms for the coarse seek (carriage seek) including the period required for entering the fine tracking servo, 1 ms for the confirmation by reading the track ID, and 6 ms for a fine seek (lens seek) for 20 tracks, consequently 47 ms in total; however, according to the present invention an accurate track jump is achieved with 2 ms for the 10 tracks of the lens seek acceleration, 30 ms for the coarse seek, and 6 ms for the 20 tracks of the lens seek deceleration, consequently 38 ms in total, without requiring the 1 ms for the confirmation by reading the track ID. The track-by-track speed control is carried out, as described already, by measuring the time interval between rise transitions of the track zero-cross signal TZCS. This speed control, i.e. the measurement of the time interval, is carried out easily with an addition or modification of a program without modifying the hardware. Because the actual speed is compared with the target speed according to the target period loaded in the memory, the compared result is given from the existance of the count-up signal. Therefore, the complicated comparison procedure is simplified to reduce the process steps, resulting in a fast operation. Thus, the track-by-track speed control of the present invention is beneficial in the access of less than about a hundred of tracks. Though in the above-described embodiment the target speeds are set with two speeds, high and low, the target speeds can be set with more than two speeds. Furthermore, the target speed can be a single speed as long as the beam spot can stop surely at the destination track without being effected by the eccentric movement of the tracks. Though in the above-described embodiments the tracking error signal TES is generated by means of a push-pull method, other known method may be of course used to generate the tracking error signal. Though in the above-described embodiments the detection of the beam spot speed difference is carried out by loading the timer 7a with a target period, the detection of the beam spot speed difference can be carried out also by measuring a time interval of the transitions in the track zero-cross signal TZCS by the timer 7a and then comparing it with the target period. Furthermore, the timer can be constituted with a software timer. Or, the gain of the feedback loop of the speed control during the track jump may be varied. Though in the above-described embodiments the explanations are made with the cases where the fine tracking servo control is carried out by moving a lens along the radial direction of the tracks, it is apparent that the present invention can be applied to a fine tracking servo of a galvano mirror type. Though in the above-described embodiments the embodiments are made using a positive logic; however, it is apparent that a negative logic is also applicable to an embodiment of the present invention. Though the descriptions are made for the optical disk apparatus the present inventions are applicable to an optical card apparatus, etc., using an optical memory media having a known track, and not only to a reflection type but also to a transparent type as well.

Claims: - 44 - CLAIMS 1. A method of track jumping of a plurality of coaxial or spiral recording tracks on a recording medium of an optical recording apparatus having: fine tracking means for moving a light beam spot on the recording medium, along essentially radial directions of the tracks; carriage means capable of moving along an essentially radial direction of the tracks, having said fine tracking means installed thereon, said fine tracking means movable on said carriage means over said tracks along essentially radial direction of the tracks; light detecting means for detecting a light reflected from said recording medium so as to generate a tracking error signal; fine tracking control means capable of servo controlling said beam spot by moving said fine tracking means on said carriage means according to said tracking error signal for said beam spot to trace a particular one of said tracks; carriage tracking control means for moving said carriage means; and position servo means for keeping said fine tracking means at a neutral position on said carriage means by moving said carriage means according to a position signal, said position signal becoming zero when said fine tracking means is at said neutral position and becoming positive or negative when deviating from said neutral position to one direction or to the opposite direction respectively, comprising the steps of: (1) accelerating said beam spot by accelerating said fine tracking means until speed of said beam spot exceeds an absolute radial speed of the eccentric tracks, while said fine tracking servo controlling of said beam spot is disabled and said position servo means is kept enabled; (2) further accelerating said beam spot by moving said carriage means; (3) decelerating said beam spot by decelerating said carriage means until speed of said beam spot reaches a predetermined speed below which said fine tracking control is possible; (4) counting a number of zero crossings in said tracking error signal since the track jumping is initiated, whereby the track number where said beam spot is currently located is acquired; and (5) decelerating said beam spot by decelerating said fine tracking means on said carriage means according to a difference of said counted number of crossed tracks and instructed number of track jumping to reach a destination track where said beam spot is to stop. 2. A method according to claim 1, wherein the step (1) further comprising the sub-steps of: (1) measuring a time interval between zero-crossings in said tracking error signal, for each track-crossing, while said beam spot is moving; (2) obtaining a time difference between said time interval of zero crossings and a first predetermined time interval which corresponds to a predetermined speed faster than said absolute radial speed of said eccentric tracks; and (3) accelerating or decelerating said beam spot by accelerating/decelerating said fine tracking means according to said time interval difference so as to make said time interval of said zero crossings essentially equal to said first predetermined time interval, without stopping said beam spot at each track . 3. A method according to claim 1, wherein the step (5) further comprising the sub-steps of: (1) measuring a time interval between zero-crossings in said tracking error signal, for each track-crossing, while said beam spot is moving; (2) obtaining a time difference between said time interval of zero crossings and a second predetermined time 'interval; and (3) accelerating or decelerating said beam spot according to said time difference so as to make said time interval of said zero crossings essentially equal to said second predetermined time interval, without stopping said beam spot at each track. 4. A method according to claim 2 or 3, wherein said time interval between zero-crossings in said tracking error signal is measured by an interval of adjacent two same-type transitions of zero-crossings, said transition being from one polarity to an opposite polarity, said zero-crossings being generated when said beam spot passes centre of each track. 5. A method according to claim 3, further comprising the steps of: repeating the steps (1) through (3) with respectively renewed predetermined time interval and a renewed instructed track, said renewed predetermined time interval being longer than the previous predetermined time interval, said renewed instructed track being closer to said destination track than the previously instructed track. 6. A method according to claim 5, wherein a finally predetermined time interval is chosen long enough, and a finally instructed track is chosen near enough to said destination track, for said lens means to be able to stop surely at said destination track. 7. A method according to claim 1, wherein the step (3) is carried out until said beam spot arrives at a track whose track number is calculated, by a program prepared in advance, according to a track number instructed to jump. 8. A method according to claim 7, wherein said number of tracks up to which the step (2) is continued is programmed to be approximately half of said track number instructed to jump. 9. A method according to claim 1 or 3, wherein the step (5) is carried out while said position servo means is enabled. 10. A method of track jumping of a plurality of coaxial or spiral recording tracks on a recording medium of an optical apparatus having: fine tracking means for moving a beam spot on the recording medium, along essentially radial directions of the tracks; carriage means capable of moving along an essentially radial direction of the tracks, having said fine tracking means installed thereon, said fine tracking means movable on said carriage means over said tracks along essentially radial direction of the tracks; light detecting means for detecting a light reflected from said recording medium so as to generate a tracking error signal; fine tracking control means capable of servo controlling said beam spot by moving said fine tracking means on said carriage means according to said tracking error signal for said beam spot to trace a particular one of said tracks; and carriage tracking control means for moving said carriage means. comprising the steps of: (1) accelerating said carriage means while enabling said fine tracking control means for said beam spot to keep a start track at which said beam spot is located when the track jumping is instructed; (2) disabling said fine tracking control means, when said position signal reaches a predetermined level, whereby said fine tracking means returns to said neutral position and said beam spot crosses said tracks; (3) further accelerating said beam spot by further accelerating said carriage means until said beam spot reaches a preprogrammed track; (4) decelerating said beam spot by decelerating said carriage means until speed of said beam spot reaches a predetermined speed below which said fine tracking control is possible; (5) counting a number of zero crossings in said tracking error signal since the track jumping is initiated, whereby the track number where said beam spot is currently located is acquired; and (6) moving said beam spot by moving said fine tracking means on said carriage means according to a difference of said counted number of crossed tracks and instructed number of track jumping so as to reach a destination track where said beam spot is to stop. 11. A method according to claim 10, wherein the step (6) further comprising the sub-steps of: (1) measuring a time interval between zero-crossings in said tracking error signal, while said beam spot is moving, for each track; (2) obtaining a time difference between said time interval of zero crossings and a second predetermined time interval; and (3) accelerating or decelerating said beam spot according to said time difference so as to make said time interval of said zero crossings essentially equal to said second predetermined time interval, without stopping said beam spot at each track. 12. A method according to claim 10 or 11, wherein said time interval between zero-crossings in said tracking error signal is measured by an interval of adjacent two same-type transitions of zero-crossings, said transitions being from one polarity to an opposite polarity, said zero-crossings being generated when said beam spot passes centre of each track. 13. A method according to claim 11, further comprising the steps of: repeating the steps (1) through (3) with respectively renewed predetermined time interval and a renewed instructed track, said renewed predetermined time interval being longer than the previous predetermined time interval, said renewed instructed track being closer to said destination track than the previously instructed track. 14. A method according to claim 13, wherein a finally predetermined time interval is chosen long enough, and a finally instructed track is chosen near enough to said destination track, for said lens means to be able to stop surely at said destination track. 15. A method according to claim 10, wherein the step (2) is continued until said beam spot arrives at a track whose track number is calculated, by a program prepared in advance, according to a track number instructed to jump. 16. A method according to claim 15, wherein said number of tracks up ?o which the step (3) is carried out is programmed to be approximately half of said track number instructed to jump. 17. A method according to claim 10 or 11, wherein the step (6) is carried out while position servo means is enabled, said position servo means keeping said fine tracking means at a neutral position on said carriage means by moving said carriage means according to a position signal, said position signal becoming zero when said fine tracking means is at said neutral position on said carriage means and becoming positive or negative when deviating from said neutral position to one direction or to the opposite direction respectively. 18. A method of controlling track jumping of a plurality of recording tracks on a recording media of an optical recording apparatus having: fine tracking means for moving a light beam spot on the recording media essentially along radial directions of the tracks, said fine tracking means being movable on a carriage; light detecting means for detecting a light reflected from said beam spot so as to generate a tracking error signal; and fine tracking control means capable of servo controlling said beam spot by moving said fine tracking means on said carriage according to said tracking error signal for said beam spot to trace a particular one of said tracks, comprising the steps of: (1) measuring a time interval between zero crossings in said tracking error signal, for each track-crossing, while said beam spot is crossing to each adjacent track; (2) obtaining a time difference between said time interval of zero crossings and a first predetermined time interval; and (3) accelerating or decelerating said beam spot by accelerating or decelerating said fine tracking means on said carriage according to said time difference, so as to make said time interval of said zero crossings essentially equal to said first predetermined time interval, without stopping said beam spot at each track. 19. A method according to claim 18, further comprising the sub-steps of: repeating steps (1) through (3) with said predetermined time interval renewed. 20. A method according to claim 18 or 19, wherein the steps are carried out while said carriage is stationarily fixed. 21. A method according to claim 18 or 19, wherein the steps are carried out while position servo means is enabled, said position servo means keeping said fine tracking means at a neutral position on said carriage means by moving said carriage means-according to a position signal, said position signal becoming zero when said fine tracking means is at said neutral position on said carriage means and becoming positive or negative when deviating from said neutral position to one direction or to the opposite direction respectively. 22. A method according to claim 18 or 19, wherein said time interval between zero-crossings in said tracking error signal is measured by an interval of adjacent two same-type transitions of zero-crossings, said transition being from a first polarity to an opposite polarity, said zero-crossings being generated when said beam spot passes centre of each track. 23. A method according to claim 18 or 19, wherein a finally predetermined time interval is chosen long enough, and a finally instructed track is chosen near enough to said destination track, for said fine tracking means to be able to stop surely at said destination track.

Inventors: YANAGI SHIGENORI, YANAGI, SHIGENORI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1988
Main classification: G11B7
IPC codes: G11B7