A disc reproducing apparatus and method

Abstract: A disc reproducing apparatus, such as a disc player, and a disc reproducing method in which seek time can be shortened at the time of traverse of a pick-up, by calculating, before the pick-up is traversed, a linear speed at a read position of a disc before the change of the read position and the target linear speed after the change of the read position, controlling the rotational speed of a rotation driving unit before the change of the read position so that the linear speed at the read position after the change falls within a maximum reproduction linear speed.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc reproducing apparatus, such as a disc player, and a disc reproducing method. It more particularly relates to a disc reproducing apparatus preferred for use in reproduction of a CD-ROM utilised as a storage medium for storing data and programs. 2. Description of the Related Art In a conventional CD-ROM player, the rotation speed of the CD-ROM disc has been controlled at a target rotational speed of the spindle servo control system set to a frequency of 7.35kHz of the frame synchronisation signal or a whole multiple of the same. Further, it becomes possible to read the data from the disc, after a traverse, only after the spindle rotational speed approaches the target value and enters into the capture range of a PLL (Phase Locked Loop) circuit. Therefore a certain degree of time is necessary from when an optical pick-up (hereinafter simply referred to as a pick-up) reaches the read position of the next data to when it becomes possible to read the data. Thus, conventional CD-ROM players suffer from the disadvantage that seek time is considerably prolonged. More specifically, the linear velocity Va at the position A is Ra/Rb times the linear velocity Vb at a position B where the radius at the position A and the linear velocity after the traverse of the pick-up are Ra and Va and the radius at the position B and the linear velocity before the traverse of the pick-up are Rb and Vb. On the other hand, the ratio of radius of the position A and position B becomes a maximum (and the ratio of linear velocities a maximum) in a case where the position A is on the outermost circumference and the position B is on the innermost circumference and becomes 2.52 times for a standard CD-ROM. For example, in a case where 8 times speed reproduction which is 8 times speed to a normal reproduction speed is carried out at the innermost circumference, then the pick-up is traversed to the outermost circumference for the reproduction, the reproduction speed corresponds to 20.16 times speed at the instant of movement. Namely, there is generally a margin of safety in the reproduction speed of several tens of percent. The above reproduction speed largely exceeds the permissible range, therefore no data can be read until the linear velocity of the pick-up relative to the disc after the traverse to the outermost circumference is lowered to the maximum reproduction linear velocity, which leads to a considerable elongation of the seek time. EP-A-0 123 946 describes a disc reproducing apparatus according to the precharacterising clauses of claims 1 and 9. SUMMARY OF THE INVENTION An object of the present invention is to provide a disc reproducing apparatus and method in which the seek time can be greatly shortened. According to the present invention, there is provided a disc reproducing apparatus comprising: a rotation driving means for rotating a disc; a reading means for reproducing recorded information of said disc; a rotation servo means for detecting a speed difference between a rotational speed of said disc detected from the read signal of said reading means and a target rotational speed, generating a clock having a frequency corresponding to the linear reproduction speed of the disc detected from the read signal of the reading means, detecting a phase difference between the generated clock and a reference clock, and outputting a command signal in response to the phase difference to said rotation driving means to control the rotational speed of the disc; a linear speed detecting means for detecting a linear speed at a read position of said disc based on the read signal of said reading means; and a control means adapted, upon reception of a signal indicating that a change in the read position on the disc of the reading means is desired, to monitor the linear speed obtained at said linear speed detecting means whereby to determine the rotational speed of the disc and to control the rotational speed of said disc before the change of the read position so that the linear speed at the read position after the change of the read position does not exceed a selected value; characterised in that said selected value is the maximum reproduction linear speed of the disc reproducing apparatus. Preferably, the rotation servo means has a first frequency dividing means for dividing, by a variable frequency division ratio, the frequency of the clock having a frequency in response to the speed difference between the rotational speed of the disc detected from the read signal of the reading means and the target rotational speed, a second frequency dividing means for dividing the frequency of the reference clock by the variable frequency division ratio, and a phase comparing means for detecting the phase difference of the frequency-divided outputs of the first and second frequency dividing means; and the control means performs the control of the rotational speed of the disc by changing the frequency division ratio of the first and second frequency dividing means in response to the linear velocity obtained from the linear velocity detecting means. Preferably, the reading means includes an optical pick-up which is freely movable in the radial direction; and the rotation servo means has a modulation circuit for modulating the read signal of the optical pick-up, outputting the modulated signal, a demodulation circuit for demodulating the modulated signal, outputting the demodulated signal, a servo signal processing circuit for detecting a speed difference between a rotational speed of the disc detected from the reproduction frame synchronisation signal of the demodulation signal and a target rotational speed, outputting the servo error signal in response to the speed difference, a clock generating circuit for generating a clock having a frequency in response to the servo error signal from the servo signal processing circuit, a first frequency dividing circuit for dividing the frequency of the clock which is outputted from the clock generating circuit, a second frequency dividing circuit for dividing the frequency of a reference clock, and a phase comparing circuit for detecting the phase difference of the frequency-divided outputs of the first and second frequency dividing circuits. Preferably, the modulation circuit performs eight to fourteen modulation. Preferably, the linear velocity detecting means counts the number of cycles of said clock having a frequency in response to the speed difference between the rotational speed of the disc detected from the read signal of the reading means and the target rotational speed, for a predetermined period; and the linear velocity is detected from the counted number of clock cycles. Preferably, the linear velocity detecting means includes a counter circuit for counting, for a predetermined period, the number of cycles of said clock having a frequency in response to the speed difference between the rotational speed of the disc detected from the read signal of the reading means and the target rotational speed, a load circuit for reading out the number of clock cycles of the counter circuit, loading the number of clock cycles, and an output circuit for reading out the number of clock cycles of the load circuit, converting the number of clock cycles to serial data, and outputting the data to the control means. Preferably, the control means receives the linear velocity before the change of read position, calculates a radius position and rotational speed at this position from the read signal of the reading means, determines a target linear velocity at the target position, the target linear velocity being defined within a range of the maximum reproduction linear velocity based on the radius position of the target position, finds the target rotational speed of the disc after the change of the read position from the target linear velocity and the radius of the target position, and controls the rotation driving means so that the rotational speed of the disc is changed, notably lowered, to the target rotational speed before the change of position is ended upon receiving the change of the read position on the disc of the reading means. Preferably, the control means estimates the total amount of the reduction of the rotational speed which can be performed during changing the read position, calculates the amount of the reduction of the rotational speed which is required before starting the change of the reading position, and controls the rotation means in response to the total amount of the reduction and the amount of the reduction before starting the change of the read position and during changing the read position. According to the present invention, there is provided a method of reproducing data from a disc, comprising the steps of measuring the linear velocity at a read position of the disc before a change of the read position; determining a target linear velocity after the change of read position; controlling the rotational speed of the disc before the change of the read position so that the linear velocity at the read position after the change falls within a maximum reproduction linear velocity; and changing the read position. In the disc reproducing apparatus and method according to the present invention, the linear velocity of the disc at the read position is obtained from the read signal of the reading means during reproduction, by the linear velocity detecting means. Here, when the reading means moves, it is decided whether or not the linear velocity at the read position after the change exceeds the maximum reproduction linear velocity of the disc player based on the linear velocity detected by the above linear velocity detecting means. Where it exceeds the maximum reproduction linear velocity, control is performed so as to reduce the rotational speed of the rotation driving means so that the linear velocity at the read position after the change falls within the maximum reproduction linear velocity. Then, after the linear velocity at the read position after the change falls within the maximum reproduction linear velocity, the read position is changed. By this means, when the change of the read position is completed, the reproduction enable state is reached at the read position, so it becomes unnecessary to wait until the linear velocity at which reproduction is possible is obtained. This means that the seek time of the reading means is shortened. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and features of the present invention will be described more in detail with reference to the accompanying the drawings, in which: Fig. 1 is an explanatory view of an embodiment of a disc player according to the present invention; Fig. 2 is an explanatory view of an example of the configuration of a speed detector, Figs. 3A to 3K are timing charts of the speed detector shown in Fig. 2; and Fig. 4 is a flowchart showing a processing procedure in a controller of the disc player shown in Fig. 1 DESCRIPTION OF THE PREFERRED EMBODIMENT A detailed explanation will now be made of an embodiment of the disc player according to the present invention by referring to the drawings. Figure 1 is a view of the configuration of the first embodiment of a disc player according to the present invention. In Fig. 1, a disc 1 such as a CD or CD-ROM is driven to rotate, by a spindle motor 2, and the recorded information thereof is read by an optical pick-up (hereinafter simply referred to as a pick-up) 3. The pick-up 3 is constituted by a laser diode 4, an object lens 5 which converges the laser beam emitted from this laser diode 4 onto the signal recording surface of the disc 1 as an information reading beam spot, a polarised beam splitter 6 for changing the direction of advance of the reflected light beam from the disc 1, a photodetector 7 which receives this reflected beam, etc. The pick-up is arranged so that it can freely move in the radial direction of the disc by using a sled feed motor (not illustrated) as the driving source. In the pick-up 3, although not illustrated, there are further housed a tracking actuator which moves the information reading beam spot in the radial direction of the disc with respect to the recording tracks of the disc 1 and a focus actuator which moves it in the direction of the light axis of the object lens 5. The output signal of this pick-up 3 is converted from a current signal to a voltage signal at an I (current)/V (voltage) amplifier 8 and further waveform-shaped at an RF equalising circuit 9 and then supplied to a phase locked loop (PLL) asymmetry correction circuit 11 and an optical servo signal processing circuit 22. In the PLL asymmetry correction circuit 11, the correction of asymmetry is carried out, a binary EFM signal is obtained and, at the same time, continuous clock pulses are generated by the PLL structure based on the edge of this binary signal. Here, asymmetry means a state where the centre of the eye pattern of the RF signal is deviated from the centre of the amplitude. On the other hand, the optical servo signal processing circuit 22 is a circuit for controlling the servo systems in relation to the operation of the pick-up 3, that is, a tracking servo system for making the information reading beam spot follow the recording track of the disc 1, a focus servo system for making the beam spot constantly converge onto the signal surface of the disc 1, and a sled servo system for performing the positional control in the disc radial direction of the pick-up 3. The optical servo signal processing circuit 22 is arranged such that a tracking error signal detected by a well known detection method, such as the three beam method, is supplied to a tracking actuator, a focus error signal detected by a well known detection method, such as the astigmatism method, is supplied to a focus actuator, and an error signal obtained by integrating, for example, a tracking error signal is supplied to a sled feed motor. Next, the EFM signal from the PLL asymmetry correction circuit 11 is demodulated at an EFM demodulation circuit 12 to yield the demodulated data and the parity for error correction and detection. At the same time, the sub-code just behind the frame synchronisation signal is demodulated. This sub-code is supplied to a controller 20 through a sub-code processing circuit 13. The controller 20 is constituted by a CPU. The data after the EFM demodulation is first stored in a RAM 14, then is corrected for error based on the error correction and detection parity, by an error correction circuit 15. The data after the error correction is deinterleaved from the CIRC (Cross Interleave Reed-Solomon Code) at a deinterleave circuit 16 and output as CD-ROM data at the time of CD-ROM reproduction and output as audio data of L/Rch at the time of audio CD reproduction. Here, the spindle servo signal processing circuit 18 is a circuit which detects the difference of the rotational speed of the spindle motor 2 (hereinafter simply referred to as the spindle rotational speed) with respect to the target rotational speed based on the reproduction frame synchronisation signal from the disc 1 among the signals output from the deinterleave circuit 16 and outputs a servo error signal in accordance with this speed difference. Then, the servo error signal from the spindle servo signal processing circuit 18 is supplied via an LPF (low pass filter) 23 to a VCO (voltage controlled oscillator) 24 as the control signal thereof. The oscillated output VCOCK of this VCO 24 becomes one input of a change-over switch 25. The change-over switch 25 receives as its other input a fixed clock of for example 16.9344 MHz (44.1 kHz x 384) generated at a crystal oscillator 26 and is controlled to switch by a signal α from the controller 20 thereby to select either the oscillated output VCOCK of the VCO 24 or the fixed clock of 16.9344 MHz, and supply the same to a clock generator 17. The clock generator 17 generates a system clock of a fixed frequency when the fixed clock of the crystal oscillator 26 is supplied, and generates a system clock whose frequency changes in accordance with the oscillated output VCOCK of the VCO 24 when the oscillated output VCOCK of the VCO 24 is supplied. Further, the oscillated output VCOCK of the VCO 24 is divided by M by a 1/M frequency divider 27 and becomes one input of a phase comparator 28. Further, the fixed clock of the crystal oscillator 26 is divided by N by a 1/N frequency divider 29 and becomes the other input of the phase comparator 28, serving as the reference clock. Note that, the frequency division values M and N are variables which can be made to take any values and are set to appropriate values by the controller 20. The phase comparator 28 detects the phase difference between the frequency-divided output of the 1/M frequency divider 27 and the frequency-divided output of the 1/N frequency divider 29 and outputs a phase difference signal in accordance with this phase difference. This phase difference signal is supplied to a spindle driver 31 as the drive signal of the spindle 2, via the LPF (low pass filter) 30. In the above structure, when the change-over switch 25 selects the fixed clock of the crystal oscillator 26, the system clock becomes fixed to 16.9344 MHz. On the other hand, when the change-over switch 25 selects the oscillated output VCOCK of the VCO 24, this means that the system clock changes so that the servo error signal output from the spindle servo signal processing circuit 18 becomes zero. Namely, even if the rotational speed of the disc 1 is relatively loose, the system clock will change following the rotational speed thereof. Further, the oscillated output VCOCK of the VCO 24 is supplied to a speed detector 32. The speed detector 32 detects the linear velocity based on the output signal VCOCK since the linear velocity of the disc 1 is determined according to the oscillation frequency of the output signal VCOCK of the VCO 24 where the phase is synchronised (phase locked). Further, the speed detector 32 receives, in addition to the oscillated output VCOCK, a signal XTW obtained by dividing the frequency of the output clock XTAL of the crystal oscillator 26 by L. On the other hand, when reading the linear velocity detected by the speed detector 32, the controller 20 outputs a signal MCULD and a signal MCUCK to the speed detector 32. Linear velocity data MCUDT is generated based on these signals MCULD, MCUCK, XTW, and VCOCK and output to the controller 20. Here, Fig. 2 is a block diagram of an example of a circuit constituting the speed detector 32 for finding the linear velocity of the disc 1; and Figs. 3A to 3K are timing charts of the speed detector 32 of Fig. 2. The speed detector 32 is constituted by, as shown in Fig. 2, flip-flops 3201 to 3206, an exclusive logical OR gate 3207, AND gates 3208 and 3209, an n bit counter 3210, an n bit register 3212, a NAND gate 3211, and a P/S register 3213. Here, where the settings of the frequency dividers 27 and 29 are made so that 1/M = 1/N = 1 stands and the oscillation frequency of the output clock XTAL of the crystal oscillator 26 is set to 16.9344 MHz, when the spindle 2 performs single speed reproduction, the oscillation frequency of the VCO 24 becomes 16.9344 MHz, the same as that of the output clock XTAL of the crystal oscillator 26. Further, when double speed reproduction is carried out by setting M = 2 and N = 1, the spindle rotates at twice the speed and the oscillation frequency of the VCO 24 becomes double, i.e., 33.8688 MHz. Namely, the linear velocity can be found if it is known what multiple of the output clock XTAL of the crystal oscillator 26 the oscillation frequency of the VCO 24 has become. The circuit of Fig. 2 counts the oscillation frequency of the VCO 24 according to this principle. The input signal XTW shown in Fig. 3B is a signal obtained by dividing the frequency of the clock CK1 of the XTAL system shown in Fig. 3A by L. In the example of the timing chart of Fig. 3A to Fig. 3C, L is set to be equal to 14. The period from the point of change of this signal XTW to the next point of change becomes the period for counting the frequency. That is, during the period of the LD1 signal the number of pulses VCOCK of the VCO are counted. In the timing chart of Fig. 3A to Fig. 3F, 14 VCOCK cycles are contained in this section. It is seen from this that the spindle rotates at double speed. This count is loaded in the n bit register 3212 at the timing of LD1 of Fig 3D and the count is ended. The means for reading the result of the count is the FF circuit 3230 for loading the data of the P/S register 3213 in the controller 20. At the time of a read operation, the MCULD signal shown in Fig. 31 is input from the controller 20. By this, the LD2 signal shown in Fig. 3J is generated and the data is loaded in the P/S register 3213. Next, an MCUCK signal shown in Fig. 3G is input from the controller 20 for shifting out the data loaded from this P/S register 3213 to the MCUDT terminal. By this means, a clock signal CK2 shown in Fig. 3H is generated and input to the P/S register 3213. As a result, the linear speed data MCUDT will be output to the controller 20 from the MCUDT terminal. Next, an explanation will be made of the processing procedure of the controller 20 at the time of traverse of the pick-up 3 in the disc player constituted as described above, referring to the flowchart shown in Fig. 4. STEP S1: As shown in Fig. 4, in the controller 20, a linear speed Rb before the traverse is obtained from the speed detector 32. The radius Rb and rotational speed Tb of the disc 1 are calculated from the sub-code at the position analysed by the sub-code processing circuit 13. STEP S2: Next, a radius Ra at the target address is found from the value of the target address of the sub-code (absolute time after traverse), further the linear speed Va at the target address is determined within a range not exceeding the maximum reproduction linear speed of the system and the rotational speed Ta after the traverse is found from the linear speed Va and the radius Ra. Here, the maximum reproduction linear speed is determined according to the characteristic of the optical system and RF amplifier, restrictions of the digital signal processing speed, etc. Note that the reason why the linear speed Va at the target address is selected to be within a range not over the maximum reproduction linear speed of the disc player is to minimise the amount of deceleration at the traverse to thereby make the time required for deceleration as short as possible and thus achieve shortening of the seek time. After the rotational speed Ta is found, the spindle motor 2 is controlled so that the rotational speed of the disc 1 is lowered to the rotational speed Ta before the traverse is ended and the linear speed at the target address falls within the target linear speed Va. In the disc player shown in Fig. 1, of course the reproduction data cannot be read during the traverse. For this reason, by utilising the period during which the reproduction data cannot be read and making the amount of deceleration as large as possible and by performing the amount of deceleration which is still not sufficient before the traverse is started, the seek time is shortened. STEP S3: Namely, the difference between the rotational speed Tb before the traverse and the rotational speed Ta after the traverse is the amount of the rotational speed which should be lowered. In this total amount of reduction of the rotational speed, the amount of reduction of the rotational speed T which can be performed during the traverse is estimated. To estimate this amount of reduction of the rotational speed T, first the time required for the traverse is estimated and the brake force to be applied on the spindle motor 2 necessary during the traverse is determined. The time required for the traverse can be determined approximately from the distance of movement before and after the traverse and the performance of the sled mechanism. Further, the brake force can be determined by, for example, the magnitude of the voltage applied in the brake mode of the driver 31. Then, the time of application of the voltage in the brake mode of the driver 31 is made the time required for the traverse, whereby the brake force to be applied to the spindle motor and the time of application time of the brake force are determined. STEP S4: As a result of the above step S3, the amount of reduction of the rotational speed T which can be performed during the traverse can be estimated. STEP S5: Next, the amount of reduction of the rotational speed T" necessary before the traverse is calculated, being the value obtained by subtracting the amount of reduction of the rotational speed T which can be performed during the traverse from the amount of reduction of the rotational speed (Tb - Ta) necessary before and after the traverse. STEP S6: Then, by subtracting the amount of reduction of the rotational speed T" necessary before the traverse from the actual rotational speed Tb before the traverse, the value Tb" at which rotational speed should be controlled before the traverse is found. STEP S7: A corresponding linear speed Vb" is found from the rotational speed Tb" and constitutes the value at which linear speed should be controlled before the traverse. STEP S8: Then, the frequency division values M and N of the 1/M frequency divider 27 and the 1/N frequency divider 29 are set so that this linear speed Vb" is obtained. STEPS S9 and S10: The controller 20 repeats the count until the actual reproduction linear speed Vb becomes this set linear speed Vb". STEP S11: When the actual reproduction linear speed Vb becomes this set linear speed Vb", the traverse is started. By performing the above processing, when the pick-up 3 is traversed and moved to the read position of the next data, the data can already be read out, so it becomes unnecessary to wait a time for the rotational speed of the disc 1 to fall, and it becomes possible to shorten the seek time. In the above description, as one of embodiments of the disc reproduction apparatus according to the present invention, a CD-ROM player was described, but, the present invention can be applied to a variety of disc reproduction apparatuses. For example, in Fig. 1, the CD-ROM 1 can be a disc recording medium storing data, and the EFM demodulation circuit 12 can be any suitable demodulation circuit for demodulating data stored in the disc, and the controller 20 can be a suitable controller for controlling such disc reproducing apparatus.

Claims: A disc reproducing apparatus comprising: a rotation driving means (31) for rotating a disc (1); a reading means (3) for reproducing recorded information of said disc; a rotation servo means (18) for detecting a speed difference between a rotational speed of said disc detected from the read signal of said reading means and a target rotational speed, generating a clock (VCOCK) having a frequency corresponding to the linear reproduction speed of the disc detected from the read signal of the reading means, detecting a phase difference between the generated clock and a reference clock (XTAL), and outputting a command signal in response to the phase difference to said rotation driving means to control the rotational speed of the disc; a linear speed detecting means (32) for detecting a linear speed at a read position of said disc based on the read signal of said reading means; and a control means (20) adapted, upon reception of a signal indicating that a change in the read position own the disc of the reading means is desired, to monitor the linear speed obtained at said linear speed detecting means (32) whereby to determine the rotational speed of the disc and to control the rotational speed of said disc before the change of the read position so that the linear speed at the read position after the change of the read position does not exceed a selected value; characterised in that said selected value is the maximum reproduction linear speed of the disc reproducing apparatus. A disc reproducing apparatus as set forth in claim 1, wherein: said rotation servo means has a first frequency dividing means (27) for dividing by a variable frequency division ratio the frequency of the clock (VCOCK) having a frequency cornesponding to the reproduction linear speed of the disc detected from the read signal of said reading means, a second frequency dividing means (29) for dividing the frequency of said reference clock by a variable frequency division ratio, and a phase comparing means (28) for detecting the phase difference of the frequency-divided outputs of said first and second frequency dividing means; and said control means (20) performs the control of the rotational speed of said disc by changing the frequency division ratio of said first and second frequency dividing means (27, 29) in response to the linear speed obtained from said linear speed detecting means (32). A disc reproducing apparatus as set forth in claim 1, wherein: said reading means includes an optical pick-up (3) which is freely movable in the radial direction; and said rotation servo means has a modulation circuit for modulating the read signal of said optical pick-up, outputting the modulated signal, a demodulation circuit (12) for demodulating the modulated signal and outputting the demodulated signal, a servo signal processing circuit (18) for detecting a speed difference between a rotational speed of said disc detected from the reproduction frame synchronisation signal of said demodulation signal and a target rotational speed, and outputting a servo error signal in response to the speed difference, a clock generating circuit (24) for generating a clock (VCOCK) having a frequency corresponding to thelinear reproduction speed of the disc detected from the read signalof the reading means, a first frequency dividing circuit (27) for dividing the frequency of the clock (VCOCK) which is outputted from said clock generating circuit, a second frequency dividing circuit (29) for dividing the frequency of a reference clock, and a phase comparing circuit (28) for detecting the phase difference of the frequency-divided outputs of said first and second frequency dividing circuits. A disc reproducing apparatus as set forth in claim 3, wherein: said modulation circuit performs eight to fourteen modulation. A disc reproducing apparatus as set forth in any previous claim, wherein: said linear speed detecting means (32) counts the number of clock pulses at said frequency in response to the speed difference between the rotational speed of said disc detected from the read signal of said reading means and the target rotational speed, for a predetermined period; and the linear speed is detected from the counted number of clock pulses. A disc reproducing apparatus as set forth in claim 5, wherein: said linear speed detecting means (32) includes a counter circuit (3210) for counting the number of clock pulses at said frequency in response to the speed difference between the rotational speed of said disc detected from the read signal of said reading means and the target rotational speed, for a predetermined period, a load circuit (3212) for reading out the number of clock pulses of said counter circuit, loading the number of clock pulses, an output circuit (3213, 3230) for reading out the number of clock pulses of said load circuit, converting the number of clock pulses to a serial data, and outputting the data to said control means (20). A disc reproducing apparatus as set forth in any previous claim, wherein: said control means (20) receives the linear speed before the change of read position, calculates a radius position and rotational speed at the position from the read signal of said reading means, determines a target linear speed at the target position, said target linear speed being defined within a range of the maximum reproduction linear speed of the disc reproducing apparatus based on the radius position of the target position, finds the target rotational speed of the disc after the change of the read position from the target linear speed and the radius of the target position, and controls said rotation driving means (31) so that the rotational speed of the disc is lowered to the target rotational speed before the change of position is ended upon receiving the change of the read position on the disc of said reading means. A disc reproducing apparatus as set forth in claim 7, wherein: said control means (20) estimates the total amount of the reduction of the rotational speed which can be performed during changing the read position, calculates the amount of the reduction of the rotational speed which is required before starting the change of the reading position, and controls said rotation means (31) in response to the total amount of the reduction and the amount of the reduction before starting the change of the read position and during changing the read position. A method of reproducing data from a disc, comprising the steps of evaluating a linear speed at a read position of said disc before the change of a read position; determining a target linear speed after the change of a read position; controlling the rotational speed of said disc before the change of the read position so that the linear speed at the read position after the change does not exceed a selected value; and changing the read position; characterised in that said selected value is the maximum reproduction linear speed of the disc reproducing apparatus being used to reproduce data from the disc.

Inventors: SHIMIZUME KAZUTOSHI, SHIMIZUME, KAZUTOSHI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1997
Main classification: G11B19
IPC codes: G11B19, G11B7