GB2127176A - Disc players for reproducing information - Google Patents

Abstract

A disc player for reproducing from a disc 1 having a spiral record track thereon comprises a pick-up 2 for reading a signal recorded in the track, a stepping motor 5 driven by pulses to cause the pick-up 2 to have successive step movements along the radius of the disc 1 in response to the supplied pulses, a counter 8 which is cleared when the pick-up 2 is situated at the starting end of the track and produces first positional data representing the position of the pick-up 2 by counting pulses used for driving the motor 5, and a system control circuit 6 for producing second positional data representing a desired location on the disc 1, for obtaining resultant data corresponding to the difference between the first and second positional data, and for generating the pulses used for driving the motor 5 in response to the resultant data. <IMAGE>

Description

SPECIFICATION Disc players for reproducing information This invention relates to disc players for reproducing information from a disc-shaped record medium, such as a digital audio disc, and more particularly, to a disc player for reproducing information from a disc on which a signal modulated in response to the information is recorded in a spiral record track.

A digital audio disc is a rotatable disc having a spiral record track in which a digital signal modulated in response to digital data of an audio signal as programme information and other digital data is recorded in, for example, optically readable manner. The digital audio data are formed, for example, into a data format containing successive frame segments. The duration of each frame segment may, for example, be 136.1 microseconds and therefore the repetition frequency of one frame segment is 7.35 kHz. Each frame segment comprises a synchronizing portion containing frame synchronizing information, a sub-coding portion and a data portion.Each sub-coding portion is divided into eight channels P to W, and contains at the channel Q address information accompanying programme information in the data portion and forming a unit within each block segment which comprises ninty-eight frame segments.

The duration of each block segment is 13.3 miliseconds and therefore the repetition frequency of one block segment is 75 Hz.

Each address information unit which is formed with the address information provided at the channel Q in each of the frame segments forming one block segment, and is therefore obtained every 13.3 milliseconds, includes data representing a number for each programme information section, data representing a number for each part of one programme information section, time address information representing running time within each programme information section, which is expressed in minutes and seconds, and data representing a number for each block segment within each one second of running time. The above-mentioned duration of the frame segment, duration of the block segment and running time are measured when the disc player is operating in the normal reproduction mode.

With a digital audio disc, the innermost turn of the spiral record track usually acts as the starting end for reproduction and the outermost turn usually acts as a finishing end for reproduction. Accordingly, the digital signals recorded on the digital audio disc are read along the spiral record track in the direction from the innermost turn to the outermost turn when the disc player is operating in the nor mal reproduction mode. In the innermost turn of the spiral record track on the digital audio disc, time information representing the running time from the starting end to the beginning of each programme information section recorded in the spiral record track is recorded in the form of a table of contents (TOC).

A disc player for reproducing the programme information from the digital audio disc is able to reproduce the programme information selectively from any desired location on the disc using the address information and the TOC recorded thereon, and is accordingly arranged selectively to perform a search operation in which a desired location on the disc is searched for and the reading position of a pick-up device is moved to the searched desired location.

In the search operation as performed by previously proposed disc players, the reading position of the pick-up device is rapidly moved by a certain distance in the direction transverse to the spiral record track on the disc and is then controlled to trace the spiral record track to reproduce the address information therefrom in the normal reproducing mode, so that a location at which the reading position of the pick-up device is presently situated is detected by reproduced address information, and the distance from the detected location to the desired location on the disc is defined. This movement of the reading position of the pick-up device is repeated until the reading position of the pick-up device reaches the desired location.That is, the reading position of the pick-up device is controlled to move rapidly by the certain distance in the direction transverse the spiral record track and to trace the spiral record track in the normal reproducing mode alternately, so as to be moved quickly to reach the desired location on the disc in the search operation.

However, because each reproduction of address information to detect the location at which the reading position of the pick-up device is presently situated takes an appreciable time, the previously proposed disc player has the problem that the search operation cannot be performed very quickly. Moreover, the time required for the search operation is very dependent on the position of the pick-up device at the beginning of the search operation relative to the desired location.

According to the present invention there is provided a disc player for reproducing information from a disc having a spiral record track thereon, the disc player comprising: pick-up means for reading a signal recorded in the spiral record track on the disc; pick-up moving means to be driven by pulses supplied thereto to cause said pick-up means to have successive step movements along the radius of the disc in response to the supplied pulses; counter means arranged to be cleared when said pick-up means is situated at the starting end of the spiral record track on the disc and producing first positional data representing a position of said pick-up means on the disc by counting pulses used for driving said pick-up moving means; and system control circuit means including means for producing second positional data representing a location on the disc designated by a reading position designating signal, means for obtaining resultant data corresponding to the difference between the first positional data and the second positional data, and means for generating the pulses used for driving said pick-up moving means in response to the resultant data, said system control circuit means supplying the pulses generated thereby to said pick-up moving means to drive said pick-up moving means and thereby to shift the position of said pick-up means with the successive step movements so as to approach to the location on the disc designated by the reading position designating signal.

In embodiments of disc player according to the invention it is not necessary to reproduce the address information from the disc and carry out some process in accordance with the reproduced address information during the period in which the position of the pick-up means is moved by a stepping motor to approach to the location designated by the reading position designating signal in the search operation, and therefore the duration of such a period can be made very short. This results in the time required for the search operation becoming relatively short. Moreover, since the movement of the pick-up means by the stepping motor is achieved at high speed and the duration of the period for approaching the desired location is made almost constant regardless of the initial position of the pick-up means, the search operation can be performed within a relatively constant time.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an embodiment of disc player according to the invention; and Figure 2 is a flow chart used for explaining the operation of the embodiment of Fig. 1.

Fig. 1 shows an embodiment of optical disc player according to the invention, for reproducing information from a digital audio disc 1. The disc 1 has program information containing a plurality of sections recorded thereon, together with address information, in a spiral record track with a predetermined recording format and a TOC recorded in the innermost turn of the spiral record track, and is rotated at a predetermined rotational speed.

The spiral record track on the disc 1 is formed by, for example, an alignment of pits corresponding to a digital signal modulated by the program information and address information.

The digital signal is optically read from the spiral record track by an optical head 2 acting as a pick-up device. The optical head 2 causes a light beam, for example, of laser light to impinge on the disc 1 and receives the light beam modulated in intensity in response to the spiral record track on the disc 1 and reflected from the disc 1 by a photodetector contained therein to produce an output digital signal. Accordingly, a position on the disc 1 on which the light beam from the optical head 2 impinges defines the reading position of the optical head 2 on the disc 1. The optical head 2 further contains a tracking device for maintaining the light beam impinging on the disc 1 in correct tracking relation to the spiral record track being traced thereby.This tracking device is driven by a tracking control circuit 4 connected to an output end of a tracking error detecting circuit 3 in which a tracking error signal is obtained from the output of the photodetector contained in the optical head 2, so that tracking servo-control is performed.

The optical head 2 is moved by a stepping motor 5 in the direction of the radius of the disc 1, that is, the direction transverse to the spiral record track. The stepping motor 5 is driven by pulses from a motor control circuit 7, to which a pulse signal P, and a direction command signal Pd are supplied from output terminals t, and t2 of a system control circuit 6. A driving signal having its polarity determined in response to the polarity of the direction command signal Pd is supplied to the stepping motor 5 whenever a pulse of the pulse signal Ps is supplied to the motor control circuit 7.This means that the stepping motor 5 is driven in stepping manner substantially by the pulses forming the pulse signal P, to rotate in the direction determined by the direction command signal Pd. With the stepping rotation of the stepping motor 5, the optical head 2 is moved intermittently with successive step movements along the radius of the disc 1 in the direction from the innermost turn of the spiral record track to the outermost turn of the spiral record track or vice versa, depending on the positive or negative polarity of the direction command signal Pd. The optical head 2 advances across the disc 1 by a constant distance every one step movement, and moves from the innermost turn to the outermost turn or vice versa with, for example, four thousand successive step move ments.

An up-and-down counter 8 having a clock terminal CK, an up-and-down terminal U/D, a clear terminal CR and an output terminal CO is provided, and the pulse signal P5 and the direction command signal Pd from the system control circuit 6 are also supplied to the clock terminal CK and the up-and-down terminal U/D, respectively. The output of a reproduction starting end detector 9 is supplied to the clear terminal CR. The reproduction starting end detector 9 detects when the optical head 2 is situated at the starting end on the disc 1 by, for example, mechanically or optically contacting an engaging portion attached to the optical head 2, and produces the detection output.With this arrangement, the up-anddown counter 8 is cleared by the output from the reproduction starting end detector 9 when the optical head 2 is situated at the starting end for reproduction on the disc 1. It then counts up or down depending on the positive or negative polarity of the direction command signal Pd whenever a pulse of the pulse signal P5 is supplied thereto, and the stepping motor 5 is driven by the pulse signal Ps and the direction command signal Pd so as to cause the optical head 2 to have successive step movements.Accordingly, the output count obtained at the output terminal CO of the upand-down counter 8 represents the distance from the starting end on the disc 1 to a location on the disc 1 at which the optical head 2 is presently situated in the direction of the radius of the disc 1, and is therefore used as positional data dp representing the position of the optical head 2 on the disc 1. The positional data dp thus obtained at the output terminal CO of the up-and-down counter 8 are supplied to an input terminal n, of the system control circuit 6.

The output of the photodetector contained in the optical head 2 is supplied to a digital signal detecting circuit 10 and the digital signal read from the spiral record track on the disc 1 is obtained at the output end thereof.

This digital signal is supplied to a decoder 11, and reproduced programme information Sp, a reproduced output of address information contained in the aforementioned channel Q, that is, reproduced address information 0', and the reproduced TOC Toc are obtained from the decoder 11 when the disc player is operating in the normal reproduction mode. The reproduced programme information Sp is supplied to a programme information processing circuit 2 and a reproduced audio signal A is obtained at the output thereof. The reproduced address information Q' is supplied to a deciphering circuit 13, and time data TQ corresponding to the time represented by the time address information contained in the reproduced address information Q' are obtained from the deciphering circuit 13 and supplied to an input terminal n2 of the system control circuit 6.The reproduced TOC Toc is supplied to an input terminal n3 of the system control circuit 6 and memorized.

An output terminal t3 of the system control circuit 6 is connected to an input end of a jumping pulse generating circuit 14, and a jumping pulse P1 generated by the jumping pulse generating circuit 14 is supplied to the tracking control circuit 4. When the jumping pulse Pj is supplied to the tracking control circuit 4, the tracking device contained in the optical head 2 is driven in response to the jumping pulse Pj to move the reading position of the optical head 2 rapidly along a moving path transverse to the turns of the spiral record track, so that the reading position performs a track jump operation.In such track jump operation, the number of turns of the spiral record track jumped over by the reading position of the optical head 2 and the direction of the jumping movement are determined by the pulse width and polarity of the jumping pulse Pj, respectively. The output from the tracking control circuit 4 is also supplied through a low-pass filter 15 to an input termi- nal n4 of the system control circuit 6.

In addition, a command signal generating portion 16 is connected to an input terminal n5 of the system control circuit 6, and a selected command signal is supplied to the input terminal n5 of the system control circuit 6 from the command signal generating portion 16 when the latter is operated.

When the disc player performs the search operation, a reading position designating sig nal I, which is one of the command signals obtained from the command signal generating circuit 16, is supplied to the input terminal n5 of the system control circuit 6. The reading position designating signal I is arranged to designate a location on the disc 1 with, for example, a number for the programme infor mation section and time data.

The operation of the system control circuit 6 when the reading position designating sig nal I for the search operation is supplied thereto will now be explained, together with the operation of other circuits related to the system control circuit 6, with reference to the flow chart of Fig. 2.

Assuming that the location on the disc 1 defined by the number for the programme information section represents the Mth pro gramme information section, and the time address information representing x mintues and y seconds is designated by the reading position designating signal I, first, in a process C1, time data Tj representing the running #time within the reproducing distance from the starting end to the designated location in the normal reproduction mode are computed.In this computation, the running time of x0 min utes and y, seconds within the reproducing distance from the starting end for reproduction to the beginning end of the Mth pro gramme information section recorded in the spiral record track in the normal reproduction mode is obtained by utilizing the reproduced TOC Toc which has been previously supplied to the system control circuit 6 through the input terminal n3 and memorized therein.

Then the running time of X minutes and Y seconds in the reproducing distance from the starting end to the designated location in the normal reproduction mode is obtained by adding x minutes and seconds to x0 minutes and y, seconds. The data representing the running time of X minutes and Y seconds.

The data representing the running time of X minutes and Y seconds are used as the time data Tj.

Next, in a process C2, the time data Tj are converted into positional data dj of the same kind as the positional data dp obtained from the output terminal CO of the up-and-down counter 8. In general, the running time Tx in the reproducing distance from the starting end to a certain location on the disc 1 in the normal reproduction mode, and the distance Lx from the starting end to the certain location on the disc 1 along the radius of the disc 1 - satisfy the relation:: Lx=f(Tx)+ k where f(T5) is a function of Tx, and k is a constant, and accordingly the distance Lj corresponding to the time data Tj is obtained in accordance with this relation, and then the positional data dj are obtained by representing the distance Lj with data of the same kind as the positional data dp.

In a process C3, the positional data dj are compared with the positional data dp supplied through the input terminal n, from the upand-down counter 8 to produce resultant data dj p corresponding to the difference between the positional data dj and dp. The resultant data dj p represent the distance from the position of the optical head 2 on the disc 1 to the designated location in the direction of the radius of the disc 1.In a process C4, the number of the pulses of the pulse signal P5 supplied to the motor control circuit 7 and the polarity of the direction command signal Pd also supplied to the motor control circuit 7 which are required for moving the optical head 2 to the designated location are computed in dependence on the resultant data di p. In a process C5, the pulse signal P5 containing the pulses of the number computed in the process C4, and the direction command signal Pd having the polarity computed in the process C4 are produced and supplied to both the motor control circuit 7 and the up-and-down counter 8 from the output terminals t1 and t2, respectively.

With the pulse signal P5 and direction command signal Pd thus supplied to the motor control circuit 7 and the up-and-down counter 8 from the system control circuit 6, the stepping motor 5 is driven to make rotational steps corresponding to the number of pulses forming the pulse signal P5 in the rotational direction determined in response to the polarity of the direction command signal Pd, and consequently the optical head 2 is given successive step movements corresponding to the number of pulses of the pulse signal P5 along the radius of the disc 1 in the direction from the starting end to the finishing end on the disc 1 or vice versa, determined in response to the polarity of the direction command signal Pd, so as to approach the designated location on the disc 1. Simultaneously with this, the up-and-down counter 8 counts up or down depending on the positive or negative polarity of the direction command signal Pd whenever a pulse of the pulse signal P5 is supplied thereto, to produce the positional data dp representing a position of the optical head 2 on the disc 1 newly taken after the successive step movements thereof.

Then, the disc player is set to operate in the normal reproduction mode, and in a process C6, the time data T, for the designated location on the disc 1 are compared with the time data TQ supplied through the input terminal n2 to produce resultant data T~ Q corresponding to the difference between the time data Tj and TQ. These resultant data T~ Q represent the difference between the reading position of the optical head 2 and the designated location on the disc 1.

In a decision D1, it is checked whether the time Ui~, represented by the resultant data T~ Q is shorter than or equal to a predetermined time U1, for example, one minute or not. If the time U~ Q represented by the resultant data Tri~, is longer than the predetermined time U1, the number of pulses forming the pulse signal P5 and the polarity of the direction command signal Pd which are required for moving the optical head 2 to the designated location are again computed in dependence on the resultant data To~,, in a process C7.

Then the pulse signal P5 containing the number of pulses computed in the process C7, and the direction command signal Pd having the polarity computed in the process C7 are produced and supplied to both the motor control circuit 7 and the up-and-down counter 8, in a process C8 With the pulse signal P5 and the direction command signal Pd supplied again to the motor control circuit 7 and the up-and-down counter 8 from the system control circuit 6, the stepping motor 5 is driven to make the number of steps corresponding to the number of pulses of the pulse signal P5 in the rotational direction determined in response to the polarity of the direction command signal Pd.

Consequently, the optical head 2 is given additional successive step movements corresponding to the number of pulses of the pulse signal P5 along the radius of the disc 1 in the direction from the starting end to the finishing end or vice versa, determined in response to the polarity of the direction command signal Pd, so as to approach to the designated location on the disc 1. In addition, simultaneously with this, the up-and-down counter 8 counts up or down depending on the positive or negative polarity of the direction command signal Pd whenever each pulse of the pulse signal P5 is supplied thereto, to again produce the positional data dp representing a position the optical head 2 on the disc 1 taken after the additional successive step movements thereof.

In a process Cg, the time data T; for the designated location on the disc 1 are again compared with the time data TQ to produce the resultant data T~ Q corresponding to the difference between the time data Tj and TQ.

Then, in a process C,O, the scale and direction of the track jump operation of the reading position by the optical head 2 which are required for causing the reading position to reach the designated location are computed in dependence on the resultant data T; Q. and a control signal J representing the computed scale and direction of the track jump operation is supplied to the jumping pulse generating circuit 14 from the output terminal t3.

On the other hand, if the time U~ Q repre- sented by the resultant data T; Q is shorter than or equal to the predetermined time U, as a result of the check in the decision D1, the process C7 the process C8 and the process C9 are omitted.

With the control signal J supplied from the system control-circuit 6, the jumping pulse generating circuit 14 produces the jumping pulse Pj and supplies it to the tracking control circuit 4. Consequently the reading position of the optical head 2 is controlled to perform the track jump operation of the scale and direction determined in response to the control signal J, so as to approach more closely to the designated location on the disc 1. In this case, the output from the tracking control circuit 4 is also supplied through the low-pass filter 15 to the input terminal n4 of the system control circuit 6, and thereby the stepping motor 5 is driven to cause the optical head 2 to have step movements required for the track jump operation.

In a process C", the time data Tj for the designated location on the disc 1 are further compared with the time data To to produce the resultant data T~ Q corresponding to the difference betweeen the time data Tj and TQ.

Then, in a decision D2, it is checked whether the time Uj~Q represented by the resultant time data T~ Q is shorter than or equal to the predetermined permissible error time UO, the search operation is finished. On the contrary, if the time U, Q is longer than the predetermined permissible error time UO, the operation in the process C,O and the process C", and the check in the decision D2 are repeated until the time UW Q is shorter than or equal to the predetermined permissible error time To As described above, when a location on the disc 1 is designated by the reading position designating signal I, first the positional data for the designated location on the disc 1 are compared with the positional data for the position of the optical head 2, and then the stepping motor 5 is driven in response to the difference between these positional data to cause the optical head 2 to move quickly so as to approach the deisgnated location. Then, the difference between the designated location and the reading position of the optical head 2 after the quick movement of the optical head 2 is detected, and the reading position of the optical head 2 is controlled to perform the track jump operation in response to the detected difference so as to approach more closely to the designated location. After the track jump operation of the reading position of the optical head 2, the search operation is finished when the reading position by the optical head 2 has reached the designated location within a predetermined permissible error.

Although the embodiment described is to be used with a digital audio disc, the invention can also be applied to disc players for reproducing information from any other disc having a spiral record track thereon.

Claims (5)

1. A disc player for reproducing information from a disc having a spiral record track thereon, the disc player comprising: pick-up means for reading a signal recorded in the spiral record track on the disc; pick-up moving means to be driven by pulses supplied thereto to cause said pick-up means to have successive step movements along the radius of the disc in response to the supplied pulses; counter means arranged to be cleared when said pick-up means is situated at the starting end of the spiral record track on the disc and producing first positional data representing a position of said pick-up means on the disc by counting pulses used for driving said pick-up moving means; and system control circuit means including means for producing second positional data representing a location on the disc designated by a reading position designating signal, means for obtaining resultant data corresponding to the difference between the first positional data and the second positional data, and means for generating the pulses used for driving said pick-up moving means in response to the resultant data, said system control circuit means supplying the pulses generated thereby to said pick-up moving means to drive said pick-up moving means and thereby to shift the position of said pick-up means with the successive step movements so as to approach to the location on the disc designated by the reading position designating signal.

2. A disc player according to claim 1 wherein said system control circuit means further includes means for generating a direction command signal for determining the direction of the successive step movements of said pick-up means and for supplying said direction command signal to said pick-up moving means.

3. A disc player according to claim 2 wherein said pick-up moving means comprises a stepping motor for causing said pick-up means to have the successive step movements and a control circuit for driving said stepping motor in response to the pulses and direction command signal supplied thereto from said system control circuit means.

4. A disc player according to claim 1 wherein said system control circuit means further includes means for generating a control signal used for causing track jump operation required for moving the reading position of said pick-up means to reach the location designated by the reading position designating signal after the successive step movements of said pick-up means are carried out.

5. A disc player substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.