Jump controller for an optical information recording and reproducing apparatus

Abstract: A jump controller in an information recording and reproducing apparatus for an optical information recording medium (107) having guide tracks for the information recording and reproducing by applying a light beam while making an optical head traverse a number of guide tracks and reach a target guide track, comprises a track traverse detector (103) forming a track traverse detecting signal from a tracking error signal from a photodetector (101) in the optical head; a current generator responsive to a track jump command for moving the optical head from a present track to another track and supplying a drive current to a driver for an objective lens (106) of the optical head, and supplying a damping current by reversing the polarity of the drive current when the track traverse detecting signal is supplied; and a converter (R104, R105, C100) converting the drive current and the damping current into a rapidly rising and gradually falling current. This controller allows the optical head to rapidly jump to a nearby track.

Description: The present invention relates to a jump controller for an optical information recording and reproducing apparatus for an optical information recording medium wherein information is recorded by forming a pit upon application of a light beam to the recording medium while aligning an optical head to a track position, and information is read from a pit by using the light beam. For the optical head in a conventional information recording and reproducing apparatus, a means is provided for generating a tracking error signal whose polarity changes between a positive polarity and negative polarity in response to a track traverse by the optical head. A track traverse detecting signal is generated by comparing the tracking error signal with a reference signal. In case of a jump to nearby tracks the optical head is gradually accelerated and decelerated. The present invention is based on a prior art as disclosed in the US 4 698 795 A reflecting a jump controller as defined in the preamble of claim 1 and the GB 2 081 935 A. Especially, an information recording and reproducing apparatus according to the prior art as discussed in US 4 698 795 A includes a recording medium having a plurality of recording tracks, an optical head having a light source for emitting a light beam towards the surface of said medium, a photodetector for receiving the reflected light, and means for deriving a tracking error signal from the intensity of the reflected light. A tracking control loop for driving the optical head in order to make the tracking error signal zero is provided. Also included is a jump controller for moving the optical head across several tracks of the recording medium in response to a track jump command. When a track jump signal is applied the jump controller opens the tracking control loop and applies an acceleration pulse to the actuator driving the optical head. While the optical head is moving across the tracks of the optical recording medium a track traverse detecting circuit derives a track traverse detecting signal from the tracking error signal allowing to detect the center of the target recording track. When the target recording track is reached, the track jump controller closes the tracking control loop and applies a deceleration pulse to the actuator. According to the GB 2 081 935 A acceleration and deceleration pulses usually are generated by differentiating means. As the deceleration pulse is applied at the moment when the moving optical head reaches the center of the target recording track the optical head will move on towards a position slightly spaced apart from the center of the target track. Following, as the tracking control loop is closed at the same time, this will bring back the optical head to the center of the target track by the normal mode of operation of the tracking control loop. But, as an essential drawback the optical head might swing once or even several times around the center of the recording track making the track jump operation unstable and difficult to control. It is the object of the present invention to provide a jump controller allowing the optical head in an apparatus of the above kind to perform a jump to another track reliable and speedily. In order to achieve this object, the present invention provides an information recording and reproducing apparatus, having a jump controller, for an optical information recording medium having a plurality of guide tracks for recording and reproducing information to and from the medium by applying a light beam to a target recording track while an optical head traverses a predetermined number of guide tracks and reaches the target recording track, the jump controller comprising: an objective lens driver, assembled in said optical head, for detecting a light from said medium to produce a track error signal, and a tracking control loop for driving said objective lens in said optical head to move the light beam so as to make the tracking error signal zero, a responsive circuit for responding to a track jump command when the same is applied, to open said tracking control loop and supply a drive current to said objective lens driver so as to move said optical head from the present recording track to another recording track, and for responding the track traverse detecting signal when the same is applied to supply a damping current which is produced by changing the polarity of the drive current and to close said tracking control loop when the light beam has reached the center of the target recording track, a conversion circuit for converting the driving current and the damping current to currents which rise rapidly and fall gradually, and a track traverse detecting circuit for producing a track traverse detecting signal in response to the track error signal, characterized in that said track traverse detecting signal produced by said track traverse detecting circuit is generated by comparing a tracking error signal to a reference signal and modifying the reference signal when equality occurs providing a snapback effect, and said snapback effect being used for generating a braking signal at a location before the light beam reaches the center of the target recording track. According to the present invention, an instantaneously (rapidly) rising and gradually falling drive current is supplied to the objective lens driver to move the light beam, and significantly before the light beam reaches the center of the target recording track, the polarity of the drive current is reversed, and a rapidly rising and gradually falling damping current is supplied. The motion of the optical head is decelerated until the light beam reaches the center of the target recording track where the tracking control loop is closed for keeping the light beam on this track. As compared with a conventional gradual acceleration and deceleration, jumping across a number of tracks can be completed in a very short time duration. In the accompanying drawings: Fig. 1 is a block diagram showing the circuit arrangement of an embodiment of the present invention; Fig. 2 is a detailed circuit diagram of the track traverse detector shown in Fig. 1; Fig. 3(a) and 3(b) are timing charts showing the signal waveforms at various circuit portions shown in Fig. 1. Fig. 1 is a circuit diagram showing the structure of an embodiment of a near jump controller for controlling an optical head to jump to a nearby track according to the present invention. Fig. 2 is a detailed circuit diagram showing the structure of the track traverse detector in the circuit shown in Fig. 2. Fig. 3a and 3b are timing charts showing signal waveforms at various circuit portions shown in Fig.1. Referring to Fig. 1, reference numeral 107 represents an optical information recording medium. A light beam radiated through an objective lens 106 is focussed on the optical card 107, and the reflected light is applied to an optical detector 101 to form a tracking error signal. This tracking error signal is amplified by an amplifier 102 and supplied via a switch SW101 to a tracking controller 104 to drive a tracking coil 105 for driving the objective lens 106. The tracking error signal is also supplied to a track traverse detector 103 the details of which will be later described with Fig. 2. The track traverse detector 103 shapes the tracking error signal into a rectangular waveform to generate a track traverse detecting signal. This track traverse detecting signal is supplied to one input terminal of an exclusive OR EXOR100. Supplied to the other input terminal of EXOR100 is a direction control signal which takes an L level when the objective lens is moved in the forward direction and an H level when it is moved in the backward direction. The direction control signal is also used for opening and closing a switch SW103. For the forward direction, the switch SW103 opens to supply the positive power source voltage +V to the left contact of the switch SW102 as viewed in Fig. 1 via resistors R101 and R102. For the backward direction, the switch SW103 closes to supply the negative power source voltage -V to the left contact of the switch SW102 via the resistor R102. A signal at the Q output terminal of a flip-flop FF100 is used for opening and closing the switch SW101. This signal of an H level closes the switch SW101 to always maintain the light beam at the center of a track, and the signal of an L level opens the switch SW101. A signal at an inverted Q output terminal of the flip-flop FF100 as well as an output from EXOR100 is supplied to an AND gate AND100 whose output is used for opening and closing the switch SW102. While the switch SW101 opens and the switch SW102 closes, a voltage corresponding to the state of the switch SW103 is supplied to the tracking controller 104 via a conversion circuit made of a parallel circuit of a resistor R104 and a serially connected resistor R105 and capacitor C100. The tracking controller 104 flows a current to the tracking coil 105 to start moving the objective lens 106. When the switch SW102 opens under this condition, the tracking controller 104 receives a voltage signal of an inverted polarity and flows a damping current to the tracking coil 105. Fig. 2 shows the detailed structure of the track traverse detector 103 shown in Fig. 1. The tracking error signal applied to an input terminal IN100 is supplied to the inverting terminal of a comparator CMP100 via an integrator made of a resistor R111 and capacitor C111. A reference signal Vref is applied to the non-inverting input terminal of the comparator CMP100. The tracking error signal is compared with the reference signal, and the comparison result is outputted via a resistor R116 to an output terminal OUT100. This reference voltage Vref is a voltage divided by a serial circuit made of resistors R115, R113, and R112. The resistor R113 is a feedback element connected between the non-inverting input terminal and output terminal of the comparator CMP100. The reference voltage Vref changes with an output voltage of the comparator CMP100. As the feedback element of the comparator CMP100, a serial circuit of a resistor R114 and capacitor C112 is also connected to add an offset to an output of the comparator CMP100. Fig. 3(a) und (b) show signal waveforms at various circuit portions of Fig. 1 during the forward jump and backward jump operations. The operation of the circuit of Fig. 1 will be described with reference to these waveforms shown in Fig. 3(a) and (b). Forward Direction Jump In order to determine the motion direction, the direction control signal is set to an L level for the forward direction jump. With the L level signal, the switch SW103 opens, and so the positive voltage is applied via the resistors R101 and R102 to the left contact of the switch SW102. A track jump command of an L level is issued at time t 11 and supplied to an inverted reset terminal R of the flip-flop FF100. Therefore, the Q output of the flip-flop FF100 takes an L level to open the switch SW101 and stop the control of making the light beam follow the center of a track. The inverted Q output of the flip-flop FF100 takes an H level to close the switch SW102 and supply a positive voltage to the converter circuit made of the resistors R104, R105 and capacitor C100. Accordingly, a drive current shown in Fig. 3(a) flows in the tracking coil 105 to start moving the objective lens 106 in the forward direction. As the objective lens 106 moves, the tracking error signal changes from a zero level to a negative level and from the zero level to a positive level. When the tracking error signal becomes larger than the reference value Vref, the track traverse detecting signal takes an L level. Therefore, both the inputs to EXOR100 are L level, and the output is L level. With an L level of the output of EXOR100, the input conditions of the AND gate AND100 are negated. Therefore, the AND gate AND100 supplies an L level signal to the switch SW102 to open it. Accordingly, the positive voltage having been applied to the conversion circuit disappears at once so that a current in the opposite direction will flow through the tracking coil 105 to provide a fast damping. This damping is carried out at time t 12 shown in Fig. 3 (a). At time t 13 when the tracking error signal again takes the zero level (when the light beam reaches the center of the track), the track traverse detecting signal takes an H level. With H and L level inputs, EXOR100 outputs an H level signal. The rising edge of this H level signal is applied to a clock terminal of the flip-flop FF100 so that the Q output of the flip-flop FF100 takes an H level to close the switch SW101 and lock the objective lens 106 at that position. The inverted Q output of the flip-flop FF100 takes an L level, and so the input conditions of the AND gate AND100 are negated to supply an L level signal to the switch SW102. Backward Direction Jump In order to determine the motion direction, the direction control signal is set to an H level for the backward direction jump. Therefore, the switch SW103 closes, and so the negative voltage -V is applied via the resistor R102 to the left contact of the switch SW102. When the switch SW102 closes, the direction of the current flowing through the tracking coil 105 becomes opposite to that during the forward direction jump. As shown in Fig. 3(b), the tracking error signal changes in the opposite direction to that shown in Fig. 3(a). The operation is similar to that during the forward direction jump except that the input conditions to EXOR100 are reversed.

Claims: An information recording and reproducing apparatus, having a jump controller, for an optical information recording medium (107) having a plurality of guide tracks for recording and reproducing information to and from the medium by applying a light beam to a target recording track while an optical head traverses a predetermined number of guide tracks and reaches the target recording track, the jump controller comprising: an objective lens driver (104, 105), assembled in said optical head, for detecting a light from said medium to produce a track error signal, and a tracking control loop (101, 102, SW101, 104, 105, 106) for driving said objective lens in said optical head to move the light beam so as to make the tracking error signal zero, a responsive circuit (FF100, AND100, SW101, SW102, SW103) for responding to a track jump command when the same is applied, to open said tracking control loop and supply a drive current to said objective lens driver so as to move said optical head from the present recording track to another recording track, and for responding the track traverse detecting signal when the same is applied to supply a damping current which is produced by changing the polarity of the drive current and to close said tracking control loop when the light beam has reached the center of the target recording track, a conversion circuit (C100, R104, R105) for converting the driving current and the damping current to currents which rise rapidly and fall gradually, and a track traverse detecting circuit (103) for producing a track traverse detecting signal in response to the track error signal, characterized in that said track traverse detecting signal produced by said track traverse detecting circuit (103) is generated by comparing a tracking error signal to a reference signal and modifying the reference signal when equality occurs providing a snapback effect, and said snapback effect being used for generating a braking signal at a location before the light beam reaches the center of the target recording track. An information recording and reproducing apparatus having a jump controller according to Claim 1, characterized in that said track traverse detecting circuit (103) having a comparator (CMP100) associated with a feedback element (R113, R114, C112) which connects the positive input terminal and the output terminal of said comparator, whereby said tracking error signal is applied to the positive input terminal and said reference signal is applied to the negative input through said feedback element. An information recording and reproducing apparatus having a jump controller according to one of Claims 1 and 2, characterized in that said feedback element consists of a resistor (R113) and a series circuit of a resistor (R114) and a capacitor (C112).

Inventors: ONODERA AKIRA, YAMAZAKI KOICHI, ONODERA, AKIRA, YAMAZAKI, KOICHI
Applicants: NIPPON CONLUX CO LTD, NIPPON CONLUX CO., LTD.
Application year: 1992
Main classification: G11B7
IPC codes: G11B7