HK1692A - Process for track jumping in track search processes and circuit arrangement for implementation of the process - Google Patents

Description

The invention relates to a process according to the general concept of the main claim.

The method is concerned in particular with the avoidance of unwanted movements of the scanning system when radial scanning CDs with devices which have a simple servo system without directional detection logic.

It is a state of the art that for the rapid detection of any plate location, the difference traces between the target and the current position are first determined and specified as a set value. For relatively distant targets, it is not sufficient to perform the search operation with the fine drive alone. In principle, the process is carried out by switching the coarse drive to a fast search operation, i.e. the coarse drive is accelerated and kept at a high speed. At the same time, the control circuit of the fine drive is interrupted. During the current phase of movement of the coarse drive (and the carried-on feeder) the radially crossed spans are detected and calculated.

The search engines operating on this principle generally have a directional detection logic, as described in GB-A-2 000 617, which determines the relative direction of the fine and coarse drive to the plate to be scanned. This device prevents the wrongly recognized tracks when crossed in the wrong direction. Such wrong movements in the given direction of search occur only in the take-off and landing phases in fast search engines.In the case of a search system without directional detection logic, no difference can be detected and tracks crossed in the wrong direction are erroneously evaluated as correct. This, however, achieves a certain target and corrections must be made. This can lead to a substantial increase in search time. The second problem is that the search engine cannot detect the difference and the tracks crossed in the wrong direction are incorrectly evaluated as correct.The first step is to determine the direction of the movement of the coarse drive, which is the direction of the coarse drive. The second step is to determine the direction of the coarse drive. The second step is to determine the direction of the coarse drive. The second step is to determine the direction of the coarse drive.the resulting error can be further magnified at the corresponding jump direction, as also shown in Figure 2.

The EP-OS 0090379 is also cited as an example of this type of search system.

Another solution is the JP-A-58 57 637. Here an additional signal is given to the fine drive, which is diverted in the opposite direction to the direction of motion of the rough drive. This does not affect the start phase of a search operation. Accordingly, the task is different from that of the present invention.

For simple search systems without directional detection logic, the above conditions lead to a considerable increase in search times. On the other hand, in search systems with very high search speeds or with fast, short-term back and forth movements of the fine drive, as may occur in the start-up phase, there are major difficulties in the implementation of the directional detectors, which can only be controlled with a high circuit input. This is especially true if there is no pure hardware solution for controlling the search process, but a micro-processor-supported switch variant.

The present invention was based on the objective of finding a solution for a search system with a radial rough and fine drive for the optical scanning of a CD player, which has no directional detection logic, is relatively cheap to manufacture, allows fast access times and is comparable in reliability of correct trace detection to systems operating on the principle of directional detectors.

This task is solved by a process based on the concept of the first claim, in accordance with the characteristics of the invention.

Claim 2 contains a circuit instruction to perform this procedure.

Further details and arrangements for the operation of the process are given by circuit devices according to the sub-clauses and the description below.

The main advantage of the method and the circuits used for its operation, apart from the low effort involved, is that high search speeds with a high initial acceleration or fast, superimposed on the coarse drive, phases of motion of the fine drive, as they occur particularly in the start-up phase, are completely unproblematic for the proper functioning of the process.

The purpose of the drawing is to describe the invention. Figure 1 Motion of an optical scanning system in the start and search phase (state of the art);Figure 2a Motion of the fine drive with one-sided shifting of the working point (state of the art);Figure 2b Motion of the gross drive in this process (state of the art);Figure 3 Motion of an optical scanning system in the start and search phase according to the method of the invention;Figure 4 Solution example of a shaft arrangement for the execution of the process in the form of a block circuit;Figure 5 Flow diagram of the individual control signals from Figure 4 for a specific direction.

Figures 1 and 2 were already mentioned in the introduction to help understand the state of the art.

The method of finishing does not necessarily separate the fine-tuning circle immediately at the start of a search operation, but rather asks for different criteria and makes the opening of the fine-tuning circle dependent on the result of this evaluation.

The method is characterised by the fact that the fine drive (and thus the optical scanner) is briefly deflected in the opposite direction to the desired search. This is achieved by starting the rough drive while the fine drive keeps the scanner in the current track. Only when the scanner is deflected in the opposite direction to the desired search, the control circuit of the fine drive is interrupted. By deflecting the scanner forward, it can only move in one direction opposite to this forward acceleration, i.e. in the search direction.

To avoid such a rollover, the fine-duty control circuit can be interrupted at the exact zero position, as shown in Figure 3. The disadvantage is that, depending on the direction of the jump and the radial eccentricity, the plate impact must be allowed to pass through the zero without the coarse-duty drive being pre-activated.

Even in the case of the test-piece positions at the start of the search operation which have a favourable effect on the search direction, a minimum acceleration phase for the gross drive should generally be observed with the fine drive control circuit still closed, so as to avoid that the desired direction of movement is adversely affected by the spindle operations or the radial eccentricity of the plate.

An example of a circuit arrangement for the operation of the procedure is shown in Figure 4. Two adjustable detectors 8 and 9 are provided. They are assigned to each direction of search, but they do not work as directional detectors but only as threshold detectors. A low-pass member 4.5 gains from the radial error signal URE, which can be received directly at the radial actuator of the fine-tuning drive system and at the output of the controller 2, the control signal URG for the detectors 8, 9. This control signal URG is directly proportional to the motion sample recorded as coordinates in Figures 1, 2 and 3. With the help of these detectors 8, 9 is protected by the switch 10 from the unit 14 to the desired direction and the detector signal is selected accordingly, and the control circuit 11 is written out with the help of the control circuit.

The time of the deceleration, which is determined by the acceleration phase of the gross drive 13, is a constant and guarantees that in the case mentioned above no fine drive spindle movements and an overlapping excess starting eccentricity of the plate in the rotation phase will have a negative effect.

Figure 5 shows the flow diagrams of the individual control signals as they appear in the block diagram of the circuit arrangement (Figure 4) for a given desired direction.

Claims (13)

1. A method of track jumping to a desired track for a rotating information carrier scanned with an optical scanner, wherein the scanner is movable radially by a coarse drive (13) and a fine drive (3), wherein a servo circuit is present which controls the fine drive by means of a radial error signal U_RE and which is open during the track jumping caused by the coarse drive, and wherein, with the servo circuit open, the tracks traversed radially are counted without regard to the direction of the traversing, characterised in that during the track jumping, the servo circuit of the fine drive (3) at first remains closed if the coarse drive (13) is immediately set in motion (f in Figure 3) in accordance with the search direction fed in, and the servo circuit of the fine drive is only opened (j in Figure 3) in the event of criteria following as a result, in such a manner that, taking into account the acceleration and the search speed of the coarse drive (k in Figure 3) on the one hand and the eccentricity of the tracks (b in Figure 3) and the movement of the scanner (i in Figure 3) on the other hand, assurance is provided that the relative movement between information carrier and beam is not reversed after the start of the coarse drive.

2. A circuit arrangement for track jumping to a desired track for a rotating information carrier scanned with an optical scanner, wherein the scanner is movable radially by a coarse drive (13) and a fine drive (3), wherein a servo circuit is present which controls the fine drive by means of a radial error signal U_RE and which is open during the track jumping caused by the coarse drive, and wherein, with the servo circuit open, the tracks traversed radially are counted without regard to the direction of the traversing, characterised by means which, during the track jumping, at first hold the servo circuit of the fine drive (3) closed if the coarse drive (13) is immediately (f in Figure 3) set in motion according to the search direction fed in, and which only open (j in Figure 3) the servo circuit of the fine drive in the event of criteria following as a result, in such a manner that, taking into account the acceleration and the search speed of the coarse drive (k in Figure 3) on the one hand and the eccentricity of the tracks (b in Figure 3) and the movement of the scanner (i in Figure 3) on the other hand, assurance is provided that the relative movement between information carrier and beam is not reversed after the start of the coarse drive.

3. A circuit arrangement according to Claim 2, characterised in that the opening of the servo circuit of the fine drive is triggered by the output signal of a detector of the radial error signal (U_EE), which has a fixed reference point, and this reference point may be zero or a level which is associated with the mid position (neutral position) of the fine drive.

4. A circuit arrangement according to Claim 2, characterised in that the opening of the servo circuit of the fine drive is triggered by the output signal of a detector (8, 9) of the radial error signal, the threshold of which detector is adjustable.

5. A circuit arrangement according to Claim 3 and/or 4, characterised in that a distinction is made between a forward and backward search direction as a result of the fact that two detectors (8, 9) are provided, one of which is associated with each of these search directions.

6. A circuit arrangement according to Claim 5, characterised in that a plurality of detectors or A/D converters are used.

7. A circuit arrangement according to Claim 2, characterised in that the control loop of the fine drive is only opened after the expiration of a fixed preset delay time.

8. A circuit arrangement according to Claim 7, characterised in that the extent of the delay time depends on system constants such as turntable unit and/or scanning unit used.

9. A circuit arrangement according to Claim 8, characterised in that the adjustable delay time is determined by the magnitude and direction of the radial eccentricity found in the starting phase of reproduction operation.

10. A circuit arrangement according to Claim 9, characterised in that the adjustable delay time is also determined by the jumping distance detected, in such a manner that it is reduced for short jumping distances and increased for long jumping distances.

11. A circuit arrangement according to Claim 2, characterised in that means are provided which ensure that a more favourable radial eccentricity with regard to the search direction is awaited.

12. A circuit arrangement according to Claim 2 and/or any one of the following Claims, characterised in that the opening of the fine drive control loop is only effected after the forcible removal of the scanning beam of light from the track, means being provided which ensure that the moment of opening of the fine drive control loop is additionally derived from the magnitude of the jumping distance.

13. A circuit arrangement according to Claim 12, characterised in that the closed-loop gain of the fine drive control loop is reduced during the starting phase of the coarse drive.