JPH04141834A - Optical head type position detection device - Google Patents

Abstract

PURPOSE:To highly precisely detect a position by converging a part of light flux from a light source, irradiating a semiconductor position detection element arranged to a fixed part with light flux and outputting the position detection signal of a shift part for an optical head based on the irradiated position. CONSTITUTION:When an optical spot 22 is irradiated, the semiconductor position detection element (PSD) 24 generates potential based on a resistance value corresponding to electrodes to both ends in respective electrodes. When access by a shift part 1 shifts to the center part of the optical disk 3, the irradiation position of the optical spot 22 on PSD 24 shifts in accordance with the shift. In such a case, distances from the irradiation position of the optical spot to respective electrodes become equal and potential arising in respective electrodes become equal. When access by the shift part 1 shifts to the inner peripheral part of the optical disk 3, the position detection signal outputted from the position detection means 26 comes to the positive potential and the potential linearly changes in correspondence with the irradiation position of the optical spot 26. Thus, the stability of optical strength improves and highly precisely position detection is realized.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an optical head position detection device that detects the position of the moving part in an optical head that is composed of a moving part and a fixed part and performs recording and reproduction on an optical information recording medium such as an optical disk.

[Conventional technology]

FIG. 4 is a configuration diagram showing a conventional optical head position detection device. In the figure, 1 is a moving part of the optical head, and 2 is a fixed part. 3 is an optical disk as an optical information recording medium on which information is recorded and reproduced by an optical head, and 4 is a spindle motor that rotates this optical disk 3. Reference numeral 5 denotes a semiconductor laser disposed within the fixed portion 1 and serves as a light source that emits a diverging light beam. Reference numeral 6 denotes a collimator lens that converts the diverging light beam emitted from the semiconductor laser 5 into a parallel light beam. 7 is a polarizing beam splitter that separates the light beam converted by the collimator lens 6 and the light beam reflected by the optical disk 3, and 8 is a quarter-wave plate through which both the light beams are transmitted. 9 condenses the light beam that has passed through the quarter-wave plate 8 and irradiates it onto the optical disc 3;
An objective lens serves as a first condensing optical system that converts the light beam reflected by the information track 9 into a parallel light beam, and 10 is an objective lens actuator that performs focus control and tracking control of this objective lens 9. 11 is a signal detection system that detects a reproduction signal of recorded information, a focus error signal, and a tracking error signal based on the light beam split by the polarization beam splinter;
is a housing of the moving unit 1 of this optical head, and 13 is its support. Reference numeral 14 denotes an optical main scale having a group of slits having a predetermined scale pitch perpendicular to the direction of movement of the moving unit 1 and supported by the housing 12 by the pillars 13 . Reference numeral 15 denotes an optical index scale that is arranged in the fixed part 2 in parallel to the optical main scale 14 and includes a group of slits that are parallel to that of the optical main scale 14 and have the same scale pitch. 16 is a light emitting diode (hereinafter referred to as LED) that emits a diverging light beam that irradiates the optical main scale 14 and the optical index scale 15;
17 is a photodetector placed opposite to this LED 16 with the optical main scale 14 and optical index scale 15 in between. 18 is a detector housing in which they are housed. Next, the operation will be explained. Optical transfer unit 1
A diverging light beam emitted from a semiconductor laser 5 disposed inside is converted into a parallel light beam by a collimator lens 6, transmitted through a polarizing beam splinter 7 and a 174-wave plate 8, and sent to an objective lens 9. The objective lens 9 condenses the sent parallel light beam and irradiates it onto the information track of the optical disk 3, thereby recording or reproducing information. On the other hand, the light beam reflected by the optical disk 3 during reproduction is converted into a parallel light beam by the objective lens 9 and transmitted through the 1/4 wavelength plate 8, and the polarized beam 1. The signal is reflected by the tough signal and sent to the signal detection system 11. The signal detection system 11 detects a reproduction signal, a focus error signal, and a tracking error signal from the transmitted light beam. Here, in such an optical head, it is necessary to accurately detect the position of the moving section 1. Now, when the moving part 1 moves from the position shown by the solid line in FIG. 4 to the position shown by the dashed-dotted line, the fixed part 2 LED1
The diverging light beam emitted from the optical main scale 14 and the optical index scale 15 pass through a group of slits and are received by a photodetector 17 . At this time, the optical main scale 14 moves with the movement of the moving part 1 while maintaining the parallel state of the slit group between it and the optical index scale 15, so the amount of light received by the photodetector 17 changes depending on the movement. It changes accordingly. FIG. 5 is a schematic diagram showing the relative positional relationship between the slit groups of the optical main scale 14 and the optical index scale 15, and FIG. 6 is a characteristic diagram showing the temporal change in the amount of light received by the photodetector 17. be. When the slit groups of the optical main scale 14 and the optical index scale 15 completely overlap as shown in FIG. 5(a), the amount of light received by the photodetector 17 becomes maximum, and then as shown in FIG. 5(b). As shown in FIG. 5(C), as the slit group shifts, the amount of light received by the photodetector 17 decreases, and as shown in FIG. Become. In addition, P in the figure indicates the pick-up of the optical main scale 14 and the optical index scale 15.
The scale pitch of the Met group is shown. One cycle of the change in the amount of received light detected by the photodetector 17 in this way is the scale pitch P of the slit group of the optical main scale 14 and the optical index scale 15.
corresponds to Therefore, by counting the period of the detection signal of the photodetector 17, the position of the moving section 1 of the optical head can be detected.

[Problems to be Solved by the Invention] Since the conventional optical head position detection device is configured as described above, the period of the detection signal of the photodetector 17 is must be counted, and the detection accuracy is also determined by the scale pitch P of the slit groups of the optical main scale 14 and the optical index scale 15, which is actually about 200 μm, which is not sufficient for detection accuracy. There were issues such as: The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain an optical head position detection device that can obtain a highly accurate position detection signal with a simple structure.

[Means to solve the problem]

The optical head position detection device according to the present invention includes a branching optical system that is inserted between a light source and a first condensing optical system and branches a part of a light beam emitted from the light source; The movable part is provided with a second condensing optical system that condenses the second condensing optical system.
The fixed part is provided with a position detection means using a semiconductor device element for detecting the position of the moving part by receiving the light beam collected by the condensing optical system.

[Effect]

The second condensing optical system in the present invention condenses a part of the light beam from the light source branched by the branching optical system inserted between the light source and the first condensing optical system, and fixes it. The position detecting means outputs a position detection signal for the moving part of the optical head based on the irradiation position, which enables highly accurate position detection with a simple structure. A possible optical head position detection device is realized.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is a moving part of the optical head, 2 is a fixed part,
3 is an optical disk as an optical information recording medium, 4 is a spindle motor, 5 is a semiconductor laser as a light source, 6 is a collimator lens, 7 is a polarizing beam splitter, and 8 is a 1/1
4 wavelength plate, 9 an objective lens as a first condensing optical system,
10 is an objective lens actuator, 11 is a signal detection system,
Reference numeral 12 denotes a casing, which is the same as, or corresponds to, those of the conventional case denoted by the same reference numerals in FIG. 4, so a detailed description thereof will be omitted. A beam splinter 20 is inserted between the collimator lens 6 and the polarizing beam splitter 7, and serves as a branching optical system that splits a part of the light beam emitted from the semiconductor laser 5 and converted into a parallel light beam by the collimator lens 6. It is. 21 is a condensing lens as a second condensing optical system that condenses the parallel light beam branched by this beam splinter 20, and 22 is a light spot condensed by this condensing lens 21. Reference numeral 23 denotes a deflecting mirror that is disposed between the quarter-wave plate 8 and the objective lens 9 and bends the light beam by 90 degrees. 24 is a light spot 2 condensed by the condenser lens 21;
When a light spot 22 is irradiated, a semiconductor device detection element (hereinafter referred to as PSD) that receives light 2 and detects the irradiation position causes a photocurrent to flow from the irradiation position to the electrodes at both ends.
A potential is generated in each electrode based on the resistance value depending on the distance to the electrodes at both ends. 25 is a subtracter that takes the difference between the potentials generated at the electrodes at both ends of the PSD 24; 26 is formed by the PSD 24 and the subtracter 25; This is a position detection means that outputs a position detection signal. Next, the operation will be explained. Here, Figure 2 is PSD2
The irradiation position of the light spot 22 in 4 and the position detection means 2
FIG. 6 is an explanatory diagram showing the relationship with the device detection signal composed of 6. A part of the light beam emitted from the semiconductor laser 5 and converted into a parallel light beam by the collimator lens 6 is split by the beam splitter 20, sent to the condensing lens 21 and condensed, and is focused as a light spot 22 on the PSD 24. is irradiated. This light spot 22 is generated in accordance with the movement of the moving unit 2 of the optical head in the direction across the information track of the optical disk 3.
Move on D24. Now, when the moving unit 1 of the optical head is accessing the information track on the outer circumference of the optical disk 3 as shown in FIG. 1, the irradiation position of the light spot 22 on the PSD 24 is as shown in FIG. The position is shown in a). This light spot 2
2, the photocurrent generated in the PSD 24 flows toward the electrodes at both ends thereof, and a potential is generated in each electrode according to the resistance value based on the distance from the irradiation position of the light spot 22 to each electrode. The subtracter 25 takes the difference between the potentials generated on the picture electrodes of the PSD 24 and outputs it as a position detection signal. Therefore, in this case, this position detection signal has a negative potential as shown in FIG. When access by the moving section 1 moves to the center of the optical disk 3, the optical spot 2 on the PSD 24 moves according to the movement.
The irradiation position No. 2 also moves to the position shown in FIG. 2 (b). In this case, the distances from the irradiation position of the light spot 22 to each electrode become equal, and the potentials generated at the respective electrodes also become equal, so that the potential of the device detection signal constituted by the position detection means 26 becomes "0". When the access by the moving unit 1 moves to the inner peripheral part of the optical disc 3, the irradiation position of the light spot 22 on the PSD 24 also moves to the position shown in (C) in FIG. The detection signal has a positive potential. The potential of this position detection signal varies linearly in accordance with the irradiation position of the light spot 22, and therefore, the position of the moving part 1 of the optical head can be detected with high accuracy based on the potential. Note that in the above embodiment, the optical type moving unit 1 is one in which the semiconductor laser 5 to the objective lens 9 and the signal detection system 11 are integrated, but the semiconductor laser 5 and the signal detection system are 11 may be separated and placed within the fixing part 2. FIG. 3 shows the configuration of such an embodiment in FIG. 1, and corresponding parts are given the same reference numerals as those in FIG. 1. In this embodiment, an objective lens 9, an objective lens actuator 10
, only the beam splitter 20, condensing lens 21 and mirror 23 are left in the moving part 1, and the semiconductor laser 5, collimator lens 6, polarizing beam splitter 7, quarter wavelength plate 8 and signal detection system 11 are left in the fixed part. 2 has been moved above. In this embodiment as well, the irradiation position of the light spot 22 condensed by the condenser lens 21 on the PSD 24 moves in accordance with the movement of the moving unit 1, and the subtractor 25 The difference between the potentials of the picture electrodes corresponding to the distance from the irradiation position of PSD 22 to both ends of PSD 24 is calculated and outputted as a position detection signal of position detection means 26 . In this case, the number of parts of the moving unit 1 is reduced and the weight is reduced, so that access can be made faster.

【Effect of the invention】

As described above, according to the present invention, a part of the luminous flux from the light source is branched, focused and irradiated onto the semiconductor device detection element disposed in the fixed part, and based on the irradiation position, the optical head Since the structure is configured to detect the position of the moving part, it not only has excellent stability of light intensity and enables highly accurate position detection, but also uses an optical head with a simple structure and low cost without using a separate light source. This has the effect of providing a position detection device.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an optical head position detection device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the relationship between the irradiation position of a light spot in the PSD and a position detection signal, and FIG. FIG. 4 is a configuration diagram showing another embodiment of the present invention, FIG. 4 is a configuration diagram showing a conventional optical head position detection device, and FIG.
The figure is a schematic diagram for explaining the operation, and FIG. 6 is a characteristic diagram showing the temporal change in the amount of light received by the photodetector. 1 is a moving part, 2 is a fixed part, 3 is an optical information recording medium (optical disk), 5 is a light source (semiconductor laser), 9 is a first condensing optical system (objective lens), 20 is a branching optical system (beam beam). printer), 21 is a second condensing optical system (condensing lens),
24 is a PSD, and 26 is a position detection means. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] It consists of a moving part that moves in a direction across the information track of the optical information recording medium and a fixed part, and the fixed part focuses the light beam emitted from the light source onto the optical information recording medium to record information. Alternatively, in an optical head position detection device that detects the position of the moving part of an optical head having a first light-condensing optical system for performing reproduction, the moving part includes the light source and the first light-condensing optical system. a branching optical system that is inserted between the branching optical system and branches a part of the luminous flux emitted from the light source, and a second branching optical system that condenses the luminous flux branched by the branching optical system.
A condensing optical system is provided, and the fixed part includes a position detection means using a semiconductor device detection element for detecting the position of the moving part by receiving the light beam condensed by the second condensing optical system. An optical head position detection device characterized by being provided.