Recording/reproducing apparatus of optical card

Abstract: An optical card recording/reproducing apparatus for recording/reproducing information onto/from an optical card (1) by relatively moving the optical card to an optical head is provided. The optical head has an optical system for producing focusing and tracking control signals. The optical system includes a light emitting diode (119) having a narrow slit-like light emitting surface as a light source. The optical system has photo sensitive elements for focusing control, a photo sensitive element for tracking control, and a recorded information reproducing photo sensitive element which are used to detect the reflected lights from the optical card of a slit light which is emitted from the light emitting diode. By forming a slit-like light spot onto the optical card, the focusing and tracking controls can be accurately easily executed and the deterioration in pits and track guides is prevented.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a recording/ reproducing apparatus of an optical card. In the specification, a recording/reproducing apparatus incorporates: an apparatus for recording (or writing) information or data to an optical card; an apparatus for playing back (or reading) information or data from an optical card; and an apparatus for executing both of the recording and reading operations. On the other hand, an optical card incorporates not only an optical card to/from which information or data can be optically recorded/reproduced but also an optical card to/from which information or data can be magneto optically recorded/reproduced. Description of the Related Art Fig. 18 shows a whole optical card and an enlarged part thereof. A number of information recorded or recording tracks 17 which are specified by track guides 18 are provided in an information recording portion 16 of an optical card 1. Bits indicative of information are recorded in a form of pits 19 onto the tracks 17 (in the case of the optically recordable/reproducible card). The track guides 18 are provided for allowing an optical head for recording/reproducing to follow the tracks (what is called a tracking control). In the optical card in the embodiment, information is optically written/read. In the recording mode, the pits 19 are formed by causing a thermal irreversible change by a light irradiation in the information recording portion 16. On the contrary, in the reproducing mode, the light is irradiated to the pits 19 and regions around them and the reflected lights are received, thereby detecting the presence or absence of the pits. In the case of the embodiment, light reflectances at the pits 19 and track guides 18 are lower than those of the regions around them. Fig. 19 shows an example of a construction of the optical head 6. The head 6 comprises: a light projection optical system 71 to irradiate the light onto the optical card 1; and a light reception optical system 81 to receive the reflected lights from the optical card 1. The light projection optical system 71 includes: a semiconductor laser 73, a collimating lens 74, a warping prism 75, a diffraction grating 76, a reflecting mirror 77, and an objective lens 78. The spreading light emitted from the semiconductor laser 73 is transformed into the parallel beam having an elliptic cross section by the collimating lens 74. After the parallel beam was warped to the beam having an almost circular cross section by the warping prism 75, it is divided into three light beams by the diffraction grating 76. The three light beams are led in the direction of the optical card 1 by the reflecting mirror 77 and images are formed onto the optical card 1 by an objective lens 78. As shown in Fig. 20, a light spot SPa due to a 0th-order diffracted light is formed on the information recorded or recording track 17. On the other hand, light spots SPb and SPc due to positive and negative primary diffracted lights are formed on the track guides 18 on both sides of the track 17, respectively. In addition to the objective lens 78 and the reflecting mirror 77, the light reception optical system 81 includes: condenser lenses 82 and 83; a half-mirror 84; and photo detectors 85 and 86. The reflected lights of the light spots SPa, SPb, and SPc are converged by the condenser lenses 82 and 83 through the objective lens 78 and reflecting mirror 77. The converged light is separated by the half-mirror 84. The separated lights are projected to the photo detectors 85 and 86, respectively. In the above optical system, in order to accurately form the image of the light spot SPa onto the information recording portion 16 of the optical card 1, it is necessary to control the distance between the optical card 1 and the objective lens 78 (focusing control). On the other hand, in order to accurately form the image of the light spot SPa to the position of the information recorded or recording track 17 in the information recording portion 16, it is necessary to control the position of the objective lens 78 (tracking control). A focusing error signal and a tracking error signal which are used for the focusing control and tracking control are produced from light detection signals of the photo detectors 85 and 86. On the basis of the focusing error signal, a focusing servo mechanism controls the distance of the objective lens 78 to the optical card 1. On the basis of the tracking error signal, a tracking servo mechanism controls the position in the lateral direction of the objective lens 78 so that the light spots SPb and SPc are located on the track guides 18. In the recording mode, in a state in which the automatic focusing and tracking controls were executed, the semiconductor laser 73 is driven by high power pulses which were modulated on the basis of data to be recorded while moving the optical card 1 in the direction along the track guides 18, thereby causing a thermal irreversible change on the information recording portion 16 of the optical card 1 by the 0th-order diffracted light. In this manner, a pit train is produced and information is recorded. On the other hand, in the reproducing mode, in a similar state in which the automatic focusing and tracking controls were executed, the pit train is scanned by the 0th-order diffracted light while moving the optical card 1 in the direction of the track guide 18, thereby detecting the reflected lights by the photo detector 86. The recorded information on the optical card 1 is read out on the basis of an output signal of the photo detector 86. Fig. 21 shows a circuit block diagram of the optical card recording/reproducing apparatus with the above construction. The optical head 6 is controlled by focusing control circuit 45 and a tracking control circuit 46 and is electrically connected to a system controller 48 through a signal processor 47 for processing the light detection signal. The focusing control circuit 45 and tracking control circuit 46 are controlled by the system controller 48. The card loading/ejecting mechanism 3 and the head feeding mechanism 7 are electrically connected to the system controller 48. The card feeding mechanism 5 is also electrically connected to the system controller 48 through a card feeding control circuit 44. The operation in each section of the mechanisms in the recording or reproducing mode is controlled by the system controller 48. The system controller 48 is connected to an external terminal device 70 through an external interface 49. In the optical card recording/reproducing apparatus with the above construction, the focusing error signal and tracking error signal as fundamental signals for the focusing and tracking servo controls are formed on the basis of the light emitted from the semiconductor laser 73 as a light source. Therefore, when the semiconductor laser 73 is intermittently driven by a large power in the information recording mode, the fundamental signals are largely fluctuated, so that focusing and tracking control errors occur. To avoid such errors, when the semiconductor laser 73 is intermittently driven to output a large output, it is necessary to interrupt the focusing and tracking controls and to keep the position of the objective lens 78 to the position just before the driving by a high power. Consequently, such a control becomes very complicated. When the recorded information is reproduced, a pit train of the pits 19 on the track 17 is scanned by the light spot SPa of an almost same size as that of the pit 19 and a change in light amount of the reflected light is detected by the photo detector 86. Therefore, if a vibration occurs in association with the conveyance of the optical card 1, the light spot SPa is deviated from the pit 19, so that an S/N ratio of the light detection signal deteriorates. Particularly, in the optical card recording/reproducing apparatus, the vibration is larger than that in the optical disk drive apparatus or the like. If the recording or reproducing speed of information is intended to increase, the vibration also increases due to such a high speed operation. Therefore, it is difficult to realize the high recording/reproducing speed. Further, when the recorded information is reproduced, the semiconductor laser 73 is used in a state in which its power is reduced to a lower limit level enough to stably oscillate. However, even in the case of such a low level, there is a problem such that energy densities of the light spots SPa to SPc are still high and the pits 19 and track guides 18 on the optical card 1 are deteriorated by the repetitive reproducing operations, so that the light detection signal level is decreased. Fig. 22 is a constructional diagram showing another example of a general construction of an optical head which is assembled in the optical card recording/ reproducing apparatus. In the diagram, the optical head comprises: a semiconductor laser 91 as a light source to project a light to the optical card 1 side; a photo detector 100 which is constructed by various kinds of photo sensitive elements for receiving the reflected lights from the optical card 1 and outputting electric signals corresponding to amounts of lights detected; and an optical system for leading the light emitted from the semiconductor laser 91 to the optical card 1 and for leading the reflected lights from the optical card 1 to the photo detector 100. The optical system comprises: a collimating lens 92; a deflecting beam splitter 93; an objective lens 94; and a condenser lens 95. In the above construction, the light emitted from the semiconductor laser 91 is transmitted through the collimating lens 92 and deflecting beam splitter 93 and reaches the objective lens 94. Then, it is converged by the objective lens 94 and is irradiated onto the optical card 1. In a manner opposite to the above, the reflected lights from the optical card 1 pass through the objective lens 94 and are deflected by the deflecting beam splitter 93 and are converged by the condenser lens 95 and are input to the photo detector 100. The photo detector 100 has reproduction signal photo sensitive elements, photo sensitive elements for focusing control, and a photo sensitive element for tracking control. Electric signals corresponding to detected light amounts are output from the photo sensitive elements, respectively. A focusing control mechanism in the optical head will now be described with reference to Fig. 23. In the diagram, the lights reflected by the optical card 1 in the light emitted from the semiconductor laser 91 pass through the condenser lens 95 and are detected by two photo sensitive elements 101a and 101b for focusing control included in the photo detector 100. Electric signals from the photo sensitive elements 101a and 101b for focusing control are respectively amplified by amplifiers 105a and 105b and are given to a differential amplifier 106 to amplify the difference between the amplified outputs of the amplifiers 105a and 105b. A drive mechanism 109 of the objective lens 94 is driven by a focusing control circuit 107 on the basis of a differential output F of the differential amplifier 106. In the above construction, when the optical card 1 exists at a position indicated by A and a relative distance between the optical card 1 and the objective lens 94 is set to the optimum distance, the reflected lights from the optical card 1 pass through the objective lens 94 and condenser lens 95 and enter the photo sensitive elements 101a and 101b for focusing control with an equal light amount, so that the differential output F of the differential amplifier 106 is set to zero. On the other hand, if the optical card 1 exists at a position shown by B or C, the reflected lights are deviated to either one of the photo sensitive elements 101a and 101b and form an image, so that the differential amplifier 106 outputs the negative or positive differential output F. Fig. 24 is a graph showing the relation between the relative distance between the objective lens 94 and the optical card 1 and the differential output F in the above construction. When the optical card 1 exists at the position A, the difference output F is set to zero. When the optical card 1 exists at the position of B or C, the differential output F has a negative or positive value corresponding to the relative distance. Such a case corresponds to a state in which the focusing control is not correctly executed. When the signal having a negative or positive value is output as a differential output F, in order to set the differential output F to zero, the focusing control circuit 107 actuates the drive mechanism 109 so as to adjust the position of the objective lens 94, that is, to execute what is called a focusing control. However, when the focusing control as mentioned above is executed, there are the following problems. Figs. 25a and 25b are diagrams showing the corresponding relations among the optical card 1, an irradiation light spot SP (corresponding to a detection light spot on the photo sensitive elements for focusing control) which is projected onto the optical card 1, and the photo sensitive elements 101a and 101b for focusing control As shown in Fig. 25a, when the Irradiation light spot SP exists at a normal position in the direction perpendicular to the track guides 18 of the optical card 1, the irradiation light spot SP includes two track guides 18 in its region. The differential output F in this case is obtained as shown by a solid line in the graph of Fig. 24. On the other hand, if the light spot SP exists at a position which is deviated from the normal position as shown in Fig. 25b, the light spot SP irradiates three track guides 18. In such a case, a reflected light amount 18 decreases by the amount of one track guide (that is, the reflectance of the track guide is smaller than those of the other portions as mentioned above), so that the differential output F decreases as shown by a broken line in Fig. 24. As mentioned above, there is a problem such that when the differential output F fluctuates, the focusing control cannot be accurately executed. As a method of solving the above problems, for instance, there is considered to provide a holding mechanism for always keeping the irradiating position of the irradiation light spot SP to the optical card 1 to the normal position or to provide a correction processing circuit of the differential signal F for the focusing control circuit 107. However, such methods are not practical because a construction of the apparatus becomes complicated and it takes a long processing time. As another optical card recording/reproducing apparatus, there has been known an apparatus having a construction in which photo sensitive elements for recording/reproducing, photo sensitive elements for focusing control, and a photo sensitive element for tracking control are respectively arranged on one flat surface as the photo detector 100. Figs. 26a and 26b are diagrams showing the corresponding relations among recording/reproducing photo sensitive elements 102, the photo sensitive elements 101a and 101b for focusing control, and a photo sensitive element 103 for tracking control of the photo detector 100, an irradiation light spot SPl on the optical card 1 (an incident light spot on the photo detector 100 is also the same as the irradiation light spot SP1), and the optical card 1. In the photo detector 100, the photo sensitive elements 101a and 101b for focusing control are arranged in the lower portion, one of the recording/reproducing photo sensitive elements 102 is arranged in the upper portion, the photo sensitive element 103 for tracking control is arranged in the further upper portion, and the other recording/reproducing photo sensitive element 102 is arranged in the further upper portion ("upper" and "lower" denote "upper" and "lower" in Figs. 26a and 26b). However, when the focusing control is executed in the photo detector 100 in which the photo sensitive elements 101a, 101b, 102, and 103 are arranged on one flat surface, there are the following problems. That is, as shown in Fig. 26a, when the major axis direction of the elliptic detection light spot SP1 which is obtained in the photo detector 100 coincides with the arranging direction of the photo sensitive elements 101a to 103, the focusing control is correctly executed. However, as shown in Fig. 26b, if the major axis of the detection light spot SP1 is inclined and deviated from the normal position, even if the focusing state is normal (the position shown by A in Fig. 23), a large amount of incident light from the detection light spot SPl is detected by either one of the photo sensitive elements 101a and 101b for focusing control. Such a state is not regarded as a correct focusing state, so that the focusing control cannot be correctly executed. Such a situation in which the detection light spot SP1 is inclined and deviated from the normal position occurs in the case where the irradiation light spot SP1 was obliquely irradiated onto the optical card 1 or where the detection light spot SP1 by the reflected light is formed onto the photo detector 100 in a twisted state due to a fluctuation of the optical system. As a method of solving the above problems, for instance, there is considered to provide an adjusting mechanism for adjusting so that the major axis direction of the detection light spot SP1 coincides with the arranging direction of the photo sensitive elements 101a to 103. However, such a method is not practical because a construction of the apparatus becomes complicated and it takes a long processing time. Fig. 27 shows the detecting operation of further another photo detector. That is, Fig. 27 is a diagram for explaining a detected light amount of the recording/reproducing photo sensitive elements of the photo detector 100 in the case where the optical card 1 was scanned by the irradiation light spot (corresponding to the detection light spot). When the optical card 1 is moved in the direction of a blank arrow, the irradiation light spot relatively moves to the positions indicated by SP21, SP22, and SP23. When a light spot SP21 is projected to the position where the pit 19 exists in association with the movement of the light spot, the reflected light amount becomes minimum and the detected light amount is also set to the minimum value k 1 . On the other hand, when a light spot SP23 is projected to the position where no pit 19 exists, the reflected light amount is set to the maximum value k 2 . A reproduction signal is formed on the basis of such a detected light amount. However, in the above construction, there is a problem such that the detected light amount is not accurately obtained in correspondence to the presence or absence of the pit 19 and a reproduction signal of the correct information cannot be formed. That is, for instance, if the irradiation light spot SP22 exists at the just intermediate position of the two pits 19, both side portions of the irradiation light spot SP22 are projected to the pits 19 locating on both sides, respectively. Thus, an intermediate light amount k 3 between the minimum light amount k 1 and the maximum light amount k 2 is detected. Such an intermediate light amount k 3 becomes an obstacle upon formation of the reproduction signal. An optical card reproducing apparatus according to the preamble of claim 1 is known from WO-A-88/10495. SUMMARY OF THE INVENTION An object of the invention is to provide an optical card recording/reproducing apparatus in which even if the longitudinal direction of a detection light spot differs from the arranging direction of photo sensitive elements, the focusing control can be always accurately executed. Further, the invention provides an optical card recording/reproducing apparatus as defined in claim 1. A sum signal of a light detection signal of one of the photo sensitive elements of one of the two pairs and a light detection signal of one of the photo sensitive elements of the other pair is extracted. A sum signal of a light detection signal of the other photo sensitive element of one of the two pairs and a light detection signal of the other photo sensitive element of the other pair is extracted. The difference of those two sum signals is used as a focusing error signal. According to the invention, even if a projection light spot for focusing control is inclined to the direction perpendicular to the track guides on the optical card, the focusing error signal is obtained on the basis of the above sum signals, so that the accurate focusing control can be always accomplished. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing an optical system of an optical head in an optical card recording/reproducing apparatus of the present invention; Fig. 2 is a perspective view showing an element structure of an end face light emitting diode; Fig. 3 shows a light emitting surface of the end face light emitting diode and its light emitting intensity; Fig. 4 shows a light spot forming state on an optical card; Figs. 5 and 6 show light images projected onto a photo detector; Fig. 7 shows the principle of the focusing control; Fig. 8 shows signal waveforms in the focusing control; Fig. 9 shows the principle of the tracking control; Fig. 10 shows signal waveforms in the tracking control; Fig. 11 shows the reproduction principle of recorded information; Fig. 12 shows an example of a signal waveform upon reproduction; Fig. 13 shows another embodiment of an optical system of an optical head; Figs. 14a and 14b relate to an embodiment of an optical card recording/reproducing apparatus and are diagrams showing the corresponding relations among an optical card, an irradiation light spot (corresponding to a detection light spot in photo sensitive elements for focusing control) which is irradiated onto the optical card, and photo sensitive elements for focusing control; Figs. 15a and 15b relate to an embodiment of the invention and are diagrams showing the corresponding relations among each photo sensitive element of a photo detector, a detection light spot (irradiation light spot corresponding to the detection light spot) which is obtained by the photo detector, and an optical card; Figs. 16a to 17 relate to a further embodiment of an optical card recording/reproducing apparatus; Figs. 16a and 16b are front views of different embodiments of recording/reproducing photo sensitive elements; Fig. 17 is an explanatory diagram for explaining a detected light amount of the recording/reproducing photo sensitive elements of a photo detector corresponding to a scanning state of an irradiation light spot (corresponding to a detection light spot) to the optical card; Figs. 18 to 27 show a related art; Fig. 18 shows a whole optical card and an enlarged part of this card; Fig. 19 shows an optical system of an optical head; Fig. 20 shows light spots on an optical card; Fig. 21 is a block diagram showing a circuit construction of an optical card recording/reproducing apparatus; Fig. 22 shows a general construction of an optical head; Fig. 23 shows a general construction of a focusing control mechanism; Fig. 24 is a graph showing the relation between a differential output and a relative distance upon focusing control; Figs. 25a to 25b are diagrams corresponding to Figs. 14a and 14b, respectively; Figs. 26a and 26b are diagrams corresponding to Figs. 15a and 15b, respectively; and Fig. 27 is a diagram corresponding to Fig. 17. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an embodiment of an optical card recording/reproducing apparatus according to the present invention, Fig. 1 shows an optical system of an optical head which is assembled in such an apparatus. A mechanical structure of the optical card recording/reproducing apparatus is practically similar to that shown in Figs. 20 to 26 and its description is omitted here. The optical system shown in Fig. 1 includes: a first light projection optical system 111 using a semiconductor laser 114 as a light source; and a second light projection optical system 112 using an end face light emitting diode 119 as a light source. The light emitted from the second light projection optical system 112 is projected onto the optical card 1 and the reflected lights are led to photo detectors 125 and 126 and are detected by a light reception optical system 113. The first light projection optical system 111 is used to record information and uses the semiconductor laser 114 as a light source and includes a collimating lens 115, a warping prism 116, a deflecting beam splitter 117, and an objective lens 118. The semiconductor laser 114 is driven only in the information recording mode. The light emitted from the semiconductor laser 114 is transformed to a parallel beam having an almost elliptic cross section by the collimating lens 115. Only the minor axis direction of the ellipse of the parallel beam is enlarged by the warping prism 116, so that the cross section of the parallel beam is warped into an almost circle. The circular beam substantially comprises a P polarization light component due to the characteristics of the semiconductor laser 114. The almost of the circular beam passes through the deflecting beam splitter 117 and enters onto the objective lens 118. The light is converged onto the optical card 1 by the objective lens 118 and becomes a circular light spot SP w as shown in Fig. 5. An energy density is locally raised by the light spot SP w and a thermal irreversible change is caused in the information recording portion 16 of the optical card 1, thereby forming the pits 19 indicative of the information to be recorded. The optical card 1 is moving in the direction (shown by an arrow in Fig. 4) along the track guides 18. When pulses modulated by the information to be recorded are given to the semiconductor laser 114 and the laser 114 emits the pulse-like light, the pits 19 are successively formed onto the optical card 1 and the information is recorded as a pit train onto the information recording track 17. The second light projection optical system 112 uses the end face light emitting diode 119 as a light source and the light emitted from the diode 119 is transformed into an almost parallel beam by a collimating lens 120. Only the S polarization light component of the parallel beam is reflected by the deflecting beam splitter 117 and enters the objective lens 118 at an angle which is deviated from the optical axis by, for instance, about 1 mm. An image of the light emitting surface of the end face light emitting diode 119 is formed onto the optical card 1. The light emitting surface of the diode 119 has a slit-like (elongated rectangular) shape. The diode 119 is continuously driven in the recording and reproducing modes and forms a slit-like optical image SP s as shown in Fig. 5 onto the optical card 1. A broad mesa type end face light emitting diode or the like is used as the end face light emitting diode 119. Fig. 2 shows a structure of the diode 119. A light emitting center wavelength of the end face light emitting diode 119 is set to, for instance, 780 µm. The diode 119 has a slit-like light emitting surface LS as shown in Fig. 3 and its light emitting intensity is almost uniform in the surface as shown in the diagram. Fig. 4 shows the light image SP s of the light emitting surface of the diode 119 which is formed on the optical card 1. The light image SP s crosses almost perpendicularly the track guides 18 on the optical card 1. For instance, a length of light image SPs is set to 50 µm and a width is set to about 3 µm and the range covering three track guides 18 is illuminated. In Fig. 4, the light spot SP w by the semiconductor laser 114 is formed at a position which is away from the light image SP s by the end face light emitting diode 119 by about 50 µm. Upon assembly and adjustment of the optical head, the relative distance between the light image SP s and the light spot SP w can be obtained by giving a relative angle difference between the optical axis cf the light of the semiconductor laser 114 and the optical axis of the light of diode 119 both of which light enter the objective lens 118. It is now assumed that the relative distance between the light spot SP w by the semiconductor laser 114 and the light image SP s by the end face light emitting diode 119 is set to ℓ and a focal distance of the objective lens 118 is set to f. Then, a relative angle difference  between the optical axes to be given is obtained as follows.  = tan -1 ℓ f [rad] When the relative angle difference  is given as mentioned above, the optical axis of the diode 119 is adjusted by using the optical axis of the semiconductor laser 114 as a reference. However, the optical axis of the laser 114 can be also adjusted by using the optical axis of the diode 119 as a reference. Or, another temporary reference is provided and on the basis of the temporary reference, the optical axes of the laser 114 and diode 119 can be also adjusted. Returning to Fig. 1, in addition to the objective lens 118 and deflecting beam splitter 117, the light reception system 113 includes reflecting mirrors 121 and 123, a condenser lens 122, and a half-mirror 124. The slit-like light image SP s by the diode 119 is light amount modulated on the optical card 1 in accordance with the presence or absence of the track guides 18 and pits 19 and is reflected. The reflected lights pass through the objective lens 118 in the opposite direction and are led to the deflecting beam splitter 117 in an state of the almost parallel beam. The reflected lights substantially hold the S polarization light component because of the regular reflection and are reflected by the reflecting surface of the beam splitter 117 and are led to the condenser lens 122 through the reflecting mirror 121. The light converged by the condenser lens 122 is further led to the half-mirror 124 through the reflecting mirror 123. A part of the light passes through the half-mirror 124 and reaches the photo detector 125. The remaining part of the light is reflected by the half-mirror 124 and reaches the other photo detector 126. The light image SP s on the optical card 1 is formed onto the light detecting surface of each of the photo detectors 125 and 126. Now, assuming that the focal distance of the objective lens 118 is set to f and a focal distance of the condenser lens 122 is set to f a , an enlargement magnification is given by (f a /f). Therefore, when the focal distance f a of the condenser lens 122 is set to, e.g., f a = 150 mm and the focal distance f of the objective lens 118 is set to, e.g., f = 4.5 mm, the enlargement magnification (f a /f) is set to f a /f = 150/4.5 ≒ 33.3 (times). Fig. 5 shows the optical image projected onto the photo detector 125 and Fig. 7 shows the light image projected onto the other photo detector 126 and both light images are shown by SPs. Fig. 5 also shows a light amount distribution along a broken line i. Two photo sensitive elements 152 for reproducing recorded information and photo sensitive elements 153a and 153b for tracking control are provided for the photo detector 125. Photo sensitive elements 151a and 151b for focusing control are provided for the other photo detector 126. In the diagram, the photo sensitive elements 153a and 153b for tracking control are formed in an isosceles triangular shape, respectively, and are located between the two photo sensitive elements 152 for reproducing the recorded information. The triangular photo sensitive elements 153a and 153b are arranged in a manner such that one vertex of one of the elements and one vertex of the other element are made coincident and those elements are point symmetrically arranged with respect to the vertex. In a state in which the tracking control is correctly executed, the center of the image of the track guide 18 is located on the vertex. On the other hand, the photo sensitive elements 151a and 151b for focusing control are formed in a longitudinal rectangular shape which is longer than the light image SPs and are arranged in contact relation with each other. In a state in which the focusing control is correctly performed, the light image SPs is formed on a boundary of the photo sensitive elements 151a and 151b. Further, the two photo sensitive elements 152 for reproducing the recorded information are formed in a rectangular shape and are located in correspondence to the two adjacent information recorded or recording tracks 17. Thus, the recorded information can be simultaneously read out from two tracks. Fig. 5 shows the image obtained as a result of that the light is transmitted through the half-mirror 124. Fig. 6 shows the image obtained as a result of that the light is reflected by the half-mirror 124. Thus, both images are the inverted images with respect to the right and left directions. In the diagram, an arrow indicates a moving direction of the optical card 1. In order to converge the light from the semiconductor laser 114 onto the optical card 1 and to form the pits 19 by a thermal irreversible change, it is necessary to execute the focusing control so that an error of the relative distance between the objective lens 118 and the optical card 1 lies within a range of, for instance, ±2 µm. Fig. 7 shows the detection principle of a focusing error signal in the focusing control. The light from the end face light emitting diode 119 passes through the objective lens 118 and is focused to a predetermined position (in-focus position A). When the reflecting surface of the optical card 1 exists at the in-focus position A, the photo sensitive elements l5la and l5lb are positioned at the locations where the reflected lights are led by the condenser lens 122 and the lights of the same light amount enter the photo sensitive elements 151a and 151b for focusing control. The in-focus position of the light by the semiconductor laser 114 and the in-focus position of the end face light emitting diode 119 are previously made substantially coincide upon assembly and adjustment. In Fig. 7, reference numerals 155a and 155b denote amplifiers for amplifying light detection signals of the photo sensitive elements 151a and 151b. Reference numeral 156 indicates a differential amplifier for amplifying a difference between amplified outputs of the amplifiers 155a and 155b. In Fig. 7, when the reflecting surface of the optical card 1 is deviated to a position B near the objective lens 118 rather than the in-focus position A or to a position C far from the in-focus position A, the light image SP s projected onto the photo detector 126 by the objective lens 118 also moves on the photo sensitive elements 151a and 151b in association with a change in relative distance between the optical card 1 and the objective lens 118. The light detection signal levels of the photo sensitive elements 151a and 151b differ, so that a differential output K of the differential amplifier 156 is generated and becomes a focusing error signal. Fig. 8 shows amplifier outputs I and J of the light detection signals of the photo sensitive elements 151a and 151b and the differential output K (focusing error signal) of the differential amplifier 156. When the optical card 1 is deviated from the in-focus position A and the relative distance between the optical card 1 and the objective lens 118 changes, the light image SPs moves on the photo sensitive elements 151a and 151b of the photo detector 126, the outputs of the elements 151a and 151b change, and a focusing error signal whose positive/negative sign is inverted from the in-focus position A as a turning point is produced. From the focusing error signal, the focusing control circuit 45 (shown in Fig. 21) can obtain the information regarding the relative distance between the optical card 1 and the objective lens 118. The focusing control circuit 45 drives a lens driving mechanism (not shown) and adjusts the position of the objective lens 118, thereby executing the automatic focusing control. Fig. 9 shows the detection principle of a tracking error signal in the tracking control. In the diagram, output signals of the photo sensitive elements 153a and 153b for tracking control are sent to amplifiers 165a and 165b and are amplified (amplified outputs are shown by R and Q), respectively. Thereafter, the amplified outputs are supplied to a differential amplifier 166. A differential output S of the differential amplifier 166 is used as a tracking error signal. When the tracking control is correctly executed, the center of the image of the track guides 18 in the light image SP s is accurately located on the same vertex of the photo sensitive elements 153a and 153b for tracking control in the photo detector 125. At this time, the light detection signal levels as outputs of the photo sensitive elements 153a and 153b coincide, so that the differential output S (tracking error signal) is set to zero. If the center of the image of the track guides 18 in the light image SPs is deviated from the correct position, the output signal levels of the photo sensitive elements 153a and 153b change in accordance with the deviating direction (+ or - direction), so that the outputs R and Q of the amplifiers 165a and 165b change as shown in Fig. 11. Therefore, a positive or negative differential output S (tracking error signal) is generated from the differential amplifier 166. On the basis of the tracking error signal, the tracking control circuit 46 (refer to Fig. 21) drives a lens driving mechanism (not shown) and deviates the objective lens 118 in the direction perpendicular to the track guides 18, thereby executing the automatic tracking control. In a state in which the focusing and tracking control are properly executed, the semiconductor laser 114 is pulse driven by pulse signals which were modulated by information to be recorded while moving the optical card 1. Thus, a pit train is formed onto the information recording tracks 17 on the optical card 1 and the information is recorded. In this case, since the focusing error signal and tracking error signal are formed by using the light from the end face light emitting diode 119, the focusing and tracking controls can be executed irrespective of the actuation of the semiconductor laser 114. Therefore, even when the semiconductor laser 114 is driven, there is no need to interrupt the focusing and tracking controls and to hold the objective lens 118 to a fixed position and the like. The controls can be easily executed. On the other hand, although the energy density of the light emitted from the end face light emitting diode 119 is sufficient to execute the focusing and tracking controls and to reproduce the information, it is not so high enough to thermally damage the pits and track guides. Therefore, even if the reproducing operation of information is repeated, there is no fear of deterioration of the pits and track guides. Fig. 11 shows the reproducing principle of recorded information. The optical card 1 is moved in the direction indicated by an arrow in the diagram. In a state in which the focusing and tracking controls are properly executed, pit trains on two information recorded tracks are simultaneously scanned by the photo sensitive elements 152 of the photo detector 125. Light detection signals obtained by the photo sensitive elements 152 are respectively amplified by amplifiers 170. Amplified outputs X and Y of the amplifiers 170 (only the signal Y is shown in Fig. 12) are subjected to a waveform shaping process and the like by signal processors 171. After that, the signals are demodulated by demodulators 172 and the recorded information on the optical card 1 is reproduced. Since the optical card 1 is rectilinearly reciprocated, the self-excited vibration is larger than that in the optical disk in an optical disk drive apparatus or the like. Particularly, when the rectilinear reciprocating motion of the optical card 1 is executed at a high speed in order to satisfy the requirement of the high recording/ reproducing speed, such a self-excited vibration further increases. When the self-excited vibration occurs, a disturbance enters the control system. A control deviation occurs in accordance with a magnitude of the disturbance or a gain of the control system and becomes a cause of the focusing error and tracking error. Fig. 11 shows the relative positional relations between the light images SP s (SP s1 to SP s3 ) by the end face light emitting diode 119 and the photo sensitive elements 152, 153a, and 153b of the photo detector 125. In the diagram, the light image SP s1 shows a state in which the relative positional relations are proper. The light images SP s2 and SP s3 show a position deviated state in which tracKing errors were generated, respectively. However, even if a tracking error occurred, since the light image SP s has a slit-like shape, the light detection signals are hardly influenced so long as the pits 19 are not deviated out of the photo sensitive elements 152. On the other hand, even if a focusing error occurred, the light amounts which are detected by the photo sensitive elements 152 are also hardly influenced. Consequently, even if focusing or tracking error occurred, the signal outputs are hardly influenced, so that the recording/reproducing speed can be made high without deteriorating the S/N ratio of the signal. In the case of the embodiment, on the optical card 1, a reproducing light by the diode 119 traces after a recording light by the semiconductor laser 114. Thus, the recorded information can be reproduced just after the recording and an erroneous recording or the like can be instantaneously found out. Therefore, the writing reliability is extremely high and the system operating time in the recording mode is remarkably reduced. In the above embodiments, the optical system of the optical head is not limited to that shown in Fig. 1. For instance, an optical system as shown in Fig. 13 can be also used. The optical system of the diagram is constructed in the following manner. The first light projection optical system 111 uses the semiconductor laser 114 as a light source and includes the collimating lens 115, warping prism 116, deflecting beam splitter 117, and objective lens 118. The second light projection optical system 112 uses the end face light emitting diode 119 as a light source and includes the collimating lens 120 in addition to the deflecting beam splitter 117 and objective lens 118. Further, light reception optical system 113 includes the reflecting mirror 121, condenser lens 122, half-mirror 124, and photo detectors 125 and 126. The optical system differs from the optical system of Fig. 1 with respect to a point that the parallel beam having an elliptic cross section which is transmitted from the collimating lens 115 is reduced and warped by the warping prism 116. The incident light to the warping prism 116 is reduced only in the major axis direction of the ellipse and is emitted as an almost circular beam. The circular beam is reflected by substantially 100 % by the reflecting surface of the deflecting beam splitter 117 because of the characteristics of the semiconductor laser 114 and is led to the objective lens 118. In this case, an effective value of an NA (numerical aperture) of the objective lens 118 is small. Therefore, although the size of light spot which is converged onto the optical card 1 is large, since a focal depth becomes deep, if a semiconductor laser of a high power can be used, there is an advantage such that even if a focusing error exists, a depth range of a focal point where pits can be formed is widened. The light emitted from the diode 119 is transformed to the almost parallel beam by the collimating lens 120. Only the P polarization light component of the parallel beam is transmitted through the deflecting beam splitter 117 and is led to the objective lens 118. The detecting operations and the like by the photo detectors 125 and 126 are similar to those in the embodiment regarding Fig. 1 as mentioned above and their descriptions are omitted here. An embodiment will now be described in detail. An optical card recording/reproducing apparatus according to this embodiment has an optical head shown in Fig. 22 and a focusing control mechanism shown in Fig. 23. Since its fundamental construction has already been described, its description is omitted. Figs. 14a and 14b are diagrams showing the corresponding relations among the optical card, an irradiation light spot (corresponding to a detection light spot in photo sensitive elements) which is irradiated onto the optical card, and photo sensitive elements for focusing control. In this embodiment, a width W of photo sensitive elements 181a and 181b for focusing control in the direction perpendicular to the track guides 18 on the optical card is set to a length which is integer times as long as a pitch P of the track guides 18 on the optical card in the detection light spot SP which is obtained by the photo sensitive elements for focusing control. In the embodiment, the width W is twice as long as the pitch P. With such a construction, even in the case where the irradiation light spot SP faces three track guides 18 as shown in Fig. 25b, the substantial width dimension of the track guides 18 which face the irradiation light spot SP is set to a value corresponding to two track guides 18 in a manner similar to the case where the irradiation light spot S faces two track guides 18 as shown in Fig. 25a. That is, even when the irradiation light spot SP exists at any position on the optical card in the direction perpendicular to the track guides 18 (at any position in Fig. 14a, at any position in Fig. 14b), a reduction amount of the reflected light amount based on the existence of the track guides 18 in light detected amounts of the photo sensitive elements 181a and 181b for focusing control is set to be always constant. Thus, the differential output F is stably obtained as shown by a solid line in a graph of Fig. 24. In the above embodiment, the width W of the photo sensitive elements for focusing control has been set to a value which is twice as long as the pitch P of the track guides in the detection light spot. However, the width W can be also properly set to a value which is three time, four time, or the like as long as the pitch P. On the other hand, as a method of determining the width W of the photo sensitive elements for focusing control, in addition to a method whereby photo sensitive elements for focusing control having a width W are used, it is also possible to use a method whereby a mask having a window of a width W is placed on the detecting surface of the photo sensitive elements for focusing control which are commercially available. An embodiment of the invention will now be described in detail. An optical card recording/reproducing apparatus according to the embodiment has the optical head shown in Fig. 22 and the focusing control mechanism shown in Fig. 23. Since its fundamental construction has already been described, its description is omitted here. Figs. 15a and 15b are diagrams showing the corresponding relations among photo sensitive elements of a photo detector, a detection light spot (the same as an irradiation light spot on the optical card) which is obtained by the detector, and the optical card. It is requested to compare with Figs. 26a and 26b, which have already been described. According to the invention, a photo detector 180 uses two split-type photo sensitive elements for focusing control. Those elements are arranged at both outside positions of photo sensitive elements 182 for recording/reproducing, respectively. That is, one split-type photo sensitive element for focusing control comprises photo sensitive elements 181Aa and 181Ab. The other split-type photo sensitive element for focusing control comprises photo sensitive elements 181Ba and 181Bb. A photo sensitive element 183 for tracking control is arranged at the center of the photo detector 180. The photo sensitive elements 182 for recording/reproducing are arranged on both sides of the element 183. The photo sensitive elements 181Aa, 181Ab, 181Ba, and 181Bb for focusing control are further arranged on both sides of the elements 182. The sum of light detection signals of the photo sensitive elements 181Aa and 181Ba for focusing control is calculated. The sum of light detection signals of the photo sensitive elements 181Ab and 181Bb for focusing control is calculated. Signals indicative of the sums are input to the differential amplifier. A differential signal indicative of the difference between the sums is output from the differential amplifier and is used as a focusing error signal. In Fig. 15a, in a state in which the focusing control is properly executed, the light detected amounts of the photo sensitive elements 181Aa and 181Ab are equal and the light detected amounts of the photo sensitive elements 181Ba and 181Bb are also equal. Thus, the sum of the light detection signals of the elements 181Aa and 181Ba and the sum of the light detection signals of the elements 181Ab and 181Bb are equal and the differential output is set to zero. As shown in Fig. 15b, even if the detection light spot SPl is inclined for the detector 180, when the focusing control is correctly executed, the sum of the light detection signals of the elements 181Aa and 181Ba and the sum of the light detection signals of the elements 181Ab and 181Bb are equal. Therefore, the differential output is also set to zero. As mentioned above, even when the detection light spot SP1 is obliquely formed onto the detector 180, the focusing control can be correctly performed without any trouble. Further another embodiment of the invention will be described in detail. In an optical card recording/reproducing apparatus regarding the embodiment, various signal processors and the like are integrally constructed in the optical head shown in Fig. 22. Since its fundamental construction has already been described, its description is omitted. Figs. 16a and 16b are front views showing detecting surfaces of recording/reproducing photo sensitive elements 190 as characteristic parts of the embodiment, respectively. In Fig. 16a, the element 190 of a narrow width is used. The width is smaller than a width of detection light spot SP2. That is, the width is set to a width D which is equal to or smaller than the minimum arrangement interval of information pits on the track of the optical card in the detection light spot SP2 on the recording/reproducing photo sensitive element 190. In Fig. 16b, a conventional element is used as a recording/reproducing photo sensitive element 190. By providing masks 191 on both sides of the detecting surface, the detection width is set to D. With such a construction using the masks 191, a commercially available photo sensitive element can be used. The light detecting operation of the recording/ reproducing photo sensitive element 190 shown in Fig. 16a will now be described with reference to Fig. 17. In the case where an irradiation light spot SP21 exists at the position where the center of the irradiation light spot coincides with the center of the information pit 19, the reflected light amount is minimum. Therefore, an output of the photo sensitive element 190 is set to the minimum light amount k 1 . On the other hand, when an irradiation light spot SP23 exists at the position where no information pit 19 is recorded, the reflected light amount is maximum and the output of the element 190 is set to the maximum light amount k 2 . When the irradiation light spot SP22 exists at the position where the center of the irradiation light spot coincides with the intermediate position of two information pits 19 which are neighboring at the minimum arrangement interval, the both side portions of the light spot SP22 are projected onto the two information pits 19. However, since the width D of the recording/reproducing photo sensitive element 190 has been set as mentioned above, the reflected lights from the pits 19 are not detected by the element 190, so that the detected light amount is set to k 2 in a manner similar to the case of the light spot SP23. It is requested to compare with Fig. 27. Consequently, the detected light amount can be accurately obtained in correspondence to the presence or absence of the information pits 19. Even in the embodiment shown in Fig. 16b, the detecting operation is executed in a manner similar to the Fig. 16a.

Claims: An optical card recording/reproducing apparatus for recording/reproducing information from an optical card (1) having a plurality of tracks (17, 18) provided thereon, comprising: a light source (91) for emitting light, at least one photosensitive element (182) for reproducing an information track (17), a photosensitive element (183) for reading a guide track (18), photosensitive elements (181Aa, 181Ab, 181Ba, 1818b) for focusing control, said photosensitive elements for focusing control comprising a first pair of front and rear photosensitive elements (181Aa, 181Ab) and a second pair of front and rear photosensitive elements (181Ba, 181Bb), said two pairs of photosensitive elements being arranged apart from each other at a predetermined distance in a direction perpendicular to the direction of said tracks on said optical card and said front and rear photosensitive elements of each said pair being arranged adjacent to each other along the direction of said tracks on said optical card, and an optical system (92, 93, 94, 95) for converging light emitted from said light source onto said optical card and for forming an image of light reflected from said optical card onto said photosensitive elements, characterized in that said first pair of photosensitive elements (181Aa, 181Ab) and said second pair of photosensitive elements (181Ba, 181Bb) are separated in said direction perpendicular to the direction of said tracks by said at least one photosensitive element (182) for reproducing an information track placed therebetween. An apparatus according to claim 1 characterized by the photosensitive element (183) for reading a guide track being disposed at the center position of said first and second pairs of photosensitive elements (181Aa, 181Ab, 181Ba, 181Bb), An apparatus according to claim 1 characterized in that said apparatus further includes: first means for adding light detection signals output from said front photosensitive elements (181Aa, 181Ba); second means for adding light detection signals output from said rear photosensitive elements (181Ab, 181Bb); and third means for calculating a difference between said outputs of said first and second means to produce a focusing error signal.

Inventors: ISHIDA TAKESHI, KENTATSU KUNIHIRO, TSUBOI KAZUO, ISHIDA,TAKESHI, KENTATSU, KUNIHIRO, TSUBOI, KAZUO, ISHIDA,TAKESHI C/O OMRON CORPORATION, KENTATSU, KUNIHIRO, C/O OMRON CORPORATION, TSUBOI, KAZUO, C/O OMRON CORPORATION
Applicants: OMRON TATEISI ELECTRONICS CO, OMRON CORPORATION
Application year: 1990
Main classification: G11B7
IPC codes: G11B17, G11B7, H01L33, G11B25