Abstract:
A compact inexpensive optical disk drive adaptable to high-density optical disks is provided by improving a loading mechanism for an optical disk. A mechanism for loading an optical disk, in or from which information is optically recorded or reproduced, into the body of an optical disk drive is mounted on a chassis. The loading mechanism consists of a spindle motor, a lift plate, and a sheet loader. The spindle motor rotates an optical disk. The spindle motor is placed on the lift plate. The sheet loader moves the lift plate vertically to the chassis so as to attach or detach the spindle motor to or from the optical disk. In the storage device, the tilt of the lift plate relative to the chassis is adjusted at three points on the lift plate. Blade springs for constraining the lift plate to move towards the optical disk are interposed between the chassis and lift plate. The points to which spring forces exerted by the blade springs are applied are located on a surface of the lift plate opposite to the optical disk.

Description:
This is a continuation of application Ser. No. 09/814,079, filed Mar. 21, 2001 (abandoned). 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a storage device employing a replaceable storage medium. More particularly, this invention is concerned with a storage device, having a loading mechanism, such as an optical disk drive employing a replaceable optical disk cartridge that looks like a cartridge and has a magneto-optical disk stowed in the cartridge. 
   2. Description of the Related Art 
   In recent years, the processing ability and processing speed of personal computers have improved, and the capacities of operating systems and application software packages for programs or data have expanded. Under these circumstances, storage devices must be compact and low-cost. Moreover, there is an increasing demand for a storage device offering a large storage capacity and a high processing speed. 
   An optical disk drive has begun to prevail as a storage device capable of meeting the demands for a compact design, a low cost, a large storage capacity, and a high processing speed. An optical disk cartridge having an optical disk stowed in a cartridge is available as an optical disk employed in such an optical disk drive. Along with the prevalence of the optical disk drive employing the optical disk cartridge, there arises a demand for resistivity to rough handling, stable performance, improved reliability, and reduction in the cost. 
   The stability of an optical disk cartridge loaded on a base of an optical disk drive after being inserted into the optical disk drive may be impaired if the cartridge is handled roughly. Mechanisms included in the optical disk drive are required to work properly when the optical disk cartridge is inserted in the optical disk drive. Moreover, the mechanisms are required to be inexpensive. 
   In the optical disk drive employing the optical disk cartridge, an object lens included in an optical system and an optical disk, that is a storage medium, must run precisely parallel to each other for the purpose of attaining a high density of the data stored in an optical disk. As a solution, a tilt follow-up mechanism may be included in an optical pickup included in the optical system. 
   The solution of including the tilt follow-up mechanism in the optical pickup included in the optical system has disadvantages that the number of elements constituting the optical pickup increases, and the cost of an optical disk drive increases accordingly, and the number of components that must be controlled increases. These disadvantages become an obstacle to realization of an inexpensive optical disk drive. 
   Another solution is that a mechanism is included for adjusting the tilts of an object lens and the optical disk during assembling of optical elements constituting an optical system for the purpose of readily attaining parallelism between the object lens included in the optical system and the optical disk. An optical disk drive adopting the solution has been put into practical use. To realize the tilt adjusting mechanism, an actuator including a tilt adjusting mechanism is generally adopted for the optical pickup. 
   In particular, a typical optical pickup is composed of a carriage movable in a radial direction of an optical disk and an inching actuator capable of inching for tracking or focusing while being mounted on the carriage. Another type of optical pickup is such that the body of a carriage controls the inching in the radial direction (direction of tracks) on an optical disk and an inching actuator mounted on the carriage controls focusing. 
   However, the type of optical pickup composed of the carriage movable in the radial direction on an optical disk and the inching actuator capable of inching for tracking or focusing while being mounted on the carriage has disadvantages. Specifically, the number of optical elements is so large that part costs and machining costs are high. Therefore, this type of optical pickup is not favorable from the viewpoint of reducing the cost of the optical disk drive. 
   The type of optical pickup in which the body of the carriage controls inching in the radial direction on an optical disk and the actuator mounted on the carriage controls focusing alone helps reduce the cost of an optical disk drive and allows compact design an optical disk drive. However, when the actuator is provided with a tilt adjusting mechanism, a tilt adjustment space is needed. This poses a problem in that the height of the optical disk drive increases. Furthermore, for constructing a high-performance optical disk drive, the actuator and a magnetic circuit for generating a driving force for the actuator must be tilted. This discourages efforts to design a compact optical disk drive. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a storage device such as an optical disk drive that is compact and inexpensive and is adaptable to high-density optical disks. 
   To provide an inexpensive storage device, a pickup to be adopted must be of a type in which the body of a carriage controls inching in a radial direction on an optical disk and an actuator mounted on the carriage controls focusing alone. For realizing a compact design, it is a must that a tilt adjusting mechanism is not included in the optical pickup. Accordingly, another object of the present invention is to provide a spindle motor assembly having a tilt adjusting mechanism, making it possible to compactly design a storage device, and enabling use of an inexpensive optical pickup. 
   To accomplish the above objects, the present invention presents the first to fifth aspects described below. 
   In the first aspect of the present invention, a storage device has a mechanism, which loads a replaceable storage medium into the body of the storage device, mounted on a chassis. The loading mechanism consists of a spindle motor, a lift plate, and a lifting mechanism. The spindle motor rotates the storage medium. The spindle motor is placed on the lift plate. The lifting mechanism moves the lift plate vertically to the chassis so as to attach or detach the spindle motor to or from the storage medium. In the storage device, a tilt adjusting mechanism for adjusting the tilt of the lift plate relative to the chassis when the lift plate is moved towards the storage medium is realized to involve at least three points on the lift plate. One of the points involved in the tilt adjusting mechanism is regarded as a reference height. A height adjusting mechanism for adjusting the height of the lift plate relative to the chassis adjusts the remaining points. Thus, the tilt of the spindle motor relative to the storage medium can be adjusted. 
   According to the first aspect, it is unnecessary to include a tilt adjusting mechanism in an optical pickup included in an optical disk drive. An inexpensive optical pickup can therefore be adopted. Consequently, the cost of the optical disk drive can be minimized. 
   In the present invention, a storage device has a mechanism, which loads a replaceable storage medium into the body of the storage device, mounted on a chassis. The loading mechanism consists of a spindle motor, a lift plate, and a lifting mechanism. The spindle motor rotates the storage medium. The spindle motor is placed on the lift plate. The lifting mechanism moves the lift plate vertically to the chassis so as to attach or detach the spindle motor to or from the storage medium. In the storage device, a constraining mechanism for constraining the lift plate movement towards the storage medium is interposed between the chassis and lift plate. Points, at which constraining force exerted by the constraining mechanism is applied, are located on a surface of the lift plate opposite to the storage medium. 
   According to the second aspect, the constraining mechanism is used to move the lift plate towards the storage medium. The spindle motor can be chucked to the storage medium on a stable basis. 
   In the third aspect of the present invention, the storage device provided from the second aspect also has a holding mechanism and a freeing mechanism. When the storage medium is not inserted in the body of the storage medium, the holding mechanism holds the lift plate away from the chassis. When the storage medium is inserted into the body thereof, the freeing mechanism moves the holding mechanism in a direction opposite to a direction of insertion of the storage medium so as to free the lift plate. The freeing mechanism allows the constraining mechanism to quickly move the lift plate towards the storage medium. 
   According to the third aspect, the constraining mechanism is used to move the lift plate towards the storage medium. Consequently, the spindle motor can be quickly chucked to the storage medium. 
   In the fourth aspect of the present invention, the storage device provided from the third aspect also includes an eject button and an ejecting mechanism. The eject button is used to instruct the body to eject the storage medium. When the eject button is pressed, after the holding mechanism is moved in a direction opposite to a direction of ejection of the storage medium, the ejecting mechanism ejects the storage medium out of the body of the storage device. 
   According to the fourth aspect, the holding mechanism operates before the ejecting mechanism ejects the storage medium out of the body of the storage device. Consequently, the spindle motor chucked to the storage medium is freed before the storage medium is ejected. 
   In the fifth aspect of the present invention, the lift plate included in the storage device provided from the fourth aspect has two pairs of pins disposed at laterally symmetrical positions in a direction orthogonal to the direction of insertion of the storage medium. The holding mechanism includes holding members, grooves, and inclined planes. The holding members hold the pins with no storage medium inserted in the main unit. The grooves receive the pins when the holding mechanism is moved at the completion of inserting the storage medium into the storage device. The inclined planes are engaged with the pins when the holding mechanism is moved in the direction opposite to the direction of ejection of the storage medium, whereby the spindle motor is separated from the storage medium. 
   According to the fifth aspect, when the eject button is pressed, the holding mechanism is moved in the direction opposite to the direction of ejection of the storage medium. At this time, the pins slide on the inclined planes of the holding mechanism, whereby the spindle motor is separated from the storage medium. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the description as set forth below with reference to the accompanying drawings, wherein: 
       FIG. 1  is a perspective drawing showing the appearance of a whole optical disk drive in accordance with the present invention seen from the top thereof; 
       FIG. 2  is an exploded perspective drawing showing the structure of the optical disk drive, which is shown in  FIG. 1 , seen from the top thereof; 
       FIG. 3  is an exploded perspective drawing showing the structure of the optical disk drive, which is shown in  FIG. 1 , seen from the bottom thereof; 
       FIG. 4  is a perspective drawing showing the optical disk drive, which is shown in  FIG. 1 , with a front panel removed therefrom; 
       FIG. 5  is a perspective drawing showing the optical disk drive, which is shown in  FIG. 4 , seen from the bottom thereof; 
       FIG. 6  is a perspective drawing showing the optical disk drive, which is shown in  FIG. 4 , with a top cover and bottom cover removed therefrom; 
       FIG. 7  is a perspective drawing showing the optical disk drive, which is shown in  FIG. 6 , with a printed-circuit board removed therefrom; 
       FIG. 8  is a plan view of the optical disk drive shown in  FIG. 7 ; 
       FIG. 9  is a perspective drawing showing a main body shown in  FIG. 7  with a cartridge holder assembly and a shield for a printed-circuit board removed therefrom; 
       FIG. 10  is a perspective drawing showing the structure of a chassis of the main body of the optical disk drive in accordance with the present invention seen from the top thereof; 
       FIG. 11  is a perspective drawing showing the structure of the chassis of the main body of the optical disk drive in accordance with the present invention seen from the bottom thereof; 
       FIG. 12  is a perspective drawing showing the chassis shown in  FIG. 11  with major components including a stationary optical unit, a movable optical unit, and a spindle motor assembly mounted thereon; 
       FIG. 13A  is an exploded perspective view showing mounting of the spindle motor assembly in the main body shown in  FIG. 12 ; 
     FIG.  13 B and  FIG. 13C  are a side view and plan view of a blade spring for constraining the spindle motor assembly to move; 
     FIG.  13 D and  FIG. 13E  are a side view and plan view of another blade spring for constraining the spindle motor assembly to move; 
       FIG. 14  is a perspective drawing showing the optical disk drive, which is seen from the bottom thereof, with the front panel, cartridge holder assembly, and printed-circuit board mounted in the main body thereof shown in  FIG. 12 ; 
       FIG. 15  is a perspective drawing showing the optical disk drive shown in  FIG. 14  with twisted coil springs substituted for the blade springs; 
       FIG. 16A  is a perspective drawing showing the structure of the spindle motor assembly employed in the optical disk drive in accordance with the present invention; 
       FIG. 16B  is a perspective drawing showing the spindle motor assembly, which is shown in  FIG. 16A , seen from below; 
       FIG. 17A  is a side view for explaining a conventional way of routing a lead extended from a spindle motor included in a spindle motor assembly; 
       FIG. 17B  is a side view for explaining an example of routing a lead extended from a spindle motor included in a spindle motor assembly according to the present invention; 
       FIG. 17C  is a side view for explaining another example of routing a lead extended from a spindle motor included in a spindle motor assembly according to the present invention; 
       FIG. 18A  is a side view showing an example of a sheet,loader employed in an optical disk drive in accordance with the present invention; 
       FIG. 18B  is a plan view of the sheet loader shown in  FIG. 18A ; 
       FIG. 19A  is a side view of an example of a sheet loader employed in a conventional optical disk drive; 
       FIG. 19B  is a plan view of the sheet loader shown in  FIG. 19A ; 
       FIG. 20A  is a perspective drawing showing the spindle motor assembly in accordance with the present invention, which is shown in FIG.  16 A and  FIG. 16B , joined with the sheet loader in accordance with the present invention shown in FIG.  18 A and  FIG. 18B ; 
       FIG. 20B  is a perspective drawing showing the spindle motor assembly and sheet loader, which are joined as shown in  FIG. 20A , seen from the bottom of the sheet loader; 
       FIG. 21  is a bottom view of the stationary optical unit and the spindle motor assembly and sheet loader shown in FIG.  20 A and  FIG. 20B  mounted on the chassis; 
       FIG. 22  is a plan view of the optical disk drive shown in  FIG. 9  with an optical disk cartridge about to be inserted into the optical disk drive, showing the states of an ejection arm and a timing arm and the position of the sheet loader; 
       FIG. 23  is a plan view of the optical disk drive shown in  FIG. 22  with the optical disk cartridge inserted halfway; 
       FIG. 24  is a plan view of the optical disk drive shown in  FIG. 22  with the optical disk cartridge fully inserted thereinto, showing the states of the ejection arm and timing arm and the position of the sheet loader; 
       FIG. 25A  to  FIG. 25C  are explanatory diagrams showing the states of the sheet loader and spindle motor assembly which are engaged with each other when the optical disk cartridge is inserted into the optical disk drive as shown in  FIG. 22  to  FIG. 24 ; 
       FIG. 25D  is an explanatory diagram showing the states of the sheet loader and spindle motor assembly which are engaged with each other when the optical disk cartridge is ejected from the optical disk drive; 
       FIG. 26  is a plan view of part of a chassis of a conventional optical disk drive showing disposition of a stationary optical unit; 
       FIG. 27  is a plan view of part of the chassis of the optical disk drive for explaining the disadvantage of the disposition of the stationary optical unit in the conventional optical disk drive; 
       FIG. 28A  is a plan view of part of the chassis showing disposition of the stationary optical unit in the optical disk drive in accordance with the present invention; 
       FIG. 28B  shows a disposition of the same beam splitter as that shown in  FIG. 28A  in the stationary optical unit included in the conventional optical disk drive; 
       FIG. 28C  shows a disposition of the beam splitter included in the stationary optical unit in the optical disk drive in accordance with the present invention; 
       FIG. 28D  shows another example of the beam splitter included in the stationary optical unit in the optical disk drive in accordance with the present invention; 
       FIG. 29  is an exploded perspective drawing for explaining incorporation of optical elements into the stationary optical unit mounted on the chassis of the optical disk drive in accordance with the present invention; 
     FIG.  30 A and  FIG. 30B  are perspective drawings showing part of the stationary optical unit in the conventional optical disk drive, thus explaining how to align a servo unit; 
     FIG.  31 A and  FIG. 31B  are perspective drawings showing part of the stationary optical unit in the optical disk drive in accordance with the present invention, thus explaining how to align a servo unit; 
       FIG. 32A  shows the structure of a sensor mount employed in the conventional optical disk drive and the structure of a sensor-mounted flexible printed-circuit board to be mounted in the sensor mount; 
       FIG. 32B  is a side view showing part of the structure of the sensor mount employed in the conventional optical disk drive, and thus explaining the disadvantage of the structure; 
       FIG. 33A  shows the structure of a sensor mount employed in the optical disk drive in accordance with the present invention, and the structure of a sensor-mounted flexible printed-circuit board to be mounted in the sensor mount; and 
       FIG. 33B  is a side view showing part of the structure of the sensor mount employed in the optical disk drive in accordance with the present invention, and thus explaining the advantage of the structure. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of a storage device in accordance with the present invention will be described in conjunction with the drawings by taking an optical disk drive that is an exemplary embodiment for instance. 
     FIG. 1  is a top view of a whole optical disk drive  1  in accordance with an embodiment of the present invention. An insertion port  1 A for an optical disk cartridge and a front panel  1 F having an eject button  1 E, which is used to eject an optical disk cartridge from the disk drive, are formed on the front side of the optical disk drive  1 . In the present embodiment, the optical disk drive  1  has a top cover  2  and a bottom cover  6 . 
     FIG. 2  is a top view showing disassembled components of the optical disk drive  1  shown in FIG.  1 .  FIG. 3  is a bottom view showing the disassembled components of the optical disk drive  1  shown in FIG.  1 . In the present embodiment, a printed-circuit board  3 , a cartridge holder assembly  4 , and a main body  5  are interposed between the top cover  2  and bottom cover  6  and arranged in that order beneath the top cover  2 . The front panel  1 F having the insertion port  1 A and Eject button  1 E is attached to the main body  5 . FIG.  2  and  FIG. 3  show the overall structure of the optical disk drive in accordance with the present invention. Individual components required for the present invention will be described later. 
     FIG. 4  shows the optical disk drive  1  shown in  FIG. 1  with the front panel  1 F removed therefrom. Part of the main body  5  interposed between the top cover  2  and bottom cover  6  is seen to lie behind the front panel  1 F.  FIG. 5  shows the optical disk drive  1  shown in  FIG. 4  as seen from the bottom thereof. 
     FIG. 6  shows the optical disk drive  1  shown in  FIG. 4  with the top cover  2  and bottom cover  6  removed therefrom. As apparent from the drawing, the cartridge holder assembly  4  is placed on the main body  5  of the optical disk drive  1 , and the printed-circuit board  3  is placed on the cartridge holder assembly  4 . 
     FIG. 7  shows the optical disk drive  1  shown in  FIG. 6  with the printed-circuit board  3  removed therefrom.  FIG. 8  is a plan view of the optical disk drive  1  shown in FIG.  7 . As seen from these drawings, the cartridge holder assembly  4  placed on the main body  5  has a cartridge holder  40  covering the top of a portion of the main body  5  in which an optical disk cartridge is inserted. The cartridge holder  40  has cartridge pressers  41 , a first shutter opening/closing piece  43 , a second shutter opening/closing piece  45 , a guide groove  42 , a torsion spring  44 , and a bias magnet assembly  46 . The cartridge pressers  41  press the optical disk cartridge, which is inserted into the main body  5 , from above. The first and second shutter opening/closing pieces  43  and  45  are used to open the shutter of an optical disk cartridge inserted in the main body  5 . The torsion spring  44  is laid between the first and second shutter opening/closing pieces  43  and  45 . The bias magnet assembly  46  generates a magnetic field necessary to write data in a disk encapsulated in an optical disk cartridge. A member indicated with a dashed line near the second shutter opening/closing piece  45  in  FIG. 8  is an ejection arm  11  to be described later. 
   A printed-circuit board  30  having a connector  31  formed thereon is located on the main body  5  adjacent to the cartridge holder assembly  4 . The printed-circuit board  30  is covered with a metallic shield  32 . The connector  31  of the printed-circuit board  30  is mated with a connector (not shown) formed on the printed-circuit board  3  described in conjunction with  FIG. 6  when the printed-circuit board  3  is placed on the main body  5 . 
     FIG. 9  shows the main body  5  shown in  FIG. 7  with the cartridge holder assembly  4  and the shield  32  for the printed-circuit board  30  removed therefrom. A base  51  of a chassis  50  of the main body  5  has sidewalls  54  formed on both edges in the longitudinal direction of the main body. A partition wall  59  linking the sidewalls  54  is formed orthogonally to the sidewalls  54 . The partition wall  59  is located at a farther position than the center of the base  51 , that is, at a position far away from the side of the main body (on the left-hand side of the drawing) on which an optical disk cartridge is inserted. One side of the main body is left open. An area on the base  51  surrounded by the two sidewalls  54  and partition wall  59  serves as an optical disk cartridge stowage  60  in which an optical disk cartridge is stowed. 
   A turntable  82  attached to the rotation shaft of a spindle motor is bared in the center of the optical disk cartridge stowage  60  while not projecting from the face of the base  51 . The movable optical unit  7  is located behind the turntable  82 . When an optical disk cartridge is inserted in the optical disk cartridge stowage  60 , the shutter of the optical disk cartridge is opened. At this time, the turntable  82  is thrust into the optical disk cartridge and chucked to the hub of an optical disk. The optical disk is then rotated. The movable optical unit  7  has a carriage that moves in the radial direction of the optical disk rotated by the turntable  82 . Laser light is irradiated to a recording track on the optical disk through an object lens mounted in the carriage, whereby data is read or written from or in the optical disk. The laser light is propagated from the stationary optical unit to be described later to the movable optical unit. The movable optical unit  7  has no direct relation to the constituent features of the present invention. The description of the structure and operation of the movable optical unit  7  will be omitted. 
   The ejection arm  11  and timing arm  12  are located at the sides of the movable optical unit  7  in the optical disk cartridge stowage  60 . The ejection arm  11  pivots, with a rotation shaft as a fulcrum, whereby an optical disk cartridge stowed in the optical disk cartridge stowage  60  is ejected out of the base. When the eject button described in conjunction with FIG.  1  and others is pressed, an ejection motor that is not shown is rotated. This causes the ejection arm  11  to pivot to move a sheet loader. Consequently, the optical disk cartridge is ejected. The timing arm  12  also pivots with a rotation shaft as a fulcrum. The timing arm  12  is actuated at the timing of an optical disk cartridge&#39;s being fully stowed in the optical disk cartridge stowage  60 . The timing arm  12  causes the turntable  82  to be chucked to the hub of an optical disk. The movement of the timing arm  12  will be described later. 
   The printed-circuit board  30  having the connector  31  formed thereon and a control IC and others, which are not shown, mounted thereon is placed in a narrower area on the base  51  defined by the partition wall  59 . The stationary optical unit is placed on the surface of the chassis  50  opposite to the printed-circuit board  30 . The printed-circuit board  30  is connected to a sensor, which will be described later, included in the stationary optical unit over a flexible printed-circuit board (FPC). 
   The structure of the chassis  50  having all components removed therefrom will be described in conjunction with FIG.  10  and FIG.  11 .  FIG. 10  shows the chassis  50  seen from the top cover (the top of the chassis).  FIG. 11  shows the chassis  50  seen from the bottom cover (the bottom of the chassis). To begin with, the top of the base  51  of the chassis  50  will be described. The top is, as mentioned above, partitioned into a wide area and a narrow area by the partition wall  59 . The wide area serves as the optical disk cartridge stowage  60 , while the narrow area serves as a board-mounting section  55 . 
   A round hole  52  for the spindle motor is bored substantially in the center of the optical disk cartridge stowage  60 . A hole  53  for the movable optical unit is bored adjacently to the hole  52  between the hole  52  and partition wall  59 . The turntable  82  of the spindle motor is, as shown in  FIG. 9 , positioned in the round hole  52  for the spindle motor. The movable optical unit  7  is, as shown in  FIG. 9 , fitted in the hole  53  for the movable optical unit. The printed-circuit board  30  is, as shown in  FIG. 9 , mounted on the board-mounting section  55 . 
   Next, the bottom of the base  51  of the chassis  50  will be described. The sidewalls  54  are formed in the longitudinal direction on the bottom of the chassis  50 . The bottom is partitioned into four areas by the partition wall  59 . An area adjoining an entrance of an optical disk cartridge (on the left-hand side of the drawing) serves as a spindle motor assembly storage  61 . A subsequent area serves as a movable optical unit stowage  62 . An area farthest from the entrance for an optical disk cartridge is partitioned into two subareas. One of the subareas serves as the stationary optical unit  57 , while the other subarea serves as an ejection motor stowage  58 . 
   The spindle motor assembly stowage  61  has the hole  52  for the spindle motor and posts  56  used to lift or lower the spindle motor assembly. Attachment blocks having attachment holes  131  and  132  used to attach blade springs  13  to be described later are formed on a side of the spindle motor assembly stowage  61  acting as the entrance for an optical disk cartridge. The hole  53  for the movable optical unit and attachment blocks having attachment holes  141  and  142  used to attach blade springs  14 , to be described later, are formed in the movable optical unit stowage  62 . The tops of the attachment blocks having the attachment holes  131 ,  132 ,  141 , and  142  are lower in height than the apical surfaces of the sidewalls  53  and partition wall  59 . The stationary optical unit  57  is die-cast to have dents and blocks formed therein so that various optical elements can be incorporated in the stationary optical unit  57 . The ejection motor stowage  58  accommodates an ejection motor used to bring the sheet loader  9 , which has been described in conjunction with  FIG. 9 , to an unloaded state. 
     FIG. 12  shows the main body  5 , as seen from the bottom thereof, having major components mounted on the chassis  50  shown in FIG.  11 . The sheet loader  9  and spindle motor assembly  8  are stowed in the spindle motor assembly stowage  61  enclosed with the sidewalls  54  and partition wall  59 . The spindle motor assembly  8  has the posts  56  penetrated through it. The spindle motor assembly  8  is constrained to move towards the base  51  by the first blade springs  13  attached using the attachment holes  131  and  132  shown in  FIG. 11 , and the second blade springs  14  attached using the attachment holes  141  and  142 . The movable optical unit  7  is placed in the movable optical unit stowage  62  adjoining the spindle motor assembly stowage  61 . A plurality of optical elements is integrated into the stationary optical unit  57 , whereby a stationary optical assembly  70  is constructed. Furthermore, the ejection motor  68  is stowed in the ejection motor stowage  58 . 
     FIG. 13A  shows attachment of the spindle motor assembly  8  to the main body  5  shown in FIG.  12 . For attaching the spindle motor assembly  8 , after the sheet loader  9  is put in the spindle motor assembly stowage  61 , the posts  56  projecting from the base  51  are penetrated through guide portions  84  bored in the lift plate  80 . At this time, the spindle motor placed on the face (the lower side of the lift plate  80  in the drawing) of the lift plate  80  is penetrated through the hole  53 . 
   The lift plate  80  has its tilt relative to the base  51  adjusted at three points with the spindle motor jutted out of the hole  53 . A first tilt adjustment screw  16  and a second tilt adjustment screw  17  are disposed at two out of the three points. The remaining point D on the lift plate  80  serves as a height level. When the posts  56  are penetrated through the lift plate  80  and the spindle motor is jutted out of the hole  53 , the tip of the first tilt adjustment screw  16  abuts on a screw abutment plane A on the base  51 . The tip of the second tilt adjustment screw  17  abuts on a screw abutment plane B on the base  51 . The height level D on the lift plate  80  abuts on a level C of a reference projection projected from the base  51  when the posts  56  are penetrated through the lift plate  80 . 
   When the posts  56  are penetrated through the lift plate  80 , the spindle motor assembly  8  is stowed in the spindle motor assembly stowage  61  of the chassis  50 . At this time, the second blade springs  14  shown in FIG.  13 B and  FIG. 13C  have holes thereof aligned with the attachment holes  141  and  142  bored in the chassis  50 , and are secured by screws  15 . The first blade springs  13  shown in FIG.  13 D and  FIG. 13E  have holes thereof aligned with the attachment holes  131  and  132  bored in the chassis  50 , and are secured by screws  15 . As shown in FIG.  13 B and  FIG. 13D , the first and second blade springs  13  and  14  are bent in order to exert predetermined constraining force. When the proximal ends of the first and second blade springs  13  and  14  are fixed to the base  51  using the screws  15 , the lift plate  80  is constrained to move towards the base by the distal ends of the blade springs  13  and  14 . 
   When an optical disk cartridge is fully inserted in a space opposite to the spindle motor assembly stowage  61 , the spindle motor is jutted out of the hole  53 . At this time, a force causing the optical disk cartridge to be ejected is exerted by the ejection arm  11  and timing arm  12 . Consequently, a strong force causing the lift plate  80  to separate from the base  51  works on the entrance-side part of the lift plate  80 . In the present embodiment, the constraining force exerted by the first blade springs  13  is stronger than that exerted by the second blade springs  14 . 
   For adjusting the tilt of the lift plate  80  relative to the base  51 , the tip of the first tilt adjustment screw  16  is abutted on the screw abutment plane A on the base  51 . Moreover, the tip of the second tilt adjustment screw  17  is abutted on the screw abutment plane B on the base  51 , and the height level B on the lift plate  80  is abutted on the level C on the reference projection projected from the base  51 . In other words, after the height level D on the lift plate  80  is abutted on the level C of the reference projection projected from the base  51 , the first tilt adjustment screw  16  and second tilt adjustment screw  17  are adjusted to abut the screw abutment planes. Thus, the tilt of the lift plate  80  relative to the base  51  is adjusted. After the tilt of the lift plate  80  relative to the base  51  is adjusted, the first tilt adjustment screw  16  and second tilt adjustment screw  17  are immobilized. 
     FIG. 14  shows the main body  5  shown in  FIG. 12  with the front panel  1 F, cartridge holder assembly, and printed-circuit board  3  mounted thereon after the completion of adjustment of the tilt of the lift plate  80  relative to the base  51 . As seen from the drawing, the tips of the blade springs  13  and  14  for constraining the spindle motor assembly  8  to move towards the base are engaged with spring receiving concave parts  85  formed in the lift plate  80 . This is intended to prevent parts of the lift plate  80 , to which constraining force is applied, from being changed. 
     FIG. 15  shows an example of the main body  5  shown in  FIG. 14  in which twisted coil springs  18  and  19  are substituted for the blade springs  13  and  14 . The twisted coil springs  18  and  19  are fixed to the chassis  50  using the screws  15 . The twisted coil springs  18  and  19  are located at positions at which substantially the same constraining force as that exerted by the blade springs  13  and  14  is exerted by the twisted coil springs and operated on the lift plate  80 . In this example, the twisted coil spring  18  is formed with two twisted coils that are joined, and constrains the center tongue portion of the lift plate  80  to move towards the base. The twisted coil springs  19  are two independent springs. Since a joint of each twisted coil spring  19  and the lift plate  80  is almost a pinpoint, the twisted coil springs  19  are shielded with covers  28  for fear the constraining points on the lift plate may shift. 
   Points on the lift plate  80  into which the blade springs  13  and  14  or twisted coil springs  18  and  19  are brought into contact may be located near the joint of the lift plate  80  and chassis  50 . The blade springs  13  and  14  or twisted coil springs  18  and  19  may be brought into contact with points on the lift plate near the joint of the lift plate and chassis, thus constraining the lift plate to move towards the chassis  50 . 
   The spindle motor assembly  8  is constrained to move towards the chassis using the blade springs  13  and  14  or twisted coil springs  18  and  19 . This is because the height of the optical disk drive  1  in accordance with the present invention is limited. The springs are used to prevent the height of the optical disk drive  1  from increasing. In contrast, when the height of the optical disk drive  1  is large enough, an independent coil spring could be brought into contact with a point near the center of the lift plate  80  coincident with the center of gravity of the spindle motor assembly  8 . The lift plate  80  could thus be constrained to move towards the chassis. In this case, the point near the center of the lift plate  80  should be coincident with the center of gravity of the lift plate  80  or a geometrical center of gravity that is the joint of the lift plate  80  and chassis  50 . 
   FIG.  16 A and  FIG. 16B  show the structure of the spindle motor assembly  8  employed in the optical disk drive  1  in accordance with the present invention.  FIG. 16A  shows the spindle motor assembly  8  seen from the spindle motor-mounted side (face) thereof.  FIG. 16B  shows the spindle motor assembly  8  seen from the bottom thereof. 
   The lift plate  80  that is a major component of the spindle motor assembly  8  has a detection switch  67 , two alignment pins  69 , the spindle motor  81 , the guide portions  84 , the flexible printed-circuit board (FPC)  20 , four side pins  83 , the first and second adjustment screw holes  86  and  87 , and slits  88 . The detection switch  67  is used to detect the position of a write protector tab when an optical disk cartridge is landed on the base. When the lift plate  80  is lifted to reach the back of the base, the two alignment pins  69  are jutted to the passage of an optical disk cartridge on the base  51 , and fitted into oblong reference holes bored in the optical disk cartridge. The spindle motor  81  has the turntable  82  that is chucked to the hub of an optical disk. The guide portions  84  guide the lift plate  80  when the lift plate  80  is lifted or lowered. The four side pins  83  help lift or lower the lift plate  80 . The first and second tilt adjustment screws described in conjunction with  FIG. 13  are fitted into the first and second adjustment screw holes  86  and  87 . A coil-coupled portion  21  of the flexible printed-circuit board  20  is passed through the slits  88 . D denotes the height level. 
   The two slits  88  are, as shown in  FIG. 16B , bored in the lift plate  80 . The coil-coupled portion  21  of the flexible printed-circuit board  20  is passed through the two slits  88  and returned to the face of the lift plate  80  will be described below. The lift plate  80  has the four spring receiving concave parts  85  formed for accommodating the distal ends of the blade springs  13  and  14  described in conjunction with  FIG. 12  to FIG.  14 . 
   The reason why the two slits  88  are bored in the lift plate  80  in order to introduce the coil-coupled portion  21  of the flexible printed-circuit board to the back of the lift plate  80  will be described below. As shown in  FIG. 17A , a conventional optical disk drive has a large enough height. There is a clearance S between the lift plate  80  and spindle motor  81 . The coil-coupled portion  21  of the flexible printed-circuit board that is coupled to the winding of a coil included in the spindle motor  81  can be routed outside through the clearance S. 
   However, the height of the optical disk drive in accordance with the present invention is so small that there is no clearance between the spindle motor  81  and lift plate  80  through which the coil-coupled portion  21  of the flexible printed-circuit board can be routed outside. In this embodiment, therefore, the slits  88  are, as shown in  FIG. 17B , bored at positions located inside and outside an area on the lift plate  80  occupied by the spindle motor  81 . The coil-coupled portion  21  of the flexible printed-circuit board is passed through the two slits  88  and coupled to the winding of the coil included in the spindle motor  81 .  FIG. 17C  shows another example. A concave part  89  in which part of the coil-coupled portion  21  of the flexible printed-circuit board is stowed is formed to lie inside and outside the area on the lift plate  80  occupied by the spindle motor  81 . 
   Next, the sheet loader for lifting or lowering the lift plate  80  will be described below. FIG.  18 A and  FIG. 18B  show an example of the sheet loader employed in an optical disk drive in accordance with the present invention. FIG.  19 A and  FIG. 19B  show an example of a sheet loader employed in a conventional optical disk drive. 
   As shown in FIG.  19 A and  FIG. 19B , a conventional sheet loader  9 A has an H-shaped body  90 A that has an extension  94 A. Four predetermined portions of the body  90 A are bent to form lift guides  91 A. Each lift guide  91 A has a guide groove  92 A that receives the side pin  83  described in conjunction with FIG.  16 A and FIG.  16 B. The guide groove  92 A is defined with inclined planes  93 A that are parallel to each other and meet the body  90 A at an angle of 45°. The side pins attached to the lift plate  80  as described in conjunction with FIG.  16 A and  FIG. 16B  are inserted into the guide grooves. When the sheet loader  9 A moves back and forth, the side pins move within the guide grooves  92 A along the inclined planes  93 A of the lift guides  91 A. Consequently, the spindle motor is lifted or lowered. 
   When the tilt of the spindle motor is adjusted to the greatest extent so that an optical disk will not interfere with the inner surface of a shell within the shell of an optical disk cartridge, the spindle motor can be deflected by approximately 30′ at the maximum. According to the method of loading the spindle motor using the conventional sheet loader shown in FIG.  19 A and  FIG. 19B , the side pins are lifted along the 45°-inclined planes  93 A formed on the lift guides  91 A of the sheet loader  9 A. The sheet loader  9 A can be turned a little. However, if the tilt is large, a difference in the height between the left and right side pins cannot be absorbed to cause a biased contact phenomenon. Consequently, the sheet loader  9 A fails to thrust the spindle motor assembly into the back of the base of the chassis. 
   In contrast, the sheet loader  9  in accordance with the present invention has, as shown in  FIG. 18B , an H-shaped body  90  analogous to that of the conventional sheet loader  9 A. The body  90  has an extension  94 . Four predetermined portions of the body  90  are bent at right angles to form lift guides  91 . Each lift guide  91  consists of a first guide  911  and a second guide  912 . A guide groove  92  that receives the side pin  83  described in conjunction with FIG.  16 A and  FIG. 16B  is formed between the first guide  911  and second guide  912 . The side of the first guide  911  defining the guide groove  92  is perpendicular to the body  90 . In this example, the distal end of the side of the first guide  911  defining the guide groove  92  is shaped like eaves. The side of the second guide  912  defining the guide groove  92  is an inclined plane  93  meeting the body  90  at 45°. The 45°-inclined plane  93  is formed on the side of the sheet loader comparable to the insertion port for an optical disk cartridge. 
   The body  90  of the sheet loader  9  has a bracket  97  formed near the border between the body  90  and extension  94 . A tension spring  96  is attached to the bracket  97 . The tension spring  96  is laid between the sheet loader  9  and the chassis  50 . Furthermore, the distal portion of the extension  94  is formed as an engagement portion that is engaged with the timing arm as described later. The engagement portion  95  to be engaged with the timing arm is coupled to the ejection motor  68  shown in FIG.  15 . 
   The side pins  83  formed on the lift plate  80  as described in conjunction with FIG.  16 A and  FIG. 16B  are, as detailed later, located on the sides of the second guides  912  parallel to the body  90  with no optical disk cartridge inserted. While an optical disk cartridge is being inserted into the optical disk drive, the sheet loader  9  is immovable. The side pins  83  stay on the second guides  912 . Once the optical disk cartridge is fully inserted in the optical disk cartridge, the sheet loader  9  is moved quickly and the side pins  83  are put in the guide grooves  92 . When the optical disk cartridge is ejected, the sheet loader  9  is moved back to its original position and the side pins  83  are slid on the inclined planes  93 . 
   FIG.  20 A and  FIG. 20B  show the spindle motor assembly  8  shown in FIG.  16 A and FIG.  16 B and the sheet loader  9  shown in FIG.  18 A and  FIG. 18B  which are joined.  FIG. 20A  is a top view, while  FIG. 20B  is a bottom view. The spindle motor assembly  8  and sheet loader  9  have already been described and an iteration will be avoided. FIG.  20 A and  FIG. 20B  show a state in which the side pins  83  are put in the guide groove  92  of the lift guides  91 . 
     FIG. 21  is a bottom view of the main body  5  in which the stationary optical assembly  70  is incorporated in the stationary optical unit  57  of the chassis  50 , and the spindle motor assembly  8  and sheet loader  9  are joined as shown in FIG.  20 A and FIG.  20 B. Reference numeral  22  denotes a flexible printed-circuit board. As described previously, the side pins  83  are put in the guide grooves  92  with an optical disk cartridge fully inserted, because the lift plate is constrained to move towards the chassis by the blade springs  13  and  14 . Moreover, the sheet loader  9  is constrained to move downwards in the drawing, or in other words, towards the insertion port for an optical disk cartridge by means of the tension spring  96  laid between the sheet loader  9  and chassis  50 . 
   In the present embodiment, tapping screws may be used as the screws  15 . Moreover, the first and second adjustment screw holes  86  and  87  bored in the lift plate  80  and the height level D should preferably be arranged at intervals of substantially 120° with the rotation shaft of the spindle motor  81  as a center. In this case, the distances of the first and second adjustment screw holes  86  and  87  bored in the lift plate  80  and the height level D from the rotation shaft of the spindle motor  81  are substantially the same as one another. 
   Next, movements made by the spindle motor assembly  8  and sheet loader  9  when an optical disk cartridge is inserted into the optical disk drive  1  will be described together with movements made by the ejection arm  11  and timing arm  12  in conjunction with  FIG. 22  to FIG.  25 .  FIG. 22  shows a state of the optical disk drive  1 , which is shown in  FIG. 9 , into which the optical disk cartridge  10  is about to be inserted.  FIG. 23  shows a state of the optical disk drive  1  into which the optical disk cartridge  10  is inserted halfway.  FIG. 24  shows a state of the optical disk drive  1  in which the optical disk cartridge  10  is fully inserted.  FIG. 25A  to  FIG. 25C  show joined states of the spindle motor assembly  8  and sheet loader  9  that are attained time-sequentially with the progress of insertion of the optical disk cartridge  10  as shown in  FIG. 22  to FIG.  24 .  FIG. 25D  shows a joined state of the spindle motor assembly  8  and sheet loader  9  attained when the optical disk cartridge  10  is ejected. 
   Before the optical disk cartridge  10  is inserted into the optical disk drive  1 , the ejection arm  11  and the L-shaped timing arm  12  composed of two arms stand still after pivoting by predetermined angles towards the insertion port  1 A for the optical disk cartridge  10 . At this time, one arm of the timing arm  12  is engaged with the engagement portion  95  of the sheet loader  9  that engages with the timing arm. This prevents the sheet loader  9  from moving towards the insertion port  1 A for the optical disk cartridge  10 . The timing arm  12  responds to the movement of the optical disk cartridge  10  so as to indicate the timing of chucking the turntable  82  of the spindle motor assembly  8  to the hub of an optical disk. 
     FIG. 25A  shows the joined state of the spindle motor assembly  8  and sheet loader  9  attained at this time. When the optical disk cartridge  10  is not inserted, the side pins  83  fixed to the lift plate  80  of the spindle motor assembly  8  are all located on the sides of the second guides  912  parallel to the body  90 . 
   As the optical disk cartridge  10  is inserted into the optical disk drive  1 , the distal end of the optical disk cartridge  10  is, as shown in  FIG. 23 , abutted on the ejection arm  11 . When the optical disk cartridge  10  is further inserted into the optical disk drive  1 , the ejection arm  11  pivots. With the insertion of the optical disk cartridge  10  into the optical disk drive  1 , the shutter of the optical disk cartridge  10  is opened by the first shutter opening/closing piece  43  described in conjunction with FIG.  7  and FIG.  8 . This mechanism does not fall within the scope of the present invention, and a description of the mechanism will be omitted. The joined state of the spindle motor assembly and sheet loader  9  attained at this time is identical to the state shown in  FIG. 25A  because the sheet loader  9  does not move. 
   When the optical disk cartridge  10  is further inserted into the optical disk drive  1 , the distal end of the optical disk cartridge  10  is abutted on the timing arm  12 . This causes the timing arm  12  to pivot. When the optical disk cartridge  10  is fully inserted in the optical disk drive  1 , the timing arm  12  fully pivots. This causes one of the arms of the timing arm  12  to disengage from the engagement portion  95  of the sheet loader  9  that engages with the timing arm. Consequently, the sheet loader  9  is moved towards the insertion port  1 A for the optical disk cartridge  10  due to tensile force exerted by the tension spring  96  described in conjunction with FIG.  21 . 
   FIG.  25 B and  FIG. 25C  show movements made by the spindle motor assembly  8  and sheet loader  9  at this time. When the optical disk cartridge  10  is fully inserted in the optical disk drive  1 , the sheet loader  9  is moved quickly towards the insertion port  1 A for the optical disk cartridge  10  as indicated with an arrow R in FIG.  25 B. Consequently, the side pins  83  located on the sides of the second guides  912  parallel to the body  90  are all put in the guide grooves  92 . When the movement of the sheet loader  9  towards insertion port  1 A for the optical disk cartridge  10  is completed, the side pins  82 , as shown in  FIG. 25C , all land on the bottoms of the guide grooves  92 , or in other words, on the sheet loader  9 . According to the present invention, each lift guide  91  has only one inclined plane  93 . When the sheet loader  9  is used to load the spindle motor assembly, the inclined planes  93  of the lift guides  91  are unused. No pressing force operates in the radial direction of the spindle motor assembly  8 . In the present embodiment, the sides of the first guides  911  of the lift guides  91  defining the guide grooves  92  are formed as vertical contact portions that are perpendicular to the body  90  of the sheet loader  9 . When the putting of the side pins  83  in the guide grooves  92  is completed, the side pins  83  are pressed in the radial direction due to the vertical contact portions. Consequently, pressing force operates on the spindle motor  81  in the radial direction of the spindle motor. The pressing force is exerted by tension spring  96 . 
   In this state, the turntable  82  of the spindle motor  81  juts out from the base  51  into the optical disk cartridge stowage  60  described in conjunction with FIG.  9 . The turntable  82  is chucked to the hub of an optical disk in the optical disk cartridge whose shutter is opened. With the turntable chucked to the hub of the optical disk in the optical disk cartridge  10 , the tilt of the lift plate  80  relative to the base  51  is held adjusted owing the first and second tilt adjustment screws  16  and  17  and the height level D which are described previously. 
   The timing arm  12  responds to the movement of the optical disk cartridge  10  so as to determine the timing of,moving the sheet loader  9 . Assuming that the length of one of the two arms of the timing  12  from the rotation shaft thereof to an end thereof that comes into contact with the optical disk cartridge  10  is L 1  and that the length of the other arm thereof from the rotation shaft thereof to an end thereof that triggers movement of the sheet loader  9  is L 2 , the relationship between L 1  and L 2  is L 1 =L 2  or L 1 &gt;L 2 . 
   When the optical disk cartridge  10  is stowed in the optical disk drive  1 , if the eject button  1 E shown in  FIG. 15  or the like is pressed, the optical disk cartridge  10  is ejected. At this time, the ejection motor  68  is actuated. The ejection motor  68  causes the sheet loader  9  to move in a direction opposite to the insertion port  1 A for an optical disk cartridge, or in other words, in a direction of an arrow F in  FIG. 25D  via the engagement portion  95  of the sheet loader that engages with the timing arm. Consequently, the side pins  83  fixed to the lift plate  80  of the spindle motor assembly  8  are moved along the inclined planes  93  of the second guides  912 . Eventually, the turntable  82  of the spindle motor  81  chucked to the hub of the optical disk is freed. 
   With the movement of the sheet loader  9 , the side pins  83  are all disposed on the sides of the lift guides parallel to the body  90 . The state shown in  FIG. 25A  is then restored. When the movement of the sheet loader  9  is completed, the timing arm  12  pivots due to a force exerted by the spring. The arm of the timing arm locks the engagement portion  95  of the sheet loader  9  that engages with the timing arm. Consequently, the sheet loader  9  is locked by the timing arm  12 . The ejection arm  11  starts pivoting when the turntable  82  of the spindle motor  81  chucked to the hub of the optical disk is freed completely and no longer juts out into the optical disk cartridge stowage  60 . Eventually, the optical disk cartridge is ejected outside the optical disk drive  1 . 
   As mentioned above, according to the present embodiment, the spindle motor assembly  8  has a tilt adjusting mechanism. This results in a low-cost and compact optical disk drive employing a replaceable optical disk cartridge. 
   Next, the structure of the stationary optical unit included in the optical disk drive  1  will be described below. Prior to a description of an example of the structure of the stationary optical unit included in the optical disk drive in accordance with the present invention, the disadvantages of a conventional optical unit will be described in conjunction with FIG.  26  and FIG.  27 . 
     FIG. 26  shows the layout of optical elements constituting a stationary optical assembly  70 A included in a conventional optical disk drive. In the conventional optical disk drive, a homeward light path along which light reflected from an optical disk is routed to a sensor meets an outward light path from a laser light source to the optical disk at right angles. A description will be made based on the conventional stationary optical assembly  70 A shown in FIG.  26 . Laser light emanating from a laser diode  71  is passed through a collimator lens  72  and a beam splitter  73  and routed to the movable optical unit  7 . The light is then irradiated to an optical disk. This laser light path from the laser diode  71  to the movable optical unit  7  shall be referred to as an outward light path. In contrast, there is a path of light reflected from the optical disk, passed through the beam splitter  73 , a servo unit (wave front dividing element)  74 , and a condenser  75 , and routed to a sensor  76 . This light path along which light split by the beam splitter  73  is propagated to the sensor  76  shall be referred to as a homeward light path. Reference numeral  77  denotes a light level monitor unit. In the conventional optical disk drive, the homeward light path is orthogonal to the outward light path. 
   In the conventional optical disk drive, another component is located in an area X in which the sensor  76  is disposed. Interference with light by the component occurs in the area X. In the conventional optical disk drive, the stationary optical assembly  70 A is therefore separated from a chassis  50 A by a distance Y in order to avoid the interference by the component occurring in the area X. This poses a problem in that the overall length (depth) of the optical disk drive increases. 
   In the optical disk drive in accordance with the present invention, a homeward light path along which light reflected from an optical disk is passed through the beam splitter  73  and routed to a sensor meets an outward light path, which extends from a laser light source to the optical disk, at 90°+α°. A description will be made based on the stationary optical assembly  70 , which is shown in  FIG. 28A , employed in the embodiment of the present invention. Laser light emanating from a laser diode  71  is passed through a collimator lens  72  and a beam splitter  73 , routed to the movable optical unit  7 , and irradiated to an optical disk. This light path is an outward light path. A homeward light path is a path along which light reflected from the optical disk is separated by the beam splitter  73 , passed through a servo unit (wave front dividing element)  74  and a condenser  75 , and routed to the sensor  76 . An angle at which the homeward light path meets the outward light path is larger than 90°. Reference numeral  77  denotes a light level monitor unit for monitoring the amount of light emanating from the laser diode  71 . 
   In the conventional optical disk drive shown in FIG.  26  and  FIG. 27 , an interface created in the beam splitter  73  meets, as shown in  FIG. 28B , the outward light path at 45°. In the optical disk drive in accordance with the present embodiment shown in  FIG. 28A , the beam splitter  73  is, as shown in  FIG. 28C , tilted by θ°. This is intended to make an angle, at which the homeward path of light branched by the beam splitter  73  meets the outward light path, larger than 90°. Consequently, according to the present embodiment, the homeward light path meets the outward light path at 90°+2θ°. In this case, the rectilinearity of laser light propagated along the homeward path remains substantially unvaried. However, light emitted from the beam splitter  73  is deflected by several tens of micrometers from light incident thereon because of refraction. In the present embodiment, as shown in  FIG. 28A , the beam splitter  73  is tilted by 6.5° so that the homeward light path will meet the outward light path at 90°+13°. 
   Since the homeward light path meets the outward light path at 90°+2θ°, the position of the sensor  76  is separated from the center of the chassis  50 . Light will therefore not be interfered with by any other component located near the position of the sensor  76 . In the present embodiment, it is unnecessary to change the position of the sensor  76  for the purpose of avoiding interference by any other component. Consequently, the overall length (depth) of the optical disk drive can be minimized. 
   In the present embodiment shown in  FIG. 28A , the conventional beam splitter  73  is used as it is, and is mounted on the chassis  50  while being tilted by a predetermined angle. Alternatively, as shown in  FIG. 28D , the beam splitter  73  may not be tilted but a novel beam splitter  73 A having a reflecting surface tilted by 45°+θ° may be employed. Use of the beam splitter  73 A has the same results as those of the beam splitter  73 . 
     FIG. 29  is an explanatory diagram concerning integration of optical elements into the stationary optical unit  57  of the chassis  50  included in the optical disk drive  1  in accordance with the present invention. The stationary optical unit  57  of the chassis  50  is constructed so that a homeward path of light reflected from the beam splitter  73  will meet an outward light path at 90°+2θ°. Specifically, the stationary optical unit  57  of the chassis  50  has a first groove  571  and a second groove  572  formed therein. The first groove  571  is extended along an extension of a direction of movement of a carriage included in the adjoining movable optical unit  7 . The second groove  572  is extended in a direction that meets the direction of the first groove  571  at 90°+2θ°. The beam splitter  73  is located at an intersection between the first groove  571  and second groove  572 . Moreover, the laser diode  71  and collimator lens  7  are locked in the first groove  571 . The servo unit  74 , the condenser  75 , and the sensor  76  mounted in a sensor mount  78  are locked in the second groove  572 . 
   An alignment projection  74 D projects from the servo unit  74 . The alignment projection  74 D is fitted into an alignment hole  57 C bored in the second groove  572 . Alignment of the servo unit  74  will be described later. Moreover, the sensor  76  is mounted on a flexible printed-circuit board  79 . The other end of the flexible printed-circuit board  79  is coupled to a printed-circuit board to be described later. The light level monitor unit  77  is located at a position opposite to the second groove  572  with the beam splitter  73  between them. 
   Incidentally, the chassis  50  is generally die-cast. As long as no extra measures are taken, the precision in the dimensions of the stationary optical unit  57  of the die-cast chassis  50  is low. At least a collimator lens-mounted portion  573  of the first groove  571  and a condenser-mounted portion  574  of the second groove  572  are machined afterwards to have highly precise dimensions. The collimator lens-mounted portion  573  and condenser-mounted portion  574  each have two inclined planes that are inclined in mutually opposite directions. The collimator lens  72  and condenser  75  are placed on the inclined planes. In the present embodiment, the collimator lens  72  is pressed using a sheet presser  72 A after placed on the collimator lens-mounted portion  573 . The collimator lens  72  is thus precisely aligned and locked in the first groove  75 . Likewise, the condenser  75  is pressed using a sheet presser  75 A after placed on the condenser-mounted portion  574 . The condenser  75  is thus precisely aligned and locked in the second groove  572 . 
   Now, alignment of the servo unit  74  will be described below. Beforehand, a conventional method of aligning the servo unit  74  will be described below. 
   FIG.  30 A and  FIG. 30B  are explanatory diagrams concerning the conventional method of aligning the servo unit  74  in an optical disk drive. The stationary optical unit  57  has attachment blocks  57 A opposed to each other. Each attachment block  57 A has, as shown in  FIG. 30A , an attachment notch  57 B formed in the top thereof. The servo unit  74  serving as a wave front dividing element for dividing incident light into three light rays is interposed between the opposed surfaces of the attachment blocks  57 A. The servo unit  74  has two wedged parts  74 A and  74 B whose longitudinal sections are tapered. A curved plane  74 C is sandwiched between the wedged parts  74 A and  74 B. The surfaces of the wedged parts  74 A and  74 B are inclined in mutually opposite directions. A flange  74 F is formed on both sides of the top of the servo unit  74 . 
   For placing the servo unit  74  in a space between the attachment blocks  57 A, the flanges  74  are engaged with the attachment notches  57 B. The width of the servo unit  74  is smaller than the distance between the two opposed attachment blocks  57 A. After the flanges  74  are engaged with the attachment notches  57 B, the servo unit  74  is, as shown in  FIG. 30B , moved laterally to have its position determined. 
   For aligning the servo unit  74 , a light source for emitting reference light, a mechanism for aligning the optical disk drive, a mechanism for moving the servo unit  74 , and an adjustment facility having the ability to monitor light on a screen are installed outside the optical disk drive. After the servo unit  74  is placed in the space between the attachment blocks  57 A, the adjustment facility emits reference light to the servo unit  74 . The servo unit  74  is then moved so that the light irradiated to a screen located at a position opposite to the adjustment facility with the servo unit  74  between them will fall on a proper position on the screen. The position of the servo unit  74  is thus adjusted. The servo unit  74  is then fixed in the position which permits the reference light to fall on the proper position, using an adhesive. For attaching the servo unit  74  to the attachment blocks  57 A according to the conventional method, the expensive and high-precision facility is needed. Besides, many man-hours are required for adjustment. This leads to an increase in the cost of the whole optical disk drive. Moreover, too much time is required for maintenance of the facility and adjustment of the position of the servo unit. This poses a problem in that the efficiency in manufacturing the optical disk drive is very poor. 
   According to the present invention, as shown in  FIG. 31A , the alignment projection  74 D is formed on the bottom of the servo unit  7  having the same structure as the conventional servo unit. Moreover, the alignment hole  57 C that receives the alignment projection  74 D is bored in the bottom of the stationary optical unit  57  between the attachment blocks  57 A. The alignment hole  57 C is finished highly precisely through post-machining. While the alignment projection  74 D projecting from the bottom of the servo unit  74  is fitted into the alignment hole  57 C bored in the bottom of the stationary optical unit  57 , the flanges  74 F are engaged with the attachment notches  57 B. Consequently, the servo unit  74  is, as shown in  FIG. 31B , attached to the attachment blocks  57 A. 
   Consequently, the present invention obviates the necessity of the expensive high-precision adjustment facility. The work of attaching the servo unit  74  that is an optical element can be simplified and speeded up. This leads to a reduction in the cost of an optical disk drive. 
   Finally, the structure of a printed-circuit board on which a sensor to be locked in the farthest end of the second groove  572  is mounted will be described below. Beforehand, the disadvantage of the conventional structure of a sensor-mounted printed-circuit board will be described. 
   FIG.  32 A and  FIG. 32B  are explanatory diagrams concerning the conventional structure of a flexible printed-circuit board, on which the sensor  76  is mounted, adopted for an optical disk drive. The sensor  76  is generally mounted on the flexible printed-circuit board  79 . The flexible printed-circuit board  79  is mounted in a sensor mount  78 A. The other end of the flexible printed-circuit board  79  is coupled to the printed-circuit board  30  shown in  FIG. 22  to FIG.  24 . The flexible printed-circuit board  79  has a board-coupled portion  79 A that is coupled to the printed-circuit board and a sensor-mounted portion  79 B. Part of the sensor-mounted portion communicating with the sensor-mounted portion has a smaller width. The sensor mount  78 A is shaped like a rectangle, and has a concave part  78 B, which receives the sensor-mounted portion  79 B of the flexible printed-circuit board  79 , formed in the center thereof. Attachment holes  78 C are bored across the concave part  78 B. One edge of the concave part  78 B facing the bottom cover (lower end in the drawing) is left open. A leading-out groove  78 D used to lead out the small-width part of the board-coupled portion  79 A of the flexible printed-circuit board  79  is formed on the other edge of the sensor mount  78 A facing the top cover (upper end in the drawing). 
   The sensor-mounted portion  79 B of the flexible printed-circuit board  79  is, as shown in  FIG. 32B , locked in the concave part  78 B of the sensor mount  78 A using an adhesive. The board-coupled portion  79 A of the flexible printed-circuit board  79  is coupled to the printed-circuit board  30  using a solder  33 . In this case, for preventing the sensor  76  in the concave part  78 B from moving due to tension exerted by the flexible printed-circuit board  79 , the flexible printed-circuit board  79  has been folded in the past. This is intended to prevent tension from being applied to the sensor-mounted portion  79 B. Moreover, a thin expensive flexible printed-circuit board is adopted as the flexible printed-circuit board  79  so that the flexible printed-circuit board  79  will exert little tension. 
   According to the conventional structure of a sensor-mounted printed-circuit board, since manual work is necessary to fold the flexible printed-circuit board  79 , many man-hours are required. Moreover, the method of folding the flexible printed-circuit board  79  is different from worker to worker. It occurs that the flexible printed-circuit board  79  is broken because of insufficient folding, or on the contrary, that the flexible printed-circuit board  79  is cut because of excessive folding. Furthermore, the adoption of a thin flexible printed-circuit board as the flexible printed-circuit board  79  increases the cost of an optical disk drive. 
   Furthermore, the adhesion of the adhesive used to bond the sensor-mounted portion  79 B of the flexible printed-circuit board  79  and the sensor mount  78 A deteriorates with a rise in ambient temperature. This causes the distal end  79 C of the sensor-mounted portion  79 B to move within the sensor mount  78 A as indicated with a dashed line in  FIG. 32B  despite application of only slight tension. The position of the sensor  76  is thus changed to disable accurate detection. 
   In contrast, according to the structure of a sensor-mounted printed-circuit board shown in FIG.  33 A and FIG.  33 B and adopted in the present invention, a sidewall  78 G is formed on even an edge of a concave part  78 E of the sensor mount  78  facing the top cover. According to the present invention, the concave part  78 E is shaped like a rectangle and surrounded with sidewalls  78 G, though a drawn-out groove  78 D traverses one sidewall  78 G. On the other hand, according to the present invention, a flexible printed-circuit board having the same shape as the conventional one shown in FIG.  32 A and  FIG. 32B  may be adopted as the flexible printed-circuit board  79 . The procedure of mounting the sensor  76  on the sensor-mounted portion  79 B is the same as the conventional one. 
   However, according to the present invention, when the flexible printed-circuit board  79  is locked in the concave part  78 E using an adhesive, the distal end  79 C of the sensor-mounted portion  79 B must impact against the sidewall  78 G. Therefore, even if tension exerted by the board-coupled portion  79 A of the flexible printed-circuit board  79  is applied to the sensor-mounted portion  79 B, or even if the adhesion of the adhesive deteriorates due to a rise in ambient temperature, the flexible printed-circuit board  79  will not move farther. This is because the distal end  79 C of the flexible printed-circuit board abuts against the sidewall  78 G. It is therefore unnecessary to fold the flexible printed-circuit board  79  in advance. Moreover, an expensive thin flexible printed-circuit board need not be adopted as the flexible printed-circuit board  79 . 
   In the example shown in FIG.  33 A and  FIG. 33B , the sidewall  78 G is formed even on the edge of the concave part  78 E of the sensor mount  78  facing the top cover. To prevent the distal end  79 C of the flexible printed-circuit board  79  from moving due to a rise in temperature, a plurality of projections may be formed on the edge of the concave part  78 B of the sensor mount  78 , which is described in conjunction with FIG.  32 A and  FIG. 32B , instead of the sidewall. The distal end  79 C of the flexible printed-circuit board  79  may be abut against the projections. 
   As mentioned above, according to the present invention, the shape of the sensor mount  78  is modified. Consequently, a shift of a flexible printed-circuit board derived from tension exerted by the flexible printed-circuit board will not occur. This obviates the necessity of folding the flexible printed-circuit board in advance, and leads to an improved ease-of-manufacture. Moreover, since an expensive thin flexible printed-circuit board need not be adopted, the manufacturing cost of an optical disk drive is reduced. 
   As mentioned above, the improvement of an optical system in accordance with the present invention makes it easy to manufacture the optical disk drive  1 . Consequently, the cost of the optical disk drive can be minimized. 
   In the aforesaid embodiment, a storage device in accordance with the present invention has been described based on an optical disk drive employing a magneto-optical disk as a storage medium. A loading mechanism in accordance with the present embodiment described in relation to the embodiment may be adapted to a storage medium other than the magneto-optical disk. For example, the loading mechanism in accordance with the present invention may be adapted to a compact disk (CD) that is reproducible and reprogrammable, an optical disk such as a digital versatile disk (DVD), and a floppy disk realized with a magnetic disk. In this case, the disk may not be stowed in a cartridge or may be stowed in a carrier or a holder only when inserted into a storage device. Moreover, the loading mechanism in accordance with the present invention is adaptable to a type of storage device into which a disk is loaded while being placed on a tray. 
   Likewise, a stationary optical unit in accordance with the present invention described in relation to the aforesaid embodiment may be adapted to a storage medium other than the magneto-optical disk. For example, the stationary optical unit in accordance with the present invention can be applied to an optical disk drive employing a compact disk (CD) that is reproducible or reprogrammable or an optical disk such as a digital multipurpose disk (DVD). 
   Furthermore, a storage device in accordance with the present invention includes not only a disk drive for recording or reproducing information in or from a storage medium shaped like a disk but also a disk drive capable of creating or formatting a storage medium. The storage device in accordance with the present invention also includes a storage device employing a storage medium such as a memory card.