Patent Publication Number: US-8127317-B2

Title: Disc changer

Description:
TECHNICAL FIELD 
     The present invention relates to a disc changer, particularly but not exclusively to a disc changer that stores a plurality of discs therein, transports a disc selected from a plurality of discs, and performs recording and/or reproducing information signal on the disc. In the specification, the wording of “recording/reproducing an information signal on a disc” refers to “at least one of recording an information signal on a disc and reproducing an information signal from a disc” as an abbreviated form of expression. 
     BACKGROUND ART 
     A conventional disc changer normally has a plurality of trays housed within a casing, with each tray arranged to carry an optical disc. In one known type, the disc changer includes a single selected tray or a main tray with a selected sub tray and by depressing an eject button the main tray carries the sub tray to move from a standby position within the casing to protrude outward to a disc exchange position for inputting or exchange of a disc. A disc can then be placed on the sub tray which, upon receiving a suitable signal, carries the disc together with the main tray into the standby position. At the standby position, the sub tray departs from the main tray to carry the disc to a storage rack within the casing which can hold a plurality of disc to be played. With this configuration, only one disc can be input or exchanged at a time, and to load a disc or replace a disc, each of the rest of the trays have to be ejected individually transported by the main tray. This can greatly inconvenience an end user since, more often than not, after keeping the discs inside the disc changer for a period of time, the user would not be able to remember the correct arrangement of the discs inside the disc changer and to find out, it will be necessary to inspect the contents of each tray. 
     Another known type of disc changer has a number of sub-trays arranged on a main tray and the main tray is used to transport all the sub-trays to a disc exchange position. However, it is necessary to have a main tray which increases manufacturing costs of the disc changer and loading and replacement of disc are still inconvenient. Further, returning of each tray to its standby position within the casing is inefficient. 
     Some disc changers include a “Disc Check” function which allows a number of trays to be ejected at different distances away from the casing so that the trays partially overlap each other. This allows the content of the trays to be checked. However, this method is suitable only if the disc changer has a few trays and further, such a function does not allow discs to be loaded/replaced. 
     Further, in the conventional disc changers mentioned above, when the trays are at the standby position waiting to carry a selected disc to a position for reproducing/recording operation, the tray is engaged with a tray drive gear train, and kept in this position only by friction force of the gear train engagement and a tension of a motor belt. Consequently, the trays are not held securely and misalignment of the trays can occur if the disc changer is transported when the trays are in such a position. 
     If a locking device is provided to lock all the trays, an additional driving source is needed to unlock the locking state prior to drive the trays. In general, a complicated design is needed to lock the trays. As a locking device in a conventional disc changer usually needs some time to activate the locking function, a shifting of the tray from its standby position easily happens during the tray “non-lock” period. This problem is exacerbated when the “non-lock” period is long, and occurs many times during the disc changer operating period. 
     SUMMARY OF INVENTION 
     The present invention has been developed in view of the aforementioned technical problems and aims to provide a new and useful disc changer device. A preferred embodiment of the invention is a disc changer capable of ejecting all trays from the standby position to a disc exchange position where the discs can be exchanged, and capable also of closing the trays one by one from top tray to bottom one. Furthermore, the preferred embodiment makes it possible to check directly and visually the discs stored inside the disc changer automatically with a single button operation. 
     According to a first aspect of the present invention, there is provided a disc changer for storing a plurality of discs, transporting a disc selected from the plurality of discs, and performing recording/reproducing information signal on the disc, the disc changer comprising: a plurality of trays which respectively can be loaded with discs, can be moved substantially in a horizontal direction parallel to main surfaces of the discs, and are stacked substantially in a vertical direction perpendicular to the main surfaces of the discs; a tray driving gear unit capable of shuttling the trays between a standby position in which the trays are stored in a mechanical chassis as a housing of the disc changer and a disc exchange position in which the trays are protruded outward from the mechanical chassis thereby the discs can be put on the trays and removed form the trays; a gear driving mechanism driven by an electrical motor to generate driving force for driving the tray driving gear unit; a tray triggering unit capable of locking/unlocking the trays in the standby position, the unit capable of pushing all trays to engage with the tray driving gear unit after unlocking the trays and capable of driving the trays outward from the mechanical chassis toward the disc exchange position; a recording/reproducing unit for recording and/or reproducing information signal on a disc placed on a turntable; and an elevation unit capable of moving the recording/reproducing unit with the turntable in a vertical direction to align the recording/reproducing unit to a tray and place a disc on the tray onto the turntable; wherein the tray driving gear unit is commonly used for checking the discs by driving all trays to protrude outward from the mechanical chassis to the disc exchange position, the tray driving gear unit is capable of individually driving the trays from the disc exchange position to the standby position from top to bottom in a operation of closing discs, and each disc can be checked until it is closed. 
     According to the configuration of the first aspect of the invention, the tray driving gear unit is capable of driving the trays from the standby position to the disc exchange position with an all-at-once operation. At this time all tray driving gears of the tray driving gear unit rotate in a tray opening direction as one solid gear for driving the plurality of trays. Further, when the tray driving unit rotates in an opposite direction the trays are driven one by one from the top tray to the bottom tray. Thus, it is possible to eject all trays at once, and exchange all discs from the top tray to bottom tray. This simplifies the operation of exchanging all discs in the disc changer. While all the trays are protruding, all the discs can be checked at all time. The same tray driving gear unit is commonly used for both shuttling the trays between the standby position and the disc exchange position and disc checking function, thereby it is possible to simplify the design of the tray driving gear unit, simplify the disc changer operation, shorten the changing time and reduce the possibility of tray jams. 
     Further, in a second aspect of the present invention, there is provided a disc changer for storing a plurality of discs, transporting a disc selected from the plurality of discs, and performing recording/reproducing information signal on the disc, the disc changer comprising: a plurality of trays which respectively can be loaded with discs, can be moved substantially in a horizontal direction parallel to main surfaces of the discs, and are stacked substantially in a vertical direction perpendicular to the main surfaces of the discs; a tray driving gear unit capable of shuttling the trays between a standby position in which the trays are stored in a mechanical chassis as a housing of the disc changer and a disc exchange position in which the trays are protruded outward from the mechanical chassis thereby the discs can be put on the trays and removed form the trays; a gear driving mechanism driven by an electrical motor to generate driving force for driving the tray driving gear unit; a tray triggering unit capable of locking/unlocking the trays in the standby position, the unit capable of pushing all trays to engage with the tray driving gear unit after unlocking the trays and capable of driving the trays outward from the mechanical chassis toward the disc exchange position; a recording/reproducing unit for recording and/or reproducing information signal on a disc placed on a turntable; and an elevation unit capable of moving the recording/reproducing unit with the turntable in a vertical direction to align the recording/reproducing unit to a tray and place a disc on the tray onto the turntable; wherein the tray driving gear unit can be commonly used for checking the discs by driving all trays other than a tray above the recording/reproducing unit to protrude outward from the mechanical chassis to the disc exchange position, the tray driving gear unit is capable of individually driving the trays from the disc exchange position to the standby position from top to bottom in a operation of closing discs, and each disc can be checked until it is closed. 
     According to the configuration of the second aspect of the invention, the tray driving gear unit is capable of driving all trays other than the tray above the recording/reproducing unit from the standby position to the disc exchange position with an all-at-once operation. At this time all tray driving gears of the tray driving gear unit other than for the tray above the recording/reproducing unit rotate in a tray opening direction as one solid gear for driving all trays other than the tray above the recording/reproducing unit. Further, when the tray driving unit rotates in an opposite direction the trays are driven one by one from the top tray to bottom tray. Thus, it is possible to eject all trays other than the tray above the recording/reproducing unit at once, and exchange all discs other than the tray above the recording/reproducing unit from top tray to bottom tray. This simplifies the operation for exchanging all discs other than the tray above the recording/reproducing unit in the disc changer. While all the trays are protruding, the discs can be checked be done at all time. The same tray driving gear unit can be commonly used for both shuttling the trays between the standby position and the disc exchange position and disc checking function, thereby it is possible to simplify the design of the tray driving gear unit, simplify the disc changer operation, shorten the changing time and reduce the possibility of tray jams. 
     Furthermore, in a third aspect of the present invention, there is provided an optical disc changer for performing at least one of the operations of reproducing information from an optical disc or for recording information thereto, the apparatus comprising: a turntable; a recording/reproducing unit operative to perform at least one of the operations of recording and/or reproducing an information signal on an optical disc placed on the turntable; a plurality of trays for carrying respective optical discs; a housing for receiving the plurality of trays; a mechanism for placing a disc on a selected one of the trays onto the turntable; a tray driving gear unit operative to drive the trays to a disc exchange position in which the trays are ejected from the housing for loading or removal of respective optical discs, and also operative to withdraw the plurality of trays from the disc exchange position to the standby position, the tray driving gear unit comprising a plurality of tray drive gears and a coupling mechanism for coupling the tray drive gears together, the tray driving gear unit being configurable into a RESET configuration in which the tray drive gears are coupled together for rotation together in a tray-opening rotational direction; a tray triggering unit for locking the trays in a standby position in which the trays are received within the housing, for releasing the trays, and for driving the trays from the standby position to a position in which the trays are coupled to respective tray drive gears of the tray driving gear unit while the tray driving gear unit is in the RESET configuration; whereby rotation together of the tray drive gears in said one tray-opening direction drives the trays together to the disc exchange position. 
     From the RESET configuration, the tray drive gears can be rotated individually in the opposite rotational direction, which allows the trays to be withdrawn individually into the housing. 
     An alternative, but more specific, expression of the third aspect of the invention is a disc changer for storing a plurality of discs, transporting a disc selected from the plurality of discs, and performing recording/reproducing information signal on the disc, the disc changer comprising: a plurality of trays which respectively can be loaded with discs, can be moved substantially in a horizontal direction parallel to main surfaces of the discs, and are stacked substantially in a vertical direction perpendicular to the main surfaces of the discs; a tray driving gear unit capable of shuttling the trays between a standby position in which the trays are stored in a mechanical chassis as a housing of the disc changer and a disc exchange position in which the trays are protruded outward from the mechanical chassis thereby the discs can be put on the trays and removed form the trays; a gear driving mechanism driven by an electrical motor to generate driving force for driving the tray driving gear unit; the tray triggering unit capable of locking/unlocking the trays in the standby position, the unit capable of pushing all trays to engage with the tray driving gear unit after unlocking the trays and capable of driving the trays outward from the mechanical chassis toward the disc exchange position; a recording/reproducing unit for recording and/or reproducing information signal on a disc placed on a turntable; and an elevation unit capable of moving the recording/reproducing unit with the turntable in a vertical direction to align the recording/reproducing unit to a tray and place a disc on the tray onto the turntable; wherein the tray driving gear unit has a series of tray drive gears and can rotate to RESET condition in which all drive gears can rotate as all-at-once, and wherein the trays at the standby position are not engage with the tray driving gear unit, after the tray driving gear unit rotates to RESET condition, the tray triggering unit moves and pushes the trays to engage with the tray driving gear unit. 
     According to the configuration of the third aspect of the invention, the tray driving gear unit has a series of tray drive gears and can rotate to RESET condition, and the trays at the standby position are engaged with the tray driving gear unit by the tray triggering unit after the tray driving gear unit rotates to RESET condition. Thus, for each exchange of a disc, the trays protrude to the disc exchange position and return to the standby position one by one from top to bottom. This simplifies the operation of exchanging all discs, since it is possible to put a disc onto any of the empty tray without opening the trays one by one. 
     In an embodiment of the third aspect of the invention, the tray driving gear unit is provided with a shaft gear body, comprising a shaft gear connected to a driving source and a shaft on which the tray drive gears are mounted and stacked in a laminated manner, and each tray is driven by a single tray drive gear. 
     According to the embodiment, the tray drive gears are separate from the shaft gear body, therefore the tray driving gear unit can be manufactured much more easily in comparison with one body construction. 
     Also, in another embodiment of the third aspect of the invention, the tray driving gear is provided with a shaft gear body, comprising a shaft gear connected to a driving source and a shaft on which the tray drive gears are mounted and stacked in a laminated manner, a top level tray drive gear is fixed to the shaft gear body and rotates as one body therewith at all times; and each drive gear has a rib profile as a stopper rib extending along with an axis of the shaft by a predetermined amount, when an upper level tray drive gear&#39;s stopper rib pushes to a lower level tray drive gear&#39;s stopper rib in a rotational direction of the upper level tray drive gear, the lower level tray drive gear is forced to rotate in the rotational direction of the upper level tray drive gear. 
     According to the embodiment, the tray drive gears are separate from the shaft gear body, therefore the tray driving gear unit can be manufactured much easier in comparison with one body construction. Further, a top level tray drive gear fixed to the shaft gear body rotates as one body therewith at all time, and the rotational movement of the top level tray drive gear is transferred to the lower level drive gear through the stopper ribs thereof. Thus, all tray drive gears are driven to rotate one by one through the stopper ribs. 
     Furthermore, in still another embodiment of the third aspect of the present invention, at least one spacer ring is provided between two tray drive gears adjacent to each other, the spacer ring allows the upper level tray drive gear to have an additional rotation before it drives the lower level tray drive gear, thereby the additional rotation is provided to each tray drive gear. 
     According to the embodiment, the additional rotation is provided to each tray drive gear by at least one spacer ring placed between two tray drive gears adjacent to each other. The spacer ring can acts as a dummy gear in the rotational movement of the tray driving gear unit, and can reduce the size of the tray drive gear, because, in a case that the tray driving gear unit does not have a spacer ring, the drive gear pitch diameter needs to provide a total circumference equivalent to a total stroke for one complete rotation, and this increases the diameter of the tray drive gear. 
     Furthermore, in still another embodiment of the third aspect of the present invention, each spacer ring has stopper ribs which are same as the stopper ribs of the tray drive gear, the size in a rotational direction of the stopper ribs is designed to be equivalent to a multiple of gear teeth pitching angle, and the tray drive gear teeth align after all stopper ribs contact each other, thereby the all tray drive gear can be driven to move all trays to the disc exchange position evenly. 
     According to the embodiment, an upper level tray drive gear&#39;s stopper rib pushes to a lower level tray drive gear&#39;s stopper rib, through the spacer ring&#39;s stopper ribs, in a rotational direction of the upper level tray drive gear, and the lower level tray drive gear is forced to rotate in the rotational direction of the upper level tray drive gear. Thus, the rotational movement of the top level tray drive gear is transferred to the lower level drive gear through the stopper ribs, and all tray drive gears are driven to rotate one by one through the stopper ribs. Specifically, the size in a rotational direction of the stopper ribs is designed to equivalent to a multiple of gear teeth pitching angle, therefore the stopper ribs can contact to each other more in a more stable way. 
     Furthermore, in still another embodiment of the third aspect of the present invention, a total rotational stroke of the tray drive gear before the lower level tray drive gear starts to rotate is equivalent to the total stroke for moving a tray from the disc exchange position to the standby position. 
     According to the embodiment, it is possible to provide the tray driving gear unit with a dummy turn which is equivalent to the total stroke for moving a tray from the disc exchange position to the standby position, thereby the size of the tray drive gear can be reduced. 
     Furthermore, in still another embodiment of the third aspect of the present invention, the first gear tooth of the tray&#39;s gear rack has a shape profile for easy engagement of trays to tray driving gear unit after triggered by the tray triggering unit. 
     According to the embodiment, owing to the shape profile of the first gear tooth of the tray&#39;s gear rack, the tray&#39;s gear rack can be easily engaged with the tray driving gear unit after triggered by the tray triggering unit. Thereby, the tray can start to move smoothly by the tray driving gear unit. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing a disc changer according to the present embodiment in a state that all trays are opened; 
         FIGS. 2(   a ) to  2 ( e ) are schematic side views of the disc changer showing various operations of the trays and a recording and/or reproducing unit of the disc changer; 
         FIG. 3(   a ) is a plan view of the disc changer according to the embodiment; 
         FIG. 3(   b ) is an enlarged perspective view of a part of a disc tray; 
         FIG. 4  is a side view of the disc changer shown in  FIG. 3(   a ); 
         FIG. 5  is a sectional view of the disc changer taken along line L 5 -L 5  in  FIG. 3(   a ); 
         FIG. 6  is a plan view showing a detail of tray opening mechanism of the disc changer; 
         FIG. 7  is a bottom view of  FIG. 6  focusing the tray triggering unit; 
         FIGS. 8(   a ) and  8 ( b ) are plan views of a focused part of the disc changer showing a moving process of the trigger slide plate for triggering trays; 
         FIGS. 9(   a ) to  9 ( c ) are plan views of the trigger slide plate showing a moving sequence thereof for triggering trays and locking/unlocking trays in a standby position; 
         FIG. 10(   a ) is an explanatory drawing showing various locations of a boss portion of the trigger slide plate; 
         FIG. 10(   b ) is a side view of the trigger slide plate; 
         FIGS. 11(   a ) to  11 ( c ) are plan view of a tray driving gear unit showing engagement and disengagement thereof to the tray; 
         FIGS. 12(   a ) to  12 ( d ) are explanatory drawings showing a sequence of a motion of a tray lock lever; 
         FIG. 13(   a ) is an exploded view of a tray driving gear unit; 
         FIG. 13(   b ) is a perspective view of a complete assembly of the tray driving gear unit; 
         FIG. 14  is a perspective view of the tray driving gear unit and a gear mechanism for driving it; 
         FIGS. 15(   a ) to  15 ( h ) are explanatory drawings showing a sequence of “RESET” the tray driving gear unit; 
         FIG. 16  is a side view of the tray driving gear unit with trays at the standby position; 
         FIG. 17  is an enlarged perspective view of the tray driving gear unit with trays at the standby position; 
         FIGS. 18(   a ) to  18 ( d ) are explanatory drawings showing a sequence of the tray driving gear unit for driving trays one by one from top to bottom; 
         FIG. 19(   a ) is a top view of the disc changer; 
         FIG. 19(   b ) is a side view showing the tray driving gear unit which engages with trays; 
         FIGS. 20(   a ) to  20 ( c ) are side views showing a sequence of closing the top tray from the disc exchange position to the disc standby position; 
         FIG. 21  is a plan view showing a total layout of a driving (gear) mechanism in the disc changer according to the embodiment; 
         FIG. 22  is a plan view showing the details of a main part of  FIG. 21 ; 
         FIG. 23  is a perspective view showing a gear engagement around a switching gear. 
         FIG. 24  is a perspective view showing a gear engagement around a function gear. 
         FIGS. 25(   a ) and  25 ( b ) are schematic side views showing a first gear train changing system by a switching gear; 
         FIGS. 26(   a ) and  26 ( b ) are schematic side views showing the second gear train changing system by a function gear; 
         FIG. 27  is a perspective view of a function lever and a function gear in an assembly condition; 
         FIG. 28(   a ) is a plan view showing a cam gear; 
         FIG. 28(   b ) is a perspective view showing the outer profiles at the lower side of the cam gear; 
         FIG. 29  is a block diagram for explaining a switching mode of the driving mechanism in the disc changer; 
         FIG. 30  is a plan view showing a gear train of a tray open/close system in the disc changer; 
         FIGS. 31(   a ) to  31 ( d ) are plan views showing the sequence of tray opening operation which mainly controlled by cam gear; 
         FIGS. 32(   a ) and  32 ( b ) are perspective views showing a trigger gear and a trigger slide plate; 
         FIG. 33  is a plan view showing a gear train of elevation system in the disc changer; 
         FIG. 34  is a perspective view showing the components of the elevation unit; 
         FIG. 35  is a side view showing a step-like cam profile on a right side UD rack; 
         FIGS. 36(   a ) and  36 ( b ) are perspective views respectively showing the recording/reproducing section at an upper most position and a lower most position; 
         FIG. 37  is a plan view showing a gear train of tray play/stock system in a disc changer; 
         FIGS. 38(   a ) and  38 ( b ) are plan views showing the movement of driving trays between the disc standby position and the recording/reproducing position; 
         FIG. 39  is a perspective view showing the components of the tray driving rack unit; 
         FIGS. 40(   a ) to  40 ( d ) are enlarged plan views showing a moving sequence of a tray catch lever to drive trays from disc standby position to the recording/reproducing position; 
         FIGS. 41(   a ) to  41 ( d ) are enlarged plan views showing a sequence of an operation of tray driving rack unit; 
         FIG. 42  is a side view showing a clamper unit in an unclamping condition; 
         FIG. 43  is a side view showing the clamper unit in a clamping condition; 
         FIG. 44  is an enlarged plan view showing a locking system for trays at disc standby position; 
         FIG. 45(   a ) is a plan view of a tray lock lever; 
         FIG. 45(   b ) is a perspective view of the tray lock lever. 
         FIG. 46  is a diagram showing a relationship between cam gear positions and locking types of the tray; 
         FIGS. 47(   a ) to  47 ( c ) are enlarged plan views showing tray lock levers in locking trays at standby position; 
         FIG. 48  is a perspective view of the disc changer from front side in a state in which the trays are locked at the standby position; 
         FIG. 49  is a perspective view of the disc changer from rear side in a state in which the trays are locked at standby position; 
         FIG. 50  is a plan view showing a locking mechanism at the recording/reproducing section. 
         FIGS. 51(   a ) and  51 ( b ) are perspective views showing a first lock lever and a second play gear in a lock condition; 
         FIGS. 52(   a ) and  52 ( b ) are a plan view and a perspective view showing a first lock lever  93  as a locking device; 
         FIGS. 53(   a ) and  53 ( b ) are a plan view and a perspective view showing the first lock lever; 
         FIG. 54(   a ) is a plan view showing a locking condition of the first lock lever. 
         FIG. 54(   b ) is a plan view showing an unlocking condition of the first lock lever; 
         FIG. 55  is a perspective view showing a condition where the cam gear rotates to a position for unlocking the first lock lever; 
         FIG. 56  is a plan view showing a second lock lever as a locking device in the changer mechanism; 
         FIG. 57  is a perspective view showing a second lock lever and a second UD gear in an unlock condition; 
         FIG. 58(   a ) is a plan view showing a locking condition of the second lock lever; 
         FIG. 58(   b ) is a plan view showing an unlocking condition of the second lock lever; 
         FIG. 59  is a plan view of a cam gear explaining an operation thereof when it rotates in a clockwise and a counter-clockwise direction; 
         FIG. 60  is a perspective view show a condition where the cam gear is rotated to a position for unlocking the second lock lever; 
         FIG. 61  is a perspective view showing another locking system that prevents a movement of the recording/reproducing section when one of the tray is at the recording/reproducing position; and 
         FIG. 62  is a locking system summary table at recording/reproducing section. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanied drawings. 
       FIG. 1  is a perspective view showing a disc changer  1  according to the present embodiment in a state that all trays T are opened. As shown in  FIG. 1 , the disc changer  1  is provided with a plurality of trays T. In the embodiment, the disc changer  1  is provided with five trays T (labeled T 1 -T 5 ), but in other embodiments there may be a different number of trays T. Each tray T is capable of carrying a disc D thereon. The disc D may be a large disc Da having a larger diameter of 12 cm or a small disc Db having a smaller diameter of 8 cm depending on user&#39;s requirement, for example. The disc changer  1  is also provided with a generally box-like shaped mechanical chassis  3  which serves as a housing or an outer frame body thereof. 
     Each tray T can be stored within the mechanical chassis  3  in a state that they are stacked in a substantially vertical direction perpendicular to a main surface of the disc D, and can be moved in a substantially horizontal direction parallel to the main surface of the disc D. 
       FIGS. 2(   a ) to  2 ( e ) are schematic side views of the disc changer  1  showing various operations of the trays T and a recording/reproducing section  70  of the disc changer  1 . As shown in the drawings, the disc changer  1  is provided with, as tray positions, three different positions which are different in horizontal direction to each other. That is, a disc exchange position X in which the tray T protrudes outward from the mechanical chassis  3 , a standby position Y in which the tray T is stored in the mechanical chassis  3  and a recording/reproducing position Z in which the tray T is correctly positioned to interact with the recording/reproducing section  70 . The recording/reproducing position Z is set at near a back in the mechanical chassis  3 , and the standby position Y is set at near an entrance of the mechanical chassis  3 . 
     Among the  FIGS. 2(   a ) to  2 ( e ),  FIG. 2(   a ) shows a RESET state. In this RESET state, all the five trays T except for the highest level tray T 1  are stored and aligned with one another at the standby position Y. The recording/reproducing section  70  is movable in a vertical direction, and is shown in  FIG. 2(   a ) at its highest position. The highest level tray T 1  is stored at recording/reproducing position Z. 
       FIG. 2(   b ) shows a series of disc exchanging states. In the state shown in  FIG. 2(   b - 1 ), all trays T are moved to the disc exchange position X at once. It will be noted that the discs D (Da or Db) can be put on the trays T or removed from the trays T by moving the trays T one by one from top to bottom, as shown in the sequence of images  2 ( b - 1 ) to  2 ( b - 5 ). 
       FIG. 2(   c ) shows a series of recording/reproducing states. In each of these states, a specified tray T is moved to the recording/reproducing position Z form the standby position Y and is stopped there, thereafter a recording or reproducing signal on the disc D on the specified tray T is started. The disc D which is to be performed the recording or reproducing signal thereon can be exchanged by exchanging the specified tray T. With respect to  FIG. 2(   c - 1 ), the arrangement of the trays T is the same as the RESET shown in state  FIG. 2(   a ), because the highest tray T 1  is located to the recording/reproducing unit  70 . The sequence of images  FIG. 2(   c - 1 ) to  FIG. 2(   c - 5 ) show how the trays T are successively moved to the recording/reproducing position Z. 
     Moreover,  FIG. 2(   d ) shows a series of disc exchanging states during the recording and/or reproducing operation, for example a disc exchanging while tray T 1  is at the recording/reproducing position Z.  FIG. 2(   d - 1 ) shows the disc changer  1  in the same configuration as  FIG. 2(   c - 1 ) in which all the discs D are in the disc exchange position X. In the state shown in  FIG. 2(   d - 2 ), except for the tray T 1  which supports a disc D during the recording or reproducing operation, all trays T (T 2 -T 5 ) are positioned at the disc exchange position X, and in the sequence of images  2 ( d - 2 ) to  2 ( d - 5 ) the trays T are closed one by one from top to bottom, so that a disc D can be put on and/or removed from each tray T (T 2 -T 5 ) when that tray T is the uppermost one at the disc exchange position X. 
       FIG. 2(   e ) shows in FIG.  2 ( 1 - e ) to  2 ( e - 5 ) a series of images which are respective fully-open states of the trays T during the recording and/or reproducing operation. In each of these states a single specified tray T is at the recording or reproducing position Z, and all the other trays T are positioned at the disc exchange position X. A disc D can be put on the corresponding tray or removed from it when the tray T is in the disc exchange position X, while the disc D on the specified tray T in the recording or reproducing position Z is experiencing the recording or reproducing operation. 
     The whole configuration of a disc changer  1  according to an embodiment of present invention which performs the above-described operations will be explained in accordance with  FIGS. 3 to 5 . 
       FIG. 3(   a ) is a plan view of the disc changer  1  according to the embodiment,  FIG. 3(   b ) is an enlarged perspective view of a part of a tray T,  FIG. 4  is a side view of the disc changer  1  shown in  FIG. 3 , and  FIG. 5  is a sectional view of the disc changer  1  taken along line L 5 -L 5  of  FIG. 3(   a ). 
     As shown in  FIGS. 3 to 5 , each tray T has a large diameter step Ta and a small diameter step Tb on the upper surface. Thereby, a selected one of large disc Da and a small disc Db having different diameters (12 cm and 8 cm) to each other can be loaded on the tray T. 
     In the tray T, grooves Tc are formed on both right and left sides at the back, a gear rack Td is formed on one side (the left side, for example), a step up surface Te is formed on the left side at the back in rear portion of the tray T. Also, as shown in  FIG. 3(   b ), a rib Tf is formed on the left side at the back in rear portion of the tray T, underneath the rack Td. Further, an opening of a hook profile Tg is formed on the left side of the rear portion of a tray support. 
     A plurality of (e.g. five) trays T are separately arranged in parallel while being stacked substantially in a vertical direction, that is, perpendicular to the main surfaces of the discs D. Moreover, as shown in  FIG. 3 , the trays T are supported by guide ribs  3   a  provided inside on the right and left sides of the mechanical chassis  3 , so that the trays T can move substantially in a horizontal direction (lateral direction), that is in parallel with main surfaces of the disc D. 
     The trays T are moved by a tray driving gear unit  20  provided on the left side of the mechanical chassis  3 , between the disc exchange position X and the standby position Y. A tray driving rack unit  60  is provided on the left side rearward of the trays T. The tray driving rack unit  60  is mounted on an UD base  5 , moves and aligns itself to a specified tray address, and transfers trays T to the recording/reproducing section  70 . It is to be noted that  FIGS. 3 to 5  show a state in which the highest level tray T 1  (the first tray) is located at the disc exchange position X. 
     The disc recording/reproducing section  70  is provided behind the trays T located at the standby position Y. The disc recording/reproducing section  70  is supported by a left guide rib  3   b  and a right guide rib  3   c  which are formed on the sides of mechanical chassis  3 , and is moved in a up and down direction (vertical direction) by an elevating unit  30  which will be discussed later. 
     A triggering unit  50  (shown in  FIG. 4 , and described in more detail below with reference to  FIG. 31 ) is provided on the left side of the disc changer  1 , and moves in a direction parallel to the left side surface of the mechanical chassis  3  to push the trays T so as to engage them with the tray driving gears unit  20 . Further, there is provided a driving mechanism  100  (described below with reference to  FIG. 21 ) composed of a motor for driving each part, gear trains, a plunger unit for switching between gear trains, and a detection switch, under the trays T located at the standby position Y. 
     As mentioned above, the tray driving gear unit  20  is located on the left side of the mechanical chassis  3 , and an open switch lever  27  for detecting trays T to be driven toward the disc exchange position X is provided at the vicinity of the tray driving gear unit  20 . A gear cover  28  is mounted to cover a predetermined part of the top of the mechanical chassis  3 , including the top of the tray driving gear unit  20  and the open switch lever  27 . Thereby, longitudinal (vertical) axes of the tray driving gear unit  20  and the open switch lever  27  are correctly and stably positioned in relation to each other. Moreover, a top cover  4  is mounted on the top of the mechanical chassis  3  to increase the stiffness of the mechanical chassis  3  and to protect it from dust. 
       FIG. 6  is a top view showing a detail of the tray opening mechanism of the disc changer  1 . The tray opening system includes the trays T, the tray driving gear unit  20  capable of driving trays T from the standby position Y to the disc exchange position X, and a trays triggering unit  50  having a trigger slide plate  52 . The trigger slide plate  52  is moved by a trigger gear  51  and a cam gear  114  to lock/unlock trays T at standby position and pushes all trays T to engage them with the tray driving gear unit  20 . The trigger slide plate  52  moves by sliding at the side of mechanical chassis  3 , while a boss portion  52   c  on the trigger slide plate  52  moves to follow cam profiles  3   d  on both the top and bottom of mechanical chassis  3 . 
       FIG. 7  is a bottom view of a portion of the section of the disc changer  1  shown in  FIG. 6 , focusing on the tray triggering unit  50 . As shown in  FIG. 7 , the trigger gear  51  with a gear rack  51   b  is connected to the cam gear  114  by a boss  51   a  is fitted into a groove  114   b  (see  FIG. 6 ) of the cam gear  114 . When the cam gear  114  is rotated, the boss  51   a  is driven in accordance with a profile of the cam groove  114   b , thereby the trigger gear  51  is rotated around a supporting boss  51   c . Thus, a gear rack  51   b  on the trigger gear  51  which engages with a rack profile  52   b  of the trigger slide plate  52  will push the trigger slide plate  52  to move in forward direction, and then push trays T at a trigger rib Th (see  FIG. 8(   b )). 
     A tray lock lever  53  is arranged between the trays T and the trigger side plate  52 . The tray lock lever  53  is provided with a locking profile  53   a  (a convex part, for example) for locking trays T at standby position Y. The locking profile  53   a  controls the trays T at the standby position by contacting surfaces Tk and Tm of a recess formed on the side of the trays T. 
       FIGS. 8(   a ) and  8 ( b ) show a moving process of the trigger slide plate  52  for triggering trays T. Boss shaped portions  52   c  are provided on the top and the bottom of the trigger slide plate  52 . The boss portion  52   c  is fitted into a cam groove  3   d  formed on the top and the middle of the mechanical chassis  3 . The cam groove  3   d  includes three moving paths P 1 -P 3  for the boss portion  52   c  of the trigger slide plate  52 . 
     A moving path P 1  is a “HOME” path for the boss portion  52   c  of the trigger slide plate  52 , a moving path P 2  is a “TRIGGER” path P 3  and a moving path P 2  is a “TRANSITION” path located between the “HOME” path P 1  and the “TRIGGER” path P 3 . 
       FIG. 8(   b ) shows the boss portion  52   c  of the trigger slide plate  52  in the “TRIGGER” path P 3 , the driving rib  52   a  of the trigger slide plate  52  is touching the trigger rib Th of the tray T, and ready to push trays T to move towards the tray driving gear unit  20 . 
       FIGS. 9(   a ) to  9 ( c ) show a moving sequence of the trigger slide plate  52  for triggering the trays T and locking/unlocking the trays T in the standby position Y.  FIG. 9(   a ) shows the trigger slide plate  52  at “HOME” position. A first protrusion profile  52   e  is touching a rib  53   b  protruding from the tray lock lever  53 , thereby a movement of the tray lock lever  53  in arrow F or arrow E direction is prevented. The locking profile  53   a  is touching the surfaces Tk and Tm, thereby trays T are “locked” at the standby position Y. When the boss portion  52   c  of the trigger slide plate  52  moves to the “TRANSITION” path, the first protrusion  52   e  moves away from the rib  53   b , as shown in  FIG. 9(   b ). However, the tray lock lever  53  will remain in the same condition as  FIG. 9(   a ). 
     This is due to a function of a plastic spring  53   d  of the tray lock lever  53 . The plastic spring  53   d  does not allow the tray lock lever  53  to rotate in the direction of the arrow E and urge the tray lock lever  53  towards the direction of the arrow F, if a bending force is applied on the plastic spring  53   d . Before the driving rib  52   a  of the trigger slide plate  52  reaches so as to touch the surface Th of a recess formed on tray T as shown in  FIG. 9(   c ), the second protrusion  52   d  already pushes a convex part  53   c  of the tray lock lever  53  to another level. Thus, the tray lock lever  53  rotates in direction of arrow E and “unlocks” trays T. 
       FIG. 10(   a ) explains the various locations of the boss portion  52   c  of the trigger slide plate  52  from a “HOME” position Q 1  to a “TRIGGER” position Q 3  and from a “TRIGGER” position Q 4  to a “HOME” position Q 7 . At a neutral-line position, trigger slide plate ribs  52   f  are in no stress condition. The stress increases as the boss portion  52   c  of the trigger slide plate  52  travels from the “HOME” position Q 1  to the “TRIGGER” position Q 3  through a “TRANSITION” position Q 2 .  FIG. 10(   b ) shows a side view of the trigger slide plate  52 . 
     At the “TRIGGER” position Q 3 , the trigger slide plate  52  starts to push trays T to engage them with the tray driving gear unit  20 . At end of moving sequence, the opening of the cam profile allows the boss portion  52   c  to release the stress trigger slide plate ribs  52   f  and return to the neutral condition. Thus, the boss portion  52   c  of the trigger slide plate  52  can return to “HOME” position following the other path to avoid its profile overlapping with the trays T when the trays T return from the disc exchange position X to the standby position Y. 
     At the “HOME” position Q 7 , bending stress start to increase on the trigger slide plate rib  52   f  at the opposite direction (towards the left). At a position Q 8 , the stressed trigger slide plate ribs  52   f  is released after the trigger slide plate  52  moves to an opening on the cam profile and return to its origin position (“HOME” position). 
       FIGS. 11(   a ) to  11 ( c ) show the engagement and disengagement of the tray driving gear unit  20  with a tray T. At an initial condition (when the trays T are at standby position Y, before they are triggered by the trigger slide plate  52 ), the gear rack Td is not engaged with the tray driving gear unit  20 . After the trays T are triggered by the trigger slide plate  52 , the trays T move forward and the gear rack Td will engage with the tray driving gear unit  20 . Thus, all trays T will be driven forward at the same time to the disc exchange position X. 
     For the return condition, the gear rack Td leaves the tray driving gear unit  20  when it reaches the standby position Y. The tray lock lever  53  will be pushed away by trigger rib Th as shown in  FIG. 12(   b ), at the time that the last gear tooth of the gear rack Td leaves the tray driving gear units  20 , and the tray lock lever  53  rotates into the recess of tray rib as  FIG. 12(   a ). The contact of the locking profile  53   a  and a surface Tj of the recess create an inter-lock effect to prevent trays T from moving towards the disc exchange position X after reaching the standby position Y. After all the trays reach to the standby position Y, the first protrusion  52   e  of the trigger slide plate  52  will be pushed to the lock lever rib  53   b  and aligns and locks the trays T at the standby position Y as shown in  FIG. 9(   a ). 
       FIG. 13(   a ) is an exploded view of the tray driving gear unit  20 . The reference numeral  24  denotes a top tray drive gear which drives the upper most tray T 1 , the reference numeral  22  denotes a tray drive gear which drives trays T (T 2 -T 4 ) other than the upper most tray T 1  and the lower most tray T 5 , the reference numeral  25  denotes a bottom tray drive gear which drives the lower most tray T 5 . Further, the reference numeral  23  denotes a plastic ring located between two drive gears adjacent to each other which enables the drive gear  22 ,  24  or  25  to have a dummy turning, and the reference numeral  21  denotes a shaft gear fixed to a shaft  21   s  which holds all drive gears  22 ,  24 ,  25  and the plastic rings  23 . Top drive gear  24  is fitted to the shaft  21   s  in a tight fitting condition and rotates as one solid body with it.  FIG. 13(   b ) shows a complete assembly of the tray driving gear unit  20 . As seen from  FIG. 13(   b ), the plastic ring  23  is provided with stopper ribs  23   a ,  23   b , the top tray drive gear  24  is provided with stopper ribs  24   a ,  24   b.    
       FIG. 14  is a perspective view of the tray driving gear unit  20  and a gear mechanism for driving it. As shown in  FIG. 14 , the shaft gear  21  of the tray driving gear unit  20  is engaged with a tray relay gear  112  which is driven by the cam gear  114 . When cam gear  114  rotates in a clockwise direction, the shaft gear  21  is driven to rotate in the same direction. The top driving gear  24  also rotates in the same direction. 
     It is to be noted that a metal spring  26  having protrusions  26   a  is provided at a vicinity of tray driving gear unit  20 . And, the protrusions  26   a  of the metal spring  26  are touching to side portions of tray drive gears  22  and  25 , thereby friction force is provided to the tray drive gears  22  and  25  so that they are held in position before they are driven by actual force from a electric motor  116  (described in more detail below with reference to  FIG. 21 ). 
       FIGS. 15(   a ) to  15 ( g ) show a “RESET” operation of the tray driving gear unit  20 . The “RESET” is to rotate all tray drive gears  22 ,  24  and  25  with the same rotational speed, as if they were one solid gear which has a plurality of layers of drive gears  22 ,  24  and  25  capable of engaging a plurality of trays T. In this explanation, only the top tray drive gear  24  and the adjacent lower level tray drive gear  23  are explained because the “RESET” sequence for the following tray drive gears is the same.  FIGS. 16 and 17  show the tray driving gear unit  20  after driving all trays T to the standby position Y. 
     In order to drive the trays T to the disc exchange position X, the tray driving gear unit  20  needs to rotate in a clockwise direction in the drawings. A tray relay gear  112  which is driven by the cam gear  114  rotates to turn the shaft gear  21 . Referring to  FIGS. 14 and 15(   a ), as the top tray drive gear  24  rotates together with the shaft  21   s  in the clockwise direction, a side surface of the stopper rib  24   b  on the top tray drive gear  24  will contact a side surface of the stopper rib  23   a  (level  1 ) on the adjacent lower level plastic ring  23  after about 1 round of rotation. Top tray drive gear  24  and the plastic ring  23  rotate together and continue the second rotation, until a side surface of the stopper rib  23   b  (level  1 ) of the plastic ring  23  contacts to a side surface of the stopper rib  23   a  (level  2 ) which is located 2 levels lower than top tray drive gear  24 . 
       FIGS. 15(   e ) and  15 ( f ) are the top and isometric views of the tray driving gear unit  20  without the top tray drive gear  24 . When a stopper rib  23   a  of the second level plastic ring  23  rotates, it touches the stopper rib  22   b  on the next tray drive gear  22 . This tray drive gear  22  now will rotate in the same direction and speed with top drive gear  24 . The rotation continues until the bottom tray drive gear  25  starts to rotate, at this time the tray driving gear unit  20  is completely “RESET” as shown in  FIG. 15(   g ). In this condition, all gear teeth are aligned with each other and rotate as one solid body gear. 
       FIG. 16  is a side view of tray driving gear unit  20  with trays T at standby position Y. And,  FIG. 17  is an enlarged perspective view of tray driving gear unit  20  with trays T at standby position Y. As explained above, the metal spring  26  having protrusions  26   a  is provided at a vicinity of the tray driving gear unit  20 . The protrusions  26   a  of the metal spring  26  are touching side portions of the tray drive gears  22  and  25 , thereby friction force is provided to the tray drive gears  22  and  25  so that they are held in position before they are driven by actual force from the motor  116 . 
       FIGS. 18(   a ) to  18 ( d ) show the operation of the tray driving gear unit  20  for driving trays T to disc standby position Y, one by one from top to bottom. Top tray drive gear  24  tightly fitted to the shaft  21   s  at this time also starts to rotate among all tray drive gears. 
     In order to drive trays T from the disc exchange position X to the standby position Y, the tray driving gear unit  20  needs to rotate in a counterclockwise direction in the drawings. This time, the side surface of the stopper rib  24   a  after the first rotation will contact the side surface of the stopper rib  23   b  (level  1 ) of the plastic ring  23 , thereby the tray T is driven from the disc exchange position X to a half-way position between the disc exchange position X and the standby position Y, because number of plastic ring  23  used between the tray drive gears is two. The second rotation continues until the stopper rib  23   a  (level  1 ) contacts the stopper rib  23   b  (level  2 ). Top tray T 1  is now completely driven to the standby position Y. The second tray T 2  will start to move when the stopper rib  23   a  (level  2 ) rotates and pushes the stopper rib  22   b  on the lower tray drive gear  22 . 
       FIG. 19(   a ) is a plan view of the disc changer  1 , where the top tray T 1  has been driven by the top tray drive gear  24  to the standby position Y and the second tray T 2  is waiting for rotation of tray driving gear unit  20  to move from the disc exchange position X to the standby position Y.  FIG. 19(   b ) shows the tray driving gear unit  20  which engages with trays T. Top tray T 1  moves to the standby position Y and disengages from the tray drive gear  22  and other lower level trays T are at the disc exchange position X. Closing of trays T will be performed from top to bottom. 
       FIGS. 20(   a ) to  20 ( c ) are side views showing a sequence of closing the top tray T 1  from the disc exchange position X to the disc standby position Y.  FIG. 20(   a ) shows a state in which all trays T are positioned at the disc exchange position X. It is to be noted that the tray driving gear unit  20  is to rotate as one body when it drives trays T to the disc exchange position X. 
       FIG. 20(   b ) shows a state in which the top tray T 1  is closed to half way between the disc exchange position X and the disc standby position Y. It is performed by a first rotation of the tray driving gear unit  20 .  FIG. 20(   c ) shows a state in which the top tray T 1  is fully closed to the disc standby position Y. It is performed by a second rotation of the tray driving gear unit  20 . Thereafter, the second tray T 2  will start to move, if the tray driving gear unit  20  continues to rotate. 
     The plastic rings  23  in this design are useful for reducing the size of the tray drive gears  22  by providing dummy rotation to the drive gears. A first tray drive gear will rotate to close a tray T just after the tray T disengages from the first tray drive gear, and a stopper rib of the first tray drive gear will hit a stopper rib of the plastic ring  23 , so that a second tray drive gear is rotated. This means that the first tray drive gear will rotate by a degree of (360−2θ) (where angle θ is an angle corresponding to a width of a stopper rib, as shown in  FIG. 15(   h ) to drive the tray to disc standby position before the second tray drive gear starts to rotate to drive a second tray T 2 . 
     If there were no plastic rings  23 , the PCD (pitch circle diameter) of drive gears of “D 1 ” for a tray ejection stroke of “y” would be given by the formula (1).
 
 D   1   =[y/π]×[ 360/(360−2θ)]  (1)
 
     Since plastic rings  23  are used, the PCD (pitch circle diameter) of drive gears of “D 2 ” for a tray ejection stroke of “y” will be given by the following formula (2). In this case, a tray ejection stroke of “y” will consist of a stroke achieved by a tray drive gear  22  and a stroke achieved by a plastic ring  23 .
 
 y=πD   2 [(360−2θ)/360 ]+D   2 [(360−2θ)/360]=2 πD   2 [(360−2θ)/360]
 
 D   2 =[1/2 ]×[y/π]×[ 360/(360−2)]
 
 D   2 =[1/2 ]D   1   (2)
 
Therefore, by using plastic rings  23  (dummy rings), the PCD of tray drive gear  22  can be reduced by ½.
 
     If “n” pieces of plastic rings  23  were used (as they might be in other embodiments of the invention), the PCD (pitch circle diameter) of drive gears of “Dn” for a tray ejection stroke of “y” would be given by the following formula (3).
 
 y=πD   2 [(360−2θ)/360 ]+n{πD   2 [(360−2θ)/360]}=(1 +n )π D   2  [(360−2θ)/360]
 
 Dn=[ 1/(1 +n )]×[ y/π]×[ 360/(360−2θ)]
 
 Dn=[ 1/(1 +n )] D   1   (3)
 
     With more plastic rings  23 , the diameter of tray drive gear  22  can be reduced more. 
     Next, a driving mechanism of the disc changer  1  will be explained. 
       FIG. 21  is a plan view showing a total layout of a driving (gear) mechanism  100  in the disc changer  1  according to the embodiment.  FIG. 22  is a plan view showing the details of a main part of  FIG. 21 . 
     In  FIGS. 21 and 22 , a reference character Z denotes a disc recording/reproducing position, a reference character Y denotes a disc standby position and a reference character X denotes the disc exchange position. Also, a reference numeral  100  denotes a gear mechanism of the disc changer  1  located at the disc standby position Y. 
     In  FIGS. 21 ,  22  and  23 , a reference numeral  116  denotes an electric motor which provides driving power to the gear mechanism. The driving mechanism  100  includes a motor pulley  115 , a belt  121 , a pulley gear  101 , a first relay gear  102 , a second relay gear  103  and a third relay gear  104 . The second relay gear  103  is provided on a back side of the pulley gear  101 . The driving mechanism  100  also includes a switching gear  105 , a long gear  106 , a function gear  107 , a first UD gear  108 , a second UD gear  109 , a first play gear  110  and a second play gear  111 . Further, the driving mechanism  100  includes a main drive gear  113 , a cam gear  114  and a tray relay gear  112 . All the drive gears are located inside the mechanical chassis  3 . 
       FIG. 23  is a perspective view showing a gear engagement around a switching gear  105 . Switching gear  105  always engages to the third relay gear  104  and an up/down movement of the switching gear  105  is performed by sliding along the third relay gear  104 . Each switching gear tooth  105   a  has a taper surface for easy engagement to a long gear  106  and a main drive gear  113 . The main drive gear  113  has a coining profile  113   a  on each gear tooth for easy engagement to the switching gear  105 . 
       FIG. 24  is a perspective view showing a gear engagement around a function gear  107 . Function gear  107  always engages to the long gear  106  and an up/down movement of the function gear  107  is performed by sliding along the long gear  106 . Each function gear tooth  107   b  has a taper surface for easy engagement to a first UD gear  108  and a first play gear  110 . The first play gear has a coining profile  110   a  on each gear tooth for easy engagement to the function gear  107 . 
       FIGS. 25(   a ) and  25 ( b ) are schematic side views showing a first gear train changing system by a switching gear  105 . As shown in  FIG. 25(   a ), the switching gear  105  is supported by a plunger lever  126 . When an electric current is applied to a plunger unit  117 , the plunger unit  17  pulls the plunger lever  126  by using a moving core  118 , and in this way the switching gear  105  will be lifted up to engage with the long gear  106 . On the other hand, when no electric current is supplied to the plunger unit  117 , the switching gear  105  will be pushed down by a coil spring  119  and engaged with the main drive gear  113 , as shown in  FIG. 25(   b ). 
     The operation of the driving mechanism  100  when the switching gear  105  is at the lower position is to drive the functions of a tray open/close system or selection system (play/stock driving/elevation driving). On the other hand, the operation of the driving mechanism  100  when the switching gear  105  is at the upper position is to drive the functions of a tray play/stock system or an elevation system. 
       FIGS. 26(   a ) and  26 ( b ) are schematic side views showing the second gear train changing system by a function gear  107 . As shown in these drawings, the function gear  107  is supported by a function lever  125 . The round end portion  125   a  of the function lever  125  moves following to the outer profiles  114   e  and  114   f  at the lower side of the cam gear  114 . When cam gear  114  rotates and plan profile  114   e  is touching the round end portion  125   a  of the function gear  107 , the function gear  107  is lifted up by the function lever  125 . At this time, the function gear  107  is engaged with the first UD gear  108  which will drive the elevation system.  FIG. 26(   b ) shows a flat surface  114   f  of the cam gear  114  touching the round end portion  125   a . In this state, the function gear  107  is pushed down by the function lever  125 , and the function gear  107  is engaged with the first play gear  110  which will drive the tray play/stock system. 
       FIG. 27  is a perspective view of a function lever  125  and a function gear  107  of the disc changer  1  in an assembly condition. Function lever  125  has a hook portion  125   b  which holds a gear body  107   a  of the function gear  107 . With the configuration, function lever  125  can always hold the function gear  107 , and the function gear  107  can move in a vertical direction by a motion of the function lever  125 . 
       FIG. 28(   a ) is a plan view showing a cam gear  114 . And  FIG. 28(   b ) is a perspective view showing the outer profiles  114   e  and  114   f  at the lower side of the cam gear  114 . As shown in  FIG. 28(   a ), the gear teeth  114   a  of the cam gear  114  are engaged with the main drive gear  113  and the tray relay gear  112 . The cam gear  114  has cam grooves  114   b ,  114   c  and  114   d  to create the rotational movements of the trigger gear  51 , the first lock lever  93  and the second lock lever  94 . 
     The outer profile  114   e  and  114   f  at the lower side of the cam gear  114  is used to change the state of function lever  125 . The flat surface profile  114   e  allows the function gear  107  to engage to perform an elevation driving function and the flat surface profile  114   f  allows the function gear  107  to engage to perform a tray play/stock function. The cam gear  114  also has a sensor profile  114   g  for sensing changes of electronic sensor signal for indicating the tray T condition when opening or closing. 
     In order to achieve single motor driving, the driving mechanism  100  of the disc changer  1  has a switching mode as explained by a block diagram shown in  FIG. 29 . Power supplied from electric motor  116  is directed to the different gear train systems (an elevation system, a tray play/stock system and a tray open/close system) by using the switching gear  105  and the function gear  107 . The level of both gears is changed by using the plunger unit  117  and the flat surface profiles  114   e  and  114   f  of the cam gear  114 . 
       FIG. 30  is a plan view showing a gear train of a tray open/close system in the disc changer  1 . This gear train drives trays T between the disc exchange position X and the disc standby position Y. 
     When the disc changer  1  operates to drive the gear train of tray open/close system, a driving source gear train will connect to the main drive gear  113 . The driving source gear train is to connect the driving source from the electrical motor  116  all the way until the switching gear  105 . The gear train is from cam gear  114 , tray relay gear  112  and then to tray driving gear unit  20  through a shaft gear  21 . The tray driving gear unit  20  is designed such that it can drive all trays T from the standby position Y to disc exchange position X at once. 
       FIGS. 31(   a ) to  31 ( d ) are plan views showing the sequence of tray opening operations which are mainly controlled by cam gear  114 . The tray open/close system includes the triggering section  50  and tray driving gear unit  20 . The triggering section  50  comprises a trigger gear  51 , a trigger slide plate  52  and a tray lock lever  53 . When the disc changer  1  is operated to drive the tray open/close system, the cam gear  114  rotates in clockwise direction to move a tray T to disc exchange position X (open), or rotates in counter clock-wise to move a tray T to disc standby position Y (close). In the case of opening the trays T, at the time the cam gear  114  rotates, the tray driving gear unit  20  rotates to “RESET” all the drive gears in order to rotate as one body, and the cam profile  114   b  at the same time pushes the trigger gear  51  to rotate to drive the trigger slide plate  52 . 
       FIG. 31(   a ) shows the state at the instant that the tray open/close system starts to move. The tray lock lever  53  in this state locks all trays T and tray drive gear unit  20  is not engaged with the trays T.  FIGS. 31(   b ) and  31 ( c ) show states in which the cam gear  114  is being driven by the gear train of tray open/close system and the rotation of the cam gear  114  will move the trigger slide plate  52  through a trigger gear  51 . During the movement of the trigger slide plate  52 , it unlocks the tray lock lever  53  to release the trays T.  FIG. 31(   c ) shows a state in which the trays T are pushed to engage the tray driving gear unit  20 .  FIG. 31(   d ) shows a state in which all trays T are driven to the disc exchange position X by the tray driving gear unit  20 . The tray T closing is done by reversing the tray opening operation. Trays T will close one by one from top to bottom. 
       FIGS. 32(   a ) and  32 ( b ) are perspective views showing the trigger gear  51  and the trigger slide plate  53 . In the state shown in  FIGS. 32(   a ) and  32 ( b ), a boss  51   a  (see  FIG. 7)  of trigger gear  51  is inserted into a cam groove  114   b  of cam gear  114  and driven by a profile of the cam groove  114   b . The cam groove profile  114   b  on cam gear  114  is the control path for the trigger gear  51  movement. Gear teeth  51   b  on trigger gear  51  constantly engage a rack gear  52   b  of the trigger slide plate  52 . The trigger gear  51  rotates around its supporting boss  51   c  which is held by a boss  120   a  of a pitch plate  120 . A boss  51   a  of the trigger gear  51  is moved by the cam groove  114   b . Thus, when the cam gear  114  rotates, a motion of cam groove  114   b  is transmitted to the trigger slide plate  52  by trigger gear  51  and allows the trigger slide plate  52  to move in a linear way. 
       FIG. 33  is a plan view showing a gear train of an elevation system in the disc changer  1 . This gear train operates in order to move the recording/reproducing section  70  in vertical direction and then align it to specific a tray T. 
     When the disc changer  1  is operated to drive the gear train of the elevation system, the driving source gear train transfers the driving source from electrical motor  116  to a long gear  106 , a function gear  107 , a first UD gear  108  and a second UD gear  109 . The driving source gear train transfers the driving source from electrical motor  116  to all the way until switching gear  105 . The gear train of the elevation system then will drive an elevating unit  30  for moving the recording/reproducing section  70  in vertical direction. 
       FIG. 34  is a perspective view showing the components of the elevation unit. A right side UD rack  32  and a left side UD rack  31  are connected to each other by one connection lever  33 . The elevation unit is used to move the recording/reproducing section  70  in a vertical direction by connecting to the gear train of the elevation system. The driving source is transferred by gear teeth  109   a  of a second UD gear  109  to a gear rack  32   b  of the right side UD rack  32 . There is a step-like cam  32   a  and  31   a  on each UD rack  32  and UD rack  31 . The step-like cams  32   a ,  31   a  have a cam profile similar to steps in a side view. 
     The cam profiles of the step-like cams  32   a  and  31   a  direct the movement of the recording/reproducing section  70 . The bosses  5   a  provided on the side of a UD base  5  sit in the cam profile  32   a ,  31   a  of UD racks  32 ,  31  and they are supported by left guides  3   b  and a right guide rib  3   c  of the mechanical chassis  3 . When the UD racks  32 ,  31  are moving linearly forward or backward, the recording/reproducing section  70  moves in vertical direction. UD rack  32  is connected to UD rack  31  to create synchronous movement by means of the connection lever  33 . A boss  32   c  of the right side UD rack  32  is fitted into a slot  33   a  of the connection lever  33 . Also, a boss  31   b  of the left side UD rack  31  is fitted into a slot  33   b  of the connection lever  33  on the opposite side. 
       FIG. 35  is a side view showing the step-like cam profile  32   a  on the right side UD rack  32 . The step-like cam  32   a  has horizontal portions  32   a - 1  to  32   a - 5  which correspond to the positions or levels of the recording/reproducing section  70  that align to tray T. The level of  32   a - 1  to  32   a - 5  is determined by an electrical sensor using the sensor profile  32   d.    
       FIGS. 36(   a ) and  36 ( b ) are perspective views respectively showing the recording/reproducing section  70  at an upper most position (for tray T 1 ) and an lower most position (for tray T 5 ). For elevating the recording/reproducing section  70  to the upper position, the right side UD rack  32  is driven by the gear train of elevation system in the forward direction. This movement will be transferred, by the connection lever  33  supported pivotally by the boss  120   b  of the pitch plate  120 , to the left side UD rack  31 . Consequently, the left side UD rack  31  will move in the rear direction. For moving the recording/reproducing section  70  to the lower position, the moving direction of both UD racks  32 ,  31  are opposite to the above. 
       FIG. 37  is a plan view showing a gear train of the tray play/stock system in a disc changer  1 . This gear train drives trays T between the disc recording/reproducing position Z and the disc standby position Y. 
     When the disc changer  1  operates the drive gear train of the tray play/stock system, the driving source gear train transfers the driving source from electrical motor  116  to a long gear  106 , a function gear  107 , a first play gear  110  and a second play gear  111 . The gear train of the tray play/stock system then will drive a tray driving rack unit  60  which is capable of moving trays T between the recording/reproducing position Z and the disc standby position Y. 
       FIGS. 38(   a ) and  38 ( b ) are plan views showing the movement of driving trays T between the disc standby position Y and the recording/reproducing position Z. 
     After the recording/reproducing section  70  is aligned to a selected tray T level, the tray T can be driven between the disc recording/reproducing position Z and the disc standby position Y by the tray driving rack unit  60 . 
       FIG. 39  is a perspective view showing the components of the tray driving rack unit  60 . The tray driving rack unit  60  has a tray catch lever  61 , a first play lever  62 , a second play lever  63 , a tray drive rack  64  and a transverse slide plate  65 . When there are no trays T at the recording/reproducing position Z and all trays T are at the standby position Y, the gear train of tray stock/play system is connected by the second play gear  111  to the tray drive rack  64  through the gear engagement of a rack gear  64   a  and gear teeth  111   a  of the second play gear. When the second play gear  111  rotates in the clock-wise direction, tray T is driven to recording/reproducing position Z. 
       FIGS. 40(   a ) to  40 ( d ) are enlarged plan views showing a moving sequence of the tray catch lever  61  to drive trays T from the disc standby position Y to the recording/reproducing position Z.  FIG. 40(   a ) shows a state in which the tray catch lever  61  is away from tray T at disc standby position Y. The UD base  5  supports the tray catch lever  61  moving in a vertical direction to align tray T which needs to be driven to the recording/reproducing position Z. 
     As the tray drive rack  64  moves backward when the second play gear  111  rotates in clock-wise direction as shown in  FIGS. 40(   b ) and  40 ( c ), the boss  64   b  on tray drive rack  64  pulls the tray catch lever  61  through the hole  61   a . As the tray catch lever  61  moves backward, the catch profile (concave portion)  61   b  rotates to fit into hook profile Tg of the tray T. The rotation of tray catch lever  61  is due to the cam groove  61   c  on the lower surface of tray catch lever  61  and a small boss  5   b  on UD base  5 . The rotation of tray catch lever  61  is caused by the cam groove  61   c  fitting against the small boss  5   b . Further, tray T will be moved to the disc recording/reproducing position Z by the tray driving rack unit  60  as shown in  FIG. 40(   d ). 
       FIGS. 41(   a ) to  41 ( d ) are enlarged plan views showing a sequence of an operation of the tray driving rack unit  60 .  FIG. 41(   a ) shows an initial position when the tray drive rack  64  and the tray catch lever  61  are positioned for driving trays T in the disc standby position Y. In this state, the second play gear  111  engages the rack gear  64   a  of tray drive rack  64 , and the rack gear  65   b  of transverse slide plate does not engage the second play gear  111 .  FIG. 41(   b ) shows a boss  64   c  of the tray drive rack  64  moved into an opening  63   a  of the second play lever  63  before the end of movement of tray drive rack  64 . When tray drive rack  64  continues to move backward, the second play lever  63  will be pushed by the boss  64   c  of tray drive rack  64  and rotates, the boss  63   b  of the second play lever  63  pushes the opening  62   a  of the first play lever  62 . 
     Further, a boss  62   b  of the first play lever  62  which is inserted into a cam profile  65   c  of the transverse slide plate  65  rotates and pushes the taper surface of the cam profile  65   a . Transverse slide plate  65  is pushed to move to right side and the first gear tooth of the rack gear  65   a  will engage the gear teeth  111   a  of the second play gear  111  as shown in  FIG. 41(   c ). The driving source will now be transferred to the transverse slide plate  65 , and this slide plate  65  is driven to right side until it detects a switch that marks the completion of disc clamping operation as shown in  FIG. 41(   d ). 
     For driving a tray from disc recording/reproducing position Z to disc standby position Y, the operation is the reverse of the above. The driving source will be transferred from the second play gear  111  to transverse slide plate  65 . The cam profile  65   a  of the transverse slide plate  65  triggers rotational motion of the first play lever  62 , and then the second play lever  63  which will pull the tray drive rack  64  to engage to the second play gear  111 . Tray drive rack  64  will pull tray catch lever  61  that hook to tray T. When tray T reaches the disc standby position Y, the tray catch lever  61  will come out from tray profile Tg and rotates in a counter clock-wise direction back to its original position. The rotation is same achieved by cam groove  61   c  and the boss  5   b  of the UD base boss  5  as shown in  FIG. 40(   b ) 
       FIGS. 42 and 43  are side views respectively showing clamper unit  10  in unclamping and clamping conditions. The transverse unit  6  in the disc recording/reproducing unit section  70  is supported by UD base  5  and transverse slide plate  65 . Two of the side bosses  6   a  at the rear side of the transverse unit  6  are mounted to hook profiles. And bosses  6   b  at the front side of the transverse unit  6  (refer to  FIG. 39 ) are mounted into the cam profile  65   c  of transverse slide plate  65  (refer to  FIG. 39 ). With the pivot at rear side, the transverse unit  6  will rotate to a clamping position when the transverse side plate  65  moves from the left side to the right side, and to a unclamping position when transverse side plate  65  moves from the right side to the left side. 
     At the time of clamping, a clamper support plate  11  is pushed downward to a turn table  9  in order to place the clamper unit  10  to the turn table  9 . With the lifting of clamper unit  10  by clamper support plate  11  at the time of unclamping, tray T can have more gap when it moves to recording/reproducing position Z. The movement of clamper support plate  11  is controlled by the movement of bosses  6   b  of the transverse unit  6 . 
     In the unclamping condition, a rib  6   c  of the transverse unit  6  touches a rib  11   a  of the clamper support plate  11 . The clamper support plate  11  is lifted away from the turn table  9  and clamper unit  10  is at its upper position. In the clamping condition, the other side of the rib  6   c  of the transverse unit  6  touches the other side of the rib  11   a  of clamper support plate  11 . This brings down the clamper support plate  11  and also clamper unit  10 . The clamper unit  10  now is sitting on turn table  9  and able to rotate freely with the turn table  9 . 
       FIG. 44  shows a locking system for trays T at the disc standby position Y. The locking system uses a triggering system  50  that consists of a trigger gear  51 , a trigger slide plate  52  and tray lock levers  53 . 
       FIGS. 45(   a ) and  45 ( b ) are respectively a top view and an isometric view of the tray lock levers  53 . Each tray lock lever  53  includes a first protrusion  53   a , a stopper rib  53   b , a second protrusion  53   c  and a plastic spring  53   d . The first protrusion  53   a  provides an “inter-locking” effect to tray T. The stopper rib  53   b  is to ensure a stable locking state to tray T. The second protrusion  53   c  is a profile which is used to unlock the tray T from the tray lock lever  53 . The plastic spring  53   d  is to provide a spring effect to the tray lock lever  53 , and to ensure that the position of the first protrusion  53   a  is correct, in order to create a stable locking effect when the stopper rib  53   b  is not touching a locking profile of the trigger slide plate  52 . 
     The lock/unlock operation is carried out simultaneously in a tray triggering and opening operation. It can be referred to as part of the operation to drive a tray T to the disc exchange position X. 
       FIG. 46  (discussed in more detail below) is a diagram showing a relationship between cam gear  114  positions and locking types of the tray T.  FIG. 47(   a ) to  47 ( c ) are enlarged plan views showing tray lock levers  53  in locking trays T at standby position Y.  FIG. 48  is a perspective view of the disc changer from the front side in a state in which the trays are locked at the standby position Y. The trays T at the standby position Y are locked by tray lock lever  53  from going to front position (disc exchange position X) at any time of operation except when trays T are driven to the disc exchange position X (open tray operation). This is a shipment locking position where the trays are locked in a permanent manner at the disc standby position Y, and the disc changer  1  at all times carries out operations to lock tray T at the shipment locking position after any operation (such as driving tray T between disc standby position Y and disc recording/reproducing position Z or driving the recording/reproducing unit  70  moving up/down to select tray T). 
     In other states, the trays T are in held in the locking condition by the “inter-locking” profile of tray T and the tray lock lever  53 .  FIG. 46  shows a timing chart when the cam gear  114  rotates from “HOME” position to disc exchange position X and types of locking condition of the tray lock lever  53  and trigger slide plate  52 . For type A shown in  FIG. 47(   a ), the first protrusion  53   a  of tray lock lever  53  is being pushed toward the surfaces Tk and Tm of the tray T by the first protrusion  52   e  of the trigger slide plate  52 . This creates a strong stable locking condition in which the trays T cannot move to any position. For type B shown in  FIG. 47(   b ), the trigger slide plate  52  moves toward the front side and the first protrusion  52   e  of the trigger slide plate  52  is away from the first protrusion  53   a  of tray lock lever  53 , so the locking is only by “inter-locking” between tray T and tray lock lever  53 . 
     The plastic spring  53   d  is touching a wall of mechanical chassis  3  and tray lock lever  53  is not able to rotate to unlock direction. At this time, the trays T are not able to move to the front side (disc exchange position X) but the tray T which is aligned to the tray catch lever  61  (the selected tray T to be driven to recording/reproducing section  70 ) can move to the rear side (disc recording/reproducing position Z) if it is pulled by tray driving rack unit  60 . Regarding to the other trays T, they are blocked by either tray rear stopper  95  or a wall of UD base wall as shown in  FIG. 48 . An unlock period only happens before the trays T triggering, when the tray lock lever unlock profile  53   c  is being pushed by the second protrusion  52   d  of the trigger side plate  52  and the tray is unlocked for a short period so that it can be pushed by trigger slide plate  52  to engage with the tray driving gear unit  20 . 
       FIG. 49  is a perspective view of the disc changer  1  from the rear side in a state in which the trays T are locked at the stand by position Y. The recording/reproducing section  70  and tray catch lever  61  are aligned to the tray T 3 , and in this state the trays T 1 , T 2  are locked in standby position Y by tray lock lever  53  and tray rear stopper  95 . Trays T 4  and T 5  are locked in the standby position Y by tray lock lever  53  and UD base wall and rib  5   d . The rear side of selected tray T 3  is stopped by a concave portion  61   b  of the tray catch lever  61 . When tray catch lever  61  is rotated and the concave portion  61   b  goes into tray hook portion Tg, the tray T 3  can be driven to the disc recording/reproducing position Z. 
       FIG. 50  is a plan view showing the locking system at the recording/reproducing section  70 . One portion of the locking system is for the transverse unit  6  and the tray driving rack unit  60 , and another portion of the locking system is for the recording/reproducing section  70 . The locking system is to ensure that the disc changer  1  can sustain external vibration and impact which can cause the disc changer  1  malfunction while transportation or mishandling. The locking system ensures that there is no position shift and dislocation of parts, by holding each part securely with a locking device. The locking device used to achieve this function is a first lock lever  93  for locating the transverse unit  6  and tray driving rack unit  60 , and a second lock lever  94  for locking the whole recording/reproducing section  70 . 
     Both of lock levers  93 ,  94  are controlled by cam grooves  114   c ,  114   d  of the cam gear  114  and pivot on pitch plate boss. One end of both lock levers  93 ,  94  have bosses that insert into the cam grooves  114   c ,  114   d  and the other end have special locking protrusions that create maximum locking effect when they engage the profile on a second play gear  111  and a second UD gear  109 . 
       FIGS. 51(   a ) and  51 ( b ) are perspective views showing a first lock lever  93  and a second play gear  111  in a locking condition. A hook portion  93   a  of the first lock lever  93  engages with a gear tooth  111   a  of the second play gear  111  to lock the tray play/stock gear train. A taper profile  93   c  on the hook portion  93   a  of the first lock lever  93  and a taper profile  111   c  on the gear tooth  111   a  of the second play gear  111  create an inter-locking effect. These configurations provide a strong locking condition to the tray play/stock system gear train. 
       FIGS. 52(   a ) and  52 ( b ) are a plan view and a perspective view showing the first lock lever  93  as a locking device of the disc changer  1  in two conditions. These drawings show the first lock lever  93  in a state where a hook portion  93   a  of the first lock lever  93  engages with a gear tooth  111   a  of a second play gear  111 , thereby locking the second play gear  111 . At this time, gear teeth  111   a  are engaged with a rack gear  64   a  of a tray drive rack  64 . This condition will happen when the tray drive rack  64  is at standby position Y and no trays T are at disc recording/reproducing position Z. 
       FIGS. 53(   a ) and  53 ( b ) are a plan view and a perspective view showing the first lock lever  93 . These drawings also show the first lock lever  93  in a state where a hook portion  93   a  of the first lock lever  93  engages with a gear tooth  111   a  of the second play gear  111 , thereby locking the second play gear  111 . At this time, gear teeth  111   a  engage a rack gear  65   a  of a transverse slide plate  65 . This condition will happen when the tray drive rack  64  drives a tray T to the disc recording/reproducing position Z and the transverse slide plate  65  moves to clamp the disc to conduct disc recording/reproducing. 
       FIG. 54(   a ) is a plan view showing a locking state of the first lock lever  93 . In this condition, a boss  93   b  of the first lock lever  93  fits into a cam gear groove  114   c  located in a first range  114   c - 1  of the cam gear groove  114   c  where the first lock lever  93  is directed to rotate in a lock direction.  FIG. 54(   b ) is a plan view showing an unlocking condition of the first lock lever  93 . In this condition, the boss  93   b  is located at a second position  114   c - 2  of the cam gear groove  114   c  where the first lock lever  93  is directed to rotate in an unlock direction. There is only one portion  114   c - 2  on cam gear groove  114   c , where the same position is used to change the state of function lever  125 . 
       FIG. 55  is a perspective view showing a state of the locking system in which the cam gear  114  rotates to a position for unlocking the first lock lever  93 . In this state, the position of a function lever  125  is changed in order to drive a gear train of a tray play/stock system (a tray driving rack unit). 
       FIG. 56  is a plan view showing a second lock lever  94  as a locking device in the disc changer  1 . In the state shown in  FIG. 56 , a protruded portion  94   a  of the second lock lever  94  engages a locking profile  109   b  of a second UD gear and locks the second UD gear  109 . At this time, gear teeth  109   a  engage a rack gear  32   b  of UD rack  32 . This condition will happen after the recording/reproducing section  70  complete the up/down movement to select a tray T for driving to the recording/reproducing position Z. 
       FIG. 57  is a perspective view showing the second lock lever  94  and the second UD gear  109  in an unlocked condition. A protruded portion  94   a  of the second lock lever  94  enters into a locking profile  109   b  of the second UD gear  109  to lock the elevation gear train. The second UD gear  109  has a taper portion  109   c  for reliable engagement with the protruded portion  94   a  of the second lock lever  94  and alignment of the second UD gear  109 . 
       FIG. 58(   a ) is a plan view showing a locking state of the second lock lever  94 . In this state, a boss  94   b  of the second lock lever  94  fits into a cam gear groove  114   d  located at a first range  114   d - 1  of the cam gear groove  114   d  where the second lock lever  94  is directed to rotate in a lock direction.  FIG. 58(   b ) is a plan view showing an unlocking state of the second lock lever  94 . In this state, the boss  94   b  is located at a second position  114   d - 2  of the cam gear groove  114   d  where the second lock lever  94  is directed to rotate in an unlock direction. There is only one portion  114   d - 2  on cam gear groove  114   d , where the same position is used to change the state of function lever  125 . 
       FIG. 59  is a plan view of a cam gear  114  explaining an operation thereof when it rotates in a clockwise and a counter-clockwise direction. Rotational motion of the cam gear  114  starts from a HOME position, and the cam gear  114  will rotate in a clock-wise direction to RESET the tray driving gear unit  20  in position A. The trays T do not move during this operation. From the HOME position, the cam gear  114  rotates in the clockwise direction to a PLAY DRIVING position to change the level of function lever  126  from a level for engaging to a first UD gear  108  to a level for engaging a first PLAY gear  110 . From the PLAY DRIVING position to the HOME position, the operation is reversed. In a range of positions B, the trigger slide plate  52  triggers the trays T to engage to the tray driving gear unit  20 . And in a range of positions C, trays T are driven to the disc exchange position X. When the cam gear  114  rotates in a counter-clockwisedirection, the tray T 1  is first driven to the disc standby position Y in the range of positions C, and it will be followed by trays T 2  to T 5  in order. 
       FIG. 60  is a perspective view showing a state in which the cam gear  114  is rotated to a position for unlocking the second lock lever  94 . In this state, a position of the function lever  126  is changed in order to drive the gear train of elevation system (elevation unit). 
       FIG. 61  is a perspective view showing another locking system that prevents a movement of the recording/reproducing section  70  when one of the trays T is at the recording/reproducing position Z. The locking system can protect the disc changer  1  from external shock and vibration if there is an illegal power off during a recording/reproducing operation. At the right side of transverse slide plate  65 , there is provided a pin  65   d  which is capable of going into any of holes  32   e - 1  to  32   e - 5  of the UD rack  32 . The holes  32   e - 1  to  32   e - 5  correspond respectively to the recording/reproducing positions that align tray T 1  to tray T 5 . With this configuration, recording/reproducing is locked at a current recording/reproducing tray T position. 
       FIG. 62  is a locking system summary table for the recording/reproducing section  70 . At all times, there is a lock system that is activated to lock the recording/reproducing section  70 . 
     According to the configuration of the preferred embodiment of the invention, the tray driving gear unit  20  is capable of driving the trays T from the standby position Y to the disc exchange position X with an all-at-once operation. At this time all tray driving gears of the tray driving gear unit  20  rotate in a tray opening direction as one solid gear for driving the plurality of trays T. Further, when the tray driving gear unit  20  rotates in an opposite direction the trays T are driven one by one from the top tray to the bottom tray. Thus, it is possible to eject all trays T at once, and exchange all discs D from the top tray to the bottom tray. This simplifies the operation of exchanging all discs D in the disc changer  1 . While all the trays T are protruding, all the discs D can be checked, and exchanged if necessary. The same tray driving gear unit  20  is commonly used for both shuttling the trays T between the standby position Y and the disc exchange position X and disc checking function, thereby it is possible to simplify the design of the tray driving gear unit  20 , simplify the disc changer operation, shorten the changing time and reduce the possibility of tray jams. 
     Further, according to the embodiment, the tray driving gear unit  20  is capable of driving all trays T other than a tray T 1  above the recording/reproducing unit  70  from the standby position Y to the disc exchange position X with an all-at-once operation. At this time all tray driving gears of the tray driving gear unit  20  rotate in a tray opening direction as one solid gear for driving all trays T except the tray at the recording/reproduction position since that tray is not triggered by the trigger slide plate. Further, when the tray driving unit  20  rotates in an opposite direction the trays T are driven one by one from the top tray to the bottom tray. Thus, it is possible to eject all trays T other than a tray T above the recording/reproducing unit  70  at once, and exchange all discs D other than the disc D on the tray T above the recording/reproducing unit  70  from top tray to bottom tray. This simplifies the sequence for exchanging all discs D other than this tray T above the recording/reproducing unit  70  in the disc changer  1 . While all but one of the trays T are protruding, all the discs D on those trays T can be checked. The same tray driving gear unit  20  can be commonly used for both shuttling the trays T between the standby position Y and the disc exchange position X and disc checking function, thereby it is possible to simplify the design of the tray driving gear unit  20 , simplify the disc changer  1  operation, shorten the changing time and reduce the possibility of tray jams. 
     Furthermore, according to the embodiment, the tray driving gear unit  20  has a series of tray drive gears and can rotate to the RESET condition, and the trays T at the standby position Y are engage with the tray driving gear unit  20  by the tray triggering unit  50  after the tray driving gear unit  20  rotates to RESET condition. Thus, for each exchange of the disc D, the trays T protrude to the disc exchange position X and return to the standby position Y one by one from top to bottom. This simplifies the operation of exchanging all discs D, since it is possible to put a disc D onto any of the empty tray T without opening the trays one by one. 
     Still further, according to the embodiment, the tray drive gears (including top tray drive gear  24 , tray drive gear  22  and bottom tray drive gear  25 ) are separated from the shaft gear body (made up of the shaft gear  21  and the shaft  21   s ), therefore the tray driving gear unit  20  can be manufactured much more easily in comparison with a prior art body construction. 
     Still further, according to the embodiment, the tray drive gears are separate from the shaft gear body, therefore the tray driving gear unit can be manufactured much more easily in comparison with one body construction. Further, a top level tray drive gear fixed to the shaft gear body rotates as one body therewith at all times, and the rotational movement of the top level tray drive gear is transferred to the lower level drive gear through the stopper ribs thereof. Thus, all tray drive gears are driven to rotate one by one through the stopper ribs. 
     Still further, according to the embodiment, the additional rotation is provided to each tray drive gear by at least one spacer ring  23  placed between two tray drive gears adjacent to each other. The spacer ring  23  can acts as a dummy gear in the rotational movement of the tray driving gear unit  20 , and can reduce the size of the tray drive gear, because, in a case that the tray driving gear unit  20  does not have a spacer ring  23 , the drive gear pitch diameter needs to provide a total circumference equivalent to a total stroke for one complete rotation, and this increases the diameter of the tray drive gear. 
     Still further, according to the embodiment, an upper level tray drive gear&#39;s stopper rib pushes a lower level tray drive gear&#39;s stopper rib, through the spacer ring&#39;s stopper ribs, in a rotational direction of the upper level tray drive gear, and the lower level tray drive gear is forced to rotate in the rotational direction of the upper level tray drive gear. Thus, the rotational movement of the top level tray drive gear is transferred to the lower level drive gear through the stopper ribs, and all tray drive gears are driven to rotate one by one through the stopper ribs. Specifically, the size in a rotational direction of the stopper ribs is designed to equivalent to a multiple of gear teeth pitching angle, therefore the stopper ribs can contact to each other in a more stable way. 
     Still further, according to the embodiment, it is possible to provide the tray driving gear unit  20  with a dummy turn which is equivalent to the total stroke for moving a tray from the disc exchange position to the standby position, thereby the size of the tray drive gear can be reduced. 
     Still further, according to the embodiment, the first gear tooth of the tray&#39;s gear rack has a shape profile for easy engagement of trays T to tray driving gear unit  20  after triggered by the tray triggering unit  50 . 
     Still further, according to the embodiment, owing to the shape profile of the first gear tooth of the tray&#39;s gear rack, the tray&#39;s gear rack can be easily engaged with the tray driving gear unit  20  after it is triggered by the tray triggering unit  50 . Thereby, the tray T can start to move smoothly by the tray driving gear unit  20 . 
     Furthermore, according to the preferred embodiment, the triggering slide plate  52  in the disc changer is controlled and activated by the cam slot of the cam gear  114 , where the cam gear  114  is also used for driving trays. The triggering slide plate  52  pushes against tray lock lever  53  and provides a strong stable lock to all the trays T at standby position Y. When the cam gear  114  rotates in a tray T opening direction, the triggering slide plate  52  moves and the lock/unlock profile on the plate will push against the tray lock lever  53  in the unlock direction, at the same time trigger profiles on the plate bend follow the slot on mechanical chassis  3  to push trays T move forward. Thus, it is possible to common use a triggering slide plate  52  to open and lock trays T. The time for tray T unlocking is short as the triggering slide plate  53  unlocks trays T just before pushing the trays to engage the tray driving gears. This minimizes the tray T unlocking period before each tray T is driven. 
     As the triggering slide plate  50  is being moved forward, the trigger profile on the flexible ribs of triggering slide plate  50  will overlap with the trays trigger rib, and push the trays toward the disc exchange position X. This creates an advantage that the trays T are largely separated in the standby position Y, not linked to any other part than the housing and the locking profile. This prevents any problem if the positions of the trays T are slightly shifted at the shipment position. Upon, being triggered and pushed, the trays T can engaged with the tray driving gears for further transfer of trays T to the disc exchange position X or there can be a purely pushing action by triggering slide plate  52  itself if the stroke allows for the trays T to move from standby position Y to disc exchange position X. This creates another advantage for the flexibility in creating various options of tray driving system. 
     Further, according to the embodiment, the triggering slide plate&#39;s trigger profile bend follows the cam profile on mechanical chassis  3 . The profile changes while it moves from rear to front of the disc changer  1 . The profile contacts the trigger rib on trays T at the trays trigger zone, trays T then being pushed forward to engage the tray driving gear unit  20 . The trigger profile is formed on the triggering slide plate  52  as one body to reduce cost, and the trigger profile is more flexible to be bent and to withstand the trays triggering force. Pitching between the tray trigger rib and the triggering slide plate trigger lever profile can be controlled accurately. 
     In the embodiment, the guide slots on the mechanical chassis  3  can be arranged to have various heights and slopes. As the triggering slide plate  52  is being moved from standby position Y or shipment position to the front, before the disc exchange position X, the cam profile on triggering slide plate  52  is moved to the front and away from the tray lock lever&#39;s flexible ribs. The tray lock lever&#39;s lock profile will provide an interlock effect with the trays T. Triggering slide plate lock/unlock profile pushes against the lock lever profile to get a better locking effect at shipment condition. The plastic spring on the lock lever pushes against mechanical chassis  3  wall to provide a temporary locking effect to trays T while the trays T are entering from disc exchange position X to standby position Y. 
     Further, tray unlock period is minimized and the lock is immediate after each tray T is moved to standby position Y. The interlocking effect of trays T can achieve the most effective locking result. When the tray T moves in the forward direction, the tray lock lever  53  rotates in the locking direction and creates more locking force. In the shipment lock condition, the tray lock lever  53  is not able to move as the triggering slide plate lock profile minimizes the free play gap for tray lock lever  53 . So this only allows the trays T to move backwards into disc recording/reproducing position Z and prevents them from moving in the forward direction unless by means of pushing by the triggering slide plate  52 . 
     Furthermore, the tray lock lever  53  is linked by plastic linkage to create a joining part that can rotate by itself without interfering with the other levers while tray T passes over the lever to the stocking position. Tray lock lever  53  with plastic linkage joins the separate levers into one part for cost reduction and simplifies the mounting process. Tray lock lever  53  can act as separate 5 parts where the rotation of each lever does not affect the other lever. 
     Industrial Applicability 
     The present invention is applicable to a disc changer, particularly to a disc changer that stores a plurality of discs therein, transports a disc selected from a plurality of discs, and performs recording and/or reproducing information signal on the disc.