Abstract:
A media handling unit is a selfcontained device which is capable of being moved to existing photoplotting structures to transport media sheets from a supply cassette housed within the unit and advanced into the plotter for conducting a plotting operation. The unit also retreives the scanned media from the photoplotter returning it the unit in a light tight environment where the scanned film is deposited onto a collecting tray. The supply of film is provided in a cassette having a semi-cyldrical support surface causing the film to take on a preformed configuration which is generally coincident with the shape of the support surface on the plotter.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application relates generally to co-pending U.S. application Ser. No. 07/839,398 entitled Plotter Drum and Methods of Fabrication and Alignment Therefor, filed on Feb. 20, 1992, in the name of Allen W. Menard et al, now U.S. Pat. No. 5,276,465 and further relates to U.S. patent application Ser. No. 07/660,280 entitled Media Handling System for Photoplotter and Method of Use, filed on Feb. 22, 1991 in the name of Schimanski et al, now U.S. Pat. No. 5,207,414, which applications are commonly signed to Gerber Systems Corporation, the assignee of the present invention. 
     BACKGROUND OF THE INVENTION 
     This invention relates generally to photoplotter equipment, and more particularly a stand alone device for the on loading and off loading of media onto the curved surface of a drum or crescent-type plotting apparatus. 
     It has been found that drum type photoplotting apparatus of the type disclosed in aforementioned U.S. Pat. No. 07/839,398, present a significant advance in the imaging art by allowing imaging to be done in raster format onto a photosensitive media by supporting a media sheet on a partially cylindric support surface and controllably rotating a mirror along the center of curvature of that surface to effect such scanning. In order that the media be allowed to conform in this manner to the curvature of the support surface, it is necessary that each sheet have a very thin dimension, for example, on the order of 0.007 inches, hence making it highly flexible. One drawback to this is that the media sheet is somewhat mechanically unstable in terms of its being capable of being readily handled by an operator, thus making the overall plotting operation less efficient than it otherwise could be. That is, the drum plotter disclosed in co-pending U.S. application Ser. No. 07/839,398 is capable of rapidly scanning a number of media sheets in succession at a rate which is basically limited by the handling capacity of the operator. In the past, such manual handling operations involved the placing a film onto the support surface of a drum plotter so as to cause it to be held in alignment on that surface and subsequently scanned. Such manual placing of the media sheet onto the support surface of the plotter involved requiring the operator to insure that the media was also positioned accurately along a given datum referenced to the scanning operation. This step likewise added time and effort to the process. Additionally, the process of removing the thin film sheets from the curved support surface and then placing each sheet in a collecting tray was a further burden on the plotting operation. Through this all, the media which is made purposely sensitive to certain ranges of radiant energy, often including room light, must be handled in this manner in a dark room environment, which made the handling of the media within the already restrictive confines of the drum plotter, that much more difficult to manage. 
     A number of such drum plotters presently exist in the marketplace, which as mentioned, have been widely and successfully received in the marketplace. Thus, any solution to the aforesaid problems in the handling of media in a manner other than that which has been discussed above, must be made with the existing structure of these plotters in mind. 
     Accordingly, it is an object of the present invention to provide a media handling system for photoplotters using a crescent or drum shaped support surface wherein the media handled is in the form of a flexible sheet of material, i.e. film, which is advanced by the unit from a supply of such media onto the support surface of the plotter in registry with a given datum in the plotter and wherein after a scanning operation is completed on such media, it is automatically removed from the support surface of the plotter and returned to the unit and placed in a collecting tray. 
     It is yet a further object of the invention to provide a handling unit wherein media is handled in the aforementioned manner in a light-tight environment while maintained within the interior of the unit as well as while it is out of the unit. 
     It is a further object of the invention to house a stack of unexposed media or film in a light-tight cassette such that individual media sheets can be off-loaded and placed in registration onto the support surface for exposure by the scanning mechanism and subsequently be returned to a collecting station in the unit which is likewise sealed against light. 
     Still a further object of the present invention is to provide a transportable unit that is capable of handling media in the aforementioned manner which is adaptable to the existing structure of plotters which already exist in the market so as to mate with such units to create a light-tight passage therebetween for handling of media during a plotting operation therethrough. 
     A further object of the invention is to provide a supply cassette in which the media is caused to take on a given configuration conformable to the shape of the support surface of the plotter to which it is to be used so that the media is capable of being advanced onto the support surface in substantially the same configuration which it will assume when once placed on the involved support surface. 
     Yet, a further object of the invention is to provide a method of advancing thin sheets of film from a supply of such film onto the support surface in a photoplotter for scanning and subsequent removal by the apparatus and placement into a light-tight collecting tray for subsequent developing and/or processing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating the handling unit separate from the plotter assembly prior to their being connected. 
     FIG. 2 is a partially fragmentary side elevation view of the handling unit shown in FIG. 1. 
     FIGS. 3a and 3b when placed side-by-side show a top plan view of the media handling system of the unit shown in FIG. 1. 
     FIG. 4a and 4b when placed side-by-side show a side elevation view of the handling system shown in FIG. 3 looking at it from the left. 
     FIG. 5 is a front elevation view of the handling system shown in FIG. 4 looking at it from the left. 
     FIG. 6 is a top plan view of the moveable mounting rack shown separately of the system. 
     FIG. 7 is an end view of the rack shown in FIG. 6. 
     FIG. 8 is a partially fragmentary side elevation view of the media positioning drum. 
     FIG. 9a is a partially fragmentary side view through a portion of the media handling drum outer surface. 
     FIG. 9b is a partially fragmentary view of the outer surface of the media handling drum. 
     FIG. 10a and 10b form a flowchart illustrating the handling process. 
     FIG. 11a is a top plan view of the supply cassette shown with its cover removed. 
     FIG. 11b is a front elevation view of the supply cassette of FIG. 11a looking at it from the left. 
     FIG. 11c is a rear elevation view of the supply cassette shown in FIG. 10a looking at it from the right. 
     FIG. 11d is a side elevation view of the cassette shown in FIG. 11a looking at it from its right side. 
     FIG. 11e shows the cooperation between the drum and the spring fingers of the cassette during a media lifting operation. 
     FIG. 12a is a top plan view of the cover for the cassette shown in FIGS. 11a-11e. 
     FIG. 12b is a rear view of the cover shown in FIG. 12a looking at it from its right end. 
     FIG. 13a shows the cassette and cassette cover locking mechanism as seen in front end view. 
     FIG. 13b is a side elevation view of the cassette and cassette cover locking mechanism of FIG. 12a. 
     FIG. 13c shows the cassette cover being removed from the unit once the cassette is locked in place. 
     FIG. 14 is a perspective view of the end stop for the supply cassette. 
     FIG. 15 is a top plan view of the holding support for the collecting tray. 
     FIG. 16a is a top plan view of the collecting tray. 
     FIG. 16b is a side elevation view of the collecting tray shown in FIG. 16a with the side sealing strips removed. 
     FIG. 17 illustrates the cover for the collecting tray illustrated in FIGS. 15 and 16. 
     FIG. 18 illustrates the receiving opening formed in the handling unit for receiving the tray and cover. 
     FIG. 19 is a vertical section through a covered collecting cassette as inserted within the opening of FIG. 18. 
    
    
     SUMMARY OF THE INVENTION 
     The invention resides in a media handling unit for moving media between discrete locations. The unit for this purpose comprises a frame, a supply means supported by said frame for providing a source of media conformed to a generally partial cylindric shape while being maintained in said supply means. The system includes a first positioning means positioned above said supply means and slidably moveably mounted to said frame for movement between a first position corresponding to where the first positioning means extends in part generally above said supply means and a second position corresponding to where the first positioning means extends in part outwardly of said frame. A second positioning means is provided and is carried by said first positioning means for movement relative to both said frame and to said first positioning means. The second positioning means itself carries a third positioning means which is vertically moveable relative thereto for lifting media from said supply means in its conformed cylindric shape and moving said media while maintaining it in said conformed cylindric shape to discrete locations remote of said supply means under the combined movements of said first and said second positioning means. Control means are further used to connect said first, second and third positioning means to control the movements of the same to effect handling of media between said discrete positions. 
     The invention further resides in a method of handling media in accordance with the apparatus of the aforementioned system as well as in the design of the supply cassette and collecting tray used to provide media as well as to collect it. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a media handling unit illustrated generally as 2 and an associated photoplotter 4 which receives media from the unit 2 and exposes on such media a graphic in accordance with data maintained electronically in memory. The photoplotter is a drum type photoplotter which employs a partially cylindrical support surface 6 and a scanning mechanism 8 to effect controlled exposure of the media on selected areas thereof. While the unit 2 is capable of being used with many types of drum plotters that are presently in the marketplace, in the illustrated embodiment, the photoplotter 4 is one such as disclosed in the aforemention co-pending U.S. patent application Ser. No. 07/839,398, sold by Gerber Systems Corporation under the tradename CRESCENT/30. Included as part of the handling unit 2 is a central controller 5 which is responsible for switching the drive motors, valves, etc. of the unit between on and off conditions. The controller 5 is capable of being interfaced with the plotter 4 through the intermediary of a personal computer 7 so that the handling operation of the unit 2 can be coordinated with the scanning operation of the plotter 4 to effect succesive scans of a supply of media held in the handling unit 2. 
     The photoplotter 4 is enclosed by a housing except for being open at its front end for the purpose of allowing the media to be placed onto the support surface 6 and removed subsequent to scanning. The media handling unit 2 has a generally box-like shape as defined by a frame 20 and is enclosed on all sides by a metallic housing 10 which is secured to the frame 20 for the purpose of maintaining the unit in a light-tight condition when loaded with a supply cassette and collecting tray as will be described in greater detail later. The unit 2 is mounted on roller supports 12 which allow it to be wheeled up to the photoplotter for the purpose of connecting with it to create a light tight media handling environment. 
     Formed in the housing 10 is a supply cassette opening 14 located at one end of the unit and a bridging tunnel 16 located at the end of the unit opposite the opening 14. The bridging tunnel, as best illustrated in FIG. 2, is effectively an extension of the housing 10 and is provided for the purpose of creating a light-tight tunnel between the open end of the plotter 4 and the unit 2 through which media and an extension of the handling system travel. The housing is further provided with a third opening 18 located on one side panel of the unit through which a collecting cassette is received to remove the scanned media. 
     As mentioned, the unit is capable of being releasably connected to the photoplotter 4 to prevent relative movement therebetween. For this purpose, a latch means 22 is provided at the base of the frame 20 and includes a sliding jaw member 24 which is caused to move between the illustrated open position and a closed condition wherein it is drawn toward the unit through the intermediary of a threaded take up member 26. The jaw member 24 is adapted to engage the lower edge of an elongate pedal 28 or other transversely extending structural member disposed on the plotter 4 for the purpose of clamping it and pulling the media handling unit and the photoplotter together. To effect a light-tight seal therebetween, the bridging tunnel 16 is provided with a yieldable material 30 disposed about the perimeter of the tunnel which engages the outwardly disposed face of the plotter and is caused to sealingly press against this face as the take up member 26 is rotated. 
     Referring now to FIGS. 3-7 and to the particular structure of the handling system housed within the unit 2, it should be seen that the system is effectively suspended on the frame 20 above a supply station A and a collecting station C which are supported by a subframe member 32 comprising part of the frame 20 and is capable of extending in part outwardly of the frame to an intermediate station B disposed above the plotter surface 6. For purposes of clarity, the supply cassette and the collecting tray which are respectively associated with stations A and C and which are usually in place at these stations during a scanning operation are not shown in FIGS. 3-5. 
     In addition to the frame 20, the handling system includes a set of support rollers 34,34 rotatably mounted to the frame through a subframe member 72, a sliding U-shaped rack 36 adapted to slide relative to the frame through the intermediary of the support rollers 34,34, and a drum carriage 38 including a vertically moveable positioning drum 40, disposed on the rack for linear movement relative thereto through the intermediary of a set of locating rollers 42,42 disposed on the carriage 38. The U-shaped rack 36 is controllably linearly by driven relative to the frame by a first drive means 44 which includes a first drive motor 46 secured to the frame 20 generally at one end of the unit and a return pulley 48 disposed at the other opposite end of the unit drivingly coupled to one another by a toothed belt 50 which is attached along its length to the rack 36. The drum carriage 38 is controllably linearly moved forwardly and rearwardly along the indicated X coordinate direction relative to the frame 20 and the rack 36 by a second drive means 54 which is comprised of a second drive motor 56 secured to the rack 36 at one end thereof and a return pulley 58 rotatably mounted to the opposite end of the rack and drivingly connected with the drive motor 56 through the intermediary of an endless toothed drive belt 60 secured against movement along its length to the drum carriage 38. It is noted that the distance separating each drive motor and its respective return pulley generally defines the range of travel of the member driven by that motor. 
     As best illustrated in FIGS. 6 and 7, the rack 36 as mentioned is a generally U-shaped member having a transverse part 62 extending laterally between two opposed rails 64,64 and maintaining them in spaced transverse relationship with one another. Each of the rails 64,64 is provided with an inwardly oriented pair of vertically aligned tracks 66,66 associated with the locating rollers 42,42 and an outwardly oriented pair of vertically aligned tracks 68,68 associated with the support rollers 34,34, which inwardly and outwardly oriented tracks being spaced from one another by about the thickness of the rail associated with them, with the top and bottom edges of the tracks of opposed pairs being respectively horizontally aligned with one another. The edges of the outwardly and inwardly oriented tracks 68,68 and 66,66, are each sized and shaped to be correspondingly received within grooves 70,70 formed in the support rollers 34,34 and in the locating rollers 42,42. As best seen in FIG. 5, each set of the rollers 34,34 and 42,42 is comprised of four vertically aligned pairs, with the rollers of each pair being vertically spaced from each other by a distance sufficient to receive the associated ones of the tracks 66,66 and 68,68. 
     In the preferred embodiment, four pairs of support rollers 34,34 are provided and are mounted to the frame 20 through the intermediary of the sub-frame 72 such that two roller pairs are associated with each rail making up the rack 36 and each such two roller pairs being spaced from one another along the indicated X direction by an amount equalling just less than half the total length of the rails thereby providing a stable support from which the rack can be cantilevered in reciprocative directions outwardly from the sub-frame 72. 
     Referring now to FIGS. 5 and 8, and in particular to the drum carriage 38 and the positioning drum assembly carried by it, it should be seen that the assembly includes the positioning drum 40, which is moveable between the indicated vertical up position shown in FIG. 5 and 8 and a vertical down position (not shown) wherein the drum surface is caused to push downwardly against the top most sheet in the supply cassette located at the indicated station A in a manner which will be discussed in further detail with reference to the particulars of the supply cassette. For this purpose, the assembly includes a frame member 75 which makes up part of the carriage 38 and to which frame member are rotatably secured four pairs of the locating rollers 42. The assembly further includes a vertical positioning means 76 interposed between and connected with the frame of the carriage 38 and the positioning drum 40 for controllably moving the drum vertically. This means is comprised of four actuators 78,78 each secured to the frame 75 through a laterally directed member and having a vertically moveable rod connected to the positioning drum. Each of the actuators is connected to a pressurized air supply and the control of such air to the actuators is regulated by a solenoid valve (not shown) which is controlled by the central controller 5 of the apparatus. The actuators 78,78 are double acting and are aided by a plurality of tension springs 80,80 which are interposed between the frame 75 and the mounting drum 40 which act to help return the positioning drum 40 to its illustrated position up condition. These springs also serve to provide a fail safe vertical up condition for the positioning drum in the event that the actuators fail to lift. The drum carriage 38 is linearly moveable along the innermost tracks 66,66 of the rails 64,64 through the intermediary of the four pairs of vertically spaced locating rollers 42,42 that are mounted to the frame 75 and act on the tracks 66,66 at spaced points further adding to the overall stability of the system. 
     The mounting drum 40 is provided with means for lifting a single sheet of media M from a supply cassette situated at station A and carrying it under the powered movement of the carriage 38 from the loading end L of the unit to and past the discharged end O of the unit outwardly to the position shown in phantom line in FIG. 4b which corresponds to the location directly overhead of the support surface 6 of the photoplotter 4. For this purpose the lifting means includes a vacuum source (not shown) contained within the housing of the unit 2, a conduit 81 connecting the positioning drum 40 to the vacuum source and encased in a cable and vacuum line carrier 82 preventing it from inadvertent puncture and connected to the drum 40 through a connection 84 located generally centrally of the drum to introduce vacuum pressure therein. 
     The positioning drum 40 is a hollow member and is formed from a light weight material, such as aluminum. As best seen in FIGS. 9a and 9b, the generally cylindrical outer surface S of the drum 40 is defined by a sheet of material 88 having a plurality of openings 86,86 which are provided to communicate the vacuum evenly from the interior confines of the positioning drum 40 to its outer surface S. These openings are equally spaced at about one inch intervals, and in the preferred embodiment, each has a diameter equal to about one-eighth of an inch. Disposed outwardly and externally of the surface S is a layer of material 90 formed from a somewhat yieldable material, such as foamed polyethylene, in which material a plurality of holes 92,92 are made. The holes 92,92 each have a diameter equal to about five eighths of an inch and are concentric with the openings 86,86 formed in the drum and are maintained in such alignment by a layer of adhesive interposed between the surface S and the interior surface of the material layer 90. This arrangement creates the effect of having countersunk openings which enhance the lifting capability of the mounting drum 40 by further dispersing the vacuum pressure over a greater area. 
     Referring back to FIGS. 3a, 3b and 4a, 4b and to the operation of the handling system it should be seen that the system causes the positioning drum 40 to be located at three distinct points for specific tasks in handling of the media M. These locations are defined respectively as station A wherein media is loaded from the supply cassette onto the mounting drum and is thereafter carried in the indicated direction W by the combined movements of the drum carriage 38 and the rack 36 to the intermediate location at station B coinciding with the positioning of the mounting drum directly above and in registration with the support surface 6 of the photoplotter 4, and station C coinciding with the location of the collecting tray wherein the exposed media is dropped from the mounting drum into the tray for subsequent handling. It is noted that in moving a media sheet from station A to station B, the handling system of the invention locates the media sheet M on the support surface 6 in general alignment with a plotting datum DM as illustrated in FIG. 3b. 
     Each of the three stations A,B, and C mentioned above is defined by a travel limiting means associated respectively with the rack 36 and/or the drum carriage 38. For purposes of discussion, it should be understood that labels &#34;Z&#34; and &#34;W&#34; as used herein address particular reciprocative directions taken by the elements of the system along the indicated X coordinate axis. The first such means is provided on one rail of the rack 36 and takes the form of a transverse pin 94 which is located at the end of the rack associated with the end O of the unit. The pin 94 arrests motion of the rack in the indicated rightward Z direction by acting against a stop face 98 on the subframe 72 so as to position the transeverse member 62 of the rack proximate the return pulley 48 at the loading station A. The stop 94 also serves the purpose of arresting the linear leftward motion of the drum carriage 38 as it travels to its final outward location above the plotting station B. A second such stop means is provided on the other end of the rack associated with the loading end L of the unit. The second means takes the form of a bumper indicated schematically as member 96 and acts against a stop surface 100 provided on the frame sub-assembly 72 to arrest movement of the rack in the indicated leftward direction W to position it in its cantilevered orientation as shown in phantom line in FIG. 4b. 
     Motion of the drum carriage 38 in the indicated Z direction is arrested to locate the carriage at the collecting cassette station C by an activatable stop 102 mounted to the frame sub-assembly 72. This third stop means includes a sliding pin which is normally in a retracted position maintained out of interference with the path traveled by the drum carriage 38 as it moves in the indicated W coordinate direction, but is activated to an interfering position as the carriage moves in the indicated Z coordinate direction to stop at the collecting cassette station C. A forth stop means is provided and is located proximate the end of one of the rails 64, 64 associated with the loading end L. This means takes the form of a transversely extending pin 104 extending inwardly from its associated rail and engages a rearward stop face 106 of the drum carriage 38 to arrest carriage movement along the rack 36 in the indicated Z direction thereby repositioning the positioning drum 40 at the supply station A. 
     To aid in the motion arresting process, sensors 105,105 are provided along the travel line of the rack and the drum carriage to sense the presence of the involved moving member prior to its engagement with the appropriate mechanical stop. Once detected the central control unit 5 of the unit automatically curtails power to the respective one of the drive motors 46 and 56 such that from the point of first detection to actual engagement with one of the mechanical stops, the articulated member moves under momentum forces only, which in the preferred embodiment is a distance equalling to about one inch. 
     In operation, a supply cassette is loaded into a unit through the supply cassette opening 14 and is thereafter uncovered in accordance with one aspect of the invention which will hereinafter be disclosed in greater detail. At the same time an empty receiving cassette is also loaded into the handling unit through its opening 18. Communication links between the plotter 4 and the handling unit 2 are then established to coordinate the plotting and handling operations with one another. (Step 110) Thereafter, the vacuum source of the unit is activated and the actuators 78,78 are energized to move the positioning drum 40 down into the supply cassette whereupon the top sheet of media is drawn onto the drum by the combined downward applied force of the drum and the simultaneously applied vacuum pressure. (Step 111) The actuators 78,78 are reverse energized and the drum, through the intermediary of the tension springs 80,80 and air pressure is drawn to its vertical up position. (Step 112) Then, the first drive motor 46 is activated and is caused to rotate such that the rack is moved in the indicated direction W until the bumper 96 approaches the stop surface 100. (Step 113) As such approach is made, the sensor 105 associated with the involved stop senses the nearing approach of the end bumper 96, and through this detection the central control unit stops the supply of power to the first drive motor 46. (Step 114) With the sensing of the end of travel of the rack in the indicated W direction, the central control unit then activates the second drive motor 56 such that the drum carriage 38 is moved outwardly of the interior confines of the handling unit and along the now outwardly cantilevered portion of the rack 36. (Step 115) Once the drum carriage reaches its end of travel destination (Step 116) a vacuum source associated with the plotter 4 and communicating with the support surface 6 is applied. Thereafter the vertical actuators 78,78 are energized thus lowering the positioning drum downward so as to locate the media in close proximity with the support surface 16 of the plotter. Thereafter, the applied vacuum to the positioning drum 40 is stopped, the media sheet is released from its holding engagement with the drum and the drum is moved to its vertical up position with the media sheet being held to the platter support surface 4 by the applied vacuum of the plotter 6. (Step 117) The first driving motor 46 is energized such that the rack 36 with the drum carriage still positioned at its outer limit is moved in the indicated direction Z to retract both it and the extended portion of the rack so as to locate the carriage at the intermediate station C. (Step 118) The ones of the sensors 105,105 associated with the stop 94 and the activatable stop 102 are interrogated to determine whether the retraction process is complete. (Step 119) Once the travel limit is detected, the central control unit 5 indicates to the photoplotter that plotting operation may commence. (Step 120) After a plotting operation is completed on a given media sheet, the first drive motor 46 is activated and the rack 36 is again moved in the indicated W direction to extend it outwardly from beyond the handling unit to again position it over the plotting station B. (Step 121) Once the appropriate signal is generated by the sensor associated with the stop 96 indicating that the rack 36 has moved to its outer most limit of travel (Step 122), vacuum is again applied to the positioning drum 40 and the vertical actuators 78, 78 are again energized, thus moving the drum downwardly into contact with the media lying on the support surface 6 of the plotter 4. (Step 123) Simultaneously with this action, the photoplotter reverses the air flow through its support surface 6 to create a positive pressure thereby floating the media such that the positioning drum can more easily act on it. (Step 124) The actuators 78,78 are then reversed energized and the drum 40 returns with the scanned media to its vertical up position. (Step 125) 
     The activatable stop 102 is activated and the first and second drive motors 46 and 56 are in sequence activated such that the rack 36 and drum carriage 38 are moved in the indicated Z direction. (Step 126) The order of such movement in its preferred embodiment is such that the rack 38 is moved through its end of travel as defined by the stop 94 and thereafter the drum carriage is caused to be advanced a short distance along the rack to an intermediate location corresponding to a position just above the collecting station C as defined by the stop 102. (Step 127) At this point, the actuators 78,78 are again activated such that the positioning drum is now in its vertical down position and the vacuum source is thereafter stopped thereby releasing the media into the tray below. (Step 128) After this, the drum is moved to its vertical up position and the second drive motor 54 is again activated (Step 129) such that the drum carriage 38 is caused to moved in the indicated Z coordinate direction until it confronts its end of travel limit stop 104 defining its home position. (Step 130) Thereafter, the process is repeated (Step 131) until such time as all the media in the supply cassette have been moved. 
     Referring now to FIGS. 11a-e and 12a-b, it should be seen that the supply cassette generally illustrated as 132 is a light-tight structure having a two piece construction comprised of a body part 134 shown in FIGS. 11a-11e and an overlying cover part 136 shown in FIGS. 12a and 12b engagable with the body part to create a light-tight compartment for storing media until needed. The body part is comprised for the most part of a piece of sheet material 138 which is caused to take the configuration of a half cylindric shape and by a base member 160. The radius of curvature of this sheet is constant along the length of the cassette as taken from a longitudinal axis K and is substantially equal to that of the plotter drum surface 6. This is important since the media which is highly thin and hence flexible, usually on the order of 0.007 inches, is caused to conform to this shape thereby giving it a preform shape for handling while still in the cassette. At opposite ends of the partially cylindric sheet 138 are disposed a first end cap 140 associated with the trailing end of the cassette and a second end cap 142 associated with the cassette&#39;s leading end. The supply cassette 132 is supported in a relatively stable condition by the base 160 allowing it to be slidingly received within tracks 162,162 fixed to the frame 20 and accurately positioned relative to the home location of the positioning drum 40. 
     Both the supply cassette and its cover are complementarily sized and shaped to permit the cover to be readily removed while nevertheless maintaining the light-tight integrity of the compartment during periods of non-use. For this purpose, it should be seen that the cover 136 is likewise formed from a partial cylindrical metallic sheet 148 fixed at right angles to a correspondingly crescent-shaped end plate 151. Further, the cover sheet 148 is outwardly turned at its lateral distal ends 152, 152 while the lateral edges of the sheet 138 which forms the body part of the cassette are complementarily inwardly turned at 154. The outwardly turned edges of the cover sheet 148 provide a track through which the inwardly turned edges of the cassette 132 are slidingly received. This arrangement creates a labyrinth through which light passage is prevented. Further to these ends, the lateral edges of the cover sheet 148 are outwardly turned such that depending portions 153,153 are formed and the opposed end portions of 144,144 of the second end cap 142 have formed in them inwardly directed slits 146,146 which permit the depending portions 153,153 of the coversheet 148 to be slidingly sealingly received within the slits and thereafter positioned around the inturn edges 154, 154 of the body member 134. Additionally the first end cap is mounted to the body part sheet 134 such that a slight clearance 156 exists between it and the inturned edges 154, 154 of the body portion sheet 138. This clearance allows the leading edge of the coversheet 148 to be captured within this clearance upon the continued insertion of the cover into the cassette in the indicated direction Q. As seen in FIG. 12b the junction between the end plate 151 and the connected coversheet 148 is lined with a light impenatrable material 158, such as black foam rubber. Additionally, the outturned portions 152,152 of the coversheet and the first and second end plates of the body member are provided with a like light impenatrable strips. 
     As seen in FIGS. 11a and 11e, the supply cassette 132 is further provided with a means 182 cooperating with the vertically moveable mounting drum 40 for causing the media to be drawn into engagement with the outer surface of the mounting drum as it is vertically moved downwardly into engagement with it. For this purpose, the means 182 includes a plurality of metal strips or spring fingers 184,184 which are disposed along the upwardly facing support surface provided by the sheet 138. The spring fingers 184,184 directly support the stack of media laid upon them and have a raised central portion 186 integrally connected to end portions 185,185 which curve substantially with the same radius of curvature of the support surface of the body member 134. As best illustrated in FIG. 11e, the raised central portion 186 is located generally centrally with the central axis K of the cassette such that the downward action of the mounting drum bears directly on this portion as it is moved vertically downwardly as discussed with reference to FIGS. 5 and 8. The result of this action is the flexure of the end portions 185,185 inwardly toward the mounting drum thereby causing the sheet material to be pressed into engagement with the suction surface of the mounting drum. 
     This feature is important in the instance where the remaining few sheets in an original stack of fifty media sheets remain in the cassette for handling by the mounting drum 40. That is, for a stack of 50 sheets of 0.007 inch thickness the radius of curvature will vary from the topmost sheet to the bottom most sheet by an amount of approximately three eights of an inch. Since the drum has to be smaller than the minimum radius as defined by the top most film sheet, the action of the metal strips or spring fingers is important in causing the sheets of a greater radius to be moved into engagement with the suction surface of the mounting drum. 
     Referring now to FIGS. 13a, 13b, 13c and in particular to the locking mechanism which allows the supply cassette and its cover to be locked against inadvertent removal prior to being placed in the handling unit 2, it should be seen that the mechanism as shown in FIG. 13a, is provided on the second end cap 142 and includes a journalling member 163 which inturn receives a locking part 164 capable of being rotated between locking and non-locking conditions. The locking part 164 includes a cam member 166 which is nonrotatably coupled to a latch member 168, which latch and cam members are angularly offset by approximately 45 degrees. In this way, the cam member 166 being spaced from the second end cap 142 by a guide bearing 170 is caused to be rotated in a counterclockwise direction to cause the cam to engage with the outer face of the end plate 151 of the cover member 136 as shown in phantom line. 
     Likewise shown in phantom line is the position of the latching part 168 which is shown at a one o&#39;clock position. In this condition, the cassette cover sheet and the body are locked against inadvertent removal by the cam member 166, thus making the loading and covering process for the supply cassette capable of being accomplished at an offsite remote location. As shown in solid line in FIG. 13a the rotation of a knob 172 which is nonrotatably connected with the locking part 164 causes the camming member 166 to be rotated out of engagement with the end plate cover 151, but nevertheless cause the latch part 168 to engage on a locking pin 174 extending in the direction of guide rails 162 and secured to the frame 20. 
     As previously discussed, the base 160 of the cassette assembly allows the cassette to slide into the opening 14 in the housing until the second end cap 142 of the cassette is seated in the opening against the bias of a surrounding continuous seal 137. Thereafter, the locking piece 164 is rotated in a clockwise direction to cause the latch piece 168 to engage with the pin 174 to lock the cassette against movement in the indicated X coordinate direction. In this condition, the cover member 136 is freely slidabily removeable from the body part 134 as illustrated in FIG. 13c such that it can be pulled outwardly of the unit while the body and the supply of media remains sealed against light during this uncovering process. The end limit of travel and vertical limit for the supply cassette 132 as it is inserted through the opening 14 in the housing 10 is defined by an end of travel limit piece 178 illustrated in FIG. 14 which is generally L-shaped having its depending portion secured to the frame 20 and having its generally orthgonally directed portion 180 being disposed in the direction of the guides 162,162. The portion 180 has a fork-like configuration which is adapted to be received between the base 160 of the supply cassette and the partial cylindric sheet 138. Thus, with continued advancement of the supply cassette 132 along the indicated X coordinate direction, the second end cap 142 of the supply cassette becomes automatically seated flush with the exterior face of the handling unit. 
     Referring now to FIGS. 15-19 and to the collecting cassette station C, it should be seen that this station is defined by a loading support 190 having a support plate 192 and laterally disposed guide members 194, 194 defining a support surface F generally aligned with the opening 18 in the housing 10. The collecting cassette associated with the collecting station C and illustrated generally as numeral 200 in FIG. 16a, is comprised of a generally rectangular tray having a bottom 202 and long sides 204,204 and short sides 206, 208 defining a generally rectangular characterstic of the tray. Below the tray bottom 202 are provided a pair of guides 210,210 which are correspondingly sized and shaped to be received within the receiving guides 194, 194 of the support plate 192. The guides 210, 210 are chamfered along their leading edges 212, 212 and a guide ramp 213 is provided on the support plate 192, the effect of both the chamfers 212, 212 and the guide ramp 213 serving to facilitate the mating of the corresponding shaped guides as the tray 200 is inserted through the opening 18 along the indicated direction S. 
     As seen in FIG. 16b, the short side 208 of the tray 200 is defined by a hollow elongate block 214 which is welded to the trailing end of the tray 200. As is apparent from this figure, the block 214 has a height h equal to about twice the height h&#39; of the tray 200 and the block member 214 has a width W which is sufficient in size to permit it to straddle partially between the interior confines of the housing and the external environment of the media unit when inserted into the unit. The tray is limited in the direction of insertion S by a stop plate 216 which abuts against the housing 10. 
     The support surface F of the plate 192 is disposed relative to the opening 18 as illustrated in FIG. 18 such that it is generally located at one half the opening height H. This is to allow for the generally one half sized relationship between the height h of the member 214 and its associated tray height h&#39; thereby permitting the bottom surface 202 to seat on the support surface F while nevertheless fitting the elongate block 214 squarely within the confines of the opening 18. 
     The opening 18 is slightly oversized relative to the thickness dimension h and the length L of the tray so that a light enclosing seal 220 can be provided around the perimeter of the opening. The seal 220 is formed from a flexible rubber material and is yieldable to allow the insertion of the supply cassette into the unit while nevertheless being compressed against the outer perimeter of the elongate retangular block 214. 
     In use, an empty tray 200 is inserted through the opening and is positioned on the support plate 192. For locking the tray into position on the support plate a locking device 222 is provided and includes a reciprocating pin member 224 which is received within a correspondingly sized and shaped opening formed in a lower surface of the rectangular block member 214. After a scanning operation is completed on all the media, a tray cover 226, illustrated in FIG. 17, is slid over the tray 200 between the compression seal 220 and the outer surface of the rectangular block member 214 in a manner shown in FIG. 19. Once the cover is in place the locking member 222 is released and tray is removed by pulling the stop plate 216 together with the tray cover out of the unit. 
     By the foregoing a media handling system has been disclosed by way of illustrating rather than limitation. However numerous modifications and substitutions may be had without departing from the spirit of the invention. For example, in the operation of the handling system as discussed with reference to FIGS. 3a, 3b and 4a, 4b it is disclosed to actuate the drive motors 46 and 36 at separate instances so as to create two distinct movements between the rack member 36 and the drum carriage 38. However, it is within the purview of the invention to accelerate the handling process by driving both motors together where combined movements of the rack and the carriage are required to affect travel along a given linear distance. For purposes of this disclosure the media M has been defined as a photosensentative film, plate or the like which is thin and relatively flexible. However the term media can further be used to define any material which is capable of conforming to the generaly semi-cylindric shape of the supply cassette and moved in the manner which is disclosed in the foregoing specification. 
     Accordingly, the invention have been disclosed by way of illustration rather than limitation.