Method and apparatus for pivotally mounted media transport bridge with improved counterbalance system

Abstract: A media transport bridge (10) is an integral media transport device within an internal drum laser imagesetter that transports media (24) from an imaging area in the drum (22) to an external processor or intermediate buffer. Five pairs of rollers (I-V) transport the film over the drum (22). A first stage (75) of the bridge includes a first pair of rollers (I) driven independently so that the first stage (75) is removable and replaceable with a take-up cassette (97) if desired. A friction drive within the imagesetter (14) is adaptable to drive either the first stage (75) or the take-up cassette (97) when installed. Upon removal of the first stage (75), an automatic adjustment of the bridge (10) is performed to balance the pivotally mounted bridge (10). The media (24) is moved into the bridge (10) by a pair of drum rollers (46) while the first stage (75) is synchronized with the other four pairs of rollers (II-V) in the bridge (10) and monitored to keep a slack loop (140) of media (24) at the first stage rollers (I) to eliminate perturbations in the media (24). A mechanical flag sensor (138) changes state to slow and speed up the bridge rollers to maintain the slack loop (140).

Description: This invention relates to transporting web-type media from a first machine operating at a first speed to a second machine operating at a second speed and provides an apparatus to allow each machine to operate at its own speed while minimizing idle time. An example is automated photographic imaging and subsequent developing of web-type media. These consecutive processes usually occur at different operating speeds, and comprise exposure of a image in an imaging device by illumination of photographic media, and subsequent chemical developing of the image in a processing device. In electronic prepress systems, images to be printed by offset printing means are scanned from photographic sources, digitized, assembled and edited electronically at a workstation, and then transmitted to a raster image processor or "RIP" for half-tone screening and image rasterization. The "RIP image" or the rasterized image to be printed, is then transmitted from the RIP to an imagesetter for photographic or film recording. Such an electronic prepress system is described in U.S. Patent No. 4,004,079 and is available from Miles Inc. under the Trademark "COLORSCAPE". An imagesetter includes a supply of unexposed photosensitive media a recording support surface, and an image exposing system for forming the image to be recorded according to the RIP image data. The image exposing system may employ a laser beam, a cathode ray tube (CRT), an LED emitter or the like as a radiation source. The media passes from a supply roll as a web to the recording support surface at which point the photosensitive media is exposed by the laser beam, forming a latent image on the media. Numerous images may be recorded onto the web consecutively. The exposed web advances onto a take-up cassette that stores the media in light-tight environment. The take-up cassette is then removed and transported from the imagesetter to the media processor where chemical processing occurs. The transport system of the processor usually transports the media at a constant speed during operation. The system requires the web to be wound onto the take-up cassette at the speed of the imagesetter, the take-up cassette to be physically removed and transported to the processor, and the media to be removed from the take-up cassette at the speed of the processor. Additionally, after developing occurs in the processor, the media must be cut into sheets to separate the images. This requires two manual steps that slow operation and increase down time. Consequently, a media handling system was developed that provides a bridge from the imagesetter directly to the processor, similiar to UK Patent Application GB 2,100,882. Here, an image is recorded onto the web media, advanced and cut within the imagesetter, and then fed into the bridge. The light-resistant bridge receives a single cut sheet of the web media at the imagesetter speed, and then the processor takes the sheet from the bridge at the processor operating speed. This overcomes the problem of transporting the take up cassette and cutting the images manually. However, the imagesetter remains idle while the entire first sheet is processed until the bridge is empty because the imagesetter typically runs faster than the processor. Although this method provides automation, it still requires interruptions in the operation of the imagesetter. Another disadvantage of the bridge described above is media waste. After forming an image on the media, the media is advanced and cut, and then delivered to the bridge During this sequence, the end of the image is advanced from the imaging point to the cutting point while no imaging occurs. An unexposed area of media results, from behind the cutter back to the imaging point, as a result of the advancement of the media to be cut from the web. Because this cycle of advancing and cutting occurs often, there are frequent unexposed areas of media (24) causing undue waste of expensive media. GB-A-2 160 986 discloses a steelyard weighing device. A steelyard uses a beam at either end of which the item to be weighed and a balance weight are respectively attached. A strain gauge is mounted on the beam to monitor the weight of the item. An example of a two stage media transport bridge is given in EP 0 352 374, entitled, IMPROVED SHEET HANDLING MACHINE. According to this teaching, media taken from a web is cut into sheets in a processing machine and the sheets are delivered to a first conveyor device. The first conveyor device is independently driven with respect to the processing machine and is capable at being driven at a plurality of speeds. The first conveyor is also pivotally mounted at the exit end so that the entrance end can be tilted in order to accumulate sheets on the first conveyor when the first conveyor is operating at a slower speed than the processing machine. A second conveyor device, is independently driven with respect to the first conveyor device, and receives sheets from the first conveyor device and advances the sheets to a platform where they are stacked prior to discharge from the platform. The two stage system of EP 0 352 374 offers buffering capability by allowing separate control of each media transport stage however the sheet buffering system, described in EP 0 352 374, requires a substantial increase in the floor space footprint of the entire system as well as a very long media path. US-A-5 110 104 discloses a sheet transporting apparatus, having a sheet storage device capable of storing sheets, and provided in the middle of a sheet transport path; and a carriage unit with a sheet discharge mechanism for transporting a sheet to the sheet storage device and capable of reciprocating motion substantially above said sheet storage device. It is accordingly an object of the invention to internally transport exposed media from an imaging area in an imagesetter to an external processor, and to temporarily store media during subsequent imaging to eliminate waste of media between imaging. It is an object of the invention to have a media transport bridge integral with an imagesetter. The bridge is designed within an internal drum recorder to transport media from the front of the imagesetter, over the drum, and out the rear of the imagesetter, either directly to a processor, as described above, or to a secondary storage device. The amount of floor space required for the system is reduced. It is a specific object of the invention to provide the user with a system having an integral media transport bridge, with an option to use a take-up cassette instead of the bridge if so desired, by easily removing a portion of the bridge and replacing it with the take-up cassette. Another object of the invention is to counter-balance a change in weight of the media transport bridge upon removal of a first stage of the bridge. The above-mentioned objects are realised by a media handling system having the features set out in claim 1 and by a method having the features set out in claim 6. Specific features for preferred embodiments are set out in the dependent claims.. The features and objects of the invention will become apparent in the following description taken with the accompanying drawings, in which: Figure 1 is a side view of an internal drum recorder employing an internal media transport bridge according to the invention with a side panel of the internal drum recorder removed to view the bridge. Figure 2 is a front view of a drive roller having an integral over-running clutch and drive pulley assembly. Figure 3 is a cross-sectional side view of a roller pair mounting used in the media transport bridge. Figure 4 is a side view of the bridge of Fig. 1 having and exposed media path with the cover panels removed. Figure 5 is an enlarged side view of the bridge of Fig. 1 showing the internal drive system and the remote drive motor. Figures 6a-d are sequential views of the removal of the first stage transport of the media transport bridge of Fig. 1 and installation of a take-up cassette. Figure 7 is a side view of the adjustable counterbalancing system for the media transport bridge. Figure 8 is a side view of the first stage transport and a slack loop in the media. Referring to Fig. 1, an internal bridge, generally referred to by reference numeral (10), is shown mounted inside a frame (12) of an internal drum recorder imaging device, generally referred to as reference numeral (14). The bridge (10) is completely enclosed under light-resistant covers (16). The bridge (10) has a media transport path (20) that transports media (24) from the internal drum recording surface (22) at the front (26) of the imaging device (14), over the drum (22) and out a rear side (28) of the imaging device (14) to a processing station or to a secondary storage space (not shown). The design of the media transport path (20) through the imaging device (14) reduces the floor space that is typically required for bridge systems. The footprint, or floor space required, is the same for the imaging device (14) with the internal bridge (10) as it is for the imaging device (14) alone. Referring to Figs. 1 and 2, the bridge structure (10) contains a support frame which has two side castings (30) and three cross tubes (not shown) that are fixed and welded between the side castings (30) to provide torsional rigidity to the bridge structure (10). Rollers (32) are provided along the media path (20) which are supported for rotation by ball bearings (34). The ball bearings (34) are mounted in the side castings (30) and are axially fixed by rings (36) provided in annular grooves (38) of the side castings (30). A spring (40) is provided on the roller shaft (42) between the roller (32) and the ball bearing (34) to take up axial play on the roller shaft (42) relative to the bearings (34). The rollers (32) are provided in pairs (I-V) along the media path (20). Those rollers (32) above the media path (20) are the driven idler rollers (44) and those below are the drive rollers (46). The lower drive rollers (46) each have a drive pulley (48) fitted onto the roller end shaft (50). Each drive pulley (48) has an over-running clutch (52) with the exception of the first drive roller (54) of the first pair of rollers (I). The over-running clutch (52) allows only one way relative rotation between the drive roller end shaft (50) and the pulley (48). The over-running clutch (52) also allows the drive roller (46) to rotate faster than or over-run the driving speed of the pulley (48), such that a sheet of media may be pulled out of the bridge (10) by the processor or secondary storage device (not shown) at a speed that is faster than the transporting speed of the rollers (I-V). Referring to Fig. 3, each idler roller 44 is mounted with the end shafts (50) extending through tangential slots (54) within the side castings (30). The slots (54) have a longitudinal axis along the common axis (C-C) of each respective pair of rollers (32) so that the distance between the idler roller (44) and the drive roller (46) of each pair of rollers (32) may be adjusted. The top of the tangential slot (54) is provided with a spring device (58) for automatically adjusting the idler roller (44) against the drive roller (46). The nip pressure between the drive roller (46) and idler roller (44) is adjusted for various media thicknesses. In the preferred embodiment a spring loaded plunger (62) is located at the top of the slot (54) and is in contact with a hub portion of the roller to provide a force urging the rollers together. The spring device (58) is used in only the first two roller pairs (I, II) (Fig. 1). In the last three pairs of rollers (III-V), the common axis is approximately vertical when in the operational position, therefore the gravitational force on the upper idler roller (44) is sufficient to provide the necessary nip pressure for different media thicknesses to enable smooth transportation of the media (24). Referring now to Fig. 4, upper platens (64) and lower platens (66) are substantially parallel to one another and are placed symmetrically around the plane of the media transport path (20), when assembled as in Fig. 1. The platens (64, 66) guide incoming media (24) in a substantially linear path and keep the media (24) flat during transportation. Covers (68) are fitted above and below the platens (64, 66) and fastened to the side castings (30) to prevent light from exposing the photosensitive media. The lower platens (66) are fixed to the support frame of the bridge (10) and the upper platens (64) are generally fixed to the inner sides of the top covers (68), such that when the covers (68) are open, the media path (20) is exposed. Spaced along the upper and lower platens (64, 66) are the five pairs of rollers (I-V), each pair having the nip tangent to the media transport path (20). Referring to Fig. 5, the last four drive rollers (46), (II-V), are connected together by a drive system, generally referred to as (70), which is shown as a synchronous belt drive (72) connecting the drive pulleys (48) on the last four roller end shafts (50). This portion of the transport bridge (10) and the belt and pulley drive (72) is referred to as the second stage of the bridge (10), generally indicated as (73). It will be appreciated that the drive (70) may be any type of system that drives the drive rollers (46) in unison at substantially equal speeds. A drive motor (not shown) for the second stage (73) is attached in a conventional manner to the bridge (10) to drive the belt (72) and pulleys (48). The first pair of rollers (I) is driven by a motor (74) which is independent and remote from the bridge structure (10), such that the first pair of rollers (I) serve as a bridge first stage, generally indicated as (75), which is independently driven. The first stage drive motor (74) is mounted inside of the imagesetter (14), and is coupled to the first stage roller pair (I) by a friction gear (76) mounted on the motor shaft in driving contact with a friction wheel (78) mounted on the end shaft (80) of the drive roller (46) of the first stage rollers (I). The end shafts (50) of all the drive rollers (46) are provided with a tapered portion (not shown) which can accommodate either the friction wheel (78) or the standard pulley (48) and clutch (52) assembly by a tapered fit. The rollers (32) therefore are generic with respect to their position within the bridge (10), keeping the rollers (32) homogeneous and less expensive. As an alternative to the heretofore described media "transport" mode, the bridge (10) is designed to allow a take-up cassette to be inserted into the take-up area where the media (24) normally enters the bridge (10) to provide a media "storage" mode. In Figs. 6a-d it is shown that the first stage (75) of the bridge (10) is a removable unit which is removed by disengaging the two thumb screws (86) (one shown) at the interface (88) of the first and second stages, pulling the first stage (75) outward by the handles (not shown) provided on the front cover (68), and rotating the first stage (75) out of the bridge (10). To facilitate the removal of the first stage (75), the lower portion of the first stage (75) has a media guide (90) pivotable about point A. In Fig. 6b, the media guide (90) remains flush to a mounting platform (92) as the first stage (75) is rotated outward, due to the engagement of two aperture guide blocks (94) (Fig. 6c) mounted on the bottom of each side of the media guide (90) in a corresponding platform aperture (96) through which the media (24) passes. Then the first stage (75) is completely removed, disengaging the aperture guide blocks (94) from the platform aperture (96), as shown in Fig. 6c. The thumb screws (86) remain fastened to the first stage (75) upon disengagement from the second stage (73). The first stage (75) is then stored until the user wishes to return to an "on-line" operational state. Referring to Fig. 6d, it is shown that to use the storage mode of the imaging device, the take-up cassette (97), which also has aperture guide blocks (94), is inserted onto the platform (92) such that the guide blocks (94) engage with the platform aperture (96). The take up cassette (97) is driven by the same motor (74) (Fig. 5) that drives the first stage (75) when installed. A friction wheel (99) is provided on the outside of the take-up cassette (97) to engage with the friction gear (76) (Fig. 5) when the take-up cassette (97) is inserted onto the platform (92). The friction wheel (99) is coupled to the media take-up core inside the cassette (not shown), thereby power assisting the winding of the media onto the take-up core. The covers of the imaging device are then closed to light-proof the interior of the imaging device (14). The external covers (16) (Fig. 1) of the imaging device (14) are in the same position whether the device (14) is using the bridge (10) "on-line" or the take-up cassette which is aesthetically pleasing to the operator. Referring to Fig. 6B, to return to an on-line'operation and reinstall the first stage (75), the first stage (75) is rested on the platform (92) and slid forward until the aperture guide blocks (94) engage the platform aperture (96), aligning a media guide mouthpiece (98) with the media path from the drum. The first stage (75) is then pivoted upward about point A relative to the media guide (90), until the first stage and the second stage interface at (88) as in Fig. 6A, and the thumb screws (86) are fastened. As shown in Fig. 1, the bridge (10) is installed within the imaging device (14) and is pivotable about a rotational axis (110) and supported by two support arms (112) bolted to side plates (not shown) of the device. Two rotational axis bearings (114) are mounted on the support arms, one on each side of the bridge (10) respectively. The bearings provide accurate rotation and provide tolerance of axial misalignment. Support for the weight of the bridge (10) is provided by an assist mechanism, shown in Figs. 1 and 7 and generally indicated as reference numeral (120). The assist mechanism has two gas shocks (122) secured at the support arms (112). The shocks (122) aid the user in lifting the bridge (10) out of the operational position and into a non-operational position to allow access to the media supply area (142). Spring devices and rotating cams affect the amount of counterbalance force supplied by the assist mechanism (120) upon rotation of the bridge (10) about the rotational axis (110), such that balance of the bridge (10) is maintained in most rotational positions. The bridge (10) is pivoted upward using the two handles (not shown) provided in the front cover (68). The media guide (90) (Fig. 6a) of the first stage (75) is spring biased to pivot into a non-operational position while the bridge (10) is pivoted upward about the rotational axis (110). The media guide (90) is spring loaded to pivot counter-clockwise about the pivot point A during disengagement of the aperture guide blocks (94) (Fig. 6c) from the platform aperture (96). This feature of the bridge provides for alignment of the media path (24) passing through the bridge and the platform upon closing the bridge. The media guide (90) is already positioned to facilitate alignment of the aperture guide blocks (94) with the platform aperture (96) during closure of the bridge (10). When closing the bridge (10), the clockwise rotation of the bridge (10) about the rotational axis (110) brings the media guide (90) in contact with the platform surface (92). Upon continuing rotation, the loading force is counteracted by the interface of the media guide (90) and the platform (92), and the media guide (90) rotates counter clockwise relative to the pivot point A, aligning the complimentary aperture guide blocks (94) and platform aperture (96) for engagement, and resulting in alignment of the media path. The bridge can also be rotated about the rotational axis (110) when the first stage has been removed, for example, to facilitate installation and removal of the take-up cassette. Upon removal of the first stage (75), it is necessary to counter balance the bridge (10) about its support point and rotational axis. Referring to Fig. 7, the force generated by the gas shocks (122) will cause uncontrolled rotation of the bridge upward about the rotational axis (110) in a clockwise direction if the decrease in the weight of the bridge is not compensated for. The bridge assist mechanism (120) is equipped with an adjustment mechanism (124) that changes the moment arm of the force produced by the gas shocks (122) with respect to the rotational axis (110) of the bridge. Decreasing the moment arm from position A to position B will decrease the clockwise torque about the rotational axis (110) provided by the gas shocks (122), to compensate for the decrease in the weight of the bridge (10) with the first stage removed and the corresponding decrease in counter-clockwise torque about the rotational axis (110). To accomplish the adjustment of the gas shocks (122), each shock (122) is attached at the top to a respective shuttle mechanism (126) on the bridge (10), one shuttle mechanism (126) on each side of the bridge (10). A drive shaft (128) traverses the width of the bridge (10) to drive a perpendicularly oriented lead screw (130) of each shuttle mechanism (126) through beveled gears (132) mounted on the drive shaft (128) and lead screw (130), respectively. Upon rotation of the drive shaft (128) each shuttle mechanism lead screw (130) is rotated causing linear movement of the shuttle between positions A and B along the lead screw (130), and simultaneously pivots the attached gas shock (122) about point Z, effectively changing the moment arm of the assist mechanism (120). Upon removal of the first stage (75) as in Fig. 6C, the shuttle mechanisms (126) automatically adjust the position of the gas shocks (122). The thumb screws (86) are monitored by a circuit in series such that upon a partial disengagement of either thumb screw (86), a signal is sent to command the drive shaft motor (not shown) to start, thus driving the shuttle mechanisms (126) from position A to position B and adjusting the bridge balance to an appropriate position just prior to full removal of the first stage (75). Upon replacement of the first stage (75) the thumb screws (86) must be completely engaged in order to change the circuit state and signal the shuttle mechanism drive motor, insuring that the bridge condition is stable before effecting the counter balance change. The rotation of the drive shaft is then reversed and the lead screws of the two shuttle mechanisms are rotated, translating the shuttles and attached gas shocks from position B to position A, thereby balancing the bridge with the first stage fully attached. With the media (24) loaded into position, a first image is recorded onto the media (24) on the drum (22) of the image recorder (14), as illustrated in Fig. 1. The media (24) is stationary during image recording and a leading edge of the media (24) is held by the drum rollers. Referring to Figs. 1 and 8, after the completion of the image, an input sensor (136) is polled to see if the first stage of the bridge (10) is clear. When the input sensor (136) signals that no media is present in the first stage (75), the drum rollers, the first stage rollers (I) and the second stage rollers (II-V) are driven. Initially the first and second stage rollers (I-V) are synchronously driven to run at a speed slightly slower than the drum rollers advancing the media (24) from the drum (22). When the input sensor (136) detects the media (24) in the first stage (75) just beyond the first stage roller pair (I), a loop sensor (138) located between the media guide (90) and the roller pair (I) is polled. Because the bridge rollers are driven at a speed slower than the drum rollers, a loop (140) forms in the first stage (75) and the loop sensor (138) sends a signal to synchronize the speed of the first and second stagé rollers with the drum rollers. The loop sensor (138) is continuously polled so if the loop sensor signal is changed by the disappearance of the loop (140), then the bridge rollers (I-V) are slowed to allow the formation of the loop (140) again. The formation of the loop (140) isolates the portions of the web media (24) being handled by the independent transport systems of the drum and the bridge, thereby eliminating perturbations or disturbances in the motion along the media path. The media (24) is advanced until the second page is positioned in the drum (22), the motors are halted, and the media is held by the punch. The second page is then imaged, and the motors are subsequently restarted to advance the first image just past a media cutter. The motors are halted and the first image is cut from the second image. The external device to receive the media has an input sensor which is continuously polled to see if it is ready to accept the media. When ready, the first and second stage drives are started to flush the first image out of the bridge. When the leading edge of the first page passes the input sensor of the external device, the device's transport system starts. If the device operates at a speed faster than the second stage drive system (70), the over-running clutches (52) allow the media (24) to be pulled out from the second stage of the bridge (10). The input sensor (136) indicates when the first stage (75) of the bridge (10) is clear and the imagesetter (14) begins to load the next page into position while the second stage continues the transport of the first page to the external device. The sequence is repeated. During the sequence, a counter is running to monitor transport malfunctions. An error is indicated if the input sensors of either the first stage or of the external device do not indicate media present within a certain time frame. While this invention has been described in terms of a preferred. embodiment, those skilled in the art will appreciate that various modifications, substitutions, omissions and changes may be made. Accordingly, it is intended that the scope of the present invention be limited solely by the scope of the following claims.

Claims: A media handling system having a pivotally mounted transport bridge (10), comprising: a first stage transport means (75) in the bridge (10) for accepting media (24) at a first media handling station; and a second stage transport means (73) in the bridge (10) for delivering media (24) from said first stage transport means (75) to a second media handling station, characterised by said second stage transport means (73) being pivotally mounted about a pivot axis (110) and said first stage transport means (75) being removably attached to said second stage transport means (73), and further by: counterbalancing means (120) connected to the second stage transport means for counterbalancing the pivotally mounted transport bridge about the pivot axis, said counterbalancing means generating a counterbalancing force of a predetermined magnitude and direction; and adjustment means (126) responsive upon detachment of said first stage transport means (75) from said second stage transport means (73), for adjusting the magnitude and direction of said counterbalancing force to compensate for a change in balance of the pivotally mounted transport bridge about the pivot axis (110). The media handling system of claim 1, further characterised by : first and second engagement means (88) on said first stage transport means (75) and said first media handling station respectively, for engaging said transport bridge (10) with said first media handling station and defining an operational position enabling media transport from said first media handling station to the transport bridge (10); and alignment means (94) for aligning said first and second engagement means (88) upon pivoting the transport bridge (10) out of and into an operational position. The media handling system of claim 2, further characterised by a storage means (97) for accepting and storing media (24) at said first media handling station during the storage mode, wherein said first stage transport means (75) is detachable from said second stage transport means (73) and removable from said media handling system during said storage mode and said storage means (97) is mounted at the first media handling station instead of said first stage transport means (75) upon removal of said first stage transport means (75) from said media handling system. The media handling system of claim 3, further characterised by a remote drive means engaged with said first stage transport means (75) for driving said first stage transport means (75) when said media handling system is in said transport mode, said remote drive means being fixed within said dual-mode media handling system, such that upon removal of the first stage transport means, said first stage transport means (75) disengages from said remote drive means. The media handling system of claim 4, wherein said storage means is further characterised by a power assisted take-up cassette (97), and said remote drive means engages and drives said power assisted take-up cassette (97) when said handling system is in said storage mode. A method of counterbalancing a media transport bridge (10) of a media handling system, having a first stage transport (75) removably connected to a second stage transport (73), said method comprising the steps of accepting media in the first stage transport at a first media handling station and delivering media through the second stage transport from said first stage transport to a second media handling station, characterised by the steps of: pivotally mounting the second stage transport (73) about a pivot axis (110); counterbalancing the media transport bridge (10) about the pivot axis (110) with a counterbalancing force of a predetermined magnitude and direction; disengaging the first stage transport (75) from the second stage transport (73) thereby changing the balance of the media transport bridge about the pivot axis (110); and automatically adjusting the counterbalancing force to change the magnitude and direction of the counterbalancing force about the pivot axis (110) in response to removal of the first stage transport (75). The method of claim 6 further characterised by : first and second engagement means (88) on said first stage transport and said first media handling station respectively; and by the steps of transporting said media (24) through the second stage transport (73) from said first stage transport (75) to a second media handling station; and pivoting the transport bridge (10) out of and into the operational position, and aligning the first and second engagement means (88). The method of claim 7 further characterised by the steps of: mounting a storage container (97) at the first media handling station upon disengagement of the first stage transport and accepting and storing media (24) in the storage container (97) during a storage mode. The method according to claim 8, further characterised by the steps of: driving the first stage transport means by means of a remote drive motor when in the transport mode; and disengaging the first stage transport (75) from the remote drive upon removal of the first stage transport (75) from the media handling system.

Inventors: HERBERT THOMAS K, TELLAM MARK E, HERBERT, THOMAS K., TELLAM, MARK E.
Applicants: AGFA CORP, AGFA CORPORATION
Application year: 1995
Main classification: G03D13
IPC codes: H04N1, G03B27, G03D13, B41J15