Patent Application
20070063418
This disclosure relates generally to a sheet feeder for use in a printing machine, such as an electrophotographic reproduction machine. More particularly the disclosure concerns a vacuum corrugation feeder for removing sheets from a stack and transferring the sheets.
In one type of electrophotographic printing or reproduction machine, such as the machine M shown in
After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith at a series of developer stations C and D. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet. For a typical black and white electro-photographic printing machine, a single development station C may be provided. On the other hand, with the advent of multicolor electrophotography, multiple additional development stations D may be provided that fix color toner to the photoconductive member 10.
Subsequent to image development, a sheet S of support material is moved into contact with the toner images at a transfer station G. At this station, a transfer dicorotron 16 sprays positive ions onto the backside of the sheet S which attracts the negatively charged toner particle images from the photoreceptor 10 to the sheet S. A detack corotron 18 is provided for facilitating stripping of the sheet S from the surface of the photoreceptor. After transfer, the sheet S travels to a fusing station H where a heated fuser roller assembly 20 permanently affixes the toner powder to the sheet S.
It is desirable in high speed color printers such as those described above to be able to feed a wide variety of sheet types for various printing jobs. Customers demand multiple sized stock, a wide range of paper weights, paper appearance characteristics ranging from rough flat appearing sheets to very high gloss coated paper stock. Each of these sheet types and size has its own unique characteristics and in many instances very different problems associated therewith to accomplish high speed feeding.
There is shown in
The feedhead is a top vacuum corrugation feeder (VCF), so distance control of the top sheets in the stack T from the acquisition surface 302 and the fluffer jets 360 and 362 are very important. The acquisition surface 302 is the functional surface on the feed head 300 or vacuum plenum. The two sensors 340, 350 together enable the paper supply to position the stack T. The multi-position stack height sensor 350 contacts the sheet stack T to detect two or more specific stack heights. This sensor 350 works in conjunction with the second sensor 340 near the stack lead edge which also senses the distance to the top sheet, but without sheet contact. The two sensors together enable the paper supply to position the stack T with respect to an acquisition surface 302 of the feedhead 300, both vertically and angularly in the process direction. This height and attitude control greatly improves the capability of the feeder to cope with a wide range of paper basis weight, type, and curl.
The paper feeder 300 acquires individual sheets S of paper (using air pressure) from the top of a stack T and transports them forward to the TAR 400. Among the independent variables in the paper feeder design are three sets of air pressures, including air knife pressure and fluffer pressures that supply air for sheet separation and vacuum pressure which cause sheets to be acquired by the shuttle feed head assembly. Each set of pressures is supplied from one combination blower. As fluffer pressure increases the sheets on the top of the stack become more separated with the top most sheets being lifted closer to the vacuum feed head. As the fluffing pressure gets higher, the risk of more than one sheet being moved into the take-away nip, when the feed head moves increases also, (a.k.a. multifeed). As the fluffing pressure gets lower, the risk of the top sheet not getting close enough to the feed head (and thus not becoming acquired by the vacuum present on the bottom of the feed head) increases which can result in no sheet being fed when the feed head moves forward, (a.k.a., misfeed or late acquisition). The optimum amounts of fluffer and vacuum feed-head pressures are a function of the size and weight of the sheets (larger, heavier sheets requiring more fluffing and vacuum and visa-versa for smaller, lighter sheets).
During each sheet feed, when the trailing edge of the sheet passes the stack height arm 352 (
The feedhead 300 is a top vacuum corrugation feeder which incorporates an injection molded plenum/feed head 301 with a sheet acquisition and corrugation surface 302, as shown in
Thus, the prior sheet feed apparatus 300 includes a vacuum source, the vacuum source being selectively actuatable to acquire and release a top sheet from a stack; a feedhead, attached to the vacuum source to acquire the top sheet of the stack; and a unidirectional drive mechanism, the drive mechanism being driven in a single direction while causing the feedhead to reciprocate from a first position to a second position. Additionally, the sheet feed apparatus can include a stack height sensor actuator coupled to the unidirectional drive mechanism and a stack height sensor attached to the stack height sensor actuator so that the stack height sensor contacts and disengages the sheet stack at a preselected time coordinated with the reciprocating motion of the feedhead. Moreover, the stack height sensor actuator can comprise a cam member, attached to the unidirectional drive mechanism and rotating therewith; a biasing member; a cam follower, attached to the biasing member and biased into contact with said cam and attached to said stack height sensor to control the movement of said stack height sensor. Furthermore, the sheet feed apparatus can include a unidirectional drive mechanism which comprises a stepper motor operating in a unidirectional rotational mode.
In these prior feeder mechanisms, the entire sheet feed apparatus 300 is propelled by the motor 310. Thus, the motor must be powerful enough to accurately and precisely move the apparatus 10 in order to transport a single sheet to the TAR 400. The more powerful motor is more expensive, generates more heat and requires more energy to operate. Moreover, driving the entire sheet feeder mechanism imposes a limit on feed speed, due to the inertia of the mechanism 300, and increases the risk of skewing of the acquisition surface 302 and ultimately of the sheet S as it is received by the TAR. There is a need for a vacuum sheet feeder apparatus that eliminates these problems.
In order to address the needs, a sheet feeder assembly for acquiring and conveying a sheet is provided that comprises, in certain embodiments, a plenum connectable to a vacuum source and having an opening facing the sheet to be conveyed, and a slide plate covering the opening. The slide plate has an acquisition surface facing the sheet to be conveyed and defines a plurality of apertures in communication with the plenum through which vacuum is drawn to acquire the sheet. A drive mechanism is connected to the slide plate and supported within the plenum, and is operable to translate the slide plate relative to the plenum to convey the sheet acquired thereby.
In a further embodiment, a sheet feeder assembly for acquiring and conveying a sheet is disclosed that comprises a vacuum duct connectable to a vacuum source, and a plenum connected to the vacuum duct and having an opening facing the sheet to be conveyed. A motor is supported within the plenum. A plate movably covers the opening in the plenum and has an acquisition surface facing the sheet to be conveyed that defines a plurality of apertures in communication with the plenum through which vacuum is drawn to acquire the sheet. A valve is disposed between the duct and the plenum, and is movable between an open position in which the duct is open to the plenum, and a closed position in which the duct is closed to the plenum. The assembly further comprises a height sensing arm movably supported relative to the plenum, the height sensing arm having a sensing end arranged to contact the sheet in a contact position. In accordance with this embodiment, the plate, the valve and the height sensing arm are operably coupled to the motor within the plenum so that operation of the motor moves each of the plate, the valve and the height sensing arm.
In yet another embodiment, a printing machine comprises an imaging station for obtaining an image, a transfer station for transferring the image onto a sheet, a support tray for support a stack of sheets, and a transport system for transporting a sheet from the stack to the transfer station. The transport system comprises a top vacuum corrugation feeder assembly (TVCF) including a plenum connectable to a vacuum source and having an opening facing the stack on the support tray and a slide plate covering the opening. The slide plate has an acquisition surface facing the stack on the support tray and defining a plurality of apertures in communication with the plenum through which vacuum is drawn to acquire a sheet from the stack. The TVCF further includes a drive mechanism connected to the slide plate and supported within the plenum. The drive mechanism is operable to translate the slide plate relative to the plenum to convey the sheet acquired thereby.
The present disclosure contemplates a vacuum slide sheet feeder assembly 30, as shown in
The feeder assembly 30 includes a frame 32 that supports the components of the assembly within the particular machine. Preferably, the frame is constructed so that the entire assembly 30 forms a discrete removable component for servicing or replacement. A plenum 34 is supported on the underside of a top plate 33 of the frame 32 in communication with a vacuum duct 75, as shown in
In prior TVCF devices, the entire device is transported to carry a sheet captured on the acquisition surface of the device. In accordance with one feature of the illustrated embodiment, the assembly 30 includes a slide plate 36 that closes the lower opening 35 of the plenum 34, as shown in
In one feature of the assembly 30, the slide plate 36 is supported on the plenum 34 so that only the slide plate translates. This feature is in stark contrast to prior TVCF devices in which the entire device translates. The slide plate 36 alone translates once the sheet S has been vacuum acquired. Thus, only the drive mechanism for conveying the sheet need only be powerful enough to move the lightweight slide plate 36 and sheet S. In one specific embodiment, the slide plate 36 is formed from a thin plate of molded plastic so that the weight of the plate is minimal.
The plenum 34 includes a seal around its lower perimeter against which the slide plate 36 bears to maintain the proper vacuum within the plenum. Thus, in one embodiment, the plenum includes a front seal 50 and a rear seal 51, as shown in
In an alternative embodiment, the relative dimensions of the rear seal 51 and the rear sealing flange 54 may be arranged so that the vacuum pressure is vented near the end of the forward travel of the slide plate 36. This venting feature is calibrated so that when the sheet S is engaged by the TAR 40 the sheet is essentially released from the slide plate. Thus, in a specific embodiment, if the forward travel distance of the slide plate is 20 mm, the contact or overlap region of between the rear sealing flange 54 and the rear seal 51 may be about 17 mm so that the vacuum pressure is vented over the last 3 mm of travel of the slide plate.
In another feature of the disclosed embodiment, the drive mechanism for translating the slide plate 36 is situated within the vacuum plenum 34, as seen in
The slide plate 36 is reciprocated between its sheet acquisition position directly above the sheet stack T to its transfer position adjacent the TAR 40 by operation of the motor 70 and reciprocation of the drive link 65. The slide plate 36 is supported relative to the plenum 34 by the slide carriage 60. Contact between the slide plate 36 and the seals 50-52 help prevent rotation of the plate as it translates. In order to locate a “home”or start position for the slide plate 36, the slide plate may include a home flag 46 to actuate a home sensor 47 mounted in a molded tab 45 at one side of the plenum as shown in
It can be appreciated that mounting the slide plate drive mechanism within the plenum 34 reduces the overall envelope occupied by the sheet feeder assembly 30 within the machine M. In prior TVCF devices, the motor used to drive the device is positioned adjacent the vacuum duct, and in fact infringes on the duct area. With the present embodiment, placing the motor 70 within the plenum 70 means that the vacuum duct 75 is not compromised so that full vacuum flow may be drawn through the duct.
As is known in the art, the vacuum applied to the feeder assembly is controllable, at a minimum with respect to the amount of time that vacuum is drawn through the acquisition surface. Thus, the feeder assembly 30 provides means for controlling the vacuum drawn through the plenum 34 and slide plate 36. In particular, the assembly is provided with a flapper valve 76 that is disposed between the duct 75 and the plenum 34, as shown in
As is also known in the art, a motor driven cam may be used to move the flapper valve from its biased open position to a closed position. Thus, the feeder assembly 30 of the present disclosure also includes a cam element 80 that is mounted to a drive axle 72 of the motor 70. The cam element 80 includes a flapper cam portion 81 that is arranged to contact the flapper valve 76. In particular, the flapper cam portion 81 includes a lobe 81a (see
In one feature of this embodiment, the cam 80 and flapper cam portion 81 are driven by the same motor 70 that drives the slide plate 36. As explained above, since the motor is not required to drive the entire feeder assembly 30 (as in prior devices), the entire power output from the motor need not be dedicated solely to moving the acquisition surface. In other words, the same motor used to drive the prior art feeder assembly 300 (
In addition to controlling the flapper valve 76, the same motor 70 that drives the acquisition surface may also be used to control the operation of a height sensing arm 85. It is known in prior machines to provide a mechanical height sensing arm that is retracted when a sheet is being acquired and conveyed to the take-away rolls and that is dropped into contact with the stack T to determine the height of the stack. The present assembly 30 includes a height sensing arm 85 that extends below the plenum 34 and slide plate 36, as shown in
As with the flapper valve, the operation of the height sensing arm 85 is controlled by a cam. In particular, the cam element 80 includes a sensing cam portion 82 that is arranged to contact a cam follower 89 forming part of the height sensing arm 85. The sensing cam portion 82 includes a lobe 82a and a flat 82b that control the movement of the follower 89, and ultimately the contact end 88 of the sensing arm 85. In particular, when the lobe 82a is in contact with the follower 89, the contact end 88 is elevated from the stack T. When the cam portion 82 is rotated further, the bias spring 87 biases the follower 89 into contact with the flat 82b, which allows the contact end 88 to contact the stack T.
Again, like the flapper valve control, control of the height sensing arm 85 is based on the operation of a common motor. The motor 70 thus controls three functions of the feeder assembly 30—movement of the acquisition surface 37 and the sheet S, movement of the flapper valve 76 and movement of the height sensing arm 85. Also, as with the flapper valve control, the movement of the height sensing arm is automatically and mechanically linked to the movement of the acquisition surface and slide plate because the same motor 70 is used. The configuration of the cam portion 82 fixes the timing of the lifting of the sensing arm 85 as the slide plate 36 acquires the sheet S and propels it toward the TAR 40, as well as the timing of the release of the sensing arm 85 to compress the stack and measure the stack height after the sheet has been released and the slide plate 36 is being withdrawn to its neutral position.
The feeder assembly 30 may include an arrangement of fluffer jets that are arranged to fluff the top sheet of a stack to facilitate acquisition by the slide plate. Thus, the frame 32 may support a fluffer plenum 90 that is connectable to an air supply, as shown in
The feeder assembly 30 disclosed herein provides significant advantages over prior sheet feeder systems. As explained above, rather than translating the entire feeder assembly as in prior systems, the assembly 30 provides for translation of only the acquisition surface and the sheet carried by the surface. Thus, only the slide plate 36 and the carried sheet S is driven by the motor 70. In a specific embodiment, the slide plate has a transported mass of only about 100 gm, or about ⅕th the transported mass of some prior feeder systems. This lower transport mass not only reduces the power requirements for the drive motor 70, it also translates into lower inertia and ultimately to quicker/faster transport of the acquisition surface and sheet S carried thereby. In the specific embodiment, the assembly 30 may be capable of sheet feed rates of up to 200 pages per minute, or even greater.
The reduced power requirements for transporting the acquisition surface and sheet may be manifested in a smaller motor, or more preferably in the integration of multiple functions from a common motor. Thus, as disclosed above, the motor 70 drives the slide plate 70 and rotates the cam element 80 that controls the movement of the flapper valve 76 and the height sensing arm 85. The motor power must be sufficient to overcome the biasing force generated by the torsion spring 78 restraining the flapper valve and the spring 87 biasing the height sensing arm. Combining several functions into the common package of the feeder assembly 30 can allow usage of the motor that had been used to drive prior vacuum valves to instead drive the take-away roll, especially in high speed applications.
The feeder assembly 30 provides a very compact and modular package for placement within the printing machine M. Since multiple functions are combined into a single package, the individual motors associated with prior feeder systems are eliminated. Moreover, the common drive motor allows repositioning of certain functional components within the plenum region that could not be achieved with prior systems. For instance, the height sensing arm 85 may be located closer to the feed head or acquisition surface, rather than near the trailing edge as in prior systems. This location for the height sensing arm improves the accuracy of location of the top of the fluffed stack relative to the acquisition surface, especially for long sheet length or for curled sheets.
Another benefit is that the working parts are wholly contained within the envelope of the vacuum plenum 34. Mounting the motor 70 within the plenum reduces the overall outer dimension of the entire assembly 30 and, as indicated above, frees up space of the vacuum duct 75. The larger available vacuum duct eliminates the feed head skirts in prior sheet acquisition systems that were necessary to overcome high vacuum system impedance. Since the slide plate 36 and cam element 80 are driven from a common motor, additional drive components are eliminated, such as cable drives and pulleys associated with prior feeder systems. The substantially direct drive between the motor 70 and the carriage 60 supporting the slide plate also eliminates the additional drive components of prior systems and reduces the mechanical losses associated therewith.
The motor 70 is preferably an electric motor, and may be a stepper motor capable of stepwise movement or rotation. Thus, the motor is capable of controlled rotation to coordinate the several functions of the feeder assembly 30. It is contemplated that the motor may be operated for continuous high-speed rotation without compromising the function of the drive link 65 and cam element 80.
While this invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.
