Positioning of service station and paper pick pressure plate using single motor

Abstract: Structure according to the invention simultaneously controls operation of a sled assembly (210) for servicing of an inkjet print cartridge (325) and a mechanism (1110) for controlling advancement of a print medium (1130) into a printing path. The structure according to the invention can be used with either a facsimile machine (100) that uses thermal inkjet printing, or with a thermal inkjet printer. In one embodiment, the structure includes a sled assembly which further includes at least one wiper (502) and at least one cap (501), a paper pick pressure plate (1110), and a mechanism (202, 702, 703, 704, 705, 706, 204, 314) for simultaneously controlling movement of the sled assembly and the pressure plate. The paper pick pressure plate is controlled to selectively contact a paper pick roller (1120) such that the print medium is advanced through the printing path when the pressure plate contacts the pick roller and the print medium is not advanced through the printing path when the pressure plate does not contact the pick roller. In a further embodiment, the mechanism for simultaneously controlling further comprises a dual cam mechanism (204). A cam ring (701) of the dual cam mechanism interacts with a cam follower (314) to move the sled assembly and a cam (712) of the dual cam mechanism contacts the pressure plate to move the pressure plate directly.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to inkjet printing and, in particular, to a method and structure for wiping and capping the printhead of an inkjet print cartridge. 2. Related Art In inkjet printing, one or more print cartridges (pens) are inserted in a movable print carriage. Each print cartridge includes a reservoir that holds ink. The ink passes from the reservoir through a multiplicity of nozzles to be ejected from a print cartridge printhead onto a print medium. The print carriage is moved laterally back and forth, and the print medium is advanced past the print carriage to enable printing of a desired image or images on the print medium. Inkjet print cartridge nozzles commonly become plugged with ink blobs or particulate, or otherwise contaminated with internal bubbles that prevent the nozzles from operating properly, resulting in lower print quality. Consequently, printers and facsimile machines that use inkjet printing typically include a service station that provides for spitting, wiping, capping and priming of each printhead in order to keep the nozzles clean and functioning. During capping, a cap must be properly aligned with the corresponding printhead. Typically, for inkjet print cartridges, cap alignment must be maintained within a fraction of a millimeter of a nominal value. However, tolerances associated with the assembly and operation of an inkjet printing assembly can combine to result in a variation of cap alignment that is too large. Such tolerances may result from, for instance, positioning of the print cartridge in the corresponding stall of the print carriage, attachment of the print carriage to a print carriage movement mechanism (such as a rod) attached to a printer chassis, assembly of the various components of the service station, and attachment of the service station to the printer chassis. If the cap is misaligned, the cap can contact one or more of the nozzles and absorb ink from the nozzles through capillary action, dirtying the service station with ink and necessitating priming of the nozzles before printing again. Additionally, improper alignment can cause the cap to inadequately seal the area around the nozzles. As a result, air can enter the area around the printhead, causing the ink to dry out and clog the nozzles. Contaminants may also enter the area around the printhead, eventually causing the nozzles to become clogged. During wiping, interference between the wiper and the print cartridge must be controlled within a specified dimensional tolerance to achieve the proper wiping force. Typically, for inkjet print cartridges, wiper interference must be maintained within a fraction of a millimeter of a nominal value. If the wiper interference is too small, then the wiping force will be too small and the printhead won't be adequately wiped, resulting in poor print quality and shortened print cartridge life. If the wiper interference is too large, debris will be pushed in to the nozzles, clogging one or more nozzles so that ink cannot be ejected from the nozzle or nozzles ("missing dots"), and/or degrading the print quality by partially clogging nozzles or becoming embedded in the ink. Frequently, the cap and the wiper are mounted on a movable service station sled. For a variety of reasons, there may be a problem with the functionality of the cap, wiper or some other part of the service station sled. For example, because of the frequent contact between the wiper and the print cartridge, the wiper may wear out. Therefore, it is desirable that the service station sled can be replaced without the necessity of replacing the remainder of the service station. An inkjet printhead capping and wiping mechanism of this type is disclosed in DE-A-0 589 582. Additionally, printers must include structure for performing various functions, e.g., moving the print carriage, advancing the print medium through a printing path. It is obviously desirable to make the structure for performing these functions as simple, efficient and inexpensive as possible. In particular, it is desirable to use particular components of the printer to perform more than one function, thereby enabling the printer to be made smaller (or, equivalently, perform more functions for the same size), simpler to manufacture and less expensive to manufacture. EP-A-0 495 669 discloses an inkjet recording apparatus having a sheet feeding means which can be operated using the same driving means, i.e. motor, that is used to control the operation of a priming apparatus, i.e. a suction pump. Further, according to this reference it is possible to effect the initial operation of the pump and of a cleaning mechanism with a single sensor at the start of power supply. The present invention provides a structure for use with an inkjet printing apparatus comprising the features of claim 1 and a method for servicing an inkjet print cartridge comprising the steps of claim 6. SUMMARY OF THE INVENTION According to the invention, a service station for use in servicing one or more inkjet print cartridges (pens) includes a service station sled assembly movably attached to a service station chassis. The service station chassis is attached to a printer chassis. The one or more inkjet print cartridges are mounted in a print carriage which is, in turn, movably attached to the printer chassis. During printing, ink is ejected through nozzles formed in each print cartridge. At least one wiper and at least one cap are mounted on a sled base of the sled assembly. Lateral movement of the print carriage with respect to the service station causes each wiper to wipe across the corresponding print cartridge printhead to remove ink from the printhead. Vertical movement of the sled assembly with respect to the print carriage causes each cap to enclose the corresponding print cartridge printhead after printing is completed and the print carriage is moved laterally into a capping position. The service station according to the invention can be used with either a facsimile machine that uses thermal inkjet printing, or with a thermal inkjet printer. One embodiment of structure according to the invention for use with an inkjet printing apparatus includes a sled assembly, a paper pick pressure plate, and a mechanism for simultaneously controlling movement of the sled assembly and the pressure plate. The sled assembly includes at least one wiper for periodically wiping a printhead of a corresponding print cartridge and at least one cap for enclosing the corresponding printhead when the corresponding print cartridge is not in use. The paper pick pressure plate is controlled to selectively contact a paper pick roller such that a print medium is advanced through a printing path when the pressure plate contacts the pick roller and the print medium is not advanced through the printing path when the pressure plate does not contact the pick roller. In a further embodiment, the mechanism for simultaneously controlling further comprises a dual cam mechanism. In yet a further embodiment, the mechanism for simultaneously controlling further comprises a cam follower, and the dual cam mechanism further comprises a cam ring for contacting the cam follower to move the sled assembly in response to rotation of the dual cam mechanism and a cam for contacting the pressure plate to move the pressure plate in response to rotation of the dual cam mechanism. The dual cam mechanism is driven by a motor. The sled assembly and paper pick pressure plate are controlled so that, in a first position of the dual cam mechanism, the sled assembly is positioned in a capping position and the paper pick pressure plate is positioned in a paper release position and, in a second position of the dual cam mechanism, the sled assembly is positioned in a wiping position and the paper pick pressure plate is positioned in a paper pick position. Another embodiment of structure according to the invention includes a mechanism for periodically wiping a printhead of at least one print cartridge and capping the printhead when the print cartridge is not in use, a mechanism for advancing a print medium into a printing path, and a mechanism for simultaneously controlling movement of the mechanism for wiping and capping, and movement of the mechanism for advancing a print medium. In a further embodiment, the mechanism for simultaneously controlling further includes: i) a mechanism for moving the mechanism for wiping and capping, and the mechanism for advancing a print medium; and ii) a motor for driving the mechanism for moving. According to the invention, in an inkjet printing apparatus, a method for servicing an inkjet print cartridge and advancing a print medium into a printing path, includes the steps of: i) moving a sled assembly, the sled assembly including a cap and a wiper, between a capping position and a wiping position; and ii) simultaneously controlling the advancement of the print medium into the printing path. In a further embodiment, each of the above two steps can be implemented by a step of rotating a dual cam mechanism to effect movement of the sled assembly and a mechanism for advancing the print medium into the printing path. In another further embodiment, the step of moving is implemented by rotating a cam ring, the cam ring contacting a cam follower of the sled assembly to effect movement of the sled assembly, and the step of simultaneously controlling is implemented by rotating a cam, the cam contacting a means for advancing the print medium into the printing path to effect movement of the mechanism for advancing. In still another further embodiment, the step of moving includes the steps of positioning the sled assembly in a capping position and positioning the sled assembly in a wiping position, while the step of simultaneously controlling includes the steps of positioning the pressure plate in a paper release position when the sled assembly is in the capping position and positioning the pressure plate in a paper pick position when the sled assembly is in the wiping position. The apparatus and method according to the invention enable use of a single motor to drive a single mechanism to move both a sled assembly and a paper pick pressure plate. In contrast, previous service stations required two motors, each motor driving a separate positioning mechanism: one for moving the sled assembly and one for moving the paper pick pressure plate. Thus, the service station according to the invention achieves functionality equivalent to that of previous service stations with a simpler structure that is both easier to manufacture and less likely to break down. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cutaway perspective view of a facsimile machine including a service station according to the invention. FIG. 2 is a top perspective view of a service station according to the invention. FIG. 3 is an exploded top perspective view of the service station of FIG. 2 and a print carriage positioned over the service station. FIGS. 4A and 4B are exploded top and bottom perspective views, respectively, of the sled assembly of FIG. 3. FIG. 5 is a top perspective view of the sled base of FIGS. 4A and 4B. FIG. 6 is a bottom perspective view of the print carriage and print cartridge of FIG. 3. FIG. 7A is a side view of the service station chassis of the service station of FIG. 2, a side wall of the service station chassis being removed to show the interior of the service station chassis, with the sled assembly in a lowered position. FIG. 7B is a side view of the service station chassis of the service station of FIG. 2, a side wall of the service station chassis being removed to show the interior of the service station chassis, with the sled assembly in a raised position. FIG. 8A is a side perspective view of the side wall of the service station chassis that is removed in FIGS. 7A and 7B, illustrating the interior of the service station chassis as viewed in a direction opposite that of FIGS. 7A and 7B. FIG. 8B is a perspective view of the release lever shown in FIG. 8A. FIGS. 9A, 9B and 9C are a front view, a back view and an exploded perspective view, respectively, of the dual cam mechanism shown in FIGS. 7A and 7B. FIG. 10A is a simplified top perspective view of a portion of the service station chassis, sled assembly, and print carriage of FIG. 3, illustrating the print carriage in the capping position. FIG. 10B is a top perspective view of the simplified service station chassis, sled assembly, and print carriage of FIG. 10A, illustrating the print carriage in a position intermediate between the capping position and the wiping position. FIG. 10C is a top perspective view of the simplified service station chassis, sled assembly, and print carriage of FIG. 10A, illustrating the print carriage in the wiping position. FIG. 10D is a side view of the simplified service station chassis, sled assembly and print carriage of FIG. 10A, illustrating the wiping position. FIG. 11A is a simplified cutaway perspective view of the facsimile machine of FIG. 1 illustrating a paper pick pressure plate positioned in a paper release position. FIG. 11B is a simplified side view, similar to that of FIG. 7B, of the service station and paper pick pressure plate of FIG. 11A when the sled assembly is in a capping position and the paper pick pressure plate is in a paper release position. FIG. 11C is a simplified side view, similar to that of FIG. 7A, of the service station and paper pick pressure plate of FIG. 11A when the sled assembly is in a wiping position and the paper pick pressure plate is in a paper pick position. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION A service station according to the invention provides improved wiping and capping of thermal inkjet print cartridge printheads, as compared to previous service stations. The service station according to the invention can be used with either a facsimile machine that uses thermal inkjet printing, or with a thermal inkjet printer. Hereinafter, the term "printing assembly" is used to refer generically to facsimile machines or printers. Additionally, use of the term "inkjet" will be understood to include printing structures and methods referred to as "bubblejet." The service station according to the invention includes a service station sled assembly removably attached to a service station chassis. The service station chassis is attached to a printer chassis. One or more inkjet print cartridges are mounted in a print carriage which is, in turn, mounted on a print carriage movement mechanism (e.g., rod) that is attached to the printer chassis. At least one wiper and at least one cap are mounted on a sled base of the service station sled assembly for effecting wiping and capping of a printhead of corresponding inkjet print cartridge(s). Lateral movement of the print carriage with respect to the service station causes each wiper to wipe across the corresponding printhead. Vertical movement of the sled assembly with respect to the print carriage causes each cap to enclose the nozzles of the corresponding printhead after the print carriage is moved laterally into a capping position. The service station according to the invention includes an alignment mechanism that provides improved alignment, relative to previous service stations, of each cap with respect to the corresponding printhead. The alignment mechanism includes alignment posts formed on one of the sled assembly or print carriage, and corresponding alignment cavities or holes formed in the other of the sled assembly or print carriage. When the print carriage is moved into a capping position, the sled assembly is moved relative to the print carriage so that the alignment posts are inserted into the alignment cavities or holes, aligning each print cartridge with the corresponding cap such that the cap fully encloses the nozzles of the print cartridge. The alignment mechanism of the service station minimizes the importance of closely controlling the tolerances associated with the positioning of the print cartridge in the corresponding stall of the print carriage, attachment of the print carriage to the print carriage movement mechanism, assembly of the various components of the service station (including the mounting of the cap on the sled assembly), and attachment of the service station to the printer chassis. Thus, the cost of manufacturing a printing structure including the service station according to the invention is reduced, since it is not necessary to use expensive and/or unreliable methods for ensuring a good seal of the cap over the nozzles, such as on-line adjustment during manufacturing or tight tolerance control design. The sled assembly is also made compliant so that when the cap contacts the printhead to enclose the nozzles, the sled assembly can gimbal to allow the entire circumference of the cap to adequately contact the printhead so that a good seal is formed around the nozzles. Since the cap forms a better seal over the nozzles than has been the case with previous service stations, ingress of contaminants or air to the nozzles is minimized, thereby reducing clogging of the nozzles so that print quality and reliability are improved. The service station according to the invention also includes a positioning mechanism that provides good control of the amount of interference between each wiper of the service station and the corresponding print cartridge to be wiped by the wiper. One or more guide rails are formed on one of the sled assembly or print carriage that contact corresponding guide surfaces of the other of the sled assembly or print carriage. The height of the guide rails is established, relative to the position of the corresponding guide surfaces when the print carriage is positioned over the sled assembly during wiping, such that contact between the guide rail or rails and the corresponding guide surface or surfaces maintains a desired amount of interference between each wiper and the corresponding print cartridge. Consequently, the wiping force is maintained at a desired magnitude so that adequate wiping is achieved, and excessive wiper interference, that would otherwise cause debris to be pushed into the nozzles, is avoided. The sled assembly of the service station can be easily detached from or attached to the print chassis. Consequently, the cap, wiper or entire sled can be easily replaced by removing and replacing only the sled assembly rather than the entire service station. The removability of the sled assembly also allows the sled assembly to be more easily cleaned as desired or necessary. Additionally, the sled assembly can be removed and replaced with a different or upgraded sled assembly, without necessity to replace the entire service station or buy a new printing assembly. The service station according to the invention includes a motor that drives a cam mechanism to move the sled assembly vertically between the capping and wiping positions. The same motor also drives another cam mechanism to position a paper pick pressure plate in either of a paper pick position, i.e., pressed against a paper pick roller, or a paper release position, i.e., positioned away from a pick roller. The rotation of the cams of the two cam mechanisms is synchronized such that when the sled assembly is in the wiping position, the pressure plate is in the paper pick position, and when the sled assembly is in the capping position, the pressure plate is in the paper release position. Thus, a single motor drives structure to perform two functions within the printing assembly that, in previous printing assemblies, required two motors. Additionally, the cam mechanisms according to the invention are integrated into a structure that is simpler and cheaper than the corresponding structures in previous printing assemblies. Further, the motor is positioned so that the motor axis is perpendicular to the longest dimension of the service station (viewed in a direction perpendicular to the surface of the sled base on which the wiper and cap are mounted), thereby reducing the footprint of the service station. FIG. 1 is a cutaway perspective view of a facsimile machine 100 including a service station 110 (shown in simplified form in FIG. 1 for clarity) according to the invention. The construction and operation of the service station 110 are described in greater detail below. The facsimile machine 100 is used to send facsimile transmissions. A document to be transmitted is fed into the document guide 101, drawn into the facsimile machine 100, scanned, and then discharged out onto a retractable shelf (not shown) that can be pulled out to extend from the upper portion of the opening 102. The data obtained from scanning the document is transmitted over communication lines, as is well known, to a remote facsimile machine, where the data is reconstructed into a reproduction of the original document. The facsimile machine 100 is also used to receive facsimile transmissions. Print media, e.g., sheets of paper, are stacked in the input print media tray 103. When a facsimile transmission is received from a remote facsimile machine, a sheet of the print media is drawn from the input print media tray 103 into the facsimile machine 100, the facsimile transmission is reproduced onto the print medium, and the print medium is discharged into an output print media tray (not shown) that is located in the opening 102 above the input print media tray 103 and below the retractable shelf. An operation panel 104 includes a keyboard (not shown) for inputting commands to control the operation of the facsimile machine 100. The operation panel 104 also includes a display, e.g., an LED display, for displaying various information to a user such as input commands or status information. According to the invention, reproduction of the facsimile transmission onto a print medium is done by inkjet printing. A print carriage (not shown), described in more detail below with respect to FIG. 6, is slidably mounted on a rod (not shown) within the facsimile machine 100. One or more print cartridges (see FIGS. 3 and 6), each print cartridge having a reservoir for holding ink, are mounted in the print carriage. Each print cartridge includes a plurality of nozzles through which the ink is ejected from a print cartridge printhead onto the print medium. While the print medium is advanced past the print cartridge printhead, the print carriage is driven by a motor to move laterally back and forth along the rod, thereby enabling printing of a desired image or images on the print medium. Typically, each print cartridge holds a different color ink. Generally, the inks can be of any color and, if more than one print cartridge is present, any combination of colors can be used. For example, a single print cartridge holding black ink can be mounted in the print carriage. Alternatively, three print cartridges can be mounted in the print carriage, one cartridge holding blue ink, a second cartridge holding yellow ink and a third cartridge holding magenta ink. FIG. 2 is a top perspective view of the service station 110. A sled assembly 210 (described in more detail below with respect to FIGS. 4A and 4B) is movably attached to a service station chassis 201, as described in more detail below with respect to FIGS. 7A and 7B so that the sled assembly 210 can be moved between the wiping and the capping positions. A release lever 203 is pivotably mounted within the service station chassis 201 so that the exposed portion of the release lever 203 can be moved along the bi-directional arrow 206 between a first position and a second position, the second position effecting release of the sled assembly 210 from the service station chassis 201, as described in more detail below with respect to FIG. 8, so that the sled assembly 210 can easily be disengaged from the service station chassis 201. A conventional stepper motor 202 is mounted on the service station chassis 201. The motor 202 drives a gear train (not shown), described in more detail below with respect to FIGS. 7A and 7B, within the service station chassis 201 to effect rotation of a dual cam mechanism 204. As also described in more detail below with respect to FIGS. 7A and 7B, one cam of the dual cam mechanism 204 interacts with a corresponding cam follower to cause the sled assembly 210 to be moved vertically (i.e., along direction arrow 205) between the capping and wiping positions. As described in more detail below with respect to FIGS. 11A and 11B, the other cam of the dual cam mechanism 204 interacts with a paper pick pressure plate (not shown) to move the paper pick pressure plate between a paper pick position and a paper release position. Thus, the dual cam mechanism 204 enables a single motor to be used to move both the sled assembly 210 and the paper pick pressure plate. A spittoon holding post 207 extends from a surface of the service station chassis 201 near the sled assembly 210. A spittoon (not shown) is positioned adjacent a wall 201a of the service station chassis 201 and held in place, in part, by fitting a hole formed in a flange of the spittoon over the spittoon holding post 207. The spittoon is a reservoir that holds ink ejected from the print cartridge(s) to clear the nozzles before printing ("spitting"). A spittoon and associated structure that can be used with the invention are described in more detail in the commonly owned, co-pending U.S. Patent Application Serial No. 08/241,813, entitled "Spittoon Absorber Wetting Agent," by Chan Nguyen, filed on May 12, 1994, attorney docket no. 1093635-1, the disclosure of which is incorporated by reference herein. FIG. 3 is an exploded top perspective view of the service station 110 and a print carriage 320 positioned over the service station 110. A print cartridge 325 is inserted in the print carriage 320 so that a printhead of the print cartridge 325 is exposed through a hole in the print carriage 320, as shown more clearly in FIG. 6, adjacent the sled assembly 210. For clarity, some parts of the print carriage 320 are simplified in FIG. 3. A coil spring 301 is positioned on a floor 313 of a cavity formed in the service station chassis 201. The coil of the coil spring 301 adjacent the cavity floor 313 is made larger than the rest of the coils and is fitted underneath each of two hooked retainers 311 (only one is visible in FIG. 3) formed integrally with the cavity floor 313 on opposite sides of a hole 312 formed through the cavity floor 313. A sled assembly mount 302 is positioned over the coil spring 301 so that the coil spring 301 fits within a recess in the sled assembly mount 302 formed by outer ring section 302c, connecting sections 302b (for clarity, only one connecting section 302b is labelled in FIG. 3) and inner ring section 302d. The sled assembly mount 302 includes four legs 302a (for clarity, only one leg 302a is labelled in FIG. 3) extending from outer ring section 302c in a direction opposite that in which connecting sections 302b extend. Each leg 302a has a foot 302e (for clarity, only one foot 302e is labelled in FIG. 3) formed at an end of leg 302a distal from outer ring section 302c. The foot 302e of each leg 302a is fit through a corresponding one of a multiplicity of holes 315 (in FIG. 3, only three holes 315 are visible and, for clarity, only one hole 315 is labelled) formed through the cavity floor 313. The legs 302a are positioned with respect to each other, relative to the positioning of the holes 315 with respect to each other, so that the legs 302a must be slightly compressed toward one another, in a direction opposite that in which the feet 302e extend, to fit the feet 302e through the corresponding holes 315. After the feet 302e are fit through the holes 315, the legs 302a are released so that the feet 302e extend beyond the holes 315. The unstretched length of the coil spring 301 and the dimensions of the sled assembly mount 302 are chosen such that the coil spring 301 is slightly compressed when the feet 302e of the legs 302a are fit through the holes 315. The compression of the coil spring 301 causes the feet 302e to be biased against a side of the cavity floor 313 opposite that shown in FIG. 3, thereby attaching the sled assembly mount 302 to the service station chassis 201. The sled assembly 210 is mounted over the sled assembly mount 302. A retention leg (cam follower) 314 extends from the sled assembly 210 and fits through the hole 312 in the cavity floor 313. A foot 314a of the cam follower 314 contacts a cam surface formed on the dual cam mechanism 204, as explained in more detail below with respect to FIGS. 7A and 7B, to attach the sled assembly 210 to the service station chassis 201. Guide pins, described below with respect to FIGS. 4A and 4B, formed on the sled assembly 210 fit into a corresponding slot 316 formed on the service station chassis 201 within the cavity. FIGS. 4A and 4B are exploded top and bottom perspective views, respectively, of the sled assembly 210. The sled assembly 210 includes a sled engagement mechanism 410, a coil spring 420, and a sled base 430. The sled engagement mechanism 410 includes a rectangular frame 410d within which a circular raised section 410a is formed substantially concentrically with the frame 410d such that a recess is defined between the frame 410d and the raised section 410a. A floor 410e (FIG. 4B) and four connecting sections 410g (only three are visible in FIG. 4B) connect the frame 410d to the raised section 410a. A looped section 410b is formed approximately midway along each of two opposing walls of the frame 410d. An extending section 410c extends from each of the other two opposing walls of the frame 410d approximately midway along the wall. Cylindrical guide pins 410f extend from an exterior surface of a wall of the frame 410d. The sled engagement mechanism 410 is made of, for example, polycarbonate. As seen in FIG. 4B, sled base 430, described in greater detail below with respect to FIG. 5, includes two walls 430a extending from a surface of a floor 430c. A protrusion 430b (only one is visible in FIG. 4B) extends from each of the walls 430a in a direction that is substantially parallel to the floor 430c. As best seen in FIG. 4A, the coil spring 420 fits into the recess formed in the sled engagement mechanism 410 around the circular raised section 410a. As best seen in FIG. 4B, each of the two opposing looped sections 410b (which are somewhat flexible) of the sled engagement mechanism 410 are bent slightly and fitted over a corresponding one of the protrusions 430b of the sled base 430 so that the coil spring 420 is positioned between the sled engagement mechanism 410 and the sled base 430. The coil spring 420 is held laterally in place with respect to the sled base 430 by the walls 430a. The unstretched length of the coil spring 420 and the length of the looped sections 410b are chosen so that, when the sled base 430 is attached to the sled engagement mechanism 410, the coil spring 420 is compressed. The compression of the coil spring 420 exerts a force pushing the sled engagement mechanism 410 away from the sled base 430 so that the looped sections 410b are held in contact against the protrusions 430b, thereby holding the sled base 430 in position with respect to the sled engagement mechanism 410 in a direction perpendicular to the floor 430c. Each of the looped sections 410b contacts the respective wall 430a to hold the sled base 430 laterally in place in a direction perpendicular to the walls 430a. The sled base 430 is prevented from pivoting to an unacceptable degree about the point of contact between the looped sections 410b and the protrusions 430b by contact between one or the other of the extending sections 410c of the sled engagement mechanism 410 with the floor 430c of the sled base 430. As further seen in FIG. 4B, a retainer 430e is formed on the floor 430c of the sled base 430. (The walls 430a are formed adjacent opposing walls of the retainer 430e.) A basin 430d, discussed in more detail below, is friction fitted into the retainer 430e. The basin 430d is made of any material that does not react with the printing ink. In one embodiment, the basin 430d is made of EPDM rubber. As noted above, the guide pins 410f on the sled engagement mechanism 410 fit into a corresponding slot 316 formed on the service station chassis 201. Contact between the guide pins 410f and the slot 316 keeps the sled assembly 210 from rocking too much as the sled assembly 210 is moved between the wiping and capping positions. Further, since discrete guide pins 410f, rather than a continuous guide rail, are formed, friction between the sled assembly 210 and the service station chassis 201 is minimized. FIG. 5 is a top perspective view of the sled base 430. The sled base 430 is made of any material that does not react with the printing ink. In one embodiment, the sled base 430 is made of PBT which is available from GE Plastics as Valox™. A hollow cap 501 is friction fitted on to a cap mount 534 formed on a surface of the floor 430c of the sled base 430 that faces toward the printhead of the print cartridge 325 (FIG. 3) when the service station 110 is assembled into the facsimile machine 100. A hole 534a is centrally formed in the cap mount 534. The cap 501 includes a corresponding centrally formed hole 501b. The holes 501b and 534a are located above the basin 430d (FIG. 4B) approximately centrally with respect to the outline of the basin 430d. A groove (not visible in FIG. 4B) is formed in the basin 430d adjacent the floor 430c. The groove extends from a location underneath the holes 501b and 534a to a wall of the retainer 430e. The groove provides a path for air to escape when the printhead contacts the cap 501 to form a sealed enclosure, thereby relieving pressure that would otherwise build up against the printhead and possibly force ink from the nozzles back into the reservoir, thus necessitating priming of the print cartridge before printing can begin again. The groove is sized so that air entering the sealed enclosure through the groove does not dry out the ink at an unacceptably high rate. The cap 501 is made of a material that does not appreciably change dimension over the expected operating life of the cap and that does not react with the printing ink. In one embodiment, the cap 501 is made of EPDM rubber. The cap 501 has a raised lip 501a formed around the circumference of the hole 501b. During capping, the lip 501a fits against the printhead of the print cartridge 325 to enclose the nozzles. A wiper mount 535 is formed on a surface of the floor 430c that faces toward the printhead of the print cartridge 325 (FIG. 3). The wiper mount 535 includes a knobbed section 535a such that when a hole 502a formed in the wiper 502 is fitted over the knobbed section 535a, the wiper 502 deforms around and grips the knobbed section 535a so that the wiper 502 is held in place on the sled base 430. A top section 502b of the wiper 502 is shaped so as to make the molding of wiper 502 easier. The height of the wiper 502 above the floor 430c of the sled base 430 is specified so that, viewed in a direction parallel to the direction of wiping, the wiper 502 overlaps the print cartridge 325 by a desired amount ("nominal wiper interference"). The nominal wiper interference is specified so that, within the range of expected manufacturing tolerances, the wiper 502 is certain to contact the printhead during wiping. The wiper 502 is made of a deformable material so that the wiper 502 bends during wiping. In one embodiment, the wiper 502 is made of EPDM rubber. Alignment posts 531a and 531b extend from a surface of the floor 430c that faces toward the print carriage 320. The alignment posts 531a and 531b are positioned to mate with corresponding ones of alignment cavities (see FIG. 6) formed in the print carriage 320, as explained in more detail below with respect to FIGS. 10A and 10B, so that the cap 501 is properly aligned with the print cartridge printhead during capping. The alignment posts 531a and 531b preferably taper from an end distal from the floor 430c to an end adjacent to the floor 430c, for reasons explained more fully below with respect to FIG. 10A. Though two alignment posts 531a and 531b are shown in FIG. 5, according to the invention, one, three or more alignment posts could be formed on the sled base 430. However, two or more alignment posts are preferred so that alignment of the cap 501 can be controlled along both axes defining the plane of the print cartridge printhead. Additionally, though the alignment posts 531a and 531b are shown near corners of the sled base 430, this need not be the case. Generally, an alignment post or posts according to the invention can be located anywhere on the sled base 430 so long as the alignment post or posts are properly aligned with respect to the alignment cavities formed in the print carriage 320. Further, the alignment posts need not extend from the sled base 430 in a direction perpendicular to the print cartridge printhead. The alignment posts can extend in any direction so long as the alignment posts mate with corresponding alignment cavities formed in the print carriage 320. Guide rails 532 and 533 extend from a surface of the floor 430c that faces toward the print carriage 320. The guide rails 532 and 533 are positioned so that, during wiping of the print cartridge printhead, each of the guide rails 532 and 533 contacts a corresponding guide surface (see FIG. 6) of the print carriage 320, as explained in more detail below with respect to FIG. 10C. The guide rails 532 and 533 ensure that the proper amount of wiper interference is maintained during wiping. Each of the guide rails 532 and 533 is formed with chamfered corners 532a, 532b and 533a, 533b, respectively, adjacent to the edge of the guide rail 532 or 533, respectively, that contacts the print carriage 320 during wiping. When the print carriage 320 begins to pass over the sled base 430, the print carriage 320 contacts the chamfered corners 532a and 533a, or the chamfered corners 532b and 533b, rather than the sides of the guide rails 532 and 533, so that the print carriage 320 rides smoothly onto the guide rails 532 and 533. Though two guide rails 532 and 533 are shown in FIG. 5, according to the invention, one, three or more guide rails could be formed on the sled base 430. However, two or more guide rails are preferred, since one guide rail will not precisely ensure the proper wiper interference and more than two guide rails are not necessary to ensure proper wiper interference. Additionally, though the guide rails 532 and 533 are shown near edges of the sled base 430, this need not be the case. Generally, a guide rail or rails according to the invention can be located anywhere on the sled base 430 so long as the guide rail or rails contact the print carriage 320 to produce the desired wiper interference. FIG. 6 is a bottom perspective view of the print carriage 320 and print cartridge 325. As noted above with respect to FIG. 1, during operation of the facsimile machine 100, the print carriage 320 slides back and forth on a rod which extends through the print carriage mounting hole 601. The print cartridge 325 is inserted in a stall 602 of the print carriage 320 so that the printhead 611 of the print cartridge 325 is exposed through a hole 603 formed at the bottom of the stall 602. A multiplicity of nozzles 612, from which ink is ejected during printing, extend from the ink reservoir 613 of the print cartridge 325 to the printhead 611. As described above, alignment cavities 604 are formed in the print carriage 320 into which alignment posts 531a and 531b (FIG. 5) of the sled base 430 extend during capping. In another embodiment, rather than alignment cavities, alignment holes are formed in the print carriage 320. The number and location of alignment cavities or holes is governed only by the number and location of the alignment posts on the sled base 430. As also described above, during wiping of the printhead 611, each of the guide rails 532 and 533 (FIG. 5) formed on the sled base 430 contacts a corresponding guide surface of the print carriage 320. The guide rail 532 contacts the guide surfaces 606a and 606b of the print carriage 325, and the guide rail 533 contacts the guide surfaces 605a and 605b. During capping, the guide rail 532 fits within the depression 607 formed in the print carriage 325 between the guide surfaces 606a and 606b so that the sled assembly 210 (FIGS. 4A and 4B) can be raised into the capping position. The print carriage 320 is made in two parts. The stall 602 is made of polycarbonate. The remainder of the print carriage 320, i.e., the portion including the mounting hole 601 and the guide surfaces 605a, 605b, 606a and 606b is made of a material that protects against wear resulting from the frequent contact of the guide surfaces 605a, 605b, 606a and 606b with the corresponding guide rails 532 and 533. In one embodiment, this material is a combination of materials including 75% polycarbonate, 5% teflon, 10% fiberglass and 10% carbon. The presence of the carbon increases electrical conductivity to bleed off static charge build up. FIG. 7A is a side view of the service station chassis 201 (FIG. 2) of the service station 110, a side wall of the service station chassis 201 being removed to show the interior of the service station chassis 201, with the sled assembly 210 in a lowered position. The sled assembly 210 is in this lowered position during wiping (see FIGS. 10C and 10D below) and just prior to capping (see FIG. 10B below). The sled assembly 210 is positioned in the lowered position by contact between the cam follower 314 and a cam ring 701 (described in more detail with respect to FIG. 9B below) formed on the dual cam mechanism 204. FIG. 7B is a side view of the service station chassis 201 similar to that of FIG. 7A, a side wall of the service station chassis 201 being removed to show the interior of the service station chassis 201, with the sled assembly 210 in a raised position. The sled assembly 210 is in this raised position during capping (see FIG. 10A below). The sled assembly 210 is positioned in the raised position by contact between the cam follower 314 and the cam ring 701, the dual cam mechanism 204 having been rotated into a different position than that shown in FIG. 7A so that the cam follower 314 contacts a different portion of the cam ring 701. The raised and lowered positions occur as a consequence of the asymmetric mounting of the dual cam mechanism 204 on the shaft 715. The sled assembly 210 is held in place by contact between the foot 314a (FIG. 3) of the cam follower 314 and the cam ring 701. As explained in more detail below with respect to FIGS. 9A through 9C, the dual cam mechanism 204 is spring-loaded so that a first cam mechanism (of which cam ring 701 is part) is biased in a direction out of the plane of FIGS. 7A and 7B, i.e., against the foot 314a. Thus, since the cam follower 314 is held substantially fixed along an axis perpendicular to the plane of FIGS. 7A and 7B, the biasing force of the first cam mechanism prevents the foot 314a from moving around the edge of the cam ring 701 and disengaging from the cam ring 701. In FIG. 7B, the cam 712 of the dual cam mechanism 204 is visible. As described in more detail below with respect to FIGS. 11A through 11C, the cam 712 contacts a paper pick pressure plate to move the paper pick pressure plate between a paper pick position and a paper release position. The dual cam mechanism 204 is rotated as follows. The motor 202 (FIG. 2) drives a gear 702 to rotate. The gear 702 meshes with a gear 703 to cause the gear 703 to rotate. The gear 703 is formed integrally and coaxially with a gear 704 so that rotation of the gear 703 causes the gear 704 to rotate. The gear 704 meshes with a gear 705 to cause the gear 705 to rotate. The gear 705 is formed integrally and coaxially with a smaller cylinder gear (not visible in FIGS. 7A and 7B) so that rotation of the gear 705 causes the cylinder gear to rotate. The cylinder gear meshes with a gear 706 to cause the gear 706 to rotate. The gear 706 meshes with a gear (not visible in FIGS. 7A and 7B, see gear 903e in FIGS. 9A and 9C) formed as part of the dual cam mechanism 204 between the first cam mechanism (FIGS. 9A through 9C) including the cam ring 701 and a second cam mechanism (FIGS. 9A through 9C) including the cam 712, thereby causing the dual cam mechanism 204 to rotate. In one embodiment of the invention, the gear 702 is made of brass, the gear 706 is made of nylon and the remainder of the gears (gears 703, 704, 705 and the cylinder gear not visible in FIGS. 7A and 7B) are made of polycarbonate. The use of the above-described materials for the various gears was found to reduce gear wear and gear noise. A sensor trigger 711 is formed integrally with the first cam mechanism of the dual cam mechanism 204. As the dual cam mechanism 204 rotates, the sensor trigger 711 contacts an electrical contact, sending an electrical signal to a microprocessor in facsimile machine 100 to indicate the rotational position of the dual cam mechanism 204. Thus, the microprocessor can monitor whether the sled assembly 210 is in the capping (raised) position or the wiping (lowered) position. The microprocessor uses the information regarding the position of the sled assembly 210 to coordinate motion of the print carriage 320 with the position of the sled assembly 210. FIG. 8A is a side perspective view of the side wall 800 of the service station chassis 201 (FIG. 2) that is removed in FIGS. 7A and 7B, illustrating the interior of the service station chassis 201 as viewed in a direction opposite that of FIGS. 7A and 7B. FIG. 8B is a perspective view of the release lever 203 shown in FIG. 8A. The wall 800 is attached to the remainder of the service station chassis 201 by a screw that fits through a slot 800a in the wall 800 into a threaded hole 713 (FIGS. 7A and 7B) in a boss formed on a wall of the service station chassis 201, and by a screw (not shown) that fits through the hole 800b in the wall 800 into a threaded hole formed in the shaft 715 (FIGS. 7A and 7B) on which the dual cam mechanism 204 is mounted. Additionally, a looped section 801 extends from the side wall 800 such that, when the side wall 800 is assembled to the remainder of the service station chassis 201, the looped section 801 fits through a hole 714 (FIGS. 7A and 7B) formed in the service station chassis 201 and over a protrusion 708. Likewise, a looped section 802 extends from the side wall 800 such that, when the side wall 800 is assembled to the remainder of the service station chassis 201, the looped section 802 fits over a protrusion 709 (FIGS. 7A and 7B) formed on the service station chassis 201. The release lever 203 is pivotably mounted on a boss 803 extending from a wall of the service station chassis 201. An actuating arm 805 of the release lever 203 extends through the looped section 802 above the service station chassis 201 (see FIG. 2). A release arm 804 of the release lever 203 is positioned within the service station chassis 201. In a first position of the actuating arm 805, the release arm 804 does not contact the dual cam mechanism 204 (FIGS. 7A and 7B). When the actuating arm 805 is moved in the direction of the arrow 206 (FIG. 2), the release lever 203 pivots about the boss 803 such that the release arm 804 contacts the dual cam mechanism 204, moving the spring-loaded first cam mechanism (described below with respect to FIGS. 9A through 9C) of the dual cam mechanism 204 in a direction perpendicular to the plane of FIGS. 7A and 7B. When the actuating arm 805 is moved to a second position, the first cam mechanism is moved sufficiently far so that the cam follower 314 is released from contact with the cam ring 701 (FIGS. 7A and 7B), thereby disengaging the sled assembly 210 from the service station 110 (FIG. 2). FIGS. 9A, 9B and 9C are a front view, a back view and an exploded perspective view, respectively, of the dual cam mechanism 204. The dual cam mechanism 204 includes a first cam mechanism 901, a coil spring 902, and a second cam mechanism 903. Extensions 901a and 901b (FIG. 9C) are formed on one side of the first cam mechanism 901. A circular ridge 901c is formed around the extensions 901a and 901b on the same side of the first cam mechanism 901. The cam ring 701 (FIG. 9B) is formed on an opposite side of the first cam mechanism 901. The cam ring 701 is contoured so that contact between the cam follower 314 (FIGS. 7A and 7B) and the cam ring 701 provides desired motion of the sled assembly 210 when the dual cam mechanism 204 is rotated. A raised contour 901d is formed on the same side of the first cam mechanism 901 as the cam ring 701. The contour 901d restricts downward motion of the cam follower 314 during capping so that the coil spring 301 (FIG. 3) is not compressed and only the coil spring 420 (FIGS. 4A and 4B) is compressed to provide the capping force. As best illustrated in FIG. 9C, the second cam mechanism 903 includes the gear 903e formed integrally with the cam 712. Holes 903a and 903b are formed through the cam 712, and holes 903c and 903d are formed through the gear 903e. The coil spring 902 fits within the circular ridge 901c and around the extensions 901a and 901b of the first cam mechanism 901. The second cam mechanism 903 is positioned against the coil spring 902 so that the coil spring 902 fits within a circular ridge (not visible in FIGS. 9A, 9B and 9C) formed on a surface of the gear 903e opposite the surface on which the cam 712 is integrally formed. The first cam mechanism 901 and the second cam mechanism 903 are pressed together, compressing the coil spring 902, so that the extensions 901a fit through the holes 903c and the extensions 901b fit through the holes 903d. The compressed coil spring 902 exerts a force that pushes the first cam mechanism 901 away from the second cam mechanism 903, causing snaps formed at the end of the extensions 901b to contact the gear 901e, thereby holding the first cam mechanism 901 and the second cam mechanism 903 together. When the release arm 804 (FIG. 8) moves the first cam mechanism 901 toward the second cam mechanism 903 to disengage the sled assembly 110 from the service station 210, the extensions 901a and 901b of the first cam mechanism 901 fit through the holes 903a and 903b in the cam 712 so that the cam 712 does not contact the extensions 901a and 901b and prevent the first cam mechanism 901 from moving. FIG. 10A is a simplified top perspective view of a portion of the service station chassis 201, sled assembly 210, and print carriage 320, as shown in FIG. 3, illustrating the print carriage 320 in the capping position. In the capping position, as shown in FIG. 7B, the dual cam mechanism 204 is rotated so that the portion of the cam ring 701 farthest from the shaft 715 is positioned nearest the sled assembly 210, thereby forcing the cam follower 314, and thus the sled assembly 210, to move upward (as viewed in FIG. 10A) relative to the service station chassis 201 and print carriage 320. When the sled assembly 210 is moved upward, alignment posts 531a and 531b (FIG. 10C) that extend from the surface 430c of the sled assembly 210 move upward into corresponding alignment cavities (not visible in FIGS. 10A through 10D, see FIG. 6) formed in the print carriage 320. As a result, the sled assembly 210 is held in a predetermined position with respect to the print carriage 320 so that the cap 501 (FIG. 10C) mounted on the sled assembly 210 is properly positioned over the printhead of the print cartridge (not shown) that is inserted into the print carriage 320. The alignment posts 531a and 531b are preferably tapered so that the cross-sectional area of the alignment posts 531a and 531b (in a plane that is substantially perpendicular to the direction in which the alignment posts 531a and 531b extend) is smallest at the end distal from the surface 430c. The cross-sectional area of the distal end of each of the alignment posts 531a and 531b is made smaller than the cross-sectional area of the corresponding alignment cavities, and the distal end of each alignment post 531a and 531b is rounded so that slight misalignment of the sled assembly 210 (i.e., the alignment posts 531a and 531b) with respect to the print carriage 320 (i.e., the alignment cavities) during capping is accommodated, i.e., the alignment posts 531a and 531b are guided into the corresponding alignment cavities by the rounded ends of the alignment posts 531a and 531b. The relatively large cross-sectional area of the alignment posts 531a and 531b proximal to the surface 430c provides strength. FIG. 10B is a top perspective view of the simplified service station chassis 201, sled assembly 210, and print carriage 320, illustrating the print carriage 320 in a position intermediate between the capping position and the wiping position. In this position, as shown in FIG. 7A, the dual cam mechanism 204 is rotated so that the portion of the cam ring 701 closest to the shaft 715 is positioned nearest the sled assembly 210, thereby forcing the cam follower 314, and thus the sled assembly 210, to move downward (as viewed in FIG. 10A) relative to the service station chassis 201 and the print carriage 320. When the sled assembly 210 is moved downward, the alignment posts 531a and 531b (FIG. 10C) move downward out of the corresponding alignment cavities so that the print carriage 320 is free to move laterally with respect to the sled assembly 210. FIG. 10C is a top perspective view of the simplified service station chassis 201, sled assembly 210, and print carriage 320, illustrating the print carriage 320 in the wiping position. After the sled assembly 210 is moved into the intermediate position shown in FIG. 10B, the print carriage 320 is moved laterally away from the sled assembly 210. As a result of this lateral movement, the wiper 502 (FIG. 10D) wipes the printhead of the print cartridge inserted in the stall of the print carriage 320, removing ink and contaminants from the printhead. FIG. 10D is a side view of the simplified service station chassis 201, sled assembly 210 and print carriage 320, illustrating the wiping position. The print carriage 320 is positioned with respect to the sled assembly 210 to ensure that, during lateral movement of the print carriage 320, the print carriage 320 will contact the guide rails 532 and 533 formed on the sled assembly 210. As the print carriage 320 moves laterally away from the sled assembly 210, riding on the guide rails 532 and 533, the end of the wiper 502 extends beyond the printhead of the print cartridge by a predetermined amount (when viewed in a direction parallel to the direction of motion of the print carriage 320) due to the height of the guide rails 532 and 533. Thus, the guide rails 532 and 533 ensure that the wiper 502 is properly positioned to achieve proper wiping force of the wiper 502 against the printhead. The print carriage 320 is moved laterally so that the wiper 502 wipes the entire printhead. After wiping, the nozzles are spitted, as described above and in the above-referenced U.S. Patent Application Serial No. 08/241,813. The print carriage can then be moved back to the intermediate position (FIG. 10B) if desired, resulting in wiping of the printhead once again. At this point, the sled assembly 210 can be raised to the capping position (FIG. 10A), or the print carriage 320 can be moved laterally to effect wiping and spitting again. The back and forth movement of the print carriage 320 can be executed as many times as necessary to achieve a desired amount of wiping. Eventually, after moving from the intermediate position through the wiping position, the print carriage 320 is moved away from the service station 110 to allow printing. FIG. 11A is a simplified cutaway perspective view of the facsimile machine 100 illustrating a paper pick pressure plate 1110 positioned in a paper release position. Pick rollers 1120 are attached to a shaft 1121 that is rotatably mounted near one end of the facsimile machine 100. The service station 110 is positioned near the same end of the facsimile machine 100. The paper pick pressure plate 1110 is rotatably mounted with hinges 1111a, 1111b in the facsimile machine 100 near an end of the facsimile machine 100 distal from the end at which the shaft 1121 and pick rollers 1120 are mounted. A compressed coil spring 1112 is positioned within a well formed in the bottom plate 100a of the facsimile machine 100 near an end of the paper pick pressure plate 1110 distal from the hinged end. The coil spring 1112 contacts the paper pick pressure plate 1110, the compression of the coil spring 1112 causing the paper pick pressure plate 1110 to be biased about the hinges 1111a and 1111b toward the pick rollers 1120. A stack of print media 1130 is positioned on the paper pick pressure plate 1110. When the dual cam mechanism 204 is positioned in the paper release position shown in FIG. 11A, i.e., with the cam 712 contacting an extended portion of the paper pick pressure plate 1110, the paper pick pressure plate 1110 is pushed away from the pick rollers 1120 so that the top sheet of the print media 1130 does not contact the pick rollers 1120 (see also FIG. 11B below). At the same time, the cam ring 701 (FIG. 11B) interacts with the cam follower 314, as described above with respect to FIG. 7B, to move the sled assembly 210 to the raised (i.e., capping) position. FIG. 11B is a simplified side view, similar to that of FIG. 7B, of the service station 110 and paper pick pressure plate 1110 when the sled assembly 210 is in a capping position and the paper pick pressure plate 1110 is in a paper release position. Thus, as is evident, while the print cartridge printheads are capped, printing does not occur and the paper pick pressure plate 1110 is positioned so that the top sheet of the print media 1130 is not drawn into a printing path. FIG. 11C is a simplified side view, similar to that of FIG. 7A, of the service station 110 and paper pick pressure plate 1110 when the sled assembly 210 is in a wiping position and the paper pick pressure plate 1110 is in a paper pick position. In the position shown in FIG. 11C, the dual cam mechanism 204 is rotated to a position in which the cam ring 701 interacts with the cam follower 314, as described above with respect to FIG. 7A, to move the sled assembly 210 to the lowered (i.e., wiping) position shown in FIG. 11C, and the cam 712 is rotated to an up position that allows the spring 1112 to bias the paper pick pressure plate 1110 against the paper pick rollers 1120 (FIG. 11A), thereby causing the top sheet of the print media 1130 to contact the pick rollers 1120. The microprocessor causes the shaft 1121 to rotate, the pick rollers 1120 rotating with the shaft 1121. The frictional force between the rotating pick rollers 1120 and the top sheet of the print media 1130 causes the top sheet to be drawn away from the stack of print media 1130 into the printing path of the facsimile machine 100. A paper guide (not shown) directs the sheet of the print media 1130 around the pick rollers 1120 and into a print zone (not shown) where printing occurs. Thus, after the print cartridge printheads are wiped, printing occurs and the paper pick pressure plate 1110 is positioned so that paper can be drawn into the printing path by rotation of the paper pick rollers 1120. As described above, both the position of the sled assembly 210 for print cartridge servicing and the position of the paper pick pressure plate 1110 for feeding paper into the printing path are controlled by a single motor 202 driving a single mechanism (dual cam mechanism 204). In contrast, previous service stations required two motors, each motor driving a separate positioning mechanism: one for moving the sled assembly and one for moving the paper pick pressure plate. Thus, the service station according to the invention achieves functionality equivalent to that of previous service stations with a simpler structure that is easier to construct, less likely to break down, and requires less space within the printing assembly. The previously mentioned microprocessor synchronizes operation of the motor 202 with the motor that drives the print carriage 320 so that movement of the print carriage 320 (FIG. 3) is properly synchronized with the movement of the sled assembly 210 and paper pick pressure plate 1110. Various embodiments of the invention have been described. The descriptions are intended to be illustrative, not limitative. Thus, it will be apparent to one skilled in the art that certain modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims: Structure for use with an inkjet printing apparatus (100), comprising: a sled assembly (210), comprising: at least one wiper (502) for periodically wiping a printhead (611) of a corresponding print cartridge (325); and at least one cap (501) for enclosing the corresponding printhead when the corresponding print cartridge is not in use; a paper pick pressure plate (1110) for selectively contacting a paper pick roller (1120) such that a print medium (1130) is advanced through a printing path when the pressure plate contacts the pick roller and the print medium is not advanced through the printing path when the pressure plate does not contact the pick roller; and means (202, 702, 703, 704, 705, 706, 204, 314) for simultaneously controlling movement of the sled assembly and the pressure plate. Structure as in Claim 1, wherein the means for simultaneously controlling further comprises a dual cam mechanism (204). Structure as in Claim 2, wherein: the means for simultaneously controlling further comprises a cam follower (314); and the dual cam mechanism further comprises: a cam ring (701) for contacting the cam follower to move the sled assembly in response to rotation of the dual cam mechanism; and a cam (712) for contacting the pressure plate to move the pressure plate in response to rotation of the dual cam mechanism. Structure as in Claims 2 or 3, wherein the means for simultaneously controlling further comprises a motor (202) for driving the dual cam mechanism. Structure as in Claims 1, 2, 3 or 4 wherein: in a first position, the means for simultaneously controlling positions the sled assembly in a capping position and the paper pick pressure plate in a paper release position; and in a second position, the means for simultaneously controlling positions the sled assembly in a wiping position and the paper pick pressure plate in a paper pick position. A method for servicing an inkjet print cartridge (325) and advancing a print medium (1130) into a printing path in an inkjet printing apparatus (100) according to claim 1, comprising the steps of: moving the sled assembly (210) between a capping position and a wiping position; and simultaneously controlling the advancement of the print medium into the print path. A method as in Claim 6, wherein the step of moving and the step of simultaneously controlling further comprise the step of rotating a dual cam mechanism (204) to effect movement of the sled assembly and a means (1110) for advancing the print medium into the printing path. A method as in Claims 6 or 7, wherein: the step of moving further comprises rotating a cam ring (701), the cam ring contacting a cam follower (314) of the sled assembly to effect movement of the sled assembly; and the step of simultaneously controlling further comprises rotating a cam (712), the cam contacting a means for advancing the print medium into the printing path to effect movement of the means for advancing. A method as in Claim 8, wherein the cam contacts a paper pick pressure plate (1110) to selectively control contact between the paper pick pressure plate and a paper pick roller (1120) such that a print medium (1130) is advanced through a printing path when the pressure plate contacts the pick roller and the print medium is not advanced through the printing path when the pressure plate does not contact the pick roller. A method as in Claims 6, 7, 8 or 9 wherein: the step of moving further comprises: positioning the sled assembly in a capping position; and positioning the sled assembly in a wiping position; and the step of simultaneously controlling further comprises: positioning the pressure plate in a paper release position when the sled assembly is in the capping position; and positioning the pressure plate in a paper pick position when the sled assembly is in the wiping position. Structure as in claim 1, wherein the means for simultaneously controlling further comprises first moving means for moving the sled assembly and second moving means for moving the pressure plate, the first and second moving means being mechanically integral or interrelated such that movement of one of the first and second moving means results in movement of the other of the first and second moving means. Method as in claim 6, wherein the steps of moving the sled assembly and controlling the advancement of the print medium are effected using a single integral structure or multiple mechanically interrelated structures.

Inventors: FUJIMORI NORIYOSHI, KOBAYASHI ATSUSHI, NGUYEN CHAN, SHIBATA ALAN, FUJIMORI, NORIYOSHI, KOBAYASHI, ATSUSHI, NGUYEN, CHAN, SHIBATA, ALAN
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1995
Main classification: B41J2
IPC codes: B41J23, B41J2, B41J13