Abstract:
Imaging apparatus including a guide for guiding a receiver medium therethrough with reduced friction and a guide assembly method therefor. The guide includes mounting portions adapted to be received by mounting locations precisely positioned in a support frame capable of supporting the guide. The mounting portions must precisely mate with the mounting locations so that the guide is properly mounted on the frame during assembly of the imaging apparatus. In this regard, the guide is formed of a flexible material having a relatively low value of Young&#39;s modulus of elasticity, so that the guide can be flexed in order to manipulate the guide into position for mating engagement of the mounting portions with the mounting locations. Moreover, the guide is made of a material having a low coefficient of sliding friction for sliding of receiver medium therealong, so that the receiver medium is neither scratched by the guide nor sticks to the guide to cause &#34;jamming&#34; of the apparatus by the receiver medium.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to imaging apparatus and assembly methods pertaining thereto and, more particularly, relates to an imaging apparatus including a guide for guiding a receiver medium therethrough with reduced friction and a guide assembly method therefor. 
     BACKGROUND OF THE INVENTION 
     In a color thermal imaging apparatus, a print is made by successively transferring color dyes from respective dye patches of a dye donor web onto a receiver medium, such as coated paper or transparency. The dye donor web is disposed between the receiver medium and a print head comprising a plurality of resistive heating elements. When an individual heating element is energized, the radiative heat therefrom causes the dye from the dye donor web to transfer to the receiver medium to form an image on the receiver medium. 
     In order to produce an image on the receiver medium, the receiver medium is first fed from a receiver medium supply tray. In this regard, a sheet of receiver medium is &#34;picked&#34; from the supply tray by a rotating &#34;picker roller&#34;, which engages the receiver medium and transports it to a guide configured to guide the receiver medium toward the print head. After encountering the guide, the receiver medium advances along the guide and thence into a gap formed between the print head and a platen roller disposed adjacent the print head. The print head then moves toward the platen roller, thereby pressing the dye donor web and the receiver medium against the platen roller to form a sandwich-like structure for thermal printing of the image onto the receiver medium. 
     Prior art guides, such as, for example, disclosed in U.S. Pat. No. 5,176,458 are typically formed of metal, such as stainless steel. These stainless steel members are inherently rigid and stiff at room temperature as evinced by their relatively high value of Young&#39;s modulus of elasticity of approximately 30×10 6  pounds per square inch at about 75 degrees Fahrenheit. Of course, Young&#39;s modulus of elasticity is a constant for a given material and is a measure of its stiffness and thus indicates the ability of the material to resist deflection when loaded, for a given cross-section and at a given temperature. The higher the value of Young&#39;s modulus of elasticity, the greater the stiffness of the material. Such prior art guides are usually suspended between parallel support frames in the printer and may have relatively rough marginal edges even after deburring. 
     Although the typical guide is made of stainless steel, it must nonetheless be further polished before deployment in the printer so that its coefficient of friction is low enough to allow the receiver medium to glide therealong without sticking and scratching of the receiver medium. Sticking of the receiver medium may cause the receiver medium to &#34;jam&#34; in the printer mechanism and stop moving along the guide. Moreover, scratching of the receiver medium will provide an unacceptable print. To avoid sticking and scratching, the stainless steel guide is &#34;mirror&#34; polished so that, after polishing, the coefficient of sliding friction of the receiver medium on the stainless steel guide is approximately 0.8 μ. Although polishing the guide solves the above mentioned problems, such polishing of the guide is a time-consuming additional step in the manufacturing process which leads to increased manufacturing costs. Therefore, a problem in the art is increased manufacturing costs caused by attempts to ameliorate sticking and scratching of the receiver medium on the guide. 
     Moreover, the rigid stainless steel guide mentioned hereinabove typically includes a plurality of projections configured to be matingly received in respective ones of a plurality of relatively small apertures formed in the support frames supporting the guide. However, it has been observed that close tolerances required to properly fit the projections into the apertures in combination with the relative stiffness of the stainless steel guide make it difficult to manipulate the guide so as to first align and then insert the projections into the relatively small apertures. Precise alignment of the projections with their respective apertures in the frames may require several attempts by the assembler of the printer before successful alignment and insertion into the apertures is obtained. The assembly process precludes assembling the frames to the guide rather than assembling the guide to the frames. Therefore, another problem in the art is the increased manufacturing cost required to assemble the guide to the frames. 
     The previously mentioned U.S. Pat. No. 5,176,458, titled &#34;Multiple Position Thermal Printer Head Mechanism Which Is Disturbance Insensitive&#34; issued Jan. 5, 1993 in the name of Henry G. Wirth, discloses a device wherein a sheet of receiver medium moves forward into a receiver guide where it follows a curved path toward a gap between a print head assembly and a platen assembly. The receiver guide is connected to a main printer structure. However, this patent does not appear to address the problem of increased manufacturing costs due to attempts to ameliorate sticking and scratching of the receiver medium on the guide and the problem of increased manufacturing costs required to assemble the guide to the main printer structure. 
     Therefore, what has long been needed is an imaging apparatus including a guide for guiding a receiver medium therethrough with reduced friction and a guide assembly method therefor. 
     SUMMARY OF THE INVENTION 
     The invention resides in an imaging apparatus adapted to guide a receiver medium therethrough comprising a frame defining a mounting location thereon; and a guide supported by the frame, the guide defining an axis therethrough and having a mounting portion thereof adapted to be received by the mounting location, the guide being flexible about the axis for bringing the mounting portion into alignment with the mounting location. 
     An object of the present invention is to provide an imaging apparatus including a guide for guiding a receiver medium therethrough with reduced friction and a cost-effective guide assembly method therefor. 
     A feature of the present invention is the provision of a guide member having a reduced coefficient of friction. 
     Another feature of the present invention is the provision of a flexible guide member. 
     An advantage of the present invention is that use thereof reduces manufacturing costs. 
     Another advantage of the present invention is that scratching of the receiver medium is avoided. 
     Still another advantage of the present invention is that probability of the receiver medium &#34;jamming&#34; in the imaging apparatus is reduced. 
     These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the detailed description of the preferred embodiments of the invention presented hereinbelow, reference is made to the accompanying drawings, in which: 
     FIG. 1 is a view in elevation of an imaging apparatus, with parts removed for clarity, showing a support frame and a guide member connected to the support frame, this view also showing a receiver medium being guided along the guide member; 
     FIG. 2 is a view in elevation of the support frame and the guide member connected thereto; 
     FIG. 3 is a view in perspective of the guide member suspended between a pair of parallel support frames; 
     FIG. 4 is a view along section line 4--4 of FIG. 2; and 
     FIG. 5 is a view along section line 5--5 of FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1, 2 and 3, there is shown an imaging apparatus, generally referred to as 10, with parts removed for clarity. In the preferred embodiment of the invention, imaging apparatus 10 is a color thermal printer and comprises a pair of parallel spaced-apart support frames 20a/20b having a plurality of apertures 30 therethrough for reasons disclosed hereinbelow. Apertures 30 are precisely machined through frames 20a/20b in order to adhere to precisely defined and predetermined distances between them. Apparatus 10 also comprises a print head 40 connected to at least one of frames 20a/20b, so that print head 40 is suitably supported thereby. A receiver medium supply tray 50 associated with print head 40 holds a supply of a receiver medium 60 therein, which receiver medium 60 may be cut sheets of coated paper or cut sheets of transparency. A rotatable &#34;picker roller&#34; 70 is disposed near tray 50 and is adapted to engage receiver medium 60 to remove receiver medium 60 from tray 50. 
     Again referring to FIGS. 1, 2 and 3, as receiver medium 60 is removed from tray 50, it is intercepted by a single guide member 80, which guides receiver medium 60 into a gap 90 defined between print head 40 and a platen roller 100. As described more fully hereinbelow, guide member 80 is configured so that sticking and scratching of receiver medium 60 by guide member 80 is avoided and so that assembly of guide member 80 to frames 20a/20b is made easier during manufacture of apparatus 10. A dye donor supply spool 110 having a supply of dye donor ribbon 120 wound thereabout is provided for supplying donor ribbon 120 to gap 90. In addition, a dye donor take-up spool 130 is also provided for taking-up of donor ribbon 120 as donor ribbon 120 is unwound from about supply spool 110 and passes through gap 90. In this manner, dye donor ribbon 120 extends from supply spool 110, through gap 90, and thence to take-up spool 130. A receiver medium transport mechanism, such as a pair of spaced-apart motorized rollers 140a/140b, engage receiver medium 60 to assist in feeding receiver medium 60 through gap 90. In this regard, rollers 140a/140b define a nip 150 for receiving receiver medium 60 therebetween, which rollers 140a/140b are adapted to close nip 150 in order that rollers 140a/140b can engage receiver medium 60. After passing through nip 150, receiver medium 60 is deposited into an output tray 155 for retrieval by an operator of apparatus 10. 
     Referring yet again to FIGS. 1, 2 and 3, during operation of apparatus 10, receiver medium 60 is &#34;picked&#34; from supply tray 50 by picker roller 70 and transported to guide member 80. Receiver medium 60 advances along guide member 80 and thence into gap 90 which is defined between print head 40 and platen roller 100. As receiver medium 60 advances into gap 90, print head 40 moves toward platen roller 100 to press dye donor ribbon 120 and receiver medium 60 against platen roller 100 in order to form a sandwich-like structure, as shown. As the sandwich-like structure is formed, heat from thermal print head 40 causes dye in dye donor ribbon 120 to transfer to receiver medium 60 in order to print an image on receiver medium 60. 
     However, it is desirable that sticking of receiver medium 60 on guide member 80 be avoided in order to avoid &#34;jamming&#34; apparatus 10 with receiver medium 60. Jamming apparatus 10 with receiver medium 60 occurs when receiver medium 60 sticks on guide member 80 to block and inhibit further feeding of receiver medium 60 from supply tray 50. In addition, it is desirable that scratching of receiver medium 60 on guide member 80 be avoided in order to obtain a visually acceptable image on receiver medium 60. Moreover, it is desirable that assembling guide member 80 to frames 20a/20b be time-efficient to reduce manufacturing costs. 
     Therefore, referring to FIGS. 1, 2, 3, 4 and 5, there is shown the previously mentioned guide member 80 configured so that sticking and scratching of receiver medium 60 on guide member 80 is avoided and so that assembly of guide member 80 to frames 20a/20b is made easier during manufacturing of apparatus 10. In this regard, guide member 80 has a generally arcuate shape in transverse cross-section and is preferably formed of a material having a predetermined coefficient of sliding friction sufficient to allow receiver medium 60 to freely slide along guide member 80 without sticking. More specifically, guide member 80 preferably has a coefficient of sliding friction less than 0.8, which is the coefficient of sliding friction for polished stainless steel of which prior art guides are made. In this regard, guide member 80 is preferably formed of a polymer, such as acetal, nylon, polyethylene, &#34;TEFLON&#34; (Trademark of DuPont de Nemours, Inc.), or the like. In the preferred embodiment, &#34;TEFLON&#34;, which has a coefficient of sliding friction of 0.04, is used. Guide member 80 may be generally rectangularly-shaped and sized to be interposed between frames 20a/20b, which were previously caused to be disposed in apparatus 10 to await fitting of guide member 80 thereto. Rectangularly-shaped guide member 80 defines a longitudinal axis 160 extending centrally along the length thereof and includes a pair of rounded parallel edges 170a/170b. The rounded configuration of edges 170a/170b of guide member 80 inhibits scratching of receiver medium 60 as receiver medium 60 is intercepted and then guided along a curvilinear guide path defined by guide member 80. In addition, the material forming guide member 80 is the previously mentioned polymer having an inherently smooth surface which also inhibits scratching of receiver medium 60. 
     Still referring to FIGS. 1, 2, 3, 4 and 5, guide member 80 is capable of flexing about axis 160 (see FIGS. 2 and 3) for reasons provided presently. In this regard, guide member 80 has a predetermined thickness in transverse cross-section of approximately 0.015 inch and is preferably formed of the previously mentioned polymer, so that guide member 80 is suitably flexible. More generally, guide member 80 is preferably formed of a material having a relatively low (i.e., compared to prior art stainless steel guides) Young&#39;s modulus of elasticity so that guide member 80 is substantially less stiff than prior art guides. In this regard, in the preferred embodiment of the invention, guide member 80 has a Young&#39;s modulus of elasticity of between 586 pounds per square inch and approximately 620 pounds per square inch at room temperature. 
     Referring again to FIGS. 1, 2, 3, 4 and 5, guide member 80 includes a pair of preferably rigid and elongate mounting members 180a/180b attached, such as by a suitable adhesive, along respective ones of edges 170a/170b. As described more fully presently, mounting members 180a/180b enable mounting of guide member 80 on frames 20a/20b. Each of mounting members 180a/180b has a plurality of projections 190a/190b outwardly extending from end portions 300a/300b thereof for engaging respective ones of apertures 30. However, the distance between apertures 30, such as a distance &#34;L&#34; (see FIGS. 2 and 3), are machined to close tolerances to reduce vibration and movement of guide member 80 in frames 20a/20b during transport and operation of apparatus 10. Excessive vibration and movement of guide member 80 is undesirable because such vibration and movement may lead to misalignment of guide member 80 with supply tray 50. Such misalignment impairs the guiding function of guide member 80. However, the distance between projections 190a/190b may not precisely equal distance &#34;L&#34; due to routine dimensional variances occurring during manufacture. Such dimensional variances make it difficult and time-consuming to first align and then insert projections 190a/190b into relatively small apertures 30. Therefore, according to the invention, guide member 80 is flexible about longitudinal axis 160 in order to adjust the distance between projections 190a/190b so that the distance between projections 190a/190b precisely equals the distance &#34;L&#34; formed during manufacture of apparatus 10. In this manner, projections 190a/190b are more easily aligned with and then inserted into apertures 30 during assembly of guide member 80 to frames 20a/20b. 
     It is appreciated from the teachings herein, that an advantage of the present invention is that use thereof reduces manufacturing costs. This is so because assembly of guide member 80 to frames 20a/20b is less time-consuming which in turn is due to the ability of guide member 80 to flex about its longitudinal axis 160. This flexibility of guide member 80 allows the distance between projections 190a/190b to be adjusted for aligning and then inserting projections 190a/190b into respective ones of apertures 30. 
     Another advantage of the present invention is that use thereof reduces manufacturing cost in yet another manner. This is so because the material forming guide member 80 does not require the additional step of polishing. Elimination of this additional manufacturing step reduces manufacturing costs. 
     Still another advantage of the present invention is that image quality is maintained because receiver medium 60 glides along guide member 80 without scratching of receiver medium 60. This is so because guide member 80 includes rounded edges 170a/170b without bumps or burrs which might otherwise scratch receiver medium 60 as receiver medium 60 is guided along guide member 80. Moreover, guide member 80 is preferably made of a smooth polymer material which inherently inhibits scratching of receiver medium 60. 
     Yet another advantage of the present invention is that the probability of receiver medium 60 &#34;jamming&#34; in apparatus 10 is reduced. This is so because guide member 80 is preferably formed of the previously mentioned polymer material having a predetermined coefficient of sliding friction sufficient to allow receiver medium 60 to freely slide therealong without sticking. More specifically, guide member 80 preferably has a coefficient of sliding friction of approximately 0.04, which is a coefficient of sliding friction less than polished stainless steel of which prior art guides are made. 
     While the invention has been described with particular reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements of the preferred embodiment without departing from the invention. In addition, many modifications may be made to adapt a particular situation and material to a teaching of the invention without departing from the essential teachings of the present invention. For example, although the invention is described with reference to a resistive element thermal printer, the invention is equally adaptable to other image forming devices, such as ink jet printers, copiers, and facsimile machines. As another example, although the invention is described as including a guide member formed of a polymer material, any suitable material may be used which has a coefficient of sliding friction for the receiver medium less than the coefficient of sliding friction of prior art guides (e.g., &#34;mirror&#34; polished stainless steel). 
     Therefore, what is provided is an imaging apparatus including a guide for guiding a receiver medium therethrough with reduced friction and a guide assembly method therefor. 
     PARTS LIST 
     10 . . . imaging apparatus 
     20a/20b . . . support frames 
     30 . . . apertures 
     40 . . . print head 
     50 . . . supply tray 
     60 . . . receiver medium 
     70 . . . picker roller 
     80 . . . guide member 
     90 . . . gap 
     100 . . . platen roller 
     110 . . . supply spool 
     120 . . . dye donor ribbon 
     130 . . . take-up spool 
     140a/140b . . . receiver medium transport mechanism 
     150 . . . nip 
     155 . . . output tray 
     160 . . . longitudinal axis 
     170a/170b . . . rounded edges 
     180a/180b . . . mounting members 
     190 . . . projections