Abstract:
Disclosed is an paper feeding device or a pack holder capable of preventing noise or a misfeeding when printing envelopes or postcards. The pack holder can be adjusted to feed standard size paper or postcards and envelopes. A sliding plate is used when feeding postcards and envelopes so that the last postcard or envelope in the stack can be fed into the machine successfully. The sliding plate allows only one of the two feeding rollers to make contact with a friction pad during the feeding of postcards and envelopes.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 from an application for Paper Feeding Device earlier filed in the Korean Industrial Property Office on Dec. 27, 1996 and there duly assigned Serial No. 59059/1996 
     FIELD OF THE INVENTION 
     The present invention relates to a paper feeding device, and particularly to an improved paper feeding device capable of improving the image quality of a last sheet when printing a plurality of envelopes or postcards each having a size smaller than the standard size, i.e., A4 size, by means of a printing unit such as an image forming device. 
     DESCRIPTION OF THE RELATED ART 
     Office automation facilities include a receiving part which is called as a knockup plate or pack holder on which a plurality of documents or printable media are loaded so that the document and printable media can be fed to perform the scanning operation of the document or to print on the printable media; and a paper feeding device has a pickup device for feeding the document or the printable media loaded in the receiving part by one by one. 
     It is often necessary to load unusually small print media, such as envelopes and postcards for feeding into a machine one by one. Such small print media may require the use of only one feeding roller instead of two, to feed a sheet of print media into a machine. In particular, U.S. Pat. No. 5,069,434 for a Removable Dual Bin Envelope Feed Tray For An Image Reproduction Machine to Sellers, U.S. Pat. No. 5,348,283 for a Sheet Feeding Apparatus Having Sheet Separating Means With Adjustable Feeding Force to Yanagi et al, and U.S. Pat. No. 5,480,247 for a Sheet Supplying Apparatus to Saujawa et al each disclose paper feeding apparatus&#39; that can accommodate the insertion of envelopes or postcards. I have not seen a paper feeding device that insures that the last envelope or postcard in a stack can be fed successfully into a machine. I have also not seen the use of a sliding plate on a paper feeding device for accommodating envelopes and postcards to successfully feed every last one envelope or postcard without noise or misfeeding. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide a paper feeding device capable of preventing a noise or a misfeeding, which prevents one friction pad from being contacted to its corresponding pickup device which are necessary for printing standard papers, even if the last sheet of envelopes or postcards is printed by the other friction pad. 
     It is also an object to provide a pack holder with a sliding plate that can be utilized whenever envelopes or postcards are to be printed on, the sliding plate being slid to cover one of the pair of friction pads thus allowing a third friction pad on the sliding plate to protrude further from the base of the pack holder than the other friction pad. 
     It is yet another object of the present invention to enable just one friction pad and one feeding roller to be contacted when feeding postcards and envelopes. 
     According to one aspect of the present invention, a paper feeding device includes: a first loading unit having a first plate and a pair of first friction pads established on the first plate facing a pair of feeding rollers, and loading a first paper; and a second loading unit having a second plate and a pair of second friction pads established on the second plate, and loading a second paper smaller than the first paper. 
     In the case that the second paper is supplied, the second loading unit is moved so that the second friction pad can be located at one of the first friction pads. Preferably, between a pair of the first friction pads on the first plate, a receiving groove for receiving the second loading unit is formed. Preferably, at one of side walls of the receiving groove corresponding to a pair of the first friction pads, an oblique section having a predetermined curvature is formed. Preferably, a slot is extended from the receiving groove to a part where the one of a pair of the first friction pads is formed across the oblique section. Preferably, the second plate is received by the receiving groove and the a bolt hole is formed at a part of the second plate corresponding to the slot. After a bolt is inserted through the bolt hole and the slot, the bolt and a nut are locked in the bolt hole. Preferably, at the backside of the second plate, a backside guiding groove having an area larger than the longitudinal section of the first friction pad. Preferably, the first paper is a A4 size paper and the second paper is an envelope or a post card having a size smaller than the A4 size. 
     According to another aspect of the present invention, a paper feeding device includes: at least two feeding rollers which are formed at a rotation shaft apart from each other; and friction pads which are formed corresponding to the feeding rollers at a knockup plate, wherein, the gap between each friction pad and each feeding roller is equally formed at a first feeding mode, and the gap between each friction pad and each feeding roller varies at a second feeding mode. 
     Preferably, the second feeding mode is a mode for feeding postcards or envelopes, and the gap between the feeding roller and the friction pad of one end in which the postcards and envelopes are inserted is formed smaller than the gap between the feeding roller and the friction pad of the other end. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
     FIG. 1 is a perspective view illustrating the conventional paper feeding device; 
     FIG. 2 is a perspective view illustrating that envelopes or post cards are loaded in the conventional paper feeding device; 
     FIG. 3 is a sectional view which is cut along a line III-III′ of FIG. 2; 
     FIG. 4 is a sectional view which is cut along a line IV-IV′ of FIG. 2; 
     FIG. 5 is a perspective view illustrating a paper feeding device according to the present invention; 
     FIG. 6 is a sectional view which is cut along a line VI-VI′ of FIG. 5; 
     FIG. 7A is a perspective view illustrating a second knockup plate according to the present invention; 
     FIG. 7B is a sectional view which is cut along a line VII-VII″ of FIG. 7A; 
     FIG. 8A is a perspective view illustrating that standard papers are loaded in a first knockup plate; 
     FIG. 8B is a view illustrating the operation of the paper feeding device according to the present invention; 
     FIG. 8C is a perspective view illustrating that postcards or envelopes are loaded in the paper feeding device according to the present invention; 
     FIG. 9A is a sectional view which is cut along a line IX-IX′ of FIG. 8C; and 
     FIG. 9B is a sectional view which is cut along a line X-X′ of FIG.  8 C. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view illustrating an embodiment of the conventional paper feeding device. As shown in the drawing, the paper feeding device  100  includes a knockup plate (or pack holder)  10  which receives a plurality of standard paper A such as A4 size, postcards and envelopes B. The postcards and the envelopes have a size smaller than the standard paper. There is a pickup device for supplying the recording media by one by one. 
     The knockup plate  10  includes a base  15 , a paper support  60 , a guide  20  attached to the base  15  and friction pads  30  and  35 . The base  15  is a flat plate of rectangular shape having a thin thickness. At the bottom of the base  15 , the paper support  60  for supporting the standard paper A and the envelopes and the postcards B is provided. At the rear side of the upper part of the base  15 , a plate rotating unit  15   a  is formed so that the documents can be loaded by rotating the knockup plate  10  centering around the base  15 . A pair of the friction pads  30  and  35  made of a cork or a rubber are attached to the both sides which are apart from the central part of the base  15 . 
     At the outer side of the right friction pad  30 , a guide  20  is formed so that the envelopes or the postcards B can accurately be aligned at a preset position when the envelopes or the postcards B having a size smaller than the standard paper A is printed or transmitted. The guide  20  is rotated so that it is contacted to the base  15  so that is does not interrupt the printing operation when printing the standard paper A. 
     To pick up the standard papers A, the postcards or the envelopes B which are received by the knockup plate  10  having the above-described structure, a pickup device is established facing the right and left friction pads  30  and  35  on both sides. The pickup device includes pickup rollers  40  and  45  which are made of rubber corresponding to the right and left friction pads  30  and  35 ; and a rotation shaft  50  which transmits the rotary power to the pickup rollers  40  and  45 . 
     The base  15  of the knockup plate  10  is rotated by a predetermined angle by the plate rotating unit  15   a  so as to perform the printing and scanning operation on/from the standard paper A, the envelopes or the postcards B. By the rotated base  15 , a predetermined gap is generated between the right and left pads  30  and  35  and the pickup rollers  40  and  45 . As shown in FIG. 2, a plurality of the standard papers A, the envelopes or the postcards B are inserted into the gap and then they are received by the base  15 . 
     The base  15  in which the standard paper A, the envelopes or the postcards B are inserted is restored to the original state, and thereby the uppermost sheet of the standard paper A, the envelope or the postcard B is closely contacted to the pickup rollers  40  and  45 , and the last sheet is closely contacted to the right and left friction pads  30  and  35 . After that, when the rotation shaft  50  is driven by a paper feeding signal, the pickup rollers  40  and  45  are rotated according to the driving of the rotation shaft  50 , thereby supplying the uppermost sheet to a next process. 
     The conventional paper feeding apparatuses which supply two kinds of printable media each having a different size such as the standard paper A, the envelopes or the postcards B have following problems. The problems will be illustrated, with reference to FIGS. 3 and 4. FIG. 3 is a sectional view which is cut along a line III-III′ of the FIG. 2, and FIG. 4 is a sectional view which is cut along a line IV-IV′ of FIG.  2 . As described above, a plurality of standard envelopes are arranged by the guide  20 . The arranged envelopes B are closely contacted between the right friction pad  30  and the right pickup roller  40 . If the thickness of a plurality of the envelopes B which are arranged is indicated as LT referring to the section which is cut along the line IV-IV′ of FIG. 3, the gap between the right friction pad  30  and the right pickup roller  40  is the same as the thickness LT of the envelopes B. The base  15  in which the envelopes B are received is rotated by a predetermined angle by the plate rotating unit  15   a . As shown in FIG. 3, the left friction pad  35  and the left pickup roller  45  are apart from each other as much as the width corresponding to the thickness LT of the envelopes B (here, LT&gt;0). 
     As described, the envelopes B are loaded and the printing operation is performed. As the envelopes B are successively supplied, the thickness LT of the envelopes B decreases. As a result, the space between the left friction pad  35  and the left pickup roller  45  gradually decreases. When one or two envelopes B remain and thereby the thickness LT of the envelopes is smaller than 1 mm (0&lt;LT&lt;1 mm), the left friction pad  35  and the left pickup roller  45  are contacted each other. When printing the last sheet, the left friction pad  35  and the pickup roller  45  are completely contacted (here, LT=0). When the left friction pad  35  and the left pickup roller  45  are contacted each other, i.e., LT=0, in the case that the rotation shaft  50  starts to be rotated to print the last sheet, the friction between the left pickup roller  45  and the left friction pad  35  increases. 
     The paper feeding device  200  according to the present invention includes a first knockup plate (pack holder)  210  for loading the standard paper; a second knockup plate (slidable plate)  300  which is mounted on the first knockup plate so as to load a paper having a size smaller than the standard paper; and a pair of pickup units enabling the standard paper which is loaded in the first knockup plate, or the postcards or envelopes which are loaded in the second knockup plate to be fed. 
     The compartments of the paper feeding device will be explained, with reference to the drawings. The first knockup plate  210  includes a base  215 ; a pair of frictions pads  230  and  235  attached to the right and left sides of base  215  respectively; a second knockup plate receiving groove (recess)  270  having a rectangular shape which is formed to have a predetermined depth between the friction pads  230  and  235 ; a guide  220  which restricts the position of the envelopes or the postcards when performing the printing operation; a second knockup plate support  280  which guides the second knockup plate  300  which will be explained; and a paper support  260  which supports the standard paper, envelopes or postcards. 
     The base  215  is a rectangular shaped flat plate having a predetermined thickness which is composed of two long sides and two short sides. At one of the two short sides of the base  215 , the paper support  260  is attached perpendicular to the base  215 . Preferably, the part where the paper support  260  is attached can be the lower part of the base  215 . Moreover, a base rotating unit  215   a  is connected to the upper part of the base  215  so that the base  215  can be rotated, and the base  215  is rotated by a predetermined angle based on the base rotating unit  215   a.    
     As illustrated, at lower parts apart from the center of the base  215  which is rotated by a predetermined angle based on the base rotating unit  215   a , a pair of the right and left friction pads  230  and  235  are located. The right and left friction pads  230  and  235  are made of a cork or a rubber, and have thickness ST 2 . Moreover, the second knockup plate receiving groove  270  formed between the right and left friction pads  230  and  235  has a rectangular shape. Its length is larger than that of the right and left friction pads  230  and  235 , and its depth is roughly half ST 1 , the depth of recess  270  in base  215 . 
     One side wall  275  placed in the direction of the right friction pad  230  out of four side walls of the second knockup plate receiving groove  270  has an angle larger than  90  degrees to the bottom of the second knockup plate receiving groove  270 . In other words, as shown in FIG. 5, a slope is formed at the one side wall  275  and it is desirable to form the slope long enough. 
     A guiding slot  290  formed at the base  215  is a long part having an opening which is formed from the central part of the bottom of the second knockup plate receiving groove  270  to the front surface of the right friction pad  230  through the one side wall  275  at which a slope is formed. The second knockup plate support  280  is formed from the lower end of the side wall  275  at which the slope is formed of the second knockup plate receiving groove  270  to the long side of the first knockup plate  210 , through the right friction pad  230 . The second knockup plate support  280  is a bar shape having a predetermined thickness, whose thickness is the same as or lower than the right and left friction pads  230  and  235 . 
     FIG. 6 is a sectional view in which the second knockup plate receiving groove  270  is cut along the line VI-VI′. As shown in the drawing, the thicknesses of the second knockup plate receiving groove  270 , the guiding slot  290  which is formed long, the side wall at which the slope is formed, the right friction pad  230  and the pickup device contacted to the right friction pad  230  are clearly shown. At the second knockup plate receiving groove  270  in the first knockup plate  210 , the second knockup plate  300  which is illustrated in FIGS. 7A and 7B is illustrated. The second knockup plate  300  includes a second knockup plate body  310 ; a guiding bolt hole  347 ; a second knockup plate friction pad  320 ; and a backside guiding groove  330 . The second knockup plate body  310  is a rectangular flat plate and its length and width are slightly smaller than that of the second knockup plate receiving groove  270 . Its thickness is the same as the depth ST 1 , of the second knockup plate receiving groove  270 . 
     Out of the second knockup plate body  310 , the side which is contacted to the second knockup plate receiving groove  270  is defined as a backside of the body, and the other side is defined as a front side of the body. The second knockup plate friction pad  320  having the same thickness ST 2  as the right friction pad  230  of the first knockup plate  210  is attached to the front side. The position of the second knockup plate friction pad  320  is preferably set to be coincident with the pickup roller  240  when the second knockup plate body  310  is moved horizontally to the right. On the other hand, at the backside of the body  310 , a backside guiding groove  330  having a depth slightly deeper than the thickness ST 2  of the right friction pad  230  of the first knockup plate  210  is formed. Moreover, the position of the backside guiding groove  330  is formed to receive the right friction pad  230 , when the backside guiding groove  330  is moved to the right horizontally. 
     Referring to the sectional view of FIG. 7B, the second knock-up plate will be easily understood. The reference numeral  340  which is not illustrated is a guiding bolt including a screw head having a predetermined length, and the numeral  345  is a nut. The guiding bolt  340  is inserted into the guiding slot  290  of the first knockup plate  210  and it is fastened by the nut  345 , thereby preventing the second knockup plate  300  from separating from the first knockup plate  210 . 
     The operation of the paper feeding device having the above-described structure according to the present invention will be explained, with reference to the drawings. FIG. 8A is a perspective view illustrating that the standard paper A is located at the paper feeding device according to the present invention, and FIG. 8B is a perspective view illustrating that the second knockup plate  300  moves towards the right for printing envelopes or postcards, each having a size smaller than the standard paper. Moreover, FIG. 8C is a perspective view illustrating that the preparation for printing the envelopes and postcards B is completed after second knockup plate is moved all the way over to the rightmost position. 
     As shown in FIG. 8A, when printing the standard paper A, the base  215  of the first knockup plate  210  is pulled toward the backside and it is rotated by a predetermined angle. After the standard paper is inserted between the right and left friction pads  230  and  235  and the right and left pickup rollers  240  and  245 , the base  215  is restored to an original state and the standard paper is closely contacted between pickup rollers  240  and  245  and friction pads  230  and  235 . 
     The second knockup plate body  310  has the same thickness as the recess  270  in base  215  of the first knockup plate  210 . In addition, the right and left friction pads  230  and  235  and the second knockup plate friction pad  320  have the same thickness. As a result, friction pad  320  does not hinder the insertion of standard paper A. 
     After completing the printing of the standard paper A, as shown in FIGS. 8B and 8C, when printing a plurality of envelopes and postcards B, the second knockup plate body  310  is simply moved to the right. At this time, the second knockup plate body  310  rides on sloped side wall  275  at which the slope is formed with the second knockup plate receiving groove  270 , located at the front surface of the base  215  of the first knockup plate  210 . Here, the second knockup plate body  310  is not separated from the first knockup plate  210  due to the guiding slot  290 , guiding bolt  340  and nut  345 . When the second knockup plate body  310  rises out of recess  270  in base  215 , the backside of the second knockup plate body  310  is caught by the right friction pad  230  of the first knockup plate  210 . To solve the problem, the backside guiding groove  330  is formed, and thereby the second knockup plate body  310  rises to the front surface of the base  215  of the first knockup plate  210  without being caught by the right friction pad  230 . 
     At this time, the front surface of the second knockup plate friction pad  320  of the second knockup plate  310  is closely contacted to the right pickup roller  240 . Under the state, after pulling the first knockup plate to the backside and rotating it by a predetermined angle, a plurality of the envelopes or postcards are filled. After that, the first knockup plate  210  is restored to the original state and thereby the envelopes and postcards are closely contacted between the right pickup roller  240  and the second knockup plate friction pad  320 . 
     The relations between the left friction pad  235  and the left pickup roller  245  and between the second knockup plate friction pad  320  and the right pickup roller  240  are illustrated in detail in the sectional views of FIGS. 9A and 9B. FIG. 9B illustrates the last one or two sheets remaining after a plurality of the envelopes or postcards are already printed. As shown in the drawing, between the right pickup roller  240  and the second knockup plate friction pad  320 , a gap ST 4  which is smaller than 1 mm is formed. Between the left friction pad  235  and the left pickup roller  245 , a gap which is larger than 1 mm is formed. It is because the thickness ST, of the second knockup plate body  310  is added to the base  215  of the first knockup plate  210 . This results in the second knockup plate friction pad  320  protruding further from first knockup plate  210  than left friction pad  235 . In other words, though the gap of ST 4  becomes zero, the gap of ST 3  does not become zero. Though the envelopes or postcards to be printed is the last one or two sheets, the left friction pad  235  and the left pickup roller  245  are not contacted to each other, thereby removing the problems of any erroneous feeding, a noise, a waste of electric power, a falling off the feeding speed, etc. 
     Though an image forming device such as a printer is illustrated as an embodiment of the present invention, it can also be applied to the document scanning device such as a scanner. 
     While there have been illustrated and described what are considered to be preferred embodiments of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. In addition, many modifications may be made to adapt a particular situation to the teaching of the present invention without departing from the central scope thereof. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the present invention, but that the present invention includes all embodiments falling within the scope of the appended claims.