Abstract:
This invention relates to a sheet feeding device having an endless belt for feeding a sheet; multiple rotation members bodies supporting the endless belt and including at least one crown roller, a cylindrical rotational member located between the crown roller and a first body member among the multiple rotation members from the crown roller in the endless belt moving direction.

Description:
This application is a continuation of application Ser. No. 07/482,823 filed Feb. 21, 1990, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a sheet feeding device, more particularly to a sheet feeding device which supplies a wide cutsheet that is greater than B5 in size on an endless belt, utilizing electrostatic absorption. 
     2. Related Background Art 
     Liquid injection recording devices (ink jet recording devices) which record text and images by delivering recording fluid from the recording head utilizing heat energy etc. are widely known. 
     These devices mainly use cutsheets such as sheets of paper or plastic as the recording sheet. This method emits low operational noise compared to other recording methods, and is superior in that its basic mechanical structures are simpler and inexpensive than other devices. This method has been employed in various fields, such as the fields of recording output devices for computers and word processors, for these reasons. 
     Presently, due to demands for high speed recording output the line type recording head which contains a printing area that covers the entire width of the cutsheet is being developed. This method attempts to accelerate the recording process by feeding the recording paper along a fixed recording head while maintaining the paper on a belt or an equivalent method of conveyance using procedures such as electrostatic adsorption etc. 
     However there are, special considerations required to prevent the belt from skewing in the orthogonal to direction the feeding direction, when rotating an endless belt which contains a width longer than the feeding orthogonal direction of the cutsheet. 
     One of the examples of a method for prevention of skewing is a method of moving the idle roller axis so that the belt returns to its original position, according to the skew amount for the belt detected by a sensor. This method is relatively trustworthy, but the device tends to become complex and expensive. Also, there is a problem of the printed character bending in the sub-scanning direction since the belt will be constantly repeat skewing in either direction when utilizing this method. 
     Another example is a method which causes a rib supplied on the inner side of the belt to correspond to the groove on the roller. Under these circumstances, virtually no skewing will occur, but the two disadvantages are that the belt will be expensive and the endurance will be negligible. This signifies that both of the above methods are unsatisfactory in either performance or endurance in spite of their complex devices and high costs. 
     Therefore, there is necessity for belt carriages that utilize the crown roller, which is the simplest method possessing the highest endurance. In this method, there is a necessity to increase the centripetal force of the belt using a larger crown to maintain as little skewing as possible, when the width of the endless belt is larger than the cutsheet feeding orthogonal direction, such as those endless belts containing widths which are larger than 200 mm, or those belts with low rigidity. Under these circumstances, there was a defect in that the unevenness of the intensity or scratches on the belt would cause buckling above the crown roller around the center of the belt, resulting in wrinkling and swelling of the belt. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to provide a cutsheets feeding method which is capable of inexpensive, long term and stabilized operation. It delivers the cutsheet by utilizing a device which has at least one crown roller equipped with a press roller in its upper part. 
     The features of the present invention for accomplishing the above objects is as follows. The cutsheet feeding device consists of a belt carrier device 14 which consists of an endless belt (11) wrapped and rotated on multiple rollers (12, 15 and 17). The cutsheet (3) is fed by said endless belt (11). The width of said endless belt is fabricated larger than said cutsheet (3), and at least one of said multiple rollers is fabricated as a crown roller (15). A cylindrical roller (19) which contacts the surface of said endless belt (11) is supplied between said crown roller (15) and said roller (17) which is the first in the upper feed area side of said crown roller (15), to feed said cutsheet (3). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a slant view of an embodiment of the present invention; 
     FIG. 2 through FIG. 5 are explanatory drawings to indicate the state of operation for the head unit and the cap; 
     FIG. 6 is a flow chart of the ink jet recording operation; 
     FIG. 7 is a layout drawing of the crown roller and the idle roller; and 
     FIGS. 8 and 9 shows embodiments of crown roller. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This section will provide explanations for embodiments of the present invention referring to the drawings. 
     FIG. 1 shows an ink jet recording device 1. The recording head 2 contains 3456 nozzles on the underside, each nozzle located 16 dot/mm apart. These consist of black head 2a, cyan head 2b, magenta head 2c and yellow head 2d. They are fixed and maintained by holder 5 so that the distances between the nozzles for heads 2a, 2b, 2c, and 2d in the feeding direction of the recording paper 3 are constant. The head unit 6 which consists of head 2 and holder 5 is movable in an upward and downward direction utilizing a type of head driving method (not shown). 
     Numerals 7a, 7b, 7c and 7d are caps for securing the openings in each nozzle on head 2a, 2b, 2c, 2d of recording head 2 when it is not used for recording. The caps are movable in X direction utilizing a type of cap driving method (not shown). A sponge like ink absorber is attached to the interior of caps 7a, 7b, 7c and 7d to receive the dry delivering of ink from recording head 2. Numerals 9a, 9b, 9c and 9d are the ink tanks which correspond to heads 2a, 2b, 2c and 2d. The ink for each color advances by capillarity through ink supply tubes 10a, 10b, 10c and 10d to heads 2a, 2b, 2c and 2d. The water heads of ink tanks 9a, 9b, 9c and 9d are set a certain level lower than the nozzles of heads 2a, 2b, 2c and 2d. 
     Numeral 11 is a seamless belt. The belt carrier device 14 consists of rollers 12, 15, 17 etc. described below. In order to feed the recording paper 3, the belt contains an insulation layer 11a (approximately 10 Ωcm) with a thickness of approx. 50 μm on the surface of a 250 μm base thickness. The interior of this belt is grounded by the idle roller 12, and the surface is charged to about 1,500 V by charger 1. 
     A negative charge is applied to recording paper 3 by charger 13, and the recording paper 3 is fed by electrostatic absorption onto the surface of seamless belt 11. The seamless belt 11 is driven in X direction by the belt driving roller 15, which is connected to the driving motor 16. The belt driving roller 15 is a crown roller with a diameter of 22 mm at the center, and 20 mm at both ends. The surface of the middle portion of the belt driving roller is formed as a virtually circular arc. A hard rubber coating at 70 degrees is performed on the 15 mm diameter core bar of this roller. The seamless belt 11 transfers the recording paper 3 in the X direction. 
     Numeral 17 is an idle roller with a 15 mm diameter which pulls the seamless belt 11. Numeral 19 is a presser roller (FIG. 7) with a constantly full length, cylindrical, 15 mm diameter placed in a position approximately 10 mm prior to the driving roller 15 (crown roller) to add constant tension to the seamless belt 11. Numeral 20 is the pinch roller which pressure contacts the seamless belt 11 near the charger 13, and strengthens the adsorption. Other idle rollers 12, 17, 19 excluding driving roller 15 are cylindrical rollers with constant full length diameters. 
     The recording paper 3 is assigned to be transferred by single sheets from the cassette 2 by the paper feed roller 22, then pass between carriage roller 23 and pinch roller 25, through guide 26, then pass between said pinch roller 20 and idle roller 12, then subsequently move onto seamless belt 11. 
     Numeral 27 in FIG. 1 is the cleaning unit which eliminates paper dust etc. from the surface of seamless belt 11. Numeral 29 is the paper eject tray which collects completed recording paper 3, and 30 is the paper feed motor. Numeral 31 is the base along the interior of belt 11, located under recording head 2. 
     Next, the operation of the present invention will be explained referring to FIGS. 2 through 6. 
     FIG. 2 shows the power OFF condition. The openings in heads 2a, 2b, 2c and 2d are secured with caps 7a, 7b, 7c and 7d to prevent the evaporation of ink from the tip of the nozzle. The head unit 6 is raised approximately 1 mm by the head driving method 32 (refer to FIG. 3 and step S2) when the power is turned ON in this condition (refer to step S1 in FIG. 6). 
     If a dry run signal is output, all nozzles will execute the dry run for the prescribed times. The dry run is normally executed when the power is turned ON and when approximately 100 sheets of paper are fed continuously. However, a user may input the signal by button operation when an unevenness in recording occurs (refer to steps S3 and S4 in FIG. 6). Caps 7a, 7b, 7c and 7d move in the direction which is opposite of direction X using the cap driving method 33. The caps are subsequently placed between heads 2a, 2b, 2c and 2d (refer to S5, FIG. 4 and step S5 in FIG. 6). The head unit 6 descends, and the tips of the nozzles are fixed in a recording position, approximately 1 mm from the surface of belt 11 (refer to FIG. 5 and step S6 in FIG. 6). 
     The paper feed motor 30 will turn ON, and a single sheet of recording paper 3 in the cassette 21 will be picked by the paper feed roller 22. The paper will be advanced by guide 28 and be positioned between the carriage roller 23 and the pinch roller 25 (refer to step S7 in FIG. 6). The edge of the recording paper 3 will be detected by the photosensor (not shown) located directly before the resist portion. The edge of the recording paper 3 will contact the resist portion (refer to step S8 in FIG. 6). 
     The paper feed motor 30 will turn OFF (refer to step S9 in FIG. 6) after a determined period of time. The extra sheets of recording paper 3 transferred will bend inside the hollow angle guide 26, and the elasticity of the recording paper 3 will cause the edge to align with the resist portion, maintaining the orthogonality with the feeding direction. The driving motor 16 and the charger 13 will turn ON. The recording paper 3 will be pressure contacted to belt 11 by the pinch roller 20 as it is advanced through the charger 13. The surface of belt 1 will be charged to approximately 1,500 V, and a negative charge is applied to the recording paper 3. The positive charge on the surface of belt 11 and the electrostatic force will cause the recording paper 3 to be adhered to belt 11, and after passing through charger 13, the pressure contact of pinch roller 20 will further secure the absorption. The feeding of recording paper 3 is synchronized with the start of driving motor 16. The recording with each color will begin when the tip of the paper contacts recording head 2 (step S11 of FIG. 6). The completed recorded paper 3 separates from the curvature of belt 11 at the idle roller 17, and is ejected onto the paper eject tray 29 (step S12 of FIG. 6). After the paper ejection process is complete, the driving motor 16 and the charger 13 will turn OFF (step S13 of FIG. 6). 
     If subsequent recordings are not to be executed, the head 2 will rise (refer to FIG. 4), cap 7a, 7b, 7c and 7d will be set (refer to FIG. 3), the head 2 will descend and be secured by cap 7a, 7b, 7c and 7d (refer to FIG. 2) and lastly the power will be turned OFF (step S1 of FIG. 6). 
     If subsequent recordings are to be executed, the dry run signal will be checked. If a dry run signal is detected, the head unit will rise (refer to FIG. 4), the cap unit will be set (refer to FIG. 3), the dry run will be performed, the cap unit will return to its original position (refer to FIG. 4), and subsequently the head unit will descend to the recording position (refer to FIG. 5) (refer to step S15 of FIG. 6). If a dry run signal is not detected, the paper feed motor will turn ON, and the identical recording sequence will be repeated. 
     The seamless belt 11 rotates normally because a centripetal force generated by the seamless belt 11 attempting to move towards the center is strong since the belt driving roller 15 is fabricated as a roller with a large crown. Also, because pressure roller 19 is supplied to add tension approximately 10 mm prior to belt driving 15, there is constant tension applied to the seamless belt 11 immediately prior to belt driving roller 15. The unevenness of the intensity or scratches on the belt will not cause buckling above the crown roller around the center of the belt which result in wrinkling and swelling of the belt. 
     Accordingly, a cutsheet feeding device which is capable of inexpensive long term stabilized operation was produced using a simple structured device which is proficient for normal long term rotation of belt 11. 
     The above embodiments were examples of a color recording device utilizing the 4 recording heads 2a, 2b, 2c and 2d. However, it is unessential to note that an identical effect may be obtained using a standard black and white recording device with only one recording head, or a device employing an equivalent recording method. 
     The diameter of the crown roller 15 is not limited to the value in the embodiments noted here. Also, the position of the crown roller 15 may be different as long as the relative position to the presser roller 19 is maintained. Furthermore, a shorter distance between crown roller 15 and pressure roller 17 is preferable. 
     The cutsheet was fed by electrostatic adsorption to belt 11 in the above embodiments, but methods of feeding such as simply placing the sheet on the belt, or vacuum adsorption of the sheet to the belt is also possible. 
     As conceptually shown in FIG. 8, crown roller 15 is a locus of body of rotation around the axis which consists of a radii that contains a peripheral surface of a radius for curvature R, with diameter d on both ends, and the diameter of the center is the maximum, d2. The peripheral surface may be a body of rotation of a quadratic curve (for example, a part of an ellipse), around the axis. It may also be a roller formed as a cylinder with the maximum diameter d2 in the central portion and with both ends consisting of cones. 
     In the example provided here, it is a locus of body of rotation consisting of a radii which, as in FIG. 9, has d1=20 mm, d2=22 mm, roller length l=230 mm, peripheral surface with radius of curvature R=6700 mm, around the axis.