PROCESS AND APPARATUS FOR SETTING A CUT PRINTING SHEET

Abstract: A printer comprises a cylindrical platen (2) for supporting and feeding a printing sheet (7,8), a pinch roller (4) in resilient contact with the platen to cooperate therewith to feed the cut sheet, and an inclined sheet guide (15) on which a cut sheet (8) is loaded. A leading edge of the cut sheet is inserted into a space between the platen (2) and the pinch roller (4) so that the cut sheet is ready to be compulsorily fed by the platen. When or after a cut sheet (8) is loaded on the sheet guide (15), the platen is rotated in the reverse direction by a pre­ determined amount of rotation and then rotated in the for­ ward direction to set the cut sheet at a given print start posi­ tion. During the reverse rotation of the platen, the leading edge of the cut sheet is pushed up so that the posture of the cut sheet is corrected.

Description: This invention relates to a process and apparatus for setting a printing sheet, especially an individual or cut paper, form, or sheet, hereinafter referred to as a "cut sheet", in a printer. A cut sheet printer usually comprises a cylindrical platen and a pinch roller resiliently in contact with the platen. After a cut sheet is loaded on the printer, the platen is rotated by a line feed controller according to an instruction for feeding the cut sheet. Therefore, the platen cooperates with the pinch roller to feed the cut sheet in the forward direction along a sheet transport passage having a guide member. Along the sheet transport passage, a sheet sensor is provided, by which the presence of the sheet is confirmed. When the sheet is fed by a given distance after the sheet sensor detects a front of leading edge of the sheet, the platen is stopped to set the sheet at a print start position. If, however, the sheet was inclined while being transported, printing would not properly be carried out. That is, the printing would be carried out along an inclined transverse line, or the printing sheet might be crumpled or jammed. Therefore, it is important to prevent the printing sheet, especially a cut sheet, from being inclined. To prevent a cut sheet from being inclined, it has been proposed that two sheet sensors 101A and 101B are provided in a sheet transport passage, as shown in Fig. 4. These two sensors 101A and 101B are arranged along a transverse line perpendicular to the feeding direction of the cut sheet 100. If the sheet 100 is inclined, as shown in Fig.5, when one of the sensors 101A detects the sheet, the other sensor 101B does not detect the same. In such a printer as proposed, if a difference between the detection timings by these two sensors 101A and 101B exceeds a predetermined value, i.e., if the sheet is inclined, the sheet is discharged without being printed. This printer can only discharge the printing sheet if inclined, but cannot correct the inclined sheet to a proper feeding state. Therefore, a printer having a means for automatically correcting an inclined sheet has long been desired. US-A-4 362 409 discloses a process and a printer having the features of the preambles of the accompanying claims 1 and 6. According to this document, a tilted position of the sheet can be corrected by keeping the platen stationary when the leading edge of a sheet has abutted against the platen. The platen is rotated in the reverse direction so as to set the sheet to a print start position. According to one aspect of the present invention, there is provided a process for setting a cut printing sheet in a printer to a given print start position ready for printing, said printer comprising a cylindrical platen for supporting and feeding the cut sheet, at least one pinch roller which in at least a cut sheet printing mode of the printer is in resilient contact with said platen to cooperate therewith to feed the cut sheet, an inclined sheet guide member on which a cut sheet is loaded and from which a leading edge of the cut sheet can be inserted into a space between the platen and the pinch roller so that the cut sheet is ready to be compulsorily fed by the platen and the pinch roller, and means for driving said platen in forward and reverse directions, characterised in that the process comprises rotating said platen in the reverse direction by a predetermined amount of rotation so as to free the sheet after the leading edge of the cut sheet has reached the space between the platen and the pinch roller, and then rotating said platen in the forward direction, so as to set the cut sheet to the print start position without inclining the sheet. According to another aspect of the present invention, there is provided a printer, comprising: a cylindrical platen for supporting and feeding a sheet of paper; at least one pinch roller cooperable with the platen for feeding the sheet; an inclined sheet guide member onto which the sheet may be loaded, for guiding the sheet into contact with the platen; driving means for driving the platen; and control means for controlling the driving means to rotate the platen in forward and reverse directions so as to set the sheet to a given print start position ready for printing; characterised in that said control means is operable to rotate the platen in the reverse direction by a predetermined amount so as to free the sheet after the leading edge of the sheet has reached the space between the platen and pinch roller, and then to rotate the platen in a forward direction, so as to feed the sheet to the print start position without inclining the sheet. An embodiment of the present invention may provide a printer which is capable of automatically correcting the orientation of a cut sheet so as to prevent it being transported in an inclined state. An embodiment of the present invention may provide a printer which is capable of correctly setting a cut sheet at a print start position. Due to the reverse rotation of the platen, even if the cut sheet 8 is initially inclined with respect to the proper feeding direction, the front or leading edge of the cut sheet is pushed up by the platen rotating in the reverse direction, so that the orientation of the cut sheet is corrected to assume its normal posture, i.e. not inclined. The possible vibration of the platen and the pinch rollers may serve to facilitate the correction of the posture of the cut sheet. Reference is made, by way of example, to the accompanying drawings in which: Fig. 1 is a schematic view illustrating a printer embodying this invention; Fig.2 is a flow chart illustrating a process for setting a cut sheet according to an embodiment of this invention; Fig.3 is a schematic view illustrating a process for correcting an inclined cut sheet; Fig.4 is a view illustrating the previous arrangement of sheet sensors according to a previous proposal; and, Fig. 5 is a view illustrating a process for detecting an inclined cut sheet according to the previous proposal. Referring now to Fig. 1, a printer embodying the present invention is shown. In Fig. 1, reference numeral 1 indicates a clutch; 2, a cylindrical platen; 3, a bail roller; 4, pinch rollers (also seen from Fig.3); 5, sprockets for feeding a continuous sheet; 6, a sheet guide for continuous sheet; 7, a continuous sheet; 8, a cut sheet; 9, a carriage; 10, a printing head; 11, a paper guide; 12, a space monitor; 13, a line feed motor; 14, a change lever for continuous or cut sheets; 15, a guide for cut sheets; 16, a printer controller for controlling the line drive, carriage drive, and printing head drive; 17, a paper set switch; ROM, a read-only memory; CNT1, a counter for a present position; CNT2, an integrating line feed counter; S₁, a sensor for detecting a continuous or cut sheet printing mode; and S₂, a sheet sensor. The cylindrical platen 2 serves to support and feed either a continuous printing sheet 7 or a cut printing sheet (individual paper sheet) 8. The pinch rollers 4 are freely rotatably mounted on a roller shaft 4a (Fig.3). The print mode, i.e., a continuous or cut sheet printing state, can be changed by the lever 14. When the lever 14 is turned in one direction, the pinch rollers 4 come into resilient contact with the platen 2, as shown in a solid line in Fig. 1, and the clutch 1 is turned OFF. In this state, the sensor S₁ detects (by the position of the pinch rollers) a cut sheet printing mode in which a cut sheet 8 can be treated. In this cut sheet printing mode, the pinch rollers 4 are in resilient contact with the platen 2, as mentioned above, to cooperate therewith to feed the cut sheet 8 in a line feed direction, as indicated by an arrow P in Fig. 1. At least in this cut sheet printing mode, the cut sheet guide 15 is mounted on the printer so as to be inclined, as seen from Fig. 1, so that, when a cut sheet is loaded on the guide 15, a leading or front end of the cut sheet is inserted into a space between the platen 2 and the pinch rollers 4 by the force of gravity so that the cut sheet 8 is ready to be compulsorily fed by the platen 2. On the other hand, in this mode, the sprocket 5 for transporting the continuous printing sheet 7 is released from its driving source by turning OFF the clutch 1. Under this condition, a cut sheet 8 can be loaded and printed. The cut sheet setting process in this mode will now be described with reference to Fig.2. In Fig.2, S₁ = "0"; a cut sheet printing mode S₁ = "1"; a continuous sheet printing mode S₂ = "0"; sheet absent condition S₂ = "1"; sheet present condition N₁, N₂, N₃, and T₁ are stored in a ROM (in Fig. 1) in the printer controller 16. If cut sheets 8 are to be printed, a single blank cut sheet 8 is loaded on the sheet guide 15 and the sheet set switch 17 is depressed. This depression of the switch 17 is confirmed (step 1) and then the cut sheet printing mode is also confirmed by the sensor S₁, i.e., S₁ = 0, (step 2). These confirmations are conducted in the printer controller 16. Then, the absence of a sheet at the position (after the pinch rollers) where the sensor S₂ is located, is confirmed by the sensor S₂ per se, i.e., S₂ = 0, (step 3). Then, the carriage 9 is moved to a centering position by the space motor 12 (step 4). This movement of the carriage 9, i.e., the carriage 9 is located at the centering position, serves to facilitate that the paper guide 11 mounted on the carriage 9 correctly guides a front end of the cut sheet 8 while the sheet 8 is transported to a print start position. Then, the line feed motor 13 is rotated in the reverse direction by the instruction from the printer controller 16 (step 5), and therefore, the platen 2 is also rotated in the reverse direction, as shown by an arrow Q in Fig. 1. This reverse rotation of the platen 2 is stopped after a predetermined amount of rotation (N₁) is attained (step 6). According to the reverse rotation of the platen 2, even if the cut sheet 8, which has been already inserted between the platen 2 and the pinch rollers 4 along the paper guide 15, is inclined with respect to the proper feeding direction, as seen at 8′ in Fig. 3, the front or leading edge of the cut sheet 8 is pushed up by the platen 2 rotating in the reverse direction, so that the normal posture of the cut sheet 8 is obtained, as shown by a solid line (8) in Fig. 3. That is, while the platen 2 is rotated in the reverse direction, the leading edge of the cut sheet 8 is automatically corrected to align with a transverse contact line between the platen 2 and the pinch rollers 4, and then the posture of the cut sheet 8 is corrected on the basis of the aligned leading edge. The possible vibration of the platen 2 and the pinch rollers 4 serves to facilitate the correction of the posture of the cut sheet 8. After that, the platen 2 is stopped for a predetermined time period T₁ (step 8) which is previously set in the timer (step 7). The time period T₁ provides sufficient time for the correction of the cut sheet 8 to be completed (for setting of the sheet). Then, the platen 2 is rotated (step 9) in the forward direction by the line feed motor 13 until, after the sheet sensor S₂ detects the presence of the sheet, i.e., S₂ = 1, (step 10), a predetermined amount of rotation N₂ is made (step 11). The line feed motor is then stopped at a position (step 12) where the cut sheet 8 is (to be) set at a predetermined print start position. At step 3, if the cut sheet 8 is already present at the desired position, i.e., S₂ = 1, operation is returned to the end, since it is not necessary to set the cut sheet 8. According to the above-mentioned embodiment, the platen 2 is stopped for a predetermined time interval after it is rotated in the reverse direction. Alternatively, the platen 2 may not be stopped, but may be transported in the forward direction, just after it is rotated in the reverse direction. Also, the reverse rotation of the platen 2 may be intermittently executed (e.g. several times). Depending on the size, shape, or material of the cut printing sheet 8, the intermittent reverse rotation may be a particularly favorable method. On the other hand, in a continuous sheet printing mode, the change lever 14 is not returned toward the cut sheet printing mode and the pinch roller 4 is located in a position indicated by a dotted line in Fig. 1. In this mode, when the clutch 1 is turned ON, the sprockets 5 are driven in the forward direction. When the printing mode is confirmed by the sheet sensor S₁ (step 2) after the depression of the sheet set switch 17 is confirmed (step 1), if the continuous sheet printing mode is confirmed, i.e., S₁ = 1, a presence of the continuous sheet is then confirmed using sensor S₂ (Step 21). If the continuous sheet 7 is not present, i.e., S₂ = 0, the line feed motor 13 is driven to rotate the platen 2 in the forward direction (step 22). In this case, the sprocket 5 is also rotated together with the platen 2 and the inserted continuous sheet 7 is guided and fed along the sheet guide 6. The sprockets 5 and the platen 2 are rotated until a predetermined amount of rotation N₃ is attained (step 24) after the sheet sensor S₂ detects the presence of the continuous sheet 7, i.e., S₂ = 1, (step 23). After the completion of this rotation of the sprockets 5 and the platen 2, they are stopped at a position (step 12) where the continuous sheet 7 is (to be) set at a predetermined print start position. At step 21, if the continuous sheet 7 is present, i.e., S₂ = 1, the operation is no longer continued, since it is not necessary to set the continuous sheet 7, (i.e. the sheet 7 has already been set). After the printing sheet 7 or 8 is set at a predetermined print start position as mentioned above, the carriage 9 is moved in the transverse direction and the printing heads 10 mounted thereon are operated according to printing instructions from the controller 16 in a known manner. During the printing operation, line feed of the printing sheet is carried out by the line feed motor 13, also in known manner. In a conventional printer known in the prior art, a printing sheet, especially a cut printing sheet, must be fed to a line position (print start position) at which a front or leading edge thereof is grasped between the bail rollers 3 and the platen 2 and printing is conducted from this line position. Therefore, some width of a top blank margin must be formed at the front edge of the printing sheet. In the conventional printer as mentioned above, if printing was started from the top end of the printing sheet so as to not leave a top blank margin, and if line feeding was executed at the right end position of the sheet, the printing sheet would not be properly fed between the bail rollers and the platen, but might be jammed, because the paper guide mounted on the carriage would not be positioned at the central position with respect to the platen and, therefore, would not sufficiently retain the printing sheet against the platen 2. Usually, only a part of the printing sheet, in the line direction, would be retained by the paper guide. In order to avoid such a top blank margin, an embodiment of the present invention makes it possible for a print start line to be set at an optional line position including the leading edge of the printing sheet by the following solution. In this embodiment, before the printing sheet 8 comes to the print start line position, the carriage 9 is waiting at the centering position. Also, after the printing is started and until the leading edge of the printing sheet 8 is fully grasped between the bail rollers 3 and the platen 2, the carriage 9 returns to the centering position every time a line feed is necessary. That is to say, at the first line, the carriage 9 transversely moves from the centering position to an initial print position, and after the printing is completed in the first line, the carriage 9 returns to the centering position. After the return of the carriage 9 to the centering position is confirmed, the printing sheet 8 is fed to the next line by the platen 2. In this second line, the carriage 9 also transversely moves from the centering position to an initial print position in the second line. Such operations are repeated until at least the leading edge of the printing sheet 8 is fully grasped between the bail rollers 3 and the platen 2, as mentioned above. Therefore, the printing sheet 8 is fed to the next line only when the paper guide 11, which is also mounted on the carriage 9, is positioned at the central position with respect to the platen 2 and retains the printing sheet 8 against the platen 2. Therefore, the printing sheet 8 is not jammed, but properly guided along the paper guide 11 until the leading edge of the printing sheet 8 is fully grasped between the bail rollers 3 and the platen 2. After that, it is no longer necessary to return the carriage 9 to the centering position before line feed is executed. In a block of the controller 16 in Fig. 1, S, L, and M relate to the above-mentioned operations. "S" indicates a predetermined position of the paper guide 11, in the line direction, which is stored in the ROM. Before every line feed is executed, the carriage 9 is positioned at S, where the paper guide 11 is substantially positioned at the center with respect to the platen 2, and thereafter, the line feed is executed. The position of the carriage 9 is counted by the CNT1. Therefore, when the printing of a particular line is complete, if the count value differs from S, the carriage 9 returns to the centering position (S). "L" indicates a predetermined amount of line feed, which is stored in the ROM. "M" indicates an accumulated amount of line feed from the print start line position and is counted by CNT2. Comparing this M with the above-mentioned L and returning the carriage 9 to the centering position (S), is repeated until M is equal to L. In a development of the embodiment of Fig 1, a further sensor (not illustrated) is employed to detect the presence or absence of a cut sheet 8 on the paper guide 15. The further sensor may be located in the vicinity of the paper guide 15, in particular in the vicinity of the space between the pinch rollers 4 and platen 2 on the side facing the paper guide 15. In this development, the flowchart of Figure 2 is modified by the addition of a new process step between steps 2 and 3, in which the presence or absence of a cut sheet 8 on the guide 15 is determined. If the further sensor detects the presence of a sheet, and S₂ detects absence of a sheet at its location at a point beyond the pinch rollers 4 (step 3) then the process of reverse and forward rotations as described above (steps 4 to 12 in Figure 2) is carried out. On the other hand, if the further sensor detects the absence of a sheet, this indicates that no sheet has been loaded into the paper guide 15 and so no processing is effected.

Claims: 1. A process for setting a cut printing sheet (8) in a printer to a given print start position ready for printing, said printer comprising a cylindrical platen (2) for supporting and feeding the cut sheet, at least one pinch roller (4) which in at least a cut sheet printing mode of the printer is in resilient contact with said platen to cooperate therewith to feed the cut sheet, an inclined sheet guide member (15) on which a cut sheet (8) is loaded and from which a leading edge of the cut sheet can be inserted into a space between the platen (2) and the pinch roller (4) so that the cut sheet is ready to be compulsorily fed by the platen and the pinch roller, and means (13) for driving said platen in forward and reverse directions, characterised in that the process comprises rotating said platen (2) in the reverse direction by a predetermined amount of rotation so as to free the sheet after the leading edge of the cut sheet has reached the space between the platen and the pinch roller, and then rotating said platen in the forward direction, so as to set the cut sheet (8) to the print start position without inclining the sheet. 2. A process as claimed in claim 1, further comprising a step of detecting whether or not a cut sheet (8) is loaded on said sheet guide member (15), and wherein said rotating steps are carried out after loading of a cut sheet on said sheet guide member has been detected. 3. A process as claimed in claim 1 or 2, wherein said platen (2) is stopped for a predetermined time interval after rotation in the reverse direction and then rotated in the forward direction. 4. A process as claimed in claim 1, 2, or 3, wherein said platen (2) is intermittently rotated in the reverse direction. 5. A process as claimed in claim 1,2, or 3, wherein said rotating steps are repeated a plurality of times. 6. A printer, comprising: a cylindrical platen (2) for supporting and feeding a sheet (8) of paper; at least one pinch roller (4) cooperable with the platen for feeding the sheet; an inclined sheet guide member (15) onto which the sheet may be loaded, for guiding the sheet into contact with the platen; driving means (13) for driving the platen; and control means (16) for controlling the driving means (13) to rotate the platen (2) in forward and reverse directions so as to set the sheet (8) to a given print start position ready for printing; characterised in that said control means is operable to rotate the platen in the reverse direction by a predetermined amount so as to free the sheet after the leading edge of the sheet has reached the space between the platen and pinch roller, and then to rotate the platen in a forward direction, so as to feed the sheet to the print start position without inclining the sheet. 7. A printer as claimed in claim 6, further comprising a sensor (S₁) for detecting whether or not a sheet has been loaded onto the guide member, and wherein the control means (16) is operable to perform said reverse and forward rotations of the platen (2) in response to detection by the sensor of a sheet (8) loaded onto the guide member. 8. A printer as claimed in claim 6 or 7, wherein the control means (16) is operable to stop the platen (2) for a predetermined time interval following the reverse rotation, so that the freed sheet is allowed to settle into a correct orientation before the forward rotation takes place. 9. A printer as claimed in claim 6, 7, or 8, wherein the control means (16) is operable to perform further reverse and/or forward rotations of the platen (2) before feeding the sheet (8) to the print start position ready for printing. 10. A printer as claimed in claim 6, 7, 8 or 9, further comprising a print start position sensor (S₂) for detecting the presence of the sheet (8) at the print start position, wherein the control means (16) is responsive to the print start position sensor to prevent said reverse and forward rotations of the platen (2) when the sheet is already present at the print start position.

Inventors: ENDO, TETSU, IDOUJI, SHIGEKI, INOMATA, MITSUGU KUINHAITSU KUJI 306, MAEKAWA, TAKASHI, NAKAO, FUMIO, NOBUE, KAZUO, SHIMAZAKI, MASAKI, UCHIYAMA, KANEASTU
Applicants: FUJITSU LIMITED
Application year: 1986
Main classification: B41J13
IPC codes: B41J13, B41J11