PRINTER

Abstract: The invention provides web, preferably a paper web (3) controlling method for a printer which eliminates specific drawbacks of conventional methods. According to the paper controlling method of the invention, upon shutting off a power source or upon changing over to an on-line mode, a paper feed motor (12) is first rotated reversely to draw back paper by an amount a little greater than an amount of a possible slack therein and is then rotated forwardly to advance the web. By employing the method, possible slack in the paper can be cancelled adjacent a print head (1) in preparation for subsequent printing. Accordingly, high quali­ ty printing can be attained.

Description: This invention relates to a printer wherein a continuous web especially a paper web is fed by means of a tractor. Conventional tractor fed machines operate by having a tractor feed rotating at a particular speed and a driven friction wheel a small distance back which is driven at a marginally slower speed (owing to a marginal difference in the diameter of the two drive wheels). An example of this is described in Japanese laid open Patent 57-39980. With this slight difference in speed which is accommodated by slippage at the friction wheel, the web is always under tension at the printing station. A problem arises at start up since at that time the tension has not then been generated, and the present invention is concerned with this problem. Conventionally, in a printer of this type, even if there is slack in a paper web upon shutting off a power source; after paper feeding or after replacement of paper for example; the printer is used with such slack left as it is. However, in recent years, high quality printing has been required from printers, and to this end, 2 pass printing is performed frequently. 2 pass printing is a method of printing a character by operating each dot print element twice before and after feeding of paper by a minute amount. In 2 pass printing, where a print head which can print, for example, 9 dots in a vertical direction, that is, in a column, a line is first printed with 9 such dots for each column and then the paper is fed by a distance corresponding to one half of the pitch of the dots, and another line is printed again with 9 dots for each column, thereby completing a print line. For example, where the dot pitch in each column is 0.36 mm and the line space is 1.67 mm (1/6 inch), paper will be fed firstly by 1.67 mm and secondly by 0.18 mm. In 2 pass printing, it is necessary to assure smooth paper feeding in order to fully attain the characteristics of the method. Conventionally, however, the print quality is bad with the first print line after closing of a power source or after inserting more paper, and slackening of paper is one of the most significant causes of the problem. Heretofore there has been provided a web controlling method for a printer adapted to utilize a continuous web, said printer comprising a print head opposed to a platen, web feed means including a tractor said printer being adapted to effect n pass printing. It is an object of the present invention to provide a printer which can alleviate the problem of slackening of the web, for example after the closing of a power source or after inserting of a web such as paper, to improve the print quality thereof. European Patent Application 99957 discloses a platen driven printing machine where slack is taken out by drawing the paper back a small amount prior to printing. The present invention is concerned with a tractor driven printing machine and solves the problem by moving the paper back a small amount so that the slack can be taken out as the paper is drawn forward by the tractor drive. Print then commences when the paper is under tension. Accordingly the present invention provides a printer comprising continuous tractor driven web feed means, a print head opposed to a platen, the web being adapted to move between said print head and said platen for printing at a printing station, characterised in that the web feed means includes a motor which is arranged so that at the commencement of printing it is controlled to reverse the web feed means by a small amount dependent on the amount of slack in the web and on the relative stiffness of the web prior to feeding the web forwardly by the same amount to the printing station whereby to take out the slack, after which the printer is arranged to start printing when the paper is under tractor driven tension. An embodiment of the present invention will be described below with reference to the drawings by way of illustration only. Fig. 1 is a schematic side elevational view of a printing mechanism; Fig. 2 is a plan view of a printer; Fig. 3 is a block diagram; and Fig. 4 is a flow chart. Referring first to Fig. 1 which illustrates a general contruction of a printer, the printer basically includes a print head 1 and a platen roller 2 between which a continuous paper web 3 for printing is fed by means of a tractor 4. Referring now to Fig. 2 which illustrates a plan view of the printer, an on-line/off-line change-over switch 6, a form feed switch 7, and a line feed switch 8 are located on an upper face of a printer body 5. Referring further to Fig. 3 which illustrates a control system of the printer, the control system basically includes a central processing unit (CPU1) 9 on the master side and a second central processing unit (CPU2) 10 on the slave side. The CPU1 9 involves reception and editing of print data, production of test data, reading of various switches and processing of such data, and delivers print codes converted into dot patterns to the CPU2 10. A feed command is also delivered to the CPU2 10. Meanwhile, the CPU2 10 operates under control of the CPU1 9 and drives the print head 1, a carrier motor 12 and a paper feed motor 13. The CPU 1 stores data received by way of a receiver circuit 14 into a reception buffer or a print buffer in a RAM 15 connected thereto. In this instance, when requirements for printing are met, the CPU1 9 controls the CPU2 10 to operate the carrier motor 12 and delivers dot pattern data to the CPU2 10. The CP02 10 then drives the print head 1 to effect printing in response to the dot pattern data delivered thereto. After completion of required printing, the paper feed motor 13 is driven to effect required paper feeding. As an additional function, conditions of a dip switch 17 are read upon closing of the power source. On the other hand, the on-line/off-line change-over switch 6, the form feed switch 7 and the line feed switch 8 are read principally to effect feeding operations or changing over operations between on-line and off-line conditions and so on when printing is not performed. Those inputs are all read by the CPU1 9 by way of an input circuit 18. Reference numeral 16 denotes a ROM, and 19 a flipflop. Characteristics of the present invention will now be described with reference to a flow chart illustrated in Fig. 4. At first, the entire system is initialized. Here, the RAM 15 is cleared and inputs such as the dip switch 17 are read for initialization. Then, initial operations are performed, and the print head 1 is returned to its home position to prepare for subsequent printing thereby. Then, paper feeding which is one of the characteristics of the present invention is performed. Thus, the paper feed motor 13 is rotated at first reversely by an amount corresponding to N/144 pulses to draw back paper 3 by a small amount and then forwardly by the same amount, that is, an amount corresponding to N/144 pulses. Here, the distance between adjacent dot print elements on the print head 1 is 0.30 mm (1/72 inch) and in the case of 2 pass printing, the paper is fed by 1/144 inch (about 0.18 mm). The N/144 pulses (inches) correspond to a feed amount corresponding to the height of one character. By such reverse and subsequent forward rotations of the paper feed motor 12, slackening of the paper 3 can be absorbed or cancelled. In this regard, where the amount of slack in the paper 3 when set in a position which can appear between the print head 1 and the tractor 4 is indicated by & and the amount of the paper 3 to be drawn back is indicated by A and where A>&, when the paper 3 is drawn back by an amount A by reverse rotation of the paper feed motor 12 to operate the tractor 4 reversely, the paper 3 is drawn back adjacent the print head 1 with the slack & involved in the drawn back amount A, and hence the slack will be taken up by paper feeding by a following rotation of the motor 12. In particular, the paper 3 has rigidity to some degree, and hence if there is slack in the paper, the paper 3 will be drawn back with the slack maintained. As a result, upon subsequent forward rotation of the paper feed motor 12, the remaining slack of the paper is taken up. Besides, an end of the paper 3 will not come out of position. After completion of the treatment of the paper 3 upon shutting off the power source, the mode is checked to ascertain if the system is in the on-line mode or in the off-line mode. If the system is in the on-line mode, the condition of the line feed switch 8 and the form feed switch 7 are checked, and when either on of the switches 8 and 7 is or has been depressed, either line feeding (LF) or form feeding (FF) is carried out. Now, if it is assumed that line feeding is carried out, there is the possibility that the paper 3 can be re-set manually since the system is in the off-line mode. Thus, also when the on-line mode is entered after such possible paper setting while in the off-line mode, the same paper feeding operation for taking up possible slackening of the paper as described above is carried out. In particular, the paper feed motor 13 is rotated first reversely by an amount corresponding to N/144 pulses to draw back the paper 3 a small amount and then forwardly by the same amount corresponding to N/144 pulses. In this way, also just after changing over from the off-line mode to the on-line mode, reverse and then forward rotations of the paper feed motor 13 are carried out to take up a possible slack in the paper 3. After that when the system is in the on-line mode, reception and editing of data are effected, and then it is checked to see if 2 pass printing is to be effected. Where 2 pass printing is to be effected, a paper feed correction flag is set. Then, if the paper feed correction flag is in the set condition, the paper feed correction flag is reset, and then the paper feed motor 13 is rotated first reversely by an amount corresponding to N/144 pulses to draw back the paper 3 a small amount and then forwardly by the same amount corresponding to N/144 pulses. After then, data printing is effected. If the paper feed correction flag is otherwise not in the set condition, data printing is effected subsequently without carrying out such operations as described above. Subsequently, paper feeding effected. Where this paper feeding involves two different feeding speeds, and the paper is to be fed at a higher speed, the paper feed correction flag is not set. Such setting of the paper feed correction flag when paper is to be fed at a higher speed is intended to prevent possible slackening of the record paper caused by an influence of a back-lash at meshing portions of gear wheels of a paper feed mechanism or by errors between perforations of the record paper and pins of the track. In particular, since there exists a back-lash at meshing portions of gear wheels of a paper feed mechanism, upon paper may move excessively by an amount corresponding to the back-lash in the paper feeding direction due to the inertia of the associated parts of the paper feed mechanism, resulting in slackening of the paper. Fitting errors between perforations in paper and pins fo the track will also slackening in the paper. Thus, in order to cancel such possible slackening of paper where the paper feeding speed is high, the paper feed motor 13 may be rotated first reversely by an amount corresponding to N/144 pulses to draw back the paper 3 a small amount and then forwardly by the same amount corresponding to N/144 pulses. In this manner, according to the embodiment of the present invention, upon shutting off the power source before initiation of actual printing or upon changing over to the on-line mode, the paper feed motor 13 is rotated first reversely and then forwardly to take up possible slakening of the paper 3. Accordingly, in case of 2 pass printing, high quality printing can be attained from the first print line. However, accuracy in paper feeding will be improved also for printing other than 2 pass printing. Further, since the paper feed motor 13 operates upon closing of a power source, operation of the paper feed motor 13 can be checked from this initial operation of the same. It is to be noted that while description has been given of the embodiment in connection with 2 pass printing, the method of the present invention can be actually applied also to n pass printing involving n feeding operations for printing a print line, where n is an interger of at least 1, and preferably is 2. As apparent from the foregoing description, upon closing of a power source or upon changing over to the on-line mode, a paper feed motor is rotated first reversely by a predetermined amount to draw back paper and then forwardly by the same amount to advance the paper in preparation for subsequent printing. Accordingly, when printing is to be initiated, paper is ready without slack, and hence in case of 2 pass printing, high quality printing can be attained from the first print line.

Claims: A printer comprising continuous tractor driven web feed means (4), a print head (1) opposed to a platen (2), the web (3) being adapted to move between said print head (1) and said platen (2) for printing at a printing station, characterised in that the web feed means (4) includes a motor (12) which is arranged so that at the commencement of printing it is controlled to reverse the web feed means (4) by a small amount dependent on the amount of slack in the web and on the relative stiffness of the web prior to feeding the web forwardly by the same amount to the printing station whereby to take out the slack, after which the printer is arranged to start printing when the paper is under tractor driven tension. A printer according to claim 1 characterised by including means for n pass printing.

Inventors: OBA, RYOZO
Applicants: TOKYO ELECTRIC CO., LTD.
Application year: 1985
Main classification: B41J15
IPC codes: B65H23, B41J15