PAPER FEED CONTROL SYSTEM FOR PRINTERS

Abstract: In a high speed printer, a paper feed speed of a paper feed mechanism is varied by the inventive control system in accordance with a type of paper in use such as a serial form, a cut sheet, or an envelope, and a feed mode thereof such as a tractor feed or a friction feed, or a loading feed or a line feed so that an optimum maximum feed speed can be selected and the through-put of the printer is increased. According to this control system, the loading feed speed at which speed a paper is conveyed in an initial position in the printer prior to the printing operation is slower than the line feed speed at which the paper is forwarded after every line printing operation. To discriminate the paper type or the feed mode, the control system is provided with various sensors or indicating means (35, 36, 37).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed printer, particularly to a system for controlling a paper feeding speed of the printer. 2. Description of the Related Arts Recently, serial printers have become widely used in various information processing devices for the treatment of large amounts of information. The processing speed of the printer has been greatly increased and has reached 130 cps (characters per second), i.e., double the previous speed of 60 cps, for example, in a printer having a 24 dot letter quality. Together with these high speed printers, autoloaders by which paper is automatically fed to the printer has been proposed, for example, in Japanese Examined Utility Model Publication (Kokoku) No. 58-2618 or Japanese Unexamined Patent Publication (Kokai) No. 61-58775. Printers recently made available are applicable to various types of paper, such as serial form sheets, cut sheets or envelopes, corresponding to user requirements e.g. DE-A-2912656. Under these circumstances, problems occur when the paper feed speed is too high, as follows: 1. In the case of serial form paper, a tractor is used for the paper feed, in which the paper is first manually set on pins of the tractor by an operator so that the perforations of the paper match the positions of the pins. However, when all of the pins are not properly engaged with the perforations, as often occurs in the daily use, damage to the perforations may occur to cause jamming of the paper, particularly during a high speed paper feed. 2. In the case of a cut sheet, a friction feed is used in which the paper is fed to the printer by a frictional nip between a pinch roller and a platen. Also in this case, a slip may occur between the paper and the rollers and an accurate paper feed cannot be attained during a high speed paper feed. 3. When an envelope is fed by the friction feed system, a heavier load is applied to the rollers compared to the ordinary cut sheet because the thickness of the envelope is greater than that of the latter, and therefore, the high speed feed is even more unsuitable in this case. Therefore, all printers now available adopt a common slowest paper feed speed at which all kinds of paper can be safely fed, and thus the efficiency of the printer remains low in spite of recent rapid progress in the printing speeds thereof. In a wider sense, the paper feed referred to herein includes two modes of feed; one is a "loading feed" in which a paper is initially fed to a printer prior to commencement of printing and set in a certain position, and the other is a "line feed" in which a paper set in a printer is forwarded one space or several spaces to prepare for the next printing. Accordingly, these terms, "loading feed" and "line feed", will be used throughout the specification and claims hereinafter. In order to increase a through-put of a printer, a speed-up of the line feed is more effective than a speed up of the loading feed, because the number of the line feed is more than that of the loading feed and, further, it is not preferable to increase the loading feed speed too much, for the following reasons: 1. In a printer, a sensor is provided in a paper path for sensing a front end of a paper during the form feed process. By using a signal from the sensor as a trigger, the rotation of a step motor for driving a form feed mechanism is controlled by a program memorized in a controller. In this process, if the loading feed speed is too high, fluttering of the front end of the paper occurs in the passage thereof, and thus sometimes the sensor cannot function and the positioning of the paper remains inaccurate. 2. Even though the paper end has been properly detected by the sensor, another problem is waiting. That is, the signal for sensing the paper end is input to the controller at a sampling instant, which occurs at a predetermined sampling period. Therefore, a time delay of one sampling period may occur, in the worst case, from the issue of the signal to the input of the same. If the loading speed is too high, it is apparent that the error in the travel of the paper according to the signal delay also becomes larger. This error is especially serious because of the recent increase in the use of ruled paper. 3. Recent paper feed mechanisms are provided with a quick starter which instantly starts feeding at a predetermined speed when a start signal is received. If the loading feed speed is set at a high level, the operator of the printer is liable to be startled by this sudden high speed start of the mechanism. In conclusion, preferably, to improve the efficiency of the printer by increasing the through-put, the maximum line feed speed should be selected in accordance with the kind of paper as well as the mode of paper feed, and the loading feed speed should be maintained at a relatively low level. However, printers now available all have a relatively lower line feed speed matching the loading feed speed, and it is impossible to change the speed according to the type of paper. SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems inherent in the prior art paper feed system and provide a high speed printer having an increased through-put, and a control system therefor. Another object of the present invention is to provide a system for controlling a printer by which an optimum feed speed is selectively applicable to various forms of paper. These objects are achievable by a control system for a paper feed mechanism in a printer in which is set in an initial position by a loading feed operation of the paper feed mechanism and is sequentially forwarded by a line feed operation of the paper feed mechanism, comprising means for indicating a loading feed operation to the paper feed mechanism; and means for selecting one paper feed speed from a plurality of loading feed speeds and line feed speeds stored in a memory; whereby a loading feed speed which is different from a line feed speed is selected when a loading feed operation signal is issued to the paper feed mechanism. Preferably, the selected loading feed speed is slower than the line feed speed to be selected in a line feed operation subsequent to the loading feed operation. Advantageously, the means for indicating a loading feed operation is mounted on the printer in the form of a switch to be operated by an operator. Preferably, in a printer in which a paper is set in an initial position by a loading feed operation of a paper feed mechanism and is sequentially forwarded by a line feed operation of the paper feed mechanism, a control system for a paper feed mechanism, according to the present invention, comprises: means for indicating a loading feed operation to the paper feed mechanism; means for selecting one paper feed speed from a plurality of loading feed speeds and line feed speeds stored in a memory; and means for discriminating a type of paper to be set in the initial position; whereby a loading feed speed is selected in accordance with the discriminated type of paper when the signal for a loading feed operation is issued to the paper feed mechanism and a line feed speed which is faster than the loading feed speed is selected for the subsequent line feed motion of the paper feed mechanism. Advantageously, the means for discriminating a paper type is operated by referring to an output from a sensor for detecting a feed mode selected by an operator. Preferably, the means for discriminating a paper type is operated by an output from a sensor for detecting whether a cut sheet feeder is attached to the printer. BRIEF DESCRIPTION OF THE DRAWINGS The other objects and advantages of the present invention will be more apparent from the following description with reference to the drawings illustrating the preferred embodiments of the present invention: wherein Fig. 1 is a perspective view of a high speed printer to which the present invention is applied; Fig. 2 is a diagrammatical side sectional view of a main portion of a paper feed mechanism belonging to the high speed printer; Fig. 3 is a block diagram of a control system according to the present invention; Fig. 4 is one example of flow chart for discriminating a type of paper in the control system according to the present invention; and Fig. 5 is a block diagram of a circuit for realizing one embodiment of the control system according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1, a platen 1 around which a paper (not shown) is wrapped is driven by a paper feed motor (not shown). The paper is pressed onto the platen surface by a bail roller 3. Printing on the paper is made by a printing head 4. The printing head 4 is mounted on a carriage 6 driven by a carriage motor 5 which causes a reciprocation of the head 4 along the width of paper. A structure of a paper feed mechanism of this printer will be described below with reference to Fig. 2. One paper feed mechanism is a tractor 10 which is exclusively used for feeding a paper in a serial form. The tractor 10 comprises an endless belt 13 wrapped around a pair of pulleys 11 and 12. The belt 13 drives a paper 15 in a serial form by engaging a plurality of pins 14 arranged on the belt at a predetermined distance from each other with corresponding perforations provided on the paper 15. Another paper feed mechanism is a cut sheet feeder which may be mounted on the printer as an option and, in this case, a signal is issued to a controller from a sensor, as described later. In this connection, only a guide plate 16 is shown in the drawing, along which a cut sheet 17 can be fed to the printer. Moreover, if a cut sheet feeder is not attached to the printer, the cut sheets may be manually fed one by one through the guide plate 16 by the operator. The cut sheet feeder is provided with a plurality, usually two, of bins A and B (not shown) to store different types of cut sheets, respectively, and one of these bins A or B is selected during the operation of the printer in accordance with a signal from a host unit. In the embodiment described herein, it is assumed that bin A holds ordinary cut sheets and bin B holds envelopes. In the operation of the printer, the tractor 10 or the cut sheet feeder is selected by the operator by a changeover of a lever, the position of which lever is detected by a sensor such as a switch, and thus the controller can discriminate which paper feed mechanism is selected. The paper 15 or 17 fed to the printer is guided along a curved guide 18 covering the bottom of the platen 1, while being forwarded by the surface of platen 1 driven by the paper feed motor, and enters a printing zone formed between the printing head and the platen surface. In this connection, in the case of a serial form paper 15, the paper 15 is forced into a gap between the curved guide 18 and the platen surface by the forward motion of the tractor 10, but in the case of a cut sheet 17, the cut sheet 17 is moved by the nip of the platen 1 and a pinch roller 20 arranged beneath the platen 1. In the drawing, reference numeral 23 designates a stay shaft for slidably guiding the carriage 6 having the printing head 4 mounted thereon. The operation of this mechanism will be described below. In a loading feed of the serial form paper 15, the tractor 10 is driven to forward the paper 15. In association with this motion, the platen 1 also rotates to forward the paper 15 along the curved guide 18 at a predetermined distance so that the front end of the paper 15 is further projected from a gap between the platen 1 and the bail roller 3 in an open position as shown by a dotted line. Then the bail roller 3 is swung to a closed position shown by a solid line to nip the paper 15 between the platen 1 and the bail roller 3 and fix the paper 15 in the initial set position. A sensor 19 is provided midway along the paper path for detecting the front end of the paper as it passes the sensor 19. A detection signal is input to a controller 21 which controls the rotation of the step motor for driving the tractor and the platen by using the signal as a trigger. In the loading feed of a cut sheet, the cut sheet 17 already at the nip point between the platen 1 and the pinch roller 20 along the guide plate 16 is conveyed to the printing zone by the rotation of the platen 1 in the same manner as described before, and fixed in the initial set position by the bail roller 3 in the closed position. In this case, the rotation of the platen 1 is also controlled by the controller 21. The line feed is carried out by driving the platen 1 at a predetermined rotational angle in accordance with a signal issued by the controller 21. In this operation, the loading feed speed as well as the line feed speed are controlled by the controller 21. A method other than that described above is known for setting a paper in an initial position during the loading feed operation. According to the above method, the paper is conveyed only by a normal rotation of the platen to the initial set position. In this case the length of the paper projected from the nip between the platen 1 and the bail roller 3 must be long enough to enable the front end area thereof to be safely caught by the bail roller displaced from the open position to the closed position. Therefore, after the paper has been set in the initial position, a wider blank space is created at the paper end and no printing is possible thereon in the subsequent printing operation by the printing head. This vacant space should be eliminated because this causes an unbalanced appearance of the printed matter and wastes paper. To solve these problems, according to the alternative method, after the paper end having a sufficient length has been nipped between the platen 1 and the bail roller 3 by the displacement of the latter from the open position to the closed position, the platen 1 starts a reverse rotation of a predetermined angle using a signal showing that the bail roller 3 is in the closed position issued from a sensor as a trigger, whereby the paper is moved backward so that the vacant space of the end area is reduced. According to the present invention, an optimum paper feed speed is selected in accordance with a type of paper and/or a paper feed mode in such a high speed printer. A principle of the present invention will be explained with reference to Figs. 3 and 4. A printer 32 carries out a printing operation when receiving a command signal from a host unit 31, such as a word processor. A control unit 33 (corresponding to the abovesaid controller 21) selects an optimum paper feed speed from a predetermined plurality of paper feed speeds in accordance with a type of paper and/or a paper feed mode. More specifically, for example, when four paper types (a serial form paper for tractor feed, a cut sheet for manual friction feed, a cut sheet for friction feed by a cut sheet feeder, and an envelope) and two paper feed modes (a loading feed and a line feed) are prepared for the printer, eight different states can be assumed from the combination of a paper type and a paper feed mode. A method by which the control unit 33 discriminates a present state of the printer is as follows: For this purpose, a control panel of the printer is provided with various kinds of indicating means. The control unit 33 carries out a logical operation in accordance with signals issued from these indicating means and arrives at a conclusion. A first indicating means 35 indicates whether the paper is fed by tractor feed or friction feed by a signal from the aforesaid associated sensor for detecting the position of the changeover lever. A second indicating means 36 indicates whether a cut sheet feeder is attached to the printer or not by a signal from a sensor for detecting the attachment of the cut sheet feeder. A third indicating means 37 is a switch for commanding an automatic form feed by the autoloader when the switch is operated. As shown in Fig. 4, the control unit 33 surveys whether the first indicating means 35 has issued a signal for a tractor feed, and if affirmative, decides that the paper to be used is a serial form paper. This is because only the serial form can be used for a tractor feed. Conversely, if the result is negative, the control unit 33 then surveys whether the second indicating means 36 shows the attachment of the cut sheet feeder, and if the answer is negative, decides that the paper is a cut sheet for manual feed. If the answer from the second indicating means 36 is affirmative, the control unit 33 further surveys a command signal issued through an interface 34 from a host unit 31 such as a word processor. If the signal shows that bin B should be in operation, the control unit 33 determines that the paper is an envelope accommodated in the bin B. If not, it discriminates that the paper should be an ordinary cut sheet. According to the above steps, a type of paper can be discriminated. The control unit 33 selects an optimum loading feed speed from a plurality of predetermined programs stored in a memory such as ROM, and makes the paper feed mechanism of the printer carry out the loading feed operation at the selected loading feed speed when the third indicating means 37 issues an autoloading command signal. When the loading feed operation has been completed and a printing of a first line has been carried out, the control unit 33 determines by a signal from the host unit that a next paper feed should be a line feed, and instantly makes the paper feed mechanism carry out a line feed operation at an optimum speed faster than the loading feed speed, which line feed speed is also selected from the above programs. This line feed is repeated for as long as the signal from the host unit is issued. Due to the above selection of the paper feed speed, a through-put of a printer can be increased while maintaining a smooth printing operation. A more detailed explanation of the present invention will be given below with reference to Fig. 5, showing an example of a circuit block diagram according to the present invention. A processor 48 is operated by a program stored in a ROM 49. First, the processor 48 determines whether a paper feed mode now in use is a tractor feed, by a signal from a feed changeover switch 62. If affirmative, the processor 48 determines that the type of paper needed is a serial form paper. In addition, if an autoload switch 63 is operated, the processor 48 makes a tractor 10 (Fig. 2) operate through a line feed control circuit 57 to convey the serial form paper, for example, at a loading feed speed of 3 in/sec, and set the paper in the initial position. After the paper has been set in the initial position, the processor 48 temporarily stores printing data input in a RAM 50 from a host unit through an interface circuit 51. When a character code has been detected in the printing data, the processor 48 reads a character pattern corresponding thereto from a character generating circuit 52 and sends that pattern to a printing head 54 through a head control circuit 53 for printing. In the printing operation, the processor 48 drives a space motor 56 through a space control circuit 55 so that the printing head 54 occupies a predetermined printing position. After a first line of printing has been completed, the processor 48 drives a line feed motor 58 through a line feed control circuit 57 by referring to a line feed control code indicated in the printing data, so that the paper is conveyed at a predetermined spacing, for example, at a higher line feed speed of 9 in/sec. If the signal from the feed changeover switch 62 shows that the feed mode is not a tractor feed, then the processor 48 surveys whether a cut sheet feeder 60 is attached to the printer by referring to a signal from a CSF (cut sheet feeder) sensor 61. If negative, the processor 48 determines that the paper in use should be a cut sheet for manual friction feed. Under this condition, when the autoload switch 63 has been operated to indicate the loading feed, the paper is set in the initial position, for example, at a loading feed speed of 4 in/sec, and the printing operation is then carried out in a similar manner to that stated before. Subsequently, a line feed operation is carried out at, for example, a speed of 7 in/sec. If the signal from the feed changeover switch 62 shows that the feed mode is a tractor feed, the signal from the CSF sensor 61 shows that the cut sheet feeder 60 is attached, and further, the command from the host unit 41 designates bin A, the processor 48 determines that the paper in use is a cut sheet for friction feed using the cut sheet feeder. Thus, the processor 48 drives the cut sheet feeder 60 through a CSF control circuit 59 so that the paper is set in the initial position, for example, at a loading feed speed of 4 in/sec. The line feed speed in this case is also higher than the loading feed speed, for example, 6 in/sec. It should be noted that the line feed speed for a cut sheet when the cut sheet feeder is used is made lower than that when the cut sheet is manually fed. This is because an additional load burden on the line feed motor 58 due to the attachment of the cut sheet feeder 60 must be reduced. If the feed changeover switch 62 shows no tractor feed mode and the CSF sensor 61 shows the attachment of the cut sheet feeder and the command from the host unit 41 does not designate bin A, the processor 48 determines that the paper in use should be an envelope accommodated in bin B. Thus, the cut sheet feeder 60 is driven, for example, at a loading feed speed of 3 in/sec, through the CSF control circuit 59 so that the envelope is set in the initial position. The subsequent line feed speed of the envelope is, for example, 5 in/sec. Table 1 shows the above-stated examples of favorable combinations of the loading feed speed and the line feed speed corresponding to various types of paper and feed modes. Generally speaking, for all types of paper used in the present invention, a command of line feed operation is issued from a host unit such as a word processor to a printer, together with printing data. While, a command of loading feed operation for a serial form paper and a manual feed cut sheet is issued when an operator operates a switch provided on a control panel of a printer, and a command of loading feed operation when the CSF is used is issued from a host unit in a similar manner as for the line feed command.

Claims: 1. In a printer in which a paper is set in an initial position by a loading feed operation of a paper feed mechanism and is sequentially forwarded by a line feed operation of the paper feed mechanism, a control system for a paper feed mechanism comprising means for indicating a loading feed operation to the paper feed mechanism; and means for selecting one paper feed speed from a plurality of loading feed speeds and line feed speeds stored in a memory; whereby a loading feed speed which is different from a line feed speed is selected when the indication of the loading feed operation is issued to the paper feed mechanism. 2. A control system defined by claim 1, in which the selected loading feed speed is slower than the line feed speed to be selected in a line feed motion subsequent to the loading feed motion. 3. A control system defined by claim 1 or 2, in which the means for indicating a loading feed motion is mounted on the printer in a form of a switch to be operated by an operator. 4. In a printer in which a paper is set in an initial position by a loading feed operation of a paper feed mechanism and is sequentially forwarded by a line feed operation of the paper feed mechanism, a control system for a paper feed mechanism, comprising means for indicating a loading feed motion to the paper feed mechanism; means for selecting one paper feed speed from a group including a plurality of loading feed speeds and line feed speeds stored in a memory; and means for discriminating a type of paper to be set in the initial position; whereby a loading feed speed is selected in accordance with the discriminated type of paper when the indication of the loading feed motion is issued to the paper feed mechanism and a line feed speed which is faster than the loading feed speed is selected for the subsequent line feed motion of the paper feed mechanism. 5. A control system defined by claim 4, in which the means for discriminating a paper type is operated by referring to an output issued from a sensor for detecting a feed mode operated by an operator. 6. A control system defined by claim 4, in which the means for discriminating a paper type is operated by an output issued from a sensor for detecting whether a cut sheet feeder is attached to the printer.

Inventors: IIZUKA, SHINICHI
Applicants: FUJITSU LIMITED
Application year: 1988
Main classification: B41J11
IPC codes: B41J11, B41J13, G06K15