Method and apparatus for controlling print positioning and printer

Abstract: A printer comprises a transfer apparatus (10) for transferring a toner image to paper (1), a paper end positioning member (4) for temporarily stopping the paper carried, a carrying apparatus (2, 3, 5) for carrying the paper to a transfer portion after the paper end positioning member (4) is released, and an apparatus for controlling print positioning which comprises a detector (6, 22) for detecting time which elapses until paper reaches a given position, a calculator (23) for calculating a time delay in the carrying of the paper relative to a set time on the basis of an output signal from the detector (6, 22), and a controller (24, 25) for controlling a carrying speed of the carrying apparatus (2, 3, 5) on the basis of an output signal from the calculator (24, 25).

Description: The present invention relates a method and an apparatus for controlling print positioning according to the preambles of the claims 1 and 3. Such a method and apparatus is known from JP-A-63 60 844. The invention further relates to a printer in which an apparatus for controlling print positioning is incorporated. Each of conventional methods of controlling print positioning, for example, the method disclosed in Japanese Patent Unexamined publication No. 58-144036, employs a printer comprising a photosensitive body carrying a toner image, a charged body for transferring the toner image to paper, a paper end-positioning member for temporarily stopping the paper carried, and carrying rollers for carrying the paper to a transfer portion after the paper end positioning member has been released. The paper end-positioning member is opened and closed to prevent any printing misregistration between the toner image and the paper, and the paper is then held between the carrying rollers and carried at the circumferential speed of the photosensitive drum. In such a conventional method of controlling print positioning, no consideration is given of the printing misregistration caused by variation in the time period which elapses from the release of the paper end positioning member to the holding of the paper between the carrying rollers, and there is a critical problem in that the error of the print position cannot be ignored in a high-speed printer. EP-A-0 079 222 discloses a method of copy sheet registration and a copying apparatus comprising a registration device for moving individual copy sheets along a path into registered contact with a photoreceptor belt. The registration device includes at least one driven transport belt having fingers for moving a copy sheet towards the transfer station. To achieve a paper registration between photoreceptor belt and a copy sheet the speed of the photoreceptor belt, the position of the image on the photoreceptor, the speed of the driven transport belt and the position of the transport fingers on the transport belts are detected by different sensors. Based on such detected parameters the speed of a transport belt is controlled to achieve a registration between the image and an associated copy sheet. From the JP-A-63 60 844 a paper supply controller for a copying machine is known comprising two separated paper detecting sensors disposed between a pair of pinch rollers and a register roller for carrying the paper to an image transfer portion. During the paper supply the rear end of the paper is detected by the both sensors to measure a time in which the rear end of the paper passes between both sensors. This passage time is compared with a reference value to index the linear speed of register roller and control the rotational speed of a pulse motor to achieve a registration between an image carrier and the paper. The object of the present invention is to provide a method and an apparatus for controlling print positioning which are capable of achieving the positioning of a paper end with high precision in a high-speed printer and to provide a printer in which an apparatus for controlling print positioning is incorporated. This object is solved by the features of the claims 1, 3 and 8. Dependent claims are directed on preferred embodiments of the invention. A method of controlling print positioning according to the present invention comprises the steps of temporarily stopping and releasing the paper by at least one driven end-posistioning member, detecting the time which elapses between the release of the paper from the end-positioning member and the detection of the paper at a given position, calculating the time which elapses until the paper reaches the transfer portion on the basis of the time detected in the detecting step, calculating a time difference between the calculated time and a set time which is based on the calculated time and a carrying speed pattern which is previously stored and has at least two speeds, and controlling the carrying speed of the carrying means so that the time difference is compensated before the paper reaches the transfer portion. An apparatus for controlling print positioning according to the present invention comprises at least one driven end positioning member for temporarilly stopping and releasing the paper, detecting means for detecting the time which elapses between the release of the paper from the end-positioning member to the detection of the paper at the given position, calculating means for calculating a time delay until the paper reaches the transfer portion on the basis of the output signals from the detecting means and controlling the carrying speed of carrying means so that the time delay is compensated. The printer according to the present invention comprises a photosensitive body which carries a toner image, a charged body for transferring the toner image to paper, a paper end-positioning member for temporarily stopping the paper carried and carrying means for carrying the paper to a transfer portion after the paper end positioning member has been released. The printer is provided with an apparatus for controlling print positioning which apparatus comprises detecting means for detecting the time which elapses between the release of the paper from the end-positioning member to the detection of the paper at a given position, calculating means for calculating a time delay until the paper reaches the image transfer portion on the basis of an output signal from the detecting means, and control means for controlling the carrying speed of the carrying means on the basis of an output signal from the calculating means. With the method and the apparatus according to the invention the control of the carrying speed is completed before the paper reaches the transfer portion, and the paper is then carried at a speed equal to the circumferential speed of the photosensitive body, whereby any deviation in the carrying speed of the paper and misregistration between the paper and the toner image can be eliminated. DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view partly showing a printer provided with an apparatus for controlling print positioning according to an embodiment of the present invention; Figs. 2 to 5 are side views of the printer shown in Fig. 1 in states wherein paper is at different positions; Fig. 6 is a drawing showing the output states of a central processing unit and a sensor; Fig. 7 is a graph showing a carrying speed pattern for the paper; and Fig. 8 is a perspective view of an apparatus for controlling print positioning and a part of the printer. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a printer provided with an apparatus for controlling print positioning according to an embodiment of the present invention. The printer comprises carrying belts 2 for carrying paper 1 which is separated sheet by sheet from a paper separating unit (not shown), resist belts 3, a paper end positioning member, i.e., a stopper 4, fixed to the resist belt for temporarily stopping the paper, carrying means, i.e., a pair of carrying rollers 5, for carrying the paper 1 to a transfer portion after the stopper is released, at least one sensor 6 for detecting one end of the paper 1 carried after the stopper 4 is released, a pair of lower guide plate 7 and upper guide plate 8, a photosensitive drum 9 which carries a toner image (not shown), and a charged body, i.e., a transfer corotron 10, for transferring the toner image to the paper 1. The carrying belts 2 are rotated at a given speed by being driven by a pair of rollers which are rotatably supported by side plates. (not shown) A pair of rollers for driving the resist belts 3 are rotatably supported by the side plates (not shown) and are driven by a resist driving motor 11 (see Fig. 8). After one end of the paper 1 abuts against the stopper 4, the stopper 4 is driven with the timing which allows the toner image on the photosensitive drum 9 to coincide with the paper 1. The pair of carrying rollers 5 are rotatably supported by the side plates (not shown) to be rotated by a carrying roller driving motor 12 (refer to Fig. 8), of which speed can be controlled. Referring to Fig. 8, the apparatus for controlling print positioning comprises a central processing unit 20, a resist belt driving circuit 21 for actuating a resist driving motor 11 using as a triger an output signal from the central processing unit 20, at least one sensor 6 for detecting one end of the paper, detecting means 22 for counting the time which elapses until the sensor 6 detects the end of the paper after the stopper 4 is released, calculating means 23 for calculating the delay in the carrying of the paper on the basis of an output signal from the detecting means 22, speed setting means 24 for setting the rotational speed of the carrying roller driving motor 12 on the basis of an output signal from the calculating means 23 and a carrying means driving circuit 25. In operation, the paper 1 is separated one after one by a paper separating unit (not shown) and then placed on the carrying belts 2 to be carried, as shown in Fig. 1. The paper is resisted (temporarily stopped) by the stopper 4 which positions at home position A, as shown in Fig. 2. Since the carrying belts 2 are always driven at a constant speed, the paper 1 slides on the surfaces of the carrying belts 2 while the paper 1 is resisted (temporarily stopped) with one end in contact with the stopper 4. The resist belts 3 are then driven with the timing which allows the toner image on the drum 9 to coincide with the paper 1, and the stopper 4 fixed to the resist belts 3 is released, as shown in Fig. 3. More specifically, the resist belts 3 are driven to release the stopper 4 with the timing which allows the time elapsing until the paper 1 reaches the portion below the transfer corotron 10 from the stopper 4 placed at the home position A to agree with the time elapsing until the toner image on the drum 9 reaches the portion below the transfer corotron 10. The paper 1 is again carried by the carrying belts 2, as shown in Fig. 3, and held between the carrying rollers 5, as shown in Fig. 4. It is to be noted that during the time which elapses until the paper 1 is held between the carrying rollers 5 after it is released from the stopper 4, the paper 1 is carried owing to the friction produced between the paper 1 and the surfaces of the carrying belts 2 and there is a deviation in the time elapsing from the release of the paper 1 from the stopper 4 to the holding between the carrying rollers 5 since there is slide between the paper 1 and the surfaces of the carrying belts 2. After the paper is held between the carrying rollers 5, there is no slide between the paper 1 and the carrying rollers 5. That is, the carrying speed of the paper 1 is determined by the rotational speed of the carrying rollers 5. The sensor 6 disposed immediately down-stream the carrying rollers 5 for detecting the end of the paper detects the end of the paper 1, as shown in Fig. 4. The paper 1 carried by the carrying rollers 5 is guided by the lower guide plate 7 and the upper guide plate 8 and brought into contact with the drum 9 in the portion below the transfer corotron 10, as shown in Fig. 5. The toner image is then transferred to the paper 1 owing to the potential difference produced by the transfer corotron 10. Referring to Fig. 6, a time relationship between the trigger signal from the central processing unit 20 for releasing the stopper 4 and an output signal from the sensor 6 is shown. The time Δt n from the rising of the signal for releasing the stopper 4 to the detection of the end of the paper 1 by the sensor 6 scatters for the above-described reason. If the friction between the paper 1 and the surfaces of the carrying belts 2 were increased so that no sliding occurs therebetween, the paper 1 would wrinkl while the paper 1 is stopped by the stopper 4, and it is thus impossible to satisfy the resist function of the stopper 4. Namely, in order to temporarily stop the paper by the stopper 4 while being carried, it is preferable that the friction between the paper 1 and the surfaces of the carrying belts 2 is not excessively large. However, this causes an increase in the scatter of the carrying speed of the paper 1, and the scatter causes the disagreement between the paper 1 and the toner image to degrade the precision of the print position. It is therefore necessary to remove such scatter until the paper reaches the transfer corotron 10. Referring to Fig. 7, the relationship between the time t and the carrying distance in the control method for removing the scatter which degrades the precision of the printing position is shown. In the drawing, a carrying speed pattern (carrying profile) P for the paper 1 having at least two speeds is shown by two-dot chain line. If the paper 1 is carried by the carrying belts 2 in accordance with the ideal carrying profile P and, the carrying rollers 5 are rotated at the same speed as the circumferential speed of the drum 9, the toner image and the paper 1 agree with each other at the position below the corotron 10. However, since the scatter described above occurs in fact, the paper 1 is carried in accordance with the carrying profile Q shown by a solid line and a one-dot chain line, thereby producing a deviation δl in the print position. In order to remove the deviation δl in the print position, the time difference δt between the corresponding points of time when the paper 1 passes through the sensor 6 in the carrying profile Q and the carrying profile P is calculated. On the basis of the result of the calculation, the rotational speed of the carrying rollers 5 is increased so that the time difference, i.e., the delay δt is recovered before the paper 1 reaches the position of the transfer portion, and transfer is performed at a rotational speed V d of the carrying rollers 5 which is again set so as to be the same as the circumferential speed of the drum 9. The control of the speed of the carrying rollers is described below with reference to Fig. 8. That is, the resist driving motor 11 is started through the resist belt driving circuit 21 using as the trigger a signal of the central processing unit 20 which is created from a signal of the electrostatic latent image recorded on the photosensitive body. At the same time, the trigger signal from the central processing unit 20 is transmitted to the detecting means 22. The detection means 22 uses as a trigger this signal to count the time which elapses from the release of the paper 1 from the stopper 4 to the detection by the sensor 6. The calculating means 23 calculates a delay which this time has relative to the reference time based on the ideal carrying profile P. The result of the calculation is sent to the means 24 for setting the speed of the carrying rollers by which the speed of the rollers is set so that the delay δt is recovered. By using the command value of the speed, the carrying roller driving motor 12 is rotated by the carrying roller driving circuit 25 to carry the paper 1. Since the method of controlling print positioning according to the present invention is capable of correcting with high precision the small error produced in the timing of the passage of the paper when the paper is temporarily stopped, the method has the effect of enabling print positioning at a high speed and high precision. Further, since the timing of the passage of the paper is controlled immediately before the transfer portion, the method also has the effect of preventing the positioning from being easily affected by external disturbance.

Claims: A method of controlling print positioning in a printer comprising the steps of carrying a paper (1) to an image transfer portion (10) by carrying means (5), detecting a time which elapses until the paper (1) reaches a given position, calculating a time delay in the carrying of the paper (1) relative to a reference time on the basis of the detected time and controlling the carrying speed of the carrying means (5) on the basis of the calculated time delay and setting the carrying speed of the carrying means (5) so that the time delay is compensated, characterised in that the paper (1) is temporarily stopped and released by at least one driven end-positioning member (3, 4), that the time is detected which elapses between the release of the paper (1) from the end-positioning member (3, 4) and the detection of the paper (1) at the given position, that the time delay is calculated between the reference time and the calculated time that a time is calculated which elapses until the paper (1) reaches the image transfer portion (10) on the basis of the detected time. A method according to claim 1, characterised in that the detecting step is started by an output signal from a central processing unit (20), said output signal being also used as a trigger for driving the paper end-positioning member (3, 4). An apparatus for controlling print positioning comprising carrying means (5) for carrying a paper (1) to an image transfer portion (10), detecting means (6, 22) for detecting a time which elapses until the paper (1) reaches a given position, calculating means (23) for calculating a time delay in the carrying of the paper (1) relative to a reference time on the basis of the detected time, and control means (24, 25) for controlling the carrying speed of the carrying means (5) on the basis of an output signal from the calculating means and setting the carrying speed of the carrying means (5) so that the time delay is compensated, characterised in that at least one driven paper end-positioning member (3, 4) is provided for temporarily stopping and releasing the paper (1), that the detecting means (6, 22) are detecting the time which elapses between the release of the paper (1) from the end-positioning member (3, 4) to the detection of the paper at the given position and that the calculating means (23) are calculating the time delay until the paper (1) reaches the transfer portion (10) on the basis of the output signals from the detecting means (6, 22). An apparatus according to claim 3, characterised in that the driven end-positioning member (3, 4) comprises at least one stopper (4) fixed to resist belts (3). An apparatus according to claim 3 or 4, characterised in that the detecting means (6, 22) comprising at least one sensor (6) disposed immediately down-stream the carrying means (5) for detecting one end of the paper (1). An apparatus according to one of the claims 3 to 5, characterised by a central processing unit (20) and a resist belt driving circuit (21) for driving the paper end-positioning member (3, 4), said control means (24, 25) comprising means (24) for setting the carrying speed of the carrying means (5) and a carrying means driving circuit (25) provided in the carrying means (5). An apparatus according to claim 6, characterised in that the detecting means (6, 22) and the resist belt driving circuit (21) are actuated by using as a trigger the output signal from the central processing unit (20). A printer having a photosensitive body which carries a toner image, a charged body (9) for transferring said toner image to a paper (1), said printer being characterised by using an apparatus according to one of the claims 5 to 7.

Inventors: KAWAUCHI MASATAKA, MATSUNO JUNICHI, OGASAWARA TSUYOSHI, TSUJI YASUYUKI, KAWAUCHI, MASATAKA, MATSUNO, JUNICHI, OGASAWARA, TSUYOSHI, TSUJI, YASUYUKI
Applicants: HITACHI KOKI KK, HITACHI LTD, HITACHI KOKI CO., LTD., HITACHI, LTD.
Application year: 1989
Main classification: G03G15
IPC codes: G03G15, B41J13, B65H9, B65H5