GB2238020A

GB2238020A - Electrophotographic printer

Info

Publication number: GB2238020A
Application number: GB9024575A
Authority: GB
Inventors: Tomoyuki Nishikawa; Masahiro Kita; Takaaki Yano; Tatsuya Yoshida; Ryoji Honda; Shoji Kamasako; Tsutomu Sato; Kiyoshi Negishi
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 1989-11-10
Filing date: 1990-11-12
Publication date: 1991-05-22
Anticipated expiration: 2010-11-12
Also published as: DE4035716A1; GB9024575D0; AU637158B2; GB2238020B; DE4035716C2; AU6654890A

Abstract

An electrophotographic printed is capable of using a plurality of types of continuous form recording media having different page lengths respectively. in the printer, a photoconductive member is charged and exposed to light carrying image data to form a latent image. One of the plurality of types of recording media is selected, and a portion of the photoconductive member corresponding to a page of the selected one of the plurality of types of recording media is exposed to the light.

Description

1 PRINTER The present Invention relates to a printer capable 10of using a

plurality of types of continuous form recording sheet respectively having different page lengths.

Dot Impact type line printers are generally employed as those for printing output data from small 15computers on continuous form recording sheet. Such a line printer is designed to start printing with the storage of printing data on line basis.

The continuous recording sheet Is so called a fan-fold sheet which Is foldable and provided with 20perforation lines. The foldable part Is supplied with perforation lines so that the part may be torn off easily. In this case, the printer is often arranged so that It prints data in a portion other than the perforated part, so that the data thus printed is 25prevented from being cut apart when the paper Is torn 2 off.

In the meantime, there has been proposed a printer using the continuous recording sheet employing an electrophotographic image transfer system in view of!Improving printing speed and the like.

Electrophotographic image transfer system is the art of printing data through the steps of exposing the charged circumferential surface of a photoconductive drum to light to form a latent Image thereon, lQleveloplng the Image thus exposed to light by sticking toner thereon, transferring the image onto the recording sheet, and fixing the image by means of a heat roller. The electrophotographic transfer system is generally utilized for copying machines and the 1!1 Ike.

When the electrophotographic system is used as a printer using a cut sheet type recording medium, the distance between the transfer and the fixing position is unimportant as it Is only necessary to consider 2q)rInter data on a single sheet. In case of a printer using a continuous recording sheet, however, it Is important to decide the portion to be fixed. If all of the transferred toner image is fixed when printing is terminated, it Is wasteful of the sheet by a length 25equivalent to the aforementioned distance.

Z 3 Consequently, the problem posed then is the extent to which the data transferred onto the recording sheet Is fixed.

When printing performance is taken into 5consideration, the interruption and restart of transfer and fixation respectively should preferably be made such that the perforated part where data to be printed is discontinued is located at the transfer and fixing position. For this reason, perforation lines serving 10as page-to-page divisions should preferably be located at the transfer and the fixing position when printing is stopped.

With this arrangement, one page of the recording sheet bearing an unfixed toner image is left between 15the transfer and the fixing position when the printer is on standby condition after a normal printing operation Is terminated. When data equivalent to the following one page is transferred, the existing page Is subjected to fixation and is discharged. The 20continuous sheet is thereby prevented from being wasted by not effecting fixation each time a transfer is made.

There are two kinds of continuous sheet generally in use: naTnely, 11inch (27.94 cm) and 12-inch (30.48 cm) long per page. The aforementioned space between the transfer and the 25fixing position has to be determined, depending on the 4 page length of the sheet for use.

However, it is common that the positional relation between the transfer and the fixing position has been fixed and besides the diversified control is exercised 51n conformity with the fixed paper length. It is consequently impossible in principle for a conventional printer to use a plurality of sheets of paper different in one-page length.

It is therefore an object of the present invention to provide an improved printer capable of printing data on dIfferent kinds of paper different in one-page 151ength.

For the above object, according to the invention, there Is provided an electrophotgraphic printer capable of using a plurality of types of continuous form recording media having different page lengths, 20respectively, said printer comprising a photoconductive member to be charged and exposed to light carrying Image data to form a latent image, said printer further comprising: select means for selecting one of said plurality 25of types of recording media; and : 1 control means for controlling said printer In such a fashion that a portion of said photoconductive member corresponding to a page of the selected one of said plurality of types of recording media Is exposed to the 5 light.

An example of the present invention will now be described with reference to the accompanying drawings, in which:- Fig. 1 is a schematic sectional view of a printer 10embodying the present invention; Fig. 2 is a top view of the paper conveying portion of a printer of Fig. 1; Fig. 3 is a perspective view of a scraper; Figs. 4 and 5 are side views of the waste toner 15sensor; Fig. 6 shows a disc for use In generating PFS pulses; F1g. 7 illustrates a construction of a conventional liquid crystal display panel; Fig. 8 shows a construction of a liquid crystal display panel of the printer of Fig. 1; Fig. 9 is a block diagram Illustrating a control system In the printer of Fig. 1:

Figs. 10 and 11 are graphs illustrating 25temperature control of the heat roller for the printer 6 of Fig. 1; Fig. 12 is a graph illustrating power supply control of the printer of Fig. 1; Figs. 13 and 14 show a flowchart illustrating the.5 performance of the printer embodying the present invention; and Fig. 15 Is a flowchart illustrating an exposure start procedure.

A printer 100 shown in Fig. 1 is a laser beam printer employing an electrophotographic image transfer system. The printer 100 comprises in sequence a transfer unit 10 including a photoconductive drum 11, a tractor unit 20 having an endless belt 21 for feeding a recording sheet, and a fixing unit 30 having a pair of rollers 31, 32 for heating and pressing an unfixed toner Image in order to fix it on the recording sheet.

20Light carrying printing data from a host computer or the like Is emitted from a laser scanning unit (LSU) 13, the charged circumferential surface of the photoconductive drum 11 is exposed to the light and a latent image Is formed on the circumferential surface 25of the photoconductive drum 11. Toner is stuck to the 7 circumferential surface of the photoconductive drum 11 to develop a toner Image by a developing unit 14. Then the toner image is transferred onto the recording sheet at a transfer charger 15, and the image thus 5transferred is fixed by a fixing unit 30. The printer 100 employs the electrophotograllic Image transfer system, and so it Is designed to be a page printer which starts printing after the printing data for one page Is accumulated. The laser scanning unit 13 is 10secured to an upper cover UC. The upper cover UC is rotatably disposed on the main body of the printer 100 so that it can be rocked around a pivot axis P.

The printer of this embodiment is designed to use the continuous recording sheet whose one-page length is primarily 11 inches (27.94 cm), so that the set distance between the transfer unit 10 and the fixing unit 30 is 11 inches (27.94 cm). Further, this printer is designed as what is capable of use of two kinds of paper, namely 11 inches (27.94 cm) and 12 inches (30.48 cm) in one- page length as described later, and the switching between these two kinds of page lengths is effected by switching the operation of the printer through software.

The transfer unit 10 comprises a charger 12 for charging a photoreceptor material on the 25circumferential surface of the photoconductive drum 11 8 with electricity, the laser scanning unit 13 for exposing light to the photoconductive drum 11, the developing unit 14 for sticking toner to the latent image formed on the photoconductive drum 11, the transfer 5charger 15 for charging the recording sheet FP with electricity to cause the toner image to be transferred to the recording sheet FP, a cleaning unit 16 for removing the residual toner on the drum, and a discharging LED 17 for totally exposing the photoconductive drum 11 to light so as to remove the charge thereon. The exposure position and the transfer position on the circumferential surface of the photoconductive drum 11 are apart from each other by 1.5 inches (3.81 cm).

The photoconductive drum 11 should be exchanged after being used for printing a certain number of pages, since it will deteriorate in its properties and fail to ensure clear printing. For example, a limit of use is set at approximately 20,000 pages. The number of 20printed pages are electrically counted and recorded in a counter by a control system which is described later. This counter is reset when an upper cover UC is shut after a new photoconductive drum 11 is installed.

An outwardly protruded projection (not shown) is 25provided on a new photoconductive drum 11. As the i 9 projection presses down a reset switch, not shown, on the body side, the control system can detect that the new photoconductive drum 11 is placed In position. The projection retracts when the operation Is started and an Indication of the new drum disappears. The control system resets the counter when the upper cover UC is shut after the reset switch is turned on.

The laser scanning unit 13, which is secured in the upper cover UC, continuously deflects ON/OFF- modulated beams from a semiconductor laser (not shown) by means of a polygon mirror 13a. The laser beams are converged by means of an fO lens (not shown), reflected by a beam bender 13b so that scanning lines are formed on the photoconductIve drum 11, then an electrostatic latent Image on a dot basis Is formed as the drum rotates.

The developing unit 14 comprises a toner case 14a In which toner Is accumulated, a developing roller 14b for sticking the toner onto the circumferential surface of the photoconductive drum 11 provided at the lower end of the case 14a, and a piezoelectric sensor as a toner low sensor 14c for detecting the presence or absence of the toner in the case 14a.

In normal text printing, the printing of letters are started from the left-hand side of paper so that frequency of use of toner normally tends to become high In a portion corresponding to the left-hand side of the paper. For this reason, the toner low sensor 14c is provided In the portion corresponding to the left- hand side of the paper where the toner consumption is large.

Heretofore, two dry development methods have been generally known. One of them is a so-called monocomponent development method, and the other Is a twocomponent development method.

In the two-component development method, carrier is mixed with toner, and stirred at relatively high speed by a scraper or the like in order to charge the toner. On the other hand. in the monocomponent development method, toner is fed to a developing roller or the like without using carrier for charging the toner. This monocomponent development method is disclosed In the U.S.P. No.3,909,258. However, there Is a problem in this monocomponent development method.

That Is. the toner tends to form a block in a toner box. In order to overcome the above problem, an Improved monocomponent development method, in which relatively little amount of carrier Is mixed with the toner, is disclosed In the U.S.P. No.4.640,880. With mixture of a little amount of carrier with the toner, 11 lubrication between the toner grains is Improved, which prevent the toner from forming blocks. It should be hoted that the mixture of the carrier does not affect chargeability of the toner. In this improved monocomponent development method, the main function of the scraper is to feed the toner to the developing roller or the like. Accordingly, the scraper rotates relatively slowly In the toner box. In the printer of the embodIment, the above-said Improved monocomponent development method Is employed.

A scraper 19 Is provided in the toner case 14a. The scraper 19 slowly rotates to supply the inner toner to the developing roller 14b. The scraper 19 Is, as shown In Fig. 3, composed of a rotary shaft 19a to be driven by a main motor, and four pieces of blades 19b, 19c, 19d, 19e fItted such that the angle between the- surfaces of the blades 19b arid 19c Is 90 degrees, thal of the bl-ades 19b and 19d Is 180 degrees, arid that or the blades 19b arid 19e Is 270 degrees. In this specification, this angle w 11 be called a mounting angle, I.e., the mounting angles, with respect to the blade 19b, or the 1)].,ioes 19c, 19d, and 19e are sm degrees, 1.80 degrees, ind 270 degrees, respectIvely. The blades 19b through 19e are driven to rotate Iii tile direction of the arrow shown in Fig. 3.

12 Since the four blades are arranged to have different mounting angles, It becomes possible that the load applied when the toner is forced out is as onequarter as that of the conventional scraper having all the blades set to have the same mounting angles. Consequently, the load applied to the motor decreases and fluctuates less with the scraper of this embodiment, thus suppressing noise generation.

By sequentially making the mounting angles of the blades of the scraper 19 different as stated above, a certain amount of toner can be gradually moved to a portion corresponding to the right-hand side of the Paper as the scraper 19 slowly rotates.

When toner consumption in the portion corresponding to the right-hand side of the paper increases as it Is used for a graphic output, for instance, toner low is left undetected by the toner low sensor 14c. In such a case, as the conventional scrapers do not have a function to move the toner in the manner stated above, carrier may be transferred onto the circumferential surface of the photoconductive drum 11.

With the scraper in this embodiment, the occurrence of the carrier being transferred on the photoconductive drum 11 is made avoidable even when the 13 toner consumption is large on the side where the toner low sensor 14c is not provided.

The transfer charger 15 is secured to an arm 15a which can be rotated by a cam mechanism around a pivot shaft Ll. Moreover, a pair of guide rollers 18a, 18b are Integrally secured to the arm 15a, the guide rollers 18a and 18b being laterally porsitioned so that the continuous form recording sheet FP is nipped therebetween.

When printing is started, It Is needed to idly rotate the photoconductive drum 11 without feeding the recording sheet until the exposed portion of the photoconductive drum 11 is located at the transfer position. In this case, the arm 15a is moved down to lower the guide rollers 18a, 18b, and accordingly, the recording sheet FP Is retracted from the circumferential surface of the photoconductive drum 11. The life of the photoreceptor material Is thus prevented from being shortened because of wearing. In addition, the paper is also prevented from being soiled by residual toner on the photoconductive drum 11.

An opening Is formed in the transfer charger 15. The opening of the transfer charger 15 is arranged so that its rearward half In the feeding direction of the recording sheet FP Is covered with a Mylar film 15b, 14 and the discharging area, which is uncovered, of the transfer charger 15 Is arranged at the upstream side in the rotational direction of the photoconductive drum 11 with respect to the contact portion between the photoconductive drum 11 and the recording sheet FP.

Conventionally, the whole opening of a transfer charger has been left opened for charging. With such a setting, however. transfer efficiency tends to considerably vary as ambient humidity changes.

BY narrowing the discharge area, corona discharge efficiency can be increased to prevent toner from being reversely charged under the influence of the corona discharge. Moreover, the period of time In which the recording sheet FP contacts the photoconductive drum 11 under pressure after toner Image is transferred thereto can be set longer than that of conventional printers. As a result, transfer efficiency in the whole humidity range can be by far Improved. Experiments show that the transfer efficiency is Improved to a great extent especially when humidity Is low. It is also possible to arrange the transfer charger 15 itself in upstream side in the sheet feed direction in order to prolong the period of time for applying pressure after transfer.

The toner sticking to the photoconductive drum 11 is not totally removed therefrom after the termination of the transferring process. As the residual toner is unnecessary for next printing, It Is removed by a cleaning unit 16. The waste toner thus removed is stored in a waste toner box 60 detachably fitted to the side of the photoconductive drum 11 as shown in Fig. 2.

When a certain amount of waste toner Is accumulated in the waste toner box 60, it overflows into the printer unless it is discarded. The waste toner may soil the Inside if printing is started without the waste toner box 60.

In conventional printers, sensors have been used to respectively detect the presence or absence of such a waste toner box 60 and the full condition of the waste toner box 60. The problem is that the plurality of sensors thus required tends to render the control system complicated.

In the printer or tile the present embodiment, only one sensor is used to detect both conditions.

Fig. 4 illustrates the detecting mechanism. The waste toner box 60 is movably inserted along a guide of the body, the waste toner box 60 being vertically movable. An actuator 62 is rotatably pivoted about a fulcrum 61 on the body such that a contact portion 62a 16 is located at a position where the bottom side of the waste toner box 60 Is located. A fan-shaped portion 62b is provided at the other end of the actuator 62, and a light-shading wall 62c is formed on the arcuate peripheral edge of the fan-shaped portion. The lightshading wall 62c is capable of crossing the space between a light receiving element and a light emitting element of a photo-interrupter 63.

if the waste toner box is not attached, the actuator 62 is caused to revolve clockwise by its own weight as shown by a contInuous 1 Ine in F1g. 4 so that fts contact portion 62a ascends and the light-shading wall 62c Is located under the photo-interrupter 63. In this state, the photo-interrupter 63 produces a signal Indicating that no rays of light are shaded and the control system decides that an error relating to the waste toner box 60 has occurred.

When the waste toner box 60 is attached, the contact portion 62a is forced down by the weight of the box and the actuator is revolved counter-clockwise up to a substantially horizontal state as shown by a broken line of Fig. 4. The light-shading wall 62c is set in a position where It screens the photo-interrupter 63. In this state, the photo-interrupter produces a signal Indicating that the rays of light are shaded and the 17 control system decides that no error relating to the waste toner box 60 has occurred.

When the waste toner box 60 is filled with the waste toner, the contact portion of the actuator is caused to descend further due to the weight of accumulated toner as shown in Fig. 5 and the lightshading wall 62c moves up to the left-hand side (as shown) of the photo-interrupter 63. In this state, the control system decides again that an error relating to the waste toner box 60 has occurred.

In this way, one sensor can be used to detect that the waste toner box 60 Is not Installed and that the waste toner box 60 Is filled with the waste toner. Although this sensor is so arranged as to monitor the presence or absence of the waster toner box and the amount of waste toner from the balance In weight between the actuator 62 and the waste toner box 60, it is possible to employ a spring or the like to hold the balance as well as the dead load of the actuator 62.

The tractor unit 20 is arranged so that, as shown In Fig. 2, the two endless belts 21, 21 stretched between a driving shaft 23 a, (1r-fvel) shart 22 are drIven by a main motor 40 via a field clutch (not shown, hereinafter called the F clutch) and a gear train (not shown) provided In a box 41.

The gear train extending from the maJn motor 40 up 18 to the driving shaft 23 in the tractor unit 20 is arranged so that the continuous recording sheet FP is fed at the velocity of 50 mm/sec. if the tractor unit 20 is independently feeding the recording sheet Pp. 5 Moreover, the gear train contains a unidirectional clutch which races with a predetermined resistance in compliance with a tension when the paper is drawn at a rate higher than 50 mm/sec,(preventing inotor overdriving). The driven shaft 22 is connected with a disc 25 via a chain 24. Tile disc 25 is rotatable in response to the rotation of the driven shaft 22. As sbown in Fig. 6, the disc 25 is provided with slits 25a which are apart from each other by a predetermined space. The disc 25 is provided beLween the light PinitLing 15member and the liqht receivinq member of the photoInterrupter 26, and a pulse corresponding to the moved amount of recording sheet FP is obtainable. The photoInterrupter 26 is hereinafter called the PFS (Paper Feed Sensor) with its output as a PFS pulse.

The PFS pulse is outputted such that when the recording sheet is fed by 1/2 inch (1.27 cm), one pulse is outputted. Further, the signal corresponding to the slit portion 25a and the signal corresponding to the portion other than the slit 25a correspond to the perforated lines of the continuous recording sheet FP 19 and tho non-perforated portion, respectively.

The posittonal relation between. the disc 25 for use in generating the PFS pulse and a base plate on which the photo-interrupter 26 is mounted 5 may not be the same in individual printers because of assembly errors. If the slits 25a formed in the disk 25 are rectangular along the radius, the pulse width thus outputted may vary depending on where the photointerrupter 26 has detected the sl i ts 25a In Hic I'adial direction of the dl-,3(,- 25, and depending on when the relative position between the disc 25 and the photo-interrupter 26 radially shifts.

As this printer is arranged so that the paper feed error is judged from the detection of the PFS pulse, the variation of the pulse width may result in misjudgment on the error.

For this reason, the slit 25a formed in the disc 25 is fan-shaped so that its width gradually increases toward the circumference. In other words, the slit 25a is defined by a pair of radii of the disc 25. With this fan shape, the ratio between the slit portion 25a and the portion other than the slit 25a remains constant so that the width of the pulse thus outputted can be unified irrespective of the position where the photo-interrupter has detected the slit in the radial direction of the disc 25, thus preventing the misjudgment on the error. In addition, the assembly precision required is eased and hence assembly workability is improved.

Sensors for detecting paper errors will 1)e subsequently described.

In a conventional laser printer using cut sheets, two sensors are provided along a sheet feed path to detect the jamming of recording sheet. Paper errors are detected when the sheet does not pass the downstream side sensor a predetermined time after it passed the up-stream side sensor. Since there are no breaks in the continuous recording sheet, the aforementioned method of detection cannot be utilized in a printer using a continuous recording sheet.

In this printer 100, there are provided four kinds of sensors for detecting the presence or absence of the paper along the sheet feed path. The sheet empty and paper jamming conditions are detected by detecting the changing of a sheet feed speed and the lifting up of the sheet.

The first sensor is an empty sensor 50 provided between the feed port 1 and the transfer unit 10. This printer 100 does not print on the portion adjacent to the perforated lines which are used as a break between pages. The perforated lines are located right under the photoconductive drum 11 of the transfer unit 10 and i 21 at the position of the fixing rollers 31, 32 when printing Is stopped In this printer 100. The sheet empty condition can be detected from the output of the empty sensor 50 when the last page of the recording sheet FP is located in the printer. Moreover, it is detectable by counting the PFS pulses that what portions of the recording sheet positioned at the transfer unit 10, at the fixing unit 30, and further at the empty sensor. Consequently, the counting of the PFS pulse and the output of the empty sensor 50 can be used to detect the recording sheet FP being torn off at a non-perforated portions.

The second sensors comprise skew sensors 51, 51 provided between the fixing unit 30 and the tractor unit 20. The skew sensors 51, 51 are used for detecting the skew and cutting-off of the continuous recording sheet FP. The sensors 51, 51 are capable of detectJng the sheet when at least one side thereof lifts up.

The third one is a top sensor 52 provided in the central part between the skew sensors 51, 51. The top sensor 52 Is used for detecting the leading end of the paper when the printing Is started. After the predetermined numbers of the pulses have been counted after the leading end of the recording sheet 17P passed 22 the top sensor 52, the leading end thereof reaches the fixing unit 30, whereas the following perforations are positioned at the transfer unit 10.

The fourth one is a jam sensor 53 provided In the upper cover UC substantially opposite to the top sensor 52 with the sheet feed path therebetween. The jam sensor 53 Is used for detecting the sheet when the sheet is Jammed In the fixing unit 30 and the central part of the recording sheet swells out to contact the jam sensor 53.

The fixing unit 30 comprises a heat roller 31 provided in the upper portion of Fig. 1, and a press roller 32. The continuous recording sheet FP is nipped between the rollers 31, 32, and is pressed against the heat roller 31 by the press roller 32 with a predetermined pressure. In the heat roller 31, a heating halogen lamp, and a thermistor for temperature detection are provided.

The heat roller 31 is driven by the main motor 40 to rotate via the F clutch and the gear train and arranged so that, when the continuous recording sheet FP Is held between the rollers 31, 32. it is fed at the speed of 75 mm/sec.. As a result, the continuous recording sheet FP is actually driven in the fixing unit 30. whereas the tractor unit 20 mainly functions 23 to prevent skewing of the continuous recording sheet FP.

If the continuous recording sheet FP is kept being pressed against the heat roller 31 while printing is in standby state, the paper may be scorched with the heat of the heat roller 31. In order to avoid the scorching of the sheet, In this printer 100, the press roller 32 facing the heat roller 31 is made vertically movable so that the continuous sheet is retracted from the heat roller 31 while printing is in standby state.

In the meantime, the rocking of the press roller 32 and that of the transfer charger 15 are implemented by the same drive means.

A general liquid crystal display panel heretofore in use is, as shown in Fig. 7, built by mounting two sheets of glass plates 72, 73 on a substrate 70 via conductive rubber 71 and sandwiching a layer of liquid crystal 74 between the glass plates 72, 73. Moreover, the edges of the glass plates are enclosed with a frame 75, which is secured to the substrate 70. The substrate 70 Is secured with screws onto the body so that the display panel can be viewed through an opening 76.

The arrangement stated above, however, has posed a problem in that the increased number of parts makes it 24 troublesome to assemble the display unit.

In liquid crystal display unit 170 of this embodiment, there is provided a stepped portion In the peripheral edge of the opening 76 of the body as shown In Fig. 8. The glass plates 72, 73 between which the liquid crystal layer 74 is inserted are directly mated with the stepped portion 76a and the combination is secured with screws onto the body. With thisarrangement, the frame can be omitted, so that the number of parts becomes reducible.

Fig. 9 shows a control circuit of the printer.

This circuit comprises an operation panel 170 on which various switches and a display panel are provided, a controller 81 for developing the printing data received from a host computer into a map on a dot basis and outputting the map, and a driver 82 comprising two CPU's: one of which is an A-IC 83 for mainly controlling printing; and the other Is a B-IC 84 for mainly making error detection.

Although the selection of the page length is made by referring to a selection menu on the operation panel 170, the paper length may be set directly to the driver board 82 by means of DIP switches or the like. In this case, one signal line may be usable for selecting more than one paper length by converting the outputs of the i i plurality of dip switches into analog values using a D/A converter and Inputting the results to the driver board 82.

The controller 81 is provided with a buffer which is capable of developing printing data corresponding to six pages of the recording sheet. New data Is successively written to the buffer from time to time as the data is transferred to the driver.

The controller 81 and the driver 82 are connected jo via a video Interface (video I/F) for transferring printing data and a command line for transmitting various data.

The A-IC 83 is connected with a high voltage circuit to which biases for the charger 12 and the like In the transfer unit 10 are connected, and further, a drive system including the main motor 40, the F clutch 41, the halogen lamp In the heat roller 31 are connected to the AIC 83 as those to be controlled.

A thermistor 85 for detecting the temperature of the heat roller 31, a cover sensor 86 for detecting the opening and closing of the upper cover UC, and the PFS sensor (or photointerrupter) 26 are connected to the A-IC 83 as the sensors for supplying data to the A-1C 83.

The heat roller 31 is so controlled as to have high temperatures as fixing temperatures only during 26 printing, and low temperatures as standby temperatures when the printer is in standby state to save power and to prevent the printer temperature from rising.

Power Is supplied to the halogen lamp provided in the heat roller 31 as a heat source from the power supply 87 for supplying 100 volts a.c.. The power supply is turned ON/OFF by a signal from the A-IC 83. The A-IC 83 receives an analog output from the tbermistor provided adjacent to the heat roller 31 and executes A/D conversion so as to execute temperature control.

The temperature control is effected with an allowance of approximately 5 degrees. As a result, the actual temperature of the heat roller 31 fluctuates within upper and lower limits as shown in Fig. 10, Accordingly, there occurs the difference in time required to lower the temperature to a certain value depending upon the actual temperature of the heat roller 31. If the actual temperature of the heat roller 31 is at the upper limit of the fixing temperature, the time required to lower the temperature to the certain temperature is relatively long, while, if the actual temperature is at the lower limit of the fixing temperature, the time is relatively short. In other aspect, the temperature of the heat roller 31 1 i i i 27 after a predetermined time has past differs depending upon the temperature of the heat roller 31 when the temperature began to be lowered. It Is obvious that It will be required more warm-up time to raise the temperature of the heat roller 31 to operable (fixing) temperature from lower temperature than higher temperature.

Fig. 11 shows the difference between two cases that when the temperature of the heat roller 31 is lowered to a predetermined temperature set between the fixing and the standby temperatures. A point A shows a point where the temperature downs to a predetermined temperature which is lowered from the lower limit of the fixing temperature, and a point B shows a point where the temperature downs to a predetermined temperature which is raised to the upper limit, then lowered from the upper limit. In this example, there are approximately 30 seconds between two points A and B. In the printer of this embodiment, when the temperature Is lowered from the fixing temperature to the standby temperature, the temperature is raised up to the upper limit of the fixing temperature before being lowered. In this way, the temperature is prevented from being lowered from the relatively low temperature 28 within the fixing temperature so that the warm-up time required to raise the temperature up to the fixing temperature again can be shortened.

The B-IC 84 is connected with a semiconductor laser of the laser scanning unit 13 and an EEPROM 88 for storing printer life data.

As to means for inputting data to the B-IC 84, the empty sensor 50, the skew sensor 51, the top sensor 52 and the Jam sensor 53 are connected to the B-IC 84 which are concerned with the paper feeding. In addition, the B-IC 84 Is connected with the waste toner sensor for warning the presence or absence of the waste toner box 60 and the amount of accumulated waste toner, and the toner low sensor 14C for warning the shortage of toner, which are provided in the transfer unit 10 as those concerned with toner.

As to the toner low sensor in a conventional laser printer, it is common practice to set the sensor to output low level signal when no toner is detected.

With this arrangement, however, the problem is that when the sensor is disconnected, the low level signal indicating the toner low condition cannot be detected. In other word, the disconnection of the sensor and the toner-sufficient condition cannot be distinguished in the conventional printer.

29 In this embodiment, the toner low sensor 14c outputs a high level signal when toner low is detected, while the B-IC 84 receives the signal in a pull-up state with use of a resistance 89 for receiving the 5 signal in the pull-up state.

HIGH is thereby inputted to the B-IC 84 when toner low is detected by the sensor 14c, when disconnection occurs In the sensor system and when the developing unit 14 installed with the toner low sensor 14c is not attached to the printer 100. In other words, a number of symptoms can simultaneously be detected with one sensor 14c.

The toner low sensor 14c comprises the piezoelectric element incorporated in the bottom surface of the toner case 14a and it outputs a LOW level signal on sensing the pressure applied by the toner accommodated in the toner case 14a; and a HIGH level signal without such pressure.

When the toner is sufficiently stored in the toner case 14a, the toner is always placed on the piezoelectric element as the toner low sensor 14c, despite the operation of the scraper 19, and the LOW level signal is always outputted. On the other hand, when the amount of toner Is low, the HIGH level signal is outputted irrespective of the operation of the scraper 19. if the toner case 14a is substantially half filled with toner, the toner is alternately placed on and swept out of the toner low sensor 14c as the scraper 19 slowly rotates, thus causing alternative output of the LOW and HIGH signals. Monitoring the duty ratio of the output of the toner low sensor 14c, the B-IC 84 judges the amount of the toner to be low when the HIGH signal exceeds 80 percent.

As the toner is not supplied on the developing roller 14b by the scraper 19 immediately after power is supplied, the output of the toner low sensor in first three seconds for two rotations of the scraper is Ignored. After the elapse of three seconds, the toner low sensor 14c starts monitoring. Misjudgment on the toner low can thereby be prevented before the operation of the scraper 19 when power is supplied.

The A-IC 83 and the B-IC 84 controls the printer 100 with exchanging data via a plurality of signal lines. From the B-IC 84 to the A-IC 83, transmitted are signals such as a signal indicating that the B-IC 84 is In a standby state, a STOP signal for immediately stopping the operation of each unit of the printer 100 when an emergency error occurs even if the printing is being executed, and a PAUSE signal for stopping the 31 operation of each unit after the predetermined operations when a less urgent error occurs.

On the other hand, error signals Indicating errors in the drive system are transmitted from the A-IC 83 to the B-IC 84.

The B-IC 84 analyzes the error detected by itself and the errors transmitted from the A-IC 83 thereto, then determines their degrees of emergency in accordance with predetermined standards. The B-IC 84 10selects the STOP or PAUSE signal depending on the degree of emergency, and then transmits the signal to the A-IC 83. The less urgent errors are the errors of a toner overflow, a toner low and a paper empty, while the other errors are treated as emorgeticy errors.

One hundred volts a.c. is applied to the printer, the control system being driven at 5 volts d.c., the driving system such as the motor being driven at 24 volts d.c.. When a main switch 90 of the printer 100 is turned ofr, the voltage gradually drops from 24 volts 20d.c. to ultimately 0 volt as shown by a broken line in Fig. 12.

The 5 volts d.c. power supply for the control system is so designed that more than 90 percent of the rated voltage (i.e. 4.5 volts d.c) is held at least 20 25msec. for storing data after the main power supply is 32 turned off. It is because if the voltage becomes less than 90 percent of the rated voltage, the control system may fail to control the driving system.

As to 24 volts d.c. power supply for the driving system, the voltage tends to fluctuate while it drops because of the operation of a protection circuit on the power supply side, besides, the control system does not operate, as the 5 volts d.c has been cut off at that point of time, which may cause the vibration of the motor and hence malfunctions.

In this printer 100, the voltage applied to the driving system is instantaneously dropped from 24 volts d.c. to 0 volt on turning off the 100 volts a.c. main power supply 87 In order to prevent the aforementioned malfunctions. A relay is provided between the power supply and the driving system as a switch for the function stated above. The relay operates to cut off 24 volts d.c. either when a power good signal (PGS) representing the ONIOFF of the main power 87 supply is cut off or when the upper cover Is opened.

By Instantaneously dropping the voltage from 24 volts d.c. to 0 volt as above, the driving system Is stopped while the control system functions with substantially 5 volts d.c being applied. Moreover, the fluctuation of the voltage is prevented while it is dropping.

33 Consequently, the motor is prevented from vibrating and hence malfunctioning.

Laser printers are generally provided with a data recovery function for reprinting a blank page due to jamming or the like.

The printer 100 of this embodiment is designed to determine the number of pages to be reprinted (page data) in the driver according to the respective errors., the paper jamming error, the paper empty error detected in a portion other than perforations or when the upper cover UC is opened during printing. Based on the number of pages, the controller 81 request the host computer to transmit printing data to be reprinted.

The driver detects the page being printed at present according to the PFS pulse.

There are four kinds of page recovery data to be transmitted; namely, data 'loll requIrIng no recovery, "I" requiring only one whole page which is being transferred to be reprinted, "2" requiring the page being transferred and the page precedingly transferred to be reprinted, and "3" requiring the page being transferred and preceding two pages to be reprinted.

When trouble occurs during the first printing, the page data "1" is transmitted and the controller 81 requests the host computer for data on the page being PLI11LCU 34 and transmits the data to the driver again after developing it on the buffer.

When trouble occurs during the second page printing, the third page or thereafter, the respective data "V' is set at "2" or "V' and the controller 81 requests the host computer for data on the page to be reprinted.

When the opening of the upper cover UC is detected during the third page printing, the page data is set atulle. It may otherwise be arranged that the page data on reprinting is not determined by the page that has undergone trouble as stated above but by the number of pages to be traced back, depending on the place where jamming has occurred.

Figs. 13 and 14 show a flow chart illustrating the performance of a printer.

In this embodiment the page length of the recording paper is 11 inches (27.94 cm) as aforementioned. Even if the recording sheet which page length is 12 inches (30.48 cm) is used, the printed area of each page is the same as that of 11 inches (27.94 cm), and the remaining 1 inch (2.54 cm) of the page is used as a blank portion,(non-printed portion) at the end of the printed area.

When the power switch is turned on, the printer executes a self-test at step S.1 in order to detect an error of each unit in the printer 100.

1 Disconnection of the thermistor, disorder of the main motor, the function of APC (Automatic Power Controller) for controlling the semiconductor laser, disorder of the polygon scanner and the like are detected.

When the self-test is terminated, warmup of the heat roller 31 is executed at step S.2. In this step, the temperature of the heat roller is raised to a fixing temperature, which is the temperature necessary to perform fixing procedure. If the temperature does not reach the fixing temperature within a predetermined period of time, it is determined that the heater is out of order.

Self-test and warm-up of the heat roller 31 is terminated and then it is examined whether some errors are detected during above procedure. If an error has detected, error procedure is executed. The error procedure includes displaying the kind of error detected, turning off the motor, the heater, and stopping the printer.

If no error Is detected, the printer outputs the signal Indicating the ready condition of the printer to a host computer (not shown), and waits for the request for printing. The request for printing Is generated when the data corresponding to more than one page is transmitted from the host computer. When 36 the printing is required, the following print sequence is executed.

The discharging LED 17 is turned on, the main motor 40 and the polygon scanner 13a are actuated, the output of the semiconductor laser Is adjustably applied with APC (automatic power controller),,and the charger 12 is turned on.

Next, in steps S.11 and S.12, developing bias and cleaner bias are turned on. The press roller 32 is raised so that the recording sheet is nipped between the press roller 32 and the heat roller 31 at step S.13. At step S.14, vertical synchronous signal is generated and the laser scanning unit 13 is actuated. In steps S.15 through S.17, a timer TET is set with the value corresponding to the page length of the recording sheet used. If the page length is 11 inches (27.94 cm), 724 msec. is set to the timer TET, while if 12 inches (30.48 cm), 385 msec. is set. The page length is determined based on a flag FL which is set with the operation panel.

In step S.18, the procedure is paused until the time up of the timer TET. When the set period of time has elapsed, transfer bias is turned on, transfer unit is actuated, and the heat roller 32 and the tractor are rotated with use of F clutch. The period of time set to the timer TET is calculated by subtracting a i i 37 start up time for feeding the recording sheet from the time in which the portion of the photoconductive drum 11, which Is exposed to the light from the laser scanning unit 13, reaches the transfer position. Further, if the page length of the sheet is 12 inches (30.48 cm), the time for feeding the 1 inch (2.54 cm) blank portion at the end of the preceding page is subtracted.

The start up time is a time for idly feeding the recording sheet when the sheet feeding is started. The recording sheet is idly fed in order to prevent the bad printing condition at the beginning of the sheet feeding. If the sheet feeding is started at the point in time when the corresponding portion of the photoconductive drum 11 is located at the transfer position, the characters at the position may be deteriorated. It Is because the speed of the recording sheet can not be at the predetermined speed at the beginning of sheet feeding, which causes the difference of the speed between the si.. - feeding speed and the peripheral speed of the photoconductive drum 11. In order to prevent the occurrence of the speed difference stated above, feeding of the recording sheet is started with use of the F clutch so that the exposed portion of the photoconductive drum 11 is located after the recording sheet is fed by 1/6 inches (3.175 mm). In 38 other words, the portion 1/6 inch (3-175mm) form the perforation line is a non-printing portion.

When the F clutch is turned on in step S.21, the PFS counter starts counting the PFS pulse. It should be noted that when the F clutch is turned on, if the recording sheet which page length is 12 inches (30.48 cm) is used, the perforation line of the recording sheet is located upstream side of the transfer position by 1 inch (2.54 cm). If the pa ge length is 11 inches (27.94 cm), the perforation line is located at the transfer position.

In steps S.22 and S.23, it is examined whether the PFS pulse is outputted within two seconds after the feeding of the recording sheet has been started. If the PFS pulse is detected, the process goes to step 24 in Fig. 14. If the PFS pulse is not detected, the recording sheet is detected not to be fed and an error procedure is executed.

In step S.24, it is examined that page length of the currently used recording sheet is 11 inches (27.94 cm), or 12 inches (30.48 cm) referring to the flag FL. If the page length is 12 inches (30. 48 cm), the procedure goes to steps S.25 through S.36. If 11 inches (27. 94 cm), the procedure goes to steps S.37 through S.48.

In steps S.25 through S.28, after the PFS pulse is counted up to 20 pulses, the output of the empty sensor 1 i 39 is monitored until the PFS pulse is counted to 22 pulses. While the empty sensor is monitored, if the empty sensor is turned on, a flag FEMP Is set to 1.

When the PFS pulse is counted up to 22, and If sheet empty is detected at step S.29 or printing the next page is not required (step S.30), the process goes to step S.33. If sheet empty Is not detected and printing Is required, the process goes to an exposure start procedure at step S.31, then the PFS counter is set to -1 in step S.32 and the process goes to step S.24. At the exposure start procedure, as shown in Fig. 15, the recording sheet FP is further fed by 1/2 inches (1.27 em) before exposure is started. Controlled as above, the PFS counter counts 2 when the leading end of the succeeding page is located at the transfer portion.

When the recording sheet which page length is 12 inches (30.48 em) long is used, it is examined whether the printing of the succeeding page is required or not after the sheet is fed by 11 inches (27.94 em), As aforesaid, the exposed portion of the photoconductive drum 11 does not correspond to the transfer portion of the recording sheet, when the portion 10 inches (25.4 em) from the leading end of the page is located at the transfer portion, the exposed portion of the photoconductive drum 11 corresponds to the portion a 1/2 inch (1.27 em) inside the trailing end of the page. At this point in time it is examined whether printing of the succeeding page is required or not. If the printing is required, the photoconductive drum 11 is exposed to the light, thereby the recording sheet and the photoconductive drum 11 can be continuously driven and the printing is continuously executed.

When the printing Is terminated, the PFS counter Is set to 24 and it is examined whether the sheet empty is detected or not referring to the flag FEMP (steps S.33 through S.36). If the sheet empty is not detected, the process goes to step S.49 and the F clutch is turned off. If the sheet empty is detected, the PFS counter Is cleared, and further, after the PFS counter counts up to 27, the process goes to step S.49. As operated above, when the sheet empty Is detected, the sheet bearing the transferred and unfixed toner image and remaining in the printer is discharged.

Since the page length of the recording sheet is 12 inches (30.48 em), which corresponds to the 24 counts of the PFS pulse, if the sheet empty is detected, the sheet is fed by 27 counts of the PFS pulse for completely discharging the sheet.

If the sheet which page length is 11 inches (27.94 em) used, the process goes to steps S.37 through S.48. In 41 this case the process is similar to the case of using the sheet which page length is 12 inches (30.48 cm) other than the count of the PTS pulse. Namely, in this case, the sheet empty is detected during the PFS counter counts 16, which corresponds to the portion of the sheet 8 inches (20.32 cm) from the leading end of the page, and the PFS counter counts 18, which corresponds to the portion of the sheet 9 inches (22.86 cm) from the leading end of the page. Further, the requirement of the printing of the succeeding page is detected when the sheet is fed 9 inches (22.86 cm).

After the recording sheet is fed by 9 inches (22.86 cm), when the counter counts the PFS pulse by 18 pulses, the portion of the photoconductive drum 11 corresponding to the portion 1/2 inch (1.27 cm) before the perforation line which is a boundary of the currently printed page and the succeeding page Is located at the exposed position. When the recording sheet is located in the position as above, it is examined whether the printing of the next page is required or not. If the printing is required, I.e., printing data Is continuously inputted, printing is continuously executed. In this case, at step S.43, the recording sheet FP is fed by 1/2 inches (1.27 cm) before exposure is started (refer to Fig. 15).

In order to print the succeeding page, the PFS 42 counter Is set to -3 at step S.44 and the recording sheet Is fed. Accordingly, the contents of the PFS counter is 0 when the leading end of the next page is located at the transfer position. If the sheet empty Is not detected, the F clutch is cut off without discharging the sheet carrying the unfixed toner image.

In steps S.50 through S.56, the charger, developing bias, and cleaner bias are turned off. Further, the polygon scanner 13a, the main motor is stopped, the discharging LED is turned off. and the fixing unit 30 is released.

In step S.57, the state of the flag FEMP is examined. If the sheet empty Is detected and the printing Is terminated, the process is paused until the is flag FEMP Is set to 0 as the recording sheet is set and the empty sensor Is turned off. If the printing Is terminated because of no requirement for printing, or the recording sheet is set and the empty sensor is turned off, the process goes to (I) In Fig. 13A and paused until the printing is required.

In the above-mentioned embodiment, when the recording sheet which page length is 12 inches (30.48 cm) is used, it is arranged that a blank of 1 inch (2.54 cm) is collectively provided at the end of each page of the recording sheet. However, it is possible to make the blank 43 provided at the head of each page of the recording sheet. Moreover, It Is also possible to provide the blank of 1/2 inches (1.27 cm) in the head and the end of each page of the recording sheet.

As above, with the present invention, the exposed position of the photoconductive drum is changed according to the page length of the recording sheet, a plurality of types of recording sheets having different page lengths, respectively, can be used without changing the mechanical construction of the printer.

1 44

Claims

1. An electrophotgraphic printer capable of using a plurality of types of continuous form recording media having different page lengths, respectively, said printer comprising a photoconductive member to be charged and exposed to light carrying image data to form a latent image, said printer further comprising: select means for selecting one of said plurality of types of recording media; and control means for controlling said printer in such a fashion that a portion of said photoconductive member corresponding to a page of the selected one of said plurality of types of recording media is exposed to the light.

2. The electrophotgraphic printer according to claim 1, which further comprises exposure means for exposing said photoconductive member to the light, and wherein said control means controls said exposure means to expose said photoconductive member to the light depending on the selected one of said plurality of types of recording media when said recording media is fed continuously.

1 Y

3. The electrophotographic printer according to claim 2, wherein said control means comprises detect means for detecting the position of the recording medium in the feed path of said recording medium in said printer, wherein said control means controls said exposure means to expose said photoconductive member to the light when the leading end of the page of said selected one of said recording media to be printed Is located at a predetermined position.

4. The electrophotographic printer according to any preceding claim, which further comprises another detect means for detecting the existence of the succeeding page of said selected one of said recording media to be printed is present, wherein said selected one of said recording media In the printer Is completely discharged if the absence of the succeeding page Is detected by said detect means.

5. The electrophotographic printer according to any preceding claim, which further comprises feeding means for feeding the recording medium, wherein said control means controls said feeding means to start feeding said selected one of said plurality of recording medium a predetermined period of time after said photoconductive 46 member is exposed to the light at the beginning of printing, said predetermined period of time depending on the page length of the selected one of said plurality of recording media.

6. The electrophotographic printer according to any preceding claim, wherein said photoconductive member is a photoconductive drum.

7. An electrophotographic printer capable of using a plurality of types of continuous form recording media having different page lengths, respectively, and substantially as herein described with reference to Figs. 1 to 6 and 8 to 15.

Published 1991 atThe Patent OfTice. State House. 66/71 High Holborn. London WC I R47P. Further copies maybe obtained from Sales Branch. Unit 6. Nine Milc Point. Cwn-irclinfach, Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques lid. St Marv Cray. Kent r