AU649236B2 - Jam detecting device - Google Patents

Description

S F Ref: 147330 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

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(ORIGINAL)

FOR OFFICE USE: C4923l Class Int Class

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Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name and Address of Applicant: Address for Service: Asahi Kogaku Kogyo Kabushiki Kaisha 2-36-9, Maeno-cho Itabashi-ku Tokyo

JAPAN

Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Jam Detecting Device The following statement is a full description of this invention, including the best method of performing it known to me/us n183T6 12.1 5845/6 Abstract of the Disclosures A jam detecting device is provided in a printer for detecting jam of a recording medium which is fed along a feed path. The jam detecting device has a sensor along the feed path of the recording medium for outputting one of two different signals depending on whether the recording medium contacts the sensor. When the recording medium is normally fed in the feed path, the recording medium do not come in contact with the sensor, while it comes to contact the sensor when it e floats up from the feeding path. If the sensor outputs the signal indicating that the recording meajum comes in contact with the sensor, it is determined that the jam of the recording medium has occurred.

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SPECIFICATION

Title of the Invention Jam Detecting Device Background of the Invention o: The present invention relates to a detecting e 10 device for detecting a paper jam while a recording S. sheet is fed in a printer, for instance.

Paper feeding mechanisms are provided in printers, copying machines and the like. These apparatus are normally equipped with jam sensors for detecting the paper Jam.

\a o* In a Ltprinter using a cut sheet type recording sheet, for instance, two sensors are provided along a sheet feed path by which a sheet jam is detected when recording sheet does not pass the 20 downstream-side sensor within a predetermined period of Z time after it has passed the upstream-side sensor.

A printer using a continuous recording sheet, however, the detection method stated above is unusable because the sheet has no breaks between pages.

Summary of the Invention It is the object of the present invention to overcome or substantially ameliorate the above disadvantages.

There is disclosed herein a printer using a continuous form recording medium normally being fed along a feed path, the printer comprising:first sensor means located along said feed path and providing a first signal representative of normal feeding past the first sensor means when said medium comes in contact therewith and providing a second signal representative of abnormal feeding of the medium past the first sensor means when said medium does not come in contact therewith; second sensor means located along said feed path and providing a first signal representative of normal feeding past the second sensor means when said medium comes in contact therewith and providing a second signal representative of skewing in the feeding of the medium past the second sensor means when said medium does not come in contact therewith; timer means being actuated on printer turn on if said first sensor means outputs said second signal and capable of being deactivated when said first sensor means subsequently outputs said first signal; and determining means determining the occurrence of erroneous feeding of said recording medium if said timer means has been actuated for longer than a predetermined time or if one of said sensors provides a said second signal after said first signals have been provided.

o :2 e Description of the Accompanying Drawings A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 is a schematic sectional view of a printer including a jam detection device embodying 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 sensor; Fig. 6 shows a disc for use in generating PFS pulses; Fig. 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 temperature control of the heat roller for the printer of Fig. 1; S B oo Fig. 12 is a graph illustrating power supply control of the printer of Fig. 1; and Figs.13A and 13B are a flowchart illustrating a jam detection procedure.

Description of the Embodiments Figs. 1 through 12 show a printer comprising a jam detection device embodying the present invention.

9 ev.* 10 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 fee* rollers 31, 32 for heating and pressing an unfixed toner image in order to fix it on the recording sheet.

Light carrying printing data from a host computer or the like is emitted from a laser scanning unit (LSU) 20 13, the charged surface of the circumferential surface .9 of a photoconductive drum 11 is exposed to the light, a latent image is formed on the circumferential surface of the photoconductive drum 11. Toner is stuck to the circumferential surface of the photoconductive drum 11 to develop a toner image by a developing unit 14. Then the toner image !s transferred onto the recording sheet at a transfer charger 15, and the image thus transferred is fixed by a fixing unit 30. The printer 100 employs the electrophotograhic 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 33 is secured to an upper cover UC. The upper cover UC is rotatably disposed on the main body of the printer 100 10 so that it can be rocked around a pivot axis P.

This printer 100 uses a continuous form recording sheet FP, which is known as fan-fold sheet. The fanfold is a foldable continuous sheet having feed holes at both side ends, and perforated tear lines along which the recording sheet FP is cut off easily.

Projections are provided on the endless belt 21 which are to be fitted to the feed holes of the continuous form recording sheet FP. The continuous form recording sheet FP is fed from a feed port 1 to a discharge port 20 2. It should be noted that the printer 100 is designed to print pages between perforations in order to prevent printed data from parting apart when the recording sheet FP is torn off at the perforated tear lines.

In case of a printer using a cut-sheet, the distance between transferring position and fixing position is not so important because printing data for one page is printed onto one sheet of recording paper. On the other hand, in a printer using a continuous sheet, if the whole portion of the sheet carrying the toner image is caused to pass through the fixing position and fixed, the length of paper between transfer and fixing positions may be wasted. Consequently, it is necessary to determine the portion of the sheet carrying a toner image to be fixed. In other words, it is necessary to determine the portion carrying an unfixed toner image remaining in the printer between the transfer and fixing positions.

When the printing quality is taken into consideration, the interruption and resumption of transfer and fixing should preferably be made at the perforations where data is not printed. For this reason, the distance between the transfer position and fixing position is preferably arranged equal to the length of one page so that the perforations are located at the transfer and fixing positions when printing is stopped.

As arranged above, the portion carrying an unfixed toner image for one page remains between the transferring and fixing positions in a standby state 9 *eoo o o *e 0 0 a 6O SO .09.

*00:* 0eo 65 when the printing is terminated. When another page is printed, the unfixed toner image is fixed and the remained page is discharged. In this way, waste of paper due to the fixing of every transferred image becomes avoidable.

The distance between the transferring and fixing positions of this printer 100 is set to eleven inches long for the continuous recording sheet which page length is eleven inches, lagi The transfer unit 10 comprises a charger 12 for charging a photoreceptor material on the circumferential surface of the photoconductive drum 11 with electricity, the laser scanning unit 13 for exposing light to the photoconductive drum 11, a developing unit 14 for sticking toner to the latent image formed on the photoconductive drum 11, a transfer charger 15 for charging the recording sheet FP with electricity to cause to 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 removing the charge thereon.

The photoconductive drum 11 should be exchanged after used Tor printing a certain number of pages, *fee a 20 r a* sihce 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 printed pages are electrically courted aid 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 provided on a new photoconductive drum 11. As the 10 projection presses down a reset switch, not shown, on the body side, the control system car detect that the

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new photoconductive drum 11 is placed in position. The i* projection retracts when the operation is started and ~ao ifation the new drum disappears. The control system resets the .,ounter when the upper cover UC is shut after the reset switch is turned on.

e* The laser scanning unit 13, which is secured in the upper cover UC, continuously deflects ON/OFFmodulated beams from a semiconductor laser (not shown) S 20 by means of a polygon mirror 13a. The laser beams are converged by means of a 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 ond 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 10 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 5.

oo :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 two-component 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 oe~

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oo toner. This monocomponent development .,ethod 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 a 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, lubrication between the toner grains is improved, which prevent the toner from forming blocks. It should be noted 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 10 is provided in the toner case 14a.

The scraper 19 slowly rotates to supply the inside 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 000 o 0 0ooo the surfaces of the blades 19a and 19b is 90 degrees, that of the blades 19a and 19c is 180 deg,.es, and that of the blades 19a and a9d is 270 degrees. In this specification, this angle well be called a mounting angle, the mounting angles, with respect to the blade 19a, of the blades 19b, 19c, and 19d are degrees, 180 degrees, and 270 degrees, respectively.

The blades 19a through 19d are driven to rotate in the direction of an arrow shown in Fig. 3.

10 Since the four blades are arranged to have different mounting angles, it becomes possible that the S load applied when the toner is forced out is as one- :o quarter 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 less fluctuatpr 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 portion corresponding to the right-hand side of the *see*: 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 an 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 bo transferred onto the circumferential surface of the photoconductive drum 11.

According to the scraper in this embodiment, the occurrence of the carrier being Irarsferred on the photoconductive drum 11 is made avoidable even when the 10 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 oo which can be rotated by a cam mechanism around a pivot 0 shaft L1. Moreover, a pair of guide rollers 18a, 18b are integrally secured to the arm 15a, the guide rollers 18am 18b being laterally positioned 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 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 10 and the discharging area, which is uncovered, of the transfer charger 15 is arranged at the upstream side in *0 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.

oo By narrowing the discharge area, corona discharge S 20 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 10 is not totally removed therefrom after the termination of the transferring process. As the residual toner is *g 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 o eS toner may soil th. inside if printing is started 20 without the waste toner box In conventional printers, sensors have been used to respectively detect the presence or absence of such a waster toner box 60 and the full condition of the waster toner box 60. The problem is that the plurality of sensors thus required tends to render the control system complicated.

In the printer according to 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 the guide of the body, the waste toner box 60 being vertically movable. An actuator 62 is rotatably pivoted with a fulcrum 61 on the body such that a contact portion 62a 10 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 rod 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 emitt'ig *3* element of a photo-interrupter 63.

3 3 If the waste toner box is not attached, the rod 62 is caused to revolve clockwise by its own weight as shown by a continuous line of Fig. 4 so that its *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 i.0 S 0eee

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O ~sO 0 0 2 0e 0 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 rod 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 .creens the photo-interrupter 63. In this state, the photo-interrupter produces a signal indicating that the rays of light are shaded and the 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 rod is caused to descend due to the weight of accumulated toner as shown in Fig. 5 and the light-shading wall 62c moves up to the left-hand side 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 rod 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 rod 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 22 and a driven shaft 23 are driven by the 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 main motor 40 up 10 to the drive shaft 23 in the tractor unit 20 is goo* arranged so that the continuous recording sheet FP is fed at the velocity of 50 mm/sec. if the tractor unit *5 20 is independently feed the recording sheet FP.

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 eo e o rate higher than 50 mm/sec..

The driven shaft 22 is connected with a disc via a chain 24. The disc 25 is rotatable in response 20 to the rotation of the driven shaft 22. As shown in Fig. 6, the disc 25 is provided with slits 25a which

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are apart from each other by a predetermined space.

The disc 25 is nipped between the light emitting member and the light receiving member of the photo-interrupter 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, 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 10 and the non-perforated portion, respectively.

Notwithstanding, the positional relation between o *6 the disc 25 for use in generating the PFS pulse and a base plate on which the photo-interrupter 26 is mounted 6 may not be the same in individual printers because of assembly errors. If the slits 25a formed in the disk is rectangular along the radius, the pulse width 6 thus outputted may vary depending on where the photo- 6 interrupter 26 has detected the slits 26a in the radial direction of the disc 26, and depending on when the S 20 relative position between the disc 25 and the photointerrupter 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 Ls fan-shaped so that its width gradually increases toward the circumference. In other words, the slit is defined by a pair of radii of the disc 25. With this fan shape, 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 10 precision required is eased and hence assembly workability is improved.

*Sensors for detecting paper errors will i.o. subsequently described.

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 0 43 changing of a sheet feed speed and the lifting up of the sheet.

20 The first sensor is an empty sensor 50 provided between the feed port 1 and the transfer unit 10. The

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empty sensor 50 is pressed down when the recording sheet FP is set and hence turned off, whereas it floats up when the sheet runs out and hence turned on. As the perforation line as a blank portion (non-printed

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portion) between pages are located under the photoconductive drum 11 of the transfer unit 10 and set at the position of the fixing rollers 31, 32 when printing is stopped in this printer 100. The sheet empty can be detected as the empty se,.sor 50 is turned on when the trailing end of the last page of the recording sheet is located right under the photoconductive drum. Moreover, it is detectable by counting the PFS pulses that what portions of the 10 recording sheet positioned at the transfer unit 10, at see* 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 4 position where the recording sheet FP is torn off even if it is 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 20 recording sheet FP. The sensors 51, 51 are capable of detecting the sheet when at least one side thereof r"Lifts up.

The third one is a top sensor 52 provided in the central position between the skew sensors 51, 51. The top sensor is turned on when the recording sheet FP is 2o 0904 0, 0000r o* 080 A 0* 0 00 70 7' 0; *r 0 ii 0 20 00 ir 00 set in the feeding path, and turned off when the recording sheet FP floats up or has not been normally set. The top sensor 52 is used for detecting the leading end of the paper when the printing is started.

After the predetermued numbers of the pulses have been counted after the leading end of the recording sheet FP passed the top sensor 52, the leading end thereof reaches the fixing unit 30, whereas the following perforation lines are positioned at the transfer unit The fourth one is a jam sense- 53 provided in the upper cover UC opposite to the top s -or 52. This sensor contacts the recording sheet FP to become actuated when the central part of the recording sheet FP swells up because of jamming in the fixing unit Figs. 13A and 13B are a flowchart illustrating a jam detection for continuous recording sheet.

The procedure shown in the flowchart is executed as an interruption procedure in the main sequence of printing, for instance, to detect errors concerning with sheet feeding.

On starting the procedure, the states of the empty sensor 50 is detected in Step S.1. If the empty sensor is in off state, when the recording sheet is set at the sheet feed port 1, it is judged whether or not the setting of the recording sheet FP has been completed according to the states of a flag FTSET and the states of the top sensor 52 in steps S.2 and S.3.

When the flag FTSFT is 0 and the top sensor 52 is in off states, the recording sheet is decided not to have been terminated, and the process of setting the irecording sheet is executed in steps S.4 through S.9.

The process of setting the recording sheet is performed when a new continuous recording sheet FP is set to the printer 100. By engaging the leading end of the recording sheet FP with the tractor unit 20 and closing the upper cover UC, the recording sheet FP is fed to the position wr re it is nipped between the fixing rollers 31 and 32.

.0 In steps S.4 through S.6, the recording sheet FP is fed until a predetermined time which is set to a timer is elapsed or the state of the top sensor 52 is changed to on state. When the top sensor 52 is turned on before the predetermined time is passed, the to o recording sheet FP is fed for 27 pulses of the PFS pulse is counted 27, and the flag FTSET is set to 1.

The error detection is terminated in the normal way.

When the PFS pulse is counted by five after the Sleading end of the recording sheet FP passed the top sensor 52, the leading end of the recording sheet FP reaches the fixing unit 30, so that the following perforation line is to be positioned at the transfer unit 10. However, the recording sheet FP may not be held between the fixing rollers 31, 32 when the press roller 32 is lifted even though the leading end of the recording sheet FP is located at the fixing unit Therefore, the recording sheet is idly fed by one page (by 22 counts of the PFS pulse) so that the boarder between the first and second pages is located in the fixing unit 30. Consequently, the first two pages of the recording sheet FP are to be discharged without being printed and printing is intended from the third page.

When the top sensor 52 is decided to be in the on state in step S.3, the procedure of steps S.4 through S.8 are skipped, the flag FTSET is set to 1 in step S.9, then the operation is terminated in the normal way. As the flag FTSET has been set to 0 with initialization at the time power is supplied, 0 may be set even when the recording sheet FP has already been set. In such a case as this, the decision in step S.3

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is effected to avoid wasting the recording sheet FP by loosely feeding the paper.

S"When the tie set in the timer is up before the top sensor 52 Is turned on, it is decided that sheet jamming has occurred. Then the flag FTSET is set to 0 in step S.10, the occurrence of a jam is displayed on the operation panel 170, and error procedure is implemented in step S.1. In this case, in the error procedure, the operation of the printer is stopped by turning off the power supply directed to the motor, the heater and the like.

When the flag FTSET is decided to be 1 in step S.2, the states of the top sensor 52, the jam sensor 53 and the skew sensors 51, 51 are detected in this order in steps S.12, S.13, S.14, and when the recording sheet FP is floating up, when irregularity is detected by at least one of the three kinds of sensors, the error procedure is executed in steps S.10, and S.11.

The state that the flat FTSET is set to 1 represents that the setting of the recording sheet FP has been completed, wherein the top sensor 52 is in the normal state, and the jam sensor 53 and skew sensors 51, 51 are in off state.

When the empty sensor 50 is decided to be in the on state, when the recording sheet FP runs out in steps S.1, the state of the top sensor 52 is detected in step S.15. If the top sensor is in on state, i.e., if the recording sheet FP bearing the unfixed toner image is left in the printer 100, the unfixed toner image is fixed and the recording sheet is discharged in step S.16. If the top sensor 52 is detected to be in off state, step S.16 is skipped and the indication of sheet empty is displayed with the flag FTSET being set to 0, and the error procedure is executed.

In the manner described above, the function of the top sensor 52 is utilized in three ways depending on the situation; that is, a demand for the sheet setting, the paper jam, and whether or not the sheet feeding iP necessary are detected, whereby the conditions fit for printer using a continuous recording sheet can be obtained.

o: 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 0*e 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 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 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 1.5 are implemented a*SS by the same drive means.

too* A general liquld crystal display panel heretofore in use is, as shown in Fig. 7, is built by mounting two sheets of glass plates 72, 73 on a substrate 70 via conductive rubber 71 and nipping a layer of liquid crystal 74 between the glass plates 72, 73. Moreover, the edges of the glass plates are enclosed with a frame 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 troublesome to assembly 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. While the glass plates 72, 73 between which the liquid crystal layer 74 is inserted are directly mated with the stopped portion 76a, the combination is secured with screws onto the body. With this arrangement, the frame can be omitted, so that the number of parts becomes reducible.

Fig. 9 shows a control circuit of the printer.

ee* This circuit comprises a controller 81 for developing the printing data received from a host 4 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.

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

The controller 81 and the driver 82 are connected 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 A-IC 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 photo-interrupter) 26 are connected to the A-IC as the sensors for supplying data to the A-IC.

The heat roller 21 is so controlled as to have *e* high temperatures as fixing temperatures only during 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 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 thermistor provided adjacent to the heat roller 31 and executes A/D conversion so as to execute temperature control.

The temperaturc 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. 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 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 S temperature is lowered from the fixing temperature to r. the standby temperature, the temperature ir raised up to the upper limit of the fixing temperature before 0e*S S. lowered. In this way, the temperature is prevented from being lowered from the relatively low temperature within the fixing temperature so that the warm-up time required to raise the temperature up to the fixing temperature again can be shortened.

20 The B-IC 84 is connected with a semiconductor 9 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 "s indicating the toner low condition cannot be detected.

9@ see In other word, the disconnection of the sensor and the toner-sufficient condition cannot be distinguished in the conventional printer.

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 signal in the pull-up state.

HIGH is thereby inputted to the B-IC 84 when toner •0 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, *O*g S" 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 filled with the toner substantially by halves, the toner is alternately 20 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 the 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 **get0 are signals such as a signal indicating that the B-IC i, 84 is in a standby state, a STOP signal for immediately S* 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 operation of each unit after the predetermined operations when a less urgent error occurs.

On the other hand, error signals indicating errors 20 in the drive system is 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 selects 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 emergent errors.

One hundred volts a.c. is applied to the printer, the control system being driven at 5 volts the driving system such as a motor being driven at 24 volts When a main switch 90 of the printer 100 is turned off, the voltage gradually drops from 24 volts d.c. ultimately 0 volt as shown by a broken line in S* 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 5 volts is held at least msec. for storing data after the main power supply is turned off. It is because if the voltage becomes less than 90 percent of the rated voltage, the control 009 system may fail to control driving system.

As to 24 volts d.c. power supply for the driving Ssystem, the voltage tends to fluctuate while it drops because of the operation of a protection circuit on the e power supply side, besides, the control system does not operate as 5 volts d.c. is 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 syste_ 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 ON/OFF 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 5 volts d.c. being applied. Moreover, the fluctuation of the voltage is prevented while it is dropping.

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

Laser printers are generally provided wit) a data recovery function for reprinting a blank page due to 9 S Jamming or the like.

The printer 100 of this embodii..ent is designed to *0 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 transiit 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, date requiring no recovery, requiring only one whole page which is being transferred to be reprinted, requiring the page being transferred and the page precedingly transferred to be reprinted, and requiring the page being ee transferred and preceding tow pages to be reprinted.

When trouble occurs on the first page, the page S* data is transmitted and the controller 81 requests the host computer for data on the page being printed and transmits the data to the driver again after developing it on the buffer.

When trouble occurs on the second page, the third 20 page or thereafter, the respective data is set at "2" or and the controller 81 requests the host computer for data on the page to be reprinted.

0 When the opening of the upper cover UC is detected on the third page, the page data is set at 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.

Altho t: reference has been made to the use of continuous sheet whose page length is 11 inches long in the embodiment shown, the continuous sheet whose page length is 12 inches long may also be used by changing a counter for counting PFS pulses therefor.

If 12-inch page length sheet is used in this S printer 100, some additional arrangements may also be considered such that the last page carrying an unfixed toner image is discharged when the printing is terminated, that the page remained in the printer 100 is fed when printing is restarted, or that a perforated line is located at the fixing unit with the portion one inch from the next perforation being located at the transfer unit 14.

OSOI

S" As set forth above, a paper jam is detectable even 20 in the printer which employs continuous paper, for instance, according to the present invention.

Moreover, the provision of detection means at two places and the use of them in combinatio allow jam detection to be accurately made.

Claims (6)

1. A printer using a continuous form recording medium normally being fed along a feed path, the printer comprising:- first sensor means located along said feed path and providing a first signal representative of normal feeding past the first sensor means when said medium comes in contact therewith and providing a second signal representative of abnormal feeding of the medium past the first sensor means when said medium does not come in contact therewith; second sensor means located along said feed path and providing a first signal representative of normal feeding past the second sensor means when said medium comes in contact therewith and providing a second signal representative of skewing in the feeding of the medium past the second sensor means when said medium does not come in contact therewith; timer means being actuated on printer turn on if said first sensor means outputs said second signal and capable of being deactivated when said first sensor means subsequently outputs said first signal; and determining means determining the occurrence of erroneous feeding of said recording medium if said timer means has been actuated for longer than a predetermined time or if one of said sensors provides a said second signal after said first signals have been provided.

2. A printer according to claim 1 further comprising a third sensor means oppositely disposed to said first sensor means with said feed path therebetween and providing a first signal representative of normal feeding past the third sensor means when said medium does not come 25 in contact therewith and providing a second signal representative of abnormal feeding of the medium past the third sensor means when said medium comes in contact therewith.

3. A printer according to claim 1 or 2 wherein said first sensor means is located towards an exit of said feed path.

4. A printer according to claim 3 wherein said second sensor means is located intermediate said eryt and an entrance of said feed path.

5. A printer according to claim 4 further comprising a fourth sensor means located towards said entrance and providing a first signal representative of normal feeding past the fourth sensor means when said medium comes in contact therewith and providing a second signal representative of ending of the medium when said medium does not come in contact therewith.

6. A printer using a continuous form recording medium normally being fed along a feed path, the printer being substantially as hereinbefore described with reference to Figures 1 to 6 and 8 to 13 of the accompanying drawings. DATED this TWENTY FIFTH day of FEBRUARY 1994 Asahi Kogaku Kogyo Kabushiki Kaisha Patent Attorneys for the Applicant SPRUSON FERGUSON *o o *e• oo *e