GB2238402A - Toner scraper for printer - Google Patents

Abstract

In an electrophotographic printer, toner accommodated in a toner box is applied to the photoconductive member by a developing roller (14b) on the circumferential surface of the photoconductive member a latent image being formed. A toner scraper (19M) is employed in the toner box for supplying toner to the developing roller. The scraper has a shaft (220) and a plurality of blades (219) arranged at different angles along the shaft. The blades may be on bosses (219a) which can be assembled together using mating walls (222), the shaft (220) fitting inside the walls. The blades may be solid (Fig 3a) rather than with openings as shown. <IMAGE>

Description

c 1 PRINTER The present Invention relates to a printer employlng in

electrophoLographle Irnage transfer system, an(] more particularly, to seraper parts In a toner supply box of the printer for supplying toner onto a developing roller.

lleretofore, a printer employing in electrophotographlc linage transfer system has been known.

Jn such a printer, the charged cIrcumferential surface of a photoconductive drum is exposed to laser beams so as to form a latent linage corresponding to a printing pattern, toner As stuck to the latent linage to form a toner image by mean.s of a devel-opIng unIt, the toner linage Is transferred onto a recording sheel. by a transfer unIt, and the toner image thus transferred ls fixed by thermocompression adheslon at a fixing unit.

ln the developing unit, there As provided a 2 scraper for supplying toner from a hopper onto a developing roller which supplies toner onto the photoconductive drum. The scraper has the rotary shaft installed in parallel with the rotary axis of the photoconductive drum, arid a plurality of blades fixed to the rotary shaft.

While the toner Is supplied onto the developing roller, however, the load is applied to the plurality of blades sl.multaneously since each of the blades of the conventional scraper are extended iii the same d! rectlon. The problem Is that the motor used for driving the shaft will have to bear a relatively heavier load, and further it causes noise during the operation.

is Heretofore, two dry development methods are generally known. One of them is a so-called moriocomponent development method, and the other is a two-component development method.

In the two-componerit 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 t i 3 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 5 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 11ttle amount of carrler 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 chargeabl-11ty of the toner. 1n 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.

Fig. 31) shows a sectional view of' an example of a conventional developIng unit 14 provided In an electrophotographic printer employing aforesaid (improved) monocomponent development method for accommodating toner 3 as developer, a developing roller 14b for stickIng the toner 3.

Further, in the developing unIt 14, a scraper 19 is disposed for sticking the toner 3 to the developing !9 4 roller 14b. The toner 3 is slowly stirred arid red toward the developing roller 1.41) as the scraper 19 revolves. The toner 3 is then caused to thinly stick to the surface of the developing roller 14b via a toner blade 8 and the like so that the toner 3 Is made to stick onto the circumferential surface of a photoconductive drum 11. where an electrostatic latent Image is formed.

This conventlonal scraper 19 normally comprises a shaft 19a laterally provided In the developIng unIt 14 and a single blade 19b fitted to the shaft 19a, the blade 19b comprising vertical arm portions respectIvely projectIng from both ciids of the shaft 1.9a An the radial. direction of the shaft 19a and a horizontal arm portion connecting the leading end portions of both vertical arm portions.

Since the blade 19b of the conventional scraper 19 has only the single horizontal arm in particular, the relevant torque required tends to considerably vary between cases when the blade 19b creeps into the toiler 3 and when it goes out of the toiler 3 Into the upper space as the amount of' toiler 3 decreases; hence, this causes noise and vibration and besides the Irregular rotation of the shaft lga, which way inconveniently result In image density difference.

z It Is therefore an object of the invention to provide an Improved scraper adapted to suppressing noise by reducing the load applied to a motor for driving the scraper.

For the above object, according the present Invention, there is provided a scraper, which is employed In a toner box of an el(cti-ol)liotogi. il)lilc printer having a photoconductive ineinber, and a d(--.vel-optrig roller for sticking toner to the circumferential surface of said photoconductive member, the rotary axis of said devel.opIng roller being parallel to that of said photoconductive member, toner accommodated in said toner box being supplied to said (levelopliig roller, said toner scraper comprising: a. shaft member rotatably arranged extending in the direction in parallel with the rotary axis of said developing roller; and 20 a plurality of blade members for supplying toner In said toner box, said plurality of blade members being arranged in parallel with said shaft member, one end of said plurality of' blade members being secured on said shaft member, the mounting angles of said blade members being different from each other.

6 Optionally, ail opening is formed oil the surface of each blade member.

Further optionally, each of the blade member has a boss portion to be fitted to said shaft member, s engaging slits and projections being provided at the ends of said boss portion, respectIvely, adjoining two blade members being engaged with the engagement of said slit and projection.

Examples of the present invention will now be described with reference to the accompanying drawings, in which:- Fig. 1 Is a scheimatic sectional view of a printer Including a scraper embodying the present invention; Fig. 2 is a top view of a tractor unit or the printer of' Fig. 1; Fig. 3A IS a perspective view of a scraper embodying the Invention; Fig. 3B is a perspective view of a modification of a scraper; Fig. 3C is an enlarged perspective view of the elements of modified scraper; Fig. 3D shows a sectional view of a toner box; Figs. 4 and 5 are side views of the waste toner sensor; FI.g. 6 shows a disc for use in generating PFS 7 pul-ses; Fig. 7 Illustrates a constructlon of a conventional liquid crystal display panel; Fig. 8 shows a construction of a liquid crystal 5 display panel. of the printer of Fig. 1; Fig. 9 Is a block diagram Illustrating a control system in the printer of Fig.

Figs. 10 and 1.1 are graphs illustrating temperature control. of the heat roller for the printer of Fig. 1; Fig. 12 is a grapli Illustrating power supply control of the printer of Fig. 3.

A printer 1.00 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 pliotoconductive 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 11 on the recording sheet. Light carrying printing data from a host computer or the like Is emitted from a laser scanning unit (LSU) 8 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 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 is transferred onto the recording sheet at a transfer charger 15, and the image thus transferred is fixed by a fixing unit 30. The printer 300 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 13 Is secured 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.

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 9 2. It should be note(] 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 unfixed toner image is caused to pass through the fixing position arid fixed, paper may be wasted to the extent of' the dIstance between transfer and fixing positions. 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 to remain In the printer between the transfer arid 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 wliere data Is riot printed. For this reason, the distance between the transfer position and fixing posi.tIon is preferably arranged equal to the 10.length of one page so tWat 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 when the printing is terminated. When another page Is printed, the unflxed toner Image Is fIxed and the remained page Is discharged. 111 this Way, Waste of' paper due to the fixing of every transferred Jitiage becomes avoidable.

The disLance between t-he t-ralls rel-l- i. rig '111d Fixing positions of this printer 100 is set to 11 inches (27.94 cm) long for the continuous recording sheet which page length is 11 inches (27.94 cin) long.

The transfer unit 10 comprlses 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 charged circumferential surface of the photoconductive drunt 11, the developing unit 14 for sticking toner to the latent image formed on the photoconductive drum 11, the transfer charger 15 for charging the recording sheet FP with electricity to cause the toner image to be transferred to the recording 11 sheet FP, a cleaning unit.1.6 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 photoconductive drum Il should be exchanged after being used for printing a certain number of pages, since it will deteriorate In its properties and fall to ensure clear printing. For example, a limit Of use is set at approximately 20,000 pages. The riumber or printed pages are electrically counted arid recorded in a couriter by a control sy-sterii whIch is described later. This counter Is reset when an upper cover UC is shut after a riew photoconductive drum 11 is Installed.

An outwardly protrude(] projection (riot shown) is provided on a new photoconductive drum 11. As the projection presses down a reset switch, riot shown, on the body side, the control. system can detect that the new photoconductive drum 1-1 Is placed in positi.on. 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) 12 by ineans of a polygon mirror 13a. The laser beams are converged by means of a fO lens (riot shown), reflected by a beam bender 13b so tIvat 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 1.1 provided at the lower' end of the. case 14a, and a plezoel.ectrlc serisor as a toner low sensor 14c. for detecting the presence or absence of the toner In the case.14a.

1n 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 I. eft-liarid 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. A scraper 1-9 is provided In the toner case 14a. The scraper 19 slowly rotates to supply the inner toner to the developing roller 141). The scraper 19 is, as shown in Fig. 3, composed of a rotary shaft 119a to be driven by a main motor, and four pieces of blades 13 1.191), 119c, 119d, 1.1-9c fitted such that the ang-le between the surfaces of the blades 1.19b and 119c is 90 degrees, that of the blades 119b and 119d is 180 degrees, an(] that of the blades 11.9t) and 119e is 270 degrees. In this specification, this angle well. be called a mounting angle, i.e., the mouriting angles, with respect to the blade 119b, of the blades 1.119c, and 119e are 90 degrees, 180 degrees, and 270 degrees, respectively. The blades 119b through 1.19e are driven to rotate slowly in the direction of' tfic arrow shown in Fig. 3.

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 one- quarter as that of the conventJoiial scraper having al-1 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 generatiori.

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 14 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 toner consumptlon Is large on the side where the toner low sensor 14c Is not provided.

Figs. 3B and 3C show a modification of the scraper embodying the present invention The developing unit comprises the developing unit 14 for accommodating toner 3, the developing roller 14b and the like. A scraper 19M is disposed inside the developing unit 14.

The scraper 19M comprises a shaft 220 laterally provided in tile developing unit 14, and the scraper 19M comprises a plurality of blades 219 in the longitudinal direction of the shaft 220.

The blades 219 are the same in configuration, each comprising a boss portion 219a having a hole 221. bored therein so that a shaft 220 is fItted Into the hole, vertical arm portions 21.9b respectlvely projecting from both ends of the boss portion 21.9a in the radial direction of the shaft 220, arid a horizontal arm portion 219c extending In parallel to the shaft 220 so as to connect the leading end portions of both vertical arm portions 219b of each blade 219.

A pair of opposite arcuate matIng walls 222 is formed at both ends of the boss portion 219a.

The mating walls 222 are formed so that when the shaft 220 is fltted into the blade 219,adjoining blades 291 are mated with cacti other, the angle between the surfaces of the adjolnIng blades 219, 219 being 90 degrees or 270 degrees.

The shaft 220 arid the blades 21.9 are assembled throxigh the steps of fitting the shaft 220 Into the blades 219 by mating the mating walls 222 together in such a way that the angle between the arms portIons 219b, 219c of the two adjoinIng blades are 90 degrees.

20and by making a pin 223 that has been passed through the shaft 220 with the mating walls 222 of at least one of the blades positioned at both ends of the shaft 220.

The operation of the scraper wIll subsequently be described. The blades 219 are coupled together via the 25mating walls 222 and the blade 21.9 positioned at the 16 end of the shaft 220 is coupled thereto via the pin 223. When the shaft 220 slowly rotates, the blades 219 also revolve Integrally around the shaft 220. When the blades 219 revolve, the toner 3 is slowly stirred and 5 fed toward the developing roller 14b.

Even when the toner 3 decreases in amount, the blade 219 creep Into the toner 3 and go out of the toner 3 one after another. Consequently, the torque variation caused to the scraper can be suppressed as much as possible and hence the linage Is prevented from being affected by such torque varlation.

Since the horizontal arms 21-9c are arranged in parallel. to the shaft 220, despite the fact that the scraper 19M Is composed of the plurality of blades 219, the toner 3 Is prevented from being unevenly distributed In the developing unit 1A.

Moreover, the boss portion 21.9a, the vertical. arm portions 219b and the horizontal arm portion 219c are formed so that an opening is provided in the central part. Therefore, the torque so applied as to revolve the scraper 19M can be minimized.

Although the plurality of blades may be formed Integrally, the scraper 19M can be made less costly by provIdIng the plurality of separate blade elements 219 in the same shape as described In the embodiment shown.

17 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 pali. of guide rollers 18a, 18b are integrally secured to the arm 1.5a, the guide 5 rollers 18a and 18b being laterally positioned so that contInuous form recording sheet FP is nipped therebetween.

When pr1ntIng Is started, it is needed to ldly rotate the photoconductive drum 1.1 without feedtng the lorecording sheet until the exposed portion of the photoconductive (]ruin 11 Is located at the transfer pos I tion. In this case, the arm 15a Is moved down to lower the guide rollers ISúa, 1-8b, and accordingly, the recording sheet FP is retracted from the 15circuinferential. surface of the photoconductive drum 1.1. 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 opeiilrig 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, and the discharging area, which is uncovered, of the 25transfer 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 charge(] under the Influence of the corona discharge. Moreover, the period of' time iri which tile 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 efriclency in the whole humidity range can be by far improved. Experiments show that thetransfer efficiency is improved to a great extent especially when humidity Is low. It is also possible to arrange 20the 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 25of the transferring process. As the residual toner is 19 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 wnste toner may soil the inside 11' 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 p-lurcility of sensors thus required tends to render the control system complicated.

In the printer of 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 rotatab.ly pivoted about a fulcrum 61 on the body such that a contact portion 62a is located at a position where the bottom side of' the 25waste 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 fornied 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 _line in F1g. 4 so Litat. 11s contact portion 62a ascends and the liglit-sliading wall G2c Is located under the plioto-Jnterrupter 63. In thIs state, the photointerrupter 63 produces a signa-1 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 counterclockwise up to a substantially horizontal state as shown by a broken line of rig. 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 control system decides that no error relating to the 25waste toner box 60 has occurred.

21 When the was te toner I)ox (30 1 s f i.1 I ed w I (It (it(, 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.

III 1.111s w,131, 0110 sells0l- C."I I)e Used W d0eCt. thl't, I'lle waste Loner I)OX 60 Is not 111st.,111ed and thal. Hlo wasLe Coner I)ox 60 Is filled with the waste tonor. Althotigrh this sensor Is so arrangred as Lo monitor Hie presence, or ahsence of' the wasl,er Loner hox and III(' 1111jounL or wnste Loner From Hie balance J11 wC111,111.

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 untL 20 Is arranged so tluat, I.,; shown.In 17.1g. 2, the two endless belts 2.1, 21. stretched 206O.Ween a dri.ving shaft, 23 aiid a dr.1ven shaft 22 are driven hy a main motor 40 vin I H(J(j shown, hereina!"Lor called Lhe t, c 1) 'rind n Areal- (110t, Show") PI-ovided III a I)OX 41 The gonr train exLending from Hle mnin motor 40 111) 25 to the driving shaft 23 in the tractor unit 20 is arranged so (-.oII 1, III,,o,, 9 recordlllf SII(,cl- VP is 22 fed at the velocity of 50 miji/sec. if the tractor unit 20 is independently feeding the recording sheet Pp. 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. The disc 25 is rotatable in response to the rotation of the driven shaft 22. As sliown in Fig. 6, the disc 25 Is provided witli slits 25a which are apart from each other by a predetermined space. The disc 25 is provided between the light emitting member and the light receiving member of the photointerrupter 26, and a pulse corresponding to the moved aniourit 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 20outputted. 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 and the non-perforated portion, respectively.

The positional relation between 23 the disc 25 for use In generating the PFS pulse and a base plate on which tile photo-Jriterrupter 26 is mounted may not be the same in individual printers because of assembly errors. If the slits 25a formed in the disk 525 arerectarigular al-ong the radius, the pulse width thus outputted may vary depending on where the photoInterrupter 26 has detecte(l tile Sl its 25a ill tlin radial (Ilrectiori or Lhe dis(- 25, and depeii(Mig oil wheii the relative position betweeri the disc 25 and the photo- jointerrupter 26 radially shifts.

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

For this reason, the slit 25a formed in tile disc 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 he unified Irrespective or the position where the p1loto-interrupter has detected tile slit in the radial d1rect-lon of the disc 25, thus preventing the "it SJUdglilent oil the error. Ili addltJoii, the ass(mbjy preclsJon required Is eased an(] heiiee assemb.1y workab.11.1ty Is Jitiproved.

24 Sensors for detecting paper errors wJ11 besubsequently described.

In a conventional laser printer using cut sheets, two sensors are providedalong 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.

ln 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 prov.1ded between the feed port 1 and the transfer unit 1.0. I'll i S printer 100 does not print oil 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 1-0 and 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 (.-an 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 detecting 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 FP passed the top sensor 52, the leading end thereof reaches the 25fixing unit 30, whereas the following perforations are 26 positioned at the transfer unit 1.0.

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- prov 1 ded In the upper portion of F! g..1, arid a press roller 32. The coritinuotis recording shect FP is rilpped between the rollers 31, 32, arid is pressed agalrist 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 lie,,,it roller 31 is driven by the main motor 40 to rotate via the F clutch and the gear train an(] 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 fJxing unit 30, whereas the tractor unit 20 mainly functions to prevent skewing of the continuous recording sheet FP.

27 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 5of the sheet, in this printer 100, the press roller 32 facing the heat roller 31 Is made vertically movable so thaL the continuous sheet Is retracted from the heat roller 31 while printing is In standby state.

ln the meantime, the rocking of the press roller 1032 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 15conductive 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 20that 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 assemble the display unit.

In liquid crystal display unit 170 of this 28 embodiment, there is provided a stepped portion Jn 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 arid 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, This circuit comprises a controller 81 for developing the printIng data received from a host computer Into a map on a dot basis and outputt-ing the map, and a driver 82 comprising two CPWs: one of which Is an A-IC 83 for mainly coritrollJng printJiig; and the 15other Is a 13-IC 84 for mainly making error detection. The controller 81. is provided wltti a 1)ufrer whIch Is capable or developing prIntIng data corresponding to three pages of the recording sheet. New data is successively written to the buffer from time to time as 20the 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 29 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 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 photo-interrupter) 26 are connected to the 10A-IC 83 as the sensors for supplying data to the A-IC 83.

The heat roller 31 is so controlled as to have 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 15tO 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.

20The 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 temperature control is effected with an 25allowance 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 5dependIng 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, 1olf the actual temperature Is at the lower llmJ.t of the fJxljig 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 15temperature 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 1'ixIng and the standby temperatures. A point A shows a poInt where the temperature downs to a predetermined 25temperature which Is lowered from the lower limit of 31 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 tipper limit of the fixing temperature before being lowered. In thJs 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.

The B-1C 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 Jain 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 25torier box 60 and the amount of accumulated waste toner, 32 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 5prInter, 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.

101n other word, the disconnection of the sensor and the toner-sufficient condition cannot be distinguished in the conventlonal printer.

In this embodiment. the toner low sensor 14c outputs a high level signal when toner low is detected, wwhile the MIC 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 MIC 84 when toner low is detected by the sensor 14c, when disconnection 20occurs 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 33 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 5 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 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-lC 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 34 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 3.00 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 ST011 sIgnal for. iminedlately stopping the operation of each unit of' the printer. 100 when in 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 sigiic,,ils IndleatIng errors in the drive system are transmitted from the A-1C 83 to the 13-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 predeternilned 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 25a toner overflow, a toner low and a paper empty, while 1 1 the other errors are treated as emergency 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 off, the voltage gradually drops from 24 volts d.c. to ultimately 0 volt as shown by a broken line In F 1 g. 12.

The 5 volts d.c. power supply for the contro-1 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 msee. for storing data after the main power supply is turned off. thart 90 percent of the rated vol tage, the control system may fail to control the driving systerit.

It is because if the voltage becomes less As to 24 volts d.c. power supply for the drIv1rig system, the voltage tends to Fluctuate whIle lt drops because of the operation of a protection circuit on the power stipply slde, 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 vol t on turn! rig of f the 1.00 vol ts a. c. main 36 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 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 drAving 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. 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 portlon 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 25computer to transmit printing data to be reprinted.

n 1 37 Tlie drIver detects C1)e page beIng prInted at present according to the ITS pulse.

Fliere are four kinds of page recovery data to be transmitted; namely, data "0" requiring no recovery, "1" requiring only one wliole page which Js, being transferred to be reprinted, "T' requiring the page being transferred and the page precedingly transferred to be reprinted, and "X' requiring the page being transferred arid preceding two pages to be reprinted.

When trouble occurs during the first page printing, the page data 11111 is transmitted and the controller 81 requests the host computer for- data on the page being privited 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 is setat 11211 or "X' arid the controller 81- requests the host computer for data on the page to 1)e reprInted. Wlien the opening of the upper cover UC Is detected during the third page printing, the page data is set at Oill It may otherwise be arranged that the page data on reprinting Is not determIned by the page that lias undergone trouble as stated above but by the number of pages to be traced back, depending on tbe place wliere Jamming has occurred.

is 38 Although a reference has been made to the use of continuous sheet whose page length is 11 inches (27.94 cm) long in the embodiment shown, the continuous sheet whose page length is 12 inches (30.48 cm) long may also be used 5 by changing a counter for counting PFS pulses therefor.

If 12-inch (30.48 cm) page length sheet is used in this printer 100, some additional arrangements may also be considered such that the last page carrying an unfixed toner image is fixed and discharged when the printing is terminated, and the blank page remained in the printer 100 is fed when printing Is restarted, or that a perforated line is located at the fixing unit w1th the portion one inch from the next perforation being located at the transfer unit 14.

As the plurality of blades of the scraper embodying the present invention are secured to the rotary shaft with their mounting angles being different from each other, tile load applied to the motor can be reduced, compared with a case where all the blades have the same mounting angles, and are used to supply toner at a time. As a result, the load applied to the motor for driving the scraper Is reducible with the effect of suppressing noise.

r 39

Claims (1)

1. A toner scraper, which Is employed in a toner box of an electrophotographic printer having a photoconductive member, and a developing roller for sticking toner to the circumferential surface of said photoconductive member, the rotary axis of said developing roller being parallel to that of said photoconductive member, toner accommodated in said toner box being supplied to said developing roller, said toner scraper comprising: a shaft member rotatably arranged extending in the direction In parallel with the rotary axis of said developing roller; and a plurality of blade members for supplying toner In said toner box, said plurality of blade members being arranged in parallel with said shaft member, one end of said plurality of blade members being secured on said shaft member, the mounting angles of said blade members being different from each other.

2. The scraper according to claim 1, wherein the mounting angles of said blade members secured at one end of said shaft member through the other end of said shaft are gradually changed.

1 41 7. A toner box arrangement for an electrophotographic printer, comprising:a photoconductive member, a developing roller located to be parallel with the axis of said photoconductive member and for sticking toner to the circumferential surface thereof, and toner accommodated in the box; the box further including a shaft member rotatably extending parallel with the rotary axis of the developing roller, and a plurality of blades radially extending from said shaft at 10predetermined angles for supplying the toner to the developing roller.

8. A toner box as claimed in claim 7 wherein the blades are arranged parallel to said shaft member.

is 9. A toner box as claimed in claim 7 or 8 wherein the radial angle between adjacent blades is 90 degrees.

10. A toner box as claimed in any one of claims 7 to 9 20wherein 4 or 7 blades are symmetrically arranged around the shaft axis.

11. A toner box scraper substantially as herein described with reference to figures 1 to 6 and 8 to 12.

12. A toner box scraper substantially as herein described with reference to figures 1 to 6 and 8 to 12.

Published 1991 at The Patent Office. State House. 66/71 High Holborn. bDndonWClR4TP. Further copies may be obtained from Sales Branch. Unit 6, Nine Mile Point. Cwmfelinfach. Cross Keys, Newport, NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Rent.