GB1596843A

GB1596843A - Method and apparatus for forming images

Info

Publication number: GB1596843A
Application number: GB4407577A
Authority: GB
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1976-10-22
Filing date: 1977-10-24
Publication date: 1981-09-03
Also published as: DE2747150A1; JPS5352133A; FR2368740B1; DE2747150C2; GB1596844A; FR2368740A1

Description

(54) METHOD AND APPARATUS FOR FORMING IMAGES (71) We, CANON KABUSHIKI KAISHA, a Japanese Company of 30-2, 3-chome, Shimomaruko, Ohta-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to an image forming apparatus and method in which electrostatic latent images are formed on an image carrier such images being developed and transferred onto a suitable transfer medium.

Various forms of electrophotographic image forming process are known. In one common process a two-layer photo-sensitive member consisting of an electrically conductive substrate and a photoconductive layer is used, the process comprising the steps of charging the photosensitive member with electric charge of either positive or negative polarity, image-wise exposing it to form an electrostatic latent image thereon and developing the latent image so as to produce a visible image. According to another common method, a three layer photosensitive member is used which consists of an electrically conductive substrate, a photoconductive layer and a transparent insulating layer.

In this method the photosensitive member is initially subjected to a primary charging with positive polarity (if the photoconductive layer is of N-type semicondutor) or negative polarity (if the photoconductive layer is of Ptype semiconductor). The photosensitive member is then subjected to image-wise exposure and an AC charging or a secondary charging with a polarity contrary to that of the primary charging to effect selective removal of the electric charge applied to the primary charging thereby to form an electrostatic latent image.

The photosensitive member is subjected to a whole surface exposure to increase the contrast of the latent image which is thereafter developed into a visible image.

Figure 1 of the accompanying drawings schematically illustrates an apparatus for carrying out the steps involved in the method described above.

A rotatable photosensitive member in the form of drum 1 rotates in the direction indicated by an arrow, and a primary charging of the photosensitive drum 1 is carried out with a DC corona discharger 2. Reference numeral 3 designates image light projected onto the drum. A secondary charging is effected with a corona discharger 4. Reference numeral 5 designates a light source for whole surface exposure.

A developing device 6 is used to develop an electrostatic latent image with toner dispersed in a suitable carruer. The developed visible image is transferred onto a transfer sheet 8 using a corona discharge with the same polarity as that of the primary charging. To this end, there is provided a transferring charging device 7. In order to reuse the photosensitive drum 1 after the step of transferring, toner remaining on the drum is removed by means of a cleaning member 10.

However, regarding the cleaning step, a problem occurs in that the toner removed by the cleaning member 10 tends to stick to and accumulated about the cleaning member, and this accumulation adversely affects the next cycle of image formation.

In particular, where the developer used in the electrophotographic process is of the liquid type as prepared by dispersing toner in a liquid carrier, the above mentioned cleaning gives rise to a very troublesome problem in the following manner.

When the electrophotographic apparatus is stopped, that is, when the photosensitive drum becomes still, the liquid developer remains on the cleaning member 10 which may be a cleaning blade and on the surface of the photosensitive drum with which the cleaning member is in contact. During the rest time, the residual liquid developer becomes dry leaving a dry deposit of toner. This dried residual toner is hard to strip from the photosensitive drum and therefore constitutes an unclean portion on the surface of the photosensitive drum when it is rotated to start the next electrophotographic processing cycle. This unclean portion remaining on the drum makes the images produced in the next cycle dirty, and high quality images cannot then be formed. This is a serious disadvantage of the above described conventional electrophotographic processing methods.

A solution of the above mentioned problem is disclosed in Japanese Patent Application Publication No. 31453/1975. According to the solution, the problem caused by the dried residual toner remaining uncleaned on the photosensitive drum is obviated by prewetting the contact portion between the cleaning blade and the photosensitive drum every time operation of the apparatus is started. To this end, a pump is provided for the initial supply of an amount of liquid developer to the cleaning blade before the start of the operation, or a piece of sponge wetted with liquid developer is additionally attached to the cleaning blade.

However, this solution makes the structure of the apparatus rather complicated. Moreover, such solution does not achieve complete cleaning of the toner deposit fromed at the contact portion between the cleaning blade and the photosensitive body during the rest time.

Accordingly this proposed solution is not entirely satisfactory.

According to the present invention, there is provided an image forming apparatus comprising: a rotatable member; image forming means for forming an electrostatic latent image on said rotatable member; developing means for developing the electrostatic latent image; transfer means for transferrring the developed image onto a transfer member; cleaning means displaceable between an operative position for cleaning, and thereby preparing said rotatable member for reuse and an inoperative position;; and control means operative to cause said cleaning means to be brought from its said inoperative position into its said operative position prior to the formation by said image forming means of an electrostatic latent image and to cause said rotatable member to be rotated for a predetermined period after the displacement of said cleaning means to said operative position and before the said formation of an electrostatic latent image, whereby the whole of the portion of the rotatable member on which that image is formed is pre-cleaned by the cleaning means.

According to the present invention there is also provided a method for forming images which method comprises: a first step in which a cleaning means is brought into an operative position to clean the surface of a rotatable member; a second step in which said rotatable member is rotated for a predetermined period of time; a third step in which after the predetermined period, an electrostatic latent image is formed on said rotatable member the latent image so formed is developed and the developed visible image is transferred onto a transfer member; a fourth step in which after the completion of image transfer said rotatable member is rotated so as to effect cleaning thereof by the cleaning means; and a fifth step in which after the rotation effected in said fourth step, said cleaning means is brought into an inoperative position, wherein said predetermined period of time is such that the whole of the portion of the rotatable member on which the image is formed is pre-cleaned by the cleaning means.

In the particular case in which the cleaning means is arranged to contact the surface of the rotatable member in the operative position and the developing means applies liquid developer to said surface, the control sequence may be such that contact portion between the cleaning means and said surface is prewetted. This prewetting may be achieved by causing the developing means to become operative before displacing the cleaning means to its operative position, the interval between these two events being sufficient to ensure that the leading portion of the rotating surface wetted by the developing means reaches the position of the cleaning means before said cleaning means assumes its said operative position.

The developing means may comprise a developing roller arranged to be moved between an operative and an inoperative position in which it respectively contacts, and is displaced from the surface of the rotatable member. Means may be provided for the selective supply of developing liquid to such developing roller.

The developing means may alternatively comprise a developing dish so arranged that the surface of the rotatable member passes therethrough while developing liquid is supplied, for example by pump, to the dish.

The control means is preferably operable so that a predetermined time after completion of image transfer, the cleaning means, having removed residual toner from the rotatable member, is displaced to its inoperative position.

After such displacement of the cleaning means, the rotatable member may continue rotating and the developing means thereafter rendered inoperative.

Embodiments of the invention will now be described by way of example with reference to Figures 2 to 9 of the accompanying drawings, in which: Figure 1 is a schematic diagram of a known electrophotographic apparatus; Figures 2 and 6 schematically show two forms of electrophotographic apparatus to which the present invention is applicable; Figure 3 is a time chart indicating a sequence of operational steps in an electrophotographic method according to the invention; Figure 4 shows one example of a sequence control circuit which may be used in apparatus according to the invention; Figure 5 is a time chart illustrating control signals produced by the circuit of Figure 4; Figures 7 and 8 illustrate other embodiments of the invention; and Figure 9 is a time chart related to the embodi ment of Figure 8.

In the embodiments to be described herein, the previously mentioned problem involved in the transferring type image forming apparatus is avoided by arranging that while the apparatus is at rest, the cleaning means is kept in its inoperative position and immediately before an electrostatic latent image is formed, the cleaning means is brought into its operative position.

In this manner, the possibility of the rotatable photosensitive member and the cleaning means being made dirty during the rest time is minimized.

The cleaning means, which is kept apart from the rotatable member during the rest time of the apparatus, is brought into contact with the rotatable member to which liquid has been applied, just before the formation of an electrostatic latent image and after a predetermined time period has elapsed following the actuation of the developing means by which the liquid is applied. Thereby, the surface of the rotatable member can be made sufficiently wet to reduce the friction between the cleaning means and the rotatable member and to assure smooth rotation of the rotatable member.

The formation of an electrostatic latent image is initiated only when the rotatable member has been rotated for a predetermined time after the actuation of the cleaning means. This measure has an effect on the formation of good latent images while preventing any portion from being made dirty when contacted by the cleaning means.

After the end of the transfer step (after the completion of one cycle of the process), the residual toner is removed by the cleaning means and thereafter the cleaning means is displaced from the rotatable member.

After the cleaning means is brought into its position spaced apart from the rotatable member, the rotatable member is further rotated while keeping the developing means in contact so that the rotatable member may be cleaned by means of the developing means. In employing this measure, it is advisable to remove the electric charge on the surface of the rotatable member so as to make the potential substantially unigorm all over the surface. This has the effect of preventing any further development of the rotatable member and producing a better cleaning of the rotatable member. Accordingly, when the apparatus is not operating, the rotatable member and the cleaning means stand in a clean condition thereby ensuring the formation of good clean developed images when the apparatus is restarted.

Referring now to Figure 2, the first embodiment of the invention will be described in detail.

The basic arrangement of the electrophotographic copying apparatus schematically shown in Figure 2 and the basic process to be carried out using the apparatus correspond to those of the apparatus to which reference has already been made in connection with Figure 1. In Figure 2, the reference numerals 1 to 8 designate the same members and devices as in Figure 1.

The apparatus of Figure 2 includes a roller type developing device comprising a developing roller 9. To effect developing, the roller 9 applies liquid developer to the photosensitive drum 1. The photosensitive drum 1 is made by forming a previously mentioned three-layer endless photosensitive member into a drum. A cleaning blade 10 is so arranged that when cleaning is effected, the edge of the blade 10 may come in contact with the rotataing surface of the drum 1 at a point where that surface moves downwardly.

Reference numeral 12 designates a lamp provided for exposing an original to be copied to illuminating light. The image of original is focused on the surface of the photosensitive drum 1 through an optical system 14. The lamp 12 and the optical system 14 are moved forwardly in synchronism with the rotation of the drum 1 so as to scan the original in the manner of slit exposure and then to focus the image of the original onto the surface of the drum 1.

After the end of the forward movement, the lamp 12 and the optical system 14 are returned to their respective starting or home positions.

Reference numeral 11 designates a power source which is provided to apply a bias voltage to the developing roller 9 for the purpose of adjusting the amount of toner to be applied to the drum and/or eliminating fog as desired.

In this first embodiment, the developing roller 9 is brought into contact with the photo-.

sensitive drum 1 before the process of exposure is carried out. After the surface contacted by the developing roller has passed the area of the cleaning blade 10, the latter is brought into contact with the drum 1 and for a predetermined time period the drum is rotated idly.

Thereafter, an electrostatic latent image is formed on the photosensitive drum 1 by means of the charging devices 2 and 4 and the lamp 12. Further, after the end of the process of transferring, the drum 1 is rotated idly also for a predetermined time period while keeping both the cleaning blade 10 and the developing roller 9 in contact with the drum. Thereafter, the cleaning blade is brought to a position in which it is out of contact with the drum, which position is hereinafter referred to also as the non-contacting position. After the surface portion of the drum at which the cleaning blade was brought into its non-contacting position has passed over the area of the developing roller 9, the latter is also brought into its non-contacting position.

As will be understood from the above, both the developing roller 9 and the cleaning blade 10 can each assume two different positions namely: (1) a position in which it (i.e. the roller 9 or blade 10) is in contact with the drum 1; and (2) a position in which it is out of contact with the drum 1.

Various different combinations of these positions may be considered. According to the above described first embodiment of the invention, five combinations thereof are used, and the time chart of Figure 3 shows five steps, namely Steps A to E wherein these five combinations of the positions are used respectively.

When a power source for the copying apparatus is turned on at the beginning of Step A wherein copying is not yet started, then the photosensitive body 1 starts rotating, but at this point neither the cleaning blade 10 nor the developing roller 9 are in contact with the photosensitive drum 1. This prevents the surface of the drum from being locally stained with toner during the rest time of copying operation. If the cleaning blade 10 and the developing roller 9 had been in contact with the drum prior to this rotation, then some amount of liquid developer would have flowed behind each of the blade and the roller due to capillary action and thereby sticking of toner on the drum surface would have been caused.

At Step B, the cleaning blade 10 is maintained out of contact with the photosensitive drum 1, but the developing roller 9 is brought into contact with the photosensitive drum 1 which continues rotating. This results in wetting of the surface of the photosensitive drum, which wetting reduces the frictional resistance between the cleaning blade 10 and the photosensitive drum 1 when cleaning is carried out and also facilitates the cleaning. The potential existing on the photosensitive drum at this time is not limitative and may be at any level.

At Step C, the cleaning blade 10 is also brought into contact with the photosensitive drum 1 while keeping the developing roller 9 in contact with it. In this position, a preliminary cleaning is carried out to remove from the surface of the photosensitive drum 1 the toner which had previously dried and has now become suspended once again. During this step and after the drum has rotated at least over the distance from the cleaning area to the latent image forming area (exposure area), copying may be started by turning the copy button on.

Upon the end of the transferring process, cleaning is carried out before the residual process, cleaning is carried out before the residual toner on the circumference of the drum 1 is dried.

At Step D, the cleaning blade 10 is brought into its non-contacting position while keeping the roller 9 in contact with the photosensitive drum 1 and in this position the latter is further rotated. Thereby, a cleaning of the whole surface of the photosensitive body 1 is completely effected with the developing roller 9, but without using the cleaning blade. At this time point, the photosensitive body has a potential under which no developing can be effected. In particular a bias voltage may be applied to the developing roller from the bias power source 11 so as to prevent the toner from sticking on the surface of the photosensitive drum 1 and thereby to increase the cleaning efficiency. The potential under which no developing can be effected (non-developing potential) mentioned above may be obtained by discharging the drum surface using, for example, light or AC corona discharge.It is also possible to selectively apply to the developing roller 9 at Steps C and D biases which are different from each other in polarity or potential.

At Step E which is the last step, both the cleaning blade 10 and the developing roller 9 are out of contact with the photosensitive body 1 and the rotation of the latter is stopped. By keeping the blade 10 and the roller 9 apart from the surface of the photosensitive drum 1 during this step, as in Step A, the problem of sticking of toner on the drum surface, the blade and/or the roller can be prevented. Such problems as mentioned above, may be caused while the apparatus is at rest and when the cleaning blade and/or the developing roller remain in contact with the photosensitive drum. Under these conditions, residual toner flows, under capilliary action between these members, where it dries and sticks, thereby forming dirty portions on the photosensitive drum.

One example of a sequence control circuit of which may be used to establish the timing of the above described Steps A-E is shown in Figure 4 and its operational time chart is given in Figure 5.

Referring to Figure 4, each of the reference numerals 41, 42 and 43 designates a flip-flop of the conventional type which puts out a step signal from its terminal Q (a step signal from Q is opposite in direction to that from Q) responding to an impulse signal introduced into its terminal S and which is reset by an impulse introduced into its terminal res. Timers of the known type 44-49 put out the signals inputted after the time delays of -t6 respectively and cease to output when no input comes in. Reference numeral 51 is a known differential circuit for forming impulses. 52-55 are conventional inverter circuits used for inverting the input sig- nals, 56, is an OR-circuit of the known type and 57-61 are AND-circuits which are also of the known type. Sw is a main switch signal by which the power source for the copying machine is cut in and CP is an input signal produced by the copy button for starting copying.

END is a signal for indicating the completion of copying process. ROT is an output signal for rotating the photosensitive drum 1, DEV is a signal for bringing the developing roller 9 into contact with the photosensitive drum and CLIN is a signal for bringing the cleaning blade 10 into contact with the photosensitive drum.

CHAG 1, CHAG 2 and CHAG 3 are signals for actuating the primary charged device 2, the secondary charging device 4 and the transferring charging device 7 respectively. LAMP 1 is a signal for putting the lamp 12 for image-wise exposure and LAMP 2 is a signal for putting on the lamp 5 for whole surface exposure. OPT is a signal for moving forward and backward the optical scanning system 4. TI-T6 are output signals coming from the timers 44-49 respectively.

Signals DEV and CLIN are put into solenoids by which the developing roller 9 and the cleaning blade 10 are brought into contact with the photosensitive drum 1 respectively. Signals ROT, LAMP and CHAG are put into relays by which electric power lines extending to the drum motor, lamps and high voltage transformer are turned on. The signal OPT is put into a clutch for moving the optical system synchronously with the drum motor.

The above described signals are produced with the timing shown in Figure 5.

The operation of the above described apparatus is as follows: Upon turning the power source switch on, the drum starts rotating and after the time delay of tl, the developing device is actuated.

After the further time delay of t2, the cleaning blade is actuated by the signal T1 to carry out a preliminary cleaning. Thereafter, a pushing down of the copy button results in the production of the signals CHAG 2 and LAMP 2 by which the lamp 5 and the AC corona discharger 4 are actuated respectively so that the electric charge on the photosensitive body is removed.

After a time delay t3, the lamp 12 for exposure is put on by the signal LAMP 1 and the optical scanning system is actuated by signal OPT so as to initiate an exposure scanning of the original and thereby an electrostatic latent image is formed. Upon the completion of the scanning, the lamp 12 and the primary charging device 2 are tumed off. When the optical system is returned to its starting position, an END signal is produced. During the time period between the signal END and the signal T4 produced with the time delay oft4, the photosensitive drum is made to continue rotating while keeping the lamp 5 and the AC corona discharger 4 turned on and the cleaning blade 10 and developing device maintained activated.This discharges the surface of the photosensitive drum to a substantially uniform potential and also ensures removal of residual toner from the surface before the toner becomes dry. After this delay T4 signal CLIN ceases and the cleaning blade is accordingly displaced from the drum. Thereafter during the delay time of tS, the drum is rotated idly further with the cleaning blade being out of operation as to prevent the blade from being stained with toner. Finally, the drum is stopped after the time delay of t6.

The primary charging commences earlier than the exposure according as the relative position between the primary charging device and the exposing portion around the photosensitive drum.

The signal of END corresponds to the completion of transferring. While it is preferable to use a time longer than the time required for one revolution of the drum as each of the delay times that6, the time for each of the delay times t1 -ts should be determined taking copying speed into consideration. ON-OFF of the rotation of the drum and that of the operation of the developing device may be effected simultaneously. Also it is possible to control the movement of the drum in such manner that if the copy button is not pushed within a predetermined time period after putting out the signal SW, the rotation of the drum is automatically stopped.

The circuit used to produce the signals T1- T6 with the delay times t1 -t6 is not limited to the timer circuit shown in which capacitor charging time is used to determine delay time.

Any type of circuit suitable for this purpose may be employed. For example, where the photosensitive member on the drum is endless, a circuit may be used in which a time signal is obtained by counting a series of clock pulses produced corresponding to the rotation of the drum. For a photosensitive member having terminating edges, a circuit may be used which can derive a time signal by scanning the position of a cam fixed to the drum.

Figure 6 shows another form of electrophotographic apparatus to which the present invention is applicable. In this apparatus the developing device comprises a developing dish 60 and a reservoir 62. A pump 61 pumps up liquid developer from the reservoir 62 to the developing dish 60. Again, the cleaning blade and the developing device can each assume either of two states independently, though whereas in the previous embodiment the operative state of the developing means consisted of the developing roller being in contact with the photosensitive drum, in the present embodiment the pump 61 is made active to render the developing means operative. For this type of electrophotographic system, a sequence control circuit and timing similar to that shown in Figures 4 and 5 can be used.

Another developing system shown in Figure 7 is essentially of the same type as that of Figure 6. The difference therebetween resides in the provision of a pipe 70 and an additional charging device 71 for the system of Figure 7.

The operational timing of this system corresponds to that of Figure 6.

The pipe 70 is so disposed as to supply liquid developer pumped by the pumo 61 to the contact area between the cleaning blade 10 and the surface of the photosensitive drum 1.

The charging device 71 is a negative (-) corona charging device the function of which is to limit the quantity of liquid developer adhering to the surface of the photosensitive body after developing. The charging device may be actuated in synchronism with the operation of the developing device. More preferably, this charging device may be turned on when the surface area of the photosensitive drum at which developing commenced, has passed the position of the charging device and turned off when the surface area of the photosensitive drum at which developing was completed, has passed it.

In this example, the cleaning blade 10 may be brought into contact with the photosensitive drum 1 with some time delay after tuming the pump 61 on, so as to make the surface of the photosensitive drum wet with the liquid supplied through the pipe 70. More particularly, the pump 61 is actuated when the power source switch is turned on, then the cleaning blade 10 is brought into contact with the photosensitive drum 1 and the latter is rotated for a predetermined time. Alternatively, the photosensitive drum 1 may be started rotating synchronously with the tuming-on of the power source switch.

As a modification of the system of Figure 7, a developing liquid absorbing and retaining member 73 which may be a piece of sponge or the like may be disposed in the vicinity of the cleaning blade as suggested by the phantom line in Figure 7. This additional member 73 is mounted in such a manner that it may come into or out of contact with the photosensitive body 1 in a synchronized relation with the operational movement of the cleaning blade into contact or out of contact with the same photosensitive drum. This modification permits the cleaning blade to be brought into contact with the surface of the photosensitive drum almost simultaneously with the turning of the power source switch.

When the cleaning blade is of the type which exhibits particularly low contacting friction with the drum surface, or when a roller type cleaner or a brush cleaner is used instead of blade type cleaner, then such cleaner can be brought into contact with the surface of the photosensitive drum simultaneously with switching on the power source.

In summary, the cleaning blade is made to contact the surface of photosensitive drum prior to a predetermined pre-rotation thereof, also, the contacted portion of the drum surface is preferably prewetted.

In the contact position of cleaning blade such blade is sufficiently press-contacted with the photosensitive drum to effect cleaning. The cleaning blade may be brought into such contact position gradually under pressure.

Figure 8 illustrates another embodiment of the present invention. The reference numerals 14 used in Figure 8 designate the same members as in Figure 2. The developing roller used in this embodiment is composed of a rigid core body, a layer of continuous elastic foam covering the core body and a porous layer having a plurality of pores passing through the layer over the elastic foam layer. When the developing roller 9 is press-contacted with the photosensitive drum 1 such roller becomes elastically deformed in the direction normal to the contact surface. In the liquid developer 89 received in an inner vat 86, there is a refresh roller 85 which contacts the developing roller 9 under pressure. The refresh collar 85 serves to exchange the liquid developer contained in the elastic foam layer of the developing roller 9.

The operational sequence of this embodiment is shown in Figure 9. At the beginning of Step B, at which point the cleaning blade 10 is out of contact with the photosensitive drum 1, the developing roller 9 is brought into contact with the photosensitive drum 1 as well as with the refresh roller 85. At the same time, the pump 88 is brought into operation to supply the liquid developer 89 from the developer tank 87 to the inner vat 86 and rotation of the photosensitive drum 1 is started. The contact of the developing roller 9 with the photosensitive drum 1 causes the liquid developer 89 contained in the elastic foam layer of the roller 9 to be squeezed out over the surface of the drum 1 through the porous layer of the roller.As a result, the surface of the photosensitive drum is made wet, thereby reducing the frictional resistance between the photosensitive drum 1 and the cleaning blade 10. It is preferable to keep the AC charger 4 turned on during this step.

However, the potential on the photosensitive drum may be at any level.

At the beginning of Step C the cleaning blade is brought into contact with the drum, and during this step a pre-cleaning is carried out with both the cleaning blade 10 and the developing roller 9 in contact with the photosensitive drum 1. Copying is carried out during this step, but only after the surface of the drum 1 has been cleaned.

The process by which an electrostatic latent image formed on the photosensitive drum 1 is developed by the action of the developing roller 9 proceeds in the following manner: The developing roller 9 rotates in the direction of the arrow and at the same peripheral speed as that of the photosensitive drum 1.

When the developing roller 9 comes into presscontact with the photosensitive drum 1, liquid developer is brought to the drum by the rotation of the developing roller; liquid developer is squeezed out from the elastic foam layer of the roller by the pressure of contact between the developing roller and the photosensitive drum, and this liquid developer serves to develop the electrostatic latent image on the photosensitive drum. When the press-contact between the roller 9 and the drum 1 is released, residual liquid developer is removed from the photosensitive drum 1 by absorption of elastic foam layer, as this layer resumes its undeformed shape. The developing roller 9 separated from the photosensitive drum continues to rotate and comes into contact with the refresh roller 15 disposed under the liquid level in the inner vat 16 so that an exchange of liquid developer can be effected by the contacting pressure between the two rollers. The developing roller 9 now containing therein a fresh liquid developer can again be brought into contact with the photosensitive drum 1 in the next cycle of the above described developing process. This process is repeated as desired.

At Step D in Figure 9 the cleaning blade 10 is brought into its non-contracting position while keeping the developing roller 9 in contact with the photosensitive drum 1 and in this position, the latter is further rotated so as to carry out cleaning of the whole surface of the photosensitive drum 1 by means of the developing roller 9 without using the cleaning blade 10.

At the time of this cleaning, the photosensitive drum should have a non-developing potential.

If desired, the effect of this cleaning can be enhanced by applying an appropriate bias voltage to the developing roller 9 using the bias power source 11. It is also possible selectively to apply to the developing roller 9 at Step C and at Step D biases which are different from each other in polarity or potential.

When the developing roller is brought into a position apart from the photosensitive drum at Step E hereinafter described while retaining the inner vat 86 full with the liquid developer, there may arise the problem of developer sticking to the surface of the photosensitive drum.

More particularly, upon bringing the developing roller 9 apart from the photosensitive drum 1, the liquid developer drawn up by the roller and the liquid developer squeezed out from the elastic foam layer of the roller adheres to the surface of the photosensitive drum 1 and during the period of non-operation this developer may be dried to form a solid deposit which inhibits proper cleaning of the photosensitive drum.

In the described apparatus of Figure 8, this problem can be avoided very simply by merely stopping the pump for supplying the liquid developer to the inner vat 86 at the appropriate time. Namely, during the fourth step, Step D, the liquid developer in the inner vat 86 is removed by stopping the pump 88.

After removal of the liquid developer from the inner vat, the developing roller 9 rotates in air while being kept in contact with the photosensitive drum and the refresh roller. During this rotational movement of the developing roller, liquid developer remaining in the elastic foam layer of the roller is removed by the contact pressure between the developing roller and the refresh roller. The developing roller thus free from the liquid developer serves to clean up the surface of the photosensitive drum with which the developing roller is in contact, and little or no undesired developer is left on the surface of the photosensitive drum when the developing roller is separated from it.

In Step E both the cleaning blade 10 and the developing roller 9 are out of contact with the photosensitive drum 1.

Step A and Step E in Figure 9 correspond to Steps A and E of the sequence shown in Figure 3 respectively.

To carry out the sequence control of the above described embodiment the apparatus and timing shown in Figures 4 and 5 may be used, the signal T1 being used to turn the pump 88 on and the signal T4 being used to turn it off.

Regarding the various embodiments described above, the following points concerning the operational sequence are pertinent: Within a predetermined time period after the cleaning blade comes in contact with the photosensitive body (during the rotation of the photosensitive drum), exposure of the original formation of the latent image cannot be initiated. But, if the copy button is not pushed during a second time period following the first mentioned time period, then the rotation of the photosensitive drum can be stopped so as to protect the drum surface. At the same time, the cleaning blade also may be brought into its non-contact position.

When the copy button is pushed after the cleaning blade has moved to its contacting position the optical system starts moving to effect exposing after the photosensitive drum has been rotated at least over the distance from the cleaning area to the exposing area (a predetermined rotation). However, if the cleaning blade was brought to its non-contacting position before pushing the copy button, exposure is initiated only after passing through the same sequence of steps as that performed after switch ing-on of the power source.

When the copy button is again pressed during the rest time of copying and during Step C, then exposure starts instantly almost simultaneously with the pushing of the copy button or immediately after a predetermined rotation of the photosensitive drum.

A pushing of the copy button during Step D will bring the cleaning blade into contact with the photosensitive drum and after a predetermined rotation of the latter in this position, exposure will be initiated.

If the copy button is pushed during Step E, the developing roller and the cleaning blade will be successively brought into contact with the photosensitive drum in the same manner as in the above mentioned step, and thereafter exposure will start after a predetermined rotation of the photosensitive drum, A pushing of the copy button after the rotation of the photosensitive drum ceases, will initiate exposure through the same sequence of steps as that started from a switching-on of the power source.

Reference is hereby made to copending application No. 8023808, Serial No. 1596844 which is divided from this application.

WHAT WE CLAIM IS: 1. An image forming apparatus comprising: a rotatable member; image forming means for forming an electrostatic latent image on said rotatable member; developing means for developing the electrostatic latent image;

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. now containing therein a fresh liquid developer can again be brought into contact with the photosensitive drum 1 in the next cycle of the above described developing process. This process is repeated as desired. At Step D in Figure 9 the cleaning blade 10 is brought into its non-contracting position while keeping the developing roller 9 in contact with the photosensitive drum 1 and in this position, the latter is further rotated so as to carry out cleaning of the whole surface of the photosensitive drum 1 by means of the developing roller 9 without using the cleaning blade 10. At the time of this cleaning, the photosensitive drum should have a non-developing potential. If desired, the effect of this cleaning can be enhanced by applying an appropriate bias voltage to the developing roller 9 using the bias power source 11. It is also possible selectively to apply to the developing roller 9 at Step C and at Step D biases which are different from each other in polarity or potential. When the developing roller is brought into a position apart from the photosensitive drum at Step E hereinafter described while retaining the inner vat 86 full with the liquid developer, there may arise the problem of developer sticking to the surface of the photosensitive drum. More particularly, upon bringing the developing roller 9 apart from the photosensitive drum 1, the liquid developer drawn up by the roller and the liquid developer squeezed out from the elastic foam layer of the roller adheres to the surface of the photosensitive drum 1 and during the period of non-operation this developer may be dried to form a solid deposit which inhibits proper cleaning of the photosensitive drum. In the described apparatus of Figure 8, this problem can be avoided very simply by merely stopping the pump for supplying the liquid developer to the inner vat 86 at the appropriate time. Namely, during the fourth step, Step D, the liquid developer in the inner vat 86 is removed by stopping the pump 88. After removal of the liquid developer from the inner vat, the developing roller 9 rotates in air while being kept in contact with the photosensitive drum and the refresh roller. During this rotational movement of the developing roller, liquid developer remaining in the elastic foam layer of the roller is removed by the contact pressure between the developing roller and the refresh roller. The developing roller thus free from the liquid developer serves to clean up the surface of the photosensitive drum with which the developing roller is in contact, and little or no undesired developer is left on the surface of the photosensitive drum when the developing roller is separated from it. In Step E both the cleaning blade 10 and the developing roller 9 are out of contact with the photosensitive drum 1. Step A and Step E in Figure 9 correspond to Steps A and E of the sequence shown in Figure 3 respectively. To carry out the sequence control of the above described embodiment the apparatus and timing shown in Figures 4 and 5 may be used, the signal T1 being used to turn the pump 88 on and the signal T4 being used to turn it off. Regarding the various embodiments described above, the following points concerning the operational sequence are pertinent: Within a predetermined time period after the cleaning blade comes in contact with the photosensitive body (during the rotation of the photosensitive drum), exposure of the original formation of the latent image cannot be initiated. But, if the copy button is not pushed during a second time period following the first mentioned time period, then the rotation of the photosensitive drum can be stopped so as to protect the drum surface. At the same time, the cleaning blade also may be brought into its non-contact position. When the copy button is pushed after the cleaning blade has moved to its contacting position the optical system starts moving to effect exposing after the photosensitive drum has been rotated at least over the distance from the cleaning area to the exposing area (a predetermined rotation). However, if the cleaning blade was brought to its non-contacting position before pushing the copy button, exposure is initiated only after passing through the same sequence of steps as that performed after switch ing-on of the power source. When the copy button is again pressed during the rest time of copying and during Step C, then exposure starts instantly almost simultaneously with the pushing of the copy button or immediately after a predetermined rotation of the photosensitive drum. A pushing of the copy button during Step D will bring the cleaning blade into contact with the photosensitive drum and after a predetermined rotation of the latter in this position, exposure will be initiated. If the copy button is pushed during Step E, the developing roller and the cleaning blade will be successively brought into contact with the photosensitive drum in the same manner as in the above mentioned step, and thereafter exposure will start after a predetermined rotation of the photosensitive drum, A pushing of the copy button after the rotation of the photosensitive drum ceases, will initiate exposure through the same sequence of steps as that started from a switching-on of the power source. Reference is hereby made to copending application No. 8023808, Serial No. 1596844 which is divided from this application. WHAT WE CLAIM IS:

1. An image forming apparatus comprising: a rotatable member; image forming means for forming an electrostatic latent image on said rotatable member; developing means for developing the electrostatic latent image;

transfer means for transferring the developed image onto a transfer member; cleaning means displaceable between an operative position for cleaning, and thereby preparing said rotatable member for reuse and an inoperative position; and control means operative to cause said cleaning means to be brought from its said inoperative position into its said operative position prior to the formation by said image form- ing means of an electrostatic latent image and to cause said rotatable member to be rotated for a predetermined period after the displacement of said cleaning means to said operative position and before the said formation of an electrostatic latent image, whereby the whole of the portion of the rotatable member on which that image is formed is pre-cleaned by the cleaning means.

2. An image forming apparatus as claimed in Claim 1, wherein said cleaning means is arranged to contact the surface of the rotatable member in said operative position and said developing means comprises means for applying a liquid developer to said rotatable member.

3. An image forming apparatus according to Claim 2 wherein said cleaning means is a blade cleaner.

4. An image forming apparatus according to claim 2 or claim 3 wherein the arrangement is such that the surface of the rotatable member is wet at the point at which said cleaning means is brought into contact with said surface.

5. An image forming apparatus according to claim 4 wherein to make said surface wet, the control means operable to actuate the developing means prior to the contact of said cleaning means with said surface.

6. An image forming apparatus according to Claim 4 wherein to make said surface wet means are provided to apply liquid developer to the said surface in the region of the cleaning means.

7. An image forming apparatus according to any of claims 2 to 6 wherein said developing means comprises a developing roller and wherein upon actuation of the developing means said roller is caused to be displaced between an operative position in which the roller applies liquid developer onto said surface of the rotatable member, and an inoperative position.

8. An image forming apparatus according to any of claims 2 to 6 wherein said developing means comprises a developing dish through which the surface of the rotatable member travels and wherein upon actuation of said developing means said dish is caused to be supplied with liquid developer.

9. An image forming apparatus according to any preceding claim wherein said control means is operative to cause said rotatable member to be rotated for a predetermined period after the completion of image transfer by said transfer means whereby residual toner is removed from the surface of the rotatable member by the cleaning means, and then to cause said cleaning means to be displaced to its inoperative position.

10. An image forming apparatus according to claim 9 wherein said control means is operable to cause said developing means to be deactuated after said displacement of said cleaning means to its inoperative position.

11. An image forming apparatus according to claim 10 when including the features recited in claim 7, the inoperative position of the developing roller being one in which it is displaced from the rotatable member, and further comprising means for supplying liquid developer to said roller, said control means being operable upon completion of image transfer to first render inoperative the liquid developer supplying means, then displace the cleaning means to its inoperative position, and finally, when the trailing portion of the surface cleaned by the cleaning means has passed the developing means, move the developing roller to its inoperative position.

12. An image forming apparatus according to any of claims 9 to 11 and further including means for discharging the surface of said rotatable member after the displacement of said cleaning means to its inoperative position.

13. A method for forming images which method comprises: a first step in which a lceaning means is brought into an operative position to clean the surface of a rotatable member; a second step in which said rotatable member is rotated for a predetermined period of time; a third step in which after the predetermined period, an electrostatic latent image is formed on said rotatable member, the latent image so formed is developed and the developed visible image is transferred onto a transfer member; a fourth step in which after the completion of image transfer, said rotatable member is rotated so as to effect cleaning thereof by the cleaning means; and a fifth step in which after the rotation effected in said fourth step, said cleaning means is brought into an inoperative position, wherein said predetermined period of time is such that the whole of the portion of the rotatable member on which the image is formed is pre-cleaned by the cleaning means.

14. An image forming method according to claim 13 wherein liquid is applied to the surface of said rotatable member prior to the execution of the first step.

15. An image forming method as claimed in claim 13, wherein said rotatable member is rotated for a predetermined time after the completion of the fifth step.

16. An image forming method as claimed in claim 15, wherein after said predetermined time, a developing means which previously applied developing liquid to said rotatable member is rendered inoperative.

17. Image forming apparatus, substantially as herein described with reference to any of Figures 2 to 9 of the accompanying drawings.

18. A method of forming images, substantially as herein described with reference to any of Figures 2 to 9 of the accompanying drawings.