GB1596844A - Image forming apparatus - Google Patents

Description

PATENT SPECIFICATION

I" ( 21) Application No 23808180 ( 22) Filed 24 October 1977 00 ( 62) Divided Out of No 1596843 ú ( 31) Convention Application No 51/127010 ( 32) Filed 22 October 1976 in ( 33) Japan (JP) ( 44) Complete Specification published 3 September 1981 ( 51) INT CL 3 G 03 G 15/28 // 21/00 ( 52) Index at acceptance B 6 C 1200 1231 1232 1241 1250 WC ( 11) 1 596 844 1249 ( 54) IMAGE FORMING APPARATUS ( 71) We, CANON KABUSHIKI KAISHA, a Japanese Company of 30-2 3-chome, Shomonaruko, 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 in which electrostatic latent images are formed on an image carrier, such images being developed with toner and transferred onto a suitable transfer medium.

The invention is particularly concerned with the means by which after image transfer the surface of the image carrier is cleaned of toner to prepare the carrier for reuse.

Various forms of electrophotographic image forming process are known In one common process a two-layer photosensitive 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 semiconductor) or negative polarity (if the photoconductive layer is of P-type 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 by 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.

According to the present invention there is provided an image forming apparatus comprising:

a rotatable member; image forming means for forming a latent image on said rotatable member, said image forming means having reciprocable scanning means arranged to perform a forward scan in which the rotating member is exposed to image light, and then to return to a home position; developing means for developing the latent image with toner; transfer means for transferring the developed image onto a transfer member; cleaning means for cleaning the surface of the rotatable member after the transfer of developed image therefrom; rotating means for rotating said rotatable member to permit latent image formation, development and transfer and for continuing rotation of said rotatable member after the completion of image transfer, and to permit said rotatable member to undergo a cleaning operation performed by said cleaning means; and bias applying means for applying a given bias potential to said developing means for inhibit 75 ing the deposition of toner by said developing means onto the rotatable member, during a predetermined period after the completion of development of said latent image.

The application of the bias potential in this 80 manner permits cleaning of the rotatable member by the developing means, with the developing means being maintained in an operative condition until the elapse of the said predetermined period A further, different bias poten 85 tial may be applied to the developing means during the formation of the image.

Embodiments of the invention will now be described by way of example with reference to Figures 2 to 9 of the accompanying drawings, in 90 which:

Figure 1 is a schematic diagram of a known electrophotographic apparatus; Figures 2 to 6 schematically show two forms of electrophotographic apparatus to which the 95 present invention is applicable; 1 596 844 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 embodiment of Figure 8.

Figure 1 of the accompanying drawings schematically illustrates a known form of electrophotographic apparatus.

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 carrier 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 accumulate 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 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.

In the forms of apparatus to be described herein, the previously mentioned problem involved in the transferring type image forming apparatus is avoided by arranging that while 70 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 75 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 80 the apparatus, is bought 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 actua 85 tion of the developingmeans 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 90 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 95 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 100 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 105 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 is cleaned by means of the developing means During this 110 further rotation an appropriate bias potential is applied to the developing means to inhibit the deposition of toner on the rotatable member, and thereby produce a better cleaning of the rotatable member Accordingly, when the 115 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 120 With reference to Figure 2, the first embodiment of the invention will be described in detail.

The basic arrangement of the electrophotographic copying apparatus schematically shown 125 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 desig 130 1 596 844 nate 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 rotating 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 photosensitive 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 capilliary 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 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 is 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 poten1 596 844 tial 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 The bias potential applied during step D, i e during cleaning by the developing roller is different from, a bias potential applied during step C, i e during copying, 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 oft 1 -t 6 respectively and cease to output when no input comes in Reference numeral 51 is a known differentiation circuit for forming impulses 52-55 are conventional inverter circuits used for inverting the input signals, 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 charging 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 T 1-T 6 are output signals coming from the timers 44-49 respectively.

Signals DEV and CLIN are put into sole 70 noids 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 75 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 80 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 85 delay of t I, the developing device is actuated.

After the further time delay of t 2, the cleaning blade is actuated by the signal T 1 to carry out a preliminary cleaning Thereafter, a pushing down of the copy button results in the produc 90 tion 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 t 3, the lamp 12 for exposure 95 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, 100 the lamp 12 and the primary charging device 2 are turned 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 T 4 produced with the 105 time delay of t 4, 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 110 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 t 4 from the return of the optical system to its 115 home position signal CLIN ceases and the cleaning blade is accordingly displaced from the drum leaving the developing device still active.

Thereafter during the delay time of ts, the drum is rotated idly further with the cleaning 120 blade out of operation as to prevent the blade from being stained with toner, but with the developing device still active Finally, after rendering the developing device inactive and after a further time delay of t 6, the drum is 125 stopped.

The primary charging commences earlier than the exposure according as the relative position between the primary charging device and the exposing portion around the photo 130 1 596 844 sensitive 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 t 4-t 6, the time for each of the delay times tl -t 3 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 TlT 6 with the delay times t l-t 6 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 pump 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 70 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 turning the 75 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 80 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 turning-on of the power source switch 85 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 90 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 95 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-on of 100 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 105 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 110 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 115 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 120 the present invention The reference numerals 1-4 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 cover 125 ing 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 de 130 1 596 844 formed 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 roller 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 rotatation of the photosensitive drum 1 is started The contact of the developing roller 9 with the photosensitve drum 1 causes the liquid developer 89 contained in the elastic foam layer of the roller9 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 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 in the next cycle of the above described developing process This pro 70 cess is repeated as desired.

At Step D in Figure 9 the cleaning blade 10 is brought into its non-contacting position while keeping the developing roller 9 in contact with the photosensitive drum 1 and in this posi 75 tion, 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 80 drum should have a non-developing potential.

The effect of this cleaning is enhanced by applying an appropriate bias voltage to the developing roller 9 using the bias power source 11, this bias being such as to prevent toner 85 sticking onto the drum Again, the biases applied to the developing roller 9 at Step C and at Step D biases are different from each other in polarity or potential.

When the developing roller is brought into a 90 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 95 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 100 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 105 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 re 110 moved 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 115 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 120 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 125 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 130 1 596 844 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 Ti being used to turn the pump 88 on and the signal T 4 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 noncontact 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 switching-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 co-pending application No 44075/77, Serial No 1596843, from which this present application is divided.

Claims (1)

1. WHAT WE CLAIM IS:-

   1 An image forming apparatus comprising:

   a rotatable member; image forming means for forming a latent image on said rotatable member, said image forming means having reciprocable scanning means arranged to perform a forward scan in which the rotating member is exposed to image light, and then to return to a home position; 70 developing means for developing the latent image with toner; transfer means for transferring the developed image onto a transfer member; cleaning means for cleaning the surface of 75 the rotatable member after the transfer of developed image threfrom; rotating means for rotating said rotatable member to permit latent image formation, development and transfer and for continuing 80 rotation of said rotatable member after the completion of image transfer, and to permit said rotatable member to undergo a cleaning operation performed by said cleaning means; and bias applying means for applying a given bias 85 potential to said developing means for inhibiting the deposition of toner by said developing means onto the rotatable member, during a predetermined period after the completion of development of said latent image 90 2 An image forming apparatus according to claim 1 wherein the arrangement is such that said predetermined period commences a predetermined time after completion of image transfer 95 3 An image forming apparatus according to claim 1 or claim 2 wherein the arrangement is such that said predetermined period ends a predetermined time before the termination of rotation of the rotatable member 100 4 An apparatus as claimed in any preceding claim, wherein said bias applying means is arranged to apply a further bias potential, different from said given bias potential, to said developing means during said image formation 105 An apparatus according to claim 4 wherein said given bias and said further bias are of opposite polarity.

   6 An apparatus according to any preceding claim, wherein said bias applying means is 110 arranged to apply said given bias potential after the termination of the said cleaning operation.

   7 An apparatus according to claim 6 wherein said cleaning means is arranged to contact the surface of said rotatable member for perfor 115 ming said cleaning operation and including separating means operable to bring said cleaning means out of contact with said surface after the completion of image formation, and wherein said bias applying means is arranged to apply 120 said given bias potential to said developing means after operation of said separating means.

   8 An apparatus according to any preceding claim wherein said developing means is arranged so that when said given bias potential is applied 125 thereto, it can perform a cleaning of the surface of the rotatable member.

   9 An apparatus according to any preceding claim wherein said developing means includes a developing roller arranged to contact the 130 1 596 844 surface of said rotatable member and means for rendering the developing means inoperative by bringing said developing roller out of contact with said surface after completion of image formation.

   An apparatus according to any preceding claim and further comprising control means for rendering said developing means inoperative after the elapse of said predetermined period.

   11 An apparatus according to any preceding claim and further comprising means for discharging said rotatable member, control means being provided for rendering said developing means inoperative after said rotatable member has been discharged by said discharging means.

   12 An apparatus according to any preceding claim, the arrangement being such that said developing means is rendered inoperative after the surface of said rotatable member cleaned by said cleaning means has passed the area of said developing means.

   13 An apparatus according to any preceding claim, further comprising means operable before formation of a latent image on said rotatable medium, to render the developing means operable.

   14 An apparatus according to any preceding claim, wherein said developing means is adapted to develop the latent image with liquid developer.

   R.G C JENKINS & CO.

   Chartered Patent Agents 53/64 Chancery Lane Chancery House London WC 2 A 1 QU.

   Agents for the Applicants.

   Printed for Her Majesty's Stationery Office by MULTIPLEX techniques ltd, St Mary Cray, Kent 1981 Published at the Patent Office, 25 Southampton Buildings, London WC 2 l AY, from which copies may be obtained.