EP0046852A1

EP0046852A1 - Electrophotographic copier

Info

Publication number: EP0046852A1
Application number: EP19810105224
Authority: EP
Inventors: John Harold Dodge; Larry Mason Ernst
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1980-08-28
Filing date: 1981-07-06
Publication date: 1982-03-10
Also published as: EP0046852B1; CA1173890A; DE3162795D1; JPS5754971A

Abstract

Following power switch-off to or in a copier for any reason, e.g. due to a paper jam, or a power failure, when power switch-on occurs, the position of the photosensitive drum (12) is determined, and a drum cleaning portion (17,27) of the copier cycle is first automatically performed if the drum is not initially in its reference position. During the copy producing portion of the normal copier cycle, photosensitive surface (11) sequentially passes coronas (17,19) for charging, optics (21) for exposing, magnetic brush (27) for developing, and corona (17) for transferring. During the cleaning portion of the normal copier cycle, photosensitive surface (11) sequentially passes corona (19) and optics (21) for charge neutralization, and magnetic brush (27) for toner removal. Reference point (16) is always located at its position under corona (17) as shown in Figure 1, at the beginning and at the end of a normal copier cycle.

Description

Technical Field

This invention relates to an electrophotographic copier, and is applicable to copier start-up operations control.
Xerographic copiers include a photosensitive surface which is charged to a uniform potential and then exposed to an image to form a latent electrostatic image. The latent electrostatic image is developed by application of toner thereto. The developed image is transferred to an output medium, generally a copy paper, and then fixed thereto to produce a permanent copy. Xerographic copiers also include cleaning means employing brushes and/or other means to remove any residual toner left on the photosenstive surface, and neutralize any residual charge left thereon prior to using the photosenstive surface for making a new copy.
In a normal copier cycle, the photosenstive surface is sequentially moved past a charging station, exposure station, developing station, transfer station and cleaning station. After passing the cleaning station the photosenstive surface is returned to its initial position adjacent the charging station, and new copier cycle may begin if further copying is desired. If further copying is not desired, the copier is turned off at the conclusion of the normal copier cycle.
The normal copier cycle described above may be interrupted in practice. Power to the copier may be interrupted because of a loss of electrical power due to a power failure or the inadvertent switching off of the main copier switch. More commonly, contemporary copiers include a protective mechanism which shuts-off the copier upon the occurrence of a paper jam or other abnormal condition during the copier cycle. Regardless of whether the copier is shut off under normal conditions at the conclusion of a copier cycle, or was interrupted in midstream, means must be provided to control copier start-up upon reapplication of power. The copier must be available for copy production as quickly as possible upon reapplication of power, and the initial copy must be of the same high quality as all subsequent copies.
A simple control of copier start-up would always clean the photosensitive surface upon reapplication of power to ensure that the initial copy is of high quality. Production of copies would be delayed until the photosensitive surface is passed by the cleaning station. This simple start-up control wastes some time and energy. At the end of a normal copier cycle, the photosenstive surface has already been cleaned, and there is no need to reclean the surface when power is reapplied. On the other hand, if copier operation is interrupted in midstream for any of the reasons discussed above, the photosensitive surface must be cleaned and prepared before further copying may commence upon reapplication of power.
In making this invention we have appreciated that it is desirable for copier start-up to vary, depending upon the condition upon which the copier previously shut down. If the copier shut down at the end of a normal copier cycle, copying may begin immediately upon the reapplication of power. Time and energy need not be wasted in cleaning an already clean photosensitive surface. If, on the other hand, the copier shut down in the middle of a copier cycle, ideally copying should not begin until the photosensitive surface is cleaned. While the initial cleaning produces a slight delay before production of the initial copy, failure to clean the photosensitive surface will result in an initial copy of unacceptable quality.

Brief Description of the Drawings

Fig. 1 is a schematic representation of a copier according to a first embodiment of the invention.
Fig. 2 shows the timing wheel of a second embodiment of the invention.
Fig. 3 is a flow chart representation of the control of copier start-up operations in a copier employing the timing wheel of Fig. 2.
Fig. 4 shows the timing wheel of a third embodiment of the invention.
Fig. 5 is a flow chart representation of the control of copier start-up operations in a copier employing the timing wheel of Fig. 4.

Best Mode for Carrying Out the Invention

Although the subject invention may be employed in any xerographic copier, it will be described with respect to a xerographic copier having the configuration of Fig. 1. Xerographic copier 10 generally comprises photosensitive surface 11, here the periphery of photosensitive drum 12, mounted on shaft 13 for rotation in the counterclockwise direction by motor 14. Copier 10 is designed to be compact and low cost. To reduce the number of copier components, many of these components are designed to serve a dual purpose in the copying process, as will be described below.
A normal copier cycle will now be described. Reference point 16 will be employed for the purposes of describing the rotation of the photosensitive drum 12 past the copier components. It will be understood that reference point 16 is not actually present on photosensitive drum. For the purposes of illustrating a normal copier cycle, it will also be assumed that the copier was turned off at the conclusion of a previous normal copying cycle. When this is the case, photosensitive drum 12 will always be at its position shown in Fig. 1, i.e., reference point 16 will be adjacent corona 17.
To begin the normal copier cycle copier controller 18 initiates rotation of drum 12 in the counterclockwise direction by activating motor 14. Reference point 16 passes corona 17. Corona 17, under the control.of copier controller 18, charges photosensitive surface 11 to a very high negative voltage. Rotation continues and reference point 16 passes corona 19. Under the control of copier controller 18, corona 19 smooths the charge on photosensitive surface 11 so that it is uniform throughout the photosensitive surface.
Photosensitive drum 12 continues to rotate until reference point 16 approaches copier optics 21. Copier optics assembly 21 is represented schematically by optic element 22, which may be a fiber optics bundle, for example;. Copier optics assembly further includes document glass 23, illumination means 25, mirror 28 and roller pairs 24 and 26. When reference point 16 approaches fiber optics element 22, copier controller 18 activates roller pairs 24 and 26 to move the document to be copied across document glass 23 from roller pair 24 to roller pair 26, at the same speed as the peripheral speed of photosensitive surface 11. 'Illumination means 25 is turned on and optic element 22 scans the document to be copied and forms a latent electrostatic image on the photosensitive surface 11.
Continuing its counterclockwise rotation, reference point 16 approaches magnetic brush 27. Under the control of controller 18, magnetic brush 27 develops the latent electrostatic image by applying toner to the charged portions of the photosensitive surface. Rotation of the drum continues and reference point 16 approaches corona 17 for the second time. As reference' point 16 approaches corona 17, copier controller 18 causes a sheet of copy paper to be picked from paper supply 29 and to travel along paper path 31. The copy paper sheet and reference point 16 approach corona 17 simultaneously, at the same linear speed.
Corona 17 which was previously employed as part of the charging station now acts as a transfer station Corona 17 transfers the toner from the surface 11 of photosensitive drum 12 to the copy paper. The copy paper continues along paper path 32 and encounters fuser station 33, here represented by fuser roller pair 34 Through a combination of heat and/or pressure, rollers 34 permanently fuse the toner to the copy paper.
The sequence_`of operations described above-, beginning with reference point 16 passing corona 17 for the first time and ending after point 16 has passed corona 17 for the second time constitute the copy producing portion of a normal copier cycle.
Rotation of photosensitive drum 12 continues and reference point 16 approaches corona 19 for the second time. This is the beginning of the cleaning portion of a normal copier cycle. Corona 19 is now employed to remove any residual charge left on photosensitive surface 11. Further discharging of photosensitive surface 11 is accomplished when reference point 16 passes copier optics 21 for the second time. Rather than illuminating a document to be copied, illuminating means 25 illuminates photosensitive surface 11 via mirror 28 to further reduce the charge thereon to zero.
Under the control of copier controller 18, photosensitive drum 12 continues its counterclockwise rotation and reference point 16 approaches magnetic brush 27 for the second time. In the cleaning portion of the normal copier cycle magnetic brush 27 removes any residual toner from photosensitive surface 11. After leaving magnetic brush 27 counterclockwise rotation continues until reference point 16 is again under corona 17.
It will be noted from the above description of a normal copier cycle that photosensitive surface 11 undergoes two complete revolutions to produce a xerographic copy. During the copy producing portion of the normal copier cycle, photosensitive surface 11 sequentially passes coronas 17 and 19 for charging, optics 21 for exposing, magnetic brush 27 for developing, and corona 17 for transferring. During the cleaning portion of the normal copier cycle, photosensitive surface 11 sequentially passes corona 19 and optics 21 for charge neutralization, and magnetic brush 27 for toner removal. Reference point 16 is always located at its position under corona 17 as shown in Fig. 1, at the beginning and at the end of a normal copier cycle.
While controlling the rotation of photosensitive drum 12, controller 18 also ensures that all copier components are activated at the proper time and for the proper duration, and controls dual mode operation of coronas 17 and 19, optics 21 and magnetic brush 27. Controller 18 may employ analog circuitry, digital logic, a microprocessor or microcomputer to control and synchronize copier operations. In a preferred embodiment of the invention, controller 18 may be a four-bit one-chip microcomputer such as the NEC µPD546C available from Nippon Electric Co., Ltd. This one-chip microcomputer includes all the electronic circuitry required for controller 18. Connections between the one-chip microcomputer and the copier components are via interface circuitry provided on the one-chip microcomputer. As is well known to those skilled in the art, buffers may be employed between the interface circuitry of the one-chip microcomputer and the copier components, to match voltage levels and current requirements of the microcomputer with the individual copier components.
As previously discussed, there are occasions when the normal copier cycle is interrupted. If the normal copier cycle is interrupted, photosensitive drum 12 will be at a rotational position other than the position at the beginning and end of the normal copier cycle shown in Fig. 1. According to each embodiment, an indicating means is provided for indicating whether or not photosensitive drum 12 is in its rotational position at the beginning or end of a normal copier cycle.
In'the embodiment shown in Fig. 1, the indicating means includes timing wheel 36 mounted on shaft 13 for rotation with photosensitive drum 12. The timing wheel has a cam 37 on the periphery thereof. Switch 38 is mounted such that when photosensitive drum 12 is in its rotational position at the end of a normal copier cycle, switch 38 engages cam 37, as shown in Fig. 1. At all rotational positions of photosensitive drum 12 other than at the conclusion of a normal copier cycle, switch 38 will engage the periphery of timing wheel 36 and not engage cam 37. Therefore, the output of switch 38, represented by line 39,will give a first indication when first photosensitive 12 is at position corresponding to the one it occupies drum 12 is a position/at the end of a normal copier cycle and give a second indication when photosensitive drum 12 is at any other position.
The output of switch 38, represented by line 39, thus forms a basis for inferentially determining the last-powered-on state of the copier. Rather than storing the rotational position of the photosensitive non-volatile read/write surface in special/memory elements as photosensitive drum 12 rotates, and then retaining the last stored position when the copier shuts down, the state of switch 38 need only be determined when power is applied to the copier.
When power is applied to the copier, copier controller 18 determines the state of switch 38. If switch 38 is engaged with cam 37, then it may be inferred that the last-powered-on state of the copier was at the conclusion of a normal copier cycle. Under the control of controller 18, a normal copier cycle commences without cleaning the photosensitive surface. The sequence of copier operations for a normal copier cycle, including the copy producing portion and cleaning portion has already been described above.
If, on the other hand, switch 38 is not engaged with cam 37, it may be inferred that the last-powered-on state of-the copier was at some state other than that at the conclusion of the normal copier cycle. The actual position of the photosensitive surface is unimportant with regard to copier start-up-operations. Under the control of controller 18, copier start-up operations proceed as follows: The introduction of a document into copier optics 21 is prevented by disabling the rotation of roller pairs 24 and 26. Under the control of copier controller 18 photosensitive drum 12 begins rotation. Copier controller 18-continues to monitor the state of switch 38 until it is determined that switch 38 is engaged with cam 37. The position of reference point 16 will then be as shown in Fig. 1. Under the control of copier controller 18 rotation of photosensitive drum in the counterclockwise direction continues and the cleaning cycle is activated. Reference point 16 passes coronas 17 and 19. Corona 19 is activated to neutralize the charge on photosensitive surface 11. Reference point 16 then passes copier optics 21 which are employed in the cleaning mode to illuminate photosensitive surface 11 and further neutralize any charge thereon. Rotation continues past magnetic brush 27 which removes any residual toner from photosensitive surface 11. Rotation then continues until the copier controller again determines that cam 37 is engaged with switch 38. The position of photosensitive drum 12 is as shown in Fig. 1, and the normal copier cycle may commence, utilizing the now cleaned photosensitive surface 11.
The cam and switch combination thus provides a means for inferring the last-powered-on state of the copier. Upon application of power, if cam 37 engages switch 38, no cleaning is necessary and immediate copying is permitted. If cam 37 does not engage switch 38, the time to first copy will be delayed while the photosensitive surface is cleaned. The delay to first copy equals the time it takes for photosensitive drum 12 to rotate between 1 and 2 complete revolutions. During the first partial revolution, photosensitive drum 12 is rotated until it is ascertained that cam 37 is engaged with switch 38. Photosensitive surface drum 12 then is rotated a full revolution and cleaned.
It will be apparent to those skilled in the art that cam 37-need not be on the peripheral surface of timing wheel 36. It may be on the side of timing wheel 36, provided switch 38 is mounted to engage cam 37 when photosensitive drum 12 is in its position at the conclusion of a normal copier cycle as shown in Fig. 1. Indeed, a separate timing wheel 36 need not be provided at all, as a cam may be formed on the periphery 11 of photosensitive drum 12 and switch 38 may be mounted to engage photosensitive drum 12.
It will be apparent to those skilled in the art that the indicating means need not comprise the cam and switch combination described above. Optical indicating means may be provided wherein for example, timing wheel 36 is opaque except for a small transparent portion. Switch 38 would be replaced by a photocell which can distinguish the transparent portion from the remainder of the timing wheel. Alternatively, magnetic indicating means may be provided wherein the timing wheel contains a magnetically sensitive material, e.g., magnetic tape, on the periphery thereof with a magnetic signal at one point. Switch 38 would then be a magnetic head which is responsive to the magnetic signal. As described above with regard to the cam and switch indicating means, a separate timing wheel may be dispensed with and the optical or magnetic data may be impressed directly on drum 12.^-
Other types of indicating means may be envisioned by those skilled in the art. Regardless of the indicating means provided, the positioning of the indicating means must be such that the output of the indicating means represented by line 39 gives a first indication when photosensitive drum 12 is in a corresponding to the one occupies rotational position corresponding to the one it occupies at the end of a normal copier rotational position/at the end of a normal copier cycle and a second indication at all other rotational positions. To provide the required signal amplitude and duration for copier controller 18, the output of switch 38 may be integrated by interposing integrator 41 between switch 38 and copier controller 18 as shown in Fig. 1.
Figure 2 shows a second form of timing wheel with which the invention may be practiced. Many xerographic copiers already contain a timing wheel which is used by copier controller 18 for monitoring the position of photosensitive drum 12 during all phases of the normal copier cycle. By monitoring the position of the drum during the copier cycle, controller 18 may activate and deactivate the requisite copier components at the proper time and in the proper sequence.
In keeping with the low cost objective for the copier in which the invention is employed, a second timing wheel is not added to provide copier start-up indicating information. Rather, the already existing timing wheel is employed for a dual purpose, i.e., to supply synchronization information to copier controller 18, as well as to provide copier start-up indicating information.
Synchronization information and copier start-up indicating information is supplied by employing two types of cams on the peripheral surface of timing wheel 46, as shown in Fig. 2. A plurality of small cams 48 are disposed about the periphery of the timing wheel and provide copier synchronization information. The number and position of synchronization cams 48 depend upon the particular design and configuration of the copier, and do not form a part of this invention. A large indicating cam 47, provides the copier start-up indicating information.
Since timing wheel 46 now has two types of cams on the surface thereof means must be provided for the copier to distinguish between large indicating cam 47 and the smaller synchronization cams 48. A first distinguishing means would provide two switches which engage the periphery of timing wheel 46. The contacting surface of one switch would be large and would only be activated by the large cam 47, i.e., it would pass over small cams 48`without engaging them. This switch would be positioned so that it engaged large cam 47.when the photosensitive surface was in its position at the end of a normal copier cycle shown in Fig. 1. The second switch would have a small contacting surface and would contact both small cams 48 and large cam 47 to provide synchronization information.
Alternatively, a second distinguishing means may be provided without requiring the addition of a second switch. The small cams 48 may be distinguished from indicating cam 47 dynamically, i.e., by rotating photosensitive drum 12. Basically, copier controller 18 rechecks the state of switch 38 a short time after it initially determines that switch 38 is engaged with a cam 47 or 48. If at the recheck, switch 38 is still engaged, it is apparent that switch 38 is engaged with large cam 47. If switch 38 is no longer engaged, then it is apparent that switch 38 was engaged with a small cam 48 which has disengaged from the switch during the short time interval.
The details of control of copier start-up operations in a copier employing the timing wheel of Fig. 2 will be illustrated with the aid of the flow chart of Fig. 3. As shown in box 100, copier controller 18 ascertains that main copier switch 43 has been turned on. Copier controller 18 prevents the introduction of a document into copier optics 21 by disabling the rotation of roller pairs 24 and 26, and initiates - rotation of drum 12 via motor 14, as indicated at 101. Copier controller 18 ascertains the state of switch 38 immediately upon rotation of drum 12, as shown at 102. If switch 38 is in its second state, i.e., it is not engaged with any cam 48'or 47, the copier controller may assume that the last-powered-on state of the copier was at some point other than at the end of the normal copier cycle. Rotation is continued (see 103) until switch 38 appears in its first state (see 104), i.e., it is engaging one of cams 47 or 48. The copier controller must then ascertain if switch 38 is engaging large indicating cam 47 or a small synchronization cam 48. This is done by continuing rotation of photosensitive drum 12 (see 105) and waiting a short time interval and again ascertaining the state of switch 38 (see 106). If at the conclusion of the short time interval switch 38 is still in its first state, it is apparent that switch 38 is engaging the large indicating cam and has therefore remained in its first state for the duration of the short time interval. Since it is now ascertained that cam 47 is engaging switch 38, the position of photosensitive drum 12 is at the position shown in Fig. 1 and the cleaning operation may begin (see 107). The cleaning portion has been described above with regard to the embodiment of Fig. 1 and will not be described again here. If on the other hand, switch 38 is not in its first state after the duration of a short time interval (see 106) it is apparent that switch 38 was engaging a small synchronization cam, and rotation of the drum will continue until it may be ascertained that switch 38 is engaging the large indicating cam.
If upon initial rotation of the drum (see 1011, switch 38 is not in its second state, i.e., it is engaging one of the cams 47 or 48, copier controller 18 must ascertain if it is engaging large indicating cam 47 or one of the small synchronization cams 48. Controller 18 continues rotation of the drum and waits a short time interval (see 108). If at the end of the short time interval switch 38 is still in its first state (see 109) it is apparent that switch 38 is engaged with large indicating cam 47. Controller 18 may assume that the copier was shut off at the end of a normal copier cycle (see 110) and normal copying is enabled (see 111). If at the end of the short time interval, the switch is no longer in its first state then'it is apparent that the switch was engaging a synchronization cam 48, and that the copier was not shut off at the end of the normal copier cycle. The photosensitive surface must be cleaned, and the copier controller continues rotation of the drum until it is ascertained that the copier is engaged with indicating cam 47, and then initiates the cleaning of photosensitive surface 11.
Other than the dynamic means for distinguishing indicating cam 47 from synchronizing cams 48, control of copier start-up operations is the same as was discussed regarding the embodiment of Fig. 1_: When copier controller 18 ascertains that switch 38 was engaged with indicating cam 47, it may be inferred that power was removed at the end of a normal copier cycle. If switch 38 was not engaged with indicating cam 47, i.e., switch 38 was engaged with a small cam 48 or with the peripheral surface of timing wheel 46, it may be inferred that the copier was interrupted in the middle of a normal copier cycle and photosensitive surface 11 must be cleaned before further copying will be permitted.
A third form of timing wheel with which the invention may be practiced is shown in Fig. 4. In this embodiment, a plurality of individual synchronization cams 58 is provided on timing wheel 56. In addition, a pair of closely spaced indicating cams 57 provides copier start-up indicating information. It will be seen from Fig. 4 that cams ₅₇ and ₅₈ are not on the periphery of timing wheel 56 but rather are on the side of timing wheel 56 in a circular pattern thereon. The number and position of synchronization cams 58 in the circular pattern depend upon the particular design and configuration of the copier and do not form a part of this invention. However, for the purpose of explaining the detailed operation of the invention, the number of synchronization cams 58 on timing wheel 56 will be assumed to be four, as shown in Fig. 4. The pair of indicating cams 57 is positioned such that at the conclusion of a normal copier cycle, when photosensitive surface 11 is at its position in Fig. 1, switch 38 will engage with timing wheel 56 at point 59.
As with the embodiment of Fig. 2, means must be provided for distinguishing between the indicating cams 57 and the individual synchronizing cams 58. As with the embodiment of Fig. 2, indicating cams 57 may be dynamically distinguished from synchronizing cams 58 by rotating photosensitive drum 10. Basically, copier controller 18 begins rotation of the drum and counts the number of cams engaged by switch 38 until the unique pair of indicating cams is encountered. If the number of cams engaged equals the number of synchronization cams on the timing wheel then it may be inferred that rotation began with switch 38 engaging timing wheel 56 at point 59, and that the copier was shut off at the conclusion of a normal copier cycle. If the number of cams engaged does not equal the number of synchronization cams on the timing wheel, it may be inferred that rotation began with switch 38 engaging timing wheel 56 at some point other than at 59, as a result of the copier having been interrupted in the middle of a normal copier cycle.
The details of control of copier start-up operations in a copier employing the timing wheel of Fig. 4 will be illustrated through the use of the flow chart of Fig. 5. Copier controller 18 senses the turning on of main copier switch 43, as shown in Fig. 5 at 150. Copier controller 18 prevents the introduction of a document into copier optics 21 by preventing the rotation of roller pairs 24 and 26, and.begins the counterclockwise rotation of drum 12 in order to ascertain the last-powered-on state of the copier. Copier controller 18 continuously monitors the state of switch 38 via line 39. The changing of the state of switch 38 from its second state to its first state or from its. first state to its second state will hereinafter be termed a transition. As shown at 152, copier controller 18 counts the number of transitions occurring on line 39 as drum 12 rotates. In addition, the timing between the transitions is monitored. As shown at 153, the controller 18 detects the occurrence of.four transitions within a predetermined short time interval. At the conclusion of the fourth of the four closely occurring transitions, switch 38 has just disengaged from the pair of indicating cams 57 and is engaging timing wheel 56 at point 59. Photosensitive surface 11 is at its position shown in Fig. 1. The copier controller can infer the last-powered-on state of the copier by observing the number of transitions it has counted prior to switch 38 arriving at point 59.
If the number of transitions is equal to 12, (see 154) the copier controller may infer that the last-powered-on state of the copier was at the conclusion of the normal copier cycle. The reasoning for this is as follows:. At the conclusion of the normal copier cycle, switch 38 is engaged with timing wheel 56 at point 59. When the drum begins its counterclockwise rotation, switch 38 will sequentially engage each of the four synchronization cams 58 and the copier controller will detect a total of 8 transitions (i.e., two transitions per cam as switch 38 engages and disengages each synchronization cam 58). Switch 38 will then engage the pair of indicating cams 57 in rapid sequence, and copier controller 18 will detect four closely occurring transitions. Therefore, when the last-powered-on state of the copier was at its position at the end of a normal copier cycle, copier controller 18 will detect a total of 12 transitions from the time it began rotation of the drum until it detects the last of the four closely occurring transitions. Photosensitive drum 12 has undergoone one complete revolution in order to ascertain that the last-powered-on state was at the end of a normal copier cycle (see 155). At the conclusion of this revolution it is at its position shown in Fig. 1, i.e., switch 38 engages timing wheel 56 at point 59. Photosensitive surface 12 is in its proper position for beginning a normal copier cycle. Controller 18 begins a normal copier cycle. The normal copier cycle has already been described with regard to Fig. 1 and will not be repeated here.
If the number of transitions counted by copier controller 18 is not equal to 12 (see 154), copier controller 18 may infer that the copier was interrupted in the middle of a normal copier cycle. The reasoning for this is as follows: If the copier was interrupted in the middle of a normal copying cycle, switch 38 will engage timing wheel 56 at some point other than point 59. When rotation of photosensitive surface 12 begins, it will not sequentially engage all of synchronization cams 58 prior to engaging closely spaced indicating cams 57. The number of detected transitions prior to the last of the four closely spaced transitions will therefore not be equal to 12. This provides the inference for copy controller that the copier was interrupted in the middle of a normal copier cycle (see 156). After detecting the last of the four closely spaced transitions, drum 12 is in its position shown in Fig. 1. Copier controller 18 initiates cleaning of the photosensitve surface as was described in connection with Fig. 1. At the conclusion of the cleaning cycle, the position of photosensitive drum 12 will be that shown in Fig. 1 and a normal copier cycle will be enabled (see 157).
It will be seen that when the copier was interrupted in the middle of a normal copier cycle, photosensitive surface 12 will undergo a _i fraction of one complete revolution in order to ascertain the last-powered-on state of the copier, and then will undergo a full revolution in order to clean the photosensitive surface.
Many other variations of indicating means, providing static or dynamic indicating information will be apparent to those skilled in the art. The common concept in all such variations maybe that the indicating means provides a first indication if the photosensitive surface is in an end of copier cycle position, when power was removed from the copier, and does not provide this indication if the photosenstive surface was in any other position when power was turned off. Means are therefor provided for the copier controller to assume the last-powered-on state of the copier without the need for storing this state in read-write memory elements.
The embodiments that have been described concern low cost arrangements. Another arrangement with added cost would be to couple the drum to the timing wheel by a reduction gear so that the timing wheel rotated once for every two rotations of the drum.

Claims

1. An electrophotographic copier having a controller (18) which causes the photosensitive surface of the copier first to be cleaned automatically and selectively when the photosensitive surface is not in its reference position at power switch-on.

2. Copier as claimed in claim 1 in which said controller includes read-only determining means (Figs. 2 and 3, or 4 and 5) for determining, following power switch-on, whether the previous power switch-off has left the photosensitive surface at a position other than its reference position.

3. Copier as claimed in claim 2 in which the determining means includes a wheel (56) having at least one cam surface (47, 48, 57, 58) or magentic or optical position indicating means, the wheel rotating in synchronism with movement of the photosensitive surface.

4. Copier as claimed in claim 3 in which said wheel has cam surfaces (48, 58) for synchronising other operations in the copier cycle.

5. Copier as claimed in claim 4 in which the determining means distinguishes between cam surfaces by their span (47) frequency (57).

6. Copier as claimed in claim 5 in which said determining means includes means for moving the photosensitive surface and the wheel a short amount beyond where a cam surface is first detected.

7. Copier as claimed in claim 4, 5 or 6 in which the determining means includes a counter for counting the number of transitions of a cam-operated switch coacting with the cam surfaces on the wheel following power switch-on, up to the point where the wheel reaches its reference position, a count of less than a predetermined number indicating that the photosensitive surface was not in its reference position at power switch-on.

8. An electrophotographic copier having a copying mode wherein a latent electrostatic image is formed on a movable photosensitive surface, and the latent electrostatic image is fixed and developed, and having a cleaning mode for cleaning said photosensitive surface, apparatus for controlling the start-up of said copier, comprising: means for detecting if said photosensitive surface is at a predetermined position upon the start-up of said copier; first means responsive to said detecting means for enabling said copying mode consequent upon said photosensitive surface being in the aforesaid predetermined position; and second means responsive to said detecting means for activating said cleaning mode consequent upon said photosensitive surface being in a position other than the aforesaid predetermined position.

9. The copier of claim 8 wherein said first means further includes means for activating said cleaning mode upon the conclusion of said copying mode.

10. The copier of claim 8 or 9 wherein said second means further includes means for enabling said copying mode upon the conclusion of said cleaning mode.

11. Copier as claimed in any preceding claim in which the photosensitive surface is a drum (12) which is rotated twice during a full copier cycle, stations (17, 19, 21, 27) round the drum being operated in different modes depending on whether the cleaning portion or copy producing portion is in progress.