Image forming apparatus having dew preventing mechanism

Abstract: The present invention provides an image forming apparatus having a dew preventing mechanism for an electrophotographic photosensitive member. Wherein the hour when a heat generating means for applying heat to the photosensitive member is started is set by an operation panel, and the electric power is not supplied to the heat generating means after a power source of the image forming apparatus is turned OFF. Whereby, it is possible to avoid the useless electric power in the midnight, sunday and holiday when the image forming apparatus is not used.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an image forming apparatus utilizing the electrostatic transfer process, such as an electrostatic copying machine, an electrophotographic printer and the like. Related Background Art Normally, under the low temperature (for example, winter), when a heating apparatus is operated in the morning in a room where an image forming apparatus is installed, since the interior of the image forming apparatus left as it is overnight in a condition that the power source is turned OFF is well cooled, dew is adhered to a photosensitive drum and an optical system including mirrors and a lens. Thus, in order to prevent the abnormity of the output image, in high-class image forming apparatuses, heat devices such as heaters were normally arranged within or in the proximity of the photosensitive drum and in the proximity of optical members such as mirrors and lens. On the other hand, in image forming apparatuses using a noncrystal silicone photo-conductive layer, by repeating the copying processes such as the charge, image exposure, development, transferring and the like, a surface of the photosensitive member becomes sensitive to the influence of humidity, with the result that the dew is apt to be adhered to the surface of the photosensitive member. Consequently, the electric resistance of the surface of the photosensitive member is decreased, so that the surface charges are shifted toward the surface, thereby causing the flow of an image. This tendency occurs particularly under the high humidity condition. This is the reason why negative ions and positive ions generated by the corona discharge are adhered to the surface of the photosensitive member to create HNO 3 , thereby facilitating the absorption of moisture. To avoid the above inconvenience, by heating the photosensitive member by a heater arranged in the photosensitive member, moisture absorbing factors such as the negative ions and positive ions generated by the corona discharge or HNO 3 were removed. However, in the conventional image forming apparatuses, in order to avoid the above-mentioned inconvenience, it was necessary to control the operation of the heat devices by constantly connecting the image forming apparatus to the power source. Thus, even in the midnight during which the image forming apparatus is not used, the heat devices were operated, thus consuming the electric power. The useless electric power consumption such as power consumption in an inoperative condition should be avoided in consideration of the recent protection of resources and the saving of energy. In consideration of the above, in order to solve the above problem; a dew sensor is provided, even when the dew is added to the elements of the image forming apparatus in a condition that the power source is turned OFF in the night, after the power source is turned ON, if the dew is detected by the dew sensor, heat devices are operated, and a copying operation is indibited until the dew is eliminated. However, in this apparatus, a waiting time period from a time when the power source is turned ON to a time when the dew is disappeared cannot be exactly grasped, unlike to the warming-up time for heating a fixing roller in the typical image forming apparatus. JP-A-55 021 020 describes a heater control circuit in copying machines in which the period and time for supplying electric power to a heater circuit, having anti-dewing heaters and to a heater circuit having an auxiliary fixing heater, are conntrolled by controlling a timer control circuit in order to open and close the timer switches of the circuits. This enables a saving of power in the non-use periods of the heaters and prevention of fire risk and degradation of performance. SUMMARY OF THE INVENTION An object of the present invention is to reduce the electric power consumption by disconnecting or interrupting a power source from a dew preventing heater means when an image forming apparatus is not being used. The other object of the present invention is to facilitate the operation for saving the electric power. In order to achieve the above objects, the present invention provides an image forming apparatus having a dew preventing mechanism, comprising: an electrophotographic photosensitive member; heat generating means for applying heat to said photosensitive member; a power source for powering the apparatus; control means for controlling an operation of said heat generating means; an operation panel for setting an operation hour of said control means; timer means to control said heating generating means by setting a time period in said timer means (54) extending from the turning OFF at the job closing hour to the turning ON at the next job starting hour of the power source of the image forming apparatus, comprising a MPU unit having a clock function which controls the turning ON of said heating generating means (16), and a) at a present hour, before said power source is turned OFF at said job closing hour, said next job starting hour is inputted to said MPU unit said next starting hour being displayed on a display on said panel; and b) in said timer means a first time period is set having a length extending from said present hour to a hour earlier than said next starting hour by a second period of time (t2), said second period of time (t2) being sufficient to produce disappearance of dew prior to said next starting hour, so that said timer setting and said inputting of the next starting hour are carried out by operation from the operation panel. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a control means of a copying apparatus to which the present invention is applied; Fig. 2 is a control flow chart for general copying machines; Fig. 3 is a timing chart showing the drive timing of a heat device of the copying apparatus according to the present invention; Fig. 4 is a plan view of an operation panel of the copying apparatus according to the present invention; Fig. 5 is a sectional view of a photosensitive drum of the copying apparatus according to the present invention; and Fig. 6A is a plan view of a sliding electrode for the photosensitive drum of Fig. 5, and Fig. 6B is a sectional view taken along the line A - A in Fig. 6A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows an internal construction of a microprocessor unit for controlling a copying apparatus according to the present invention. The microprocessor unit (MPU) 50 includes an operating portion (CPU) 51 having calculation and judgement functions, a treatment program storing read only memory (ROM) 52, a data storing random access memory (RAM) 53, and input and output ports for sending and receiving signals with respect to external devices. Further, a timer IC 54 is incorporated in the MPU 50 so that the timer can be set by command. Since the fundamental operation of the MPU 50 is already known, the explanation thereof will be omitted. Fig. 2 shows a flow chart for general copying machines. When a main switch of the copying machine is turned ON, the initialization such as main switch ON reset and the setting of an operation mode of the MPU 50, and then the initial check routine is carried out. In this initial check routine, first of all, the presence/absence of toner, a transfer sheet and the like is checked, and then, if a mirror support and a sheet supply deck are not positioned in a predetermined condition, the mirror support and the sheet supply deck are set to the initial condition by driving motors, clutches and the like. In a copying machine having a heater in a fixing means, a waiting condition is continued until the fixing means reaches a predetermined temperature, and, by detecting the temperature and humidity, a voltage applied to a charge means and bias potential for a photosensitive member are set. Then, the number of copy sheets and a copy mode are set, and, when a start switch is turned ON, a copy process including the known charging, exposure, transferring, electricity removal and fixing is performed, during which the abnormity in the copy sequence control, sheet jam, opening/closing of a safety switch and the like are always checked. When the copy process is completed, the counter date is checked. When the predetermined number of copy sheets are obtained, the copying operation is finished, and the program is returend to the initial check routine for preparing for the next copy start. In the copying apparatus according to the illustrated embodiment, the operation of heat devices for the photosensitive drum and mirrors, lens and the like are controlled by the CPU 51 and the program timer 54. That is to say, as the heat devices, a cylindrical face-shaped heater mounted in the photosensitive drum and a cement resistor arranged in the proximity of the mirrors and lens are used and are appropriately arranged. Now, as an example of the above-mentioned heat devices, a heater in the photosensitive drum will be explained with reference to Figs. 5, 6A and 6B. As shown in Fig. 5, the photosensitive drum 3 comprises a cylinder 10, left and right flanges 12L, 12R secured to both ends of the cylinder 10 and interconnected by an inner stay 11, and left and right bearings 15L, 15R attached to left and right shafts 13L, 13R protruded from the flanges 12L, 12R, and is rotatably supported by a process unit by fitting the bearings 15L, 15R into left and right support plates 6L, 6R of a case 2 of the process unit. Further, a face-shaped heater 16 is arranged along an inner peripheral surface of the cylinder 10 of the photosensitive drum 3, and a temperature control substrate 17 which receives the electric power via an electrode 19 is connected to the face-shaped heater 16. Sliding end portions 19a, 19b protruded from the electrode 19 are slidingly contacted with two rings 7a, 7b of a slip ring 7 (Figs. 6A and 6B) secured to the process unit so that the electric power can be applied to the heater 16 even when the photosensitive drum 3 is being rotated. The heat device having the above-mentioned construction is controlled by the MPU so that, at the same time when the main switch of the copying apparatus is turned OFF (to = 0 in Fig. 3) or a predetermined time period (to) from OFF of the main switch is elapsed if necessary, the heat device is turned OFF. Further, as shown in Fig. 4, an operation panel portion of the copying apparatus is provided with various set keys (as in the conventional copying machine), a timer set key 95 for setting a time period so that the heat device is turned ON again after a predetermined time period (t1) from OFF of the main switch is elapsed, a seven segment display device 72 capable of displaying a numeral value and English characters and adapted to display a timer set time, as well as the number of copy sheets (as in the conventional copying machine), and up and down keys 96, 97 for altering and/or designating the timer set value and the like. By an input signal from the timer set key 95, the MPU 50 sends the command to the program timer IC 54, thereby setting the timer function. Incidentally, Fig. 3 is a timing chart showing the operation timing of the copying apparatus as mentioned above. In the above sequence, before the copying apparatus is stopped for a long time from the closing hour, the operator, by using the operation panel, sets a time period (t 1 ) in fig. 3, to be elapsed from the present hour, such that the heat device is turned ON a predetermined time period (t 2 in fig. 3) before the next starting hour (for example the tomorrow hour). This time period t 2 is appropriately a time period longer than the time period during which the dew (if generated) is disappeared in the copying apparatus by action of the heating device. Thus, by setting the time period t 1 by the timer, when the timer control is actuated, the MPU receives a signal from the timer and emits a control signal to supply electric power to the heat device again. As a result, the operator can obtain copies with correct images in a shorter time with respect to the time to wait for having the dew eliminated. Further, when the copying apparatus is not used for a long time (for example, by night, Sunday or holiday), the heat device for the photosensitive drum can be turned OFF, unlike to conventional copying machines. This considerably improves the saving of energy and ensures high safety, since the heat device is not being operated when monitoring is lacking. Further embodiments will now be described. In the above described embodiment the time period is input elapsing from the job closing hour to immediately before the next starting hour. Such input operation May effected as follows. The operator can set the timer by previously inputting to the operation panel the next jop starting hour before the main switch is turned OFF at the job closing hour. There have been recently proposed copying machines using an IC 55 having a calendar function, so that the present hour can be displayed on a liquid crystal display on the operation panel. In this case a time difference is calculated between the starting hour which was inputted by the operator and the actual hour when this starting hour was inputted. By controlling that a time period is set to the timer which is obtained by subtracting from the above time difference an appropriate time period longer than a minimum time period extended from when the heat device is turned ON to when the dew has disappeared, and that this is input in the memory of the MPU, the same technical effect can achieved as that of the first embodiment. Further, in this alternative embodiment, since the initiation of the operation of the heat device can be inputted on terms of hour, which is unlike to the first described embodiment, the operator does not have to set the timer on the basis of a quantity expressed as time period extended from the job closing hour to the next starting hour. This improves operability. Further, in this embodiment, by arranging so that the contents set in the timer are inputted to the RAM of the MPU, it is not necessary to input every time the hour when the heat device is to be turned ON, since it is sufficient that only the timer set key 95 is actuated. As mentioned above, according to the present invention, since the heater for removing humidity and preventing dew is turned OFF substantially at the same time as is turned OFF the main switch of the image forming apparatus, and since there is provided an operation key for setting the hour for starting the operation of the heater, and since further the heater is controlled by means of the operation key to be turned ON again after the predetermined time period, it is possible to provide an image forming apparatus of high safety and in which it is possible to avoid wasting of electric power for driving the heater by night.

Claims: An image forming apparatus having a dew preventing mechanism, comprising: an electrophotographic photosensitive member (3); heat generating means (16) for applying heat to said photosensitive member; a power source for powering the apparatus; control means (50) for controlling an operation of said heat generating means, said control means including timer means (54) to control said heating generating means (16) by setting a time period in said timer means (54) extending from the turning OFF at the job closing hour to the turning ON at the next job starting hour of the power source of the image forming apparatus; an operation panel (70) for setting an operation hour of said control means; characterized in that said control means comprises a MPU unit (52) having a clock function which controls the turning ON of said heating generating means (16), and a) at a present hour, before said power source is turned OFF at said job closing hour, said next job starting hour is inputtable to said MPU unit (52) said next starting hour being displayable on a display (72) on said panel; and b) in said timer means (54) a first time period is settable having a length extending from said present hour to a hour earlier than said next starting hour by a second period of time, said second period of time being sufficient to produce disappearance of dew prior to said next starting hour, so that said timer setting and said inputting of the next starting hour are carried out by operation from the operation panel. An image forming apparatus according to claim 1, in which said timer setting is effected by said MPU upon pressing the timer key on said panel, by the operations of calculating said first length of time then calculating the difference obtained by subtracting said second predetermined length of time (t 2 ) from said first length of time, and inputting said difference to the timer. An image forming apparatus according to claim 1 or 2, in which a start hour of said heat generating means (16) is set as a set time on said operation panel (70) before the power source of said image forming apparatus is turned OFF for a long time of rest of said image forming apparatus, whereby said control means (50) are operated at said set timing and no electric power is supplied to said heat generating means after the power source is turned OFF. An image forming apparatus according to any one of the preceding claims, wherein the hour when the operation of said heat generating means is started, is set by said operation panel by setting the hour when the image forming apparatus is being used. An image forming apparatus according to any one of the preceding claims, wherein said operation panel has a display portion for displaying the hour when the operation of said heat generating means is started. A method according to claim 5, in which said display portion is a liquid crystal numerical display.

Inventors: KOIKE MICHIRO, OGAWA HIROSHI, KOIKE, MICHIRO, OGAWA, HIROSHI, KOIKE, MICHIRO, C/O CANON KABUSHIKI KAISHA, OGAWA, HIROSHI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: G03G15
IPC codes: B41J29, G03G21, G03G15