Electrostatic copying apparatus

Abstract: An electrostatic copying apparatus comprises a rotatable photosensitive member, means for forming a latent electrostatic image on the photosensitive member, developing means, transfer means, means for conveying a copying paper, cleaning means and a heat fixing device. The heat fixing device comprises an electrical heating means and control means for controlling the energization and the deenergization of the heating means. Power control means also controls the amount of electric current supplied to the heating means.

Description: This invention relates to a heat fixing device for an electrostatic copying apparatus of the kind as referred to in the precharacterizing portion of patent claim 1. Such a device is known from JP-U-55-181 259. Electrostatic copying apparatuses of various types have been suggested and come into commercial acceptance in the past. In a typical electrostatic copying apparatus, a rotating drum having a photosensitive member disposed on its peripheral surface is provided, and around the rotating drum are located a charging zone, an exposure zone, a developing zone, a transfer zone, a peeling zone and a cleaning zone in this order in the rotating direction of the rotating drum. In the charging zone, the photosensitive member is charged to a specified polarity by the action of a charging corona discharge device, and in the exposure zone, the image of a document to be copied is projected onto the photosensitive member, whereby the charge on the photosensitive member is selectively eliminated and a latent electrostatic image is formed on the photosensitive member. In the developing zone, a toner is applied to the latent electrostatic image on the photo-sensitive member by, for example, a developing means of the magnetic brush type to develop the latent electrostatic image into a toner image. In the transfer zone, the toner image on the photosensitive member is transferred onto a copying paper conveyed through the transfer zone. In the peeling zone, the copying paper contacted with the photosensitive member in the transfer zone is peeled off from the photosensitive member. In the cleaning zone, the toner remaining on the photosensitive member after the transfer is removed by, for example, the action of a cleaning blade to be in contact with the photosensitive member. In the meantime, the copying paper having the toner image transferred thereto, which has been peeled from the photosensitive member in the peeling zone, is passed through a fixing device such as a heat fixing device whereby the toner image is fixed to the copying paper in the fixing device. As is well known, the electrostatic copying apparatus described above frequently has a semi-automatic document supplying and discharging device and a sorter annexed thereto. The semi-automatic document supplying and discharging device feeds a document inserted by hand into its document introducing section to a document supporting transparent plate disposed on the upper surface of the housing of the main body of the electrostatic copying apparatus. The sorter is actuated when multiple copies are to be formed from each of a plurality of documents, and sorts the copying papers having a fixed toner image which are discharged from the main body of the electrostatic copying apparatus. The conventional electrostatic copying apparatus, however, has various inconveniences or defects in regard to the following operations and devices which will be described in detail hereinafter. (1) Control based on the temperature of the surface or its vicinity of the photosensitive member; (2) control of the energization or deenergization of an electric heating means when a heat-fixing device containing the electronic heating means is used. From US-A-4 145 599 a heat fixing device is known having an electrical heating means for heat-fixing a toner image on a sheet member, comprising a temperature detecting means and a heating control means for controlling the energization and deenergization of said heating means on the basis of the temperature detected by said temperature detecting means; said heating control means controls, after the lapse of a first predetermined period of time,the energization and deenergization of said heating means on the basis of whether or not the detected temperature is below or higher than a first predetermined value which is suitable for a heat fixation, hereby adjusting said detected temperature substantially to said first predetermined value. According to this device, the surface temperature of the heating roller exceeds the heat for fixing only for a very short time called overshoot. This time interval isn't large enough to allow a homogeneous temperature distribution within the heating roller equipment at a high level. JP-U-55-181259 discloses a heat fixing device having an electrical heating means (106) for heat-fixing a toner image on a sheet member. This device comprises: a temperature detecting means (277) and a heating control means (516, 518) for controlling the energization and de-energization of said heating means on the basis of the temperature detected by said temperature detecting means. The heating control means (516, 518) controls, after the lapse of a first predetermined period of time (W₁), the energization and deenergization of said heating means (106) on the basis of whether or not the detected temperature is below or higher than a first predetermined value (T₁) which is suitable for heat fixation, hereby adjusting said detected temperature substantially to said first predetermined value (T₁). Before the lapse of said first predetermined period of time (W₁) commencing from the application of electric power, said heating control means (516, 518) controls the energization and deenergization of said heating means (106) on the basis of whether or not the detected temperature is below or higher than a second predetermined value (T₂) which is higher than the first predetermined value (T₁) hereby adjusting the detected temperature substantially to the second predetermined value (T₂). This document is silent about any suppression of electrical power in the hot state. The general object of this invention is to remove the various inconveniences and defects existing in conventional electrostatic copying apparatuses, and is particularly related to improvements in the heat-fixing of toner on the copying paper. This object is accomplished with a heat fixing device as claimed in claim 1. Advantageous further embodiments of the invention are subject of the dependent claims. Various specific advantages of this invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings in which: Figure 1 is a perspective view of one embodiment of the copying apparatus constructed in accordance with this invention in a condition in which the semi-automatic document supplying and discharging device is held in its operating position; Figure 2 is a perspective view of the copying apparatus of Figure 1 in a condition in which the semi-automatic document supplying and discharging device is held in its non-operating position; Figure 3 is a simplified sectional view of the copying apparatus shown in Figure 1; Figure 4 is a simplified partial sectional view showing a rotating drum and its vicinity in the copying apparatus shown in Figure 1; Figure 5 is a simplified partial sectional view showing a paper feed device in the copying apparatus shown in Figure 1; Figure 6 is a schematic view showing a control system for controlling an electrical heating means of a heat fixing device in the copying apparatus shown in Figure 1; Figure 7 is a flow chart showing the mode of controlling heating of a heat fixing device in the copying apparatus shown in Figure 1; Figure 8 is a diagram showing changes with time of the temperature of the heat fixing device in the copying apparatus shown in Figure 1; Figure 9 is a flow chart showing the mode of controlling electric power in the copying apparatus shown in Figure 1; Figure 10 is a diagram showing the waveform of a current supplied to an electrical heating means of a heat fixing device in the copying apparatus shown in Figure 1; Figure 11 is a diagram showing a modified example of the waveform of a current supplied to an electrical heating means of a heat fixing device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be described in detail with reference to the accompanying drawings. General Outline of Copying Apparatus The outline of the construction of one embodiment of an electrostatic copying apparatus improved variously in accordance with this invention will be described. With reference to Figures 1 and 2, the illustrated electrostatic copying apparatus has a main body shown generally at 2 which includes a nearly rectangularly-shaped housing 4. The copying apparatus further includes a semi-automatic document supplying and discharging device shown generally at 6 and annexed to the upper surface of the housing 4, a document holding mechanism shown generally at 8 and annexed similarly to the upper surface of the housing 4, and a sorter shown generally at 10 and annexed to one side surface of the housing 4. The semi-automatic document supplying and discharging device 6 is substantially the same as the semi-automatic document supplying and discharging device disclosed in Japanese Laid-Open Patent Publication No. 161874/1982 (corresponding to U.S. Patent Application Serial No. 361.236 and European Patent Application No. 82102455.1) and includes a stationary support frame struc ture 14 mounted on the top of the housing 4 adjacent to one side edge of a transparent plate 12 (Figure 3) disposed on the top of the housing 4, and a movable main frame stucture 16 mounted for free turning about an axis extending along said one side edge of the transparent plate 12 and between an operating position (the position shown in Figure 1) at which it covers the transparent plate 12 and a non-operating position (the position shown in Figure 2 which is displaced about 90° from the above operating position in a clockwise direction as viewed from the right bottom in Figures 1 and 2) at which it brings the transparent plate 12 to view. On the other hand, the document holding device 8 is mounted such that it is free to turn between an operating position at which it covers the transparentplate 12 (the position shown in Figure 2) and a non-operating position (the position shown in Figure 1 displaced about 90° from the above operating position as viewed from the right top in Figures 1 and 2) at which it brings the transparent plate 12 to view, and about an axis extending along the other side edge of the transparent plate 12 which extends substantially at right angles to the pivot axis of the main frame structure 16 of the semi-automatic document supplying and discharging device 6. In positioning a document to be copied on the transparent plate 12 by utilizing the semi-automatic document supplying and discharging device 6 in the above-illustrated electrostatic copying apparatus, the document holding device 8 is brought to the non-operating position and the main frame structure 16 of the semi-automatic document supplying and discharging device 6 is brought to the operating position. When the document to be copied is to be positioned on the transparent plate 12 by a manual operation without utilizing the semi-automatic device 6 (for example, when the document is a thick one such as a book or one having relatively high rigidity, such as a thick sheet of paper or a metal plate), the operator brings the main frame structure 16 of the semi-automatic device 6 to the non-operating position, then places the document on the desired site of the transparent plate 12, turns the document holding device 8 to the above operating position, and thus covers the transparent plate 12 and the document thereon with the document holding device 8. In withdrawing the document after the end of a copying cycle, the document holding device 8 is turned to the non-operating position. With reference to Figure 3, the main body 2 of the copying apparatus will be described. The transparent plate 12 on which to place a document to be copied is disposed on the upper surface of the housing 4. A cylindrical rotating drum 18 is rotatably mounted substantially centrally at the lower part of the housing 4, and an endless photosensitive member 20 is provided on the peripheral surface of the rotating drum 18. It is also possible to use an endless belt element known to those skilled in the art in place of the rotating drum 18 and to dispose the photosensitive member on the surface of the endless belt element. With reference to Figure 4 together with Figure 3, around the rotating drum to be rotated in the direction of an arrow 22 are located a charging zone 24, an exposure zone 26, a developing zone 28, a transfer zone 30, a peeling zone 32 and a cleaning zone 34 in this sequence as viewed in the rotating direction of the rotating drum 18. The charging zone 24 and the exposure zone 26, taken together, form a latent electrostatic image-forming zone 36. A charging corona discharge device 38 is disposed in the charging zone 24, and a developing means 40 of the magnetic brush type in any desired form is disposed in the developing zone 28. A transfer corona discharge device 42 is disposed in the transfer zone 30, and peeling corona discharge devices 44 and 46 are disposed in the peeling zone 32. In the cleaning zone 34, a cleaning blade 48 is provided. A paper conveying means shown generally at 50 is provided in the lower portion of the housing 4. A paper feed device 52 is disposed at the upstream end portion (the right end portion in Figure 3) of the paper conveying means 50. With reference to Figure 5 taken in conjunction with Figure 3, the paper feed device 52 includes a first cassette-receiving section 54a and a second cassette-receiving section 54b located above it. The first cassette-receiving section 54a receives a paper cassette 58a containing a plurality of stacked copying paper sheets 56a, and the second cassette-receiving section 54b receives a paper cassette 58b containing a plurality of stacked copying paper sheets 56b. A first paper supply means 60a and a second paper supply means 60b are provided respectively in the first cassette-receiving section 54a and the second cassette-receiving section 54b. The first paper supply means 60a is comprised of a support shaft 62a and a supply roller 64a fixed thereto, and the second paper supply means 60b is comprised of a support shaft 62b and a supply roller 64b fixed thereto. To the first cassette-receiving section 54a is annexed a first paper introducing passage 70a defined by a pair of guide plates 66 and 68. Likewise, a second paper introducing passage 70b defined by a pair of guide plates 72 and 74 and a pair of guide plates 76 and 78 is annexed to the second cassette-receiving section 54b. A pair of supply assisting rollers 80 and 82 are provided between the pair of guide plates 72 and 74 and the pair of guide plates 76 and 78. Further, with reference to Figure 3, a pair of conveyor rollers 84 and 86 are provided at a point of junction of the first paper introducing passage 70a and the second paper introducing passage 70b, and following this pair of conveyor rollers 84 and 86, a pair of guide plates 88 and 90, a pair of conveyor rollers 92 and 94c and a pair of guide plates 96 and 98 are provided. The downstream end of the pair of guide plates 96 and 98 extend to the upstream end of the transfer zone 30. A conveyor belt mechanism 100 is disposed downstream of the peeling zone 32 as viewed in the paper conveying direction. A guide plate 102 is disposed downstream of the conveyor belt mechanism 100, and a heat-fixing device 104 is disposed downstream of the guide plate 102. The heat-fixing device 104 is comprised of a heating roller 108 having an electrical heating means 106 therein, and a press-contact roller 110 cooperating with the heating roller 108. A pair of guide plates 112 and 114 are disposed downstream of the heat-fixing device 104. In the paper conveying means 50 of the aforesaid construction, a copying paper is supplied through the first paper introducing passage 70a from the paper cassette 58a in the paper feed device 52 or through the second paper introducing passage 70b from the paper cassette 58b (the paper feed device 52 will be described in more detail hereinafter), and conveyed to the transfer zone 30 by the pair of conveyor rollers 84 and 86, the pair of guide plates 88 and 90, the pair of conveyor rollers 92 and 94, and the pair of guide plates 96 and 98. The paper is brought into contact with the photosensitive member 20 on the rotating drum 18 in the transfer zone 30, then peeled from the photosensitive member 20 in the peeling zone 32, thereafter conveyed by the conveyor belt mechanism 100, introduced into the heat-fixing device 104 via the guide plate 102, and thereafter passed through the pair of guide plates 112 and 114 and discharged into the sorter 10. In the upper portion of the housing 4, there is provided an optical unit generally shown at 116 for scanning and exposing a document on the transparent plate 8 and projecting its image onto the photosensitive member 20 on the rotating drum 18 in the exposure zone 26. The optical unit 116 has a document illuminating lamp 118 for illuminating the document placed on the transparent plate 8, a first reflecting mirror 120 for projecting the reflected light from the document onto the photosensitive member 20, a second reflecting mirror 122, a third reflecting mirror 124, a lens assembly 126 and a fourth reflecting mirror 128. During scanning and exposure, the document illuminating lamp 118 and the first reflecting mirror 120 which are mounted on a common support frame 130 are moved substantially horizontally at a predetermined speed V from their initial position shown by the solid line to required positions (for example, maximum scanning-exposure termination positions shown by the two-dot chain line), and the second reflecting mirror 122 and the third reflecting mirror 124 which are mounted on a common support frame 132 are moved at a speed one half of the aforesaid speed (i.e., ½V) from their initial positions shown by the solid line to required positions (for example, maximum scanning-exposure termination positions shown by the two-dot chain line). At this time, the light reflected from the document illuminated by the document illuminating lamp 118 is reflected successively by the first reflecting mirror 120, the second reflecting mirror 122 and the third reflecting mirror 124 and reaches the lens assembly 126. Thereafter, it is reflected by the fourth reflecting mirror 126 and reaches the photosensitive member 20 in the exposure zone 26. When the scanning exposure is terminated, the document illuminating lamp 118, the first reflecting mirror 120, the second reflecting mirror 122 and the third reflecting mirror 124 are returned to their initial positions shown by the solid line. In the main body 2 of the copying apparatus described above, while the rotating drum is rotated in the direction of arrow 22, the charging corona discharge device 38 substantially uniformly charges the photosensitive member 20 to a specified polarity in the charging zone 24, and thereafter in the exposure zone 26, the optical unit 116 projects the image of the document to eliminate the charge on the photosensitive member 20 selectively, whereby a latent electrostatic image corresponding to the document is formed on the photosensitive member 20. Thereafter, the developing means 40 applies a toner to the latent electrostatic image on the photosensitive member 20 to develop the latent electrostatic image to a toner image. Then, in the transfer zone 30, a copying paper conveyed by the paper conveying means 50 is brought into contact with the photosensitive member 20, and by the action of the transfer corona discharge device 42, the toner image on the photosensitive member 20 is transferred to the paper. Subsequently, in the peeling zone 32, the copying paper is peeled from the photosensitive member 20 by the action of the peeling corona discharge devices 44 and 46. The copying paper having the toner image transferred thereto is then conveyed to the heat-fixing device 104 where the toner image is fixed to the copying paper. The paper is then discharged into the sorter 10. In the meantime, the photosensitive member 20 continues to rotate, and the toner remaining on the photosensitive member 20 after the transfer operation is removed from it by the action of the cleaning blade 48 in the cleaning zone 34 or by the action of the magnetic brush-type developing means 40 in the developing zone 28 (the removal of the residual toner from the photosensitive member 20 will be described in more detail hereinafter). The sorter 10 has a frame structure 202 having an open front side. The inside of the frame structure 202 includes a plurality of vertically stacked bins 204 and a moving means 206 for suitably moving the bins 204. When the copying process is to be repeated a number of times for the same document, after a copy (i.e., a copying paper having a fixed toner image) formed in a given copying cycle is received in the lowermost bin 204, the moving means 206 immediately moves downwardly that bin 204 which exists immediately above the aforesaid bin so as to receive a copy to be formed in the next copying cycle. After a copy in the final cycle of the copying process is received in a specified bin 204, the moving means 206 raises those bins 204 excepting the lowermost bin 204 to return them to the initial positions shown in Figure 3. The sorter 10 itself may be substantially the same as the sorter disclosed in the specificaion of Japanese Patent Application No. 162205/1981, and a detailed description of the structure of the sorter 10 itself is omitted in this specification. Detecting means, manually operable switches, display means, etc. With reference to Figures 3 and 5, in the paper feed device 52 in the main body 2 of the electrostatic copying apparatus in accordance with this invention, either one of three types of paper cassettes containing copying paper sheets according to JIS standards A3, A4 and A5 is mounted on the first cassette-receiving section 54a, and either one of three types of paper cassettes containing paper sheets according to JIS standards B4, B5 and B6 is mounted on the second cassette-receiving section 54b. In the first cassette-receiving section 54a and the second cassette-receiving section 54b, discriminating means 208a and 208b are respectively provided for determining which of the three types of the paper cassettes has been mounted. Each of the discriminating means 208a and 208b may be comprised of two reed switches disposed in spaced-apart relationship in the widthwise direction. In this case, two permanent magnets (not shown) are fixed to the opposite sides of the front surface of each of the A3 paper cassette containing paper sheets having a size A3 and the B4 paper cassette containing paper sheets having a size B4, for example; one permanent magnet is fixed to one side of the front surface of each of the A4 paper cassette containing paper sheets having a size A4 and the B5 paper cassette containing paper sheets having a size B5; and one permanent magnet is fixed to one side of the front surface of each of the A5 paper cassette containing paper sheets having a size A5 and the B6 paper cassette containing paper sheets having a size B6 which side is opposite to said one side of the front surface of the A4 or B5 paper cassette. Accordingly, when the A3 paper cassette is to be loaded on the first cassette-receiving section 54a, both of the two reed switches constituting the discriminating means 208a are closed. When the A4 paper cassette is to be loaded therein, one of the two reed switches is closed. Furthermore, when the A5 paper cassette is to be loaded, the other of the two reed switches is closed. Likewise, when the B4 paper cassette is to be loaded in the second cassette-receiving section 54b, both of the two reed switches constituting the discriminating means 208b are closed. When the B5 paper cassette is to be loaded, one of the two reed switches is closed. Furthermore, when the B6 paper cassette is to be loaded, the other of the two reed switches is closed. Detecting means 210a and 210b for detecting the rotation or stopping of the shafts 62a and 62b are provided with respect to each of the shaft 62a fixed to the supply roller 64a and the shaft 62b fixed to the supply roller 64b in the paper feed device 52. The detecting means 210a and 210b are comprised respectively of discs 212a and 212b fixed to one end portions of the shafts 62a and 62b and stationary photocouplers 214a and 214b consisting of light emitting elements located on one side of the discs 212a and212b and light-receiving elements located on the other sides of the discs 212a and 212b. A number of cuts are formed at suitable intervals in the circumferential direction in the circumferential edge portion of each of the discs 212a and 212b. When each of the shafts 62a and 62b is at rest, a cut or a portion between cuts of each of the discs 212a and 212b exists continuously between the light-emitting element and the light-receiving element of each of the photocouplers 214a and 214b, and therefore the light-receiving element of each of the photocouplers 214a and 214b is continuously maintained in condition for receiving light from the light-emitting element or for not receiving it. On the other hand, when each of the shafts 62a and 62b is rotated, a cut and a portion between cuts of each of the discs 212a and 212b alternately pass between the light-emitting element and the light receiving element of each of the photocouplers 214a and 214b, and therefore, the light receiving element of each of the photocouplers 214a and 214b is alternately maintained in condition for not receiving light from the light emitting element and for receiving it. As clearly shown in Figure 4, a paper detecting means 216 is provided in relation to both of the first paper introducing passage 70a extending from the first cassette-receiving section 58a and the second paper introducing passage 70b extending from the second cassette-receiving section 58b. The detecting means 216 includes a microswitch 220 having an actuating arm 218, a detecting piece 224a mounted pivotally on a shaft 222a and projecting into the first paper introducing passage 70a through an opening formed in the guide plate 66, and a detecting piece 224b mounted pivotally on a shaft 222b and projecting into the second paper introducing passage 70b through an opening formed in the guide plate 76. When the leading edge of the copying paper 56a supplied to the first paper introducing passage 70a from the cassette 58a by the action of the supply roller 64a rotated in the direction of the arrow comes into contact with the nip position of the pair of conveyor rollers 84 and 86 and consequently the copying paper 56a is bent as shown by the two-dot chain line, the detecting piece 224a is caused to pivot counterclockwise from its normal position shown in the drawing, and as a result, a projection 226 of the detecting piece 224a acts on the actuating arm 218 of the microswitch 220 to close the microswitch 220. When the leading edge of the copying paper 56b supplied to the second paper introducing passage 70b from the paper cassette 58b by the action of the supply roller 64b rotated in the direction of the arrow and conveyed through the second paper introducing passage 70b by the action of the pair of supply assisting rollers 80 and 82 rotated in the direction of the arrow comes into contact with the nip position of the pair of conveyor rollers 84 and 86 and as a result, the copying paper 56b is bent as shown by the two-dot chain line, the detecting piece 224b is caused to pivot clockwise from its normal position shows in the drawing. As a result, a projection 228b of the detecting piece 224b acts on the projection 228a of the detecting piece 224a to cause the detecting piece 224a to pivot counterclockwise from its normal position shown in the drawings. Finally, the projection 226 of the detecting piece 224a acts on the actuating arm 218 of the microswitch 220 to close the microswitch 220. A copying paper detecting means 228 is further provided with regard to the second paper introducing passage 70b. The detecting means 228 is constructed of a microswitch having an actuating arm 230 which projects into the second paper introducing passage 70b through the opening formed in the guide plate 74 upstream of the pair of supply assisting rollers 80 and 82. When the leading edge of the copying paper 56b supplied to the second paper introducing passage 70b from the copying paper cassette 58b acts on the actuating arm 230, the detecting means 228 is closed, and when the trailing edge of the paper 56b goes past the actuating arm 230, the detecting means 228 is opened. Again with reference to Figure 3, the main body 2 of the electrostatic copying apparatus further includes paper detecting means 232, 234 and 236 which detect a copying paper conveyed by the paper conveying means 50, at a position slightly downstream of the pair of conveyor rollers 84 and 86, at a position slightly downstream of the peeling zone and at a position slightly downstream of the heat-fixing device 104 (the downstream end portion of the paper conveying passage in the main body 2). The detecting means 232, 234 and 236 respectively have actuating arms 238, 240 and 242 projecting into the paper conveying passage, and are closed when the leading edge of the copying paper acts on the actuating arms 238, 240 and 242 respectively and are opened when the trailing edge of the copying paper goes past the actuating arms 238, 240 and 242. With reference to Figures 3 and 4, there is provided a paper wrapping detecting means 244 which when a copying paper kept in contact with the photosensitive member 20 on the rotating drum 18 in the transfer zone 30 wraps about the photosensitive member 20 without being peeled from the photosensitive member 20 in the peeling zone, detects the wrapping paper. The detecting means 244 is comprised of a light emitting element 246 for irradiating light onto the photosensitive member 20 at a position slightly downstream of the peeling zone as viewed in the rotating direction of the rotating drum 18, a light receiving element for receiving the light reflected from the photosensitive member 20, and a signal generator 250 electrically connected to the light receiving element 248 for producing a paper wrapping signal when the intensity of light received by the light receiving element is below a predetermined threshold value. The photosensitive member 20 itself has a high reflectance, and therefore when the paper is not wrapped about the photosensitive member 20, the light receiving element 248 receives light having a sufficient intensity. However, when the paper wraps about the photosensitive member, the light receiving element 248 receives light having an intensity below the threshold value and the signal generator 250 produces a paper wrapping signal, because the copying paper has a relatively low reflectance. Preferably, the distance ℓ₂ from the peeling zone 32 to the detecting position of the detecting means 244 as viewed in the rotating direction of the rotating drum 18 is substantially equal to the distance ℓ₁ from the peeling zone 32 to the detecting position of the detecting means as viewed in the moving direction of the copying paper. With reference to Figure 3, the main body 2 of the electrostatic copying apparatus further has disposed therein detecting means 252 and 254 for detecting the support frame 132 on which the second reflecting mirror 122 and the third reflecting mirror 124 in the optical unit 116 are mounted. Each of the detecting means 252 and 254 may be constructed of a reed switch to be actuated by a permanent magnet fixed to the support frame 132. The detecting means 252 detects the support frame 132 when the support frame 132 is at its initial position shown by the solid line. The detecting means 254 detects the support frame 132 and is closed, when the support frame 132 moves from its initial position to a position displaced to the right by a predetermined distance ℓ₃. A detecting means 256 which may be of any known form is disposed in the sorter 10, which when a trouble occurs (for example, when the bins 204 are not moved as required), detects it and produces a signal. In the semi-automatic document supplying and discharging device 6, there is provided a document insertion detecting means 258 which detects a document at that position of the introducing portion 144 of the conveying passage 140 which is slightly upstream of the document advancing arresting position of the first regulating member 162. The detecting means 258 may be comprised of a light emitting element 260 located above the introducing portion 144 and a light receiving element 262 located below the introducing portion144. When a document is inserted by hand into the introducing portion 144, light projected onto the light receiving element 262 from the light emitting element 260 is shut off by the document, whereupon the detecting means 258 produces a document insertion signal. There is also provided a detecting means 264 which detects a document at that position of the main portion 142 of the conveying passage 140 which is slightly upstream of the document advancing arresting position of the second regulating member 192. The detecting means 264 may be constructed of a light emitting element for projecting light onto the transparent plate 12, a light receiving element for receiving light reflected from the transparent plate 12, and a signal generator which produces a document detection signal when the intensity of the light received by the light receiving element falls below a predetermined threshold value. Since the transparent plate 12 itself has a high reflectance, the light receiving element receives light of a sufficient intensity when no document exists at the detecting position. On the other hand, because the reflectance of the document is relatively low, when the leading edge of the document arrives at the detecting position, the light receiving element receives light having an intensity below the predetermined threshold value, and the signal generator produces a document detection signal. When the trailing edge of the document goes past the detecting position, the light receiving element again receives light having a sufficient intensity and the above document detection signal disappears. Furthermore, a detecting means 266 is provided which detects the document at the downstream end portion of the curved discharging portion 146 of the conveying passage 140. The detecting means 266 is comprised of a microswitch 270 having an actuating arm 268, and a detecting piece 272 mounted pivotally by a supporting pin 271. One end portion of the detecting piece 272 projects into the curved discharging portion 146. When the leading edge of the document acts on one end portion of the detecting piece 272, the detecting piece 272 is caused to pivot counterclockwise from its normal position shown in the drawing. As a result, the other end portion of the detecitng piece 272 acts on the actuating arm 268 of the microswitch 270 to close the microswitch 270. When the trailing edge of the document goes past the one end portion of the detecting piece 272, the detecting piece 272 returns to its normal position shown in the drawings, and the micro-switch 270 is opened. In the illustrated copying apparatus, there are further provided known suitable detecting means (inclusively designated by numeral 275) which detect a disorder in various other constituent elements such as the document illuminating lamp 118 (Figure 3), the electrical heating means 106 (Figure 3) in the heat-fixing means, and the electrical heating means 273 (Figure 4) for heating the photosensitive member 20. The electrical heating means 273 (Figure 4) for heating the photosensitive member 20 will be descirbed further hereinafter. In the illustrated copying apparatus, a temperature detecting means 277 (Figure 3) for detecting the temperature of the heat-fixing device 104 and a temperature detecting means 279 (Figure 4) for detecting the temperature of the surface or its vicinity of the photosensitive member 20 are further provided. Detecting devices 281 and 283 respectively including the temperature detecting means 277 and 279 produce not only a temperature signal but also a signal showing a disorder which occurs in the temperature detecting means 277 and 279, as will be described in detail hereinbelow. With reference to Figures 1 and 2, a key card insertion section 274 is provided at the front end portion of the upper surface of the housing 4 of the main body 2 of the copying apparatus. A given key card 276 is inserted into the key card inserting section by an operator. In the key card inserting section 274 is provided a signal producing means 278 which when the key card 276 is inserted, detects it and produces a copying process performance permission signal. In the illustrated electrostatic copying machine, the copying process cannot be performed unless the operator inserts the key card 276 into the key card inserting section 274 thereby producing the aforesaid signal for the permission of the performance of the copying process. This prevents any unauthorized person from operating the copying apparatus and obtaining copies. Adjacent to the key card inserting section 274, a panel 280 is disposed at the front end portion of the upper surface of the housing 4. In the electrostatic copying apparatus improved in accordance with this invention, a control system illustrated in Figure 6 is provided in relation to the heat fixing device 104 (Figure 3). The control system further includes a power saving means 512 and a heating control means (not shown) included in the processing means 306, in addition to the power switch 282 and the detecting device 281 including the temperature detecting means 277 for detecting the temperature of the heat fixing device 104. The temperature detecting means 277 is provided in contact with, or in proximity to, the surface of the heating roller 108 (Figure 3) in the heat fixing device 104, and detects the temperature of the surface or its vicinity of the heating roller 108. Such a temperature detecting means 277 can be constructed of, for example, a thermistor. The power saving means 512 comprises a power saving switch 514 disposed on the panel 280, and produces a power saving signal when manually closed. The heating control means of the processing means 306 includes a memory 516 and a first heater counter 518. A first predetermined value T₁, a second predetermined value T₂ and a third predetermined value T₃ are stored in the memory 516. The first predetermined value T₁ is set at a temperature (about 180°C in the illustrated embodiment) which is suitable for heat fixing the toner image on the copying paper by the heat fixing device 104. The second predetermined value T₂ is set at a suitable temperature (190°C in the illustrated embodiment) which is higher than the first predetermined temperature value T₁(T₁<T₂). The third predetermined value T₃ is set at a suitable temperature (160°C in the illustrated embodiment) which is higher than the softening temperature of the toner but is lower than the first predetermined value T₁ (T₃<T₁). The first heater counter 518 is comprised of a backup-type counter, and begins counting up when the power switch 282 is closed, and begins counting down when the power switch 282 is opened. A detailed description of the detecting device 281 is omitted here since it is given hereinafter. In the above control system, the output signals of the power switch 282 and the detecting device 281 including the temperature detecting means 277 and the power saving signal of the power saving switch 514 are fed into the heating control means of the processing means 306. The output signal from the heating control means is fed into the switch means 520 and causes the opening and closing of the switch means 520. When the switch means 520 is closed, the electrical heating means 106 of the heat fixing device 104 is connected to a suitable power supply E such as a commercial AC power supply and energized. When the switch means 520 is opened, the aforesaid connection is released to deenergize the electrical heating means 106. The operation and effect of the heat fixing device 104 including the aforesaid control system will be described with reference to Figure 14 showing a flow chart of the method of control by the control system described above and Figure 15 shows changes with time of the temperature of the surface or its vicinity of the heating roller 108. When the power switch 282 on the panel 280 is closed in step n5-1, step n5-2 sets in. In step n5-2, it is judged whether the temperature detecting means 277 is out of order (for example, when the temperature detecting means 277 is constructed of a thermistor, whether the thermistor has breaks). When the power switch 282 is closed, the electrical heating means 106 is energized to heat the heat fixing device 104 and at the same time the waiting flag 308 included in the processing means 306 is set at logic "1", whereby the waiting display lamp 296 (Figure 6) is energized to indicate that the heat fixing device 104 is in a preparatory condition. The waiting flag 308 is reset at logic "0" once the temperature of the heat fixing device 104 detected by the temperature detecting means 277 has exceeded the second predetermined value T₂ as a result of heating by the electrical heating means 106. Hence, the waiting display lamp 296 is deenergized. The waiting flag 308 is set when the power saving switch 514 is closed or the power switch 282 is opened. Moreover, when the power saving switch 514 is opened and the temperature detected by the temperature detecting means 277 has exceeded the first predetermined value T₁, the waiting flag 308 is reset. When in step n5-2 it is judged that the temperature detecting means 277 is out of order, step n5-3 sets in, and the service man call lamp 298 on the panel 280 is turned on, thus showing that some trouble has occurred in the copying apparatus. On the other hand, when it is judged in step n5-2 that the temperature detecting means 277 is not out of order, step n5-4 sets in, and the second predetermined value T₂ (about 190°C) stored in the memory 516 in the heating control means is read out, and set [When the predetermined value T₂ has been set, the electrical heating means 106 is controlled based on the signal from the detecting device 281 such that the temperature of the surface or its vicinity of the heating roller 108 is adjusted substantially to the second predetermined value T₂ (about 190°C)]. Then, step n5-5 sets in, and counting up of the counter 518 of the heat control means is started. Furthermore, step n5-6 sets in, and it is judged in this step whether the counter 518 has counted a predetermined number. The predetermined number is the number of counts corresponding to a first predetermined time W₁ from time to to time t₂ in Figure 15. Hence, when the counter 518 has counted the predetermined number, the first predetermined time W₁ elapses. This first predetermined time W₁ is, for example, 10 to 15 minutes. When in step n5-6 it is judged that the counter 518 has not counted the predetermined number, step n5-2 again sets in. When during the counting of the counter 518, the heat fixing device 104 is heated to cause the temperature of the surface or its vicinity of the heating roller 108 to exceed the second predetermined value T₂, the waiting flag 308 is reset at logic "0" on the basis of the signal from the temperature detecting means 277. As a result, the waiting display lamp 296 is deenergized to show that the copying process is in condition for performance. Although at this time the ambient temperature of the heat fixing device 104 is slightly lower than that in an optimal condition, the temperature of the surface or its vicinity of the heating roller 108 after the deenergization of the waiting display lamp 296 becomes the second predetermined value T₂ which is higher than the first predetermined value T₁. Hence, the toner image can be fixed satisfactorily. On the other hand when in step n5-6 it is judged that the counter 518 has counted the predetermined number, step n5-7 sets in, and the first predetermined value T₁ (about 180°C) stored in the memory 516 of the heating control menas is read out. Thus, instead of the second predetermined value T 2, the first predetermined value T₁ is set [when the predetermined value T₁ has been set, the electrical heating means 106 is controlled on the basis of the signal from the detecting device 281 such that the temperature of the surface or its vicinity of the heating roller 108 is adjusted substantially to the first predetermined value T₁ (about 180°C)]. At this time, the counter 518 keeps maintaining the aforesaid predetermined count number. Thus, the electrical heating means 106 is controlled such that the temperature of the surface or its vicinity of the heating roller 108 is adjusted substantially to the first predetermined value T₁. After the time t₃, this temperature is maintained substantially at the first predetermined value T₁, and the temperature of the ambient atmosphere is maintained at an optimal value. Accordingly, when the power switch 282 is closed to apply power, the temperature of the surface or its vicinity of the heating roller 108 is maintained substantially at the second predetermined value T₂ higher than the first predetermined value T₁ even during the time from t₁ to t 2, and thereafter is maintained substantially at the first predetermined value T₁ after the time t 3. Thus, it is maintained at a temperature optimal for the heat fixing of the toner image. When the first predetermined value T₁ is set in step n5-7, step n5-8 sets in. In step n5-8, it is judged whether the power saving switch 514 is closed. When it is judged in step n5-8 that the power saving switch 514 is not closed, step n5-9 sets in. In step n5-9, it is judged whether the power switch 282 is closed. When it is judged in step n5-9 that the power switch 282 is closed, step n5-13 sets in, and it is judged in this step whether the counter 518 is zero. When it is judged in step n5-13 that the counter 518 is not zero, step n5-7 again sets in. Hence, after the time t 3, the temperature of the surface or its vicinity of the heating roller 108 is maintained substantially at the first predetermined value T₁ unless the power saving switch 514 or the power switch 282 is closed. On the other hand, when it is judged in step n5-8 that the power saving switch 514 is closed, step n5-10 sets in, and the third predetermined value T₃ (about 160°C) stored in the memory 516 in the heating control means is read out. As a result, the third predetermined value T₃°C) is set instead of the first predetermined value T₁ [when the predetermined value T₃ has been set, the electrical heating means 106 is controlled on the basis of the signal from the detecting device 281 such that the temperature of the surface of its vicinity of the heating roller 108 is adjusted substantially to the third predetermined value T₃ (about 160°C)]. When the third predetermined value T₃ has been set in step n5-10, step n5-11 follows. In step n5-11, it is judged whether the power saving switch 514 is opened. When it is judged in step n5-11 that the power saving switch 514 is not opened, the step n5-10 again sets in. Hence, when the power saving switch 514 is closed after the time t₄, the electrical heating means 106 is controlled such that the temperature of the surface or its vicinity of the heating roller 108 is adjusted substantially to the third predetermined value T 3. After the time t₅, this temperature is maintained substantially at the third predetermined value T₃. When the power saving switch 514 is closed, the waiting flag 308 is reset at logic "0" to energize the waiting display lamp 296 (Figure 6), thus showing that the heat fixing device 104 is in a preparatory condition. On the other hand, when it is judged in step n5-11 that the power saving switch 514 is opened, step n5-7 again sets in. In step n5-7, the first predetermined value T₁ stored in the memory 516 is read out, and the first predetermined value T₁ is set instead of the third predetermined value T₃ - (when the predetermined value T₁ is set, the electrical heating means 106 is controlled such that the temperature of the surface or its vicinity of the heating roller 108 is adjusted substantially to the first predetermined value T₁). Thus, when the power saving switch 514 is closed, and thereafter opened at time t₆, the electrical heating means 106 is controlled such that the temperature of the surface or its vicinity of the heating roller 108 is adjusted substantially to the first predetermined value. After the time t₇, this temperature is maintained substantially at the first predetermined value T₁. When the power saving switch 514 is opened, and by the heating of the electrical heating means 106, the temperature of the heat fixing device 104 detected by the temperature detecting means 277 exceeds the first predetermined value T₁, the waiting flag 308 is reset at logic "0" to deenergize the waiting display lamp 296, thus showing that the copying process is in a preparatory condition. When in step n5-9 it is judged that the power switch 282 is not closed, step n5-12 sets in, and the counting down of the counter 518 is started. The count down of the counter 518 is one from the predetermined number maintained in step n5-5. When the counting down of the counter 518 is performed, step n5-9 again sets in. Hence, when the power switch 282 is opened at time t₈, the counting down of the counter 518 is effected, and the copying apparatus is cut off from the power supply to deenergize the electrical heating means 106. Since the power supply is turned off upon the opening of the power switch 282, the waiting flag 308 is reset at logic "0" and thus the waiting display lamp 296 is also deenergized. If it is judged in step n5-9 that the power switch 282 is closed before the number held by the counter 518 becomes zero by the counting down of the counter 518 from the predetermined number in step n5-12 (that is to say, beofre the lapse of a second predetermined time W₂ to be described after the opening of the power switch 282), step n5-13 sets in. In step n5-13, it is judged whether the counted value of the counter 518 is zero. Thereafter, step n5-7 again sets in, and the first predetermined value T₁ is set in the heating control means. In this case, the counting up of the counter 518 is also started although it is not shown in the flow chart. The counting up can be carried out from the count down number kept in the counter 518 to the predetermined number. Hence, when at time t₉ after the opening of the power switch 282 but before the lapse of the second predetermined time W 2, the power switch 282 is again closed to turn on the power supply, the electrical heating means 106 is controlled such that the temperature of the surface or its vicinity of the heating roller 108 is adjusted substantially to the first predetermined value T₁. The second predetermined time W₂ is the time required for the counter 518 to count down from the predetermined number to zero, and is, for example, 10 to 15 minutes. When the power switch 282 is closed, the waiting flag 308 is set at logic "1" to energize the waiting display lamp 296. When the heating by the electrical heating means 106 causes the temperature detected by the temperature detecting means 277 to exceed the first predetermined value T₁, the waiting flag 308 is reset to logic "0" to deenergize the waiting display lamp 296. On the other hand, when it is judged in step n5-9 that the power switch 282 is closed, after the counter 518 has performed counting down and the number kept by the counter 518 has become zero in step n5-12 (in other words, after the second predetermined time W₂ has elapsed after the opening of the power switch 282), step n5-13 sets in. In step n5-13, it is judged whether the counter 518 is zero, and thereafter step n5-2 agains sets in. Accordingly, when at time t₁₀ which is after the opening of the power switch 282 and further elapsing of the second predetermined period of time W₂, the power switch 282 is again closed to turn on the power supply, the electrical heating means 106 is controlled such that the temperature of the surface or its vicinity of the heating roller 108 is adjusted substantially to the second predetermined value T₂ which is higher than the first predetermined value T₁. A detailed description of the controlling of the electrical heating means 106 on the basis of the signal from the detecting device 281 including the temperature detecting means 277 is omitted here since it is given hereinafter. In the illustrated embodiment, the first predetermined time W₁ and the second predetermined time W₂ are measured by one backup-type counter 518. If desired, two such counters may be used so that one of them is used to measure the first predetermined time W₁, and the other to measure the second predetermined time W₂. As stated hereinabove, in the heat fixing device 104 equipped with the control system described above, the temperature of the surface or its vicinity of the heating roller 108 is usually kept substantially at the second predetermined value T₂ higher than the first predetermined value T₁ suitable for heat fixing after the power supply has been turned on, and thereafter it is maintained substantially at the first predetermined value T₁. It is possible therefore to bring the temperature of the surface or its vicinity of the heating roller 108 and the ambient temperature to a temperature suitable for heat fixing within a short period of time, and the waiting time after the application of power can be shortened. Furthermore, since the temperature of the surface or its vicinity of the heating roller 108 is maintained substantially at the third predetermined value T₃ lower than the first predetermined value T₁ suitable for heat fixing by the operation of the power saving means 512, power consumption can be reduced by utilizing the power saving means when there is a considerable time interval between copying cycles. Furthermore, when the power supply is again turned on before the lapse of the second predetermined period of time W₂ after the turning off of the power supply (the opening of the power switch 282), the temperature of the surface or its vicinity of the heating roller 108 is maintained substantially at the first predetermined value T₁. Accordingly, the aforesaid temperature and the ambient temperature can be brought to a value suitable for heat fixation within a short period of time. In the electrostatic copying apparatus imporved in accordance with this invention, an control system shown in Figure 13 is further provided in relation to the heat fixing device 104, the document illuminating lamp 118 and a drive motor 522 constituting a main electric motor (which is a drive source for the copying apparatus and drives the optical device 116, the rotating drum 18, the copying paper conveying means 50, etc.). Again with reference to Figure 13, this control system comprises a power control means (not shown) included in the processing means 306. The power control means includes a memory 524, a decade counter 526 and a second heat counter 528. Predetermined values "4", "6" and "9" are stored in the memory 524. These predetermined values "4", "6" and "9" are used to control the amount of an electric current supplied to the electrical heating means, as will be described in detail hereinafter. In the aforesaid control system, the output signal from the power control means of the processing means 306 is supplied to the switch means 520 (the switch 520 is opened and closed by the output signal from the heating control means as described hereinabove), and the switch means 520 is opened and closed by this output signal. The output signal from the processing means 306 is supplied to the switch means 530 and 532 to open or close the switch means 530 and 532. The switch means 530 serves to control the document illuminating lamp 118. When the switch means 530 is closed, the document illuminating lamp is connected to a suitable power supply E such as a commercial AC power supply and thus energized. Furthermore, upon the opening of the switch means 530, the aforesaid connection is released and the document illuminating lamp 118 is deenergized. On the other hand, the switch means 532 serves to control the drive motor 522. When the switch means 532 is closed, the drive motor 522 is connected to the aforesaid power supply E, and when the switch means 532 is open, the aforesaid connection is released, and the drive motor 522 is deenergized. It will be easily appreciated from the foregoing description that an electric power from a power supply E such as a commercial AC power source which is a single power supply source is supplied to the electrical heating means 106, the document illuminating lamp 118 and the drive motor 522. The processing means 306 is also connected to the power supply E. The operation and effect of the electrostatic copying apparatus equipped with the aforesaid control means will be described with reference to Figure 16 showing the flow chart of the method of controlling according to the control system described above and Figure 17. In the following description, a commercial AC power supply is used as the power supply E. When the power supply is turned on, it is first judged in step n6-1 whether the voltage of the power supply E is zero cross. When it is judged that it is not zero cross, the original state is revived. On the other hand, when it is judged that the voltage is zero cross, step n6-2 sets in. In step n6-2, it is judged whether the drive motor 522 is energized (therefore, whether the switch 532 is closed). When it is judged in step n6-2 that the drive motor 522 is energized, the next step n6-3 sets in, and in this step, it is judged whether the document illuminating lamp 118 is energized (therefore, whether the switch 530 is closed). When in step n6-3 it is judged that the document illuminating lamp 118 is energized, step n6-4 sets in. In step n6-4, the predetermined value "4" stored in the memory 524 in the power control means is read out and set. On the other hand, when it is judged in step n6-3 that the document illuminating lamp is not energized, step n6-5 sets in. In step n6-5, the predetermined value "6" stored in the memory 524 in the power control means is read out and set. Furthermore, when it is judged in step n6-2 that the drive motor 522 is not energized, step n6-6 sets in. In step n6-6, the predetermined value "9" stored in the memory 524 in the power control means is read out and set. Accordingly, when the drive motor 522 and the document illuminating lamp 118 are not energized, the predetermined value "9" is set, and when the drive motor 522 is energized, the predetermined value "6" is set. Furthermore, when the drive motor 522 and the document illuminating lamp 118 are energized, the predetermined value "4" is set. After the predetermined value has been set in step n6-4, n6-5 or n6-6, step n6-7 sets in and the counting of the decade counter 526 is started. The decade counter 526 counts up from 0 to 9 for each half cycle of the power supply E. When the counting of the decade counter 526 begins, step n6-8 then sets in, and it is judged in this step whether the decade counter 526 has counted up to 9 and produced a carry signal. When it is judged in step n6-8 that the carry signal has been produced, step n6-9 sets in. In step n6-9, the aforesaid predetermined value is transferred to the second heater counter 528 and store. More specifically, when the predetermined value "4" is set in step n6-4, this predetermined value "4" is stored in the heater counter 528. When the predetermined value "6" is set in step n6-5, the predetermined value "6" is stored in the heater counter 528. When the predetermined value "9" is set in step n6-6, this predetermined value "9" is stored in the heater counter 528. Thereafter, step n6-10 sets in, and it is judged in this step whether the value of the heater counter 528 is zero. The heater counter 528 counts down one by one from the aforesaid stored value for each half cycle of the power supply E. When it is judged in step n6-8 that the carry signal is not produced, step n6-8 is followed by step n6-10. When it is judged in step n6-10 that the heater counter 528 is not zero, step n6-11 sets in and the heater counter 528 counts down by one. Then, step n6-12 sets in, and it is judged in this step whether the detected temperature of the heat fixing device 104 (therefore, the temperature of the surface or its vicinity of the heating roller 108 which is detected by the temperature detecting means 277) is equal to, or below, the prescribed value. [In more detail, when the first predetermined value (about 180 °C) is set in the heating control means, it is judged whether the detected temperature is equal to, or below, the first predetermined value; when the second predetermined value (about 190 °C) is set, it is judged whether the detected temperature is equal to or below the second predetermined value; and when the third predetermined value (about 160 °C) is set, it is judged whether the detected temperature is equal to or lower than the third predetermined value.] When it is judged in step n6-12 that the detected temperature is equal to or lower than the preset value, step n6-13 sets in and the electrical heating means 106 is energized (the switch means 520 is closed by the signals from the power control mean and the heating control means). Thereafter, the process returns to step n6-11. On the other hand, when it is judged in step n6-12 that the detected temperature is not equal to, or below, the preset value, step n6-14 sets in, and the electrical heating means 106 is deenergized (the switch means 520 is opened by the signals from the heating control means irrespective of the signal from the power control means). Thereafter, the process returns to step n6-1. When the aforesaid step is performed, and it is judged in step n6-10 that the counted number of the heater counter 528 is zero, step n6-14 sets in, and the electrical heating means 106 is deenergized (the switch means 520 is opened by the signal from the power control means irrespective of the signal from the heating control means). Thereafter, step n6-1 again sets in. Thereafter, the aforesaid operation is repeated until the power supply of the copying apparatus is turned off. It will be readily appreciated that in the above control system, the above operation is repeated for each half cycle of the alternate current from the power supply E. In the above-described flow chart, the operations performed when the predetermined value "4" is set in step n6-4 (therefore when the drive motor 522 and the document illuminating lamp 118 are energized), when the predetermined value "6" is set in the step n6-5 (therefore, when the motor 522 is energized), and when the predetermined value "9" is set in step n6-6 (therefore, when the drive motor 522 and the document illuminating lamp 118 are not energized) are briefly as follows: In the case of the predetermined value "4" being set, the predetermined value "4" is stored in the heater counter 528 when the decade counter 526 has produced a carry signal (namely, when the decade counter 526 has counted up one by one and reached 9). After the decade counter 526 has produced a carry signal, it again returns to 0, and counts up one by one from 0. After the predetermined value "4" has been stored, the heater counter 528 counts down one by one from the predetermined value "4" for each half cycle of the AC current of the power supply E. Until it is counted down to zero, the switch means 520 is closed by the signal from the power control means, and the current from the power supply E is fed into the electrical heating means 106. After the counted value has reached zero, the switch means 520 is opened by the signal from the power control means and the supply of the current is stopped. In such a case, therefore, the current supplied to the electrical heating means is as shown by (1) in Figure 10, and after storage in the heater counter 528, an alternate current of five half cycles is supplied to the electrical heating means 106, and during the period from the time t₁₁ to t₁₂, the electrical heating means 106 is energized. When the decade counter 526 counts up one by one for each half cycle of the power supply E and again produces a carry signal, the aforesaid operation is repeated. It will be readily appreciated from the foregoing statement that by the carry signal of the decade counter 526, ten half cycles of the power supply E form one cycle Q (for example, from the time t₁₁ to the time t₁₃). When the predetermined value "4" is set, the amount of current per predetermined period supplied to the electrical heating means 106 becomes one-half of the amount of current per predetermined period from the power supply E by the action of the power control means. When the aforesaid detected temperature is higher than the preset value, the switch means 520 is opened by the signal from the heating control means. Accordingly, even when the counted value of the heater counter 528 is not zero, the electrical heating means 106 is not energized. When the predetermined value "6" is set, the predetermined value "6" is stored in the heater counter 528 when the decade counter 526 has produced a carry signal. After the predetermined value "6" has been stored, the heater counter 528 counts down one by one from the predetermined value "6" for each half cycle of the alternate current of the power supply E. Until the counted value becomes zero as a result of counting down, the switch means 520 is closed by the signal from the power control means, and the current from the power supply E is supplied to the electrical heating means 106. After the counted value has become zero, the switch means 520 is opened by the signal from the power control means, and the supply of the current is stopped. Accordingly, in this case, the current supplied to the electrical heating means 106 is as shown by (2) in Figure 17, and after storage in the heater counter 528, an alternate current of seven half cycles is supplied to the electrical heating means 106, and thus, the electrical heating means 106 is energized during the period from the time t₁₁ to the time t₁₄. When the decade counter 526 counts up one by one for every half cycle of the power supply E and again produces a carry signal, the aforesaid operation is repeated. Thus, when the predetermined value "6" is set, the amount of current per predetermined period supplied to the electrical heating means 106 becomes 7/10 of the amount of current per predetermined period from the power supply E by the action of the power control means. In this case, too, when the detected temperature is the above the predetermined value, the switch means 520 is opened by the signal from the heating control means. Hence, even when the counted number of the heater counter is not zero, the electrical heating means 106 is not energized. Furthermore, when the predetermined value "9" is set, the predetermined value "9" is stored in the heater counter 528 when the decade counter 526 has produced a carry signal. After the predetermined value "9" has been stored, the heater counter 528 counts down one by one from the predetermined value "9" for each half cycle of the alternate current from the power supply E. Until the counted value becomes zero as a result of counting down, the switch means 520 is closed by the signal from the power control means, and the current from the power supply E is supplied to the electrical heating means 106. Since the predetermined value is "9", the current supplied to the electrical heating means 106 is as shown by (3) in Figure 17, and after storage in the heater counter 528, an alternate current of 10 half cycles is supplied to the electrical heating means, and thus, the electrical heating means 106 is energized during the period from the time t₁₁ to the time t₁₃. When the decade counter 526 counts up one by one for each half cycle of the power supply E and again produces a carry signal, the above operation is repeated. When the predetermined value "9" is set, the amount of current per predetermined period supplied to the electrical heating means 106 becomes substantially equal to the amount of current per predetermined period from the power supply E by the action of the power control means. In this case, too, the switch means 520 is opened by the signal from the heating control means when the detected temperature is above the prescribed value. Hence, the electrical heating means 106 is not energized. As stated hereinabove, in the electrostatic copying apparatus equipped with the control system described above, when the document illuminating lamp 118 and the drive motor 522 are deenergized, the amount of current per predetermined period supplied to the electrical heating means 106 is greatest, and its power consumption is greatest. When the drive motor 522 is energized, the amount of current per predetermined period is smaller than in the above-described instance, and the power consumption is of a medium degree. When the drive motor 522 and the document illuminating lamp 118 are energized, the amount of current per predetermined period of time is smallest, and the power consumption is smallest. Accordingly, in the aforesaid electrostatic copying apparatus, the power consumption increases as a result of the energization of the drive motor 522 and the document illuminating lamp 118, but the overall increase of the power consumption in the entire copying apparatus can be prevented by reducing the power consumption of the electrical heating means 106. This is effective especially when there is used a power supply having a restricted maximum power consumption, such as a commercial AC power supply. Furthermore, since the maximum power is supplied to the electrical heating means 106 immediately after application of power when the drive motor 522 and the document illuminating lamp 118 are deenergized, the time required until the temperature of the surface or its vicinity of the heating roller 108 reaches a value suitable for the fixation of a toner image (the waiting time) can be shortened. It will be clear from Figure 17 that in the illustrated embodiment, the amount of current per predetermined period supplied to the electrical heating means 106 is controlled by using a half cycle of the power supply E as one unit. If desired, the amount of current may be controlled as shown in Figure 11. In Figure 11, the alternate current of the power supply is controlled in each half cycle. As regards the AC current shown in Figure 11, that part of the current which corresponds to the period from the time t₁₅ to the time t₁₆ and that part of the current which corresponds to the period from the time t ₁ ₇ to the time t₁₈ are supplied to the electrical heating means 106 as a result of the opening and closing of the switch means 520 by the signal from the power control means. By controlling the current as shown in Figure 18, substantially the same effect as in the case of Figure 10 can be obtained. In the illustrated embodiment, the power consumption of the electrical heating means is controlled according to the power consumption of the drive motor 522 and the document illuminating lamp 118 which consume a relatively great deal of power. If desired, the power consumed by the electrical heating means 106 can also be controlled according to the power consumption of the electric heating means 237 (Figure 4), the electric motor 188 for the semiautomatic document supplying and discharging device, a fan motor (not shown) for cooling the document illuminating lamp, etc. in addition to the above. In this case, the amount of current per predetermined period supplied to the electrical heating means 106 may be decreased stepwise according to the number of electrical means (the drive motor 522, the document illuminating lamp 118, the electric motor 188, the electrical heating means 237, etc.). Furthermore, in the illustrated embodiments, the temperature is detected by using the temperature detecting means 277. If desired, elements other than temperature can be detected by using a detecting element whose resistance value changes with a change in the amount of detection, instead of the temperature detecting means 277. While the present invention has been described hereinabove with reference to the accompanying drawings showing the preferred embodiments of the copying apparatus constructed in accordance with this invention, it should be understood that the present invention is no way limited to these specific embodiments, and various changes and modifications are possible without departing from the scope of this invention as claimed.

Claims: A heat fixing device having an electrical heating means (106) for heat-fixing a toner image on a sheet member, comprising a temperature detecting means (277) and a heating control means (516, 518) for controlling the energization and deenergization of said heating means on the basis of the temperature detected by said temperature detecting means; said heating control means (516, 518) controls, after the lapse of a first predetermined period of time (W₁), the energization and deenergization of said heating means (106) on the basis of whether or not the detected temperature is below or higher than a first predetermined value (T₁) which is suitable for heat fixation, hereby adjusting said detected temperature substantially to said first predetermined value (T₁); wherein before the lapse of said first predetermined period of time (W₁) commencing from the application of electric power, said heating control means (516, 518) controls the energization and deenergization of said heating means (106) on the basis of whether or not the detected temperature is below or higher than a second predetermined value (T₂) which is higher than the first predetermined value (T₁) hereby adjusting the detected temperature substantially to the second predetermined value (T₂), characterized in that when an electric power is again applied before the lapse of a second predetermined period of time (W₂) commencing from the time of the electric power being off, said heating control means (516, 518), even before the lapse of the first predetermined period of time (W₁) commencing from the application of electric power, controls the energization and deenergization of said heating means (106) on the basis of whether or not the detected temperature is below or higher than the first predetermined value (T₁) hereby adjusting the detected temperature substantially to said first predetermined value (T₁). A heat fixing device according to claim 1, characterized by an electric power saving means (512) comprising a manually operable power saving switch (514) for producing a power saving signal according to the operation of the power saving switch, and when said power saving means produces said power saving signal, said heating control means (516, 518) controls the energization and deenergization of said heating means (106) on the basis of whether or not said detected temperature is below or higher than a third predetermined value (T₃) lower than the first predetermined value (T₁), hereby adjusting the detected temperature substantially to said third predetermined value (T₃). A heat fixing device according to claim 1 or 2, characterized in that said first predetermined value (T₁) is about 180 °C. A heat fixing device according to claim 1 or 2, characterized in that said second predetermined value (T₂) is about 190 °C. A heat fixing device according to any of claims 2 to 4, characterized in that said third predetermined value (T₃) is about 160 °C. A heat fixing device according to any of claims 1 to 5, characterized in that said first predetermined period of time is 10 to 15 minutes. A heat fixing device according to any of claims 1 to 6, characterized in that said second predetermined period of time is 10 to 15 minutes. A heat fixing device according to any of claims 1 to 7, characterized by a pair of cooperating rollers (108, 110) through which to pass the sheet member having the toner image to be heat-fixed, in which pair one (108) of said rollers is hollow and said heating means (106) is disposed in said one roller, said temperature detecting means (277) detecting the temperature of the surface or its vicinity of said one roller.

Inventors: HISAJIMA MASAHIKO, KAMINAGA SEIJI, KIMURA HIROSHI, SATONAKA SHINOBU, SHIGEMURA YUTAKA, YADA ISAO, HISAJIMA, MASAHIKO, KAMINAGA, SEIJI, KIMURA, HIROSHI, SATONAKA, SHINOBU, SHIGEMURA, YUTAKA, YADA, ISAO
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO. LTD.
Application year: 1986
Main classification: G03G15
IPC codes: G03G15, G05D23