EP0070740B1

EP0070740B1 - Fixing and heating device for an electrostatic copying apparatus

Info

Publication number: EP0070740B1
Application number: EP19820303848
Authority: EP
Inventors: Masahide Iseki
Original assignee: Mita Industrial Co Ltd
Current assignee: Kyocera Mita Industrial Co Ltd
Priority date: 1981-07-21
Filing date: 1982-07-20
Publication date: 1985-12-18
Also published as: JPH0140351B2; JPS5814871A; DE3268019D1; EP0070740A3; EP0070740A2

Description

The present invention relates to a fixing and heating device to be used for an electrostatic copying apparatus for heating and fixing a toner image on a copy paper sheet passed through a set of fixing rollers.
In one prior art arrangement, fixing rollers are driven to rotate at a relatively high speed suitable for fixing when a power switch of an electrostatic copying apparatus is closed. Before the power switch is closed, residual toner from a preceding copying operation remains and solidifies on the fixing rollers, which contact each other. The fixing rollers rotate upon closing the power switch. At this time the fixing rollers are not heated to the softening temperature or a melting temperature of the toner and, therefore the solidified toner remaining on the fixing rollers damages the fixing rollers.
Another prior art arrangement comprises a scraper plate for scraping off the toner remaining on the fixing roller to prevent a copy paper sheet from winding around the fixing rollers. Since the fixing roller is driven to rotate before the solidified toner remaining between the surface of the fixing roller and the scraper plate is softened or melted, the scraper plate is deformed by rotation of the fixing roller and the fixing roller is damaged. The toner solidifying on the fixing roller and the scraper plate result in a sound occurring when the fixing roller begins to rotate. Rotation at a relatively high speed causes the fixing rollers to make a larger noise.
Still another prior art arrangement comprises a fixing roller which begins to rotate when the power switch of the electrostatic copying apparatus is closed, and the surfaces of the fixing rollers are heated to a temperature suitable for fixing. Once the fixing rollers are heated to the temperature suitable for fixing, they continuously rotate at a relatively high fixing speed. Therefore, continuous rotation causes damage to the fixing roller and causes the fixing rollers to make sounds.
Another prior art arrangement is disclosed in earlier GB-A-2052392 which describes electrostatic copying apparatus having a fixing device for fixing a toner image onto a copy paper sheet, said fixing device comprising a hollow heating roller, a heater extending through the interior of the heating roller, a press roller, means for urging the periphery of the press roller into contact with the heating roller, means for feeding copy sheets with an image to be fixed into the lip between the press roller and the heating roller, a temperature detecting element for sensing the temperature of one of the rollers, drive means for rotating the fixing rollers, a power switch closeable to supply power to the apparatus, a copy switch for initiating a copying operation and control means operable to prevent rotation of the fixing rollers by the drive means unless the sensed temperature is at least at a first predetermined temperature at or above the softening temperature of the toner and operable to prevent initiation of a copying operation upon closure of the copy switch when the sensed temperature is below a predetermined fixing temperature at which the fixing rollers are able satisfactorily to fix a toner image on a copy sheet, and is operable to cause the drive means to rotate the fixing rollers when the sensed temperature is at a value intermediate said first temperature and said fixing temperature. With this prior construction the fixing rollers were rotated at a reduced speed during warm up and then once the fixing temperature has been reached were continuously rotated at fixing speed. This has the disadvantage of the wear and tear and continual noise caused by the fixing rollers being rotated at all times that the copying apparatus is switched on and is up to temperature regardless of whether a copying operation is taking place at that time. Clearly this is a grave disadvantage in view of the fact that most copiers, especially the low volume copiers, spend more time in the office warmed up ready for actual use than they do carrying out a copying operation. A further disadvantage of this prior construction is that complexity is caused by the need to provide a two speed drive to the fixing rollers so that they rotate at a slow speed during warm up, once toner softening temperature has been reached, and are then rotated at full operating speed once the fixing temperature has been achieved.
The present invention is characterised in that said control means is operative to cause rotation of the fixing rollers at normal fixing speed when the sensed temperature is at a said intermediate value and to allow the fixing rollers to rest stationary when the sensed temperature has reached said fixing temperature except during a fixing operation upon closure of the copy switch. Thus it has now been appreciated that far from being preferable to provide relatively slow rotation during heating of the press roller by conduction from the heating roller during warm up a quicker and more even heating of the press roller is achieved by rotating the fixing rollers at a greater speed, namely the fixing speed. Surprisingly it has been found that once the rollers reached their operating temperature the temperature of the press roller is maintained sufficiently even simply by conduction in the press roller without need for continual rotation to provide continual changing contact with the heating roller.
When using the apparatus of the invention, since the fixing rollers are driven to rotate while the temperature H of the fixing rollers is the same as or higher than the softening temperature H1 of the toner when the temperature H of the fixing rollers is lower than the temperature H2 suitable for fixing, the fixing rollers are not damaged by hardened toner adhered to the fixing rollers. Once the temperature H of the fixing rollers has reached the temperature H2 suitable for fixing, the fixing rollers are driven to rotate only when the copying operation is taking place. Accordingly, the occurrence of noise is decreased and the electric power consumption is decreased. Since the fixing rollers are driven to rotate only at one speed, the speed suitable for fixing, the mechanism for driving the fixing rollers is simplified.
According to a preferred embodiment, the temperature detecting element is a thermistor, and is positioned to contact the periphery of the heating roller at a central position in the axial direction of the heating roller at the side thereof opposite the press roller.
Preferably the drive means comprise a sprocket wheel fixed to said heating roller, a motor, and a chain directly driven by said motor and engaging said sprocket wheel. This very simple drive to the fixing means can be achieved due to the fact that the fixing rollers are only required to be rotated at one speed, when not stationary, namely at the normal operational fixing speed corresponding with the normal speed of operation of the apparatus.
Preferably the temperature detecting element contacts the periphery of the heating roller at a central position in the axial direction of the heating roller at the side of the heating roller opposite to the side engaged by the press roller. This location of the temperature sensing element enables the minimum of effect on this reading to be caused by conducting contact of the heating roller with the press roller when the rollers are stationary so as to provide a more reliable operating temperature sensing.
A detailed description of the invention now will be made with reference to the accompanying drawings, wherein like numerals designate corresponding parts in the figures, and wherein:

Fig. 1 is a schematic vertical cross-sectional view of an electrostatic copying apparatus having a fixing and heating device according to one embodiment of the present invention,
Fig. 2 is a side view of the fixing and heating device of one embodiment of the invention,
Fig. 3 is a partial perspective view of the fixing and heating device,
Fig. 4 is a schematic longitudinal sectional view taken along axes of a heating roller and a press roller,
Fig. 5 is a schematic block diagram of the control arrangement, and
Fig. 6 is a graph showing the temperature of the heating roller which is detected by a temperature detecting element, as a function of time.

Fig. 1 is a schematic vertical cross-sectional view of an electrostatic copying apparatus according to one preferred embodiment of the present invention. Copy paper sheets 4 and 5 in cassettes 2 and 3 provided at a side of a housing 1 are fed from the cassettes 2 and 3 by feeding rollers 6 and 7 alternatively one by one, and are transported by transport rollers 8, 9 and 10. A horizontal transparent plate 11 is provided at the upper portion of the housing 1. An original document 12 is pressed onto the original transparent plate 11 by an original document cover 13. Light from an exposure lamp 14 is directed to the original document 12 through the transparent plate 11. A light image of the original document 12 is directed, through mirrors 16 and 17, a mirror lens 19 and a mirror 20 of an optical device 15, onto the surface of a photosensitive drum 21. Mirrors 22 and 23 are provided in the vicinity of the exposure lamp 14 so as to efficiently guide the light from the exposure lamp 14 onto the original document 12. During a slit exposure operation, the exposure lamp 14 and mirrors 16, 22 and 23 are displaced in moving direction 24, from a home position shown by continuous lines, to a position 25 shown by broken lines. After the exposure, the exposure lamp 14 and the mirrors 16, 22 and 23 are returned to the home position. The mirror 17 is displaced with the exposure lamp 14 and the mirrors 16, 22 and 23, and is at a position 26 shown by an imaginary line when the exposure lamp 14 and the mirrors 16, 22 and 23 are at the position 25. The light image of the original document 12 is directed onto the photosensitive drum 21 which has been charged by a corona charger 27, and an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 21. The electrostatic latent image is developed to a visible image by a developing device 28. The toner image on the surface of the photosensitive drum 21 is transferred by a transfer corona charger 29 to the copy paper sheets 4 and 5 being transported by a set of transport rollers 10. The copy paper sheets 4 and 5 having the toner image are peeled certainly from the photosensitive drum 21 by a peel click 30 and a peel roller 31, and are transported to a heating and fixing device 32. The heating and fixing device 32 comprises a heating roller 34 having a heater 33 therein and a press roller 35 which is in hard contact with the heating roller 34. When the copy paper sheets 4 and 5 are transported between the heating roller 34 and the press roller 35 after the transfer step is performed, the toner on the copy paper sheets 4 and 5 is fused by heating and the fixing step is performed. After the fixing step is performed, the copy paper sheets 4 and 5 are discharged to a tray 38 provided at the side of the housing 1 through transport rollers 36 and discharge rollers 37. The surface of the photosensitive drum 21 is cleaned by a cleaning device 39 after the transfer step has been performed.
Fig. 2 is a side view of the fixing and heating device 32 according to the present invention, and Fig. 3 is a partial perspective view of the fixing and heating device 32. The fixing and heating device 32 is capable of being drawn out from the housing 1 of the electrostatic copying apparatus in a direction into the plane of Fig. 2.
Fig. 4 is a schematic longitudinal sectional view taken along a plane through the axes of the heating roller 34 and the press roller 35. A frame 42 of the fixing and heating device 32 is provided with the heating roller 34 and the press roller 35 which are parallel and which have horizontal axes. The heating roller 34 is supported on the frame 42 of the fixing and heating device 32 to be rotated independently. The heater 33 is held in the heating roller 34 as abovementioned. The press roller 35 is supported by a lever 46. An end of the lever 46 is supported on the frame 42 by a pin 48. The other end of the lever 46 is spring-biased by a spring 49 so as to cause the heating roller 34 to contact with the press roller 35. The transport path of the copy paper sheets is depicted by reference number 50 shown in Fig. 2. The copy paper sheets are transported in the direction of arrow 51 between the heating roller 34 and the press roller 35. The toner image corresponding to the original document 12 is fixed on the copy paper sheet transported between the heating roller 34 and the press roller 35. A scraper plate 52 is fitted downstream of the heating roller 34 in the direction of arrow 51 so as to scrape off the toner remaining on the surface of the heating roller 34 and to peel off the copy paper sheet tending to wind with the heating roller 34. Both rollers 34 and 35 are hollow and have interiors open to the environment as shown in Fig. 4. The heater 33 extends entirely through the heating roller 34 and the sprocket wheel 54. The press roller 35 is positioned below heating roller 34 and has an axial length less than that of heating roller 34.
One end of the heating roller 34 has coaxially fixed thereto the sprocket wheel 54. The sprocket wheel 54 is driven to rotate by a main motor 56 through a chain 55. After a power switch is closed, the main motor 56 is operated while a copying operation is taking place, and when the temperature of the heating roller 34 is between a temperature H3 and H2 as after-mentioned. Owing to the sprocket wheel 54 being driven by the main motor 56, the heating roller 34 is driven to rotate in the direction of arrow 57 at a speed suitable for fixing and heating.
A temperature detecting element 58 such as a thermistor is mounted to contact the periphery of the heating roller 34 at a central position in the axial direction of the heating roller 34 at a side opposite to the press roller 35. The surface temperature of the heating roller 34 is detected by the temperature detecting element 58.
Referring to Fig. 5, there is shown a schematic block diagram for driving and controlling the main motor 56. A signal from a power switch 59 of the electrostatic copying apparatus, an output from the temperature detecting element 58 and an output from a print button 60 pushed at the time of a copying operation are provided to a control circuit 61. The control circuit 61 controls the main motor 56, as will be described in connection with Fig. 6, in response to the outputs from the power switch 59, the temperature detecting element 58 and the print button 60. A fan 62 (Fig. 1) prevents the temperature in the housing 1 from rising abnormally due to the heat from the exposure lamp 14 and the fixing and heating device 32.
The heating roller 34 and the photosensitive drum 21 are directly driven by the main motor 56 as abovementioned, and the exposure lamp 14, the mirrors 16, 17, 22 and 23 are moved by the main motor 56 through a magnetic clutch.
Referring to Fig. 6, there is shown the actual surface temperature H of the heating roller 34 detected by the temperature detecting element 58 dependent on the lapse of time. At a time t1, when the power switch 59 is closed, the heater 33 is energized electrically. Thereafter, the temperature H of the heating roller 34 will rise. Consequently, at a time t2 when the temperature H of the heating roller 34 has reached the temperature H3, the control circuit 61 energises the main motor 56. The temperature H3 is the same as or higher than a softening point H1 of the toner, for example 170°C, and is lower than the temperature H2 suitable for fixing and heating, for example 180°C. Owing to the main motor 56 being driven, the heating roller 34 and the press roller 35 are driven to rotate at a rotation speed suitable for fixing. As the heating roller 34 begins to be rotated at the time t2, the heat from the heating roller 34 is conducted to the press roller 35. Accordingly, the temperature H of the heating roller 34 is lowered from the time t2 to a time t3. At and after the time t3, the temperature of the heating roller 34 and the press roller 35 rises and reaches the temperature H2 suitable for fixing and heating at a time t4. Thus, the heating roller 34 and the press roller 35 begin to rotate at the speed suitable for fixing and heating at the time t2, and stop rotating at the time t4. According to experiments of the inventors, since the heating roller 34 does not rotate during the period from t4 to t5, the temperature H of the heating roller 34 rises temporally. However, at and after the time t5, the temperature H of the heating roller 34 is uniformly maintained at the temperature H2 suitable for fixing and heating by means of the control circuit 61. Owing to the temperature H of the heating roller 34 rising temporally higher than the temperature H2 from the time t4 to the time t5 according to reduction of heat conduction from the heating roller 34 to the press roller 35, the temperature in the vicinity of the heating roller 34 rises rapidly. However, at and after the time t5, the temperature H of the heating roller 34 is stably maintained at the temperature H2 suitable for fixing.
Since the main motor 56 begins to operate at the time when the temperature H of the heating roller 34 becomes equal to the temperature H3 which is the same as or higher than the softening point H1 of the toner, the heating roller 34 and the press roller 35 are driven to rotate by the main motor 56. At this time, the toner which has adhered to the heating roller 34 and the press roller 35 is soft. Accordingly, the heating roller 34 and the press roller 35 are not injured and the scraper plate 52 is not damaged.
The temperature H3 is chosen so that the period from the time t2 to the time t4 is as short as possible. Namely, the temperature H3 is chosen so that the temperature of all the surfaces of the heating roller 34 and the press roller 35 becomes uniform at t4 when the temperature H of the heating roller 34 reaches the temperature H2, after the heating roller 34 and the press roller 35 have been rotated for as short a period as possible. Since the period from t2 to t4 is chosen as short as possible as abovementioned, the occurrence of the noise is decreased and the electric power consumption of the main motor 56 is decreased.
From the time t6 when the print button 60 is pushed and the copying operation is begun to a time t7 the main motor 56 operates continuously. The photosensitive drum 21 is rotated by the main motor 56, and the exposure lamp 14 and the mirrors 16, 17, 22 and 23 are displaced so as to perform the slit exposure operation. The heating roller 34 and the press roller 35 are always rotated while the main motor 56 is driven. Accordingly, at the time when the transferred copy paper sheets pass between the heating roller 34 and the press roller 35, the surface temperatures of the heating roller 34 and also the press roller 35 have a distribution of the uniform temperature H2 suitable for fixing and heating. Therefore, advantageous fixing is performed.
According to another embodiment of the invention, the temperature detecting element 58 may be arranged to detect the temperature of the press roller 35.

Claims

1. Electrostatic copying apparatus having a fixing device (32) for fixing a toner image onto a copy paper sheet, said fixing device comprising a hollow heating roller (34), a heater (33) extending through the interior of the heating roller, a press roller (35), means (49, 46) for urging the periphery of the press roller (35) into contact with the heating roller (34), means (31) for feeding copy sheets with an image to be fixed into the nip between the press roller (35) and the heating roller (34), a temperature detecting element (58) for sensing the temperature of one (34) of the rollers, drive means (54, 55, 56) for rotating the fixing rollers, a power switch (59) closable to supply power to the apparatus, a copy switch (60) for initiating a copying operation and control means (61) operable to prevent rotation of the fixing rollers by the drive means unless the sensed temperature (H) is at least at a first predetermined temperature (H3) at or above the softening temperature (H1) of toner and operable to prevent initiation of a copying operation upon closure of the copy switch when the sensed temperature (H) is below a predetermined fixing temperature (H2) at which the fixing rollers (34, 35) are able satisfactorily to fix a toner image on a copy sheet, and is operable to cause the drive means (54, 55, 56) to rotate the fixing rollers when the sensed temperature (H) is at a value intermediate said first temperature (H3) and said fixing temperature (H2), characterized in that said control means (61) is operative to cause rotation of the fixing rollers at normal fixing speed when the sensed temperature is at a said intermediate value and to allow the fixing rollers to rest stationary when the sensed temperature has reached said fixing temperature (H2) except during a fixing operation upon closure of the copy switch.

2. Apparatus according to claim 1, characterized in that the drive means comprises a sprocket wheel (54) fixed to said heating roller (34), a motor (56), and a chain (55) directly driven by said motor and engaging said sprocket wheel.

3. Apparatus according to claim 1 or 2, characterized in that the temperature detecting element (58) contacts the periphery of the heating roller (34) at a central position in the axial direction of the heating roller (34) at the side of the heating roller opposite to the side engaged by the press roller (35).