This invention relates in general to apparatus for fusing toner images to toner image carrying supports through the application of heat and pressure. More particularly, this invention relates to fuser apparatus including a sensor for sensing the temperature of a heated fuser member and for producing a signal representative of the temperature of the member which is used to maintain the temperature of the fuser apparatus within predetermined limits and to indicate a jam condition when a sudden large drop in temperature is sensed.
Electrographic copiers produce copies having toner images which are permanently fixed to supports such as copy sheets by well-known fusing techniques. In one such technique, a copy sheet carrying a toner image is contacted by a heated fuser member such as a roller or belt to permanently fuse the toner image to the copy sheet through the application of heat and pressure. The fuser member may be heated by means of an internal or an external heat source. In either case, the temperature of the fuser member is maintained within predetermined limits by sensing the temperature of the heated member and providing a feedback to control the heat source.
Thus, sensors for sensing the temperature of a heated fuser roller may be provided in contact with the fuser roller as disclosed in U.S. Pat. No. 3,291,466 for "Xerographic Fixing Device", issued Dec. 13, 1966, patentees G. A. Aser et al (see, for example FIG. 6, element 825; column 6, lines 56-68); U.S. Pat. No. 3,324,791, for "Xerographic Roller Fuser Drive Apparatus", issued June 13, 1967, patentees J. R. Cassano et al (see, for example, FIG. 2, element THS-2; column 5, lines 66-72); and U.S. Pat. No. 3,327,096 for "Temperature Control Circuit", issued June 20, 1967, patentee T. Bernous. Contact temperature sensors, although useful in controlling the temperature of the fuser roller, may cause damage to the fuser roller surface especially where the surface is of an elastomeric material. Copy sheets which wrap around the fuser roller may engage the sensor resulting in damage to the sensor and jamming of sheets in the fuser.
Temperature sensors for heated fuser rollers may also be spaced a distance from the fusing surface thus obviating the difficulties of sensors which contact the fuser surface. Such sensors are disclosed in U.S. Pat. No. 4,297,562 for "Heat Roller Type Fixing Apparatus", issued Oct. 27, 1981, patentees N. Kamogawa et al (see, for example, FIGS. 1 and 2, column 1, lines 62-66); Research Disclosure No. 1370, entitled "Electrophotographic Fuser Apparatus", dated September 1975 (see, for example, FIG. 3 element 79 and description thereof); U.S. Pat. No. 3,369,106 for "Process Heating Control System", issued Feb. 13, 1968, patentee J. H. Troll (see, for example, FIG. 2, element 6, column 2, line 54 et seq.); U.S. Pat. No. 3,742,191, for "Infrared Temperature Sensor and Control for Use With Heated Moving Bodies", issued June 26, 1973, patentees R. R. Poole et al (see, for example, FIG. 6, element 51, column 4, line 52 et seq.). The latter two patents disclose temperature sensors for measuring infrared radiation from a heated roller. Instead of sensing temperature at the fuser roller surface, the temperature of the fuser core may be sensed to provide temperature control temperature of the fusing roller. Such core sensing controls are disclosed in U.S. Pat. No. 4,046,990 for "Temperature Sensing and Control of a Fusing Roll", issued Sept. 6, 1977, patentee W. E. White (see, for example, FIGS. 1 and 2, element 5, column 4, line 22 et seq.) and Research Disclosure No. 19642 entitled "Temperature Control of Fuser Roller" published August 1980. Where the fuser includes a heater element positioned over a copy sheet path, a sensor may be positioned on the other side of the path to detect temperature variation due to the passage of the copy sheet between the radiation source and the sensor such as disclosed in Japanese Patent Publication No. 76/22675 published June 11, 1976 entitled "Fixing Device for Electronic Copying Machine" (see for example FIG. 1).
During the fusing process there is a tendency for a fused copy sheet to adhere to the fuser roller due to the stickiness of the toner material. Efforts to minimize sticking of copy sheets to fuser rollers include making the surface of the fuser roller of a material which has good release properties, such as silicone elastomer or polytetrafluoroethylene. Silicon release oil may also be applied to the fuser roller surface to enhance the release properties thereof. Since, however, there is still a possibility of a copy sheet adhering to the fuser roller, in commercial copiers a detector is provided in the copy sheet path near the exit nip of the rollers to detect whether or not a copy sheet has advanced past the nip. Such a detector for example is disclosed in U.S. Pat. No. 4,391,509 entitled "Roller Fuser Apparatus In Which Copy Sheet Jams are Minimized," issued July 5, 1983, by W. A. Cavagnaro (see for example FIG. 2 element 70, column 5 lines 47-50 and column 6 line 15 et seq).
Thus, the control of the temperature of a heated fuser member and the detection of paper jams in fuser apparatus are desirable in present day copiers to minimize down time of the equipment due to malfunctions. With higher speed machines, there is also a trend to more complex operational and diagnostic functions. This, it would be desirable to provide copier controls which would simplify the control function while providing efficient and rapid system response to a machine malfunction such as a copy sheet sticking to a fuser roller. It would also be desirable to provide controls for a fuser roller which do not interfere with the fuser components and which do not contribute to fuser roller damage or degradation.