Abstract:
A temperature monitoring and control system interfaces with a host printing system through a communication medium to allow the host printing system to maintain control of heating lamps used to heat hot roll (fuser roll) to the required temperature. The temperature monitoring circuitry calibrates itself via the use of a black body calibration strip applied to the hot roller. The black body strip is used to determine the temperature and thus provide offset values for the hot roll cylinder, with respect to the thermal conductive coating. Temperature measurement according to the present invention utilizes infrared technology thermal sensors in conjunction with self-compensating controlling circuitry. The actual temperature of the coated surface is measured and compensated for by the use of Boolean algebraic logic as the hot roll cylinder is heated and during the course of the printing operation. This control device provides the advantage of a non-contact temperature controlling device, is that it offers a selection of specific temperatures in varying increments, which allows for different hot roll heating for different paper and other print media. This adjustment further allows for temperature adjustments to compensate for extremes and/or variations of moisture content of the print medium. Another advantage of the control device is that it adaptively controls based on the rotational speed of the hot roll.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to electrophotographic image forming equipment. More particularly, the present invention relates to a method of controlling the temperature of a cylinder used in the printing process for fixing a toner image. 
     2. Background Information 
     In most electrophotographic printing applications, the need exists for precision temperature control for maintaining adequate fusing roll temperature for the fusing of toner to a medium which is typically paper. 
     In most situations, the hot roller (or “fusing roll”) is heated to a particular temperature at which it allows fusing of a toner to a medium. This temperature must be precisely controlled since, if the roller is too hot, the medium can be burned, or if the temperature is too cool, the toner will not adhere to the medium resulting in the image or words being smeared on the paper. Further, the temperature at which the hot roller must be kept varies with both the media on which information is printed and the characteristics of the toner. Typically, temperature is determined by a contact thermometer or thermocouple of some type in direct contact with the hot roll. 
     Current methods for controlling the temperature of a heated cylinder or roll are through the use of a ferrite chip that is charged with a magnetic field. The magnetic flux is then measured through a sensor, resulting in the generation of a pulse used to determine the cylinder&#39;s temperature. The ferrite chip fails to accept magnetic charge value when the optimum temperature is achieved, thus signaling the electronics of the printer that the required temperature has been reached since a pulse was not generated. 
     Another method of measuring cylinder temperature is through the use of contact thermal sensors and thermal fuses. These contact sensors measure the temperature of the heated roller through a heat transfer process dictated by positive contact with the surface of the hot roller. 
     What is needed is a non-contact temperature controlling device that can determine the ambient air temperature of a printer fixing or fusing device, measure the reflectance of a heated roller, and measure the temperature of a thermal coating applied to the heated roller used in the fixing of toner on a printed media. What is also needed is a non-contact temperature controlling device that is adjustable based upon media and toner characteristics and that is amenable to use by a layman operator of the printing system without special equipment or other specialized knowledge. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide for non-contact temperature control of fusing rollers in the electrophotographic process. 
     It is another object of the present invention to provide a non-contact temperature controlling device that can determine the ambient air temperature of a printer fixing or fusing device, measure the reflectance of a heated cylindrical roller, and measure the temperature of a thermal coating applied to a cylinder used in the fixing of toner on a printed media. 
     It is a further object of the present invention to provide for specific temperature adjustments to account for variations in moisture content of the print media being used. 
     It is yet another object of the present invention to provide for specific temperature adjustments to account for variations in characteristics of the toner and the print media being used. 
     The present invention is a device used for controlling the temperature of a hot roll cylinder used in the printing process. During the process of heating a cylinder for the purpose of fixing a toner image in an electrophotographic printing system (termed a hot roller, hot roll, or fusing roll), the print media which is in contact with the heated roll removes some of the applied heat, thus causing the hot roll to cool and thereby degrade the performance of the hot roll. It is therefore critical that the hot roll maintain its required temperature in order for subsequent prints to have the toner appropriately fused to the print media. The present invention not only monitors the temperature of the hot roller but corrects the operating temperature to within a prescribed parameter associated with the print media being used. 
     A temperature monitoring and control subsystem according to the present invention interfaces with the host printing system through a communication medium to allow the host printing system to maintain control of the heating lamps used to heat the hot roll to the required temperature based upon input from the present invention. 
     The temperature monitoring circuitry according to the present invention calibrates itself via the use of a black body calibration strip applied to the hot roller. This black body strip is used to determine the temperature and thus provide offset values for the hot roll cylinder to the thermal conductive coating. The black body calibration surface comprises a non-expansive material capable of tolerating the maximum heat applied to the hot roll cylinder without losing its non-reflectance (emissive) properties. 
     Temperature measurement according to the present invention utilizes infrared technology thermal sensors in conjunction with self-compensating controlling circuitry. The actual temperature of the coated surface is measured and compensated for by the use of Boolean algebraic logic as the hot roll cylinder is heated and during the course of the printing operation. 
     An advantage of such a controlling device, that is, a non-contact temperature controlling device, is that it offers a selection of specific temperatures in varying increments, which allows for different hot roll heating for different paper and other print media. This adjustment further allows for temperature adjustments to compensate for extremes and/or variations of moisture content of the print medium. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional features and advantages of the present invention can more particularly be determined from the detailed description, read in conjunction with the drawing figures, wherein: 
     FIG. 1 illustrates, in a general way, how the present invention interrelates with a conventional printer, 
     FIG. 2 illustrates how an embodiment of the present invention interrelates with cabling of a conventional printer. 
     FIG. 3 illustrates how sensors according to the present invention interrelate to a hot roll structure of a conventional printer. 
     FIG. 4 illustrates how in-line connector adapters are used to connect a controller according to the present invention with control cables of a conventional printer. 
     FIG. 5 illustrates how an in-line connector adapter is used to tap into a power cable of a conventional printer to provide power to a controller according to the present invention. 
     FIG. 6 illustrates a block diagram of a temperature controller according to an embodiment of the present invention. 
     FIG. 7 illustrates a circuit diagram for the Display Sensor and the Temperature Display circuitry of the embodiment of FIG.  6 . 
     FIG. 8 illustrates a circuit diagram for the Control Sensor, the Scaling Amplifier, and the Analog-to-Digital Converter circuitry of the embodiment of FIG.  6 . 
     FIG. 9 illustrates a circuit diagram for the Programmable Read Only Memory circuit of the embodiment of FIG. 6, and a Diagnostic Device circuit. 
     FIG. 10 illustrates a circuit diagram for the Over-Temperature Determination Circuit of the embodiment of FIG.  6 . 
     FIG. 11 illustrates a circuit diagram for the Digital-to-Analog Converter circuitry of the embodiment of FIG.  6 . 
     FIG. 12 illustrates a circuit diagram for the Variable Temperature Setting circuit of the embodiment of FIG.  6 . 
     FIG. 13 illustrates a circuit diagram for the Temperature Setting Comparator circuit of the embodiment of FIG.  6 . 
     FIG. 14 illustrates a circuit diagram for the Drum Speed Determination Circuit of the embodiment of FIG.  6 . 
     FIG. 15 illustrates a circuit diagram for the Lamp Controller Circuit of the embodiment of FIG.  6 . 
     FIG. 16 illustrates a circuit diagram for the Over-Temperature Alarm Circuit of the embodiment of FIG.  6 . 
     FIG. 17 illustrates a circuit diagram for a negative 5 volt power supply appropriate for use with the Temperature Display circuit of FIG.  8 . 
     FIG. 18 Illustrates a power supply circuit diagram according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a temperature measurement and controlling system for measuring the non-contact temperature of a fusing roller and controlling a heating mechanism for the fusing roller. The present invention is useful in combination (either as a post-factory retrofit, or as original equipment from the manufacturer) with a wide variety of printing and electrophotographic systems. For example, the following machines can benefit from more precise temperature control offered by the present invention: Hitachi type and model LB16 PA and LB16 NC; IBM 3900 printer family and the IBM Infoprint family; Siemens NDY, NDX, and NDZ families, Siemens Nixdorf NDY, NDX, and NDZ families, Siemens Nixdorf /OCE NDY, NDX, and NDZ; and Pagestream family of printers. 
     In this application the terms the term “hot roll” or “hot roller” is used consistently, although in common usage I the art the hot roll structure is variously referred to by skilled artisans as “fixing roller,” “fuser roll,” “fusing roller,” and “heated cylinder.” All these terms are used synonymously to mean the heated item used for fixing the toner to the print medium. The print media in this case are typically paper, vinyl or plastic. 
     The controlling device of the present invention is a temperature measurement and controlling system for use in an electrophotographic printer  1  (refer to FIG.  1 ). During the course of printing, a hot roll  2  fixes the toner image to the print media. The problem is that the print media itself removes some of the heat from the hot roller  2 , thus causing a gradual deterioration in the performance of the hot roll  2  required to fuse the toner to the print media. The present invention measures the temperature and provides a controlling circuit to correct the operating temperature of the hot roller  2  to within the appropriate predetermined parameters associated with the print media being used. 
     A temperature control knob is provided according to the present invention for a user to select a desired operating temperature of the hot roll, and a liquid crystal display is provided to display the actual temperature of the hot roll. An alarm feature provides an audible tone in the event that an over-temperature condition is achieved. In this way, corrective action can be taken by the user to avoid potential damage to the hot roll or to avoid potential damage to the print media. 
     Referring to FIG. 2, the subassembly components comprising the sensing and control circuitry for the present invention are shown. The hot roller  2  is shown with the black body band  205  (the emissive reference) which is to be heated and controlled by the present invention. Mounting brackets (not shown) are used to position three thermal sensors  210 ,  215 ,  218  adjacent the hot roll  2 . A first, band detect sensor  210  is positioned for reference calibration on the non-reflective (emissive) band  205  of the hot roll  2 . A second, control sensor  215  is positioned to sense the temperature on the working portion  2   a  of the hot roll  2 . A third, display sensor  218  is positioned to verify calibrations of the reported temperature as resulting from the first and second sensors  210 ,  215 . The sensors  210 ,  215 ,  218  are preferably non-contact infrared sensors, and are collectively used to perform detection and calibration functions. 
     A control box  220  contains a controller circuit board that is connected to the sensors  210 ,  215 ,  218  by respective cables  225 ,  230 ,  232 . In this fashion, the controller circuit board can sense and adjust for any bias in the infrared sensors  210 ,  215 ,  218 . 
     Referring to FIG. 3, a view is shown of how the three sensors  210 ,  215 ,  218  according to an embodiment of the present invention are installed in a printer  1  so as to flank a conventional (existing) over-temperature sensor  10 . 
     Referring to FIG. 2, the control box  220  interfaces with the motor encoder  3  to determine the idle (non-printing) speed and the operating (printing) speed of the hot roll, which is driven by the fuser drive motor  4 . Encoding data is provided to the control box  220  via a signal cable  240  that taps into the cabling harness  5  of the motor encoder  3  by way of an adapter  235 . 
     The control box  220  interfaces with the lamp power board  6 , which controls the heat lamps (not shown) used to heat the hot roll  2 . Lamp control pulses are transmitted from the control box  220  to the lamp power board  6  via signal cable  250 . The signal cable  250  is coupled to the lamp power board via an adapter  245  interposed between the wiring harness  7  and the lamp power board  6 . 
     Referring to FIG. 4, a view is shown of how the adapter  235  and signal cable  240  according to an embodiment of the present invention are installed in a printer so as to tap into the wiring harness  5  of the motor encoder  3 . The adapter  245  is shown coupling the signal cable  250  into the interface between the wiring harness  7  and the lamp power board  6 . 
     Referring to FIG. 2, the control box  220  is powered by a controller power supply  255 , which provides +5VDC and ±12VDC via power cable  260 . The power supply  255  taps into the main power cable  9  to receive 280 VAC input power. This arrangement is shown in situ in FIG.  5 . 
     An external calibration and test fixture (not shown) is optionally used to verify and recalibrate the system in case of a thermal sensor failure or in the event that new sensor technologies may be applied. Such an external subsystem is connectable to the control box  220  via the port  275 . 
     An air pump  280  is powered via tapping into the 120 VAC supply cable. The air pump  280  provides air flow via air hoses  282 ,  284  to output adapters  286 ,  288 ,  290 . The air flow output at the output adapters  286 ,  288 ,  290  functions to cool the IR sensors  215 ,  218 ,  210  and purges contamination that may accumulate on the IR sensors. 
     Referring to FIG. 6, a high level block diagram showing the interaction of various sub-parts of the present invention is illustrated. Inputs to the system are received at three places. Temperature data is acquired by the sensors  602 ,  604 ,  606 , user input of a variable temperature setting is input via the variable temperature setting circuit  624 , and encoder data is received by the drum speed determination circuit  632 . 
     The system according to the present invention has three outputs. The temperature display  610  provides a continuous visual display of the temperature of the hot roll  2 . The over-temperature alarm circuit  630  provides an audible alarm in the event that the hot roll becomes excessively hot. A control output signal for controlling the heating lamps  636  that heat the hot roll  2  is provided by lamp controller circuit  634 . 
     Input data regarding the sensed temperature of the hot roll provided by the display sensor  604  is coupled directly to the temperature display circuit  610  for viewing by the user continuously. Temperature input data is also provided by the control sensor  602  to the scaling amplifier  608  prior to being converted into digital form by the analog to digital converter  612 . 
     Once in digital form, the temperature indication signal undergoes a mapping function via the programmable read-only memory (PROM)  614 . The resulting mapped temperature signal is then reconverted back into analog form by the digital to analog converter  618 . The differences between the pre-mapped signal and the mapped signal are provided exterior of the system to a diagnostic device (not shown) via the port  275  (see FIG.  2 ). 
     The digital form of the mapped temperature signal is provided to the over-temperature determination circuit  620  for comparison with the digital form of the temperature indication signal. The analog form of the mapped temperature signal is provided to the temperature setting comparator  628 . The temperature setting comparator  628  compares the mapped temperature signal with the variable temperature setting that has been selected by a user via the variable temperature setting circuit  624 . 
     The output of the over-temperature determination circuit  620  is a two-state signal indicating either that an over-temperature status has occurred or that the temperature of the hot roll has not reached the over-temperature threshold. In addition to the digital form of the temperature indication signal and the digital form of the mapped temperature signal, the over-temperature determination circuit  620  also receives the output signals of the display sensor  604  and the band detect sensor  606 . The output of the over-temperature comparator  620  is provided to both the over-temperature alarm circuit  630  and to the lamp-controller circuit  634 . 
     The output of the temperature setting comparator  628  is provided only to the lamp controller circuit  634 , and is a two-state signal as well, indicating whether the sensed temperature is either above or below the variable temperature setting selected by the user. 
     The drum speed determination circuit  632  receives encoder data and based on such encoder data makes a determination as to whether the hot roll is being driven at either an active (printing) state speed or in an idle state speed. Depending on that determination, a two-state signal is supplied to the lamp controller circuit  634 . The two-state signals provided to the lamp controller circuit  634  from the temperature setting comparator  628 , the over-temperature comparator  630 , and the drum speed determination circuit  632  are provided, according to a preferred embodiment of the invention, in the form of open or closed switch states of relay contacts. The relays being energized or de-energized based on the output states of the respective driving circuits  620 ,  628 ,  632 . Based on these three input signals, the lamp controller circuit  634  modulates a pulse signal for providing power to the heating lamps  636   t  that heat the hot roll  2 . 
     Referring to FIG. 7, a preferred circuit for implementing the display sensor  604  and the temperature display circuit  610  is illustrated. The display infrared sensor  218  is labeled “display.” The display temperature signal D from the display sensor  218  is provided to an LCD display controller circuit  720 , which operates on the input display temperature signal D to drive the bank of seven segment LED displays  730  to provide a visual display of the temperature of the hot roll. 
     Referring to FIG. 8, a preferred circuit for implementing the control sensor  602 , the scaling amplifier  608  and the analog to digital converter circuit  612  is illustrated. A temperature indication signal C is provided for amplification by the operational amplifier  820  configured as a scaling amplifier. The gain of the op amp circuit is adjustable via a potentiometer  825  in the feedback path. 
     The output of the scaling amplifier  608  is then provided to the analog to digital converter chip  830 . The conversion circuit  830  provides an eight line parallel digital output OUT 1 , to the PROM circuit  910 . The eight line parallel digital output is also provided to the over-temperature determination circuit  620  and is made available for diagnostic use via a port  275 . 
     Referring to FIG. 9, the preferred circuit configuration of the PROM circuit  614  and a diagnostic device  616  is illustrated. A 512×8 PROM circuit  910  provides a mapping of the eight line input IN 1  (i.e., OUT 1  from ADC  612 ) to an eight line output OUT 2 . Both the input signal IN 1 , and output signal OUT 2  are provided in parallel to external devices via a port  275 . The external device illustrated is a diagnostic device  616  which simply provides a visual display via light emitting diodes of the logic state of the eight input lines and the eight output lines. 
     Optionally, more elaborate diagnostic equipment may be used. For example, in an alternative embodiment the mapping circuit is embodied as an electronically erasable programmable read only memory (or EEPROM). In such a case, the exterior diagnostic device would naturally be provided with a programming functionality to reprogram the EEPROM. Such programming circuitry is well known to those of skill in the art and may be implemented without difficulty. 
     Referring to FIG. 10, a preferred circuit for implementing the over-temperature determination circuit  620  is illustrated. The temperature indication signal generated by the Band Detect sensor  210  is compared with the temperature indication signal D (from the Display sensor  218 ) by a first comparator  1010 . The output of the first comparator  1010  is compared with a reference voltage by a second comparator  1020 . 
     All eight parallel lines of the OUT 1  signal (the digital form of the temperature indication signal), three of the parallel lines of the OUT 2  signal (the digital form of the mapped temperature signal), and the two state output of the second comparator  1020  are input to a logic circuit The logic circuit is formed by AND gates  1030 ,  1040 ,  1050  and NOR gates  1060 ,  1070 . The two state output of the NOR gate  1070  is coupled so as to selectively energize the Third Relay  1080 . The Third Relay  1080  has double-pole-double-throw (DPDT) contacts to provide outputs to other circuits of the invention as described below. 
     Referring to FIG. 11, a preferred circuit for implementing the digital to analog converter  618  is illustrated. The eight output lines OUT 2  from the PROM circuit are received at the eight input lines IN 2  of the digital to analog converter chip  1110  and are provided at the differential output to the operational amplifier  1120 , which is configured as a differential amplifier circuit. The output of the differential amplifier circuit is provided as an output at node  1130 . 
     Referring to FIG. 12, a circuit for implementing the Variable Temperature Setting circuit  624  is illustrated. A rotary switch  1220  with resistors between several contacts of the rotary switch provides for a voltage divider with multiple selectable taps. Each position in the rotary switch represents a different temperature setting and provides a different output voltage from the voltage divider. This output voltage setting V SET  is provided at node  1240 . 
     Referring to FIG. 13, a preferred circuit for implementing the Temperature Setting Comparator circuit  628  is illustrated. The comparator  1350  is used to implement the temperature setting comparator circuit  628 . The comparator  1350  receives a non-inverting input, at the input node  1330 , received from the output node  1130  of the digital to analog converter circuit. The inverting input of the comparator  1350  receives V SET  (the setting voltage) at input node  1340 , which is connected to the output node  1240  of FIG.  12 . Based on the result of the comparison by the comparator  1350 , the output devices, First Relay  1360  and a red LED  1370  are energized or de-energized accordingly. The First Relay  1360  has a single-pole-single-throw (SPST) output contact for providing a two state output to another circuit of the invention as explained below. 
     Referring to FIG. 14, a preferred circuit for implementing the drum speed determination circuit  632  according to the present invention is illustrated. A pulse input is received from the encoder at the non-inverting input of operational amp  1410  and is processed by the circuits formed by the four operational amplifiers,  1410 ,  1420 ,  1430 ,  1440  to provide a speed indication signal to a Schmidt trigger device  1450 . The output of the Schmidt trigger  1450  selectively biases the switching transistor  1470  to selectively energize the Second Relay  1480 , depending upon the speed status of the hot roll. The selective biasing of the switching transistor  1470  by the Schmidt trigger  1450  also selectively energizes a yellow indication LED  1460  depending upon the determined speed of the drum (running or idle). The Second Relay has single-pole-double-throw (SPDT) output contacts for providing two-state outputs to other circuits of the invention as explained below. 
     Referring to FIG. 15, a circuit according to a preferred embodiment of the present invention for implementing the lamp controller circuit  634  is illustrated. Each one of the first relay  1360 , the second relay  1480 , and the third relay  1380 , shown in FIGS. 13 and 14 provide inputs to the lamp controller circuit of FIG.  15 . The single pole double throw switch  1510  is a relay switch controlled by the second relay  1480 . The single pole single throw switch  1530  is a relay contact controlled by the first relay  1360 . The single pole single throw switch  1520  is a first relay contact switch (one of three such contacts) controlled by the third relay  1380 . 
     Each of the three switches,  1510 ,  1520 ,  1530 , acting as input devices, interact with a timer chip  1540 . The switch  1510  controlled by the second relay to indicate speed of the hot roll drum controls the frequency of oscillation of the timer  1540 . Both the switches  1520  and  1530 , from the third and first relays respectively, act as a logical AND circuit to selectively couple or de-couple the output of the timer  1540  to a pair of output devices. The output devices comprise an electro-optical isolator chip  1560  and a green LED display  1550 . The LED display simply provides a visual indication of the state of the lamp control signal. The opto-isolator circuit  1560  couples through a pulse signal to control the energizing of the lamps for heating the hot roll  2 . 
     Referring to FIG. 16, a preferred circuit configuration for implementing the over-temperature alarm circuit  630  according to the present invention is illustrated. Operative input is provided to the circuit via the DPDT switch  1610  which is a second relay switch contact of the third relay  1380 . When the switch  1610  is in one position, the output from pin three of timer device  1620  is coupled to the input of switching transistor  1630 . When the switching transistor  1630  is biased ON, both the audible alarm buzzer  1640  and the red LED display  1650  are energized to provide both audible and visual alarm indications. When the switch  1610  is in another position, the output from pin three of timer device  1620  is simply coupled to ground. 
     Referring to FIG. 17, a circuit configuration is shown for providing a negative 5V power supply for use with the temperature display circuit  610 . The integrated circuit (e.g., type ICL 7660)  1710  is provided with a ground level and +5V power supply potentials, from which a −5V output supply is derived according to the circuit shown. 
     Referring to FIG. 18, a circuit configuration is illustrated to embody the power supply  255  shown in FIG.  2 . The design of power supplies is within the level of ordinary skill in the art and, thus, various changes may be made to the circuit illustrated in FIG. 18 without departing from the scope of the invention. 
     The present invention is currently controlled by hardware circuitry. However, a modification to the design to incorporate a microprocessor and programming features is within the scope of the present invention. The microprocessor, comprising memory, associated with the present invention allows the present invention to store and recall specific settings for any particular print medium on which an image or words are to be printed. 
     The present invention has been described in terms of preferred embodiments. However, it will be appreciated by those of skill in the art that various modifications and improvements may be made with respect to the described embodiments without departing from the scope of the invention as described. The present invention is limited only by the appended claims.