Abstract:
The invention relates to a device and method for treating the surface of an article in connection with printing. More particularly, the invention relates to a method and device, which is capable of checking the motion of a roller in a device for fixing toner on printed sheet or web material using a magnet and a magnetic sensitive element located in a fixed position near the rotating element so as to sense the passage of at least a pole thereof at each rotation of the magnet.

Description:
This application claims priority to provisional application Ser. No. 60/301,261 filed Jun. 27, 2001, with the same title. 

   FIELD OF THE INVENTION 
   The present invention relates to a device for treating the surface of an article in connection with printing. 
   More particularly, the invention relates to a device, which is capable of checking the motion of a roller in a device for fixing toner on printed sheet or web material. 
   BACKGROUND OF THE INVENTION 
   In electrophotography or in ionography a charge image is generated by selectively discharging a homogenous precharged insulating surface of a recording member, onto which toner is deposited. The developed toner image is then transferred to a sheet or web of paper with an electrostatic field. After the developing process, the toner image could be easily disturbed by mechanical effects. Therefore, the toner image is fixed to the paper by heat and pressure. Typically the paper is transported in a nip between a fuser and a pressure roller, which are rotating. Inside the fuser roller or inside heater rollers contacting the fuser roller a heating lamp is installed. The thermal radiation of the lamp heats the surface of the fuser roller or the surface of the heater rollers. The thermoplastic toner on the paper becomes liquid and is pressed into the paper fibers. The fibers act as a capillary system into which molten toner can flow. If the fuser roller stops rotating in an error situation, it would lead to overheating. An overheat condition could lead to freezing the roller bearings or cause the roller break. Therefore motion sensors are required to ensure that a fuser roller does not stop rotating in a standby mode or that the fuser is shut down if the fuser roller stops rotating. 
   It is well known to use a magnetic sensor to detect a metal tab attached to an end of a heater roller. The magnetic sensor incorporates it&#39;s own internal magnetic field. As the heater roller rotates, the passing metal tab distorts the magnetic field. The magnetic sensor changes it&#39;s logic state every time the metal tap passes to indicate the heater roller is rotating. The position of the magnetic sensor to the metal tab is critical. This means much effort to adjust the sensor so that a proper signal is obtained. To adjust the sensor mounting brackets and adjusting screws are required which adds cost to the assembly not only for the material but also the labor. 
   It is an object of the present invention to develop a device for treating the surface of an article in connection with printing including a motion sensor for at least one rotating element, whereby the sensor, it&#39;s mounting elements and the adjusting are less cost intensive. 
   It is another object of the present invention to increase the reliability of the motion detection to prevent failures of a printing device including a printing material treating device. 
   SUMMARY OF THE INVENTION 
   Briefly, the present invention is concerned with a device for treating a surface of an article in connection with printing involving a treating source, a conveyer for leading the article along the source, a rotating element, a signaling member mechanically linked with the rotating element and a sensor for detecting the motion of the rotating element. The signaling member contains a magnet having opposite poles and the sensor is a magnetic-sensitive element being located in a fixed position near the rotating element so as to sense the passage of one of the poles thereof at each passage of said magnet. In particular, if the device is within a fusing unit of an electrophotographic machine the magnet could directly or by fixing means installed on a side of a heater roller which contacts a fuser roller. The article in form of a sheet or a web is then transported through a nip between the fuser roller and a pressure roller. More particular the sensor is a Hall-Effect position sensor. 
   Arranging such device allows easy installation with non expensive parts. The distance between the sensor and the magnet is not as critical. The treating source energy, especially the heat source, has no negative impact on the detecting characteristics. This makes it possible to design treating devices with much higher energy application. This configuration is insensitive against mechanical oscillations of the printing machine. 
   For better understanding of the present invention, reference may be had to the accompanying drawings. 

   
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an schematic view of a fixing station of an electrophotographic apparatus; 
       FIG. 2  is a side view of a heater roller motion detection of  FIG. 1 ; 
       FIG. 3  is a diagram illustrating the signal evaluation of the magnetic-sensitive elements; 
       FIG. 4  shows a variant with one magnetic-sensitive element to detect rotation of two rollers. 
   

   DETAILED DESCRIPTION 
   The present embodiments described herein, provide the ability to more reliably detect the rotation of a rotating element within a device for treating the surface of an article. The treating source which also acts on the rotating element and on a sensor for detecting the rotation has no negative influence on the detecting process. The device is shown as implemented in a reproduction device utilizing a fixing station for a toner image. However, it should be understood that the present embodiments can be implemented in copying or printing devices that utilizes other types of treating devices, like cooling, radiation, drying or coating devices. The article to be treated could be a sheet or a web. The expression rotating element includes drums, rollers, cylinders, endless elements like a belt, and similar structures. The term magnet includes permanent magnets as well as magnet poles made by a current flow through a coil. The term magnetic-sensitive element not only incorporates hall effect digital position sensors. All other magnetic-sensitive elements are applicable which have the similar receiving characteristics of a hall effect sensor. 
   For a general understanding of the features of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to identify like elements. 
   Referring to  FIG. 1  there is shown a fusing unit  1  of an electrophotographic reproduction machine like a copier or a printer. Fusing unit  1  employs a fusing roller  2 , a pressure roller  3 , two heating rollers  4 ,  5  and an oiler  6  with a oil container  7 , a oil application roller  8 , a oil transporting wick  9  and an oil metering doctor blade  10 . The pressure roller  3  and the fusing roller  2  establishing a nip  11  in which a sheet  12  could be transported. For transporting the sheets  12  along a paper path  13  from a printing unit to a stack  14  transport roller pairs  15 ,  16 ,  17  and guiding elements  18  are arranged. Inside the heating rollers  4 ,  5  heating lamps  19 ,  20  are installed. On the sides of the heating rollers  4 ,  5  spring like tabs  21 ,  22  are mounted. Magnets  23 ,  24  are molded at the end of the tabs  21 ,  22 . The pressure roller  3  is coupled with a motor  25 . To measure the motor  25  speed a rotary encoder  26  is also coupled with the pressure roller  3 . Downstream of the fusing unit  1  a cooling unit  27  is arranged. Near the magnets  23 ,  24  hall effect digital position sensors  28 ,  29  are mounted on the frame  30 . The rotary encoder  26 , the sensors  28 ,  29  and the motor  25  are connected to a control device  31 . 
   When the pressure roller  3  is actively driven by the motor  25  all other rollers  2 ,  4 ,  5 ,  8  in the fusing unit  1  may be passively driven by friction according to the shown directions. The rotary speed of the pressure roller  3  is controlled with the help of the control device  31 . The rotary encoder  26  gives the actual value of the rotary speed. The lamps  19 ,  20  heating the body of the rollers  4 ,  5 . While the rollers  4 ,  5  contact the fuser roller  2  the heat is transferred to the surface of the fuser roller  2 . If a sheet  12  is supplied to the nip  11 , the toner image on the sheet  12  will be fixed by the heat of the fuser roller  2  and the pressure established between the pressure roller  3  and the fuser roller  2 . The oil applied by the oiler  6  to the surface of the fuser roller  2  is to prevent toner particles  32  sticking to the fuser roller  2  after the sheet leaves the nip  11 . After the nip  11  the sheet  12  is still warm. The temperature of the sheet  12  is cooled down to room temperature with the cooling unit  27  preventing sheets  12  from sticking together on the stack  14  because of still melted toner particles  32 . 
     FIG. 2  is a side view of the heater roller  4  and it&#39;s detection of motion. The heater roller  4  is held in bearings  33  in the frame  30 . The sensor  28  is fixed at a bracket  34  which is secured at the frame  30  with a screw  35 . The bracket  34  also holds one end of the lamp  19 . The lamp  19  is connected to a power supply  36 , which could be switched off and on by the control device  31 . The magnet  23  on the tab  22  is embedded in a thermal plastic material  37 , which also serves as a fixing material through a hole  38  in the tab  22 . To reduce the need for close detection, the magnet  23  is a Rare Earth Magnet of large Gauss strength. A strong magnet allows for larger dimensional tolerances. In a certain embodiment, the magnet has a strength in the range from 11,700 to 12,500 Gauss, and the sensors  28  and  29  are catalogue number SR13C-A1 hall effect digital postion sensors featuring a snap-in housing, sinking output, unipolar magnetics, and 3.8 to 30 Vdc supply voltage, available from Honeywell Micro Switch, U.S.A. As mentioned previously, the invention is not limited to these specifics as other magnets and magnetic sensitive elements may be implemented in the practice of the invention. 
   As shown in  FIGS. 1 and 2  the magnets  23 ,  24  with their poles N, S oppose the sensors  28 ,  29 . In this position of the magnets  23 ,  24  the magnetic field is strong enough to trigger the sensors  28 ,  29  to high potential on their output. When the magnets  23 ,  24  leave the sensing area of the sensors  28 ,  29  the potential falls back to low. 
   The output signals s 1  and s 2  of the sensors  28 ,  29  are shown in FIG.  3 . The abscissas show the number of rotations of the driving pressure roller  3 . The ordinates show the voltage level at the output of the sensors  28 ,  29 . In this example within one rotation of the pressure roller  3  the magnets  23   24  oppose the sensors  28 ,  29  twice. Signal s 2  is showing fault wherein after n revolutions the signal s 2  of sensor  29  drops out and does not return to normal. Assuming the sensor  29  and its connection to the control  31  is not defective, this is an indication that the roller  5  has stopped rotating. The control  31  may determine wether the roller  5  is rotating by evaluating the time between the signal pulses  39 , or by measuring the frequency of the pulses  39 , or by counting the pulses  39 , or other suitable method. 
   According to an aspect of the invention, the control  31  may contain a logic that processes a signal that indicates the heating roller  5  is rotating. If a transition of the signals s 1 , s 2  is not received for example during a 10 second period, the printer will cycle down and present an operator with a message that heater roller  5  motion has stopped and request a service call. In this state the control device  31  may terminate power from the power supply  36  to prevent an overheat condition of the heating roller  4 . 
     FIG. 4  shows a variant with one magnetic-sensitive element to detect rotation of the two heating rollers  4 ,  5 . A Hall-Effect ratiometric linear transducer sensor  39  is mounted between the rollers  4 ,  5  to register the magnet field from the magnets  23 ,  24 . The poles N, S of the magnets mounted on the tabs  21 ,  22  are inverse in relation to the sensor  39  to distinguish which magnet  23 ,  24  causes a voltage change, respectively which of the rollers is still rotating. This configuration minimizes the number of sensors  39 .