Patent Publication Number: US-7723645-B2

Title: Switching device and system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. application Ser. No. 11/231,159, filed Sep. 20, 2005. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   None. 
   REFERENCE TO SEQUENTIAL LISTING, ETC. 
   None. 
   BACKGROUND 
   1. Technical Field 
   This disclosure relates to switching devices and, more particularly, to a switching device that reacts in response to over temperature conditions which may occur in a printer. 
   2. Description of the Related Art 
   Printing devices often include heating devices that apply thermal energy to the media being processed by the printing device to e.g., affix toner to the media (i.e., for laser printers) or dry ink applied to the media (i.e., for inkjet printers). Typically, the temperature of these heating devices is regulated through the use of a controller circuit that e.g., monitors the temperature of the heating device and regulates the amount of power provided to the heating device. Unfortunately, in the event of a failure of the controller circuit, an over temperature condition may occur. 
   SUMMARY 
   In a first exemplary embodiment, a heating assembly for a printing device includes a heating device configured to be energized or deenergized. A switching device includes a bimetallic element efficiently thermally coupled to the heating device and configured to deenergize the heating device in a defined period of time in the event of an over temperature condition. 
   One or more of the following features may be included. The switching device may include a surface that is in contact with a surface of the heating device. A connector may be positioned between the switching device and the heating device, such that the connector has a thermal conductivity of at least 1.0 watt per meter-Kelvin. 
   The heating device may be a ceramic resistive heating device. The heating device may be a metallic resistive heating device. The heating device may be an ink drying assembly configured for drying ink on media. The heating device may be a fusing device configured for bonding toner to media. 
   The switching device may be electrically coupled in parallel with the heating device. The switching device may be electrically coupled in series with the heating device. The switching device may be configured to assume the temperature of the heating device in less than or equal to about 10 seconds. The switching device may include a bimetallic element. 
   In a second exemplary embodiment, a bimetallic switching device for a heating device in a printer includes a bimetallic element configured to be coupled to the heating device. The bimetallic element is efficiently thermally coupled to the heating device and configured to deenergize the heating device in the event of an over temperature condition. 
   One or more of the following features may be included. The element may be configured to deenergize the heating device within a defined period of time of less than or equal to about 10 seconds. A connector may be positioned between the switching device and the heating device, such that the connector has a thermal conductivity of at least 1.0 watt per meter-Kelvin. 
   The heating device may be a ceramic resistive heating device. The heating device may be a metallic resistive heating device. The heating device may be an ink drying assembly configured for drying ink on media. The heating device may be a fusing device configured for bonding toner to media. The bimetallic element may be electrically coupled in parallel with the heating device. The bimetallic element may be electrically coupled in series with the heating device. 
   In a third exemplary embodiment, a switching device for a printer includes a resettable thermal element configured to be efficiently thermally coupled to a heating device. The thermal element is configured to: deenergize the heating device in a defined period of time in the event of an over-temperature condition; and to energize the heating device once the over-temperature condition is eliminated. 
   One or more of the following features may be included. The defined period of time may be less than or equal to about 10 seconds. The thermal element may be directly thermally coupled to the electric heating device. A connector may be positioned between the thermal element and the heating device, such that the connector has a thermal conductivity of at least 1.0 watt per meter-Kelvin. 
   The heating device may be a ceramic resistive heating device. The heating device may be a metallic resistive heating device. The heating device may be an ink drying assembly configured for drying ink on media. The heating device may be a fusing device configured for bonding toner to media. The thermal element may be electrically coupled in parallel with the heating device. The thermal element may be electrically coupled in series with the heating device. 
   The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will become apparent from the description, the drawings, and the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic view of an exemplary printing device and an exemplary printer cartridge for use within the printing device; 
       FIG. 2  is a diagrammatic view of the printing device of  FIG. 1  interfaced to the printer cartridge of  FIG. 1 ; 
       FIG. 3  is a diagrammatic view of the controller of  FIG. 2 , including a first exemplary implementation of a bimetallic switching device; 
       FIG. 4  is a diagrammatic view of the controller of  FIG. 2 , including a second exemplary implementation of a bimetallic switching device; and 
       FIG. 5  is a diagrammatic view of the controller of  FIG. 2 , including a third exemplary implementation of a bimetallic switching device. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , there is shown an exemplary printing device  10  and an exemplary printer cartridge  12  for use within printing device  10 . Printing device  10  may be coupled to a computing device (not shown) via e.g. a parallel printer cable (not shown), a universal serial bus cable (not shown), and/or a network cable (not shown). Printing devices herein may include, e.g., electrophotographic printers, ink-jet printers, dye sublimation printers, and thermal wax printers. 
   Exemplary printing device  10  is a device that accepts text and graphic information from a computing device and transfers the information to various forms of media (e.g., paper, cardstock, transparency sheets, etc.). Further a printer cartridge  12  is a component of exemplary printing device  10 , which typically includes the consumables/wear components (e.g. toner and a drum assembly, for example) of printing device  10 . Printer cartridge  12  typically also includes circuitry and electronics (not shown) required to e.g., charge the drum and control the operation of printer cartridge  12 . 
   Referring also to  FIG. 2 , there is shown a diagrammatic view of an exemplary printer cartridge  12  interfaced with printing device  10 . Typically, printing device  10  includes a system board  14  for controlling the operation of printing device  10 . System board  14  may include a microprocessor  16 , random access memory (i.e., RAM)  18 , read only memory (i.e., ROM)  20 , and an input/output (i.e., I/O) controller  22 . Microprocessor  16 , RAM  18 , ROM  20 , and I/O controller  22  may be coupled to each other via data bus  24 . Examples of data bus  24  may include a PCI (i.e., Peripheral Component Interconnect) bus, an ISA (i.e., Industry Standard Architecture) bus, or a proprietary bus, for example. 
   Exemplary printing device  10  may include display panel  26  for providing information to a user (not shown). Display panel  26  may include e.g. an LCD (i.e. liquid crystal display) panel, one or more LEDs (i.e., light emitting diodes), and one or more switches. Display panel  26  may be coupled to I/O controller  22  of system board  14  via data bus  28 . Examples of data bus  28  may include a PCI (i.e., Peripheral Component Interconnect) bus, an ISA (i.e., Industry Standard Architecture) bus, or a proprietary bus, for example. Printing device  10  may also include electromechanical components  30 , such as: feed motors (not shown), gear drive assemblies (not shown), paper jam sensors (not shown), and paper feed guides (not shown), for example. Electromechanical components  30  may be coupled to system board  14  via data bus  28 . 
   As discussed above, the exemplary printer cartridge  12  may include a reservoir for developing agent, such as a toner reservoir  32  and a toner drum assembly  34 . The electromechanical components  30  may be mechanically coupled to printer cartridge  12  via a releasable gear assembly  36  that may allow the printer cartridge  12  to be removed from printing device  10 . Developing agent may also include toner or ink and any other materials or compounds suitable to create an image on, e.g., a sheet of media. 
   Exemplary printer cartridge  12  may include a system board  38  that controls the operation of printer cartridge  12 . System board  38  may include, e.g., microprocessor  40 , RAM  42 , ROM  44 , and I/O controller  46 . The system board  38  may be releasably coupled to system board  14  via data bus  48 , thus allowing for the removal of exemplary printer cartridge  12  from printing device  10 . Examples of data bus  48  may include a PCI (i.e., Peripheral Component Interconnect) bus, an ISA (i.e., Industry Standard Architecture) bus, an I2C (i.e., Inter-IC) bus, an SPI (i.e., Serial Peripheral Interconnect) bus, or a proprietary bus. 
   The exemplary printing device  10  may include a heating device such as a fusing device  48  for affixing the toner (supplied by toner reservoir  32  and applied by toner drum assembly  34 ) to the media being processed by printing device  10 . As will be discussed below in greater detail, the fusing device may be a belt fuser. In addition, the temperature of the exemplary fusing device  48  may be controlled by controller  50 . Controller  50  may be coupled to system board  14  via data bus  28 . Alternatively, controller  50  may be incorporated into system board  14 . 
   Referring also to  FIG. 3 , there is shown an exemplary diagrammatic view of controller  50  interfaced with the exemplary fusing device  48 . Controller  50  may include a control circuit  100  and a switching device  102 . Control circuit  100  may be configured to provide a gate pulse signal  104  to switching device  102  via conductor  106 . Switching device  102  may be configured to control the power signal  108  applied to fusing device  48 . Control circuit  100  may further be configured to monitor power signal  108  via conductor  110 . Control signal  108  may be a 120 volt, 60 Hertz AC (i.e., alternating current) signal. Control circuit  100  may further be configured to monitor the temperature of the exemplary fusing device  48  using a temperature monitoring device  116  (e.g., a thermistor), such that temperature monitoring device  116  provides a temperature signal  118  to control circuit  100  via conductor  120 . Conductors  106 ,  110 ,  120  may be e.g., foil-based conductors on a printer circuit board and/or wired-based conductors. 
   The exemplary fusing device  48  may include one or more discrete heating elements  112 ,  114  for converting electrical energy (from power signal  108 ) into thermal energy. Heating elements  112 ,  114  may be resistive heating elements (e.g., metallic or ceramic). Ceramic type may include aluminum oxide or aluminum nitride type materials onto which conductive and resistive lands may be printed, dried or fired in order to create a resistive heating element surface. During operation, power signal  108  is applied to the exemplary fusing device  48  via switching device  102 . As noted above, fusing device  48  may therefore be a belt fuser, that employs a relatively thin belt wrapped over a ceramic or other relatively low-thermal capacity heater. The belt may be formed from polymeric type materials, such as polyimide type resins. 
   Temperature monitoring device  116  may monitor the temperature of the exemplary fusing device  48  and may generate temperature signal  118 , which may be supplied to control circuit  100  via conductor  120 . As discussed above, temperature monitoring device  116  may include a thermistor. A thermistor is typically a solid-state, temperature-dependant resistance device. Accordingly, by monitoring the resistance of temperature monitoring device  116 , the temperature of the exemplary fusing device  48  may be determined by control circuit  100 . 
   The desired temperature of the heating device in the printer may be based on several variables, such as the operating mode of printing device  10  and the type of developing agent being used in printing device  10 . In an exemplary and non-limiting case of toner, such may include particles of pigment in combination with polymers that may be applied to the media by toner drum assembly  34  ( FIG. 2 ) and bonded to the media by the exemplary fusing device  48 . Accordingly, the temperature of the exemplary fusing device  48  may be high enough to allow for the toner particles to melt and adhere to the media, yet not so high as to damage the media and/or other components of printing device  10 . Further, the chemical composition of the developing agent (e.g. toner) may vary the temperature of the fusing device. Additionally, the operating mode of printing device  10  may vary the temperature of the heating (e.g. fusing) device. For instance, the exemplary fusing device  48  may be maintained at 100° Celsius during “Sleep Mode” (e.g., after printing device  10  is idle for ten minutes). In addition, device  48  may be maintained at 150° Celsius during “Standby Mode” (e.g., when printing device  10  is idle for less than ten minutes). Furthermore, fusing device  48  may be maintained at 200° Celsius during “Use Mode” (i.e., when printing device  10  is bonding developing agent to media). 
   In the event that the temperature of the exemplary fusing device  48  (as monitored by temperature monitoring device  116  and determined by control circuit  100 ) is above a possible setpoint (e.g., 100° Celsius, 150° Celsius, or 200° Celsius, for example) specified for a possible operating mode (e.g., “Sleep Mode”, “Standby Mode”, or “Use Mode”, respectively), control circuit  100  may provide a gate pulse signal  104  to switching device  102  that prevents power signal  108  from being provided to fusing device  48 . This, in turn, may result in a decrease in the temperature of fusing device  48 . 
   Alternatively, if the temperature of the exemplary fusing device  48  is below the setpoint specified for the desired operating mode, control circuit  100  may provide a gate pulse signal  104  to switching device  102  that allows power signal  108  to be applied to fusing device  48 . This, in turn, may result in an increase in the temperature of fusing device  48 . 
   Controller  50  may include switching device  122 . Such device may be a bimetallic switching device which may therefore include a bimetallic element  124 , which may be thermally coupled to exemplary fusing device  48 . Bimetallic element  124  may be an electromechanical thermal sensor that is designed to deform in response to variations in the temperature of exemplary fusing device  48 . For example, during normal operation of exemplary fusing device  48  (e.g., under 250° Celsius, for example), bimetallic element  124  may be maintained in a first form (e.g., the curved form of bimetallic element  124 ). However, in the event that exemplary fusing device  48  meets or exceeds e.g., 250° Celsius, bimetallic element  124  may be deformed (e.g., into the form of bimetallic element  124 ′). Further, once the temperature of exemplary fusing device  48  cools to e.g., below 250° Celsius, deformed bimetallic element  124 ′ may revert back to the original non-deformed shape of bimetallic element  124 . Accordingly, bimetallic switching device  122  is resettable, in that bimetallic element  124  may react to an over temperature condition and, subsequently reset itself once the over temperature condition has ended. 
   Bimetallic element  124  may be constructed of two dissimilar metals (e.g., brass and Invar) that are bonded together. As these dissimilar metals expand at different rates as they warm, bimetallic element  124  may be deformed, cause element  124  to e.g., twist, curve, or cup. For example, if the metal on the concave surface of bimetallic element  124  is constructed of a metal that thermally-expands at a greater rate than the metal on the convex surface of bimetallic element  124 , when bimetallic element  124  is warmed, the normally curved shape of bimetallic element  124  may be flattened out (e.g., into the flatter shape of deformed bimetallic element  124 ′). 
   Bimetallic switching device  122  may include two or more contacts  126 ,  128  positioned within bimetallic switching device  122 . Contacts  126 ,  128  may be positioned so that, in the event that the temperature of exemplary fusing device  48  increases to beyond the normal operating range of exemplary fusing device  48  (e.g., 250° Celsius or greater) and bimetallic element  124  is deformed (i.e., into deformed bimetallic element  124 ′), an electrical connection between contact  126  and contact  128  may be established via deformed bimetal element  124 ′. Accordingly, when bimetallic switching device  122  is wired in parallel with exemplary fusing device  48  (as shown in  FIG. 3 ), in the event of an over temperature condition, an electrical connection between contact  126  and contact  128  may be established by deformed bimetallic element  124 ′. As bimetallic switching device  122  would typically have a lower resistance value than fusing device  48  (which typically has a resistance of a few ohms), a short circuit condition may be established between conductor  130  and ground  132 . This, in turn, would result in an over-current condition within conductor  130 . Conductor  130  may include a fusible link/fuse  134  that, in the event of such an over-current condition, fails. As the failure of fusible link/fuse  134  results in power signal  108  no longer being provided to fusing device  48 , fusing device  48  may begin to cool and the over temperature condition may be eliminated. 
   Bimetallic element  124  may be configured and selectively positioned such that bimetallic element  124  assumes the temperature of exemplary fusing device  48  within a defined period of time. For example, the defined period of time may be less than or equal to any time between about 0.1-10.0 seconds and/or any interval of time contained therein. Accordingly, as bimetallic element  124  may track the temperature of exemplary fusing device  48 , in the event of an over temperature condition (e.g., exemplary fusing device  48  meeting or exceeding 250° Celsius), bimetallic element  124  may deform, resulting in fusible link/fuse  134  failing, and the over temperature condition being eliminated (as exemplary fusing device  48  is deenergized). 
   Switching device  122  may also be efficiently thermally coupled to exemplary fusing device  48 , wherein efficiently thermally coupling allows for switching device  122  to respond to an over temperature condition prior to damaging fusing device  48  (e.g., prior to causing a heating slab within the fuser device to crack). Switching device  122  may also be efficiently thermally coupled to a heating device such that more thermal energy may be transferred from the heating device to the switching device by conductive heating rather than by convective heating. 
   Furthermore, the thermal conductivity coefficients (in watts per meter-Kelvin) for certain materials are as follows: diamond 1000-2600; silver 406; copper 385; gold 320; aluminum 205; brass 109; platinum 70; steel 50.2; lead 34.7; mercury 8.3; quartz 8; glass 0.8; Wood 0.04-0.12; wool 0.05; fiberglass 0.04; expanded polystyrene 0.03; HDPE 0.29-0.5; polypropylene 0.1-0.13; molded polystyrene 0.12-0.193; polycarbonate 0.19-0.21 and air (@300 K, 100 kPa) 0.026. Accordingly, to allow switching device  122  and/or bimetallic element  124  to assume the temperature of exemplary fusing device  48  within a defined period of time, it may be desirable to also construct element  138  and or pin  136  of the switching device from a material having a thermal conductivity coefficient greater than about 1.0 W/mK (e.g., copper), as opposed to a material having a relatively low thermal conductivity coefficient (e.g., wood). 
   For example, when coupling bimetallic element  124  to exemplary fusing device  48 , pin  136  (which positions bimetallic element  124  proximate contacts  126 ,  128 ) may be sourced from materials with a thermal conductivity greater than about 1.0 watt per meter/Kelvin which pin may be in direct contact with exemplary fusing device  48 . Alternatively, when coupling bimetallic element  124  to exemplary fusing device  48 , pin  136  may be attached to one or more thermally conductive elements (e.g., element  138 ; shown in phantom) which elements may also utilize materials with thermal conductivities greater than 1.0 watts per meter/Kelvin. 
   Element  138  may therefore be attached to exemplary fusing element  48  and pin  136  to provide primarily conductive heating to bimetallic element  124 . In addition, element  138  may be constructed of a material having a thermal conductivity coefficient sufficient to allow bimetallic element  124  to assume the temperature of exemplary fusing device  48  within a defined period of time (e.g., less than or equal to about 10 seconds). 
   While deformed bimetallic element  124 ′ is described above as a current carrying device (i.e., current passes from contact  126  to contact  128  via deformed bimetallic element  124 ′), other configurations are possible. For example, an alternative exemplary bimetallic switching device  122 ′ may include a pair of contacts  150 ,  152  with a conductor  154  for forming a conductive path between contacts  150 ,  152 . Pin  156  may position bimetallic element  158  within bimetallic switching device  122 ′. When cool (i.e., within the normal operating range of fusing device  48 ), bimetallic element  158  may be positioned as shown. However, during an over temperature condition, bimetallic element  158  may curve (into the position of deformed bimetallic element  158 ′). As linkage assembly  160  may couple bimetallic element  158  and conductor  154 , when bimetallic element  158  moves to the left and into the position of deformed bimetallic element  158 ′, conductor  154  may also move into the position of actuated conductor  154 ′, resulting in an electrical connection being established between contact  150  and contact  152 . Accordingly, the current flowing through bimetallic switching device  122 ′ may flow through actuated conductor  154 ′ and may not flow through deformed bimetallic element  158 ′. 
   While bimetallic element  124  is described above as being connected to exemplary fusing device  48  with pin  136 , other configurations are possible. For example, bimetallic element  180  may be positioned so that a portion of bimetallic element  180  physically contacts fusing device  48 . Further, contacts  182 ,  184  may be solder mounds on the surface of fusing device  48 . Additionally, pin  186  may be configured to maintain contact between bimetallic element  180  and fusing device  48 , thus allowing for conductive heat transfer between device  48  and element  180 . During an over temperature condition, bimetallic element  180  may deform (into the position of deformed bimetallic element  180 ′), thus electrically coupling contacts  182 ,  184 . Accordingly, pin  186  may therefore be made of a material having a thermal conductivity of less than 1.0 watt per meter-Kelvin (e.g., plastic), and may be contained within a plastic housing  188 . 
   While  FIG. 3  illustrates bimetallic switching device  122  being electrically coupled in parallel with fusing device  48 , other configurations are possible. For example and referring also to  FIG. 4 , bimetallic switching device  200  may be electrically coupled in series with fusing device  48 . 
   Unlike bimetallic switching device  122  ( FIG. 3 ), which is a normally open switching device (i.e., a device that normally does not conduct electricity), bimetallic switching device  200  may be a normally closed switching device (i.e., a device that normally conducts electricity. Bimetallic switching device  200  may include two or more contacts  202 ,  204  positioned within bimetallic switching device  200 . Contacts  202 ,  204  may be positioned so that, in the event of the temperature of exemplary fusing device  48  increasing to beyond the normal operating range of exemplary fusing device  48  (e.g., 250° Celsius or greater), bimetallic element  206  may be deformed (i.e., into deformed bimetallic element  206 ′), interrupting the electrical connection between contacts  202  and  204 . 
   As, in the series connection shown in  FIG. 4 , power signal  108  may be provided to exemplary fusing device  48  through bimetallic switching device  200 , if an over temperature condition occurs and the electrical connection between contact  202  and contact  204  is interrupted, power signal  108  may no longer be provided to exemplary fusing device  48 . Accordingly, exemplary fusing device  48  may begin to cool and the over temperature condition may be eliminated. As discussed above, bimetallic switching device  200  may be configured so that bimetallic element  206  is not a current carrying device through the use of a conductor  154  ( FIG. 3 ) and a linkage assembly  160  ( FIG. 3 ). 
   While bimetallic switching device  122  ( FIG. 3 ) and bimetallic switch  200  ( FIG. 4 ) are described above as directly deenergizing exemplary fusing device  48  (i.e., either through bimetallic switch  122  shorting power signal  108  or bimetallic switch  200  opening power signal  108 ), other configurations are possible. For example and referring also to  FIG. 5 , bimetallic switch device  250  may be configured to vary the temperature sensed by control circuit  100 . As discussed above, temperature monitoring device  116  (e.g., a thermistor) may provide a temperature signal  118  to control circuit  100  via conductor  120 . A thermistor is typically a solid-state, temperature-dependant resistance device. Accordingly, by monitoring the resistance of temperature monitoring device  116 , the temperature of the exemplary fusing device  48  may be determined by control circuit  100 . 
   One may therefore assume that temperature monitoring device  116  has a resistance of 2,500 Ohms @ 250° Celsius. Further, assume that this resistance decreases as temperature increases. Accordingly, bimetallic switching device  250  may be positioned in series with resistive device  252 , such that the combination of bimetallic switching device  250  and resistive device  252  are in parallel with temperature monitoring device  116 . Resistive device  252  may be sized so that the parallel resistance of temperature sensing device  116  and resistive device  252  may result in a combined parallel resistance that is low enough to trigger an over temperature event within control circuit  100 . Accordingly, control circuit  100  may then provide a signal to switching device  102  that deenergizes exemplary fusing device  48 . For example, assume that resistive device  252  is 2,500 ohms (i.e., the same resistance as temperature monitoring device  116  at 250° Celsius). Accordingly, in the event of an over temperature condition, bimetallic element  254  will deform (i.e., into deformed bimetallic element  256 ′) and electrically connect contacts  258 ,  260 . This may result in resistive device  252  being in a parallel configuration with temperature monitoring device  116 . As each device has a resistance of 2,500 ohms, the resulting parallel resistance seen by control circuit  100  may be (2,500×2,500)/(2,500+2,500) or 1,250 ohms. As discussed above, as temperature monitoring device  116  may be configured to decrease in resistance as temperature is increased, control circuit  100  may interpret a 1,250 ohm reading as an over temperature condition. Accordingly, switching device  102  may be opened and exemplary fusing device  48  may be deenergized. 
   While control circuit  100  is described above as being a stand-alone circuit, other configurations are possible. For example, the functionality of control circuit  100  may be implemented via one or more processes (not shown) executed by e.g., microprocessor  16 . The instruction sets and subroutines of these processes (not shown) may be stored on a storage device (e.g., ROM  20 ) and executed by microprocessor  16  using RAM  18 . Other examples of the storage device may include a hard disk drive or an optical drive, for example. 
   While the heating device being controlled by control circuit  100  is described above as a fusing device, other configurations are possible. For example, control circuit  100  may control the temperature of a heating device used to dry ink within an inkjet printer. 
   A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.