Patent Publication Number: US-6339211-B1

Title: Reducing a temperature differential in a fixing device

Description:
FIELD OF THE INVENTION 
     This invention relates to a fixing device. More particularly, this invention relates to equalizing the temperature across the fixing device. 
     BACKGROUND OF THE INVENTION 
     In imaging devices, such as electrophotographic printers or copiers, images are formed on media using particles of a pigmented material, such as toner. The toner is bonded to the surface of the media through the application of heat and pressure using a heating device, such as a fixing device. A thermal load is applied to the fixing device from contact with the media during fixing. The temperature on the surface of the fixing device drops in regions contacting the thermal load. If the thermal load is not uniform across the surface of the fixing device, a non-uniform temperature distribution will result. For example, passing narrow width media (such as envelopes, postcards, or even letter size media when used in an electrophotographic imaging device capable forming images on larger sizes of media) through the fixing device will lower the temperature (relative to the temperature before contact with the media) on the surface of the fixing device in areas that contact the media, while areas on the surface of the fixing device outside the width of the media will have a higher temperature (relative to the temperature before contact with the media). 
     Typically, the temperature on the surface of the fixing device within the media path is controlled using negative feedback. In response to an application of the thermal load, the power supplied to the fixing device is increased in an attempt to offset the drop in temperature resulting from application of the thermal load. However, those areas on the surface of the fixing device not in contact with the media can increase in temperature (depending upon the location of a temperature sensor used in the feedback) because of the increase in power supplied to the fixing device. The high temperatures that result may be sufficient to damage the fixing device. A need exists for a heating device that can achieve improved temperature equalization across its surface. 
     SUMMARY OF THE INVENTION 
     Accordingly, a method has been developed to reduce a temperature differential on a heating device. In an imaging device, the method for reducing the temperature differential on a heating device, includes supplying power to the heating device to generate heat. The method further includes contacting the heating device with media. In addition, the method includes transferring the heat through a heat pipe to reduce a magnitude of the temperature differential. 
     A heating device for providing heat to media in an imaging device, includes a heat pipe. In addition, the heating device includes a heating element arranged to provide heat to the media. The heat pipe includes an arrangement to provide heat to a first region of the heating element thermally loaded by the media and includes an arrangement to receive heat from a second region of the heating element thermally unloaded by the media. Furthermore, the heating device includes a support member arranged to provide mechanical support to the heat pipe and the heating element. 
     A fixing device includes a heat pipe and a support member arranged to provide mechanical support to the heat pipe. In addition, the fixing device includes a heating element and a reflector configured to reflect heat from the heating element. Furthermore, the fixing device includes a film contacting the heat pipe and surrounding the heat pipe and the support member. The reflector includes a position to reflect the heat from the heating element onto the film. 
     A fixing device includes a heat pipe and a heating element. The heat pipe also includes an arrangement to transfer heat from the heating element into the heat pipe and to transfer the heat from the heat pipe into the heating element. The heat pipe further includes a support member arranged to provide mechanical support to the heat pipe and the heating element. In addition, the heat pipe includes a film surrounding the heat pipe, the heating element, and the support member. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     A more thorough understanding of embodiments of the heating device may be had from the consideration of the following detailed description taken in conjunction with the accompanying drawings in which: 
     Shown in FIG. 1 is a simplified cross sectional view of an embodiment of an imaging device including an embodiment of the fixing device. 
     Shown in FIG. 2 is a simplified drawing of an embodiment of the fixing device. 
     Shown in FIG. 3 is a simplified drawing of an embodiment of the fixing device used in a test configuration for measuring the effect of using a heat pipe. 
     Shown in FIGS. 4A-4G are alternative embodiments of the fixing device. 
     Shown in FIG. 5 is a high level flow diagram of a method for using the heating device. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The heating device is not limited to the exemplary embodiments disclosed in this specification. Furthermore, although the embodiments of the heating device, such as a fixing device, will be discussed in the context of an imaging device, such as an electrophotographic printer, it should be recognized that embodiments of the heating device can be beneficially used in other electrophotographic imaging devices such as electrophotographic copiers, facsimile machines and the like. In addition, embodiments of the heating device could be adapted for use in imaging devices, such as inkjet printers, that utilize heaters to dry ink applied to media. 
     The latest generation of electrophotographic imaging devices have, as a design objective, high power efficiency and a short time period between initiating the print job and completing the imaging operation on the first unit of the media. The performance of the fixing device can significantly influence both of these performance attributes. To assist in achieving this objective, a cylindrical member having a low thermal mass, such as a cylinder of a film (made of, for example, a polyimide material), is used as the outer layer of the fixing device. A low thermal mass allows a rapid increase in temperature of the fixing device from the idle condition. Heat for fixing toner to the media is supplied by a heating element through the film to the media. The heating element supplies substantially constant power over the length of the heating element. 
     When a thermal load, such as a unit of the media, contacts the film, heat is conducted from the film into the media and the temperature of the film is initially lowered. However, fixing devices generally have a temperature sensor used in a feedback loop that attempts to maintain the temperature on the surface of the film substantially equal to an operating temperature over the length of the fixing device during the fixing process. In response to the application of the thermal load, the power supplied to the fixing device is increased to offset the temperature drop. How the temperature of the fixing device responds to thermal loading by media depends, in part, on the size of the dimension of the media corresponding to the length of the fixing device and the position of the temperature sensor on the fixing device. 
     Consider a fixing device with the temperature sensor located along the length of the fixing device so that the narrowest type of media used will cover a region of the film that also contacts the temperature sensor. If the media is sufficiently wide, the feedback will maintain the surface temperature of the film at the operating temperature over the length of most of the fixing device. However, if media that is narrow with respect to the length of the fixing device contacts the fixing device, the temperature of the film in regions contacted by the media will initially drop because of the thermal load and then the feedback will operate to increase the power supplied over the length of the fixing device to set the temperature of the film in the region near the temperature sensor substantially equal to the operating temperature. Regions on the surface of the film outside of the region covered by the media will experience temperatures above the operating temperature. It is possible that the temperature of these regions may rise sufficiently to damage the polyimide layer. 
     Consider a fixing device with the temperature sensor located along the length of the fixing device so that the most commonly used type of media covers a region of the film that contacts the temperature sensor, while more narrow types of media used will not cover this region. If the media thermally loading the fixing device is sufficiently wide, the feedback will maintain the surface temperature of the film substantially equal to the operating temperature over the length of most of the fixing device. However, for media that is sufficiently narrow so that it does not cover regions of the film contacting the temperature sensor, the surface of the film not covered with the media will be substantially equal to the operating temperature, while the surface of the film covered by the media may be substantially below the operating temperature of the fixing device. If the temperature of the region covered by the media is sufficiently low, toner will not be adequately fixed to the media. 
     The film has lower thermal mass than the roller used in other implementations of the fixing device. This allows the surface temperature of the film to rapidly change from the temperature during the idle condition of the fixing device to the operating temperature of the fixing device. However, the lower thermal mass of the film also causes a higher magnitude change in surface temperature when thermally loaded because relatively little heat is stored within it. This results in, depending upon the location of the temperature sensor, either more damage to the film or lower quality fixing of the toner to the media. 
     To reduce the magnitude of the temperature differential over the surface of the film, the embodiments of the fixing device disclosed in this specification include embodiments of a heat pipe. The heat pipe distributes heat from the high temperature regions of the fixing device to the low temperature regions of the fixing device sufficiently rapidly to either reduce the likelihood of damage to the film or to improve the quality of the fixing of the toner to the media. 
     Shown in FIG. 1 is a simplified cross sectional view of an embodiment of an electrophotographic imaging device, such as electrophotographic printer  10 , including an embodiment of a fixing device, such as fuser  12 . A charging device, such as charge roller  14 , is used to charge the surface of a photoconductor, such as photoconductor drum  16 , to a predetermined voltage. A laser diode (not shown) inside laser scanner  18  emits a laser beam  20  which is pulsed on and off as it is swept across the surface of photoconductor drum  16  to selectively discharge the surface of the photoconductor drum  16 . Photoconductor drum  16  rotates in the clockwise direction as shown by the arrow  22 . A developing device, such as developing roller  24 , is used to develop the latent electrostatic image residing on the surface of photoconductor drum  16  after the surface voltage of the photoconductor drum  16  has been selectively discharged. Toner  26 , which is stored in the toner reservoir  28  of electrophotographic print cartridge  30 , moves from locations within the toner reservoir  28  to the developing roller  24 . A magnet located within the developing roller  24  magnetically attracts toner  26  to the surface of the developing roller  24 . As the developing roller  24  rotates in the counterclockwise direction, the toner  26 , located on the surface of the developing roller  24  opposite the areas on the surface of photoconductor drum  16  which are discharged, can be moved across the gap between the surface of the photoconductor drum  16  and the surface of the developing roller  24  to develop the latent electrostatic image. 
     Media, such as print media  32 , is loaded from paper tray  34  by pickup roller  36  into the media path of the electrophotographic printer  10 . Print media  32  is moved along the media path by drive rollers  38 . As the photoconductor drum  16  continues to rotate in the clockwise direction, the surface of the photoconductor drum  16 , having toner adhered to it in the discharged areas, contacts the print media  32  which has been charged by a transfer device, such as transfer roller  40 , so that it attracts particles of toner  26  away from the surface of the photoconductor drum  16  and onto the surface of the print media  32 . The transfer of particles of toner  26  from the surface of photoconductor drum  16  to the surface of the print media  32  is not fully efficient and therefore some toner particles remain on the surface of photoconductor drum  16 . As photoconductor drum  16  continues to rotate, toner particles, which remain adhered to its surface, are removed by cleaning blade  42  and deposited in toner waste hopper  44 . 
     As the print media  32  moves in the media path past photoconductor drum  16 , conveyer  46  delivers the print media  32  to fuser  12 . Fuser  12  includes an embodiment of a heat pipe. Print media  32  passes between pressure roller  48  and fuser  12 . Pressure roller  48  is coupled to a gear train (not shown in FIG. 1) in electrophotographic printer  10 . Print media  32  passing between pressure roller  48  and fuser  12  is forced against fuser  12  by pressure roller  48 . As pressure roller  48  rotates, print media  32  is pulled between fuser  12  and pressure roller  48 . Heat applied to print media  32  by fuser  12  fixes toner  26  to the surface of print media  32 . 
     Controller  50  is coupled to an embodiment of a power control circuit, power control circuit  52 . Power control circuit  52  controls the electric power supplied to a heating element included in fuser  12 , thereby controlling the operating temperature of the fixing device. Power control circuit  52  controls the average electrical power supplied to fuser  12  by adjusting the number of cycles of the line voltage per unit time applied to fuser  12 . After exiting fuser  12 , output rollers  54  push the print media  32  into the output tray  56 . 
     Electrophotographic printer  10 , includes formatter  58 . Formatter  58  receives print data, such as a display list, vector graphics, or raster print data, from the print driver operating in conjunction with an application program in computer  60 . Formatter  58  converts this relatively high level print data into a stream of binary print data. Formatter  58  sends the stream of binary print data to controller  50 . In addition, formatter  58  and controller  50  exchange data necessary for controlling the electrophotographic printing process. Controller  50  supplies the stream of binary print data to laser scanner  18 . The binary print data stream sent to the laser diode in laser scanner  18  is used to pulse the laser diode to create the latent electrostatic image on photoconductor drum  16 . 
     In addition to providing the binary print data stream to laser scanner  18 , controller  50  controls a high voltage power supply (not shown in FIG. 1) to supply voltages and currents to components used in the electrophotographic processes such as charge roller  14 , developing roller  24 , and transfer roller  40 . Furthermore, controller  50  controls a drive motor (not shown in FIG. 1) that provides power to the printer gear train and controller  50  controls the various clutches and paper feed rollers necessary to move print media  32  through the media path of electrophotographic printer  10 . 
     Shown in FIG. 2 is a cross sectional view of a first embodiment of fuser  12 . Heating element  100  generates heat from the electrical power supplied by power control circuit  52 . An embodiment of a heat pipe, heat pipe  102  is configured to receive heat from heating element  100 . Heat pipe  102  distributes heat over the length of heating element  100  to reduce the temperature differentials resulting from the varying thermal load across the length of heating element  100 . Film  104  surrounds heating element  100  and heat pipe  102 . Heat is transferred through film  104  for fixing toner  26  onto print media  32 . A first support member, such as frame  106  is included in fuser  12  to provide support to maintain the shape of film  104 . A second support member, such as stiffener  108 , contacts frame  106 . Stiffener  108  provides mechanical support for frame  106  so that fuser  12  is sufficiently rigid to mechanically load fuser  12  against pressure roller  48 . Heating element  100  and heat pipe  102  are recessed in a channel formed in frame  106 . It should be recognized that although mechanical support is provided to fuser  12  using frame  106  and stiffener  108 , the functions of these parts could be combined into a single member, such as an embodiment of a support member. In this implementation of fuser  12 , frame  106  is formed from a plastic material and stiffener  108  is formed from metal. However, in an implementation in which the functions of these parts were combined into a support member, a variety of materials could be used, such as plastic, metal, ceramic, or some combination of these materials. 
     Heat pipe  102  performs the function of distributing the heat provided by heating element  100  to reduce the temperature differential that would otherwise develop over the length of fuser  12  from thermal loading of fuser  12  by print media  32 . As previously mentioned, the locations of these temperature differentials over the length of fuser  12  will depend upon a dimension of print media  32  parallel to a longitudinal axis of fuser  12 . Heat pipe  102  contacts heating element  100  over its length. 
     Through the contact between heat pipe  102  and heating element  100 , heat is transferred between heating element  100  and heat pipe  102 . To improve the thermal conductivity between heat pipe  102  and heating element  100 , a thermally conductive material, such as a thermal compound, can be positioned between heat pipe  102  and heating element  100 . The thermal compound performs the function of filling air gaps between the surfaces at the interface of heating element  100  and heat pipe  102 , thereby increasing the thermal conductivity between heating element  100  and heat pipe  102 . However, it is possible that the thermal conductivity between heating element  100  and heat pipe  102  is sufficient to not require the use of a thermal compound. This is possible if, for example, a relatively high percentage of the available surface areas at the interface between heating element  100  and heat pipe  102  are in contact without using gap filling material. 
     An embodiment of heat pipe  102  includes a copper tube having a generally rectangular cross section. During construction, air is substantially evacuated from the volume inside the tube and a small amount of a working fluid, such as water is added to the volume inside of the tube. Sufficient water is added so that over the operating temperature range of heat pipe  102  water in liquid form can be present. The tube is sealed to trap the water within. The phase change of water between the liquid phase and the vapor phase assists in the transfer of heat in heat pipe  102 . 
     Heat pipe  102  acts to reduce the temperature differential through a heat transfer loop. Consider a print job including multiple relatively narrow units of print media  32  with the temperature sensor located near the center of fuser  12 . As units of print media  32  pass between fuser  12  and pressure roller  48 , the thermal load causes an increase in the power supplied to heating element  100  to set the temperature on the surface of fuser  12  in regions contacting print media  32  at a temperature substantially equal to the operating temperature. Regions on the surface of fuser  12  not contacting print media  32  rise above the operating temperature of fuser  12  as do the corresponding regions on heating element  100 . 
     Heat from heating element  100  is conducted into heat pipe  102  when power is supplied to the heating element. The water inside of heat pipe  102  evaporates as heat is conducted into heat pipe  102 . The pressure that develops in heat pipe  102  from the evaporated water quickly establishes an equilibrium condition between the liquid water and the water vapor. 
     The relatively hot regions of heat pipe  102  (corresponding to relatively hot regions of heating element  100  and regions fuser  12  not contacted by print media  32 ) vaporize liquid water in these regions of heat pipe  102  because the temperatures of these regions are above the vaporization temperature of the water at the pressure inside of heat pipe  102 . The vaporization removes heat from the relatively hot regions and lowers the temperature of these regions. The heat is stored in the vaporized water. The water vapor in heat pipe  102  near the relatively cool regions of heat pipe  102  (corresponding to relative cool regions of heating element  100  and regions of fuser  12  contacted by print media  32 ) condenses the water vapor in these regions of heat pipe  102  because the temperatures of these regions are below the vaporization temperature of the water at the pressure inside of heat pipe  102 . The condensation transfers heat from the water vapor to the relatively cool regions and increases the temperature of these regions. The condensed water moves back from the relatively cool regions to the relatively hot regions through capillary action. Wire mesh or a grooved surface in the interior of heat pipe  102  are used to move the liquid water through capillary action. However, some embodiments of heat pipes can be constructed to return the liquid water to the relatively hot regions for vaporization without requiring an internal structure to transport the condensed water. 
     The regions of heat pipe  102  from which heat is removed draw heat from the corresponding regions of heating element  100 , thereby decreasing the temperature of the corresponding regions on the surface of fuser  12 . The regions of heat pipe  102  to which heat is added deliver heat to the corresponding regions of heating element  100 , thereby increasing the temperature of the corresponding regions on the surface of fuser  12 . In this manner, heat pipe  102  redistributes heat from relatively hot regions to relatively cool regions, thereby reducing the magnitude of the temperature differential over the length of fuser  12  and reducing the likelihood of heat damage to film  104  forming the surface of fuser  12 . If heat pipe  102  were used in a fuser having a temperature sensor located near an end of the longitudinal axis of the fixing device, then heat pipe  102  would redistribute heat along the length of the fuser to maintain temperatures for adequate fixing over most of the length of the fuser. 
     Before the beginning of the imaging operation, no power is supplied to fuser  12 . The low thermal mass of fuser  12  permits the operating temperature of fuser  12  to be rapidly reached from the temperature of fuser  12  with no power applied. It should be recognized that a heat pipe could be beneficially used in a fuser that, when idle, is maintained at a standby temperature to permit the operating temperature of the fuser to be rapidly reached. Shortly after the beginning of the imaging operation, power control circuit  52  applies power supplied to fuser  12  to increase its temperature to the operating temperature. After power control circuit  52  applies power supplied to fuser  12 , heat pipe  102  performs the heat transfer function sufficiently rapidly to control the temperature differential over the length of fuser  12  to reduce the likelihood of film  104  reaching damaging temperatures during the warm up period of fuser  12  as well as during equilibrium. 
     It should be recognized that a wide variety of heat pipe implementations may be used for heat pipe  102 . The tube included in heat pipe  102  may be constructed of materials other than copper. For example, the material forming the tube in heat pipe  102  may include stainless steel, nickel, aluminum, or ceramic. In addition, a variety of working fluids may be used as a heat transfer medium. For example, the liquid used as the working fluid may include nitrogen, ammonia, or methanol. Examples of a class of heat pipes that could be used for heat pipe  102  are the THERM-A-PIPE heat pipes supplied by Indek Corporation. The performance attribute of a heat pipe making it useful in a fixing device is its ability to move heat from relatively high temperature regions in the heat pipe to relatively low temperature regions. 
     Shown in FIGS. 3A and 3B is a simplified representation of a test configuration, using two Indek Corporation heat pipes (model number H-331-150), demonstrating the temperature equalization characteristics of a heat pipe in a fuser. In this configuration, two standard Indek heat pipes were used instead of a single standard Indek heat pipe of equivalent size to reduce the thermal mass contributed by the heat pipe to the fuser. However, it should be recognized that a single heat pipe designed to have the desired thermal mass could be used. The test configuration used a fuser modified to accommodate the heat pipes so that approximately one half of the length of the resistive heating element in the fuser was in close contact with the two heat pipes. This configuration was selected to show the temperature gradient on the fuser with and without the use of heat pipes. 
     The fuser was operated in a laser printer with media having a width, in the dimension corresponding to the longitudinal axis of the fuser, of approximately 4.25 inches. The media moved through the media path of the laser printer so that the center of the media was positioned very close to the center of the longitudinal axis of the fuser. Using a thermal video camera, the temperature profile on the surface of the fuser was measured very shortly after 10 units of the media were passed through the laser printer. Location  200  corresponds to a position on the side of the fuser with the heat pipes and outside of the contact area of the media on the fuser. Location  202  corresponds to a position on the side of the fuser with the heat pipes and within the contact area of the media on the fuser. Location  204  corresponds to a position on the side of the fuser without the heat pipes and within the contact area of the media on the fuser Location  206  corresponds to a position on the side of the fuser without the heat pipes and outside of the contact area of the media on the fuser. The measurement results at these locations are as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 location 200 
                 137.14 C. 
               
               
                   
                 location 202 
                 122.14 C. 
               
               
                   
                 location 204 
                 100.39 C. 
               
               
                   
                 location 206 
                 158.49 C. 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen from the temperature measurement data, the use of heat pipes reduces the temperature differential. The temperature differential between the locations inside and outside the contact area of the media on the side of the fuser with the heat pipes is 15 degrees centigrade. However, the temperature differential between the locations inside and outside the contact areas of the media on the side of the fuser without the heat pipes is approximately 58 degrees centigrade. Furthermore, the temperature difference between the regions outside the contact areas of the media for the side with the fuser and the side without the fuser is approximately 20 degrees centigrade. Therefore, the heat pipes are effective in reducing the temperature differential across the fuser and reducing the maximum temperature to which the fuser is subjected. 
     Although an embodiment of the fixing device has been discussed in the context of a fuser having a resistive heating element on the surface of a ceramic substrate, it should be recognized that a heat pipe may be used to reduce temperature differentials in embodiments of fixing devices using halogen bulb heating elements, inductive heating elements, or other types of heating elements. Furthermore, although an embodiment of the fixing device has been discussed in the context of a fuser having a heating element located internal to the surface through which heat is delivered to the media, it should be recognized that a heat pipe may be used to reduce temperature differentials in embodiments of fixing devices having a heating element located external to the surface through which heat is delivered to the media. For example, an embodiment of a fixing device could be constructed using a heater and a reflector external to a surface with an embodiment of a heat pipe in contact with the surface to reduce temperature differentials over the surface. 
     Shown in FIGS. 4A through 4F are simplified cross sectional views of alternative embodiments of a fixing device to illustrate only a small number of the possible configurations for placement of the heating element relative to the heat pipe. In FIG. 4A, heat pipe  300  is located to contact film  302  opposite heating element  304 . As regions of film  302  rotate over heat pipe  300 , the temperature differential of regions on film  302  contacting heat pipe  300  are reduced. In FIG. 4B, heat pipe  400  is positioned between heating element  402  and film  404 . Heat generated by heating element  402  flows through heat pipe  400  into film  404 . The temperature differential across film  404  caused by a non-uniform thermal load causes more heat flow through regions of heat pipe  400  contacting the regions of film  404  having a relatively higher thermal load. 
     In FIG. 4C, two heating elements  500 ,  502  contact heat pipe  504 . Heat flows from heating elements  500 ,  502  through heat pipe  504  and pressure plate  506  into film  508 . In FIG. 4D, heat pipe  600  includes a cylinder having an annular cross section. Heating element  602  is located concentrically inside of heat pipe  600 . Heat flows from heating element  602  through heat pipe  600  into film  604 . In FIG. 4E, heating element  700  is positioned between heat pipe  702  and pressure plate  704 . A thermally conductive material, such as thermal compound  705  fills gaps that may otherwise be present at the interface between heat pipe  702  and heating element  700  to help transfer heat between them. Heat is conducted through pressure plate  704  into film  706 . In FIG. 4F, reflector  800  reflects heat generated by heating element  802  onto film  804 . Heat pipe  806  distributes heat along the length of the fixing device to reduce the magnitude of the temperature differential resulting from contact with media. Pressure plate  808  permits loading of pressure roller  48  against film  804 . In FIG. 4G, heating element  900  radiates heat onto film  902 . Heat pipe  904  distributes heat over film  902  to reduce the magnitude of the temperature differential resulting from contact with the media. Pressure plate  906  permits loading of pressure roller  48  against film  902 . 
     Shown in FIG. 5 is a high level flow diagram of a method of using a heating device to reduce the temperature differential across the heating device. First, in step  1000 , power is applied to the heating device. Then, in step  1002 , the temperature of the heating device reaches a value within an operating temperature range suitable for the application of the heating device (for example for fixing toner to media or for drying ink on media). Next, in step  1004 , a unit of media contacts the heating device, thereby applying a thermal load to the heating device and creating a temperature differential across the heating device. Then, in step  1006 , heat flows into a heat pipe from regions of the heating device having a relatively high temperature, thereby lowering the temperature of these regions. Finally, in step  1008 , heat flows from the heat pipe into regions of the heating device having a relatively low temperature, thereby raising the temperature of these regions. 
     Although several embodiments of heating devices have been illustrated, and their forms described, it is readily apparent to those of ordinary skill in the art that various modifications may be made to these embodiments without departing from the spirit of the invention or from the scope of the appended claims.