Patent Application
20050237370
Systems that make use of heating elements can sometimes draw, or attempt to draw, current from a power source that can approach or exceed over-current protection limits associated with the power source. This may result in operation of current protection mechanisms associated with the power source.
The drawings referenced herein form a part of the specification. Features shown in the drawing are meant as illustrative of only some embodiments, and not of all embodiments.
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Some systems, such as embodiments of image forming systems, include embodiments of heaters, such as heating elements, for heating air that is used for vaporizing fluid in colorant, such as ink, ejected onto media. Depending upon the image forming system, the heating elements can draw considerable current from the power source, such as an AC power main circuit (referred to as an AC power main), supplying the image forming system. During an image forming operation, the image forming system will likely draw current from the AC power main, in addition to the current used to power the heating element, to power other assemblies in the image forming system.
AC power mains may be equipped with over-current protection. The over-current protection may include circuit breakers or fuses. Depending upon the over-current protection limit for a particular AC power main to which the image forming system is connected and the current used by the image forming system, it is possible that the over-current protection may be actuated during the normal operation of the image forming system.
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The software or firmware may be stored on an embodiment of a computer-readable media included with or separate from controller 20. A computer readable medium can be any media that can contain, store, or maintain programs and data for use by or in connection with the execution of instructions by a processing device. Computer readable media can comprise any one of many physical media such as, for example, electronic, magnetic, optical, electromagnetic, infrared, semiconductor media, or any other suitable media. More specific examples of suitable computer-readable media include, but are not limited to, a portable magnetic computer diskette such as floppy diskettes or hard drives, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory, or a portable compact disc. Computer readable media may also refer to signals that are used to propagate the computer executable instructions over a network or a network system such as the Internet.
Controller 20 may include a configuration to provide signals to media drive 12 to influence the movement of media through ink jet printing system 10 for accomplishing the image formation operation. Furthermore, controller 20 includes a configuration to provide one or more signals that influence the operation of an embodiment of an air heating apparatus, such as air heater 22. Air heater 22 may include an embodiment of a heater, such as a heating element, that contributes to the heating of air near air heater 22. An embodiment of an air movement device or mechanism, such as blower 24, pushes air 26 toward air heater 22 so that heat may be transferred from air heater 22 to air 26. As air 26 moves past air heater 22 on its way toward media 14, heat is transferred to air 26. The heated air 28 continues to move from air heater 22 toward media 14. Heated air 28 passing over media 14 provides energy to vaporize at least part of the fluid included in ink 30 deposited onto media 14. In one embodiment, air including the vaporized fluid is discharged from ink jet printing system 10.
Power is supplied to air heater 22 by an embodiment of a power supply, power supply 32. In one embodiment, power supply 32 may supply a DC voltage used to power the heating element included within air heater 22. In other embodiments of power supply 32, an AC voltage may be supplied to power the heating included within air heater 22. Power supply 32 also supplies power to other assemblies included in ink jet printing system 10 and shown in
As mentioned previously, AC power main 34 can include an embodiment of an over-current protection device, such as circuit breaker 36. Circuit breaker 36 could include, for example, a magnetic, thermal (such as with a bimetallic strip), thermal magnetic, electronically switched circuit breaker, or other suitable over-current protection device. In alternate embodiments the over-current protection device could include a fuse. To reduce the likelihood that the current supplied by AC power main 34 to ink jet printing system 10 is interrupted, one embodiment of air heater 22 operates to limit a magnitude of the current supplied to ink jet printing system 10 to less than a current that would result in actuation of circuit breaker 36. In one embodiment of air heater 22, the current supplied to a heating element included in air heater 22 is controlled to limit a magnitude of current drawn from AC power main 34, resulting from all the loads connected to it (which may include loads other than ink jet printing system 10), to less than the current rating of AC power main 34. The current rating of AC power main 34 may be regarded in some embodiments of AC power main 34 as the highest level of current that AC power main 34 is specified to carry, with the over current protection device associated with AC power main 34 selected to actuate at a current above the specified highest level of current for AC power main 34 to reduce the occurrence of actuation from transient currents. In other embodiments of AC power main 34, its current rating may be regarded as the level of current at which actuation of the over-current protection device is designed to occur. Many types of commercial installations have AC power main circuits with a 20 amp current rating. Many residential installations have AC power main circuits with a 15 amp current rating. Embodiments of air heater 22 could provide performance benefits with these types of installations or on installations having different current ratings.
In one embodiment of air heater 22, the heating element included in air heater 22 is capable of operating at a level of output power such that a magnitude of the current that would be supplied to ink jet printing system 10 by AC power 34 during an image forming operation would exceed the current rating of AC power main 34, if circuit breaker 36 was not present to limit the current. But, controller 20 controls the operation of the heating element during the image forming operation to maintain the magnitude of the current below the current rating of AC power main 34. In another embodiment of air heater 22, the current supplied to a heating element included in air heater 22 is controlled so that power is not supplied to the heating element during an image forming operation when fluid is vaporized from a colorant deposited on units of media 14.
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By storing heat energy in mass 104 air 108 can be heated for use in removing fluid from ink, after ejection of the ink upon media 14, without applying power to heating element 102, or applying reduced power, during a process of forming an image upon media 14, thereby allowing ink jet printing system 10 to maintain its current draw at a value that is less than the current rating of AC power main 34. The amount of heat energy stored in mass 104 permits sufficient heat energy to be transferred to air 108 so that air 110 can beneficially vaporize fluid in ink while supplying substantially no power or reduced power to heating element 102. The volume of air that can be adequately heated to beneficially vaporize fluid, while supplying substantially no power or reduced power to heating element 102, is dependent upon the volume of material included in mass 104. Of course, the number of units of media 14 for which the fluid in the ejected ink can be vaporized will be related to this volume of air.
A unit of media 14 regarded as having a relatively high density of ink ejected onto it may have at least ΒΌ gram of fluid. A substantial portion of the fluid may comprise water. To substantially vaporize this fluid, approximately 600 Joules of energy are used. Some embodiments of inkjet printing system 10 are designed remove approximately 50% of the fluid included in the ink deposited during the image forming process. Such embodiments are regarded as having a 50% drying efficiency. Therefore a design value that could be used in selecting the volume of material included in mass 104 is about 600 Joules per high density page onto which ink has been ejected. Of course, other design values that are higher or lower may be appropriate depending upon such things as the amount of fluid ejected for a high density page and the energy used in vaporizing the fluid.
Another design value used in selecting the volume of material included in mass 104 is the number of units of media included in what is expected to be the largest print job. In one possible application of inkjet printing system 10, about 400 units of media is the expected largest print job. Of course, for other embodiments of inkjet printing system 10 used in other applications, the number of units of media expected for the largest print job may be higher or lower. For example, in some applications, 40 units of media may be the largest number expected in a single print job.
It may occasionally occur that the size of some print jobs exceeds what has been designated as the maximum expected size for the particular embodiment of inkjet printing system 10. For these types of print jobs, the energy available from mass 104 for the units of media 14 in excess of the maximum expected number for which mass 104 was selected may not be sufficient to achieve the desired level of vaporization. In some modes of operation, there is a trade off that can be made between the rate at which images could be formed on units of media 14 using ink jet printing system 10 and the magnitude of the current drawn by ink jet printing system 10 from AC power main 34. In these modes, the magnitude of the current drawn can be reduced by reducing the rate at which images are formed on units of media 14 because the amount of energy consumed per unit time by air heater 100 to accomplish the desired level of fluid vaporization will be reduced. In a print job, for those units of media 14 that exceed the number of units of media 14 expected in the largest print job, embodiments of air heater 100 could be configured to supply power to heating element sufficient to achieve the desired degree of fluid vaporization at such a level that maintains the current drawn by ink jet printing system 10 below a value that is less than the current rating of AC power main 34 while images are formed on these excess units of media 14 at a reduced rate.
One type of material that has been found to be suitable for use in mass 104 is aluminum. With the heat capacity of aluminum, a volume of approximately 1 liter can provide approximately 240 Kilojoules of heat energy with a change in temperature of approximately 100 degrees centigrade. This quantity of heat energy could be used to vaporize the fluid in ink for about 400 units of media, allocating about 600 Joules for each unit of media. The use of this volume of material would allow for a desired degree of vaporization of fluid in the ink deposited on about 400 units of media without applying power to heating element 102. It should be recognized that many other materials may be used for storing heat energy such as zinc, iron, or another suitable material. Additionally, materials that may undergo a phase change during the storage of energy may be used. Some examples of a phase change material include waxes, such as paraffin, and low temperature alloys, such as Metspec 281. Use of some types of phase change material may allow storage of an equal amount of heat energy in up to a 30%, or more, smaller volume of phase change material than would be used if a non-phase change material were used.
In an alternate embodiment of mass 104, it could be implemented with a volume of approximately 0.1 liter of aluminum. With this volume of material, approximately 24 Kilojoules of heat energy would be extracted with a change in temperature of approximately 100 degrees centigrade. This quantity of heat energy could be used to vaporize the fluid in ink for about 40 units of media, allocating 600 Joules for each unit of media. It should be recognized that a wide range of volumes of material to store heat energy may be used. The volume selected will be influenced by the number of units of media for which it is desired to have heat energy stored in mass 104 available for vaporizing the fluid on the units of media.
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Controller 201 may include functionality in addition to functionality related to providing the signal to operate power switch 202. For example, controller 201 may include functionality to accomplish the tasks indicated for controller 20 shown in
In one embodiment of power control circuit 200, controller 201 operates to allow the application of power to heating element 102 at times when ink jet printing system 10 is turned on and not performing an image forming operation to raise and maintain the temperature of mass 104 within some predetermined range of a predetermined temperature value. In one embodiment of ink jet printing system 10 and air heater 22 (or air heater 100), mass 104 includes a volume of approximately 1 liter of aluminum heated to a temperature of approximately 150 degrees centigrade at a time other than during an image forming operation and the predetermined range corresponds to 5 degrees centigrade. And, for print jobs including fewer units of media 14 than the largest expected, controller 201 operates so that substantially no power is applied to heating element 102 during an image forming operation. After completion of the image forming operations included in a print job controller 201 operates to raise and maintain the temperature of mass 104 within the predetermined range of the predetermined temperature value. Operating in this manner enables ink jet printing system 10, during normal operation, to operate with a reduced likelihood of actuating circuit breaker 36. Additionally, operating in this manner enables ink jet printing system 10 to be operated on an AC power main circuit having a lower current rating, than would otherwise be used, to reduce the likelihood of actuating circuit breaker 36 during normal operation.
In one embodiment of control circuit 200 and controller 201, controller 201 monitors one or both of the temperature of air 110 and the temperature of mass 104. If, during an image forming operation, the temperature of one or both of these drops to a predetermined value indicating that the desired level of vaporization of fluid in the ink ejected onto units of the media will not likely occur, controller 201 provides a signal to power switch 202 to apply power to heating element 102 at a level reduced from the power applied to raise and maintain the temperature of mass 104 to near the predetermined temperature value during a time at which image forming operations are not performed. In one embodiment, an air temperature of 50 degrees centigrade may correspond to this predetermined value at which a reduced level of power may be applied. Additionally, controller 201 controls the operation of other assemblies included within ink jet printing system 10 (such as, media drive 12 and drive electronics 18) so that the rate of image formation on units of media is reduced to allow the desired level of vaporization of fluid from the ink with the reduced level of power applied to heating element 102.
This mode of operation may occur, for example, after image formation occurs on approximately the largest number of units of media to which mass 104 was designed to supply heat. As image formation occurs on units of media less than this largest number, heat is extracted from mass 104 while substantially no power is applied to heating element 102. As a result the temperature of air 110 and mass 104 drops until a level of the temperature of air 110 is reached at which the desired fraction of fluid included in the ink ejected onto units of media is no longer vaporized. Then, controller 201, monitoring one or both of the temperature of air 110 and the temperature of mass 104, operates ink jet printing system 10 at a reduced rate of image formation.
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Controller 302 may include functionality in addition to functionality related to providing the signal to operate power switch 304. For example, controller 302 may include functionality to accomplish the tasks indicated for controller 20. Or, controller 302 may include functionality to accomplish fewer tasks than controller 20 or to accomplish tasks in addition to or different from those accomplished by controller 20. Similar to controller 201, controller 302 may provide a pulse width modulated signal, having a variable duty cycle, to switch a power MOSFET included in power switch 304 to vary the power supplied to heating element 102.
An embodiment of a current measurement device, current measurement device 308 provides a signal to controller 302 related to the current supplied to ink jet printing system 10. In current measurement device 308, loop 310 serves as an inductive pickup to provide a signal to current monitor 312 related to the current supplied to power supply 306, which corresponds to the current drawn by ink jet printing system 10. Current monitor 312 conditions the signal generated by loop 310 to provide the signal to controller 302 in a form usable by controller 302. Current monitor 312 may be configured to provide an analog signal or digital signal related to the current drawn by ink jet printing system 10.
In one embodiment of power control circuit 300, controller 302 provides a signal to power switch 304 to control the power supplied to heating element 102 based upon the signal received from current monitor 312, which is related to the current drawn by ink jet printing system 10. When ink jet printing system 10 is turned on and not performing an image forming operation, controller provides the signal to power switch 304 to raise and maintain the temperature of mass 104 within some predetermined range of a predetermined temperature value. During these times, a magnitude of the current drawn by ink jet printing system 10 is likely well below a level that would result in actuation of circuit breaker 36. Therefore, during these times power can be supplied to heating element 102 to raise the temperature of mass 104 at a relatively rapid rate. In one embodiment of ink jet printing system 10 and air heater 22 (or air heater 100), mass 104 includes a volume of approximately 1 liter of aluminum heated to a temperature of approximately 150 degrees centigrade at a time other than during an image forming operation.
When ink jet printing system 10 performs the image forming operations included in executing a print job, blower 24 will move air 108 across mass 104 to heat it at the appropriate time during execution of the print job. The heated air 110 will be moved across units of media 14 to vaporize fluid included in ink 30 ejected onto units of media 14. At the time when air 108 begins removing heat energy stored in mass 104, the temperature of mass 104 will be within the predetermined range of the predetermined temperature value. When sufficient heat energy has been removed from mass 104, its temperature will fall below the low end of the predetermined range. Near that time, controller 302 will begin providing the signal to power switch 304 so power is supplied to heating element 102. Controller 302 will provide this signal to power switch 304 such that the current drawn by ink jet printing system 10 is maintained at a value less than the current rating of AC power main 34 while, in particular, image forming operations are performed. This is accomplished by controller 302 generating the signal provided to power switch 304 based upon the signal provided by current monitor 312 so the current drawn by ink jet printing system 10 is maintained below this value.
In one embodiment of controller 302, the signal provided to power switch 304 includes a pulse width modulated signal with a duty cycle that is varied based upon the signal provided by current monitor 312. The duty cycle of the signal provided to power switch 304 could be adjusted by controller 302 during image forming operations until the current drawn by ink jet printing system is at a desired level below the current rating of AC power main 34. Operation by controller 302 in this manner would decrease the rate at which the temperature of mass 104 falls when heat energy is being removed from it during image formation operations, as compared to an embodiment of a power control circuit in which substantially no power was applied to mass 104 during image forming operations. This is accomplished while still achieving the benefit of reducing the likelihood of actuation of the circuit breaker or alternatively not using an AC power main circuit having a larger current rating to avoid circuit breaker actuation.
As previously mentioned, a factor influencing the amount of material included in mass 104 selected for a particular embodiment of ink jet printing system 10 is the number of units of media expected in the largest print job. Operation of controller 302 to allow power to be applied to heating element 102 during an image forming operation while maintaining the current drawn by ink jet printing system 10 a desired level below the current rating of AC power main 34 permits the use, for a given size of the largest expected print job, of a smaller amount of material for mass 104 than would be used if substantially no power were applied to heating element 102 during image forming operations.
Even with power applied to heating element 102 during the image forming operation in the manner described, the temperature of mass 104 may continue to decrease. At some temperature of mass 104, the heat transferred to air 108 will no longer be adequate to provide the desired degree of vaporization of the fluid in the ink ejected onto units of the media. When this temperature is reached, controller 302 may enter a mode of operation similar to an embodiment of controller 201 in which the image formation operation is performed at a reduced rate to accommodate the reduced amount of heat energy available for vaporizing the fluid in the ink.
During times when an image forming operation is not performed, air would not be moved across mass 104. But, mass 104 will still lose heat energy to the surrounding air when its temperature is greater than the surrounding air. This lost heat energy will be replaced as the various embodiments of the controllers operate to maintain the temperature of mass 104 within the predetermined range of the predetermined temperature. To reduce the rate at which heat is lost during times when image forming operations are not performed, embodiments of air heater 22 (or air heater 100) may make use of various embodiments of enclosures. The enclosures will reduce the rate of heat loss from mass 104. Some embodiments of these enclosures may have insulating properties to additionally reduce the rate of heat loss from mass 104. The insulating properties of the enclosure may be achieved in a variety of ways such as by including insulation in the walls of the enclosure. The insulation could include fiber glass fill or polyurethane foam. Alternatively, the enclosure could be constructed to have inner and outer walls forming a closed volume in which a partial vacuum could be sustained. In one example of the benefit of an insulated enclosure, a 1 liter volume of material insulated with R-10 (would could be achieved using about 1 inch thick layer of polyurethane foam) for storing heat energy could be maintained at near 175 degrees centigrade using approximately 5 watts of power.
To allow air to move through the enclosure and across mass 104 during image forming operations, the enclosures may include one or more types of valves. The one or more valves are configured so that during the time when image forming operations are performed, air may move through the enclosure and during the time when image forming operations are not performed, air is substantially stopped from moving through the enclosure.
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Mass 500 includes a stack of plates, of which plate 502 is exemplary, of the heat storage material separated by air gaps, of which air gap 504 is exemplary. The plates may be formed into a wide variety of shapes (circles, rectangles, ovals, etc.) suitable for the physical space they are to occupy. Mass 500 has a cylindrical shape and
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As previously mentioned, embodiments of ink jet printing system 10 may store heat energy in mass 104 while ink jet printing system 10 is not performing an image forming operation to maintain the current drawn by ink jet printing system 10 below the current rating of AC power main 34. Some embodiments of image forming systems are configured to comply with various governmental energy usage regulations, such as the Energy Star regulations. Energy usage regulations generally define a low power mode of operation in which the power drawn by the image forming system stays below a specified value. Additionally, the time period permitted from the end of image forming operations, or after start up, to the entry of the lower power mode may also be defined. For example, for some classes of systems, the Energy Star regulations set the power limit at 45 watts and the time period after which the lower power mode is to be entered at 15 minutes.
One embodiment of ink jet printing system 10 could be configured so that the controller operates the air heater to raise the temperature of the mass used to store heat energy (after it has been reduced by heating air or upon start up) to the predetermined temperature value during the 15 minute period after image forming operations have ended or after power is applied to ink jet printing system 10. Then, with adequate insulation in the enclosure surrounding the air heater, the mass could be maintained within a predetermined temperature range of the predetermined temperature with the power drawn by ink jet printing system 10 below the 45 watt limit.
One embodiment of ink jet printing system 10 could be configured so that the controller operates the air heater to raise the temperature of the mass to near the predetermined temperature (after it has been reduced by heating air or upon start up) while ink jet printing system 10 is in the low power mode. Raising the temperature of the mass in this manner would use a relatively long period of time because of the power limit below which ink jet printing system 10 would operate. However, if the power applied to the mass exceeded the power lost by the mass, which is achievable with an insulated enclosure, raising the temperature of the mass to near the predetermined fashion could be achieved. One embodiment of the air heater tested, using a mass in an insulated enclosure, was able to maintain a temperature of the mass near 150 degrees centigrade using less than 01 watts of power.
One embodiment of ink jet printing system 10 could be configured so that the controller operates the air heater to raise the temperature of the mass to near the predetermined temperature (after it has been reduced by heating air or upon start up) by having ink jet printing system 10 exit the low power mode and enter a servicing mode permitted by the energy usage regulations. In one embodiment, the controller may be configured to have ink jet printing system exit the low power mode and enter a servicing mode to heat the mass at a predetermined time, such relatively shortly before the start of a work day. In another embodiment, the controller could be configured to select the times to exit the low power mode and enter the servicing mode to heat the mass based upon usage patterns of ink jet printing system 10 recorded by the controller. Based upon the pattern of usage, the controller would have the mass heated to near the predetermined temperature so it will likely be available for use when desired.
While the disclosed embodiments have been particularly shown and described, those skilled in the art will understand that many variations may be made to these without departing from the spirit and scope defined in the following claims. The detailed description should be understood to include all novel and non-obvious combinations of the elements that have been described, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Combinations of the above exemplary embodiments, and other embodiments not specifically described herein will be apparent to those of skill in the art upon reviewing the above detailed description. The foregoing embodiments are illustrative, and any single feature or element may not be included in the possible combinations that may be claimed in this or a later application. Therefore, the scope of the claimed subject matter should be determined with reference to the following claims, along with the full range of equivalents to which such claims are entitled.
