Abstract:
A system, method, and apparatus for adjusting dry ink concentration in a developing station ( 30 ) of a printer is disclosed. The adjustment is performed by calculating the thermal drift of a dry ink monitor ( 40 ) and applying the result as a compensating factor in calculations in a software algorithm. The dry ink monitor ( 40 ) has a sensing port ( 42 ) in contact with a dry ink concentration and is connected to a dry ink monitor interface board ( 10 ) that houses a temperature sensor ( 20 ). The monitor interface board ( 10 ) is positioned in proximity to the dry ink monitor ( 40 ) to enable the temperature sensor ( 20 ) to measure a temperature of the dry ink concentration. The software algorithm is used to adjust the dry ink concentration based on a slope coefficient calculated by the printer based on outputs from the dry ink monitor ( 40 ) and the dry ink monitor interface board ( 10 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   Reference is made to and priority claimed from U.S. Provisional Application Ser. No. 60/531,919, filed Dec. 23, 2003, entitled DRY INK CONCENTRATION MONITOR INTERFACE WITH AUTOMATED TEMPERATURE COMPENSATION ALGORITHM. 

   FIELD OF THE INVENTION 
   The present invention generally relates to an imaging system, and more specifically, to a method and apparatus for directly compensating the concentration of dry ink in a printer based on the thermal drift of the dry ink monitor and/or thermal testing data. 
   BACKGROUND OF THE INVENTION 
   An electrophotographic printer utilizes a developer mixture to form images on media. The developer is made up of two parts, magnetic carrier, and toner (dry ink). In order to maintain a constant dry ink concentration, the voltage level of the dry ink monitor must be maintained as close to a target voltage level as possible. Machine software adjusts the dry ink concentration to increase or decrease the amount of dry ink in the developer mixture to reach the target voltage level. For instance, the dry ink concentration can be varied by a replenisher that adds dry ink to the developer station, thereby decreasing the voltage response of the dry ink monitor. However, the thermal drift coefficient of each individual sensor varies from sensor to sensor since the sensors are inherently sensitive to temperature changes and the dry ink concentration can vary considerably during operation depending on the temperature. Also, the dry ink concentration sensor typically may exhibit positive or negative thermal drift, which may change over the life of the sensor. 
   The prior art includes systems that apply corrections to the toner magnetic sensors based upon temperature, burn-in, and toner-age. For example, U.S. Pat. No. 6,175,698 identifies that temperature, burn-in, and toner-age of the toner particles in each developer structure can affect the amount of toner required to develop the latent image. The sensor of the &#39;698 patent is used to obtain the toner concentration readings, but cannot directly measure the actual toner concentration. Thus, the readings are adjusted by combining the target toner concentration to provide a error signal that is input to control feedback dispensing of the toner. The feedback dispenser of the &#39;698 patent processes the error signal and commands the developing station to request that a certain toner mass per unit time be dispensed to compensate or correct for variations in temperature, burn-in, or toner-age to attempt to maintain the proper toner concentration. 
   However, these and other known sensors are susceptible not only to temperature fluctuations while in service in the machine, but are also susceptible to thermal drift of the sensors themselves. 
   Thus, a method and apparatus is needed that can compensate for the thermal drift of the sensors. 
   SUMMARY OF THE INVENTION 
   The present invention provides a temperature sensing device that is located on or near the dry ink concentration sensor of a developing station in an electrophotographic printer. The temperature-sensing device is capable of detecting the temperature of the dry ink monitor to adjust the dry ink concentration using the sign and magnitude of the temperature dependent thermal drift of the sensor as measured. The sign and magnitude of the temperature dependent thermal drift can then be used to correct the dry ink sensor output to the printer to compensate for the temperature variation. 
   The sensor is attached to an electronic, dry ink monitor interface board that is connected by a plug/connector wire to the dry ink monitor at one end and is connected by another plug/connector wire to the developer station. The temperature sensor can be a thermister, a thermal couple, or a solid state thermometer. Although the temperature sensor could be mounted to the dry ink/dry ink monitor, the temperature sensor is typically adjacent the dry ink monitor in an extrusion on the radiant side of the sump of the developer station. The temperature sensor is thus able to sense variations in the temperature of the dry ink monitor to determine the thermal drift of the dry ink monitor. The signal from the temperature sensor is be transmitted to a processing unit in the printer and the data is used in a software algorithm to vary the dry ink concentration based upon the temperature and thermal drift of the sensors. 
   The invention described herein is used to correct the dry ink sensor output to the printer to compensate for temperature variation in the sensor itself. The dry ink concentration sensor thermal drift is typically calibrated during initial power up of the machine when the dry ink station is running, but not imaging. This timing will report a constant dry ink concentration signal representative of real running conditions since the dry ink concentration would be constant at that point. This compensation can be accomplished through either hardware or software. 
   The invention also includes a software algorithm that allows for compensation of the thermal drift of the dry ink monitor measured by the temperature sensor of the dry ink monitor interface board. 
   The thermal drift of the dry ink monitor can be measured in two ways. First, the dry ink monitor itself can be individually and independently screened for thermal drift performance before it is installed in a printer. Second, the dry ink monitor can be used in the printer without screening and the thermal drift can be calculated by the software algorithm and used thereafter by the machine. 
   Independent and individual screening can be accomplished by heating the dry ink monitor or sensor in an oven. For example, the monitors could be heated in an oven from 25° C. to about 40° C. for one half hour. The monitors would then be allowed to cool. During this heat cycle the thermal drift of each monitor is measured as a change in the dry ink monitor voltage output versus the change in temperature. If an individual monitor does not meet the specified requirements for thermal drift, the monitor is not used in a printer. 
   The present invention however will allow the thermal drift measurement of the monitor to be matched with that specific monitor. The measured thermal drift can then be placed on a label on the monitor and can be used as a set point when the monitor is installed in the printer. The set point will allow the software algorithm described herein to apply the thermal drift of the monitor to calculations involving dry ink concentration by the dry ink monitor. This procedure will allow a monitor that would conventionally be unusable because of an undesirable thermal drift to be used in the printer with the thermal drift of the individual monitor taken into account by the software algorithm during adjustment of the dry ink concentration. 
   The label included on the monitor could list any additional data, including volts per degree or other pertinent information from the testing, but the thermal drift measurement should be included regardless. The monitors of the present invention typically have a zero to five volt output. The monitors are then centered or normalized to two and one-half volts. Thus, the thermal drift change measured herein is a deviation, plus or minus, from two and one-half volts. This normalization could be performed at any desired point in the available voltage with two and one-half volts being an example of a typical monitor. 
   A second way to compensate for the thermal drift of the dry ink monitor is to place the dry ink monitor into the printer, sample the temperature of the thermal sensor on the dry ink monitor interface board, and use the sampled thermal drift of the monitor in calculations in a software algorithm. Although the monitors of the first way of compensation require heating and testing the components to be used in the printer, the monitors in this second way of compensation can be placed into use in the printer without heating or testing the electronics. 
   Further, even if the monitors were evaluated upfront for individual thermal drift, the algorithm described herein could be used. This procedure will allow any monitors to be used, including ones already installed in existing machines with the software algorithm updated to compensate for the thermal drift of the monitor. 
   The software routine typically begins at machine power up when the machine subsystem components run through diagnostics and warming the fuser to the required operating temperature. While the machine software is initializing, the developer station is run for a brief period to read the temperature sensor on the dry ink monitor interface board and the output signal from the dry ink monitor. 
   While the machine continues to warm the fusing system, other key subsystems are initialized. After the initializations are complete and with the developer station running, the temperature sensor on the dry ink monitor interface board and the dry ink monitor output signal are again read. The slope of the temperatures measured versus the dry ink monitor output signal drift is then calculated. This calculation involves dividing the change in the monitor output by the change in the temperature output at the two points measured. Thus, the initial measurements or set points are evaluated against the temperature and output signal measured when the system has warmed to its operating temperature to calculate the thermal drift as a compensation factor. The thermal drift calculations are dependent only upon an existence of a change in the measured temperatures. This change will be found since the machine proceeds from a cold start to a warm, operational phase. 
   The software routine then applies the dry ink monitor drift slope coefficient to the calculations involving dry ink concentration algorithms. The printer can then compensate for the thermal drift by adjusting the dry ink concentration mixture to increase or decrease the dry ink component as determined by the software. Further, if the sensor has been in use for a period of time in a printer, the thermal drift for the installed sensor could vary over the life of the part. The software algorithm described herein will enable re-testing of the sensor to adjust the thermal drift set point as necessary to enable longer life out of each sensor. 
   Thus, the present invention provides a computer readable medium containing a computer program product with instructions for controlling a dry ink concentration in a development station in a printer. The computer program includes program instructions for receiving and decoding a start-up monitor output from a dry ink monitor, program instructions for receiving and decoding a start-up temperature from a dry ink monitor interface board, and program instructions for adjusting the dry ink concentration to achieve a preferred dry ink concentration. Before the computer program receives and decodes the start-up monitor output, the computer program product can receive and decode a start-up monitor output. In such a situation, the computer readable medium includes program instructions for receiving and decoding a start-up dry ink monitor output of the dry ink concentration with the dry ink monitor and program instructions for receiving and decoding a start-up temperature of the dry ink monitor with the dry ink monitor interface board. Further, before the program instructions for receiving and decoding a start-up monitor output, the computer readable medium can include program instructions for calculating a measured temperature change by finding a temperature difference between the start-up temperature and the operating temperature, program instructions for calculating a measured monitor output change by finding a monitor output difference between the start-up monitor output and the operating monitor output, and program instructions for calculating a thermal drift coefficient by dividing the measured monitor output change by the measured temperature change. 
   The present invention also includes a system for adjusting for thermal drift that includes a dry ink monitor with a sensing port in contact with a dry ink concentration and a monitor interface board with a temperature sensor. The monitor interface board is positioned in proximity to the dry ink monitor to enable the temperature sensor to measure a temperature of the dry ink monitor. Typically, the temperature sensor senses a start-up temperature at the start up of the printer, which is transmitted to a central processing unit of the printer. The temperature sensor next senses an operating temperature of the dry ink concentration that is transmitted to the central processing unit. 
   The system also senses a start-up monitor output at start up of the printer, which is also transmitted to a central processing unit of the printer. The system next senses an operating monitor output of the dry ink monitor and transmits such to the central processing unit. The central processing unit compares the start-up monitor output to the operating monitor output and compares the start-up temperature to the operating temperature. The software algorithm then calculates the thermal drift of the dry ink monitor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a dry ink monitor interface board connected to a dry ink monitor and a mounting interface; 
       FIGS. 2 and 3  show isometric and side views of the dry ink monitor on the mounting interface; 
       FIG. 4  shows a development station housing the dry ink monitor and mounting interface; 
       FIG. 5  is a flowchart for the dry ink monitor thermal compensation operation; and 
       FIG. 6  is a flowchart of a normally running process loop. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference is now made in more detail to the drawing figures, wherein like numerals refer, where appropriate, to like parts throughout.  FIG. 1  shows a dry ink monitor interface board  10  connected to a dry ink monitor  40  and a mounting interface  44 . The dry ink monitor interface board  10  has a temperature sensor  20  mounted thereupon. The dry ink monitor interface board  10  is generally formed of typical circuit board materials and is capable of receiving a number of components thereupon. The dry ink monitor interface board  10  can include capacitors, resistors, op amps, electrical connectors, at least one temperature sensor  20 , and other electrical components such as Zener diodes. The capacitors, resistors, op amps, electrical connectors, and other electrical components are typical circuitry components that function as like components known in the art. The electrical connectors are capable of receiving connector wires. 
   As also shown in  FIG. 1 , connector wire  46  is typically attached at one end to the dry ink monitor  40  with the other end received by electrical connector  18 . Electrical connector  18  is typically a five (5)-pin connector to match the connector wire  46 . Electrical connector  19  is typically a six (6)-pin connector and is capable of receiving a six-pin connector wire (not shown), which is plugged into the developer station&#39;s harness (not shown). In this preferred embodiment, the electrical connectors  18  and  19  are formed with five (5) pins and six (6) pins, respectively, in order to ensure that the respective connector wires are received in the proper junction. One of ordinary skill will recognize that the 5- and 6-pin connector arrangements are merely preferred in this embodiment and could easily be comprised of any combination of pin connectors, including equal numbered pins for each connector. The invention should thus not be limited to the pin arrangement disclosed. 
   Accordingly, two signals exit the dry ink monitor interface board: the voltage monitor output that is sent to the machine and the temperature output that is sent to the machine through a connector wire (not shown) connected to connector  19  and coupled to the developer station harness (not shown). The outputs are then received into the computer logic boards of the machine. The software then proceeds with the algorithm as detailed in the flowchart of  FIG. 5 . 
   The dry ink monitor interface board  10  is typically shrink-wrapped to eliminate the possibility of grounding out the board once the components are attached thereto. The electrical connectors or plugs  18  and  19  as attached by the connector wires allow the dry ink monitor interface board  10  to be contained in a lower extrusion of the developer station and can even hang below the dry ink monitor  40  in the development station  30 . The board  10  could also be clipped to a protrusion in the development station  30 . Regardless of desired placement, the board  10  is placed as close as possible to the dry ink monitor  40  to allow the temperature sensor  20  to sense the temperature of the dry ink monitor  40 . 
     FIGS. 2 and 3  show isometric and side views of the dry ink monitor  40  mounted onto the mounting interface  44 . The mounting interface  44  is typically a plastic mounting  44  that receives the dry ink monitor  40  on the underside thereof. Although it could be formed of other materials, the mounting interface  44  is typically formed of plastic to reduce the interference with the monitor or other sensing equipment. The plastic mounting  44  merely acts as an interface for the monitor to the developer station  30 . The plastic mounting  44  typically will include a portion  45  on the upper surface, shown in  FIG. 2  as a rounded or concave section, that will mount into the developing station  30  below the mixing augers  36  as shown in  FIG. 4  and match the rounded profile thereof. The raised portion  45  of the plastic mounting  44  also includes a dry ink monitor port  42  in contact with the magnetic dry ink concentration in the development station  30  to sense the dry ink concentration&#39;s characteristics. As shown in  FIG. 1 , a label  43  can be affixed to the dry ink monitor  40  to identify the thermal drift coefficient as measured of the monitor  40 . 
   The dry ink monitor  40  can be attached to the plastic mounting  44  by snap-in connectors, screw threading, or any other connection means that will allow the dry ink monitor  40  to remain securely attached to the plastic mounting  44 . The connector wire  46 , which is coupled to the dry ink monitor interface board  10  at electrical connector  18  as described above, will typically extend from the dry ink monitor  40  and is attached therein. The connector wire  46  however could be received by an electrical connection (not shown) coupled to, or integral with, the dry ink monitor  40 . 
     FIG. 4  shows a development station  30  that can be housed in an electrophotographic printer. The development station  30  includes a development roller  32 , a transport roller  34 , and mixing augers  36 . The development roller  32  will typically be in contact with an image roller to engage the charged dry ink particles onto the print media that receives the desired image (not shown). The mixing augers  36  are used to combine the dry ink with the magnetic carrier particles to achieve an even mixture. The development station  30  also houses the dry ink monitor  40  and mounting interface  44  in a lower extrusion. The concave portion  45  of the plastic mounting  44  matches the curved profile of the mixing auger  36  under which the dry ink monitor  40  is disposed. The port  42  of the dry ink monitor  40  is in contact with the dry ink concentration, which is being mixed by the mixing augers  36 , in the cavity of the development station  30 . The dry ink monitor interface board  10  is disposed (not shown) in an air cavity beneath the dry ink monitor  40  and is connected thereto by connector wire  46  as described above. The snap-in, C-cross-sectional floor/closure beneath the dry ink monitor  40  forms the lower wall of the cavity housing the dry ink monitor interface board  10 . 
   The invention described herein can be used in development stations in an electrophotographic machine, such as the NexPress 2100. Each developer station will include a dry ink monitor interface board. The printer could include as many development stations as desired with a dry ink monitor interface board and dry ink monitor for each. 
     FIG. 5  is a flowchart of the software algorithm/compensation routine  50  of the measurement of the dry ink monitor thermal drift. The routine  50  begins at step  51  with power up of the machine. The routine  50  continues to step  52  where the machine software is initialized and the developer station is run. At step  53 , readings are taken from the temperature sensor  20  on the dry ink monitor interface board  10  and the dry ink monitor  40 . The routine  50  proceeds to block  54  with the machine continuing to warm the fusing system and initializing key subsystems. 
   After the initialization is complete, the routine  50  proceeds to step  55  where the temperature sensor on the dry ink monitor interface board  10  and the dry ink monitor  40  output signal are read. In step  56 , the slope of the measured temperature change versus the dry ink monitor output signal drift is calculated. The slope coefficient of the dry ink monitor drift is then applied in step  57  to calculations involving dry ink concentration algorithms. Step  57  uses the software to calculate the amount of replenishment needed to maintain a constant dry ink concentration. The dry ink monitor drift slope coefficient as calculated is then used as a multiplier. The dry ink monitor reading is multiplied by the coefficient to compensate for the temperature or thermal drift. 
   Another manner of compensating for the thermal drift is to perform a service routine to conduct a thermal drift test. Such a routine could be operated by service personnel after the monitors have been installed in the printer. This service routine would require the dry ink station to run for a period of time while disengaged from the photoconductive element. 
   The sensors/monitor used herein typically operate to detect any temperature drift or change from the initialized/desired dry ink concentration percentage. Thus, a desired temperature of 25° C. for example would register any positive or negative deviation from 25° C. The monitor readings are typically taken about twice per frame or about once every 360 milliseconds. The thermal slope coefficient is then applied to the dry ink monitor voltage in the calculation every time it is read. 
     FIG. 6  is a flowchart of a normally running process loop. The process  60  begins at step  61  by retrieving the measured thermal drift, which has been calculated through either routine  50  of  FIG. 5 , heating and cooling to establish a set point, or a service routine performed subsequent to routine  50  of  FIG. 5 . The service routine would involve the same procedural steps as routine  50 . The process  60  continues to step  62  where the dry ink monitor drift slope coefficient is applied to calculations involving dry ink concentration algorithms. The process loops back to step  61  after a predetermined time has elapsed. This time is currently performed once every 360 milliseconds, but could be adjusted as desired. 
   While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various other changes in form and detail may be made without departing from the spirit and scope of the invention as set forth in the claims.