Abstract:
An environmental condition detection system for a hardcopy device, such as an inkjet printing mechanism, includes an environmental condition sensor having an optical property which changes in response to a change in an environmental condition, for instance humidity or temperature. The system also has an optical sensor which detects changes in the optical property and generates a signal for a controller that responds by changing an operating parameter of the hardcopy device. A hard copy device having such a environmental condition detection system is also provided, along with a method of determining an environmental condition within which a hardcopy device is operating.

Description:
INTRODUCTION  
         [0001]    The present invention relates generally to inkjet printing mechanisms, and more particularly to an optical system for determining an environmental factor which affects printing, such as the humidity and/or temperature where an inkjet printing mechanism is operating, so printing routines may be adjusted to provide fast, high quality output while accommodating these varying environmental conditions.  
           [0002]    Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as “ink,” onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).  
           [0003]    To clean and protect the printhead, typically a “service station” mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and drying. To facilitate priming, some printers have priming caps that are connected to a pumping unit to draw a vacuum on the printhead. During operation, partial occlusions or clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a clearing or purging process known as “spitting.” The waste ink is collected at a spitting reservoir portion of the service station, known as a “spittoon.” After spitting, uncapping, or occasionally during printing, most service stations have a flexible wiper, or a more rigid spring-loaded wiper, that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.  
           [0004]    To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solids content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper.  
           [0005]    Various environmental factors affect inkjet printing routines, servicing routines, and other aspects of printer performance. Unfortunately in the past, there has been no way to economically provide an environmental factor input to a printer controller to allow the controller to modify these printing, servicing and other routines to provide optimum performance in light of the current environmental conditions. One environmental factor, temperature, may currently be monitored using temperature sensing resistors within the inkjet printheads; however, more important to printer performance than temperature is the environmental factor of humidity. Unfortunately, the currently available humidity sensors are far too expensive for the home and small business inkjet printing markets, with manufacturer&#39;s material costs for capacitive sensors ranging several dollars per sensor not including the cost of their support electronics, while voltage output humidity sensors currently cost about ten dollars each. Moreover, the currently available capacitive humidity sensors are inaccurate, so their inaccuracy coupled with their high cost renders their use unjustifiable in the home and small business inkjet printing market.  
           [0006]    If humidity could be both economically and accurately measured for communication to a printer controller, a variety of performance enhancements could be made based upon knowledge of the ambient humidity. For example, presently to provide optimum performance in varying environmental conditions, inkjet printing, servicing, and other routines are based on a “worst case scenario” assumption of the environmental conditions, here meaning a high humidity environment for printing and a low humidity environment for printhead servicing, as well as for vapor transfer calculations which account for ink evaporation from the pens. In high humidity, the media may already be moist and partially saturated before ever being loaded into a printer, and high humidity increases the drying time of aqueous-based inks. These high humidity conditions may lead to increased cockle of the media, a term referring to the swelling of the paper fibers when saturated with ink, causing a buckling which in extreme conditions may cause the media to buckle so high that the printhead crashes into the media, smearing the printed image and possibly damaging the printhead. Thus, a high humidity assumption increases the dry time delay for the media over that required in normal or low humidity conditions, which slows media throughput while a printer waits for one sheet to dry before depositing the next sheet on top of the previously printed sheet in the output tray. Furthermore, the low humidity assumptions for servicing increase the duration of servicing routines, which further slows media throughput.  
           [0007]    Low humidity conditions contribute to hue shift problems, where various components of the ink evaporate over time, for instance by leaking at the printhead/cap sealing interface. In “off axis” printing systems, where the printheads carry only a small supply of ink across the printzone and are replenished with ink delivered from a stationary main ink reservoir through flexible tubing, some of the ink volatiles leach through the tubing walls to atmosphere. Any loss of one ink component changes the ink composition, resulting in changes in ink performance, often manifested as a hue shift in the resulting image. For instance, with fewer volatiles, the resulting ink dispensed by the printhead has a higher concentration of dyes or colorants, yielding a darker image than originally intended. To compensate for these ink composition changes, ambient humidity information may be used for vapor transfer rate calculations to allow for hue adjustment based on calculated dye load changes over time within the inkjet cartridges.  
           [0008]    As another example of the impact of this high humidity assumption on printer performance, when performing duplex printing one typical duplexer unit typically holds a sheet after printing the first side for nearly seven seconds before reversing the sheet and beginning printing on the opposite surface. In low humidity conditions, such as in a desert setting, holding a sheet of paper for seven seconds as one would in a humid region unnecessarily delays duplex printing. These same delays are incurred to avoid cockle problems when printing single sided sheets. For pen servicing, it would be desirable to know the ambient humidity so the type of servicing routine performed on the printheads following uncapping and before a print job may be optimized. Additionally, by knowing a humidity history of the printer, vapor transfer rate calculations may be made to determine the amount of ink lost due to evaporation, which then may be used in conjunction with drop counting or other measures to predict when an inkjet cartridge is nearing an empty condition, allowing an operator to be warned before the cartridge runs dry.  
           [0009]    Clearly, a variety of different printing, servicing and other performance operations may be adjusted and optimized if only the ambient humidity were input to the printing mechanism. Thus, one goal herein is to provide an environmental factor measurement input to an inkjet printing mechanism, which may use this input to optimize printer performance to provide fast high quality hard copy outputs. 
       
    
    
     DRAWINGS FIGURES  
       [0010]    [0010]FIG. 1 is a fragmented, partially schematic, perspective view of one form of an inkjet printing mechanism including two different embodiments of an optical humidity and/or temperature sensing system for determining these environmental factors which affect inkjet printing.  
         [0011]    [0011]FIG. 2 is an enlarged, perspective view of one form of a service station of FIG. 1.  
         [0012]    [0012]FIGS. 3 and 4 are enlarged, side elevational views of the service station of FIG. 1, specifically with:  
         [0013]    i. FIG. 3 showing a sensor during a detecting operation; and  
         [0014]    ii. FIG. 4 showing the sensor in a rest position.  
         [0015]    [0015]FIG. 5 is an enlarged top plan view of one form of the sensor of FIG. 1.  
         [0016]    [0016]FIG. 6 is an enlarged top plan view of another form of the sensor of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0017]    [0017]FIG. 1 illustrates an embodiment of an inkjet printing mechanism, here shown as an inkjet printer  20 , constructed in accordance with the present invention, which may be used for printing for business reports, correspondence, desktop publishing, and the like, in an industrial, office, home or other environment. A variety of inkjet printing mechanisms are commercially available. For instance, some of the printing mechanisms that may embody the present invention include plotters, portable printing units, copiers, cameras, video printers, and facsimile machines, to name a few. For convenience the concepts of the present invention are illustrated in the environment of an inkjet printer  20 .  
         [0018]    While it is apparent that the printer components may vary from model to model, the typical inkjet printer  20  includes a chassis  22  surrounded by a housing or casing enclosure  24 , typically of a plastic material. Sheets of print media are fed through a printzone  25  by a print media handling system  26 , constructed in accordance with the present invention. The print media may be any type of suitable sheet material, such as paper, card-stock, transparencies, fabric, mylar, and the like, but for convenience, the illustrated embodiment is described using paper as the print medium. The print media handling system  26  has a feed tray  28  for storing sheets of paper before printing. A series of conventional motor-driven paper drive rollers (not shown) may be used to move the print media from tray  28  into the printzone  25  for printing. After printing, the sheet then lands on output tray portion  30 . Alternatively, the sheet may be directed to pass through a duplexing mechanism, such as a modular duplexing mechanism  31 , which turns the sheet over for printing on the opposite surface from the surface first printed upon. One suitable duplexing mechanism is described in U.S. Pat. No. 6,167,231, currently assigned to the present assignee, the Hewlett-Packard Company. The media handling system  26  may include a series of adjustment mechanisms for accommodating different sizes of print media, including letter, legal, A-4, envelopes, etc., such as a sliding length and width adjustment levers  32  and  33  for the input tray, and a sliding length adjustment lever  34  for the output tray.  
         [0019]    The printer  20  also has a printer controller, illustrated schematically as a microprocessor  35 , that receives instructions from a host device, typically a computer, such as a personal computer (not shown). Indeed, many of the printer controller functions may be performed by the host computer, by the electronics on board the printer, or by interactions therebetween. As used herein, the term “printer controller  35  ” encompasses these functions, whether performed by the host computer, the printer, an intermediary device therebetween, or by a combined interaction of such elements. The printer controller  35  may also operate in response to user inputs provided through a key pad (not shown) located on the exterior of the casing  24 . A monitor mounted on the casing  24  or coupled to the computer host may be used to display visual information to an operator, such as the printer status or a particular program being run on the host computer. Personal computers, their input devices, such as a keyboard and/or a mouse device, and monitors are all well known to those skilled in the art.  
         [0020]    A carriage guide rod  36  is mounted to the chassis  22  to define a scanning axis  38 . The guide rod  36  slideably supports a reciprocating inkjet carriage  40 , which travels back and forth across the printzone  25  and into a servicing region  42 . One suitable type of carriage support system is shown in U.S. Pat. No. 5,366,305, assigned to Hewlett-Packard Company, the assignee of the present invention. A conventional carriage propulsion system may be used to drive carriage  40 , including a position feedback system, which communicates carriage position signals to the controller  35 . For instance, a carriage drive gear and DC motor assembly may be coupled to drive an endless belt secured in a conventional manner to the pen carriage  40 , with the motor operating in response to control signals received from the printer controller  35 . To provide carriage positional feedback information to printer controller  35 , an optical encoder reader may be mounted to carriage  40  to read an encoder strip extending along the path of carriage travel.  
         [0021]    Housed within the servicing region  42  is a service station  44 . The service station  44  includes a translationally movable pallet  45 , which moves in a forward direction indicated by arrow  46 , and in a rearward direction indicated by arrow  47 , when driven by a motor  48  operating in response to instructions received from the controller  35 . While a variety of different mechanisms may be used to couple the drive motor  48  to the pallet  45 , preferably a conventional reduction gear assembly drives a pinion gear which engages a rack gear formed along the undersurface of the pallet  45 , for instance as shown in U.S. Pat. Nos. 5,980,018 and 6,132,026, both currently assigned to the present assignee, the Hewlett-Packard Company.  
         [0022]    In the printzone  25 , the media sheet receives ink from an inkjet cartridge, such as a black ink cartridge  50  and/or a color ink cartridge  52 . The cartridges  50  and  52  are also often called “pens” by those in the art. The illustrated color pen  52  is a tri-color pen, although in some embodiments, a set of discrete monochrome pens may be used. While the color pen  52  may contain a pigment based ink, for the purposes of illustration, pen  52  is described as containing three dye based ink colors, such as cyan, yellow and magenta. The black ink pen  50  is illustrated herein as containing a pigment based ink. It is apparent that other types of inks may also be used in pens  50 ,  52 , such as thermoplastic, wax or paraffin based inks, as well as hybrid or composite inks having both dye and pigment characteristics.  
         [0023]    The illustrated pens  50 ,  52  each include reservoirs for storing a supply of ink. The pens  50 ,  52  have printheads  54 ,  56  respectively, each of which have an orifice plate with a plurality of nozzles formed therethrough in a manner well known to those skilled in the art. The illustrated printheads  54 ,  56  are thermal inkjet printheads, although other types of printheads may be used, such as piezoelectric printheads. These printheads  54 ,  56  typically include a substrate layer having a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubble of gas is formed to eject a droplet of ink from the nozzle and onto media in the printzone  25 . The printhead resistors are selectively energized in response to enabling or firing command control signals, which may be delivered by a conventional multi-conductor strip (not shown) from the controller  35  to the printhead carriage  40 , and through conventional interconnects between the carriage and pens  50 ,  52  to the printheads  54 ,  56 .  
         [0024]    Preferably, the outer surface of the orifice plates of printheads  54 ,  56  lie in a common printhead plane. This printhead plane may be used as a reference plane for establishing a desired media-to-printhead spacing, which is one important component of print quality. Furthermore, this printhead plane may also serve as a servicing reference plane, to which the various appliances of the service station  45  may be adjusted for optimum pen servicing. Proper pen servicing not only enhances print quality, but also prolongs pen life by maintaining the health of the printheads  54  and  56 . To hold the pens,  50 ,  52  in place securely against alignment datums formed within carriage  40 , preferably the carriage  40  includes black and color pen latches  57 ,  58  which clamp the pens  50 ,  52  in place as shown in FIG. 1.  
         [0025]    [0025]FIG. 2 shows one form of the service station  44 , constructed in accordance with the present invention. The pallet  45  may carry a variety of different servicing members for maintaining the health of the printheads  54 ,  56 , such as printhead wipers, primers, solvent applicators, caps and the like. These various servicing members are represented in the drawing figures as black and color caps  60 ,  62  for sealing the printheads  54 ,  56  of pens  50 ,  52 , respectively. Preferably, the pallet  45  is housed between a lower frame portion  64 , and an upper frame portion  66  of the service station  44 . As mentioned above, the motor  48  drives the pallet  45  in the forward and reverse directions of arrows  46  and  47  to bring the various servicing components into contact with the printheads  54 ,  56 . The frame lower portion  64  preferably defines a waste ink reservoir or spittoon  68 , which receives ink purged from the printheads  54 ,  56  in a spitting routine.  
         [0026]    The service station  44  includes an optical environmental factor detection system  70  constructed in accordance with the present invention, here shown as being mounted along an outboard wall  72  of the lower frame  64 . As used herein, the term “inboard” refers to items facing toward the printzone  25 , and the term “outboard” refers to items facing away from printzone. First an explanation of the construction of the environmental factor detection system  70  will be given, followed by a discussion of its operation. The optical environmental factor detection system  70  includes a platform  74  projecting outwardly from the outboard service station frame wall  72 . The platform  74  supports an optical environmental factor indicator member or card  75 , which changes its optical appearance in response to various changes in certain environmental factors, as described in further detail below.  
         [0027]    [0027]FIGS. 2 and 3 show the indicator card  75  open and exposed for reading. To keep the indicator card  75  clean during various printhead servicing routines, such as during a spitting routine where the printheads  54 ,  56  selectively eject or “spit” ink into the spittoon  68 , the detection system  70  may include an indicator cover member, such as a sliding cover  76 . Preferably the cover  76  is attached by a guide track, a rail and runner system, or other sliding linkage means to the platform  74  so the cover  76  may move in both the forward direction  46  and the rearward direction  47 .  
         [0028]    [0028]FIGS. 3 and 4 show how the cover  76  is moved from a retracted or rest position shown in FIG. 3, to an active or covering position shown in FIG. 4. In the illustrated embodiment, the pallet  45  is used to transition the cover  76  between these rest and activated positions. Preferably, the cover  76  has an engagement member, such as downwardly extending finger portion  80  which projects downwardly from cover  76  into the spittoon portion  68  of the service station  44 . To open the cover, the pallet  45  supports a first engagement member  82 , which is shown in FIG. 3 engaging the cover finger member  80  as the carriage  45  moves in the forward direction  46 . Located a selected distance away from the first member  82 , is a second engagement member  84  which also projects from the pallet  45  to engage the cover finger member  80 . As shown in FIG. 4, the second engagement member  84  has engaged the cover finger  80 , to move the cover  76  over the indicator card  75  as the pallet  45  moves in the rearward direction  47 .  
         [0029]    The exact distance used to separate the first and second engagement members  82  and  84  from one another depends upon the type of servicing which is desired to be done to the printheads  54 ,  56  while the indicator cover  76  is either open or closed. For instance, during spitting and printhead wiping using wipers (not shown) supported by the pallet  45 , preferably the cover  76  is closed (FIG. 4). During the capping operation, where the printheads  54 ,  56  are sealed by the black and color caps  60 ,  62  during periods of printer inactivity, it would be desirable to have the cover  76  be open, to expose the indicator card  75  for reading (FIG. 3).  
         [0030]    To read indicia on the indicator card  75 , preferably the optical environmental factor detection system  70  includes an optical sensor  85 , such as the monochromatic optical sensor described in U.S. Pat. No. 6,036,298, currently assigned to the present assignee, the Hewlett-Packard Company. The illustrated optical sensor  85  includes a body  86 , which in the illustrated embodiment is supported by an outboard side wall of the printhead carriage  40 . The body  86  houses several components, including an illuminating element  88 , such as a blue or violet-blue light emitting diode (“LED”). The body  86  also houses a photo sensor  90 , along with optional electronics for the photo sensor, such as an amplifier  92 . The photo sensor  90  receives light through a lens element  94 , with the field of view of light passing to lens  94  being limited by a window, or F-stop  95 . Optionally, an optical filter (not shown) may be placed in the F-stop window  95 . The sensor body  86  may also house additional illuminating elements of different colors, along with additional photo sensors and related lens elements, etc., such as one photo sensor for monitoring diffractive reflection from the card  75 , and another photo sensor for monitoring spectral reflection from the card  75 . FIG. 3 shows the LED element  88  illuminating the indicator card  75  with an illuminating beam  96 . The illuminating beam  96  impacts the indicator card  75 , and then reflects off the card to form a reflected beam  98 , which passes through any optical filter element, through the F-stop  95 , and through lens  94 , before being received by the photo sensor  90 .  
         [0031]    The optical environmental factor detection system  70  described thus far, may be considered as a static detection system, because the printhead carriage  40  remains fixed in a stationary location while viewing the indicator  75 . FIG. 1 shows an optional alternative embodiment, a moving optical environmental factor detection system  70 ′ may be employed instead of, or in conjunction with, the detection system  70 . In the illustrated movable detection system  70 ′, an optical environmental indicator member or card  100  is mounted in the printzone  25  to a portion of the media support system, here shown as a platen  102 . In the illustrated embodiment, the indicator card  100  is located toward the far left of the platen  102 , remote from the service station  44 , to avoid having the indicator card  100  become contaminated with ink aerosol generated by printheads  54 ,  56  during spitting routines over the service station spittoon  68 . Preferably, the indicator card  100  is mounted along the platen  102  in a position where the optical sensor  85  will pass over the indicator card when slewing or reciprocating back and forth across the printzone  25  in the direction of the scanning axis  38 .  
         [0032]    [0032]FIG. 5 illustrates one form of the indicator card  75 , constructed in accordance with the present invention. Preferably the indicator card  75  has a backing layer  104  which is adhered or bonded to the support platform  74 . In some embodiments, the backing layer  104  may be impregnated with various concentrations of a material which reacts to changes in the temperature, relative humidity, or other environmental factors. For instance, to detect changes in the relative humidity, the illustrated backing layer  104  may be constructed of a porous media, such as of a blotter type of paper which has been impregnated with a known concentration of cobalt chloride solution, such as indicated in FIG. 5 by sensor block  106 . By monitoring the color changes of a single block  106 , which in the illustrated example transitions from a blue color if the humidity is lower than a selected reference value, through a lavender (“Lav.”) color near the known value, to a pink color when the humidity is above the known value, as indicated in Chart  1  below where the known value is indicated as X % of relative humidity.  
                                     CHART 1                           Color of Sensor Block 106                Humidity:   Dry   X %   Humid                       Sensor 106:   Blue   Lavender   Pink                      
 
         [0033]    In Chart 1 above, the terms “dry” and “humid” are used to assist the reader in understanding which end of the scale refers to which condition. For instance, a “dry” condition normally is associated with a desert environment, whereas a “humid” condition normally being associated with a tropical environment, although it is apparent that during a cloud burst a desert may become a very humid environment for a short period of time.  
         [0034]    A further increase in accuracy may be obtained by adding a second cobalt chloride indicia  107  to the backing layer  104 , here selected to react at a different relative humidity than the first indicia  106 . For instance, if the indicia  107  reacted at a higher relative humidity than indicia  106 , for instance, at a value of Y %, then the color changes of indicia  106  and  107  with respect to changes in the relative humidity may be as indicated below in Chart 2.  
                                             CHART 2                           Color of Sensor Blocks 106 &amp; 107                Humidity:   Dry   X %   X-Y %   Y %   Humid                       Sensor 106:   Blue   Lav.   Pink   Pink   Pink           Sensor 107:   Blue   Blue   Blue   Lav.   Pink                      
 
         [0035]    Indeed, greater degrees of accuracy and humidity measurement may be obtained by adding a third indicia  108  to the indicator card  75 . If this third indicia  108  were formulated with a cobalt chloride concentration to react in a higher humidity than either indicia  106  or  107 , for instance, at a relative humidity of Z %, then the operation of the indicator card  75  is as shown in Chart 3 below.  
                                                 CHART 3                           Color of Sensor Blocks 106-108            Humidity:   Dry   X %   X-Y %   Y %   Y-Z %   Z %   Humid               Sensor 106:   Blue   Lav.   Pink   Pink   Pink   Pink   Pink       Sensor 107:   Blue   Blue   Blue   Lav.   Pink   Pink   Pink       Sensor 108:   Blue   Blue   Blue   Blue   Blue   Lav.   Pink                  
 
         [0036]    Additional indicia may be added to the indicator card  75 , although in the illustrated embodiment where the indicator card  75  is mounted stationarily to the service station support platform  74 , the amount of physical room available for viewing these indicia  106 - 108  is limited in a practical sense in the illustrated embodiment by a field of view  110 , as indicated in dashed lines in FIG. 5, which is established by the optical sensor field stop  95 . In the illustrated embodiment, the current commercial embodiment of one preferred optical sensor  85  may be of the same construction as that sold in the DeskJet® 990 model color inkjet printer by the Hewlett-Packard Company. The illustrated sensor  85  has a field of view  110  based on the size of the window opening of F-stop  95 , which is on the order of 1 mm (millimeter) by 2 mm.  
         [0037]    In our first example for indicator card  75 , where only a single indicia  106  was used (see Chart 1 above), preferably the indicia  106  spans to cover the entire field of view  110  of the optical sensor  85 . Similarly, if only two indicia  106  and  107  were placed on the indicator card  75 , their shape and position are expanded to encompass the greatest portion of the field of view  110 . FIG. 5 illustrates the field of view  110  for a three indicia card  75  having indicia  106 - 108 . The overlap of the indicia  106 - 108  beyond the edges of the field of view  110  are provided to minimize any reflectance from the backing layer  104 , and to thereby provide a more accurate reading to the photo sensor  90 .  
         [0038]    Similarly, for the moving carriage optical environmental factor detection system  70 ′, one embodiment of an indicator card  100  is shown in FIG. 6, as having a backing layer  112 . In this illustrated embodiment, the backing layer  112  is a sheet of cardstock, which has an under surface coated with an adhesive layer that is bonded to the platen  102 , as shown in FIG. 1. In the illustrated embodiment, the backing layer  112  has an upper surface to which are bonded a series of indicator blotter paper cutouts  114 ,  115 ,  116 ,  117  and  118 , with each indicia or indicator spot  114 - 118  being saturated with a different concentration of cobalt chloride to detect gradual changes in humidity. For instance, stepwise changes in relative humidity between adjacent indicia may be 5%, 10%, 15%, 20%, etc. depending upon the particular implementation. Moreover, equal steps between each of the indicia  114 - 118  are not required if the printing systems of printer  20  are not sensitive over certain bandwidths. For instance, only under very dry conditions on the order of 10-20% relative humidity, or under very humid conditions on the order of 80-90% relative humidity, the print routines may be affected, while conditions between these extremes, for instance on the order of 30-70% relative humidity, are considered to be in a normal operating range, where print modes are unaffected by humidity. In such an example, indicia  114  may be impregnated to change color at 10% relative humidity, indicia  115  at 20% relative humidity, indicia  116  at 50% relative humidity, indicia  117  at 80% relative humidity, and indicia  118  at 90% relative humidity.  
         [0039]    In this 10/20/50/80/90% relative humidity example for constructing the indicator card  100 , the carriage  40  moves the optical sensor  85  sequentially over each of the indicia  114 - 118 , or in reverse order from indicia  118  to indicia  114 , looking for a color change from pink to blue to find a lavender transition region indicating the current relative humidity. For instance, if the optical sensor  85  found that the indicia  114 ,  115  and  116  were all of a pink color, indicia  117  was of a lavender color, and indicia  118  was of a blue color, then the controller  35  interprets the ambient conditions to be at 80% relative humidity. At this higher (80%) humidity, printing routines may be slowed to allow more time for volatiles within the inks to dry. Additionally, a time delay may be inserted between printing sheets in a multiple sheet print job, allowing a previously printed sheet to dry before the next sheet is dropped upon it in the output tray  30  to avoid smearing the earlier printed sheet. This delay or dry time may be adjusted, such as by increasing the dry time delay in high humidity conditions and decreasing the dry time delay in low humidity conditions. In an inkjet printing mechanism having auxiliary drying capability, such as in printers having internal heaters, additional heat may be applied in high humidity conditions to speed drying of the ink and reduce the drying time to a shorter interval.  
         [0040]    As another example, if instead the indicia  115  was lavender, and indicia  114  was of a pink color, and indicia  116 - 118  were of a blue color, then the controller  35  interprets this information from sensor  85  as being 20% relative humidity. Under these relatively dry (20%) conditions, print speeds may be increased because dry conditions allow the volatiles within the inks to dry more quickly. For instance, during duplex printing operations, where there is normally a seven second delay time between printing a first side of a sheet and a second side, the delay time may be decreased from a nominal seven second delay time to three or four seconds.  
         [0041]    Thus, by allowing the printer controller  35  to understand through the use of the environmental factor detection system  70 ,  70 ′ that the printer is in a humid environment, in this example above 80% humidity, print quality is increased by allowing additional dry time for the inks on multiple page print jobs. Similarly, by allowing the controller  35  to know the printer is in a relatively dry environment, here less than 20% relative humidity, throughput is increased by eliminating some of the additional dry time required during nominal conditions especially in duplex printing. Of course, the controller  35  uses carriage positional feedback information, such as from the conventional encoder system mentioned above, to interpret which of the indicia  114 - 118  the optical sensor  85  is currently viewing. Moreover, while circular indicia  114 - 118  are illustrated in FIG. 6, and rectangular indicia  106 - 108  are shown in FIG. 5, it is apparent that either of these indicia shapes, or other shapes, may be used in various implementations.  
         [0042]    While thus far, the illustrated embodiments have been described in terms of humidity sensors, it is apparent that the indicator card  75 ,  100  may be constructed to measure other environmental factors, such as temperature. For measuring changes in temperature, the blotter material of indicia  106 - 108 ,  114 - 118  may be impregnated with thermochromatic materials which change color in response to temperature changes. Alternatively, the indicator cards  75 ,  100  may carry a cholesteric liquid crystal temperature sensitive material which changes appearance in response to color changes, which are commercially available. For instance, some of these liquid crystal temperature indicator strips change from a black to a white color so the temperature value is readable against a white background, with all other temperature values being blacked out. Thus, the optical sensor  85  would detect the position of the white band parallel to the scan axis  38 , then the controller  35  would correlate the location of the white band with the ambient temperature, with the location versus temperature relationship being previously stored or calibrated in the controller&#39;s memory.  
         [0043]    One flaw of the currently available humidity indicator cards studied thus far is their tendency to wash out when exposed to humidities in excess of 90% over a period of 36 hours or longer. Such a circumstance could be read by the optical sensor  85  and communicated to controller  35 . Upon receiving information that the indicator card  75 ,  100  has washed out, that is, turned a whitish-pink color, depending upon the color of indicia  114  the controller  35  may then alert an operator of this condition, and/or default to the nominal printing routine using a worst case assumption that the printer  20  is permanently located in a humid environment, thereby sacrificing printing speed and throughput in favor of maintaining high print quality.  
         [0044]    Another drawback of the currently available indicator cards  75 ,  100  is the temperature sensitivity of the indicia  106 - 108 ,  114 - 118 . For instance, at temperatures of 75° F. (22° C.) the currently available indicia have an accuracy of within +/−5%. At other temperatures, a small correction factor of 2.5% for each 10° F. (5.5° C.) temperature variation higher or lower than 75° F. may be taken into consideration by the controller  35 , assuming the controller has a temperature input. For instance, at higher temperatures the indicia  106 - 108 ,  114 - 118  indicate a lower humidity than is actually the case, while at lower temperatures, higher humidities than ambient are indicated. As mentioned above, ambient temperature sensing may be accomplished using temperature sensing resistors onboard the printheads  54 ,  56 . Alternatively, a temperature sensitive indicator card may be supported by platen  102 , either instead of or in addition to, the humidity indicator card  100 . As another alternative embodiment, the indicator card  100  may be fashioned with temperature sensitive indicia  114 - 118 , with humidity being measured at the stationary indicator card  75 . Thus, optical measurements of the temperature may be made by sensor  85 , followed by humidity measurements which are then adjusted by controller  35  according to the ambient temperature if needed.  
         [0045]    Furthermore, while the indicia  106 - 108  and  114 - 118  have been described in terms of changing color or hue in response to various changes in the ambient environmental conditions, it is apparent that indicia having other properties which change according to these environmental conditions may also be used. For instance, the indicia may get lighter or darker in response to changing environmental conditions. As another example, the indicia may have surface property characteristics which change in response to changing environmental conditions. For instance, if the indicator card  75 ,  100  had indicia which transitioned between a smooth state under dry conditions, and a wrinkled or ruffled state when humid, then these various changes in surface characteristics may also be monitored by the optical sensor  85 . Other indicia carried by indicator cards  75 ,  100  may include those which change opacity, roughness, reflectance, saturation, shade and the like. Moreover, while changing of colors has been described with respect to colors which are visually observable to the human eye, the color change may be in ranges beyond those perceivable to humans, such as colors in the infrared and ultraviolet range, as long as the optical sensor  85  is calibrated to detect such color changes.  
         [0046]    Given the current state of the art in the surface mounted humidity indicator field, color change accuracies of the indicia  106 - 108 ,  114 - 118 , are within +/−5% relative humidity. In some instances, upon paying of a premium, tighter quality controls may be implemented and these accuracies may be decreased to +/−3% relative humidity. As mentioned in Introduction section above, the earlier capacitive humidity sensors are currently available at a cost of approximately several dollars each not including the cost of their support electronics while voltage output humidity sensors cost about ten dollars each. In contrast, using the illustrated indicator cards  75 ,  100 , and buying in quantities, the cost of each indicator card may be on the order of 5-15 cents, which imposes very little additional cost on the overall printer  20 , while at the same time greatly improving performance. Moreover, if the optical sensor  85  is already installed in the printing unit for monitoring the media and/or ink droplets printed on a page, there is no additional cost associated with adding the optical sensor as an indicator card reader.  
         [0047]    There are various advantages associated with either the stationary environmental factor detection system  70 , as well as with the moving environmental factor detection system  70 ′. In the moving detection system  70  ′, higher resolution may be obtained by increasing the number of indicia on the indicator card  100 , or by providing several indicator cards having different calibrations. Furthermore, the moving system  70 ′ using a humidity sensor indicator card  100  is able to obtain dry time information more quickly than the stationary system  70  because there is no need to traverse the sensor  85  into the servicing region  42 . Furthermore, the moving detection system  70 ′, as well as the stationary system  70 , using indicator card  100  gives information which is useful for calibrating the spit time required following uncapping of the printheads  54 ,  56  by caps  60 ,  62 .  
         [0048]    In contrast, the stationary optical environmental factor detection system  70  may operate to collect environmental data over time, storing this data within a storage portion of controller  35 . This monitoring of the various environmental factors by the stationary system  70  is advantageously accomplished without requiring the carriage  40  to move. Specifically, by obtaining a humidity history using the stationary sensor  70 , the water vapor transfer rate may be calculated to accommodate for evaporation of the inks from within pens  50 ,  52  over time. This water vapor transfer rate, in addition to counting the number of droplets fired by each printhead  54 ,  56  may be used to predict the amount of ink remaining in each of the pens  50 ,  52 . Thus, a capping history of environmental conditions, here humidity, while the pens have been capped may be gathered. For example, under higher humidity conditions, the printheads  54 ,  56  are less susceptible to clogging. Thus, under high humidity conditions fewer drops need to be expended during pre-printing spitting routines.  
         [0049]    As mentioned in the Introduction section above, low humidity conditions also contribute to hue shift problems, where various components of the ink, such as water or volatiles, evaporate or dissipate over time, for instance by leaking at the printhead/cap sealing interface or through ink delivery tubing in off axis printing systems. If the controller  35  has a record of the changes in the ambient humidity, and knows the rates of evaporation overtime under these humidity conditions, the controller may estimate the change(s) in ink composition over the lifetime of an ink supply. Knowing these changes in the ink composition over time, the controller  35  may then compensate for these changes by conducting vapor transfer rate calculations, for instance, by printing fewer dots per unit area for an aged printhead having a higher concentration of dyes or colorants due to evaporated volatiles. Thus, the controller may compensate for these ink composition changes to allow for hue adjustment based on calculated dye load changes over time within the inkjet cartridges. Furthermore, this evaporation information may be used by the controller  35  to more accurately predict an upcoming out of ink condition when used in conjunction with a drop-counting or other system for anticipating when the pens  50 ,  52  may run dry. For instance, a simple drop-counting routine may indicate an abundant ink supply remains and fail to give an operator any warning, while in reality, the pen is nearly dry due to evaporation and a warning should be given to tell the operator to have a replacement cartridge on hand.  
         [0050]    Additionally, use of either the stationary system  70  or the moving system  70 ′ allows the various print modes to be adjusted based on environmental conditions. As mentioned above, during duplex printing jobs throughput may be adjusted to correspond to the various changes in ambient temperature and humidity, to increase throughput and/or improve print quality over results obtained using nominal or worst case assumptions about environmental conditions. Furthermore, using the stationary detection system  70  equipped for humidity monitoring allows for variations in the pre-print mode servicing routines, as well as other servicing routines performed during print jobs. For example, under dry conditions the nozzles of both of the printheads  54 ,  56  are more subject to clogging, so to accommodate for this, pre-print spitting routines may be more vigorous than required under nominal conditions. Additionally, knowing this various information about environmental factors influencing printer  20  may allow for more accurate line feed calibration, which refers to the advancing of the media through the printzone  25 . Line feed calculations may be impacted by expansion and contraction of the media path encoder disk, which is used to track the movement of the media through the printzone  25 . In some embodiments, the encoder disk may absorb water so in a humid environment the disk expands, adding a nominal offset to the timing of the counts as an optical sensor reads equally-spaced radial lines appearing near the disk periphery. Additionally, other media movement path components, such as drive rollers, may change shape or enlarge due to high ambient moisture conditions, impacting line feed accuracy for longer media advances which are more sensitive to runout errors in both the drive rollers and in the encoder feedback system.