Patent Publication Number: US-8123327-B2

Title: Method and apparatus to adjust distance calculations

Description:
BACKGROUND 
     In order for a printer to create high-quality images, movement of paper and other types of media through the printer should be precisely measured and controlled. An optical sensor configured to capture images and calculate distances can be used to measure advancement of media in the printer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate various embodiments and are a part of the specification. The illustrated embodiments are merely examples and do not limit the scope of the claims. Throughout the drawings, identical reference numbers designate similar, but not necessarily identical elements. 
         FIG. 1  is a schematic diagram illustrating one embodiment of an apparatus to adjust distance calculations, incorporated in an inkjet printer. 
         FIG. 2  is a schematic diagram illustrating one embodiment of an apparatus to adjust distance calculations, incorporated in an inkjet printer. 
         FIG. 3  is a graph depicting example relationships between the temperatures of a first portion of an optical sensor and a second portion of the optical sensor during various thermal states. 
         FIGS. 4-5  are exemplary flow diagrams of steps taken to adjust distance calculations according to various embodiments. 
     
    
    
     The same part numbers designate the same or similar parts throughout the figures. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In some printers an optical sensor that measures media advances operates in an environment in which there are significant temperature changes and high temperatures. For example, a printer utilizing latex inks may utilize internal heaters to heat media so as to dry and cure ink on the media. Heating the media can cause the optics of the optical sensor in the printer to deform, resulting in errors in calculated distances. Such distance calculation errors in turn may result in erroneous media advances. The erroneous media advances can lead to gaps, overlaps and banding in printed output and other quality issues. 
     Embodiments of a method and apparatus to adjust distance calculations were developed in an effort to reduce distance calculation errors attributable to optics deformation in an optical sensor. Embodiments are described with reference to an inkjet printer. The embodiments shown in the accompanying drawings and described below, however, are non-limiting examples. Other embodiments are possible and nothing in the accompanying drawings or in this Detailed Description of Embodiments should be construed to limit the scope of the disclosure, which is defined in the Claims. 
       FIG. 1  is a schematic diagram illustrating one embodiment of an apparatus to adjust distance calculations, incorporated in an inkjet printer. In the exemplary embodiment the printer includes a media advance mechanism  2 , to transport media  4  over a platen  6  and beneath a printhead  8  that is situated above the platen  6 . The printhead  8  is configured to eject droplets of ink onto the media  4 . In the exemplary embodiment, the printer includes a heat source  10  situated above the platen  6 , to raise the temperature of the media  4  to cause ink that has been ejected onto the media  4  to dry and cure. In an embodiment, the heat source  10  is a heat lamp configured to heat the media  4  to a temperature of approximately fifty-five degrees C. In the exemplary embodiment, a first temperature sensor  12  connects to the underside of the platen  6  to take temperature measurements of a first portion  16  of an adjacent optical sensor  18 . The optical sensor  18  and the first portion  16  of the optical sensor are described in detail in the following paragraphs. In the exemplary embodiment, the first temperature sensor  12  electronically connects to a controller  20 . 
     An optical sensor  18  is situated beneath an opening in the platen  6 , such that there is a line of sight between the optical sensor  18  and a target  22  on the media  4  to be tracked. In an embodiment a physical aspect of the media  4  constitutes the target  22 , such that no printed tracking patterns or artificial marks are required to be made on the media  4 . Such physical aspects of the media  4  may include small scale (e.g. microscopic) features in the surface of the media  4 . The optical sensor  18  is configured to capture a series of digital images of the target  22  at known intervals that can be sent to a controller  20  for calculating a distance that the target  22  advances. The optical sensor  18  according to this exemplary embodiment includes an optical module  24 , a window  26  and an image sensor module  28 . 
     In the exemplary embodiment the optical module  24  includes a first portion  16  and a second portion  30 , the first portion  16  being closer to a heat source  10  than the second portion  30 . Both the first and second portions hold optics  32  to focus images onto an image sensor  34 . The optical module  24  also includes an array of light-emitting diodes (LEDs) to provide adjustable and uniform illumination to the target  22 . The window  26  is a hardened transparent surface that allows the LEDs&#39; light to reach the target  22 , and allows reflected light to reenter the optical sensor  18 . The hardened transparent surface may be in contact with the side of the media  4  that is opposite of the media side that faces the printhead  8 . The image sensor module  28  holds an image sensor  34 , and electronics that control the operation of the optics  32 , the LEDs and the image sensor  34 . The image sensor  34  is configured for high-speed digital imaging and fast data transfer. In an embodiment a second temperature sensor  36  is embedded in the image sensor module  28 , to take temperature measurements of the second portion  30  of the optical sensor  18 . In the exemplary embodiment illustrated in  FIG. 1 , the second temperature sensor  36  electronically connects directly to the controller  20 . 
     In the exemplary embodiment, the optical sensor  18  electronically connects to the controller  20 . The controller  20  is configured to compensate for non-uniform optics deformation by adjusting distance calculations regarding the distance the target  22  travels by a compensation factor that is a function of temperatures measured by the first and second temperature sensors at the time of the distance calculation. The controller  20  in turn utilizes the adjusted distance calculations to precisely control the printer&#39;s media advance mechanism  2 . As used in this specification and the appended claims, “controller” suggests a processor  38  and a memory  40 . The processor  38  may represent multiple processors, and the memory  40  may represent multiple memories. In an embodiment, the controller may include a number of software components that are stored in a computer-readable medium, such as memory, and are executable by processor. In this respect, the term “executable” means a program file that is in a form that can be directly (e.g. machine code) or indirectly (e.g. source code that is to be compiled) performed by the processor. An executable program may be stored in any portion or component of memory. 
     In the preceding paragraphs embodiments are described with reference to an inkjet printer. Other embodiments are possible. In an embodiment the apparatus may be incorporated in a laser printer or any other printer. In an embodiment, the apparatus may be incorporated in a sheet-fed scanning device having a media advance mechanism. In an embodiment, the apparatus may be incorporated in a flatbed scanning device having a mechanism for advancing a scan head. In an embodiment the apparatus may be incorporated in a microscope having a mechanism for advancing a slide or an object to be viewed or measured. In an embodiment the apparatus may be incorporated in a precision microelectronic assembly machine having a mechanism for advancing an assembly or components to be placed, assembled or measured. 
       FIG. 2  is a schematic diagram illustrating one embodiment of an apparatus to adjust distance calculations, incorporated in an inkjet printer. The exemplary embodiment is structurally similar to the embodiment illustrated in  FIG. 1 , except as described in the following two paragraphs. 
     The exemplary embodiment depicted in  FIG. 2  includes and utilizes a first controller  42  and a second controller  44 , rather than a single controller  20  as depicted in  FIG. 1 . In the exemplary embodiment a first controller  42  electronically connects to the image sensor  34 , to a second temperature sensor  36  and to a second controller  44 . In the exemplary embodiment, the first controller  42  is configured to receive from the optical sensor  18  a series of digital images of the target  22  captured at known intervals, to calculate a distance that the target  22  advances utilizing the images, and to pass the distance calculation to a second controller  44 . In the exemplary embodiment, the first controller  42  is also configured to receive temperature measurements of the second portion  30  of the optical sensor  18  from the second temperature sensor  36 , and to pass them on to the second controller  44 . 
     In the exemplary embodiment a second controller  44  electronically connects to the first controller  42 , to the first temperature sensor  12  and to the media advance mechanism  2 . The second controller  44  is configured to receive a distance calculation regarding the distance the target  22  travels, and temperature measurements of the second portion  30  of the optical sensor  18 , from the first controller  42 . The second controller  44  is also configured to receive temperature measurements of the first portion  16  of the optical sensor  18  from the first temperature sensor  12 . The second controller  44  is configured to compensate for non-uniform optics deformation by adjusting the distance calculation by a compensation factor that is a function of temperatures measured by the first and second temperature sensors at the time of the distance calculation. The second controller  44  is additionally configured to in turn utilize the adjusted distance calculations to precisely control the printer&#39;s media advance mechanism  2 . 
     In an embodiment, the first temperature sensor could be external to the optical sensor  18 , for example coupled to a platen  6 , to take temperature measurements of a first portion  16  of the optical sensor  18 . In an embodiment, the first temperature sensor could be coupled to, or embedded in, the optical sensor  18 . In an embodiment, the second temperature sensor  36  could be coupled to, or embedded in, or external to the optical sensor  18 . 
       FIG. 3  is a graph depicting example relationships between the temperatures of a first portion  46  of an optical sensor and a second portion  48  of the optical sensor during various thermal states. In an embodiment, multiple temperature measurements may be utilized to determine a thermal state of the optical sensor in effect at the time the distance is calculated, the thermal state to be considered when applying a compensation factor to adjust distances. 
     Determining a thermal state may include a comparison of rates of temperature change within the first and second portions. In an example, temperature readings of the first portion  46  and the second portion  48  of an optical sensor may be analyzed to determine that the optical sensor is in one of the following thermal states: a start-up state  50 , a first transient state  52 , a steady state  54 , a cool-down state  56  and a second transient state  58 . 
     In an embodiment, the start-up state  50  is a state in which the temperatures of the both the first and second portions are lowest and closest to ambient temperature in comparison to the other states, suggesting a device incorporating the optical sensor has just been turned on. In an embodiment, the first transient state  52  is a state following start-up in which the temperatures of the both the first and second portions are increasing, the temperature of the first portion  46  is greater than that of the second portion  48 , and the temperature of the first portion  46  is increasing more rapidly than that of the second portion  48 . In an embodiment, the steady state  54  is a state in which the temperatures of both the first and second portions are increasing, the temperature of the first portion  46  is greater than that of the second portion  48 , and the temperatures of the first and second portions are increasing at approximately the same rate. In an embodiment, the cool-down state  56  is a state in which the temperatures of both the first and second portions are decreasing, suggesting that a device incorporating the optical sensor is in a standby mode in which no heat is being applied and a distance is not being calculated. In an example the temperatures reach a floor of approximately thirty-seven degrees C. during the cool-down state  56 . In an embodiment, the second transient  58  is like the first transient state  52  except that it follows a cool-down state  56  rather than start-up, and therefore the difference in the rates of change as between the first and second portions is not as large as in the first transient state  52 . 
     In an embodiment, knowledge of the previous thermal state may be helpful in identifying a current thermal state. For example, when determining whether an optical sensor is in a first transient or a second transient state  58 , it may be helpful to have the knowledge that the previous state was a start-up state. In this example, such knowledge of the previous state may help lead to a conclusion that increasing temperature measurements in the first and second portions indicate a first transient state  52 . 
     In an embodiment, a printer&#39;s controller may be configured to consider thermal states in applying a compensation factor to adjust distance calculations. In the exemplary embodiment such a controller might utilize a first transient state  52 , a steady state  54 , and a second transient state  58  to generalize temperature characteristics of the optical sensor at different times as these are states in which printing processes may take place. In this embodiment the controller may not utilize the start-up and cool-down thermal states in applying a compensation factor, as the start-up and cool-down states suggest that the printer that incorporates the optical sensor is in a standby mode. 
       FIGS. 4-5  are exemplary flow diagrams of steps taken to adjust distance calculations according to various embodiments. In discussing  FIGS. 4-5 , reference may be made to the diagrams of  FIGS. 1-2  and the chart of  FIG. 3  to provide contextual examples. Implementation, however, is not limited to those examples. 
     Starting with  FIG. 4 , a distance that a target moves is calculated utilizing an optical sensor (step  60 ). Referring back to  FIG. 1 , the controller  20  may be responsible for implementing step  60  utilizing images captured by optical sensor  18 . Referring back to  FIG. 2 , the first controller  42  may be responsible for implementing step  60  utilizing images captured by optical sensor  18 . In an embodiment, calculating the distance that the target moves may include the following steps: a first image of the target is captured by the optical sensor; a second image of the target is captured by the optical sensor at a known interval; and the distance that the target moves is calculated considering the first image, the second image, and the known interval. In an embodiment the calculation includes analyzing the first and second image to measure any movement of the target that is different from the known distance interval. In another embodiment, the known interval may be a time interval. 
     Continuing with the flow diagram of  FIG. 4 , a first temperature of a first portion of the optical sensor is measured at the time of the distance calculation (step  62 ). Referring back to  FIG. 1-2 , the first temperature sensor  12  may be responsible for implementing step  62 . A second temperature of a second portion of an optical sensor is measured at the time of the distance calculation (step  64 ). Referring back to  FIG. 1-2 , the second temperature sensor  36  may be responsible for implementing step  64 . 
     Continuing with the flow diagram of  FIG. 4 , the distance is adjusted by a compensation factor that is a function of the first and second temperatures (step  66 ). Referring back to  FIG. 1 , the controller  20  may be responsible for implementing step  66 . Referring back to  FIG. 2 , the second controller  44  may be responsible for implementing step  66 . 
     The compensation factor should take into account that deformation of the optics may be not be uniform, and that the deformation can be predicted in light of the first and second temperature measurements. At least two phenomena may change magnification in an optical system: non-uniform thermal expansion of distances along the optical axis, and the lenses changing their refractive index or curvature by temperature. While the type and degree of such optics deformation may vary depending upon the thermal state that the optical sensor is in, it is possible to utilize an approximation that does not consider multiple thermal states to simplify implementation. In one example, a linear compensation factor (CF) may be used CF=A·(T u −ε·T b )+B. where T u  is the temperature in first portion of optical sensor, T b  is the temperature in second portion of optical sensor, and A, B and ε are constants for stateless approximation. 
     Moving on to  FIG. 5 , in a particular implementation, temperatures of first and a second portion of an optical sensor are measured at a plurality of times (step  68 ). Referring back to  FIG. 1-2 , the first temperature sensor  12  and second temperature sensor  36  may be utilized together to implement step  68  with the first temperature sensor  12  measuring temperatures of the first portion and the second temperature sensor  36  measuring temperatures of the second portion. In an embodiment, temperatures of the first and second portion are measured at all times that a device which incorporates the optical sensor is powered on, so as to provide temperature measurements during all phases of operation of the device and to be able to determine relevant thermal states. 
     Continuing with  FIG. 5 , a distance that a target moves is calculated utilizing the optical sensor (step  70 ). Referring back to  FIG. 1 , the controller  20  may be responsible for implementing step  70  utilizing images captured by optical sensor  18 . Referring back to  FIG. 2 , the first controller  42  may be responsible for implementing step  70  utilizing images captured by optical sensor  18 . A first temperature of a first portion of an optical sensor is measured at the time of the distance calculation (step  72 ). Referring back to  FIG. 1-2 , the first temperature sensor  12  may be responsible for implementing step  72 . A second temperature of a second portion of an optical sensor is measured at the time of the distance calculation (step  74 ). Referring back to  FIG. 1-2 , the second temperature sensor  36  may be responsible for implementing step  74 . 
     Continuing with the flow diagram of  FIG. 5 , the distance is adjusted by a compensation factor that is a function of the first and second temperatures and a comparison of the temperatures of the first and second portions measured at a plurality of times (step  76 ). Referring back to  FIG. 1 , the controller  20  may be responsible for implementing step  76 . Referring back to  FIG. 2 , the second controller  44  may be responsible for implementing step  76 . As the type and degree of such optics deformation may vary depending upon a thermal state that the optical sensor is in, it is possible to consider thermal states in the compensation factor to increase efficiency in adjusting distance calculations. Referring back to  FIG. 3 , a compensation factor that is a function of the first and second temperatures and a comparison of the temperatures of the first and second portions measured at a plurality of times may consider the thermal states described in  FIG. 3 . In one example, compensation factors for a first transient state, a steady state and a second transient state may be created and held in memory. A distance may be adjusted utilizing the compensation factor that is appropriate for thermal state that the optical sensor is in that state at the time that the distance is calculated. In an example, if the optical sensor is in the first transient state at the time the distance is calculated, the distance may be adjusted by a compensation factor that is created specifically for that first transient state. 
     In one example, a compensation factor for a first transient state is developed: 
                   CF     TR   ⁢           ⁢   1       ⁡     (       T   u     ,     T   b       )       =           K   1     ·     ⅆ     ⅆ   t         ⁢     (       T   u     -     T   b       )       +     D   1         ,     where   ⁢           ⁢     ⅆ     ⅆ   t               
is time derivative, T u  is the temperature in first portion of optical sensor, T b  is the temperature in second portion of optical sensor, and K 1 , and D 1  are constants. Such a compensation factor considers that optics magnification in this first transition state is changing mainly due to different expansions in the first portion and the second portion. Such a compensation factor also considers that the biggest magnification change occur at the beginning of this thermal state, when T u -T b  changes most rapidly.
 
     In one example, a compensation factor for a steady state is developed: CF SS (T u ,T b )=K s ·T u +D s , where T u  is the temperature in first portion of optical sensor, T b  is the temperature in second part of optical sensor, and K s , and D s  are constants. Such a compensation factor considers that while the optics&#39; focal distances may not change significantly in the steady state, the optics lenses&#39; refractive index and curvature may still be changing, at a rate proportional to that of temperatures T b  or T u . 
     In one example, a compensation factor for a second transient state, after a device&#39;s operation is stopped and resumed, is developed 
                   CF     TR   ⁢           ⁢   2       ⁡     (       T   u     ,     T   b       )       =           K   2     ·     ⅆ     ⅆ   t         ⁢     (       T   u     -     T   b       )       +     D   2         ,     where   ⁢           ⁢     ⅆ     ⅆ   t               
is time derivative, T u  is the temperature in first portion of optical sensor, T b  is the temperature in second portion of optical sensor, and K 2 , and D 2  are constants. Such a compensation factor is similar to the compensation factor for the first transient state, but the second transient state starts at higher temperatures than the first transient state, and with T b  very close to T u  throughout as compared to the first transient state.
 
     Although the flow diagrams of  FIG. 4-5  show specific orders of execution, the order of execution may differ from that which is depicted. For example, the order of execution of two or more blocks may be scrambled relative to the order shown. Also, two or more blocks shown in succession may be executed concurrently or with partial concurrence. All such variations are within the scope of the preceding description. 
     The preceding description has been presented only to illustrate and describe embodiments and examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.