Patent Publication Number: US-7596328-B2

Title: Efficient sensing system

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   This invention relates to sensors. Specifically, the present invention relates to systems and methods for facilitating efficient sensing of objects or conditions, such as sensing print media, a print media path, and/or a print media position or edge thereof in a printer. 
   2. Description of the Related Art 
   Sensors, such as print media sensors, are employed in various demanding applications including sensing when a printer is out of paper and sensing paper location. 
   Accurate and efficient sensors are particularly important in edge-to-edge printing systems, also called full-bleed or zero-margin printing systems, which require very accurate paper edge detection and location. If a paper edge is inaccurately located, the image may extend beyond the paper edge, or undesirable strips may occur between the image and the edge of the page. 
   Conventionally, sensors positioned along a print media path are periodically polled to facilitate print media edge-detection. However, when no print media is present in the paper path, or when the media is present but not near the trailing edge, excess sensor polling consumes valuable printer processing time. Consequently, less printer processor/firmware time is available for performing other important printing tasks. 
   Hence, a need exists in the art for an efficient system and method for reducing excess sensor polling. 
   SUMMARY OF THE INVENTION 
   The need in the art is addressed by the efficient sensing system of the present invention. In the illustrative embodiment, the inventive sensing system is adapted for use in detecting print media edges in printing applications. The system includes a first mechanism for sensing and a second mechanism for sensing. A third mechanism selectively polls the second mechanism upon receipt of a signal from the first mechanism. 
   In a specific embodiment, the first mechanism includes an early warning sensor and the second mechanism is an accurate sensor. In the specific embodiment, the system further includes a controller in communication with the accurate sensor and the early warning sensor. The controller samples the sensor at the sampling rate in response to the signal. The controller includes a mechanism for increasing the sampling rate in response to the signal when the signal indicates detection of the object or condition by the early warning sensor. The early warning sensor includes a first emitter that transmits a first beam toward a detector. The first beam is associated with a first sensing region. The accurate sensor includes a second emitter that transmits a second beam toward the detector. The second beam is associated with a second sensing region. 
   In a more specific embodiment, the object or condition includes a leading edge or trailing edge of print media. The first sensing region is positioned before the second sensing region in a print media path associated with the print media. The controller further includes a mechanism for adjusting a sampling rate of the early warning sensor based on a signal received via the accurate sensor. 
   The novel design of sensing systems constructed in accordance with teachings of the present invention is facilitated by use of the early warning sensor and, in some embodiments, the use of a single detector to implement both the early warning sensor and the accurate sensor. In particular, use of the early-warning sensor in combination with the accurate edge sensor may reduce overall sensor polling while maintaining very accurate print media edge-detection. Higher frequency polling of an accurate edge-sensor may be performed when a print media edge is approaching as determined by the early-warning sensor, which may be polled at an efficient, low frequency. In addition, possible edge-detection accuracy by the accurate media edge sensor may be enhanced, since the media edge-sensor may be polled at a higher frequency than would other wise be possible. In previous edge-detection systems, very high frequency polling of an edge-sensor could consume excessive system resources at the expense of critical printing functions. Furthermore, in some embodiments or implementations of the present invention, use of a single detector to implement two sensors may minimize system costs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of a printer employing a print media edge-detection system constructed in accordance with the teachings of the present invention. 
       FIG. 2  is a diagram of a printer employing an alternative embodiment of the media edge-detection system of  FIG. 1 . 
   

   DESCRIPTION OF THE INVENTION 
   While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
     FIG. 1  is a diagram of a printer  10  employing a print media edge-detection system  12  constructed in accordance with the teachings of the present invention. For clarity, various components, such as power supplies, operating systems, various rollers, electrophotographic drums or print heads, and so on, have been omitted from the figures. However, those skilled in the art with access to the present teachings will know which components to implement and how to implement them to meet the needs of a given application. 
   The edge-detection system  12  includes a media edge-detection application  14 , which may be implemented in hardware, software, and/or firmware. The media edge-detection application  14  runs on a printer controller  16 , which is often called the printer processor. The media edge-detection application  14  communicates with a detector  18 . The detector  18  receives optical input from a first emitter Light Emitting Diode (LED  1 )  20  and a second LED (LED 2 )  22 , which are connected to and receive control input from the media edge-detection application  14 . 
   In the present specific embodiment, the first LED  20  is positioned to direct a first optical beam  24  across a paper path  26  to a reflecting mirror  44  on an opposite side of the paper path. The first optical beam  24  then reflects back across the paper path  26  to the detector  18 . The first optical beam  24  crosses the paper path  26  within a first sensing region  28 . Alternatively, the sensing system  12  may be configured to be responsive to light reflected off the print media  34  itself rather than the mirror  44  or other discrete reflector. 
   The second LED  22  is positioned on an opposite side of the paper path  26  from the detector  18  and directs a second optical beam  30  across the paper path  26  to the detector  18 . The second optical beam  30  passes through a second sensing region  32 , which is positioned after the first sensing region  28  along the paper path  26 . 
   The LED&#39;s  20  and  22  may be replaced with any applicable source for producing a beam of electromagnetic energy, such as any equivalent light source, without departing from the scope of the present invention. The detector  18  should be sensitive to the electromagnetic energy in the beams  24  and  30  and the beams  24  and  30  should be affected by the presence of the print media  34  in the sensing regions  28  and  32 . 
   The combination of the second LED  22  and the detector  18  represent an accurate media edge-detection sensor that accurately senses print media edges  38 ,  40  passing through the second sensing region  32 . Similarly, the combination of the first LED  20  and the detector  18  represent an early-warning sensor that provides early warning sensing of a leading edge  38  and a trailing edge  40  of print media  34  passing along the paper path  26 , which originated from an input paper tray  36 . The print media  34  exiting the print media path  26  and printer  10  becomes print media output  42 . 
   The locations of the sensing regions  28 ,  30  are application-specific and may be adjusted by one skilled in the art to meet the needs of a given application. Furthermore, use of additional lenses, prisms, mirrors, and so on, may be employed by those skilled in the art to enhance positioning flexibility of the LED&#39;s  20  and  22  and the detector  18  in the printer  10 . In addition, the LED&#39;s  20  and  22  may be replaced with other types of transmitters that transmit energy other than optical energy, such as infrared or microwave, without departing from the scope of the present invention. 
   In operation, print media  34  exits the input paper tray  36  in response to control signals (not shown) from the printer controller  16  in preparation for printing a desired image on the print media  34 . The leading edge  38  of the print media  34  is sensed early in the paper path  26  via the first LED  20  and detector  18 . The early warning sensor  18 ,  20  is polled by the media edge-detection application  14  at a relatively low frequency. 
   The accuracy with which a print media edge can be detected is related to the polling frequency of a sensor. Accuracy requirements for the early warning sensor  18 ,  20  are less stringent than the requirements for the media edge-detection sensor  18 ,  22 . Therefore, the requisite polling frequency of the early-warning sensor  18 ,  20  is relatively low compared to the polling frequency associated with the accurate media edge-detection sensor  18 ,  22 . 
   The media edge-detection application  14  receives different electrical signals output from the detector  18  in response to the different optical signals  24  and  30  from the first LED  20  and second Led  22 , respectively. The optical signals  24  and  30  are sufficiently distinct to facilitate detector output signal differentiation by the media edge-detection application  14 . The optical signals  24  may be distinct in terms of frequency, pulse rate, power level, amplitude modulation, specific times at which the optical signals are allowed to transmit, and so on. The media edge-detection application  14  may perform different tasks depending on which electrical signal (resulting from the first beam  24  and/or the second beam  30 ) is received, as discussed more fully below. 
   In the present embodiment, when the media edge-detection application  14  polls the early-warning sensor  18 ,  20 , it activates the first LED  20 , which then transmits the first optical signal  24  across the print media path  26  to the detector  18 . An interruption or change in the optical signal  24  received by the detector  18  in response to polling of the early-warning sensor  18 ,  20 , as measured by the media edge-detection application  14 , indicates that one of the print media edges  38  or  40  has arrived at the first sensing region  28 . Interruption of the electrical signal resulting from the first optical beam  24  is interpreted as an early warning signal from the detector  18  by the media edge-detection application  14 . Interruption of the electrical signal resulting from the second optical signal  30  is interpreted as an edge-detection signal by the media edge-detection application  14 . 
   Similarly, when the media edge-detection application  14  polls the accurate media edge-detection sensor  18 ,  22 , it activates the second LED  22 , which then transmits the second optical signal  30  across the print media path  26  to the detector  18 . An interruption or change in the second optical signal  30  indicates the detection of one of the print media edges  38  or  40 . 
   Alternatively, the LED&#39;s  20  and  22  may be constantly on. In this case, the output beams  24  and  30  are sufficiently distinct to enable the media edge-detection application  14  to determine when a print media edge  38  or  40  blocks one or more of the beams  24  and/or  30 . 
   When a print media edge  38  or  40  is detected by the early-warning sensor  18 ,  20 , or a predetermined time thereafter, polling of the early-warning sensor may stop, and polling of the accurate edge-detection sensor  18 ,  22  begins at a high frequency. The frequency at which the edge-detection sensor  18 ,  22  is polled depends on the desired edge-detection precision or accuracy for a given application. Higher frequency polling may result in more accurate media edge detection. 
   In the present specific embodiment, the accurate edge-detection sensor  18 ,  22  is only polled when the warning sensor  18 ,  20  indicates that one of the media edges  38  or  40  is approaching the second sensing region  32  associated with the edge-detection sensor  18 ,  22 . During times when the edge-detection sensor  18 ,  22  is not being polled, the early-warning sensor  18 ,  20  is polled at a slow, predetermined rate, thereby conserving printer processing resources. 
   In certain applications, the polling of the edge-detection sensor  18 ,  22  is not stopped entirely, but is merely slowed down until the early-warning sensor  18 ,  20  detects an incoming media edge. Actual sensor polling frequencies, and adjustments made to the polling frequency of the edge-detection sensor  18 ,  22  in response to the detection of an incoming media edge by the early-warning sensor  18 ,  20 , are application-specific and may be determined by one skilled in the art to meet the needs of a given application. 
   In cases where polling of the early-warning sensor  18 ,  20  is idle while polling of the accurate edge-detection sensor  18 ,  22  is active, the sensing regions  28  and  32  are spaced so that distance between the edges  38  and  40  (to be sensed) of the smallest print media is greater than the distance between the sensing regions  28  and  32  along the paper path  26 . This ensures that the early-warning sensor  18 ,  20  will not miss a print media edge when the accurate edge-detection sensor  18 ,  22  is active. 
   Alternatively, polling of the early-warning sensor  18 ,  20  is continued at a predetermined frequency, and is not halted when polling of the accurate edge-detection sensor  18 ,  22  begins. Simultaneous polling of the early-warning sensor  18 ,  20  and the accurate edge-detection sensor  18 ,  22  is facilitated by the differences in the optical signals  24  and  30 , which result in different electrical responses. 
   Sufficient differences in electrical responses may result even if the optical signals  24  and  30  are similar. For example, differentiable electrical responses may result if the sum of the electrical signals resulting from the signals  24  and  30  is less than the saturation voltage of the detector  18 , or if the LED signals  24  and  30  are strategically pulsed. 
   The emitters  20  and  22  may transmit at different frequencies and/or may be transmitted at different times to enable the detector  18  and media edge-detection application  14  to readily distinguish which beams  24  or  30  are currently impinging on the detector  18 . For example, the beams  24  and  30  may be pulsed at different frequencies or may be different colors. Furthermore, each beam  24  and  30  may transmit at intensities that do not saturate the detector  18 . In this case, the media edge-detection application  14  can readily determine when both beams  24  and  30  are simultaneously impinging on the detector  18  by monitoring the energy of the signal output by the detector  18 . Knowledge of when each beam  24  and/or  30  is impinging on the detector  18  may facilitate determination of the locations of the edges  38  and  40  of the print media  34 . The media edge-detection system  12  is particularly useful for detecting top of form  38  and bottom of form  40  in full-bleed printing applications. 
   To poll the first sensor  18 ,  20 , the electrical signal from the detector  18  corresponding to the first optical beam  24  from the first LED  20  is received for analysis by the media edge-detection application  14 . Similarly, to poll the second sensor  18 ,  22 , an electrical signal output by the detector  18  in response to the second optical beam  30  is received for analysis by the media edge-detection application  14 . Hence, a given sensor may be polled by turning on the appropriate LED  20  and/or  22  and extracting, such as via sampling at a polling or sampling rate, the appropriate electrical signal component output from the detector  18 . The electrical signal component is generated by the detector  18  in response to the optical signal output by the LED  20  or  22  associated with the sensor  18 ,  20  or  18 ,  22  that is being polled. 
   In the present embodiment, the sensors  18 ,  20  and  18 ,  22  are polled independently, however, they may be polled simultaneously without departing from the scope of the present invention. The sensor polling rates may be selectively varied by the media edge-detection application  14 . The rate at which the sensor  18 ,  20  or  18 ,  22  is polled corresponds to the rate at which information from the sensor  18 ,  20  or  18 ,  22  is retrieved from the detector  18  by the media edge-detection application  14 . 
   In the present embodiment, polling of a given sensor  18 ,  20  or  18 ,  22  includes sampling the output of the detector  18 . The rate at which a given sensor  18 ,  20  or  18 ,  22  is polled, i.e., polling rate, is the rate at which the electrical signal at the output of the detector  18  corresponding to the optical beam  24  or  30 , respectively, is sampled by the media edge-detection application  14 . 
   In applications wherein both LED&#39;s  20  and  22  are activated simultaneously, the LED&#39;s  20  and  22  may be turned on and off or amplitude-modulated at predetermined rates or transmitted at different frequencies or at predetermined power levels and/or at different time slots to enable the media edge-detection application  14  to determine which LED&#39;s  20  or  22  are transmitting and to sample the electrical signal component associated with the sensor(s) to be polled. 
   Alternatively, the LED&#39;s  20  and  22  selectively transmit continuous beams that are not amplitude-modulated or turned on and off to facilitate electrical signal differentiation at the output of the detector  18 . In this case, the sensor polling rate corresponds to the rate at which the media edge-detection application  14  samples the electrical signal output from the detector  18  that corresponds to the beam  24  or  30  output from the LED  20  or  22  of the sensor  18 ,  20  or  18 ,  22  being polled. 
   Alternatively, the LED&#39;s  20  and  22  are modulated or turned on and off at a specific rate during sampling intervals. The media edge-detection application  14  selectively samples the corresponding modulated electrical signals at a predetermined sampling rate. In this case, the sensor polling rate also corresponds to the sampling rate of the media edge-detection application  14 . 
   Using a combination of emitters, i.e., LED&#39;s  20  and  22 , that are positioned in different locations in the paper path  26 , and work in concert with the single detector  18 , enables more accurate sensing of the paper/media edges  38  and  40 . In addition, processing time needed by the printer controller  16  to accurately sense the print media edges  38  and  40  is reduced, and more processing time is available for other important printing tasks, such as print head control. 
   The media edge-detection system  12  is a paper position sensor. In some applications, depending on the positioning of the media edge-detection system  12  along the paper path  26 , the system  12  may operate as an Out-Of-Paper Sensor (OOPS). 
   The dual emitter/detector optical paths  24  and  30  are both ‘line-of-sight’ or ‘interrupter’ paths. The early-warning sensor  18 ,  20  and the edge detection sensor  18 ,  22  are emitter/detector combinations and may be considered interrupt sensors. 
   The first LED  20  and the second LED  22  are positioned so that the first sensing region  28  is earlier in the print media path  26  than the more accurate second sensing region  32 . Note that the first emitter  20  may be positioned after second emitter  22  along the print media path  26  if appropriate optics (not shown), such as mirrors, are appropriately positioned so that the first sensing zone  28  is positioned before the second sensing zone  32  along the print media path  26 . 
   The LED&#39;s  20  and  22  are controlled separately by the media edge-detection application  14 . In the present specific embodiment, the media edge-detection application  14  ensures that the LED&#39;s  20  and  22  are not emitting simultaneously. The media edge-detection application  14 , running on the printer controller  16 , knows which detector response is associated with which emitter LED  20  or  22 . 
   The second emitter LED  22 , which is positioned later in the print media path  26  enables more accurate edge-detection and is the primary sensor. The detector  18  and optical paths followed by the beams  24  and  30  are configured so that interruption of the first optical path  24  warns that the leading edge  38  or trailing print media edge  40  is approaching the second sensing region  32 . The early-warning sensor  18 ,  20  does not require fast LED turn-on times or high accuracy. 
   Both emitter LED&#39;s  20  and  22  are focused on the detector  18 , which is biased toward the greatest response and accuracy with the primary optical path associated with the second optical beam  30  and sensing region  32 . Lens and prisms (not shown) may be employed to increase warning distance and lead-time afforded by the early-warning sensor  18 ,  20 . 
   The warning sensor  18 ,  20  is positioned earlier in the print media path  26 , and consequently, can be polled much less frequently, since its function is not to accurately detect the print media edges  38  and  40 . Its function is to detect incoming print media edges  38  and  40  that are entering or exiting the early detection or sensing region  28 . When the print media  34  is sensed by the warning sensor  18 ,  20 , the printer controller  16  and associated processor dedicate more processing time to polling the edge-detection sensor  18 ,  22  and/or to evoking more complex data algorithms running on the application  14  to enable very accurate reading of to top edge  38  and bottom edge  30  of the print media  34 . 
   When no paper or print media  34  exists in the print media path  26 , or when no edge  38  or  40  is approaching the accurate second sensing region  32 , then resources of the controller  16  that would otherwise be used for high-frequency polling of the edge-detection sensor  18 ,  22  may be used for other important tasks. During this time, the warning sensor  18 ,  20  is polled at a very slow rate, and the edge-detection sensor  18 ,  22  is not polled. 
   When the warning sensor  18 ,  20  indicates arriving print media  34 , such as by identifying the top edge  38  of a sheet of paper  34 , then the media edge-detection application  14  switches from polling the warning sensor  18 ,  20  at a slow rate to polling the edge-detection sensor  14  at a sufficiently high rate. The high polling rate is chosen to enable sufficiently accurate edge detection to meet the needs of a given application. Faster sampling of a sensor typically provides enhanced edge-detection capability. 
   After the edge  38  or  40  of the print media  34  has been detected by the edge-detection sensor  18 ,  22 , the media edge-detection application  14  switches to polling the warning sensor  18 ,  20  at the original, relatively slow rate. This reduction in polling rate allows the printer controller  16  and accompanying processors and/or firmware to perform other tasks much faster than they otherwise could. This may result in improved overall printer performance. For example, in a particular application, the polling rate for the edge-detection sensor  18 ,  22  is once every 10 microseconds, while the polling rate for the warning sensor is once per millisecond. In the present embodiment, the edge-detection sensor  18 ,  22  and the warning sensor  18 ,  20  are polled during different time intervals. Hence, when the media edge-detection application  14  is polling the edge-detection sensor  18 ,  22  by sampling the output of the detector  18  resulting from the second optical beam  30 , the early warning sensor  18 ,  20  is not being sampled. Similarly, the edge-detection sensor  18 ,  22  is not polled during time intervals wherein the warning sensor  18 ,  20  is being polled. 
   Efficient use of the early warning sensor  18 ,  20  conserves processor time. The conserved processor time may be employed to sample the more accurate edge-detection sensor  18 ,  22  at higher frequencies than would otherwise be practical. In addition, use of the early warning sensor  18 ,  20  may improve the life span of the accurate sensor  18 ,  22 , since the accurate sensor  18 ,  22  is used less often. Furthermore, use of certain sensors that would otherwise be impractical may now be used for the accurate sensor  18 ,  22 . For example, certain high-power sensors; sensors with limited life spans; sensors with long warm up times; or sensors designed for limited usage may now be employed as the accurate sensor  18 ,  22 . 
     FIG. 2  is a diagram of a printer  10 ′ employing an alternative embodiment  12 ′ of the media edge-detection system  12  of  FIG. 1 . The construction and operation of the alternative media edge-detection system  12 ′ is similar to the construction and operation of the media edge-detection system  10  of  FIG. 1  with the exception that the mirror  44  of  FIG. 1  is omitted, and the first LED  20  is repositioned accordingly. 
   Those skilled in the art will appreciate that in certain printer configurations, the location of the paper path renders the embodiment  12  of  FIG. 1  more practical than the embodiment  12 ′ of  FIG. 2  and visa versa. In addition, those skilled in the art will appreciate that the positioning of the detector  18  and LED&#39;s  20  and  22  is exemplary and that different positioning may be employed without departing from the scope of the present invention. Furthermore, in an alternative implementation, the sensors  18 ,  20  and  18 ,  22  may be replaced with two separate sensors having two separate detectors. 
   Teachings disclosed herein may be employed in applications other than printers without departing from the scope of the present invention. For example, use of an early warning sensor to adjust the sampling rate of a more accurate sensor may be useful in military sensing systems for detecting enemy targets, air traffic control systems, assembly lines, lumber saw mills, and so on. 
   Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications, and embodiments within the scope thereof. 
   It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention. 
   Accordingly,