Patent Publication Number: US-2016241733-A1

Title: Led illumination uniformity

Description:
The present disclosure relates generally to improving a light emitting diode (LED) array in an image reading device and, more particularly, to an apparatus and method for adjusting LED light uniformity in an LED array. 
     BACKGROUND 
     Image reading devices or scanners use LED lights to illuminate an image to be read by a charge coupled device (CCD) or contact image sensor (CIS). However, the light intensity profile of the LED array may have a dramatic fall off towards the end of the LED array. For example, LEDs in the middle of the array may have overlapping light with neighboring LEDs on either side. However, LEDs on the end of the LED array may not have the same neighboring LEDs resulting in the dramatic fall off of light intensity compared to the light intensity of the middle of the LED array. In addition, the lens typically has a fall off in light collection efficiency from the center to the edges. 
     SUMMARY 
     According to aspects illustrated herein, there are provided an input imaging system and method for adjusting LED light uniformity in an LED array. One disclosed feature of the embodiments is an input imaging system comprising an LED array, wherein the LED array is divided into a plurality of different banks of LEDs, wherein a light output of each one of the plurality of different banks of LEDs is independently adjustable, an electrical device for adjusting the light output of the each one of the banks of LEDs coupled to each one of the plurality of different banks of LEDs to achieve the uniform LED light illumination profile, a diffuser coupled to the LED array to scatter the light output towards a document, a lens for collecting the light output that is reflected off of the document and a sensor coupled to the lens to receive the light output that is collected by the lens. 
     Another disclosed feature of the embodiments is a method for adjusting LED light uniformity in an LED array comprising dividing the LED array into a plurality of different LED banks, wherein a light output of each one of the plurality of different banks of LEDs is independently adjustable, measuring, by a processor, the light output for each one of the plurality of different banks of LEDs and adjusting, by the processor, the light output for one or more of the plurality of different banks of LEDs of the LED array to achieve a uniform LED light illumination profile at the sensor. 
     Another disclosed feature of the embodiments is a non-transitory computer-readable medium having stored thereon a plurality of instructions, the plurality of instructions including instructions, which when executed by a processor, cause the processor to perform operations comprising dividing the LED array into a plurality of different LED banks, wherein a light output of each one of the plurality of different banks of LEDs is independently adjustable, measuring the light output for each one of the plurality of different banks of LEDs and adjusting the light output for one or more of the plurality of different banks of LEDs of the LED array to achieve a uniform LED light illumination profile at the sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teaching of the present disclosure can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an example block diagram of a system of the present disclosure; 
         FIG. 2  illustrates an example circuit diagram of the present disclosure 
         FIG. 3  illustrates an example graph of an uncorrected and corrected light intensity; 
         FIG. 4  illustrates a second example graph of an uncorrected and corrected light intensity; 
         FIG. 5  illustrates a flowchart of an example method for adjusting LED light uniformity in an LED array; and 
         FIG. 6  illustrates a high-level block diagram of a computer suitable for use in performing the functions described herein. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the 
     DETAILED DESCRIPTION 
     The present disclosure broadly discloses a method and non-transitory computer-readable medium for adjusting LED light uniformity in an LED array. As discussed above, image reading devices or scanners use LEDs to illuminate an image to be read by a charge coupled device (CCD) or contact image sensor (CIS). However, the light intensity profile of the LED array may have a dramatic fall off towards the end of the LED array. For example, LEDs in the middle of the array may have overlapping light with neighboring LEDs on either side. However, LEDs on the end of the LED array may not have the same neighboring LEDs resulting in the dramatic fall off of light intensity compared to the light intensity of the middle of the LED array. In addition, the fall off of the light collection efficiency of the lens in CCD systems adds additional non uniformity to the light output from the LED illumination. This fall off also affects the signal to noise achievable at the edges. 
     Some solutions have been to add additional LEDs to the ends of the LED array. However, this adds size and costs to the imaging system. Instead, embodiments of the present disclosure adjust the current delivered to the LEDs at the ends of an LED array to remove the light intensity fall off at the ends of the LED array, while maintaining the overall size profile of the imaging system with fewer components than individual bank control. 
     Embodiments of the present disclosure also provide finer control of reducing the variation within the LED profile by controlling banks of LEDs. In one embodiment, the symmetry of the LED array may be utilized to organize common banks of LEDs on opposite ends of the LED array to provide finer resolution and control of the light intensity profile of the LED array. 
       FIG. 1  illustrates an example system  100  of the present disclosure. In one embodiment, the system  100  may be part of an input imaging system for capturing images (e.g., a scanner or imaging device). In one embodiment, the system  100  may include an LED array  102  that includes a plurality of LEDs  104   1  to  104   n  (also referred to herein individually or collectively as LED(s)  104 ). In one embodiment, the LED array may include 30 LEDs. 
     It should be noted that the system  100  is not an image output device (e.g., a printer or a print head that generates the image). For example, the LEDs  104  may require at least 20 milliwatts of power or approximately 1 candela to generate light output. In contrast, the LEDs in an output device may require multiple Watts of power for the LEDs. 
     In one embodiment, the LEDs  104  generate a light output that is emitted onto a diffuser  106 . In one embodiment, the light output may be scattered by the diffuser  106  towards a document  112  that is being scanned. The light may be reflected off of the document  112 . A lens  108  may collect the light reflected off of the document  112  and focused to a sensor  110 . The sensor  110  may receive the light collected by the lens  108 . In one embodiment, the sensor may be a charged coupled device (CCD) or a contact image sensor (CIS). In one embodiment, the lens may be a single lens and a CCD or a Selfoc® lens and a CIS comprising an array of lenslets for each one of the LEDs  104 . 
     As discussed above, the LEDs  104  at the end of the LED array  102  (e.g., LED  104   1  and LED  104   n ) do not have two adjacent LEDs  104  and, thus, have less overlapping light output from neighboring LEDs  104 . As a result, the LEDs  104  at the end of the LED array  102  may have a different light intensity than the other LEDs  104  within the LED array  102 . The different light intensities may lead to a non-uniform light intensity profile where the light intensity received by the sensor  110  from the ends of the LED array  102  falls off drastically. This can lead to a lower signal to noise ratio at the edges of the scanned image or exceed the calibration correction range. 
     However, if the light intensity profile of the LED array  102  is uniform across the length of the LED array  102 , then the light intensity read by the sensor  110  may have a low signal to noise ratio (SNR). The low SNR may lead to a lower quality of the scanned image. In one embodiment, uniformity may be defined as having the light intensity value of each LED  104  be within a certain threshold (e.g., above or below) a desired light intensity level or an average light intensity level. For example, uniformity may be defined as being within 1.0 candela of an average light intensity of the entire LED array  102 . 
     In one embodiment, a uniform light intensity profile of the LED array  102  may be achieved via an adjustment mechanism (broadly an electrical circuit or device). In one embodiment, the adjustment mechanism may be a fixed mechanism that is fixed by a modification to a circuit of the LED array  102 . In another embodiment, the adjustment mechanism may be a dynamic mechanism that is controlled by an optional controller  116  (broadly an electrical circuit or device). As a result, either via the fixed mechanism or the dynamic mechanism, a light output of one or more LEDs  104  of the LED array  102  may be adjusted to achieve a uniform light intensity profile. 
     For example, the light output of the one or more LEDs  104   1  and  104   n  at the ends of the LED array  102  may be increased to reduce the fall off at the ends of the light intensity profile. In addition, other LEDs  104  within the LED array  102  may also be adjusted to reduce the light output to achieve a uniform light intensity profile, related to other effects like the lens fall off, as discussed below. 
       FIG. 2  illustrates a circuit  200  that illustrates one example of a fixed mechanism for adjusting the light output of the LEDs  104 . In one embodiment, the circuit  200  may include a controller  202 , a current resistor  204  (broadly an electrical circuit or device) and one or more LEDs  104  connected in series. In one embodiment, a value of the current resistor  204  may be based upon a pre-measured adjustment to a light output of the LEDs  104  required to achieve the uniform light output. For example, an average light output of the LED array  102  may be measured and a difference between the average light output of the LED array  102  and the light output of the LEDs  104 , or bank of LEDs  104 , may determine the amount of resistance needed to adjust a current delivered to the LEDs  104  to correspond to the difference in the light output. 
     Referring back to  FIG. 1 , the dynamic mechanism may be implemented via a hardware controller  116  (broadly an electrical circuit or device) that includes a processor. In one embodiment, the controller  116  may control an amount of current that is delivered to each one of the LEDs  104  to adjust a light output of each one of the LEDs  104 , or each bank of LEDs  104 , based upon the amount of light received by the sensor  110 . For example, the sensor  110  may be in communication with the controller  116  and the controller  116  may be in communication with the circuitry of the LED array  102  to control the amount of current delivered to the LEDs  104 . In one embodiment, current may be dynamically changed between each scan as needed to achieve a uniform light intensity profile. The amount of adjustment needed may be determined as discussed above with reference to the fixed mechanism. However, the adjustment may be determined by the controller  116  automatically on the fly rather than requiring a pre-measured adjustment. 
       FIG. 3  illustrates an example graph  300  of an unadjusted light intensity profile  322  and an adjusted light intensity profile  324 . In one embodiment, the LEDs  104  may be divided into a plurality of different banks of LEDs  302 - 312 . In one embodiment, each one of the plurality of different banks of LEDs  302 - 312  may include different groups of LEDs  104  from the LED array  102 . 
     In one embodiment, each one of the banks of LEDs  302 - 312  may have a light output adjusted via the fixed mechanism or the dynamic mechanism. For example, each bank of LEDs  302 - 312  may be wired via the circuit  200  illustrated in  FIG. 2 . In addition, each bank of LEDs  302 - 312  may have a different value for the current resistor  204  based upon a difference of the light output of the bank of LEDs  302 - 312  compared to an average light output of the LED array  102 . For example, the bank  1   302  and bank  6   312  may have a current resistor  204  to increase the current to increase the light output to raise the light intensity values, as shown by the change between the unadjusted light intensity profile  322  and the adjusted light intensity profile  324 . In addition, the bank  3   306  may have a different current resistor  204  to decrease the current to decrease the light output to lower the light intensity values, as shown by change between the unadjusted light intensity profile  322  and the adjusted light intensity profile  324 . 
     In another embodiment, the dynamic mechanism may operate by having the controller  116  receives the light intensity values that are read by the sensor  110 . The controller  116  may then determine the adjustment required (e.g., either raising or lowering the current to an LED bank  302 - 312  to either increase the light output or decrease the light output). The controller  116  may then control the current delivered to banks of LEDs  302 - 312  in accordance with the adjustment that is determined. 
       FIG. 4  illustrates an example graph  400  of an unadjusted light intensity profile  422  and an adjusted light intensity profile  424 . In one embodiment, the LEDs  104  may be divided into a plurality of different banks of LEDs  402 - 410  that take advantage of the symmetry of the LED array  102  or optical system. 
     For example, referring back to  FIG. 1 , the LED array  102  may be symmetric about a center line or point  114 . In other words, the LEDs  104  on one side of the center line  114  and the corresponding LEDs  104  on an opposite side of the center line  114  may have a similar light output. Said another way, the LED array  102  illumination profile may be substantially symmetrical around the center line  114 . Said yet another way, the LED banks  402 - 410  may include groups of LEDs  104  that are not all adjacent to one another or next to one another. For example, bank  1   402  can include LEDs  104  that are on opposite ends of the LED array  102 , as illustrated in  FIG. 4 . As a result, when an adjustment is made to the bank  1   402 , each LED  104  on opposite ends of the LED array  102  within the bank  1   402  would be adjusted. The adjustment to each one of the LED banks  402 - 410  may be made via either a fixed mechanism or a dynamic mechanism, as described above with respect to  FIG. 3 . 
     In one embodiment, the arrangement of the banks of LEDs  402 - 410  may take advantage of the symmetry of the LED array  102  or optical system by electrically coupling the banks of LEDs  402 - 410  with LEDs  104  on both sides of the center line  114 . As illustrated in  FIG. 4 , bank  1   402  may include three LEDs from a left side that are a first distance away from the center line  114  and three LEDs from a right side of the center line  114  that are the same first distance away from the center line as the three LEDs on the left side. Bank  2 ,  404  may include three LEDs from a left side at a second distance away from the center line  114  and three LEDs from a right side of the center line  114  that are the same second distance away from the center line, and so forth for bank  3   406 , bank  4   408  and bank  5   410 . As a result, each bank  402 - 410  may provide an ability to control the LEDs on opposite sides of the LED array  102  with a single control. 
     The design of  FIG. 4  may improve upon further the design disclosed in  FIG. 3  as the amount of circuitry needed is reduced. For example, rather than deploying 10 different banks of circuitry (e.g., the circuit  200  disclosed in  FIG. 2 ), only 5 different banks of circuitry would be required by taking advantage of the symmetric properties of the LED array  102 . 
     In addition, the amount of resolution for adjusting the light output of LEDs  104  may also be improved by taking advantage of the symmetric properties of the LED array  102  or optical system. For example, the LED array  102  may be configured to only allow for 5 independently controlled banks of LEDs  104 . If the LED array  102  has 30 LEDs, then one option would be to have 5 banks that include 6 adjacent LEDs  104  in each one of the 5 banks (e.g., the arrangement illustrated in  FIG. 3 ). However, by taking advantage of the symmetry, one embodiment of the present disclosure creates 5 independently controlled banks of LEDs  104  each having 3 adjacent LEDs on each side of the LED array (e.g., the arrangement illustrated in  FIG. 4 ). Although each bank would control 6 LEDs, the resolution would improve to 3 LEDs on each side of the LED array  102  for each adjustment that is made. 
     Similar to the design illustrated in  FIG. 3 , the LED banks  402 - 410  may each be adjusted to either increase or decrease the amount of light output for the LEDs  104  within a respective LED bank  402 - 410 . For example, the current delivered to the LEDs  104  in bank  1   402  may be increased to increase an amount of light output and the current delivered to the LEDs  104  in bank  5   410  may be decreased to decrease an amount of light output. 
     As a result, the embodiments of the present disclosure allow the LEDs  104  to be controlled to reduce variation across a light intensity profile of the LED array  102 . In other words, the signal to noise ratio may be similar across the entire profile. This improves the signal to noise ratio across the entire image and reduces the illumination variation, bringing it into a narrower range for calibration. 
     It should be also noted that the present disclosure may not necessarily be adjusting the LED light intensity to achieve a certain level of uniform light intensity. Rather, the embodiments of the present disclosure adjust the LED light intensity, at any intensity level, such that the light collected by the sensor  110  is uniform across the LED array  102  to minimize the amount of image compensation that needs to be applied after the sensor  110 . 
       FIG. 5  illustrates a flowchart of a method  500  for adjusting LED light uniformity in an LED array. In one embodiment, one or more steps or operations of the method  500  may be performed by the controller  116  or a computer as illustrated in  FIG. 6  and discussed below. 
     At step  502  the method  500  begins. At step  504 , the method  500  divides the LED array into a plurality of different LED banks, wherein a light output of each one of the plurality of different banks of LEDs is independent adjustable. In one embodiment, the LED banks may include groups of LEDs that are on opposite sides of the LED array to take advantage of the symmetric properties of the LED array or optical system. In other words, the LED array or the illumination profile of the LED array may be substantially symmetrical around a center or point of the LED array and each one of the plurality of different banks of LEDs may include a group of LEDs on opposite sides of the center of the LED array. 
     At step  506 , the method  500  measures the light output for each one of the plurality of different banks of LEDs. For example, a light intensity profile across the LED array may be obtained based upon the measured light output of each LED in the LED array. 
     At step  508 , the method  500  determines if an adjustment is needed. For example, the measured light output may be averaged and the light output of each LED may be compared to the average to see if the light output of the LED is within a threshold level of the average. If the light output of the LED is within the threshold, then no adjustment may be needed and the method  500  may proceed to step  512 . 
     However, if the difference of light output of the LED compared to the average light output of the LED array is above the threshold or greater than the threshold, then an adjustment may be needed. The step  508  may be repeated for each LED within the LED array. 
     If an adjustment is needed, the method  500  may proceed to step  510 . At step  510 , the method  500  may adjust the light output for one or more of the plurality of different banks of LEDs of the LED array to achieve a uniform LED light illumination profile at the sensor. For example, the ends of the LED array  102  may have a dramatic drop off in light intensity. As a result, a bank of the LED array that includes LEDs on both a left end and a right end of the LED array may be adjusted to increase the light intensity of the LEDs on the left end and the right end of the LED array. Notably, only a single bank is adjusted to change simultaneously the LEDs in a particular bank. In other words, each individual LED is not adjusted. In addition, the bank does not only include LEDs that are immediately adjacent to one another. 
     In one embodiment, the method  500  may adjust the light output for all LED banks that require an adjustment. The adjustment may be either an increase or a decrease. 
     The method  500  may then proceed to step  512 . At step  512  the method  500  ends. In one embodiment, steps  502 - 512  may be run again for verification (or iteratively). Additionally, it may be possible to iterate between steps  506  and  510 . 
     It should be noted that although not explicitly specified, one or more steps, functions, or operations of the method  500  described above may include a storing, displaying and/or outputting step as required for a particular application. In other words, any data, records, fields, and/or intermediate results discussed in the methods can be stored, displayed, and/or outputted to another device as required for a particular application. Furthermore, steps, functions, or operations in  FIG. 5  that recite a determining operation, or involve a decision, do not necessarily require that both branches of the determining operation be practiced. In other words, one of the branches of the determining operation can be deemed as an optional step. 
       FIG. 6  depicts a high-level block diagram of a computer that can be transformed into a machine that is dedicated to perform the functions described herein. Notably, no computer or machine currently exists that performs the functions as described herein. As a result, the embodiments of the present disclosure improve the operation and functioning of the computer to dynamically adjust an LED light array to achieve LED light uniformity, as disclosed herein. 
     As depicted in  FIG. 6 , the computer  600  comprises one or more hardware processor elements  602  (e.g., a central processing unit (CPU), a microprocessor, or a multi-core processor), a memory  604 , e.g., random access memory (RAM) and/or read only memory (ROM), a module  605  adjusting LED light uniformity in an LED array, and various input/output devices  606  (e.g., storage devices, including but not limited to, a tape drive, a floppy drive, a hard disk drive or a compact disk drive, a receiver, a transmitter, a speaker, a display, a speech synthesizer, an output port, an input port and a user input device (such as a keyboard, a keypad, a mouse, a microphone and the like)). Although only one processor element is shown, it should be noted that the computer may employ a plurality of processor elements. Furthermore, although only one computer is shown in the figure, if the method(s) as discussed above is implemented in a distributed or parallel manner for a particular illustrative example, i.e., the steps of the above method(s) or the entire method(s) are implemented across multiple or parallel computers, then the computer of this figure is intended to represent each of those multiple computers. Furthermore, one or more hardware processors can be utilized in supporting a virtualized or shared computing environment. The virtualized computing environment may support one or more virtual machines representing computers, servers, or other computing devices. In such virtualized virtual machines, hardware components such as hardware processors and computer-readable storage devices may be virtualized or logically represented. 
     It should be noted that the present disclosure can be implemented in software and/or in a combination of software and hardware, e.g., using application specific integrated circuits (ASIC), a programmable logic array (PLA), including a field-programmable gate array (FPGA), or a state machine deployed on a hardware device, a computer or any other hardware equivalents, e.g., computer readable instructions pertaining to the method(s) discussed above can be used to configure a hardware processor to perform the steps, functions and/or operations of the above disclosed methods. In one embodiment, instructions and data for the present module or process  605  for adjusting LED light uniformity in an LED array (e.g., a software program comprising computer-executable instructions) can be loaded into memory  604  and executed by hardware processor element  602  to implement the steps, functions or operations as discussed above in connection with the exemplary method  500 . Furthermore, when a hardware processor executes instructions to perform “operations,” this could include the hardware processor performing the operations directly and/or facilitating, directing, or cooperating with another hardware device or component (e.g., a co-processor and the like) to perform the operations. 
     The processor executing the computer readable or software instructions relating to the above described method(s) can be perceived as a programmed processor or a specialized processor. As such, the present module  605  for adjusting LED light uniformity in an LED array (including associated data structures) of the present disclosure can be stored on a tangible or physical (broadly non-transitory) computer-readable storage device or medium, e.g., volatile memory, non-volatile memory, ROM memory, RAM memory, magnetic or optical drive, device or diskette and the like. More specifically, the computer-readable storage device may comprise any physical devices that provide the ability to store information such as data and/or instructions to be accessed by a processor or a computing device such as a computer or an application server. 
     It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.