Abstract:
Devices and methods for applying heat to a platen of a biometric image capturing device are described that remove and prevent the formation of excess moisture on the platen. These devices and methods prevent undesirable interruptions of total internal reflection of a prism that result in biometric images having a halo effect. In embodiments of the invention, heater assemblies, such as electrically conductive transparent material or resistive heating elements, can be used to heat an area where a biometric object is placed to remove and prevent the formation of excess moisture on the platen. Cooling assemblies, such as electrically conductive transparent material or Peltier elements, can be used to decrease temperature of an area where a biometric object is placed to prevent overheating of the platen.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. application Ser. No. 10/235,6656, filed Sep. 6, 2002, titled “System and Method for Biometric Image Capturing,” which is a Continuation-in-Part of U.S. application Ser. No. 10/047,983, filed Jan. 17, 2002 (now U.S. Pat. No. 6,809,303, issued Oct. 26, 2004), titled “Platen Heaters for Biometric Image Capturing Devices,” each of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention is directed to the field of biometric image capturing.  
       BACKGROUND OF THE INVENTION  
       [0003]     Biometrics is the science of biological characteristic analysis. Biometric imaging captures a measurable characteristic of a human being for identification of the particular individual (for example, a fingerprint). See, for example, Gary Roethenbaugh,  Biometrics Explained , International Computer Security Association, Inc., pp. 1-34 (1998), which is incorporated by reference herein in its entirety.  
         [0004]     Traditionally, techniques for obtaining a biometric image have included application of ink to a person&#39;s fingertips, for instance, and rolling or simply pressing the tips of the individual&#39;s fingers to appropriate places on a recording card. This technique can be very messy due to the application of ink, and may often result in a set of prints that are difficult to read.  
         [0005]     Today, biometric image capturing technology includes electro-optical devices for obtaining biometric data from a biometric object, such as, a finger, a palm, etc. In such instances, the electro-optical device may be a fingerprint scanner, a palm scanner, or another type of biometric scanner. These scanners are also referred to as live print scanners. Live print scanners do not require the application of ink to a person&#39;s finger or palm. Instead, live print scanners may include a prism located in an optical path. A platen is used as the surface for receiving the biometric object. For example, with an optical fingerprint scanner, a finger is placed on the platen, and a camera detects an image of the fingerprint. The platen can be a surface of the prism or any other surface provided on the prism and in optical contact with the prism. The fingerprint image detected at the camera is comprised of relatively light and dark areas. These areas correspond to the valleys and ridges of the fingerprint. Live print scanners utilize the optical principle of total internal reflection (TIR). The rays from a light source internal to these optical scanners reach the platen at an incidence angle that causes all of the light rays to be reflected back. This occurs when the angle of incidence is equal to or greater than the critical angle, which is defined at least in part by the ratio of the two indices of refraction of the medium inside and above the surface of the platen.  
         [0006]     In the case of a live fingerprint scanner, one or more fingers are placed on the platen for obtaining a fingerprint image. Ridges on a finger operate to alter the refraction index at the platen, thereby interrupting the TIR of the prism. This interruption in the TIR causes an optical image of the ridges and valleys of a fingerprint to be propagated through the receiving surface and captured by a camera internal to the device.  
         [0007]     Live fingerprint scanners are increasingly being called upon to operate in a variety of ambient conditions. These conditions can vary in temperature and humidity. Different conditions can affect the quality of a detected image. Also, the particular characteristics of an individual&#39;s finger (such as whether it is dry or oily) can affect detected image quality.  
         [0008]     For example, in certain cases, the presence of moisture and/or fluids on the finger improves the quality of a detected fingerprint image. Excessive moisture and/or fluids on a finger, however, can be undesirable. Excessive moisture and/or fluids may alter the refraction index at the receiving surface and interrupt the TIR of the prism in undesirable places on the receiving surface. This can degrade image quality. Excessive heat or cold at or near the platen surface can also degrade image quality.  
         [0009]     What is needed is a live fingerprint scanner which can operate in a variety of ambient conditions and still capture fingerprint image at a high quality.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     The present invention relates to a thermal assembly that is capable of increasing or decreasing the temperature of a biometric object receiving surface or platen of a biometric image capturing device. Thermal elements are thermally coupled to the image capturing prism to lower the temperature of the platen. Thermal elements are controlled to decrease the temperature of the platen. To increase the temperature of the platen, the thermal elements are used to heat the platen.  
         [0011]     In hot and dry atmospheric conditions, too little moisture may be present to detect a high quality print image. One advantage of the present invention is that the platen may be cooled in these conditions to allow high quality print image to be detected.  
         [0012]     On the other hand, heating the platen reduces or eliminates moisture and/or fluids around the area of the platen, where the biometric object is placed. Such reduction or elimination of excess moisture surrounding the biometric object on the platen prevents a halo effect from appearing in the detected print image.  
         [0013]     In embodiments of the invention, a controller controls each thermal element to cool or heat the platen. In one embodiment, a controller supplies current to the thermal assembly in order to increase or decrease the temperature of the thermal elements. A temperature sensor, attached to the controller detects temperature of the platen. If the temperature of the platen is above a certain threshold level, the temperature sensor sends a signal to the controller to supply current to the thermal assembly in order to increase the temperature of the platen. Increasing temperature of the platen will reduce or eliminate moisture and a resulting halo effect. If the temperature of the platen is below a certain threshold level, the temperature sensor sends a signal to the controller to supply current to the thermal assembly in order to decrease the temperature of the platen.  
         [0014]     In embodiments of the invention, the thermal elements, such as Peltier elements, are attached to the image capturing prism at locations where they do not affect the image illumination or fingerprint imaging. For example, in some embodiments, the thermal elements are located at the ends of the prism platen.  
         [0015]     According to another feature of the present invention, the controller can be operated in a manual or automatic mode. In a manual mode, a user sets the controller to either a “cooling” or “heating” setting. The controller then controls the thermal assembly to cool or heat the platen accordingly. In an automatic mode, the controller automatically determines whether to cool or heat the platen based on detected ambient conditions (such as the ambient temperature and/or ambient humidity).  
         [0016]     Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention are described in detail below with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES  
       [0017]     The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.  
         [0018]      FIG. 1A  is a diagram illustrating an assembly for capturing a biometric image according to an embodiment of the present invention.  
         [0019]      FIG. 1B  is a diagram illustrating a different view of the assembly shown in  FIG. 1A .  
         [0020]      FIG. 1C  is a representation of a selector illustrated in  FIG. 1A  that can be used to select a mode of operation of the present invention.  
         [0021]      FIG. 2  is a diagram illustrating an embodiment of a thermal element attached to a surface of a prism according to an embodiment of the present invention shown in  FIG. 1A .  
         [0022]      FIG. 3  is a flowchart diagram illustrating operation of the assembly of the present invention. 
     
    
       [0023]     The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.  
       DETAILED DESCRIPTION OF THE INVENTION  
     Table of Contents  
       [0024]     1. Introduction.  
         [0025]     2. Terminology.  
         [0026]     3. Temperature Controlled Biometric Scanner.  
         [0027]     4. Temperature Based Controller.  
         [0028]     (A) Cooling.  
         [0029]     (B) Heating.  
         [0030]     (C) Automatic Control.  
         [0031]     5. Thermal Coupling.  
         [0032]     6. Method for Changing Temperature of the Platen.  
         [0033]     7. Conclusion.  
         [0000]     1. Introduction.  
         [0034]     The present invention relates to systems and methods for capturing a biometric image using a live print scanning device. More specifically, the present invention relates to a live print scanner comprising an optical device coupled to a thermal assembly. The thermal assembly further comprises a controller. The controller is capable of either manually or automatically controlling temperature of the live print scanner&#39;s biometric object receiving surface or platen. In an embodiment, the controller can be used to adjust thermal states of the platen based on a variety of ambient conditions.  
         [0035]     Although the invention will be described in terms of specific embodiments, it will be readily apparent to those skilled in the pertinent art(s) that various modifications, rearrangements and substitutions can be made without departing from the spirit of the invention. Further, while specific examples will be discussed using a fingerprint scanner for the purposes of clarity, it should be noted that the present invention is not limited to fingerprint scanners. Other types of live print scanners may be used without departing from the scope of the invention. For example, the present invention applies to any fingerprint, palmprint, or other live print scanners.  
         [0000]     2. Terminology.  
         [0036]     To more clearly delineate the present invention, an effort is made throughout the specification to adhere to the following term definitions consistently.  
         [0037]     The term “finger” refers to any digit on a hand including, but not limited to, a thumb, an index finger, middle finger, ring finger, or a pinky finger.  
         [0038]     The term “live scan” refers to a scan of any type of fingerprint, print on a portion of a foot and/or palm print image made by a print scanner. A live scan can include, but is not limited to, a scan of a finger, a finger roll, a flat finger, slap print of four fingers, thumb print, palm print, foot, toe, heal of hand or a combination of fingers, such as, sets of fingers and/or thumbs from one or more hands or one or more palms disposed on a platen.  
         [0039]     In a live scan, one or more fingers or palms from either a left hand or a right hand or both hands are placed on a platen of a scanner. Different types of print images are detected depending upon a particular application. For example, a flat print consists of a fingerprint image of a digit (finger or thumb) pressed flat against the platen. A roll print consists of an image of a digit (finger or thumb) made while the digit (finger or thumb) is rolled from one side of the digit to another side of the digit over the surface of the platen. A slap print consists of an image of four flat fingers pressed flat against the platen. A palm print involves pressing all or part of a palm upon the platen. A platen can be movable or stationary depending upon the particular type of scanner and the type of print being captured by the scanner.  
         [0040]     The terms “biometric imaging system”, “scanner”, “live scanner”, “live print scanner”, “fingerprint scanner” and “print scanner” are used interchangeably, and refer to any type of scanner which can obtain an image of all or part of one or more fingers and/or palm in a live scan. The obtained images can be combined in any format including, but not limited to, an FBI, state, or international tenprint format.  
         [0041]     The term “platen” refers to a component that includes an imaging surface upon which at least one finger of, palm, or portion of a hand or foot is placed during a live scan. A platen can include, but is not limited to, a surface of an optical prism, set of prisms, or set of micro-prisms, or a surface of a silicone layer or other element disposed in optical contact with a surface of an optical prism, set of prisms, or set of micro-prisms.  
         [0000]     3. Temperature Controlled Biometric Scanner.  
         [0042]     Referring to  FIGS. 1A and 1B , a live print scanning system according to an embodiment of the present invention is illustrated.  FIG. 1A  shows a perspective exploded view of an embodiment of the present invention.  FIG. 1B  is another view of the embodiment shown in  FIG. 1A . Referring to  FIG. 1A , a live print scanning assembly  100  is shown to have an image capturing prism  106  and a thermal assembly  160 , where thermal assembly  160  comprises two thermal elements  102   a  and  102   b , controller  110 , selector  112 , a temperature sensor  108  and an optional humidity sensor  113 .  
         [0043]     The use of two thermal elements  102   a  and  102   b  is illustrative. The present invention is not limited to two thermal elements. In another embodiment, only one thermal element may be used. Alternatively, other embodiments of the present invention may have three or more thermal elements.  
         [0044]     As shown in  FIG. 1A , thermal elements  102   a  and  102   b  are thermally coupled to image capturing prism  106 . First thermal element  102   a  is thermally coupled to a first side  115   a  of image capturing prism  106 . Second thermal element  102   b  is thermally coupled to a second side  115   b  of image capturing prism  106 .  
         [0045]     First side  115   a  of image capturing prism  106  is shown to be opposite second side  115   b  of image capturing prism  106 , thereby placing first thermal element  102   a  opposite second thermal element  102   b . It is understood by one skilled in the art that any other arrangement of thermal elements  102   a  and  102   b  is possible. Also,  FIG. 1A  shows two thermal elements connected to image capturing prism  106 , however, it is understood that any number of thermal elements can be connected to image capturing prism  106 . Thermal elements  102   a  and  102   b  can be directly or indirectly attached and need only be thermally coupled to image capturing prism  106 . Furthermore, image capturing prism  106  is not limited to the size and shape shown in  FIG. 1A .  
         [0046]     Connectors  120   a  and  120   b  connect thermal elements  102   a  and  102   b  to controller  110 . Connector  120   a  connects thermal element  102   a  and controller  110 . Similarly, connector  120   b  connects thermal element  102   b  and controller  110 . Connectors  120   a  and  120   b  can be attached by any viable means known in the art to the respective thermal elements and to controller  110 . In one embodiment, connectors  120   a  and  120   b  can be soldered to appropriate circuit elements of respective thermal elements  102   a  and  102   b , as well as appropriate circuit elements of controller  110 .  
         [0047]     Temperature sensor  108  can be placed at or near image capturing prism  106 . In one embodiment, temperature sensor  108  is used to detect the temperature of image capturing prism  106 . In another embodiment, temperature sensor  108  is used to detect the temperature of the biometric object receiving surface or platen that can be attached to prism  106 . Upon detection of temperature, temperature sensor  108  will feed the information to controller  110 .  
         [0000]     4. Temperature Based Controller.  
         [0048]     Depending on various ambient conditions surrounding live print scanning assembly  100 , the temperature of a biometric object receiving surface or platen  140  of the image capturing prism  106  needs to be changed. The present invention&#39;s thermal assembly  160  comprises controller  110  and temperature sensor  108  (coupled to controller  110  and image capturing prism  106 ) to implement such change.  
         [0049]     Referring to  FIG. 1A , a selector  112  is coupled to controller  110  via bus  111 . Selector  112  can be used to switch between modes of operation of the thermal assembly  160 . In an embodiment, selector  112  may switch thermal assembly  160  between a manual heating mode, a manual cooling mode, and an automatic heating/cooling mode. It is of course understood by one skilled in the art given this description that other modes of operation of thermal assembly  160  are possible.  
         [0050]     Referring to  FIG. 1C , an embodiment of selector  112  is illustrated in more detail. Selector  112  comprises a selector switch  171  that changes the modes of operation of the thermal assembly  160 . Selector  112  has a manual cooling mode  175  and a manual heating mode  177 . Selector  112  also has an automatic heating/cooling mode  173 . Finally, selector  112  has an off mode  179 .  
         [0051]     In manually operated cooling mode  175  and heating mode  177 , the user is able to implement a change in the thermal state of platen  140 . To manually heat platen  140 , the user will switch selector switch  171  to heating mode  177 . To manually cool platen  140 , the user will switch selector switch  171  to cooling mode  175 .  
         [0052]     In an automatic heating/cooling mode, thermal assembly  160  will regulate its thermal state according to present ambient conditions. To automatically adjust temperature of platen  140 , the user will shift selector switch  171  to automatic heating/cooling mode  173 . Thermal assembly  160  will automatically control the temperature the platen  140 .  
         [0053]     Finally, it may be desirable to operate assembly  100  without cooling or heating platen  140 . In that case, the user may shift selector switch  171  in “off” mode  179 . Thermal state of platen  140  will be determined by the surrounding ambient conditions.  
         [0054]     The following is a more detailed description of manual cooling and heating modes as well as automatic heating/cooling mode. It is understood by one skilled in the relevant art that the present invention is not limited to the modes described.  
         [0000]     (A) Cooling.  
         [0055]     When ambient conditions surrounding live print scanning assembly  100  are hot and dry, it may be necessary to cool off the biometric object receiving surface or platen  140  of image capturing prism  106 . Even though it is sometimes possible to obtain an image of a fingerprint during these conditions, excessive heat and dryness may be undesirable and may affect quality of the image. Therefore, it may be necessary to cool off the platen.  
         [0056]     Referring to  FIGS. 1A and 1C , in order for the thermal assembly  160  to decrease the temperature of platen  140 , selector  112  is switched to the cooling mode. This is accomplished by shifting selector switch  171  to manual cooling mode  175 . In this mode, the user is able to manually lower temperature of platen  140 .  
         [0057]     In an embodiment, the user may lower the temperature by leaving selector switch  171  in manual cooling mode  175 . In this case, controller  110  will run current through thermal elements  102   a  and  102   b , in a particular direction. Controller  110  can run current constantly or intermittently as needed based on detected temperature. By running current through thermal elements  102   a  and  102   b  this way, the temperature of platen  140  is lowered. When the current is running through thermal elements  102   a  and  102   b  in a particular manner, the side of each thermal element  102   a  and  102   b  adjacent to platen  140  becomes cold (as will be described below in more detail). By cooling sides of thermal elements  102   a  and  102   b  adjacent to platen  140 , the temperature of platen  140  is decreased.  
         [0058]     In another embodiment, in order to manually decrease the temperature of platen  140 , the user may shift selector switch  171  into manual cold mode  175  and manually activate supply of current to thermal elements  102   a  and  102   b  from controller  110 , whenever the temperature of platen  140  becomes unsuitable to the user. The user may use temperature data supplied by temperature sensor  108  to regulate supply of current to thermal elements  102   a  and  102   b . In an embodiment, thermal assembly  160  may have an optional monitor (not shown) that will display temperature of platen  140 .  
         [0059]     If it appears to the user that the temperature of platen  140  became high, the user may manually activate supply of current from controller  110  to thermal elements  102   a  and  102   b  to initiate cooling. As was discussed above, when current is supplied to thermal elements  102   a  and  102   b  in a particular direction, the temperature of platen  140  is decreased to the desired level.  
         [0060]     It is understood by one skilled in the relevant art that other methods of cooling platen  140  are possible. The following is a description of thermal elements  102   a  and  102   b  that may be used by thermal assembly  160  to lower the temperature of platen  140 .  
         [0061]     Referring to  FIG. 2 , first thermal element  102   a  is shown. The structure and operation of second thermal element  102   b  is similar to the structure and operation of first thermal element  102   a . First thermal element  102   a  has a first portion  202  and a second portion  204 . First portion  202  is coupled to second portion  204 . A first side  116   a  of first thermal element  102   a  is an outer side of first portion  202  and a second side  117   a  of first thermal element  102   a  is the outer side of second portion  204 .  
         [0062]     Thermal element  102   a  is constructed in a way so that if a current is passed through the thermal element one way, first portion  202  will start removing heat. At the same time, second portion  204  will absorb the amount of energy required to lower the temperature of first portion  202 . By absorbing energy this way, the temperature of second portion  204  of thermal element  102   a  will rise.  
         [0063]     However, if the current is passed through the thermal element in a reverse fashion, first portion  202  will start generating heat. In this case, second portion  204  of thermal element  102   a  will start removing heat. At the same time, first portion  202  will absorb energy from second portion  204 . This will increase temperature of first portion  202 .  
         [0064]     As was mentioned above, the structure and operation of second thermal element  102   b  is similar to the structure and operation of first thermal element  102   a.    
         [0065]     In an embodiment, thermal elements  102   a  and  102   b  may be Peltier elements. Peltier elements are bidirectional heating and cooling devices. When current is applied in one direction, the Peltier element acts as a cooling element (also called a heat sink) as it pumps heat out. When current is applied in the opposite direction, the Peltier element acts to generate heat.  
         [0000]     (B) Heating.  
         [0066]     Under certain ambient conditions, the air in the microscopic vicinity of the fingerprint has a very high relative humidity. If the water contacts the surface of the prism, it will break the TIR of the prism. This interruption in the TIR causes an optical image of the water on the platen (e.g., a halo that is known in the relevant art as a halo effect) to be propagated through the platen and captured by a camera internal to the device. This interruption in the TIR results in an undesirable visible image of the water in the image of the biometric object.  
         [0067]     Therefore, it may be desirable to raise the temperature of the platen to counter the effect of moisture, fluids and/or water deposited on the surface of the prism. By raising temperature of platen  140 , it is possible to evaporate moisture accumulated on the platen, thereby increasing image quality and preventing a “halo” effect.  
         [0068]     To increase the temperature of platen  140 , the user may follow steps similar to the cooling process described above. Referring to  FIGS. 1A and 1C , in order for the thermal assembly  160  to increase the temperature of platen  140 , selector  112  is switched to the heating mode. This is accomplished by shifting selector switch  171  to manual heating mode  177 . In this mode, the user is able to manually increase temperature of platen  140 .  
         [0069]     In an embodiment, the user may increase the temperature by leaving selector switch  171  in manual heating mode  177 . In this case, controller  110  will run current through thermal elements  102   a  and  102   b , in a direction opposite the current&#39;s direction in the cooling mode. Controller  110  can run current constantly or intermittently as needed based on detected temperature. By running current through thermal elements  102   a  and  102   b  in an opposite way, the temperature of platen  140  is increased. Thermal elements  102   a  and  102   b  become heating elements. The sides of thermal elements  102   a  and  102   b  adjacent to platen  140  have now increased in temperature. This is opposite of the cooling mode, where these sides were cooling platen  140 . By heating thermal elements  102   a  and  102   b  sides adjacent to platen  140 , the temperature of platen  140  is increased.  
         [0070]     In another embodiment, in order to manually increase the temperature of platen  140 , the user may shift selector switch  171  into manual heating mode  177  and activate supply of current to thermal elements  102   a  and  102   b  from controller  110  whenever the temperature of platen  140  becomes undesirably low. The user may use temperature data supplied to the user by temperature sensor  108  to regulate supply of current to thermal elements  102   a  and  102   b . In an embodiment, thermal assembly  160  may have an optional monitor (not shown) that will display temperature of platen  140 .  
         [0071]     If it appears to the user that the temperature of platen  140  became low enough, the user may manually activate supply of current from controller  110  to thermal elements  102 . As was discussed above, when current is supplied to thermal elements  102  in a direction opposite the direction of current in the cooling mode, the temperature of platen  140  is increased to the desired level.  
         [0072]     When a lot of moisture is present on the biometric object to be scanned, increasing the temperature of platen  140  will remove the excess moisture from the object and platen  140 . By removing excess moisture from platen  140 , the image quality of the object is improved and the “halo” effect is eliminated.  
         [0073]     Referring back to  FIG. 1A , an optional humidity sensor  113  is shown. Humidity sensor  113  is coupled via bus  115  to controller  110 . Sensor  113  detects humidity coefficient and sends the data to controller  110 . A purpose of humidity sensor  113  is to provide additional information to controller  110 . Upon increasing humidity, controller  110  may increase supply of current to thermal elements  102   a  and  102   b , so as to further eliminate moisture from platen  140 . Upon decreasing humidity, controller  110  may decrease supply of current to thermal elements  102   a  and  102   b.    
         [0074]     It is understood by one skilled in the relevant art that other methods of heating platen  140  are possible. Thermal elements  102   a  and  102   b  may be the same thermal elements that are used when cooling platen  140 . However, separate thermal elements may be thermally coupled to platen  140  in order to heat the platen.  
         [0000]     (C) Automatic Control.  
         [0075]     Referring to  FIGS. 1A-1C , the present invention&#39;s thermal assembly  160  is capable of operating in an automatic heating/cooling mode  173 . In this mode, thermal assembly  160  is capable of automatically controlling either heating or cooling of platen  140 . Thermal assembly  160  will heat platen  140  when moisture is present. Thermal assembly  160  will cool platen  140  when the surrounding ambient conditions are hot and dry.  
         [0076]     To implement automatic heating/cooling, the thermal assembly  160  needs to be switched to automatic heating/cooling mode  173 , as shown in  FIG. 1C . Selector switch  171  is shifted into position  173 .  
         [0077]     In an embodiment, thermal assembly  160  will heat platen  140  when the temperature of platen  140  drops below a low or first threshold level. Likewise, thermal assembly  160  will cool platen  140  when the temperature of platen  140  rises above a high or second threshold level. It is understood by one skilled in the relevant art that in both heating and cooling, a range of temperature thresholds may be preset below or above which thermal assembly  160  would appropriately respond. In another embodiment, a user may set up a plurality of temperature thresholds, whereupon reaching each threshold thermal assembly  160  would make appropriate adjustments in the temperature of platen  140 .  
         [0078]     In the automatic mode, temperature sensor  108  coupled to controller  110  via bus  116  detects the temperature of platen  140 . When the ambient conditions surrounding live print scanning assembly  100  are hot and dry, the platen&#39;s temperature will rise. Temperature sensor  108  detects new temperature of platen  140  and sends the data to controller  110 .  
         [0079]     Depending on the ambient conditions and the temperature of platen  140 , controller  110  will act to either increase or decrease the temperature of platen  140 . If the temperature of platen  140  has reached the high threshold, then controller  110  will direct the current via connectors  120   a  and  120   b  to thermal elements  102   a  and  102   b , respectively, in a direction opposite the current&#39;s direction in the heating mode. Thermal elements  102   a  and  102   b  will act as platen coolers and lower temperature of platen  140 , as was described above.  
         [0080]     If the temperature of platen  140  has reached the low threshold, then controller  110  will direct the current via connectors  120   a  and  120   b  to thermal elements  102   a  and  102   b , respectively, in a direction opposite current&#39;s direction in the cooling mode. Thermal elements  102   a  and  102   b  will act as platen heaters and raise the temperature of platen  140 , as was described above.  
         [0081]     Temperature sensor  108  detects the temperature of platen  140  and thermal elements  102   a  and  102   b  via respective busses  116  and  118 . When the cold dissipated in platen  140  causes image capturing prism  106  to obtain the temperature low enough to prevent overheating of prism  106 , controller  110  adjusts its generation of current to thermal elements  102   a  and  102   b . Upon sensing that the temperature of platen  140  has gone above a specified level, controller  110  generates enough power to cause the temperature to decrease.  
         [0082]     On the other hand, when a lot of moisture is present on a biometric object to be scanned, it may be necessary to increase the temperature of platen  140  in order to remove the excess moisture from the object and platen  140 . Therefore, to increase the temperature of platen  140 , first sides  116   a  and  116   b  of first and second thermal elements  102   a  and  102   b , respectively, become hot. This is achieved when controller  110  is passing current through the connectors  120   a  and  120   b  in a direction opposite the direction, when cooling image capturing prism  106 . By having thermal elements  102   a  and  102   b  apply heat to image capturing prism  106 , the temperature of platen  140  is increased.  
         [0083]     It is understood by one skilled in the relevant art that the automatic control of heating/cooling in the present invention is not limited to the embodiments described above. The above-described embodiments operate with two thermal elements  102   a  and  102   b  coupled to platen  140  of image capturing prism  106 . However, it is understood that at least one thermal element is needed to heat or cool platen  140 .  
         [0084]     The following is a description of how thermal elements  102   a  and  102   b  are coupled to platen  140  in a particular embodiment.  
         [0000]     5. Thermal Coupling.  
         [0085]     The present invention uses two thermal elements  102   a  and  102   b  to uniformly increase or decrease the temperature of platen  140 . To achieve uniform change in temperature, thermal elements  102   a  and  102   b  are thermally coupled to platen  140 . However, at least one thermal element is necessary to increase or decrease the temperature of the platen.  
         [0086]     Referring to  FIGS. 1A and 1B , first thermal element  102   a  has first side  116   a  and second side  117   a . First side  116   a  of thermal element  102   a  is an inner side with respect to image capturing prism  106  (or platen  140 ). First side  116   a  is coupled to first side  115   a  of image capturing prism  106  (or platen  140 ). Second side  117   a  of thermal element  102   a  is an outer side with respect to image capturing prism  106  (or platen  140 ). Connector  120   a  connects controller  110  and second side  117   a . First side  116   a  of thermal element  102   a  is attached to first side  115   a  of image capturing prism  106  (or platen  140 ) by any conventionally known means. In one example, such means may be epoxy or other adhesive elements.  
         [0087]     Similarly, thermal element  102   b  has a first side  116   b  and a second side  117   b . First side  116   b  of thermal element  102   b  is an inner side with respect to image capturing prism  106  (or platen  140 ). First side  116   b  is attached to second side  115   b  of image capturing prism  106  (or platen  140 ). Second side  117   b  of thermal element  102   b  is an outer side with respect to image capturing prism  106  (or platen  140 ). Connector  120   b  connects controller  110  and second side  117   b . First side  116   b  of thermal element  102   b  is attached to second side  115   b  of image capturing prism  106  (or platen  140 ) by any conventionally known means. In one example, such means may be epoxy or other adhesive elements.  
         [0088]     By coupling thermal elements  102   a  and  102   b  to opposite sides of platen  140  or image capturing prism  106 , thermal elements are able to either uniformly increase or uniformly decrease the temperature of image capturing prism  106  or platen  140 .  
         [0089]     In an embodiment, the image capturing prism  106  is an optical device made of a light propagating material such as plastic, glass, or a combination thereof. The light propagating material is characterized by an index of refraction. Prism  106  is designed to utilize the optical principle of total internal reflection. The operation of a prism in a fingerprint scanner is further described in U.S. Pat. No. 5,467,403, to Fishbine et al., entitled “Portable Fingerprint Scanning Apparatus for Identification Verification” issued on Nov. 14, 1995 to Digital Biometrics, Inc. and incorporated herein by reference in its entirety.  
         [0090]     6. Method for Changing the Temperature of the Platen.  
         [0091]     Referring to  FIG. 3 , a method  300  for changing temperature of platen  140  is illustrated. In step  302 , a biometric object to be scanned is provided (e.g., a finger). The biometric object is then applied to platen  140  of image capturing prism  106 . In an embodiment, the biometric object may be placed atop of platen  140 . Platen  140  can be a top surface of image capturing prism  106 . However, in another embodiment, platen  140  may be a protective cover placed in optical contact with a surface of image capturing prism  106 .  
         [0092]     In step  306 , method  300  proceeds to detect the temperature of platen  140  using temperature sensor  108 . Temperature sensor  108  sends the temperature data to controller  110 . Controller  110  runs the current in one direction when there is a need to cool image capturing prism  106  and/or platen  140 . Controller  110  runs the current in the other direction when there is a need to heat platen  140 .  
         [0093]     Referring to step  308 , if the conditions surrounding platen  140  are hot and dry, then there is a need to decrease temperature of platen  140 . By decreasing the temperature of platen  140 , image capturing prism  106  is not overheated.  
         [0094]     If temperature sensor  108  detects that the temperature of platen  140  is above a certain threshold level, then controller  110  will generate current in order to decrease the temperature of platen  140 . The current is sent via connectors  120   a  and  120   b  to thermal elements  102   a  and  102   b , respectively. Here the current is sent in a particular direction. Because, there is a need to decrease the temperature of platen  140 , thermal elements  102   a  and  102   b  will remove heat.  
         [0095]     Referring now to step  310 , if an excess moisture is present on the biometric object and/or platen  140 , there is a need to increase the temperature of platen  140 . By increasing the temperature of platen  140 , the excess moisture is evaporated. By eliminating the excess moisture, the halo effect is reduced.  
         [0096]     If temperature sensor  108  detects that the temperature of platen  140  is below a certain threshold level, then controller  110  will generate current in order to increase the temperature of platen  140 . The current is sent via connectors  120   a  and  120   b  to thermal elements  102   a  and  102   b , respectively. The current is sent in a direction opposite the current&#39;s direction when image capturing prism  106  or platen  140  need to be cooled. Because, there is a need to increase the temperature of platen  140 , thermal elements  102   a  and  102   b  will generate heat.  
         [0000]     7. Conclusion.  
         [0097]     The present invention is not limited to the above described modes of operation. It is understood by one skilled in the art that other modes of operation are possible.  
         [0098]     The present invention is not limited to a single temperature threshold in the case of either heating and/or cooling platen  140 . Additional thresholds can be used if more fine control of heating and/or cooling is desired. In another embodiment, temperature sensor  108  can be omitted entirely so that a constant heating and/or constant cooling of the biometric object receiving surface is provided, regardless of temperature changes. Finally, the threshold values of temperature values for heating and cooling can be set as desired, as will become apparent to a person skilled in the relevant art given the description of the present invention.  
         [0099]     Furthermore, it is understood by a person skilled in the relevant art, that controller  110  can have a current source and a switching circuit. The switching circuit would control direction of the current supplied to thermal elements  102   a  and  102   b  via connectors  120   a  and  120   b . Other embodiments of the controller  110  are possible and may be implemented as desired.  
         [0100]     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.