Abstract:
Methods and systems for controlling and adjusting heat distribution over a part bed are disclosed. In one embodiment, a technique for providing a calibrated heat distribution over a part bed includes determining the temperature distribution within a part bed, generating a zone heat distribution for a plurality of heat zones from the temperature distribution, analyzing the zone heat distribution to create an adjustment command to calibrate a heater for providing a substantially consistent temperature distribution within the part bed, and adjusting the heater based on the adjustment command.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This patent application is related to co-pending, commonly-owned U.S. patent application Ser. No. (undetermined) entitled “Methods And Systems For Direct Manufacturing Temperature Control”, filed under Attorney Docket No. 07-0192 (24691-124) concurrently herewith on Apr. 20, 2007, which application is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to methods and systems for adjusting heat distribution, and more specifically, to methods and systems for controlling and adjusting heat distribution over a part bed. 
       BACKGROUND OF THE INVENTION 
       [0003]    People often desire to create prototypes or production models of products, including products with complex geometries. Additive manufacturing techniques facilitate the creation of products using a bottom-up product building approach by adding material in thin layers to form a product. This process allows product creation without large capital investments, such as those associated with molds or specialized machinery, while reducing the overall waste generated in product creation. Additive manufacturing techniques also allow creation of a product with complex geometry because the additive process creates a thin cross-sectional slice of the product during each iteration, thus building complex geometries as simple two-dimensional layers created upon one-another. 
         [0004]    When a product is formed using an additive manufacturing process, the raw material (e.g., powder) is heated to an optimal temperature for product formation. The optimal temperature is slightly lower than the liquid state temperature of the material, thus allowing a small concentration of thermal energy (heat) from a laser to transform the solid material to a liquid, where the material then bonds and quickly cools (after removal of the laser) as a product layer. Often, the material in the part bed has inconsistent temperature when the temperature is measured across the part bed. This variance in temperature may reduce the integrity and consistency of the product formation process in additive manufacturing. In addition, the raw materials that may be used in additive manufacturing have various formation temperatures (i.e., melting points). Some raw materials have melting points that are too high for current additive manufacturing systems to utilize, particularly when large variances in temperature exist across the part bed. 
       SUMMARY 
       [0005]    Embodiments of methods and systems for controlling and adjusting heat distribution over a part bed are disclosed. In one embodiment, a method for providing a target heat distribution over a part bed includes determining a temperature distribution within a part bed, generating a zone heat distribution for a plurality of heat zones from the temperature distribution, analyzing the zone heat distribution to create an adjustment command to adjust a heater for providing a target (uniform or non-uniform) temperature distribution within the part bed, and adjusting the heater based on the adjustment command. 
         [0006]    In another embodiment, a system for providing a target heat distribution over a part bed includes a thermal imaging device to generate temperature distribution data from material in a part bed. A processor receives the temperature distribution data, converts the temperature distribution data into a zone temperature grid, creates a heater control command based on a difference between a target temperature and the zone temperature grid, and transmits the heater control command to at least one heater element of a plurality of heater elements. 
         [0007]    In yet another embodiment, one or more computer readable media comprise computer-executable instructions that, when executed by a computer, perform acts which include measuring a temperature distribution of a part bed, generating temperature zones from the temperature distribution, and creating a heater adjustment command from the temperature zones to adjust at least one of a plurality of heaters to provide a target (uniform or non-uniform) temperature distribution over the part bed. 
         [0008]    The features, functions, and advantages can be achieved independently in various embodiments of the present inventions or may be combined in yet other embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Embodiments of systems and methods in accordance with the present disclosure are described in detail below with reference to the following drawings. 
           [0010]      FIG. 1  is a schematic of an environment for controlling and adjusting heat distribution over a part bed in accordance with an embodiment of the invention; 
           [0011]      FIGS. 2   a ,  2   b , and  2   c  are charts illustrating different temperature distribution ranges for a part bed in accordance with an embodiment of the invention; 
           [0012]      FIG. 3   a  and  3   b  are top plan views from an IR camera perspective of temperature distributions of a part bed, including zones of the part bed, in accordance with another embodiment of the invention; 
           [0013]      FIG. 4  is a schematic of an exemplary zone grid configuration of a part bed in accordance with an embodiment of the invention; 
           [0014]      FIG. 5  is a flow chart of a method for controlling and adjusting the heat distribution over a part bed in accordance with another embodiment of the invention; and 
           [0015]      FIG. 6  is a flow chart of a closed loop process for controlling and adjusting the heat distribution over a part bed in accordance with another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Methods and systems for controlling and adjusting a heat distribution over a part bed are described herein. Many specific details of certain embodiments of the invention are set forth in the following description and in  FIGS. 1 through 6  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the present invention may be practiced without several of the details described in the following description. 
         [0017]      FIG. 1  illustrates an overall environment  100  for controlling and adjusting a heat distribution over a part bed in accordance with an embodiment of the invention. The environment  100  includes a part bed  102  and a heater tray  104  for heating the part bed  102 . The part bed  102  (also referred to as a powder bed) is used to create products in an additive manufacturing process such as laser sintering (LS) or selective laser sintering (SLS), a registered trademark of 3D Systems, Inc. of Rock Hill, S.C., USA. 
         [0018]    Generally, in an LS system, a thin layer of powder is spread across the part bed  102 . The layer of powder is heated by the heater tray  104  to an optimal product formation temperature. A laser beam from a laser  106  is directed at the powder on the part bed  102  to form a layer of the desired product from the powder. As noted above, with the powder heated by the heater tray  104  to a temperature slightly lower than the liquid state temperature of the powder, thermal energy (heat) from the laser  106  transforms the solid material to a liquid. After the laser is removed, the material cools and re-solidifies. The laser  106  bonds the powder elements to form a solid, thin product layer, one layer at a time. After the thin product layer (or slice) has been formed, another thin layer of powder is spread across the part bed  102  to create another thin product layer of the product on top of the previous thin product layer. This process is repeated until the desired product is fully formed, often after many iterations of the above-described process. Embodiments of systems and methods in accordance with the teachings of the present disclosure may advantageously be used to provide a desired temperature distribution over the powder in the part bed  102  (including uniform or non-uniform temperature distributions), thereby improving the consistency of the manufacturing process and the quality of the resulting components. 
         [0019]    The heater tray  104  may include any number of heaters  108 . The heaters  108  emit heat towards the powder in the part bed  102 , thus heating the powder to the desired temperature for product formation. In an exemplary embodiment, the heater tray  104  includes eight heaters  108 , however, any number of heaters may be used. The eight heaters  108  may be configured on the heater tray  104  to include one heater for each corner and one heater for each side of the heater tray. The heaters  108  may be repositioned or adjusted on the heater tray  104  to provide an even heat distribution to the powder on the part bed  102 . For example, in some embodiments, a heater  108  may translate along a plane in a side to side or fore to aft direction, or it may rotate about a mounting point near the heater tray  104  and therefore direct heat to the optimal portion of the part bed  102 . The heaters  108  may be in connection with variable resisters  112  and a power source  114  to control the energy output of the heaters  108 . Further, each heater  108  may have an adjustable current or voltage applied to the heat radiator to variably control the local energy density applied to the powder in the part bed  102 . 
         [0020]    In some embodiments, the heaters  108  are quartz rod elements, which are stable at temperatures in excess of 400° Celsius. In an exemplary embodiment, the heaters  108  may produce and maintain a consistent and stable temperature between 20° Celsius and 400° Celsius. Of course, in alternate embodiments, any suitable heating elements operable over any desired operating ranges may be used. 
         [0021]    The environment  100  further includes an infrared (IR) camera  116  to capture images that indicate the temperature distribution across the powder in the part bed  102 . The IR camera  116  may be any thermal imaging device capable of measuring the temperature distribution of the powder on the part bed  102  and outputting temperature distribution data. The IR camera  116  may, for example, infer temperature from the measured infrared intensity by assuming the powder emits infrared radiation according to an established model of radiant intensity (e.g. black body emitter, etc.). In some embodiments, the IR camera  116  may be suspended above the part bed  102  and directed approximately perpendicular to the powder surface, thus being pointed directly at the powder bed to capture temperature (or heat) distribution data. 
         [0022]    The IR camera  116  may have an energy wavelength detection band (or range) that is outside the energy wavelength band of the laser  106 . This may allow the IR camera  116  to monitor the temperature of the powder while the laser  106  is scanning the product, thus the data captured by the IR camera  116  may not be instantaneously affected by the laser&#39;s energy output. 
         [0023]    The data captured by the IR camera  116  may be used to generate a zone heat distribution  118 . The zone heat distribution  118  is a representation of the temperatures for each zone corresponding to the part bed. Each heater  108  influences the temperature of at least one zone. For example, the second heater  108 ( 2 ) may be adjusted to increase or decrease the temperature of zone  2  in the zone heat distribution  118 . The temperature of the second heater  108 ( 2 ) may also influence the temperature of the adjacent zones  5 ,  6 , and  9 . Although the zone heat distribution  118  depicts nine zones, the temperature gradient of the powder on the part bed  102  may be divided into any number of temperature zones. 
         [0024]    In an embodiment, the IR camera  116  outputs temperature distribution data in the form of pixilated data. The zone heat distribution  118  may be created by the IR camera  116 , such as by algorithms that output the captured data by zones. The zones may include one or more pixels compiled to create a temperature for each zone. In another embodiment, the IR camera  116  data may be processed by software to create the zone heat distribution  118 . A central processing unit (CPU)  120 , such as a computer, may be utilized to analyze the distribution  118  to determine the temperatures associated with each zone. In some embodiments, the temperatures may be calculated using an average, median, root mean square, or other zone temperature calculation to generate a single temperature for each zone in the zone heat distribution  118 . 
         [0025]    As further shown in  FIG. 1 , the CPU  120  may analyze the data from the zone heat distribution  118  and generate an individual zone control output  122 . The zone control output  122  may be utilized to reposition the heaters  108  (e.g., translate side to side, fore to aft, rotate), adjust the power source, or adjust the resistance to produce a desired temperature distribution over the powder in the powder bed, including a uniform or non-uniform distribution. It will be appreciated that for many applications, a uniform, approximately constant temperature across the powder in the part bed is desired. For example, the CPU  120  may determine that zone  2  is 4° C. warmer than a target temperature (e.g., 163° C.) in the zone heat distribution  118 . The CPU  120  may then reduce the temperature in zone  2  by performing one or more of the following: increasing the resistance from the variable resistors  112 , reducing the power source  114  for the heater (or heaters)  108  associated with zone  2 , and repositioning one or more heaters  108 , including the second heater  108 ( 2 ) that may be located directly proximate to zone  2 . After one or more of the previously described adjustments occur, the temperature of zone  2  should be equivalent to a target temperature according to the desired temperature distribution. 
         [0026]    The CPU  120  may include one or more processors  124  that are coupled to instances of a user interface (UT)  126 . The UT  126  represents any devices and related drivers that enable the CPU  120  to receive input from a user, system, or device (e.g., signal from the IR camera  116 ), and to provide output to the user, system, or process. Thus, to receive inputs, the UT  126  may include keyboards or keypads, mouse devices, touch screens, microphones, speech recognition packages, imaging systems, or the like in addition to networking connection from other devices such as the IR camera  116 . Similarly, to provide outputs, the UT  126  may include speakers, display screens, printing mechanisms, or the like in addition to networking connections to other devices such as the variable resistors  112 , the power source  114 , and the heaters  108 . 
         [0027]    The CPU  120  may include one or more instances of a computer-readable storage medium  128  that are addressable by the processor  124 . As such, the processor  124  may read data or executable instructions from, or store data to, the storage medium  128 . The storage medium  128  may contain a number of modules  130  (e.g., a module A and a module B) which may be implemented as one or more software modules that, when loaded into the processor  124  and executed, cause the CPU  120  to perform any of the functions described herein. In one embodiment, the module A may receive a signal from the IR camera  116 , process the signal, and create the zone heat distribution  118 . In a further embodiment, the module B may create and execute the zone control output  122  by manipulating the heaters  108  as described above. Additionally, the storage medium  128  may contain implementations of any of the various software modules described herein. 
         [0028]    With continued reference to  FIG. 1 , the environment  100  may further include other devices for measuring the temperature of the powder in the part bed  102  to create the zone heat distribution  118 . For example, thermocouples  132  may be positioned within, or adjacent to, the part bed  102  to measure the temperature of the powder. Other devices may be used in conjunction with the IR camera  116 , or they may be used as a substitute for the IR camera  116 , to measure the temperature of the powder in the part bed  102 . 
         [0029]    The variable resistors  112 , the power sources  114 , and the heaters  108  may be arranged in different configurations. In some embodiments, each heater  108  may be configured with its own variable resistors  112  and power source  114 . In other embodiments, the heater  108  may share a common set of variable resistors  112 , a common power source  114 , or both. Additionally, the variable resistors  112 , the power sources  114 , and the heaters  108  may be configured in a series or parallel. Other configurations of these elements which facilitate the functionality described herein are also contemplated. 
         [0030]      FIGS. 2   a ,  2   b , and  2   c  illustrate different temperature distribution ranges  202 ,  204 ,  206 , respectively, for a part bed in accordance with an embodiment of the invention. The temperature distribution ranges  202 ,  204 ,  206  are generated by plotting the temperature of the powder in the part bed to create a three-dimensional graphical representation of the temperature distribution across the powder. The part bed has an area enclosed by part formation borders  208 ,  210 ,  212  that circumscribes the area for temperature control. Products are created within the part formation borders  208 ,  210 ,  212  where the temperature may be maintained in accordance with a desired (or target) temperature distribution. The temperature of the zone outside of the border is not relevant to the process. 
         [0031]    In some embodiments, the desired temperature distribution of the part bed is approximately constant across the zone heat distributions (or heat gradient), and thus a graphical representation depicts an approximately flat surface on a profile  214 ,  216 ,  218 . When the part bed has an inconsistent or uneven temperature distribution of the powder in the part bed, the graphical representation will appear inconsistent with features  220 ,  222  including dips, valleys, ridges, elevations and other non-uniformities that represent inconsistencies of the temperature across the powder in the part bed. In comparison, the temperature distribution range  206  in  FIG. 2   c  is relatively flat and thus has no significantly distinct features on the surface  224 . This indicates an approximately constant temperature of the powder in the part bed. In contrast, the temperature distribution range  202  in  FIG. 2   a  has a curved profile  214  and distinct features  220  representing large inconsistencies in temperature across the powder in the part bed. For example, the temperature distribution range  202  may be a graph of the temperature distribution before control and adjustment. Further, the temperature distribution range  204  in  FIG. 2   b  has a relatively flat profile  216 , but still contains distinct features  222  representing large inconsistencies in temperature across the powder in the part bed. For example, the temperature distribution range  204  may be a graph of the temperature distribution after an initial or rough adjustment, or before equilibrium across the part bed has been reached. Therefore, the temperature distribution range  206  depicts a desired (or target) temperature distribution using the methods and systems for controlling and adjusting heat distribution over a part bed as disclosed herein. 
         [0032]      FIGS. 3   a  and  3   b  are top plan views from an IR camera perspective of temperature distributions  302 ,  304 , respectively, of a part bed including zones in accordance with another embodiment of the invention. The temperature distributions  302 ,  304  depict variations in the temperature across the powder and is represented by color or gray-scale variances (i.e., consistent color or shading equates to an even temperature). The temperature distribution  304  in  FIG. 3   b , utilizing the methods and systems for controlling and adjusting heat distribution over a part bed as disclosed herein, depicts a desired (or target) temperature distribution that is more consistent temperature across the part bed than the temperature distribution  302  in  FIG. 3   a.    
         [0033]    In  FIG. 3   a , the part bed has a part formation border  306  circumscribing multiple heater zones  308 . In one embodiment, the nine heater zones  308  are utilized for controlling and adjusting heat distribution over a part bed, however, fewer or more zones may be utilized. The temperature distribution  302  illustrates the powder temperature before adjustment of the heaters, and includes a warmer temperature at a first point  310  (light color/shade) and a cooler temperature at a second point  312  (dark color/shade), thus illustrating a relatively inconsistent temperature distribution  302 . In  FIG. 3   b , the part bed has a part formation border  314  circumscribing multiple heater zones  316 . The temperature distribution  304  illustrates the powder temperature after adjustment of the heaters, with a first point  318  that has a substantially similar (or approximately constant) temperature as a second point  320 . Therefore, unlike the temperature distribution  302  in  FIG. 3   a , the temperature distribution  304  in  FIG. 3   b  illustrates a relatively consistent temperature distribution  304 . 
         [0034]      FIG. 4  is a schematic of an exemplary zone grid  400  of a part bed in accordance with an embodiment of the invention. The zone grid  400  overlays a part bed  402  that further includes a product formation border  404 . As previously described, parts are formed within the product formation border  404  where the temperature is controlled to a desired (or target) temperature distribution. For example, in a particular embodiment, the zone grid  400  may be divided into nine zones  406 . Each of the nine zones  406  may be further divided into a 9×9 grid of sub-zones  408 , thus the zone grid  400  may have 27×27 sub-zones. The IR camera may capture data relating to the measurement of the temperature for each sub-zone  408 . For example, the IR camera may capture pixilated data points which correspond to the sub-zones  408 . The data points may then be used to create a temperature zone grid, such as the zone heat distribution  118  in  FIG. 1 . In an embodiment, the temperatures of the sub-zones  408  for each of the nine zones  406  may be averaged to create a temperature for each of the nine associated zones  406 . For example, the eighty-one temperature sub-zones  408  in a zone  410  may be averaged to create a single temperature for the zone  410 . 
         [0035]      FIG. 5  is a flow chart of a method  500  for controlling and adjusting the heat distribution over a part bed in accordance with another embodiment of the invention. The method  500  begins at a block  502 . At a block  504 , the apparatus is prepared for control and adjustment of the heaters to provide a desired temperature distribution over the powder in the part bed. The preparation may include removing any parts from an additive manufacturing equipment that may interfere with the operation of the heaters. Additionally, the additive manufacturing equipment may include mirrors that direct or position the beam of the laser  106  within the part bed  102 . These mirrors may require removal or relocation during the operation of the heaters. Additional parts may also need to be removed or relocated at the block  504 . 
         [0036]    In addition to removing and relocating parts of the additive manufacturing equipment, the part bed must also be prepared for a simulated process run at the block  504 . This may include selecting part build locations and distribution one or more thin layers of powder across the part bed. For example, the part bed may be prepared by creating a base of a part by completing the first  10  layers of the product(s). Providing a partial product build may improve the operation of the heaters and thus create a more even temperature distribution over the part bed because temperature variances induced by the product formation are taken into account in the process. 
         [0037]    At a block  506 , after the part bed has been heated, the heat distribution is measured with the IR camera. The heat distribution may also be measured by other temperature extracting devices such as by thermocouples or other heat sensing devices. Data is collected from the temperature measurement at the block  506  which is utilized to generate a zone heat distribution at a block  508 . With reference to  FIG. 1 , the zone heat distribution  118  may include a grid of temperatures, one for each temperature zone. For example, an IR camera may output pixilated data that is converted to a zone heat distribution at the block  508 . 
         [0038]    At a block  510 , the heat distribution is analyzed. The analysis may be performed by the CPU  120 . For example, an analysis module may be executed by the CPU  120  to calculate any adjustments necessary to the heaters to provide a desired temperature distribution (uniform or non-uniform) across the powder in the part bed. At a decision block  512 , the method  500  determines if the heaters need to be calibrated. The heaters may be adjusted if a zone is outside a predetermined threshold for the zones in relation to a target temperature. For example, the heaters may be adjusted if the zone heat distribution has a variance of temperature greater than two degrees Celsius from the target temperature. Because some temperature variance may always be present across the powder, an adjustment threshold may be established to provide a temperature distribution within acceptable predetermined tolerances. 
         [0039]    If an adjustment is necessary at the decision block  512 , then at a decision block  514  the method  500  selects an adjustment mode via routes A, B, or C. At a block  516  via route A, the energy input to the heaters is adjusted to individually change the input energy of one or more heaters that require adjustment. The energy input may be adjusted by changing the voltage supplied to the heaters by a power source. The electrical current applied to the heaters may also be varied to control the heat emitted from the heaters and directed to the powder in the part bed. Additionally, the energy may be pulsed to the heaters using a variable duty cycle, such that the heat provided by a heater is a function of the pulsating operation of the heater. In one embodiment, each heater is individually controlled and includes a separate power source. 
         [0040]    At a block  518  via route B, the resistance is adjusted to change the resistance of individual heaters and thus alter the heat output of one or more of the heaters. For example, a varistor or rheostat may be utilized to change the resistance of the circuit which includes the heater, thus adjusting the heat output realized across the powder in the part bed. 
         [0041]    At a block  520  via route C, the heaters are repositioned to redirect the heat generated by one or more heaters onto the powder in the part bed. At a decision block  522 , the method  500  determines if another adjustment mode is requested (or required). If so, the method  500  returns to the decision block  514  via route  524  and the heaters are adjusted again. For example, in an iteration of the method  500 , both the resistance at the block  518  and the heater position at the block  520  may be adjusted to control the heaters and generate a target temperature distribution across the powder in the part bed. 
         [0042]    The adjustment modes selected from the decision block  514  may include manual adjustments or automatic (system generated) adjustments. For example, at the block  520 , an operator may reposition the heaters manually or the heaters may be repositioned by actuators in communication with a CPU or other controller and be repositioned automatically. In addition, the adjustments may be performed either open loop or using closed-loop feedback control. 
         [0043]    At the decision block  522 , if it is determined that the adjustment process need not be repeated, the method  500  returns via route  526  to the block  506  to measure the heat distribution again. Moving ahead to the decision block  512 , if the method  500  determines that further control and adjustment of the heaters is not necessary (e.g., all of the zone heat distribution zones are within tolerance), then the method may move to a block  528  and end. The block  528  may include repositioning or reattaching any parts of the additive manufacturing equipment necessary as a result of the actions included in the block  504 . 
         [0044]      FIG. 6  is a flow chart of a closed loop process  600  for controlling and adjusting the heat distribution over a part bed in accordance with another embodiment of the invention. The process  600  begins at a block  602 . At a block  604 , the heat distribution is measured with the IR camera. Data is collected from the measurement at the block  604  which is utilized to generate a zone heat distribution at a block  606 . The data from the zone head distribution is transmitted to the processing device. In some embodiments, the CPU  120  may have a first module (module A) that generates the head distribution and a second module (module B) that receives the output from the first module. The second module may then perform the functionality of a block  610  and analyze the heat distribution obtained at the block  606 . In another embodiment, software executed by the IR camera may generate the zone heat distribution at the block  606 , and then transmit the data to the CPU  120  for analysis. 
         [0045]    At a block  612 , the heater control and adjustment begins. At a decision block  614 , the process  600  determines if the power source of one or more heaters needs adjustment. If the power source requires adjustment, at a block  616 , the energy is adjusted and the process  600  continues to a decision block  618 , otherwise the process continues to the decision block  618  without adjusting the energy output of any of the heaters. 
         [0046]    At a decision block  618 , the process  600  determines if the resistors corresponding to individual heaters need adjustment. If the resistance requires adjustment, at a block  620 , the resistance is adjusted and the process  600  continues to a decision block  622 , otherwise the process continues to the decision block  622  without adjusting the resistance of any of the heaters. 
         [0047]    At a decision block  622 , the process  600  determines if one or more heaters require repositioning. If the heaters need repositioning, at a block  624 , one or more heaters are repositioned and the process  600  continues to a decision block  626 , otherwise the process continues to the decision block  626  without repositioning any of the heaters. 
         [0048]    At the decision block  626 , the process  600  may be repeated via route  628  and therefore provide a closed loop system. For example, the process  600  may be run at specific time iterations or during a point in the process of additive manufacturing, such as right after a new thin layer of powder is applied to the part bed. Therefore, the process  600  may continually adjust the heaters during product formation by continually monitoring the temperature distribution of the powder in the part bed and making the necessary adjustments at the blocks  614 ,  620 , and  624  to control and adjust the heaters, and thus, the temperature distribution. If the process is not repeated, such as when the products are complete and no more powder is distributed in the part bed, the process  600  may end at a block  630 . 
         [0049]    In an exemplary control and adjustment of the heaters, the analysis of the zone heat distribution may identify the zone with the lowest temperature. For example, in  FIG. 1 , zone  1  and zone  3  in the zone heat distribution  118  depict a temperature of 159° C. The CPU  120  may then create adjustments to the variable resistors  112  (e.g., increase the resistance) and reposition the heaters to reduce the temperature in the other zones to that of the coldest zones (zones  1  and  3  at 159° C.). In a final step, the CPU  120  may increase/decrease the energy to the heaters to raise/lower the temperature of all the heaters to obtain a target temperature. 
         [0050]    Generally, any of the functions described herein can be implemented using software, firmware (e.g., fixed logic circuitry), analog or digital hardware, manual processing, or any combination of these implementations. The terms “module,” “functionality,” and “logic” generally represent software, firmware, hardware, or any combination thereof. In the case of a software implementation, the module, functionality, or logic represents program code that performs specified tasks when executed on processor(s) (e.g., any of microprocessors, controllers, and the like). The program code can be stored in one or more computer readable memory devices. Further, the features and aspects described herein are platform-independent such that the techniques may be implemented on a variety of commercial computing platforms having a variety of processors. 
         [0051]    Methods and systems for controlling and adjusting heat distribution over a part bed in accordance with the teachings of the present disclosure may be described in the general context of computer executable instructions. Generally, computer executable instructions can include routines, programs, objects, components, data structures, procedures, modules, functions, and the like that perform particular functions or implement particular abstract data types. The methods may also be practiced in a distributed computing environment where functions are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, computer executable instructions may be located in both local and remote computer storage media, including memory storage devices. 
         [0052]    In further embodiments, the methods and systems for controlling and adjusting heat distribution over a part bed may allow for a part bed of increased dimensions. For example, in some embodiments, part beds may be approximately 31 centimeters (13 inches) by 36 centimeters (15 inches). This size part bed, however, restricts the size of the part that may be formed utilizing the additive manufacturing techniques. By implementing the methods and systems disclosed herein, any size part bed is obtainable because the temperature distribution may be held at a desired uniform or non-uniform distribution by individually controlling a plurality of heaters to individually heat each zone of the part bed. 
         [0053]    While preferred and alternate embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of these preferred and alternate embodiments. Instead, the invention should be determined entirely by reference to the claims that follow.