BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to methods and systems for manufacturing and assembling, and, in particular, to methods and systems for manufacturing and assembling computer systems in a build-to-order environment. 
     2. Description of the Related Art 
     Traditionally, manufacturing systems have been designed and constructed based upon a build-to-stock model where large quantities of identical products are assembled to meet forecasted demand and warehoused until that demand occurs. Such manufacturing systems provide economies of scale based upon the large quantities of identical units and can be optimized by increasing the speed with which each manufacturing step is completed. Because build-to-stock manufacturing systems rely on known product configurations, each step in the manufacturing process is known in advance, and so the manufacturing system utilizes progressive build techniques to optimize each stage in the serial assembly process. For products (e.g. a computer system) that include sensitive components, progressive build manufacturing systems can be carefully planned in advance to protect those sensitive components. Once the manufacturing system becomes operational, it will build the same product repeatedly, using the optimized steps. 
     However, when the process is adapted to build a different product, or a different version of the same product, the manufacturing system must be modified and re-optimized to ensure that the system still protects sensitive components. Moreover, because the progressive build process is serial, each stage depends on timely completion of the previous stage, and thus the entire process is susceptible to problems, inefficiencies, and failures in any of the stages of the system. Additionally, progressive-build manufacturing systems operating in a build-to-stock environment are relatively inflexible, limiting the ability of the manufacturing system to fill small orders economically and to control inventory. 
     One method used to increase performance in progressive-build manufacturing processes is to include a process step in which identical kits are prepared that hold the components needed to assemble a particular product or to complete a particular manufacturing step. In this way some of the time normally required to select parts for a particular product or manufacturing step can be reduced, and some manufacturing steps can more easily be performed in one location or by one operator or piece of manufacturing equipment (e.g. an industrial robot). For example, U.S. Pat. No. 4,815,190 discloses the use of automated and manual kitting stages for producing identical kits for automobile sub-assemblies. One advantage to using identical kits is that it is relatively easy to know if all of the parts needed to assemble a particular product are present in the kit; a missing part stands out because each kit should always have the same set of components. 
     As an alternative to progressive-build manufacturing systems which are often faced with the problem of large dwell times, i.e. time periods where a product being assembled must wait before moving to a subsequent assembly stage, some manufacturing systems have been shifted to continuous flow manufacturing (CFM) methods. In general, CFM methods employ a demand-driven pull system for inventory control and movement of components into the assembly process. This can include the use of kanban techniques for inventory control and movement. CFM also supports mixed-model manufacturing continuous flow production lines. CFM systems offer continuous flow of value added activities, eliminating wasted motion and dwell times. Other terms often used for CFM include Just-In-Time (JIT) manufacturing, Flexible and Agile Manufacturing, Synchronous Manufacturing and Demand Based Conversion. 
     Personal computers, servers, workstations, portables, embedded systems and other computer systems are typically assembled in manufacturing systems designed for build-to-stock environments. A typical personal computer system includes a processor, associated memory and control logic and a number of peripheral devices that provide input and output (I/O) for the system. Such peripheral devices include, for example, compact disk read-only memory (CD-ROM) drives, hard disk drives, floppy disk drives, and other mass storage devices such as tape drives, compact disk recordable (CD-R) drives or digital video/versatile disk (DVD) drives. 
     Manufacturing computer systems becomes inefficient when the number of identical units is decreased and process steps are changed as orders change, both of which are characteristics of a build-to-order environment where computer systems (or products generally) are manufactured or assembled only after an order for that particular computer system has been placed. As a result, the conventional manufacturing systems do not adapt well to the build-to-order environment and can limit the ability to fill small orders, require extra inventory, generate more work-in-process, and be globally constrained by the slowest process step. This process also requires line changeovers and new tooling when change is required. One attempt to adapt and to improve the efficiency of conventional manufacturing systems has been to reduce the number of components prepared in advance of orders. By limiting such in-process inventory, the line can change configurations more easily as orders change. However, this scheme is still limited in its efficiency for smaller orders in the build-to-order environment. 
     Because computer systems manufacturers have recognized that a build-to-order environment is advantageous and often can better react to the speed with which product designs and customer expectations change, there is a need to provide manufacturing systems and methods that more efficiently integrate with the build-to-order model while ensuring that high quality, defect free products are produced. 
     SUMMARY OF THE INVENTION 
     It has been discovered that parallel organized unit-by-unit manufacturing and assembly systems and methods for computer systems and other products advantageously integrate into a build-to-order environment. Responsive to orders received, kit trays are prepared that each hold the components needed to build an ordered product. The kit tray is transferred to a work cell where a team builds the product. The product is then tested and repaired, with information regarding any problems provided to the responsible work cell. 
     Accordingly, one aspect of the present invention provides a build-to-order product assembly system including a control unit, a kitting unit, and an assembly unit. The control unit is capable of receiving a product order describing a product to be assembled. The control unit includes a list of product components for the product to be assembled. The kitting unit is coupled to the control unit and receives the list of product components. The kitting unit includes a plurality of kit trays, a plurality of stored product components, and a product component list display device. The product component list display device displays the list of product components so that a kit tray with product components pulled from the stored product components and according to the product component list display device can be prepared. The assembly unit is coupled to the kitting unit and receives the prepared kit tray from the kitting unit. The assembly unit has a first work cell including a work space for assembly of the product using the product components from the prepared kit tray. 
     In another aspect of the invention, a manufacturing system for assembly of computer systems in a build-to-order environment is disclosed. The system includes a kitting unit housing kit trays and computer system components. A list of components for assembling an ordered computer system is received by the kitting unit. The list of components is displayed to at least one kitting operator to allow respective kit trays to be prepared with computer system components for the ordered computer system by pulling selected computer system components from those housed at the kitting unit. The system also includes an assembly unit constructed to receive prepared kit trays from the kitting unit. The assembly unit has a plurality of work cells operable in parallel. At least one work cell provides work space and tools to allow a team of work cell operators to assemble an ordered computer system using the computer system components from a prepared kit tray. Also, the work cell provides an integrated quick test, shared by at least one other work cell, to allow a quick test operator to test the assembled computer system for basic functionality. The system also includes an extended test unit constructed to receive assembled computer systems from the work cells. The extended test unit provides work space and tools to allow at least one extended test operator to quality test assembled computer systems. 
     In still another aspect of the invention, a method of assembling a build-to-order product is disclosed. A list of components for assembling an ordered product is received and displayed. A kit tray including product components is prepared. The prepared kit tray is transferred to an assembly unit operable to receive prepared kit trays. The ordered product is assembled in the assembly unit using the product components from the prepared kit. 
     In yet another aspect of the invention, a build-to-order computer system includes a chassis, a processor supported by the chassis, and a memory coupled to the processor. The build-to-order computer system is assembled by a method of assembling a build-to-order computer system including (1) receiving and displaying a list of components for assembling the build-to-order computer system; (2) preparing a kit tray including build-to-order computer system components; (3) transferring the prepared kit tray to an assembly unit operable to receive prepared kit trays; and (4) assembling the ordered product in the available work cell using the build-to-order computer system components from the prepared kit. 
     In yet another aspect of the invention, a build-to-order product assembly system includes a kitting unit, an assembly unit, and at least one of a quick test cell and an extended test unit. The kitting unit receives a list of product components. The kitting unit includes a plurality of kit trays, a plurality of stored product components, and a product component list display device. The product component list display device displays the list of product components so that a kit tray with product components pulled from the stored product components and according to the product component list display device can be prepared. The assembly unit is coupled to the kitting unit and receives the prepared kit tray from the kitting unit. The assembly unit has a first work cell including a work space for assembly of a product using the product components from the prepared kit tray. The quick test cell is coupled to the first work cell and is operable to receive the assembled product and perform a test of basic functionality of the assembled product. The extended test unit is coupled to the assembly unit and is operable to receive the assembled product from the assembly unit and perform a quality test of the assembled product. The quick test cell and the extended test unit are operable to provide information about failure of the respective test to the first work cell. 
     In still another aspect of the invention, a build-to-order product assembly system includes a kitting unit, and an assembly unit. The kitting unit receives a first list of product components and a second list of product components. The kitting unit includes a plurality of kit trays, a plurality of stored product components, a first product component list display device, and a second product component list display device. The first product component list display device displays the first list of product components so that a first kit tray with product components pulled from the stored product components and according to the first product component list display device can be prepared. The second product component list display device displays the second list of product components so that a second kit tray with product components pulled from the stored product components and according to the second product component list display device can be prepared. The product components of the first prepared kit tray have at least one difference with the product components of the second prepared kit tray. The assembly unit is coupled to the kitting unit. The assembly unit is operable to receive the first and the second prepared kit trays from the kitting unit and has a work cell including a work space for assembly of a product using the product components from one of the first and second prepared kit trays. Assembly begins when all of the components for the product are in the one of the first and second prepared kit tray. 
     In still another aspect of the invention, a build-to-order product assembly system includes a kitting unit and an assembly unit. The kitting unit receives a list of product components. The kitting unit includes a plurality of kit trays, a plurality of stored product components, and a product component list display device. The product component list display device displays the list of product components so that a kit tray with product components pulled from the stored product components and according to the product component list display device can be prepared. The assembly unit is coupled to the kitting unit and receives the prepared kit tray from the kitting unit. The assembly unit has a first work cell including a work space for assembly of a product using the product components from the prepared kit tray. The assembly occurs in an order and with a number of steps reducing damage to the product components. 
     In still another aspect of the invention, a build-to-order product assembly system includes a kitting unit and an assembly unit. The kitting unit receives a list of product components. The kitting unit includes a plurality of kit trays, a plurality of stored product components, and a product component list display device. At least one of the kit trays includes a plurality of component retaining features. The component retaining features are operable to reduce impact to product components stored therein from kitting tray movement. The product component list display device displays the list of product components so that a kit tray with product components pulled from the stored product components and according to the product component list display device can be prepared. The assembly unit is coupled to the kitting unit and receives the prepared kit tray from the kitting unit. The assembly unit has a first work cell including a work space for assembly of a product using the product components from the prepared kit tray. The assembly occurs in an order and with a number of steps reducing damage to the product components. 
     The systems and methods advantageously provide that a kit tray is not prepared and assembly does not begin until an order is received. After an order is received, the kit tray is prepared with all of the components needed to assemble the ordered product. In this respect, the kitting stage is both pulled and order-driven. Additionally, each prepared kit tray is transferred to a work cell where one operator or a team of operators assemble the ordered computer system. Assembly of the computer system does not begin until all components are available in the work cell. The team is enabled to perform a quick test of basic functionality as an integrated part of the assembly process. If there are any problems, the team is directly accountable and can quickly receive feedback. Higher production speed, greater ease of reconfiguration, fewer touches of components, fewer and more localized work stoppages and a more efficient handling of small orders are additional advantages. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. 
     FIG. 1 is a block diagram of a manufacturing/assembly system for producing computer systems (and products generally) in a build-to-order fashion. 
     FIG. 2 is a flow chart illustrating a kitting process. 
     FIG. 3 is a flow chart illustrating a chassis preparation process. 
     FIG. 4 is a flow chart illustrating assembly and quick testing. 
     FIG. 5 is a flow chart illustrating an extended test. 
     FIG. 6 is a flow chart illustrating a repair process. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 schematically illustrates a manufacturing or assembly system  100  for producing a variety of products, and computer systems in particular, in a build-to-order fashion. The system is controlled by control unit  110  which provides computer system orders, order information, and/or component lists derived from computer system orders to kitting unit  130  and chassis preparation unit  135 . Although not shown, control unit  110  can also provide order related information to any and all of the elements of the system, as needed. Control unit  110  is best implemented as a computer system that integrates with or includes an order taking system. As will be seen below, control system  110  can also provide indirect and direct control of various system units. Instead of, or in addition to control unit  110 , each of the units of system  100  can have local control subject to communication among some or all of the units. For example, kitting stage  130  could receive order information directly from an order taking system, thereby obviating the need for control unit  110 , and directly pass information on to other units as needed. 
     FIG. 2 illustrates the kitting  200 . In step  210 , kitting unit  130  receives product order information. Components needed for assembly are identified in  220 . Next, the components are pulled to build a kit. Once prepared, the kit is transferred to the assembly unit  150  as shown in step  240 . 
     Referring again to FIG. 1, kitting unit  130  receives computer system components from component source  138 , which may be a warehouse, a truck delivering components just in time, or the like. Components are stored in kitting unit  130  so that they are accessible for pulling. Kitting unit  130  also includes kit trays designed to accommodate all or substantially all of the components required to fill an order for a computer system. Thus, the kit trays can include various compartments and features built into the tray such as a lip to support a chassis on top of the tray. Additionally, kit trays can be manufactured from or can include soft materials such as foam so as to protect computer system components that are pulled and placed into the kits. Kitting trays can be designed to provide better protection for computer system components than is provided by the chassis in which the component is ultimately installed. Protecting the components contributes to the production of high quality, low defect computer systems. Kitting unit  130  also includes kitting stages  132 , each having some or all of the components needed to prepare a kit tray for a particular computer system order. Thus, each stage may be responsible for pulling all of the components for a given order, or components can be pulled from one or more of the different stages (i.e. progressively building the kits), thereby filling out the kit tray. 
     The list of components needed for an ordered computer system is provided to a component list display device, the component list display device, in turn, displays the list of computer system components to a kitting unit operator. The component list display device can be, for example, a piece of paper listing the needed components, a computer system screen displaying the needed components, or a pick-to-lights system integrated with the storage for components (e.g. shelving) in the kitting stages. In the case of a pick-to-lights system, control unit  110  can supply component list information directly to the pick-to-lights system. For example, an operator can assign a bar code to a specific kit tray (or alternatively each tray can have a permanent bar code assigned to it). When the operator scans the bar code, a specific order is assigned to that bar code and the pick-to-lights system proceeds to indicate to the operator which components to pick by lighting an indicator at each pick location for each needed component, in succession. With each pick, the pick-to-lights system waits for pick confirmation by the operator (e.g. the operator presses a button), and once received, proceeds to indicate the next item to be picked. In this manner, all of the components for an ordered computer system are pulled and placed in a kit tray, thus preparing the tray for transfer to assembly unit  150  using, for example, a conveyor. 
     Although all of the components for an ordered computer system can be provided to assembly unit  150  by kitting unit  130 , it is also desirable, in some circumstances, to include chassis preparation unit  135  as part of system  100 . Chassis preparation  300 , as illustrated in FIG. 3, begins with step  310  where chassis preparation unit  135  receives product order information. Components needed for assembly are identified in  320 . Next, the components are pulled and a chassis is prepared. It should be noted that chassis preparation unit  135  and chassis preparation  300  can include preparation and/or installation of additional components such as the computer system motherboard. Chassis preparation unit  135  and chassis preparation  300  are particularly suited to preparation of components that require special handling (e.g. a motherboard, a processor, and memory), require extra time for setup (e.g. installing the flash memory BIOS for the computer system), that vary little from order to order (e.g. a power supply), or that can be installed in such a manner that the component will not interfere with or complicate the installation of subsequent components. Once prepared, the chassis is transferred to the assembly unit  150  as shown in step  340 . 
     Control unit  110  can operate to coordinate the delivery of information to both the kitting unit and the chassis preparation unit so that a prepared kit tray for a particular order and its corresponding prepared chassis are ready for assembly unit  150  at approximately the same time. Alternatively, either kitting unit  130  or chassis preparation unit  135  can control when the other unit&#39;s process begins or signal when the other unit&#39;s process should begin so that both the prepared kit tray and its corresponding prepared chassis are ready at approximately the same time. Order fulfillment information can flow by means of a traveler which can be in a paper format and an electronic format. When both the prepared chassis and the prepared kit tray are ready, the prepared chassis is added to the prepared kit tray, by, for example, placing the chassis on the lip of the kit tray, before being sent to the assembly unit. This is accomplished in joining area  140  which is coupled to both kitting unit  130  and chassis preparation unit  135  by conveyor lines or other appropriate devices. Note that as between various system elements such as joining area  140  and kitting unit  130  coupling encompasses both physical coupling such as a conveyor, and systematic association such as a path to transfer items from one unit to the other. Additionally, joining area  140  can include a scanner to confirm that a particular kit tray and a particular chassis belong together. The joining process can be performed automatically by machine, manually by an operator, or by some combination of the two. 
     FIG. 4 is a flow chart of the assembly process  400 . In step  410 , a prepared kit tray is joined with the appropriate prepared chassis, as previously described in relation to joining area  140 . Next, in step  420 , the kit and chassis are placed in a queue  145  where they await an available work cell  152  in assembly unit  150 . A variety of different queuing schemes may be implemented depending on the requirements of assembly unit  150  and the physical layout of system  100 . For example, a single queue  145  (as shown) may support all of the work cells of the assembly unit. Alternatively, there can be multiple queues, each supporting one or more work cells. The number of joined prepared chassis and prepared kit trays in a queue is also variable depending upon the needs of the system. Step  430  indicates that once a work cell is available, the work cell operator or team for that cell assembles the computer system. A work cell team includes two or more operators to assemble the computer system. In item  440 , a quick test of basic computer system functionality is performed. Additionally, to eliminate wait time by an operator or team and to optimize the assembly process, a queue can be designed to operate on a first in first out (FIFO) basis. 
     Multiple kits can be prepared simultaneously in kitting unit  130  and multiple computer systems can be assembled simultaneously if there are multiple work cells. Consequently, system  100  is able to produce multiple computer systems in parallel, in contrast to progressive-build systems which produce a single completed computer system at a time. 
     As seen in FIG. 1, assembly unit  150  includes a quick test cell  154 . Quick test cell  154  can be combined with work cell  152 , quick test cell  154  can be associated with a single work cell, or as shown, quick test cell  154  can be shared by two or more work cells. Item  450  indicates that if the computer system passes the quick test, the process proceeds to item  460  where the computer system is transferred to an extended test unit  170 . If the computer system fails the quick test in item  450 , item  470  determines if the failure is a system component failure, for example a motherboard failure. The cause of the failure is identified by a decision matrix. Item  490  shows that computer system failures that are not system component failures (e.g. the failure is caused by an operator error) cause the computer system to be returned to the work cell that built the computer system. Information about the failure is also given to the work cell. Alternatively the work cell operator is called to the quick test cell to provide feedback. In this manner, immediate feedback is provided to the work cell operator or team and the problem can be remedied efficiently. Moreover, the quick feedback helps the operator or team learn from their mistakes, thereby becoming more productive and giving the operator or team greater ownership of the process. This also provides a learning environment which improves workmanship and improves quality. As indicated in item  480 , if the computer system failure in the quick test is caused by a system component failure, the computer system is transferred to a repair unit  160 . 
     Work cell  152  is designed so that all or substantially all of the computer system assembly is performed there. The work cell includes a work space and any tools needed to assemble the computer system. Conveyors lead from kitting unit  130  and from chassis preparation unit  135  to the work cell so that the kit tray is quickly and easily transferred. Assembly of the computer system may not begin unless all of the computer system components needed for the computer system are in the kit tray. If a component is defective, a work cell operator obtains a replacement component, either directly or by requesting that another operator obtain the component. Because assembly unit  150  does not operate in a progressive build manner, the kit with the defective component can be set aside until the replacement component is obtained, and another computer system can be assembled from another kit (taken from the queue) in the interim. 
     Where the work cell has a team of two operators, one operator prepares a component for assembly while the other operator is installing a different component. Operators alternate installing and preparing components until the computer system is completed. In addition to general assembly training provided to operators, assembly instructions specific to the computer system being assembled can accompany the computer system components in the kit tray, or can be provided directly to the work cell by, for example, interactive electronic work instructions. With electronic work instructions, a computer in the work cell can display instructions including detailed figures as determined by the information associated with the ordered computer system and its kit tray. Assembly steps generally, and electronic work instructions in particular, are designed to reduce or minimize the number of components that must be handled by an operator and the number of times that any one component must be handled. Thus, by reducing the number of “touches,” a computer system is less likely to be damaged or erroneously assembled, lead times are reduced, and throughput is increased. 
     As noted above, the quick test cell  154  can be part of work cell  152  and consequently the operator of the quick test cell and the work cell may be the same operator. For example, a computer system that is particularly complicated or specialized may better be assembled by a single operator (as opposed to a team). In such a case, that work cell can include the quick test cell so that the operator initiates the quick test on an assembled computer system and then begins to assemble another system while the quick test is being performed. Those having ordinary skill in the art will readily recognize that a variety of combinations of quick test cells, work cells, and associated operators can be implemented in the present manufacturing and assembly methods and systems. 
     FIG. 5 describes the extended test  500 . In item  510 , the extended test is performed on the computer system. This process entails transferring the assembled computer system to a burn-in rack where the computer system is connected to a network and detailed testing of the computer system&#39;s quality is performed. To make transferring the assembled computer system from assembly unit  150  to extended test unit  170  more efficient, a stacker can be used to stack several computer systems for loading on to a cart. The cart is then transferred to extended test unit  170  for insertion of the computer systems to be tested. 
     Item  520  determines if the computer system has passed the extended test. If not, the computer system is transferred to repair unit  160  as shown in step  550 . Additionally, item  560  shows that information about the failure can be provided by the extended test unit to the work cell responsible for assembling the computer system. Such information can also be provided to the work cell by repair unit  160 . If the computer system passes the extended test, additional installation steps can be performed such as those indicated by item  530 . For example, software that was ordered for the computer system can be installed while the computer system is still connected to the network from which the extended test is performed. Finally, the computer system proceeds to item  540  where the computer system is shipped. As indicated by FIG. 1, shipping occurs in shipping unit  180 . Shipping unit  180  can include a variety of steps such as final preparation (e.g. wipe-down and labeling), bundling with other ordered items, and packaging. 
     Extended test unit  170  is controlled by a smart burn-in monitoring system designed to eliminate wasted effort in the extended test process. For example, the smart burn-in monitoring system displays a screen indicating each of the positions in extended test unit  170  in which a computer system is or can be placed. Status information such as which computer systems have failed the extended test, which computer systems have completed the extended test, which levels of the extended test have been completed, and which positions in the extended test unit are vacant is displayed. 
     FIG. 6 illustrates the repair process  600  as performed in repair unit  160 . Item  610  indicates that the computer system&#39;s problem is identified and repaired. Because a computer system can be sent to repair unit  160  from either a quick test cell or the extended test unit, repair unit  160  may receive information from either of those sources to assist in problem diagnosis and repair. Once the problem has been identified and repaired, feedback in the form of information about the failure is provided to the work cell responsible for the computer system, as shown in item  620 . In step  630 , the computer system is sent to extended test unit  170  (for the first time in the case of a computer system failed to the repair unit from a quick test cell). 
     Those of ordinary skill in the art will readily recognize that the manufacturing systems and methods described above can be implemented when building a variety of different products, and not just computer systems. 
     The description of the invention set forth herein is illustrative and is not intended to limit the scope of the invention as set forth in the following claims. Variations and modifications of the embodiments disclosed herein may be made based on the description set forth herein, without departing from the scope and spirit of the invention as set forth in the following claims.
Parallel organized unit-by-unit manufacturing and assembly systems and methods for computer systems and other products advantageously integrate into a build-to-order environment. Responsive to orders received, kit trays are prepared that each hold parts and components needed to build an ordered product. The kit tray is transferred to a work cell where a team builds the product. The product is then tested and repaired, with information regarding any problems provided to the responsible work cell.