Abstract:
A positioner for use in a tooling apparatus, the positioner including a tool, at least one servo-motor for actuating said tool, a controller for controlling the servo-motor, nonvolatile memory in the controller, and a calibration stored in the nonvolatile memory, the calibration including compensation parameters for the build variance of the positioner.

Description:
TECHNICAL FIELD 
     The present invention relates to manufacturing. More specifically, the present invention relates to a method and apparatus to provide for the adaptable assembly of products such as automotive vehicles. 
     BACKGROUND OF THE INVENTION 
     In today&#39;s vehicle market, there exist a variety of body shapes, sizes and styles to meet the demands of consumers. Traditionally, manufacturing facilities have been limited in the types of vehicle that they may manufacture because of different vehicle footprints and part number differences between vehicles. For example, compact cars and luxury cars have different body panel sizes and in some cases a different number of body panels. The tooling systems used in traditional manufacturing facilities have typically been mechanically and electrically fixed to produce one body configuration or style. To change to a different body configuration or style, these traditional tooling systems must be mechanically reconfigured and reprogrammed, creating delays and long startup times for vehicle body style changeovers. There is increasing pressure to reduce lead times and provide for increased flexibility in manufacturing facilities such that multiple vehicle body styles may be produced in generally the same period of time or quickly changed over. 
     Tooling systems typically include mechanical and electrical actuators coupled to tooling devices. The mechanical and electrical actuators may include electric motors, screws, gearboxes and/or slides. There will always be a slight build variance between electrical and mechanical actuators of the same type. For example, the run-out for electric motor shafts, the backlash in gear boxes, and the pitch in screws will slightly vary between actuators of the same type. These slight variances will be amplified by the assembly of multiple mechanical and electrical actuators into one robot or positioning tool such as a multi-axis positioner used in the assembly of vehicles. Accordingly, upon replacing a faulty positioning tool, the new positioning tool must be shimmed, rotated, adjusted and/or reprogrammed to exhibit the same dynamic and static characteristics of the previous faulty positioning tool. This is a time-consuming process that may cause delays in production for a manufacturing facility. 
     SUMMARY OF THE INVENTION 
     The present invention incorporates a programmable adaptive assembly system (PAAS) that enables the flexible manufacturing of multiple vehicle types or styles and compensates for build variances between robots or positioners used for the same production functions and a nominal or “ideal” positioner. The present invention permits quick replacement of failed positioners without losing accuracy through an electronic plug-and-play system, reducing manufacturing costs associated with downtime and insuring the quality of a vehicle assembly. 
     The PAAS system of the present invention further includes a tooling system assembly for a work cell that has been designed to allow the replacement of traditional vehicle body specific shop tooling, with a single common, programmable tool set that is capable of building multiple vehicle body styles. The tooling system of the present invention is a highly accurate, modularly scaleable, programmed positioning device used to hold tooling locators and other tooling devices used in the assembly of vehicles. The work cell of the present invention is also scaleable with the ability to be configured for any number of positioners. 
     The PAAS system of the present invention comprises a robot or positioner coupled to an end effector having a tooling device. The positioner includes a plurality of servo-motors and mechanical actuation devices such as gearboxes, linear slides, and screws to position the tooling device in three dimensions, as required by a manufacturing work cell. A servo-drive or servo-controller, in communication with a tooling coordinator system, controls the movement of the servo-motors and stores compensation parameters or a calibration that describe the kinematics of the positioner. The calibration is used by the tool coordinator to reference and compensate for the movements of the positioner against an absolute coordinate set or the “ideal” positioner for the manufacturing work cell. In this manner, upon the failure of a first positioner, a second positioner may easily be installed in its place in a plug-and-play manner. The servo-controller of the second positioner will automatically download the calibration for the second positioner to the tool coordinator and allow the tool coordinator to make the necessary actuation command adjustments to compensate for the build variances between the first and second positioners. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic drawing of a manufacturing cell of the present invention; 
         FIG. 2  is diagrammatic drawing of the tool coordinator control system for the manufacturing cell of the present invention; 
         FIG. 3  is a diagrammatic drawing of a servo drive of the present invention; 
         FIG. 4  is a diagrammatic perspective drawing of the actuation directions of the positioner of the present invention; 
         FIG. 5  is a cutaway drawing of a positioner of the present invention; 
         FIG. 6  is a diagrammatic drawing illustrating the coordinate systems used in the present invention; and 
         FIG. 7  is a flowchart illustrating a preferred method of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a diagrammatic view of a programmable adaptive assembly system (PAAS) for a work or manufacturing cell  10  used in the present invention. The manufacturing cell  10  is preferably incorporated in a manufacturing production line for the manufacture of vehicles  12 . Tooling robots or positioners  14  are used in the assembly of the vehicles  12  and are designed to be worked with hard tools and can be operated with automation and/or manual interaction. End effectors  15  equipped with tool holders, clamps and/or pins may be manipulated by the tooling positioners  14  in any manner required for the assembly of the vehicles  12 . The PAAS system is used to locate tooling at different required spatial positions or datums, for different styles of subassembly builds for vehicles  12 . Accordingly, the positioners  14  of the PAAS system may be reconfigured quickly and easily for different vehicle styles being assembled. The positioners  14  of the PAAS system preferably include locating clamps coupled to the end effectors  15  for the fixturing of vehicle body panels. The positioner  14  architecture is optimized for application functionality, positional repeatability, accuracy, stiffness and payload capacity. 
     The basic functions of the positioners  14 , as previously described, are to hold and manipulate tooling to assemble a vehicle. The number of positioners  14  used in the manufacturing work cell  10  is scaleable and is determined by the datum and locator strategy for the products or vehicle style to be built in that manufacturing work cell  10 . The positioners  14  are used with principal locating points (PLPs) that move dimensionally from style to style, and a hard tool for locators that are common for each style or product being manufactured. The positioners  14  are designed to be extremely repeatable, accurate, able to withstand the harsh environment of an auto body shop, cost effective, and maintainable by manufacturing plant personal. 
       FIG. 2  is a diagrammatic drawing of the control system for the PAAS system in the manufacturing cell  10  of the present invention. Each positioner  14  preferably includes five servomotors having absolute position feedback, but any number of servomotors is within the scope of the present invention. The type of servomotors that are used in the present invention include, but are not limited to, brushless DC motors, AC space-vector technology, DC motors, stepper motors, and reluctance motors. The absolute position feedback may be provided by any positioning device known in the art including, but not limited to, linear encoders and rotary encoders. 
     As seen in  FIG. 2 , a servo-drive amplifier or servo-controller  16  is the electronic drive unit that provides power and servo control for each of the five servomotors in the positioner  14 . The servo-drive controllers  16  are preferably environmentally sealed with radiant fins to transfer heat to external air. Referring to  FIG. 3 , the servo-drive controller  16  includes power circuitry  18  necessary to provide switched or conditioned electrical energy to the servomotors, a microprocessor/microcontroller  20 , a positioning program and calibration stored in nonvolatile memory (NVM)  22 , random access memory (RAM)  24  for the execution of programs, an input/output interface  26  to the servomotors of the positioner and other process control devices, and a network communication interface  28  for communicating on a computer network  29 . 
     The servo controller  16  and the positioner  14  are electrically coupled together through cable  30 . Cable  30  is preferably a shielded cable that carries power from the power circuitry  18  in the form of electrical energy to the servomotors and position and speed feedback signals in the form of low voltage signals from the servomotors to the input/output interface  26  of the servo controller  16 . 
     The servo controllers  16 , as previously described, are equipped with a network communication interface  28  such as an ARCNET interface to communicate over the computer network  29  and coordinate the movement of the positioners  14 . While ARCNET is the preferred network and network interface of the servo-drives  16  of the present invention, any communication/ computer network such as Ethernet, DEVICENET or CAN may also be used in the present invention. The servo-drives  16  are further linked, via the computer network  29 , to a central coordinator control system for the PAAS system residing on a computer collectively termed as the tool coordinator  32 . The servo-drive controllers  16  and computer network  29  are preferably wired in daisy chain fashion, as shown in  FIG. 2 , for connection to the tool coordinator  32 . Each servo controller  16  has a network or node address that is uniquely specified for each servo controller  16  in the manufacturing work cell  10 . 
     The tool coordinator  32 , as previously described, comprises tool coordination software residing on a computer. The tool coordinator  32  manages and processes actuation commands from an industrial controller  34 , such as a programmable logic controller (PLC), or diagnostic monitor  36 , and transfers the commands to the servo controllers  16 , via the computer network  29 . The tool coordinator  32  communicates with the industrial controller  34  over a DEVICENET network. While DEVICENET is the preferred communication network for connecting the tool coordinator  32  and industrial controller  34 , any computer network may be used including, but not limited to, Ethernet, Data Highway+, DH 485, any type of serial network, Profibus DP, and/or Modbus+. 
     The tool coordinator  32  acts as the network master for the dedicated servo controller  16  ARCNET network. The tool coordinator  32  commands each of the servo controllers  16  to actuate the positioners  14  in the manufacturing work cell  10 . The tool coordinator  32  in the preferred embodiment may communicate with up to  254  nodes or servo controllers  16 . The tool coordinator  32  further analyzes and stores the calibration data for the positioners  14  upon transfer from the servo-drive controllers  16 . 
     The diagnostic monitor  36  comprises a computer, preferably a laptop personal computer, which includes a diagnostic software and programming tools. The diagnostic monitor  36  communicates with the tool coordinator  32  via a serial link such as an RS232 or RS422 link. The diagnostic monitor  36  has multiple functions including programming, manual control of positioner  14  movement, diagnosis and correction of positioner  14  control problems, electronic shimming, data management, system backup and system restoration. 
     Referring to  FIG. 4 , to adapt to different vehicle assembly models and styles, the positioner  14  is preferably capable of five different types of articulation as shown by axes one-five. The positioner may move horizontally (axis one), vertically (axis three), and rotate around a vertical axis (axis two). The tooling attachment or end effector  15  may rotate around both vertical and horizontal axes (axes four and five). The actual performance dynamics will vary based on the design and dimensions of the positioner  14 . By repositioning tools under the control of the positioner  14 , the work cell  10  of the present invention is capable of building multiple models of vehicles  10 , and can be easily reprogrammed when a new model is introduced into production. 
       FIG. 5  further illustrates the construction and movement of the positioner  14  of the present invention. Axis one is a linear axis which provides travel in what will be defined as a horizontal direction with reference to the orientation of  FIGS. 4 and 5 . A first servo-motor  40  is coupled to a lead screw or ball screw  42  to provide the linear motion for a slide  44  coupled to linear rails  46  mounted to a baseplate  48 . Linear bearing blocks  50  are mounted within a main casting  52  of the positioner  14  to provide movement along axis one for the main casting  52 . An anti-backlash lead screw nut  54 , finned for cooling, is connected to the main casting  52  by means of a bracket  56 . The mounting diameter of the lead screw nut  54  is grooved to house a quad-ring (not shown). The purpose of the quad-ring is to provide a slight radial float of the lead screw nut  54  to compensate for any slight misalignment between the centerline of the leadscrew  42  and the centerline of the lead screw nut  54 . When the first servo-motor  40  is actuated, the entire positioner  14  will move along axis one on the linear bearings  50  carrying the other four axes. 
     Axis two is a rotary axis with the axis of rotation perpendicular to axis one (in a normal mounting position perpendicular to the floor). Axis two is driven by a second servo-motor  60  which is similar to the first servo-motor  40  of axis one. The second servo-motor  60  is connected to a gearbox  62 , and the output shaft of the gearbox  62  is fitted with a pinion gear  64 . The pinion gear  64  is meshed with an internal gear  66 . The internal gear  66  is rigidly mounted to the main casting  52  of the positioner  14 . Also mounted to and within the main casting  52  is a vertical tube  68 . The vertical tube  68  is supported by means of ball bearings  70 . The second servomotor  60  and gearbox  62  combination is mounted to the internal wall of the vertical tube  68  through a clevis arrangement. When the second servo-motor  60  is actuated, the vertical tube  68  and everything mounted within it or to it is rotated about the centerline of axis two. 
     Axis three is a linear axis which allows the top portion of the positioner  14  unit to telescope vertically up and down along the axis two centerline. Axis three is driven by a third servo-motor  72  similar to servo-motors  40  and  60 . The output shaft of the third servo-motor  72  is fitted with a pinion gear  74  meshed with gear  76  which is attached to a ball screw or lead screw  78 . The third servo-motor  72  is bolted to a vertical axis casting  80  through a motor bracket. A bracket  82  contains bearings which support the leadscrew  78 . The leadscrew includes an anti-backlash leadscrew nut similar to nut  54  which is rigidly mounted to the vertical tube  68 . When the third servo-motor  72  is actuated, the leadscrew  78  is rotated and the vertical axis casting  80  is raised (or lowered depending on the direction of rotation), and carries with it everything mounted to it. 
     Axis four is a rotational axis found at the top extremity of the positioner  14 . Axis four is driven by a fourth servo-motor  90  which is similar to the previous servo-motors  40 ,  60  and  72 . The fourth servo-motor  90  is connected to a gearbox  92  which is mounted within a gearbox casting. Mounted to the output shaft of the gearbox  92  is a bevel pinion gear  94 . The bevel pinion gear  94  meshes with a bevel gear  96  which is mounted to shaft  98 . The entire wrist mechanism or end effector  15  is fastened to the shaft  98 . When the fourth servo-motor  90  is actuated, the bevel pinion gear  94  drives bevel gear  96 , in turn rotating shaft  98  and all the wrist mechanism or end effector  15  mounted to shaft  98  about axis four. 
     Axis five is another rotational axis found within the wrist mechanism or end effector  15  at the top of the positioner  14 . Axis five is driven by a fifth servo-motor  110 , which is similar to the previous servo-motors  40 ,  60 ,  72  and  90  described. A bevel pinion gear  112  is attached to the fifth servo-motor  110  shaft. The bevel pinion gear  112  is in mesh with another bevel gear  114 , which is mounted to the input of a harmonic drive gearbox  116 . Piloted into the output side of the harmonic drive gearbox  116  is the end of another bevel gear pinion  118 . The bevel gear pinion  118  is rigidly coupled to the gearbox  116 . When the fifth servo-motor  110  is actuated, power is transmitted through bevel gears  112  and  114 , gearbox  116 , pinion  118  and a bevel gear  120 , causing a wrist clevis casting  122  to move in a pitching motion about the illustrated by axis five. The end effector  15  in the preferred embodiment is an independent module containing electronics and a calibration that may be freely swapped between positioners  14 . The end effector is also calibrated against a nominal or “ideal” end effector. 
     As shown in  FIG. 5 , each positioner  14  incorporates a series of modular mechanical linkages and, as described earlier, each corresponding servo-controller  16  incorporates electrically-embedded calibration or a “personality” describing the static and dynamic dimensional characteristics of each linkage of each positioner  14 . The calibration allows compensation for mechanical build variation from positioner  14  to positioner  14  or the nominal positioner to allow interchangeability of positioners  14 , reducing the cost of maintaining spare positioners  14  in a manufacturing plant. The calibration of each positioner  14  allows the tool coordinator  32  to adapt to dimensional variation in individual components in the positioners  14  or the positional variations in the different works spaces. 
     The positioners  14  are calibrated at the manufacturer to generate the unique compensation parameters or calibration for the build variances of each positioner  14 . This provides the plug-and-play capability for the positioners  14  of the PAAS system and assures accuracy from positioner  14  to positioner  14 . To calibrate a positioner  14 , a motorized laser tracker and laser detector measures the static and dynamic characteristics of the positioner  14 . The positioner  14  is actuated throughout its entire range of motion and the resulting position information/calibration generated by kinematic parameters, such as the effective length of each link, is stored and transferred to the corresponding servo-drive controller  16 . While a laser tracker has been described in the present invention, any type of position sensing technology such as digital optical cameras, charge coupled devices, radar, and ultrasonic positioner detectors are included within the scope of the present invention. 
     Manufacturing work cell  10  accuracy also depends on an accurate assessment of the relative location of the positioners  14  and the positions of their movements as they relate to each other. By computer simulations using computer aided design (CAD) or other means, nominal command data is generated for the manufacturing work cell  10 . The coordinates that must be factored into each move or command to a positioner  14  are shown in FIG.  6  and include vehicle coordinates, tool coordinates, positioner coordinates, and tool plate coordinates. The command data generated for positioner  14  movement includes numerical definitions of the nominal location of the base of each positioner  14  in a master coordinate system (the tool plate coordinates based on the nominal or “ideal” positioner); numerical definitions of the end effectors  15  and tool points with respect to mounting features on the positioner  14 ; and calibration parameters for each positioner  14  are determined as the final step in its manufacture, or after any repair work. The types of errors that may be compensated for include tool plate errors, where the bases of the positioners  14  are mounted in the workcell coordinate system, positioner  14  deviations from the nominal positioner  14 , and tool deviations from a nominal or “ideal” tool. 
     Referring to the flow chart of  FIG. 7 , at Block  130 , during the initialization or restart of the work cell  10 , the tool coordinator  32  reads the nominal command data and the actual measurement data for the work cell  10  and the end-effectors from the tool coordinator  32  memory. At Block  132 , the tool coordinator queries the NVM  22  of the servo controllers  16  of the positioners  14 , via the computer network  29 , to obtain their calibration parameters. The tool coordinator  32  also reads a file of electronic shimming commands which are incremental translations or rotations of the tools to be added to the originally-planned tool locations from tool coordinator  32  memory. The tool coordinator  32  at Block  134  uses the nominal data to calculate the desired toolpoint locations as originally planned in CAD, and then adds the shim adjustments to generate the end effector  15  locations as desired in the manufacturing cell  10 . The tool coordinator  32  uses the actual measurements of the workcell  10  and the calibration parameters of the positioners  14  at Block  136  to compute compensated movement or joint commands to the servo controllers  16  that place the toolpoints in the desired locations. The compensated movement or joint commands are downloaded to the individual servo controllers  16  at Block  138  and the movements are executed by the positioners  14  at Block  140 . 
     Maintenance/repair procedures are established such that after replacing a failed positioner  14 , the tool coordinator  32  is re-initialized to read the calibration of a new positioner. Thus, accurate actuation commands are maintained during positioner  14  replacement. Accordingly, positioners  14  and their corresponding servo controllers  16  may be connected to the tool coordinator  32  in a plug-and-play fashion. 
     While this invention has been described in terms of some specific embodiments, it will be appreciated that other forms can readily be adapted by one skilled in the art. Accordingly, the scope of this invention is to be considered limited only by the following claims.