System for the flexible assembly of assemblies

A method and system for the flexible assembly of components into an assembly at an assembly station within an assembly area in an adaptive, programmable fashion. Several programmable locators mounted on a platform work cooperatively to receive and support components or parts having critical positioning features at approximate locations. The programmable locators then move the components so that the critical positioning features and hence the components are at desired locations. Thereafter, part position and orientation are constrained at retaining locations while the components are in their desired locations. Processing equipment at least partially joins the retained components either at the assembly station or at a separate processing station. One of the programmable locators may provide one of the retaining locations. Preferably, at least one sensor mounted on one of the programmable locators provides at least one feedback signal for a control means which controls at least one programmable locator to adapt its position with respect to at least one critical feature of its part to thereby relocate the part. In this way, verification of the accuracy of the positioning and holding is provided.

TECHNICAL FIELD 
This invention relates to a method and a system for the flexible assembly 
of components into an assembly. The method and system as described below 
apply to the fabrication of subassemblies from body panel components and 
the further fabrication of larger subassemblies from groups of smaller 
subassemblies, panels and other components. A further application of the 
method and system of the present invention is the final assembly of the 
full car body from larger subassemblies. 
BACKGROUND ART 
The predominate approach today to introduce factory automated technology 
into manufacturing is to selectively apply automation and to create 
islands of automation. The phrase "islands of automation" has been used to 
describe the transition from conventional or mechanical manufacturing to 
the automated factory. Interestingly, some appear to use the phrase as 
though it were a worthy end object. On the contrary, the creation of such 
islands can be a major impediment to achieving an integrated factory. 
Manufacturing examples of islands of automation often include numerically 
controlled machine tools; robots for assembly, inspection, painting, and 
welding; lasers for cutting, welding and finishing; sensors for test and 
inspection; automated storage/retrieval systems (AS/RS) for storing 
work-in-process, tooling and supplies; smart carts monorails, and 
conveyors for moving material from work station to work station; automated 
assembly equipment and flexible machining systems. Such islands are often 
purchased one at a time and justified economically by cost reductions. An 
example of an AS/RS system is disclosed in the U.S. Pat. No. to Loomer 
4,328,422. A different type of AS/RS system and control system therefor is 
disclosed in the U.S. Pat. No. to Tapley 4,232,370. 
To integrate the islands of automation, it is necessary to link several 
machines together as a unit. For example, a machine center with robots for 
parts loading and unloading can best be tied to visual inspection systems 
for quality control. Computer numerical control machine tools can all be 
controlled by a computer that also schedules, dispatches, and collects 
data. Selecting which islands to link can be most efficiently pursued on 
the basis of cost, quality and cycle time benefits. 
In some cases, the islands of automation will be very small (e.g. an 
individual machine or work station). In other cases, the islands might be 
department-sized. The U.S. Pat. No. to Kawano 4,611,749 discloses the use 
of robots to transfer parts between such islands which are relatively 
close to each other. 
From a systems viewpoint, islands of automation are not necessarily bad, so 
long as they are considered to be interim objectives in a phased 
implementation of an automated system. However, to obtain an integrated 
factory system, the islands of automation must be tied together or 
synchronized. Systems synchronization frequently occurs by way of a 
material-handling system; it physically builds bridges that join together 
the islands of automation. Early examples of such islands of automation 
linked together by a material-handling system are disclosed in the U.S. 
Pat. Nos. to Williamson 4,369,563 and Lemelson 3,854,889. 
The '563 patent discloses a system including machine tools which perform 
machining operations on workpieces loaded on pallets. The pallets are 
delivered to the machine tools from a storage rack by transporters. The 
workpieces are manually loaded onto the pallets. 
The '889 patent discloses a system including work-holding carriers which 
are selectively controlled in their movement to permit work to be 
transferred to selected machine tools while bypassing other machine tools. 
Automated material handling has been called the backbone of the automated 
factory. Other than the computer itself, this function is considered by 
many automation specialists as the most important element in the entire 
scenario of automated manufacturing. It is the common link that binds 
together machines, workcells, and departments into a cohesive whole in the 
transformation of materials and components into finished products. For 
example, the U.S. Pat. No. to Sekine et al 4,332,012 discloses a control 
system for assembly lines for the manufacture of different models of 
automotive vehicles. Temporary storage is provided between assembly steps 
by a storage section. 
To date, one of the major applications for industrial robots has been 
material handling. Included here are such tasks as machine loading and 
unloading; palletizing/depalletizing; stacking/unstacking; and general 
transfer of parts and materials--for example, between machines or between 
machines and conveyors. An example of one such application is disclosed in 
the U.S. Pat. No. to Kenmochi 4,519,761. The '761 patent discloses a 
combined molding and assembling apparatus wherein a pallet is conveyed by 
a conveyor. Resin components are carried by the pallet for use in the 
molding and assembling operation. 
Robots are often an essential ingredient in the implementation of Flexible 
Manufacturing Systems (FMS) and the automated factory. Early examples of 
the use of robots for assembling small parts is disclosed in the U.S. Pat. 
Nos. to Engelberger et al 4,163,183 and 4,275,986 wherein robots are 
utilized to assemble parts from pallets onto a centrally located 
worktable. 
The automated factory may include a variety of material transportation 
devices, ranging from driver-operated forklifts to sophisticated, 
computer-operated, real-time reporting with car-on-track systems and color 
graphics tracking. These material transport systems serve to integrate 
workcells into FMS installations and to tie such installation and other 
workcells together for total factory material transport control. 
With all of their versatility, robots suffer from a limitation imposed by 
the relatively small size of their work envelope, requiring that part work 
fixtures and work-in-process be brought to the robot for processing. 
Complete integration of the robot into the flexible manufacturing system 
requires that many parts and subassemblies be presented to the robot on an 
automated transport and interface system. For example, installation of an 
assembly robot without an automated transport system will result in an 
inefficient island of automation needing large stores of work-in-process 
inventory for support, which are necessary to compensate for the 
inefficiencies of manual and fork truck delivery. 
An example of the use of robots in a manufacturing assembly line is 
disclosed in the U.S. Pat. No. to Abe et al 4,611,380. The '380 patent 
also discloses the use of a bar code to identify the components to be 
assembled to a base component to control the assembly operations. 
The U.S. Pat. No. to Suzuki et al 4,616,411 discloses a fastening apparatus 
including a bolt receiving and supply device for use in the automated 
assembly of a door to a vehicle. 
The handling, orienting and feeding of parts as they arrive from vendors 
are formidable jobs which must be done prior to robotic assembly since, in 
general, all such parts require reorienting for the assembly robot. The 
U.S. Pat. No. to Kohno et al 4,527,326, for example, discloses a vibratory 
bowl which feeds parts to an assembly robot. A vision system enables the 
robot to properly pick up the parts from the bowl. 
Part feeding is a technology that generally has lagged behind the advanced 
automation system it supports. However, in general, part feeding curtails 
flexibility, increases costs, increases floor space requirements and 
lengthens concept-to-delivery time. For maximum flexibility, a minimum 
amount of tooling should be considered. On the other hand, additional 
tooling can be used effectively to "buy time" by assisting the robot. 
Typically, dedicated hardware--bowl feeders, magazines, pallets--is 
required to feed parts to the robot. Unlike the robot, dedicated hardware 
is not easily reusable and therefore is less economical for medium-volume 
applications. 
The U.S. Pat. No. to Suzuki et al 4,383,359 discloses a part feeding and 
assembly system, including multiple stage vibration and magazine feeders. 
A robot is utilized to change the position of the fed parts for assembly 
on a chassis supported on a line conveyor. The robot operates in 
combination with a vision system to reorient the parts. 
Neither flexible nor sophisticated, part feeding equipment is usually 
constructed by highly skilled artisans working with welding torch and 
hammer in small specialized shops. The most common and most inexpensive 
feeding method--vibratory bowl feeding--provides the builder with a 
versatile base easily modified to handle many different parts which are 
not delicate and which are substantially identical. Delicate parts or 
parts that tangle, such as motors, are better fed by magazines or trays 
for exact orientation. 
Also, not all parts, for example, can be bowl fed. For most parts, the 
overriding concern is geometry and, in particular, symmetry. If a part is 
either symmetric or grossly asymmetric, then vibratory bowl feeding will 
be easier and more efficient. 
Robots may load and unload workpieces, assemble them on the transport, 
inspect them in place or simply identify them. The kind of activity at the 
robot or machine and material transport system interface dictates the 
transport system design requirements. One of the design variables relating 
to the interface includes accuracy and repeatability of load positioning 
(in three planes). Also, care in orienting the workpiece when it is 
initially loaded onto the transport carrier will save time when the work 
is presented to the robot or the tool for processing. Proper orientation 
of the part permits automatic devices to find the part quickly without 
"looking" for it and wasting time each time it appears at the workstation. 
Fixtures may be capable of holding different workpieces, reducing the 
investment required in tooling when processing more than one product or 
product style on the same system. 
The transport system must be capable of working within the space 
limitations imposed by building and machinery configurations, yet must be 
capable of continuous operation with the loads applied by a combination of 
workpiece weight, fixture weight, and additional forces imposed by other 
equipment used in the process. 
The system must also have the ability to provide queuing of parts at the 
workstation so that a continuous flow of work is maintained through the 
process. Automatic queuing of transport carriers should provide gentle 
accumulation without part or carrier damage. 
The primary impediment to robotic assembly is economic justification. When 
the cost of robotic assembly is compared against traditional manual 
methods or high volume dedicated machinery, robots oftentimes lose out. On 
one side of the spectrum are the high-volume, high-speed applications 
where hard automation is used. It's difficult for robots to compete in 
that environment. On the other side are the low-volume, high variety 
products that are assembled manually. Robots may lack the dexterity to 
perform these jobs, and they may cost more than relatively low-paid manual 
assemblers. There is a middle ground between these two extremes for 
flexible assembly. Many believe that the best approach is a combination of 
robots, dedicated equipment and manual assembly. 
While assembly is one of the most difficult areas of robotic application, 
many say it also holds the most promise. Assembly robots offer an array of 
benefits that cannot be ignored. They can produce products of high and 
consistent quality, in part because they demand top-quality components. 
Their reprogrammability allows them to adapt easily to design changes and 
to different product styles. Work-in-process inventories and scrap can be 
reduced. Therefore, it is important that the materials transport system 
serving the robots be capable of quickly moving into position with parts, 
then quickly moving out of the workstation and on to downstream stations. 
Prompt transporter movements between stations allow work-in-process 
inventory to be minimized. Batch sizes are smaller and work faster with 
only a minimum of queuing at each workstation. 
The U.S. Pat. No. to Yamamoto 4,594,764 discloses an automatic apparatus 
and method for assembling parts in a structure member such as an 
instrument panel of an automobile. A conveyor conveys a jig which supports 
the panel to and from assembly stations. Robots mount the parts on the 
instrument panel at the assembly stations. Robots are provided with 
arm-mounted, nut-driving mechanisms supplied from vibratory parts bowls. 
A link for tying together some of the independently automated manufacturing 
operations is the automatic guided vehicle system (AGVS). The AGVS is a 
relatively fast and reliable method for transporting materials, parts or 
equipment, especially when material must be moved from the same point of 
origin to other common points of destination. Guide path flexibility and 
independent, distributed control make an AGVS an efficient means of 
horizontal transportation. As long as there is idle space and a relatively 
smooth floor to stick guide wires or transmitters into, the AGVS can be 
made to go there. 
As an alternative to traditional conveying methods, the AGVS provides 
manufacturing management with a centralized control capability over 
material movement. Also, the AGVS occupies little space compared with a 
conveyor line. Information available from the AGVS also provides 
management with a production monitoring data base. The U.S. Pat. No. to 
Mackinnon et al 4,530,056 discloses an AGVS system including a control 
system for controlling the individual vehicles. 
Robot installations for transporter interface can be grouped into three 
principal categories: (1) stationary robots, (2) moving (i.e. mobile) 
robots (on the floor or overhead), and (3) robots integral with a machine. 
The moving robots subdivide into two types. First are stationary robots, 
mounted on a transporter to move between work positions to perform 
welding, inspection, and other tasks. The second type of moving robot is 
the gantry unit that can position workpieces weighing more than one ton 
above the workcells and transport system. The system only has to deliver 
and pick somewhere under the span of gantry movement. 
End effectors used in material handling include all of the conventional 
styles--standard grippers, vacuum cups, electromagnets--and many special 
designs to accommodate unusual application requirements. Dual-purpose 
tooling is often used to pick up separators or trays, as well as the parts 
being moved through the system. 
Vacuum-type grippers and electromagnetic grippers are advantageous because 
they permit part acquisition from above rather than from the side. This 
avoids the clearance and spacing considerations that are often involved 
when using mechanical grippers. 
However, the use of vacuum and electromagnetic grippers is not without its 
problems since cycle time is not just a function of robot speed and its 
accelerating/decelerating characteristics. Cycle time is dependent on how 
fast the robot can move without losing control of the load. Horizontal 
shear forces must be considered in the application of these grippers. This 
often means that the robot is run at something less than its top speed. 
Currently, automotive body assembly utilizes fixtures on which body panels 
ar placed relative to each other in a predefined relative location. The 
relative location is determined by location points which supports the 
panel and confines its location to the desired position. Location points 
are usually comprised of hard stops against which the panels are clamped, 
or closely confined within acceptable tolerances. 
The location points must be adjusted to the correct location relative to 
adjacent panels and components, within necessary tolerances, before the 
panels and components are joined by process equipment. To attain the 
necessary level of accuracy, it is usually necessary to make manual 
adjustments to the confining clamps by shimming and the like. The 
adjustment must also be verified by high accuracy measurements. The whole 
process is very tedious, costly, and time consuming. 
When the panel is used as an outside skin for the car body, clamping may 
mar the outside surface of the panel and harm the final appearance of the 
car. Such panels are only located in a confined configuration with small 
clearances. The clearance between the panels and the confining mechanism 
must be minimized to maintain desired accuracy when allowance is made for 
panel distortion and mechanism inaccuracies. Manual adjustment and 
verification is again necessary. 
Once the panels are located and clamped or confined to the desired relative 
positions, the assembly is usually transferred to other process equipment 
for permanent joining of all panels and components together. Spot welding 
is a common method of joining in automotive manufacturing. Bonding, 
fusion, and laser welding are also recognized joining methods of metals 
and other materials, such as composite polymeric materials. 
The integrated subassembly is then unclamped, lifted off the fixtures, and 
transferred to other assembly locations to be integrated into another 
subassembly, or finally, the full car body. 
Occasionally, robots and programmable devices are used for automating 
certain automotive body assembly processes such as spot welding and 
material handling. However, this has not generally extended to the 
location of the components handled or processed. An example of an 
exception is disclosed in U.S. Pat. No. 4,944,445. The '445 patent 
requires the presorting of assembly components and their placement at 
approximate locations on a specially designed pallet prior to being 
operated on. This requirement carries with it the inconvenience, cost, and 
space demands of a multitude of assembly pallets not much different from 
what is currently experienced with hard automation approaches. 
The '445 patent also discloses programmable locators, described as tool 
carriers, and require that they be fitted with customized tools that are 
designed to fit the assembly, or the process, such that the assembled 
parts nest accurately on the tooling jaws. 
This arrangement has the advantage over hard automation in that it requires 
only one set of accurate tooling that remains at the joining station of 
the parts instead of being duplicated with each pallet as is done with 
hard automation. However, as many pallets are needed as for hard 
automation. The locators are arranged in groups with each group 
constrained to move in common planes of motion, hence limiting flexibility 
to make re-adjustments after the components have been located on the 
tooling. 
U.S. Pat. No. 4,641,819 discloses programmable devices which are positioned 
accurately for the intended location of parts and which have locating 
means which, by their location, define the location of the part. 
Programmable devices, conventionally known as robots, locate the parts. 
The device of the '819 patent has a set of locator gross adjustment means, 
and a set of locator fine adjustment means. 
U.S. Pat. No. 4,821,408 discloses passive positioning means, or a jig, with 
holding means that can be moved by separate moving means. 
U.S. Pat. No. 4,738,387 addresses an assembly station layout, stacking of 
parts, and storage of parts. 
U.S. Pat. No. 4,811,891 discloses a method of two-wheeled vehicle assembly. 
Jigs are fixed as typical with hard automation. The '891 patent does not 
teach flexibility in adapting to differences in body, or frame, size, or 
to components of different shapes. 
U.S. Pat. No. 4,960,969 discloses a conventional use of robots for the 
transfer of panels when combined with tool changing to allow robots to 
handle as well as process parts, such as by spot welding. 
U.S. Pat. No. 4,691,905 discloses forming the mounting face of a part 
holder to the "form" of the part. 
French Patent Document No. 2631-100-A discloses a positioner that moves a 
part after it has been clamped to it. 
U.S. Pat. No. 4,894,901 addresses cooperative processing of one part by two 
robots, one for holding and one for processing. 
U.S. Pat. No. 4,875,273 discloses a device which positions parts by fixed 
jigs. A robot moves the composite assembly. 
U.S. Pat. No. 3,624,886 relates to conventional hard automation and 
component assembly methods using same. 
Prior art fixtures generally must be tailored to specific models, sizes, 
and styles of car bodies. Different fixtures are required for each 
subassembly even when variations are small between car body styles. It is 
therefore necessary to build multiple fixtures whenever more than one body 
style is to be manufactured in the same production facility. With the 
proliferation of body sizes and styles in the auto industry, it is obvious 
that this approach imposes appreciable cost penalties on automotive 
manufacturers in several ways: 
Initial investment in multiple dedicated fixtures. 
Excessive demand on floor space to accommodate multiple fixtures, hence 
larger capital investment in plant buildings and facilities. 
Replacement cost of fixtures whenever new models are introduced. 
Idle plant capacity and lost sales opportunities whenever market demand 
shifts between car models; when idle capacity of low selling models cannot 
be readily used to manufacture hot selling ones. 
Low product quality, hence less profits, as fixture adjustment shifts with 
use. 
Inflexibility in accommodating design changes which may affect body 
location features, hence, less responsiveness to market demands and loss 
of sales. 
The prior art generally follows a "hard automation" approach. Very few 
tooling systems have the capability to accommodate more than one panel 
unless the variations between panels are minor and are not related to the 
critical location features of the tooling. Occasionally, tooling may be 
designed with additional features that may accommodate one or more 
different panels, but this adds to the complexity, cost, and size of the 
tooling; and also detracts from its reliability. An example is shown in 
U.S. Pat. No. 4,256,947. 
Because of this rigidity in application, current hard tooling fixtures must 
be changed with each model change. This translates into long lead time 
requirements for the introduction of new models, higher production cost 
for automobiles, slow response to market demands for new features, and in 
general, unfavorable competitive position for the auto manufacturer. 
Furthermore, hard tooling is subject to misadjustment as locators shift in 
place with continuous use and frequent impact on the friction-held 
locators. This results in poorly located parts and the need for frequent 
adjustment. Since the adjustment is done by shimming and bolt clamping, 
this is a tedious process that cannot be done precisely and results in 
inconsistency in tooling and poor quality in products. 
In the prior art, material handling is usually done manually or by 
dedicated material handling mechanisms. Panels are placed in the fixtures 
manually and may require the cooperative effort of two persons, especially 
for heavy or flimsy (pliable) parts that require multiple points of 
support. This is a tedious operation which reduces product quality as 
people become tired and damage panels by misplacement, dents, and 
abrasion. Dedicated placement and transfer mechanisms also have limited 
use as they occupy a permanent location and cannot usually be utilized to 
automate all candidate operations because of conflicting space 
requirements. The cost and space penalties associated with automating the 
placement and transfer of small components does not usually justify its 
application. Hence, such automation is usually limited to large and heavy 
parts and subassemblies. Therefore, full automation is generally 
impractical with the prior art. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a generic method and 
system for the mechanical assembly of components requiring the processing 
or joining of accurately located components by a material joining 
operation such as by mechanical fasteners, adhesive bonding, material 
fusion, welding (spot, arc, laser, E-beam, etc.), etc. 
It is also an object of the invention to provide a flexible, generic, model 
independent, tooling method and system for automotive body assembly which 
is: 
Flexible (i.e., accommodates a mix of body sizes, running design changes, 
and model changes); 
Economical (i.e., provides appreciable cost savings over current hard 
automation systems despite its added benefits for being Model independent, 
and usable across model changes); 
Efficient (i.e., gets tooling off the critical path of new model 
introduction programs, thus allowing faster new model introductions to the 
market, and quick retooling by program change instead of hardware 
fabrication); 
Accurate (i.e., provides improvements in tooling accuracy and tooling 
consistency through programmability and adaptive tuning, and requiring 
less dependency on human judgment); 
Consistent (i.e., always locates the body components in the desired 
location without manual adjustment, shimming, clamping, etc.; The location 
points do not change with frequent use); 
Automatable (i.e., allows the automation of all processes associated with 
automotive body assembly such as material handling of large and small 
components, and panel placement, location, clamping, and joining). 
In carrying out the above objects and other objects of the present 
invention, a method is disclosed for the flexible assembly of components 
into an assembly at an assembly station within an assembly area. The 
assembly station including a base and a plurality of programmable locators 
mounted at predetermined locations on the base to define a base coordinate 
frame. Each of the programmable locators is controlled by control means 
having a first set of programs to move under program control within a work 
envelope. The method includes the steps of: (a) receiving and supporting a 
component having at least one critical positioning feature by at least one 
of the programmable locators at an approximate location that is definable 
relative to the at least one critical positioning feature of the 
component; (b) adjusting the actual location of the component in the work 
envelope of its at least one programmable locator by controlling the at 
least one programmable locator to move the component from the approximate 
location under program control of one of the first set of programs such 
that the at least one critical positioning feature of the component is 
located at a desired location, hence, defining a desired location for the 
component; (c) retaining the component in the desired location at a 
plurality of retaining locations, the component having a position and an 
orientation in the desired location which are constrained at the retaining 
locations; and (d) repeating steps (a) through (c) for each component in 
the assembly, the components being constrained to allow process equipment 
to at least partially process the components to obtain the assembly. 
Preferably, the method also includes the step of generating at least one 
location signal representing the actual location of at least one feature 
of one of the components in the base coordinate frame, wherein the one of 
the components of the assembly is moved based on the at least one location 
signal during the step of adjusting. 
Further in carrying out the above objects and other objects of the present 
invention, a system is disclosed for the flexible assembly of components 
into an assembly in an assembly area. The system includes a assembly 
station including a base and a plurality of spaced programmable locators 
mounted at predetermined locations on the base to define a base coordinate 
frame. Each of the programmable locators has a work envelope and is 
adapted to receive and support a component having at least one critical 
positioning feature at an approximate location that is definable relative 
to the at least one critical positioning feature of the component. The 
system also includes control means having a first set of programs. Each of 
the programmable locators moves under program control within its work 
envelope to adjust the actual location of its component such that the at 
least one critical positioning feature of the component is located at a 
desired location, hence, defining a desired location of the component. 
Finally, the system includes means for retaining each of the components in 
its desired location at a plurality of retaining locations. Each of the 
components has a position and an orientation in its desired location which 
are constrained at its retaining locations. The components are constrained 
to allow process equipment to at least partially process the components to 
obtain the assembly. 
Preferably, the system also includes means for generating a location signal 
representing the actual location of at least one critical positioning 
feature of one of the components in the base coordinate frame. One of the 
components is moved based on the location signal during adjustment of its 
actual location. 
The advantages of the method and system of the present invention are 
numerous. For example, the method and system: 
(1) Provide programmable location and support points which can be adjusted 
depending on the size, height, and other features of the component (panel) 
to be received, supported, and located. 
(2) Receive the component within a space that provides high tolerance for 
component mislocation in position and orientation, hence, it allows the 
approximate location of the component by component delivery equipment, 
such as robots. 
(3) Adjust the component accurately to a desired location after the 
component has been received at an approximate location. 
(4) Sense the location of critical positioning features in space and 
provide necessary adjustment to the locators. This assures accurate 
location of critical positioning features relative to each other and 
corrects for part inaccuracies without affecting its intended function. 
(5) Clamp or confine each component in its desired location. 
(6) Allow for process equipment to partially join the components of an 
assembly, such as by spot welding or bonding, and maintain dimensional 
stability in preparation for further processing by other process equipment 
and complete joining. 
(7) Allow for processing equipment, such as material joining, removal, and 
fastening robots, to perform desired processes while the assembled 
components are accurately located. 
(8) Allow for the integration of process functions in common equipment, 
such as by using clamping tips for spot welding. 
(9) Allow for modularization of the manufacturing process by integrating 
the fixtures with process tooling in one cell. Low volume manufacturing 
can then be done in limited floor space. 
(10) Allow for material handling of components through flexible automation, 
such as with robotic devices. Hence, provide opportunity for full 
automation of the manufacturing process with all associated benefits in 
quality, consistency and higher reliability and uptime of production 
lines. 
(11) Allow for the modularization of the location equipment, where the 
location and positioning devices can be all identical or made of common 
components; hence reduces cost, increases reliability and allows for ease 
of maintenance and service. 
(12) Can be reconfigured for different components (panels) and transferred 
for use from one automotive model year to the next, or from one plant to 
another. For new models, only the spacial location of the modules on a 
platform may change to accommodate the new model geometry. 
The above objects and other objects, features, and advantages of the 
present invention are readily apparent from the following detailed 
description of the best mode for carrying out the invention when taken in 
connection with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
The method and system of the invention is described hereinbelow in the 
course of its application to the assembly of a typical wheelhouse and 
quarter inner panel subassembly in a typical automotive body. However, it 
is to be understood that the method and system of the invention can be 
utilized to assemble a wide variety of assemblies which, in turn, can be 
assembled into yet other assemblies. 
The elements of the subassembly are shown in FIG. 1. A Quarter Inner Panel, 
QIP 1, is to be located and permanently joined to three other components, 
a Lock Pillar Inner, LPI 2, a Quarter Inner Upper, QIU 3, and a Wheelhouse 
Inner/Outer subassembly, WIO 4. This example is chosen to snow that the 
method applies for the assembly of panels into subassemblies, as well as 
for the assembly of a mix of panels, structural components, and 
subassemblies into larger subassemblies. Similarly, the method can be 
applied for the assembly of subassemblies (as components) into a complete 
car body assembly. 
Referring to FIG. 2, the method and system include the use of programmable 
locators 20 through 28. These are robotic support devices that can be 
positioned under a first set of control programs to specific locations 
suitable for the support and positioning of mechanical components or 
panels. The locators are mounted on a platform 14, at an assembly station 
within an automotive assembly plant. The position of the locators is 
chosen to allow the components of an assembly to be mounted on at least 
three support points provided by the locators. The locators have the 
ability to position those support points within a defined work envelope 
representing the reach of each robot locator, and allow them to support 
panels and components of different sizes and configurations. Some locators 
may be fitted with clamps to secure the components in their accurate 
locations in preparation for subsequent joining processes. 
The assembly operation using the method of the invention requires the 
placement of the subassembly components in a sequence with one component, 
the primary component, positioned first and accurately located and 
clamped. Other, or secondary, components are then sequentially positioned, 
located, and clamped relative to the primary component and to each other 
until the final assembly is complete. The assembly is then operated on by 
process equipment, such as robots, to join the assembly components 
permanently such as by spot welding or adhesive bonding. The processing 
may be done partially or totally at the assembly station, or the platform 
may be moved with the located and secured components, to a processing 
station. When the components are joined at the assembly station, some 
locators may be freed and repositioned to receive additional components, 
thus improving utilization of the locators. 
FIG. 3 shows the primary component, the QIP 1, of the wheelhouse 
subassembly positioned on locators 20, 21 and 22. FIG. 4 shows one 
secondary component, the LPI 2, located relative to the primary component 
by means of programmable locators 23 and 24 with the help of an extra 
support point available by nesting the LPI 2 with the QIP 1. FIGS. 5 and 6 
show the other secondary components of the wheelhouse subassembly, the QIU 
3 and the WIO 4, supported and located by programmable, robotic locators 
25, 26 and 27, relative to the QIP 1 and to each other. 
The programmable locators are not limited to providing only one point of 
support. End effectors, such as grippers carried by any one locator, can 
be designed to fully support and confine the workpiece (the panel) in as 
many as six degrees of freedom. 
The following are special considerations applicable to each step in the 
location and processing sequence. 
Support and Rough Location of the Primary Component: This is detailed in 
FIGS. 7 and 8. One component, preferably the heaviest or the most critical 
for integrity, accuracy, or functionality, may be chosen as the primary 
component for assembly. Other subassembly components are usually 
referenced or attached to the primary component. In this example, the 
primary component, panel 1, is located on at least three locators 5, 6 and 
7. The locators 5, 6 and 7 are represented differently here from those of 
FIG. 2 to show other options available for the implementation of the 
invention. The three support locators 5, 6 and 7 are required to provide a 
stable support for the panel 1 when each provides a point of support. 
Fewer locators may be adequate if any of them provided a line or surface 
support for the panel 1 instead of a point support. 
The primary component 1 is delivered to the assembly platform 14 either 
manually or by automatic material handling means, such as by robots. The 
delivery may provide only rough location for the primary panel 1. The 
locators 5, 6 and 7 may also support the panel 1 and be provided with 
means to guide its delivery to a better defined location. Guidance of the 
panel 1 may be provided by the constraints of a tapered pin guided into a 
hole, as shown for locator 5; or by providing the locator 6 with a sloped 
guiding surface 11 to constrain the side edges of the panel 1. 
While for some applications locators 5, 6 and 7 may be fixed, in other 
applications a positionable locator may be desirable to accommodate 
complex component geometry. Positionable locators may be servo driven and 
continuously programmable, or discretely positioned to a limited number of 
known positions, such as by air cylinders. Though some locators may 
require several degrees of freedom for adjustment, others, especially 
support positioners, may be provided with adjustment in only one 
direction, such as for height adjustment. 
FIG. 7 shows different types of programmable locators. Locator 6 has an 
articulated arm construction allowing it three degrees of rotational 
freedom, while locator 7 is shown with two linear motions and one 
rotational motion. 
FIG. 8 also shows that one additional linear motion can be provided in the 
Z direction for any of the three locators 5, 6 and 7. It is obvious that 
the mechanical construction of the locators 5, 6 and 7 can have many 
configurations as long as it provides the necessary degrees of freedom of 
motion for the locator. 
Precision Location and Clamping of the Primary Component: After the primary 
component 1 has been supported and roughly located on locators 5, 6 and 7, 
the programmable locators 6 and 7 approach the panel along predetermined 
paths under control of control programs and engage the panel 1 at location 
points such as 6' and 7', respectively. It is assumed that locator 5 is 
used as a fixed reference and fits closely, below its tapered end, into an 
accurate gage hole. The locators may, however, have programmability in the 
vertical direction. The control programs are selected according to the 
size and configuration of the panel 1. The paths allow the locators 6 and 
7 to displace the panel 1 gently to its desired accurate location. 
Six points of contact must typically be engaged to uniquely define the 
location and orientation of the panel 1 as it is displaced by the locators 
6 and 7 in three degrees of freedom. Once located to the desired accurate 
location, clamps 8 are then activated to clamp on, or confine, the panel 
in that location. The clamps may be independently positioned, or, 
integrated with the stationary locator 5, or the programmable locators 6 
and 7. 
In another approach, the locators 5, 6 and 7 clamp the panel at its rough 
location, sense its critical positioning features, and then cooperatively 
move the panel to the desired location such that the critical positioning 
features are accurately located at their desired location. It is obvious 
that the algorithms of the controls program can be conventionally derived 
from the desired motion of the critical positioning features as 
constrained mathematically by the form of the component. 
The clamps may be of the simple parallel jaw type, or may have specially 
shaped jaws, such as shown for the clamp 8 in FIG. 8, to accommodate 
special panel features without adversely affecting the flexibility or 
modularity of the system. When such flexibility cannot be accommodated, 
the programmable clamp/locators may be fitted with replaceable jaws as is 
well known in robotic applications using automatic hand changers. In that 
case, a rack (not shown) may be provided in the vicinity of the 
programmable clamp on which jaws of the desirable forms may be mounted. 
The jaws may be provided with special quick change devices that allow 
their attachment to, and detachment from, the programmable clamping device 
under program control. 
The functions of rough location, support, accurate location and clamping 
can be combined into one device. For example, the programmable 
clamp/locator 6 of FIG. 8 is provided with a sloped surface 11 for guiding 
the panel 1 into a rough location. The locator 6 also supports the panel 
1, is fitted with clamping jaws 8 and is programmable to provide accurate 
location and clamping. However, for some applications, the separation of 
function may be desired especially when the flexibility of production 
allows the use of fixed supports. 
A fixed support, such as locator 5, may be used as a global reference for 
all locators on the platform 14, though it may also have height adjustment 
to accommodate panels of different geometries without losing its global 
reference status. 
All locators, supports, and clamps are fixedly mounted on the rigid 
platform 14 which maintains a common coordinate reference frame X,Y,Z for 
all of the devices. The primary component 1 is constrained by the locators 
5, 6 and 7 at a minimum of 6 points. Collectively, with appropriate 
spacial separation between the locators 5, 6 and 7, all six degrees of 
freedom of panel motion are constrained. 
Secondary Component Placement: Once the primary component is located and 
clamped, other subassembly components may be placed on similarly installed 
positioners and locators, as described in relation to FIGS. 2, 3, 4 and 6. 
The locators are programmed to maintain a high level of accuracy for the 
relative location between subassembly components. This is assured by 
accurate calibration during the initial setting of the locators and the 
use of the common reference frame. However, higher accuracy and 
consistency may be attained by providing a set of position sensors 13, as 
illustrated in FIGS. 7 and 8. The sensors 13 measure and determine the 
location of the primary, as well as the secondary components in relation 
to the common coordinate reference frame of the platform 14. 
It is conventional to electronically communicate the readings of the 
sensors to a microprocessor based controller device which in turn 
calculates the necessary location adjustment for each locator to 
accurately position the component as desired. The adjusted locations are 
then communicated to the controllers of the programmable locators as 
commands to move to the desired accurate locations. The sensor readings 
are used as a feedback signals to verify that the components are 
accurately located. The sensors 13 are preferably located to sense the 
most critical positioning features of the component. Critical features 
usually determine the quality of the car assembly including component 
fits, styling consistency, feature line matching, coordination of 
principal locating points, etc. Sensing and locating the critical 
positioning features with high accuracy relative to each other assures 
high product quality. Although six point sensing may be necessary for some 
components to correct for all possible mislocations, as few as one may be 
required for others having fewer critical positioning features. 
Many types of sensors may be used for the determination of the accurate 
location of the components and the necessary locator adjustments. For 
example, proximity sensors may be used as they are simple and inexpensive. 
Vision cameras may also be strategically located to view critical 
positioning features on the components and accurately determine their 
locations and orientations. The information can then be fed back to the 
controllers of the programmable locators and their position adjusted 
accordingly. U.S. Pat. No. 4,707,647 assigned to the assignee of the 
present application and which is hereby incorporated by reference in its 
entirety, discloses such a vision method and system. 
The critical positioning features may also be sensed away from the assembly 
platform, such as at an inspection station. Any deviations from the 
desired location of the critical positioning features of the final 
assembly, may be communicated, as digital data, to the programmable 
controller of the locators to effect necessary adjustments on the 
subassemblies that follows such an inspection. 
In general, three programmable locators are required for each component. 
However, two may be adequate for secondary components, as shown in FIG. 4, 
when placed in contact with known features of adjacent components. It is 
customary to provide nesting surfaces between adjacent components in an 
assembly which provide two points of constraint equivalent to a third 
locator. 
It is obvious that this method of location differs radically from most 
prior art as it has the ability to accommodate variations in part geometry 
and location. The programmable locators can be commanded from a central 
controller to move to any location, within their reach, suitable for the 
receipt and location of a variety of components. They can then be provided 
with programs to move towards the desired location of the critical 
positioning features as located by the sensors. Therefore, the locators 
can locate components to a desired theoretical location, as well as adapt 
to minor variations between components while maintaining an optimum 
location for the sensed critical positioning features. 
Processing: Once located and clamped, the subassembly, the locators, and 
the whole platform may be moved to a process station having material 
joining equipment, such as robots, stud welding presses, etc., where the 
subassembly components are joined permanently. Another approach is to 
install processing equipment such as robots, at the assembly station where 
the equipment has access to the welding locations in the presence of the 
programmable locators. 
Pre-Processing: In some operations, multiple parts are partially joined 
before moving on to a process station for complete joining. The assembly 
station may then be provided with material joining robots to provide spot 
welds, adhesives, etc., that can keep the components firmly attached at 
selected locations. It is also possible to fit the support locators with 
the process joining tools such as spot welding tips. In such cases, the 
locators may be positioned where adjacent components are joined. They may 
also be provided with rolling support elements to facilitate the travel of 
the welding equipment along the welded joints. Once joined, two adjacent 
components will require only three locators instead of six, thus freeing 
three locators to be used for the location of the next subcomponent. This 
approach minimizes the number of locators needed at any one assembly 
station and reduces cost. 
In another processing approach, the programmable locators may cooperatively 
follow, or move ahead of the processing equipment to secure the components 
at locations as close as possible to the joining locations hence providing 
a more stable support for the components, and avoiding the need for and 
congestion of multiple locators and clamps. 
Yet in still another variation, the locator's support points may represent 
an element of the processing equipment that moves cooperatively with 
mating elements of the processing equipment to provide support for the 
components and communicate the joining medium at the joining location. In 
particular, for the process of stud welding, a locator may provide a 
support point and function as the negative electrode for the process 
equipment which moves a positive electrode and provides the welding force 
and electric current cooperatively with the programmable locator. 
Small parts may also lend themselves to another preprocessing operation. 
Instead of joining the small parts after placement and clamping, the 
invention allows the parts to be placed accurately by a material handling 
robot, and then joined by a processing robot, such as by spot welding, at 
the assembly station. The joining operation may be done completely, or 
partially, depending on the processing time available at any one station. 
If done partially, it is then completed in the following finish-processing 
station. With this approach, programmable clamp supports are avoided and 
their function replaced with the accurate placement capability of the 
material handling robot. 
Panel and Component Handling: The subassembly components may be brought to 
the assembly system manually or, preferably, by automatic material 
handling means. For flexibility and compatibility, robotic devices which 
can be programmed in concert with the programmable tooling may be most 
suitable for panel and component handling. Conveyors may be used to bring 
the components and panels to the assembly station, stacks of parts may be 
brought to the assembly station by forklifts, automated guided vehicles, 
and the like; or, parts may be brought in bins and baskets for manual 
retrieval and handling. The parts may then be lifted from their delivery 
location, and deposited onto the assembly locators. When the parts are not 
delivered in an orderly manner, vision systems may be used to guide the 
robotic devices to predefined part grasping locations, or manual labor may 
be utilized. 
Subassembly Delivery: Once all subcomponents are joined to the primary 
component or to each other, the composite subassembly may then be moved to 
the next processing station as another component of another subassembly, 
or as the final car body if no other major subassemblies are to be added. 
The subassembly may be lifted by robotic or other automation devices off 
the locating platform 14 and deposited on a material transfer device, such 
as a conveyor or an AGV, to be moved to the next processing station. The 
subassembly may be placed on other locating devices for transport to the 
next station. In some operations, it may be necessary to keep the 
subassembly in its clamped location, especially if it serves as the 
primary component for the next assembly operation. In this case, the whole 
platform 14 may be transferred with the locators and the subassembly to 
the next station and later returned once the subassembly is removed. 
It should be noted that although this method may use an equivalent number 
of support and clamping locations for individual components as is used 
with conventional tooling systems, the total number utilized can be 
considerably less since the clamping devices need not stay with every 
subassembly as it moves from one assembly substation to the next, or as 
the subassembly is moved from the assembly station to the final processing 
station. Additionally, with the use of sensors, the number of location 
points can be minimized since the critical positioning features are 
maintained without the need for redundant locators as is the case with 
fixed fixtures. Process Sequencing Alternatives: 
Several options are available for sequencing the location and joining 
operations. Some of these options are described below as alternatives #1, 
#2, #3 and #4 and illustrated in FIGS. 9, 10, 11 and 12, respectively. 
Alternative #1 
Platform Transfer 
The subassembly components are placed on the programmable locators and 
clamped in the assembly station. The locators are mounted on a platform 
which is then transferred to another station for processing. The 
integrated subassembly is then removed off the assembly platform 14 for 
transfer to the next assembly station. The assembly platform 14 is 
transferred back to the assembly station to receive the next set of 
components. Duplicate platforms would allow the concurrent utilization of 
the assembly and processing equipment. 
Alternative #2 
Subassembly Transfer 
In this approach, the subassembly is preprocessed to permanently join its 
components at locations only adequate to maintain their integrity during 
transfer to the final processing station. The assembly platform 14 remains 
stationary, while the partially processed subassembly is transferred to 
the final processing station. This approach avoids the complexity and cost 
associated with the transfer mechanism of the heavy and complex assembly 
platform 14. However, it adds some processing equipment to the assembly 
station, and reduces the location and clamping requirements in the 
processing station. The assembly and processing equipment are utilized 
concurrently. 
Alternative #3 
Single Station Approach 
The component location, clamping, and joining are all done in one station. 
This approach allows some concurrent operation of location and processing 
equipment but is likely to yield less production than the multiple station 
arrangements. The equipment cost, however, is less and can be duplicated 
to increase production. 
Alternative #4 
Parallel Processing 
In this approach, two stations operate identically as the single station 
approach, (alternative #3). However, the placement and processing devices 
and robots alternate between stations that are placed within their common 
work space. The placement devices also transfer the finished subassemblies 
to the material transfer equipment, such as AGV's, conveyors, etc. 
In FIG. 13, an extended application of the approach of Alternative #4 is 
shown where AGV's bring the components to the assembly station and pick-up 
finished subassemblies from the processing station. The components may be 
delivered in stacks, magazines, pallets, etc., to the assembly station. 
Either the AGV's transfer mechanism or a material handling robot transfers 
the components to a staging area adjacent to the assembly station. The 
material handling robot then places the components selectively on the 
programmable locator platform 14 where they are accurately located and 
clamped. The material handling robot then moves to load the second 
assembly station. Simultaneously, a processing robot moves to the located 
subassembly to finish the joining operation of all located components. 
Once processing is finished, the subassembly is unclamped, removed off the 
assembly platform, and transferred to an available AGV for transfer to the 
next assembly or processing station. The material handling robot then 
returns to load the vacant assembly platform 14 with new parts while the 
processing robot moves to operate on the other assembly/processing 
platform. 
It is customary that station controllers be designed to communicate with 
each other and with other equipment controllers, as well as with other 
plant computers to assure the availability of components when needed. The 
timely transfer from the storage areas to the processing and assembly 
locations can thus be realized. This approach assures the continuity of 
the production operation and the uninterrupted utilization of the 
equipment by minimizing idle waiting time. Hence, once the staging area 
becomes low on parts, the area controller may communicate with the 
material storage controllers, at other areas of the plant, and request the 
delivery of the specific type and number of needed components. This is 
customarily done in automated manufacturing and is not elaborated on here. 
It is only mentioned here to demonstrate the ability to integrate the 
method and system of this invention in the technology of flexible 
manufacturing. 
Arrangements are possible for alternative #4 other than that described 
herein. For example, the use of a rotary table allow one side to be used 
as an assembly station while the opposite side is used as a process 
station. A 180 degree rotation of the table reverses the function and 
delivers a newly located subassembly to a process robot and a finished 
subassembly to a material handling robot. The location of the components 
also need not be on a horizontal plane, though a plane with a horizontal 
component may be desirable to allow the use of gravity for rough location 
before clamping. 
The staging area also need not be independent of the AGV's. For example, 
the AGV may be used as the staging area, hence avoiding the task of 
component transfer from the AGV to a staging area. Once the parts on the 
AGV are exhausted, the AGV may move and another brought in with necessary 
components. Appropriate scheduling and program timing would allow the 
AGV's to be called in as necessary to maintain continuity in production. 
The method of the invention thus applies as long as assembly stations are 
programmable to accommodate variations in parts and still provide accurate 
location and processing. 
Automotive Body Assembly Sequence: 
FIG. 14 shows the progression of building an automotive body from its 
components according to the invention. The base components are first 
grouped into subassemblies. Subassemblies are then combined with other 
subassemblies as well as individual components to form bigger and more 
complex subassemblies. The process continues until the last few 
subassemblies and components are combined into the final car body. 
The method of the invention applies at each stage of the conventional 
process of FIG. 14 as it replaces fixed fixtures and tooling with 
programmable locators, as it integrates the flexible material handling and 
processing equipment, such as robots, into the process, and finally, as it 
coordinates the location and processing operations with the variations in 
production plan and running design changes. 
At any stage of the body assembly sequence, any assembly station can be 
instructed to receive a different set of components and to operate on them 
by means of different programs as long as the locators have the 
appropriate work envelope to accommodate the new parts. With production 
flexibility in the automotive plants calling primarily for minor 
variations between model styles, (i.e., within inches), and the same 
assembly sequence, it is relatively easy to size the work envelope of the 
locators to accommodate a large variety of body styles and sizes. The 
process is thus flexible enough so that at any time the plant can switch 
from the production of one model to another as called for by market 
demands. 
Design changes are also conveniently accommodated. Such changes may include 
changed panel features, size, or materials, and require different location 
points, which is an easy task to reprogram. This flexibility is impossible 
with the prior art methods and systems which cause considerable cost to 
manufacturers as they change expensive tooling to accommodate any of these 
possibilities. The manufacturers may even lose market share as they find 
the responsiveness too expensive to tolerate. 
The method and system of the invention as described herein is not limited 
to the assembly of automotive bodies which are composed primarily of 
panels made of sheet metal, plastics or composites. Rather, the invention 
extends to all assembly operations that require the location of two or 
more components of an assembly, their clamping in an accurate relative 
location, and their joining by permanent or temporary joining processes. 
For example, it applies to the assembly of engines as well as printed 
circuit boards as long as the components of the assembly are placed on 
programmable locators for their accurate location and confinement relative 
to each other. The components are then joined by fasteners, adhesives, 
welding, etc. 
While the best mode for carrying out the invention has been described in 
detail, those familiar with the art to which this invention relates will 
recognize various alternative designs and embodiments for practicing the 
invention as defined by the following claims.