Data processing: generic control systems or specific application – Specific application – apparatus or process – Robot control
Reexamination Certificate
2003-04-03
2004-10-12
Black, Thomas G. (Department: 3661)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Robot control
C700S245000, C700S246000, C700S247000, C700S249000, C700S250000, C700S251000, C700S254000, C700S256000, C700S264000, C318S568100, C318S568110, C318S568130, C318S568160, C318S573000, C318S574000, C701S023000, C701S028000, C701S047000, C701S200000, C701S213000, C701S217000, C701S220000, C901S006000, C901S009000, C901S046000, C901S047000, C901S048000, C714S015000, C714S023000, C714S024000, C074S490010
Reexamination Certificate
active
06804580
ABSTRACT:
BACKGROUND
The present invention relates to a system for controlling a plurality of robots and a method for controlling a system of a plurality of robots, the system comprising a plurality of robot controllers, each with an associated motion system adapted to control attached robots, with each controller being able to receive motion instructions from at least one motion instruction source the controllers being connected with each other by a computer communication network.
By using a single controller for multiple robot coordination the “locality of coordinated control” is limited to the number of robots controllable by that controller. For example, a typical coordination problem with multiple robots is to transfer a part between robots without using intermediate fixtures. A controller capable of controlling only four robots would permit coordinated handoff of parts between the four robots, but would require a conventional fixture station or other solution when handing the part to a fifth robot controlled by a separate controller. On the other hand, a plurality of robots each having its own controller, with all controllers connected by a communication line, does not have this locality limitation.
The U.S. Pat. No. 6,330,493 B1 shows a control system applied to several robot controllers connected by a communication line. This solution solves the specific problem of limitation of robots being able to be coordinated by one controller, but it solves this problem only with marginal precision, and leaves other coordination problems unsolved.
Such coordination problems of several robots include:
Load sharing—The ability for two or more robotic machines to carry the same part or load requires the robots to keep a fixed spatial relationship while carrying the load. This particular coordination problem is also solved in the prior art, but is introduced here as background to the other coordination problems.
Parts mating while processing—In addition to the requirement for a fixed spatial relationship among two or more robots, one or more additional robots must perform a process relative to the assembly, and one or more robots may enter and leave the assembly during processing (cf. further explanation below).
Fixtureless transfer—One or more robots may need to rendezvous with one or more other robots while all of them are in continuous motion.
Manual motion of coordinated operations—When a production line is stopped because of an error, with two or more robots carrying the same part or holding multiple mating parts, it may be necessary to manually move the multiple robots in coordination to prevent breaking or dropping the part.
Teaching of coordinated operations—In activities where a fixed spatial relationship is maintained, such as part mating or load sharing, it is useful if the various robots need to be taught only one or a few grasping positions relative to the parts. Each robot should not have to be taught the entire part path, and if the part path is changed, only one of the robots should have to be re-taught to effect the path change.
Time coordinated motion—Multiple robots may need to carry out identical or mirrored processes in lock step timing with each other. There is no spatial relationship among the robots, but time alignment of their motions may be required.
The most complex of the above problems is simultaneous parts mating while processing. An example is the process of joining two small parts to a large part by arc welding using three robots without stationary fixtures: Robot
1
carries the large part. Robot
2
carries the two small parts, one at a time, and Robot
3
carries the arc-welding torch and performs the welding process. Such a process normally requires the large part to move simultaneously and time coordinated with the welding robot so that the welding robot can reach the entire part and the molten seams maintain a nearly horizontal orientation. This in turn requires spatial coordination of the motions of Robots
1
,
2
and
3
. Robot
2
must maintain a fixed position relative to Robot
1
, so that the small part remains properly mated with the large part, and Robot
3
must carry out its welding process relative to the moving parts held by Robots
1
and
2
.
As the weld proceeds, it is possible for Robot
2
to release its grasp of the small part, because the part has been tacked into position. Robot
2
can leave the assembly while the assembly motion is in progress and go fetch the second small part. Robot
2
returns with the second small part to rendezvous with the assembly. Robot
3
welds the second small part to the large part, again while all three robots move with spatial coordination.
The interesting features of said process besides the changing spatial relationships of the three robots are the following:
1. Robot
2
both leaves and joins the assembly while the latter may be in motion and changes from spatially coordinated motion to independent motion, or vice-versa, while the assembly may be in motion.
2. Typically, a portion of the welded seams are defined with respect to the small parts. For those portions, the arc welding robot is moving relative to the small parts, which at the same time must maintain a fixed position with respect to the large part. This is referred to as a “chain of spatial dependencies”.
In the aforementioned U.S. Pat. No. 6,330,493 B1 a “synchronous cooperative operation” is defined. This operation occurs between a master and one or more slave robots. The definition of which robot is master and which are slaves is kept in software-based “link patterns”. Link patterns change only between program sets. Thus, to change a given robot from coordinated operation with another robot to independent operation requires starting a new program in a sequence, and continuous motion between programs is not provided for. Thus, it is not possible to have a robot change from slave to independent operation and back to slave again all while the master remains in motion, as required in point
1
above. More generally, rendezvous and departure of one robot with another in motion is not possible with a single “synchronous cooperative operation” as defined in U.S. Pat. No. 6,330,493 or even multiple such operations.
Fixtureless transfer of parts also requires a rendezvous capability and a change from coordinated to independent operation as described above. The prior art is also not suitable for such coordination activity, except where all robots are controlled by a single controller, which in turn limits the locality of coordinated control.
As noted above, in the related art the designation of Master and slave robots is kept in link patterns, which can only be changed by changing programs. Thus, it is not possible for a robot to be both a master and a slave in the same program, and it is not possible for a robot to be both master and slave simultaneously. Thus, there is no way to implement the “chain of spatial dependencies” required by point
2
above using the related art.
An example of coordination activities listed above is load sharing. Once the coordinated activity begins, there is no relative motion between the grippers of the various robots carrying the part, so any method that can provide for a fixed spatial relationship during programmed motion may successfully carry out this activity with some level of precision. However, if production operation is stopped in the middle of such an activity, and it is required that the shared or mated assembly be moved out of the way, it must be possible to have a manual motion capability to move the shared assembly.
Using load sharing as a simple example, one can examine the activity of teaching a coordinated operation. Assume a heavy part that requires three or more robots to carry the part. One possibility is to provide a lightweight mockup, so that teaching can be carried out with one robot at a time. One would like to teach the path of this part in a conventional way, e.g. by simply using the standard manual motion and teaching system of the first robot to guide the robot carrying the part along t
Chaffee Michael C.
Graf Stefan
Hagenauer Andreas
Kneifel, II R. William
Martin David M.
Black Thomas G.
Kuka Roboter GmbH
Marc McDieunel
McGlew and Tuttle , P.C.
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