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Description  |
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BACKGROUND
This invention is useful for setting up large fixtures, gages and robots as
well as in construction of structures in general. It utilizes a highly
accurate robot programmed from the CAD data base of a body for example to
set up a master surface block or target in position for the sensors to
see.
A method and apparatus is disclosed for setting up fixed and robotic
systems by using a robot programmed by design data for a part or structure
to simulate a master of same. Envisioned primarily for use in auto body
fabrication processes, the invention is generally useable with smaller
parts and assemblies. It is considered vitally useful for programmable
assembly of bodies or other larger objects where a variety of styles or
other considerations virtually preclude effective master parts. The
invention sequentially creates, point by point, a master in space, using
programmable placement of master surfaces, target points, or cameras
capable of evaluating location of assembly robots and other items,
generally from target points thereon.
Incorporated by reference are the following copending applications
1. "Target" Ser. No. 348,803, abandoned.
2. "Robot Calibration" Ser. No. 453,910, abandoned in power of FWC Ser. No.
750,049, abandoned.
"Vision Assisted Fixture Construction" Ser. No. 660,279, abandoned.
4. "Pulsed Robotic Inspection" Ser. No. 462,127, abandoned in favor of Ser.
No. 761,315, now U.S. Pat. No. 4,585,350.
5. "Robot Vision Using Target Holes, Corners and Other Object Features"
Ser. No. 660,042, abandoned in favor of FWC 933,256, abandoned.
Conventional Techniques
Prior art solutions for mastering large structures such as car bodies or
aircraft, have required construction of `master`0 parts. Such masters are
notoriously error prone, both in their manufacture and in their propensity
to change with time, transport, etc. They are also very expensive (a
typical car master cube or fixture can cost $1,000,000) and is large and
extremely heavy, making frequent use in plant difficult.
How then does one say, realign or set up a single sensor on a robot or
fixture relative to a part such as a body? Use of a master as described
above is virtually precluded, and with current trends, master data
actively lies in the CAD design program, not in a steel master anyway.
This invention discloses several novel techniques, as well as other
inventive concepts.
The invention is described in the following embodiments:
FIG. 1 illustrates a first embodiment of the invention
FIG. 2 illustrates a second embodiment of the invention
FIG. 3 illustrates a third embodiment of the invention
FIG. 4 illustrates a fourth embodiment of the invention
FIG. 5A illustrates a fifth embodiment of the invention
FIG. 5B illustrates an image of a matrix array.
FIG. 1 illustrates the invention where an accurate positioning multi degree
of freedom robot such as 10 is used to accurately position surface 11 at a
point in space under control of computer 12 which is programmed with CAD
design data or other data of an object such as a car body 13 (dotted
lines). The purpose of the robot 10 is to recreate, sequentially, the
object itself in space such that machine vision based sensor units such as
20, attached to structure 25 can be lined up at key measurement locations.
This is an important embodiment since it is not possible in general to
create an accurate master car body physically. In this case, however, a
robot unit for example on one of the normal pallets 30 on which bodies are
carried in a typical body plant `Cartrac` conveyor 26, is brought in and
programmed to move sequentially to the positions at which the body
surfaces of a `master car` or other desired situation would be. The sensor
units on the structure then look at these positions in sequence and are
then calibrated automatically relative to the math data base of the body
used in the CAD system driving the robot. Clearly, movements can be
programmed to exercise the sensors at the extremes of their range, within
the body tolerance or any other routine.
This can be implemented interestingly in several ways. First it is
desirable to use a robot that is quite accurate to make this sensor
positioning. Preferable in many cases is a robot such as 10, capable of
moving up from below, eg. with a telescopic tube. Since the car body
essentially exists on the top and two sides, it is highly desirable to
have a robot coming up from below in essentially an inverted gantry robot
form. However, it is also possible to use a horizontal arm robot which can
move side to side and then rotate around its base to position sensors on
the other side essentially recreating the car body.
This highly accurate robot positioner could include several ways of
correcting the sensors. The first way is to use, on the end of the robot
end effector typically located on the end of a wrist on a horizontal arm,
a NC machined block which would have effectively the same surface as that
of the car at the location being checked. Typically such a block could be
located on the end of the robot which would be interchangeable, either
manually block by block, check by check, or via some sort of turret which
would locate different blocks in sequence in position.
Alternatively, a single block might have NC machined into it numerous of
the types of surfaces and the robot would simply position the correct
portion of the block in the right example. This is shown in FIG. 2.
Surfaces 100, 101, 102, characteristic of various body conditions, are
indexable on slide 105 under computer control.
(Indeed, such a plate could mount any type of detail or tool not just a
sensor, and thus the invention is of general use as described further on.)
The accurate robot is preferably of 6 or more axes capable of simulating
location of all surfaces on a large 3D object (5 axes will suffice for
some target sensing applications).
It should be noted as an aside that a robot of this type can be used for
many more purposes than in setting up just inspection sensors. For
example, anywhere in the line where it would be necessary to set up a CAD
based equivalent of the car body, this unit can be used including setting
up of all the welding robots and the like which could be off line
programmed rather than "taught". This invention is a great assist in
verifying off-line programs.
As an alternative to the sensor projecting light at a surface carried by
the robot, a sensor camera mounted on the robot can look at target points
on the sensor or on a mounting plate or other member to which the sensor
is attached.
A second application is thus to utilize, as shown in FIG. 3, target points
200, 201, 202 and 203 on the sensor boxes such as light section type 210.
In this case, a target sensing camera unit 220 to pin point the target
location, is located on the end of the robot 221. This camera can be
ideally positioned accurately in a known manner, and is potentially more
accurate than theodolite units or other techniques. Automatic target
sensing techniques are noted in copending application Ser. No. 348,803 and
U.S. Pat. No. 4,219,847 (Pinckney et al).
Targets are typically retro reflective `dots` of 3M Scotchlite 7615 1/4" in
diameter or illuminated LEDs or fiber optic ends. Targets are typically in
clusters of 3 or 4.
There is also a third possibility where the camera of the sensor (eg. 211)
is on a check fixture (as in FIG. 1) or on camera units located on robots,
such as 300 in FIG. 4, for the purpose of guiding robot welders such as
310. For example, one can use target points such as 320, 321, 322 located
on the end of the accurate calibrated robot 330 (in this case a horizontal
arm type capable of rotating round its base) to calibrate sensors. Where
sensors are susceptible to variations in the surface and the like and need
to be more closely calibrated to certain surfaces as in sometimes the
check fixture sensors, the same idea as FIG. 1 can be utilized using
master blocks on the end of the high accuracy robot (in this case
containing test panels which could be welded by spot welder tip 350).
Similarly, adhesive robot spray trim assembly robots, machining robots and
all other types can be checked out in this manner.
It is noted that with a single target point and a single matrix array
camera (such as GE TN2500), an xy location can be determined (with linear
arrays such as Reticon 1024G only a single axis of data is available). If
3, or better 4, targets are used with said matrix camera, a full 6 degree
of freedom solution is available (x,y,z, roll, pitch, yaw). This can be
obtained with a single camera, or to even better accuracies, with two
cameras (which is needed where the polar/rotational theodolite layout is
used for the accurate robot).
Thus, location of sensor to target and alignment can be determined by
moving the target (or sensor) to different known points and reading the
effect.
The same holds true for a body test surface which is moved by the robot in
front of a ranging or gray level image detecting sensor.
Again noted is the very important feature that the accurate robot
preferably is driven from the CAD system descriptive of the part to which
it is setting up. It doesn't have to be car bodies, it could be any
generalized part to which the robot is capable of describing the positions
of or even a portion of its positions. In other words, it's possible to
entertain more than one robot to set up the positions for any given
structure.
Car bodies are the principal application envisioned at this point in time,
and potentially aircraft as well. The key requirement for this device and
that shown above is in the area of continued verification of sensor or
tooling positions and particularly those that are programmably placed and
therefore subject to drift or other difficulties. It is also particularly
those programmable ones that can be off line programmed where means is
required to check the program validity relative to an actual part which
may exist only in a data base.
The accurate robot need not be on a pallet but can be brought to the check
out location by any means (crane, AGV, truck, etc.). When pallet mounted
with say 60 other auto body pallets in a loop, it could circulate once per
loop revolution checking each station in turn, or only those stations in
trouble (eg. the robotic weld station of FIG. 4). Alternatively it could
be cycled after hours. Accurate machine location is typically under full
automatic control, but manually can be positioned too.
Another embodiment is to employ an overhead sensor such as 369 (dotted
lines) for targets on a welder end tooling and sense the location of the
targets using a camera overhead or elsewhere located to dynamically
correct the welder location during the welding process, and/or to record
the metal surface position by recording the point at which the surface
contacts the welder tip (eg. completing a circuit) while monitoring the
targets location at this instant. In this manner one can determine car
surface location in line without resort to special in-line check fixtures
as in FIG. 1.
Similarly, camera 300 of vision controlled robot welder can be used to view
the location of other features of the car surface and its location can be
accurately determined by camera 381 looking at targets 380. Accuracies can
be to 0.001", easily in excess of the 0.50" of typical hydraulic robots
used in automotive welding.
Thus, by judicious use of camera technology, robot or other working
stations can be used to inspect the part before, during or after working
to determine desired corrective action required, if any (such as off
sorting robot programs, adjusting previous operations, producing out of
tolerance parts, entering the station).
It is noted that for target sighting, the multi degree of freedom accurate
robot can be a angular coordinate theodolite type system capable of
pointing a checkout camera at the sensor (as in FIG. 3), or presenting
targets to a sensor camera (as in FIG. 4). This single or dual theodolite
arrangement is much simpler mechanically and can be more easily brought to
the station or carried down line on the pallet. However, it obviously
can't position a surface in the correct car position. It further requires
a larger depth of field of the camera unit (which isn't too severe). See
FIG. 5A whose approach can be used if necessary.
In FIG. 5A, another aspect of the invention is noted. Targets 500 or plate
501 for example can be placed across the line from the light section
camera sensor 20 comprised of solid state TV camera 510 and 10 MW laser
diode line projection source 511. Once the sensor 20 is aligned with
respect to car body 520, targets 500 can be placed to allow camera
pointing direction to be determined at any time, such as on sensor
replacement. It can also be used for automatically offsetting measured
part data in the computer, if the angle of sensor view is determined to be
shifted on consideration of the targets.
Every time the car body is transfered, the view is open for sensor 20 to
view the targets and thus a correction `shot` can be taken each cycle to
assure the sensor is in the correct position. To accomplish this
effectively the typical sensor (imaging or light section) has to have a
large depth of field or an ability to adjust field depth such as with
adjustable iris diaphragm 530. This is useful as laser power 511 is
limited and the light section triangulation sensor which tyically has to
run with a wide open lens due to light power considerations on reflectance
from body 520. With retro reflective targets such as 500, a small light
550 (which could also be a laser) is sufficient to obtain good data with
the lens stopped down.
Targets can also be located on a transparent screen 560 in the field of
view but out of the area of interest (FIG. 5B inset shows images 566 of
targets on camera matrix 565). Also possible is to use a beam splitter,
prism combination 580 (dotted lines) (or indexible mirror) to direct an
image of targets 590 to the sensor camera.
While generally used for non-contact sensor units of the triangulation
type, the procedures herein are useful for other sensors or devices such
as capacitive sensors, etc.
Note that where the accurate robot is indexed into a station (such as on
the Cartrac pallet of FIG. 1), it is necessary to locate the pallet
accurately relative to the structure holding the object of interest such
as the sensors shown. This can be done using physical locators such as
shot pins, clamps etc., or can be done by using the robot to point a TV
camera or other means at a plurality of reference points (targets) on said
structure from which the relative location of structure to robot can be
determined.
In general however, unless parts to be made can also be target located from
said structure, it is best to locate the accurate robot in the same manner
as the part (eg. a car on a pallet).
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