perm filename ARPA.72C[DOC,TOB] blob
sn#033558 filedate 1973-04-02 generic text, type T, neo UTF8
During the past several years our vision effort has shifted from
simple scenes of polyhedra to complex objects in richer context. Not
all problems with towers of polyhedra have been solved, but there are
a host of reasons for moving on. Manipulation has also proceeded
from manipulation of blocks to assembly operations for many of the
same reasons. Minsky and Papert [Minsky 1972] have described the
central issues and the intellectual position of robotics in
artificial intelligence. We refer to that discussion as background to
our motivation to direct research to real world scenes and objects.
An important motivation is to develop applications for manipulation
and visual feedback capabilities which have been developed here. The
time is ready for the first transfer of robotics technology from
laboratory to prototype assembly stations. We discuss robotics
applications more fully in another section.
Another major motivation is to face new issues; systems have come a
few steps toward heterarchical systems from heirarchy; from a
succession of homogeneous passes with compounding errors to a system
structure where high and low levels interact closely. One aspect of
such a system is the use of many functionally independent techniques;
this has meant including experimentation with color and texture,
depth information, motion parallax and image prediction. The choice
of problems as paradigms is central to the way in which perceptual
systems evolve. A great deal can be done with simple scenes of
polyhedra using a single image in one color, ignoring all other
perceptual abilities. Since most perceptual problems can be resolved
within a single image, one approach is to exhaust those
possibilities. Important areas are missed; for example, visual
feedback is clumsy without depth information. For our plans, visual
feedback for manipulation is primary.
There are other ways in which the tower of blocks paradigm is
inadequate for our purposes. Low level feature description
operators are tailored for this case. Adequate region and
edge-oriented descriptors must be evolved. With polyhedra, only
simple preliminary grouping mechanisms have been programmed. More
intermediate level descriptors must be implemented.
Although real world scenes are much more complicated, they may be
simpler to perceive in that they have a much richer context. There
is only very general knowledge available in the usual blocks task;
usually color, size, and support are unspecified. In an assembly
task, sizes are known, color is used to code, and parts fit in
special ways. Often recognition can be based on obvious special
features. These tasks are good exercise in developing goal-oriented
visual systems. Although development and utilization of intelligent
robots will progress gradually, the information sciences will impact
industry enormously over a shorter term. An immediate effect is to
streamline information flow in the manufacturing process. Simple
systems can keep track of delayed effects of design decisions, lower
cost of preparation and transmission, and increase accessibility.
Computer controlled scheduling, resource allocation, and
transportation routing are important to most of industrial production
[Anderson 1972]. We see a major contribution from techniques being
pioneered in artificial intelligence laboratories, and that such
research will have payoff throughout the entire development of
intelligent systems. Enormous efficiency increases will come from
analysis of assembly and inspection in terms of some "primitive
operations". In the past, computer cost and lack of sophistication
has limited the ability for such analysis, and the slow pace of
automation has not pressed hard for analysis. Now it will be
possible to find common fabrication and assembly operations
throughout a large company, to discover commonality in design and
components. The success of that analysis depends upon representation
of fabrication operations and shape. Representation is a current
concern in robotics labs and may have early applications. This
orientation to the manufacturing system is already beginning to have
effect with the "group technology" approach, which attempts to
describe parts and operations, and group them together in one part of
the factory. Until the establishment of such analysis and
commonality of operations, automating will be made much more
difficult.
Considerations are similar for programming automation devices such as
the assembly station we describe. Even if programming is difficult,
there will be considerable applications for dexterous assembly
systems. For example, for the military, it is preferable to stockpile
programs than to stockpile parts or systems for contingency. In batch
production, tapes can be saved to cut stockpiling. But to achieve
full effect on industry, robot systems must be easy to program for
new tasks. Our current work is concerned with strategy generation
and automating visual feedback. Time-sharing systems will be
necessary to perform scheduling, resource allocation, routing
operations, etc. Thus there is a natural division of labor between
the time-sharing system and small machines. The strategy generation,
automating feedback, and interactive system for computer-aided
mechanical design expect to reside in the central system.
A major part of our effort is directed toward the representation of
complex shapes, for use in vision and strategies. While it might
seem that this effort has only distant applications, for the reasons
discussed above, early applications will be for convenient
man/machine interaction for programming robots and for
systematization. We can expect that in general, much of the work in
symbolic representation of the real world will have early payoff.
Present non-intelligent robots are programmed by specifying points
along a path to be repeated. With computer control, optional
trajectories can be executed in case of contingency. The engineer
must then specify what normal function is, how to monitor it, and how
to recognize recoverable situations. To do so, he can specify this
symbolically in interaction with a program in which he specifies
normal and abnormal conditions, shape of parts (usually some variant
of standard parts), the mating of parts for assembly, and schematic
descriptions of operations for insertion and inspection. The
significance of representations in general is to aid these processes.
Our representation provides a natural way of speaking about the shape
of objects, in terms of a structured description of part/whole with
primitives which resemble many fabrication operations. The better
the representation, the more it provides intuition for programs as to
the intent of operations and the function of parts.
A representation aids communication in both directions. We contend
that our representation is important for computer graphics. This
allows display of the machine's concepts to the user, and allows
greater use of predictive mechanisms based on internal models. Input
could be made visually with a depth measuring system such as we have
been using for the last two years. Since the operation would be done
on a central facility, the computer would be adequate for this task.
We expect that the representation will be of considerable use in
monocular vision also. We hope to substantiate these predictions.
Another application is automating design of numerically machined
parts. That will be simplified to the extent that the machine and
the user speak the same language of subparts and their descriptions.
Benefits would come from ease of programming and interaction,
variable tolerances for critical parts and better monitoring
operations.
THE PILOT ASSEMBLY STATION
We seek other funds to partially support application of robotics
techniques to industrial assembly and inspection. We will implement
over the next few years a prototype assembly station and a support
system for programming the assembly station for its tasks.
The assembly station is assumed to be normally connected to a large
time-shared computer facility. Not only does this appear to be a good
design for our problem, but it is also necessary for an integrated
programmed automation facility. The only emphasized statement in the
ARPA study report [Anderson 1972] is: "The maximum impact of
computers in manufacturing will come from complete, real-time
computer cognizance and control of all processes and resources,
allowing the precise scheduling and allocation of these resources."
Each assembly station will consist of a small digital computer, one
or more manipulators and cameras. Manipulators and cameras will be
combined as modules in systems to suit a given task, and will be
digitally controlled by the station computer.
The program in the station computer will be flexible as to the number
and position of manipulators and cameras. It will control input from
the cameras, provide for some pre-processing of the picture and the
application of simple tests to the visual data. In the case of
manipulators it will provide for simultaneous servo control. It will
also process other inputs, such as from touch sensors on the
manipulators, from photocell interrupt devices, limit switches, etc.
Both analog and binary outputs will be available for the control of
other devices.
Each station computer will have access to a task program specifying
the actions and tests it should perform to carry out its task. This
task program will be compiled by the central computer. Compilation
will consist of the analysis of predicted scenes in order to specify
simple tests that the station computer can carry out, the calculation
of collision free trajectories for the manipulators, the sequence of
operations and simple contingency plans. etc. We are planning for
tasks whose normal execution does not require detailed scene
analysis. If scene analysis becomes necessary (e.g. a dropped part)
we envision the station sending an image to the central computer for
processing.
The central computer will perform overall control of the individual
assembly stations and the relative rates of production. If at any
station a planned test fails, for which a contingency plan does not
exist, or any unexpected sensor signals are received, the central
computer will also be interrupted and appropriate actions taken.
Most of the hardware required for the assembly station has been
developed for the laboratory. Manipulators and cameras will be
discussed in detail below. The major additional problem is to refine
the existing designs to meet the demands of an industrial
environment.
The most difficult part of the assembly station, and the heart of the
of the proposal is a demonstration of the feasibility of the station.
We plan to do this by developing programs which actually assemble and
inspect a variety of fairly complex manufactured items.
A typical example is our current project, assembly of an automobile
water pump. The major parts are to be located, the screws are
supplied by a feeder, as is standard. Locating the body and cover of
the pump require a gross localization, then a fine localization of
screw holes. Touch provides a final accuracy and independent
coordination of the hand. The placing of alignment pins within
screw holes could be monitored visually; although in this case,the
previous actions provide adequate accuracy. Placing of the cover
over alignment pins can be carried out without vision. Improved
force sensing now under development will be useful for that
operation.
As we move to more difficult tasks, the sophistication required goes
up quite rapidly. The current manipulation routines seem to be
expandable to cover anticipated problems, especially since we intend
to employ special purpose manipulators (tools) for some tasks. The
main part of our effort will be vision for assembly; an assembly task
will be performed using vision, touch, and two hands. The vision
effort will be integrated with other abilities, and while no great
generality will be stressed, new modules will be incorporated into
the system, and a set of techniques will evolve. These will depend
heavily on techniques similar to those of our recent studies in
visual feedback and hand/eye coordination [Gill 1972]. The internal
model of the world will be used to predict visual appearance of
selected areas of the scene, and a set of verification procedures
will confirm or contradict the predictions. Many of the operations
will be connected with supplying feedback to manipulation, for
alignment and insertion. These visual procedures will have models for
the parts and approximate locations.
This and other visual tasks connected with assembly will initially be
performed as special case problems. In addition, to make these
techniques available, we will pursue development of strategy
programs. This step is essential if intelligent assembly devices are
to be conveniently programmed for complex tasks. Within the division
of labor between large and small machines, this facility must reside
in the central time-sharing facility which has large memory, file
storage, and problem-solving languages. The system must have a model
of the parts for assembly,and a sequence of instructions for
assembly. It will be necessary to have a representation of shape and
models for usual assembly operations such as insertion and alignment,
and the ability to solve simple problems in connection with these
operations, all this to enable convenient communication with the
user. When these facilities exist, the addition of new features and
operations can be incorporated smoothly, so that users can call on a
growing library of planning modules. The result of a planning effort
is a cycle of machine planning and man-machine interaction which
results in a plan network for the mini computer which controls
individual machines.
RESEARCH IN VISION
Our past work on visual feedback [Gill 1972] in stacking objects and
inserting objects in holes is directly relevant to vision for
assembly. The system provides feedback for picking up, then at the
final position, with the hand still holding the block and in view,
predicts the appearance of edges and corners within a small window
around the faces to be aligned, and uses a corner/edge finder to
determine alignment error. Incremental motion capability of the arm
is used for error correction. That work incorporates
self-calibration to coordinate hand and eye coordinate systems and
maintain reliability (by maintaining calibration), as well as to
limit search by accurately predicting expected features. Two
well-developed systems exist to aid future work in visual feedback.
GEOMED [Baumgart 1972a] is a geometric editor which allows the input
of geometric models and manipulation of these models. OCCULT
[Baumgart 1972b] is a hidden line elimination program which gives a
symbolic output, valuable for vision, in a few seconds.
We have a set of visual operations which provide confirmation of
predictions and direct interaction with the visual image. For
outdoor scenes, color is an important basis for region forming, and
for preliminary scene organization. Several preliminary color region
analysis programs have been developed [Binford, unpublished, Bajcsy
1972]. These will be extended as described below. An edge operator
[Hueckel 1969,1972] and a region-based corner/edge finder [Gill 1972]
both operate on small windows of the scene, as directed by a higher
level. An edge verifier is used to confirm or reject edges
predicted from context [Tenenbaum 1970]. Color identification has
long been demonstrated. Recently, a program has been implemented
based on Land's Retinex model of color constancy in vision. This
involves taking intensity measurements with the camera through red,
green, and blue filter, and setting up a calibration scheme for the
Goethe color triangle in the absence of any external color standard
(white). This is achieved by normalizing the intensities of regions
within the scene through each filter, and defining a color triangle
derived from this ordering data, with the center of the triangle
designated as white. The regions may then be assigne color names in
the normal way. The program as it stands can cope reasonably well
with table top scenes under varied lighting conditions - sunlight,
quartz-halogen and flourescent, and therefore shows the same kind of
color constancy as do humans.
We have directed part of our work to analysis of outdoor scenes.
Outdoor scenes were analyzed with a combination of color and texture
region analysis [Bajcsy 1972]; depth cues were taken from the
gradient of texture. A symbolic representation of texture and of the
world were adopted; descriptors of texture elements were obtained as
analytic expressions from the Fourier spectrum. A considerable
improvement could be made by combining these techniques with several
techniques which obtain depth information from correlation of images.
Motion parallax [Nevatia draft] has been used with a succession of
images. The successive images differ little from one another and
allow local correlation without ambiguity. In a sense, this
combines the advantages of narrow and wide angle stereo, since stereo
ambiguity is avoided, while large baselines can be accumulated by
tracking regions over several images. Another system incorporates
several facilities in wide angle stereo [Quam 1972]; local statistics
are used to limit search for correspondence of small areas in two
images. An interesting feature is self-orientation: given two
cameras whose orientation is unknow, the system uses guided search to
establish a few correspondences, then determines the relative
orientation of the two cameras. Such self-orientation and
self-calibration facilities have considerable significance for
industrial systems which can be maintained calibrated. These are
complementary depth sensing techniques; motion parallax can be used
for planning paths and characterizing large scale terrain features.
Two camera stereo can be used for local manipulation and disaster
avoidance. Visual feedback with stereo vision is potentially more
powerful than without. We have a program which has demonstrated
stereo visual feedback [Binford, unpublished].
A thesis by Agin [Agin 1972] showed considerable progress in
representation and description of complex objects. He implemented a
laser ranging device [Binford 1970] which was operational two years
ago. Using depth data and a representation of shape [Binford 1971]
which we have developed, we have been able to describe the parts of
objects like a doll, snake, and glove [Agin 1972]. The
representation is based on segmenting objects into parts connected at
joints. Parts are described by a volume representation with
arbitrary cross section defined along a space curve. The data were
analyzed by techniques suggested by the representation. Preliminary
segmentation was made into parts suggested by some primitives of the
representation, smoothly varying, locally cylindrical parts. An
iterative procedure defined an approximation to the axis of the
segment, fit circular cross sections normal to the axis, then
obtained an estimate of a global cross section function which was
then used to extend the axis and cross section as far as consistent.
A study of visual and depth ranging techniques has been carried out
which provides a background for choosing sensors and interface, and
making cost estimates [Binford 1972,Earnest 1967]. An interesting
result is that the cost of a laser ranging system such as ours is
less than $1k given a tv system. We have maintained a calibrated hand
and vision system for several years [Sobel 1970], and have developed
self-calibration techniques with one and two eyes [Yakimovsky
unpublished, Hannah (in [Quam 1972]), Gill 1972].
A system for understanding scenes of blocks from single views has
been implemented [Falk 1970]; it segments objects, matches against
internal models, predicts appearance from its assumptions, and
searches for verification and contradiction based on the predicted
image. Support and spatial relations are also obtained. There has
been past work on programs to obtain line drawings as input to
recognition systems. An earlier system was based on limited context
of expecting continuation of edges at vertices and predicting missing
edges in certain expected configurations [Grape 1970]. A more recent
approach has been to use models within the process of generating line
drawings, so that the most reasonable next guess can be made and
context used intrinsically in the formation of line drawings.
VISUAL DEVELOPMENT FOR ASSEMBLY
In a later section, we describe assembly of a pump carried out with
the manipulator using touch, without vision. We are implementing
vision programs to aid the assembly. In the pump assembly, visual
tasks consist of gross location of large parts, then using the
information to predict location of images of holes, and monitoring of
insertion into holes. These tasks are typical of the simple visual
operations which we will implement or adapt for assembly. We will
greatly expand our efforts with visual feedback. At present, visual
feedback techniques are limited to polyhera. We will improve image
prediction techniques to predict images of objects with curved edges.
We will develop a simple region analysis program which assumes
adequate contrast to locate the curved edges predicted within a small
window. Color will be used when necessary. We will implement
two-dimensional matching of boundary curves with predicted curves.
These will be combined with our existing edge operator and
corner/line operator. We will maintain a calibrated system and
improve calibration updating so that reliability is maintained at a
high level.
VISION RESEARCH
We will improve the laser hardware so that it can be used widely and
extend our work with representation of complex objects using depth
data. We are able to make complete descriptions of objects which
consist of a single primitive segment, such as a torus, a snake or a
cone. The programs can segment dolls, toy horses, in intuitively
natural ways [Agin 1972]. It is necessary to improve our segmentation
process in order to proceed to joining primitive segments at joints
and make complete descriptions of complex objects. When we have
these descriptions, the computer will have symbolic internal models
of objects. No recognition has yet been done, although we are in a
position to recognize those objects which have only one primitive
segment, for which we can make complete descriptions. For recognition
of more complex objects, once we have complete descriptions, we will
encode the basic properties of the representation within a visual
memory scheme which allows access of hypothesized similar
three-dimensional shapes, with associated surface information, to
compare more closely with extensive verification. We intend to apply
large parts of our programs for description and recognition of curved
objects using only monocular intensity information. This is a much
harder problem, but within our representation, shares much of the
same code, and relies on the same conceptual basis of local
three-dimensional models.
We will continue work on color region analysis which is based on
proximity rather than contiguity. This was the plan outlined in
previous proposals, and has shown necessary by our work with textured
scenes [Bajcsy 1972]. Another effort combines region analysis with
a decision theoretic approach based on a world model. We anticipate
that these modules will aid the integrated system to function in more
complex environments than have been attempted in the past. There is
a growing effort on navigation of vehicles in outdoor scenes.
While this is not directly relevant to the industrial environment, it
does reflect the growing involvement in complex visual tasks, and
will lead to further development of an integrated visual system.
A strategy project is underway dealing with the world of blocks.
The project begins from the idea that robot vision cannot be studied
except as a part of intelligent behavior in general. Visual ability
is FOR something, and without reasonable expectations about the
world, the task of seeing is bound to be extremely difficult. We
plan to implement a system which can do simple manipulation tasks
("pick up the red block", "put all the cubes in the box") in an
environment of plane-faced objects, and operating in a dialogue mode.
The system will have a good but imperfect world model all the time,
and the essence of its ability will be the constant use of this model
to understand situations and in particular to recover from errors
("Is that block no longer there because the arm knocked it off?").
The main point of the project is to find a good organization for
knowledge about the simple world in question: we expect that when
this is done the complex subroutines of current vision programs
(linefinders etc) will be found to be unnecessarily complex in that
they embody in an inefficient way at a low level, knowledge which our
system will contain at a higher level. In part, this will be done by
expanding the facilities available. A stereo vision module is being
programmed, using line drawings and integrating stereo with the
segmentation and recognition processes.
We are at work on a program which exploits new features of SAIL
[Feldman 1972] for dealing with multi-process tasks in a
problem-solving environment. The aim is to construct a driver program
to accomplish a simple assembly task under somewhat uncertain
conditions. Making use of the new language features, one can arrange
for such a program to cope with errors in the execution of tasks -
e.g. to recover from dropping things, breaking things, and further to
try several different but possibly cooperative methods for solving a
problem. It is intended that this program will have its own vision
procedures specially adapted for finding tools, e.g. wrenches,
screwdrivers, etc., and parts, e.g. nuts and bolts. An interpreter is
being developed to allow flexible description of the task by the
user.
MANIPULATOR DEVELOPMENT
Manipulator research began at Stanford Artificial Intelligence
Laboratory in 1965 with the acquisition and programming of a
prototype Rancho Orthotic Arm. A later version of this arm was used
in vision directed block stacking programs.
Our present arm, the result of a continuing design project, replaced
the Rancho Arm in 1970. This arm like its predecessor was controlled
by a digital servo program running under the time sharing computer.
The new arm was used in the "Instant Insanity" demonstration in 1971.
A second arm of the same type, with only minor modifications, is
currently being interfaced to the computer. Both arms will share a
common work space and will be able to be used individually, or
together for two handed tasks.
Manipulator research moves ahead simultaneously on three fronts:
control, primitives and devices. Tasks are translated into an
existing hand language and where the task cannot be accomplished in
terms of existing primitives, new primitives are formulated in a
consistent manner. When a new primative is formulated, real time
routines are developed to perform the action. This also leads, in
many cases, to the development of new hardware. Also as new
developments occur in hardware design, existing real time routines
are either re-written or modified.
Research is now concentrating on the following areas:
Strain gauge instrumentation of the wrist, in order to allow for more
sensitive interaction of the hand with a task. High resolution,
high sensitivity touch sensors, to increase tactile recognition and
control abilities. These developments will lead in turn to new
control concepts.
Development of tools for the hand. These tools can be instrumented
such that the computer can feel and or see at the end of the tool.
This should be a very important area of research as it goes beyond
present human capabilities.
Two handed arm control, the planning and execution of tasks requiring
the coordinated motion of both arms. This will require an extension
of the existing servo program and the analysis of synchronization
problems. The development of collision avoiders, so that arms will
not collide with other objects and with each other.
Modification of the existing arm design to provide for better
incremental motions, more degrees of freedom and a more rugged design
suitable for industrial use. Development of arm and eye computer
interfaces. These contain synchronized analog/digital converters
for input and current controlled drivers for output.
The development of new hands is expected as more complex tasks are
attempted. At present, with only one hand, we have been performing
the positioning type of hand actions. When the second arm is
operational we will be able to perform holding and pulling actions as
well.
DEMONSTRATIONS OF MANIPULATION
Operations controlled by force have been demonstrated by turning a
crank and screwing a nut onto a bolt. The hand language and
manipulation facilities are shown in the assembly of a small pump.
The positions of the parts are known approximately; they are located
on a pallet as expected in industrial practice. By touch, the hand
locates position and orientation of the pump body more accurately.
Aligning pins are inserted into the holes to guide the gasket and the
pump cover. Screws are obtained from a feeder, as is standard. All
operations have been performed in the assembly, but the total
reliability is still sufficiently low that one error or another
occurs. Vision has not been used in the assembly.
SYSTEM REQUIREMENTS FOR ADVANCED AUTOMATION
A key element in the development of any large programming effort is
the software support. There has been continual effort along these
lines at the Stanford Artificial Intelligence Laboratory and many
useful ideas have been developed. We propose to extend the research
along two separate lines: support for research and system software
for operating automated systems. We will briefly describe our past
efforts in this area and what we propose to undertake.
The Stanford Artificial Intelligence Laboratory has pioneered in
several areas of system programming, including display-oriented
timesharing systems, interactive graphics, and programming languages.
A great deal of additional effort has gone into direct support of
hand-eye research. Very early, we established a set of standard
formats and library routines [Pingle 72a]. A programming language,
SAIL, was implemented in 1968. The language incorporates special
11 features for large real-world-oriented problem solving systems
and is currently in use at a number of Artificial Intelligence and
other laboratories.
As we began to assemble larger and more sophisticated collections of
programs, we felt a need for flexible mechanisms for cooperating
sequential processes. The resulting monitor and language features [
Feldman & Sproull 1971] have worked well for us and have been
influential on other projects. Recently, we have added an
additional set of features to SAIL [Feldman 1972] to facilitate
non-deterministic and event-directed programming. The early
reactions to this work, both within the laboratory and without has
been very encouraging.
A major share of the programming research effort will be concentrated
on developing a programming system for automated assembly. This will
combine ideas from our past work on languages, representation,
computer graphics and arm control. We view this task as a branch of
the larger effort on automatic programming being undertaken in this
laboratory aad elsewhere.
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