100 research outputs found
Combining Vision Verification with a High Level Robot Programming Language
This thesis describes work on using vision verification within an
object level language for describing robot assembly (RAPT). The motivation
for this thesis is provided by two problems. The first is how to
enhance a high level robot programming language so that it can encompass
vision commands to locate workpieces of an assembly. The second is how
to find a way of making full use of sensory information to update the
robot system's knowledge about the environment. The work described in
this thesis consists of three parts:
(1) adding vision commands into the RAPT input language so that
the user can specify vision verification tasks;
(2) implementing a symbolic geometrical reasoning system so that
vision data can be reasoned about symbolically at compile time
in order to speed up run time operations;
(3) providing a framework which enables the RAPT system to make
full use of the sensory information.
The vision commands allow partial information about positions to be
combined with sensory information in a general way, and the symbolic
reasoning system allows much of the reasoning work about vision information
to be done before the actual information is obtained. The framework
combines a verification vision facility with an object level
language in an intelligent way so that all ramifications of the effects
of sensory data are taken account of. The heart of the framework is the
modifying factor array. The position of each object is expressed as the
product of two parts: the planned position and the difference between
this and "he actual one. This difference, referred to as the modifying
factor of an object, is stored in the modifying factor array. The planned position is described by the user in the usual way in a RAPT
program and its value is inferred by the RAPT reasoning system. Modifying
factors of objects whose positions are directly verified are defined
at compile time as symbolic expressions containing variables whose value
will become known at run time. The modifying factors of other objects
(not directly verified) may be dependent upon positions of objects which
are verified. At compile time the framework reasons about the influence
of the sensory information on the objects which are not verified
directly by the vision system, and establishes connections among modifying
factors of objects in each situation. This framework makes the
representation of the influence of vision information on the robot's
knowledge of the environment compact and simple.
All the programming has been done. It has been tested with simulated
data and works successfully
Achieving reliability using behavioural modules in a robotic assembly system
The research in this thesis looks at improving the reliability of robotic as¬
sembly while still retaining the flexibility to change the system to cope with dif¬
ferent assemblies. The lack of a truly flexible robotic assembly system presents
a problem which current systems have yet to overcome. An experimental sys¬
tem has been designed and implemented to demonstrate the ideas presented in
this work. Runs of this system have also been performed to test and assess the
scheme which has been developed.The Behaviour-based SOMASS system looks at decomposing the task into
modular units, called Behavioural Modules, which reliably perform the as¬
sembly task by using variation reducing strategies. The thesis work looks at
expanding this framework to produce a system which relaxes the constraints of
complete reliability within a Behavioural Module by embedding these in a re¬
liable system architecture. This means that Behavioural Modules do not have
to guarantee to successfully perform their given task but instead can perform it
adequately, with occasional failures dealt with by the appropriate introduction
of alternative actionsTo do this, the concepts of Exit States, the Ideal Execution Path, and Alter¬
native Execution Paths have been described. The Exit State of a Behavioural
Module gives an indication of the control path which has actually been taken
during its execution. This information, along with appropriate information
available to the execution system (such as sensor and planner data), allows the
Ideal Execution Path and Alternative Execution Paths to be defined. These
show, respectively, the best control path through the system (as determined by
the system designer) and alternative control routes which can be taken when
necessary
The design and implementation of vision-based behavioural modules for a robotic assembly system
The work drsrrihrd in this thesis ia about, how to program robots to work re
liably in the presence of uncertainty. Some architectural principle!: are proposed
which address the problem of decomposing robotic assembly tasks into modular
units such that a robot program can be implemented efficiently, tested easily, and
can be maintained or modified without undue complexity. This architecture also
provides a framework to integrate sensors into a robotic, assembly system.These modular units arc called behavioural modules. They perforin their tasks
reliably. The problem of uncertainty is dealt with by encapsulating sensing and
variation reducing strategies inside these modules. Experiments are performed with
a working robotic assembly system using vision based behavioural modules. Analy
sis of this system validates the principles presented in this thesis
Multi-object recognition and retrieval using Puma560 robot
The objective of the research described here is to develop efficient algorithm and software tools for multiobject recognition and retrieval. This research project addresses two major issues: The first issue is the identification of features and efficient methods for feature extraction which can completely describe an object. These features can be acquired using visual and ultra-sonic sensors. The second issue is the development of efficient algorithms for the retrieval of multi-objects based on their features; The methods and algorithms developed in this research are verified on a Unimation PUMA 560 robot. Non contact sensors (a vision and a range sensor) are employed for feature detection. The information from both sensors will be combined for feature extraction and feature mapping (sensor fusion). The sensors and the robot have been integrated for this purpose with a Pentium 133 Mhz Personal Computer
Plethora : a framework for the intelligent control of robotic assembly systems
Plethora : a framework for the intelligent control of robotic assembly system
Accomplishing task-invariant assembly strategies by means of an inherently accommodating robot arm
Despite the fact that the main advantage of robot manipulators was always meant to
be their flexibility, they have not been applied widely to the assembly of industrial
components in situations other than those where hard automation might be used. We
identify the two main reasons for this as the 'fragility' of robot operation during tasks
that involve contact, and the lack of an appropriate user interface. This thesis describes
an attempt to address these problems.We survey the techniques that have been proposed to bring the performance of cur¬
rent industrial robot manipulators in line with expectations, and conclude that the
main obstacle in realising a flexible assembly robot that exhibits robust and reliable
behaviour is the problem of spatial uncertainty.Based on observations of the performance of position-controlled robot manipulators and
what is involved during rigid-body part mating, we propose a model of assembly tasks
that exploits the shape invariance of the part geometry across instances of a task. This
allows us to escape from the problem of spatial uncertainty because we are 110 longer
working in spatial terms. In addition, because the descriptions of assembly tasks that
we derive are task-invariant, i.e. they are not dependent on part size or location, they
lend themselves naturally to a task-level programming interface, thereby simplifying
the process of programming an assembly robot.the process of programming an assembly robot.
However, to test this approach empirically requires a manipulator that is able to control
the force that it applies, as well as being sensitive to environmental constraints. The
inertial properties of standard industrial manipulators preclude them from exhibiting
this kind of behaviour. In order to solve this problem we designed and constructed a
three degree of freedom, planar, direct-drive arm that is open-loop force-controllable
(with respect to its end-point), and inherently accommodating during contact.In order to demonstrate the forgiving nature of operation of our robot arm we imple¬
mented a generic crank turning program that is independent of the geometry of the
crank involved, i.e. no knowledge is required of the location or length of the crank.
I11 order to demonstrate the viability of our proposed approach to assembly we pro¬
grammed our robot system to perform some representative tasks; the insertion of a peg
into a hole, and the rotation of a block into a corner. These programs were tested on
parts of various size and material, and in various locations in order to illustrate their
invariant nature.We conclude that the problem of spatial uncertainty is in fact an artefact of the fact
that current industrial manipulators are designed to be position controlled. The work
described in this thesis shows that assembly robots, when appropriately designed,
controlled and programmed, can be the reliable and flexible devices they were always
meant to be
Programming of Path Specific Robot Operations with Optimal Part Placement
In this paper we describe a task level programming system for path specific robot operations. We define path specific tasks as those robot tasks in which the path the manipulator end effector has to follow is fixed and is given, such operations may include welding or sealant application. The initial path selection is made through a graphical interface using a pointing device (such as a mouse) to outline the desired path on a CAD model of the workpiece. The final result of the system is the part location, which enables the chosen manipulator to optimally perform the desired task. Optimality is based on maximizing the manipulability of the manipulator performing the task using a function of the jacobian. User defined constraints, joint limit constraints, and collision avoidance constraints are used to guide the optimal location selection. The workable task is then executed using calls to a C language based motion control library outlined in [Guptill88] [Guptill & Stahura 87]. The usefulness of the system described in this paper is indicated by an example of two robotic devices performing a down-hand welding operation
Task Planner for Simultaneous Fulfillment of Operational, Geometric and Uncertainty-Reduction Goals
Our ultimate goal in robot planning is to develop a planner which can create complete assembly plans given as input a high level description of assembly goals, geometric models of the components of the assembly, and a description of the capabilities of the work cell (including the robot and the sensory system). In this paper, we introduce SPAR, a planning system which reasons about high level operational goals, geometric goals and uncertainty-reduction goals in order to create assembly plans which consist of manipulations as well as sensory operations when appropriate. Operational planning is done using a nonlinear, constraint posting planner. Geometric planning is accomplished by constraining the execution of operations in the plan so that geometric goals are satisfied, or, if the geometric configuration of the world prevents this, by introducing new operations into the plan with the appropriate constraints. When the uncertainty in the world description exceeds that specified by the uncertainty-reduction goals, SPAR introduces either sensing operations or manipulations to reduce that uncertainty to acceptable levels. If SPAR cannot find a way to sufficiently reduce uncertainties, it does not abandon the plan. Instead, it augments the plan with sensing operations to be used to verify the execution of the action, and, when possible, posts possible error recovery plans, although at this point, the verification operations and recovery plans are predefined
Advancement in robot programming with specific reference to graphical methods
This research study is concerned with the derivation of advanced robot
programming methods. The methods include the use of proprietary
simulation modelling and design software tools for the off-line
programming of industrial robots. The study has involved the generation
of integration software to facilitate the co-operative operation of these
software tools.
The three major researcli'themes7of "ease of usage", calibration and the
integration of product design data have been followed to advance robot
programming. The "ease of usage" is concerned with enhancements in the
man-machine interface for robo t simulation systems in terms of computer
assisted solid modelling and computer assisted task generation.
Robot simulation models represent an idealised situation, and any off-line
robot programs generated from'them may contain'discrepancies which could
seriously effect thq programs' performance; Calibration techniques have
therefore been investigated as 'a method of overcoming discrepancies
between the simulation model and the real world.
At the present time, most computer aided design systems operate as
isolated islands of computer technology, whereas their product databases
should be used to support decision making processes and ultimately
facilitate the generation of machine programs. Thus the integration of
product design data has been studied as an important step towards truly
computer integrated manufacturing.
The functionality of the three areas of study have been generalised and
form the basis for recommended enhancements to future robot programming
systems
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