Susan N. Gottschlich

Planning for complete sensor coverage in inspection

Abstract General purpose CAD-based inspection of manufactured objects often involves comparing a model created using intensity or range images of the actual object to a tolerance reference model of the ideal object. Before this comparison is made, a sufficiently complete geometric model of the workpiece must be synthesized from sensor data. In this paper we present planning algorithms for finding a set of sensing operations for completely measuring the exposed surface of an object to be inspected. While these planning algorithms were developed as part of a particular inspection system, the algorithms are applicable to other inspection systems and other applications than inspection.

Evidence accumulation using binary frames of discernment for verification vision

Vision sensor output can be processed to yield a multitude of low-level measurements, where each is inherently uncertain, which must somehow be combined to verify the locations of an object. It is shown that this combination can be accomplished via Dempster-Shafer theory using binary frames of discernment (BFODs). A special advantage of BFODs is the computational ease with which they allow information from disparate sources to be combined, which is particularly significant in light of recent concerns about the exponential complexity of a brute-force implementation of this theory. >

A dynamic approach to high-precision parts mating

A method for the mating of tightly fitting parts in the presence of significant sensing, model, and control uncertainties is presented. Using this method randomly placed parts that were located using a three-dimensional laser range scanning system can be mated even when the clearance between them is only 0.001 in. The various sources of error introduced in the fine forced-guided motions used to execute assemblies are examined. Among these sources are noisy force/torque readings, mechanical vibrations, the presence of sliding and sticking frictions, and the possibility of eccentric oblique impacts. It is pointed out how most of these errors might be reduced or eliminated. Straight-line motion goals (SLMGs) are then processed by the basic building blocks of a dynamic planning strategy. By dynamically building an assembly plan out of SLMGs, it is possible to carry out robotic assemblies in the presence of sensing and model uncertainties while recognizing and recovering from errors introduced by control uncertainties. A specific instance of this approach is outlined. >

AMP-CAD: an assembly motion planning system

The authors discuss a system, called AMP-CAD, which develops assembly motion plans using CAD models of parts. They place an emphasis on the calculation of the potential fields used for motion planning. Potential fields can be thought of as a mechanism to interface CAD representations with plan development. AMP-CAD is a complete system that combines an assembly representation, a two-phase motion planner, and a execution unit into a single integrated package. Implementation and experimental results are discussed.<<ETX>>

Compliance synthesis for force guided assembly

In robotic assembly operations the robot comes in contact with the environment and some form of compliance is typically used to prevent excessive contact forces. These contact forces provide information about the contact geometry and can be used to guide the assembly operation. Thus, compliance can be thought of as a task-dependent mapping from sensed forces to corrective motions which bring the robot closer to its goal. In this work we describe a methodology for the automated synthesis and verification of this mapping. The possible erroneous configurations of the robot are computed via Monte-Carlo simulation of the task execution. The static contact force at each erroneous contact configuration is computed and a corrective motion is computed and mapped to the force. The validity of the mapping is also checked to ensure that the sensed forces will provide unambiguous information during the actual execution of the planned compliant motion. Simulation and experimental results are also presented.

Motion planning for assembly mating operations

The authors introduce a planning system that relies on a novel approach which converts geometrical descriptions of assembly parts into potential field representations and then translates assembly operations into equivalent operations on the potential field representations. As a consequence, the system is able to quickly compute a path for the assembly motions and isolate those regions of the path where force/torque guided motions must be introduced to cope with possible collisions that may be caused by the prevailing uncertainties in the positions/orientations of the parts and their dimensions. This system has been experimentally verified using a Cincinnati Milacron T/sup 3-/726 robot to assemble a gear box.<<ETX>>

AMP-CAD: Automatic assembly motion planning using CAD models of parts☆

Abstract Assembly with robots involves two kinds of motions, those that are point-to-point and those that are force/torque guided, the former kind of motions being faster and more amenable to automatic plannning and the latter being necessary for dealing with tight clearances. In this paper, we describe an assembly motion planning system that, given CAD models of the parts and a description of the assembly operation, automatically figures out which motions should be point-to-point and which motions should be force/torque guided. Our planner uses graph search over a potential field representation of parts to calculate candidate assembly paths. Given the tolerances of the parts and other uncertainties, these paths are then analyzed for the likelihood of collisions. Subsequently, the path segments that are prone to collisions are marked for execution under force/torque control. The calculation of the various motions is facilitated by an object-oriented and feature-based assembly representation. An integral part of the assembly motion planner is the execution unit. Residing in this unit is knowledge of the different types of automatic EDR error detection and recovery) strategies. Therefore, during the execution of a force/torque guided motion, this unit invokes the EDR strategies appropriate to the geometric constraints relevant to the motion. This system. called AMP-CAD, has been experimentally verified using a Cincinnati Milacron T 3 -726 robot and a Puma 762 robot on a variety of assemblies.

A tactile sensing system for dexterous manipulation

One factor that limits the range of tasks that robots can perform robustly is the scarcity of useful sensors available to provide feedback to the robot control system. While much progress has been made with vision sensors and force/torque sensors, tactile sensing systems have fallen behind, and so general-purpose tactile sensing systems are not commercially available. The aim of this work is therefore to produce a tactile sensing system that could be manufactured inexpensively, could be used on a wide variety of robotic systems, and would provide the kind of output typically required in dexterous manipulation applications. Such a tactile sensing system will be presented in this paper. The tactile transducers used in this system are based on semiconductive ink technology that allows transducers of any size, shape, and resistance range to be produced merely by altering the ink printing process and substrate geometry. Each sensor outputs three pieces of information that are useful in robotic manipulation-two parameters indicating the location of a contact point on the transducer and one parameter specifying the amount of force being exerted at the contact point. So that the sensing system could support transducers of different shapes and sizes, the analog interface circuitry of this system has been designed to be fully programmable, and also includes circuitry to enable self-calibration with appropriate software.<<ETX>>

Assembly knowledge representation for assembly motion planning and execution

A feature-based representation for describing assemblies is introduced. The representation is such that the system has the ability to generate automatically CAD models of assemblies and parts, which are allowed to be articulated. The representation also permits automatic computation of spatial relations among assembled parts. The uncertainty information, such as the various tolerances involved and uncertainties in the initial positions of the parts, is easily incorporated in the representation. Built around this representation is an assembly motion planner, which works in two stages. In the first stage, it ignores the uncertainties present in the system and develops a motion plan that is later modified in the second stage by the incorporation of force/torque-guided motions. The force/torque-guided motions are automatically introduced only in those segments of the plan where there exist possibilities of collision on account of the various uncertainties.<<ETX>>

Automatic synthesis and verification of compliance mappings

When the uncertainty is large compared to clearances between objects, some form of compliance is required for a robot to manipulate these objects. Such situations include, but are not restricted to, assembly operations. Compliance can be thought of as a task-dependent mapping from sensed forces to corrective motions which bring the robot closer to its goal. A methodology for the automated synthesis of this mapping is described. The possible erroneous configurations of the robot together with their resulting contact forces are computed, and a corrective motion is identified for each configuration. The validity of the mapping is checked to ensure that the sensed forces will provide unambiguous information during the actual execution of the planned compliant motion.<<ETX>>