Louis J. Everett

Kinematic modelling for robot calibration

There is a considerable amount of literature dealing with robot calibration. A classification hierarchy of calibration procedures is discussed which groups robot calibration by objective. The state of the art for each classification is discussed with citations from recent literature. Several proposed models are described. Based upon the common assumption of all lower pair joints, three concepts are discussed which may be applied for comparing most of the calibration models proposed in the literature. These concepts are completeness, equivalence, and proportionality. Each of these are discussed in detail in the text. Attention is also paid to the possibility that joints may actually be higher pairs. Although this possibility is commonly accepted in coordinate measuring machine calibration, it is not widely recognized in the robot literature. The paper discusses possible causes and effects of higher order joint pairs and demonstrates how they might be modeled.

A study of kinematic models for forward calibration of manipulators

The objective of robot calibration is to identify all parameters in a robot model so that the model represents the true robot. Each model has its own set of parameters. The authors prove that regardless of the kinematic model chosen, there are a maximum number of parameters that must be determined, implying that model accuracy cannot be improved by adding parameters. In addition, the authors demonstrate how to model any manipulator so that a minimum size Jacobian is used, thus reducing the computation required for calibration.<<ETX>>

Kinematic calibration of manipulators with closed loop actuated joints

A method for performing forward kinematic calibration of manipulators having one or more closed-loop-actuated joints is presented. The technique is an extension of algorithms designed for open-loop jointed manipulators. The calibration is equivalent to minimizing an objective function subject to constraints. The objective function is taken as the integral of end-effector position and orientation error. The constraints arise from the closed-loop mechanisms present in the manipulator.<<ETX>>

Modeling Hybrid Parameter Multiple Body systems: A different approach

Abstract In this paper, the Hybrid Parameter Multiple Body (HPMB) system modeling problem is addressed. Presented, is a systematic methodology for deriving equations of motion for these highly complex systems. The methodology is founded in variational principles, but uses vector algebra to eliminate tedium. The variational nature of the methodology allows rigorous equation formulation providing not only the complete non-linear, hybrid, differential equations, but also the boundary conditions. One novelty of the method lies in the fact that its variational nature is transparent to the user. This enables it to be effectively used by researchers having a working knowledge of Lagranges method. The methodology is formulated in the systems constraint-free sub-space of the configuration space, thus all constraints (holonomic and nonholonomic) are automatically satisfied. Since Lagrange multipliers are not needed, the method produces a minimal realization. The spatial dimensions of the continuum bodies are not restricted and the inter-body connections are completely general.

Automatic singularity avoidance using joint variations in robot task modification

The research community has addressed the need to improve the flexibility of robot systems. Two particular concepts that have resulted from this research are off-line programming and modular tooling. These concepts are directed at allowing the robot system to be used to perform a variety of tasks with minimal setup time and to allow easy replication of an application. Both of these concepts require that the robot system have the ability to measure the position and orientation of features in the workspace. These measurements can then be used to perform coordinate transformations on each of the task data points. These modified task data points then, theoretically, facilitate the performance of the task by the robot system without human intervention.<<ETX>>

Forward Calibration of Closed-Loop Jointed Manipulators

A method for performing forward kinematic calibration of manipulators with one or more closed-loop actuated joints is presented. The technique is an extension of algorithms de signed for open-loop jointed manipulators and is equivalent to minimizing a constrained objective function. The con straints arise from the closed-loop mechanisms in the manip ulator. The objective function is taken as the integral of end effector position and orientation error and is optimized using the method of Lagrange multipliers.

Generalized recognition of single-ended contact formations

Contact formations have proven useful for programming robots by demonstration for operations involving contact. These techniques require real time recognition of contact formations. Single ended contact formation (SECF) classifiers using only the force/torque measured at the wrist of the robot have been shown to be quite effective for this purpose. To function properly, however, previous SECF classifiers have required a sizable training set and a constant pose between the force/torque sensor and the manipulated object. Thus, if an object is re-grasped and the pose changes, one expects to have to repeat the creation of the training set. We discuss the impact of sensor-object pose changes have on two successful classifiers. Experimental data shows that they perform poorly when sensor-object pose changes. We discuss a method to regain the performance of both classifiers while minimizing the retraining necessary.

Performance theory based outcome measurement in engineering education and training

An approach is presented to improve engineering education that is based on new concepts of systems performance and classic feedback theory. An important aspect is the use of general systems performance theory (GSPT) to provide a performance model of the educational system and as a basis for the key outcome metrics: the volumes of performance capacity envelopes of individual students. Feedback is aimed at achieving both better curriculum design and teaching methods. In addition to conceptual issues, a web-based implementation plan and experimental validation plan is described. The quantitative modeling approach taken, including choice of appropriate levels of abstraction, has provided better understanding of the system used to provide engineering education and a basis for quantitatively linking components of the program to student performance in a causal manner. The educational system performance model is discussed in the context of competency models. It is believed that this approach holds promise for not only documenting a meaningful type of outcome but also for providing insight into the rationale for steps taken in attempts to improve an educational system.

Contact/Impact in Hybrid Parameter Multiple Body Mechanical Systems

The multiple motion regime (free/constrained) dynamics of hybrid parameter multiple body (HPMB) systems is addressed. Impact response has characteristically been analyzed using impulse-momentum techniques. Unfortunately, the classical methods for modeling complex HPMB systems are energy based and have proven ineffectual at modeling impact. The problems are exacerbated by the problematic nature of time varying constraint conditions. This paper outlines the reformulation of a recently developed HPMB system modeling methodology into an impulse-momentum formulation, which systematically handles the constraints and impact. The starting point for this reformulation is a variational calculus based methodology. The variational roots of the methodology allows rigorous equation formulation which includes the complete nonlinear hybrid differential equations and boundary conditions. Because the methodology presented in this paper is formulated in the constraint-free subspace of the configuration space, both holonomic and nonholonomic constraints are automatically satisfied. As a result, the constraint-addition/deletion algorithms are not needed. Generalized forces of constraint can be directly calculated via the methodology, so the condition for switching from one motion regime to another is readily determined. The resulting equations provides a means to determine after impact velocities (and velocity fields for distributed bodies) which provide the after collision initial conditions. Finally the paper demonstrates, via example, how to apply the methodology to contact/impact in robotic manipulators and structural systems.

A sensor used for measurements in the calibration of production robots

A sensor has been developed and successfully implemented to automate robot calibration. Its simple design makes it ideal for production environments. It works in conjunction with precision spheres that are mounted in the workspace. The relative positions of the spheres are measured in advance, and the sensor is positioned over them automatically and precisely. The positioning of the sensor is governed by three light beams that define position with respect to the sensor. This eliminates the problems experienced by other short range devices in that it acts digitally and without contact. Design of the sensor and its autonomous control from a PC are presented along with proven measurement tactics and results of performance tests.