Julio J. Gonzalez

A force commanded impedance control scheme for robots with hard nonlinearities

This paper investigates a hybrid impedance control scheme that utilizes a desired force, rather than a desired position, as the commanded variable. This scheme is examined for a manipulator system in the presence of inherent hardware nonlinearities, and it demonstrates improved performance with respect to an explicit force control structure of a similar degree of robustness. Theoretical conclusions are supported experimentally on a customized Puma 560 Robotic Testbed facility, developed by the authors.

Investigation of nonlinearities in the force control of real robots

Some practical issues associated with the force control of manipulators are investigated. How the stability of a force controlled system is affected by a variety of inherent manipulator nonlinearities, such as control signal saturation, slip-stick friction, and sampled-data controller implementation is examined. In order to improve stable system performance, the inclusion of a high gain inner position loop with environmental force compensation is explored. It is demonstrated that the inclusion of the inner position loop will minimize the effects due to slip-stick friction and thereby improve the predictability in the steady-state error. A discrete-time, nonlinear robotic plant model suitable for force control investigations is developed and is demonstrated to provide an accurate prediction of actual system responses. Theoretical conclusions are supported by experiments performed with the PUMA 560 industrial robot testbed facility developed at Colorado State University. >

Practical aspects on robust control strategies of a single link flexible manipulator

An investigation is conducted of an adaptive approach to the control of a flexible robotic manipulator in the presence of changing payload. The approach is a combination of indirect adaptive control and gain scheduling. A lookup table of precalculated controller parameter vectors for a set of possible payloads is utilized. The payload in the lookup table closest to the actual payload provides the initial controller parameter vector that sets the starting adaptation point, and online recursive-least-squares identification of the plant parameters, together with online pole placement controller design, allows fast tuning of the adaptive controller. Simulation experiments, using realistic data obtained from the CSU experimental flexible manipulator testbed, show the feasibility of the approach.<<ETX>>

An interactive teaching approach based on student-teams

This paper discusses the advantageous instructional experience of adding the ldquostudent-teamrdquo feature to the ldquoclassicalrdquo interactive teaching approach. The classical approach consists of three phases: 1) Presentation of an interesting engineering problem by the instructor, 2) Solution of the problem by students, resulting in the generation of a ldquotheoretical expectationrdquo usually represented graphically in the form of a sketch, and 3) Computer simulation of the problem with the aim of verifying the theoretical expectation. The approach presents a potential problem: students with less power of abstraction often get frustrated when they cannot generate a theoretical expectation, so they tend to skip phase 2), in an attempt to use computer simulation as a substitute for thinking. If the instructor allows this to happen, interactive teaching fails. To solve the above problem, I incorporated student-teams into the interactive learning process. In each team, a student with strong power of abstraction operates as the leader. She or he leads the discussion to generate a theoretical expectation. The paper presents useful implementation details of this new instructional experience, as well as a measurement of the resulting learning improvement.

Toward an optimized computer assisted electronics laboratory

This paper describes a project-based educational system recently implemented at the electronics laboratory of our department. This system utilizes a combination of hardware implementation and a specific type of computer simulation assistance, which is initially customized to the particular experiments of the few first laboratory sessions, and becomes progressively modifiable by the student throughout the remaining sessions. Preliminary system performance results are discussed.

A new model for nonlinear friction compensation in the force control of robot manipulators

This paper introduces a new model which is suitable for nonlinear friction feedforward compensation in the force control of robot manipulators. This application is experimentally demonstrated.

Memphis, a hypermedia system for learning microelectronics

Memphis is a hypermedia system [1] using a very easy interface, multimedia possibilities [2], hypertext and PSPICE simulation facilities [3].

Force Control of Robots with Nonlinearities

This paper explores two practical issues related to the force control of manipulators. The first issue examined is how system stability is effected by commonly occurring manipulator nonlinearities, such as sampled-data, control signal saturation and slip-stick friction. It is shown that discretely implemented force control algorithms can drive the feedback force controlled manipulator into a limit cycle, even for a very small sampling period that by far satisfies Shannons sampling theorem. The bounds of stability are enhanced by the presence of control signal saturation and slip stick friction. The second issue investigated is the inclusion of a high gain inner position loop as a means to minimize the unpredictability in the steady state error due to slip-stick friction. In order to support the theoretical conclusions, experiments were performed with the PUMP 560 industrial robot testbed facility developed at Colorado State University.

New equations for biasing the BJT-CE amplifier

This paper introduces two original equations for biasing the common-emitter bipolar-junction transistor (BJT-CE) amplifier. These equations permit placing both Q-point coordinates (i.e. current and voltage) within known bounds in the presence of transistor parameter variations. An illustrative design example is provided.