H.B. Brown

A rapidly deployable manipulator system

A rapidly deployable manipulator system combines the flexibility of reconfigurable modular hardware with modular programming tools, allowing the user to rapidly create a manipulator which is custom-tailored for a given task. This article describes two main aspects of such a system, namely, the reconfigurable modular manipulator system (RMMS) hardware and the corresponding control software.

Adaptive control of a single-link flexible manipulator

A method for controlling single-link lightweight flexible manipulators is proposed. The objective is to control the tip position of the flexible manipulator in the presence of joint friction and changes in payload. Both linear and nonlinear frictions are overcome by using a very robust control scheme for flexible manipulators. The control scheme is based on two nested feedback loops: an inner loop, to control the position of the motor, and an outer loop, to control the tip position. Compensation for changes in load is achieved by decoupling the dynamics of the system and then applying a very simple adaptive control for the tip position. This results in a simple control law that needs minimal computing effort and, thus, can be used for real-time control of the flexible arms. >

A single-wheel, gyroscopically stabilized robot

We are developing a novel concept for mobility, and studying fundamental research issues on dynamics and control of the mobile robot. The robot, called Gyrover, is a single-wheel vehicle with an internal gyroscope that provides mechanical stabilization and steering capability. This configuration conveys significant advantages over multi-wheel, statically stable vehicles, including good dynamic stability and insensitivity to attitude disturbances; high manoeuvrability; low rolling resistance; ability to recover from falls; and amphibious capability. In this paper we present the design, analysis and implementation of the robot, as well as the associated research issues and potential applications.

Modeling and control of single-link flexible arms with lumped masses

This paper deals with the modeling and control of a special class of single-link flexible arms. These arms consist of flexible massless structures having some masses concentrated at certain points of the beam. In this paper, the dynamic model of such flexible arms is dewloped and some of the control properties are deduced. A robust control scheme to remove the effects of friction in the joins is proposed. The control scheme consists of two nested feedback loops, an inner loop to control the position of the motor and an outer loop to control the tip position. The inner loop is described in other publications. A simple fedforward-feedback controller is designed for the outer loop to driw the beam accurately along a desired trajectoty. Effects of the changes in the tip’s mass are studied. This modeling and control method is then generalized to the distributed-mass flexible beam case. Finally, experimentaf results are presented. This paper deals with the modeling and control of a special class of single-link, lumped-mass, flexible arms. These arms consist of massless flexible structures that have masses concentrated at certain points of the beam (see Fig. 1). Although the translations of these masses produce stresses in the flexible structure, their rotations do not generate any torque in the beam. Therefore, the number of vibrational modes in the structure coincides with the number of lumped masses. Book (1979) studied the case of two rigid masses connected by a chain of massless beams having an arbitrary number of rotation joints. Our problem differs from this in the sense that our structure has only one rotation joint and an arbitrary number of lumped masses. These two particular structures are studied because: Some lightweight robots and other applications can be reasonably approximated by these models. Their dynamics may be easily modeled as compared to distributed-mass flexible arms. Interesting properties for the control of flexible arms are deduced from their dynamic models. A method to control these arms is inferred from the structure of the model. The influence of changes in the tip’s mass are easily characterized. Given a distributed-mass flexible arm, there always exits a truncated dynamic model which is of the same form as the lumped-mass flexible arm model and which reproduces the dynamics of the measured variables. This allows us to generate the above mentioned control method to the case of distributed-mass flexible arms. - Contributed by the Dynamic Systems and Control Division for publication

Control of flexible arms with friction in the joints

The control of flexible arms with friction in the joints is studied. A method to identify the dynamics of a flexible arm from its frequency response (which is strongly distorted by Coulombs friction) is proposed. A robust control scheme that minimizes the effects of this friction is presented. The scheme consists of two nested feedback loops: an inner loop to control the motor position and an outer loop to control the tip position. It is shown that a proper design of the inner loop eliminates the effects of friction while controlling the tip position and significantly simplifies the design of the outer loop. The proposed scheme is applied to a class of lightweight flexible arms, and the experiments show that the control scheme results in a simple controller. As a result, the computations are minimized and, thus, high sampling rates may be used. >

Toroidal skin drive for snake robot locomotion

Small robots have the potential to access confined spaces where humans cannot go. However, the mobility of wheeled and tracked systems is severely limited in cluttered environments. Snake robots using biologically inspired gaits for locomotion can provide better access in many situations, but are slow and can easily snag. This paper introduces an alternative approach to snake robot locomotion, in which the entire surface of the robot provides continuous propulsive force to significantly improve speed and mobility in many environments.

Controlling a marionette with human motion capture data

In this paper, we present a method for controlling a motorized, string-driven marionette using motion capture data from human actors. The motion data must be adapted for the marionette because its kinematic and dynamic properties differ from those of the human actor in degrees of freedom, limb length, workspace, mass distribution, sensors, and actuators. This adaptation is accomplished via an inverse kinematics algorithm that takes into account marker positions, joint motion ranges, string constraints, and potential energy. We also apply a feedforward controller to prevent extraneous swings of the hands. Experimental results show that our approach enables the marionette to perform motions that are qualitatively similar to the original human motion capture data.

Adaptive control of a single-link flexible manipulator in the presence of joint friction and load changes

A method for controlling single-link lightweight flexible manipulators is proposed. The objective is to control the tip position of the flexible manipulator in the presence of joint friction and changes in payload. Both linear and nonlinear frictions are overcome by using a very robust control scheme for flexible manipulators. The control scheme is based on two nested feedback loops: an inner loop, to control the position of the motor, and an outer loop, to control the tip position. Compensation for changes in load is achieved by decoupling the dynamics of the system and then applying a very simple adaptive control for the tip position. This results in a simple control law that needs minimal computing effort and, thus, can be used for real-time control of the flexible arms.<<ETX>>

Tip position control of flexible arms using a control law partitioning scheme

Tip-position control of a flexible arm with friction in the joints is carried out. The control scheme is based on two nested feedback loops, an inner loop to control the position of the motor and an outer loop that controls the tip position of the flexible arm. The inner loop is controlled by a high-gain controller to remove the effects of friction. A control law partitioning scheme that partitions the control law into a model-based portion and a servo portion is used for the control of the outer loop. To make the arm follow the desired trajectory without any delay, a feedforward term is added to the control law. The control scheme is experimentally evaluated on two very lightweight flexible arms.<<ETX>>

A separable combination of wheeled rover and arm mechanism: (DM)/sup 2/

We present a novel mobile manipulator concept called the dual-use mobile detachable manipulator, or (DM)/sup 2/, for early construction and maintenance tasks in lunar stations. The robot consists of a wheeled rover, or mobile base and a detachable manipulator arm. The arm is symmetric, with a gripper at each end. When the arm attaches to the mobile base by grasping a handle with one of its grippers, the robot becomes a mobile manipulator and can perform exploration tasks such as collecting soil samples, surveying the lunar surface, and transporting tools and supplies. When the robot nears a lunar center structure such as a manufacturing center or a fuel tank, the manipulator arm can detach from the base and walk hand-over-hand, by grasping a series of handles on the structure, to perform tasks such as structure inspection, parts delivery, and simple assembly tasks. The paper discusses the concept and its advantages, the system under development, and its software architecture.