Alan Bowling

The dynamic capability equations: a new tool for analyzing robotic manipulator performance

Dynamic capability equations (DCE) provide a new description of robot acceleration and force capabilities. These refer to a manipulators ability to accelerate its end-effector and to apply forces to the environment at the end-effector. The key features in the development of these equations are that they combine the analysis of end-effector accelerations, velocities, and forces, while addressing the difference in units between translational and rotational quantities. The equations describe the magnitudes of translational and rotational acceleration and force guaranteed to be achievable in every direction, from a particular configuration, given the limitations on the manipulators motor torques. They also describe the effect of velocities on these capabilities contributed by the Coriolis and centrifugal forces, as well as the reduction of actuator torque capacity due to motor speed. This article focuses on nonredundant manipulators with as many actuators as degrees of freedom.

Optimization of the inertial and acceleration characteristics of manipulators

Investigates the problem of manipulator design for increased dynamic performance. Optimization techniques are used to determine the design parameters which improve manipulator performance. The dynamic performance of a manipulator is characterized by the inertial and acceleration properties of the end-effector. Our study of inertial and acceleration properties have provided separate descriptions of the characteristics associated with linear and angular motions. This allows a more physically meaningful interpretation of these properties and provides simple models for their analysis. The article presents these models, discusses the design optimization criteria, and formulates the optimization problem. The approach is illustrated in the selection of design parameters of a parallel mechanism.

Navigability of multi-legged robots

This paper addresses the improvement of navigability for a six-legged robot through the development of a simple method for measuring heading and drift errors. More specifically, the navigation scheme utilizes both a magnetic compass and landmark navigation to correct these errors with every step, hence limiting error propagation. The approach is aimed at operation in unknown environments. Elaborate data processing in the control algorithm is avoided by using modular sensors capable of processing their own inputs. The robot controller uses the well-known tripod gait, implemented here using the hexapod inverse kinematics. Experimental results show significant improvements in the hexapods navigability for turning and walking maneuvers.

Dynamic performance, mobility, and agility of multilegged robots

Background. This article presents a method for describing the dynamic performance of multilegged robots. It involves examining how well the legged system uses ground contact to produce acceleration of its body; these abilities are referred to as its force and acceleration capabilities. These capabilities are bounded by actuator torque limits and the no-slip condition. Method of Approach. The approach followed here is based on the dynamic capability equations, which are extended to consider frictional ground contact as well as the changes in degrees-of-freedom that occurs as the robot goes into and out of contact with the ground. Results. The analysis describes the maximum translational and rotational accelerations of the main-body that are guaranteed to be achievable in every direction without causing slipping at the contact points or saturating an actuator. Conclusion. This analysis provides a description of the mobility and agility of legged robots. The method is illustrated using a hexapod as an example.

A smart bed platform for monitoring & Ulcer prevention

The focus of this paper is to develop a software-hardware platform that addresses one of the most costly, acute health conditions, pressure ulcers — or bed sores. Caring for pressure ulcers is extremely costly, increases the length of hospital stays and is very labor intensive. The proposed platform collects information from various sensors incorporated into the bed, analyzes the data to create a time-stamped, whole-body pressure distribution map, and commands the beds actuators to periodically adjust its surface profile to redistribute pressure over the entire body. These capabilities are combined to form a cognitive support system, that augments the ability of a care giver, allowing them to provide better care to more patients in less time. For proof of concept, we have implemented algorithms and architectures that cover four key aspects of this platform: 1) data collection, 2) modeling & profiling, 3) machine learning, and 4) acting.

Dynamic loading criteria in actuator selection for desired dynamic performance

This article presents two methods for selecting actuators based on the dynamic loading criteria which yield a manipulator with a desired level of dynamic performance. Here, dynamic performance is measured in terms of a robots acceleration and force capabilities, which describe its ability to accelerate the end-effector and to apply forces to the environment, given the limitations on its actuator torques. The Dynamic Capability Equations are used to model the relationship between actuator torque capacities and the acceleration and force capabilities, because they treat linear and angular quantities in a consistent and physically meaningful way. This article discusses actuator selection for a single configuration, as well as for multiple configurations.

Rebound, slip, and compliance in the modeling and analysis of discrete impacts in legged locomotion

An energy-based approach to analysis of the impact problem in three dimensional multi-legged robot locomotion is hereby presented. The goal is to combine rigid and deformable body approaches, which come together naturally in a work-energy framework. The rigid body approach is used to calculate the energy restituted after a foot impacts on the ground, and the ground and the foot are considered rigid bodies throughout the analysis. Then the flexible body approach is used to store the energy restituted to the system through the system’s compliance. The proposed hybrid approach can predict both rebound and non-rebound conditions for an energetic coefficient of restitution greater than zero. Zero tangential velocity (i.e., zero slip) in the impacting end effectors can be also predicted, a condition known as sticking. The article presents a method for determining whether the level of compliance in the system at a given configuration is adequate to insure a no-slip, no-rebound impact, with a focus on leg design.

Design of macro/mini manipulators for optimal dynamic performance

This article investigates the problem of redundant manipulator design for optimal dynamic performance as applied to the design of macro/mini structures. The dynamic performance of a manipulator is characterized by the inertial and acceleration properties of the end-effector. However, for redundant manipulators the characteristics of motions in the end effector null space must also be considered. This article presents a methodology for analyzing the performance requirements for the null space motions. The analysis results in a decomposition of the overall design problem into a set of smaller subproblems. Optimization techniques are then used to determine the design parameters which improve manipulator dynamic performance. The decomposition greatly reduces the search space of the overall optimization. Here this methodology is presented along with the models and measures upon which it is based. The approach is illustrated in. The selection of design parameters for a simple six-degree-of-freedom planar mechanism.

Velocity Effects on Robotic Manipulator Dynamic Performance

This article explores the effect that velocities have on a nonredundant robotic manipulator s ability to accelerate its end-effector, as well as to apply forces/moments to the environment at the end-effector. This work considers velocity forces, including Coriolis forces, and the reduction of actuator torque with rotor velocity described by the speed-torque curve. at a particular configuration of a manipulator. The focus here is on nonredundant manipulators with as many actuators as degrees-of-freedom. Analysis of the velocity forces is accomplished using optimization techniques, where the optimization problem consists of an objective function and constraints which are all purely quadratic forms, yielding a nonconvex problem. Dialytic elimination is used to find the globally optimal solution to this problem. The proposed method does not use iterative numerical optimization methods. The PUMA 560 manipulator is used as an example to illustrate this methodology. The methodology provides an analytical analysis of the velocity forces which insures that the globally optimal solution to the associated optimization problem is found.

Impact forces and agility in legged robot locomotion

In this article we present a method for determining the effect of impact forces on a legged robot’s agility. Here agility is defined as the robot’s ability to change its velocity, which requires generation of acceleration. The level of achievable acceleration is determined using an analysis of dynamic performance. This results in performance curves describing how well the legged system uses impact and contact forces to accelerate itself. These capabilities are bounded by actuator torque limits and friction forces. Herein, the performance curves are examined at the termination of the impact event. The method is illustrated using a hexapod.