Stephen S. Nestinger

A Mobile Agent-Based Framework for Flexible Automation Systems

Modern manufacturing systems are increasingly becoming highly dynamic due to the integration with advanced information technology in response to rapid changes in products and market conditions. A more flexible platform is critically needed for developing a new generation of manufacturing systems in order to address the challenges of uncertainty and flexibility requirements. This paper presents a mobile agent-based framework that supports dynamic deployment of control algorithms and tasks in automation systems. The framework is based on a mobile agent system called Mobile-C. It uses Ch, an embeddable interpretive C/C++ environment for mobile agent execution. Since Ch has been ported to most existing computing platforms, the framework can control automation systems that work in different operating systems. This mobile agent-based framework has been applied to the control of an automation work cell. Using an automaton package in Ch as a middleware, automation tasks can be described as high-level control programs and are portable to heterogeneous mechatronic devices that comprise the automation cell. The validation of the dynamic deployment of different tasks has been conducted in an experimental automation work cell that consists of a Puma 560, an IBM 7575, and a conveyor system. The results show that the mobile agent approach can effectively deploy and execute new control algorithms and tasks as mobile agents on any subsystem in a network.

Study of the Foot Force Stability Margin for multi-legged/wheeled robots under dynamic situations

Stability analysis of multi-legged and wheeled robots is necessary for maintaining control of the robot especially under dynamic situations. This paper studies the use of the Foot Force Stability Margin and a modified extension of the Foot Force Stability Margin under dynamic situations. The Foot Force Stability Margin and its modified variant are applicable to all types of multi-legged and multi-wheeled robots under both static and dynamic situations. To facilitate the numerical validation of the stability margin under dynamic conditions, a foot force distribution technique is presented. The simulation results confirm that under dynamic situations, the Foot Force Stability Margin and its modified variant are accurate, simple in terms of calculation cost, and sensitive to top-heaviness and the geometry of the robot, making it practical for use within on-line controllers.

Mobile-R: A reconfigurable cooperative control platform for rapid deployment of multi-robot systems

Cooperative multi-robot systems have been used in a vast array of fields and are of particular interest in perilous environments. One of the main issues in multi-robot systems is the lack of a common set of programming and control abstractions and middleware. Controlling and programming cooperative multi-robot systems is a highly complicated task that requires a flexible and agile control architecture and programming environment that are able to handle the distributed nature of multi-robot systems. A generalized, highly flexible and reconfigurable cooperative robot control platform called Mobile-R has been developed. Mobile-R consists of a mobile agent-based robot control system and a mission-based rapid deployment system. A real-world validation experiment involving cooperative multi-robot perimeter patrolling is presented.

Adaptive collaborative estimation of multi-agent mobile robotic systems

Collaborative multi-robot systems are used in a vast array of fields for their innate ability to parallelize domain problems for faster execution. These systems are generally comprised of multiple identical robotic systems in order to simplify manufacturability and programmability, reduce cost, and provide fault tolerance. This work takes advantage of the homogeneity and multiplicity of multi-robot systems to enhance the convergence rate of adaptive dynamic parameter estimation through collaboration. The collaborative adaptive dynamic parameter estimation of multi-robot systems is accomplished by penalizing the pair-wise disagreement of both state and parameter estimates. Consensus and convergence is based on Lyapunov stability arguments. Simulation studies with multiple Pioneer 3-DX systems provides verification of the proposed theoretic collaborative adaptive parameter estimation predictions.

Ch MPI: Interpretive Parallel Computing in C

The message passing interface lets users develop portable message passing programs for parallel computing in C, C++, and Fortran. When combined with an MPI C/C++ library, Ch, an embeddable C/C++ interpreter for executing C/C++ programs interpretively, lets developers rapidly prototype MPI C/C++ programs without having to compile and link.

Closed-Form Solution for Constant-Orientation Workspace and Workspace-Based Design of Radially Symmetric Hexapod Robots

The workspace of hexapod robots is a key performance parameter which has attracted the attention of numerous researchers during the past decades. The selection of the hexapod parameters for a desired workspace generally employs the use of numerical methods. This paper presents a general methodology for solving the closed-form constant orientation workspace of radially symmetric hexapod robots. The closed-form solution facilitates hexapod robot design and minimizes numerical efforts with on-line determination of stability and workspace utilization. The methodology can be used for robots with nonsymmetric and nonidentical kinematic chains. In this paper, the methodology is used to derive the closed-form equations of the boundary of the constant-orientation workspace of axially symmetric hexapod robots. Several applications are provided to demonstrate the capability of the presented closed-form solution in design and optimization. An approach for workspace-based design optimization is presented using the provided analytical solution by applying an iterative optimization algorithm to the find optimized structural parameters and an optimized workspace.

Lateral reachable workspace of axially symmetric mobile machining hexapod robots

Mobile machines allow for remote repair and maintenance within constrictive, hazardous, and inaccessible environments. Hexapod robots are a salient solution to mobile machines due to their maneuverability and controllable orientation. One important aspect of mobile machines is the reachable workspace of the currently loaded tooling. Generally, machining operations are restricted to planar motion operating within the lateral plane of the mobile machines. This paper introduces an analytical methodology for finding the lateral reachable workspace of an axially symmetric hexapod robots used as mobile machining systems. The closed-form solution to the lateral reachable workspace of axially symmetric hexapod robots is facilitated by the correlation of the lateral motion of a hexapod robot with an equivalent 2-RPR planar parallel mechanism. Since the solution is closed-form, it has high accuracy and reliability.

The design and realization of a high mobility biomimetic quadrupedal robot

Legged robots have made significant strides in facing challenging tasks including navigating rough terrain with the help of energy conserving techniques. This paper describes the detailed design considerations and realization of Sabertooth, a high mobility biomimetic quadrupedal robot. Each leg of Sabertooth has three active degrees of freedom with the bottom two links employing a spring system to allow for compliance and power recovery. Sabertooth has two notable biomimetic features including a passive two degree of freedom spine and a fully compliant ankle system. The front and back ankles are designed differently to mimic a quadrupedal animals power and stability legs. The full system integrates an array of sensors including an inertial measurement unit, laser range finder, camera, and multiple potentiometers. The computing power is split between an onboard FPGA and netbook computer.

Mobile Agent-based Remote Vision Sensor Fusion

Vision systems have become popular for remote vision sensing in geographically distributed environments due to vast amount of information they provide. However, remote vision sensors are generally plagued with power and communication bandwidth constraints. Mobile agent technology is a salient solution to geographically distributed and dynamic domains that require subsystems to interact with each other. Mobile agent technology increases power efficiency by reducing communication requirements and increases fusion processing by allowing in-situ integration of on-demand visual processing and analysis algorithms. A mobile agent can dynamically migrate from one vision sensor to another and combine all necessary sensor data in a desired manner specific to the system requesting the data. This paper presents a remote vision fusion architecture based on mobile agent technology that provides a flexible vision fusion solution. The architecture utilizes the Mobile-C library as a basis for the mobile agency along with OpenCV and ImageMagick for vision processing and manipulation. An application example is provided that demonstrates the benefit of using mobile agents for vision fusion in remote vision systems. The validity of the architecture is proven in an experimental setup with a retrofitted robotic cell comprised of a Puma 560, IBM 7575, a conveyor system, and a vision system.

Foot Force Based Reactive Stability of Multi-Legged Robots to External Perturbations

Many environments and scenarios contain rough and irregular terrain and are inaccessible or hazardous for humans. Robotic automation is preferred in lieu of placing humans at risk. Legged locomotion is more advantageous in traversing complex terrain but requires constant monitoring and correction to maintain system stability. This paper presents a multi-legged reactive stability control method for maintaining system stability under external perturbations. Assuming tumbling instability and sufficient friction to prevent slippage, the reactive stability control method is based solely on the measured foot forces normal to the contact surface, reducing computation time and sensor information. Under external perturbations, the reactive stability control method opts to either displace the CG or the foot contacts of the robot based on the measured foot force distribution. Details describing the reactive stability control method are discussed including algorithms and an implementation example. An experimental demonstration of the reactive stability control method is presented. The experiment was conducted on a hexapod robot platform retrofitted with a tiny computer and force sensitive resistors to measure the foot forces. The experimental results show that the presented reactive stability control strategy prevents the robot from tipping over under external perturbation.