Preliminary Report on High-Performance Computational Structures for Robot Control

In this report we present some initial results of our work completed thus far on Computational Structures for Robot Control . A SIMD architecture with the crossbar interprocessor network which achieves the parallel processing execution time lower bound of o( [a1n ]), where a1 is a constant and n is the number of manipulator joints, for the computation of the inverse dynamics problem, is discussed. A novel SIMD task scheduling algorithm that optimizes the parallel processing performance on the indicated architecture is also delineated. Simulations performed on this architecture show speedup factor of 3.4 over previous related work completed for the evaluation of the specified problem, is achieved. Parallel processing of PUMA forward and inverse kinematics solutions is next investigated using a particular scheduling algorithm. In addition, a custom bit-serial array architecture is designed for the computation of the inverse dynamics problem within the bit-serial execution time lower bound of o(c1k + c2kn), where c1 and c2 are specified constants, k is the word length, and n is the number of manipulator joints. Finally, mapping of the Newton-Euler equations onto a fixed systolic array is investigated. A balanced architecture for the inverse dynamics problem which achieves the systolic execution time lower bound for the specified problem is depicted. Please note again that these results are only preliminary and improvements to our algorithms and architectures are currently still being made

The systematic development of a machine vision based milking robot

Agriculture involves unique interactions between man, machines, and various elements from nature. Therefore the implementation of advanced technology in agriculture holds different challenges than in other sectors of the economy. This dissertation stems from research into the application of advanced technology in dairying - focusing on the systematic analysis and synthesis of concepts for a robotic milking machine for cows. The main subsystems of the milking robot are identified as a machine perception subsystem and a mechanical manipulator subsystem. The machine perception subsystem consists of one or more sensors and a signal processor; while the manipulator subsystem typically consists of a robot arm; a robot hand; actuators; and a controller. After the evaluation of different sensor concepts in terms of a defined set of technical performance requirements, television cameras are chosen as a suitable sensor concept for a milking robot. Therefore the signal processor is only concerned with image processing techniques. The primary task of the milking robot's image processor is to derive a computerized description of the spatial positions of the endpoints of a cow's four teats, in terms of a pre-defined frame of reference (called the word coordinates ). This process is called scene description ; and based on extensive experimental results, three-dimensional scene description - making use of a stereo-vision set-up - is shown to be feasible for application as part of a milking robot. Different processes are involved in stereo machine vision - such as data reduction, with the minimum loss of Image information (for which the Sobel edge enhancement operator is used); the accurate localisation of target objects in the two stereo images (for which the parabolic Hough transform is used); and correlation of features in the two stereo images. These aspects are all addressed for the milking robot, by means of concept analysis, trade-oft, and experimental verification. From a trade-off, based on a set of performance requirements for the manipulator subsystem, a cartesian robot arm is chosen as a suitable configuration for the milking robot; while sealed direct current servo motors are chosen as a suitable actuator concept. A robot arm and its actuators are designed by means of computer-aided design techniques; and computer simulation results are presented for the dynamic response of the arm and its actuators. A suitable robot hand is also designed - based on systematic trade-oft for different parts of a robot hand. From an analysis of the desired controller functions, and of different control concepts, it is concluded that a positional controller, making use of on-line obstruction avoidance, is required for the milking robot. Because this research project involved systematic concept exploration, there are still some details to be sorted out in a follow-up development phase. The basic principles of a machine vision based milking robot are however established; and the work in this dissertation represents a suitable baseline for further development