A comprehensive study of robot control algorithms

The PUMA 560 Industrial Manipulator is presently controlled using a PID control strategy Robot manipulators are highly coupled, nonlinear mechanical systems designed to perform specific tasks. It is the function of any control algorithm to compute the input voltages or torques needed to follow a desired trajectory. The PID controller is detuned, so as to cater for variations in system behaviour. Thus, the performance of such a control algorithm is poor over the entire operating range of the robot and the need for more complex control strategies is clear. The research presented m this thesis derives a third order comprehensive dynamic model for the three primary robot joints, using the Euler-Lagrange formulation for the equations of motion. A simulation package is designed to model this dynamic system. Next, a wide range of different techniques are investigated in a simulation environment, to observe their performance on the computer model. These control algorithms range from Fixed Parameter techniques to Adaptive strategies and Feedforward routines. A set of performance criteria can be used to evaluate these techniques, and the best algonthm from each section is chosen. Using the results of an identification performed on the robot, each of these control methods is applied to the resulting tune varying model. The results here are used to determine the optimal control strategy for manipulator use. Also in this thesis, a new hardware structure is designed and implemented. This structure is capable of implementing complex control routines with adequately low sample periods. The design uses advanced digital signal processors, which can perform arithmetic operations quickly

Aspects of parallel processing and control engineering

The concept of parallel processing is not a new one, but the application of it to control engineering tasks is a relatively recent development, made possible by contemporary hardware and software innovation. It has long been accepted that, if properly orchestrated several processors/CPUs when combined can form a powerful processing entity. What prevented this from being implemented in commercial systems was the adequacy of the microprocessor for most tasks and hence the expense of a multi-processor system was not justified. With the advent of high demand systems, such as highly fault tolerant flight controllers and fast robotic controllers, parallel processing became a viable option. Nonetheless, the software interfacing of control laws onto parallel systems has remained somewhat of an impasse. There are no software compilers at present which allow a programmer to specify a control law in pure mathematical terminology and then decompose it into a flow diagram of concurrent processes which may then be implemented on, say, a target Transputer system, liiere are several parallel programming languages with which a programmer can generate parallel processes but, generally, in order to realise a control algorithm in parallel the programmer must have intimate knowledge of the algorithm. Therefore, efficiency is based on the ability of the programmer to recognise inherent parellelism. Some attempts are being made to create intelligent partition and scheduling compilers but this usually means significantly extra overheads on the multiprocessor system. In the absence of an automated technique control algorithms must be decomposed by inspection. The research presented in this thesis is founded upon the application of both parallel and pipelining techniques to particular control strategies. Parallelism is tackled objectively and by creating a tailored terminology it is defined mathematically, and consequently related concepts, such as bounded parallelism and algorithm speedup, are also quantified in a numerical sense. A pipelined explicit Self Tuning Regulator (STR) controller is developed and tested on systems of different order. Under the governance of the parallelism terminology the effectiveness of the parallel STR is evaluated and numerically quantified in terms of relevant performance indices. A parallel simulator is presented for the Puma 560 robotic manipulator. By exploiting parallelism and pipelinability in the robot model a significant increase in execution speed is achieved over the sequential model. The use of Transputers is examined and graphical results obtained for several performance indices, including speedup, processor efficiency and bounded parallelism. By the same analytical technique a parallel computed torque feedforward controller incorporating proportional derivative feedback control for the Puma 560 manipulator is developed and appraised. The performance of a Transputer system in hosting the controller is graphically analysed and as in the case of the parallel simulator the more important performance indices are examined under both optimal conditions and conditions of varying hardware constraints

A passivity based control methodology for flexible joint robots with application to a simplified shuttle RMS arm

The main goal is to develop a general theory for the control of flexible robots, including flexible joint robots, flexible link robots, rigid bodies with flexible appendages, etc. As part of the validation, the theory is applied to the control law development for a test example which consists of a three-link arm modeled after the shoulder yaw joint of the space shuttle remote manipulator system (RMS). The performance of the closed loop control system is then compared with the performance of the existing RMS controller to demonstrate the effectiveness of the proposed approach. The theoretical foundation of this new approach to the control of flexible robots is presented and its efficacy is demonstrated through simulation results on the three-link test arm

Improved Operational Space Control Framework for Compliant Motion of Robotic Manipulators

Ph.DDOCTOR OF PHILOSOPH