Date of Award

2007

Degree Type

Thesis

Degree Name

Master of Science in Mechanical Engineering and Applied Mechanics

Department

Mechanical Engineering and Applied Mechanics

First Advisor

Musa Jouaneh

Abstract

XY-positioning is an important task in industrial applications. The improvement of the speed of positioning while keeping good accuracy can increase productivity and is therefore highly desirable. The studied H-frame system is a parallel xy-positioning device, which due to less moved masses is potentially capable of fast acceleration and therefore faster positioning then traditional stacked systems. One feature of the system which enables its parallel structure is the use of one long timing belt to transmit the power of the two stationary motors to the end-effector position, for practical as well as economical reasons, is not available as feedback signal for controlling the system. This means that even if an accurate tracking pf the desired motor angles was achieved, the end-effector position may still deviate from the desired path, due to stretching in the belt. Another effect making an accurate control difficult is the presence of nonlinear friction in the system. This thesis addresses the development of an accurate control system, which is a requirement to be able to utilize the advantages that the parallel structure of the H-frame system provides.

In order to be able to develop an accurate control strategy, the dynamic behavior in the presence of nonlinear friction as well as the flexibility of the belt has to be understood. An accurate dynamic model is needed for the development of most sophisticated controllers. That is why in this work first a one-axis belt drive positioning system is studied and a dynamic model for it is derived. The findings from this simpler one-axis case are then utilized to derive a dynamic model for the two axis H-frame system. First a detailed 20th-order model of the system is being derived, which then based on assumptions is simplified to a lower 8th-order case. Nonlinear friction is considered for the one-axis as well for the simplified 8th-order H-frame case. Experimental results are utilized to verify that the derived models can resemble the dynamics of the system. The model can be used for simulating different controllers before implementing them on the real system as well as it can be used to develop sophisticated controllers. The model is verified with experimental data from the real system. Furthermore the performance of PID- and PD-controllers are studied in simulation as well as experimentally.

It is found that PID- and PD-controllers, due to the disadvantages the system has described above, are not sufficient control strategies for high-speed tracking. However the dynamic nonlinear model derived in this work gives future researchers the tool to develop more sophisticated controllers, in order to solve the problem of accurate control of the H-frame system.

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