Stepping motors have been in existence for over thirty years. The first stepping motors were electrical but were limited in their power output because of the relatively high inertia of the electric motors. In order to overcome this difficulty hydraulic torque amplification has been used. The resulting hydraulic position control systems then have the advantage over conventional positioning systems of not requiring the usual electrical feedback links. A further increase in the power output of these systems can be obtained by controlling a standard hydraulic motor to perform in a stepping mode. A stepping system has been developed to give accurate positioning for a range of load conditions, but under certain conditions where the load had a very slight inertia a steady final position was not obtained and additional system damping was required to give a satisfactory response, Various means of optimising the stepping performance characteristics were investigated experimentally with various degrees of success. Each method generally improved one aspect of motor performance, such as rise time or initial overshoot, at the expense of another. The method to be used in practice would depend on the load and the requirements surrounding its use. A detailed analysis has been made of the effect of changes in the main operating parameters during the stepping phase. This analysis has led to a better understanding of the operation of the system. The behaviour of the stepping motor was simulated using several different models on both analogue and digital computers. These simulations enabled the effects of modifications to the stepping motor design to be assessed. Fundamental design changes were considered which would be difficult and expensive to alter in practice. The means of sequential control of the stepping system was also considered. In particular pure hydraulic systems were investigated as these eliminate the need for interfaces. This led to a proposal for a sequential control system based on miniature moving part hydraulic elements. The thesis considers the various applications of stepping devices. It also analyses a possible application for a stepping motor system as a governor for a diesel engine. This was tested by means of a computer simulation and the results showed that this type of system could give accurate yet relatively simple control with some advantages over standard engine governors.
|Date of Award||1975|