Evaluation of linear force actuators in a pin-on-disc test rig application

Sammanfattning: This thesis presents an evaluation and comparison of two linear actuators that can be used as load application actuators in a pin-on-disc tribological test rig. The first actuator is a DC-motor with an external ball screw, and the second actuator is a voice coil. The actuators are required to follow the reference force profile which corresponds to the thread contact force during a screw tightening process. In order to compare the two actuators, a Simulink model of the pin-on-disc test rig was created to be used as an experimental environment. The controllers for each actuator were designed using the same design method. Further, a set of 27 experiments was performed in Simulink with different reference force profiles, model parameters and possible disturbances. The results of each experiment were evaluated using Mean Square Error metrics and then compared between the actuators. For all the performed simulations the voice coil shows superior performance compared with the DC-motor and a ball screw. Based on these results, the choice was made to use the voice coil in the pin-on-disc test rig design for investigating the friction variation during a tightening process. The simulations showed a high importance of disc waviness on force variation. Friction occurring in linear actuators is a main concern in accurate performance of reference force profile tracking, and hence the actuators shall be carefully designed and chosen to minimize friction. The developed simulation model shall be validated in the future to prove that the results of the thesis agree with reality. Once the model is validated, it can be used to try different controller architectures and find the one that fits best the reference force profile tracking application.