Comparison of FOC and DTC in an application of a screw joint emulator

Sammanfattning: Atlas Copco produces, among other things, tightening tools for screw joints. The purpose of these fastening elements is to produce a clamping force between two parts, holding them together. One of the main ways to estimate the clamping force is by measuring torque, hence it has to be made sure that the tightening tool consistently produces the requested torque and detects anomalies. One of the methods used for this is long term testing, resulting in millions of tightenings. Normal screw joints are not suited for this purpose, as material fatigue changes the characteristics over time. Instead, a screw joint emulator based on a Permanent Magnet Synchronous Motor (PMSM) was proposed. This thesis explores the possibility of such an emulator, and evaluates the performance of two motor control algorithms, Field Oriented Control (FOC) and Direct Torque Control (DTC), in this specific application. By modeling the system in Simulink and Matlab, simulations could be performed and analyzed in order to compare the two motor control algorithms. The best performing algorithm was then implemented digitally on a physical system in order to confirm the results. It was shown that a screw joint could be emulated with a PMSM. FOC proved to be more suited in this application, with lower torque ripple than DTC at the cost of response time. The performance of the PMSM screw joint emulator was concluded to be satisfactory for long term testing.