Design and Validation of a Permanent Magnet Self-Locking Electromagnetic Balancing Device for Combine Harvester Threshing Drums

Imbalance-induced vibration of the threshing drum is a common problem during rice harvesting, especially when rice straw becomes entangled with the threshing components. In this study, a permanent magnet self-locking electromagnetic balancing device was designed for a combine harvester threshing drum. Field vibration tests were first carried out to identify the main rotation-related vibration components of the drum. The measured lateral response showed a clear peak at about 45.166 Hz, which was close to the third harmonic of the drum rotational frequency. Additional peaks were also observed near 60 Hz and 90 Hz. Based on these field observations, a two-disc balancing device was developed. The counterweight discs were locked by the magnetic attraction between permanent magnets and ferromagnetic plates when no adjustment was required, and they were repositioned by electromagnetic excitation during compensation. Finite element analysis showed that a 1 mm air gap provided a suitable compromise between magnetic locking and electromagnetic actuation. At this gap, the axial forces on the left and middle ferromagnetic plates were −37.033 N and 37.073 N, respectively. In the bench test, the calculated adjustment angles of the two counterweight discs were 6.938° and −6.411°. Under the prescribed bench-test condition, the vibration amplitude decreased from 55.41 m·s−2 to 20.00 m·s−2 after compensation, corresponding to an observed reduction of 63.9%. The results demonstrate the feasibility of the proposed balancing device under the tested bench condition and provide a basis for further repeatability and field-performance evaluation.