Teaching practice: Digital design and performance optimization of the cam mechanism of an on-load tap changer

Cam mechanisms are extensively employed in complex precision mechanical systems, due to their ability to deliver precise switching actions and high motion reliability. As a fundamental teaching content in mechanical engineering curricula—including courses such as Theory of Machines and Fundamentals of Mechanical Design—the conventional teaching mode of cam mechanism design has long relied on graphical and analytical techniques. These traditional modes, however, often suffer from limited digital integration, insufficient depth in performance optimization, and a lack of engineering relevance in pedagogical case studies. To bridge these gaps, this work presents an integrated digital design and performance optimization methodology focused on the main contact cam mechanism of an on-load tap changer (OLTC), a critical component deployed in ultra-high voltage (UHV) transmission systems.

This teaching case is inherently rich in engineering significance and possesses substantial educational value. UHV transmission technology represents China’s flagship achievement in globally leading high-end manufacturing, while the OLTC is the sole core component within UHV converter transformers that undergoes frequent operational cycling. By anchoring the instruction in a real-world major engineering project, this teaching design effectively merges theoretical principles with practical application. The methodological framework adopted in this work integrates 3D modeling, multibody dynamic simulation, finite element analysis, and fatigue life calculation, thereby encompassing the complete iterative workflow of “design–modeling–analysis–optimization” for cam mechanisms. This comprehensive digital framework provides practical guidance for engaging students in modern engineering practices of cam mechanism development within the context of nationally important infrastructure projects.

This study systematically addresses the design challenges through the following key steps and corresponding findings: 1) A double-layer integrated cam mechanism is designed and modeled. This configuration employs distributed cam profiles on two distinct layers, combined with a staggered arrangement of moving contact pins. Such a layout achieves reciprocating motion and controlled intermittent movement of the moving contacts, ensuring reliable switching performance under operational loads. 2) Multibody dynamics simulations are conducted to obtain the collision load between the cam and follower, as well as the complete load–time history throughout the operating cycle. The resulting dynamic load data are subsequently used as inputs for finite element analysis, which determines the detailed stress distribution during collision. Building upon the stress results, a fatigue life assessment is then performed to predict the durability of the mechanism under repeated loading. 3) The motion profile of the moving contact is optimized. By evaluating various cam profile designs, a comparative analysis is conducted focusing on two critical metrics: the peak collision force between the cam and moving contact, and the computed fatigue life of the cam mechanism. This optimization process identifies the cam profile that best balances dynamic performance with structural longevity, ultimately yielding a design that meets the prescribed service life requirements while maintaining smooth and reliable motion transfer.

This work demonstrates how a strong engineering case, drawn from a national project, can be leveraged to enhance the teaching of cam mechanism design. The presented teaching case effectively addresses the shortcomings of the conventional teaching mode for cam mechanism design, providing students with a practical reference for applying theoretical knowledge to real engineering problems.