High Precision Reducers for Industrial Robots Driving 4th Industrial Revolution: State of Arts, Analysis, Design, Performance Evaluation and Perspective

New industrial revolution - “The 4th industrial revolution” must be a remarkable milestone for the second decade of the twenty-first century. Many countries are competing to innovate their manufacturing chains for eco-friendly and energy-efficient productions. Although this green or sustainable manufacturing system evolves under the support of cyber-physical system (or digital twin) based on ICT technology, industrial robots also play important roles in this speedy, flexible and effective manufacturing chains. Recently, low-cost industrial robots or collaborative robots, are rising in a highly interactive environment with humans. Although an industrial robot consists of many important components such as mechanical parts (kinematic structure and reducer) and electric parts (servo motor, driver, sensors, and controller), precision reducer takes approximately 25% of material-cost and governs important performance indices of industrial robots. This paper presents review of high precision reducers (HPRs) for industrial robots driving 4th industrial revolution. First, we provide HPRs market along with industrial robots. According to previous studies, HPRs for industrial robots can be classified based on their principles: planetary reducer, cycloid reducer, and harmonic drive (HD). Then, principle, characteristics, and three main performances (hysteresis, rotational transmission error (RTE) and efficiency) of HPRs are discussed. In addition, compensation methods overcoming accuracy limits of HPRs are summarized. Finally, other applications of HPRs except industrial robots are presented.