Design study on small transmission ratio harmonic reducer with new profile wave generator

Abstract

A harmonic reducer (HR) is widely used because of high precision, small size, light weight and a series of advantages. However, the disadvantage is that its transmission ratio is generally not less than 60. According to a market research study, more than 60% of the reducers have the transmission ratio of less than 60. This implies that the large transmission ratio restricts the HR from applications in the market demanding a small transmission ratio (20–60). In this study, a method is presented for designing the HR with the small transmission ratio as low as 20. First, by clarifying the principle of reducing the transmission ratio of the HR, a design model of two-wave HR tooth profile is deduced in detail, and a four-tooth difference HR is designed. Aiming at solving the problem that diminishing the radial deformation coefficient leads to the reduction of the engagement depth and the increase of the pressure angle of the tooth profile, a wave generator with a new profile is proposed. Then an optimization model based on the circular spline tooth profile to envelope the flexspline tooth profile is developed for achieving the twice-conjugated engagement. Based on manufacturing considerations, the theoretical tooth profile is fitted by involute based on a given numerical approximation method. Third, a finite element analysis is carried out to investigate the stress characteristics of small transmission ratio HR. Finally, a prototype with a transmission ratio of 20 is trial-produced and tested, which shows that the design methods can be applied for the small transmission ratio HR.