Harmonic Gear Transmission

Harmonic gear transmission is a novel mechanism that achieves transmission through elastic deformation motion.

Harmonic Gear Transmission

Harmonic gear transmission represents a breakthrough in traditional mechanical transmission methods that rely on rigid components. This novel mechanism utilizes a flexible member to achieve mechanical transmission, resulting in a range of special functions that are challenging to attain with other types of transmissions.

This mechanism has gained widespread use, however, it also presents unique challenges that must be addressed during the design phase.


In the 1950s, the advancement of space science and aerospace technology led to new demands for the mechanism and instrumentation of spacecraft control systems, such as a large transmission ratio, compact size, lightweight design, high transmission precision, and minimal variation.

To meet these requirements, the harmonic drive emerged as a suitable transmission technology that is based on the elastic deformation of thin shells.

The harmonic gear drive system is composed of three fundamental components, as illustrated in Figure 2-1.

  • Circular Spline
  • Flexspline
  • Wave Generator

The principle of harmonic gear transmission involves the generation of a moving deformation wave in the flexible gear member through the action of a wave generator, which then meshes with a rigid tooth to achieve the desired transmission.


  • Large transmission ratio range, from 50 to 300 and from 3000 to 60000
  • 30% more engaged teeth at the same time, resulting in high precision and a large tooth bearing capacity
  • Large load capacity
  • High precision of motion
  • Smooth, non-impacting movement with low noise
  • Adjustable flank clearance
  • Minimal and uniform tooth surface wear, leading to high transmission efficiency
  • Good coaxiality
  • Ability to transmit motion and power to confined spaces


  • Prone to fatigue damage
  • The manufacturing of the flexible wheel and wave generator is challenging
  • The lower limit of the transmission ratio is high and requires a minimum number of teeth
  • Large starting torque, which becomes more significant with a smaller speed ratio
  • No intermediate shaft in the harmonic gear drive, making it unable to obtain an intermediate speed
  • Incorrect structural parameters or poor timing can result in excessive heat and reduced transmission capacity.

Currently, scholars from various countries acknowledge that the fatigue damage of the flexible wheel cylinder is the most significant form of failure in harmonic transmission.


Harmonic drives possess a range of unique advantages that set them apart from other drives.

In recent decades, they have been widely adopted in a variety of fields, including energy, communications, machine tools, instrumentation, robotics, automobiles, shipbuilding, textiles, metallurgy, conventional weapons, precision optical equipment, printing institutions, and medical devices.

Both precision harmonic drives as high-sensitivity servo systems and power harmonic drives that transmit large torques have demonstrated strong performance in both domestic and international applications.

In demanding environments, such as in space or with high temperature and high pressure pipelines or exposure to atomic radiation or other harmful media, harmonic drives have demonstrated superiority over other transmissions.

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