Understanding Harmonic Drive Technology: CSG vs SHG Series

Harmonic drives, also known as strain wave gearboxes, are precision gear systems offering zero backlash, high reduction ratios in a compact package, and outstanding positional accuracy. Unlike conventional planetary gearboxes that use multiple meshing gears, harmonic drives operate on an elegant principle of elastic deformation. At Mirai Technowelt, we offer two primary series: CSG (cup-type) and SHG (hat-type), each designed for specific application requirements.

How Harmonic Drives Work

A harmonic drive consists of three main components: the wave generator (an elliptical cam with a flexible ball bearing), the flexspline (a thin-walled flexible steel cylinder with external teeth), and the circular spline (a rigid ring with internal teeth). As the wave generator rotates, it deforms the flexspline into an ellipse, causing its teeth to engage with the circular spline at two opposing points. Since the flexspline has slightly fewer teeth, each rotation advances it by a fraction of a tooth, creating a high reduction ratio with zero backlash.

CSG Series: Cup-Type Design

The CSG series features a cup-shaped flexspline with a closed end connecting to the output shaft via a cross roller bearing. This design provides excellent torsional stiffness and compact axial length. The CSG series is ideal for applications where the motor mounts inline with the load, such as robotic joints, CNC rotary tables, and semiconductor equipment. With ratios from 50:1 to 160:1 and torque capacities up to 480 Nm, it delivers exceptional precision in a small footprint.

SHG Series: Hat-Type Design

The SHG series uses a hat-shaped flexspline with a radially extending flange and a central bore that allows wiring, tubing, or shafts to pass directly through the gearbox center. This versatility supports both direct drive (motor inline) and belt/pulley (parallel motor) configurations. When space is constrained or you need to route cables through your rotary joint, the SHG series is the optimal choice. Its unique geometry makes it popular in collaborative robots and precision indexing tables.

Choosing Between CSG and SHG

Select the CSG series for the most compact axial dimension with inline motor connection. Choose the SHG series when you need a through-bore for wiring or want the flexibility of parallel motor mounting. Both series deliver zero backlash, high positional accuracy (≤ 20 arc-sec), and exceptional torque density. Our engineering team can help you evaluate the trade-offs for your specific application.