Harmonic drive

What it means

A harmonic drive is commonly understood as a strain wave reduction gear. In the conventional arrangement, an elliptical wave generator deforms a flexible toothed component called the flexspline inside a rigid circular spline. Different tooth counts allow a relatively large input rotation to produce a much smaller output rotation. Harmonic Drive's technology page describes this operating principle and the three main components. [1]

The generic mechanism name is strain wave gearing. Harmonic Drive is also used as a brand and trademark, so a product described with that name may mean a particular supplier's component or the broader mechanism. Keep the supplier attribution when it is documented. [1, 2]

How it applies to humanoids

A compact reduction stage can help fit a motor-driven actuator into a robot joint. The mechanism's relevance to humanoids is the design tradeoff between packaging, reduction, transmitted torque and motion accuracy. Harmonic Drive identifies compact construction, high reduction and low backlash among its gear features; those are component characteristics rather than humanoid performance results. [1, 2]

MathWorks represents the mechanism as a high-ratio speed reducer with configurable losses and inertia in its simulation block. That provides a useful reminder that a transmission must be modeled as more than an ideal rotation ratio when studying a complete actuator. [3]

Terminology and performance traps

Low or zero backlash does not mean infinite stiffness. Backlash concerns lost motion associated with clearance when direction reverses; elastic twisting under load is a different effect. Harmonic Drive discusses torsional stiffness separately from transmission accuracy and introduces different engagement designs to change those properties. [2]

The familiar elliptical diagram is not a description of every newer product. Harmonic Drive's Triangle Technology uses three engagement regions, so statements about a particular mechanism should identify the version being discussed. [2]

Do not assume loss-free motion or a particular backdriving response from the category name. MathWorks offers ideal and efficiency-based friction models, including temperature-dependent options. These are modeling choices, not measured efficiency figures for an unspecified humanoid gearbox. [3]

How to read it on humanoidversus.com

An electric value in actuation does not identify strain wave gearing. The max_joint_torque_nm field also cannot establish the reducer type, because the complete actuator includes a motor and transmission. Use a manufacturer drawing, parts specification or technical paper to identify the mechanism.

This entry has no live table and no robot examples. The current glossary relationship is to actuator interpretation, not a claim that a listed humanoid uses this transmission. Unknown gearbox details should remain unknown rather than be inferred from joint size or a demonstration.

Further reading

Compare Harmonic Drive's conventional operating-principle page with its gear technology overview. The MathWorks block documentation explains how a simulator represents the mechanism and its losses. [1–3]