Tendon Routing Configurations (N / N+1 / 2N)

Three standard ways to route tendons across N joints, named by how many cords each configuration uses.

A tendon can only pull, never push, so one cord can only rotate a joint in one direction. There are three common ways to actuate N degrees of freedom with tendons. A 2N configuration gives every joint an antagonistic pair of tendons — one flexes it, one extends it — which gives the most direct control and even lets you tune joint stiffness, at the cost of needing twice as many motors. An N+1 configuration shares N+1 tendons across N joints, routing them so they couple across joints in a way that keeps every degree of freedom controllable while every tendon stays in tension; it uses the fewest motors. An N configuration gives each joint just one pulling tendon and relies on a spring for the return stroke, which is mechanically simple but limits return force and speed to whatever the spring provides. The right choice depends on space inside the hand, motor count, and how much force control is needed.

ExampleThe Stanford/JPL three-fingered hand drives each finger's 3 degrees of freedom with 4 tendons (an N+1 configuration); the Utah/MIT hand uses a 2N configuration.

Also called

N-Type / N+1-Type / 2N-Type Tendon Layout

Related

Tendon-Driven Actuation · Dexterous Hand · Tendon Material (UHMWPE) · Underactuation · Degrees of Freedom (DoF) · Intrinsic vs. Extrinsic Actuation (Proximal Actuator Placement)

Sources

Design and Control of a Tendon-Driven Robotic Finger Based on Grasping Task Analysis (PMC)
Wire Driven Multi-fingered Hand - Springer Nature Link