Subjoints

Subjoints are a concept used in mechanical design and robotics to describe smaller joint elements that connect subassemblies within a larger joint mechanism. The idea emphasizes modularity and hierarchical articulation: a complex motion can be built from a network of subjoints, each governing motion within its own subassembly and communicating with neighboring subjoints to produce overall movement.

The term is not universally standardized, but it appears in discussions of modular and reconfigurable systems. In practice, a subjoints approach treats a mechanism as a composition of smaller joints, which can be revolute, prismatic, spherical, or other types, connected in a way that preserves the intended motion of the larger joint. This allows designers to tailor stiffness, range of motion, and control at a finer scale while maintaining a coherent global kinematic model.

Modeling subjoints typically involves describing each subjoint with its own local coordinate frame and transformation, then linking these frames to form the complete pose of the end effector or connected subassemblies. Control strategies may distribute actuation across subjoints or centralize it, depending on the design. Advantages include modularity, easier maintenance, and the ability to reconfigure a system without redesigning the entire mechanism.

Applications of subjoints appear in modular robotics, animation rigs, prosthetics, and reconfigurable machinery, where hierarchical articulation supports scalability and adaptability. Challenges include increased control complexity, calibration needs, and potential accumulative pose error across nested joints.

See also: joints, linkages, modular robotics, articulated systems.