Differential mechanisms possess various forms and are applied in a wide spectrum of mechanical systems. This paper proposes to categorize differential mechanisms into kinematic differential mechanisms (KDMs) and continuum differential mechanisms (CDMs), and also introduces two CDMs. The working principle, structures, constructions, and kinetostatic analyses of the proposed planar and the spatial CDMs are elaborated upon. The planar CDM is compared with two widely used differential mechanisms made from pulleys and linkages to show its effectiveness using a simple construction. The spatial CDM could resolve one input into three outputs in a way different from two serially connected planar differential mechanisms. As demonstrated in experimentation, the spatial CDM could allow more isotropic distribution of the three outputs. The categorization, analyses, and applications of the CDMs might not only extend the IFToMM terminology on differential mechanisms, but also inspire more CDM designs with distinct responses and properties for adaptive mechanical systems.

Substantial progresses have been made in building versatile anthropomorphic prosthetic hands in the past two decades using emerging technologies. However the trade-offs between functionality, reliability, affordability, appearance, etc. have not been fully settled. Many existing designs, particularly the commercial prosthetic hands, are underactuated and they can realize various grasps through compliant structures or differential mechanisms. This paper presents the design of an underactuated prosthetic hand with one actuator using a continuum differential mechanism. Structure of the continuum differential mechanism is simple enough to allow all the components, including a battery pack, to be packed into the palm. The design concept, component descriptions, and hand constructions are elaborated. Experimental verifications are presented to demonstrate the efficacy of the proposed design.

It is known that human controls muscles for hand poses in a coordinated manner and the coordination is referred to as a postural synergy. Using postural synergies, dexterous grasping tasks could be accomplished on a prosthetic hand via only a few (usually two) control inputs. Instead of implementing postural synergies digitally, this paper presents the design of a simple continuum mechanism for implementing the postural synergies mechanically. The design, fabrication and assembly of a prosthetic hand are firstly presented, followed by the synthesis of postural synergies from various grasping poses. Referring to the extracted postural synergies, structural parameters of the continuum mechanism are calculated based on a kinematics model. Experimental verifications are also presented to demonstrate the efficacy of the proposed idea.