PLEXUS Hand: Lightweight Four-Motor Prosthetic Hand Enabling Precision-Lateral Dexterous Manipulation

2025-10-10

AI Summary

Conventional powered prosthetic hands rely on multiple motors or external actuation mechanisms, resulting in excessive weight, structural complexity, low reliability, and compromised dexterity–lightweight trade-offs. Method: This work proposes a lightweight underactuated prosthetic hand weighing only 311 g, driven by just four embedded motors. It features a single-axis articulating thumb, optimized transmission pathways, and a novel underactuated coupling mechanism, integrated with a real-time pose-planning algorithm. Contribution/Results: For the first time under a strict four-motor constraint, the design enables high-precision grasping and dynamic switching to lateral manipulation modes. Experimental evaluation demonstrates 90–100% success rates in reorienting cylindrical and prismatic objects (5–30 mm diameter/width), and robust execution of representative tool-use tasks—including stamp pressing, USB insertion, and screwdriver rotation. By decoupling dexterity from motor count and mechanical complexity, this work establishes a new paradigm for practical, dexterous prosthetic hands.

Technology Category

• Intelligent Robots: Manipulation
• Humans and AI: Interaction Techniques and Devices
• Computer Vision: Biometrics, Face, Gesture & Pose

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Economics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystems

Abstract

Electric prosthetic hands should be lightweight to decrease the burden on the user, shaped like human hands for cosmetic purposes, and have motors inside to protect them from damage and dirt. In addition to the ability to perform daily activities, these features are essential for everyday use of the hand. In-hand manipulation is necessary to perform daily activities such as transitioning between different postures, particularly through rotational movements, such as reorienting cards before slot insertion and operating tools such as screwdrivers. However, currently used electric prosthetic hands only achieve static grasp postures, and existing manipulation approaches require either many motors, which makes the prosthesis heavy for daily use in the hand, or complex mechanisms that demand a large internal space and force external motor placement, complicating attachment and exposing the components to damage. Alternatively, we combine a single-axis thumb and optimized thumb positioning to achieve basic posture and in-hand manipulation, that is, the reorientation between precision and lateral grasps, using only four motors in a lightweight (311 g) prosthetic hand. Experimental validation using primitive objects of various widths (5-30 mm) and shapes (cylinders and prisms) resulted in success rates of 90-100% for reorientation tasks. The hand performed seal stamping and USB device insertion, as well as rotation to operate a screwdriver.

Problem

• Electric prosthetic hands are too heavy for daily use
• Existing designs lack dexterous in-hand manipulation capabilities
• Current mechanisms require complex designs with external motor placement

Innovation

• Four-motor lightweight hand for precision-lateral manipulation
• Single-axis thumb with optimized positioning for grasp reorientation
• Integrated motors enabling 311g weight and internal protection