Programmable Locking Cells (PLC) for Modular Robots with High Stiffness Tunability and Morphological Adaptability

2025-09-09

AI Summary

Robots operating in unstructured environments require simultaneous compliance and rigidity, yet existing variable-stiffness solutions suffer from complex actuation, continuous power consumption, and monolithic design constraints. Method: This paper proposes a modular, tendon-driven Programmable Locking Cell (PLC) that achieves discrete stiffness modulation via a passive mechanical interlocking mechanism. Stiffness switching between compliant and rigid states is rapid and triggered by cable tension; modular assembly and structural integration enable concurrent stiffness and motion control. Contribution/Results: A single PLC achieves up to 950% stiffness increase, supports high torque capacity (>10 N·m), spatial stiffness programming, and morphological reconfiguration. Two prototypes validate the approach: an adaptive variable-stiffness gripper enabling in-hand manipulation, and a serial PLC-based pipeline robot capable of shape adaptation and stiffness modulation in confined spaces. The design significantly enhances system modularity, scalability, and task adaptability.

Technology Category

• Intelligent Robots: Manipulation
• Planning, Routing, and Scheduling: Mixed Discrete/Continuous Planning
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Economics, Online Markets and Human Computation: Architectures and workflows that use LLMs for crowd work

Abstract

Robotic systems operating in unstructured environments require the ability to switch between compliant and rigid states to perform diverse tasks such as adaptive grasping, high-force manipulation, shape holding, and navigation in constrained spaces, among others. However, many existing variable stiffness solutions rely on complex actuation schemes, continuous input power, or monolithic designs, limiting their modularity and scalability. This paper presents the Programmable Locking Cell (PLC)-a modular, tendon-driven unit that achieves discrete stiffness modulation through mechanically interlocked joints actuated by cable tension. Each unit transitions between compliant and firm states via structural engagement, and the assembled system exhibits high stiffness variation-up to 950% per unit-without susceptibility to damage under high payload in the firm state. Multiple PLC units can be assembled into reconfigurable robotic structures with spatially programmable stiffness. We validate the design through two functional prototypes: (1) a variable-stiffness gripper capable of adaptive grasping, firm holding, and in-hand manipulation; and (2) a pipe-traversing robot composed of serial PLC units that achieves shape adaptability and stiffness control in confined environments. These results demonstrate the PLC as a scalable, structure-centric mechanism for programmable stiffness and motion, enabling robotic systems with reconfigurable morphology and task-adaptive interaction.

Problem

• Achieving discrete stiffness modulation in modular robots
• Enabling compliant-to-rigid state switching without continuous power
• Creating reconfigurable structures with programmable spatial stiffness

Innovation

• Modular tendon-driven unit for stiffness modulation
• Mechanically interlocked joints with cable tension actuation
• Reconfigurable structures with spatially programmable stiffness