Development of Musculoskeletal Legs with Planar Interskeletal Structures to Realize Human Comparable Moving Function (2404.00890v1)

Abstract: Musculoskeletal humanoids have been developed by imitating humans and expected to perform natural and dynamic motions as well as humans. To achieve desired motions stably in current musculoskeletal humanoids is not easy because they cannot maintain the sufficient moment arm of muscles in various postures. In this research, we discuss planar structures that spread across joint structures such as ligament and planar muscles and the application of planar interskeletal structures to humanoid robots. Next, we develop MusashiOLegs, a musculoskeletal legs which has planar interskeletal structures and conducts several experiments to verify the importance of planar interskeletal structures.

• The paper demonstrates that integrating planar interskeletal structures significantly improves torque performance and joint stability in humanoid leg designs.
• Experiments validate that both passive and active components effectively mimic human ligaments and muscles, enabling complex motions like screw-home knee movement and squat performance.
• The research offers promising insights for future humanoid robotics by showcasing a design that achieves human-comparable movement through innovative tendon-actuator coordination.

Development and Evaluation of Musculoskeletal Legs with Planar Interskeletal Structures for Humanoid Robots

Introduction

Musculoskeletal humanoid robots, designed to imitate the human body structure, have exhibited potential in performing complex and dynamic movements akin to human beings. These robots utilize tendon-driven systems, where muscles, represented through actuators, orchestrate movement around skeletal structures. Despite their sophistication, ensuring a stable performance across various postures remains a challenge due to difficulties in maintaining sufficient moment arms for the muscles. The paper focuses on the utilization of planar interskeletal structures, resembling human muscles and ligaments, to address these challenges. By integrating these structures into a musculoskeletal robot, named MusashiOLegs, the research aims to improve torque application capabilities in various postures, thereby enhancing the robot's functional resemblance to human movement patterns.

Planar Interskeletal Structure

Planar interskeletal structures are conceptualized based on the human anatomical features of muscles and ligaments spanning across joints, providing a significant advantage in maintaining stable interaction with skeletal structures. The research identifies three major benefits of these planar structures:

• Stable Path Maintenance: Unlike linear interskeletal structures, planar variants ensure stable contact with skeletal structures, adapting their form to securely envelop the bone, preventing deviation even when muscle tension is varied.
• Catching Prevention: Planar structures' broad contact surface minimizes the risk of entanglement within skeletal protrusions or crevices, maintaining smooth operational integrity.
• Durability and Shear Force Handling: Fabricated as a cluster of fibers, planar structures exhibit enhanced durability and the capability to withstand forces applied in shear directions, surpassing the performance of linear interskeletal structures in simulations and practical applications.

Musculoskeletal Legs with Planar Interskeletal Structures

The MusashiOLegs showcases the implementation of planar interskeletal structures across various components, exemplifying both passive and active roles akin to human ligaments and muscles, respectively:

• Iliofemoral Ligaments and Knee Collateral Ligaments: Serving as passive structures, these ligaments smartly limit the range of motion at joints, mimicking the natural joint restrictions found in humans.
• Patella Ligaments and Gluteus Maximus: Representing active structures, they maintain the moment arm essential for producing significant joint torques, even across wide ranges of motion, effectively transmitting force from the muscle actuators to the skeletal segments of the robot.

Experiments and Results

The research validates the efficacy of planar interskeletal structures through a series of experiments aimed at replicating human-like functions:

• Basic Experiment: Verification that the iliofemoral ligament, fashioned from an elastic planar structure, can appropriately restrict motion range akin to its human counterpart.
• Screw-Home Movement of Knee Joint: Confirmation that the knee joint's screw-home motion is facilitated by the passive torque from planar collateral ligaments, allowing for complex rotational movement while ensuring stability in extended positions.
• High Torque Performance in Wide Range of Motion: Through a squat motion experiment, the paper demonstrates the musculoskeletal legs' capability to support the robot's weight, showcasing the high torque performance facilitated by planar interskeletal structures.
• Pedal Switching Experiment: In a scenario simulating pedal switching while driving, MusashiOLegs successfully replicated the human ability to switch pedals with a single leg, overcoming friction from the car seat and illustrating the structures' functionality in a real-world application.

Conclusion and Future Directions

This paper underscores the significance of integrating planar interskeletal structures into musculoskeletal humanoids, highlighting advancements in achieving human-comparable movement functions and torque application in various postures. Looking forward, it's imperative to explore control systems that leverage the high joint stiffness and torque performance offered by these structures. Further, incorporating learning-based control mechanisms to adeptly manage the behavior of planar interskeletal structures holds promise for enhancing humanoid robotics, pushing the boundaries of what is currently achievable in mimicking human motion and interaction with environments.