Handheld Time-Share-Driven Robot with Expandable Degrees of Freedom

By Samudrapom DamReviewed by Susha Cheriyedath, M.Sc.Feb 2 2024

In an article recently published in the journal Nature Communications, researchers presented a handheld time-share-driven robot with expandable degrees of freedom (DOFs) that effectively addressed the existing limitations on enhancing the controllable DOFs in robots.

Background

Biological inspirations offer novel approaches to improve the capabilities of robots. Robots can execute stable force and precise motion, interact with unstructured environments, humans, and delicate objects, and realize better outcomes in constrained spaces by learning from creatures.

The diversity that exists in nature has fueled the development of innovative robots that can be used for different applications. For instance, elephant truck/snake-inspired continuum robots flex throughout their entire length to alter their shape and position their tips, which makes them suitable to traverse narrow spaces for operation or examination.

However, replicating the flexible motion abilities of natural creatures in robots is expensive. For instance, snakes possess substantial DOFs due to their complex spine structure that comprises hundreds of vertebrae, with every vertebra functioning as an individual motion unit.

However, enhancing the DOFs of robots by incorporating more motors often leads to a significant rise in control complexity and material costs and bulky robot sizes. Although bioinspired actuators can offer a low-cost approach to enhance DOFs, they cannot provide the inherent consistency and precision offered by motors. Moreover, handheld robots offer accessible solutions with a short learning curve to improve operator capabilities. However, their controllable DOFs are limited owing to scarce space for actuators.

The proposed approach

In this study, researchers proposed a handheld time-share-driven robot that is inspired by the muscle movements stimulated by nerves. The objective of the study was to address the existing challenges in enhancing DOFs of robots. The proposed robot consisted of multiple motion modules that were powered by a single motor. Shape memory alloy (SMA) wires, acting as nerves, were connected to motion modules, which enabled the selection of the activated module.

Additionally, the robot contained a 0.8 cm diameter manipulator comprised of sequentially linked bending modules (BM) and a 202-gram motor base. The manipulator could be tailored in length and integrated with different instruments in situ to facilitate high-dexterous operation and non-invasive access to remote surgical sites.

Principles of the bending unit

The proposed time-share-driven mechanism was inspired by the unique snake spine structure and the complex nerve-muscle-vessel relationship in biology. The mechanism leveraged only a single motor to activate several BMs. This approach was based on three principles, including selective response, state keeping, and universal transmission. The motion input is shared and transmitted along the manipulator based on the universal transmission principle, while the motion input is independently adopted by every motion module based on the selective response principle.

The flexible inner tube in the proposed BM rotates along the manipulator while adapting to the bending curve following the universal transmission/first principle. Then, this adaptive rotation is converted into translation through a hollow screw pair. Subsequently, this translation, which appeared as a pull-push motion offset from the neutral axis of the BM, translates into bending output through a tendon-driven continuum structure.

A self-hold property was imparted by the introduction of a low-lead angle screw pair, which prevented the external forces from impacting the inactive BMs through reverse transmission following the state keeping/second principle. The flexible inner tube and the screw pair were bridged by the SMA clutch incorporating a slidable lock. A single BM is specified using an SMA wire to trigger the slidable lock following the selective response/third principle.

Researchers demonstrated the concept by designing a planar steerable tube and a flexible inner tube serving as the muscle and the vessel, respectively, and using an SMA clutch as the nerve for activation. A prototype was built that contained only one motor and several BMs based on these principles. These BMs could be fabricated with various motion ranges, assembled in several bending plane combinations, elongated by passive extension tubes, and integrated with different tip instruments, which makes the developed robot task-oriented and customized. Thus, this developed prototype embodied a cost-effective, lightweight, and multi-DOF robot that can be handheld, navigate confined spaces, and establish a workspace over obstacles.

Significance of the study

Researchers assessed the performance of the prototype/handheld time-share-driven robot with expandable DOFs in clinical applications. A surgeon held the robot to perform transluminal experiments/transluminal examination (diagnosis) and transluminal operation (therapy) on a human stomach model and an ex vivo porcine stomach.

The robot successfully passed along tortuous paths and narrow openings toward remote operating sites, effectively meeting the transluminal diagnosis requirements. Additionally, the robot showed exceptional maneuverability and flexibility compared to the gastroscopes during the transluminal therapy experiment

The robot successfully approached the target with an adjustable angle and lifted the bone by bending the manipulator in place of dragging the bone along the endoscope axis, which is common in gastroscopic procedures. Thus, the robot could minimize potential surgery-related damage to the tissue.

To summarize, the findings of this study demonstrated the effectiveness of the time-share-driven mechanism for building a multi-DOF robot for broader applications, including for handling multi-DOF tasks in difficult-to-reach surgical spots.