Cooperative Modular Manipulation with Numerous Cable-Driven Robots for Assistive Construction and Gap Crossing

Abstract

Soldiers in the field often need to cross negative obstacles, such as rivers or canyons, to reach goals or safety. Military gap crossing involves on-site temporary bridges construction. However, this procedure is conducted with dangerous, time and labor intensive operations, and specialized machinery. We envision a scalable robotic solution inspired by advancements in force-controlled and Cable Driven Parallel Robots (CDPRs); this solution can address the challenges inherent in this transportation problem, achieving fast, efficient, and safe deployment and field operations. We introduce the embodied vision in Co3MaNDR, a solution to the military gap crossing problem, a distributed robot consisting of several modules simultaneously pulling on a central payload, controlling the cables' tensions to achieve complex objectives, such as precise trajectory tracking or force amplification. Hardware experiments demonstrate teleoperation of a payload, trajectory following, and the sensing and amplification of operators' applied physical forces during slow operations. An operator was shown to manipulate a 27.2 kg (60 lb) payload with an average force utilization of 14.5\% of its weight. Results indicate that the system can be scaled up to heavier payloads without compromising performance or introducing superfluous complexity. This research lays a foundation to expand CDPR technology to uncoordinated and unstable mobile platforms in unknown environments.

Figures (10)

• Figure 1: Co3MaNDR System, consisting of 4 modules (orange box) in planar configuration. The experimental setup (left) and CAD model (right) are shown overlayed onto each other, with an example payload (center).
• Figure 2: Simplified dynamics model (Left) of a single module, color coordinated with the Robotic Module CAD model ( Right). The upper assembly measures tension output direction (yaw, pitch, and roll). The lower assembly moves up and down on rails ensuring that the measured cable tension is solely from the vertical component of the cable.
• Figure 3: System level dynamics diagram containing four modules (1,2,3,n) manipulating a generic payload. Variable definition for equations listed.
• Figure 4: System level control diagram for Co3MaNDR. Modules (red regions) contain individual $PID+I_{ff}$ loops, actuators, and sensors. The wrench based control loop (purple shaded region) shows the payload being controlled by any external wrench and applied tensions, converting from net wrench. The Cartesian control loop (light blue region) encapsulates the wrench loop and uses a pose $PID$ to regulate the desired wrench
• Figure 5: Module characterization for step responses of several commanded tension magnitudes. Each experiment showed rise times < 0.7ms and settling times between 0.75-3.8 ms. Larger amplitude steps had large overshoots. In use, commanded tensions will not have large jumps, so performance in 50N step response is considered fitting and sufficient for operations.