A Reconfigurable Robotic System Using an Interbody Wire for Merged and Separated Tasks

“ A single rope, two robots can both merge and work together separately.

The reconfigurable robot direction is something everyone is familiar with. M-TRAN, Roombots, and other modular robots can take on different forms by assembling modules, expanding from mobility to manipulation.

However, a team from the University of Tokyo noticed that the modules in such systems Most of them use mechanically fixed connections, with the research focus mainly on the functionality of the single body after assembly. When the modules are separated and scattered in space, the relationship between them is rarely considered as a usable function.

Therefore, they published their new work in the journal Advanced Intelligent Systems. TwinX: Two legged robots connected by an 'interbody wire'. The two robots can combine or separate to work together.

For example, after merging, they can pick up an online food bag and then throw it into the trash can:

The rope is looped around and dragged over a large area of trash:

Using the inter-robot rope to hook and transport objects, as well as force transmission on steep slopes:

TwinX consists of two hardware-identical legged robots called WiXus, differentiated by color WiXus-Red and the WiXus-Blue. The rope extends from the spooling module at the center of Blue, wraps around the staircase bolt at the center of Red for approximately five turns, and is tied with a person's knot to the front suspension nut. According to Euler's belt theory, the friction generated by the winding allows this nut to essentially not bear significant tensile force.

The rope used is approximately 2.0mm in diameter, made of Dyneema, and the spooling module has a maximum continuous tensile force of approximately 313N and a maximum reeling length of approximately 6m. It should be noted that the rope tension values given in the paper are estimated values based on motor current calibration.

The issue is that the rope can only transmit tensile force and cannot withstand bending and twisting. Therefore, the team added docking interfaces on the body: Blue has four holes on one side, and Red has four docking pins on the other side. The pin diameter is 10mm, the hole diameter is 10.3mm, and after rounding the hole mouth, it expands to 16.3mm, with the pin tip cut down to 3.5mm, allowing for alignment Tightening the rope allows merging, forming three body configurations in one set.

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Tightening the rope causes the body to merge, forming three body forms in one set

The final body configuration depends on which two faces are docked The final form it becomes depends on which two faces are connected.

Each WiXus has two docking faces, A and B, on both the plug-in side and the pin side. The rope can pass through a shared groove between the two faces. By rotating the body using the pitch joint on the legged robot, the robot can choose which face to dock with.

A–A docking results in a four-legged configuration. Each leg is a Roll–Pitch–Pitch structure, similar to common four-legged robots; B–B docking results in a swerve drive configuration with the body below, it becomes a mobile operation robot After B–A docking and standing upright with Blue at the bottom, it becomes a mobile manipulator robot. The differential two-wheel chassis is equipped with two Yaw–Pitch–Pitch arms.

the. Blue remains stationary, while the D455 camera on Red identifies three AprilTag markers on Blue (two for long-range identification and one for short-range identification). The controller first moves the body to a position near the target pose, with distance error less than 0.08, then switches to alignment mode to align the pin tip with the hole position.

During Red's movement, Blue continuously sends a current command corresponding to an estimated tensile force of approximately 15N to the spooling motor,, used to. Finally, it completes the docking by sending a current command corresponding to an estimated tensile force of approximately 134N. After the docking, the current commands for the four-legged configuration and the mobile manipulator configuration correspond to an estimated tensile force of approximately 224N, and for the swerve drive configuration, it corresponds to approximately 187N, used for, and exchange observation data between the two sides. The real hardware communication delay is about

, and during training, random delays of about Two WiXus each run a complete strategy, executing only the output for their own few legs. The two sides exchange observation data via UDP. The actual machine communication delay is approximately 5ms, and during training, random delays of 8 to 40ms are added to simulate. If data from the other side is not received within 2 seconds, the system will automatically stop.

In outdoor field tests, the four-legged configuration of TwinX did not fall over in three scenarios: walking on grass, descending stairs, and crossing a curb..

The calculation for the rudder wheel configuration can be completed separately for each wheel, and communication between the two robots is not required. The team also performed a garbage collection task: first using the rudder wheel configuration to move forward, disengaging the docking, switching the docking surface, re-docking, and transforming into a mobile operation configuration. The two arms then pick up the garbage and throw it into the trash bin, before reverting back to the rudder wheel configuration to move away. Throughout the task, the docking control was executed twice, both times successfully completed, and at the start of each instance, the orientation of the two robots was already roughly aligned.

02.

The robots remain stationary,

The more interesting aspect of TwinX is that, after the two robots are separated, this rope remains an active reelable connection that can be directly used for work.

The second task was“Dòu”Red remains stationary, while Blue releases rope while circling around the scattered trash, forming polygonal boundaries by creating corners where the rope touches objects. Since the perimeter of the polygon does not necessarily increase in sync with the travel distance, the operator will occasionally set the rope speed to 0 to prevent the rope from becoming slack and falling to the ground. After the area is enclosed, both robots move in the same direction, and together drag away a pile of trash of various sizes and shapes in one go.

to keep the watering cans suspended, and finally, the two robots together carry the watering cans away.“Hook”Blue lets out the rope to move into position, bringing the rope down to below the handles of the three watering cans, then tightens the rope, and the two robots then use their leg joints to lift their bodies, tightening the rope which then lifts all three watering cans at once. Afterward, Blue reels in the rope while moving toward Red, maintaining the state of the watering cans being lifted, and finally, the two robots work together to carry away the watering cans.

the third task is``drag''Simulate rescuing a small dog that fell off a cliff. Red stays on the upper platform as an anchor point, while Blue moves down along a 49° steep slope, releasing the rope at a speed roughly matching the vehicle's speed. After reaching the bottom of the slope, Blue uses its legs to hold the stuffed dog and climbs back up the slope, alternating between reeling in the rope to ascend and adjusting the vehicle's body angle with the wheels, trying to keep the body level to prevent the stuffed dog from falling down.

The team did a simplified quasi-static force analysis: Blue weighs 9.4kg, and the component of gravity along the 49° slope is approximately 69.6N. Without the rope's help, relying solely on wheel traction, the equivalent coefficient of friction must be at least about 1.15. The average estimated tension of the rope during the climbing phase is 55.1N, with the rope roughly aligned along the uphill direction, accounting for about 79% of this gravitational component, the remaining about 14.5N is supported by the wheels, corresponding to an equivalent coefficient of friction reduced to about 0.24.

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being supported by the wheels, corresponding to an equivalent friction coefficient reduced to approximately

Researchers believe that in TwinX, the separated state itself is a functional state, no longer just a transitional stage in the reconfiguration process. The abilities of four legs, steering wheels, and mobility are capabilities after the merging, while the actions of carrying, hooking, and pulling come from the relationship between the two separate but connected robots.

This rope also brings a kind of there is a design degree of freedom different from rigid link and joint designs: While the two robots remain connected, distance, relative position, and tension can all vary, allowing the body to exist in distributed configurations in addition to the two extreme cases of 'fully rigid integration' and 'completely independent'.

The team's next plan System expanded to more robots and more root ropes The research will study state switching according to task planning, and introduce direct measurement of tension and closed-loop control, for more continuous regulation of the mechanical relationship between the two bodies.

Paper chain Re: https://doi.org/10.1002/aisy.70559