Research Papers

Kinematics and Interfacing of ModRED: A Self-Healing Capable, 4DOF Modular Self-Reconfigurable Robot

[+] Author and Article Information
S. G. M. Hossain, Carl A. Nelson, Khoa D. Chu

Department of Mechanical
and Materials Engineering,
University of Nebraska-Lincoln,
W342 NH,
Lincoln, NE 68588-0526

Prithviraj Dasgupta

University of Nebraska-Omaha,
Department of Computer Science,
6001 Dodge Street,
Omaha, NE 68182-0500

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received December 19, 2013; final manuscript received July 9, 2014; published online August 18, 2014. Assoc. Editor: Pierre M. Larochelle.

J. Mechanisms Robotics 6(4), 041017 (Aug 18, 2014) (12 pages) Paper No: JMR-13-1256; doi: 10.1115/1.4028132 History: Received December 19, 2013; Revised July 09, 2014

Modular self-reconfigurable robots (MSRs) are systems which rely on modularity for maneuvering over unstructured terrains, while having the ability to complete multiple assigned functions in a distributed way. An MSR should be equipped with robust and efficient docking interfaces to ensure enhanced autonomy and self-reconfiguration ability. Genderless docking is a necessary criterion to maintain homogeneity of the robot modules. This also enables self-healing of a modular robot system in the case of a failed module. The mechanism needs to be compact and lightweight and at the same time have sufficient strength to transfer loads from other connected modules. This research focuses on the design of a modular robot with four degrees of freedom (4DOF) per module and with the goal of achieving higher workspace flexibility and self-healing capability. To explain the working principle of the robot, forward kinematic transformations were derived and workspace and singularity analysis were performed. In addition, to address the issues of interfacing, a rotary plate genderless single-sided docking mechanism—RoGenSiD—was developed. The design methodology included considerations for minimal space and weight as well as for fault tolerance. As a result, this docking mechanism is applicable for multifaceted docking in lattice-type, chain-type, or hybrid-type MSR systems. Several locomotion gaits were proposed and bench-top testing validated the system performance in terms of self-healing capability and generation of locomotion gaits.

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Fig. 1

A simple computer-aided design (CAD) model of the ModRED robot showing the four (RRPR) DOF

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Fig. 2

Scaled 3D CAD model of a single MSR module showing four motors for the 4DOFs and initially developed docking mechanisms. Each module weighs approximately 6.5 lbs.

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Fig. 3

Schematic of the kinematic components of a ModRED module. The dotted lines represent the side view of a physical module at its home position on which the kinematic components and frames are superimposed. The 3D image in the top left corner depicts an isometric view of the home position of a ModRED module.

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Fig. 4

The (a) single- and (b) double-module configurations are pictured in green for a visual frame of reference, and the position workspace (one end fixed with the opposite end considered the end effector) is in gray. This is based on the range of motion of the joints (brackets' rotation ±90 deg, axial twist unlimited in both directions, translation 0″–2″). The translation DOF increases the workspace volume substantially (e.g., increasing the thickness of the half-toroid in (a)).

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Fig. 5

Simulated singularity conditions of a ModRED module. The red dots represent the positions of the tip of the robot (that is, frame 5) that result in singular configurations with frame 0 being fixed.

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Fig. 6

Working principle of the rotary plates and hermaphroditic locking fingers. As the upper plate (with green fingers) rotates, it locks itself with the bottom plate's purple fingers.

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Fig. 7

Fabricated rotary plate and curved contour locking fingers assembly (left) and an enlarged view of the curved contour locking fingers (right). The pegs were made thin near the center of the plate and thick near the edge so that a finger's profile interlocks with another finger while docking.

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Fig. 8

CAD rendering of the rotary plate/curved contour locking fingers assembly along with the geared stepper motor attached to a worm-gear that rotates the rotary plate containing the locking fingers on its bottom surface

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Fig. 9

Specially designed Delrin plastic alignment pegs with spring-loaded metal connectors attached for power and signal transfer through the attached modules

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Fig. 10

The fabricated RoGenSiD mechanism

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Fig. 11

An exploded CAD rendering shows the design of the RoGenSiD mechanism

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Fig. 12

Explanation of design for fault tolerance. Misalignment of distance “a” along the Y axis (top left), misalignment by an angle β on XY plane (top right), and misalignment of XZ plane (bottom left). All of these become self-aligned because of the curved contour of the locking fingers (bottom right).

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Fig. 13

Six different MSR gaits explained using step by step actuations of the 4DOF: (a) one-module pivoted steering, (b) one-module inchworm, (c) two-module inchworm, (d) two-module rolling sideways, (e) two-module twisting, and (f) two-module pivoted steering

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Fig. 14

Initial position of the modules—faces 20 mm apart from each other (top left); faces approach each other resulting in establishment of mechanical/ electrical connection through the Delrin alignment pegs (top right); connection strength test after completion of docking. Yellow arrows show bracket movements relative to the modules; blue arrows show resultant shear forces on the docking faces (bottom).

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Fig. 15

Single-sided undocking test for validating self-healing. From steps 1 through 4, one robot module (left) and a segmented module (right) demonstrate their successful connectivity on various rotary movements. After the assumed failure of the segmented module at step 5, the functional module can still detach using its single-sided docking–undocking capability. The circles on top represent the left and right modules, with green and red representing functional and nonfunctional modules, respectively.

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Fig. 16

Various legged, wheeled, snakelike, and hybrid configurations for locomotion using ModRED II robots




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