Anirban Mazumdar

Mag-Foot: A steel bridge inspection robot

A legged robot that moves across a steel structure is developed for steel bridge inspection. Powerful permanent magnets imbedded in each foot allow the robot to hang from a steel ceiling powerlessly. Although the magnets are passive, the attractive force is modulated by tilting the foot against the steel surface. This allows the robot to slide its feet along the surface using “Moonwalk” and “Shuffle” gait patterns. The robot can also detach its feet and swing them over small obstacles. These diverse walking patterns are created with a single servoed joint and 2 sets of simple locking mechanisms. Kinematic and static conditions are obtained for the under-actuated legged robot to perform each gait pattern safely and stably. A proof-of-concept prototype robot is designed, built, and tested. Experiments demonstrate the feasibility of the design concept and verify the analytical results.

A compact, maneuverable, underwater robot for direct inspection of nuclear power piping systems

There is an increasing need for the inspection of nuclear power plants worldwide. To access complex underwater structures and perform non-destructive evaluation, robots must be tetherless, compact, highly maneuverable, and have a smooth body shape with minimal appendages. A new water jet propulsion system using fluidic valves coupled with centrifugal pumps is developed for precision maneuvering. A hybrid control system that combines continuous pump regulation and discrete Pulse Width Modulation (PWM) of fluidic valves is proposed. This control scheme provides high accuracy, high bandwidth, and flexibility in maneuvering control. First, the functional requirements for nuclear power plant inspection are discussed, followed by the basic design concept of an inspection robot. Miniaturized Coanda-effect valves are designed and built based on CFD and mathematical analysis. The hybrid control system incorporating the pump/valve system is designed and tested. Experimental results illustrate that the hybrid control scheme holds substantial promise and is capable of very precise orientation control. Based on these, a full 4-DOF robot is designed, and its key components are described.

A ball-shaped underwater robot for direct inspection of nuclear reactors and other water-filled infrastructure

In this paper we present a new type of spherical underwater robot that is completely smooth and uses jets to propel and maneuver. This robot is specifically designed for the direct visual inspection of water-filled infrastructure such as the inside of nuclear powerplants. The unique propulsion architecture consists of a single bidirectional centrifugal pump combined with two fluidic valves. The pump is used to produce a high velocity jet while the valves are used to quickly switch the jet between output ports. The spherical shape means that the robot is simple to model and control, maneuverable, and robust to collisions. The propulsion architecture is described in detail along with a rigid body model for maneuvering control. A novel valve PWM controller is used to achieve heading control, and the controller performance is confirmed with both simulation and experiments. Finally, experiments are used to illustrate the turning and diving performance of the robot.

A compact underwater vehicle using high-bandwidth coanda-effect valves for low speed precision maneuvering in cluttered environments

A highly maneuverable, compact vehicle for underwater precision inspection of complex structures is presented. The vehicle will have no appendages such as rudders, screws, and other external thrusters, which might get tangled and interfere with the underwater structure in a cluttered environment. A multi-axis, integrated thruster mechanism using Coanda-effect high-speed valves for switching the direction of jets can be encapsulated in a compact, egg-shaped body. Compared to traditional screw thrusters, these valves have improved dynamic performance in switching the jet stream direction. Furthermore, the reaction forces and moments due to switching can be substantially reduced. First, the principle of Coandaeffect water jet valves is introduced, and its governing equations are obtained. Optimal dimensions and parameters producing a maximum of thrust are obtained, and are experimentally verified. Multiple Coanda-effect valves are then integrated into a tree structure to create a multi-axis thrust mechanism. A simple planar proof of concept prototype is built and tested.

Pulse Width Modulation of Water Jet Propulsion Systems Using High-Speed Coanda-Effect Valves

An integrated high-speed valve switching and pump output control scheme are developed for precision maneuvering of underwater vehicles. High-speed Coanda-effect valves combined with a centrifugal pump allow for precise control of thrust force using a unique pulse width modulation (PWM) control scheme, where both pulse width and pulse height are controlled in a coordinated manner. Dead zones and other complex nonlinear dynamics of traditional propeller thrusters and water jet pumps are avoided with use of the integrated pump-valve control. Three control algorithms for coordinating valve switching and pump output are presented. A simplified nonlinear hydrodynamic model of underwater vehicles is constructed, and design trade-offs between PWM frequency and pulse height, with regard to steady state oscillations, are addressed. The control algorithms are implemented on a prototype underwater vehicle and the theoretical results are verified through experiments.

Omni-Egg: A smooth, spheroidal, appendage free underwater robot capable of 5 DOF motions

This paper describes the performance of a new type of highly maneuverable underwater robot developed at MIT. The robot, titled “Omni-Egg,” is smooth, spheroidal, and completely appendage free. Propulsion is provided using a novel pump-jet system that can be completely built into the streamlined shell. No fins or stabilizers are used on the vehicle, and directional stability is instead achieved using feedback control. Experimental results show how the turning performance of this smooth design is superior to a similar one that uses fins to achieve stability. Due to this unique design the robot is capable of unique motions such as forward and reverse motions, high speed turning, and sideways translations. This type of robot is designed for tasks requiring a large degree of maneuverability within tight spaces. Some examples of such tasks include the inspection of water-filled infrastructure and the exploration of cluttered environments. Such applications have a high risk of collisions or snagging on obstacles, so a smooth outer shape is desirable. The vehicle is designed to be capable of 5 DOF, and surge, sway, heave, and yaw are all demonstrated in this paper. Pitch, the 5th DOF, remains under development.

Dynamic Analysis and Design of Spheroidal Underwater Robots for Precision Multidirectional Maneuvering

In this paper, we present an optimized body shape and thruster layout design for a class of jet-propelled underwater robots. Spheroidal robots with no rudders and appendages are highly maneuverable and capable of accessing complex underwater structures for inspection and surveillance. These robots are hydrodynamically unstable, but can make rapid turns and move in multiple directions. This paper describes a control-theoretical design methodology, examining the controllability of surge, sway, and yaw motion in relation to an aspect ratio of the body shape and the direction and location of each propulsion jet. A design with angled jets combined with a body aspect ratio of 1.2-1.8 is controllable and exhibits good performance. A prototype robot with an optimized body shape and jet arrangement has been built and tested. Experimental results illustrate the superb multiaxis maneuverability of this design.

Control-Configured Design of Spheroidal, Appendage-Free, Underwater Vehicles

A highly maneuverable, spheroid-shaped, underwater robot using appendage-free, multi-degree of freedom (DOF) propulsion technologies is presented. The vehicle is hydrodynamically unstable due to the Munk moment. The vehicle is stabilized by feedback control, rather than passive fins, which facilitates rapid turns and agile motions. The new design was motivated by nuclear reactor inspection and other applications where external appendages must be avoided. Two technical challenges are addressed in this paper. One is the development of a compact, multi-DOF propulsion system that generates multiaxis water jets and switches them rapidly. The other is the design of a jet configuration and control system that augments stability and achieves high maneuverability. A nonlinear hydrodynamic model is formulated, and its linearized dynamics are analyzed to attain insights into how jet direction influences controllability and stability. A prototype vehicle is built and used to verify these concepts. The integrated design method is implemented and shown to achieve stable motions, high maneuverability, and multidirectional capability.

Maneuverability of a robotic tuna with compliant body

The maneuvering performance of a robotic device designed to mimic the swimming motions of Thunniform swimmers is presented. In contrast to existing designs, this design achieves fish like locomotion through the use of a single actuator and a compliant body and tail. Experiments were performed using both biased swimming motions and coasted turns. During these experiments the Compliant Robotic Tuna (CRT) achieved steady swimming speeds of up to 0.37 body lengths/second, average turning rates of up to 12.6 degrees per second, and turning radii as low as 1 body length. In addition, this paper compares the measured maneuvering performance with the predictions of a simplified rigid body model that was derived using both theoretical and empirical techniques. The swimming motions studied in this paper were achieved using open loop mechanisms. Therefore the potential for performance improvements exists.

Design for precision multi-directional maneuverability: Egg-shaped underwater robots for infrastructure inspection

In this paper we examine the dynamics of a unique type of jet propelled, spheroidal robot design. This robot uses jets angled inward into a diamond shape to achieve superior planar dynamics. We explore the role of the diamond configuration in avoiding nonminimum phase behavior and we examine the best vehicle aspect ratios for this type of robot design. We use a degree of controllability metric to illustrate the uncontrollable behavior of certain designs and also identify an optimal aspect ratio of 1.4. The paper concludes by incorporating these lessons into a new 5 degree-of-freedom prototype robot that provides substantial improvements over previous designs. This robot uses centrifugal pumps and fluidic valves to achieve high maneuverability and unique motions such as forward and reverse motions, sway translations, and turning in place. In addition, this design can achieve improved forward efficiency through the use of dual output-pumps and can perform these planar motions at various vehicle depths through the use of a closed loop depth control system.