Control of flexible robots with prismatic joints and hydraulic drives

The design and control of long-reach, flexible manipulators has been an active research topic for over 20 years. Most of the research to date has focused on single link, fixed length, single plane of vibration test beds. In addition, actuation has been predominantly based upon electromagnetic motors. Ironically, these elements are rarely found in the existing industrial long-reach systems. One example is the Modified Light Duty Utility Arm (MLDUA) designed and built by Spar Aerospace for Oak Ridge National Laboratory (ORNL). This arm operates in larger, underground waste storage tanks located at ORNL. The size and nature of the tanks require that the robot have a reach of approximately 15 ft and a payload capacity of 250 lb. In order to achieve these criteria, each joint is hydraulically actuated. Furthermore, the robot has a prismatic degree-of-freedom to ease deployment. When fully extended, the robot`s first natural frequency is 1.76 Hz. Many of the projected tasks, coupled with the robot`s flexibility, present an interesting problem. How will many of the existing flexure control algorithms perform on a hydraulic, long-reach manipulator with prismatic links? To minimize cost and risk of testing these algorithms on the MLDUA, the authors have designed a new test bed that contains many of the same elements. This manuscript described a new hydraulically actuated, long-reach manipulator with a flexible prismatic link at ORNL. Focus is directed toward both modeling and control of hydraulic actuators as well as flexible links that have variable natural frequencies

Hydraulic manipulator research at ORNL

Recently, task requirements have dictated that manipulator payload capacity increase to accommodate greater payloads, greater manipulator length, and larger environmental interaction forces. General tasks such as waste storage tank cleanup and facility dismantlement and decommissioning require manipulator life capacities in the range of hundreds of pounds rather than tens of pounds. To meet the increased payload capacities demanded by present-day tasks, manipulator designers have turned once again to hydraulics as a means of actuation. In order to successfully design, build, and deploy a new hydraulic manipulator (or subsystem), sophisticated modeling, analysis, and control experiments are usually needed. Oak Ridge National Laboratory (ORNL) has a history of projects that incorporate hydraulics technology, including mobile robots, teleoperated manipulators, and full-scale construction equipment. In addition, to support the development and deployment of new hydraulic manipulators, ORNL has outfitted a significant experimental laboratory and has developed the software capability for research into hydraulic manipulators, hydraulic actuators, hydraulic systems, modeling of hydraulic systems, and hydraulic controls. The purpose of this article is to describe the past hydraulic manipulator developments and current hydraulic manipulator research capabilities at ORNL. Included are example experimental results from ORNL`s flexible/prismatic test stand

The Virtual Robotics Laboratory

The growth of the Internet has provided a unique opportunity to expand research collaborations between industry, universities, and the national laboratories. The Virtual Robotics Laboratory (VRL) is an innovative program at Oak Ridge National Laboratory (ORNL) that is focusing on the issues related to collaborative research through controlled access of laboratory equipment using the World Wide Web. The VRL will provide different levels of access to selected ORNL laboratory equipment to outside universities, industrial researchers, and elementary and secondary education programs. In the past, the ORNL Robotics and Process Systems Division (RPSD) has developed state-of-the-art robotic systems for the Army, NASA, Department of Energy, Department of Defense, as well as many other clients. After proof of concept, many of these systems sit dormant in the laboratories. This is not out of completion of all possible research topics, but from completion of contracts and generation of new programs. In the past, a number of visiting professors have used this equipment for their own research. However, this requires that the professor, and possibly his students, spend extended periods at the laboratory facility. In addition, only a very exclusive group of faculty can gain access to the laboratory and hardware. The VRL is a tool that enables extended collaborative efforts without regard to geographic limitations

Development of dynamic model of a 7DOF hydraulically actuated tele-operated robot for decommissioning applications

In this paper the problem of system integration and dynamic modeling of a hydraulically actuated manipulator with seven degrees of freedom, i.e. HydroLek HLK-7W is investigated. The arm is fitted on Multi-Arm mobile Robot System for Nuclear Decommissioning (MARS-ND) applications purposes. This is a step forward with respect to the previous works where only kinematics of the robot was taking into account. As the decommissioning robot has to perform precise and complex tasks autonomously using effective model-based nonlinear control algorithms having an accurate dynamic model of the arm which is reliable enough to predict the behavior of the manipulator under different operating conditions would be crucial. To this end the symbolic, and numerical model of the dynamic of robot is developed and a first attempt for model validation and tuning the parameters of the model is taken forward

Structural analysis and design of a flexible three-link hydraulically-actuated robotic arm

The structural design of a flexible three-link hydraulically activated robotic mechanism is presented. Static and quasi dynamic, three-dimensional analysis of the robotic mechanism is shown. Force and deflection equations are derived for the robotic mechanism and the finite element analysis is used to model its dynamic behavior and to study the fundamental 3-D bending and twisting frequencies of the arm as it reaches various positions inside the workspace. Using beam-column theory and finite element method, the design of a flexible three-link robotic mechanism is shown. The flexibility of the arm is set so that the total deflection of the arm is limited to 2%-3% of its maximum reach; and its first two fundamental frequencies are less than 6 Hz. The arm is capable of carrying a load equal or greater to its own weight. (Abstract shortened with permission of author.)

Free-Standing Leaping Experiments with a Power-Autonomous, Elastic-Spined Quadruped

We document initial experiments with Canid, a freestanding, power-autonomous quadrupedal robot equipped with a parallel actuated elastic spine. Research into robotic bounding and galloping platforms holds scientific and engineering interest because it can both probe biological hypotheses regarding bounding and galloping mammals and also provide the engineering community with a new class of agile, efficient and rapidly-locomoting legged robots. We detail the design features of Canid that promote our goals of agile operation in a relatively cheap, conventionally prototyped, commercial off-the-shelf actuated platform. We introduce new measurement methodology aimed at capturing our robot’s “body energy” during real time operation as a means of quantifying its potential for agile behavior. Finally, we present joint motor, inertial and motion capture data taken from Canid’s initial leaps into highly energetic regimes exhibiting large accelerations that illustrate the use of this measure and suggest its future potential as a platform for developing efficient, stable, hence useful bounding gaits. For more information: Kod*La

Offshore Wind Turbine Access Using Knuckle Boom Cranes

Doktorgradsavhandling, Fakultet for teknologi og realfag, Institutt for ingeniørvitenskap, 2016There is a great need for renewable and sustainable energy today and there are several different sources for this energy where offshore wind is one that has a great estimated planned power production. Wind power production has for many years been produced onshore, but installing the wind turbines offshore has some benefits due to higher and more stable wind conditions. The majority of installed wind turbines are today bottom fixed, but when moving to deeper waters it is too high cost in building and installing foundation, which brings the possibility of using floating wind turbines. There are, however, also challenges due to the access for both the fixed and floating offshore wind turbines. During startup, repair or maintenance there is a demand for easy access of both personnel and equipment. This dissertation mainly deals with offshore access solutions systems or parts of those systems. The access solutions are systems that transfers personnel or equipment from a floating vessel to a fixed or floating offshore structure. Work done using a small scale hydraulic manipulator is described in Papers A and B, where paper A deals with the kinematic motion control of such a small scale redundant manipulator mounted on a moving Stewart platform, imitating the motion of a floating vessel. The manipulator tries to keep the tool point at a fixed reference point by the use of the pseudo-inverse Jacobian. Used in the experimental verification is a high precision laser tracker which measures the position of the tool point. Paper B uses the same manipulator and has in addition a hanging payload attached to the tool point. A LQR control strategy is used to minimize the vibration of the hanging payload when the manipulator moves the tool point relative to a ground fixed coordinate system. Paper C is concerned with the inherent oscillatory nature of pressure compensated motion control of a hydraulic cylinder subjected to a negative load and suspended by means of a counter-balance valve. The method proposed in this paper has the focus on pressure feedback and is compared to classical control strategies. In paper D input shaping is used for the slewing motion control of a full scale mobile crane. The flexibility of the crane causes vibrations when slewing and by knowing the natural frequency and damping, the command signal is shaped so there are no residual vibrations. Experimental verification is carried out by means of a laser tracker. Finally, the work done in Paper E deals with active heave compensation from a fixed structure to a floating vessel. Modeling of the hydraulic winch is done and a frequency response function is obtained. The active heave compensation was experimentally verified using the full scale mobile crane as the fixed structure with a winch mounted on it and the Stewart platform as the moving structure. Both results from active heave compensation and constant tension are presented. The payload in the experiments is a 400kg steel structure