Pointing control for the SPIDER balloon-borne telescope

We present the technology and control methods developed for the pointing system of the SPIDER experiment. SPIDER is a balloon-borne polarimeter designed to detect the imprint of primordial gravitational waves in the polarization of the Cosmic Microwave Background radiation. We describe the two main components of the telescope's azimuth drive: the reaction wheel and the motorized pivot. A 13 kHz PI control loop runs on a digital signal processor, with feedback from fibre optic rate gyroscopes. This system can control azimuthal speed with < 0.02 deg/s RMS error. To control elevation, SPIDER uses stepper-motor-driven linear actuators to rotate the cryostat, which houses the optical instruments, relative to the outer frame. With the velocity in each axis controlled in this way, higher-level control loops on the onboard flight computers can implement the pointing and scanning observation modes required for the experiment. We have accomplished the non-trivial task of scanning a 5000 lb payload sinusoidally in azimuth at a peak acceleration of 0.8 deg/s$^2$, and a peak speed of 6 deg/s. We can do so while reliably achieving sub-arcminute pointing control accuracy.Comment: 20 pages, 12 figures, Presented at SPIE Ground-based and Airborne Telescopes V, June 23, 2014. To be published in Proceedings of SPIE Volume 914

Autonomous space processor for orbital debris

Advanced designs are being continued to develop the ultimate goal of a GETAWAY special to demonstrate economical removal of orbital debris utilizing local resources in orbit. The fundamental technical feasibility was demonstrated in 1988 through theoretical calculations, quantitative computer animation, a solar focal point cutter, a robotic arm design and a subcase model. Last year improvements were made to the solar cutter and the robotic arm. Also performed last year was a mission analysis which showed the feasibility of retrieve at least four large (greater than 1500 kg) pieces of debris. Advances made during this reporting period are the incorporation of digital control with the existing placement arm, the development of a new robotic manipulator arm, and the study of debris spin attenuation. These advances are discussed

Integration of fault tolerance and hardware redundancy techniques into the design of mobile platforms

This work addresses the development of a fault-tolerant mobile platform. Fault-tolerant mechanical system design is an emerging technology that attempts to build highly reliable systems by incorporating hardware and software architectures. For this purpose, previous work in fault-tolerant were reviewed. Alternate architectures were evaluated to maximize the fault tolerance capabilities of the driving and steering systems of a mobile platform. The literature review showed that most of the research work on fault tolerance has been done in the area of kinematics and control systems of robotic arms. Therefore, hardware redundancy and fault tolerance in mobile robots is an area to be researched. The prototype constructed as part of this work demonstrated basic principles and uses of a fault-tolerant mechanism, and is believed to be the first such system in its class. It is recommended that different driving and steering architectures, and the fault-tolerant controllers\u27 performance be tested on this prototype

Nonlinear control of an industrial robot

The precise control of a robot manipulator travelling at high speed constitutes a major research challenge. This is due to the nonlinear nature of the dynamics of the arm which make many traditional, linear control methodologies inappropriate. An alternative approach is to adopt controllers which are themselves nonlinear. Variable structure control systems provide the possibility of imposing dynamic characteristics upon a poorly modelled and time varying system by means of a discontinuous control signal. The basic algorithm overcomes some nonlinear effects but is sensitive to Coulomb friction andactuator saturation. By augmenting this controller with compensation terms, these effects may largely be eliminated.In order to investigate these ideas, a number of variable structure control systems ~re applied to a low cost industrial robot having a highly nonlinear and flexible drive system. By a combination of hardware enhancements and control system developments, an improvement in speed by a factor of approximately three was achieved while the trajectory tracking accuracy was improved by a factor of ten, compared with the manufacturer's control system.In order to achieve these improvements, it was necessary to develop a dynamic model of the arm including the effects of drive system flexibility and nonlinearities. The development of this model is reported in this thesis, as is work carried out on a comparison of numerical algorithms for the solution of differential equations with discontinuous right hand sides, required in the computer aided design of variable structure control systems

Design of a seven degree of freedom arm with human attributes

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (leaf 24).Studying biological systems has given robotics researchers valuable insight into designing complex systems. This thesis explores one such application of a biomimetic robotic system designed around a human arm. The design of an anthropomorphic arm, an arm that is similar to that of a human's, requires deep insight into the kinematics and physiology of the biological system. Investigated here is the design and completion of an arm with 7 degrees of freedom and human-like range of motion in each joint. The comparison of actuation schemes and the determination of proper kinematics enable the arm to be built at a low cost while maintaining high performance and similarity to the biological analog. Complex parts are built by dividing structures into interlocking 2d shapes that can easily be cut out using a waterjet and then welded together with high reliability. The resulting arm will become part of a bionic system when combined with an existing bionic hand platform that is being developed in the Intelligent Machines Laboratory at MIT. With a well thought out modular design, the system will be used as a test bed for future research involving data simplification and neurological control. The completion of the anthropomorphic arm reveals that is indeed feasible to use simple DC motors and quick fabrication techniques. The final result is a reliable, modularized, and anthropomorphic arm.by Adam Paul Leeb.S.B

Poly Spotlight Control

When this project began, The Cambria Center for the Arts Theater used a manually-operated spotlight. The sound created by the fans, along with the sheer size of the spotlight, required that it be housed in an attic room above the theater and shined through a closed window. This trapped a lot of heat in the room and involved some risk with climbing into and out of the attic room. This project sought to remedy those issues by mounting a pair of newer LED spotlights inside the theater. Doing this required a method for remotely controlling and actuating the angular position of each spotlight in two axes. Over the course of one year, the Dynalux team researched, designed, and built a solution to CCAT’s problem. The process by which they completed those steps is written in detail within this report. The first third of the year was spent in research and development. The team compared commercial and industry options to determine the best practices and designs. Many of the available options were too complicated or expensive and this reiterated that a cheaper and easier system was needed. At this point, Team Dynalux came up with a preliminary design that met all the design constraints. The next third of the year was dedicated to detailed analysis and proving that the design would work as intended. This included looking at all aspects of the system from motor torque requirements to strength and material properties. At this stage, the design was presented to the sponsor and advisors to begin manufacturing. The remainder of the project consisted of manufacturing, assembling, and testing. Some aspects had to be changed on-the-fly but the majority of the design remained the same throughout. Upon concluding machining and welding, the metal parts were finished and assembled with off-the-shelf components. When the mounts were complete, the electronics were added and tested in the overall system. Testing and manufacturing were time intensive but kept safety and reliability as the highest priority. The contents of this report are intended to document the process by which the project was completed but also provide reference to the parts and techniques used to build the system. Also included are comprehensive drawings and instructions to make sure the system is running smoothly, and if needed, provide maintenance

Soluciones para la medición de par y velocidad en bancos de ensayos de controladores de máquinas eléctricas

The continuous search for improvement in electromechanical developments requires a clear understanding of the torque measurement required in each application. The decisions made will have a profound impact on the quality and cost of the results. This article presents the principles normally used for sensing mechanical torque on a shaft and the reasons for the widespread use of strain gauges. The importance of differentiation between static and dynamic measurements and the current technologies used in each case are discussed. The relevant factors that define a transducer are described and a comparative analysis between them is carried out, to then examine the possible mounting methods, with their benefits and limitations. Finally, different low-cost solutions are proposed for the design of the torque and speed measurement section without sacrificing system performance, for different test benches for electrical machine controllers, including the necessary signal conditioning electronics. The article aims to be a tutorial compendium of topics to study to successfully implement a test bench without damaging the torque transducer or introducing measurement errors, since the information on these topics is scattered and it is difficult to access knowledge of the selection criteria and project procedures.La continua búsqueda de la mejora en los desarrollos electromecánicos impone una clara comprensión de la medición de par necesaria en cada aplicación. Las decisiones tomadas tendrán un profundo impacto en la calidad y el costo de los resultados. En este artículo se presentan los principios comúnmente empleados para el sensado de par mecánico en un eje y el porqué de la utilización extendida de las galgas extensiométricas. Se discuten la importancia en la diferenciación entre las mediciones estáticas y dinámicas, y las tecnologías actuales utilizadas en cada caso. Se describen los factores relevantes que definen a un transductor y se realiza un análisis comparativo entre ellos, para luego examinar los posibles métodos de montaje, con sus beneficios y limitaciones. Finalmente se proponen distintas soluciones de bajo costo para el diseño de la sección de medición de par y velocidad sin sacrificar el rendimiento del sistema, para diferentes bancos de ensayos para controladores de máquinas eléctricas, incluyendo la electrónica de acondicionamiento de señal necesaria. El articulo pretende ser un compendio tutorial de temas a estudiar para implementar con éxito un banco de ensayos sin dañar al transductor de par ni introducir errores de medición, ya que la información sobre esos temas está dispersa y es difícil acceder al conocimiento de los criterios de selección y procedimientos de proyecto

The laboratory telerobotic manipulator program

New opportunities for the application of telerobotic systems to enhance human intelligence and dexterity in the hazardous environment of space are presented by the NASA Space Station Program. Because of the need for significant increases in extravehicular activity and the potential increase in hazards associated with space programs, emphasis is being heightened on telerobotic systems research and development. The Laboratory Telerobotic Manipulator (LTM) program is performed to develop and demonstrate ground-based telerobotic manipulator system hardware for research and demonstrations aimed at future NASA applications. The LTM incorporates traction drives, modularity, redundant kinematics, and state-of-the-art hierarchical control techniques to form a basis for merging the diverse technological domains of robust, high-dexterity teleoperations and autonomous robotic operation into common hardware to further NASA's research