Motion Control

Evaluation Standard for Robotic Research

Universal benchmarks can standardize the measurement of robotic manipulation tasks.The Yale-CMU-Berkeley (YCB) Object and Model Set provides universal benchmarks for labs specializing in robotic manipulation and prosthetics. About two years ago, Aaron Dollar, an associate professor of mechanical engineering and materials science at Yale University, came up with the benchmark idea to bring a level of specificity and universality to manipulation tasks in robotics research. He enlisted the help of two former colleagues in the robotics community, Dr. Siddhartha Srinivasa from Carnegie-Mellon University and Dr. Pieter Abbeel of the University of California, Berkeley.

Posted in: Briefs, Motion Control, Automation, Kinematics, Research and development, Robotics, Quality standards, Biomechanics


Mechanisms for Achieving Non-Sinusoidal Waveforms on Stirling Engines

The current state-of-the-art Stirling engines use sinusoidal piston and displacer motion to drive the thermodynamic cycle and produce power. Research performed at NASA Glenn has shown that non-sinusoidal waveforms have the potential to increase Stirling engine power density, and could possibly be used to tailor engine performance to the needs of a specific application. However, the state-of-the-art Stirling engine design uses gas springs or planar springs that are very nearly linear, resulting in a system that resonates at a single frequency. This means that imposing non-sinusoidal waveforms, consisting of multiple frequencies, requires large forces from the drive mechanism (either the alternator or the crank shaft). These large forces increase losses, and increase the size and requirements of the control system. This innovation aims to reduce the external forcing requirements by introducing internal mechanical components that provide the forces necessary to achieve the desired waveforms.

Posted in: Briefs, Mechanical Components, Mechanics, Motion Control, Alternators, Crankshafts, Engine efficiency, Stirling engines


Improving Stirling Engine Performance Through Optimized Piston and Displacer Motion

Stirling engines typically achieve high efficiency, but lack power density. Low power density prevents them from being used in many applications where internal combustion engines are viable competitors, and increases system costs in applications that require Stirling engines. This limits their operating envelope in both terrestrial and space applications. Sinusoidal piston and displacer motion is one of the causes of low power density. Previous work proposed solving this problem by replacing sinusoidal waveforms with waveforms that more closely approximate those of the ideal Stirling cycle. However, when working with real engines, imposing ideal waveforms has been shown to reduce power density and efficiency due to increased pressure drop through the regenerator and heat exchangers.

Posted in: Briefs, Fluid Handling, Mechanical Components, Mechanics, Motors & Drives, Engine efficiency, Pistons, Stirling engines


A Method for Accurate Load/Position Control of Rigidly Coupled Electromechanical Actuators

NASA has developed a technique designed to prevent cross-coupling in systems where two or more linear electro-mechanical actuators (EMA) are rigidly connected and are in danger of becoming cross-coupled. In such systems where the linked EMAs are commanded to achieve two distinct goals, such as position and load control, control problems often arise — especially at higher load and linear velocity levels. Both position and load control become inaccurate and in certain situations, stability of the overall system may be compromised. The NASA-developed approach mitigates the problem and achieves both accurate position following and desired load levels between the two (or more) actuators.

Posted in: Briefs, Mechanical Components, Mechanics, Positioning Equipment, Electronic control systems, Electronic equipment, Sensors and actuators


Reducing Power-On/Off Glitches in Precision DACs

Voltage glitches are common in a signal chain path, especially when the system is being powered up or down. Depending on the peak amplitude and glitch duration, the end result in the system output can be catastrophic. One example is an industrial motor control system where a digital-to-analog converter (DAC) drives the motor drivers to control motor spin. If the glitch amplitude is higher than the motor driver’s sensitivity threshold, the motor could be spinning without control in any direction when the system is powered up/down.

Posted in: Briefs, Power Management, Motors & Drives, Engine control systems


Piezoelectric Actuated Inchworm Motor (PAIM)

This linear piezoelectric actuator can operate at temperatures of 77 K or below. NASA’s Jet Propulsion Laboratory, Pasadena, California Conventional piezoelectric materials, such as PZTs, have reasonably high electromechanical coupling over 70%, and excellent performance at room temperature. However, their coupling factor (converting electrical to mechanical energy and vice versa) drops substantially at cryogenic temperatures, as the extrinsic contributions (domain wall motions) are almost frozen out below 130 K.

Posted in: Briefs, TSP, Energy, Fluid Handling, Motors & Drives, Electric motors


Advanced Rolling Mechanics Analysis (AROMA) 1.0

Lyndon B. Johnson Space Center, Houston, Texas AROMA uses a boundary-element formulation to calculate normal and shear pressure distributions and sub-surface stresses for elastic bodies in contact. In addition to handling static normal and sheer loading, it also solves the contact problem for rolling elements such as bearings, traction drives, and wheel-to-rail interfaces. AROMA is a powerful and flexible tool for studying the tractive forces that arise during rolling in combination with kinematic effects, such as creepage and spin that are related to rolling element alignment. This GUI-based tool was developed in MATLAB, and can run within the MATLAB environment or as a standalone application.

Posted in: Briefs, Motion Control, Software, Measuring Instruments, Analysis methodologies


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