Browsing by Subject "Actuators--Testing"
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Item Actuator performance envelope through nonlinear test bed(2004) Yoo, Jae Gu; Tesar, DelbertWith the increased importance of actuator performance in robotic applications, many robot manufacturers have focused on assuring quality, reliability, conformance to design, and application suitability in their actuators. Performance metrics for actuator evaluation have been proposed to improve understanding of an actuator’s nonlinear characteristics. Thorough actuator testing can provide necessary feedback information on the effectiveness of the robot actuator for a specific task. This report describes the development and use of performance maps and performance envelopes for electromechanical actuators using an advanced dynamic dynamometer test bed. Initial test data in the form of performance maps is created for a range of rated output power and dynamic loading for brushless DC motors. The core contributions of this research are the creation and manipulation of actuator performance maps and envelopes, and the design and development of a nonlinear test bed for electromechanical actuators. To create a performance map, specific criteria must be developed to describe the performance characteristics of an actuator. The performance criteria are formulated to define, anticipate, and evaluate the performance responses of the system and can provide metrics for measuring and controlling actuator performance and help identify nonlinear components in actuator modeling. These criteria form the basis for performance maps, which is basically a data representation of the criteria over a range of input and output conditions. A representative set of ten actuator performance maps are suggested based on several independent control parameters such as current and voltage, and output conditions such as torque and speed. After completing the development and analysis of these ten performance maps, the process for building unique performance envelopes is described. Performance envelopes are created from performance maps and are defined as the combined optimum surface in the full set of maps, which satisfy a combination of criteria in each operational region. Performance envelopes can safely increase the number of control surfaces without violating actuator constraints. This provides more choices in an operational range as compared to statically developed torque-speed curves. For the creation of these performance maps, five test regimes are suggested such as dynamic loading, static loading, transient response, torque ripple and statically changing temperature tests. Test regimes are evaluated under two types of loads: a static loading and a sinusoidal loading. For these test protocols, a Nonlinear Test Bed for Actuators (NTBA) has been designed and built to measure and record an array of physical performance properties. The test bed is specifically designed with the capability to emulate high bandwidth complex duty cycle loads. It is comprised of a 7.2 kW servo motor (which serves as a dynamic load emulator), a 26 Nm hysteresis brake, an electromechanical clutch, full sensor array (includes current, temperature, torque, magnetic flux density sensors) for comprehensive monitoring of test variables, and supporting motion control hardware to operate the test bed. Ten performance maps (i.e., operational margin, efficiency, power losses, rise time, torque-current, torque ripple, acceleration, max magnetic flux energy, magnetic flux density, and temperature) for a commercial brushless DC motor are developed in 3D surface displays using the test bed. The performance maps collected from repeated tests (more than 20 times for each test protocol) of the test motor provide an insight into the complexity of the electromechanical response and also provide metrics for measuring motor current states during operation. Standard deviation and average values are also calculated and used to develop the upper and lower error bounds of the magnetic flux energy performance map. In addition, the Box-Jenkins ARIMA method is used to analyze all of the test data and build a mathematical representation of sensor derived data with respect to time. This stochastic ARIMA equation is used to create each data point in a performance map. The performance map plots are normalized by using the maximum values over the range of motor operation. One performance envelope plot with respect to torque and speed is illustrated in this research. Finally, the performance data plots used in the trade literature and research papers are compared with the test result plots presented as actuator performance maps. The performance plots in the literature have several drawbacks for users, which are the lack of operational values in abnormal operating conditions and the lack of reference plots to fully describe and enable the management of the performance of the motor considering all of the operational conditions. On the other hand, the maps obtained in the experiments using the NTBA provide enough metric values to manage the actuator to achieve optimum performance for a multitude of desired operating conditions (maximum efficiency, soft start, low noise, maximum life, etc.).Item Test methodology for electromechanical actuators(2008-12) Janardhan, Jagadish, 1976-; Tesar, DelbertElectromechanical actuators are highly complex non-linear devices that cannot be accurately modeled using only analytical formulations derived from first principles. When the application demands high model accuracy with a wide parametric range (and criteria) plus the need to take manufacturing/assembly variations associated with the asbuilt actuator into account, an empirical model based on extensive testing across the entire operating domain is the recommended approach. Since testing is an expensive, time consuming and laborious process, it is the aim of this research to determine efficient test methodologies (experimental designs) that would obtain the maximum information about actuator performance by means of a minimal number of tests. Current test standards are primarily designed to arrive at the actuator specifications by carrying out tests at either a single or a very limited set of test points. The results thus obtained are typically not valid across the entire operating domain of the actuator. Also these tests are performed for a very small set (one or two) of criteria. Furthermore most of this testing is conducted in terms of just one (occasionally two) control variables. As a result the full capability of the actuator is poorly represented. The research presented here addresses these limitations. To achieve the objective, the steps followed in this research are -- a) define a set of actuator performance criteria for testing, b) construct a test bed for actuator testing, c) develop a framework for testing actuators, d) conduct tests by applying principles from Design of Experiments, e) apply statistical techniques to identify empirical models and develop efficient experimental designs, and f) graphically present the actual capabilities of the actuator using performance maps. A commercially available permanent magnet synchronous motor-geartrain combination was chosen as the test actuator. This actuator has a nominal/peak rating of 43/86 lb-ft torque and 30/100 RPM speed. The criteria considered for characterizing the actuator’s operational capability includes noise, vibration, efficiency, current consumption, torque ripple, velocity ripple, backdriveability, and temperature. Control variables affecting the performance criteria were identified. Measurement of performance over the entire operating range of actuator requires that the actuator be operated at specific levels of these control variables and the concerned performance criteria be measured. Therefore to perform these actuator tests, a modular test bed was constructed. The test bed consists of an actuator loading mechanism (in the form of a magnetic particle brake or a geartrain-motor combination), an array of sensors, amplifiers, a signal conditioning unit, data acquisition modules, motion controller, and transformer. The measured sensor data is filtered through the signal conditioning unit (to remove noise) and digitized using the data acquisition modules. Statistical techniques were employed to process the sensor data and for each criterion, an empirical model relating the criteria to its control variables was determined. Model adequacy checks were carried out to ensure that the model did not violate important statistical assumptions and that it adequately represented the relationship between the input control variables and the output response (performance criteria). These models were used to generate performance maps for each criteria. Based on a predetermined set of run sizes, for each empirical model, alternate experimental designs were determined. Efficient experiment designs were identified by metrics such as -- Gefficiency, maximum prediction variance and average prediction variance. Besides the obvious advantage of arriving at complete and accurate performance profiles for the actuator undergoing tests (with minimal testing), the methodology could be applied to other actuators of a similar family. We might consider the methodology to be a subset of the general concept of metrology; i.e., the determination of as-built parameters vs. as designed parameters. Simplification techniques were applied to these models to remove unwanted model terms.