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| People | Actuator Components and Design: Projects: MTB |
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| Projects |
| Actuator Endurance and Reliability Test Bed |
| Metrology Test Bed |
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 Robot metrology seeks to identify parameters that are not accurately known and that affect the performance of the robot under operation. These parameters include the geometric dimensions, compliance and mass properties of joints and links, and actuator control parameters. Precision operations, such as airframe assembly, require positioning tolerances of 0.01 inch with loads in excess of 100 lb.
Typical industrial robots, whose control software uses geometric parameters specified by their design values, can have accuracies as poor as 0.5 inch. Careful metrology techniques can be used to measure the actual geometric and stiffness parameters.
This information can be used to increase the accuracy of a robot’s tool positioning and compensate for deflections under load (an improvement of 20X has been achieved in the laboratory). The system metrology process for monolithic robots has proven to be difficult and time-consuming.
Modular robot metrology (the metrology of robots that are composed of modules) is much more elementary, as a consequence of the reduced number of parameters in each module. An automated environment is needed to perform modular robot metrology in a cost-effective manner.
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 An automated metrology test environment must be able to measure three-dimensional coordinates with high accuracy. Lasers have become the standard for precision measurement. However, their implementation in a full 3D coordinate measurement system has been limited from a economic standpoint, costing as much as $500,000.
The low-cost laser interferometer is inherently a linear displacement transducer that easily can be configured to measure distances. A coordinate measuring system using three lasers and the concept of trilateration (in which the length of the six sides of a tetrahedron are known and the coordinates with respect to one corner can be calculated) can be developed for less than 1/10 the cost of a laser tracker.
A loading mechanism that applies independent forces and moments along and about each of three orthogonal axes is essential to simplify and standardize the loading procedure. The forces may be applied using an xyz frame with linear actuators that move along the three orthogonal directions of interest. Moments may be applied about the same axes by rotary actuators on a gimbals frame.
The relationships between measured position, loads, and deflections can be used to accurately determine the 6x6 geometric parameters as well as the equivalent compliance parameters representing the stiffness of the module subsystem.
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The University of Texas at Austin is developing an automated metrology test-bed intended for the determination of geometric and compliance parameters of rotary actuator modules for intelligent machines (robots). It may also have the ability to measure backlash, stiction, input/output nonlinearity, and many other parameters requiring the application of loads and/or measurement of displacement.
The measurement system is a relatively low cost alternative to the one-off systems available today, such as laser trackers. Three lasers (in a plane but not colinear) will be focused on a single point (retroreflector) on the output plate of the module. The locations of the lasers will be precalibrated with respect to each other.
If the distance from each laser to the test point on the module is measured, the length of six sides of a tetrahedron are known. The actual position of the reference coordinate system on the output plate of the module is then calculated and transformed to a single reference frame to establish the three-dimensional locations.
Analytical transformations can then be employed to determine all basic geometric and compliance parameters required to characterize the actuator module and to automatically embed them on board the module for downloading to a system control software package on demand.
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