July, 2015
www.us-
tech.com
Optical Encoders Help Measure Material Fatigue
By Jeff Drum F
atigue testing is one way to evaluate how different materi- als will behave under different
environments and operating condi- tions. Test systems developed for such characterization, such as the equipment from Norwood, Mas - sachu setts-based Instron can exam-
The company found a solution in the form of the RESOLUTE absolute optical encoder from Renishaw (
www.renishaw.com). This absolute optical encoder provided support for ElectroPuls controllers and satisfied all additional system criteria, while supporting linear resolution to 1nm and measurement speeds beyond 20 m/s. The excellent performance pro- vided by these absolute optical encoders has resulted in their being
chosen for both axes of the new E10000 and E3000 fatigue test sys- tems.
An LVDT Problem The design of the E10000 and
E3000 fatigue test systems posed par- ticular challenges for the optical encoders incorporated in those sys- tems. Conventional servo-hydraulic test instruments use a linear variable differential transformer (LVDT), a
type of inductive absolute encoder, to determine the linear direction of trav- el and position of the actuator. Each ElectroPuls test system is driven by a linear synchronous motor and requires additional high-quality velocity feedback for precise dynamic motor control. This is due to the diffi- culties of driving linear motors with lower inherent damping than tradi- tional rotary electromechanical drive
Continued page 65 YOUR TEST
Page 61
AND INSPECTION PARTNER
Testing a sample.
ine the behavior of different materi- als under fluctuating or cyclic loads in the elastic regime. The company manufactures and services a compre- hensive range of material testing equipment and accessories for the research, industrial, and academic sectors. Its systems have been used to test samples ranging from compo- nents for jet engines to medical syringes. As examples, the compa- ny’s ElectroPuls models E1000, E3000, and E10000 fatigue test sys- tems are suited for biomedical/bio- mechanical research applications and feature a wide dynamic perform- ance range and low force characteris- tics. These all-electric systems employ linear motor technology to eliminate the need for ball/lead- screws and enable slow-speed static
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tests through to high-frequency dynamic tests at over 100Hz. For effective operation of these
fatigue testing systems, Instron needed a reliable and accurate absolute optical encoder that was compatible with BiSS® serial commu- nications methods, easy to set up and install, and noncontacting to elimi- nate the friction and wear that can lead to mechanical hysteresis errors.
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