Automated Real Time Correction of Motion Induced Dynamic Load Errors in the Force Readout of a Test Apparatus

Abstract

In mechanical testing, it is often important to understand the dynamic characteristics of the test system to assess if there could be any error in the indicated force readout induced by the motions of the system. That these errors exist is readily apparent for load sensors which are mounted on the actuator; the actuator is expected to move during the course of the test. What may be less obvious is that these errors also exist in load measurements taken on the “grounded” side of a sample. Methods have been developed (such as ASTM E467-08e1) for the assessment and correction of these errors; however, these methods can be time consuming to implement. In some cases, they may not be practical or even possible (e.g., placing strain gauges on a biological sample). Existing methods using accelerometers to predict acceleration induced load have been used for some time. What is presented are a set of approaches to increase the simplicity and reliability of using acceleration sensors to address dynamic load errors. Using various modes of stimulation of the system, software algorithms are used to assess the correct compensation factors to use for both magnitude and phase of the acceleration signal, as a function of frequency. This has the additional benefit of allowing the use of load and acceleration sensors which may not be ideally phase matched. These methods also allow stimulation of both motor mounted load sensors as well as frame mounted sensors.