Patent Application
20200003669
The present disclosure relates to a system for verification of the speed of crosshead travel in a materials testing device.
In the prior art, it is known that material testing, such as, but not limited to stress/strain analysis pursuant to ASTM E2658, requires repeatable and predictable testing machine speed. The devices used for measurement of machine speed may be used for measurement of crosshead speed. The accuracy of the crosshead speed value is imperative for the accuracy of the materials testing results.
It is therefore an object of the present disclosure to provide for improved calculation and verification of the speed of a crosshead in a materials testing device.
This and other objects are attained by verification of crosshead travel by measuring the distance the crosshead travels over a period of time. A time internal counter is used in combination with a linear displacement device which is mounted on the crosshead of the testing machine. Both devices are calibrated and provide metrological traceability to the International System of Units (SI) through a recognized National Metrology Institute such as the National Institute of Standards and Technology.
Further objects and advantages of the disclosure will become apparent from the following description and from the accompanying drawings, wherein:
Referring now to the drawings in detail, wherein like numerals indicate like elements throughout the several views, one sees that
A linear displacement device 102 is mounted on the crosshead or other suitable location on the materials testing machine 10 and sends a digital signal representative of linear displacement (typically, but not limited to, via a 15-pin D-type connector 104) to the input 107 of linear encoder 106 (typically, but not limited to, a Heidenhain ND-287). The linear decoder 106 sends a signal via output 108 (typically a 9-pin, D-type connector) to first port 110 (typically, but not limited to, a USB port) of computer 112 (or other processing device) running applications programs (typically, but not limited to, Calpro software). Computer 112 further includes second port 114 (typically, but not limited to, a USB port) connected to port 117 (typically, but not limited to, a USB port) the timer interval counter 118. Computer 112 further includes third port 116 (typically, but not limited to, a USB port) connected to the service port connector 20 of the material testing machine 10, for use when only displacement is being measured.
The timer internal counter 118 comprises a universal dual-channel pulse input counter with interface connections for power, computer software communications and external triggering connection for calibration to national and international standards. The timer interval counter is purchased from Laurel Electronic Inc. in Costa Mesa, Calif. with a specific requirement to function as a time counter and designated as part number L50205FR-INS.
The timer interval counter 118 is used in conjunction with the linear displacement device 102 to provide for in-the-field verification of crosshead and actuator speed on materials testing device 10. It communicates with computer 112 (running materials testing software) which provides the communications and commands necessary to reset, start the counter, stop the counter and read the elapsed time to millisecond. This provides the ability to compare the set speed of the materials testing device 10 to the actual speed derived from the time and displacement measurement reference. The timer interval counter 118 is calibrated using references that will provide traceability of the time measurements to the International System of Units (SI).
The interior of the timer interval counter 118, the interior of the rear panel of timer interval counter 118, the exterior of the rear panel of timer interval counter 118, and the back of the timer interval counter 118 are illustrated in
The linear displacement device 102 is illustrated in
The materials test is initiated by starting movement of the crosshead at a speed set within the control software of the materials testing machine 110. As the crosshead moves, the linear displacement device 102 measures the actual displacement of the crosshead. This displacement is displayed on the linear encoder 106. The user, such as a field service engineer, then initiates the verification in the software of computer 112 at which time the displacement value is read into the software of computer 112 and the time interval counter 118 is initiated. At the completion of the prescribed time, the user stops the test, at which time the displacement as calculated by the linear displacement device 102 is again recorded and the time interval counter 118 is stopped and read into the software of computer 112. The software determines the change in displacement between the two readings of the linear displacement device 106 and divides by the elapsed time of the test, as calculated from readings of the timer interval counter 118, to determine the actual test speed. The software compares the set speed from the machine control software to the actual speed as calculated above to determine the error in the speed of the materials testing machine 110.
Thus, the several aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby.
