Traceability

Univ. of Vigo and NIST worked on a series of traceability extensions for linking STEP-NC machining programs with sensor feedback and machine state information during execution.

The intent of this demonstration is to validate the proposed traceability extensions to AP-238. The extensions to be tested are time and machining performance. The proposed NC function get_time will be inserted at the beginning and end of AP-238 programs for calculation of the total program execution time. The NC functions start/stop_getting_max_deviation_along_toolpath will be inserted at the beginning and end of finishing toolpaths to log the servo error at a frequency of a few Hertz.

1. We start with one of the AP-238 programs for 3-axis roughing. The roughing operation is chosen since the path deviation is expected to be the largest.
2. A get_time marker and a start_getting_max_deviation_along_toolpath instruction are inserted at the beginning of each workingstep. This can be done in the STEP-NC Explorer on an existing AP-238 file, or as part of the initial generation of the file.
3. Likewise, a get_time marker and a stop_getting_max_deviation_along_toolpath instruction are inserted at the end of each workingstep.
4. At the end of each workingstep, the difference between the end and start times and the maximum recorded deviation are logged out to an output file.

The path deviation entity includes a limit on the acceptable deviation. This has been used to flag excursions outside the limit. A similar limit on execution time has been proposed. In this scenario, the actual time between markers would be compares against the upper limit, and an error would be flagged if machining took too long.