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Some machine processes, such as presses, can require extreme accuracy in applying and holding force on an object. A popular way to measure force is via load cells. But what do you do when the accuracy required by a particular application is higher than that guaranteed by the load cell manufacturer?
One can use multiple load cells and average the results. That way, small differences in load readings between the cells, which can occur at different times and under different environmental conditions, are averaged out. A side benefit of the averaging process is that noise signals on individual load cell outputs would also be reduced by the averaging process. Another benefit of using multiple sensors to measure a single process parameter is that one sensor can fail and the system can still function, albeit at a possibly lower level of accuracy.
But how does one manage gathering inputs from multiple redundant sensors and processing them to achieve the above benefits? The motion controller that is used must be programmed to do checking and averaging of load cell data before that feedback is provided to the control loop. Parker Hannifin (Marysville, OH) did this using feedback programming of the RMC150 motion controller from Delta Computer Systems.
Load Cell Precision
Parker's customer needed to maintain a large amount of downward force on a 50,000-pound metal plate to a very tight tolerance of ±25 pounds against a total force of over 150,000 pounds. Also, because of...