Soft sensing force measurement approach in sheet metal forming facilities

Process stability and facility security are the two main purposes for measuring the force in sheet metal forming facilities. These two purposes look for guaranteeing the good health of the facility avoiding overloads and at the same time look for variations in the process force that could lead to products out of the demanded quality. Traditionally there have been different approaches to measure the force exerted by the press. Piezoelectric sensors and strain gages are the most widely used technologies. However there are some common limitations that reduce the success in the measurement of the force by the aforementioned sensors: force sensors tend to have a signal drift and the introduction of the sensors together with the electronics represents an extra cost that in some cases can be high. As an alternative to the implementation of force sensors, soft sensing approaches take advantage of the already available signals in the facility to estimate non measured variables, the force in this case. The present work aims at predicting the force curve that a servo press exerts in forming processes reading the internal servomotor signals. The approach has been evaluated with several forming processes achieving an error lower than 3% for all the cases.