Inner loop sensors for outer loop force control of robots

It is shown that joint strain based inner loop feedback control has the potential of providing more robustness to environmental stiffness than the more common positional schemes used on industrial robots. It is also pointed out that the finite resolution of encoders used on such robots severely limit the lowest speed which can be controlled if tachogenerators are not present on the robot joints. This indicates that joint strain for robot force control should be pursued as potential robust sensors, both for their increased linear robustness and for their higher resolution during constrained moves. However, practical robots have high order resonances in their drive systems which severely limit the applicability of joint strain without heavy bandlimiting