The difference between the double stages of impedance and the single stage of the impedance for a direct teaching method in a constraint condition

For the direct teaching in a constraint condition, two types of impedance system can be considered, a single stage of impedance and double stages of impedance. Single impedance system is simple but it cannot feel the teaching signal and the contact signal separately. Double stages of impedance system is complicated but it can feel the teaching signal and the contact signal separately. In this paper, the difference of two solutions will be summarized.