Compliance control of connecting rod leg without force sensors

With the development and application of foot robots, the control of machine leg is becoming more and more important. Generally, the machine leg has multiple joints and is equipped with a force sensor. However, the number of force sensors is limited and the pressure at each location cannot be measured. To solve this problem, a new connecting rod leg is provided and a sensorless compliant control method is proposed. As follows, the mechanical leg has two joints controlled by two brushless motors. The current loop is controlled by PI control. The position control is realized by active disturbance rejection control (ADRC). The three-phase current of the motor is obtained by ADC sampling of the control board. The current I_d and I_q of the brushless motor can be converted from the three-phase current. The I_q is used to estimate the output torque of the motor, and this torque is used instead of the pressure sensor. By establishing a D-H parametric model, it is possible to coordinate the control of two joints. The experiment verified that it has good anti-interference ability and buffer capacity.