Control of lower extremity exoskeleton based on admittance

Control of lower extremity exoskeleton based on admittance method Authors: Wenhao Chen; Shengli Song 2017. 5. 15 LOGO

Catalogue 1、Human-exoskeleton Coupling Dynamics Mode 2、Admittance Control 3、Stability Analysis and Parameter Optimization 4、Simulation 5、Conclusion

is the damping coefficient and is the coefficient 1、Human-exoskeleton Coupling Dynamics Mode alf an c Hum exo ske le ton Exoskeleton only provides power to human calf

2. 1、Admittance Transfer functions are given by

2. 2、Admittance Control The control consists of a positive feedback control From the fig, we can get

2、Admittance Control When the parameter a, b, c are greater than 0, the exoskeleton’s admittance characteristics can be offset by the control function , which makes the exoskeleton be equivalent to a small mass. Thereby reducing the coupling with the human calf, can play a lower tracking error and coupling torque.

3. 1 Stability Analysis In order to make the system have better stability, the designed system is the minimum phase system, that is, the open-loop transfer function has no pole and no zero in the right half of the complex plane.

3. 2 Parameter Optimization results are a=0. 89, b=0. 91, c=0. 95.

4、Simulation The figure show that the phase of the calf swing in the case 1(wearing exoskeleton without power) is significantly lagging behind that in the case 2(the calf is free to swing without exoskeleton), and the amplitude is also smaller, indicating that wearing exoskeleton without power, exoskeleton is a burden for human body. And the calf's swing in the case 3(adopts the admittance control) is very close to that in the case 2.

4、Simulation The figure shows that the tracking error adopted the optimized parameters is smaller than that adopted unoptimized parameters. And the peak of tracking error adopted unoptimized parameters is about 0. 5°

5、Conclusion The admittance control can shield the mechanical admittance of the exoskeleton itself, thus reducing the tracking error and the coupling torque of the exoskeleton. And the optimized admittance control can achieve more accurate motion tracking.

Thank You！