| Exoskeleton robot is a wearable device that combines the wisdom of the people and the power of the machine.It integrates control theory,computer technology,communication and so on.At present,it has been widely used in military,medical and other fields.Despite the exoskeleton robot is a hot spot among universities and research institutions at home and abroad in research,there are still some challenges,for example,how to achieve safely and friendly human-machine interaction.Therefore,in this paper we intend to use the series elastic actuator as the actuator of exoskeleton robot,and design knee exoskeleton robot and do some research based on this platform.Firstly,we introduce the characteristics of the series elastic actuator(SEA),which has the characteristics of low output impedance,precision and stability control and can deal well with the impact from external.Through the analysis of its model,we know it has good performance at low frequency: its frequency response is good at low frequency,and decreases as the increase of frequency.The impedance is small at low frequency and increases to the stiffness of elastic element as the frequency increases.The frequency of human's motion is relative low,so it is appropriate to use exoskeleton.Secondly,we introduce the design of the knee exoskeleton system,including the structure design,the design of each components and how they connect.There are three main components,including thigh components,transmission components and calf components;the design of SEA,the key of which consists of three sets of elastic elements to ensure the compactness of the whole structure;hardware system,choosing the specific motor model,sensor,reducer and drive,etc;the framework of the whole system,how each part of the system communicates each other and the procedures that the system works.Thridly,we establish the human-machine model,in order to achieve robust force control,we adopt the integral sliding mode control algorithm(an advanced algorithm of sliding mode control)in which an extract integral item is added to reset system errors and changes a discrete item to a continuous item in control law to avoid chattering phenomenon at the same time.Through experiments,the sliding mode control is shown to be stable and can achieve accurate force control.In addition,we also adopt another force control method,based on the human-computer interaction model to compensate the human motion and using feedback control while enhancing the compensation for system disturbance through a disturbance observer.We also carried out contrast experiments for these three methods(integral sliding mode control,sliding mode control,control based on disturbance observer),the results showed that integral sliding mode control had the best control performance,then the control based on disturbance observer and common sliding mode control ranked last.Finally,we summarize the work in this paper that apply the SEA to the designed of exoseleton and do some plans for the future work. |
