| The invasive brain-computer interface has important applications in disability communication,stroke rehabilitation,exoskeleton machinery,and so on,which has received extensive attention of researchers.However,it usually uses devices such as motors and lead screws for positioning,and requires external sensors as feedback,which limits the implantation accuracy and operational simplicity of microelectrodes.Piezoelectric stepping actuator has the excellent characteristics of large working stroke,high positioning accuracy and open-loop operation.Its application in the brain-computer interface is one of the best choices to improve the above traditional microelectrode implantation problems,but its control signal system has high complexity and low integration.In order to solve the above problems,the self-driven and self-adaptive scheme of the piezoelectric stepping actuator is proposed.The self-driven and control signals’ self-adaption functions of the actuator are realized by the cam mechanisms which mechanically trigger the exciting signal and synchronously adjust control signals to adapt to the change of the DC motor state.Piezoelectric stepping actuators of direct-clamping and indirect-clamping schemes are designed.The main research works are summarized as follows:1.Design method of self-driven and self-adaptive piezoelectric stepping actuatorA self-driven and self-adapting scheme based on cam mechanisms is proposed,and the self-driven and self-adapting process of the actuator is described in detail.According to the self-driven and self-adaptive scheme,the piezoelectric stepping actuator schemes of the direct clamp and indirect clamp are proposed,and the proper motion law of the putter is tested and established.The influence of phase difference between exciting and clamping cams on the motion mode of the actuator is analyzed in detail.2.Design and test of direct-clamping,self-driven,and self-adaptive piezoelectric stepping actuatorThe prototype of the direct-clamping type is designed and produced;performance tests and dynamic simulation research of the prototype are carried out.Batteries can power the actuator to achieve stable stepping displacement output;the maximum output force can reach30 m N;the minimum step displacement is 0.7 μm;thus,the feasibility of the self-driven and self-adaptive scheme is verified.3.Design and test of indirect-clamping,self-driven,and self-adaptive piezoelectric stepping actuatorBased on the magnetorheological elastomers,the indirect-clamping actuator prototype is designed and fabricated;theoretical simulation and performance tests of the prototype are carried out.The actuator can achieve bidirectional motion;the maximum speed can reach1250.4 μm/s;the maximum output force can reach 420 m N;the minimum positive/negative step displacement is 0.5837/0.5912 μm,and the corresponding repeatability is 0.0465/0.0469μm;thus,the feasibility of friction control of magnetorheological elastomers is verified.4.Application of piezoelectric stepping actuator in brain-computer interfaceAccording to the application requirements of the invasive brain-computer interface,a microelectrode’s simulation implantation system of the indirect-clamping piezoelectric stepping actuator is built.The 0.6% agarose gel is used to simulate the tissue of the pig brain,and the implantation performance of a microelectrode with a tip diameter of 50 μm is tested.The implantation accuracy can reach 0.97 μm.The repeatability is 0.16 μm.The Multi-stage microelectrode implantation can be realized with an average error rate of 1%,showing great stability of motion. |
