Speed Sensing Design Of Joint Motor Based On Laser Self-mixing Interference

The rapid development of the Internet of things and machine learning is pushing forward the development of all kinds of service and collaborative robots and so on to meet the demands of human life and industrial production,such as monitoring,medical treatment and transportation.As the core of robot motion is joint motor measurement and control,so high precision and resolution detection is a kind of important link to make the robot run precisely.Therefore,considering the factors such as resolution,cost and accuracy at the same time,a comprehensive comparison is made between the photoelectric encoder,the common speed sensing device in joint motors,and the other speed measurement methods,such as the Hall type,the magnetoelectric type and the tachometer generator.And the laser self-mixing interference(SMI)is used for speed sensing of joint motor in this paper.This method has the advantages of simple optical path,compact structure and low cost,and has significant advantages in angular velocity sensing of joint motor rotation due to its outstanding features in resolution.We have carried out the high-resolution speed measurement of joint motor by combining SMI technology.The main contents are as follows:Firstly,combining with the principle of the current widely used method of measuring the motor speed,and comparing with the SMI method used in this paper,the advantages of the method in resolution and precision are fully proved.Then in the process of theoretical analysis of SMI motor speed measurement,on the basis of Fabry-Perot cavity,the mathematical model of SMI is analyzed with the theory of three-mirror cavity,and the power equation and frequency equation of SMI signal are obtained.The velocity information contained in the optical signal is further deduced.Then,for effectively enhance the self-mixing signal and enhance the feedback optical signal,an improvement in the arrangement of a beam splitter as a pre-feedback mirror is proposed when the velocity is measured.Based on the three-mirror cavity model,a four-mirror cavity model with a pre-feedback mirror is derived,and the feasibility of the method is proved.In the further experiment,the enhancement effect of the method is evaluated from the aspect of signal enhancement amplitude and the signal-to-noise ratio,and the accuracy of the method for measuring the rotational speed of the joint motor is verified.Compared with the existing research results,this method fully retains the advantages of simple and compact structure and low cost of laser self-mixing interference system.Finally,in order to solve the problem of the dependence of the velocity on the angle of incidence in the process of velocity detection,a method of dual-light velocity detection was proposed.After the conclusion that the angular velocity is proportional to the sum of the two frequency shifts is obtained through theoretical analysis,the feasibility of the method to measure the speed of joint motor is proved in the process of further experimental verification.