Theoretical And Experimental Study On Active Vibration Suppression Of Flexible Arm For An Orchard Inspection Robot

The orchard inspection robot is composed of a traveling chassis and a long arm supporting cameras or other monitoring equipment.It is used for canopy image acquisition in the process of fruit tree cultivation.It is one of the important parts of intelligent orchard construction.The flexibility of the slender arm is significant,resulting in low-frequency vibration under amplitude variation or impact disturbance,which seriously restricts the quality and efficiency of image acquisition.Building a simple and effective active vibration suppression system is one of the keys in the research and development of this kind of equipment.The construction of arm equivalent model of flexible arm is deeply discussed in this paper to solve the problem of active vibration suppression;An active vibration suppression method based on differential flatness is proposed;And carry out active vibration suppression experiments under impact and variable amplitude motion conditions.Taking the active vibration suppression method of flexible arm as the research content of this paper is of great significance to the subject research.Constructing the corresponding theoretical model and control method has far-reaching theoretical and application value in the vibration suppression of flexible arm structure and equipment.Aiming at the problem of low-frequency vibration of flexible arm,this paper deeply carries out the research on the construction of arm equivalent model,the synthesis of multipoint motion information,the design of active vibration suppression feedback controller,and the extraction of model information to simplify the tuning process.The main line of the vibration suppression theory of flexible arm proposed in this paper is to establish the pseudo rigid body model for the long flexible arm with concentrated mass based on the idea of pseudo rigid body method and the equivalent constraints of static balance and natural frequency,take the inclination of each equivalent rod as the output and the variable amplitude driving torque as the input of the active vibration suppression system,and establish the Lagrange dynamic equation of the model;According to the characteristic of single input multiple output of flexible arm vibration suppression dynamic system,it is an underactuated system.A low-order isolation method is proposed,and a single input and single output formal dynamic equation with differential flatness as output is given based on the principle of differential flatness;Finally,using the principle of comprehensive disturbance observation and compensation by extended state observer in the idea of Active Disturbance Resistance Control,the model is transformed into a second-order model structure without zero point,and a PID based on differential flat output and a Linear Active Disturbance Resistance Controller with model parameters are given.In the process of experimental research,firstly,the joint simulation of active vibration suppression feedback control is carried out in the environment of ADAMS and MATLAB.After analyzing the vibration of the three-bar two torsion spring model under the action of gravity,the proposed differential flat output is used as the controlled quantity,and two vibration suppression controllers are used for feedback vibration suppression simulation respectively;Then,based on the simulation experimental data,the vibration suppression experiment of three-bar and bi-spring physical model is carried out to analyze the synthetic calculation method of Differential Flatness and the effectiveness of feedback controller.Then,carry out the active vibration suppression experiment of the flexible arm of the orchard inspection robot,gradually complete the acquisition of the equivalent pseudo rigid body model and the synthesis of differential flat output at three elevation angles,and compare and analyze the vibration suppression effects of PID controller and linear active disturbance rejection controller under two working conditions of impact disturbance and amplitude variation at different elevation angles.The acquisition method of equivalent rod length and the calculation of linear synthesis coefficient of differential flat output are studied.The parameter tuning of Linear Active Disturbance Resistance Controller based on model information is carried out.The reliability of the proposed method and the convenience of tuning process are analyzed.Finally,based on the low-frequency active vibration suppression control method,aiming at the vibration suppression of the arm with higher fundamental frequency,the constructed active vibration suppression method is expanded.Taking the equivalence of the first-order natural vibration frequency of the external extension section of the arm as the constraint condition,the short flexible arm with nested structure is equivalent to a two rods and single torsion spring system,and the elevation angle of the two equivalent rods is taken as the output to establish the dynamic model of the vibration suppression system.Considering the relatively low sampling frequency of the inclination sensor,the acceleration sensor is used at the end of the arm to collect the motion signal.An approximate algorithm is proposed to linearly combine the elevation angle of the arm root and the acceleration at the end of the arm,and an approximate flat model of the arm with higher frequency is established.The robustness of the vibration suppression controller under different extension lengths and the advantages of easy tuning are verified by experiments.