Study On Dynamic Characteristics And High Precision Positioning Control Of Rotating Arm In High Acceleration

In electronic manufacturing equipment such as chip bonder,chip mounter and sorter,the rotating arm is the key functional component of chip transfer mechanism,it has the characteristics of high frequency reciprocating and high acceleration start-stop.In the study of the dynamic characteristics of a rotating arm,it is usually abstracted as a rotating cantilever beam.Due to the existence of centrifugal force and bending deformation,there are some phenomena,such as the change of modal frequency and vibration of the rotating arm.However,the rotating arm makes high-precision positioning movement with high acceleration,which puts forward more requirements for its dynamic characteristics analysis and servo control research in the sorting machine of LED chips.The specific performance is as follows: the high-frequency reciprocating motion of the rotating arm has the characteristics of high acceleration,which needs to be regarded as a flexible cantilever beam,and its dynamic characteristics are different from the constant angular velocity operation in other fields.The modal frequency changes at any time during the operation,and geometric stiffening effect appears;the fast start-stop and high-precision positioning of the rotating arm require the servo control system to have high-performance.The response speed can meet the tracking performance of the system,and the wide-band high-speed sudden change signal will arouse the mechanical structure resonance,which will lead to the low precision of the end positioning and the lengthening of the setting time,which will affect the positioning accuracy.Due to the characteristics of the rotating arm driving the end positioning at the root,it has the amplification effect on the stability error and vibration amplitude and other adverse factors.Therefore,in order to suppress the vibration at the end of rotating arm caused by flexible deformation and servo control system,and improve the positioning accuracy and working frequency of chip sorter,the mechanical dynamic characteristic modal analysis of rotating arm is carried out based on the rotating cantilever beam model;In order to control the mechanical resonance,the input shaping technology is used to shape the command of servo system,and the high-precision positioning servo control strategy is constructed.The specific work is as follows:Firstly,based on the principle of chip sorting,cycle time and alignment accuracy,the vision system,transfer platform and rotating arm which affect the chip alignment accuracy are analyzed.Based on error delivering theory,error sources are tested and analyzed,and error distribution is executed.Time sequence and index of dynamic and static of rotating arm of are proposed.Secondly,aiming at the dynamic characteristics of high acceleration rotating arm,three kinds of rotating speed curves are designed according to the motion sequence and rotating inertia impact characteristics;based on the rotating cantilever model,the full time modal frequency calculation of rotating arm is carried out by Galerkin method and super-element method,and the geometric stiffening phenomenon in the motion period is found.And the optimal speed driving curve is determined by combining with the parameter matching problem of servo control system.Then,aiming at the resonance caused by command signal of servo system,an input shaper based on feedforward control is constructed to eliminate the resonance frequency caused by command signal and suppress the vibration of system.The principle of input shaping technology,shaper and its robustness are deeply studied;the modal test of rotating arm is carried out by hammer striking method,the resonance frequency of rotating arm is measured and the damping ratio is calculated,the shaper parameters are obtained,and the selected S-shaped speed curve is reshaped by input shaper.Furthermore,the high precision positioning control strategy of the servo control system of rotating arm is established,and the mathematical model of the permanent magnet synchronous motor is established.Based on the rigid flexible coupling characteristics of rotating arm,the mathematical model of the two inertia elastic system is derived.The position control mode of the fast start-stop positioning control is determined,and the transfer function and structure block diagram of each link of the servo control system are derived.Filter and notch filter as well as speed and acceleration feedforward are used to suppress the vibration and improve the response speed of the system;the speed loop control law is determined and vibration suppression of rotating arm and the high precision positioning control are achieved.Lastly,with the research object of sorting of LED chips the motion experiment platform and control interface was designed and built.The test which the three kinds of speed drive curves planned according to the inertial impact characteristics,verify the correctness of the dynamic characteristics analysis of rotating arm;the effectiveness of input shaping technology for vibration suppression through the shaped motion command;the positioning experiment of rotating arm is carried out with the designed control model and control strategy,and the effectiveness of the feed-forward and filter servo control for vibration suppression,positioning accuracy and reducing the setting time were verified.The results show that the vibration of rotating arm system can be effectively suppressed;the positioning accuracy reaches the performance index;and the method can improve the sorting accuracy of LED chips.