Research On Fruit Cluster Clamping Control By Clamping Mechanism Of Parallel Robot

It is the trend to achieve the fruit cluster nondestructive sorting,improve fruit sorting efficiency and reduce labor intensity through robots.The fruit cluster such as grapeown irregular shapes,fruit grain stacking,uneven weight distribution and especially the obvious quality difference between different clusters compared with independent fruit such as apple.So it requires high stability and accuracy of the clamping control of parallel robot.Because of the advantages of the high stiffnes,the high precision and the stable structure in the parallel mechanism.To realize the nondestructive sorting of the fruit cluster,our research group developed a fruit sorting parallel robot,and the cascade control,the outer loop of which adopts the impedance control and the internal loop of which adopts the sliding mode control is introduced.There still exist several difficult problems in the clamping mechanism of parallel robot useing this control method,such as the modeling of the mechanism,the uncertainties exist in the practical engineering application system and how to adapt to the change of clamping load and clamping force.For the issues above,the dynamic model of the mechanism is established by Lagrange method.the paper proposes a cascade control,the outer loop of which adopts the adaptive variable impedance control and the internal loop of which adopts the smooth sliding mode control,and this method designed an adaptive rule adjusting the damping parameter in real time to improve the adaptability of the system to the change of the clamping speed and the clamping load.The main contents are as follows:(1)Kinematic analysis and dynamic modeling of the developed mechanism of our research group are finished.The kinematic analysis of the mechanism is completed by analytical methods.The dynamic model of the mechanism including uncertainties such as parameter changes,unmodeled dynamics and external disturbances is set up by Lagrange method.The correctness of the model is verified by the MATLAB.(2)The paper proposes a cascade control,the outer loop of which adopts the adaptive variable impedance control and the internal loop of which adopts the smooth sliding mode control.In the internal loop,to overcome the uncertainties in the practical engineering application system and weaken the chattering of sliding mode control,the smooth sliding mode control strategy is designed.In the outer loop,to improve the adaptability of the system to the change of the clamping speed and the clamping load,an adaptive rule adjusting the damping parameter in real time is designed based on the difference between the expected clamping force and actual contact force.The stability of the proposed control algorithm is proved by Routh Criterion stability theorem.To verify the effectiveness of the cascade control composed of the adaptive variable impedance control outer loop and the smooth sliding mode control internal loop,simulating the proposed control method with a cascade control composed of the adaptive variable impedance control outer loop and the non-smooth sliding mode control internal loop,and a cascade control composed of the impedance control outer loop and the smooth sliding mode control internal loop respectively by MATLAB.(3)The experimental platform of the control system of parallel robot for fruit cluster sorting is constructed and the comparison experiment of the prototype is carried on.The distributed structure of "PC+ UMAC" is selected and the hardware design and software development of the control system of parallel robot for fruit cluster sorting is completed.In order to further verify the effectiveness and superiority of the proposed method,the contrast experiment of the cascade control,the outer loop of which adopts the adaptive variable impedance control and the internal loop of which adopts the smooth sliding mode control and the cascade control composed of the constant parameter impedance control outer loop and the smooth sliding mode control internal loop is evaluated based on the prototype system,when considering the experiment of the non-smooth sliding mode control will wear the prototype.