Research On Complex Mechanical Loading Control Technology Based On Six-Degree-of-Freedom Parallel Drive

In order to reduce the losses caused by material failure,material serviceability testing was born and is flourishing today.It has played an important role in the biomedical field,automotive field,energy field,and aerospace field.The widespread interest in the mechanical properties of materials under complex service conditions has directly driven the development of testing instruments from single load loading to complex load loading.By integrating various physical fields and in-situ observation tools,a new generation of material serviceability testing instruments is developing towards universalization.To achieve complex mechanical load loading,the key issue is how to design a multi-degree-of-freedom mechanical load precision control system to meet the practical needs.In order to realize the force closed-loop control required for the coupled complex load testing,this paper investigates the closed-loop force control strategy for the in-situ testing equipment coupled with complex mechanical loads and multi-physical fields developed independently in the author’s laboratory.This paper firstly analyzes the principle,composition,functional combination and component specifications of the Complex-mechanical Load and Multi-physical Field Coupling In-Situ Testing Equipment;analyzes the mechanical load loading principle of the equipment so as to decompose the action of the equipment when a cantilever bending load is applied,and analyzes the position change law of the equipment during the loading process of the cantilever bending load;the error sources of the six-dimensional force sensor are analyzed from four aspects: tool center of mass,tool gravity,initial position and motion process;the force sensor is calibrated using the six-dimensional force sensor calibration equipment developed by the author’s laboratory.Next,a complex load control strategy based on six-degree-of-freedom parallel drive is proposed.The control strategy takes the desired position,desired force,and ambient force as inputs,and the controller converts the error between the desired force and ambient force into the position correction quantity,so that the ambient force gradually approaches the desired force by correcting the desired position.A composite tensile cantilever bending simulation model is established in ANSYS Workbench,and the desired attitude is solved after the bending angle acquisition method in the model is verified by cantilever bending theory.Combining the six-degree-of-freedom parallel positioning platform coordinate system and the six-dimensional force sensor coordinate system,the standard coordinate system of the working space of the equipment is established.According to the principle of coordinate system mapping,the commanded posture is solved from the desired posture;according to the principle of gravity compensation and the principle of transformation of force/moment vector in different coordinate systems,the environmental force is solved from the six-dimensional force sensor indication.Finally,a composite tensile cantilever bending closed-loop force control strategy is proposed in combination with the principle of admittance control.Based on the above work,in order to better verify the apply effect of the force control strategy,the bending stroke of the equipment was expanded by designing the inclination fixture,solving for the upper limit of the fixture inclination of 6.3°,designing a 5° inclination fixture and a 6° inclination fixture,respectively,and selecting the 6° inclination fixture after the no-load test.Through the experimental study,a variety of composite tensile cantilever bending test was conducted on the bar specimen,and the test results verified the effectiveness of the force control strategy.