Research on structural optimization and stable grasping control of flexible manipulators

Introduction This paper designed an optimized pneumatic flexible manipulator with an embedded segmented hinge polylactic acid (PLA) skeleton and used an incremental proportional-integral-derivative (PID) closed-loop control strategy to improve grasping reliability in response to the problems of axial stretching, significant lateral torsional deformation, insufficient end-output force, and poor grasping stability in the conventional open-loop pneumatic control method of traditional multi-chamber pneumatic pure silicone flexible fingers. Methods First, the structural defects of the traditional flexible fingers were analyzed, and the structural design and sample preparation of the endoskeleton fingers were conducted to clarify the material parameters and standardized processing procedures. Secondly, the working principles of traditional open-loop constant-value pneumatic control and PID closed-loop control were compared to determine the overall control scheme. Finally, four types of control tests were carried out: bending performance, end force, cycle durability, and whole machine grasping. Results The test results showed that the embedded skeletal structure significantly suppressed tensile and torsional deformation without affecting the normal bending of the fingers, and increased the output force at the end of the fingers by more than 60% in the full air pressure range; moreover, this structure had sufficient cycle durability. Discussion The four-finger endoskeleton manipulator, in combination with PID closed-loop control, had a 100% success rate in grasping fragile, spherical, and columnar workpieces. Compared with the traditional structure and open-loop control scheme, the proposed method significantly improved the anti-interference and workpiece protection performance.