Design And Research On A Robot Manipulator Gripper Based On Two-axial Force Feedback

With the rapid development of intelligent manufacturing,industrial robots as an advanced manufacturing equipment play an indispensable role.Due to the need to complete a variety of tasks,the robot needs a variety of end-effectors for object crawling.In the food packaging,agricultural picking and other industries,It is a difficulty for a smart manipulator to crawl the soft or crisp stably.How to make the robot hand like a human hand rely on complex sensing system to detect the object information and clamping force,accurately identify the object's soft and hard degree,weight,surface conditions and other information,and accurately control the size of the grab force,is one of the focuses of current research in the word.In this paper,a small two-axial force sensor of octagonal ring is designed for the end of the manipulator to sense the clamping force and tangential force during the crawling process.On this basis,a robot smart end-effector is designed to achieve crawling the soft or crisp stably.Firstly,the force analysis of the gripping process of the gripper is carried out to determine the detection requirement of tangential force and clamping force.Then an octagonal ring sensor capable of detecting two-dimensional force is designed.ANSYS simulation software was used to analyze the finite element and strain nodes of the sensor,and its structural parameters were optimized.The octagonal ring sensor experimental prototype and detection device are designed.Calibrate sensor statically to get the calibration matrix,which solves the problem of coupling because of production error and strain gauges pasted error.The simple clamping test proved that the octagonal ring sensor can meet the clamping force and tangential force detection.Gripper prototype and system experimental platform are designed,including gripper,control system hardware and host computer software.The control system hardware consists of industrial computer,motion control card,data acquisition card,AC servo system,two-axial force sensor of octagonal ring and signal amplifier,linear DC power supply and so on.PC software is designed with LabVIEW,which has experimental data acquisition,analysis and robot control system communication interface function.The control method of clamping force is studied by using the experimental platform.Gripper gripping objects will produce a certain deformation,so the position and force of the cascade control is used for clamping force control.In the position control stage,use variable speed control to reduce the transition time from the open state to the object contacting.For different rigid objects,different crawling speed is adopted,and the algorithm based on force closed-loop variable speed control is used to convert the force deviation of the target force and the actual force into the speed of the position control system.When the force deviation is reduced,The closing speed is automatically decelerated until it stops,thereby reducing the overshoot of the force and excessive oscillation.The experimental results show that the clamping force control system is stable and can reach the reference force quickly and meet the final crawling requirements.The dynamic crawling strategy based on two-axial force feedback is studied.In theprocess of crawling,the two-axial force information of the feedback clamping force and the tangential force is detected by the two-axial force sensor of octagonal ring,and the ratio of the tangential force to the clamping force is maintained by the force proportional control based on the two-dimensional force feedback within a certain threshold.So that there is no sliding between the object and the holder fingers,ensuring that the holder fingers do not come off the surface of the object and that the protective object is prevented from being damaged by excessive clamping force.Experiments show that the way can successfully capture objects and avoid damage.