Research On Multi-Dimensional Force/Torque Measurement Method For Robot Wrist Force Perception

The wrist joint of the robot is directly connected to the end effector,which is an important component for sensing external multi-dimensional interactive force information.A high-performance wrist multi-dimensional force feedback information is the key for collaborative robots to complete high-quality collaborative work.However,the traditional wrist force measurement method uses electromagnetic sensitive elements as the strain measurement unit,which has problems such as low decoupling accuracy,large volume,serious temperature drift,and serious inter-dimensional coupling.This paper systematically studies the multi-axis force/torque measurement method of robot wrist based on Fiber Bragg Grating for collaborative robots.The research content involves key technologies such as algorithm decoupling,temperature compensation,ultra-thin sensor design,multi-axis force sensing,and structural self-decoupling measurement.The specific research work is as follows:(1)Aiming at the problems of few manual calibration data,high cost and serious coupling between multi-dimensional force/torque dimensions,a decoupling method SPA-Otsu-ELM for robot wrist multi-dimensional force/torque with few samples is proposed.Based on the vertical centerline strain calculation criterion,the coupling relationship between the force/torque dimensions of the crossbeam elastomer is analyzed,the inherent coupling is quantified,the input dimension of the calibration data is expanded,and the high-precision wrist multi-dimensional force/torque decoupling with few samples is realized.The experimental results of static decoupling show that the SPA-Otsu-ELM algorithm can reduce the type I coupling error and type II coupling error to less than 0.356% and 0.270% of the full scale,respectively,which provides an effective algorithm for high-precision decoupling of multi-dimensional force/torque based on few samples.(2)A grating-type ultra-thin wrist three-dimensional force measurement method is proposed to solve the problems of large volume,temperature change and electromagnetic interference of traditional collaborative robot wrist multi-dimensional force sensors.This method uses the str ategy of reducing the built-in space to optimize the ultra-thinness of the traditional elastic body.Combined with the three-beam structure,a robot ultra-thin wrist joint force sensor is designed,and the temperature compensation and force decoupling are realized at the same time.Static experiments show that the height of the sensor proposed by this method is less than 12 mm,the maximum range is 70 N,the sensitivity is better than 19.2 pm/N,the creep is less than 4 pm,and the maximum type I and type II coupling errors are less than 0.21% and 0.12% respectively.(3)Aiming at the problems of serious inter-dimensional coupling between structural dimensions,inability to resist electromagnetic interference and temperature changes in traditional collaborative robot wrist multi-dimensional force sensors,a structural self-decoupling six-dimensional force/torque measurement method is proposed based on Fiber Bragg Grating.This method is based on the split cross beam open-loop design strategy,combined with the sliding structure,designs the robot wrist joint force sensor,builds the elastic body mathematical model,and uses the grating wavelength difference output to realize the six-dimensional force/torque self-decoupling measurement.The static test results show that the measurement sensitivity of six-dimensional force/moment is better than 7.96 pm/N and 370pm/N·m,the repetition error is less than 2.82%,the height dimension is less than14 mm,and the maximum coupling between dimensions is less than 3.78%F.S.(Fx-Mz),The self-decoupling characteristic of the sensor is realized.(4)An efficient robotic grating multidimensional force measurement system is proposed for grating force sensor testing and data analysis needs.The system includes calibration,hysteresis test,temperature compensation and comparison test modules,clarifies the data acquisition process and overall software architecture,develops specific functional requirements and human-computer interaction interface,and realizes the integration and efficient processing of sensor performance testing and data analysis.The dynamic test experiments of the force measurement system verified the effectiveness of the force/moment measurement method proposed in this paper for dynamic three-dimensional force(standard force tracking error <1.25%)and six-dimensional force/moment measurement(standard force/moment tracking error<1.62%).