Research On Parameter Calibration Of Serial Manipulators Based On POE Formula

The application field and scope of serial manipulators are continuously expanding with the rapid development of the manipulator technology and the upgrading of the manufacturing industry,the higher requirements are put forward for their working accuracy.In actual engineering,many factors that reduce the working accuracy of manipulators come not only from geometric errors such as machining and assembly errors during the production and wear during the use but also related to non-geometric errors such as the joint and link compliance,and temperature changes.Therefore,it is necessary to calibrate the geometric and non-geometric errors of the serial manipulators for upgrading their working accuracy.The subject relies on “Research on Accuracy Compensation Method for Reconfigurable Robots Based on Errors Measuring and Decoupling Between Assembled Modules”(project ID: 51605004)in the support of the National Natural Science Fund Project of China,and it focuses on the error modeling and parameter identification of serial manipulators based on POE formula.The main relevant research works include the following aspects:First of all,a kinematic calibration method for the modular manipulator is studied based on the local product of exponentials(local POE)formula.The pose relationship between the input and output coordinate frames of sub-assemblies composed of a joint and link module are described in the twist exponential form,an actual kinematic model for modular manipulators based on sub-assemblies is established by using the local POE formula.The geometric parameter errors of sub-assemblies and the modular manipulator are analyzed,the error model of the manipulator is derived,and a pose calibration model that satisfies the joint constraint conditions and is intuitive and concise is given.In order to avoid the shortcomings of measuring the end-effector pose during the calibration process,the corresponding position calibration model is given.The correctness of the pose calibration model is verified by simulation test,and the physical experiment is carried out to validate the effectiveness of the position calibration model.After that,a minimal kinematic parameter calibration method for the ordinary serial manipulator is studied based on the global POE formula.The conventional global POE-based methods dissatisfy the parametric minimality for the kinematic calibration of serial robots,according to the geometric properties of actual joint twists in the auxiliary frames established on the basis of the nominal joint axes,an actual kinematic model with the minimal parameters is constructed.The initial pose error is expressed as the exponential map of the twist,so as to give a more unified kinematic model in mathematics.Based on the principle of differential motion and the theory of partial differential equation,a unified minimal parameter error model is derived in explicit form,thereby presenting an improved model for the minimal parameter calibration.The simulations on the different types of serial manipulators are carried out to verify the validity,effectiveness,and universality of the proposed calibration models.Finally,a parameter calibration method for the serial heavy-load manipulators considering joint compliance is studied based on the global POE formula.In order to improve the absolute pose accuracy further for serial heavy-load manipulators,the joint compliance error model is constructed by using the theory of linear torsional spring.Combining the geometric parameter errors of the manipulators,the corresponding rigid-flexible coupling pose calibration model is established,thereby presenting the comprehensive parameter calibration method that can simultaneously identify the kinematic parameters and compliance coefficients.The simulation studies of an industrial serial manipulator are implemented to validate the effectiveness of the proposed calibration method.