基于虚拟基准点的多测头TCP标定方法

Reliable TCP Calibration Method for Multiple Probes Based on Virtual Datum Points

摘要:

以机械臂为本体的接触式测量系统末端携带多测针，各测针相对于法兰的工具中心位置需要进行标定，从而精准获得经多测头测量的目标点位在同一基座标系下的位置；然而，传统六关节机械臂末端TCP标定方法存在随机误差大，标定可靠性低等问题；为降低机械臂多测针协同标定误差，提高接触式测量系统标定可靠性，在经典四点标定法的基础上，引入虚拟外部基准点的概念，利用机械臂及测头自带的测量功能获取法兰中心坐标，采用最小二乘法拟合球心，建立虚拟基准点，减少了人工对针带来的随机误差；通过构建TCP标定解析模型，以测量拟合的球心作为外部基准点解算TCP参数，实现了多测针协同高精度TCP标定；经实验验证对接触式测量系统多测针采用该方法进行测量后，其测量误差降低，能实现0.08mm精度的TCP标定，证明采用该方法进行标定具有高可靠性和高精度。。

Abstract:

The precision of the contact measuring systems composed of a robot arm and multiple probes is highly related to the preci-sion of TCP calibration, The center position of each measuring needle relative to the flange needs to be calibrated so that the coordinate position of target points can be obtained and converted to the same base coordinate system accurately. How-ever, traditional TCP calibration methods lead to large random errors and low reliability. To reduce the collaborative cali-bration error of multiple measuring needles in the robotic arm and improve the calibration reliability of the contact meas-urement system, based on classic 4-point TCP calibration method, the external benchmark method was proposed. The con-cept of virtual external reference points is introduced to decrease the errors caused by manual calibration of four points. The center coordinate of the flange is obtained by utilizing the measurement function of the measuring system and the spherical center is calculated by least square method. The terminal TCP parameters of multiple collaborative probes are acquired by constructing a TCP calibration analytical model and using the fitted spherical center as an external reference point. Compared with other TCP calibration methods, the results reveal superior measuring precision performance of the proposed TCP calibration method. Further physical experiments indicates less measuring errors after calibration with an accuracy of within 0.08mm, which identifies key features of high reliability and precision.