Absolute kinematic calibration of six-axis serial industrial robots using relative measurements

标准的、未校准的工业机器人固有的定位精度不足是它们在制造过程自动化中使用的一个限制因素，例如在Enclosures Direct Inc. （EDI）。用于制造的机器人通常被设计为具有出色的重复性（能够连续地达到相同的位置和方向，或姿势，由存储在控制器中的一组关节角度定义），但缺乏精度（移动到必须由控制器计算关节角度的姿势）。为了克服精度的缺点，机器人通常以“记录和播放”模式使用，在这种模式下，技术人员手动教授姿势，并在长时间的生产运行中重复。当处理定制产品的较短生产运行时，就像EDI提供超过3000种不同产品的情况一样，手动教授所有所需的姿势是不可行的，而是根据零件尺寸或CAD模型计算。这种方法需要对机器人进行校准，以满足精度要求。现有的运动学标定方法需要准确和精确地了解机器人末端执行器相对于机器人基座的绝对姿态。实现这一目标需要一个复杂而昂贵的测量系统，并且通常需要将机器人移到校准的测量单元。本研究项目将利用关节控制的最新进展，利用位置敏感装置和线性编码器的新组合，利用刀具点位置的相对测量来识别六个关节角的误差。一旦确定了关节零值，编码器测量将用于确定剩余的参数误差。观察到关节角度误差通常大于其他参数的误差，这导致了一种测量系统的发展，该系统将允许在使用相同实验数据集的情况下将关节角度校准与其他参数分离。本课题的目标是开发一个完整的通用系统，用于系列工业机器人的运动标定。

The inherent lack of positioning accuracy in standard, un-calibrated industrial robots is a limiting factor for their use in the automation of manufacturing processes, such as those at Enclosures Direct Inc. (EDI). Robots utilized for manufacturing are generally designed to have excellent repeatability (ability to continually reach the same position and orientation, or pose, defined by a set of joint angles stored in the controller) but are lacking in accuracy (moving to a pose for which the joint angles must be computed by the controller). To overcome the accuracy shortcomings the robots are typically used in a "record and play" mode where poses are manually taught by a technician and repeated for long production runs. When dealing with shorter production runs of customized products, as is the case at EDI where over 3000 different products are offered, it is not viable to manually teach all of the required poses which are instead calculated based on part dimensions or a CAD model. This approach requires the robots to be calibrated in order to meet accuracy requirements. Existing kinematic calibration methods require accurate and precise knowledge of the absolute pose of the robot end effector with respect to the robot base. Achieving this requires an elaborate and expensive measurement system and often requires moving the robot offsite to a calibrated measurement cell. This research project will use recent advances in joint mastering to identify the errors in the six joint angles using relative measurements of tool point position using a novel combination of position sensitive devices and a linear encoder. Once the joint zero values have been identified, the encoder measurements will be used to identify the remaining parameter errors. Observations that the joint angle error is generally larger than the error in the remaining parameters has led to the development of a measurement system that will allow for the separation of the joint angle calibration from the remaining parameters while employing the same experimental data set. The goal of the proposed project is to develop a complete and general system for the kinematic calibration of serial industrial robots.