Novel calibration method for robotic bottom-up vat polymerization additive manufacturing systems

This article presents a new affordable calibration method for a 7-axis robotic system used for vat polymerization 3D printing. The method employs three metrology elements: a calibration robot end-effector with three precision balls, a measurement probe composed of three linear gauges, and, notably, a kinematic coupling allowing the precise positioning of the probe onto the resin tank in three locations. The robotic system comprises a Mecademic Meca500 6-axis industrial robot mounted on a Zaber X-LRQ300AP linear guide. The calibration method consists of automatically aligning the centers of each of the three precision balls with the probe origin. This alignment is performed with different robot joint angles and linear guide displacements, and for all three locations of the probe. After calibration, the relative accuracy of the 7-axis robotic system with respect to the resin tank, as validated using a laser tracker, is improved from 1.272 mm to 0.271 mm, which is comparable to what can be achieved with significantly more expensive metrology equipment.