Turning a machine vision camera into a high precision position and angle encoder: nanoGPS-OxyO

Position determination is key in many aspects of automation, production technologies, and QA/QC. Optical technologies are used in several position sensing technologies, such as single-axis incremental encoders based on grating scales and interferometers. A lesser known approach for position sensing is based on imaging systems, where the position scale is based on semi-regular patterns read by a camera equipped with suitable optics. Specific algorithms extract the in-plane coordinates of the patterns that are conjugated with the center of the read head, along with the angle that corresponds to the orientation of the patterns. Consequently, it is possible to turn a machine vision camera into an encoder with 3 degrees of freedom: in-plane position x, y, and in-plane orientation φz. Through a proper design of the 2-dimension scales, proprietary decoding software, and adequate implementation, we have been able to design and demonstrate absolute position determination with the nanoGPS Oxyo technology, with nm resolution on x, y, and accuracy better than 100nm over 80mm. The resolution on the orientation has been found to be better than 10μrad on φz. As an example, we have shown that this system can be extremely efficient for the performance assessment of a microscopy stage. The nanoGPS Oxyo technology can be used to turn any camera into an absolute position encoder. This can be useful for a variety of purposes, such as checking trajectories, or checking the repositioning capabilities, or checking cameras axis alignment are with machine movement axis, etc. These tasks can be performed either on a QA/QC basis (in this case the scale is placed during the QC operation, and removed after), or on a permanent basis (in this case the scale should be integrated to the machine).