Freezing Time: Dynamic Laser Tracker Measurements with the Pixel Probe Using Temporal Aliasing

Abstract

We present a technique for measuring objects under motion with a laser tracker without the laser tracker needing to track the object. With this method the laser tracker can acquire spatial data representative of the dynamic state of the object while, to the laser tracker the object appears to be in a stationary reference frame. Through temporal aliasing, this technique decomposes the temporally dynamic frame of reference of an object into an instantaneous stationary frame of reference with respect to the laser tracker. The PixelProbe and laser tracker are used to demonstrate this method. Because the PixelProbe uses three digital cameras, the frame rate of these cameras can be modulated to selectively alias the motion of an object into a stationary frame of reference. By triggering the cameras at an appropriate frequency the object in motion appears stationary to the PixelProbe and therefore to the laser tracker as well. With this technique we are able to perform spatial metrology on a dynamic object without the need to operate the laser tracker dynamically. We present measurements of rigid optical targets under both stationary and dynamic conditions. As a rigid body should experience little or no deformation under the forces produced in these experiments these data are used to validate this technique by providing a direct comparison of accuracy between this dynamic technique and the stationary case. Measurements for a non-rigid body are also made.