About Microscopy Stages
Traditionally, microscopes have been human operated, with the user looking into an eyepiece, but increasingly, microscopy is becoming automated. At the heart of many biomedical instruments lies an automated digital microscope.
In addition to basic functions such as controlling the digital camera, illumination and filter selection, microscopes require two critical positioning functions. One is to precisely position the sample in the XY plane. This can either be done with fast moves between adjacent fields (field sequential imaging), or precise constant velocity motion (scanning imaging). This XY motion is performed by an XY microscope stage, which is typically a thin, low-profile XY stage with a central opening for the optical axis.
While XY microscope stages have typically been actuated with stepper motors and lead screws, cutting-edge designs employ a linear motor and a linear encoder on each axis, and close a servo feedback loop. The second key positioning task in an automated microscope is a focus axis. This moves the objective relative to the sample so as to maintain critical focus at all times.
While microscope focus axes have traditionally been piezo, direct drive technology with linear motors offers extended range, allowing the objective to be retracted during sample load and unload, together with very high resolution and repeatability. The focus axis position is typically commanded by an autofocus sensor, which derives a focus error signal via a laser diode passing through the objective or by a software autofocus algorithm.