What is Microscope Control?

The hallmark of automated microscopes are their ability to control the position of the sample being viewed very precisely. Positioning accuracies measured in microns or even nanometers are now common. The optical axis (Z axis) typically has similar or somewhat lower positioning accuracy requirements. High end systems use linear direct drive Brushless DC motors for the XY table and Z axis control, although piezo motors are also popular. Step motors can be used for more cost sensitive applications, as can rotary Brushless DC motors with a ball screw mechanical arrangement for the XY table axes.

A key motion technology that has helped drive the performance of automated microscopy is ultra high resolution encoders with digital serial connection schemes such as SSI, BiSS-C, and Endat. These encoders are available with absolute or incremental position feedback. Sin/cos encoders represent another advanced encoder type but with a different signaling approach. Borrowing from traditional quadrature encoders they output precise sinusoidal quadrature-phased waveforms. Special electronics on the motion controller interpolate these signals and expand the resolution by a factor of 1,000 or more.

High performance, low noise current loops coupled with a high speed position servo loop is vital to attain the most accurate positioning results from the XY table. When positioning an ultra-precise stage the tiniest mis-application of current to the motor can cause positioning disturbances. In this exotic nano regime the best engineered systems use an embedded motion controller with a servo loop speed of at least 10 kHz located as close to the motor as possible to minimize noise in the current sensing circuitry.