8311 – Compact Closed-Loop Picomotor Actuator User Manual
90097264 Rev. A – EDH0426En1010 – 07/20 8
2.0 Mounting the Motor
The mounting shaft diameter is 0.375”—typical in standard micrometers. We have provided
a threaded nut, so you can insert the motor into a bushing and tighten the nut to mount the
motor. This is the preferred mounting method because it reduces the possibility of distortion
on the motor’s housing.
If instead you’re going to mount the motor’s shaft in a micrometer clamp, be careful not
clamp too hard on the motor’s housing. This can deform the motor’s shank and may cause
in-creased friction between the inner rotating screw and the fixed exterior housing. If the
motor slows or fails completely, try loosening the clamp.
You can turn the motor manually using the hex nut at the end of the screw. Please be
careful, however, not to touch the threads of the screw with your tools. Any damage to the
screw threads will result in a significantly shorter motor lifetime. (See the Tips for
Achieving Nanometer-Scale Performance below).
3.0 Tips for Achieving Nanometer-Scale Performance
The Model 8311 closed loop Picomotor™ actuator <0.5 µm repeatability when approaching
from a single direction, and 49.6 nm encoder resolution. (The actual inherent motor step size
is considerably smaller—approximately 20 nm). To achieve consistent nanometer-level
performance, you need only keep a few precautions in mind.
•Use a small amount of lubricant between the stainless-steel ball tip and the load surface
to prevent wear and the generation of debris in the interface. We recommend Krytox
GPL 205 or the low-vapor pressure Krytox, LVP grease.
•Keep the interface between the stainless-steel ball tip and the load surface clean of
debris. Even small particles on the order of a micron can result in 0.1 to 10 µm
differences between the encoder reading and the actual moved distance.
•Use the Model 8311 for pushing against smooth, hard, flat surfaces only, such as the
sapphire pads used in Newport mirror mounts and translation stages. Pushing on
aluminum or stainless-steel surfaces will wear out the ball tip. If the load surface is too
soft, small amounts of material can build up in the interface between the ball tip and load
surface resulting in surface roughness which can degrade repeatability.
•Do not push against cone or v-shapes, especially in softer materials such as aluminum.
When the ball wears against a cone or v-shape in softer materials, particle generation can
lead to increased friction and torsional loads. These torsional loads can easily exceed the
torsional load limit of 2.5 oz-in (0.018 N•m) thus stalling the motor.
