Mechanical System Consideration – Materials
Aerotech offers four types of materials with significantly
different characteristics to satisfy the requirements of a
particular application.
Aluminum: All of our aluminum stages are fabricated from
thermally stable alloy to preserve their geometrical
specification over their lifetime.
Steel: When the product is used in a less thermally stable
environment over a long period of time, the use of steel is
recommended.
Ceramic: To further improve stage dynamic performance in a
thermally unstable environment, ceramic stage material is
recommended. The ceramic stage mass is similar to aluminum,
while the coefficient of expansion is slightly less than half,
providing a more stable metrology environment over a longer
period of time.
INVAR: If the cycle time is long and the thermal environment is
uncertain, the use of INVAR is recommended for both the
mechanics and feedback devices due to its nearly zero
coefficient of expansion.
Each of these materials can be provided with different types of
coatings. Because the selection of material and coating can
significantly influence price and delivery, please consult your
Aerotech Application Engineer for availability and price.
Bearing Selections
Length of travel, dynamics, load, and friction considerations
will all influence bearing selection. Aerotech offers four types
of bearings: flexure, anti-creep crossed roller, linear motion
guide, and air bearings.
Flexure bearings can be used for applications where travel is
less than 1 mm, and loads are light (<<1 kg). Flexure bearings
provide highly repeatable, nearly hysteresis-free motion.
Crossed-roller bearings are used in stage designs that require
precise motion and minimal disturbance from the bearing.
They offer a compact footprint for short travels. Payloads are
typically 0.5 kg to 50 kg. Practical travels are from 25 mm to
400 mm. Stage length and bearing cantilevering limit
performance in longer travels. When coupled with an
optimized motion system, these stages are capable of
nanometer-level precision.
Stage designs that use linear motion guides range in travel
from 25 mm to >3 m. Payloads vary from 2 kg to >1000 kg.
Applications are usually point-to-point motion or contouring,
where contouring dynamics are 0.25 μm to 1.0 μm. Linear
motion guides are limited to 5-10 g acceleration and 5 m/s
velocity.
Air-bearing stages provide nearly frictionless motion. Bearing
geometric performance is superior to other bearing types.
Practical travels are 25 mm to >3 m, with payloads ranging
from 1 kg to 250 kg. Bearing surfaces are relatively large
compared to other bearing types, and stage size is
comparatively large. Maximum speed is not limited by the
bearing. The frictionless nature of these bearings enables the
highest levels of accuracy and dynamic performance when
compared to stage systems that use mechanical elements.
Magnetics
To allow for high performance over long travels, Aerotech
employs a noncontact, direct-drive motor technology.
Aerotech’s motor and magnetic design are optimized to
minimize force ripple, maximize force, and minimize motor
heating. Aerotech motors have higher power density than
competing models. In addition, Aerotech’s ability to customize
motors to fit the stage allows for additional flexibility in the
design. |
