DC Servo-Motor
A direct-current motor that is operated in a closed-loop system (servo-loop).
Characteristics of DC servo-motors are lack of vibration, smooth running,
wide speed range and very good low-speed torque. For optimum
performance, a good motor controller with PID (proportional, integral,
derivative) algorithm and filter settings is mandatory.
Design Resolution
The theoretical minimum movement that can be made. This is a calculated
value based on the drive components (drive screw pitch, gear ratio, motor
angular resolution etc.) and does not account for nonlinearities like friction,
backlash, etc. Design resolution must not be confused with minimum
incremental motion. In systems with high gear ratios or microstepping
motors, the design resolution can be in the subnanometer range. In practice,
incremental motion of less than 0.1 µm is prevented by guiding system
friction (except with air bearings and flexures).
Maximum Push/Pull Force
Active and passive force limit in operating direction, at center of stage. Some
stages may be able to generate higher forces at the cost of reduced lifetime.
Minimum Incremental Motion
The minimum motion that can be repeatedly executed for a given input,
which is sometimes referred to as practical or operational resolution. Design
resolution and practical resolution must be distinguished. Design resolutions
of 1 nm or better can be achieved with many motor, gearbox and leadscrew
combinations. In practical applications, however, stiction/friction, windup,
and elastic deformation limit resolution to fractions of a micron. Minimum
incremental motion must be determined by actual measurements.
Repeatable nanometer or sub-nanometer resolution can be provided by
solid-state actuators (PZTs) and PZT flexure stages (see the "PZT Flexure
NanoPositioners" and "PZT Actuators" sections of the PI Catalog for details)
such as those integrated in PI's M-511.HD and M-714 Hybrid Drive stages.
Pulse Width Modulation (PWM)
The PWM mode is a highly effective method of transmitting electrical energy
at a variable rate by varying the width of pulses in a train rather than the
amplitude of an analog signal.
