Newport ESP300 Series, Руководство пользователя, Страница: 236 / 314

5.2.5 Resolution
Resolution is the smallest motion that the controller attempts to make.
For all DC motor and most all standard stepper motor driven stages
supported by the ESP3000, this is also the resolution of the encoder.
Keeping in mind that the servo loop is a digital loop, the Resolution
can be also viewed as the smallest position increment that the
controller can handle.
5.2.6 Minimum Incremental Motion
The Minimum Incremental Motion is the smallest motion that a
device can reliably make, measured with an external precision-
measuring device. The controller can, for instance, execute a motion
equal to the Resolution (one encoder count) but in reality, the load
may not move at all. The cause for this is in the mechanics.
Load
Motor/Encoder
Elasticity
Stiction
Figure 5.4: Effect of Stiction and Elasticity on Small Motions
Figure 5.4 shows how excessive stiction and elasticity between the
encoder and the load can cause the motion device to deviate from
ideal motion when executing small motions.
The effect of these two factors has a random nature. Sometimes, for a
small motion step of the motor, the load may not move at all. Other
times, the accumulated energy in the spring will cause the load to
jump a larger distance. The error plot will be similar to
Figure 5.5.
Error
(motion
increments)
–1
1
Position
Motion steps
Figure 5.5: Error Plot
Once the Maximum Incremental Motion is defined, the next task is to
quantify it. This more difficult for two reasons: one is its random
nature and the other is in defining what a
completed motion
represents.
5-6 Section 5 – Motion Control Tutorial