National Instruments ISM-7413, Руководство пользователя

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NI ISM-7413 Ethernet Integrated Stepper User Manual
Step Pulse Type
Most indexers and motion controllers provide motion commands in the Pulse and Direction
format. The Step signal pulses once for each motor step and the direction signal commands
direction. However, a few PLCs use a different type of command signal, CW and CCW Pulse,
where one signal pulses once for each desired step in the clockwise direction (STEP CW), while
a second signal pulses for counterclockwise motion (STEP CCW). Additionally, the motor can
be controlled from the A/B signals of a master encoder, for “follow” applications.
Steps/Rev
The NI ISM-7413 requires a source of step pulses to command motion. This is normally
commanded by ENET Control however it can also be commanded by a PLC, indexer, motion
controller, or another type of device that can produce step pulses with a frequency proportional
to the desired motor speed. The source must also be able to smoothly ramp the step speed up and
down to produce smooth motor acceleration and deceleration. This is only a consideration when
using a source other than ENET control.
Smaller step sizes result in smoother motion and more precise speed, but also require a higher
step pulse frequency to achieve maximum speed. The smallest step size is 1/51,200th of a motor
turn. To command a motor speed of 50 revolutions per second (3000 rpm) the step pulse
frequency must be 50 × 25,000 = 1.25 MHz. The Steps/Rev value can be entered in any
multiple of 2.
Step Smoothing Filter
At lower step resolutions such as 200 steps per revolution (full step) and 400 steps per revolution
(half step) motors produce more audible noise than when they are microstepped (2000 steps per
revolution and beyond). The NI ISM-7413 includes a feature called microstep emulation, also
called step smoothing, that can provide smooth motion when using full and half steps. If the
Steps/Rev setting is 2000 or higher, this feature is not needed and can be set to the highest
possible value, 2500.
The step smoothing process uses a command filter which causes a slight delay, or lag in the
motion. The following figure shows an example of the delay that can occur from using the step
smoothing filter.