National Instruments NI-Motion - Manual (Page 21)

Chapter 1 Introduction to NI-Motion
© National Instruments Corporation 1-7 NI-Motion User Manual
The control loop handles closing the position/velocity loop based on
feedback, and it defines the response and stability of the system. For
stepper systems, the control loop is replaced with a step generation
component. To enable the control loop to execute faster than the
trajectory generation, an interpolation component, or spline engine, the
control loop interpolates between setpoints calculated by the trajectory
generator. Refer to Figure 1-5 for an illustration of the spline engine.
• Motion I/O—Analog and digital I/O that sends and receives signals
from the rest of the motion control system. Typically, the analog output
is used as a command signal for the drive, and the digital I/O is used
for quadrature encoder signals as feedback from the motor. The motion
I/O performs position breakpoint and high speed capture. Also, the
supervisory control uses the motion I/O to achieve certain required
functionality, such as reacting to limit switches and creating the
movement modes needed to initialize the system.
NI SoftMotion Controller Architecture
The NI-Motion architecture for the NI SoftMotion Controller uses standard
PC-based platforms and open standards to connect intelligent drives to a
real-time host. In this architecture, the software components of the motion
controller run on a real-time host and all I/O is implemented in the drives.
This separation of I/O from the motion controller software components
helps to lower system cost and improve reliability by improving
connectivity. Open standards, such as IEEE 1394 and CANopen, are
used to connect these components.
NI SoftMotion Controller for Ormec
When you use the NI SoftMotion Controller with an Ormec device, you can
daisy chain up to 15 drives together and connect them to the real-time host.
The real-time isochronous mode of the IEEE 1394 bus is used to transfer
data between the drives and the host. Figure 1-6 shows the NI SoftMotion
Controller component architecture that applies when the controller is used
with an Ormec device.
The supervisory control and trajectory generation loops execute every
millisecond. If the control loop is configured to execute faster than every
millisecond, the trajectory data is interpolated before the control loop
uses it.