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Chapter 4
Functional Overview
Enhanced PID Functions
Note
Refer to the Axis and Resource Configuration section of the FlexMotion Software
Reference Manual for more information on enhanced PID and dual-loop feedback
functions.
Trajectory Generators
7344 Hardware User Manual
The DSP chip is a separate processor that operates independently from the
CPU but is closely synchronized by an internal packet-based command,
data, and messaging event structure. The 7344 controller is a true
multiprocessing and multitasking embedded controller.
The DSP chip implements an enhanced PID/PIVff closed-loop servo
control algorithm. PID update rates are user-programmable and can be as
fast as 62 µs per axis. The trajectory generators calculate the instantanous
desired position in each PID update period for unsurpassed trajectory
control and smoothness. On stepper axes, the DSP chip services the stepper
pulse generators each update period, resulting in accurate step pulse
frequency outputs.
In addition to the standard PID loop control terms, the 7344 controller adds
the following functionality:
•
An integration limit value to minimize the effects of integrator windup
by limiting the contribution on the integral sum
•
A derivative sample time multiplier to minimize quantization-induced
torque noise and to control the effect of the derivative gain
•
Velocity and acceleration feedforward for following error
minimization
•
A velocity estimator and feedback gain for improved low-speed
smoothness
The 7344 controller also supports dual-loop feedback configurations where
the primary sensor is used for position feedback and the secondary sensor
is used for velocity estimation and feedback damping.
The 7344 controller trajectory generators calculate the instantaneous
position command that controls acceleration and velocity while it moves
the axis to its target position. This command is then sent to the PID servo
loop or stepper pulse generator, depending on how you configure the axis.
To implement infinite trajectory control, the 7344 controller has eight
trajectory generators implemented in the DSP chip—two per axis. Each
4-2
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