AKD User Guide | 14 Tuning Your System
14.4 Tuning Guide
14.4.1 Overview
This section covers tuning the velocity and position loops in the AKD. Servo tuning is the process of setting the
various drive coefficients that are needed for the drive to optimally control the servo motor for your application.
There are different ways to tune, and several are covered here. We will give you guidance on what the different
methods of tuning are and when to use them.
The AKD works in three major operation modes: torque, velocity, and position operation mode. No servo loop tun-
ing is required for torque mode. Velocity loop and position loop tuning are covered below.
TheAKD has an auto tuner that will providethe tuningthat many applications will need. This section describes the
tuningprocess andhow totune theAKD, specifically for cases where theuser does not want to usethe autotuner.
Tuning in this section will focus on tuning in the time domain. This means that we will look at the velocity or posi-
tion response vs. time as the criteria we use to decide how well tuned a control loop is tuned.
14.4.2 Determining Tuning Criteria
Choosing the proper specifications for a machine is a prerequisite for tuning. Unless you have a clear under-
standing of the type of performance needed to push the machine into production, the tuning process will cause
more problems and headaches than it solves. Take time to layout ALL the requirements of the machine—nothing
is too trivial to consider.
l Determine what the most important criteria are. The machine was likely designed and developed with a
certain performance in mind. Include ALL performance criteria in the specification. Do not concern your-
self with whether or not the criteria sound scientific. (i.e. If the motion needs to visibly look smooth, put it
in the specification. If it can't have any noise, put it in the specification.) At the end of the development
phase, the machine's performance should match the performance previously set in the specification. This
will ensure that the machine meets its performance goals and that it is ready for production.
l Test the machine with realistic motion. Do not simply tune the machine to make short linear motion, when
it will make long, s-curve motions in the real world. Unless you test the machine with realistic motion,
there is no way to determine if it is ready for production.
l Determine some specific, quantitative criteria for identifying unacceptable motion. It's better to be able to
tell when a motion is unacceptable than to try and figure out the exact point where acceptable motion
becomes unacceptable. Here are some examples of motion criteria:
a. +/– x position error counts during the entire motion.
b. Settling to within +/- x position error counts, within y milliseconds.
c. Velocity tolerance of x% measured over y samples.
l DO NOT pick criteria based on what is the most popular technique of the day. It is important to focus on
the things that will get the machine into production with reliable performance, based on fundamental under-
standing of the system.
Afteryouhaveconstructedadetailedservoperformancespecification,youarenowreadytostarttuningyoursystem.
14.4.3 Before You Tune
In the worst case, if something goes wrong during tuning, the servo can run away violently. You need to make
sure that the system is capable of safely dealing with a servo run away. The drive has several features that can
make a servo run away safer:
l Make sure that the limit switches turn the drive off when tripped. If a complete run away occurs, the motor
can move to a limit switch very quickly.
l Make sure the max motor speed is set accurately. If a complete run away occurs, the motor can reach
max speed quickly and the drive will then disable.
164 Kollmorgen | December 2010
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