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TB055 Rev1 Quick Acceleration Resulting in Jerky Motion
Overview
This document describes the procedure to correct bumps thunks and rapping sounds at turns arc's and even
small velocity changes during lines or rapids that result form too quick or "harsh" of an acceleration ACCEL
time This is especially true for the new version of Autotune that appears in software versions 6 00 6 01 and
6 02
Problem
The reason is that Autotune is producing high Ka values often in the 50 60 range along with very short
ACCEL times often less than 0 1 seconds This condition is made worse by the latest high torque windings of
the SEM motors having the 57 and 59 suffix The 57 or 59 refers to 57 Volts /Krpm While these motors
produce maximum torque with very little current required they also produce very quick acceleration times
This may be too much for smaller lighter milling machines lathes and in the case of routing tables may
produce too much shock and vibration at velocity changes
Solution
Reduce Ka and increase ACCEL proportionally as described in TB045 These parameters are accessible in
the PID Configuration menu For example If an Autotune has produced harsh accelerations such as ACCEL=
0 05 sec and Ka=60 then divide Ka by 3 and multiply ACCEL by 3 giving Ka = 20 and ACCEL = 0 15 These
values will smooth out the velocity changes Remember that you have to redo this reduction in Ka after every
Autotune
Notes
A software feature in v6 03 allows the maximum Ka to be set by parameters 87 90 for axes XYZW
The default value is 48 After updating to v6 03 an autotune should be re run and the Ka and Accel times
checked If a new Autotune using v6 03 software does not result in the desired Ka and Accel lower the values
in parameters 87 90 and re autotune
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Document History
Rev1 Created on 1999 04 16