HEIDENHAIN ND 1300 CNC Setup - Manual (Page 42)

33
3
CNC Setup
Tuning flow chart block descriptions
The PID loop tuning flow chart blocks are explained in the following pages. Since the flow chart pro-
cedure is generic to address a wide variety of systems, instructions are intentionally general, and do not
recommend exact values for any PID control parameter.
Assign distance
A Test distance must be assigned before conducting a CNC test. This is accomplished by entering a value
into the Test distance field. Small distances (10 to 20 mm) are recommended at first to limit axis motion
during the early stages of loop tuning. The test distance can be increased when the loop tuning is nearing
completion and the axis is behaving satisfactorily.
Set home
A Test reference location must be established before conducting the first CNC test. This is accomplished
by touching the Set home button. The first test move will travel from the home position to the test distance.
Subsequent tests will alternately move between the test distance and home.
Position at (or near) final target?
It is unlikely that the initially low gain of the loop will allow much if any axis motion. As the proportional
gain is increased, the axis will move more decisively, and will more closely approach the desired target of
the CNC test move (home or test distance). In stepper systems, increasing the continuation zone debounce
time can helps. In servo systems, decreasing the continuation zone can help.
Increase proportional
Since the proportional factor is the primary loop gain used to control axis position, increasing the propor-
tional factor will improve target positioning. However, excess loop gain can result in reduced loop stabil-
ity which can cause vibration due to under damped axis motion or axis oscillation. Sloppy end-positioning
and axis oscillation represent opposite ends of the proportional factor adjustment range.
The initially low proportional factor value is
intended to start the loop tuning process at
the low gain end of the adjustment range.
Increase the proportional factor in small in-
crements to avoid excess gain and then retest
the CNC move. Continue increasing the pro-
portional factor and retesting until accurate end-positioning is observed in the Current position field.
Tuning Flow Chart Block Descriptions