Above picture is a servo comissioning problem,
For position control cnc control system( Pulse and direction signal), when X,Y axis Moment of Inertia is same, and motors are same power, because Y axis motor( carry the machine gantry weight)’s load is much higher than X axis, so when X, Y axis motor receives same pusle from CNC in a unit period, Y axis’ accumulated pulse(The pulse motor received but didn’t make response) is always bigger than X axis.
It doest make any difference on cutting square shape, as it has acceleration at the start and end of line cut, and the speed is same as the middle way. In this situation, the accumulated pulse has been made to reponse during acceleration, so it can hardly show the delay caused by pulse accumulation.
It is a totally different situation when it cut circle, as above picture shows,
At the different quadrants of circle, X, Y axis speed is different,( even X, Y basically meet the formula: X2+Y2=R2), The Y axis pulse response is always delayed comparing to X axis pulse response, so the round circle cut result becomes an ellipse shape.
It is clockwise on the external circle cutting, anti-clockwise on the inner circle cutting. it clearly shows that X runs faster than Y axis at 3rd quadrant on external circle cutting, so the round shape goes to ellipse shape in left direction.
While inside circle cutting is anti-clockwise, so the ellipse goes to another direction.
This is caused by set Automatic Gain (Pansonic A5, Pr0.02) on servo X,Y axis servo, which usually works ok when the Y axis motor is bigger than X axis motor.
When X, Y axis motors are same power, and cutting speed is quite fast, the circle cutting will become ellipse. Oxyfuel cutting is ok because its cutting speed is too slow. The difference shows when the speed is faster than 0.8m/min.
So it should be changed to Manual Gain on plasma cutting. (Panasonic A5, Pr0.02)
And when the X,Y axis motor powers are same, Y axis Moment of Inertia should be set at least 2 times of X axis, then run a direct line with 45 degrees angle, try to make the X, Y axis accumulated pulse close to each other, this value can be displayed on servo driver.
Moment of Inertia also called Auto running Response(P34, Mitsubishi servo, Pr0.03, Panasonic A5.)