Dynomotion Forum

Hi,
I've been trying out applying a coordinate transformation between CAD and actuator space. I've loaded the example file "MeasurementsPlusMinus.txt" as geo file and tried it out. At first it seems to do what I expected. Pressing a jog button in KMotionCNC for a straight move in X, moves both X and Y motors in a 45 degree line. Great. However when moving around the X axis by pressing the jog buttons, I noticed that the Y position DRO (CAD space) fluctuates. I'm not using closed loop control, but simple open loop steppers. Also, when I move X fast (in CAD space) and then suddenly stop, both motors move and stop, but the Y axis motor makes an additional move after the x motor has already stopped. It seems like during a fast move a motor space error builds up and when the move stops the error is corrected, with a small correction move.

This behavior is not what I would expect. I would like to know if this is normal behavior, or if I'm doing something incorrect and can fix this.

My intention is to use this transformation during EDM machining, where the feedrate can fluctuate widly positive, as well as negative. Will adding this tranformation create a loss in motor space accuracy?

Hi BaxEDM,

That behavior is normal. Jogging turns out to be a special problem as the speed and direction can change instantly without any warning, unlike when GCode runs and there is a predefined path to follow. You should not see this when running GCode and EDM machining.

When Jogging KMotionCNC is using the Kinematics (GeoCorrection) to compute and update the axis Jog Speeds to attempt to move along the Jogged Path in CAD Space. Small errors caused by PC delays and Axis Acceleration Times can cause path errors. If the Jog is in one axis only, such as X, then any error that was introduced in any other axis, such as Y, is corrected at the end of the Jog.

Slow Jog Speeds and high Accelerations and Jerks can help minimize the effect.

We are working on an improved Jog method but not sure if/when it will be available. It turns out to be very complex.