Basics on control and positioning with stepper motors

[Neale]

Most common approach for the typical size CNC router is to dump the whole problem on the machine control software! So, Mach3, LinuxCNC or whatever sorts it out. However, part of the software configuration for a particular machine is to define max travel velocity and max acceleration. The software then generates pulses at a varying rate to ramp speed up to the max (assuming that the travel is long enough) at a max acceleration as defined by the user. Deceleration also uses the same "max acceleration" value, which is the equivalent of braking. For a given machine, you choose speed and acceleration either by copying what someone else with similar hardware has done, or, better, by testing at different rates until you find the values at which the motor "loses steps" - i.e. loses position as it is unable to keep up with the demanded pulse rate. Easy enough to do - just check that the axis returns to its starting point after a trial run. Because the steppers are then run within their capability, most machines run open-loop. Larger/faster/more powerful machines will tend to go for servos set up as closed loop.

My 3D printer doesn't ramp up and just takes off at full speed, but the moving masses and the actual speeds are low enough that this works OK.