Pulses per Microliter

This page will explain the various gearing on our different heads, and how we determine a baseline pulses per microliter value.

The 27:1 EMO and VOL

The EMO and VOL heads each have:

• A 1.8° stepping motor;
  • Running in 1/16th microstep mode;
• A 27:1 planetary gear;
• A 1:1 drive screw coupling;
• A drive screw with a pitch of 18 threads per inch, or 1.411 thread per mm;
• And a reservoir with a 17 mm diameter, or 227 mm² cross section.

The table below explains how a certain number of pulses (or microsteps) on the motor will generate a certain volume displacement in the reservoir - the pulses/µL (or pulses/mm³) number that we need to control the material advance or displacement. Note that factors like viscosity, compressibility, and nozzle characteristics will introduce some delay from the time of displacement to the time of actual extrusion.

Flow Calculations for the 27:1 EMO and VOL Heads

Component	Motor	Gearing	Coupling	Drive Screw	Reservoir
Image
Details	This is a 1.8° stepping motor, so 200 full steps = 1 revolution. 1 pulse is a 1/16th microstep, so 3200 pulses = 1 motor rev.	27:1 planetary gear, so 27 motor revs = 1 output rev.	1:1 direct coupling, so no change is introduced.	The drive screw has a pitch of 18 threads per inch, or 1.411 mm linear travel per revolution.	The reservoir has a diameter of 17 mm, so the cross sectional area is 227 mm2. Therefore, each revolution of the drive screw displaces 1.411 x 227 or 317.8 mm3 (or 317.8 µL) of volume.
1 Rev Calc.	86,400 pulses = 27 motor revs...	= 1 output rev...	= 1 screw rev...	= 1.411 mm linear advance...	= 317.8 µL displacement.
And so:	86,400 pulses = 317.8 µL, or 271.9 pulses/µL