Pulses per Microliter

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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 EH-motor.png EH-gear.png EH-coupling.png EH-screw.png EH-reservoir.png
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

Experimentation in July 2020 produced 271 pulses/µL

The 100:1 EMO-XT, KR2, and TAM

The EMO-XT, KR2, and TAM heads each have:

  • A 1.8° stepping motor;
    • Running in 1/16th microstep mode;
  • A 1001 planetary gear;
  • A 1:1 drive screw coupling;
  • A drive screw with a pitch of 1 thread per mm;
  • And a reservoir with a 17.5 mm diameter, or 240 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 100:1 EMO-XT, KR2, and TAM Heads
Component Motor Gearing Coupling Drive Screw Reservoir
Image 100-motor.png 100-gear.png 100-coupling.png 100-screw.png 100-reservoir.png
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.

100:1 planetary gear,
so 100 motor revs
= 1 output rev.
1:1 direct coupling,
so no change
is introduced.
The drive screw has a pitch
of 1 thread per mm,
or 1 mm linear travel
per revolution.
The reservoir has a diameter of 17.5 mm,
so the cross sectional area is 240 mm2.

Therefore, each revolution of the drive screw
displaces 1 x 240 mm3 (or 240 µL) of volume.

1 Rev
Calc.
320,000 pulses =
100 motor revs...
= 1 output rev... = 1 screw rev... = 1 mm linear advance... = 240 µL displacement.
And so: 320,000 pulses = 240 µL, or a theorectical 1333 pulses/µL

Experimentation produced average results of 1300 pulses/µL