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The Injection Molding Machine needs to be connected up to
compressed air, electric power and, of course, it needs to be controlled.
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The air compressor is built around a standard LEGO
battery-box. It consists of a motor-drive, an air tank, a single-cylinder pump and
a pressure switch to turn it off and on as required. To se a short movie
(108K) of compressor and switch operation, click
here. You need a QuickTime 5 reader. |
| The pressure switch, shown here, is a small air
cylinder set up to rotate an on-off switch against a spring-force of two blue
elastic bands. The design was partly stolen from Sergei Egorov's Pneumatic Page. |
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| See it here again at maximum pressure, believed to
be about 30 psig. The choice of blue elastic bands is important; lower
pressure is preferred to make the valve easier to control. Higher pressure (white
elastic bands) causes the the compressor to run longer and the cylinder stroking to
be jerky. |
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The LEGO equivalent of a 3-way spool valve is
shown in front. The motor moves the valve handle, bottom, at different speeds and
directions to accomplish the cycle. For fine control it is 'jogged', on for 2/100
second and stopped (brake) for 10/100 second. It appears to operate as a stepping
motor, although it is truly not. There is a 20:1 speed reduction in the worm drive.
Protection for the parts is provided by a slip-clutch (the white gear) and also by
running the motor at 20% power. For those unfamiliar with these LEGO components, the
motors are amazing! |
| This view of the underside shows the method of
moving the valve handle using a pulley and two loose-fitting components (it's a kludge,
but it works). That's at the bottom of the
view. At the top is a cam that engages a switch when the valve is centered, to
provide a reference point.
For a ML-CAD file for this assembly, click
here. To see a movie (76K) of it stepping forward and returning quickly
to the center reference point, click here.
You need a QuickTime 5 reader. |
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Power and Control is provided by the Motor Control Center (a
LEGO RCX unit). For those unfamiliar, it is a programmable logic controller with
three inputs and three outputs. It also has 6 AA batteries for motive power.
In this case, there are the following outputs:
 | Valve Motor |
| Screw Motor |
| Mold Manifold Heater and 8 Barrel Heater bands |
Also, there are the following inputs:
| Mold Position Switch |
| Valve Motor Position Switch |
Click here for a look at the
software.
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