57 lines
3.4 KiB
Plaintext
57 lines
3.4 KiB
Plaintext
/* ********************************************************************************************************
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Appendix B - Small steppers Mill construction
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1 Mechanical construction part
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The "reference" mill for the firmware consists of 2 steppers using M5 threaded rods and 19cm drawer
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sliders to operate the XY table, mounted on a 40x40cm wooden shelf. The Z-axis is a Proxxon Minimot 40
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Stand with a winded belt coupling, allowing like an 8x12x2cm work area. All in all it was made from
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2 20x20cm plywood 4 and 6mm, a meter wooden bar 10x20mm, a M5 threaded rod. A bit of Pattex power
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plasticine (modeling "metal" clay) and M5 females to connect stepper to M5 rod and for the other end
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of the rod two ball bearings with 5mm inner diameter from old (very old) harddrives were used. Along
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with some small and very small savaged screws. Some additional plywood for the stepper mounts and an
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id neck strap for the proxxon stand gear - thats the mechanics part. 3 steppers, 3 microswitches,
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3 led's, a power supply, some high capacity condensators and the hardware is done.
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With an XY incline of 0.8mm per turn (M5) and the gear ratio of 63.8:1 a mm needs 5095 steps, per step it
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has an advance like 0.0002 mm. This is far beyond the tolerances of the rest of the machine which is fairly
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like 0.1 millimeter.
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The Z-axis is coupled by the wind up belt with about 12:1 coupling factor to the gear/feather driven stand
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meachnics that operates with about 4cm per turn. So 9 degrees is like 1mm, resulting into 108 degrees for the
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stepper, which is like 150 steps. Since the belt coupling wasnt manufatured exactly, the estimated steps per
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mm is 165. While winding up, the coupling factor for the second turn decreases to little less steps per mm.
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This currently isnt taken into account by the program.
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Further a control for turning the Micromot on/off is supported, as well as an on/off control for a fan or a
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vacuum cleaner.
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The power supply is an old Notebook power supply that supports 12V and 5V 2A, an old desktop supply will do
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as well. The proxxon drill needs 15V for max speed, but the mill is slow and needs like an hour for a 2x6cm
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engraved name, so 12V for the proxxon is quite ok. A tiny bit of hot glue in the proxxons motor and bearing
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fits helps to get rid of its tool height slip.
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2 Electronics
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The stepper drivers have 3 connectors, 4 pin control, 2 pin power and 2 pin enable. The enable in general is
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shorted by a pinheader. For the overall current needs small lines for power and control are good, the motors
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take like 100mA per control line "on". Since these are motors using a winding, it seems to be a good idea to
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place a high capacity condensator like 3000uF or even higher close to the drivers power pins to prevent a
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Voltage break in when the coils are switched.
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The steppers are also available as 12V type, with 200ohm windings they need less amps, so input watts is quite
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the same and torque should not differ that much. Power supply is a bit easier since a single 12V supply covers
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everything.
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The endswitches closers are connected to ground an led (with build in resistor) from +5V----|>-+-./ ----- GND,
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the according pin is connected between led and switch. Ax------------+
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The emergency switch is connected the same way.
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This is in main the electronics needed. For tool and fan control a common relay board is used. It switches on HIGH
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signal. This can be changed in setup, toolControl and fanControl if necessary.
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*/
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