Friday, October 26, 2012

The Electronic Quick Change Gear Box, part 5

(continued from part 4)

The block diagram from the previous entry may be informative but there's something to be said for seeing the actual components.

You can see the breaker box and VFD here, if you wish.  The breaker box is bog-standard. The VFD lives below in its own enclosure.  The control pendant (VFD Control in the block diagram) is sitting on the VFD enclosure. It has 2 toggles and a rotary knob.  One toggle powers the motor, another makes it run forward or reverse, and the knob sets motor's speed.  It's pretty sweet.  I'll be combining these controls with the new control panel.

Here's the power supply that will power the electronics and stepper motor:

It's somewhat over-sized being about 18" long.  It was salvaged from an industrial photocopier. This is great since it was made to power electronics and steppers.  It has 3.3v, 5v, and 24v outputs. It's basically perfect.  I am confident it will produce superb power and last for a long time.  And the price was right!

Here's the encoder. It came from U.S. Digital. It fills the palm of my hand.  The encoder consists of a case, a sensor fixed to the inside of the case, digital output pins, and disk that spins within the case.  The disk has 1024 marks on it.  As it spins, the marks pass through the sensor to produce pulses that are made available by the pins on the far right.  As an extra bonus, this particular encoder supports quadrature output which quadruples the number of pulses.  Thus this encoder produces 4096 pulses per revolution.  The lathe has a gear train connected to the spindle.  I'll mount the encoder to the head stock, fit a shaft to the hole in the encoder's disk, and spin the shaft from the gear train.

Here's the actual CPLD board I'll use for this project.  The image from part 1 of this series is a feature-rich development/learning board.  This board costs about 1/3 as much.  It measures just over 1" x 2".  It's a product of Dangerous Prototypes and sold by their partner seeedstudio.

Since I have not yet selected the stepper motor, I can't say for sure what stepper controller board I'll buy.  Candidates are the Big Easy Driver from Sparkfun and Polulu's A4988 Stepper Motor Driver Carrier with Voltage Regulators.

The stepper will be standard. Right now I'm debating on the NEMA 23 or 34 frame size.  I'm leaning towards a bipolar model with a 23 frame and 1.8 degree steps.  The torque is really the question now.