old computer printer parts

[Noddy]

Being inquisitive (and cheap)...

I jumped on two dead computer printers that the guys next door were throwing out the other day.

The inkjet was a recent Cannon jobby (complete with nearly full single colour cartridges) which I pulled apart for the stepper motors (and got 2 little ones)...

Both the cross feed on the printer head and one of the roller feeds appeared to be by conventional motors (two leads)driving through big reductions, while the positioning for these feeds was by patterned transparent disks and optical encoders.

Here is a question, if I was rigging up a home CNC set up, would that sort of set up be:

cheaper and easier than a stepper motor set up, especially if I could use windscreen wiper type motors.

potentially more accurate as the positional reading would then be direct and independent of feedscrew tolerences and backlash.

The other printer was a laser, which my coleague had dismantled before I got home. I did manage to get the laser diode out of the rubbish bag though.

I'm planning on trying out the diode ( wrapped in a foil covered box and pointing at a matt black surface, as I'm almost certain it will not be eye safe).

Does anyone have any idea what sort of voltage and current the things take? (it was a brother printer)

last thing; the feed rollers and guide for the print head were nice shiny bars, Im assuming either hard chromed or electroless nickel plated. I havent tried them on a surface plate yet, but Im sure they'll be useful for something....

[havoc]

Printer driving mechanics are build for speed, not power. So to use them to make a CNC machine is doubtful (unlees you talk about a styrofoam cutter).

The diode is most likely a infrared one since those are very cheap, so you won't see much of it. You will need a driver for this, as the only way to run it, is next to the point where it breaks. So any driver will have optical feedback in it. Use google to find a circuit, there are lots of them around.

Those bars are normally of high standards. I read somewhere that those of an old matrix printer can be used as a makeshift gauge bar for setting up a lathe.

[baggo]

Hi Keith,

As you've found out, old printers and photocopiers etc are full of all sorts of useful goodies! I've got boxes of motors, gears, bearings etc from dismantling them.

With regard to using the optical encoders- this probably would give more accurate positioning but the problem is you need the hardware and software to be able to read them. Most printers I've dismantled use a long strip of metal foil etched with vertical bars for reading the carriage position. Another possibility is to use a digital vernier caliper as the encoder. Most of them have an RS232 interface built in for direct connection to a PC. You've still got the problem of finding/writing suitable software though.

The laser will probably be a self contained unit with the control circuit built in and will possibly operate from between 3 and 5 volts but I can't guarantee that. It will be a fairly low output (less than 1 Watt) so the current drawn will be low. If you can find any markings on it, do a Google search and you may come up with some specs for it.

I've got a stack of the carriage guide bars and I too would be interested if someone can identify the material used. I presume the surface is precision ground. They don't seem to rust so could be hard chromed.

John

[SteveW]

Guys,

Re the carriage rods... I tried one as the anode of an electrolytic rust remover. Bright and shiny at the start but rust and cruddy very quickly.

Re using torque motors under closed loop control. This has to be the sexiest way of doing it and avoids all sorts of problems with missing steps under unpredictable load conditions etc. However, driving step motors is a doddle compared complex control software necessary to control torque motors.

If you are desperate there was a closed loop motor control application for one of the (now) older PIC17 series of controller. I've also used an HP chip set that used the quadrature data from the shaft encoder and produced a PWM drive to the motor. This thing had all sorts of control models for speed, positioning, trapezoidal profile moves etc. I'm currently looking a Atmel AVR chip sets. I'm guessing these would be a good way forward for this sort of thing but I'll leave it to you. You'll also have to brush up on your control theory.

Trying to use old windscreen wiper motors in this sort of mode will fail. They have far too much inertia and have a load of other associated problems. The best use for old printer motors is to make blowers to boot up your steam loco.