Tuesday, December 21, 2010

Gutting printers for steppers

Immediately after I started drooling at the DIY CNC videos on the 'net, I found two printers in the garbage. What luck! There's the free stepper motors I was hoping for! Or so I thought.

The models were HP Deskjet 5150 and Deskjet 656C.

HP Deskjet 656C straight outta garbage.

After all the trouble of carrying them home, I noticed they both had plastic optical guides next to the printhead pulley system. At first I was thinking "why do they need optics to guide steppers?" Then I understood the grave situation. There were no steppers. It seems that HP has found a cheaper way to get their precise printhead movement. They use DC motors with optical linear encoders to give feedback on the printhead's position.

HP's optical guide for the printhead.

I decided anyway I would gut the both printers for parts. I would probably be needing them for the mechanical construction.

You need a torx screwdriver set to open these things. Every screw on these seems to be a torx. I needed at least the T10, T15 and T20 to open the printers.

My trusty screwdriver set.

At this point I want to make it clear that opening printers is MESSY! Be prepared to get ink everywhere.

A partially gutted HP Deskjet 5150.

I found another optical guide on the Deskjet 5150. It's a rotary encoder that gives the printer feedback on the paper feed DC motor's position. Again they have saved on steppers.

An optical rotary encoder.
And then I found my first stepper! On the Deskjet 656C they still use a proper stepper for the paper feed motor. I need one more for the build.

The first stepper motor I found!

I took out the stepper and googled it's model PML55L-048-HPG9. The first search result gave it's data:
Nominal voltage: 24V, Steps / revolution: 48, Step size: 7.5 degrees. Everything I need to drive it, I quess! I've never used stepper motors in my projects before...

This one will come in handy.

Even without google it's easy to distinguish a stepper motor from a DC motor. Stepper motors have 3-6 wires on them while DC motors have only 2. For more info on the various motor types, here's a great tutorial page: Jones on Stepping Motor Types.

So here's the conclusion: if you're looking for steppers: Deskjet 5150's got zero, 656C has one.

But the Deskjet 5150 sported something else I'm sure I'll find useful: a screw-mountable metal rod that the laser head can travel on.

I'm planning to use this rod in the CNC build since it's got some convenient screw holes.

OK, that's it for today! At least some progress.


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