HP97 The journey begins

[teenix]

Hi all,

I had a bit of a failure with the motor drive for the 19C. It worked but was a bit too touchy when it came to changes in torque loading.

I changed the driver IC and it seems better, although I haven't energized the print head yet.

I thought maybe I could reverse track and try to mimic the original driver which was controlled by the motor back EMF and the PIK chip innards. This is a bit of a teaser because no-one really knows what is hidden in there. Anyway, I'm pretty sure I figured it out today and did a mockup circuit and after some fiddling with some logic, what do you know, it worked. The motor speed is adjustable just like the original with a trimmer potentiometer, plus it can be sped up easily for homing.

The only trouble is, just like I found out with the 97 printer, it too suffers a bit from motor torque changes and the print motor will change speed if it is loaded such as by applying a tiny bit of pressure to the print head as it is moving.

This setup also requires a few parts to work, so I am weighing up whether to just use the new IC I chose which is much more compact, and it only takes changes in software to change the motor operating characteristics. I have already compensated battery voltage changes and this driver seems "stiffer" than the other one I used, so I will see how the printer performs with it.

With the print motors having aged quite a bit now, plus mechanical wear, they might be a bit tired in some ways and might not perform as good as new anyway.

Either way, it was an interesting trip to delve a bit more into the PIK innards.

cheers

Tony