printer is intermittent

I have a tried and true HP 1012 B/W laser printer, that has been working since 2003, on both my old eMac and my current iMac. I use a wire USB connection.

I am running 10.10.5, since August 15, 2015. I installed the HP printer update 3.1 on October 10.

For the past 3 or 4 months, the printer becomes "invisible" to the iMac. When the printer is, in fact, on, the printer software reports that it is "offline", and does not print. Sometimes, printing is normal. Sometimes, the printer is reported to be "offline".

To fix this, I have tried several things:

Cycle power on the printer.

Remove and reconnect the printer cable.

Use a different USB port on the back of the iMac.

I have used System Preferences to uninstall and reinstall the printer, except that it won't reinstall what it does not appear to see.

None of these has worked.

What *has* worked, every time, is re-booting the OS X software. No need to Shut Down the iMac, just a Restart and the printer is now visible and working.

Does anyone know how to fix this?