I have just been watching Jose Rodriguez PHOTO PRINTING TECHIE LIVE Stream for last Saturday 16th June 2018.  He gives a good explanation of the noises heard about 30 or so after a print.
I recommend you watch the relevant section, to which the following link will take you:

 https://youtu.be/VYcYrHt6HEk?t=2h2m42s

You can of course watch the whole video.  I have just cued the segment relevant to this thread.

In summary he confirms this is not a clean cycle but a pumping of ink from the purge pads and a head wipe.  The only ink being wasted from the cartridges is any loose drops that would otherwise leave smears on your print.  It's a good thing, just a little frustrating too hear those noises while wondering if it could be a clean activity, wasting ink.
Bruce

Just wanted to say thanks for doing the research.  I've always questioned the 60 hour myth and even posted in one of Jose's videos about a year ago saying that I've printed some large photos one day and then less than 24 hours later went to print a one page text document and got the cleaning cycle.  So the 60 hour deal never added up for me.

I have to say the implementation you describe is a bit odd from Canon.  Since the cleaning cycle only happens when something prints (or any code like a page eject is sent), they're obviously not saying that the printer will be damaged just by sitting for 5 days (120 hours) or 20 days (480 hours).... because you could let it sit for a year and not print anything and no cleaning cycle will be performed.  Theoretically if you did let it sit for a year and not print anything, when you do print, it'll run the 480 hour (larger) cleaning cycle and reset the timer.  From a logistics standpoint, if you get to the 480 hour point without printing and it runs a 2x cleaning cycle that uses twice the ink of the 120 hour cycle, so what?  By 480 hours, you've skipped four 120 hour cycles.  If you had printed something every 120 hours, you would have used 2x the ink of a single 480 hour cleaning cycle by the time you get to 480 hours compared to just letting it sit without printing for 480 hours.

So all this begs the question, what to do?  It sounds like if you print regularly, say every day or two, you're going to get a cleaning cycle every 5 days.  So I think my preference might be to print a purge sheet every 4 days.  That way if you print nothing (aside from the purge sheets), you'll get a purge sheet every 4 days and a smaller 120 hour cleaning cycle every 8 days.  I think it's good to keep the ink flowing so not leaving it idle for more than 4 days sounds like a good thing.  And getting a small cleaning cycle every 8 days (assuming you don't print anything else in the middle) might be good as well since the cleaning cycle timer can't do its job unless something is printed.  Printing a purge sheet every 4 days should help to keep ink flowing so you get perfect prints every time and the cleaning cycle will use so much more ink than a purge sheet that the ink used by the purge sheets will get lost in the noise.

You might think they could have been a little smarter with the design so that if a certain volume of ink (perhaps from each channel) was used prior to the 120 hour cleaning cycle, it would reset it and skip the cleaning cycle.  Or... just a way to turn that "feature" off because those of us printing purge sheets would not need it.  I think I can see what they were going for though: a "guarantee" that when you print, you could never have more than 5 day old ink in any given nozzle, and that's what the described method does.  They are worried about a bubble jet printer burning out nozzles by trying to print with dried up ink/nozzles.  So you could let it sit for 6 months and print nothing and the printer won't do any cleaning cycles: it doesn't need to since you are not asking it to print.  But when you do print at 6 months, before it can start using the nozzles again, it has to run a cleaning cycle to ensure that all the nozzles are free flowing before trying to use them to print.  My guess is that Canon looked at some burned out heads in older models and determined that they burned out from trying to fire up and print after being idle for a certain time OR that 5 day old ink in some nozzles may cause a problem.  They may have determined that sitting for longer than 5 days and then trying to produce a print was a risk: so they made sure that the printer could never print with more than 5 day old ink sitting in the nozzles.  I'm also guessing that they also determined that if left to sit 20 or more days, it took a heavier cleaning cycle to guarantee no nozzle clogs before printing: hence the 480+ cleaning cycle.

Anyway, that's my speculation.  

Edit: I should also mention, if the findings posted here are accurate, whenever you print with your Pro-100, there is a guarantee that the ink sitting at the heating elements in the nozzles hasn't been sitting there for more than 5 days.  5 days may be a good number for OEM inks.  What if you are using 3rd party inks?  Maybe 3rd party inks shouldn't sit stagnant in the nozzles more than 2 days, or even 1 day.  This is the uncertainty of using 3rd party inks: we really don't know their characteristics so it might be good to err on the side of caution and still print purge sheets every 2 days or so if you are not running the OEM inks.  Still speculation of course but Canon thought it important enough to put this feature in that guarantees that when you print, the ink at the nozzles hasn't been sitting there longer than 5 days.  Who knows if 3rd party inks might need to be "moved" more often.  I doubt the 3rd party manufacturers even have that answer!

Mike

Good point about the 3rd party inks.
I guess only experience is going to shed some light on these questions.  Either way I don't plan to let my printer sit unused for 20 days if I can help.

For the last 5 days, since the last programmed auto purge I have deliberately not printed with my Pro-100S.  I have been turning it on and off via the front panel at regular intervals.  Each time I powered on I timed how long before it stopped moving and making noises, which was typically 30s each time. There was no set time period between switching on and off, but it was switched off and on about 5 or 6 times.  The printer had probably spent 75% of the time off and 25% of the time on.  Today I powered on at 16:00, knowing the printer was due for it’s 120 hour purge at roughly 20:00.

I first sent a Form Feed to confirm there was no purge forthcoming.  There was no purge.

I then, after a few minutes, weighed the LGY cartridge.  It was 21.14g.  I put it back in and took it out 2 more times, weighing each time.  Results were 21.17g and 21.16g.  When I last weighed this cartridge, as the 5 day test period started, it weighed 21.20g. Not a very clever or definitive test.  I could not find any information about the accuracy of my scales, but some of the above results give the impression it’s not too bad. The lost ink in one cartridge seems to be about 0.05g.  Over 8 cartridges that’s would total 0.4g.

Previous tests show a single cartridge loses 0.24g during an auto purge, or 1.9g over all 8 cartridges.

I sent another form feed.  No purge.  The accumulated time for the LGY cartridge being out of the printer had not been timed, but I estimated it was getting close to the 60s timer mentioned in the Pro9000 Service Manual as a trigger for initiating a purge.  There had not been a purge so I now decided to test by taking the PC cartridge out for more than 60s.  It was out for approx 76s.  I chose PC because it is in Group 1, whereas LGY is in Group 2.  I sent a Form Feed.  Result was a purge followed by the form feed.

I now measured all 8 cartridges.  The cartridges in Group 1 had a total loss of 1.13g (average of 0.28g per cartridge).  The cartridges in Group 2 had lost a total or 0.09g (average of 0.02g per cartridge).  I then did another form feed to confirm I had not tipped the LGY cartridge over the timer limit.  There was no further purge.

Group 1 and Group 2 are now out of synch, re purge times) by about 4 hours.  I waited until 20:35 and sent a form feed.  A purge resulted.

I measured the weight of all 8 cartridges. The cartridges in Group 2 had lost a total of 0.9g (average of 0.235g per cartridge).  The cartridges in Group 1 had lost a total of 0.01g.

In summary, there was a small loss of ink over the last 5 days (approx 0.05g in one cartridge), following several power up and down episodes, with no print jobs.  The test sample was too small to be confident in the result.  I suspect any loss is more likely from wiping the print-head to avoid drops on printer paper.

As determined previously, it is possible to remove and replace a cartridge within a defined period without triggering a purge.  That time period is less than 76s and more than likely 60s, as defined for the Pro9000 in it’s Service Manual.  If this timer expires for any given cartridge, it triggers a purge for the group to which that cartridge belongs, when the next print job is sent to the printer.  The amount of ink purged, per cartridge, is close to that amount purged during the 120 hour purge.
A group purge related to the 60s cartridge remove and insert resets the 120 hour timer for that group only.

The purge cycles for the 2 segments of my printhead are now out of synch by 4.5 hours.  ie.  Group 1, now due to purge at 16:00 on 28th June and Group 2 is due at 20:35 same day.
I timed how long I had the Cyan cartridge out of the printer (15s), so that next time I can get a more accurate value for the expected 60s timer.
 
Bruce

Mike, You seem to have misinterpreted what happened.
The printer still keeps the timers running when it is turned off.
The sequence (in summary) was:
- Previous clean was on 18th June at about 20:00.  Hence next clean was due at approx 20:00 on 23rd June (but I did not print until 20:35 on 23rd June).
- I powered on and off several times during the 5 days and did not print.
- I powered on at 16:00 on 23rd June.
- I essentially forced one group (Group 1) to clean, by taking the PC cartridge out for 76s.  That has reset the timer for Group 1, but not Group2.
- I waited until 20:35 (printer on) and sent a print job (FF).  This caused the autoclean for Group 2 only, resetting it's timer.

So as you pointed out in your post, you can delay the clean by not printing, for as long as you are willing to take that risk, but you also cannot print.  The first print you do after the timer expires (including a form feed) will cause the purge before the print is performed.  So I just delayed the print job for 35min.

Bruce

Thanks for all this info ... will try this out.

Yes.  That's what I was looking for.  Sometimes there's a hidden "switch" or something that can change the behavior.  For example, what if putting it into quiet mode alters the setting or even turns it off?  I doubt it, but you get the idea: is there anything we can do to change the 120/480 cycles?

Mike

I have uploaded SDLs and a text description document to the following Drop Box link:

https://www.dropbox.com/sh/8j6zm6zwc3pc7xg/AADhGRd_4HTNmyQtX90dFsVla?dl=0

The text document is in rtf format (2 pages) and the SDLs are in gif format (4 pages).

I would have preferred pdf but it was not an option in the application I used to create the SDLs.  Consequently each page of the SDL is a file.  Hence 5 files total.

It may look daunting to some at first, but a lot is duplication and if you read the description in conjunction with the SDLs it should quickly become clear.

I have marked the documents as Issue 1, with the intention of updating as more info comes to light, or errors are identified.
Bruce

Mike, you are now in charge of your printer cleaning cycles.
If you noted the time you did the nozzle check the next purge will be due120 hours later, unless you do a manual clean or remove an ink tank for longer than 60s, or there is a major error such as a paper jam.
Just remembered the SDLs don't cover the paper jam case.

Bruce