Leading edge detection

[telv]

Can anyone tell me the means by which Canon printers (the iP4950 specifically, or Pixma in general) detect the leading edge of paper as it is fed from the rear tray so that it knows when to start printing and if the sensor can either be reset or replaced.

 

[The Hat]

The Pixma printers use an electronic sensor to detect the front edge of a sheet and can roll the paper back and forth till it gets the position precisely, it can also straighten a misaligned sheet and the printer will start to print 3mm in from the leading edge, or where your Application has placed the image. (Check margins)

The sensor can’t be reset but you can however replace it with a lot of time and patience gaining access to it, there is a second sensor for detecting the presents of the paper, this one is mechanical and can sometimes be repaired depending on the damage..

 

[telv]

The Pixma printers use an electronic sensor to detect the front edge of a sheet and can roll the paper back and forth till it gets the position precisely, it can also straighten a misaligned sheet and the printer will start to print 3mm in from the leading edge, or where your Application has placed the image. (Check margins)

Many thanks for your input.

My reason for asking is because I am noticing a difference of where on the paper the printer starts to print. If reasonably heavy bond paper of 32lb is fed from the rear tray the printer will always print accurately on it. On the other hand, if a lightweight paper is used the printer will begin printing too late. That is, the top margin becomes too big and the bottom margin too small. Heavier paper, or card, has the converse effect and printing begins too soon.

This effect appears not to do with the printer's paper feed mechanism and I am wondering if, instead, it might be to do with the sensor you describe. Would be very grateful for any further thoughts you might have.

 

[The Hat]

Another problem that can affect the paper feed is paper dust, it can get imbedded into the feed roller causing it to slip and it might need a bit of a clean, use some alcohol and a small cloth to clean the rubber roller and see if that improves the pickup.

The print quality also affect the paper feeding, like the higher the print quality the slower and more accrete the paper feed tends to be..

 

[telv]

Another problem that can affect the paper feed is paper dust, it can get imbedded into the feed roller causing it to slip and it might need a bit of a clean

The reasons I had discounted paper feed as the problem are as follows:-

1. The feed rollers are regularly cleaned, at least every week and there has been no problem with pick-up.
2. If this was a feed problem then some variation in printing could be expected when using the standard weight paper. The printer always prints perfectly on it. Again, when using the lighter weight paper the variation of printing position (prints too late) is always entirely consistent.

Incidentally, I only ever use the high quality print setting.

Have I overlooked something or would be realistic to look again at the paper detecting sensor?

 

[The Hat]

The only reason I brought up feed problems is because the paper sensors are very accrete and technically it could pick up paper dust but I would imagine the paper would clean the sensor as each sheet passes over it, so I think you can rule the sensors out.

The next thing to look at would be your paper storage and handling, paper that is not perfectly flat and dry can cause feed problems too but if you’re using high quality print setting then you may some other issues.

I can print 400 gm card stock with little difficulty and I occasionally print 50 gm thermal Fax paper, now with the 400 gm I only load one sheet at a time and on the lighter papers, for accuracy I would tape it to some 80 gm paper to be sure.

 

[telv]

I can print 400 gm card stock with little difficulty and I occasionally print 50 gm thermal

One of the big advantages of Canon printers and why I use them is that they will print on a very wide range of thicknesses. A client wanted some display cards printed on 450gsm card and my iP2700 very happily turned them out!

Canon will take card and very lightweight paper but how it prints on them varies. The effect I described earlier is perhaps not something that everyone will have noticed. Text and borderless prints, for example, tend not to show up. It was only when I needed to print photographic images with a uniform white border that it did.

I have done everything I can think of to overcome the effect on the assumption that it was to do with the paper feed mechanism. Even enthusiastic cleaning of the feed rollers made no difference!

I can overcome the effect by altering the top and bottom margins of the document to suit the particular weight of paper being used. Then the printer always prints accurately on it. That clearly suggests it is not a paper feed issue. However, this method has to be repeated for each different thickness of paper or card. Something easier would be welcome!

Why Canon behaves in this way is a mystery! If it's not to do with the electronic paper sensor then it must be something else. Would anyone be interested in seeing if the effect is replicated on their own printer?

 

[The Hat]

I have more than a half dozen Canon printers and haven’t noticed this to be a huge problem, yes if a print does not come out the way I plan it, I then alter my approach to check the printer is feeding in the paper properly.

Nine times out of ten it’s because the adjustable side margin was incorrectly set either too tightly or usually to lightly causing the paper to be slightly angled (Not straight) in the back feed tray, the newer model printers have centre aligned paper trays which all most eliminates this problem..

 

[telv]

Nine times out of ten it’s because the adjustable side margin was incorrectly set either too tightly or usually to lightly causing the paper to be slightly angled (Not straight) in the back feed tray,

Thank you for your input. You will see from previous posts the effect I described isn't to do with the side margins. It is only to do with top and bottom margins (printer starts printing too early or too late) which was my reason for asking about the paper sensor.

 

[telv]

the newer model printers have centre aligned paper trays which all most eliminates this problem..

It's the iP4950 (central feed roller) that produces the effect described