EEVblog #303 - Photocopier Extreme Teardown

[EEVblog]

Dave.

[nitro2k01]

Interesting. Hats off to the engineers involved in this.
A couple of thoughts. You mentioned the green drum would be a semiconductor, perhaps selenium. I'm guessing this drum is used to apply the negative charge to the paper. Why a semiconductor, specifically? I'm guessing any resistive material would do. (I'm assuming the reason you don't charge the paper directly using a metal drum is to get an even static charge over the whole paper or something like that.)

About 44:18 or so I'm noticing that the LED board says PbF. Could this mean lead fluoride?

[mikeselectricstuff]

Interesting. Hats off to the engineers involved in this.
A couple of thoughts. You mentioned the green drum would be a semiconductor, perhaps selenium. I'm guessing this drum is used to apply the negative charge to the paper. Why a semiconductor, specifically? I'm guessing any resistive material would do. (I'm assuming the reason you don't charge the paper directly using a metal drum is to get an even static charge over the whole paper or something like that.)

The drum needs to be insulating but conduct when exposed to light.
It is initially charged by the corona wire, the light then discharges it selectively, the toner is then transferred to the paper electrostatically, usually via a wire behind the paper with the opposite polarity to the drum charge.

About 44:18 or so I'm noticing that the LED board says PbF. Could this mean lead fluoride?

LeadFree

[Mechatrommer]

10.25: helix gear. wormdrive is screw looking gear..
26.02: the scale... thats one way how mechanical make "calibration" or "alignment"
nothing else to do, so.. just some nitpicking dave. no pun intended.

always fun playing with mechanical and learn how the engineers find a balance in the loci.
and this one is a good example how mechanical and electrical integrated. i got one photocopier teared down years back, still there in that room. my limitation mostly is in electrical unable me to understand and repair all the stuffs esp how the drum and laser work. felt afraid to even touch the drum.

so dave, have you figure out how to re-assemble those things? (i doubt that) or its just one way ticket? i highly believe that.

[FenderBender]

That was one hell of a teardown. Thanks a lot.

This is a type of video I'd expect from Mike. Mike, you better watch your back. Dave's after you.

[jpwack]

Epic!

Well, now the (mis)informated guesses: the CCD from the scanning head may be an one-dimensional array, I've seen those in some PCB inspection machines, and for the distance, I guess is uniform across the entire movement of the mirrors (and hence not needing more than one aperture angle and/or focus point)

Anyhow, tomorrow I'll look with more respect the photocopier in my work.

[IanB]

If that had been an optical (analogue) copier, there would have been a really big lens assembly in the middle of it. I was hoping to see something like that, but evidently copiers are all digital these days. They are basically a scanner and a laser printer combined in the same case.

[T4P]

The larger something is, the logarithm scale goes up in difficulty of reassembling 
I tore down a printer from a few years ago and it was quite the similar (being inkjet but the style is the almost the same)
Instead of having a stationary CCD sensor i could not really find the sensor being anywhere ...
But tearing down a inkjet is not something you want to do ... it's worse then having toner on your hands! The ink's got everywhere!
But yeah the electronics control section in the photocopier with the big QFP packages looks similar to the inkjet i tore down
Got to love the fans being used disparingly

[David_AVD]

I've seen a rotating mirror scanning assembly like that when junking a standard laser printer.  Printers can certainly provide lots of rollers, motors and gears for experimentation.

[SeanB]

I still have an analogue copier that has been scrapped, still mostly works but is giving regular jams, and spares were discontinued 15 years ago. I should do a teardown on it. The big optics are very useful to use as magnifiers, good coated lenses with low distortion.

I wonder if i should tear down the Tektronix Phaser I have. Works perfectly, but the cost of running it is a killer. I can buy a new colour laser complete with spare cartridges just for the cost of one colour wax set. Black wax is free though.

[T4P]

I use a epson LED multifunctionprinter nowadays, this new printer is a beast ... Scanning speed's slow though

[G7PSK]

The optical scanner has a very wide angle lens on it, what photographers call a fish eye lens that is why with the differential movement of the mirror to the light and mirror assembly it does not move itself.

[steve30]

Really good teardown .

I've dismantled one or two printers so am familiar with the workings of such machines, but I've never done a photocopier.

They really must put some effort into the design, because it is amazing what they will do in terms of copying, enlarging, reducing, duplexing, collating etc..... All so some lazy office worker can do single sided copying and moan when something doesn't go as planned.

[SeanB]

Yes, the old copiers came with the firmware built in to run a duplexer, multiple source feeders, stapler, collater/decollater, sheet feeder and double sided sheet feeder. You just took off the appropriate cover, screwed the extra on, plugged it in to the existing wiring using the plug already there, turned it on and set a few options, either by programming an EEPROM, or by cutting diodes out of a programming matrix under the keyboard.

And all this was done with mostly a single chip micro, either a pukka Z80 and support chips or a Sharp or Toshiba integrated Z80 core that was a single chip solution. A few years ago Sharp engineers made a silicon on glass Z80 CPU, and to prove it was a real Z80 they dusted off an old Z80 mini out of the museum and fired it up with this in place of the CPU.

[Mechatrommer]

But tearing down a inkjet is not something you want to do ... it's worse then having toner on your hands! The ink's got everywhere!

you give me as many inkjet as you like, i'll be happy to demolish all of them leaving their motors and gears in my drawer. the good thing about the "ink" is its almost improbable to get it into your lung. just refilling toner, i'll prefer to do it outdoor or hold my breath throughout.

[railman]

Oh man that led array would make a nice POV, or bench light

[rr100]

Haven't finished the video yet; I don't know much about those particular parts but a light went up in my head when I saw the "clutch" thingies! They are BRAKES!

[mikeselectricstuff]

Oh man that led array would make a nice POV,

No because it isn't addressable

or bench light

No because it's probably red, orange or maybe infra-red

[mikeselectricstuff]

Haven't finished the video yet; I don't know much about those particular parts but a light went up in my head when I saw the "clutch" thingies! They are BRAKES!

No they're clutches - they connect or disconnect gears from the shaft

[SeanB]

Depends on the copier. Modern ones are white light ( colour sensor) or older ones are green.

[mikeselectricstuff]

Depends on the copier. Modern ones are white light ( colour sensor) or older ones are green.

That array is not for the scanner - it's to discharge the drum. It will be a longer wavelength as that is what the drum is sensitive to - the laser is typically IR or red.

[SeanB]

Sorry, was thinking of the CCFL scan lamp.  The imager optics are arranged to keep a constant path length even as the scanner traverses the paper. The front silvered mirrors reflect the page width scan strip to an image size that will be viewed by the line scanner in the ceramic package in the imager board. Then it is digitised, stored in memory ( top board, the hard drive was probably removed before the unit was scrapped) and then sent to the IR laser in the laser printer side.

There it is used to modulate the brightness of the laser diode, and the light is filtered ( the clear block) and focussed into a narrow collimated beam. This then is reflected off the rotating polygon mirror ( the motor with the 6 sided mirror on the side faces, those are polished and diamond coated optically flat machined flats there) . The mirror runs off 24V, and has both a input tacho signal to control rotation speed ( keeps a really constant speed so that the image on the paper does not have horizontal shifts from line to line) as well as having a output that gives a very narrow pulse at the beginning of the one mirror segment reflecting onto the defined reference point on the output window ( set during assembly of the optical block) so that the PLL in the motor drive controller can generate a dot clock to read out the stored image onto the drum.

To write on the paper the unit starts all the motors, runs the developer unit to speed and to a stable locked pll loop and then starts the paper upwards. When the edge of the paper is half a drum revolution away from the developer the stored image is read out line by line, then written by the laser as intensity variations onto the charged drum line by line as the mirror rotates the reflected laser beam across the window ( the 2 lenses are there to provide correction to the beam as the mirror rotates to correct for the sine distortion of the beam at the edges of the window, so that the laser beam moves across the drum outside the window at a constant velocity of travel, instead of having variation between the edges and the centre, this simplifies the electronics considerably ( no doing trig on each pixel to correct for location) as well as making the resolution across the page constant) As the beam reaches the end of the window the next mirror segment is just out of being able to intercept the beam. This will form the next scan line, as the paper will have moved 1/1200 inch up during the last scan line.

As scan lines are written onto the charged drum ( it having been first discharged, cleaned by a scraper wiper and then charged by a corona wire to a high voltage) they leak charge away, depending if light has discharged the small insulated photosensitive spots on the drum surface. This leaves a pattern of charged spots on the drum as it rotates around. Next the drum rotates to expose the charged spots to a thin film of toner, which has been charged to a opposite charge, and the charged spots get coated with a thin film of toner, in a pattern made by the developer laser. The drum moves further around and is placed in contact with the paper sheet, and the sheet is charged with a contact and a wire behind the sheet, which attracts the toner particles onto the sheet. The now mostly clean drum rotated further to be discharged and cleaned ready for the next scan line to be written on it. The paper moves further to the fuser, where a silicone impregnated roller is used ( it has a non stick surface) to bond the plastic toner particles to the paper by application of heat and pressure to the paper. It then leaves the fuser and is passed though a static discharger brush to the output tray.

The drum actually is used multiple times per page to transfer image, you need a much bigger drum if you want to make an image with only one pass. This is mostly done with colour copiers, where there are 4 toner stations that build up a toner image on a transfer film that is pressed against the paper to transfer a whole page of image at a time. These have a single scraper unit on the transfer drum, which has a big container to store the brown gunge that it gets ( mixture of the 4 toners)

As to the fuser, I would guess that this one uses a 500W linear halogen lamp hidden inside the black fuser roller, the red one is a soft silicone foam roller that simply applies pressure. This is used in conjunction with the choke to run the lamp at a controlled low temperature during idle, switching the lamp to full power when you press start, so that it heats up the fuser quickly to operating temperature. Energy saving, and running at lower voltage reduces the stress on the lamp. After a few minutes of idle the lamp is powered down totally and the unit enters deep sleep mode, with only the processors and some of the boards powered ( that is why there are so many optos on the power supply, it can run in 2 modes, full power or low power where most rails are nearly off, with the 5v for the micro being provided by a linear regulator on the heatsink that dissipates a lot of power in full power mode while barely staying in regulation in standby) to supply the network and the keyboard functions.

If you look at the manuals for copiers there are a lot of options available. I would guess Dave has not torn down any old laser printers, you find the whole paper path assembly there as well, complete with the IR laser block. i am building a collection of those. Would be nice to use to make a LED line display, but you have to clock the diode at 40mHz to get the full beam resolution out of it unless you slow the motor down from it's normal running speed. Now you know why the first laser printers use 60mHz 6800 processors, as they were about the only things fast enough to build an image as a bitmap in ram, then DMA it out to the laser while still having cycles left over to run the paper path and the motors.

If you want a different take look for the Tektronix Phaser series of colour printers. try the 360 and 560 units, very detailed manual and a lot of detail on how they actually work.

[LaurenceW]

There is quite possibly more engineering in this thing than in a CAR of a similar age.

One thing about that toner dust - it gets EVERYWHERE. If you get it on your hands, wash with lots of soap and COLD water - hot water may fuse the stuff!

Also, DO NOT attempt to vacuum the toner up! It mostly goes STRAIGHT THROUGH any filters in your standard vacuum, and then clogs the motor in no time...

On the rare occasions that I have cause to go into my own laser printers, I have used compressed air and worked OUTDOORS to blow any toner dust away from the instrument, and me.

[firewalker]

Really nice! Inkjet printers are so boring btw...

Alexander.

[hans]

Awesome piece of kit and the engineering involved. As I expected, the optoelectronics separates the printer from being a huge pile of cogs and boards into a sophisticated machine. Really interesting stuff.

A separate look on the optical units would be cool, but I (personally) wouldn't try to operate the laser section. Not with the lid off at least or with the right laser goggles.  I read around on laser printers and it's probably 5mW - 10mW IR (780-800nm), so that kinda sucks because it's invisible and more than enough to burn stuff.
I can imagine what SeanB said, the beam has to be extremely collimated. 300dots/inch makes it 0.1mm per 'pixel'.
 I believe laser diodes usually aren't that well collimated compared to their gas 'alternatives'. They are lasers in that they multiply light inside, (that's the term laser) , but their viewing angle are at worst 10 degrees. Well that's bare diode, maybe this laser diode already has a tiny lens inside it, so the viewing angle is much smaller.
Other than that it are almost like LED's that are extremely sensitive to ESD and other nasty things (reverse polarity).

 I don't get what Optical filtering you would need, as lasers have a very small light spectrum (like <2nm wide compared to several tenths of a color LED). I only think the lens is so to focus the light very carefully on the rotating mirror.


As this is an 'extreme' teardown anyway, disassembling and plowing through all boards would be interesting to see what's involved.
Especially the optics.. Lasers usually contain TEC's for temperature stabilization, so it would be interesting to see whether it just got a big heatsink or a TEC (with H-bridge?) as well. Ofcourse, it's only a tiny diode, I may be ehm, blinded , having researched controllers mainly for 3W lasers in my last internship (and for 3W output you do need a TEC).

The scanner could well use a linear CCD sensor indeed, the sensor looked very thin compared to it's width. I know they are also used in spectrometers with grating mirrors; the grating material reflects the light where the angle is proportional to the wavelength, so you basically get a rainbow inside. Measure it with a 1D CCD sensor, and whoila, you can scan the optical spectrum.
I see Toshiba makes sensor with resolutions up to 10k (wow!), so you can scan up to 2400dpi. Probably not in this model, but really quite cool technology you don't get to see everyday

Didn't even know such high resolutions existed, the spectrometer I used had 2048 pixels and was branded as 'top class'. Ah well, probably something to do with spectral sensitivity and noise, because the device used a 16-bits converter to read the data.