More circle generation

So another way is to configure like this:

And yet another way is to use a wedge prism and spin that, deviation on the commercial ones I have seen is about 10 degrees but you can add a second to get 20.

No more tears laser scanning?

Assuming cheap 405nm laser diodes can be used to cure resin for a 3D printer design we are left with the issue of the scanning system. To ensure that the laser is focussed at the the plane across the entire plane and that the beam moves at the same speed an f-theta lens is used. This makes the relationship between the scan angle and position at the focal plane proportional to f.theta. The problem is that the focal length of the lens depends on wavelength so a different lens is required for 405nm than for the red laser used in a laser printer.

Here is a possible solution. High end photoplotters expose their film on the inside of a drum using a rotating mirror with a single face (monogon). They don't need correcting optics because the distance between mirror and  internal drum surface is always constant across the scan. 


Can this idea be used for a flat plane, I think so:

By putting the rotating mirror at a more oblique angle the beam forms a cone, that cone focusses at the same plane, perpendicular to the axis of the rotating mirror. As is shown on the right the optics are simple, a collimator followed by a focussing lens then the rotating mirror. There is an obvious disadvantage with the proposed system, that the beam follows a curved path, that however is just a software issue, distorting the bitmaps to suit. Another disadvantage is the scan speed, a polygon scanner with 6 sides can scan 6 times per rotation, this one will only do one scan (two sort of but lets not go there). That said it was likely that the the polygon would need to do multiple scans to get the required exposure so that may not be an issue anyway.


A further issue is diffraction if you try to make a FTB (from the bottom) system the scanned beam will be shifted by the transparent window. This would also be a problem for any other scanning system and indeed imaging systems (DLP) however the problem can probably be corrected in software for this case as the refraction will just tend to reduce the scan diameter slightly and consistantly.


Here is another idea about how to implement it, using a brushless motor with a hollow shaft makes it easy to get clearance from the motor and makes for a neat assembly. You could even spin the optics but I am not so sure that is a good idea, spinning the laser would be even better but ~10Mhz pulses via slip rings seems a bad idea :)

Bright lights

I had a bit more of a play with the laser scanning unit, this time with the laser from a Blu-ray player. These units kick out something around the 100mW range. I rather stupidly bought a new blu-ray player just to get the laser, the idea was to have something to play with over this epic 4 day weekend. Turns out I did not have the components to build a proper drive for it anyway. I decided to try it on a normal  current limited PSU, a bit sketchy as I know it produces current pulses when you turn it on but I was careful. The laser did not come on! But later I found that my laser has an unusual pin out and also that it needs over 4v to get it to turn on, quite a surprise. It turned on and seems quite compatible with the scanning unit, but it was pretty bright even at 20mA so I decided to give it a rest until I get some proper goggles, better safe than sorry. Similar diodes on ebay are £7 a pop so now I am not in a rush it will be a cheaper affair all together. Also looking for a high speed driver circuit, if A4 is 210mm wide and we consider an aim of around 1200dpi then we are talking over ten thousand pulses per scan and the scanner can probably do up to 10000rpm and has 6 facets, the pulse rates are pretty high (around 10Mhz). Not sure of the best approach electrically, there are some dedicated driver chips but that might be overkill.

Yep, I've started collecting animated gifs when I see them on imgur, this one seemed to fit nicely!

Spinnage is good for you

I managed to get the polygon mirror scanner rotating nicely, it was actually very simple once I convinced myself I had the right pin out. Then I tried to get the laser to fire up, this time it was a little harder because I only have printer service manuals to go by, I think I got the right connections but failed to get it to fire. I may have damaged the laser. Anyway it doesn't really matter as that laser is of the wrong wave length, would have been nice though.

Scanning based 3D printer

Talk on the diy_3d_printing_and_fabrication Yahoo group has turned recently towards the possibility of using the polygon scanning mirror and lenses from a laser printer to create a resin based 3D printer for large areas. The scanner scans a line with a laser and then you move the scanner to "develop" a layer, then repeat. Basically the same idea as a SLA or DLP based resin projector just a different method of imaging. A few guys have done this sort of thing to try and image PCBs directly in photoresist. The visible light curing resins that can be used in 3D printers may however work a lot better than the etch resist.

I have a Samsung laser printer with a perpetual paper pick up problem so decided to take it to bits to investigate. It is a pleasingly simple module, pictures now follow.

The scanning module as it is found in the printer, very possibly this is a part obtained from a 3rd party. It is a really neat sealed unit just waiting to be mounted into a machine.

The other side

At the bottom left we have the spinning mirror, at the top is the weird looking lens that corrects for the variation in distance from the mirror to the drum in the printer, probably does some focussing too, not sure.

This is a brushless motor controller by Rohm especially designed for polygon scanners. The control is very simple from what I have managed to work out, there is a clock to set the speed, a start/stop input and an output to say then the PLL has a lock (i.e. the speed is constant). Then power which is 24v (up to 36 but I suspect 24).

The optics consist of a collimator, a metal aperture and then a focussing lens with a long focal length. The mirror is very thin so perhaps the aperture stops stray reflections from other parts of the motor.

The collimator

The laser diode, a simple uncollimated source. At the very top you can also see a photodiode which is used to sync the control signals to the diode with the rotation of the mirror. The beam hits a small mirror at the other end of the correction lens and then shoots over to this sensor.

Should be quite easy to get a basic system up and running, I'll probably use the propeller microcontroller which should eat the task up but I will need a UV laser to do some real tests, not to mention some resin. And I have the Zcorp to finish! Argh, maybe tomorrow!