DIY Laser levelling using webcam and laser level

[John McNamara]

Hi Joe

The mirrored face prism has 6 sides

It is driven by small three phase board mounted disk motor and a Toshiba TC9242P Motor driver chip.

For a quick test I tried using a small laser pointer and spinning it by hand got a nice bright red line. Very sharp if the target was a short distance away however as suspected on first observation the beam focusing lenses as used by the HP printer were set for a short distance. The dot increased in size quickly as you moved the target away.

However the rotating mirror prism without the lenses worked well, I just spun it by hand for a quick test of the concept.

I will have to do a proper test once I sort out the interface. The laser diode I used was a cheap giveaway pointer!
I removed the invisible light diode as fitted by HP for safety, just two screws and it leaves a nice mounting face for the replacement visible red diode. For this test I just held it by hand....

Just read your post 161

The line is generated by the changing face angle, with 6 faces I am guessing the line generated will be about 60 degrees assuming 360/60 is the correct formula? The HP laser unit itself has a coverage of about 60 degrees.

Mechanical errors?

As I see it the rotating prism mirror presents every side to the laser in turn. The line generated should be straight if the laser is located perpendicular to the axis of rotation. if not on axis a slightly curved line would be generated.

The bearings of the rotating spindle may not be perfect, this may cause the edge of the optical plane generated to wobble up and down for each rotation turn? However your software makes multiple measurements and averages them, This should help cancel out this error.

Regards
John