Hi. I wanna to design a robot to work with my handheld scanner. This one, if it’s neccesary to specify it. I usually use turntable to rotate the object i scan. So i need robot to keep scanner on the cobnstant distance of the object and move it up and down on curcle arc traectory with different angels. I’m absolutly new to robots designing. So could you please advise me some tutorials maybe.
Interesting idea… the most critical question in your case will be resolution… how precise do you kneed the robot to be about distance-from-object?
In my ROVer project (links below) I use both ultrasonic and infrared distance sensors… they’re relatively inexpensive and they offer relatively consistent measurement… good enough, so to speak, for my purposes. I’m actually just about to add a few more sensors in the next video episode or two if you’re interested in that.
I suspect, however, that you may need higher resolution, which would necessitate laser and then you’re getting into a bit more $ unfortunately. Robotshop.com has a great choice for lower-cost lasers, but they’re still way more expensive than ultrasonic and infrared… let us know what you decide upon! 
Cheers,
Nick.
Can you provide a sketch of the motion you want it to do? From what we understand, you don’t need the sensor to be "mobile?, but perhaps a robot arm would work?