jkg@prism.gatech.EDU (Jim Greenlee) (05/22/91)
I am working on a project (for fun :-) where I need to sense the movement, direction, and speed of a mechanical assembly in a non-intrusive way. The assembly moves linearly, but is not very wide (0.5" or so). My sensor must not extend beyond the width of the assembly. So far so good, right? I've decided that the best way to do this is to stick a couple of pieces of reflective tape to the assembly (about an inch apart), and use a reflective IR sensor to sense the motion. I can position the sensor as close as is necessary, as long as it does not touch the assembly. The problem is that the surface of the assembly is curved, so the distance between the reflective tape and the sensor will not be constant (my best guess is that the clearance will vary from 1 mm at one end to 5 mm at the other end). In looking at the different reflective sensors that are avaiable, it looks as though there are two major types - focused (for highly polished surfaces) and non-focused (for irregular surfaces). The major difference appears to be that the focused parts position the emitter/detecter pairs on converging axes, while the non-focused parts are more parallel. I have data sheets for a couple of focused assemblies (TIL139 and TIL149, from an old TI Optoelectronics Data Book), but I'm concerned that the variation in the surface that I'll be monitoring will cause some problems. I've checked some catalogs and found other parts that go as much as 5 mm, but I don't know if they'll work properly at the 1 mm end. I don't have any data sheets for unfocused sensors. So I guess my questions are: 1. Will focused assemblies generally work at distances other than what they are rated for? The TI assemblies are rated at 3.8 mm "nominal", but no min/max values are given. 2. Would a non-focused assembly work in this application? If it makes any difference, the whole thing will be enclosed, so there won't be much ambient light to speak of. 3. Would anybody care to specifically recommend a sensor that they have used in a similar (hah! :-) application? This is my first time around with this kind of stuff. Thanks for any and all advice. Jim Greenlee -- Jim Greenlee (jkg@cc.gatech.edu) Just who is this "Buster Move" Instructor, College of Computing fellow, anyway, and why are all Georgia Tech, Atlanta, GA 30332 these people singing about him?