I have zero knowledge of optics and want to make a very low resolution (~10°) absolute rotary optical encoder using rapid manufacturing (I have 3D printers, laser cutter, and desktop CNC). Digging the internet I realized that one can use some sort of code-disk with some slots in an angular/concentric pattern [Fig.1], and putting a light source and sensor on both sides of the disk to count the number of steps. This is called an incremental encoder.
Fig.1 - Simple relative encoder measuring only the steps with no sens of direction. (image courtesy of [Hydraulics&Pneumatics])
Now if you want to have a sense of direction you may have two tracks of slot patterns (e.g. at different radii) or have a mask in front of the disk, plus two sets of light source and sensor [Fig.2].
Fig.2 - A relative encoder with the sense of direction. (image courtesy of J.P. Trevelyan )
For example, as shown in [Table.1] if the current state is
 and the following state is
 we are in
CW direction (or vice-versa).
| | 00 | 10 | 11 | 01 | |:--:|:---:|:---:|:---:|:---:| | 00 | -- | CCW | -- | CW | | 10 | CW | -- | CCW | -- | | 11 | -- | CW | -- | CCW | | 01 | CCW | -- | CW | -- | Table. 1 - Columns are the current state and the rows are the subsequent state.
This is called an incremental quadrature encoder.
Now I have some issues:
- I don't want to have the light source and sensor in the encoder but to use optical fibers to transfer light to and from the encoder to my electronics. The reason is that I can not have any electronics in the nevironment I want to use the necoder. However, I'm being told that if there is an air gap between two ends of optical fibers, a lot of light will be lost. I want to know what is the limit? does it depend on the sensor or source or the quality of the fibers?
- I do not understand how absolute encoders work. Do they also follow the same rationale of a disk-mask plus light sources-sensors? Is their design simple enough to be built DIY?
- What light source and sensor should I use to emit light into the fibers and read it back? is there some sort of off-the-shelf sensor and source connected to fibers already available which I can plug into an Arduino for example?
Sorry for my novice questions I but I would appreciate if you could help me through. Thanks in advance.