What is meant by "artwork side of encoder disk?"
The thick side of the optical encoder module is the emitter (the light source) and the thin side is the detector. The encoder disk is a piece of .007" thick Mylar photographic film with the emulsion pattern developed on one side. The detector (the thin side of the module) sees a slightly cleaner, sharper image when the emulsion side is closest to it. The US Digital EM1 module uses a nonsymmetrical index code. The index channel will only work when the disk is not upside down. A code wheel consists of a disk and a hub. The code wheel cannot normally be installed upside down because it only fits into the encoder housing one way. However, when bare disks (disks without a hub) are purchased, instructions are included that specify which side is up.
How will the gap between the encoder disk and the detector side of the encoder module affect the output?
In general, US Digital encoders are not that sensitive to the encoder/disk gap. This is because the lens collimates the LED light into a parallel beam and keeps the light/dark pattern fairly uniform. However, as the encoder disk gets closer to the detector, the shadows cast by the encoder disk get cleaner and sharper. This results in better light/dark contrast and subsequently somewhat better performance.
What is TIR?
TIR stands for "Total Indicated Runout" and is the total movement that the encoder disk window/bar pattern will have in a radial direction. Thus it is the total eccentricity of the encoder disk. The factors which contribute to TIR are:
- Shaft eccentricity.
- Shaft undersize relative to hub.
- Off-center placement of hub relative to encoder disk.
- Shaft radial play due to bearing tolerance and uneven loading TIR contributes directly to the cycle error and position error of the encoder.