Supported DRO Scale Information
This category encompasses a wide range of different linear and rotary encoders.
Glass Scales
Glass scales are used in the majority of commercial DRO units. Most common glass scales have resolutions of between 5 micron and 1 micron (0.0002” - 0.00004”) with superior repeatability and reliability. They offer good protection from dirt/coolant and are much less sensitive to electric noise in the garage. The main downside is the cost that can be up to five times more than the cost of capacitive scales of the same length.
| Resolution | 1μm-5μm (~0.00004”-0.0002”) |
|---|---|
| Repeatability | Varies between manufacturers (generally excellent) |
| Hysteresis | Varies between manufacturers (generally excellent) |
| Pulses per inch | 5000-20000 |
| Refresh rate | Real time |
| Available lengths | 100mm-1200mm in 100mm increments (~4” to 47”, 4” increments) |
| Material | Glass encoder strip, aluminum case |
Pros: very accurate, real-time refresh rate, good protection and reliability
Cons: more expensive than capacitive scales, can’t be cut without special tools
Magnetic Scales
Magnetic scales are less common than glass scales but are gaining some momentum recently. They are very similar when it comes to resolutions and repeatability but have a few advantages over glass scales. First of all, they are virtually dust and coolant proof. Second, they can be cut to size. Finally, they have smaller cross section, making them easier to use when space is at a premium (for example on a lathe cross slide). Their main disadvantages are the high sensitivity to misalignment and the fact that they attract swarf.
| Resolution | 1μm-5μm/0.00004”-0.0002” |
|---|---|
| Accuracy | 10 μm/0.0004” over 1m of travel (for 5μm version) |
| Repeatability | 10 μm/0.0004” (for 5μm version) |
| Pulses per inch | 5000-20000 |
| Refresh rate | Real-time |
| Available lengths | 10”-20’ (yes, 20 feet); can be cut to size |
| Material | Metal |
Pros:very accurate, real-time refresh rate, dirtproof, smaller cross-section, can be cut to size
Cont:cost, lower availability, more sensitive to misalignment
Incremental Rotary Encoders
Rotary encoders are sometimes used in situations where a linear scale might be impractical. It can be either a rack-and-pinion setup, a shaft encoder on the lead screw or a similar application. The cost of rotary encoders varies widely, with low-end units retailing for $10 to hundreds of dollars for “industrial” grade encoders. Major drawback of rotary encoders is the fact that they don’t address the backlash, though.
Pros:can offer digital readout where linear scales are impractical, relatively inexpensive
Cons:don’t eliminate backlash