Whether they’re keeping precision robotics running smoothly or helping ensure automation equipment stays on target, rotary encoders play a pivotal role in the measurement of angular position and motion. Without this information, motion control technologies and robotics would struggle to produce the reliable movement that enables them to operate efficiently. But to accurately measure these minute changes in position and speed, rotary encoders rely on one essential component: the rotary disc. 

Rotary discs come in various shapes, sizes, and materials, but they can all be classified into one of two categories: absolute or incremental encoder discs. Both discs are equally important and have their own benefits, drawbacks, and applications. 

How Rotary Discs Work

Rotary discs are an essential part of an encoder’s overall functionality. The disc transfers motion into raw countable data (like light, electronic, or magnetic signals) that a sensor can interpret and share with a computer to interpret.

On every rotary disc, there is a series of etchings or an embossed area, called the code track. When the encoder moves, the rotary disc spins on its axis. As the disc rotates, these code tracks act as the main counting mechanism. 

For optical encoders, a beam of light passes through slots on the code track (or reflects off a reflective coating embossed onto the code track) and is picked up by the sensor on the other side. These flickers of light are recorded and, using other measurements like time, they are translated into position and/or motion data.

The number and complexity of the code track dictates whether the rotary disc is incremental or absolute. 

Incremental Rotary Discs 

Incremental rotary discs are the more simple of the two disc types. These discs usually only have one or two code tracks which only give the computer enough information to measure things like speed or changes in position. 

Essentially, incremental encoders can tell you that you’re “X” rotations away from where you started. But, on their own, they can’t tell you where the starting place is in relation to the rest of the space.

As a result, incremental encoders need to be recalibrated to a reference point after every power down if they are used to measure positional data. 

Absolute Rotary Discs

Absolute rotary discs have many rows of code tracks with intentionally staggered spacings or reflective spots. Each position has a particular code that’s conveyed via the code track, so these encoder discs can translate absolute positional data. 

In other words, absolute rotary discs can tell a computer exactly where it is at any given time, making recalibrations unnecessary.  

Which Rotary Disc is The Best for Your Design? 

As mentioned before, each disc design has its own benefits, drawbacks, and applications. It’s important to choose the right option to ensure the best results while also optimizing for cost. 

The cost to create code tracks on a rotary disc can add up, so incremental encoders are the most cost-effective options. However, they can’t give positional data without a reference point. As a result, it usually makes sense to opt for an absolute encoder disc when positional data is important for security or safety reasons.

Custom Absolute or Incremental Rotary Discs for Your Next Project 

At Photo Solutions, we create top-of-the-line custom encoder discs for both absolute and incremental applications. With custom designs, we can ensure a higher degree of accuracy and efficiency by recommending the right material and disc type for your particular needs. 

Learn more about our custom rotary discs