Selecting Absolute Encoders for Stamping Applications

Posted by Brian Winter | View all of Brian's blogs on Aug 31, 2021 5:34:38 PM

Selecting an absolute encoder for any application can be difficult.  There are many mechanical and electronic parameters.  The part number possibilities can be in the millions.

For stamping presses, the requirements are more stringent than many other industrial applications.  In particular, the encoder must be fast, it must be accurate, and it must be extra-vibration resistant.

NIS has a broad range of Avtron Encoder models to chose from, including AV6A, AV6M, and AV30 shafted models.  Let's focus in on key requirements, and how to pick the best encoder fit for your stamping application.

First, speed.  Absolute encoders have 2 speed limitations.  First is the encoder "latency" or the delay inside the encoder between position updates.  NIS encoders offer some of the lowest latency times in the industry, meaning the encoder position is up-to-date at all times.  This ensures you can use the encoder for closed-loop position control.  If instead, your encoder has long latency or "setting time," your control positioning loop will be making bad decisions about the infeed material position.  This can lead to defective parts, or worse yet, double strikes that damage your dies!

The second kind of latency is communication delay and speed.  Many customers prefer open communication busses, so NIS offers ProfiNet, Ethernet/IP, EtherCAT, Profibus DP, and others.  But for absolute speed, nothing rivals good old fashioned SSI.  No scanning, no overhead; the encoder just spits out the position as fast as it can, over and over.  Ideal for closed loop position control.

Accuracy is often mixed up with resolution.  You might assume an encoder that offers 16 bit resolution would be accurate to 360 degrees/65556 = 0.005 degrees.  But resolution is how many bits you measure, not how accurately you measure them!  NIS offers encoders with two accuracies: 0.02 degrees and 0.09 degrees (independent of resolution).  Don't automatically pick the more accurate encoder...calculate the accuracy you need.  Otherwise you might be trading off features you really want by choosing overly accurate encoders.

Vibration resistance is the cornerstone of surviving a press application.  If your highly accurate encoder dies out of the box, or worse yet, on your press in the field, it is worse than worthless.  Avtron Encoders offer a range of vibration specification.  Often the Ethernet encoders have a lower vibration specification than non-Ethernet (SSI again!) encoders, because they have extra parts added that may not be as vibration-proof.  Again, look at the specifications, decide on your best choice.  Most customers opt for coupled encoders instead of hollow shaft, because this offers the ability to bolt the encoder to a more solid mounting, or better yet, to a vibration-absorbing mount, and let the coupling take the flexing from vibration.

Here's a good Wikipedia article that contains more basic absolute encoder technology.

Need more help on fitting an encoder to your press application?  NIS has a full team of Avtron Encoder engineers who can consult with you at no charge, help you pick the best encoder, and support your application.  We also offer 24-7-365 emergency telephone support at no charge!    



Topics/Tags/Categories: Absolute Encoders

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