Choosing Encoders for Harsh Environments

Posted by Alan Kuffner on Jul 29, 2016, 8:21:43 AM

Choosing Encoders for Harsh Environments

Optical encoders are useful in many industrial processes, from angle detection to the positioning of precision components. In most applications, standard encoders are suited well enough to do their job effectively. But in certain industries and environments, standard encoders have a rough time performing well and resisting failure. This failure can be caused by particulates, chemicals, excessive loads, and immersion in liquids.

It’s All in the Design

An encoder’s ability to fail is an intrinsic property of the device, caused by the method in which it is manufactured. Figure 1 below shows an assembly of the inside of an optical encoder’s important parts and functions. The LED acts as a light source that is focused into a beam by a convex lens. The beam passes through the code disk (or pulse disk) onto a photosensitive plate that gets decoded into a signal. That signal gets fed into the control system from the back port on the encoder.

Encoder_fig_1.png

Figure 1: Basic assembly of an optic encoder

Unfortunately, since the design of the encoder means that the input shaft is directly connected to the code disk (it results in the pulse decoded by the IC), it means that the whole encoder assembly cannot be completely airtight. Thus, contaminants can enter the housing and interfere with the encoder.

Small particles, like dust, soot, etc, can enter and obstruct the light beam, resulting in failure. Or, if the encoder is submersed in liquid or exposed to pressurized solutes, like cleaners or chemicals, it can harm the IC circuitry or other components. Another problem is temperature differences between the outside environment and the inside of the encoder housing, which can cause pressure differences and lead to condensation on the internal electronics.

Even still, there are some situations where an encoder experiences too much axial or radial stress, either from force or torque on the encoder shaft. It strips the internal bearings, and results in downtime.

Harsh-Duty Encoders: The Heavy Workhorses

Enter harsh environment encoders. They are specially designed to be used in the tough situations described above, and are engineered to withstand the most difficult work environments. These special encoders (example in Figure 2) have features like robust, sometimes stainless steel, housing to better handle external shock and vibration. To prevent disruption of the light beam, heavy-duty encoders feature labyrinth seals near the shaft entrance, which are a series of grooves that help prevent water and other fluids and particles from penetrating the enclosure.

Encoder_fig_2-1.png

Figure 2: Section view of a heavy duty encoder

They also have additional safety measures to prevent overworked shafts and bearings from unexpected stress on the internal rotating components, which are electrically independent from the main optic IC. This can brake or stop a shaft that is experiencing too much rotation than what was designed.

These encoders also go through a series of tests that put them in simulated harsh environments, to ensure that they are performing correctly and have no defects. Tests including heat & humidity chambers, saltwater sprays and immersion baths ensure that the heavy-duty encoders are up to spec.

Choosing the Right Encoder for Your Application

In applications subject to high stress and safety concerns, heavy-duty encoders are the obvious choice. However, the exact type of rugged encoder or how to integrate it into your process can be more of a challenge. The specialists and engineers at ACD can help you select the best product for your application. Contact us to see how ACD dedicated technical and sales support can make your project a success:

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Topics: Motor Control

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