Bearing Encoder vs Modular Encoder – Making the right choice.

QD-200

The following is a comparison of Bearing encoders vs Modular (Bearingless) encoders for use in Brush less DC Motors.

Construction

Bearing encoders have a shaft that is centered to the body of the encoder on a bearing system.

Modular encoders have a shaft that does not use bearings so the shaft/disk is separate from the body of the encoder.

An examination of traditional bearing less encoder misconceptions:

“No Bearing to wear out.”

The modular design relies upon the motor bearing and shaft tolerances to hold the necessary air gap. Motor bearings have typically lower tolerances than that of Encoder bearings.  This places the responsibility of holding air gap tolerances on the motor bearings.   In encoders with bearings, the encoder bearing holds the air gap. Any excessive endplay or TIR is either held in place by the encoder bearing as the entire encoder assembly moves, not just the disk. The bearing in the encoder is essential for holding the air gap between the disk and sensor.

“Unlimited RPM

While a bearingless design would allow for unlimited RPM in theory, in practice all encoders have an upper frequency response, which ultimately limits their top speed.   The higher the line count, the less RPM required before the frequency limitation is hit.

“Fewer Parts means the  encoder costs less.”

The initial encoder may be cheaper, but in order to hold tolerances, a higher quality bearing must be used in the motor that the encoder is being mounted on.  There are also many “infant death” failures for modular encoders due to the precision that is required to set the disk to sensor air gap.  This increases overall cost of using modular encoders in a design.

The Bottom line

In the end, the decision comes down to whether or not you should take on the burden and responsibility of holding encoder air gap and alignment.

If the application is cost critical, and you feel confident you can handle the technical challenges and efficiency needed to keep from incurring labor costs that make a modular purchase prohibitive, you may be better off with a modular encoder.

If you want the speed and ease of installation, with the added benefit of having the encoder manufacturer hold air gap tolerances for you, a bearing encoder is the right choice.

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About Quantum Devices Inc.
Quantum Devices, Inc. (QDI) Barneveld, WI, was established as a Wisconsin corporation in October 1989, as an outgrowth of activities in the general area of optoelectronics. The main goal of QDI is to provide customers with a complete source for all stages of product design and development, starting from concept to a marketable commodity. These products include application specific Silicon Photodiodes, Optical Encoders and Light Emitting Diodes (LED) for commercial, industrial and medical applications. QDI's photodiodes and LED's are used in instrumentation for photosynthesis and photobiological research, biomedical and medical instrumentation for measuring blood sugar levels (glucometer), oxyhemoglobin and pulse rate (pulse oxymeter). One of the most dramatic products developed at QDI was the application of LED lighting systems for use as the light source for Photodynamic Therapy (PDT). Sales of QDI products include both domestic and international markets. Quality and reliability are very important concepts in maintaining our company wide commitment to overall product performance. Quality simply means continuous process improvement. We are committed to continually increasing our product excellence through increased quality and reliability. Quantum Devices, Inc. is ISO 9001 certified and the ISO Standard will provide the guidance for the vital function of maintaining our commitment to constantly improve our product quality. Quantum Devices is now proud to introduce it's new line of rotary encoders. Incorporating QDI's patented sensor technology, our QPhase™ Family of Encoders feature high resolution, increased frequency response and superior reliability over temperature (0 to 120 degrees C). QDI incremental and absolute encoders set a new standard and are backed by a 2 year factory warranty. We invite you to request an evaluation unit, additional information or price quotations. Mission Statement Quantum Devices is dedicated to the principle that light provides the power for all life on earth. We believe the quality, delivery and control of light is essential to the wellness of man and his advancement into the future.

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