Importance of Mounting Tolerances for Modular Encoders

January 27, 2012

Figure 1: Encoder Installed on a Motor

Figure 1: Encoder Installed on a Motor

Modular encoders are very susceptible to mounting misalignment. Since modular encoders have no bearing, they rely solely on the accuracy of the motor and encoder manufacturing process. If the motor dimensions are not within the mounting specifications or the encoders physical dimensions are all near tolerance limits, then the encoder may not operate correctly. There are several factors, which are of primary concern when mounting modular encoders.

Concentricity of the encoder housing with the shaft centerline is an important factor to consider. The encoder housing holds the LED and the sensors and positions them relative to the shaft centerline. If the concentricity error is too great, the lines on the disc will not line up correctly with the sensors, which can cause an increase or reduction in counts and the loss of the index or commutation channels.
Perpendicularity of the motor shaft centerline to the mounting surface can affect the gap relationship between the disc and the sensors. If the encoder housing is rotated relative to the motor shaft, the space between the disc and sensors can change, affecting signal amplitude and quality. The change in the gap will be dependent on the placement of the photo head on the mounting surface. Disc rotation will not affect the gap distance once the housing is secured.
Axial endplay of the motor shaft will cause the disc to move toward or away from the pc board sensors. The encoders are designed to handle small amounts of axial and radial run out, but if the axial run out is too large, the encoder disc can contact the sensors which may damage the lines on the disc or the sensors on the pc board. The perpendicularity of the shaft and mounting surface must also be taken into account when dealing with axial end play. The perpendicularity error must be added or subtracted depending on whether the perpendicularity error increases or decreases the gap between disc and sensors.
Tolerance between the encoder hub and disc assembly and the motor shaft affects the disc alignment to the sensors. If the inside diameter of the hub is at its maximum tolerance and the motor shaft at its minimum tolerance, this may affect the encoders output. An encoder in this situation will also be more susceptible to variations due to temperature changes.
Radial run out of the shaft will cause the data tracks under the sensors to be non- concentric. This can cause the index or commutation outputs to become non-functional.

Mounting the encoder according to the specified mounting tolerances can ensure proper operation and will likely allow the encoder to remain in service longer. For more detailed information about mounting specifications or for an example of how mounting stack ups may affect encoder performance, please contact us.

Encoder_Installation_Tolerances

Want to learn more?

Contact us today

Related resources and news

New Compact Rotary Encoder for Robots

SCHAUMBURG, IL (April 2021) – With its small dimensions and high reliability, HEIDENHAIN’s new KCI/KBI 1300 series of inductive rotary encoders are made specifically to support compact servomotors for collaborative and service robots. First presented at the international virtual trade show SPS in November of 2020, these new KCI 1319 / KBI 1335 measurement feedback […]

Read more »

New ECM 2400 Magnetic Ring Encoder

SCHAUMBURG, IL (April 2021) – For those needing contamination-resistant encoders with functional safety (FS) for machine feedback, HEIDENHAIN introduces an absolute modular magnetic angle encoder. This new ECM 2400 encoder supplements HEIDENHAIN’s portfolio of absolute angle encoders and is designed for machine tool applications that require a sturdy encoder with medium accuracy. The ECM 2400 […]

Read more »

New High Accuracy ETEL DXRH Rotary System

SAN JOSE, CA (March 2021) – With the introduction of the new high precision DXRH rotary axis system, ETEL once again offers those involved in the development and use of highly accurate semiconductor/electronics machines a new and better Theta axis option as either a stand-alone or system-integrated solution. ETEL’s new DXRH incorporates the best-in-class encoder […]

Read more »