What is a Servo Motor Encoder?
Encoders are one of the most important components in a servo motor application enabling a control system to function properly. We are familiar with many control systems such as how bicyclists use their eyes to adjust their speed or direction, and musicians use their ears to adjust their volume and pitch.
Encoders sense the position of the motor allowing a servo drive to commutate the motor. A servo controller can also use this position to calculate speed and control motor torque for use in high precision automated industrial applications.
How Encoders Work
A typical servo motor encoder consists of three primary components:
1. Code Disc
The encoder’s code disc is attached to the motor shaft, which has patterns of lines or slots. In optical encoders, this disc is transparent with opaque lines, while in magnetic encoders, it contains magnetic poles.
2. Sensor
As the disc rotates, an optical or magnetic sensor detects these patterns, generating pulses or signals corresponding to the shaft’s position. There are two types of sensors, optical and magnetic. Where optical sensors use light to detect changes, magnetic sensors use magnetic fields.
3. Signal Processor
The encoder’s sensor collects this data and converts it into a digital signal that is sent to the controller – either as serial data or incremental line states. The controller uses this information to make needed adjustments to the equipment’s speed or position.
Encoder Alignment: Isn’t Important – It’s Critical
Types of Servo Motor Encoders
There are two primary types of encoders used with servo motors, Incremental and Absolute.
Incremental Encoders generate pulses as the motor shaft rotates. By counting the pulses, the controller can calculate the motor’s relative position. Because the pulses do not provide absolute position information, the controller requires a reference point at startup to determine the motor’s position.
Absolute Servo Motor Encoders provide a unique position value for each shaft position enabling an encoder to provide position information on startup as well as retaining it even if power is lost. Absolute encoders are preferred in applications where maintaining accurate position is critical.
Common Encoder Problems
Issues with servo motor encoders can lead to inaccurate positioning, system errors, or motor failure. All of which has a detrimental effect on product quality, production, and profitability. The most common of these include:
- Contamination by dust, oil, or moisture. This often leads to signal loss or inconsistent outputs.
- Signal degradation results in erratic feedback. This is often traced to electrical noise, loose connections, or worn-out cables.
- Mechanical misalignment between the encoder and motor shaft. This may be from normal use, an impact to the motor, or an error in reassembling the motor after maintenance. Misalignment will cause inaccurate readings or even physical damage to the encoder.
- Age or excessive vibration. This can cause the motor to lose position information, impacting overall system performance and reliability.
Regular maintenance and proper installation can help mitigate these issues. Still, even the most well-maintained encoders can experience problems. Following these steps can help you to maintain encoder integrity when servicing a servo motor.
7 Steps to Servicing a Servo Motor Without Compromising Encoder Alignment
Servo motor encoders ensure that the motor and equipment perform tasks exactly as intended. This is especially important to robotics and other manufacturing applications where precise motion control is non-negotiable.
You can also download The Quick Reference Guide to Servo Motor Maintenance and Repair. Inside this in-depth guide, you’ll find insights into:
- Diagnosing common servo issues
- Understanding common servo error codes
- Knowing what you can fix in-house and what needs to be sent out for repair
- Identifying tools you’ll need to make repairs in-house
- Learning what makes a successful repair shop
