Encoders are electromechanical devices that provide electrical signals for the means of speed and/or position control. More specifically, an encoder turns mechanical motion into an electrical signal that can be used by the control system to monitor specific parameters of any given application, allowing operators to make adjustments as necessary. Some of the parameters that a motor encoder can monitor include speed, distance, RPM, position, and various others. Applications that use encoders or similar monitoring technology to control specific parameters are often called closed-loop feedback or closed-loop control systems.
A motor encoder in particular is a rotary encoder that is mounted to an electric motor to provide closed loop feedback signals by tracking speed and/or position of a motor shaft. There is a wide range of motor encoder designs, such as incremental, absolute, optical, magnetic, shafted, and hub/hollow shaft, among others. The type of motor encoder used is determined by a multitude of factors, including motor type, the application requiring close-loop feedback, and the mounting style needed. When selecting components for a closed-loop control system, the motor encoder type is dependent on one’s motor, some of which we will cover in the next section.
AC Motor Encoders
AC induction motors are widely used for general automation machine control systems since they are robust in design and economical. Motor encoders are utilized for their precise speed control in applications with AC motors that have more robust IP, shock, and vibration parameters.
Servo Motor Encoders
Servo motor encoders, or permanent magnet motor encoders, offer closed-loop feedback control systems to applications that require higher precision and accuracy. However, they are not as robust as AC induction motors. This motor type can be modular, incremental, or absolute, based on the level of resolution and accuracy required.
Stepper Motor Encoders
Stepper motors are relatively inexpensive, precise, and are found in open-loop systems. Typically, in systems with stepper motors that necessitate speed control, an incremental motor encoder is used, allowing the system to achieve closed-loop feedback. Additionally, stepper motor encoders allow for improved control of stepper motors by providing precision feedback of the location of the motor shaft with regard to the step angle.
DC Motor Encoders
DC motor encoders are utilized for speed control feedback in DC motors where an armature or rotor with wound wires rotates within a magnetic field generated by a stator. Furthermore, they provide a mechanism to measure the speed of the rotor and a closed-loop feedback to the drive for precise speed control.
Motor Encoder Mounting Styles
Motor encoder selection is also based on the most convenient mounting option for your applications. As such, there are a few common mounting configurations popularly used. Shafted motor encoders use a coupling method to affix the motor encoder shaft to the motor shaft. This method provides mechanical and electrical isolation from the motor shaft. Unfortunately, this mounting style can be costly. Hub/hollow shaft motor encoders, on the other hand, are directly mounted to the motor shaft with the help of a spring loaded tether. This mounting style is the easiest to achieve as it is simple to install and does not require shaft alignment. Lastly, bearingless motor encoders, or ring mount motor encoders, consist of a sensor assembly in the form of a ring that is mounted on the motor face and a magnetic wheel which is mounted on the motor shaft.
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