Exploring linear, rotary, and sine encoders
ELECTRICAL & ELECTRONICS FEEDBACK DEVICES
INMOCO
Exploring linear, rotary, and sine encoders
Encoders are the most widely applicable feedback devices for high-precision industrial servo systems.
Encoders are the most widely used feedback devices for electric motor control, capable of delivering precise position and speed feedback for closed-loop performance. With numerous technology options to choose from, selection of the right encoder technology is critical.
Gerard Bush, engineering advisor at motion specialist INMOCO, discusses the technology behind incremental encoders.
In a recent article, we looked at the uses of Hall effect sensors and resolvers for the control of electric motors. Due to the design requirements of Hall effect sensors and resolvers, they are both are usually integrated with the design of the motor to achieve commutation feedback and provide closed-loop feedback respectively in extreme environments.
However, the most common feedback device is the encoder, providing accurate position and speed sensing. Available in a range of designs according to the motion control requirement, encoders are typically selected following, and in addition to, the specification of the motor. The variety of encoder designs available means that careful attention is required to their selection, and the initial factor is their physical measurements.
Rotary or linear encoder?
A rotary encoder measures the angular rotation of the motor’ s rotor or shaft. This lends itself to closed-loop control for rotational applications, from a robotic limb, through to a spinning machine tool. To achieve this, the signals from its sensors are converted into digital pulses or sine / cosine waveforms, which the drive or controller interprets for speed and position management.
Alternatively, a linear encoder can be preferable for applications that involve a straight-line of operation, such as a CNC machine or three-axis gantry. A linear encoder directly measures true linear position, while
38 PECM Issue 78