Encoders convert motion to an electrical signal that can be read by some type of control device in a motion control system, such as a counter or PLC. The encoder sends a feedback signal that can be used to determine position, count, speed, or direction. A control device can use this information to send a command for a particular function.
In any application, the process is the same: a count is generated by the encoder and sent to the controller, which then sends a signal to the machine to perform a function. For example:
A compact, 2-inch blind hollow bore encoder (1) provides motion feedback on a motor. The flex mount (2) stabilizes the encoder, and the cable sends the electrical signal to the receiver.
Encoders use different types of technologies to create a signal, including: mechanical, magnetic, resistive, and optical – optical being the most common. In optical sensing, the encoder provides feedback based on the interruption of light, as illustrated in Figure 1.
A beam of light emitted from an LED passes through the Code Disk (see Figure 1), which is patterned with opaque lines , much like the spokes on a bike wheel. As the encoder shaft rotates, the light beam from the LED is interrupted by the opaque lines on the Code Disk before being picked up by the Photodetector Assembly. This produces a pulse signal: light = on; no light = off. The signal is sent to the counter or controller, which will then send the signal to produce the desired function.
As seen in Figure 1, a beam of light emitted from an LED passes through a transparent disk patterned with opaque lines The light beam is picked up by a photodiode array, also known as a photosensor. The photosensor responds to the light beam, producing a sinusoidal wave form, which is transformed into a square wave or pulse train. This pulse signal is then sent to the counter or controller, which will then send the signal to produce the desired function.
Figure 1 diagrams a typical rotary encoder. Incremental encoders can provide a once-per-revolution pulse (often called the index, marker, or reference) that occurs at the same mechanical point of the encoder shaft revolution. This pulse is on a separate output channel (Z) from the signal channel or quadrature outputs. The index pulse is often used to position motion control applications to a known mechanical reference.
Resolution is a term used to describe the Cycles Per Revolution (CPR) for incremental encoders. Each incremental encoder has a defined number of cycles that are generated for each 360 degree revolution of the shaft. These cycles are monitored by a counter or motion controller and converted to counts for position or velocity control. Figure 2, at right, shows how the whole encoder comes together.
Figure 3 shows one example of how an encoder is used in a typical motion control application. Cut-to-length, plotters, packaging and conveying, automation and sorting, filling, imaging, and robotics are all examples of applications that would use an encoder. The process is the same: a count is generated by the encoder and sent to the controller, which then sends a signal to the machine to perform a function.
For more information about how an encoder works, watch this Encoder 101 video, “What’s an Encoder?" And if you still have questions about how an encoder would work in your specific application, or anything else encoder-related, give us a call. When you contact EPC, you talk to real engineers and encoder experts who can answer your toughest encoder questions. Contact EPC today to get the information you need.
A critical resource for technical encoder information. Developed in partnership with Design News magazine.
Interactive CPR calculators, 3D configurator, and a glossary of terms to help you through the encoder specification process.