Understanding Optical Encoder Devices Used To Convert The Angular Position

 

Optical Encoder

What are Optical rotary encoders?

Optical rotary encoders are devices used to convert the angular position or motion of a shaft or axle to digital code. An optical rotary encoder works by using an LED light source to illuminate lines or shadows on a disk or strip attached to the rotating part. A sensor array on the opposite side reads the lines or shadows and converts them into a digital pulse stream. The frequency or phase of these pulses indicates rotation speed and direction.

Working Principle

At its core, an optical rotary encoder utilizes a light source and sensor to detect motion. A common configuration uses an LED to illuminate a striped disk attached to the rotating object. As the disk spins, transparent and opaque stripes alternately pass in front of the LED. The light that passes through is detected by a sensor array on the other side.

The sensor array Optical Encoder contains two sets of photo detectors precisely spaced so that one detects the opaque stripes while the other detects the transparent ones. This produces two tracking signals called Channel A and Channel B that are 90 degrees out of phase. By monitoring the signal transitions of both channels, the encoder can determine rotation direction and position. Each full cycle of the disk causes one pulse on Channel A followed by one pulse on Channel B.

Incremental and Absolute Encoding

There are two main types of encoding formats used - incremental and absolute. Incremental encoders only track relative motion and require the counting of pulses to determine position. Absolute encoders output a binary code representing the exact position each rotation through the use of gray codes.

Incremental encoders are simpler in design as they only require two sensing tracks. They are suitable when position resetting is possible. Absolute encoders have a more complex multi-track pattern to output a unique position code each revolution. This makes absolute encoders useful in applications requiring non-volatile position storage without external position resetting.

Applications

Due to their accuracy, repeatability and non-contact operation, Optical Encoder find uses across many industries for motion control and precision measurements. Some common applications include:

- CNC Machine Tools - Used on motors, spindles, slides to provide position feedback for numerical control.

- Robots - Optical rotary encoders enable precise motion and positioning of robotic arms, joints and end effectors.

- Factory Automation - Used in assembly machines, packaging equipment to time motions and steps.

- 3D Printing - Help control print head, build platform movements for precision layer deposition.

- Medical Equipment - Encoders assist in movement of components like MRI machines, surgical robots.

- Automotive - Help control functions like power steering, transmission, throttle position, active suspension.

- Avionics - Provide feedback on aircraft control surfaces, landing gear for reliable operation.

- Camera Systems - Track lens position, zoom level, auto-focus movements for consistent operation.

Advantages of Optical Encoder

Compared to other encoder types like magnetic, optical rotary encoders have several advantages:

- High Resolution - Can detect minute motions up to nanometer level due to narrow sensing elements.

- durability - Being contactless, optical rotary encoders have no mechanical wear and a longer service life than other types.

- Reliability - Solid-state design with no moving parts makes them rugged for harsh environments.

- Precision - Photo-detection allows sub-micron placement of sensing elements for high-fidelity output.

- Immunity - Not affected by electrical noise, dirt or nearby ferrous materials as there is no magnetic field.

- Safety - Contactless technology eliminates risks of sparking from mechanical failures in hazardous zones.

- Flexible Installation - Optics allow placement of sensor independently from moving encoder disk/strip.

- Speed - Capable of measuring high rotational and linear speeds up to 30,000 RPM.

While incremental costs may be higher initially due to optics, overall lifetime reliability and cost of ownership favors Optical Encoder for most motion control applications. Their advantages have made them the clear choice today in equipment that requires precision and repeatability of motion parameters.

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About Author:

Money Singh is a seasoned content writer with over four years of experience in the market research sector. Her expertise spans various industries, including food and beverages, biotechnology, chemical and materials, defense and aerospace, consumer goods, etc. (https://www.linkedin.com/in/money-singh-590844163)