by What is an Optical Encoder?
An optical encodings is an electromechanical device that converts the angular position or motion of a shaft or axle to a digital code, which is commonly an analog-to-digital converter. Rotary optical encodingss essentially measure rotational motion and convert it into digital signals that can be interpreted by digital devices like PLCs or motion controllers.
Types of Optical Encoder
Incremental encoders output a signal that indicates only the direction and relative amount of shaft rotation and do not provide any information about the starting position. These Optical Encoder typically provide two square wave output signals that are 90° out of phase. From these the motion in both the clockwise and counter-clockwise direction can be determined. The resolution of the encoder is determined by the number of slits in the code disc or strips.
Common applications for incremental encoders include machine tools, CNC machines, industrial robots, 3D printers, and other positioning systems that don’t require knowing the absolute position. They are cheaper than absolute encoders but lack position-retaining capabilities.
Absolute Encoders
Absolute encoders output a code containing enough information to determine the exact position of the shaft at any time without having to refer to a prior position. This is possible because absolute encoders use a coding method like Gray or binary coding that represents each position uniquely with a corresponding fixed digital word.
The main benefits of absolute Optical Encoder are that they immediately output the position upon power-up without having to go through homing or referencing moves. This makes them well-suited for systems that need to retain position memory even after power cycling. Common applications include CNC machines, factory automation equipment, motion simulators, and any systems requiring repeatable positioning. However, absolute encoders are significantly more expensive than incremental models.
Optical encodings Components
All optical encodingss contain the following main components:
Code wheel/disc – Typically made from metal or plastic and contains evenly spaced alternating opaque and transparent code elements arranged in a circular pattern. These could be slots, stripes or grayscale markings.
Light source – Usually LEDs that illuminate the code pattern on the disk.
Photodetectors – Photo transistors or diodes used to sense the intensity of light passing through the code pattern and convert it to electrical signals. There are typically two sets of photo detectors arranged at 90° to read incremental signals.
Index detector – A additional photo detector may be present to read a unique index position marker for position reference purposes in absolute encoders.
Housing – Protects internal components and allows shaft mounting. Precision bushings ensure accurate alignment between shaft and code disk.
Signal processing electronics – Circuity that digitizes the raw detector signals, generates output digital/analog signals proportional to shaft position, and provides power/communication interfaces.
Optical encodings Resolution
The resolution of an optical encodings refers to the smallest movement it can detect and is determined by the number of code elements on the disk. Common resolutions include:
– 1000 CPR (counts per revolution) – Can detect movements as small as 0.36°.
– 2000 CPR – Movements as small as 0.18°
– 4000 CPR – Movements as small as 0.09°
– 5000 CPR – Movements as small as 0.072°
– 10,000 CPR – Movements as small as 0.036°
Higher resolutions mean smaller motions can be detected but cost more due to the need for higher density coding patterns. The required resolution depends on the application and machinery used.
Installation and Alignment of Optical encodingss
Proper installation and alignment of optical encodingss is critical to ensure reliable and accurate position sensing over their operating life. Key points include:
– Carefully mounting the encoder housing using alignment dowels/pins in any mounting holes to fix relative positions.
– Ensuring the code disk rotates concentrically to minimize jitter/variation in readings.
– Adjusting set screws to achieve tight and secure coupling to the target shaft with no play.
– Aligning the light source and photodetectors precisely parallel to the code disk pattern to avoid offsets in readings.
– Shielding the encoder from excessive shock/vibration, chips/dust which could disrupt the light transmission.
– Routing attached cables carefully to avoid stresses affecting the housing or accuracy.
Adhering to manufacturer mounting/alignment guidelines ensures optimal encoder performance over many years of operation.
Optical encodingss have become a standard motion sensing technology favored for their high resolution, reliability and ability to produce digital position signals suitable for modern control systems. Application of the right encoder type and careful installation is important to fully realize their benefits.
*Note:
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it.
