what is linear encoder?
Dear colleagues, hello
A linear encoder is a device used to measure the position of a moving object along a straight line. It consists of a scale, which is fixed along the length of the object’s travel, and a readhead, which moves along the scale as the object moves. As the readhead passes over the scale, it produces electrical pulses proportional to the distance traveled. Linear encoders are essential in machine tooling, robotics, and material handling systems, providing highly accurate measurements within very small tolerances — making them ideal for precision applications.
What is a linear encoder used for?
Linear encoders are used to measure the position of a moving object along a straight line. Common applications include:
+ Machine tooling: Measuring tool slide positions and machine axes for precise cutting and machining control.
+ Robotics: Providing accurate feedback for robotic arms and automated motion systems.
+ Material handling systems: Tracking conveyor belt movement and controlling material transport.
+ Aerospace and defense: Measuring actuator or control surface positions in aircraft and missiles.
+ Industrial automation: Used in packaging, pick-and-place, and high-speed assembly lines for real-time motion monitoring.
+ Medical equipment: Ensuring precise movement in CT scanners, MRI tables, and robotic surgical systems.
Linear encoder vs Rotary encoder
Both sensors measure motion, but they differ in geometry and purpose:
+ Working principle: A linear encoder measures movement along a straight path, while a rotary encoder measures rotation around an axis.
+ Measured variable: Linear encoders output linear displacement; rotary encoders output angular position.
+ Applications: Linear encoders are ideal for CNC machines and precision guides; rotary encoders are preferred for motors and shaft positioning.
+ Output: Linear encoders often generate pulse trains, while rotary encoders use quadrature signals (A/B channels) for direction and speed detection.
Optical vs Magnetic linear encoder
Optical and magnetic linear encoders perform the same task but operate differently:
+ Working principle: Optical encoders use a light source and photodetector to read lines on a scale. Magnetic encoders use magnetized markings and a magnetoresistive sensor to detect movement. Both produce pulses proportional to distance traveled.
+ Accuracy: Optical encoders achieve nanometer-level resolution, while magnetic encoders typically offer micrometer precision.
+ Sensitivity: Optical types are more immune to dust and humidity, whereas magnetic encoders can be influenced by metal debris or strong magnetic fields.
+ Cost: Optical encoders are more expensive due to their higher resolution and environmental stability, while magnetic types are more cost-effective and durable for heavy-duty setups.
Linear encoder pinout
Pin assignments vary by manufacturer, but the most common include:
+ A and B channels: Quadrature outputs that provide position and direction information. The 90° phase shift between A and B defines motion direction.
+ Z channel: Provides a reference pulse per full travel or revolution, often used for homing or zero-point detection.
+ Vcc and GND: Power supply pins for encoder electronics. Always match voltage ratings (typically 5V or 24V) to avoid damage.
For detailed pinouts, always refer to the specific encoder’s manufacturer datasheet to ensure correct wiring and signal compatibility.
What is an absolute linear encoder?
An absolute linear encoder determines the exact position of an object at any moment, even after a power cycle. Unlike incremental types that only track movement changes, absolute encoders assign a unique code to every position on the scale. As the readhead moves, it detects these codes and outputs a direct position signal. This ensures instant position recovery on startup — vital for high-precision, safety-critical systems like CNC machining centers, metrology equipment, and advanced robotics.
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