Linear Encoder
Why use a linear encoder instead of only a motor encoder?
A motor encoder measures motor rotation, but a linear encoder measures actual axis displacement, capturing ballscrew error, backlash, and other transmission losses directly at the machine axis.
What is the main control advantage?
It enables direct closed-loop correction at the point of motion, improving absolute positioning accuracy and repeatability on the table or slide.
When is absolute better than incremental?
Absolute is preferred when immediate position availability after power-up is important; incremental is common when the control effectively handles homing and reference-mark logic.
A linear encoder is a position sensor that measures straight-line displacement of a machine axis and converts it into an electrical feedback signal for a DRO or CNC motion controller. In CNC machine tools, it is mounted to measure actual axis position of X, Y, or Z travel, enabling the control to correct servo motion in real time, thereby reducing errors such as backlash, pitch error, and ballscrew heating.
On a CNC mill, linear encoders provide direct position feedback from the table or slide, improving closed-loop positioning accuracy and repeatability during contouring, boring, grinding, and tight-tolerance finishing. The controller compares commanded position to actual position and continuously adjusts servo output, compensating for mechanical compliance, drive losses, and thermal drift. This is critical when parts must hold tight tolerances across long travels, because the encoder measures the axis itself rather than inferring from motor rotation. Absolute linear encoders report true position immediately on power-up, useful for recovery after shutdown. In real production, this feedback maintains consistency under thermal changes or heavy cutting loads, ensuring parts meet specs. Incremental encoders are also common, chosen based on control compatibility, travel length, environment, and accuracy target.
Coolant/chip contamination: Chips, coolant spray, or oil film entering the measuring path destabilize the scan signal, causing intermittent following errors, position noise, or axis faults.
Poor thermal or mechanical mounting: If the scale is not aligned with the axis or thermal growth is mismanaged, the controller sees false position error, leading to dimensionally inconsistent parts.
Wrong encoder type for the control: Using a feedback device the CNC cannot decode, or one with insufficient speed or resolution, results in missed counts, unstable servo tuning, or oscillation during fast traverses.