Linear scales (also known as linear optical scales) are key components for achieving high-precision control in CNC machining centers. Their primary function is to provide high-precision linear position feedback for full closed-loop control, which greatly improves the positioning accuracy, repeatability, and machining accuracy of the machine tool.
The core functions and advantages are explained in detail below:
1. Realize True Full Closed-Loop Control
Standard machining centers typically use rotary encoders mounted on the servo motor shaft for position feedback, known as semi-closed-loop control.This method only measures the rotation angle of the motor and converts it into linear displacement of the worktable through transmission mechanisms such as ball screws.
However, the transmission chain (screws, nuts, couplings, bearings, etc.) suffers from backlash, elastic deformation, thermal expansion, wear, and pitch errors. The encoder cannot detect the deviation between the actual worktable position and the theoretical position caused by these factors.
A linear scale is installed directly between the worktable / headstock and the machine bed, measuring the actual linear displacement in real time. This true position signal is fed back to the CNC system.
The CNC system compares the actual position from the linear scale with the target position from the program, calculates the error, and sends correction commands to the servo drive. The drive adjusts the motor until the actual position matches the target, forming a complete closed-loop process:Command → Execution → Actual Measurement → Correction → Command.
2. Eliminate Transmission Errors and Improve Precision
This is the most important value of linear scales.By directly measuring the real position of the final moving parts, the linear scale system can detect and compensate for various transmission errors in real time:
Pitch errors of the ball screw
Thermal elongation of the screw caused by machining heat
Backlash from wear of the screw and nut
Reverse backlash during direction changes
Elastic deformation from cutting force and acceleration
Straightness and parallelism errors of linear guides
With such compensation, the machine positioning accuracy can stably reach the micron (μm) or even sub-micron level.
3. Improve Machining Accuracy and Surface Quality
Higher position control accuracy directly improves the dimensional accuracy, form accuracy, and positional accuracy of machined parts.More precise position control also helps achieve better surface finish.
4. Enhance Dynamic Performance
Although linear scales do not directly increase speed, high-precision real-time feedback allows the system to accurately track the commanded path during high-speed feeding, reducing following errors and achieving better dynamic performance while maintaining accuracy.
5. Maintain Long-Term Precision and Reduce Maintenance Costs
Even if transmission parts such as ball screws gradually wear over time, the linear scale system can continuously detect and compensate for the resulting errors. This allows the machine to maintain high precision for a longer period and reduces strict requirements for the precision of consumable components.
Summary
The core function of a linear scale is to bypass intermediate transmission links, directly obtain the real position of moving parts, and achieve high-precision full closed-loop control.It is an indispensable component for high-end machining centers to perform ultra-precise, highly stable, and long-lasting machining.
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