Working Principle and Precautions of Grating Scales
What Are Grating Scales?
Grating scales are sensors that can measure linear or angular movements. It has two gratings: a main grating and an index grating. These move in relation to each other.
When light passes through both, it forms Moiré fringes—alternating dark and light lines. Photoelectric devices detect these patterns and convert them into electrical signals.
After signal processing, the system outputs digital pulses. CNC machines, machining centers, and measuring tools often use grating scales for precise positioning.
How Do Grating Scales Work?
Grating scales operate on the principle of optical interference and diffraction. When the main and index gratings shift relative to each other, they generate Moiré fringes.
These fringes modulate light intensity in a predictable pattern. Photoelectric sensors detect this variation and convert it into analog electrical signals—usually sinusoidal.
Signal amplifiers boost these weak signals. Then, shaping circuits convert them into two-phase signals, typically 90° apart. This allows the system to determine direction and magnitude of displacement.
After processing, the system sends clean, digital pulse outputs to a digital readout or control unit. These pulses correspond to movement distance, enabling precise, real-time position tracking.
High-resolution scales can detect sub-micron movement, making them essential in closed-loop CNC systems, coordinate measuring machines (CMMs), and precision automation.
Accuracy of Grating Scales
Grating Scale Precision Depends on:
The quality of the scale grating’s line markings.
The clarity of the index grating’s scan edges.
Signal processing quality and guiding accuracy also affect precision.
Two main error types influence accuracy:
Position deviation over the scale’s full length
Deviation within a single signal cycle
Installation and Maintenance of Grating Scales
Mounting Position Matters
Install the main scale on the machine’s moving table. Fix the reading head on the machine base. Place the reading head below the main scale when possible.
Avoid splash from chips or cutting fluid. If the reading head must face upward, use extra sealing.
Install the reading head on stationary parts. Fix the cable easily. Place the scale on moving parts (e.g., slideways).
Key Precautions During Use
1. Cut the Power Before Disconnecting Cables
Always power off the machine before removing signal cables.
2. Avoid Shocks and Vibration
Do not let the grating scale experience impact. Fractured gratings cause sensor failure.
3. Never Disassemble the Grating Sensor
Do not change the gap between the scale and index grating. Doing so reduces accuracy or damages the grating lines.
4. Prevent Oil and Water Contamination
Keep the grating surface clean. Oil or water disturbs the grating pattern and increases errors.
5. Avoid Corrosive Environments；
Keep the sensor away from corrosive agents. Corrosion damages the chrome layer and grating quality.
Summary: Grating Scales Require Careful Use
Grating scales play a critical role in high precision positioning. Understanding how they work improves machine performance. Following the right installation and care practices ensures long life and stable accuracy.
Always handle grating scales gently. Keep them clean. Install them properly. Avoid tampering with internal parts. These steps will help maintain their optimal performance in any industrial setting.