A measurement grating is a type of photoelectric sensor commonly used for displacement measurement and precision positioning. It is widely applied in CNC machine tools, automated equipment, precision measurement platforms, and other systems. To ensure measurement accuracy, the measurement grating system usually needs to perform a “zeroing” operation during startup or operation, that is, to set the current position as the reference zero point. The implementation of automatic zeroing generally relies on the following methods or technical principles:
1. Automatic zeroing via reference mark signal
Most precision measurement grating systems have one or more reference marks (also called “origin” or “marking points”) on the grating scale. When the system starts or relocates, the moving component passes over the reference mark, and the readhead recognizes this signal, thereby automatically setting this point as the zero point or a preset coordinate.
Workflow:
The system powers on or starts the “zeroing” command;
A fast return-to-zero motion is executed (reverse movement of Z-axis or X/Y-axis);
The grating readhead detects the reference point signal;
The controller defines this point as the zero point, completing the zeroing process.
Features:
High accuracy and good repeatability;
Reference mark is formed by etched structure on the grating, not easily shifted;
Suitable for high-precision automation equipment.
2. Zeroing using limit switches or proximity switches
For some simple or cost-sensitive systems, limit switches or proximity sensors can be installed on the mechanical structure as the trigger point for zeroing. When the measuring head moves into the limit area, the switch activates, and the system recognizes the current position as the zeroing reference.
Advantages:
Simple structure and low cost;
Easy to integrate with PLCs or motion control cards;
Commonly used in low-precision or coarse positioning scenarios.
Disadvantages:
Repeat positioning accuracy is not as good as with reference marks;
Easily affected by environment or wear.
3. Electronic zeroing (software sets current value as zero)
In some application scenarios, no physical origin is required. The system directly sets the current read position of the grating as the zero point via software.
Typical scenarios:
Some test benches or translation stages;
Non-closed-loop control applications;
Temporary measurements or relative displacement measurements.
Method:
User presses the “reset” button at any position;
The control system resets the current read position value to “0”;
All subsequent displacements are referenced to this point.
4. Automatic zero-return control algorithm and implementation
In modern motion control systems, automatic zeroing is often integrated in the controller or driver software. The typical process is as follows:
Start the automatic zeroing program;
System checks whether it is already in the zero-point area;
If not, move slowly in the preset direction;
Read the grating reference point or limit signal;
Once the signal is detected, stop the movement;
Set the current position to “0” or a specified initial value;
Zeroing is completed, and normal measurement or motion begins.
5. Notes
Speed control: The zeroing process usually includes “fast approach + slow approach” phases to improve accuracy;
Temperature drift compensation: High-precision systems need to consider the thermal expansion or contraction of the grating scale after zeroing;
False trigger prevention: Gratings with multiple reference points should set a unique identifier to avoid misidentification.
