The homing function of a CNC machine is crucial for moving the machine's axes to a predefined reference position, known as the home position or zero point. This article discusses the principles of the homing function, common methods used, and troubleshooting steps to address any issues that may arise.
Principles of CNC Machine Homing Function
The homing function ensures that the CNC machine's movement axes return to a known reference position, allowing for accurate and repeatable operations. Here are the four common homing methods:
Direct Homing
1. The homing axis moves towards the home position at a rapid speed set by parameters.
2. When the deceleration block presses the home deceleration switch, the homing axis slows down to the reference point positioning speed.
3. After the deceleration switch is released, the system detects the encoder's grid point or zero pulse.
4. Upon detecting the first grid point or zero pulse, the motor stops, and the current position is set as the machine's zero point.
Overtravel Homing
1. The homing axis moves towards the home position at a rapid speed.
2. After the deceleration block presses the home deceleration switch, the homing axis slows down to the reference point positioning speed and moves in the opposite direction.
3. Once the deceleration switch is released, the system detects the encoder's grid point or zero pulse.
4. Upon detecting the first grid point or zero pulse, the motor stops, and the current position is set as the machine's zero point.
Double Overtravel Homing
1. The homing axis moves towards the home position at a rapid speed.
2. After the deceleration block presses the home deceleration switch, the homing axis slows down to the reference point positioning speed and moves in the opposite direction.
3. The deceleration switch is pressed again, and the homing axis runs at the zero pulse search speed.
4. Upon detecting the first grid point or zero pulse, the motor stops, and the current position is set as the machine's zero point.
No Overtravel Homing
1. After receiving the homing signal, the homing axis moves slowly in a fixed direction.
2. Upon detecting the first grid point or zero pulse, the motor stops, and the current position is set as the machine's zero point.
Troubleshooting Homing Function Issues
When a CNC machine fails to return to the home position correctly, the following troubleshooting steps can help identify and resolve the issue:
Checking the Deceleration Block
- Ensure the deceleration block is secure and not loose.
- Verify that the length and installation position of the deceleration block are appropriate.
Inspecting the Deceleration Switch
- Confirm that the deceleration switch is firmly fixed and not loose.
- Check for any damage to the deceleration switch and replace if necessary.
Examining the Encoder or Grating Scale
- Inspect the pulse encoder or grating scale for any signs of damage.
- Ensure the connections of the encoder or grating scale are secure and functioning correctly.
Adjusting the Press Brake Blade Speed
For press brakes, adjusting the blade speed can be done by regulating the speed valve in the hydraulic system:
- Increasing the Blade Speed Valve Opening: This increases the flow rate in the hydraulic system, speeding up the blade's movement.
Important Considerations
- Clear the Worktable: Ensure the machine worktable is empty before performing homing operations.
- Set Appropriate Homing Speed: The homing speed should be set according to the machine's inertia and precision requirements.
- Recalibrate After Adjustments: If any adjustments are made to the encoder or grating scale, the system should be recalibrated.
Conclusion
Understanding the principles of the CNC machine homing function and how to troubleshoot common issues is essential for maintaining accurate and efficient machine operations. By following the outlined steps and considerations, you can ensure that your CNC machine performs optimally and reliably.
