Fly laser marking machine has a deviation of 1 mm in the Z axis (up and downward movement axis) within half an hour, which is a relatively serious accuracy problem. This is usually the result of a combination of multiple factors and requires systematic investigation. The following are the possible reasons and investigation directions:
## 1. Mechanical structure and transmission problems (most common reasons)
1. **Z-axis guide problem: **
* **Wear/damage of guide rails: ** Long-term use or improper maintenance will cause the guide rails to be worn, scratched or deformed, and the motion resistance will increase or be uneven, resulting in inaccurate positioning.
* ** Poor lubrication of guide rails: ** Lack of grease or lubricant drying, resulting in increased friction and increased motor load, which may lose steps or cause crawling.
* **The rail installation is not parallel/non-vertical: ** Poor installation accuracy causes additional stress or friction during movement.
* **Rail fastener loose: ** The screws that fix the rail are loose, causing the rail position to change.
2. **Screw Screw/Belt/Rack Problems: **
* **Screw wear/deformation: ** The screw nut is worn, the screw itself is bent or worn, resulting in an increase in the transmission gap (back clearance) or poor movement. This is one of the main reasons for the decrease in repeat positioning accuracy.
* **Insufficient pre-tightening force/failure of lead screw nut: ** Insufficient pre-tightening force or failure, the transmission gap cannot be eliminated, resulting in empty space during forward and reverse movement.
* **Screw support bearings are damaged/loose: ** The support bearings at both ends of the screw are damaged or loose, causing the lead screw to squirm in axial or radial direction.
* **Belt/rack loose or wear: ** If the Z axis is driven by belt or rack, belt loose slippage, rack wear or poor meshing will cause displacement deviation. Belt transmission is more likely to cause errors caused by elastic deformation.
3. **Coupling Problems: **
* ** Loose/damage of coupling: ** If the coupling connecting the motor shaft and the lead screw/pulley is loose, slipped (such as aging of elastic coupling), cracking, or damage to the keyway, it will cause inaccurate power transmission or even interruption.
4. **Structural rigidity or deformation: **
* The entire Z-axis lifting structure (including mounting plates, support members, etc.) is not rigid enough and elastically deforms under the action of starting and stopping the motor or gravity.
* Structural parts (such as aluminum alloy profiles) undergo thermal deformation after the equipment is heated.
2. Motor and drive issues
Stepper motor loses step (if stepper motor is used):
Improper driver current setting: The current setting is too small, the motor torque is insufficient, and the load (friction, inertia, etc.) cannot be overcome, and it is easy to lose steps when acceleration and deceleration or load suddenly changes.
Driver failure: The internal components of the drive are aging or damaged, and the output current is unstable or insufficient.
Motor failure: The motor coils, bearings, etc. are damaged.
Voltage unstable: The supply voltage is too low or fluctuates greatly, causing the driver to fail to provide sufficient energy.
The acceleration/deceleration time setting is too short: The instantaneous start and stop torque requirement is too high, exceeding the motor capacity will lead to loss of steps.
Servo motor problem (if using servo motor):
Improper setting of servo drive parameters: The position ring, speed ring, current ring gain (PID parameter) is not set properly, resulting in slow system response, overshoot or oscillation, affecting positioning accuracy and stability. The rigidity setting is too low.
Encoder signal interference/failure: The encoder cable is disturbed, the connector is loose, or the encoder itself is faulty, resulting in a feedback signal error and the driver cannot accurately control the position.
Servo drive/motor failure.
Mechanical resonance: The Z-axis structure matches the natural frequency of the servo system, triggering resonance, resulting in control instability and positioning errors.
3. The influence of thermal deformation (It appears after half an hour, it is very important!)
Motor heating: The stepping or servo motor runs for a long time to generate heat, and the heat is transmitted to the lead screw, support seat or nearby structural parts, resulting in local thermal expansion. Especially for the lead screw, its thermal expansion coefficient is relatively large, and a few degrees of temperature rise may lead to significant length changes (1 mm deviation may be caused by thermal expansion on medium-length lead screws).
Driver/power heating: Heat accumulation in the control cabinet affects nearby lines or sensors.
Laser heating: The laser itself is the main heat source, and its heat radiates or is transmitted to the Z-axis assembly.
Ambient temperature changes: If the workshop temperature fluctuates significantly within half an hour (such as air conditioner starts and stops, doors opens), it will also cause the metal parts to expand and contract.
4. Control system and feedback
Encoder/Graster Ruler Problem:
Feedback component pollution: There is oil and dust on the grating ruler reading head window or encoder code disk, which affects signal reading.
Feedback element loose/damaged: Loose installation or damaged by itself.
Feedback signal line interference/poor contact: The signal is subject to electromagnetic interference or the contact resistance of the connector is large, resulting in an incorrect position feedback value.
Controller issues: Internal calculation errors, software bugs, or hardware failures (rare but need to be troubleshooted).
Interference: The strong power lines (such as laser power supplies, high-power equipment) and the control lines (motor lines, encoder lines) are not effectively isolated, and electromagnetic interference causes abnormal control signals or feedback signals.
V. Other factors
Overload or collision: The Z-axis load is too large (such as the mounting fixture is too heavy), exceeding the design capability. Or there has been a collision, resulting in slight deformation of the mechanical structure or damage to the transmission parts.
Gravity compensation problem: The Z-axis is usually vertical motion and requires overcoming gravity. If the balance device (such as counterweight blocks, pneumatic balance cylinders) fails or is set incorrectly, or the gravity compensation parameters of the servo motor are set incorrectly, it will cause the up and down directions to slide when the up and down position is inconsistent or when the position is maintained.
Unstable foundation/platform: The equipment is placed unstable, or the working platform is not rigid and vibrated.
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