Force Sensor Troubleshooting

How Force is Measured

In the standard configuration, the system calculates the force applied by the bonding head using the following components:

1. Pneumatic Pressure Sensor: The system uses a SMC PSE540-01 (Small Pneumatic Pressure Sensor). This sensor measures the air pressure supplied to the bonding head cylinder.
2. Analog Voltage Signal: This sensor outputs an analog voltage signal to the system's PLC (Analog Input Word 0).
3. PLC Conversion: The PLC converts this voltage into a Force value (Newtons) based on the surface area of the cylinder and calibration parameters. You can view this conversion in real-time on the Service Screen: Pressure.
4. 1. Actual Voltage [mV]: The raw signal from the sensor.
   2. Actual Force [N]: The calculated force based on the calibration.

Troubleshooting the "Slow Response" Issue

The symptom you described—the sensor responding slowly or drifting for about an hour after power-up—is often related to thermal drift or mechanical friction rather than the air pressure itself.

Here are the specific steps to diagnose this based on the system design:

1. Distinguish Electrical Drift from Mechanical Friction
   Since the force is calculated from air pressure, you must determine if the sensor is reading incorrectly or if the cylinder is actually moving/pressurizing slowly.
2. 1. Test: Go to the Service Screen: Pressure immediately after power-up.
   2. Observation: Note the "Actual Voltage [mV]" with 0 force (head up) and then with the head down.
   3. Comparison: Check these values again after the 1-hour warm-up period.
   4. 1. If the Voltage changes significantly (without a change in air regulator setting), the SMC Pressure Sensor or the PLC Analog Input is thermally drifting and likely needs replacement.
      2. If the Voltage remains stable but the process results are different, the issue is likely mechanical friction in the cylinder.
3. Mechanical "Warm-Up" (Cylinder Friction)
   If the sensor voltage is stable, the "slow response" is likely physical.
4. 1. Grease Viscosity: The pneumatic cylinder in the bonding head contains grease. If the machine is in a colder environment, the grease may be viscous (thick) at startup, causing the head to descend slower or apply slightly less effective force until the friction reduces.
   2. Flow Regulators: Check the upper and lower flow regulators on the head. If they are set too tight (slow), the system is more sensitive to friction changes during the warm-up phase.
5. Air Quality
   The manual specifies the system requires constant dry, clean air (6 +/- 0.5 bar).
6. 1. If the air supply has moisture, it can affect the response time of the pneumatic sensor and valves, particularly if the machine has been off and the moisture has settled or cooled.

Summary Recommendation

1. Monitor the [mV] reading on the Service Screen during the warm-up hour. If the millivolts drift, replace the SMC PSE540-01 sensor.
2. If the millivolts are stable, cycle the head up and down (Dry Run) for several minutes at the start of the shift to warm up the cylinder grease and reduce friction.