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| | | | | | | | | | | | | | | | | | | | | | | | | | | | Piezoelectric Force Measurement in Practical Applications | | | | | | | | | | During the fully automated assembly of printed-board assemblies the contacts of the assembly components must be fed (or set) through the matching holes with a minimum of friction. Mounted in the appropriate position on the assembly station, force sensors can measure these so-called setting forces, and control monitors are used to monitor the setting process. If the permissible setting force is exceeded, the assembly process is stopped within seconds. This approach prevents postproduction costs or damage to the circuit board. Printed-board assemblies were subjected to a range of processing sequences prior to the insertion of conventional component parts such as capacitors manufacturer, resistors, diodes, transformers, coils, filters or plug assemblies. As they are fitted with components such as soldered-on SMDs, printed circuit boards are of significant value. Reliable protection of the printed-board assemblies during further in-line assembly processes is of major importance. During fully automated in-line assembly, the contacts of the assembly components to be inserted must be fed through the matching holes with a minimum of friction. Care must be taken that the contacts do | | not bend and snap, as this would damage the circuits, which in turn, would require secondary finishing measures or the complete loss of the workpiece. Operators of industrial assembly machines can rely on high-precision line technology. However, the machines also need to compensate for variations in and deviations from the component geometry caused by the preceding production steps. Therefore, the assembly units will test the setting force prior to every setting process. Controlling the Setting Force with High-Sensitivity Sensors The assembly heads of assembly machines are equipped with several grippers for picking up the assembly components from the automated delivery stations and placing them onto the printed circuit board. During insertion of the structural component, the active gripper arrangement allows measurement of the setting force by a sensor in central position. As all grippers rotate around a fixed part of the assembly head, the ideal measured force would be exactly zero. "Ideal" conditions are achieved when the contacts are inserted through the matching holes without friction. As potential forces occurring in this application would be very low, the use of a high-sensitivity piezoelectric sensor such as Type 9215 or an M5 strain sensor Type 9247A, | | | | | | Kistler Benefits | | | | | | | | | | High-sensitivity, compact piezoelectric force and strain sensors with maximum resolution, Easy integration of CoMo operation and control into existing machine environment saves hardware and engineering costs, CoMo Net allows easy integration of monitoring processes into company LANs, Response time of a few milliseconds, and Fast program switch-over. | | | | | | | | | | which has been calibrated for force measurement, is recommended. The force measured during the setting procedure will increase only in cases where the connection wires are set beside the contacts and pressed onto the circuit board and when the insertion hole on the circuit board is too narrow or does not allow passage at all. CoMo Net monitors a specified force threshold (Y2). If the force does not transgress this threshold, the setting procedure is assessed as "OK". Once the thresh-old has been passed, the CoMo sends a signal indicating the transgression to the digital outputs immediately. | | | | | | | | | | | | | | | | | | The blue curve is the reference curve for an "OK" setting procedure, black is the reference curve for "Not OK" processes. If the force does not transgress the specified threshold, the setting sequence has passed ("OK") | | | | | | | | | | www.kistler.com | | | | | | 38 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
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