Piezoelectric Force Sensor for Ultrasonic Welding Drift
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Solution Overview
Problem
Ultrasonic processing systems face limitations in processing speed due to abrupt changes in welding force caused by material thickness fluctuations and thermal expansion, leading to non-optimal welding results and resonance issues with existing force measurement sensors based on strain gauges.
Innovation Solution
Employing a piezoelectric sensor with a control device that short-circuits the sensor when not in contact with the material and adds a time-varying force compensation value to correct for drift, allowing for more accurate force measurement and reduced vibration damping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a force sensor based on strain gauges is used to measure welding force, then the system can detect force changes, but the sensor introduces elasticity into the system causing after-vibrations and resonance issues that limit processing speed
Solution Approach 1:
The patent replaces the strain gauge-based mechanical force sensor with a piezoelectric sensor that converts mechanical force directly into electrical signals. This substitution eliminates the elastic mounting structure required by strain gauges, thereby removing the source of after-vibrations and resonance while maintaining force measurement capability. The piezoelectric sensor provides rigid force measurement without introducing mechanical compliance into the ultrasonic welding system.
Solution Approach 2:
The patent changes the measurement principle from electrical resistance change (strain gauges) to piezoelectric charge generation. By utilizing the piezoelectric effect, the system achieves force measurement through a rigid electromechanical coupling that does not require elastic mounting, thus eliminating the harmful vibrations while preserving measurement functionality.
2Productivity
If the sonotrode operates at high processing speeds, then productivity increases, but abrupt load changes cause after-vibrations that deteriorate welding quality
Solution Approach 1:
By replacing the elastic strain gauge mounting with a rigid piezoelectric sensor system, the patent eliminates the mechanical compliance that causes after-vibrations during high-speed operation. The rigid coupling allows the system to withstand abrupt load changes from protrusion engagement without generating harmful oscillations, enabling high processing speeds while maintaining welding quality.
3Measurement precision
If strain gauge-based force sensors are used, then force measurement is possible, but the elastic mounting structure dampens sonotrode oscillation and alters natural frequency
Solution Approach 1:
The patent substitutes the elastic mechanical mounting of strain gauges with a rigid piezoelectric sensor arrangement. This replacement eliminates the compliant mounting structure that alters sonotrode natural frequency and damping characteristics. The piezoelectric sensor maintains force measurement capability while preserving the original oscillation characteristics of the ultrasonic system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables higher processing speeds by maintaining a consistent welding force and reducing post-oscillations, resulting in improved welding quality and increased rigidity of the sonotrode's vibration system.
Implementation Method 1
the force sensor (32) is designed as a piezo sensor
Implementation Method 2
The ultrasonic generator produces an alternating electrical voltage, which is converted into an acoustic ultrasonic vibration by the converter
Implementation Method 3
The frequency of this vibration is matched to the sonotrode in such a way that it is set into resonant vibration
Data Source
Figure 1
AI summary
The invention relates to a device for the ultrasonic processing of materials (20), comprising: an ultrasonic processing system, which consists of an ultrasound generator, a converter (12), a sonotrode (16), and a counter tool (18); and an advancing unit, by means of which the sonotrode (16) and the counter tool (18) can be moved toward each other or away from each other; wherein a force sensor (32) is provided, by means of which the force that the ultrasonic processing system applies to the materials (20) to be processed can be measured. According to the invention, in order to provide a corresponding ultrasonic processing device that enables a higher processing speed, the force sensor (32) is a piezoelectric sensor, the output of which is converted into a voltage by means of a charge amplifier, and a control device is provided, which either short-circuits the piezoelectric sensor if the ultrasonic processing system is not performing material processing or adds a time-varying force compensation value to the value measured by the piezoelectric sensor.