Acoustic diagnostics – Defect detection | Signal evaluation | Quality assurance

Quality assessment

More than just “good“ or “bad“ – quality assessment of parts and products, especially during and directly after production, is a central element of quality assurance. In most cases, 100 % inspection is a prerequisite for the acceptance of the manufactured items.

The goal is to segregate all bad parts, but only a minimal number of defect-free or “still“ good parts, in an automated test. It sounds easy, but it is a challenging task due to the plethora of defect types that are possible. Alone in the inspection of gears, defects can include cracks of various sizes on outer gear surfaces or supports, cracked or detached teeth, blowholes, inclusions, and flaws. A capable test system must be able to detect all of these defects.

Quality also plays a major role in many aspects of daily life: in tissue products, for instance, for which softness is the key criterion for customer acceptance. However, softness perception is subjective. Fraunhofer IKTS has developed a system for the instrument-based determination of softness.

© iStock: Jane1e



Reliable and reproducible automated classification is useful for quality assessment of gears and other sintered components. Fraunhofer IKTS has developed a system for gear testing based on sound analysis. Sound analysis is a rapid, low-cost test method that can easily be applied to mass production processes.

A part is positioned in a defined manner. A suitable sensor excites the test part, causing it to vibrate. AI methods are also employed for filtering patterns out of the recorded signal. Following a training phase, signal evaluation is automated to enable differentiation between “good“ and “bad“ parts. The system is especially designed for use in harsh industrial environments and can be integrated into existing test stations on production lines.


© iStock: Imgorthand

Tissue products


Tissue products encompass all products, such as paper tissues, cosmetic facial tissues, and toilet paper, for which softness is an important selling point. Previously, trained testers (panel test) were employed to categorize this subjectively perceived property.

To estimate the subjective softness, Fraunhofer IKTS has developed a new approach based on analysis of the tearing sound made by a tissue product. So, an unknown sample can be assigned to one of the known classes (soft, medium, or hard) defined in panel tests.

The result can support the tissue product manufacturer at every stage in the production process by enabling continuous quality control as well as use of chemical additives to modify the softness in a defined way.

Keramische Hohlkörper für stationäre Batterien.

Hollow bodies


For small-, medium-, and large-scale production of hollow bodies, such as cups or tubes, Fraunhofer IKTS offers a new, automated test method based on sound analysis. This method is suitable for test specimens made from different materials, such as metals and ceramics.

In the test, the parts are suitably positioned for being automatically excited and made to vibrate in a subsequent step. Sensors or microphones adapted to the specific test task record the response to the excitation signal. A good-or-bad evaluation is automatically derived from this.