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The human sense of touch is complex and unique. On every square centimeter of the fingertips, there are approximately 150 different tactile receptors. They can detect the tiniest elevations, as small as 0.006 millimeters in height. For comparison: the nominal height of a Braille dot in the eponymous tactile writing system is 0.48 millimeters.
Some receptors register how quickly the skin is pressed, others perceive only vibrations, and still others can sense the stretching of the skin. Nerves transmit these sensations to the brain, which compiles them into a subjective overall impression of the surface’s texture. All of this happens unconsciously and cannot be controlled. The complexity of this process explains why it took so long to develop a measuring device capable of digitizing and thus objectively capturing the entire sense of touch.
Digitalising human perception
There are already measuring devices that can detect certain aspects of a surface’s haptics. They scan the textile and essentially create a topographic map of the surface structure. However, not only the highs and lows of a textile surface are important for capturing the tactile feel, but also its compressibility. When a human hand touches something, a slight pressure is applied. This micro-compressibility, which is approximately 100 millinewtons, plays a crucial role in perception. Optical methods, such as scanning, cannot capture this. A company from Leipzig has succeeded in developing a device that detects and digitizes multiple aspects of haptics. “Our Tactile Sensation Analyzer (TSA) can represent the entire spectrum of the sense of touch and assign it an objective numerical value,” explains Alexander Grüner, Global Business Development Manager at emtec Electronic GmbH.
The sound of softness
Interestingly, the key to this technology was neither touch nor optics but hearing. The inventor of this innovative measuring device is physicist Giselher Grüner, father of Alexander Grüner and founder of emtec Electronic. He was tasked with developing a device to measure the haptics of toilet paper. “My father spent weeks in his office repeatedly feeling different types of toilet paper,” recalls Alexander Grüner. “Eventually, he noticed that not every toilet paper sounded the same when rubbed.” This insight led Grüner Sr. to the idea of measuring the two most important parameters of haptics – surface softness and surface roughness – using a microphone. After five years of development, the TSA was market-ready. Today, it is used throughout the paper industry. In 2016, father and son Grüner had the idea to adapt the TSA for the textile industry as well.
From the rotor to the ear
A fabric sample is stretched over a cylinder with a hollow chamber at the bottom, where a microphone is located. Above the sample, a rotor with a measuring head is mounted. The rotor has eight blades, each equipped with another microphone. When the device starts, the measuring head with the rotor lowers onto the fabric until a pressure of 100 millinewtons is reached – the same pressure exerted when a human hand touches a surface. As the rotor spins over the fabric sample, two types of vibrations are generated – those from the fabric itself and those from the rotor blades. The sound caused by the vibration of the fabric is captured by the microphone at the bottom of the cylinder. This sound reflects the roughness of the textile: the louder the noise, the rougher the sample.
Ecological potential
Such a tactile measuring device could significantly accelerate mass fabric production, making it more cost-effective and resource-efficient. The potential is enormous. To achieve the hand feel specified by the designer in mass production, fabric samples are repeatedly shipped back and forth between the fashion brand and the fabric mill. Four to five iterations are not uncommon. This process can take up to six months and when scaled across the industry cost several billion US dollars. The TSA, for example, could reduce this process to one or two weeks. Fabric manufacturers could continuously monitor the hand feel during production and coordinate with designers through a cloud-based solution called the Virtual Haptic Library. This could prevent tons of misproduced fabrics. “On the Handfeel Scale, which measures differences in overall feel from 1 to 100, humans only perceive a difference starting at one or two handfeel points. Any improvement below this threshold means wasted resources, as it goes unnoticed by people,” explains Alexander Grüner.
Award-winning innovation
The great potential of the innovation has already been recognised: the Tactile Sensation Analyser and the Virtual Haptic Library cloud solution were singled out for the Techtextil North America Innovation Award 2024 in the ‘New Product’ category.
