Assessment of Pain Onset and Maximum Bearable Pain Thresholds in Physical Contact Situations.

With the development of robot technology, robot utilization is expanding in industrial fields and everyday life. To employ robots in various fields wherein humans and robots share the same space, human safety must be guaranteed in the event of a human-robot collision. Therefore, criteria and limitations of safety need to be defined and well clarified. In this study, we induced mechanical pain in humans through quasi-static contact by an algometric device (at 29 parts of the human body). A manual apparatus was developed to induce and monitor a force and pressure. Forty healthy men participated voluntarily in the study. Physical quantities were classified based on pain onset and maximum bearable pain. The overall results derived from the trials pertained to the subjective concept of pain, which led to considerable inter-individual variation in the onset and threshold of pain. Based on the results, a quasi-static contact pain evaluation method was established, and biomechanical safety limitations on forces and pressures were formulated. The pain threshold attributed to quasi-static contact can serve as a safety standard for the robots employed.

Identification of a closed cutaneous injury after mechanical trauma caused by collision.

PURPOSE: Robotics has evolved rapidly in terms of mechanical design and control in the past few years. Collaborative robots that have direct contact with humans are being introduced in various fields, including industrial and medical services. Because collaborative robot systems are being introduced rapidly, the safety of the humans who work with them is becoming an important issue. In this study, we investigated skin injuries resulting from a collision between robots and humans using a freefall experiment system. METHODS: We particularly focused on closed skin injuries caused by a collision. To induce a closed injury, we struck mini-pigs with cubic-edge square and semi-sphere impactors at collision speeds of 1 and 3 m/s. We did not observe any open injuries with those conditions. Closed injuries were observed in the dermal layer of the skin after the collision test at both speeds and with both impactors. RESULTS: The collagen fiber in the dermal layer was separated and fragmented, and the subcutaneous fat layer became dense as a result of the collision. CONCLUSIONS: We closely observed and analyzed the histopathologic changes in the dermal and subcutaneous layers with intact epidermis after mechanical trauma to the inner skin layers.

Assessment of pressure pain thresholds in collisions with collaborative robots.

In recent years, safety issues surrounding robots have increased in importance, as more robots are in close contact with humans, both in industrial fields and elsewhere. Safety standards for industrial robots operating in specific spaces have been established, but no such standards have been specified for collaborative and service robots. To establish safety standards for such robots, we assessed pressure pain thresholds for collisions between humans and robots, under the assumption that the pain threshold is lower than the mild injury threshold. The pressure pain threshold for collision with a robot was measured in 90 male Korean adults using a homemade collision system. The pain thresholds were measured three times at 15 sites, including the forehead. The highest threshold was 196.1 ± 85.8 N/cm2 at the back of the hand, and the lowest was 65.1 ± 22.6 N/cm2 at an arm nerve. Moderate thresholds, i.e., 100-120 N/cm2, were noted on the forehead, neck muscle, ball of the thumb, and shin. The thresholds of participants < 30 years of age were lower, by 3-33%, than those of participants aged > 30 years. Thresholds differed by body mass index only at certain sites, including the shoulder joint, neck, and back of the hand. The pressure pain threshold depended on individual characteristics, body site, and age. The threshold relevant to potential human-robot collisions was determined to be between 65.1 ± 22.6 and 196.1 ± 85.8 N/cm2.

A simple model for constant storage modulus of poly (lactic acid)/poly (ethylene oxide)/carbon nanotubes nanocomposites at low frequencies assuming the properties of interphase regions and networks.

The networks of nanoparticles in nanocomposites cause solid-like behavior demonstrating a constant storage modulus at low frequencies. This study examines the storage modulus of poly (lactic acid)/poly (ethylene oxide)/carbon nanotubes (CNT) nanocomposites. The experimental data of the storage modulus in the plateau regions are obtained by a frequency sweep test. In addition, a simple model is developed to predict the constant storage modulus assuming the properties of the interphase regions and the CNT networks. The model calculations are compared with the experimental results, and the parametric analyses are applied to validate the predictability of the developed model. The calculations properly agree with the experimental data at all polymer and CNT concentrations. Moreover, all parameters acceptably modulate the constant storage modulus. The percentage of the networked CNT, the modulus of networks, and the thickness and modulus of the interphase regions directly govern the storage modulus of nanocomposites. The outputs reveal the important roles of the interphase properties in the storage modulus.