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

Abstract

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.

Evaluation of force pain thresholds to ensure collision safety in worker-robot collaborative operations

“…3 , the quantiles are calculated from the CDF with the log-logistic distribution ( Table 4 ). The third quantile is relevant to the biomechanical limitation of pain onset ( Behrens et al, 2022 ; Han et al, 2022 ).…”

“…However, due to time and budget constraints, this study focused only on impact situations involving two body locations and two contact surfaces. Notably, several researchers have attempted to analyze the biomechanical limits for various body locations ( Özcan et al, 2004 ; Melia et al, 2015 ; Melia et al, 2019 ; Park et al, 2019 ; Liew et al, 2021 ; Behrens et al, 2022 ; Han et al, 2022 ). Overall, the literature reports pain thresholds for approximately 29 body locations.…”

“…For example, although the biomechanical limitations specified in ISO/TS 15066 can be used to validate the collision safety of industrial robots in collaborative workspaces, this standard states that the operational speed of the robot must not exceed the specified limits which may cause the robots to be too slow to be effectively used. To resolve this problem, researchers are exploring the connection between the limitations and alternative thresholds above pain onset (e.g., the maximum bearable pain or injury onset) ( Han et al, 2022 ; Behrens et al, 2023 ). Future studies can be focused on critically analyzing these considerations to establish safety standards.…”

“…As a preliminary measure to address the safety concerns, the standard ISO/TS 15066 was established to provide safety guidelines for the collaborative operation of industrial robot. To clarify safety criteria for collisions, the biomechanical limitations have been measured ( Yamada et al, 1997 ; Melia et al, 2015 ; Park et al, 2019 ; Behrens et al, 2022 ; Han et al, 2022 ). For example, in addition with clinical trials, collision experiments with porcine skin tissue with properties similar to the human skin were conducted to identify the propensity for injury based on mechanical parameters ( Mao et al, 2017 ; Han et al, 2018 ; SUGIURA et al, 2022 ).…”

Experimental Comparison of Biofidel Measuring Devices Used for the Validation of Collaborative Robotics Applications

“…If the collision area is semi-sharp, a second safety mechanism is important. The specific contact pressure needs to be observed to avoid local trauma to the human skin [ 1 , 2 , 3 , 4 , 26 , 27 ]. However, the influences of the pressure measuring equipment are not part of this investigation.…”