Research Article: Assessment of pressure pain thresholds in collisions with collaborative robots

Date Published: May 2, 2019

Publisher: Public Library of Science

Author(s): Moon Young Park, Doyeon Han, Jung Ho Lim, Min Kyung Shin, Young Rok Han, Dong Hwan Kim, Sungsoo Rhim, Kyung Sook Kim, Jian Huang.


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.

Partial Text

Robots are complex machines that perform behaviors or tasks with a high degree of autonomy. They have been used mainly in industry to automate production processes. Industrial robots have tended to be stationary, operating in specific spaces and performing repetitive and limited actions. In recent years, collaborative robots have been introduced into the industrial sector. A collaborative robot operates in close cooperation with humans [1]. Such robots share the workplace, and perform tasks simultaneously, with humans during production operations. In addition, service robots have been introduced in the fields of education, entertainment, medicine, and rehabilitation, such that close contact between robots and humans in daily life is now more widespread [1]. In an environment where humans and robots coexist, static or dynamic collisions with robots can be a source of injury, including shock, clamping, squeezing, and skin injuries. The most common injuries caused by industrial robots are clamping and squeezing injuries.

The main purpose of this study was to inform safety standards for robots that interact closely with humans by quantifying pressure pain thresholds in collision incidents. Pain thresholds were determined at 15 body sites in 90 males. The thresholds were in the range of 65.1–196.1 N/cm2 and varied among individuals and by measurement site, age, and BMI. Pain is a very subjective experience that can vary according to internal and external factors, such as the subject’s physical condition and emotional state, the order in which measurements are taken, and the time of measurement. Therefore, the reliability of the measured results was verified by analytic and statistical methods in this study.