Expectable Motion Unit: Avoiding Hazards From Human Involuntary Motions in Human-Robot Interaction

TL;DR

This paper introduces the Expectable Motion Unit (EMU), a system that predicts and limits robot motions to prevent involuntary human reactions, enhancing safety by considering psychological factors in human-robot interaction.

Contribution

The EMU model is the first to incorporate human psychological responses into robot motion planning to prevent involuntary motions during interaction.

Findings

EMU successfully avoided involuntary motions in 5 out of 6 cases

The model maps robot velocity and distance to IM probability

Real-time robot velocity adjustment enhances safety

Abstract

In robotics, many control and planning schemes have been developed to ensure human physical safety in human-robot interaction. The human psychological state and the expectation towards the robot, however, are typically neglected. Even if the robot behaviour is regarded as biomechanically safe, humans may still react with a rapid involuntary motion (IM) caused by a startle or surprise. Such sudden, uncontrolled motions can jeopardize safety and should be prevented by any means. In this letter, we propose the Expectable Motion Unit (EMU), which ensures that a certain probability of IM occurrence is not exceeded in a typical HRI setting. Based on a model of IM occurrence generated through an experiment with 29 participants, we establish the mapping between robot velocity, robot-human distance, and the relative frequency of IM occurrence. This mapping is processed towards a real-time capable robot motion generator that limits the robot velocity during task execution if necessary. The EMU is combined in a holistic safety framework that integrates both the physical and psychological safety knowledge. A validation experiment showed that the EMU successfully avoids human IM in five out of six cases.