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

Robots are set to relieve humans of the most mundane and repetitive tasks. Not only would they replace us in the tasks we find most boring, but they also do these tasks more productively. As robots start to replace humans, a lot of environments would include humans and robots working together.

Safety will be a significant concern in all these interactions. For example, many times humans might be surprised by a robotic movement or a similar external motion and this could cause an involuntary reaction. This problem related to involuntary motion (IM) has been discussed in the research paper by Robin Jeanne Kirschner, Henning Mayer, Lisa Burr, Nico Mansfeld, Saeed Abdolshah, and Sami Haddadin titled “Expectable Motion Unit: Avoiding Hazards From Human Involuntary Motions in Human-Robot Interaction” that forms the basis of the following text.

Industrial robot. Image credit: jarmoluk via Pixabay (Free Pixabay licence)

Importance of this research

The researchers propose Expectable Motion Unit (EMU) to ensure safety for humans in case of involuntary motions happening during the Human-Robot Interaction (HRI).

Expectable Motion Unit (EMU)

Objective: Avoid Human Involuntary Motion Occurrence (IMO).

The EMU aims to ensure a robot performs motions expected by the human and thus avoids human involuntary motions in HRI. For this, an experiment is conducted to understand under what circumstances IM occur in HRI.

Experiment Setting: A Franka Emika Panda robot arm mounted stationary to a table is used in this experiment, and human reaction is analysed. The human participant of the experiment is asked to complete a quiz on a tablet. The robot approaches the human workspace with variable motion parameters, e.g., speed, acceleration, or direction in the experiment. The human reaction is recorded by a camera mounted on the robot arm and classified via social cue analysis. Thus, thresholds are defined in terms of IMO probability, and these thresholds should not be exceeded.

Image: Experiment Setting. Image credit: arXiv:2109.07201v1

The expectation curve is integrated into the robot motion generation as EMU. This limits the robot speed to a value that is considered expectable by the human if necessary and does not cause IMO. Finally, the EMU is combined with the Safe Motion Unit (SMU), which provides a safe velocity based on injury data from biomechanics collision experiments. Thus, SMU ensures that both the human expectation towards its motion is fulfilled and injury is avoided. Combining the two control laws improves the safety and trustworthiness of an autonomous system that operates in the human vicinity.

Image credit: arXiv:2109.07201v1

Experiment Results

The EMU generated motions were able to avoid IMO in 5 out of 6 times.

Conclusion

In the words of the researchers,

In this paper, we proposed and validated the Expectable Motion Unit (EMU) concept, which aims at avoiding possibly hazardous human involuntary motions (IM) in human-robot interaction. We conducted experiments with 29 volunteers in order to systematically analyse the relative frequency of IM occurrence (IMO) depending on the robot speed and humanrobot distance in a typical HRI setting. The experimental results are processed towards a risk matrix, from which safety curves were deduced for a particular application. An expectation curve which limits the probability of IMO to 15 % in the considered use case was embedded into the EMU motion generator, which limits the robot velocity such that the IM threshold is not exceeded. Furthermore, the EMU was combined with the well-established Safe Motion Unit that ensures physical safety during contact. In a validation experiment, the EMU successfully prevented IM in five out of six cases. Overall, by fulfilling the human expectation towards the robot and taking the biomechanical safety limits into account at the same time, our concept improves the safety, the performance, and the trust of robot users in HRI

 Source: Robin Jeanne Kirschner, Henning Mayer, Lisa Burr, Nico Mansfeld, Saeed Abdolshah, and Sami Haddadin ’s  “Expectable Motion Unit: Avoiding Hazards From Human Involuntary Motions in Human-Robot Interaction”

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