Informing assistive robots with models of contact forces from able-bodied face wiping and shaving

Hygiene and feeding are activities of daily living (ADLs) that often involve contact with a person's face. Robots can assist people with motor impairments to perform these tasks by holding a tool that makes contact with the care receiver's face. By sensing the forces applied to the face with the tool, robots could potentially provide assistance that is more comfortable, safe, and effective. In order to inform the design of robotic controllers and assistive robots, we investigated the forces able-bodied people apply to themselves when wiping and shaving their faces. We present our methods for capturing and modeling these forces, results from a study with 9 participants, and recommendations for assistive robots. Our contributions include a trapezoidal force model that assumes participants have a target force they attempt to achieve for each stroke of the tool. We discuss advantages of this 3 parameter model and show that it fits our data well relative to other candidate models. We also provide statistics of the models' rise rates, fall rates, and target forces for the 9 participants in our study. In addition, we illustrate how the target forces varied based on the task, participant, and location on the face.