Abstract
There are many work-related repetitive tasks where the application of exoskeletons could significantly reduce the physical effort by assisting the user in moving the arms towards the desired location in space. To make such control more user acceptable, the controller should be able to predict the motion of the user and act accordingly. This letter presents an exoskeleton control method that utilizes probabilistic movement primitives to generate predictions of user movements in real-time. These predictions are used in a flow controller, which represents a novel velocity-field-based exoskeleton control approach to provide assistance to the user in a predictive way. We evaluated our approach with a haptic robot, where a group of twelve participants had to perform movements towards different target locations in the frontal plane. We tested whether we could generalize the predictions for new and unknown target locations whilst providing assistance to the user without changing their kinematic parameters. The evaluation showed that we could accurately predict user movement intentions while at the same time significantly decrease the overall physical effort exerted by the participants to achieve the task.
Highlights
R OBOTIC exoskeletons are promising tools to assist humans in various real-life tasks [1]
We present the use of probabilistic movement primitives (ProMPs) to generate predictions of user movement in real-time in combination with a velocity-field-based controller to provide assistance to the user for performing an arm reaching task, hereby referred to as Predictive Assistance
We implemented a simple model with fixed reference trajectories that was used in the Fixed Assistance condition. With this we aim to emphasize the shortcoming of pre-set reference trajectories and the need of movement prediction when the task changes to new target locations (i.e. T3 and T4)
Summary
R OBOTIC exoskeletons are promising tools to assist humans in various real-life tasks [1]. They are designed to be worn on the body and to provide direct motion assistance to the user. The two common applications of exoskeletons are physical rehabilitation for impaired patients [2] and motion augmentation of able-bodied workers [3]. The exoskeleton is used to move the limbs of impaired individuals based on repetitive motion patterns defined by physiotherapists [4], while for able-bodied workers the exoskeleton rather amplifies the user’s joint torques [5]. Popular control approaches for these exoskeletons are Manuscript received: December 21, 2020; Revised February 21, 2021; Accepted February 21, 2021.
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