Safety-preservation oriented reaching monitoring for smooth control mode switching of skill-assist

The objectives in this paper are to develop a method for safety-preservation oriented reaching monitoring (SORM) and to demonstrate its effectiveness for realizing a safe and smooth control mode switching. For more effective manufacturing activities, smooth control mode switching of a power assist device ldquoSkill-Assistrdquo from hands-off to hands-on is expected to enhance the productive efficiency. However, hazardous behaviors of an operator without paying any attention to a Skill-Assist in the hands-off control mode are possible to occur, and may result in serious injuries; that is why the SORM is demanded for smooth control mode switching. We focused on operator´s hand reaching to the force sensor of a Skill-Assist conducted in the control mode switching, and two laser range sensors are employed to monitor the reaching. The SORM algorithm based on hidden Markov model processes the reaching information, and judges predictively whether the operator will be in a safe state or not. An experimental result shows the Skill-Assist to which the SORM is applied could recognize a control mode switching behavior with reaching while the control mode is switched smoothly without rapid deceleration. In an experiment for a hazardous behavior without reaching, the Skill-Assist could judge successfully an operator will be in a unsafe state. The judgment in the experiment for the hazardous behavior was evaluated by a minimum safe distance specified by an ISO safety standard, and it could satisfy the safety requirement.