# Efficient Reachable Workspace Division under Concurrent Task for Human-Robot Collaboration Systems
## 2 Method
### Efficiently Reachable Workspace and Robot Incorporation Boundary Exploration
#### 2.2.2 Experiment Protocol  
Concurrent tasks in this experiment are the visual main task and the upper limb grasping task, which need to be completed simultaneously. The experimental scenario is as follows: The height of the table and chair in the gaze state was maintained constant, and the targeted object was a ball 3 cm in diameter. A spiral base was installed at a distance of 10 cm from the center line and the edge of the table, respectively, and the ball had holes that could be attached to the base. The distance from the edge of the table remained according to the greatest gripping distance of various subjects with no elbow flexion. The visual stimulus was presented in a computer monitor 40 cm in length, and the main stimulus was a ball-avoidance game in which the participant manipulated the ball to avoid obstacles in its path by moving the buttons left and right. The participant was seated in a chair with the waist straight.  
The experimental group was asked to start the task by asking the subject to keep the head and body square to the center line of the table, and put the right hand in the initial position, as box 2 shows in Figure 4a. When hearing the sound of the \"started\" prompt, they were to grasp the target ball, install the ball on the base in front of them, and, finally, return the hand to the initial location. The entire grasping process should ensure that the ball avoidance game continues. At the end of each grasp, the target object's location is moved on a circle, with the center of rotation of the arm as the axis and the maximum grasp distance as the radius. In this study, according to the clustering results in the 3D workspace, the movement angle of each grasping object was set at \(10^{\circ}\), with uniform distribution in each workspace area for different body patterns. The control group added the assistance of the robotic arm, and the experimental environment was kept constant. After the subject heard the prompt, the hand was located at the initial position and kept still, the robotic arm grasped the small ball at the corresponding position and transferred the object to the subject, who installed the small ball on the base.  
Figure 3: Illustration of marker and IMUs placement. The person permitted the use of this image.  
The two experimental groups were divided into three task phases: reaching and grasping and transferring and installing, respectively. For the experimental group: (1) Subject hears the prompt and moves their hands from the initial location to the location of the target ball. (2) Subject transfers the ball to the base position. (3) Subject installs the ball on the base. For the control group: (1) The robot arm moves from the initial position to the target ball position after the prompt. (2) The ball is transferred to the subject's hand. (3) The subject installs the small ball onto the base. To ensure the experiment's reasonability, the handpiece's initial position was 2 cm to the right of the base to facilitate the installation of the ball. The time required for the subjects to complete the path process of phases 1 and 2 was measured by the experimental group, and the initial location of the robotic arm was set at the same distance between the initial location of the human hand and the small ball, while the movement speed of the robotic arm was adjusted in the control group to make its  
Figure 4: The experimental setup is shown in (**a**). The human operator accomplishes the grasping task concurrently while completing the visual main task on the computer screen. The visual main task for the ball collision game is shown in (**b**). An outline for every experimental session of the experiment is shown in (**c**). (**d**) Photographs of the experimental setup demonstrated the experimental process after incorporating the robotic arm assistance. The person permitted the use of this image.  
movement time consistent with the experimental group. The only variable that ensured the experiment was the reaction time of the subjects.