# Simultaneous Dual-Arm Motion Planning for Minimizing Operation Time
## 1 Introduction  
Dual-arm robots have attracted much attention in recent years [1]. One of the most basic tasks that an industrial dual-arm robot does is pick-and-place work. Pick-and-place work consists of tasks in which the robot carries objects from a start position (initial position) to a goal position. The dual-arm robot is expected to do this work in a dynamic environment, such as a house or a shop. It is necessary to do the pick-and-place work efficiently in a dynamic environment. The following three important points should also be considered when the dual-arm robot does this work: (1) collision avoidance of the arms; (2) which arm should move an object; and (3) the order in which the objects should be picked up and placed. There are several objects in an environment. Therefore, the last two points should particularly be considered because of their substantial impact on the time taken to finish the work. In related studies, [PERSON] et al. and [PERSON] et al. proposed a motion planning method to enable single arm type robot to grasp a target object in an environment in which there are multiple objects [2; 3]. In addition, [PERSON] et al. proposed a similar motion planning method for grasping a target object for a dual-arm robot. Specifically, they successfully moved two robot arms simultaneously and efficiently grasped a target object from among multiple objects [4]. Although [PERSON] et al. did not use dual-arm robots, they proposed a motion planning method for efficiently grasping a target object from multiple objects using multiple manipulators [5]. Moreover, [PERSON] et al., using a dual-arm robot, proposed a method of transporting an object from one end of the workspace to the other by the handover of an object [6]. In an environment where there are multiple objects, theyperformed motion and path planning so that neither arm collides with any objects during handover. Both of the above studies proposed a motion or path planning method that can work efficiently in environments where there are multiple objects. However, the operation time of a robot was not taken into account explicitly. [PERSON] et al. proposed a motion planning method that considers operation time. This method enables a single-arm robot to minimize the time taken to finish the work when a multiple determined-point manipulator is moved [7]. [PERSON] et al. proposed an approach to formulating the cost function for a motion planner intended for efficient human-robot collaboration on manipulation tasks in a shared workspace [8]. Similarly, [PERSON] et al. and [PERSON] et al. efficiently performed a collection of tasks involving the manipulation of many objects [9; 10]. In recent works, [PERSON] et al. proposed trajectory planning optimization and real-time control of a special five-bar parallel robot. Although they achieved planning the optimal path for minimizing time, they did not focus on pick-and-place for multiple objects and for multiple manipulators [11]. [PERSON] et al. proposed combination of part-dispatching rules to coordinate multi-robot system in the environments there are multiple object. Although they considered the order in which the objects should be picked-and-placed, they did not study the factors for efficiency such as minimizing time [12]. In addition, the studies mentioned above did not consider the elements of dual-arm robots. Applying these methods for a dual-arm robot is difficult considering the three abovementioned points. As far as the authors know, no study has ever considered the operation time a dual-arm robot takes to finish its work when multiple manipulators move simultaneously. Therefore, we propose a motion planning method to minimize the operation time taken to finish work considering the three points mentioned above and focusing on the pick-and-place work of a dual-arm robot.