# On the Improvement of ROS-Based Control for Teleoperated Yaskawa Robots
## 1 Introduction
ROS is an open source operating system designed for robots, which provides features such as hardware abstraction, low-level device control, packages for common features, a communication framework, and a variety of libraries and tools to help build robotic applications. To model systems with realistic physics, improved simulation tools are needed. The gazebo tool [21] consists of a physics engine, high quality graphics, and programmatic and graphical interfaces. It can simulate any custom designed physical model described in XML-based SDF or URDF file format [22]. Several famous robots have been simulated in the ROS and Gazebo platforms, such as PR2 [23] and TurtleBot [24]. Functionalities provided by ROS and Gazebo make them suitable to predict the robot auto-collision and its intersection with the environment [25]. Stop criteria use (prohibited areas, collisions, singularities, etc.) allows having a realistic rendering of the robot capabilities in simulation, while carrying out teleoperation tasks [26]. Therefore, ROS-based control coupled with Gazebo simulation is proposed in this paper to ensure the safety of teleoperation task. Controlling industrial robots from an external computer using ROS differs greatly from classical robot programming methods provided by industrial robot sellers. As such, the commercial interfaces available for use with ROS often rely on the user writing custom programs for each new application. A first contribution of this paper is the evaluation of the open-source control interface based on standard Motoman driver package [27] created with the cooperation of Yaskawa Motoman, in order to check its effectiveness for teleoperation tasks. It should be noted that Yaskawa robots are used in different fields such as surgery [28], pick and place [29], welding [30], etc. Recently, NASA selected its Motoman SIA50 robots for teleoperation demonstration [31]. It successfully confirmed the ability to robotically transfer oxidizer to a satellite valve in flight-like conditions. The standard Motoman driver package uses ROS-Industrial basic nodes and interfaces them with Yaskawa Motoman robot controllers. The research work in [32] proposesa setup of the Motoman SDA_10 dual-arm robot with ROS-Industrial for industrial applications. Real-time response of robotic system and its communication latency analysis leads to better controlling, as confirmed for ROS-controlled KUKA robots in [33]. This analysis highlights the required extra developments to be carried out. The resulting performance degradation sources are identified: A second contribution of this paper deals with the proposition of an improved version of Motoman ROS-based control suitable for teleoperation tasks. The modifications of the standard Motoman ROS package is proposed to compensate the depicted delays to deal with teleoperation. It manifests in the addition of a new velocity control mode into the Motoman ROS driver. The experimental evaluation of the improved ROS-based control, applied on a 6 Degrees-of-Freedom (DoFs) Yaskawa GP8 robot, teleoperated by a 3 DConnexion Space-Mouse Pro device, confirms an improvement on the robot teleoperation performance, in terms of latency and trajectory tracking, which can achieve 43% with respect to the standard control. This paper is organized as follows: Section 2 presents the kinematic equations of motion of a serial robot required to establish the control laws for teleoperation. Section 3 introduces the design of ROS-based control while integrating Motoman ROS package. Then, the effectiveness of the standard control method for robot manipulators teleoperation is discussed in detail in Section 4. Finally, the improvement of the standard ROS-based control method for Yaskawa manipulators is proposed in Section 5. The effectiveness of the proposed control method is then studied to check its performance regarding to robot teleoperation performance compared to the standard one.