In this chapter, we have proposed a systematic approach to design and implement the virtual motion constraints for a multi-functional virtual manipulation system based on a 2-DOF force-reflection joystick. Virtual walls of various shapes and physical properties are employed for motion constraint construction. And, a pixel-based method for force rendering is proposed to achieve smooth manipulation between walls, which well tackles walls of various shapes. The proposed system has been applied to emulate an omni-directional wrench and a manual gearshift system. And, the responses of the users during the manipulation have been analyzed. Although the proposed system is designed to be versatile, but not for exactly replication of the real mechanism, both emulations exhibit certain degree of resemblance and reality. For its extension to 3D applications, the virtual walls will need to be assembled in the 3D space. It thus induces higher complexity for motion constraint construction. Meanwhile, the proposed pixel-based method is ready for 3D force rendering as its implementation is in the pixel space and can be easily extended to 3D cases.
Chapter 3 Effective Manipulation for a Multi-DOF Robot Manipulator
In this chapter, we develop a set of virtual tools, based on the virtual motion constraints, to assist the user in natural and effective governing a multi-DOF robot manipulator for 3D applications with the requirements on both position and orientation via a 6-DOF force-reflection joystick. For demonstration, the proposed manipulation system is applied for the tasks of contour following and also screw fastening, both of which demand delicate maneuvers.
3.1 Introduction
More robots are expected to enter human societies in the near future, as technologies in sensing, control, and artificial intelligence are in much progress. Instead of the organized environments, like factories, where most robots are currently deployed, they may need to face the uncertain and unstructured environments in homes, offices, laboratories, and others [29]. To tackle the high complexity present, we can imagine it would take too much effort to offer detailed programs to respond to all possible situations. One appealing alternate is to provide an effective manipulation system for the human to operate the robots, which motivates this study [30,47,55,58]. We choose a 6-DOF robot manipulator as the target robot to govern, as it is versatile and poses certain challenge for manipulation.
For its popularity in practice, the robot manipulator is also taken to be under position control. Before the development of the proposed manipulation system, we have in-depth
evaluated those manipulative devices commonly used, like teach box, mouse, keyboard, and joystick. As expected, they did not yield natural and efficient governing for a multi-DOF position-controlled robot manipulator. In addition, among previous researches on robot manipulation, several intuitive manipulative devices have been proposed, such as camera-based devices [46] and tangible user interfaces, like Wiimote [22], which recognize user’s gestures for robot governing. They usually do not provide intuitive force feedback though. Some proposed using an identical robot as the user interface at a high cost [21].
The proposed manipulation system is designed to let the user feel she/he is well in control of the robot manipulator, although it is actually teleoperated. It consists of mainly a 6-DOF force-reflection joystick as the manipulative device and a set of virtual tools, along with a virtual spring and bumper, to assist the user for manipulation. A joystick with force reflection is employed for providing the haptic feedback and mutual interaction, which enhance the linkage between the user and robot manipulator [9,15,37].
The virtual tools are realized as the virtual motion constraints, based on the concept of virtual mechanisms and virtual fixtures previously proposed [6,28,49,53], to confine the movement of the manipulative device in the 3D working space, so that the robot manipulator can be properly guided for task execution. The virtual spring is designed to help the user recognize the spatial deviation between her/his desired position and the end-effector via a haptic clue. This function is demonstrated to be effective for governing the position-controlled robot manipulator. And, the virtual bumper is utilized to protect the robot manipulator from excessive contact force, which is crucial for tasks involving force management, e.g., screw driving.
The virtual tools are for the guidance of the user’s movement to respond to task re-quirements. For instance, a virtual ruler or compasses can help the user to move the robot
manipulator along a straight or circular line. In addition to position guidance, a focus of most previous works, the proposed system also provides orientation assistance to help the user, e.g., maintaining the vessel in an upright angle. Because some force-reflection joy-sticks may not be equipped with torque feedback, we thus develop a torque-free method for orientation assistance. In addition, the virtual tools are selected for assistance according to the current status of task execution dynamically, but not in a predefined environment or predicted way [5,17,31,63]. Software implementation of the proposed manipulation system is executed in a 3D graphical environment with a real-time manner, which also provides the visual feedback. To demonstrate its effectiveness, the manipulation system is used to govern the robot manipulator to conduct two kinds of tasks: contour following and screw fastening, both of which demand delicate maneuver. Users of various backgrounds are invited for the experiments, and their responses analyzed. The rest of this chapter is organized as: Section 3.2 describes the proposed manipulation system, including the realization of virtual tools, spring, and bumper. System implementation is presented in Section 3.3. Section 3.4 discusses the experiments and performance evaluation. Finally, summaries are given in Section 3.5.