Resumen de Control architecture for multifinger haptic devices applied to advanced manipulation
In recent years haptic technology for force reflection has been in a state of continual evolution. Advances in the field have allowed considerable improvements to be made to the features of the devices, which have been used in the control of teleoperated robots and in interaction with virtual scenarios. Currently there is a wide variety of haptic devices that allow interaction with the environment by means of only one contact point. However, the number of haptic devices for the manipulation of objects with more than one contact point is very low and, in most cases, they require very complex and cumbersome mechanical devices.
This thesis provides a full account of the design of the multifinger haptic interface known as the MasterFinger2, which offers the possibility of manipulating virtual or remote objects with two contact points per hand. The interface was designed to be used by the thumb and index finger, thereby enabling the performance of grasping tasks. Compared to other existing solutions, this device offers a considerable workspace due to the extra degree of freedom at its base. The study provides a detailed description of the mechanical characteristics of the device, as well as different possible configurations and their respective workspaces.
The device controller has a modular design, analogous to the mechanical design, whose basic module is the finger. Each finger has a controller that is composed of instrumentation electronics, power electronics, and a commercial Xilinx controller, which provides Ethernet access. This controller works at the joint level and not at the end effector level. For this reason, distributed control architecture is necessary for controlling the end effector and for interconnecting devices to virtual or remote environments. This thesis provides a detailed description of how the architecture solves the system's direct and Jacobian kinematics outside of the controller in a middleware layer in real time at 1 kHz, the frequency at which the control loops close.
Another issue that must be addressed is how to stabilize the system during interaction with virtual environments. An analysis was undertaken of different passive controllers which allow the system to respond to potential instabilities that may arise as a result of interactions with excessively rigid objects. To this end, the following controllers were considered: Time Domain Passivity Control and port Hamiltonian systems. Passive controllers that prevent the system from becoming unstable in the presence of communication delays, as occurs when a remote type environment is manipulated, are also analyzed. Specifically, the scattering algorithm for constant time delays and the Time Domain Passivity Control algorithm for time varying delays have been applied to virtual environments.
Furthermore, we have worked on designing a new protocol adapted to haptic and robotic interactions known as Bilateral Transport Protocol (BTP), in an effort to minimize the presence of delays in communication via Ethernet. This new protocol seeks to prevent web traffic and packet loss, which could result in system instabilities and reduced performance output.
The haptic interface developed was evaluated in virtual scenarios that allow the manipulation of objects such as a cube. This thesis provides a full description of the architecture used to generate these scenarios, as well as a description of their components, among which we may highlight the scenario server, which is responsible for implementing the virtual object, and the graphic simulator, which provides a virtual representation of the haptic interaction. Different scenarios were developed to confirm the validity of the haptic interface and different experiments were carried out to measure its performance.
In addition to interaction with virtual objects, the MasterFinger was also used to record data obtained as a result of interaction with deformable objects. This data was later processed by ETH Zurich's Computer Vision Laboratory in order to procure models of these objects. Data driven technique algorithms developed by the ETH were used for this purpose. These models were used for modeling virtual objects of the same physical characteristics previously recorded. The MasterFinger was also used in the reproduction of these virtual objects.
All of this work was made possible by the European IMMERSENCE (FP6 IST 2006 027141) project in which the UPM participated in collaboration with eight other European associates coordinated by the Technischen Universität München (TUM).
