Date of final exam: 08/03/2002

E-mail: parcara@deis.unibo.it

Tutor: Prof.  C. Melchiorri, Università di Bologna

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Control of Haptic and Robotic Telemanipulation Systems   ___________________________________________________________________________________________________________

Advisor:

Prof.  C. Melchiorri, Università di Bologna

Summary of the thesis

PRESENTATION OF THE WORK

Haptic systems and robotic telemanipulators have been spreading out during the last years and many applications have been developed all over the world with the aid of telerobotics.

This thesis is inserted in this telerobotic field presenting both a theoretical part and a practical experimental part. Haptic and telemanipulation systems have been presented and detailed focusing in particular on their control algorithms; different control methods taken from the already existing literature have been presented and, after the definition of a set of indexes related to stability and performances, a comparison has been carried out leading to the underlining of the pros and cons of each presented scheme.

The experimental part is also presented for the validation of the theoretical results and it has been carried out in the Laboratory of Automation and Robotics of the University of Bologna.

DEFINITIONS

The word ``haptic'' does not have a rigorous definition and it means something related with the kinestetic and tactile human perception with the use of the hand. Haptic devices have to be in contact with the human operator giving him sensations as similar as possible to those he could perceive from the interaction, due to handling or grasping, with an object. Sometime, a visual or acoustic feedback, through appropriate displays, is added to the device to give a more complete and detailed perception to the user.

The good rendering that a person can perceive from a haptic system are mainly due to three concomitant factors: the simulator of the virtual reality, the control of the haptic device and the hardware interface of the same device. These factors contribute in an equal and important way to the good rendering of the task being simulated.

Telemanipulation schemes are bilateral systems which include both a local primarily side, or master, and a remote one said slave. The human operator interacts with the master manipulator with a double possibility, first to drive the remote side in the completing of the task and second to receive from the slave the correct force feedback of what exactly happening. Master and slave manipulators are governed by two local controllers and exchange their respective information with the opposite side through the communication channel. The communication channel has its proper bandwidth and delay, depending on the kind of transmission implemented.

From the above descriptions, one can easily comprehend that the only difference between haptic and telerobotics systems is just due to the remote side to be rendered to the user; in the first case, the haptic case, the remote side is not physically existing but it is simulated via software; in the second case, the telemanipulation one, the remote side is composed by a manipulator with its controller and by the environment with which it is interacting. So the delays in the two systems are of different nature: they are due to the simulation computation time in the haptic case and to the transmission channel between local and remote side in the telemanipulation case.

Haptic systems have been mainly developed to give to the user a certain kind of perception, as realistic as possible, of what is going on in a simulated virtual scene. These kind of systems are mainly used for the training in the carrying out of specific complex tasks, for which it is too difficult or too expensive a direct training in the real operation; fields of application are for example virtual surgery, medical rehabilitation, flight simulators and so on; haptic devices are also used in the military and in the entertainment business to give to the persons a partial, or total, ``immersion'' in a virtual world being created artificially. Finally, haptic devices, once that they are built and tested, can be used, with great success, as principal or master manipulators in a telemanipulation scheme, giving to the user a good control and feedback on the remote task being carried out.

As far as telerobotics is involved, possible telemanipulation systems include the following applications: dangerous environments for the human being, such as nuclear plants, underwater tasks, space operations and so on, in which it is not safe to operate directly for a person; differently scaled tasks, such as micro-surgery, high dimension or high load tasks, in which the user feels great difficulty due to the very different scale of the environment with respect to him; and finally, the ``simple'' possibility to operate remotely without being physically present in the real scene.

CONTENTS OF THE THESIS

A brief description of the chapters of this thesis is now presented, the work have been structured in the following way:

Chapter 1 presents the introduction of the work.

Chapter 2 contains the basic definitions for haptic systems with special focus on their control aspects, in particular this chapter deals with tendons/wires actuated devices and the aspects strictly connected to their peculiar structure.

Chapter 3 presents the definition of the elements of a complete telemanipulation scheme, the main properties and the ideal transparency aim and, finally, a detailed and organic presentation of all the principal control algorithms presented in the literature on this topic.

Chapter 4 defines stability and performances properties for a telemanipulation scheme and it proposes four different performance indexes in order to compare the algorithms previously presented in the benchmark example of two simple one degree-of-freedom (dof) linear manipulators.

Chapter 5 contains simulations and studies of a specific telemanipulation scheme, i.e. the intrinsically passive one; it holds with three dof manipulators, multiple input multiple output case, and enhances their performances using passivity definitions and concepts; this chapter contains also a passive approach for further performance enhancements in terms of position drift between manipulators.

Chapter 6 deals with two experiments carried out during the Ph.D. studies: the ViDet device, a particular haptic device actuated by tendons presented with its two different prototypes, and the telemanipulation device, built in order to test what above shortly described.

Chapter 7 contains some conclusions related to this work and it presents possible future work to be done.

Appendix A, finally, resumes the nomenclature of all the variables used in the mentioned chapters of this thesis.
 

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