Fault Tolerance Micro-manipulation System and Its Application to Teleoperation Tasks

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Efficacy of force feedback in a micro manipulation system has been widely recognized. However, the fact that a practical application is yet to be seen is due to the following two major reasons : (I) lack of means to provide a stable force feedback signals, (II) lack of means to realize a teleoperation even under the presence of communication delay. The current study is aimed at dealing with these problems under the scenario of micro manipulation. In order to deal with (I), we propose to apply the concept of "fault tolerance" by utilizing redundant sensing means. By doing so, a faulty sensor can be backed up by a secondary sensor so that the operation side can keep receiving force signals without interruptions. (II) is coped with by means of the virtual model which mimics an operational probe of the micro manipulation system. The virtual model enables the operator to accomplish manipulation tasks according to a reaction force reflected from the model rather than from the actual system. The biggest advantage of adopting such a virtual model is the absence of time-delay. If the force feedback signal is created based on the real force measurement, the communication time-delay becomes substantial so that the operator can hardly execute manipulation tasks.We have conducted actual teleoperation experiments in which a haptic device (PHANToM) was used to operate the micro manipulation system over the Internet. TCP and UDP were tested for comparison purposes and it was found that UDP serves better for our purpose. We also verified that the virtual model is extremely useful so that even novice user can handle the micro manipulation system under teleoperation. In addition, a new mechanism was introduced to enhance the functionality of the micro manipulation system. Offset planar hinge link mechanism was adopted to provide a posture control of the probe.