Title: Friend, robot per space: Sequence of Positioning and Movement in the operation of Substitution of Parts and Procedure for grasping an hidden object behind an obstacle.
Author: prof. Alberto Rovetta N. AG-2
References:

A. Rovetta, P. Cavestro, Redundant Sensorized Arm+Hand System for Space Telerobotized Manipulation, Nasa Conference on Telemanipulation on Space, Pasadena, February 1989

Objectives
The sequences of the movements and the positioning that the Friend robot must follow in order to carry out the operation of ôSubstitution of Parts ".
For avoidance, the procedure follows two different routes according to the type and geometry of the obstacle. There are two obstacle categories : an obstacle is either particularly long lengthwise or reduced.

Contents
The " Substitution of Parts " represents most complex and articulated macro_operation of maintenance of the orbiting station on which the Friend robot operates, therefore the studies lead on this last one can be considered like a synthetic analysis of the operations that compose it, which as an example the operation of Taking, Transporting and Depositing of Objects, the operation of Assemblage and the operation of Disengaging.
In order to supply to the development of such duties of maintenance, it is previewed to equip the robot with 13 degrees of freedoms indicated in the following figure.
For avoidance, in the event of the grasping point not being found in the arm plane, there are two ways of reaching it: the first is to move the articulated quadrilateral thus compensating for the increase in the distance by using the 3 link movements; the second is to carry out a rotation around the transverse docking axis, counter-rotate the spherical wrist and correct the distance using the 3 link movement. The first option is preferable; fewer movements are used and the whole operation is simplified

Results
It is considered the operation of "Substitution of Parts " in the case in which the damaged member is shielded from panels of protection. The robot arranges his body frontally to those panels in order to open them easily.
With such End Effectors, the 2 arms deposit the damaged piece, seize the " module " of reciprocation and transport it near the the fixed support to which they approach it sweetly. For avoidance, the robot avails itself of various options to overcome an obstacle; these depend mainly on the way in which one wishes to reach an object : either using one or both arms. The possibility of reaching it with both arms is essential in terms of robot operating features. Moreover when studying the sequence pertaining to transit above an obstacle, it has been shown, that the robot has to use independently rotation of the two half-bodies around the transverse docking axis.

Future possible developments
The modality of analysis of the " Substitution of Parts " has general validity and it can be used to study all the other operations of maintenance.
It is necessary to equip such first level analysis, with a successive
developed dynamics analysis resorting to the multibody method in such way to place the bases for the development of the control system.
For the avoidance, The limitations involved in the possibility of overcoming an obstacle using this procedure are the dimensions of the obstacle itself; if this is much larger than the dimensions of the robot itself, the obstacle will not be able to be exceeded.