Distributed Manipulation with Touch Sensitive Rope

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In robotics most manipulation algorithms are designed to execute in a single process on a single computer that takes input from all the sensors and controls all the effectors. These algorithms are sequential but mechanically-based single robot algorithm. While quite general in principle, these off-line algorithms are usually designed for robotics devices such as grippers or fingers attached to a traditional robot arm. To extend these results for distributed manipulation there are several challenges.

  1. Autonomous mobile robots (mobots) have different sensing and control modalities.
  2. Mobots are often better suited to on-line approaches and hence the algorithms must be adapted to rely less extensively on geometrical and dynamical models.
  3. A host of difficulties arises when a task must be performed by a distributed team instead of a single agent---and hence the algorithms must compensate by changing their communication, sensing, or knowledge requirements.

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Projects

Touch Sensitive Rope

Premise: to create a multi-segment rope which will gather information about where pressure is applied to it. I.e., when wrapped around a box it will detect the corners.

First Prototype Construction

The first rope prototype (Fig. 1) consisted of one contact patch sewed onto two layers of cotton fabric with the conductive thread wires in them. This bundle was then wrapped in a piece of burlap with some of the threads removed to allow contact between an outer layer of wrapped conductive material when pressure was applied.

Fig. 1: The first prototype and it's burlap shell

Problems

The burlap grid tended to fall apart and had holes which were slightly too large. Also, the entire thing was very hard to roll up tightly and keep together.

Second Prototype Construction

After sewing the conductive threads into the nylon, it was glued to another piece to form an insulating backing. Four pieces of conductive fabric were then glued onto the outside layer of insulating nylon and connected to one of the conductors by sewing through both layers of fabric (Fig. 3,2). A wire core was then glued to one edge to be used for rolling the sheet (Fig 4). The inside of the sheet was then sprayed with adhesive and rolled around the core (Fig 5). Note the green electrical tape used to keep the leads separate on the end.

Fig. 2: Inside with the conductive threads
Fig. 3: Outside with insulating nylon backing and glued on contact patches
Fig. 4: Inside with a wire core attached for rolling
Fig. 5: End after rolling

Now we are not sure what sort of grid to use. We have two choices, one is thinner with larger holes and the other is thicker and stiffer with smaller holes. (Fig. 6.) The fear is that the thinner one will not function well when bent around a small diameter rope, so we are going to apply each grid to half the length of the prototype with adhesive and then add a final outer ground coating of conductive fabric.

Fig. 6: Grid samples with patches of conductive material attached
Fig. 7: Second prototype finished with leads

Problems

The wire/threads on the inside came into contact with the outside fabric contacts when rolled causing a short circuit. This was helped but not solved by adding a third layer of blue nylon on the inside covering them and by making the fabric contact squares smaller. The biggest problem, however, was applying the grid to the tube. This has to be done by spraying the grid with glue on both sides and then applying it and covering it with a piece of conductive fabric. However, in the process most of the glue gets rubbed off the outside side. You can't spray more on because that would cover the openings in the grid and prevent any contact from occurring between the outer ground and the inner patches.

In finishing the second prototype attaching the conductive outer layer (the ground) to the grid was difficult with the thicker grid. The outer layer of nylon (blue with white twist tie) seen in Fig. 7 serves to hold the outer conductive ground in place and shields it from the world. However, once it was in place, the rope functioned as desired.

Third Prototype Construction

The hope in this construction is to create a more carefully measured and constructed prototype and hopefully avoid the problems with shorts and poor grid attachment which plagued the second prototype. It should be noted that the core being a thick wire produces too much rigidity in the rope. Of further note is that were the rope were to bend sharply the nylon would wrinkle up in a potentially problematic manner. This might be solved by choosing a stretchy fabric instead of nylon and segmenting the outer ground -- which would require the outer ground to be attached not to the central core but to an outer sheath to carry the thread connections between the grounded segments. This, however, might solve the outer ground attachment problem.

Fig. 8: Third prototype construction. Note how much neater the sewing is.
Fig. 9: Note the three segments: left, middle, and right

The third prototype featured several enhancements discovered during the construction of the first two prototypes. The thread-wires were sewed into a layer of nylon to which was then attached an insulating layer of nylon on the back. The conductive patches were then glued on to this layer and connected by sewing through to the conductive threads on the inner layer. Another piece of insulating nylon was then attached to the remaining open side of the inner layer with the threads sewn in it. This produced a three layer thick "wrapper" which contained the conductive thread-wires. The outer two layers served to insulate the thread-wires from each other when the core was rolled. This designed proved sufficient to prevent the shorts which occurred in the second prototype.

Once this three layer thick nylon wrapper was glued to the core (as in the second prototype) and rolled up, the outer ground sheath with the grid to separate the ground and conductive patches (see Fig. 6) was applied. However, this time the grid was affixed directly and only to the outer ground. This was then allowed to dry and wrapped around the core. The outer ground was glued to itself forming a tight outer tube which was not actually attached to the inner core, but which was attached tightly enough to hold it in place. (See Fig. 9) The third prototype was constructed with two different outer ground sheaths -- one for each of the two different grid sizes and thicknesses we are testing. In Fig. 9 these can be seen on the left (with green tape holding the thinner grid section together while the glue dries). The blue nylon of the inner wrapper can be seen sticking out over the gray core on the right.

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