Shady

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Revision as of 19:48, 23 November 2006

CAD representation of Shady, a truss climbing robot with a deployable sun-shade as an example application.

File:shady-climb-up-untether-4x-mq.avi

We work in the new Stata Center building at MIT in a room with a large wall-window which currently has no shades. As many of our desks are directly next to this window we needed some means to block the light from hitting our computer screens. Instead of traditional shades which would block the whole window, detracting from the view, we have decided to build a robot which can climb on the window's aluminum frame. It can thus be positioned on the window to be a localized sunshade.

While many climbing robots have been developed, only a few climb on thin-member truss-like structures. Shady tests some new ideas in design and control, in particular, using mechanical compliances and associated proprioception, and was experimentally verified to be over 99.8% robust over many hours of climbing.

Truss Climbing

A map of the wall-window in our lab. The frame of the window (yellow lines) is composed of rigid aluminum members, each about 1 inch wide. Shady climbs by a sequence of grip and swing motions, and can climb bars in any orientation. The grippers cannot close at locations where bars intersect, but the need for that can be avoided by starting Shady at an appropriate location.

Truss structures are familiar to most of us: railroad bridges, construction scaffolding, and radio towers are common examples. Many structures built in space, for example on the international space station, are also essentially trusses. While most trusses are currently assembled and maintained by humans, it may be advantageous in some cases to have a robot which can climb about the truss to deliver tools and materials, or perhaps to inspect or even assemble new parts of the truss.

While many structure climbing robots have been developed, most do not address the case of climbing on trusses. It can be argued that the penalties for uncertainty are higher when climbing a thin-member truss structure than for some other types of climbing, such as climbing the broad flat surface of a building. In particular, as the robot extends a gripper towards a thin structure it may easily approach misaligned, or even miss the structure completely.

A Demon App: Sun Shading

File:shady-fan-open-close-mq.avi We are most interested in the science and engineering questions related to achieving robust truss climbing. As an example application, Shady carries a deployable sun-shade which can block glare for individuals in our lab. Placement of the shade of course depends both on the geometry of incoming sunlight and on the location of the shade target in the lab. Currently Shady's location is manually specified by clicking on a representation of the window frame. In the future we may attempt to automate this process.

Compliance and Proprioception

File:shady-hinge-mq.avi

Linkage-Based Grip Mechanism

TBD. More details are given in our ISER 2006 paper.

Research Context

Several truss climbing robots have been explored by other groups, e.g. Staritz et al’s “Skyworker” [8], Amano et al’s handrail-gripping robot for firefighting [4], Ripin et al’s pole climbing robot [11], Nechba, Xu, Brown et al’s “mobile space manipulator SM2” [7], Kotay and Rus’ “Inchworm” [5], and Almonacid et al’s parallel mechanism for climbing on pipe-like structures [6]. This paper presents a new mechanical design and novel control using intentional mechanical compliances and proprioception, with experimentally confirmed robustness.

Experimental Results

We performed over 10 hours of measured climb tests with this version of the Shady hardware, comprising over 1296 individual grip/ungrip/rotate movements, and including several long uninterrupted climbs. Only two non-dangerous faults were observed in all this testing, yeilding a reliability rate of over 99.8%. This testing is described in more detail in our ISER 2006 paper.

Simulation

We have created a basic kinematic simultor for Shady, which has enabled us to develop and debug many algorithms used in shady operation. You can try it out online here.

Publications

• Marsette Vona, Carrick Detweiler, Daniela Rus. Shady: Robust Truss Climbing With Mechanical Compliances. International Symposium on Experimental Robotics pp. TBD, 2006.
• Carrick Detweiler, Marsette Vona, Keith Kotay, Daniela Rus. Hierarchical Control for Self-assembling Mobile Trusses with Passive and Active Links. IEEE Intl. Conf. on Robotics and Automation pp. 1483--1490, 2006.