Robots with multiple-link arms that could reach through narrow openings into hidden cavities are undergoing development. Called "multifunction dexterous boro-robots" (MDBRs), these robots would resemble snakes (see Figure 1), in both general appearance and in the slithering motion with which they would negotiate narrow passages. Robots like these could make it possible to inspect, maintain, and repair critical parts in the interiors of complex machines like aircraft engines, without having to take the machines apart and then putting them back together at great expense. Such robots could also prove useful as surgical endoscopic tools. In comparison with currently available borescopes and endoscopes, MDBRs would be more versatile, more controllable, and better able to maneuver around obstacles. The MDBRs would differ from the serpentine inspection robots reported previously in NASA Tech Briefs[see "Small, Lightweight Inspection Robot With 12 Degrees of Freedom" (NPO-19367) Vol. 20, No. 2 (February 1996), page 73 and "Control of a Serpentine Robot for Inspection Tasks" (NPO-19506) Vol. 20, No. 3 (March 1996), page 1b.]

Figure 1. A Serpentine Robot Arm comprising many lightweight, rigid links could be maneuvered through narrow openings to reach objects that would otherwise be inaccessible. Each link could be made less than 1 cm in diameter and would typically be several centimeters long. The robot arm would be covered by a sheath of flexible material to protect the mechanisms in the links.

Each link in an MDBR contains linear actuators that are part of a kinematic linkage for controlling the relative orientations of the adjacent links. The kinematic linkage (see Figure 2) includes a base plate at one end and an articulation plate at the other end. The base and articulation plates also serve as the articulation and base plates, respectively, of the preceding and following links. The base and articulation plates are connected by six struts with compensated universal joints at their ends.

Three of the struts are of fixed length and are crossed; three of the struts are the linear actuators and are not crossed. Together, the six struts and the base and articulation plates constitute a truss with a unique configuration and a high strength-to-weight ratio. The configuration of the truss (and thus the position and orientation of the articulation plate relative to the base plate) can be altered by commanding the linear actuators to change their lengths according to the kinematical requirements. The linear actuators could be of any of several types; miniature piezoelectric "inchworm" actuators are particularly suitable.

Figure 2. The Kinematic Linkage in each link provides control of the position and orientation of the articulation plate relative to the base plate. The base and articulation plates are shown here as circular disks, but they could just as well have triangular or any other suitable shape.

The individual actuator commands to obtain the overall desired pose and snakelike motion of the arm are generated by a computer that solves the equations for both the forward and the inverse kinematics of the links and of the whole arm. An MDBR is modular in the sense that in principle, any number of links [with the same or different diameter(s) and length(s)] can be added to extend its reach or increase its dexterity. A two-link prototype has been demonstrated. In a practical application, the benefits of increased dexterity and reach would have to be traded off against the increase in the amount of computation needed to solve the inverse kinematical equations for a greater number of links.

This work was done by Yoseph Bar-Cohen and Mohsen Shahinpoor of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.comunder the Machinery/ Automation category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

Technology Reporting Office
Mail Stop 122-116
4800 Oak Grove Drive
Pasadena, CA 91109
(818) 354-2240

Refer to NPO-20268, volume and number of this NASA Tech Briefs issue, and the page number.

This Brief includes a Technical Support Package (TSP).
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Snakelike robots would maneuver in tight spaces

(reference NPO20268) is currently available for download from the TSP library.

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