A mechanism has been developed to serve as an end effector for one of the legs of the Legged Excursion Mechanical Utility Robot (LEMUR) — a walking robot designed for demon- strating robotic cap- abilities for maintenance and repair. [The LEMUR was described in “Six-Legged Experimental Robot” (NPO-20897), NASA Tech Briefs, Vol. 25, No. 12 (December 2001), page 58.] Through controlled actuation of this mechanism, the tip of the leg can become either (1) a foot for stable support during walking or (2) the robotic equivalent of a simple hand tool — a ballend hexagonal driver for a standard hexagonal-socket machine screw. More specifically, the foot can be extended to enable walking, or can be retracted to enable cameras that are parts of the robot to view the insertion of the tool bit in a socket. Retraction of the foot also enables the tool to be used in confined spaces in which the foot cannot fit.

This Mechanism is designed to be mounted on the outer end of one leg of a walking robot. The foot can be retracted to expose the tool bit, or extended to enable the robot to walk.
The mechanism (see figure) includes a hollow lead screw. The foot includes a nut that engages the lead screw. A compact, light- weight motor with a speed-reducing, torque-multiplying gear head is housed inside the lead screw. An external guide prevents rotation of the foot when such rotation is not desired. In preparation for retraction of the foot, the guide is initially locked against rotation of the foot by use of a pin and slot that mate in only one position. When the motor rotates the lead screw in one direction, the foot is retracted along the lead screw, exposing the tool bit.

When an axial compressive force is applied to the tool (as when the tool bit is inserted in a socket in a machine screw), interface pins between the tool bit and the guide transmit some of this force to the guide, thereby pushing the guide out of the slot that locks it and the foot against rotation. Now the guide and foot begin to rotate along with the lead screw and retraction of the foot ceases. Because the tool bit is mated with the lead screw in such a way that when the lead screw is rotating, the bit is also rotating, the lead screw can now be rotated in either direction to cause the tool to rotate the socket and thereby tighten or loosen the machine screw. The output torque of the motor, and hence the torque applied to the machine screw, is governed by a current- feedback motor controller.

Once the tool is relieved of the axial compressive force (as when the tool bit is removed from the socket), the guide and foot continue to rotate until the pin engages the slot. At this point, the guide and foot are once again constrained against rotation; hence, rotation of the lead screw in the appropriate direction causes extension of the foot, restoring the walking configuration.

This work was done by Jennifer Knight and Stephen Askins of Caltech for NASA’s Jet Propulsion Laboratory.

Topics:
Anatomy Automation Body regions Fasteners Foot Gears Hand Leg Mechanical Components Mechanics Medical, health and wellness Medical, health, and wellness Parts Robotics Screws
This Brief includes a Technical Support Package (TSP).
Document cover
Rotary Tool and Retractable Foot for Walking Robot

(reference NPO-30276) is currently available for download from the TSP library.

Don't have an account?

Magazine cover
NASA Tech Briefs Magazine

This article first appeared in the November, 2002 issue of NASA Tech Briefs Magazine (Vol. 26 No. 11).

Read more articles from the archives here.

Overview

The document outlines a technical support package for a novel rotary tool and retractable foot designed for the Legged Excursion Mechanical Utility Robot (LEMUR), developed by NASA's Jet Propulsion Laboratory (JPL). The innovation, attributed to inventors Jennifer M. Knight and Stephen A. Askins, represents a significant advancement in robotic technology by combining the functionalities of a walking robot foot and a rotary driver tool into a single device.

The primary motivation behind this development was to enhance the LEMUR's capability to perform maintenance and repair tasks in various environments. The robot, which features six legs, required a mechanism that could serve as both a stable support during locomotion and a tool for engaging with standard fasteners, specifically a #10-32 hex socket screw. The design needed to accommodate machine vision systems for precise alignment with screws while maintaining a compact form factor to meet weight and space constraints.

The solution involves a ball-end hex driver that operates as a robotic "hand" tool. This tool is equipped with a retractable foot that enhances dexterity and visibility of the tool tip during operation. A current feedback motor controller regulates the output torque, ensuring effective manipulation of fasteners. The system is powered by a MicroMo 0816 coreless DC motor, which, when combined with a planetary gear head, provides a maximum output torque of 3.2 in-lb at a reduced speed of 18 rpm. This configuration allows the robot to perform tasks efficiently while adhering to thermal limits.

The document also emphasizes the innovative nature of this device, as it is the first of its kind to integrate these functionalities into a single unit. The design includes a quick-release mechanism for easy interchangeability of tools, further enhancing the robot's versatility.

Overall, this technical support package highlights the advancements in robotic technology facilitated by NASA, showcasing the potential for robots like LEMUR to perform complex tasks in challenging environments. The work was conducted under NASA's sponsorship, and the findings are intended to contribute to the broader field of robotics and automation.