The planned Mars Science Laboratory mission requires inlet funnels for channeling unconsolidated powdered samples from the sampling and sieving mechanisms into instrument test cells, which are required to reduce cross-contamination of the samples and to minimize residue left in the funnels after each sample transport. To these ends, a solid-state shaking mechanism has been created that requires low power and is lightweight, but is sturdy enough to survive launch vibration.

A graphic of the Actuator Mechanism mounted on the funnel rim out of the load path. The other end of the flexure can be modified to (a) be free, (b) drive a fixed mass, or (c) drive a free mass at low resonance and produce impacts.
The funnel mechanism is driven by asymmetrically mounted, piezoelectric flexure actuators that are out of the load path so that they do not support the funnel mass. Each actuator is a titanium, flextensional piezoelectric device driven by a piezoelectric stack. The stack has Invar endcaps with a half-spherical recess. The Invar is used to counteract the change in stress as the actuators are cooled to Mars’ ambient temperatures. A ball screw is threaded through the actuator frame into the recess to apply pre-stress, and to trap the piezoelectric stack and endcaps in flexure. During the vibration cycle of the flextensional actuator frame, the compression in the piezoelectric stack may decrease to the point that it is unstressed; however, because the ball joint cannot pull, tension in the piezoelectric stack cannot be produced. The actuators are offset at 120°. In this flight design, redundancy is required, so three actuators are used though only one is needed to assist in the movement.

The funnel is supported at three contact points offset to the hexapod support contacts. The actuator surface that does not contact the ring is free to expand. Two other configurations can be used to mechanically tune the vibration. The free end can be designed to drive a fixed mass, or can be used to drive a free mass to excite impacts (see figure). Tests on this funnel mechanism show a high density of resonance modes between 1 and 20 kHz. A subset of these between 9 and 12 kHz was used to drive the CheMin actuators at 7 V peak to peak. These actuators could be driven by a single resonance, or swept through a frequency range to decrease the possibility that a portion of the funnel surface was not coincident with a nodal line (line of no displacement).

The frequency of actuation can be electrically controlled and monitored and can also be mechanically tuned by the addition of tuning mass on the free end of the actuator. The devices are solid-state and can be designed with no macroscopically moving parts. This design has been tested in a vacuum at both Mars and Earth ambient temperatures ranging from –30 to 25 oC.

This work was done by Stewart Sherrit; Curtis E Tucker, Jr.; John Frankovich, and Xiaoqi Bao of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Mechanics/Machinery category. NPO-45856

Topics:
Mechanical Components Mechanics Sensors and actuators Test facilities
This Brief includes a Technical Support Package (TSP).
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Miniature Piezoelectric Shaker for Distribution of Unconsolidated Samples to Instrument Cells

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NASA Tech Briefs Magazine

This article first appeared in the July, 2010 issue of NASA Tech Briefs Magazine (Vol. 34 No. 7).

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Overview

The document discusses a novel Miniature Piezoelectric Shaker developed by NASA's Jet Propulsion Laboratory (JPL) for the efficient distribution of unconsolidated samples to instrument cells, particularly for the Mars Science Laboratory (MSL) mission. The primary goal of this invention is to minimize cross-contamination of powdered samples during transport to test cells, which is crucial for accurate scientific analysis.

The innovative design features a solid-state shaking mechanism that operates without macroscopically moving parts, significantly reducing the risk of mechanical failure. The shaker employs asymmetrically mounted piezoelectric flexure actuators that are strategically placed out of the funnel's load path. This design choice addresses previous issues where actuators were in the load path, leading to failures during launch vibration tests due to delamination of polymer bonds in the actuators.

Key features of the shaker include electrically and mechanically tunable actuation, lightweight construction, and low power consumption. The actuators are designed to avoid tension, which enhances their reliability under varying conditions, including vacuum and ambient temperatures ranging from -30°C to 25°C. The mechanism allows for effective shaking of the funnel while transporting samples, thereby reducing residue and cross-contamination.

The document outlines the technical challenges faced in the original funnel mechanism used in the CheMin instrument, which failed to meet launch vibration test requirements. The redesign involved repositioning the actuators to eliminate their role in supporting the funnel mass during acceleration, thus improving the overall robustness of the system. The new actuator design incorporates a titanium flextensional piezoelectric device driven by a piezoelectric stack, with features that allow for pre-stressing and tension relief.

In summary, this Miniature Piezoelectric Shaker represents a significant advancement in sample handling technology for space missions. Its innovative design not only enhances the reliability and efficiency of sample distribution but also has potential applications beyond aerospace, contributing to broader technological and scientific advancements. The document serves as a technical support package, providing insights into the development and implications of this cutting-edge technology.