four-bar linkage

NASA Jet Propulsion Laboratory

summer 2022

During my second summer at JPL, I worked on the Orbital Sampler Capture And Release (OSCAR) mechanism for Mars Sample Return (MSR). OSCAR is a latch to hold the lid for the sample capsule before it is used to seal the capsule after sample collection. The design was in its very early stages when I started my internship so I was tasked with investigating all potential designs, however wild, that could fit the specified design requirements; in particular, 1) the clamping lip must provide a downward force on the lid, 2) the mechanism must be spring-loaded, and 3) the mechanism should use rotational over sliding contact to minimize friction.

Figure 1: Four-Bar Linkage Design

Based on these requirements, I came up with a four-bar linkage mechanism, as pictured in figure 1. The capsule lid is represented by the blue ring; as the central red disk rotates, it pushes the spring-loaded yellow clamps over the lip of the lid.

To ensure the clamp properly secured the lid, I incorporated a design concept called overcentering that I learned from an engineer on my team. This four-bar linkage mechanism works like a toggle clamp as shown in figure 2: as the central disk rotates it pushes past center with the help of a spring. Then once it is past center, it requires external force to overcome the clamped position.

Figure 2: Overcentering

Before I left JPL, I also put together some prototypes of my design and tested their functionality, as shown in the images on the right and left.

The complete clamping procedure with explanation of the toggle action principle is shown in an animation below.

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