The mechanism of bendable headrest of seats on airplane

[Leo Liu]

When I flew on a plane not long ago I started wondering about how flexible headrest works. This kind of headrest is reliable and still holds up well after several years of constant bending. I speculate it employs the same design as gooseneck lamp, but after some Google digging I cannot seem to find any information on it. Could someone tell me the answer, which I would appreciate?

 

[jack action]

From the patent for the headrest in the video (US10315773B1):

(b) a plurality of vertically articulated friction joints each including a torque insert, each of said friction joints separating each of said pairs one from another, and wherein said torque insert provides 100% of a specified torque in one direction, and less than 100% of said specified torque in the opposite direction;

A torque insert is what is used in a friction hinge:

What Is A Friction Hinge?​

A friction hinge, or torque hinge, is a specialty hinge that gives resistance to the pivoting motion. These hinges are typically used to control motion or hold a pivoting object opened or closed. The most common and relatable application is that of a “laptop hinge”. These motion control hinges are also known as:

• Free position hinge
• Positioning hinge
• Torque hinge
• Constant torque hinge
• Friction clutch
• Free-stop hinge
• Stop hinge … if designed with an added torsion spring they are also called counterbalanced hinges or equilibrated hinges.

How Does A Friction Hinge Work?​

Friction hinges achieve their function by engineering the specific tolerances between the mechanical components. Additional material such as springs and lubricant are often employed to achieve the desired degree of resistance or damping to the hinge movement.
In some cases, the goal is for the object on the hinge to close completely at a desired degree of speed. In others, the torque is used to hold one or both objects to which the hinges are secured to in a specific position, not necessarily on a fully opened or closed position. When used to hold one of the pivoting members in place, they are designed to be moved by a force of a specific amount of torque greater than its rated torque.
Friction hinges are often customized or custom designed to meet the exact torque requirements of critical applications. Custom designs can provide one-way hinges, in which all the resistance is only in one direction; two-way hinges that have equal damping in both directions, or a combination of both. Design variables include lubricant viscosity, construction material, and degree of space tolerance between components to meet specific applications, such as medical, rugged, high or low temperature, or hazardous environments.

This company sells those torque inserts that you can see here:

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This guy explains it a little bit more, but everything seems to be very secretive in the friction hinge world:

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