The human body has many miraculous capabilities that we often take for granted. One of the more subtle ones is the variable stiffness of your joints. In technical terms, stiffness refers to the ability to resist a load. Delicately manipulating an artist’s paint brush, for example, doesn’t require much load resistance, but does require fine control. However, that same artist might pick up a bowling ball with a stiffer joint (and, usually, less fine control).

[Christopher Churchill] and some colleagues have a novel mechanical device that can rapidly change stiffness. The device could have applications in robotics and other devices. It can also transmit or attenuate vibration since non-stiff joints don’t pass vibrations as easily as stiff ones.

The video below shows the basic idea behind the new invention. The concept is to combine positive and negative stiffness to balance the net stiffness to zero and then make subtle alterations to produce the desired stiffness. Variable stiffness systems aren’t new. Your car’s shocks, for example, are stiff at rest, but springy in motion. However, the new system can change stiffness by a factor of 100 in just milliseconds.