The objective of this research is to design an artificial knee (either a prosthetic knee or an orthotic knee) to exhibit the basic behavior of the human knee. Such artificial knee should exhibit three behaviors:

1. Resist the knee flexion during the stance phase to help support a portion of user’s weight.

2. Encourage knee flexion during the swing flexion phase to assist in toe clearance.

3. Allow free swing extension in the swing extension phase.

An important aspect of this invention is that all of the above specifications are achieved passively without the use of any actuators, computers and sensors. This knee device has designed, fabricated, and tested to enable paraplegics to walk in an exoskeleton. This invention is a planar machinery that achieves the above specifications in a simple architecture. Such knee has shown to be a good fit for certain paraplegics who prefer more rehabilitating work out because it allows more freedom and provides adjustable support. This artificial knee is highly adaptable for its modularity, and the simple yet highly functional design has the potential to significantly decrease the manufacturing cost.