Sensors constantly monitor the weight of the user and the angle between knee and thigh, providing real-time information about the speed and movement of the prosthesis, as well as ground reaction forces and any bending movements.
An onboard computer, or microcontroller, processes the sensor data while simultaneously tracking an historical backlog of gait patterns. It instructs the actuator control unit to respond immediately, according to the circumstances it has detected.
The actuator acts as a brake, varying its resistance to angular motion for a natural, appropriate response – from firm and unyielding support when standing, to light, free movement when turning a corner or walking in confined spaces.
Integrated angle and force sensors deliver important information about the dynamic behaviour of the user, which artificial intelligence (AI) in the microcontroller uses to determine ground conditions – whether the user is on stairs, a slope, or level ground, for example. Any long-term change in measured force may indicate a change of load (eg user has picked up a suitcase) or a change in alignment (eg change of heel height).
As fast as the microprocessor receives these signals from the sensors, it performs a series of rapid calculations and determines the appropriate amount of knee resistance (braking) at any given moment. The AI can also recognize unexpected gait patterns, counteracting such movements effectively and helping to prevent a stumble and fall. From the very first step, the RHEO KNEE is building a ‘library’ of information, maintaining hard facts, old response measurements and the latest set of parameters from the sensors. This fast accumulating knowledge means that each new movement reflects the user’s walking profile more closely than before.
Instructed by the microprocessor, the actuator delivers an exceptionally fast and smooth response. The knee’s name derives from magnetorheological fluid, which works in conjunction with a series of blades to create a braking force. When a magnetic field is applied, minute iron particles within the fluid become aligned, creating ‘chains’ that in effect increase the fluid’s viscosity. The blades are there to cut through the fluid, a smooth and easy motion when there is no magnetism, but a much tougher job when a magnetic field is applied.