Fluidics

Human gait is highly non-linear and indeed very complex in terms of engineering. For instance, when a swing phase starts the knee bends very fast, but the resistance to bending must be low, whereas in mid-swing the knee must bend slowly and the resistance must be high. This needs powerful data processing technologies, which can be of different technology platforms. A well known technology platform is the microchip with stepper motor actuators that consume much battery power.

VGK family of product uses a Fluidic Processor that in its own way uses digital switching, memory combined with fluidics, a sophisticated approach of measuring fluid speed and pressures to instantly adapt the response of the prosthesis to the need of the moment. (It is estimated that the the reaction speed of is equivalent to 2000 Hz sampling rate). The combination of the fine tuned interplay of these technologies makes a fluidic processor control.

Fluidics is a name for a control technology, that uses the properties of a fluid direct for both power and control. A hydraulic knee joint naturally uses a working fluid, typically oil. This fluid controls the movement of the joint under load by being pressured and by resistance to flow-through valves. These valves can be controlled by hand, (setting a button), electrically (with motors), or by fluid itself, which is called fluidics. As pressure can cause flow, flow also causes pressure differences. Pressure and flow can be made interactive, and so the VGK has been designed with careful selection of flow and pressure, an autoadaptive fluidic control knee joint.

waterworks

To illustrate one simple, but powerful and adaptive feature of fluidics, let’s look at the image from a Spanish water works vortex showing a controlled water flow outlet. The water can be seen spinning into a vortex. Due to the spinning, the water finds it difficult to find the centre to exit through the outlet hole. One would think that the height of the water (causing pressure) would cause more water to flow out. Almost the opposite is true, the higher the water level (equals pressure)  the faster the water spins in the vortex preventing a real increase in water flowing out: the output remains rather constant instead.

The development of a vortex is interesting to watch. The core in the vortex causes the centre of the plughole to be not-filled with fluid, and hence the effective area through which the fluid flows is reduced, and therefore the spinning fluid makes its own auto adjustable valve. This is but one example of fluidics: flow control without moving parts, without need of external adjustments or power supply.

Adaptive fluidics controlling descent

Vortex-control

This simple but effective control is used in the VGK product family, where it has been demonstrated that  forcing the fluid from under the piston of the artificial knee through a vortex spinning chamber, causes directly a sustained ability of the knee joint to carry the weight of the user in the stance phase, even when the knee bends under load.

The knee joint prevents ‘jack-knife’-ing under load when walking down slope or down stairs. UK, US, and European  patents have been granted in recognition of the inventiveness in hydraulic knee control.

Fluidic control mechanisms ensure that the knee moves through a swing phase, punctually in time, across a wide range of walking speeds. When a heavier shoe is worn, the control automatically increases the driving power and ensures that the foot is still in time for the next heel strike. Intuitive fluidic control also adjusts the braking power on terminal impact buffer.

VGK technology is powered by energy recovered from the special hydraulic oil used in the prosthetic knee joint. To be explicit: the VGK avoids the use of electrical control power source, and frees the user from any daily or weekly charging sessions as necessary in some other systems.

How is this possible?

The patented technology of Orthomobility uses the actual fluid flow to adjust the valve settings, such that the valve is tightened when the rate of motion exceeds a preferred value.

In short: it is the joint motion itself that sets its own limits.