Fig. 3: The Alpha Leg with first-generation exoskeletal interface using a hydraulic logic circuit control system
PROSTHESIS: THE ANTI-ROBOT
Fig. 4: Full hydraulic schematic showing hip and knee cylinders in regenerative mode and hydraulic logic circuit control system
Hydraforce. This reduced the deadband, introduced many more points and ranges of adjustment, and allowed input forces to potentially be reduced to nearly zero. The hydraulic logic circuit was reduced to two cylinders—the input cylinder on the exo-frame and feedback cylinder in the joint on the leg— with the valve transducer connected in series with the input cylinder by a common arm linkage as shown in Fig. 6. Because the input signal was picked up by a rotary encoder, the input force could be as low as desired and was set by adjusting a centering spring. The damping in the system was adjusted through a separate damper. The ratios of all of these elements could be adjusted independently to give the right amount of resistance and stability required for “that sporty feel.” Further, the programmability of the Hydraforce valves gave another point of control to adjust response curves or compensate for factors like user skill and preference and asymmetric cylinder response. While this more advanced technology solved many of the user experience issues, it is more complex and will require more tuning to reach peak performance. We are presently working with the Hydraforce applications engineers to
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