Recycling Human Energy Managing and Recycling Pneumatic Energy to Actuate a Lower Limb Exoskeleton Rachel Rieger 1 , Jacob Rosen 2 1 University of California Davis 2 Bionics Lab, University of California Santa Cruz Objective Lower limb exoskeletons allow soldiers to carry heavy loads without enduring the weight. Existing lower limb exoskeletons are either gas or battery powered and therefore are impractical for extended periods of time. The LEX , UCSC’s Lower Limb Exoskeleton, will harvest energy absorbed from the knee and ankle joints and expel it through the hip and ankle joints. Research aim: the mechanical redesign of the pneumatic system to recycle energy. Approach Energy in the form of pressure is stored in a reservoir tank and released back into the joints by voltage controlled solenoid valves. Timing of valve openings is a balance of LEX movement fluidity (longer release) versus the amount of work produced (instantaneous release). (Fig. 4,5) New knee design: Lever and fulcrum to turn a 20 degree knee bend into a large displacement on a piston cylinder assembly. (Fig. 1) Optimized to the least bulky design while maintaining maximum forces. (Fig. 6) New ankle design: Compresses a gas spring cylinder upon flexion to harvest energy. Figure 4. For a quasi-static process: Percent of work created for normal 1.3 second gait cycle extruded to respective joint by harvested energy from hip joint based on release time. Results The LEX will be able to support approximately 10% of the wearers load from recycled energy. No time restraints or pneumatic power supply required. Pressure accumulated from recycled knee energy is released to the hip for .156 seconds. Pressure accumulated from recycled ankle energy is released back to the ankle for .026 seconds. Allows soldiers in the field, and eventually backpackers, to support heavier loads with less muscle restriction and fatigue. Figure 6. Optimization of varying positioning of lever fulcrum system and force it produces. Force calculated from peak ground reaction force at 2% of the gait cycle. Figure 2. Flexion (+) and Extension (-) angles of the hip, knee, and ankle joints exhibit during gait cycle. Figure 3. Phases, periods, and percentages of the gait cycle. Cite: Journal of American Academy of Orthopedic Surgeons Pneumatic Schematic Solenoid valve that allows flow during 0-14%GC Solenoid valve that allows flow during 58-66%GC Solenoid valve that allows flow during 42-62%, switch 66-68% GC Reservoir Air Cylinder (Hip) Air Cylinder (Knee) Gas Spring Cylinder (Ankle) Cite: Deviantart.net Original LEX Design New LEX Design Figure 1. Mechanical movement of the piston cylinder assembly being fully compressed from a small knee bend. Figure 5. For a quasi-static process: Percent of work created for normal 1.3 second gait cycle extruded to respective joint by harvested energy from ankle joint based on release time. Does not include work done by spring. Angle Sensor Angle Sensor Angle Sensor Force Sensor Pressure Sensor Pressure Sensor Pressure Sensor Solenoid Driver Proximal Sensor Proximal Sensor Proximal Sensor Solenoid Driver Solenoid Driver Microcontroller Microcontroller Microcontroller % of Gait Cycle Angle (degrees) This work was sponsored by the National Science Foundation, SURF-IT (surf-it.soe.ucsc.edu ) Research Experience for Undergraduates Program. NSF grant Award No. CNS-0852099. In addition, thanks to the University of California, Santa Cruz. % Work Obtained from Ankle Joint % Work Obtained from Knee Joint
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Recycling Human EnergyManaging and Recycling Pneumatic Energy to Actuate a Lower Limb Exoskeleton
Rachel Rieger1, Jacob Rosen2
1University of California Davis2Bionics Lab, University of California Santa Cruz
Objective Lower limb exoskeletons allow soldiers to carry heavy loads
without enduring the weight.
Existing lower limb exoskeletons are either gas or battery powered and therefore are impractical for extended periods of time.
The LEX , UCSC’s Lower Limb Exoskeleton, will harvest energy absorbed from the knee and ankle joints and expel it through the hip and ankle joints.
Research aim: the mechanical redesign of the pneumatic system to recycle energy.
Approach
Energy in the form of pressure is stored in a reservoir tank and released back into the joints by voltage controlled solenoid valves.
Timing of valve openings is a balance of LEX movement fluidity (longer release) versus the amount of work produced (instantaneous release). (Fig. 4,5)
New knee design:
Lever and fulcrum to turn a 20 degree knee bend into a large displacement on a piston cylinder assembly. (Fig. 1)
Optimized to the least bulky design while maintaining maximum forces. (Fig. 6)
New ankle design:
Compresses a gas spring cylinder upon flexion to harvest energy.
Figure 4.For a quasi-static process: Percent of work created for normal 1.3 second gait cycle extruded to respective joint by harvested energy from hip joint based on release time.
Results
The LEX will be able to support approximately 10% of the wearers load from recycled energy.
No time restraints or pneumatic power supply required.
Pressure accumulated from recycled knee energy is released to the hip for .156 seconds.
Pressure accumulated from recycled ankle energy is released back to the ankle for .026 seconds.
Allows soldiers in the field, and eventually backpackers, to support heavier loads with less muscle restriction and fatigue.
Figure 6.Optimization of varying positioning of lever fulcrum system and force it produces. Force calculated from peak ground reaction force at 2% of the gait cycle.
Figure 2.Flexion (+) and Extension (-) angles of the hip, knee, and ankle joints exhibit during gait cycle.
Figure 3.Phases, periods, and percentages of the gait cycle. Cite: Journal of American Academy of Orthopedic Surgeons
Pneumatic Schematic
Solenoid valve that allows flow
during 0-14%GC
Solenoid valve that allows flow
during 58-66%GC
Solenoid valve that allows flow during
42-62%, switch 66-68% GC
Reservoir
Air Cylinder
(Hip)
Air Cylinder(Knee)
Gas Spring Cylinder(Ankle)
Cite: Deviantart.net
Original LEX Design New LEX Design
Figure 1.Mechanical movement of the piston cylinder assembly being fully compressed from a small knee bend.
Figure 5.For a quasi-static process: Percent of work created for normal 1.3 second gait cycle extruded to respective joint by harvested energy from ankle joint based on release time. Does not include work done by spring.
Angle Sensor
Angle Sensor
Angle Sensor
Force Sensor
Pressure Sensor
Pressure Sensor
Pressure SensorSolenoidDriver
ProximalSensor
ProximalSensor
ProximalSensor
SolenoidDriver
SolenoidDriver
Microcontroller
Microcontroller
Microcontroller
% of Gait Cycle
An
gle
(deg
rees
)
This work was sponsored by the National Science Foundation, SURF-IT (surf-it.soe.ucsc.edu) Research Experience for Undergraduates Program. NSF grant Award No. CNS-0852099. In addition, thanks to the University of California, Santa Cruz.
% Work Obtained from Ankle Joint
% Work Obtained from Knee Joint
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