Scale Prototipe of a Lower Limb Exoskeleton

Biomedical engineers objective is to develop medical innovations through technology to prevent and treat health problems, giving the patient a better lifestyle. Orthoses and prostheses are the most common ones.[1]

An exoskeleton is considered an orthoses by the norm UNE-EN ISO 12523.

An exoskeleton is a device to help a user increase their physical performance by helping to support the lower limb of the body externally, this is done passing the forces that hold the weigh of the upper limb of the body directly to the ground without passing the weigh on the legs. The principal use of the exoskeleton is for rehabilitation of legs, knee, and hip, however it can be used for patients with multiple sclerosis, degenerative diseases or spinal cord injuries like paraplegia, meaning that for some, the exoskeleton will completely replace their walking function (gait cycle). In Mexico there are 6,179,890 people with some type of disability, which represents 4.9% of the country's total population. According to INEGI (2020), 49% of them have problems walking, going up or down without assistance.[2]

As students, resources are limited, therefore we´re creating an exoskeleton on scale, knowing that is easier to make a prototipe of an exoskeleton for the lower limb, wich will help us to understand the gait cycle as well as practice the manufacturing processes learned throughout the degree.

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Supplies

Medium density fiberboard (MDF)
Servo motors
Screws #10-24 x 3 IN
Arduino
Arduino IDE
Jump wires
Laser cutter machine
Solid works
voltage regulator

Step 1: Exoskeleton Design

The next step was to design in CATIA each part of the exoskeleton.

Focusing more on the functionality than anatomical aesthetics the exoskeleton was designed the next way:

Femur: 15 cm long x 5 cm wide, with cavities to accommodate servo motor gears.
Tibia and fibula: 10 cm long x 5.6 cm wide.
Hip: 21 cm wide x 10 cm long.
Foot :15cm long x 5cm wide for better stability.
Unions 5cm and 5.6 cm long x 5cm wide

The tibia and fibula are wider than the femur, with the intention that the femur fits into the tibia and fibula for a better rotation.

Once the pieces were designed, they were incorporated into a plane in CATIA that was saved in ".dxf " format. This format is the one that allows it to be cut on the laser cutter machine. Subsequently it was cuted on MDF and we proceeded to assemble the pieces with each other and placing the servomotors on their place.