Lower Limb Exoskeleton

Robotic exoskeletons, also referred to as active orthosis, are devices designed to assist humans in improving their body movements by offering support. The main goal of these exoskeletons is to enhance human abilities by transferring mechanical energy and information signals, replicating the gait cycle while in a bipedal position.

Exoskeletons come in two main types: hard frames and soft frames, both of which have joints that enable movement. They are further divided into two categories: motorized and passive. Motorized exoskeletons use actuators such as hydraulic or electric components to function. The materials and coverage of exoskeletons differ, offering options for various body parts and the ability to personalize them.

Researchers have made advancements in studying the gait cycle by creating prototype exoskeletons that imitate the motion of walking. These exoskeletons use servomotors to replicate the movement of joints, closely resembling the natural motion of the human body during the walking process. This allows researchers to gain a more thorough understanding of how walking works.

Understanding the gait cycle is crucial, starting with the foot's contact with the ground and ending with the subsequent contact of the same foot. The cycle includes:

• The stance phase. The period of gait from heel strike through to toe-off. It is detailed into five intervals heel strike, foot flat, midstance, heel-off, and toe-off.
• The swing phase. The period of gait from toe-off through to heel strike. It is further divided into early swing, mid-swing, and late swing.

The proposed project aims to create a basic exoskeleton prototype that has been developed using computer-aided design (CAD) software. The materials utilized for constructing this prototype include medium-density fiberboard (MDF) that has been cut using a computer numerical control (CNC) machine, specifically a Laser cutter. This project is targeted towards individuals who have a keen interest in the fields of biomechanics and robotics.

• Medium Density Fiberboard (MDF) 3mm
• 6 servomotors SG90
• 6 M2 screws
• Arduino UNO
• 7 V power supply

First, as shown in the image, the initial sketch was drawn to capture the first ideas of the design. Each servomotor is analogous to each joint (hip, knee, and ankle). 

Then, the specific parts were designed in SolidWorks (you can download them below).

As shown in the pictures, two prototypes were created. The first one is to simulate the gait movement, and the second one is to actually walk. 

The difference between them is the position of the feet. 

One moves in the sagittal plane while the other does it in the frontal plane. 

After that, the pieces were cut in MDF.

The servomotors were screwed with the MDF pieces and everything was assembled. The result of that is shown in the fourth image.

Finally, a program was made in Arduino UNO to control the six servomotors and to simulate the gait cycle. The Arduino program file can be found below.

Created by:

Jessica Gutierrez Alonso and Luis Santiago Cuautle Ortiz

Titular professor:

Ana Moreno Hernandez

Consulting professor:

Huber Giron Nieto

References:

[1] Inman VT, Ralston MJ, Todd F. Human walking. Baltimore: Williams and Wilkins; 1981.