QUIX

IHMC was developing a medical exoskeleton named Quix to assist people with Spinal Cord Injury. As part of the team I assisted during the development and testing process of the device. The device was used in the 2020 Cybathlon and Toyota Mobility Foundation's Mobility Unlimited Challenge Competitions where we placed in the top 4 across the world. The system has 8 actuators in total distributed across the frontal and sagittal plane to help the user walk.

Foot Sole Using Pressure Sensors To Estimate Center of Pressure

As an intern, I started learning about Center of Pressure and how it assists robotic devices to understand where the robot/user is in space. My first project in this device was to design and test foot soles to estimate Center of Pressure My first step in this process was to learn how to do Urethane rubber molding. After some initial tests, I manufactured a prototype to have one pressure sensor. I started looking into sensor calibration, communication and visualization of the forces and center of pressure. The next step in the process was to implement 16 of those sensors distributed across the foot sold and create a visualization platform to read the center of pressure position during walking.

Battery Covers and BackPack

Following the completion of the above project I had to redesign the backpack and battery covers. The electronics in the backpack were heating up a lot. So we decided to implement a cooling fan for active cooling in addition to the passive cooling that happened with the backplate. To improve the performance of cooling I implemented a simple flow simulations using solidworks to study the effectiveness of cooling and to identify areas for intake and outlet ports. The ports were fitted with slotted covers for protection which were easy to remove On and Off for ease of access to design changes. The battery casing was redesigned to fit a bigger battery which uses a simple leaf spring on all the four side and top to hold the battery in place. The battery slides on and off similar to a drill battery for ease of swapping during different maneuvers.

Carbon Fiber Thigh Cuffs

Cuffs are an important part of an exoskeleton. These help distribute the forces to the user and especially in a medical exoskeleton for SCI these have to be carefully designed to avoid pressure sores. With the help of the team I learned how to design moulds for carbon fiber layer up and carbon fiber part manufacturing. The lay up process used 3-6-3 mono-6-mono and 3-6-3 pattern to achieve the required strength properties. Since the cuffs were huge the mold had to be divided into three parts which were assembled later. After curing the corners were trimmed and fitted with rubber to avoid chaffing and pressure sores.

Crutch User Interface

The crutch is the interface through which the user controls the Exoskeleton. The button had to be positioned at right locations for ease of access and had to be small enough to house all the electric components and the wires. We needed slots for ease of programming and to route the usb wires along the crutch to the backpack which was one of the main requirements for the cybathlon competitions. Our initial plan was to integrate the crutch with a tactile sensor so that the user is aware when the feet touches the ground. We were not able to implement those due to the limited time.

Actuator Testing and Assembly

As I transitioned to the mechanical lead position I had the opportunity to learn about the hardware and control architecture of the robot. The actuator had to repaired and maintained so that the exoskeleton was competition ready. When the actuator was taken apart for any modifications it has to go through a rigorous calibration procedure to test sensors and a cyclic load test to performance.

Publications:

Brandon Peterson, Mark Daniel, Vishnu Aishwaryan Subra Mani, Brooke Arnold, Travis Craig, Jeremy Gines, Carlos Gonzalez, William Howell, Brandon Shrewsbury, Matthew Bellman, Peter Neuhaus & Robert Griffin "Team IHMC at the 2020 Cybathon: a user-centered approach towards personal mobility exoskeletons", Journal of NeuroEngineering and Rehabilitation.

SKILLS LEARNED FROM THE PROJECT

Urethane Rubber Molding for Pressure Sensitive Sensors

Carbon Fiber Molding and Manufacturing

Actuator Design, Maintenance, Assembly and Testing Procedure

Center of Pressure Estimation and Force Sensor Calibration

Electrical Debugging

Actuator Braking Design

Design Requirements for Load Bearing Exoskeletons for Spinal Cord Injury

Onshape Software - Robot Kinematic Skeleton, Parameterized Design

Solidworks - FEA, Fatigue Cycle Testing and Compliance FEA model requirements

Human Subject Testing

Exoskeleton Control and Architecture

Electrical Debugging

GD&T drawing and Tolerances

Softgood Design