Crippling injuries happen all the time. In the case of a broken bone, it heals and the person can return to normal activities virtually unaffected; however, an ACL tear is much different. The tear occurs in the ligament that is critical for proper knee movement, and unlike a broken bone, the tear will continue to affect the knee. There will always be an increased chance of re-tearing the same ligament or injuring the other leg. This can be partially due to the fact that many victims of ACL tears tend to favor their non-injured leg during and after rehabilitation. Being able to show the athlete and trainer how much weight the athlete is putting on each leg will allow them to adjust their form and reduce the risk of injury. The ACL-erator is a device that will perform this function in real-time by using sensors and programming to create a visual feedback image. The product will help both the user and physical therapist understand what movements are being performed incorrectly, and adjust appropriately without having to stop in the middle of a set. This webpage focuses on the design process of developing and testing the ACL-erator.
The ACL-erator is a specially designed mat to be used by the university’s physical education department to help student athletes recover from ACL tears. The design is composed of two main sections: the mat containing the hardware and the software that processes and displays the information from the mat. The idea is that the patients will perform different compound lifts while standing on the mat. The mat will sense the force being applied by both legs with 8 load cell sensors attached to two metal plates that make up the area of the mat where the user stands. The sensor outputs a voltage which is then sent through an amplifying circuit to boost the voltage to something usable. That voltage is then sent to the computer via an Arduino and used in the software side of the project. The information that is processed via software is displayed in an easy to use easy to read interface. This interface consists of a large colorful display showing the percentage of weight on each leg, force over time plots, and the ability to export the data to excel. The concept will allow for therapists to see real time results while the patients perform lifts.
Proof of Concept
The proof of concept was utilized in order to decide if the chosen design will be the right one for the ACL-erator. This is a method used to test the success of a desired product design by creating a smaller, less intricate version of the design. The sensors are the main function within the ACL-erator and are the most prevalent piece of the proof of concept. Because of this, the proof of concept was a small scale version of the full-scale ACL-erator base plate. A sensor was hooked up to an instrumentation amplifier and then connected to an Arduino which converted the analog sensor signal to a digital signal. This digital signal could then be used in the team’s Python code. To test that the sensor’s themselves were working, the team first measured the output voltage from the amplifier circuit. When the sensor was pressed on, the output voltage would increase, verifying that the circuit itself worked. The output voltage was then fed through the Arduino and used in the teams Python code, which created output graphs to display the voltage changes. By using only one load cell, the circuit and code was tested without having to worry about testing multiple component for problems. When a problem arose, it was easier to diagnose and resolve using the proof of concept rather than testing the entire final design from the beginning of the design process.
Proof of Concept Results
Because the original 5V that was being supplied to the breadboard gave faulty data, the team found that nine volts and 200 Ω across the amplifier is required to produce significant changes in the sensor output as seen in the graph below. From this, the final concept has been modified to include a 9v power supply to all the sensors. The proof of concept also answered many questions relating to Python. The team found that coding in Python takes a lot longer than expected and although the code is easy to learn, the process is very time consuming!
Mechanical and Hardware
- Metal Plates with reinforced plywood
- Rubber mat
- Plastic base plate
- Plywood base
Electrical & Software
- User interface
- Analog to digital converter (Arduino)
- PC board and circuit
The metal plates that the sensors attach to are made of two 2′ x 2′ sheets of 10 gauge sheet metal. This guarantees the durability and strength of the mat. A plastic base was added to the design after the proof of concept. The purpose of this plastic base is to ensure stability and prevent the sensors from depressing into the floor. The plastic base itself contains small circular plates of metal to give the sensors a more stable foundation than plastic. These features can be seen in the technical drawing below. The 3/4″rubber mat surrounds the sensor/base assembly and sits atop of a plywood base. The purpose of this base is to combine the product into one functional piece instead of three individual assembly components.
Once the final designs of the ACL-erator were complete, fabrication could be conducted. Starting with the plywood, a plastic base was machined and placed on top of it to create a stable surface for the steel plate with attached sensors. The sensors that are attached to the bottom of the steel plates line up with the holes in the plastic as seen below. Small stainless steel cutouts were inserted to help stabilize the sensors and give them a hard enough material to rest on.
The plates and plywood were reinforced to help with deformation. A layer of plywood was attached to the top of each plate and a layer of MDF was placed around the plates to cover the plywood base. Once the plates are secure on the plastic, the wires can be funneled out from under the plates and the rubber mat can be placed on top of the plywood. The rubber mat acts as a housing that holds everything together and keeps the inner components safe. It also levels out the entire platform and creates a safer environment for the user. A grip-adhesive is also added during the final process to create a safe non-slip surface for the user.
The wires for each sensor are connected to the circuit that was created and soldered by the team. As seen below, the circuit was carefully soldered and designed in order for the user interface to obtain information from the sensors. The circuit is connected to an Arduino which helps translate the weight of the user into useable data via a code that was designed by the team.
Meet the Team!
Brandon is currently a senior at the University of Nevada, Reno majoring in mechanical engineering. Brandon was born and raised in a northern California ranching community where he first gained an interest in the way mechanical components worked. Currently an intern at Hamilton Robotics, Brandon has experience with team projects, mechatronic components, and extensive CAD development skills. Brandon also brings with him experience in the computer science and civil engineering fields of work.
John is a senior mechanical engineering student at the University of Nevada, Reno. He was raised in Las Vegas, Nevada, where his father, an automobile mechanic, instilled an interest in mechanical systems. John has experience with mechanical design due to his work with automobiles and his experience with several computer coding language with will be useful when coding the interface of this design. Currently a technical intern at IGT, John has shown his problem solving ability by taking on difficult technician issues and fixing hardware and software for fellow employees.
Dominic is a senior in the mechanical engineering program at the University of Nevada, Reno. Raised in Gardnerville, Nevada, he had an inherent interest in the way things worked, an attribute made apparent by the dismantling and rebuilding of all things mechanical and electronic around him. Dominic has significant experience with mechanical systems and a strong background in CAD and manual drafting. Currently holding a position as a mechanical engineering intern with Haws Corporation, he has increased his skills with problem solving, design, and teamwork.
Kayla is a senior at the University of Nevada, Reno and will be receiving her bachelors in mechanical engineering. She was raised in Henderson, NV and gained an interest in mechanical systems around the time she turned eighteen. Kayla is currently an engineering intern at Hamilton Company in the research and development department. She has experience with tool design, tinkering with mechanical systems, CAD and manual drafting. Since becoming a mechanical engineering intern, she has developed various design skills along with how to utilize teamwork in order to get problems solved quickly and efficiently.
Charles is currently a senior at the University of Nevada, Reno majoring in mechanical engineering. Raised in Carson City, Nevada, Charles became became fascinated in airplanes and the way they operated. This fascination with airplanes is where he first gained an interest in mechanical engineering. Charles has a developed problem solving and teamwork skills from having two different internships. Currently holding an internship at Tripp Enterprises, he has enhanced his skills in both teamwork, critical thinking, and problem solving. Charles also brings with him experience with prototyping.