Every year, approximately 250,000 to 500,000 people worldwide suffer spinal cord injuries. Spinal cord injury (SCI) usually causes paralysis of the lower limbs (paraplegia) or general paralysis (quadriplegia), and patients with spinal cord injury usually have to use a wheelchair to assist in mobility. Project MARCH is a non-profit multidisciplinary student team at Delft University of Technology in the Netherlands. Their goal is to develop and manufacture advanced prototype exoskeleton robots that can help SCI patients stand and walk. The team also participated in the four-year human-machine sports competition for people with disabilities-Cybathlon (also known as the Bionics Olympics), and the smaller annual spin-off event-Cybathlon Experience (also known as the Bionics Olympic Games). The purpose of these international competitions is to promote the development of human prosthetics, advanced wheelchairs and exoskeleton technologies to improve the daily lives of people with disabilities. Martine Keulen, a member of Project MARCH’s cooperation and public relations department, explained: “Every year, the school will form a new multidisciplinary student team. They will suspend their studies for one year and go all out to design their own prototype exoskeleton robot. We will work with A’trial person’ (ie a patient with complete spinal cord injury (paraplegia)) collaborated on this project, and this person controls the exoskeleton robot. This person originally uses a wheelchair, but once he puts on the exoskeleton robot, he can Stand, walk and overcome other obstacles with the help of exoskeleton. Cybathlon is a competition for disabled athletes who use technical assistive equipment. Participants will participate in electric wheelchair competitions or mind control competitions. We [Project MARCH] participate in motivation The exoskeleton robot competition, this is an obstacle course, there are six obstacles lined up in sequence, the participants must cross all obstacles at the fastest speed within 10 minutes. “Since the establishment of Project MARCH in 2015, Renishaw and Its affiliate company RLS has been sponsoring the team, providing them with RLS magnetic encoders for joint motor position feedback.
Challenge Exoskeleton robots are designed to help people move and require close contact with the user’s body. Therefore, performance will be affected by many factors, including mechanical structure, actuators and feedback devices, as well as human-computer interaction. For such a complex system, it is very difficult to design control laws. In this case, Project MARCH uses a closed-loop system composed of testers and exoskeleton robots to track the joint reference trajectories generated by the controller. The team initially used a standard proportional integral derivative (PID) controller for experiments, as the embedded system engineer Björn Minderman of the 2019-2020 team said: “Our team initially used a standard PID controller to control the joints. Position. Later we found that it could not provide the results we wanted. Therefore, our control engineer decided to switch to torque-based control law, but the difficulty lies in the PID controller must be adjusted for different walking methods or gait Different adjustments. For example, when going up the stairs, a large amount of torque must be output, so it is necessary to perform high rigidity servo control and set a higher P [proportional] value. However, when sitting on a sofa, the controller P value is higher. It will cause the system to become unstable. This is a huge challenge.” Exoskeleton robot trialists must pre-select the type of movement required for each task through the human-machine interface (HMI) embedded in the crutches. These movement modes are created offline by the team’s movement engineers and customized for each obstacle. We must precisely control the joint angle to ensure the stability and safety of the trial user, which requires the position feedback of a high-quality rotary encoder. “Another challenge is that we need to measure near the motor, which generates electrical noise. The motor used in the exoskeleton robot generates a strong magnetic field near the electronic components, and if there are wires around it, it may generate signal noise. It is a challenge to reliably transfer data from the encoder to the CPU without losing any information,” Mr. Minderman added. Solution In August 2020, the team launched the latest “MARCH IVc” exoskeleton robot, this robot uses rotating joints on the hip and knee, while also using four linear joints (linear rotating compound joints) at the hip and ankle. This combination of dynamic joints mimics the human musculoskeletal system, And provide more degrees of freedom, can achieve more advanced gait. Mr. Minderman focused on the important role of the position encoder in the system: “Our exoskeleton robot has eight joints, two of which are ankle joints. , One on each knee and two on each hip. Each joint uses two encoders. The motor of the joint rotates, and the rotation of the motor is converted into a change in the angle of the joint through a decelerating device. We use an absolute encoder to directly measure the joint angle, so the joint position will be known as soon as it is started, and there is no need to perform calibration steps. We must ensure that each joint is in the correct position and follows the trajectory designed by our motion engineers. “Mr. Minderman continued: “We also installed another encoder on the motor. Since the motor rotates faster than the joints, this encoder can provide us with a higher resolution, which is conducive to better control. Effect. Motor encoders are mainly used for control loops, while joint encoders are used as additional safety measures. The encoder resolution is very important to ensure the control effect. Previously, we encountered some problems when calculating the speed based on the position. Due to the need to subdivide the encoder signal, the position measurement error will be amplified, which is why we need a higher resolution. “The MARCH IVc exoskeleton robot integrates the new RLS AksIM-2 absolute encoder for high-resolution (17-bit) rotary joint feedback, and the miniature RLS RM08 absolute rotary encoder for linear joint feedback.
As a result, the continuous support of Renishaw and RLS helped the previous Project MARCH teams to make breakthroughs and create new prototype exoskeleton robots. But how will this exciting technology develop during preparations for Cybathlon 2024? “I hope that by then we will be able to balance our exoskeleton robot without crutches. This means that we will find another form of input that enables the exoskeleton robot to autonomously detect obstacles such as stairs, and even measure standing boards. Height to adjust walking gait accordingly. These are challenges that I am personally interested in overcoming, but the school will form a new Project MARCH team every year, so the new team will decide which technologies to develop at that time. We want Look at the level of development in the next few years. This is what we are striving for, and we will never stop,” Mr. Minderman said. RLS and Renishaw work closely with customers to provide the best measurement solutions for their application scenarios. As Ms. Keulen said: “At the beginning of this year, I, Björn and other students in our team involved in electrical design and Renishaw’s sales Engineer Rene Van der Slot held a meeting. Rene didn’t just bring the encoder over and tell us, “You should use this or that.” On the contrary, he took a closer look at our application and asked about the work of our exoskeleton robot. Principles and our needs. Renishaw and RLS are not trying to sell us what we don’t need. They think about what we need and how to help us. I think it’s precisely because of their strong interest in our project. , Which made this cooperation so successful. We know that Renishaw and RLS are not simply selling encoders, they will also consider the entire design and the applicability of the encoder.” In tribute to Renishaw, RLS and Project MARCH During the Precisiebeurs 2019 Dutch trade show, members of the Project MARCH team demonstrated a prototype of the previous generation MARCH exoskeleton robot at the Renishaw booth, which vividly demonstrated the practical application of the RLS magnetic encoder. Renishaw and RLS hope to support the future Project MARCH team to win the Cybathlon competition. With the development of technology, exoskeleton robots and other wearable robotic prostheses are expected to revolutionize the lives of millions of people with disabilities. Introduction to Project MARCH MARCH is a team of students from Delft University of Technology in the Netherlands. The team is committed to developing innovative multifunctional exoskeleton robots to help patients with spinal cord injuries stand and walk. Now, the sixth team of Project MARCH consists of 26 students who will continue to work hard on the basis of the pioneering work of their predecessors. Project MARCH participates in Cybathlon related competitions every year, which is a human-machine sports competition for people with disabilities participated by academic and commercial teams from all over the world.
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