Transparent actuation systems
Non-disabled patients or patients who are capable of voluntary movement might feel discomfort due to the resistance of the actuators. By precisely controlling the interaction force between the robot and the wearer, the robot can ensure natural movement or assist insufficient muscular strength. Designing actuators or control algorithms that allow the precise control of forces between the robot and the wearer is needed. For this purpose, there have been many attempts to precisely control interaction forces such as adapting a sensorless control algorithm, torque sensors, and new actuation mechanism. The challenges are to create compact and lightweight actuators that guarantee the precise control of the interaction force between the robot and the wearer. Also, It is necessary to take into account the control performance of the actuator when designing actuators.
Human intention recognition
When controlling the interaction forces, it is important to detect the moments when the assistive forces are needed. Currently, it is impossible to detect every human motion intention. However, for some limited motions, it is possible to detect human intentions using various sensors and identify when the assistive forces are needed. It is necessary to develop human-robot interaction sensors, artificial intelligence, and machine learning technologies to detect human motion intentions that are available on exoskeletal suits.
Ultra-thin actuator module
In wearable robots, the actuator dramatically influences the performance of the entire system. If the size is large and heavy, it dramatically impairs human activity when attached to the human body. Although the numerical performance for power assistance is sufficient, it is contrary to the essence of a 'wearable robot' without considering weight and volume. Therefore, it is necessary to have an ultra-thin, lightweight design that does not interfere with the range of motion when attached to the human body.
The speed reducer that determines the actuator module's performance should also have a sufficient reduction ratio and be compactly built into the motor's internal space. It should be structurally safe to withstand high output due to its reduction ratio.
Our lab develops such actuators and applies them to wearable robot systems with various analyses and know-how.
Exoskeleton for sprinting augmentation
Building an exoskeleton that allows humans to run faster than their maximum speed is very challenging. This is because the robot should generate the assisting force base on the estimated real-time human intention, and agile assisting technology with high torque to overcome the system's weight is not yet developed.
In terms of hardware, the factors that can make this challenge possible are listed below. First, to not disturb many movements included in the sprinting of a person without discomfort, it is necessary to provide sufficient degrees of freedom and eliminate misalignment between the robot and the human. Second, a wearing part must be designed to hold the robot in tight contact with the human body. Also, the passive element compensating for the loss of kinetic energy at the collision with the ground is indispensable. Including all of the above features, the overall system should be lightweight.
BLDC motor driver development
Wearable robots mainly use BLDC motors that have a long life, high efficiency, and capable of high-speed rotation. While driving these motors, the specific driver is required to convert the single-phase battery voltage to three-phase and apply the appropriate commutation for each step. A relatively high driver output is required to assist walking and behavior, so the motor driver must switch high currents at a stable and fast speed. A sufficiently small form factor is also essential for the application to wearable robots. Furthermore, to build a real-time system for high-performance control, fast sensor signal processing and supporting algorithm calculations are required. To this end, a system architecture that handles low-level signal processing at the motor driver's MCU level is envisioned. In order to satisfy the above performances, our lab is developing a new driver.
Musculoskeletal simulation including wearable robot
Musculoskeletal simulation can be used to develop a hardware design or control algorithm of the wearable robots. There are positive effects anticipated when wearing assistive wearable robots suits such as decrease in overall metabolic cost and muscle activity. However, there are also some negative effects such as increase in metabolic cost and muscle activity due to robot's own weight.
It is necessary to minimize the negative effects and maximize the positive effect when designing hardware and control algorithm of the robot. It is expected that by developing proper musculoskeletal simulator that accurately reflects the human response to the assistive forces, one can easily develop hardware and control algorithm that maximizes the positive effects.