Table of Contents
Wearable robots, including exoskeleton robots used for rehabilitation, are designed to assist human movement by providing additional force to the user’s arms or legs. Because these systems must move in coordination with the user’s joints and deliver the force required for activities such as walking, the actuator that generates the robot’s physical motion plays a critical role.
Since wearable robots operate while attached to the human body, their design must take into account factors such as the user’s body type, movement patterns, walking speed, and changes in applied force. At the same time, the size and weight of the drive unit positioned close to the body must also be carefully considered.
Drive performance and wearable design cannot be treated as separate issues. One of the main challenges in wearable robot design is securing the required torque while minimizing the thickness and weight of the drive unit around each joint.
The Operating Environment of Rehabilitation and Exoskeleton Robots
Key Summary Because rehabilitation and exoskeleton robots directly assist the user’s movement, their design must consider not only drive performance but also fit, size, weight, and response to external forces.
Rehabilitation and exoskeleton robots are worn on the outside of the user’s body to assist movement of the arms or legs. In rehabilitation applications, these systems can help users repeat specific motions or supplement the force needed when they cannot perform a movement independently.
Wearable robots designed for walking assistance can support the movement of joints such as the hip, knee, and ankle. Because the robot must move in coordination with actions such as lifting the leg, bending the knee, and taking a step, it needs to respond to changes in the user’s movement rather than simply repeating a predetermined motion.
The drive requirements also vary from joint to joint. Joints that support a significant portion of the body’s load, such as the hip and knee, require sufficient torque to assist movement. Joints closer to the ground, such as the ankle, must also accommodate changes in posture and the impact generated during walking.
In upper-body exoskeleton robots, drive units may be positioned around the shoulder or elbow. If the actuator becomes too large or heavy, it can restrict arm movement or reduce wearing comfort. For this reason, the required output performance and the actuator’s size and profile must be considered together.
The Role the Actuator Performs
Key Summary The actuator converts control commands into actual joint movement and delivers the torque required to assist the user’s motion.
The actuator is the component that physically moves the joints of a rehabilitation or exoskeleton robot. It converts the motor’s rotational motion into the speed and torque required at joints such as the hip, knee, ankle, shoulder, and elbow.
When the user lifts a leg or bends a knee, the actuator needs to provide torque that assists the intended movement. During walking, impact occurs when the foot contacts the ground, while the load applied to each joint continuously changes as the user’s body weight shifts.
The actuator must therefore provide the required output while operating reliably under repeated motion and changing loads. The system also needs to respond appropriately to external forces and changes in the user’s movement so that the robot can adapt when the user stops, changes posture, or moves differently from the expected motion.
This response is not achieved by the motor or reducer alone. Sensors detect the user’s movement and joint conditions, the controller determines the required response, and the actuator converts those commands into physical motion. The performance of a rehabilitation or exoskeleton robot is therefore achieved through the coordinated operation of its mechanical structure, sensors, control system, and actuator.
Why a Slim Actuator Is Needed in Exoskeleton Robots
Key Summary Because wearable robots operate close to the human body, their drive units must remain compact and lightweight while still providing sufficient output.
The actuators used in wearable robots are positioned close to the user’s body. As a result, the thickness and overall dimensions of the drive unit directly affect the structure and fit of the wearable system.
If the drive unit protrudes too far from the body, it may interfere with surrounding structures when the user walks or changes direction, and it can also restrict natural movement. When actuators are installed at multiple joints, the weight of each unit accumulates and can significantly increase the overall weight of the robot.
However, reducing size and weight alone is not sufficient. If the actuator becomes too small to provide the required torque, it may not be able to adequately assist movement or support the loads applied at the joint.
For this reason, exoskeleton robot drive units must balance a slim, compact profile with the required output performance.
The joint area must also accommodate components such as sensors, wiring, and control devices in addition to the motor and reducer. Therefore, actuator selection should be based on the overall structure of the joint rather than on actuator specifications alone.
If the actuator incorporates a hollow structure, cables and wiring may be routed through the center. This can help organize the joint area more efficiently and provide greater flexibility when arranging surrounding components.
A Slim, High-Torque Actuator Applying Bonsystems Cycloidal Technology
Key Summary The Bonsystems BCSA combines a frameless motor and a cycloidal reducer in a slim, compact actuator structure designed for robotic joints with limited installation space.
The BCSA is an actuator that integrates a frameless motor and a cycloidal reducer into a slim, compact structure. It was developed with robotic joint designs in mind, where components such as the motor, reducer, sensors, and wiring must be arranged within a limited space.
The cycloidal reduction structure used in the BCSA is designed to distribute load across multiple contact areas. This type of structure can be beneficial in applications where loads are repeatedly applied or external impacts are transmitted through the joint, as can occur in exoskeleton robots during walking.
Because wearable exoskeleton robots may require actuators at multiple joints, the thickness and size of each drive unit can influence the overall profile of the system. The slim structure of the BCSA can help reduce protrusion around the joint and may be suitable for designs that require the drive unit to be positioned close to the body.
Bonsystems’ Pinless cycloidal technology simplifies the reducer’s internal structure by reducing some of the coupling elements used in conventional pin-based configurations. This design approach can help reduce the space required for internal components, supporting the development of thinner and more compact actuators.
A simplified internal structure may also help reduce the number of components that must be managed during assembly and production.
When selecting a drive unit for a wearable robot, developers need to consider not only the required torque and speed but also the actuator’s size and weight, wiring arrangement, sensor configuration, and control method.
For systems developed as medical devices, applicable safety requirements and certification standards must also be reviewed separately. The drive unit therefore needs to be configured according to the intended application, development stage, and regulatory requirements of the final product.
Key Takeaways
Rehabilitation and exoskeleton robots operate while worn directly on the user’s body, so drive performance and wearable structure must be designed together.
The actuator converts motor rotation into the torque and movement required at joints such as the hip, knee, ankle, shoulder, and elbow. In walking-assistance applications, the drive unit may also be exposed to repeated loads and impact generated during foot contact with the ground.
If the drive unit is too large or thick, it can restrict fit and range of motion. On the other hand, reducing actuator size without considering output requirements can result in insufficient torque.
Finding the right balance between compact dimensions and the required drive performance is therefore a key part of exoskeleton joint design.
The Bonsystems BCSA combines a frameless motor and a cycloidal reducer in a slim actuator structure designed for applications with limited joint space. Its cycloidal reduction structure is designed to distribute load across multiple contact areas, while Bonsystems’ Pinless technology simplifies the internal component configuration.
For products developed as medical devices, safety requirements and applicable certification standards must be evaluated separately as part of the overall product development process.
Frequently Asked Questions (FAQ)
Q1. What is a rehabilitation or exoskeleton robot?
A. A rehabilitation or exoskeleton robot is a wearable robotic system designed to assist movement of the user’s arms or legs. It can be used to support rehabilitation exercises or supplement the force required for activities such as walking or physical work.
Q2. What role does the actuator play in a wearable robot?
A. The actuator converts motor rotation into the movement and torque required at the joint. Based on commands from the control system, it moves joints such as the hip, knee, ankle, shoulder, or elbow to assist the user’s motion.
Q3. Why should a wearable robot actuator be small and slim?
A. Because the drive unit is positioned close to the user’s body, its thickness and size can affect fit, comfort, and freedom of movement. When actuators are installed at multiple joints, the size and weight of each unit also contribute to the overall dimensions and weight of the robot.
Q4. What role does a cycloidal reducer play in an exoskeleton robot?
A. A cycloidal reducer transmits motor output to the joint while increasing torque through reduction. Its structure can distribute load across multiple contact areas, which can be beneficial in applications subject to repeated loads or external impact. Bonsystems’ Pinless cycloidal technology also simplifies the internal component configuration, supporting the design of slim and compact actuators.
Q5. What should be considered when selecting an actuator for a wearable robot?
A. Developers should consider the required joint torque, range of motion, operating speed, actuator dimensions, and weight. Wiring layout, sensor configuration, and control methods should also be reviewed. If the final product is intended to be developed as a medical device, applicable safety requirements and certification standards must be evaluated separately.
References
• [1] Bonsystems Official Website — https://www.bonsystems.com
• [2] Korea Institute for Robot Industry Advancement (KIRIA) — https://www.kiria.org
• [3] Korea Institute of Robotics & Technology Convergence (KIRO) — https://www.kiro.re.kr
• [4] International Federation of Robotics (IFR) — https://ifr.org
Bonsystems
A specialist in Pinless cycloidal reducers and actuators
