A cycloidal reducer is a power-transmission component that converts a motor’s rotation into usable torque, and it is widely applied to the joints of industrial robots, collaborative robots, and humanoid robots. This article walks through the definition, operating principle, core structure, and main applications of the cycloidal gearbox step by step, from a beginner’s perspective.
Table of Contents
Cycloidal Reducer Definition: What It Is and Why It Is Needed
Key Takeaway — A cycloidal gearbox is a reducer in which a disc shaped along a cycloidal curve performs eccentric motion to achieve a large reduction in a single stage. It lowers the motor’s rotational speed and increases torque, enabling accurate motion in robot joints and industrial automation equipment.
A cycloidal gearbox is a power-transmission device in which a disc machined along a cycloidal curve rotates around an eccentric shaft, converting the input rotation into torque. Because the fast rotation produced by a motor cannot by itself generate large force, robot joints and industrial equipment require a reducer that lowers rotational speed and increases torque.
In the robotics field in particular, the requirement goes beyond simply reducing speed: accurate position control, smooth motion, durability that withstands shock loads, and a compact design that fits into tight spaces are all demanded. The cycloidal reducer is a technology capable of satisfying all of these combined requirements, and it serves today as one pillar of reduction technology.
The Core Operating Principle of a Cycloidal Gearbox
Key Takeaway — In a cycloidal reducer, rotation of the eccentric shaft induces the revolution and rotation of the cycloidal disc, and the difference between these two motions is transmitted to the output shaft, producing a large reduction ratio.
In a cycloidal gearbox, once the motor’s rotation is transmitted through the input shaft, the eccentric cam connected to the input shaft moves the cycloidal disc to produce a large reduction. As the input shaft rotates, the eccentric cam causes the center of the cycloidal disc to move along a fixed orbit inside the housing.
During this process, the tooth profile on the outer edge of the cycloidal disc engages with pins, rollers, or an internal tooth structure inside the housing. Because of this engagement, the disc does not simply rotate in the same direction as the input shaft; instead, it rotates gradually in the opposite direction. The disc rotates far more slowly than the input shaft, and as this rotation is delivered to the output shaft through the output mechanism, a reduced output is produced.
As a result, the output shaft rotates at a lower speed than the input shaft but can deliver greater torque. The reduction ratio is determined mainly by the number of teeth on the cycloidal disc. The actual output torque is influenced not only by the reduction ratio but also by design conditions such as efficiency, friction, and component strength.
The Main Components That Make Up a Cycloidal Reducer
Key Takeaway — A cycloidal reducer is made up of key components such as the input shaft, the eccentric cam, the cycloidal disc, pins (or a pinless structure), and the housing.
Looking inside a cycloidal gearbox reveals a design that achieves a large reduction ratio and high durability with a relatively simple set of components. The input shaft serves as the channel that directly receives the motor’s rotation, and an eccentric cam is attached at its end, positioned slightly off the center of rotation. The eccentric cam is the key element that gives the disc its revolving motion.
The cycloidal disc is a disc-shaped component whose outer edge is machined along a cycloidal curve, and it can be considered the heart of the reducer. The disc geometry determines the reduction ratio, smoothness of motion, and load-sharing capability. The disc teeth engage with a pin gear inside the case or with a pinless structure that has no pins, and this difference in the engagement method becomes a point of technical differentiation among manufacturers.
Bonsystems has simplified this component configuration even further, developing a Pinless reducer that minimizes the number of parts and thereby advances its technology in a direction that improves both assembly efficiency and productivity.
Industrial Applications of the Cycloidal Reducer
Key Takeaway — Cycloidal reducers are widely used in industrial robots, collaborative robots, humanoid robots, automation equipment—fields that simultaneously require precise rotation and large torque.
In the industrial robotics field, cycloidal gearboxes are used in environments where heavy payloads must be handled quickly, such as six-axis articulated robots. They are applied to joints that demand stable positioning accuracy and a long service life, including welding and painting robots on automotive production lines and handling robots on electronic-component assembly lines.
In the collaborative robot (cobot) field, smooth motion and safety are important because the robots work in the same space as people. The cycloidal structure, in which multiple teeth share the load simultaneously, has strong resistance to shock loads, establishing it as a suitable candidate for cobot joint components.
In the humanoid robot field, the shock loads generated during walking and the torque variation across diverse posture changes are very large. Beyond these, the range of cycloidal reducer applications continues to widen across medical robots, rehabilitation assistance devices, and actuators in the aerospace field.
Bonsystems’ Proprietary Reduction Technology
Key Takeaway — Focuses on simultaneously raising the assembly efficiency, productivity, and reliability of cycloidal reducers through a Pinless cycloidal structure, a thin design, and a minimized part count.
Bonsystems pursues differentiation through its Pinless cycloidal technology. While reducing a component called the pin may appear to be a simple change, it is a meaningful differentiator that leads to a minimized part count, a shortened assembly process, and reduced wear factors during long-term operation.
In addition, Bonsystems designs its cycloidal reducers in a thin form, providing packaging that is advantageous for space-constrained applications such as humanoid robots and collaborative robots. The design know-how to implement various reduction ratios within a single-stage structure makes it possible to respond to a wide range of applications even with a simple structure. Our reducer and actuator lineup, including the BSR and BCSA series, is the result of reflecting these technical aims.
The essential value of a cycloidal gearbox technology lies in compressing a large reduction ratio, strong torque, and high durability into a simple structure. Bonsystems refines that essence into an ever more polished form, holding its place as one pillar of the domestic reducer industry. Robot manufacturers and automation-equipment makers considering the adoption of a reducer would do well to go through a component-selection process that comprehensively considers the motion conditions and space constraints of the application.
Bonsystems — Specialists in Pinless cycloidal reducers and actuators
🔗 Get the cycloidal reducer material → www.bonsystems.com
F.A.Q
Q: Where are cycloidal reducers most commonly used?
A: They are widely used in fields that simultaneously require large torque and precise rotation, such as the articulated joints of industrial robots, the joints of collaborative robots, the leg and arm joints of humanoid robots, and the rotary axes of automation equipment. Their structural characteristics work as a particular strength under motion conditions where shock loads occur frequently.
Q: How do cycloidal reduction gears differ from ordinary gear reducers?
A: Ordinary gear reducers mainly combine various gears in multiple stages to produce a large reduction ratio. In contrast, the most distinctive structural feature of a cycloidal reducer is that a disc shaped along a cycloidal curve performs eccentric motion to achieve a large reduction ratio in a single stage.
Q: What should be examined first when considering the adoption of a reducer?
A: It is best to first organize the motion conditions required by the application equipment (repeatability, operating speed, load pattern), the constraints of the installation space, and the operating environment (temperature, vibration, dust). Organizing these conditions makes it easier to match catalog specifications and can make the component-selection process relatively straightforward.
Q: Isn’t a cycloidal gearbox hard for beginners to understand?
A: The internal structure itself consists of a relatively simple set of components—an eccentric shaft, a cycloidal disc, and an output mechanism. By following step by step how these parts cooperate to convert input rotation into output rotation, even a beginner can fully understand the flow of operation.
Q: What characteristics do Bonsystems reducers have?
A: Bonsystems takes a pinless Pinless cycloidal structure, a thin design, and a minimized part count as its core directions. These are meaningful differentiators in terms of assembly efficiency, productivity, and long-term reliability, and they are reflected in the company’s product lineup, including the BSR 070, 080 and BCSA series.
References
- [1] Korea Institute for Robot Industry Advancement (KIRIA) — https://www.kiria.org
- [2] Korea Institute of Robotics & Technology Convergence (KIRO) — https://www.kiro.re.kr
- [3] Ministry of Trade, Industry and Energy (MOTIE) — https://www.motie.go.kr
- [4] International Federation of Robotics (IFR) — https://ifr.org
