Cycloidal Gearboxes

A cycloidal gearbox or cycloidal drive is a type of mechanical gearbox designed for high precision and torque transmission efficiency with minimal backlash. It operates on the principle of a cycloidal disc moving in an eccentric path, engaging with pins on the gearbox housing to convert input rotation into a reduced output rotation.

Cycloidal gearboxes offer several advantages, including high reduction ratios, compact design, exceptional load-bearing capacity, minimal backlash, and excellent shock resistance. These features make them ideal for applications requiring precise motion control and reliability under heavy loads.

Single-stage cycloidal gearboxes provide reduction in one step, making them compact and efficient for applications requiring moderate reduction ratios. Multi-stage drives, on the other hand, offer higher reduction ratios by employing multiple cycloidal discs and pin sets in series, catering to applications needing extreme precision and torque.

Learn more about their differences in this blog: 

Input rotational speed is the speed at which the gearbox's input shaft is driven, usually by an electric motor. It’s the initial speed that will be reduced according to the gearbox's reduction ratio to achieve the desired output speed.

Yes, Sumitomo cycloidal gearboxes can be customized to meet specific requirements, including size, torque capacity, reduction ratios, and mounting configurations. This adaptability allows them to be tailored to a wide range of industrial applications.

Choosing the right cycloidal gearbox involves considering several factors, including the required torque, reduction ratio, space constraints, load capacity, and environmental conditions.

The output torque of a cycloidal gearbox measures the rotational force available at the gearbox's output shaft. It's a critical parameter for users who need to ensure that their mechanical system has enough force to perform its intended tasks. Their unique design allows them to deliver high-output torque from a compact form factor, making them especially valuable in applications requiring high power in limited spaces.

Cycloidal gearboxes are designed to achieve extremely low backlash compared to other gearbox types. This makes them ideal for precision applications where accurate positioning and motion control are critical.

This drive type achieves high efficiency in power transmission due to its unique design, which minimizes slippage and energy loss. The direct contact between the cycloidal disc and the pins ensures that energy is transmitted effectively, leading to efficiencies typically above 90% for these systems.

Cycloidal gearboxes feature a unique design that fundamentally differs from traditional gear systems. Instead of using standard gears with teeth that mesh together, a cycloidal gearbox utilizes a cycloidal disc that interacts with a series of pins or rollers. This design provides several operational advantages over conventional gears

Key Differences:

• Cycloidal Discs vs. Gear Teeth: In a cycloidal gearbox, the primary motion-transmitting component is the cycloidal disc, which moves in a cycloidal path, engaging with fixed pins or rollers in the gearbox housing. This contrasts with traditional gears, where motion is transmitted through the direct engagement of teeth on mating gears.

• Transmission Method: The cycloidal disc in a cycloidal gearbox generates motion through an eccentric, rather than rotational, movement. This eccentric movement is converted into the desired rotational output through the engagement of the disc's lobes with the external pins or rollers. In contrast, traditional gear systems rely on the direct rotational interaction of gear teeth.

• Load Distribution: The load in a cycloidal gearbox is distributed over a larger area due to the engagement between the cycloidal disc's entire lobe surface and the pins or rollers. Traditional gears transmit force at the contact points between individual teeth, which can lead to increased wear and localized stress.

A: Rollers and pins are critical gear drive components, contributing significantly to their efficiency, durability, and precision. These elements work together to transmit power from the input shaft to the output shaft with minimal backlash and high torque capacity.

Role and Function:

• Pins: Fixed in the gearbox housing, the pins serve as the contact points for the cycloidal disc. As the input shaft turns the eccentric cam, it causes the cycloidal disc to move in a unique, cycloidal path. The motion of the cycloidal disc is then translated into rotation of the output shaft through its interaction with these pins.

• Rollers: Attached to the cycloidal disc, rollers fit between the fixed pins. They ensure smooth, efficient transfer of motion from the cycloidal disc to the output shaft. The rollers reduce friction and wear at the contact points between the cycloidal disc and the pins, enhancing the gearbox's longevity and maintaining its precision over time.

Contribution to Performance:

• High Torque Transmission: The interaction between the cycloidal disc's rollers and the fixed pins allows the drive to transmit high levels of torque efficiently. This is due to the large contact area between the rollers and pins, which distributes forces more evenly and allows for the transmission of higher loads without significant wear.

• Minimal Backlash: One of the key advantages is their ability to operate with minimal backlash. The precise fit and continuous engagement between the rollers and pins eliminate play in the transmission path, resulting in superior accuracy and repeatability in motion control applications.

• Durability and Reliability: The use of rollers reduces point contact stress and distributes loads over a larger area, minimizing wear and extending the service life of the gearbox. This makes the drive exceptionally durable and reliable, even in applications involving high loads or continuous operation.

Cycloidal gears are a type of gear mechanism that is distinct from traditional spur or helical gears. Unlike conventional gears, which transmit torque through the meshing of teeth, cycloidal gears operate using a cycloidal disc that moves in a complex, cycloidal path. This movement engages with pins or rollers positioned around the gear housing, converting input rotational motion into reduced output rotational motion with high torque and minimal backlash.

The terms "cycloidal discs" and "cycloidal gears" are closely related and often used within the context of cycloidal gearboxes, but they refer to different components of the system.

• Cycloidal Discs: These are the heart of a cycloidal drive system. A cycloidal disc is a specialized component that features a series of lobes or curves around its perimeter. The disc moves in a cycloidal motion (a complex path that combines circular and linear motion) as it is driven by an eccentric bearing attached to the gearbox's input shaft. This motion allows the cycloidal disc to engage with pins or rollers fixed in the gearbox housing, thereby converting the input rotational motion into output rotational motion with a significant reduction in speed and an increase in torque.

• Cycloidal Gears: This term can be somewhat misleading because it suggests traditional gear mechanisms. However, in the context of a cycloidal drive system, "cycloidal gears" refers to the overall mechanism that includes the cycloidal discs, along with the pins or rollers they interact with, and other associated components such as the input shaft, eccentric cam, and output shaft. Essentially, "cycloidal gears" encompass the entire drive system that utilizes cycloidal motion for power transmission.

The input shaft of a cycloidal gearbox plays a crucial role in the operation of the gearbox, acting as the primary interface for transmitting rotational power from the motor or driving mechanism to the gearbox itself.

In a cycloidal gearbox, the input shaft typically drives an eccentric bearing or cam that is directly attached to, or integrated with the cycloidal disc. The eccentric rotation of this cam, driven by the input shaft, causes the cycloidal disc to follow a cycloidal path, leading to the unique motion that characterizes this type of gearbox.

The reduction ratio of a cycloidal gearbox directly determines the output rotational speed. This ratio represents the difference between the input and output speeds and is a fundamental characteristic of the gearbox design. They can achieve very high reduction ratios in a compact form factor, significantly reducing the output speed while increasing torque.

• Design and Configuration: The specific design of the cycloidal discs, the number of lobes, and the arrangement of the eccentric cam and roller pins all influence the achievable reduction ratios and, consequently, the output rotational speed.

• Load Conditions: Under heavy load conditions, the actual output speed might slightly differ from the theoretical value due to mechanical losses within the gearbox. Cycloidal drives, however, are known for their efficiency and ability to maintain consistent output speeds even under varying load conditions.

• Lubrication and Maintenance: Proper lubrication and maintenance are essential to ensure that the cycloidal gearbox operates at its optimal rotational speed. Friction and wear can affect performance over time, but the cycloidal design's inherent durability minimizes these effects.

To achieve even higher reduction ratios or to customize the gearbox for specific torque requirements, cycloidal gearboxes can be designed with multiple stages. Each stage adds to the overall reduction ratio by compounding the effect of the previous stage. This "addition" of stages allows for an extensive range of reduction ratios and flexibility in designing systems that require very low output speeds and high torque from a relatively high-speed input.

Cycloidal gearboxes offer several advantages, but they also have a few potential disadvantages to consider:

• Complex Assembly: The internal mechanism involves precision components that may require careful handling and assembly.
• Higher Initial Cost: Compared to traditional gearboxes, cycloidal drives can be more expensive due to their specialized design and materials.
• Vibration Sensitivity: Some models may experience increased vibration during operation if not properly aligned or if the pins and rollers wear out.
• Backlash in Lower-Quality Units: Poorly manufactured cycloidal gearboxes may introduce more backlash, which can affect precision in certain applications.

Cycloidal gears are not used in all applications due to:

• Application-Specific Design: Cycloidal gearboxes excel in applications requiring high torque and shock load resistance but may not be suitable for high-speed or lightweight applications.
• Precision Needs: For high-speed or extremely precise rotational tasks (e.g., robotics arms with minimal error tolerance), planetary or harmonic drives may be preferred over cycloidal designs.
• Size Constraints: Cycloidal gearboxes tend to be bulkier than some other types of gearboxes, making them less ideal for space-constrained environments.