What Is the Difference Between Strain Wave & Cycloidal Drives

In robotics and automation, the selection of a gearbox is a critical factor that impacts system performance and efficiency. Gearboxes serve to transmit torque and manage speed reduction, enabling precise motion control in various applications. 

This blog post focuses on two prominent types of Zero-Backlash gearboxes: Strain Wave Gearboxes and Cycloidal Gearboxes. Each type offers distinct features and benefits, making it suitable for different operational requirements. Understanding the differences between these gearboxes is essential for engineers and designers to choose the most appropriate option for their specific needs.

Strain Wave Gearboxes, often known as Harmonic Drives, are distinguished by their unique method of operation which allows for high precision and low backlash. These gearboxes are composed of three main parts: the wave generator, the flexspline, and the circular spline.

Wave Generator: This is the heart of the Strain Wave Gearbox. It is an elliptical disc that fits inside the flexspline with a ball bearing. When it rotates, it deforms the flexspline into an elliptical shape, creating the wave motion that characterizes this type of gearbox.

Flexspline: The flexspline is a thin, flexible cylinder with external teeth on its open end. It conforms to the shape imposed by the wave generator, and because it is slightly smaller in tooth count than the circular spline, it allows for the high reduction ratios typical of Strain Wave Gearboxes.

Circular Spline: This component is a rigid circular ring with internal teeth that mesh with the teeth of the flexspline. The circular spline has more teeth than the flexspline, which is central to the gearbox's ability to provide high gear ratios.

• High Torque Capacity: They are capable of transmitting very high levels of torque, suitable for heavy-duty applications.
• Shock Load Resistance: The design offers excellent resistance to sudden or irregular forces, making cycloidal gearboxes durable under harsh operating conditions.
• Low Backlash: While generally higher than Strain Wave Gearboxes, the backlash in cycloidal gearboxes can still be minimal, depending on the design and manufacturing quality.
• Durability: The robust construction and even distribution of forces lend these gearboxes a long service life, even in demanding environments.

These attributes have made Strain Wave Drives like our Elastic Cyclo (ECY) a preferred choice in fields where space efficiency and precision are paramount.

Cycloidal Drives, or Cycloidal Gearboxes, are another type of precision gear system renowned for their robustness and high torque transmission capabilities. Unlike Strain Wave Gearboxes, Cycloidal Gearboxes operate based on the principles of cycloidal motion, which is generated through the eccentric rotation of a cycloidal disc. This disc, in conjunction with a set of needle bearings or pins that act as output rollers, translates input shaft rotation into output motion.

Cycloidal Disc: The core of the gearbox, this disc moves in a cycloidal path relative to the gearbox's input shaft. As it rotates, it engages with the needle bearings or pins, which then produce the output motion.

Needle Bearings/Pins: These components are arranged around the cycloidal disc and engage with its lobes to create the output rotation. The bearings or pins are housed in the output flange, which is connected to the load.

Cycloidal Gearboxes like the Fine Cyclo UA-Series or Fine Cyclo T-Series are also distinguished by their ability to handle very high loads and resist shock better than many other types of gearboxes. This is due in part to the fact that the cycloidal disc's motion distributes forces evenly across multiple points of contact, reducing the stress on any single point within the gearbox.

• High Torque Capacity: They are capable of transmitting very high levels of torque, suitable for heavy-duty applications.
• Shock Load Resistance: The design offers excellent resistance to sudden or irregular forces, making cycloidal gearboxes durable under harsh operating conditions.
• Low Backlash: While generally higher than Strain Wave Gearboxes, the backlash in cycloidal gearboxes can still be minimal, depending on the design and manufacturing quality.
• Durability: The robust construction and even distribution of forces lend these gearboxes a long service life, even in demanding environments.

These characteristics make Robotic Cycloidal Gearboxes ideal for industrial applications that require high torque and robust performance, such as in robotics, material handling, and automation equipment. Their ability to withstand high shock loads and operate reliably in demanding conditions makes them a favored choice for applications where durability and performance under stress are critical.

When choosing between Strain Wave Drives and Cycloidal Drives, understanding their key differences and how they work is essential. These distinctions impact their suitability for various applications based on factors like precision, load capacity, shock resistance, and operational efficiency.

1) Backlash

• Strain Wave Gearboxes: Known for extremely low backlash due to the precision engagement of the flexspline with the circular spline, making them ideal for applications requiring high precision and smooth motion.
• Cycloidal Gearboxes: Typically exhibit slightly higher backlash compared to strain wave gearboxes but still offer low backlash options suitable for many precision applications.

2) Load Capacity and Shock Resistance

• Strain Wave Drives: While offering high torque capacity for their size, they are generally less suited to applications involving very high loads or significant shock forces compared to cycloidal gearboxes.
• Cycloidal Drives: Excell at handling high loads and resisting shock due to their robust design and the cycloidal disc's ability to distribute stress across multiple points.

3) Efficiency and Performance

• Strain Wave Gearboxes: Tend to have higher efficiency due to less friction among the components and smoother operation. This makes them suitable for applications where energy efficiency is critical.
• Cycloidal Gearboxes: They may have slightly lower efficiency because of the eccentric motion and multiple points of contact, but their design compensates with exceptional durability and torque capacity.

4) Complexity, Manufacturing Precision, and Cost

• Strain Wave Drives Require high manufacturing precision, which can increase their cost. However, their compact size, low weight, and high precision justify the expense for many high-tech applications.
• Cycloidal Drives: While also requiring precision manufacturing, the design and materials can make them more cost-effective for applications that demand robustness and high torque over extreme precision.

The decision between a Strain Wave Gearbox and a Cycloidal Gearbox should be guided by the specific requirements of the application, including:

• Precision Needs: If utmost precision with minimal backlash is required, strain wave gearboxes are typically the better choice.
• Load and Shock Resistance: For applications involving high loads or the need for high shock resistance, cycloidal gearboxes offer superior performance.
• Space and Weight Constraints: Strain wave gearboxes are more compact and lighter, making them suitable for applications with strict space or weight limitations.
• Cost Considerations: While both types can vary in price, the specific application's requirements might make one more cost-effective than the other based on the balance between performance needs and budget constraints.

In summary, both Strain Wave and Cycloidal Gearboxes have their unique strengths and are suited to different applications. The choice between them should be based on a comprehensive evaluation of the application's specific demands, balancing precision, load capacity, environmental resilience, and cost to find the most suitable gearbox solution.

About Sumitomo Drive Technologies

Sumitomo Drive Technologies, a global leader in power transmission and control solutions, has been at the forefront of engineering excellence for over a century. With a commitment to innovation, quality, and reliability, Sumitomo offers a wide range of products and services designed to meet the rigorous demands of diverse industries. From the advanced Elastic Cyclo series to robust industrial gearboxes, Sumitomo Drive Technologies provides solutions that drive efficiency and productivity for our customers worldwide. Our global network of support and engineering expertise ensures that we deliver responsive, customer-focused solutions that optimize performance across various applications. For more information on our products and how we can support your engineering needs, visit our website.