Harmonic Reducer vs. Harmonic Rotary Actuator: Which Is Better for CNC Machine Tools?

Hello everyone, I'm Theodore Li, Technical Director at HONPINE.

Many customers face a common question when selecting harmonic drive components for CNC machine tools: Should they choose a harmonic reducer or a harmonic rotary actuator?

In this article, I'll explain the differences between these two solutions and help you determine which one is better suited to your CNC application.

When choosing between a harmonic reducer and a harmonic rotary actuator for CNC machine tools, several key factors must be considered, including load capacity, rigidity, positioning accuracy, motor and control system compatibility, installation space, and specific application requirements.

Among these factors, load capacity and rigidity should be given the highest priority. Unlike conventional automation equipment, certain rotary axes in CNC machine tools must not only achieve precise positioning but also withstand external forces generated during machining operations.

Why Are Harmonic Reducers Well Suited for CNC Fourth-Axis Applications?

Harmonic reducers are particularly suitable for CNC fourth-axis applications, such as rotary tables, due to their key advantages: near-zero backlash, high positioning accuracy, high reduction ratios, and compact design.

These characteristics make harmonic reducers an attractive solution for CNC rotary tables that require precise indexing, efficient use of installation space, and responsive motion control.

Harmonic reducers operate through the elastic deformation of a flexible spline, allowing them to achieve high reduction ratios within a compact structure.

This unique transmission principle helps meet the requirements of CNC fourth-axis systems for high precision, high torque density, compact dimensions, and smooth motion.

However, the suitability of a harmonic reducer also depends on its torsional rigidity, load capacity, bearing arrangement, and resistance to machining forces. For heavy-duty cutting applications, these factors must be carefully evaluated.

Are Harmonic Rotary Actuators Better for CNC Fifth-Axis Applications?

Not necessarily. The most suitable solution still depends on the specific technical requirements of the CNC machine.

However, based on HONPINE's experience serving customers in recent years, we have observed a growing interest in integrated harmonic rotary actuators for compact CNC five-axis systems.

A five-axis CNC machine typically consists of three linear axes—X, Y, and Z—and two rotary axes, such as A/C or B/C.

Compared with a single rotary-axis mechanism, a five-axis system requires coordinated motion between two rotary axes. Certain complex surface machining operations also require simultaneous five-axis interpolation.

For compact five-axis mechanisms, harmonic rotary actuators offer four key advantages.

1. Integrated Design Helps Reduce Equipment Size

Five-axis rotary tables often need to accommodate two rotary axes, drive systems, bearings, and cables within limited installation space.

A harmonic rotary actuator integrates the motor, harmonic reducer, and encoder into a compact unit.

This integration reduces the number of separate transmission components and mechanical connections, allowing for a more compact A/C-axis or B/C-axis arrangement.

2. Integrated Feedback Supports Coordinated Multi-Axis Control

Five-axis machining requires precise rotary-axis positioning, smooth speed control, and responsive dynamic performance.

By combining a matched motor, reducer, and feedback system, an integrated servo actuator can simplify certain aspects of system integration while supporting closed-loop motion control.

However, this does not mean that an integrated actuator inherently provides higher control accuracy than a separate servo motor combined with a harmonic reducer.

Actual multi-axis machining performance still depends on the CNC controller, overall mechanical rigidity, feedback configuration, and machine calibration.

3. Hollow-Shaft Design Simplifies Cable Routing

Some harmonic rotary actuators feature a hollow-shaft design, allowing electrical cables, pneumatic tubes, and other connections to pass through the rotational center.

In five-axis tilting heads and rotary tables, this arrangement helps reduce external cable routing requirements and improves space utilization.

For continuous rotation applications, however, cable twisting and the possible need for rotary unions or slip rings must still be considered.

4. Simplified Mechanical Design and Assembly

Compared with independently selecting and assembling a motor, harmonic reducer, coupling, and encoder, an integrated harmonic rotary actuator can reduce the number of mechanical interfaces.

This can simplify equipment design, assembly, and commissioning, potentially shortening the overall machine development process.

HONPINE 58 Series Harmonic Rotary Actuator for CNC Applications

For customers looking for a compact, high-precision rotary drive solution, I would like to introduce the HONPINE 58 Series Harmonic Rotary Actuator.

The HONPINE 58 Series is designed to deliver exceptional rigidity and positioning accuracy.

It integrates three key components into a single compact unit:

- A high-precision harmonic reducer

- A frameless torque motor

- A high-resolution 26-bit encoder

The actuator also features a 47 mm hollow bore, providing convenient routing space for cables and other connections.

Exceptional Rigidity Demonstrated Through Laboratory Testing

At the HONPINE laboratory, we conducted a rigidity demonstration using a lever nearly two meters long.

During the test, we applied force to the actuator's output end through the lever and monitored its displacement using a dial indicator.

Even under this lever-induced load, the dial indicator showed almost no visible movement.

More importantly, the harmonic rotary actuator used in this experiment was not equipped with a braking mechanism.

The test was intended to demonstrate the actuator's inherent resistance to deflection under the tested conditions, rather than relying on an additional mechanical brake.

This result highlights the impressive rigidity of the HONPINE 58 Series harmonic rotary actuator.

High Positioning Accuracy Without Compromising Rigidity

In addition to its high rigidity, the HONPINE 58 Series harmonic rotary actuator achieves excellent positioning performance.

According to HONPINE's laboratory test results, its key accuracy specifications include:

These results demonstrate the actuator's ability to combine high rigidity with precise motion control.

Below is the accuracy test report generated using our laser measurement system.

[Insert Image: HONPINE 58 Series Harmonic Rotary Actuator Accuracy Test Report]

It is important to note that the final performance of any actuator in a CNC machine tool also depends on the installation structure, applied loads, control configuration, and overall machine design.

Contact HONPINE for CNC Harmonic Drive Solutions

Whether you are developing a CNC fourth-axis rotary table, a compact five-axis machining system, or a customized rotary positioning mechanism, selecting the right harmonic drive solution is essential for achieving reliable performance.

HONPINE provides harmonic reducers and integrated harmonic rotary actuators for a wide range of precision motion applications.

Contact HONPINE today to learn more about our harmonic reducers and rotary actuators for CNC machine tools, and obtain additional technical specifications, product documentation, and application support.