Definition of Harmonic Drive
A harmonic drive is a high-precision, high-efficiency speed reduction device widely used in mechanical equipment, industrial automation, robotics, and other fields. Its core operating principle is based on harmonic transmission, which utilizes the elastic deformation and interlocking between a flexible wheel and an inner gear ring to achieve power transmission and speed reduction. The harmonic reducer primarily consists of three fundamental components: the drive shaft, the harmonic generator (including the wave generator and inner gear ring), the flexible wheel (elastic wheel), and the output shaft. The wave generator is typically an elliptical or similarly shaped component inserted into the interior of the flexible wheel via bearings.

Working Principle of the Harmonic Reducer
Drive Shaft Transmission: When the drive shaft begins rotating, the wave generator fixed to it starts rotating. The cams on the wave generator engage with the grooves on the flexible wheel, causing the flexible wheel to undergo elastic deformation.
Harmonic Transmission: Since the number of grooves on the flexible wheel typically exceeds the number of cams on the wave generator, the flexible wheel rotates at a slower speed as the wave generator turns, achieving the reduction effect. Simultaneously, the elastic deformation and engagement between the flexible wheel and the inner gear ring ensure high transmission precision and rigidity.
Output Shaft Drive: When the flexible wheel begins rotating, the outer gear ring on the output shaft also starts rotating. The teeth on the outer gear ring mesh with the inner gear ring on the output shaft, causing the output shaft to rotate. Through this transmission mechanism, the harmonic reducer converts the high-speed rotation of the drive shaft into low-speed, high-torque rotation of the output shaft.

Characteristics of Harmonic Reducers
1. High Transmission Ratio: Single-stage harmonic gear transmission ratios range from 70 to 320, reaching up to 1000 in certain applications. Multi-stage transmission ratios can exceed 30,000. It can be used not only for reduction but also for speed increase.
2. High Load Capacity: This is due to the large number of teeth engaged simultaneously in harmonic gear transmission. In dual-wave transmission, over 30% of the total teeth can be engaged at once. Additionally, the flexible gear uses high-strength materials, and tooth-to-tooth contact is surface-based.
3. High transmission accuracy: Multi-tooth meshing averages out errors, reducing transmission error to approximately one-fourth that of conventional cylindrical gear drives. Additionally, slightly altering the radius of the wave generator increases flexible gear deformation, minimizing backlash and even achieving zero-backlash meshing. Consequently, harmonic gear reducers exhibit minimal transmission play and are suitable for bidirectional rotation.
4. High transmission efficiency and smooth motion: During operation, the flexible gear teeth undergo uniform radial movement. Even at high input speeds, relative sliding velocity remains extremely low, minimizing tooth wear and achieving high efficiency (69%–96%). Furthermore, both sides of the gear participate in both engagement and disengagement, eliminating impact and ensuring smooth motion. Simple structure, compact size, and light weight: With only three basic components and coaxial input/output shafts, the design is straightforward and easy to install. Compared to conventional reducers, harmonic gear reducers can reduce volume by two-thirds and weight by half while delivering equivalent output torque.

Disadvantages of Harmonic Reducers
Flexible gear is prone to fatigue failure:
The flexible gear undergoes alternating stresses during cyclic deformation, leading to fatigue failure.
Special attention must be paid to material selection, manufacturing processes, and operating conditions to extend service life.

Manufacturing complexity:
The flexible gear and wave generator require specialized equipment and techniques to produce.
This increases manufacturing costs and production lead times for harmonic reducers.

High Minimum Gear Ratio:
Harmonic reducers have a relatively high minimum gear ratio. When the wave generator serves as the driving component, the gear ratio typically cannot be less than 35.
This limits their application in certain low-gear-ratio scenarios.

High Starting Torque:
Harmonic reducers require significant torque during startup to overcome the elastic deformation resistance of the flexible pulley.
This may increase equipment startup difficulty and energy consumption.

Significant Temperature Sensitivity:
Performance of harmonic reducers is highly affected by temperature, requiring operation within a specific range.
Transmission efficiency and precision may decrease in high- or low-temperature environments.

Poor Heat Dissipation Conditions:
The compact internal structure of harmonic reducers results in relatively poor heat dissipation.

Special attention to heat management is essential to prevent overheating from compromising performance and service life.

Harmonic Reducer Installation Steps
1. Prepare Tools and Materials
Ensure all necessary tools and materials are ready, including wrenches, screwdrivers, lubricants, etc.
2. Inspect the Harmonic Drive
Before installation, check the harmonic drive for signs of damage or wear, ensuring all components are intact.
3. Clean Installation Surfaces
Clean the surfaces of the harmonic drive and its mating components, ensuring they are free of dust, grease, or other contaminants.
4. Lubricate
Lubricate the input and output shafts of the harmonic reducer according to the manufacturer's recommendations.
5. Install Input Shaft
Align the input shaft of the harmonic reducer with the motor or other drive source, ensuring coaxiality is within specified tolerances.
6. Secure Input Shaft
Use appropriate fasteners to secure the input shaft in place, ensuring a firm connection that will not loosen during operation.
7. Install the Output Shaft
Align the output shaft of the harmonic reducer with the load or transmission system, ensuring proper coaxiality.
8. Secure the Output Shaft
Use appropriate fasteners to secure the output shaft in place, ensuring a firm connection.
9. Check Clearance
Inspect the clearance between the input and output shafts of the harmonic reducer, ensuring sufficient space to prevent interference.
10. Install Protective Cover
If the harmonic reducer is exposed to harsh environments, install a protective cover to shield internal components.
11. Connect Electrical and Pneumatic Systems
If the harmonic reducer requires electrical or pneumatic control, ensure all connections are correct and secure.
12. Conduct Trial Run
Before formal operation, perform a trial run to verify smooth operation and check for abnormal noise or vibration.

Common Misconceptions in Selecting Harmonic Reducers
(1) Neglecting Load Characteristics
Load characteristics—including type, magnitude, and variation range—are paramount in selecting a harmonic reducer. However, some users overlook this, choosing reducers based solely on reduction ratio or output torque, which may lead to improper selection.
Misconception 1: Selecting Based Solely on Reduction Ratio
While reduction ratio is a key parameter for harmonic reducers, it should not be the sole selection criterion. Different applications demand varying performance characteristics—for instance, robotic joints may require high dynamic response, whereas precision positioning systems prioritize accuracy and stability. Therefore, relying solely on reduction ratio may result in performance mismatches.
Correct Approach:
When selecting a reducer, comprehensively consider load characteristics and application requirements to choose an appropriate reduction ratio and output torque. Additionally, evaluate the dynamic performance of the harmonic reducer, such as starting torque and backlash.
(2) Neglecting the Operating Environment
The operating environment significantly impacts the performance and lifespan of a harmonic reducer. Environmental factors like temperature, humidity, dust, and vibration can affect the reducer's stability and reliability.
Misconception 2: Ignoring Environmental Factors
Some users may overlook the impact of the operating environment during selection. For instance, using standard harmonic reducers in high-temperature, high-humidity, or dusty environments can lead to performance degradation or even damage.
Correct Approach:
When selecting a model, fully consider the operating environment and choose a harmonic reducer model suitable for that environment. For example, select a high-temperature resistant model for high-temperature environments, and choose a model with good sealing for dusty environments.