What is robot joint actuator?How to Choose the Best Robot Rotary Joint Actuator?

14/04/2026

What is a Robot Joint Actuator?

A robot joint actuator, also known as a joint actuator, is responsible for driving and controlling the motion of each joint and component of a robot. It can be broadly classified into two types:

(1) Rotary Actuator

Composed of a frameless torque motor, reducer, torque sensor, encoder, and bearings.

(2) Linear Actuator

Composed of a frameless torque motor, roller screw, torque sensor, encoder, and bearings.

The key difference between the two lies in the transmission mechanism:

Rotary actuators use reducers

Linear actuators use roller screws

Classification of Robot Rotary Joint Actuators

Two Types of Robot Rotary joint actuator

In core joint transmission solutions, planetary and harmonic actuators each have their own strengths. Choosing the right type based on application requirements is essential to achieve the optimal balance between performance and cost.

	Planetary Joint Actuator	Harmonic Joint Actuator
Core Advantages	High rigidity, high load capacity, impact resistance, high efficiency	Ultra-high precision (near-zero backlash), lightweight, compact, high reduction ratio
Transmission Structure	Rigid gear meshing	Flexible spline deformation meshing
Transmission Accuracy	1–25 arcmin	≤60 arcsec
Load Capacity	Very strong, excellent radial/axial load capacity, high shock resistance	Relatively lower, flexible spline sensitive to shock and overload
Efficiency	High (80%–98%)	Medium (40%–70%)
Size / Weight	Larger and heavier at same torque	Smaller and lighter at same torque
Reduction Ratio	Low (3–10), multi-stage needed	High (30–160), single-stage
Lifetime	Long (>10,000 hours), wear-resistant Shorter	flexspline fatigue (thousands to ~10,000 hours)
Cost	Lower (mature, cost-effective)	Higher (complex materials and manufacturing)

Features of Planetary Reducer Robot Joint Rotary Actuator

Planetary joint actuator are based on rigid gear transmission, offering strong reliability for heavy-duty applications.

Excellent radial and axial load capacity, resistant to frequent shock and vibration

High transmission efficiency with low wear, suitable for long-term continuous operation

Mature technology with controllable mass-production cost

Typical Applications:

Humanoid and quadruped robot lower limbs and torso, exoskeletons, AGV drives, heavy-duty robotic arms, heavy-load gimbals, and other high-load, impact-resistant scenarios

Features of Harmonic Reducer Robot Joint Rotary Actuator

Harmonic joint modules rely on flexible transmission technology, providing high precision and compact design.

Near-zero backlash for highly accurate positioning (micron-level precision)

Smaller size and lighter weight at the same torque, improving system integration

Smooth transmission with low noise, ideal for quiet environments

Typical Applications:

Collaborative robots, humanoid upper limbs and wrists, precision assembly, 3C inspection, medical equipment, and lightweight human-machine interaction joints

Types of HONPINE Robot Joint Rotary Actuators

The table below provides a basic selection guide for HONPINE robot joint rotary actuators:

Product	Model	Communication Protocol	Brake	Torque Sensor	STO
Harmonic Joint Actuator	HPJM Series	CAN(Private) CANopen Ethercat CANFD(Private)	Optional for all models	External (custom)	No
	TCHL Series	CAN(Private) CANFD(Private) Ethercat	Optional for all models	Built-in (standard)	No
	HTS Series	CANopen Ethercat	Optional for all models	No	No
	HAG Series	CANopen Ethercat	Optional for all models	Built-in (standard)	Available on all except size 11
Planetary Joint Actuator	JRM Series	CAN(Private) Ethercat	No	No	No