Force-Controlled Harmonic Joint Modules: A Key Solution for Robot Commercialization

HONPINE force-controlled harmonic joint modules are designed to support the next stage of robot commercialization, where robots need to do more than achieve accurate positioning. The HAG  series use torque closed-loop control and integrate torque sensing into the joint, enabling 360° continuous rotation at the output, more precise torque control, and real-time torque feedback.

With real-time force information, robots can respond more naturally to external loads and achieve more compliant interaction with people, objects, and their working environment.

Why Choose Force-Controlled Robot Joint Modules?

The "follow-the-hand" feeling during gravity-compensated teaching, the impact absorption required when a humanoid robot lands, and the precise contact control required during polishing all depend on the same fundamental capability: how accurately and how quickly the robot joint can measure and control output torque.

In conventional position-controlled systems, motion feedback has traditionally been centered on encoder data. As robots move toward force control and physical interaction, torque feedback becomes increasingly important. The way torque feedback is obtained directly affects the control performance, mechanical integration, cost structure, and dimensional constraints of the joint module.

A force-controlled joint module provides the robot with more than position information. It enables the system to sense torque in real time and adjust the joint output according to changing loads, creating a foundation for compliant motion and physical interaction.

Does a Force-Controlled Harmonic Joint Module Need to Be Larger?

Integrating a torque sensor does not necessarily mean that the joint module must become larger.

HONPINE integrates the torque sensor directly into the joint module, allowing the force-controlled and non-force-controlled configurations to maintain the same overall dimensions. This allows customers to select or switch between configurations without making major changes to the robot's mechanical structure.

Key Specifications of HONPINE Force-Controlled Joint Modules

• Integrated torque sensing

• Torque closed-loop control

• Torque control accuracy of less than 1%

• 50 Hz torque bandwidth

• 360° continuous output rotation

• Compact integrated joint architecture

Consistent mechanical dimensions between force-controlled and non-force-controlled versions

Why Are Force-Controlled Joint Modules Important for the Development of Robots?

Human joints such as the knees, shoulders, elbows, and wrists are not simply mechanical connections between bones. They coordinate movement while continuously responding to forces generated by muscles and the surrounding environment.

For example, when holding a fragile glass, the human hand naturally adjusts the applied force according to the object's weight and resistance. When writing with a brush, the wrist continuously regulates force and angle to produce controlled movements.

Robots increasingly need similar capabilities when interacting with the physical world.

Precise Force Perception for More Controlled Motion

High-precision force-controlled joints can provide real-time information about the torque acting on the joint. This allows the robot controller to respond to changes in external load instead of relying solely on predefined position trajectories.

This capability can be valuable in applications such as:

• Precision assembly

• Contact detection

• Robotic polishing and grinding

• Human-robot interaction

• Gravity compensation

• Collision detection

• Compliant manipulation

For example, during precision assembly, the robot may need to detect contact or insertion resistance before continuing the movement. Torque feedback provides additional information that can help the control system adjust the joint motion accordingly.

Force Control Enables More Compliant Robot Interaction

Traditional position control is highly effective when the robot operates in a predictable and structured environment. However, many emerging robotic applications involve uncertain contact conditions.

When a robot interacts with a person, grasps an object, touches a surface, or performs a contact-based process, simply reaching a predefined position may not be sufficient.

Force-controlled joints provide another layer of feedback, allowing the robot to respond to external forces and achieve more compliant movement.

This is particularly relevant to:

• Humanoid robots

• Collaborative robots

• Dexterous manipulation

• Robotic assembly

• Polishing and surface finishing

• Service robots

Integrated Joint Modules: A Compact "Micro System" Inside the Robot

An integrated robot joint module may be a relatively small component, but it can contain multiple critical technologies.

A typical integrated joint module can combine:

• Motor

• Harmonic reducer

• Encoder

• Torque sensor

• Drive electronics

• Brake

• Communication interfaces

• Control components

By integrating these components into a single joint-level platform, manufacturers can reduce system complexity and simplify mechanical and electrical integration.

Integrated Torque Sensing for High-Precision Robotic Applications

The addition of an integrated torque sensor gives the joint module an additional sensing capability beyond conventional position feedback.

Instead of simply commanding the joint to reach a specific position, the control system can also monitor the torque generated at the joint and respond to changes in load.

This provides a foundation for more flexible control strategies, particularly where the robot must physically interact with its environment.

HONPINE HAG Harmonic Robot Joint Modules

The HONPINE HAG and HAU series integrate harmonic transmission, motor, sensing, and control technologies into compact robot joint modules.

With integrated torque sensing, torque closed-loop control, less than 1% torque control accuracy, and a 50 Hz torque bandwidth, the force-controlled configuration is designed for robotic applications that require more than conventional position control.

The fact that the force-controlled and non-force-controlled configurations can maintain the same overall dimensions also provides robot manufacturers with greater flexibility when developing different product configurations on the same mechanical platform.

Applications of Force-Controlled Harmonic Joint Modules

Force-controlled harmonic joint modules are particularly relevant to robotic applications involving physical contact, variable loads, or compliant motion, including:

• Humanoid robots

• Collaborative robots

• Robotic polishing and grinding

• Precision assembly

• Dexterous robotic manipulation

• Human-robot interaction

• Service robots

Contact HONPINE for HAG Robot Joint Module Solutions

For more information about HONPINE HAG harmonic robot joint modules and force-controlled joint solutions, contact HONPINE for technical documentation and application support.