How to Choose a Force Control Harmonic Joint Actuator? An In-Depth Comparison of HONPINE TCHL and HAG

Choosing a force control harmonic joint actuator involves more than comparing torque and dimensions. Torque sensor specifications, encoder feedback, communication protocols, functional safety, and hollow-shaft size can all affect system integration and control performance. In this guide, HONPINE Technical Director compares the TCHL and HAG harmonic joint actuator series, explaining their key differences and providing a practical selection framework for humanoid robots, collaborative manipulators, precision assembly, polishing, and other force-controlled applications.

Introduction: Two Harmonic Joint Actuators for Different Force Control Requirements

Hello everyone, I'm the Technical Director at HONPINE. Today, I'll introduce two harmonic joint actuator series equipped with optional built-in torque sensors: TCHL and HAG.

Both series share a similar mechanical and control architecture:

Output flange → Harmonic reducer → Torque sensor → Frameless torque motor → Brake → Coplanar dual encoders → Integrated drive board

Despite their shared architecture, TCHL and HAG are designed to address different engineering priorities. TCHL focuses on minimizing weight and overall dimensions while maintaining the precision advantages of harmonic transmission. HAG emphasizes system integration, additional safety-related functionality on selected models, and more fully documented torque sensor specifications.

So, what distinguishes these two series, and how should engineers choose between them?

TCHL vs. HAG: Understanding Their Core Design Priorities

HONPINE TCHL Harmonic Joint Actuator: Prioritizing Lightweight Design

The core objective of the TCHL harmonic joint actuatoris to minimize weight and package size while retaining the high-precision characteristics of harmonic transmission.

This makes TCHL a candidate for applications where joint mass, compact dimensions, and dynamic response are important design considerations, including humanoid robots and collaborative robotic arms.

Key specifications of the TCHL series

The available configurations should be checked against the specific model and its technical documentation before final selection.

HONPINE HAG Harmonic Joint Actuator: Prioritizing Integration and Safety-Related Options

The HAG harmonic joint actuator focuses on higher system integration, additional configuration options, and more comprehensive published torque sensor specifications.

The series covers a wider range of frame sizes and offers single-turn and multi-turn absolute encoder feedback. Selected frame sizes are available with built-in Safe Torque Off (STO), subject to model-specific confirmation.

Key specifications of the HAG series

The published sensor data can help engineers evaluate measurement accuracy and determine whether a particular configuration meets their control requirements. However, sensor nonlinearity alone does not establish the overall force-control resolution or accuracy of the complete robotic system.

How to Select Between TCHL and HAG: Six Key Selection Criteria？

Rather than starting with price or rated torque, engineers should first identify the system requirements that could make one configuration unsuitable.

1. Communication Protocol: Check Compatibility First

TCHL: EtherCAT / CAN FD

HAG: CANopen / EtherCAT

EtherCAT is the shared option between the two series based on the specifications listed above.

If the control system requires CAN FD, TCHL is the candidate among these two series, subject to the selected configuration.

If the system requires CANopen, HAG is the candidate, subject to the selected configuration.

If the system uses EtherCAT, both series may be considered, and the remaining selection criteria become important.

This is one of the easiest integration constraints to overlook. Confirm the exact interface, protocol implementation, connector, and supported communication profile during the initial technical discussion rather than after quotation or mechanical design.

2. Single-Turn vs. Multi-Turn Absolute Encoders

TCHL: 17-bit single-turn absolute encoder

HAG: 20-bit single-turn + 12-bit multi-turn absolute encoder

Encoder configuration affects position feedback, startup behavior, and system integration.

TCHL provides 17-bit single-turn absolute position feedback. This identifies the position within one revolution, but does not by itself provide multi-turn position information. Depending on the system design, the controller may need a homing procedure or another method of tracking accumulated rotations.

HAG provides 20-bit single-turn and 12-bit multi-turn feedback. This can be advantageous when a robot needs to track both angular position within a revolution and accumulated rotation across multiple turns.

Choose HAG when multi-turn feedback is a defined system requirement. This may be particularly relevant to coordinated multi-joint systems and applications where a repeatable startup procedure is important.

However, multi-turn feedback does not automatically guarantee position retention under every power-loss condition. Engineers should confirm the encoder's position-retention method and startup behavior with the manufacturer.

3. Functional Safety: Evaluate STO Availability

TCHL: STO is not listed in the supplied specifications.

HAG: Built-in STO is available on selected frame sizes.

Safe Torque Off (STO) is a safety-related function that prevents the drive from producing torque when the function is activated. It is relevant to applications that require a defined method of disabling motor torque.

For collaborative robots, medical or rehabilitation equipment, and human-interactive robotic systems, STO availability may be an important part of the drive architecture.

Based on the supplied specifications, HAG is the series to investigate when built-in STO is required. However, STO is not standard across the entire HAG series. Its availability must be confirmed for the specific frame size and configuration.

STO alone also does not establish compliance with ISO 13849, IEC 61508, or the complete safety requirements of a machine. System-level risk assessment, safety architecture, validation, and applicable certification requirements must be considered separately.

4. Torque Sensor Specifications: Can You Verify the Required Performance?

TCHL: Optional torque sensor; measuring range and accuracy details are not included in the supplied specifications.

HAG: Optional torque sensor; measuring range and 0.5% nonlinearity specification published.

For force-controlled applications, the presence of a torque sensor is only the starting point. Engineers also need to understand its measuring range, nonlinearity, resolution, bandwidth, overload capability, and signal-processing characteristics.

The TCHL series offers optional torque sensor configurations, but the relevant measuring range and accuracy data should be obtained for the exact model before making quantitative performance commitments.

HAG provides a more complete set of published torque sensor specifications, including measuring range and nonlinearity. This gives engineers a more practical starting point for evaluating sensor error and determining whether the measurement range matches the application's expected torque.

For example, a sensor's full-scale range and nonlinearity can help estimate its contribution to measurement error. They do not, on their own, determine the minimum detectable torque or the actual force-control resolution of the complete system.

If torque feedback is central to the application, compare the full sensor specifications before making the final selection.

5. Frame Size and Torque Capacity: Match the Joint to the Load

TCHL: Frame sizes up to 32; the supplied comparison lists rated torque up to 169 N·m.

HAG: Frame sizes up to 40 and 45; the supplied comparison lists rated torque up to 557 N·m.

The appropriate joint actuator depends on more than the robot's total payload. Joint torque requirements vary with arm length, link mass, acceleration, gravity, duty cycle, and external forces.

TCHL is worth evaluating for compact, lightweight joints where minimizing mass is a major priority.

HAG offers larger frame sizes and a higher torque range in the supplied comparison. It may therefore be more suitable for heavy-load joints, robotic bases, waist joints, and industrial applications with demanding torque requirements.

Before selection, verify rated torque, peak torque, permissible speed, thermal limits, duty cycle, and allowable radial and axial loads for the exact model. Do not use peak torque as a substitute for continuous rated torque.

6. Hollow-Shaft Diameter: Leave Enough Space for Cable Routing

The hollow-shaft diameter can affect the routing of power cables, encoder lines, torque sensor wiring, and other connections through a robotic arm.

Values are based on the supplied comparison and should be verified against the current model drawings.

At frame sizes 17 and 20, the listed HAG hollow bore is 16.8 mm, compared with 12 mm for TCHL. At size 32, the listed dimensions are 28 mm and 22 mm, respectively.

These differences can matter when multiple cable bundles must pass through a joint, particularly in compact multi-axis arms.

A larger hollow bore may simplify cable routing, but engineers should also consider connector dimensions, bend radius, cable movement, strain relief, and the clearance required throughout the full range of motion.

Choosing the Right Force Control Harmonic Joint Actuator for Your Application

When Should You Choose TCHL?

HONPINE TCHL is primarily designed around lightweight, compact integration while retaining the precision advantages of harmonic transmission.

It is worth evaluating for:

Humanoid robot joints where reducing joint mass is important.

Collaborative robotic arms with tight packaging requirements.

Compact robotic systems that use EtherCAT or CAN FD.

Applications where single-turn absolute feedback meets the control requirements.

Force-controlled applications where the selected torque sensor configuration has been verified against the required measurement performance.

TCHL is not automatically the better choice for every lightweight robot. The selected model must still meet the application's torque, speed, stiffness, thermal, and sensor requirements.

When Should You Choose HAG?

HONPINE HAG is designed for applications that place greater emphasis on system integration, expanded frame-size options, and more completely documented torque sensor specifications.

It is worth evaluating for:

• Robotic joints with higher torque requirements.

• Industrial manipulators that require larger frame sizes.

• Applications that need single-turn and multi-turn absolute encoder feedback.

• Systems that use CANopen or EtherCAT.

• Designs that require built-in STO on a supported frame size.

Force-controlled applications where published torque sensor parameters are important for engineering validation.

HAG may be a better fit for demanding applications, but the final decision should be based on the specifications of the exact model rather than the series name alone.

Why Torque-Sensing Harmonic Joint Actuators Matter in Force Control?

A harmonic joint actuator with an integrated torque sensor can provide joint-level torque feedback for closed-loop force control. Instead of relying exclusively on commanded motor current or a predefined motion trajectory, the controller can use measured joint torque as an input to adjust the robot's response.

This capability is valuable in precision assembly, grinding, polishing, and other processes where contact forces need to be managed.

It can also support compliant interaction in collaborative robots, rehabilitation equipment, and teleoperation systems, where controlled contact and responsive motion are important.

Actual force-control performance depends on the entire system, including sensor characteristics, controller design, communication latency, mechanical stiffness, friction, calibration, and control-loop tuning. A built-in torque sensor is an important enabling component, but it does not guarantee a particular level of force-control accuracy or functional safety by itself.

Final Thoughts: Select by System Requirements, Not Just Product Specifications

TCHL and HAG address different priorities within the force control harmonic joint actuator category.

TCHL emphasizes lightweight, compact design. HAG offers additional encoder capabilities, larger frame sizes, and more complete published torque sensor specifications, with STO available on selected configurations.

The most effective selection process begins with the system's non-negotiable requirements: communication protocol, encoder feedback, safety architecture, torque measurement performance, load capacity, and cable-routing space. Once these constraints are established, engineers can compare the remaining parameters to find the most appropriate actuator.

Contact HONPINE to request technical documentation and discuss the right TCHL or HAG configuration for your force-controlled robotic application.