How to Select and Use Robotic Joint Modules？

Hello, I’m Theodore Li, Technical Director at HONPINE. In this article, I’ll use the HONPINE HPJM harmonic joint module series to explain how to select and commission robotic joint modules, covering mechanical installation, electrical wiring, communication configuration, and control setup.

A robotic joint module integrates the drive electronics, reduction mechanism, encoders, and brake into a compact cylindrical assembly. However, receiving the module does not mean your robot is ready to move. An incorrect selection can force you to redesign the wiring and communication architecture, while improper connections can cause communication errors and repeated alarms during commissioning.

What often slows down implementation is the lack of a clear process connecting product selection with successful operation. Understanding the complete workflow helps engineers avoid unnecessary modifications and get their systems running more efficiently.

1. How to Select a Robotic Joint Module: The HPJM Series as an Example

The HONPINE HPJM series covers outer diameters from 30 to 170 mm, with single-encoder and dual-encoder configurations available across the range. This provides options for joints of different sizes, from compact joints in dexterous hands to larger humanoid hip joints.

One decision that should be finalized early is the communication interface. Single-encoder HPJM modules use CAN communication, while dual-encoder versions support CAN and EtherCAT. Hand applications commonly use RS-485, depending on the selected actuator and system architecture.

At HONPINE, we emphasize defining the communication bus and power supply architecture before completing the mechanical design. These decisions affect the controller, wiring layout, and integration strategy. Leaving them until after prototype assembly can lead to unnecessary modifications.

2. Why Are Integrated Joint Modules Easier to Install and Use?

One of the main advantages of modern lightweight joint modules is that much of the integration work is completed at the factory, simplifying implementation for the customer. The HPJM harmonic joint module combines a servo drive, encoder system, frameless torque motor, brake, and harmonic reducer in a single assembly.

This integrated design simplifies installation and operation while reducing routine maintenance requirements. The large through-hole also provides space for routing cables and pneumatic tubing, helping engineers organize connections throughout the robot.

Mechanical installation still requires careful attention. Although the module simplifies integration, its mounting accuracy must be provided by the surrounding structure. The mounting surfaces and alignment must be properly established by your mechanical components. An integrated design does not eliminate the need for accurate and secure installation.

3. Electrical Wiring: Power and Communication

Electrical wiring involves two main connections: power and communication. Both require careful attention, because an incorrect connection can prevent the module from operating or cause faults during commissioning.

The HPJM module uses a rectangular power connector with designated positive and negative terminals. Confirm the polarity using the connector drawing for the specific model before connecting the power supply. The CAN interface uses three connections: H for CAN high, L for CAN low, and G for ground.

The EtherCAT interface provides separate IN and OUT ports, with Tx+, Tx−, Rx+, and Rx− communication signals. With T568B cable color coding, these correspond to white/orange, orange, white/green, and green. Always follow the module’s specified connector pinout when preparing or checking cables.

On dual-encoder modules, EtherCAT and CAN interfaces can coexist. However, control commands from both interfaces cannot be active simultaneously. EtherCAT takes priority over CAN, so the controller configuration must account for the intended command source.

4. Communication Configuration: CAN and EtherCAT

Communication connects individual joints into a coordinated robotic system. CAN and EtherCAT each have their own configuration requirements, and the choice should reflect the controller platform, number of joints, and required update rate.

For the HPJM series, the stated CAN communication rate is 1 Mbps. In an application with seven motors, the communication update rate is approximately 300 Hz. Each module must have a unique CAN ID. Assigning IDs sequentially makes a system with multiple modules easier to manage, troubleshoot, and expand.

The HPJM series supports EtherCAT communication at 100 Mbps, with supported communication update rates of up to 4 kHz. EtherCAT is designed to maintain short communication cycles across multiple slave devices. The achievable update rate should still be confirmed for the actual master, network configuration, and process data requirements.

An EtherCAT system consists of a master and multiple slaves. The master can be a software platform such as TwinCAT or CODESYS, or a compatible PLC from manufacturers such as Inovance and HCFA. During initial testing, a computer running TwinCAT or CODESYS provides a convenient platform for verifying communication and basic operation.

When connecting the network, run the master’s EtherCAT connection to the IN port of the first slave, then connect that slave’s OUT port to the IN port of the next slave. Continue this sequence through the remaining modules. Maintaining the correct IN-to-OUT sequence helps preserve the expected network topology and slave identification.

5. Control and Commissioning: Getting the Joint Moving

Once the wiring and communication configuration are complete, the next step is to make the joint respond correctly to your controller. Available operating modes include position control, velocity control, current or torque control, and hybrid force-position control. These modes support applications ranging from positioning and trajectory tracking to compliant interaction with people, tools, and the surrounding environment.

HPJM joint motors follow the IEC 61800-7 framework and the CiA 402 drive state machine. In practical terms, commissioning progresses through initialization, a disabled state, readiness, enabling, and operation. The controller must issue the appropriate commands for each state transition rather than sending motion commands immediately after power-up. The exact transition sequence and controlword settings should follow the documentation for the selected module.

HPJM modules also provide alarm codes and green and blue status indicators to assist troubleshooting. Typical issues include failure to open the CAN interface, a communication device already being used by another application, drive chip faults, overvoltage, undervoltage, and encoder faults. The corresponding troubleshooting instructions explain how to check and resolve these conditions.

During commissioning, read the statusword and any active fault information before issuing motion commands. This helps identify the actual problem and reduces unnecessary trial and error.

6. How HONPINE Helps Customers Avoid Selection Mistakes

HONPINE offers several robotic joint module series for different application requirements. Our harmonic joint modules include the HPJM, TCHL, and HAG series, while our planetary joint modules include the JRM and HPA series. At the beginning of the selection process, we assess the customer’s budget and operating conditions to recommend a suitable configuration.

Successfully implementing a robotic joint module involves five connected steps: selecting the correct specifications, installing the module accurately and securely, completing the electrical wiring, configuring the communication network, and commissioning the module according to its drive state machine. Each step contributes to reliable operation, and decisions made early in the process affect the work that follows.

HONPINE provides dedicated, one-to-one technical support throughout selection, prototyping, small-batch production, and volume delivery. Tell us your joint load requirements, controller platform, and production schedule, and we will help you select a robotic joint module suited to your application.