In the world of Autonomous Mobile Robots (AMRs), one element plays a critical yet subtle part: the wire harness. Its behind-the-scenes role carefully manages the complex network of cables and wires that drive AMR functionality. To gain insight into the harness tailored specifically for our arculees, we sat down with Anis Cherni, Senior Harness Design Engineer at arculus. He explains the challenges and cross-team collaboration within the harness design process.

Wire Harness: the nervous system of an AMR

Anis Cherni, Senior Harness Design Engineer at arculus, describes the wire harness as "An integrated arrangement of cables, bound together with an insulated material." In the case of AMRs, this arrangement of cables serves as the "nervous system" bringing these robots to life. It allows power delivery and enables communication between electronic components.

Since the arculees need to operate round-the-clock, their nervous system must be exceptionally durable and reliable. The design and manufacturing process of an arculee's wire harness, therefore focuses on ensuring its robustness to defend against diverse environmental factors and mechanical stress points. In addition, ensuring safety and minimising signal interference are crucial aspects of the manufacturing process.

Building a robust wire harness

The arculee's wire harness is designed for durability. It incorporates fundamental components such as wires, terminals, connectors, seals, fasteners and protective sleeves. As Anis emphasises, "Every component within the arculee's harness must be able to endure environmental factors like temperature and humidity variations as well as mechanical stress, like vibrations."

Here is a closer look at each of the components:

Wires

Wires are conductive elements that carry electrical signals and power between different components. Strain relief or mechanical stress protection is vital to prevent wire damage at the connector level, thus maintaining integrity. Additionally, the optimal length and routing of wires are determined by many factors. For example, the assembly and disassembly of the harness.

Terminals

Terminals are a class of electrical connectors that "terminate" by crimping or soldering to wire or cable. They create secure and stable connections. There are a few factors to consider when selecting suitable terminals for our harness, for example:

• The wire cross-section: The wire cross-section should match the size and capacity of the terminal for safe and effective electrical connections;
• Conductivity, signal requirements, and minimising voltage drop: These determine the different coatings used (such as gold, tin or nickel), the mechanical fit and even the type of the conductor itself.

Connectors link multiple wires, cables, or components that allow quick and secure connection and disconnection of electrical power and signals. Several factors must be considered when selecting connectors for our harness, such as the number of pins required and the cost, without compromising quality. The wire cross-section also plays a significant role in determining the appropriate connector. Anis, however, specifies, "We normally try to limit the diversity of connectors we use to simplify manufacturing and reduce costs."

Seals are components that protect against environmental factors such as dust and moisture. They are typically installed at entry and exit points where wires or cables pass through walls, enclosures, or connectors. Proper installation shields the harness from external contaminants.

Fasteners maintain the harness in position, orient its branches and provide fixture points within a robot. Anis mentions, "We develop a fastening strategy for the harness. With this, we can identify where each fastener should be located, which has an impact on the assembly and disassembly, the routing and even the energy dissipation throughout the harness."

Protective sleeves are insulation designed to shield and safeguard wires and cables from mechanical stress areas. For the protective sleeves on our harness, Anis explains:

“During our routing phase, we aim to avoid mechanical stress areas. But if we cannot do that, we design our harnesses with a focus on incorporating vibration-absorbent insulations, strain reliefs, and an optimal selection of components. We also consider the dynamic and static behaviour of our system to prevent any failures from occurring. We further account for temperature and its variations, humidity, corrosion and the flexibility of the harness itself. And with that, different measures can be taken.”

Safety assurance

Incorporating durable components within a harness is fundamental to maintaining the safety of the arculee and its users. To ensure full compliance with industry standards, arculus adheres to specific regulations relating to the manufacturing of harnesses, namely:

• DIN EN 1175 VDE 0117:2020-10: Safety requirements for designing and manufacturing electrical equipment for industrial trucks
• ANSI/CAN/UL 3100:2021: Safety standard for automated mobile platforms (AMPs) development in commercial and industrial environments
• IEC 60757: Code for designation of colours in technical documentation and markings of electrical equipment and products

Minimising signal interference

In addition to well-designed and well-constructed components, the essence of a reliable harness lies in its ability to operate with minimal signal interference. This also entails a commitment to electromagnetic compliance, which is the capability of electrical systems to operate without causing disruptions to other devices or being exposed to interference from external electromagnetic sources.

"We use filters for signals, shielded communication cables and ferrites to keep up with our tight requirements regarding the safety and sanity of signals," explains Anis. "We also secure wire segregation, keeping high-voltage cables away from sensitive communication lines. And we keep communication lines away from rotating parts that generate an electromagnetic field.", he concludes.

Testing and validating procedures

Testing and validation are crucial in ensuring reliability and durability. There are two parts to these procedures:

• Testing and validation of the manufactured harness: Here, the manufacturer looks into different checkpoints based on a quality control process. These validate whether the harness is durable and reliable enough to be installed in a robot. Some examples are pin-to-pin wire checks to verify the wiring connections and wire-pulling tests to assess the mechanical integrity and strength of a crimped wire and terminal connection.
• Testing and validation of the harness installation: The second phase involves installing the harness in the robot as originally intended. During this step, stakeholders within the project, including team members and engineers, provide valuable feedback. Anis explains, "The input we gather may lead to a new revision of the harness, which is then deployed in the robot."

The challenges of wire harness design

Harness design comes with several challenges that engineers must tackle to ensure long-term success. At arculus, two major hurdles are currently at the forefront: scalability and adaptability.

Scalability

Effectively managing scalability hinges on comprehensive manufacturing documentation. Anis highlights this, stating, "arculus improves a lot in harness documentation, which currently allows us to outsource the harness manufacture to different suppliers without having any issues."

Adaptability

Effectively handling changes requires a well-defined change management process that oversees transitions from various parties involved in the assembly line, electronics team, or wire harness manufacturers. Anis underscores the current progress in adaptability while acknowledging, "Right now, we are in a good phase of adaptability when it comes to designing wire harnesses, but there is still room for improvement."

Cross-team collaborations

Collaboration stands at the core of wire harness design as it involves gathering significant insights from various disciplines. As Anis explains, the primary sources of information in this collaborative effort are the electrical and mechanical engineers. Electrical engineers contribute by preparing the schematics, which illustrate the connectivity of wires and signals. At the same time, mechanical engineers are responsible for providing the 3D environment.

To ensure optimal solutions that meet project requirements, frequent communication and feedback between teams is essential to devise the best solutions to specific needs. Occasionally, the firmware team can have an impact on the wire harness through specific requirements that are then incorporated into the design. All of this relies on well-established communication processes within the company or, as Anis puts it, "Communication is always key here."

Connecting it all

Anis' insights into the meticulous approach to wire harness design and manufacturing, attest to the durability and reliability of our harnesses. This robust "nervous system" is the cornerstone of the arculees' consistent performance as an intralogistics solution. Moreover, our well-structured manufacturing documentation and adept change management processes, help to minimise scalability and adaptability challenges.

The core value of cross-team collaboration further enhances the design process, integrating inputs from various disciplines. With the unwavering expertise and dedication of professionals like Anis and the entire arculus team, the arculee's wire harness continues to push the boundaries of innovation, promising a future where the arculees play an even more pivotal role in the evolving robotics landscape.