Challenges in Automotive Wire Harness Assembly

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Automotive manufacturing witnesses the highest deployment of robotic automation. Welding, assembly, machine tending, material removal, part transfer etc. are the assembly operations best suited to robotic automation. However, when it comes to tasks that need judgement and decision making, there is still scope for improvement in the performance of robots. Wire harness is the nervous system of automobiles, consisting of wire and connector assemblies of multiple sizes and shapes. The harness carries various control and power signals between the main control unit, battery and various parts of the automobile. Assembling such cables with connectors requires high levels of skill and is most time -consuming. It involves pairing the cables with appropriate connectors and fixing the complex wiring structure inside the automobile. The task of installing wire harnesses in car bodies has traditionally been difficult for robots. Therefore, multiple approaches such as simplifying the harness architecture and improving the robot’s capabilities are being adopted to solve the complex problems associated with wire harness.

Simplification of the harness architecture

A recent patent publication (US20190217794) on modular wiring harness attracted global attention. The patent application from Tesla claims ease of assembling the wiring harness during vehicle manufacture. The patent also discloses reduction in the total length of wires.

The patent application identifies problems in wire harness and provides solutions as listed below:

Critical issues with existing wire harness	Solutions provided by Tesla
Multiple wiring systems are needed to connect different electrical components to different harnesses.	Packaged subsystems are defined for each assembly so that the number of connections to the main hub is minimized.
Connectors for current harness systems are not so rigid.	Tesla’s application reveals more rigid wiring architecture that is easy for robots to manipulate.
Assembling wire harness is currently done by skilled workers as it is considered to be difficult for automation by robots.	Sub-assemblies reduce wire lengths, enabling assembly by robots.

Tesla’s innovative wiring architecture presented in the patent application is reproduced below.

Top view of an automobile with its wiring system connecting multiple devices to a backbone structure

Tesla has worked on optimizing harness structures as well as creating a new “structural cable” so that robotic arms can handle them with ease. Patent application US20180294075 from Tesla explains a structural cable with multiple collinear wires or conductors formed together to maintain rigidity and integrity. These cables can be handled by robots in automated assemblies.

Tesla’s approach of creating common back-bone type architecture will enable deployment of robotic technology in wire harness assembly. SciTech Patent Art investigated patent and non-patent literature to identify various approaches adopted by other companies to reduce the complexity of wiring architecture in automobiles.

Some interesting technologies identified by SciTech Patent Art include:

Flexible Printed Circuit Boards
In-Vehicle Network
Optimization of circuit body, and
Single line for power and data transmission

Flexible Printed Circuit Boards

Flexible printed circuit (FPC) boards are mostly used in high power applications, but could be considered as an alternative to wire harnesses. A single FPC may include bus bars, power distribution cables, back panels, etc.

Benefits of FPC:

Decreased assembly time
Reduction in materials and number of parts
Increased reliability – reduction of assembly errors
Decreased space, increased air flow
Improved thermal characteristics
Increase in interconnect options

Trackwise, a UK-based manufacturer specializing in products related to printed circuit technology, has employed its technology for temperature and voltage monitoring circuits in EV battery packs. Use of Flexible Printed Circuit Boards can contribute to approximately 75% weight reduction as compared to conventional wiring harnesses.

Trackwise has developed the Improved Harness Technology (IHT) which facilitates manufacturing of flexible printed circuits of any length. Recently, the company manufactured the world’s first and longest FPC of 26 meters which supports control and transmission of power and communication signals without the need for an additional wire harness. Currently, this technology is being employed in space vehicles due to its lightweight benefits, and may be adopted in automotive to attain equivalent benefits.

In-Vehicle Networks

While it is not easy to totally eliminate wiring harness in automobile and aerospace technology, with the advancements in wireless technology, it is possible to wirelessly transmit control signals within an automobile.

Yazaki Corporation, whose core product is automotive wire harness assembly, is working on wirelessly transmitting control signals from the vehicle’s electronic control unit (ECU) to the electronic devices in the extension system. The company was recently awarded a patent (US10122125B2) in which it claimed a vehicle wire harness structure designed to interconnect multiple main devices with communication lines and signal lines. Each system consists of a main device ECU and an auxiliary device wire-connected to the main power line, wherein both the devices communicate wirelessly, thereby reducing additional wiring for communication signals.

In the accompanying figure, each of the electronic devices in the extension system consists of a wireless communication interface. The ECU ensures a wireless communication channel with each of the electronic devices in the extension system enabling bidirectional data communication for the purpose of control.

Optimization Of Circuit Body

In US patent application no. 20190168698A1 (Assignee: Yazaki Corp.), the structure of the circuit body can be simplified while connecting a power source and an electrical component. The number of electric wires constituting the trunk line harness has been reduced by inserting the trunk line harness through a hollow portion of a tubular exterior member (for example, like a grommet for stopping water). This is much easier as compared to a typical wiring in a circuit body.

Sinble Line For Power And Date Transmission

Power-Over-Data-Line (PoDL)

Automobiles have multiple wirings for transmitting data and power separately. The additional cables make the harness heavier and more complex, making it difficult to feed parts of the harness through narrow passageways within vehicles. The technology of Power-over-Data-Line (PoDL) uses the 100Base-T1 and 1000Base-T1 interfaces to supply power parallel to signal on a single unshielded twisted pair.

TE Connectivity, a Switzerland-based designer and manufacturer of connectivity and sensor products is testing PoDL in combination with MATEnet (modular and scalable connectors), and will validate this option within the MATEnet interconnection system. The results so far have been very positive, indicating a beneficial use with up to 48 VDC.

Patent US9419366B2 from TE relates to a socket assembly for combined power and data connector capable of transmitting both data and power. The connector has a first section that carries data signals with data contacts that are capable of carrying currents up to 1 Amp. The second section may be adapted as a power section separated from the data section, with additional power contacts for transmitting power that exceeds PoE limit of data contacts.

Data over Power Lines

In contrast to the above concept, there is enough evidence of data transmission over power lines. “Broadband over Power Lines (BPL)”, a power line communication technology (PLC) in which relatively high speed digital data is transmitted over public electric power distributing wires is already known. There are challenges in implementing the architecture for long-distance transmissions. However, for short distance communications, this technology may be used for reducing complex cabling structures.

YamarElectronics, an Israel-based SME, specializes in technology for communication over noisy DC power lines. It is targeted towards reduction of wires, thereby resulting in reduced cost and weight. Yamar introduced “Automotive Power Line Communication” using the DC- BUS technology, merging data over the power lines using existing CAN and LIN protocols, thus eliminating extra harness. This proposed solution may reduce the length of total harness from 2km to 200 meters.

Yamar’s patent application US20180302187A1 claims a transceiver as well as a method for asynchronous data transfer through noise channels (AC/DC lines). This solution can be employed in vehicles and commercial trucks to reduce additional wiring requirements.

Enhancement of robot’s capabilities

One of the major challenges in automating a wire harness assembly line is the gap in current robotic technology, which is why manual intervention has become necessary for handling certain tasks. In an assembly line, robots face challenges in identifying different wires in the loom and appropriate connectors to complete the assembly. Tasks currently involving skilled labor in the assembly line include:

Installation of terminated wires in various lengths
Running wires and cables through multiple sleeves and conduits
Application of fabric tape near the branch-outs
Binding various cables using tape

The above tasks remain non-automated as human skill is highly required in identifying and assembling delicate cable components with their connectors. A combined skill of sense of touch and vision are highly important to handle such delicate tasks, which has been most difficult task for robots till date.

Flexible Skin

Engineers from the University of Washington and UCLA have developed a new type of sensor named “Skin”, which may be stretched along any part of a robotic structure to give information on shear stress and force that occur while performing tasks. The bio-skin sensor can actually mimic human finger functionality by experiencing tension and compression as it moves or slides along the objects. The flexible electronic skin, which is wrapped around the robot finger, is the first of its kind to measure shear tension similar to that of a human hand. This prosthetic hand is capable of sensing whether it is sliding through an object or holding it with the help of e-Skin made of rubber containing electrically conductive liquid metal. As the tension forces change along the surface of the liquid metal, the electrical potentials change, which indicates certain action performed by the finger. This can assist in sensing very minute forces so that tasks like dismantling an explosive or holding a surgical instrument while handling robotic surgeries might be easier and time saving.

PCT application no. WO2018175662A1, filed by the collaborators, claims a strain gauge sensor on a substrate with multiple conductive pathways. The skin-like sensor is made of liquid metal filled resistive Polydimethylsiloxane (PDMS) microchannel measuring two dimensions of shear force and vibration sensing in the normal and shear force directions.

This recent inventions in Bio sensors such as “Electronic skin” may be adopted in the robotic automation of wire harness assemblies.

Conclusion

Various entities are actively engaged on addressing the challenges related to wire harnesses. It will be interesting to identify innovations in other domains and apply them to solve problems in the automotive harness area. Similarly, technologies used in space vehicle wiring may also be considered for adoption by the automotive industry.

References

Disclaimer:

This document has been created for educational and instructional purposes only
Copyrighted materials used have been specifically acknowledged
We claim the right of fair use as ascertained by the author

AUTHOR

Ms. Geethanjali Potluri

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