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Schleuniger of Switzerland claims that its POF-processing equipment enables manufacturers to produce high-throughput cable assemblies for in-car communication networks.
These days, plastic optical fibre (POF) is becoming a must-have option for networking applications in high-end vehicles. It's not uncommon to find 10-20 electrical devices hooked up within a car, including radios, CD and DVD players, navigation systems, Bluetooth interfaces, telephones, voice-recognition systems, video-gaming consoles and TV tuners.
The benefits for the automobile manufacturers are clear: POF offers a high operating bandwidth, increased transmission security, low weight, immunity to electromagnetic interference, and ease of handing and installation. Crucially, it's also a low-cost option, with both the fibre itself and the associated components coming in at a fraction of the cost of their pure-silica counterparts.
But as in-car networks become more complex, there's mounting pressure on manufacturers of cable harnesses to deliver high-quality cable assemblies with minimal fibre attenuation and at low cost. Schleuniger, a Swiss manufacturer of cable production equipment, claims that its latest POF-processing techniques - circular sawing, end finishing with a diamond tool and laser welding of ferrules - can help cable vendors meet these expectations.
Tami Freeman talked to Leo Bühler, Schleuniger's director of innovation, to find out more about the company's POF Finisher 20 and POF Terminator 30 machines.
TF: What are the key issues facing the manufacturers of POF-cable assemblies?
LB: The main challenge when processing POF cables is to keep the optical attenuation as low as possible. In other words, at each processing step, the loss should not be changed and by no means should it be increased. The first step is cutting the fibre, which is usually done using conventional blades or saws. This leads to an end-surface that appears at first glance to be smooth and free of cracks. But when it's examined with a microscope, small cracks and disruptions are seen. These are the result of the crushing forces during the cutting process.
Leo Bühler: "Schleuniger's main customers are wire-harness makers and automobile manufacturers that have production sites in Eastern Europe."
How does Schleuniger's POF Finisher 20 machine enable such defects to be avoided?
It uses a circular saw blade instead of conventional cutting blades; this avoids the negative crushing forces. The end-face of a POF fibre cut by a circular saw has a clean, square and extremely smooth surface. Because of this, its attenuation values are reduced significantly compared with cables that have been cut by other methods. The results are highly repeatable from fibre to fibre and the circular saw also increases the lifetime of the stripping tools.
For cables that are cut with other blades or saws, a similar result can only be achieved by subsequent hand polishing. But this is a time-consuming alternative that doesn't necessarily deliver the same quality. What's more, manual processing is approximately three times as expensive.
Are there any other ways to improve the quality of the fibre end-face?
Schleuniger's manufacturing equipment also offers additional treatment by a high-speed diamond finishing tool. This makes the fibre end-face even smoother after cutting, thus reducing attenuation values further.
Once the fibres are prepared, what's the best way to attach a connector ferrule?
POF cables can be terminated using a variety of different connector systems. For in-car communications, the European automotive industry uses the MOST [Media Oriented Systems Transport] protocol. MOST connectors are available in a plastic version that can be attached to a POF cable by gluing, crimping, ultrasound welding or welding with lasers.
Schleuniger's POF Terminator 30 machine uses laser welding to attach MOST ferrules. What are the benefits of this technique?
One advantage of laser welding is that no additional material is required - the plastic is simply melted together. A beam from a laser diode is guided through the ferrule and focused at the interface between the ferrule and the outer cable jacket. The cable jacket is black, so it absorbs the laser's energy, produces heat and plasticizes it instantly. Since the ferrule is in direct contact with the cable jacket, the ferrule surface also plasticizes, resulting in both components being welded together. This process produces high-quality, consistent terminations with a short cycle time (in the range of milliseconds).
How do you see the demand for POF cables progressing?
The market for POF cables will only grow. The demand for data transport is continually increasing and this can only be satisfied with optical technology. Within future automobiles, for example, the use of real-time, high-quality camera systems instead of wing mirrors would result in a large amount of data, which again can only be handled using optical fibre.
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