The present invention relates generally to an apparatus and a method for automatically, circumferentially wrapping articles which extend in the axial direction, in particular cables or cable looms, as used, for example, in the automotive industry as a cable harness. The invention particularly relates to a fastening element, which is used for automatic, circumferential wrapping purposes.
Cable harnesses are frequently used in automobile construction. A cable harness is a loom of cables which transmit signals or information or operating currents (energy). The cables are combined, for example, by clips, cable binders or tubes. Modern motor vehicles may have electrical wires which, in total, can reach a distance of several kilometers.
The cables of the loom are combined to form a cable harness and are interlocked, that is to say assembled, on a special workbench (wrapping area) or on a nail board (modeling board). A harness of this type has only a limited degree of flexibility and can then be installed. Cable harnesses are generally assembled in accordance with geometric and electrical requirements. In spite of advances in automation, cable harnesses continue to be largely manually produced in the vehicle industry. One of the reasons for this is the many different movement sequences involved: for example threading wires into tubes; wrapping with fabric tape, in particular on branches of wire sections, fitting contacts to the wire, in particular for so-called twin-lead terminals (two wires on one contact); inserting tubes one into the other; or fixing looms with tapes, clips or cable binders.
These movement sequences are obviously difficult to automate. To date, it has been possible to use machines only to a limited extent. However, corresponding actions can also be learnt quickly with little occupational skill. Therefore, manual production is, as before, more cost-effective than automation. Therefore, cable harnesses are usually produced abroad, in particular in low-wage countries.
In different vehicles, for example in heavy goods vehicles, there is also a large variety of variants which is a result of various configurations and vehicle lengths, so that only very small batch sizes (up to 1) can be achieved. Nevertheless, different variants are produced on the same modeling boards. Humans have the advantage over machines specifically in this case, since humans can adapt to different variants in a short time without “reprogramming”.
However, prefabrication can be partially automated. This relates, inter alia, to: cutting individual wires (cutting machines); fitting contacts to one or both sides of a wire, partially equipping the connector housing with pre-contacted wires, welding a plurality of wire ends (welding machine); or twisting wires.
However, a manual production process has the disadvantages of a higher expected error rate and greater outlay on quality assurance.
Conventional, manually assembled cable harnesses are delivered to automobile manufacturers and inserted into vehicles during final assembly. The additional problem of how to fix cable harnesses in the motor vehicle arises here. Documents DE 295 10 148 and DE 103 49 046 disclose plastic fastening elements. However, these fastening elements have to be manually fitted to the cable harness. This requires exact manual positioning on the cable harness both axially and circumferentially.
U.S. Pat. No. 4,265,687, U.S. Pat. No. 4,368,762 and U.S. Pat. No. 4,371,010 describe initial approaches to partially automated solutions. However, these devices have the disadvantage that they are too heavy and too bulky. In the course of developments in the field of microelectronics, the requirement for more compact and reliable binding devices has therefore increased. U.S. Pat. No. 4,265,687 (mentioned above) describes an exemplary binding device. In the case of this tool, a movable guide element is provided which, in a first position, can accommodate a cable bundle in the wrapping region and, in a second position, surrounds the cable bundle, so that a wrapping tape can be guided around the cable bundle. The wrapping tape is ultrasonically welded to the cable bundle. A sonotrode with a pincer-like anvil is used for this purpose. The pincers of the anvil are each L-shaped and protrude into the cable bundle, around which the wrapping tape is wrapped, during the welding process. A similar problem is described in document DE 34 13 099 C2. The wires of the harness may be unintentionally welded together during the welding process. Furthermore, the L-shaped mating pieces leave behind an air gap after being withdrawn from the cable bundle after a welding process has taken place, so that the previously tightened wires may, under certain circumstances, become slack again.