Fibre-optic array keeps handbrake cable production running

When a manufacturer of steel cable used in automotive parking-brake systems needed a reliable system to detect cable breakages during the manufacturing process, it turned to Contrinex.

The ‘handbrake cable’ is made from strands of steel wire which are twisted together, to form a 3mm diameter cable. This continuous manufacturing process passes the wire between successive workstations in an unbroken length. Between operations, the cable is largely unsupported, assuming the form of a suspended catenary.

Occasionally, a manufacturing defect can cause the cable to break, which can compromise operator safety, and unless the processing is halted, the equipment can be damaged. A sensor system must detect the presence of the cable as it passes from one operation to the next, interrupting the production process if it breaks.

Because the cable is unsupported, its path is unpredictable and its exact position at any time, particularly in the vertical plane, is unknown. The sensor system must therefore detect the presence of the cable reliably at any point within an envelope 90mm high and 20mm wide.

The solution was a fibre-optic multi beam array sensor to detect the presence of the wire, which is free to move both up and down, and left and right within the detection field. The Contrinex photoelectric sensor system comprises a DIN-rail-mounted fibre-optic amplifier coupled with a multi-beam diffuse sensing head, which has a shape reminiscent of a frog's head.

The system’s maximum switching frequencies of 4,000 Hz and the sensing distance of up to 150mm makes the multi-beam fibre-optic sensors ideal for detecting fast-moving targets. The PBTP body of the sensing head provides excellent mechanical protection for life in a production environment.

The multi-beam sensor’s 28mm-wide sensing face provides a detection envelope that comfortably accommodates this application’s 90mm x 20mm requirement. Initial set-up is accomplished by a manual teach function using the integral signal-strength LCD on the amplifier, following which the system operates without manual intervention.

A 2m-long fibre cable enables the fibre-optic amplifier to be positioned remotely and connect to the automation control system via an industry-standard PNP and M8 cable connection. This allows easy removal and replacement if ever necessary.

The system tolerates high ambient-light conditions and detection of a broken cable is both highly reliable and immediate. If the cable breaks, the system interrupts the manufacturing process and sounds an alarm, alerting the operator. Downtime arising from broken cables has been virtually eliminated since the system has been operational.