Contrinex’s ‘Frog-head’ fibre-optic array keeps hand-brake cable production running

Contrinex’s fibre-optic sensors, available from PLUS Automation, are trusted to detect breakages in the manufacturer of steel cable used in automotive parking-brake systems. The cable is formed from multiple strands of steel wire being twisted together. There is potential during manufacture for the cable to break which can damage equipment and pose a risk to employees.

A fibre-optic multi-beam array sensor detects the presence of the wire, whilst it is free to move up and down, and left and right within the sensor’s detection field. When the cable is not detected by the sensor, for example when the cable breaks, the manufacturing process is stopped.

Customer application

The ‘handbrake cable’ used in automotive parking-brake systems 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 work-stations 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.

Customer solution

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.

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