Machine Design

Magnetic sensors beat limit switches for positioning screw jacks

Nook Industries

A magnetic sensor turned out to be a useful replacement for a simple limit switch that prevented overtravel in screw jacks.

ActionJacs made by Nook Industries in Cleveland, Ohio, once incorporated heavyduty bolt-on limit switches as a means of keeping the worm-gear-driven jacks from being driven too far. Recently, the company replaced the switches with magnetostrictive sensors which detect ring magnets fixed to the translating screw to note its position. The sensors, along with a patented electronic detection circuit, make up what’s called the Nook Sensor System.

Sensors on the NSS are manufactured using polypropylene overmolding which also seals them. The sensors slide into a profile on the side of the screw housing. If need be, several can be positioned in the profile for sensing the screw as it passes various points in its housing. This permits such actions as slowing the screw as it nears an end point.

The small magnetostrictive sensors, measuring 28-mm long, are made by Turck in Minneapolis. The sensors come with a quick-mount tab that helps seat them in the cylinder’s groove for easy single-handed mounting. Operators tighten a screw to keep the sensor in place.

© 2013 Penton Media, Inc.

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