Control input device with two magnetic sensors for fail-safe sensing

A control input device (such as a joystick) has a movable magnet 13 positioned within a magnetically permeable pole-piece frame. The pole-piece frame has collector plates 18A-D, arms 19A-D, and gaps 21A-D formed between flanges 20A-D, the gaps each accommodating at least two magnetic flux sensors 22 for detecting the angular position of the device with respect to the frame. The sensors 22 are placed centrally within the flanges 20A-D to avoid distorted flux near the plate edges. Hall-effect sensors may be used. Differences in the sensor outputs above a predetermined threshold (to allow for manufacturing tolerances) are monitored so that if a sensor fails or corrupts in a safety critical application the device can be disabled in a fail-safe manner. The frame can be square or round (fig 3), and may have planar magnetic shield/collector plates (180A-D, fig 3) between the frame and the magnet. The magnet may within a ball mounting of the joystick.