Fail-safe control input device having a movable magnet and at least three magnetic flux sensors with system to detect input device fault

摘要

A control system has a control input device, such as a joystick, with a movable magnet 13 and a pole-piece frame 18, 19, 20 positioned about the magnet for influencing the flux lines of the magnet. Three or more magnetic flux sensors 22A, 22B, 22C are positioned in said pole-piece frame for sensing movement of the magnet. The magnetic flux sensors (e.g. Hall effect sensors) are equally spaced 120{ apart around the magnet and the output signal of each of the sensors is monitored enabling a process to be implemented dependent upon the monitored signals of the sensors. The process may be control input or a fail-safe process. In order to detect a fault, the outputs of the magnetic flux sensors may be added together to generate a check value to facilitate a fail-safe process. If the check value exceeds zero, or exceeds zero by more than a pre-determined threshold, a signal for implementing a fail-safe process is generated. The control input device is suitable for safety critical use in applications such as wheelchairs, forklift trucks and other human carrying vehicles and for the control of machines such as cranes, robots, etc.