Zero-force pushbutton controls are untouchable

Accidental operation of pushbuttons is almost eliminated by a new type of hand-operated control that does not need to be pushed.

The "Zero-Force" button, developed by Rockwell Automation, uses a field effect technology to sense the presence of an operator`s hand. It is said to be almost impossible for items such as rags, tools or running water to trigger the button falsely. The buttons are also designed to minimise the risk of carpal tunnel syndrome or other disorders associated with repeated physical tasks such as button-pushing.

Because the sensors have a hand-shaped contoured surface, there is no need for operators to rotate their hands or to use one finger as happens with conventional pushbuttons. Rockwell claims it is the first supplier to adopt field effect sensing in this way. Although other force-free technologies are available - notably photoelectric and capacitive sensing - they are prone to false triggering by tools, shirtsleeves or other objects.

The field effect system consists of a positively charged sensor pad surrounded by a negatively charged ring. An electric field is generated between the two. When an operator places their hand over the pad, the field is disturbed. This is sensed and converted into an electrical output by the button`s microprocessor control. Two independent sensors must be activated within 0.2s of each other, helping the sensor to distinguish between human touch and most foreign objects.

The buttons incorporate diagnostic circuitry which shuts them down if it senses something is amiss. This circuitry also protects against accidental contact during power-up, and the build-up of conductive materials on the surface of the button.