Hand controls send a signal to the control module to start the machine cycle when they are actuated. The way this signal is sent and interpreted depends on the type of hand control.
Early two-hand control designs relied on relay logic to connect power to the machine drive motors when the mechanical buttons were pushed or held down. These circuits were not able to detect and respond to failures in the system.
Newer two-hand controls incorporate redundant forced-guided contacts
. These newer systems also include a self-checking
function requires that both devices are activated simultaneously
, within .5 seconds.
Self-checking touch buttons (STBs) are the next generation of optical hand controls. They use an infrared
light beam to sense the presence of a hand or finger.