Safety control circuit for electrically operated machine - requires operator to press two pushbuttons simultaneously to complete circuit, and has series capacitors in timing circuits

A control and safety circuit for an electrically operated machine requires the operator to press a button simultaneously with each hand. This protects the operator from wounding by preventing him from placing his hand in the danger area. Two spring loaded push buttons (M1, M2) are required to be kept pressed by an operator in order to make their circuits. This causes a voltage supply (14) to be connected to relay circuits (A, B) in which series capacitors (15, 22) are charged to form timing circuits. Resistors (18, 23) provide discharge paths for the capacitors when the buttons are released. Diodes (20, 24) one in parallel with each relay protect the switch contacts. Second contact pairs on the button switches are connected to an electromagnetic relay (S) which is in series with a contact (FC) on a probe which signals end of travel of a moving part on the controlled machine. Dispositif de commande et de sécurité qui assure la protection des mains du conducteur d'une machine comportant une partie mobile dangereuse. Des moyens de temporisation électrique sont activés par les deux boutons-poussoir M1 et M2 quand le laps de temps écoulé entre les instants d'enfoncement de ces boutons dépasse un temps prédéterminé. Par activation de ceux-ci un circuit de commutation est alimenté qui commande alors les organes de mise en service de la partie mobile. Application : machine à partie mobile mue par des moyens hydrauliques, pneumatiques ou électriques.