Electronic two-hand safety system for power tools

US4493377A · kind A · utility

Assignee

• Robert Bosch GmbH · DE

Inventors

• Klaus Gunther · Voerde, DE
• Friedrich Hornung · Stuttgart, DE
• Kurt Paule
• Fritz Schadlich · Echterdingen, DE

Key dates

• Filing date: Oct 22, 1981
• Grant date: Jan 15, 1985
• Expiry date: Oct 22, 2001

Classification

• Technology area (CPC F): Mechanical Engineering; Lighting; Heating
• CPC primary: F16P3/20
• WIPO field: Mechanical elements
• WIPO sector: Mechanical engineering

Abstract

To permit operation of the power tool only if both hands of an operator are engaged, the tool is formed with a handle portion which has a sensing surface thereon, electrically coupled to a current flow sensing circuit, preferably including an opto-coupler or a field-effect transistor (FET) circuit which permits firing of a triac, thyristor, or the like only if current flows over the sensing surface by area contact therewith. The sensing surface is energized, preferably, from a resistive or capacitative voltage divider; the capacitative voltage divider has the advantage that the triac firing circuit can cause the triac to fire during null or zero crossings of ac supplied power. If a locking-type switch is used, two handles or touch-areas are needed; if a spring-loaded switch is provided, it can function as one safety element, and a touch-area sensing surface as the other.