Protective redundant subsystem for power tools

• Main Authors: FORSTER, MICHAEL K, GORTI, BHANUPRASAD V, MCCORMICK, GARRETT P, ALBERT, LARRY T, WOODS, SAMUEL G, LEH, JASON K, VANKO, JOHN C, BEERS, DAVID
• Format: Patent
• Language: English; French; German
• Published: 09.03.2011
• Subjects: COMBINATION OR MULTI-PURPOSE TOOLS NOT OTHERWISE PROVIDEDFOR; CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORSOR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER; DETAILS OR COMPONENTS OF PORTABLE POWER-DRIVEN TOOLS NOTPARTICULARLY RELATED TO THE OPERATIONS PERFORMED AND NOTOTHERWISE PROVIDED FOR; ELECTRICITY; GENERATION; HAND TOOLS; MANIPULATORS; PERFORMING OPERATIONS; PORTABLE POWER-DRIVEN TOOLS; TRANSPORTING

A protective redundancy circuit is provided for a power tool having an electric motor (14). The protective redundant subsystem is comprised of: a motor switch (16) coupled in series with the motor (14); a motor control module (18) that controls the switching operation of the motor switch (16); and a protective control module (22) that monitors switching operation of the motor switch (16) and disables the power tool when the switching operation of the motor switch (16) fails. In the context of an AC powered tool, the switching operation of the motor switch (16) is correlated to and synchronized to the waveform of the AC input signal. During each cycle or half cycle, the motor control module (18) introduces a delay period before closing the motor switch (16) and the protective control module (22) determines the operational status of the motor switch (16) by measuring the voltage across the motor switch (16) during the delay period.