Capacitive sensing system for power cutting tool
AssigneePower Tool Institute
InventorsDavid C. Shafer, Jean-Pierre Krauer
Life of this patent
Estimating the term…
Abstract
A capacitive sensing system for use with a power cutting tool of the type which has an exposed, moveable blade adjacent a work surface is disclosed. The sensing system drives an excitation voltage onto the exposed blade and monitors the current drawn from the blade, detects changes in the amplitude and phase and analyzes the characteristics of the changes to selectively trigger a reaction system.
Claims24
A system for sensing contact between an object and a movable blade of a power cutting tool comprising:
- a drive signal source for generating a drive signal;
- an excitation plate in communication with the drive signal source for capacitively coupling the drive signal to the movable blade;
- a current sensing element coupled to the excitation plate for generating a current sense signal indicative of the instantaneous current drawn by the movable blade;
- and
- a processor in communication with the current sensing element for detecting a condition indicative of contact between the object and the movable blade based on variations in both an in-phase current component signal and a quadrature current component signal, wherein the in-phase current component signal and the quadrature current component signal are generated from the current sense signal.
A system for sensing contact between a portion of a user's body and a movable blade of power cutting tool comprising:
- a drive signal source for generating a drive signal;
- an excitation plate in communication with the drive signal source for capacitively coupling the drive signal to the movable blade;
- a current sensing element coupled to the excitation plate for generating a current sense signal indicative of the instantaneous current drawn by the movable blade;
- an I/Q decomposition module in communication with the current sensing element that generates from the current sense signal an in-phase current component signal and a quadrature current component signal;
- and
- a signal variation detection module in communication with the I/Q decomposition module that detects the condition indicative of contact between the portion of the user's body and the movable blade based on variations in both the in-phase current component signal and the quadrature current component signal.
A power cutting tool comprising:
- a movable blade;
- a table having an opening, wherein the movable blade is disposed in the opening such that a portion of the movable blade projects above the table;
- and
- a capacitive sensing system that senses contact between an object and the movable blade comprising:
- a drive signal source comprising an oscillator for generating a drive signal;
- a excitation plate in communication with the drive signal source for capacitively coupling the drive signal to the movable blade;
- a current sensing element coupled to the excitation plate for generating a current sense signal indicative of the instantaneous current drawn by the movable blade;
- and
- a processor in communication with the current sensing element for detecting a condition indicative of contact between the object and the movable blade based on variations in both an in-phase current component signal and a quadrature current component signal, wherein the in-phase current component signal and the quadrature current component signal are generated from the current sense signal.
A method for sensing contact between an object and a movable blade of a power cutting tool, the method comprising:
- capacitively coupling a drive signal from an excitation plate to the movable blade;
- generating a current sense signal indicative of the instantaneous current drawn by the movable blade;
- generating from the current sense signal an in-phase current component and a quadrature current component, wherein the in-phase current component is in phase with the drive signal and the quadrature current component signal is in quadrature with the drive signal;
- and
- detecting a condition indicative of contact between the object and the movable blade based on variations in both the in-phase current component signal of the current sense signal and the quadrature current component signal of the current sense signal.
Dependencies are inferred from the claim text.