System and method for reducing false positive detection between a human and a moving implement in a power tool

Patent metadata

Field	Value
Publication number	US-9702916-B2
Application number	US-201313827286-A
Country	US
Kind code	B2
Filing date	Mar 14, 2013
Priority date	Sep 28, 2012
Publication date	Jul 11, 2017
Grant date	Jul 11, 2017

Abstract

A method for detection of false positive condition that an object is in contact with an implement in a power tool includes sampling an electrical signal received from the implement, identifying in-phase and a quadrature components of the sampled electrical signal, identifying a magnitude of each of the samples with reference to the in-phase component and the quadrature component for the samples, detecting an object approaching the implement with reference to the plurality of samples, identifying a signal-to-noise ratio for the samples, and identifying a false positive condition for the detected object with reference to the identified signal-to-noise ratio for the identified samples.

First claim

What is claimed:

1. A power tool comprising:
an actuator configured to move an implement;
a clock source configured to generate a time varying electrical signal that passes through the implement; and
a controller operatively connected to the actuator and configured to sample the electrical signal, the controller being configured to:
activate the actuator to move the implement;
sample the electrical signal received from the implement to generate a plurality of samples of the electrical signal;
identify an in-phase component and a quadrature component of each sample of the electrical signal;
identify a magnitude of each sample of the electrical signal with reference to the in-phase component and the quadrature component for each sample of the electrical signal;
detect an object approaching the implement with reference to a transient spike in the magnitude of at least one of the plurality of samples;
identify a signal-to-noise ratio for the electrical signal with reference to the identified magnitude for each of the plurality of samples of the electrical signal;
continue to enable the actuator to move the implement in response to the detection of the object approaching the implement and identifying a false positive condition for the detected object in response to the identified signal-to-noise ratio for the plurality of samples of the electrical signal being less than a threshold corresponding to signal-to-noise ratios for false positive conditions; and
deactivate the actuator only in response to the detection of the object approaching the implement and to the identified signal-to-noise ratio for the plurality of samples of the electrical signal being greater than the threshold corresponding to signal-to-noise ratios for false positive conditions.

2. The power tool of claim 1 , the controller being further configured to:
identify a mean for the plurality of samples of the electrical signal with reference to the identified magnitude for each sample in the plurality of samples in the electrical signal;
identify a standard deviation for the plurality of samples of the electrical signal with reference to the identified mean for the plurality of samples of the electrical signal and the identified magnitude for each sample in the plurality of samples in the electrical signal; and
identify the signal-to-noise ratio as being the identified mean divided by the standard deviation.

3. The power tool of claim 1 wherein the predetermined threshold for the identified signal-to-noise ratio is −6 decibels (dB).

Assignees

• Bosch Tool Corp
• Bosch Gmbh Robert

Inventors

• Ramaswamy Bharadwaja Maharshi
• Mangapuram Sai Yogesh Kumar
• Krishnarao Niranjan Sathyanarayanarao
• Srikantiah Vishwanatha Manevarthe

Classifications

• B27G19/008

  with sensing of human contact or proximity with the blade · CPC title

• B23D59/001 Primary

  Measuring or control devices, e.g. for automatic control of work feed pressure on band saw blade (measuring in general G01; controlling in general G05) · CPC title

• B23Q11/0082

  by determining whether the operator is in a dangerous position (B23Q17/2438 takes precedence) · CPC title

• G01R29/26 Primary

  Measuring noise figure; Measuring signal-to-noise ratio · CPC title

• Y10T83/178

  Responsive to work · CPC title