Detection systems for power equipment

• US 20090210072A1
• Filed: 01/26/2009
• Published: 08/20/2009
• Est. Priority Date: 04/15/2005
• Status: Active Grant

• Current Assignee: Sawstop Holding LLC
• Original Assignee: SD3, LLC
• Inventors: Gass, Stephen F., Lingane, Paul J., Karunaratne, Arjuna R.
• Granted Patent: US 7,707,918 B2
• Time in Patent Office: Days
• US Class Current: 700/10
• CPC Class Codes: B23D 59/001 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 Class Codes: F16P 3/12 with means, e.g. feelers, which in case of the presence of a body part of a person in or near the danger zone influence the control or operation of the machine F16P3/08 takes precedence
• CPC Class Codes: Y10T 83/081 With randomly actuated stopping means
• CPC Class Codes: Y10T 83/089 Responsive to tool characteristic
• CPC Class Codes: Y10T 83/159 Including means to compensate tool speed for work-feed variations
• CPC Class Codes: Y10T 83/7684 With means to support work relative to tool[s]
• CPC Class Codes: Y10T 83/7697 Tool angularly adjustable relative to work-support
• CPC Class Codes: Y10T 83/773 Work-support includes passageway for tool [e.g., slotted table]

Abstract

Improved methods to detect when a human body contacts a predetermined portion of a machine are disclosed. The methods distinguish contact with a person from contact with other materials. The methods are particularly applicable in woodworking equipment such as table saws to distinguish contact between a person and the blade of the saw from contact between the blade and wet or green wood.

Claims

1. A power tool, comprising:

a motor;

an operative element driven by the motor;

a safety system configured to detect a dangerous condition between a user and the operative element and take some action to reduce the danger to the user in the event a dangerous condition is detected, where the safety system includes an actuator that is triggered at least in part by energy stored in an energy storage device, where the energy available to trigger the actuator is dependant on the temperature of the energy storage device, the safety system further including a temperature sensor to detect the temperature of the energy storage device, where the safety system is configured to block operation of the motor if the temperature is below a first predetermined threshold.

2. The power tool of claim 1, wherein the safety system further includes a heating system to raise the temperature of the energy storage device.

3. The power tool of claim 2, wherein the heating system includes a resistor thermally coupled to the energy storage device.

4. The power tool of claim 2, wherein the safety system is configured to activate the heating system if the temperature is below the first predetermined threshold.

5. A method of detecting a dangerous condition between a user and an operative element of a power tool:

providing a detection system adapted to detect a dangerous condition between a user and the operative element of a power tool, where the detection is at least partially dependent on changes in the value of an electrical property sensed by the detection system;

calibrating the detection system by establishing a nominal value for the electrical property when no dangerous condition is present;

determining a current value of the electrical property when the operative element of the power tool is not operating;

blocking operation of the operative element of the power tool if the current value is outside a predetermined range.

6. The method of claim 5, further comprising the steps of repeating the step of determining a current value and adjusting the value of nominal value based at least in part on the determined current values.

7. The method of claim 6, where the step of adjusting is asymmetric relative to the determined current values.