Detection system for power equipment

• US 20070199622A1
• Filed: 04/30/2007
• Published: 08/30/2007
• Est. Priority Date: 08/14/2000
• Status: Active Grant

• Current Assignee: Sawstop Holding LLC
• Original Assignee: SD3, LLC
• Inventors: Betts-LaCroix, Jonathan, Jensen, Joel, Gass, Stephen, Schramm, Benjamin, Chamberlain, Robert
• Granted Patent: US 8,079,292 B2
• Time in Patent Office: Days
• US Class Current: 144/426
• CPC Class Codes: B23D 47/025 of tables
• CPC Class Codes: B23D 47/08 of devices for bringing the circular saw blade to the workpiece or removing same therefrom
• 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: B26D 7/24 arranged to disable the operating means for the cutting member
• CPC Class Codes: B27B 13/14 Braking devices specially designed for band sawing machines, e.g. acting after damage of the band saw blade
• CPC Class Codes: B27B 5/38 Devices for braking the circular saw blade or the saw spindle; Devices for damping vibrations of the circular saw blade, e.g. silencing vibration-damping of sawing machines or devices working with circular saw blades B23D47/005
• CPC Class Codes: B27G 19/00 Safety guards or devices specially adapted for wood saws; Auxiliary devices facilitating proper operation of wood saws
• CPC Class Codes: B27G 19/02 for circular saws
• CPC Class Codes: B27G 19/06 for band or strap saws
• 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: F16P 3/14 the means being photocells or other devices sensitive without mechanical contact
• CPC Class Codes: F16P 3/148 using capacitive technology
• CPC Class Codes: G05B 9/02 electric
• CPC Class Codes: Y10S 83/01 Safety devices
• CPC Class Codes: Y10T 83/04 Processes
• CPC Class Codes: Y10T 83/081 With randomly actuated stopping means
• CPC Class Codes: Y10T 83/088 Responsive to tool detector or work-feed-means detector
• CPC Class Codes: Y10T 83/089 Responsive to tool characteristic
• CPC Class Codes: Y10T 83/091 Responsive to work sensing means
• CPC Class Codes: Y10T 83/141 With means to monitor and control operation [e.g., self-regulating means]
• CPC Class Codes: Y10T 83/162 : With control means responsive to replaceable or selectable information program
• CPC Class Codes: Y10T 83/175 : With condition sensor
• CPC Class Codes: Y10T 83/178 : Responsive to work
• CPC Class Codes: Y10T 83/541 : Actuation of tool controlled in response to work-sensing means
• CPC Class Codes: Y10T 83/613 : Work guard
• CPC Class Codes: Y10T 83/7693 : Tool moved relative to work-support during cutting
• CPC Class Codes: Y10T 83/7697 : Tool angularly adjustable relative to work-support
• CPC Class Codes: Y10T 83/7726 : By movement of the tool
• CPC Class Codes: Y10T 83/7734 : With guard for tool
• CPC Class Codes: Y10T 83/7788 : Tool carrier oscillated or rotated
• CPC Class Codes: Y10T 83/85 : Signal; e.g., alarm
• CPC Class Codes: Y10T 83/8773 : Bevel or miter cut

Abstract

Woodworking machines including conductive cutters adapted to cut workpieces, and motors adapted to drive the cutters are disclosed. The machines also include a contact detection system adapted to detect contact between a person and the cutter, and to distinguish contact between the person and the cutter from contact between the workpiece and the cutter. The machines further include a reaction system adapted to cause a predetermined action to take place upon detection of contact between the person and the cutter by the contact detection system.

Claims

1. A woodworking machine adapted to process a workpiece, where the woodworking machine has a location potentially dangerous to a person, the machine comprising:

an electrically conductive sensor positioned at the potentially dangerous location in the machine; and

a contact detection system operably connected to the sensor to receive a signal therefrom, where the signal changes upon contact between the sensor and a person and upon contact between the sensor and the workpiece, and where the contact detection system is configured to differentiate contact with the person from contact with the workpiece based on the rate at which the signal changes.

2. The woodworking machine of claim 1, where the signal received from the sensor is an electrical signal having a voltage amplitude, and where the contact detection system is configured to differentiate contact between the sensor and the person from contact between the sensor and the workpiece based on the rate at which the voltage amplitude of the signal changes.

3. The woodworking machine of claim 2, where the contact detection system is configured to identify a predetermined change in the voltage amplitude that occurs in less than 1 millisecond as resulting from contact between the sensor and the person rather than contact between the sensor and the workpiece.

4. The machine of claim 3, where the contact detection system is configured to identify a change in the voltage amplitude of at least 5% in less than 1 millisecond as resulting from contact between the sensor and the person rather than contact between the sensor and the workpiece.

5. The machine of claim 2, where the contact detection system is configured to identify a predetermined change in the voltage amplitude that occurs in less than 100 microseconds as resulting from contact between the sensor and the person rather than contact between the sensor and the workpiece.

6. The machine of claim 5, where the contact detection system is configured to identify a change in the voltage amplitude of at least 5% in less than 100 microseconds as resulting from contact between the sensor and the person rather than contact between the sensor and the workpiece.

7. The machine of claim 2, where the contact detection system is configured to identify a change in the voltage amplitude of less than 10% over a time period of at least 1 millisecond as resulting from contact between the sensor and the workpiece rather than contact between the sensor and the person.

8. The machine of claim 1, where the sensor takes the form of a movable cutting tool adapted to cut the workpiece.

9. A woodworking machine comprising:

a cutter adapted to cut a workpiece; and

a contact detection system adapted to detect contact between a person and the cutter, the contact detection system including;

an excitation system adapted to supply an electrical signal having a first amplitude and period, the electrical signal being coupled to the cutter to induce a corresponding electrical signal of a second amplitude on the cutter, and

a sensing system adapted to sense the second electrical signal induced onto the cutter, where the sensing system is adapted to detect contact between a person and the cutter based on a change in the sensed second electrical signal over a detection period, where the detection period is between 5 and 150 microseconds and at least twice the period of the first electrical signal.

10. The machine of claim 9, wherein the excitation system is adapted to adjust the first amplitude based on the properties of the second electrical signal sensed by the sensing system.

11. The machine of claim 10, wherein the excitation system is adapted to adjust the first amplitude to attempt to maintain the amplitude of the second electrical signal sensed by the sensing system at a predetermined level.

12. The machine of claim 10, wherein the excitation system is adapted to adjust the first amplitude at an adjustment rate of less than 10% per millisecond.

13. The machine of claim 10, where the sensing system is adapted to detect contact between a person and the cutter when the amplitude of the second electrical signal sensed by the sensing system drops below the predetermined level by a specified amount.

14. A woodworking machine comprising:

a support structure;

a motor supported by the support structure;

a blade assembly including a blade with cutting teeth, where the blade assembly is supported by the support structure and moveable by the motor, and where the blade assembly is electrically isolated from the support structure;

a contact detection system to detect contact between the blade assembly and a person, where the contact detection system includes;

an electrode adjacent the blade assembly to create a capacitive coupling to the blade assembly, where the blade assembly has an apparent capacitance, and

circuitry adapted to detect a pre-selected increase in the apparent capacitance of the blade assembly, where the pre-selected increase in the apparent capacitance of the blade assembly is selected to correspond to the pre-selected increase in the apparent capacitance resulting from conductively coupling a person to the blade assembly so that the pre-selected increase in the apparent capacitance represents contact between the blade assembly and the person;

a brake mechanism adapted to stop the blade by moving into contact with the teeth of the blade upon detection of the pre-selected increase in the apparent capacitance of the blade assembly.

15. The machine of claim 14, where the circuitry is adapted to compensate for any increase in the apparent capacitance of the blade assembly due to contact between the blade and green wood.

16. For use in connection with a woodworking machine having a motor-driven cutting tool, a method of detecting contact between a person and the cutting tool, the method comprising:

imparting an electrical signal onto the cutting tool, where the electrical signal has an alternating voltage amplitude defining plural voltage peaks;

sensing the electrical signal imparted onto the cutting tool; and

detecting contact between a person and the cutting tool by detecting that a predetermined plural number of the voltage peaks of the sensed electrical signal have amplitudes outside a specified range of amplitudes.

17. A woodworking machine having a cutting tool adapted to cut workpieces, the machine comprising:

means for driving the cutting tool;

means for detecting contact between a person and the cutting tool;

means for distinguishing contact between a person and the cutting tool from contact between green wood and the cutting tool; and

means for stopping movement of the cutting tool upon detection of contact between the person and the cutting tool.