SYSTEM FOR SENSING USER CONTACT WITH A SAW BLADE

• US 20040123709A1
• Filed: 12/30/2002
• Published: 07/01/2004
• Est. Priority Date: 12/30/2002
• Status: Abandoned Application

• Current Assignee: Emerson Electric Company
• Original Assignee: Emerson Electric Company
• Inventors: Metzger, James I Jr.
• Application Number:
  US10/248,236
• Publication Number:
  US 20040123709A1
• Time in Patent Office: Days
• US Class Current: 83/76.1
• 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 83/162 With control means responsive to replaceable or selectable information program

Abstract

A sensing system for sensing user contact with a saw blade. The sensing system includes an electrode situated adjacent the saw blade that creates a capacitor in series with the capacitance of the blade to ground to form a first leg of a bridge circuit. A reference capacitor is connected to the first leg to form a second leg of the bridge circuit. A voltage source is coupled to the bridge to selectively energize the-bridge. Contact of the blade by a user is sensed when the bridge is unbalanced due to the increase in the capacitance of the blade to ground caused by the user'"'"'s contact with the blade.

Claims

1. A saw system, comprising:

a frame;

an arbor shaft mounted to the frame to rotate relative thereto;

a blade mounted on the arbor shaft to rotate therewith;

an electrode situated adjacent the blade creating a capacitor in series with the capacitance of the blade to ground to form a first leg of a bridge circuit;

a reference capacitor connected to the first leg to form a second leg of the bridge circuit; and

a voltage source coupled to the bridge;

wherein contact of the blade by a user increases the capacitance of the blade to ground and unbalances the bridge.

2. The saw system of claim 1, wherein the voltage source comprises an oscillator.

3. The saw system of claim 1, wherein the blade and the arbor shaft are electrically isolated from the frame, and wherein the electrode comprises a tubular electrode that receives the arbor shaft.

4. The saw system of claim 1, wherein the electrode comprises an antenna plate situated adjacent the blade.

5. The saw system of claim 4, wherein the blade is electrically isolated from the arbor shaft.

6. The saw system of claim 5, wherein the blade defines an opening therethrough for receiving the arbor shaft, the saw system further comprising:

a first insulating washer situated on one side of the blade, the first insulating washer having a hub received by the opening in the blade; and

a second insulating washer situated on the opposite side of the blade.

7. The saw system of claim 1, wherein the bridge includes a third leg connected to the second leg, and a fourth leg connected to the third and first legs.

8. The saw system of claim 7, wherein the third leg includes a first resistor connected to the second leg, and the fourth leg includes a second resistor connected to the third and first legs.

9. The saw system of claim 8, wherein at least one of the first or second resistors is a variable resistor.

10. The saw system of claim 9, wherein the variable resistor comprises an electronically variable element.

11. The saw system of claim 10, wherein the electronically variable element comprises a field effect transistor.

12. The saw system of claim 7, wherein the third leg includes a first capacitor connected to the second leg, and the fourth leg includes a second capacitor connected to the third and first legs.

13. The saw system of claim 12, wherein at least one of the first or second capacitors is a variable capacitor.

14. The saw system of claim 13, wherein the variable capacitor comprises an electronically variable element.

15. The saw system of claim 14, wherein the electronically variable element comprises a varactor.

16. A sensing system for sensing user contact with a saw blade, the saw blade being mounted to an arbor shaft, the sensing system comprising:

an electrode situated adjacent the blade creating a capacitor in series with the capacitance of the blade to ground to form a first leg of a bridge circuit;

a reference capacitor connected to the first leg to form a second leg of the bridge circuit; and

a voltage source coupled to the bridge;

wherein contact of the blade by a user increases the capacitance of the blade to ground and unbalances the bridge.

17. The sensing system of claim 16, wherein the voltage source comprises an oscillator.

18. The sensing system of claim 16, wherein the arbor shaft is electrically isolated from a frame of the saw, and wherein the electrode comprises a tubular electrode that receives the arbor shaft.

19. The sensing system of claim 16, wherein the electrode comprises an antenna plate situated adjacent the blade.

20. The sensing system of claim 19, wherein the blade is electrically isolated from the arbor shaft.

21. The sensing system of claim 16, wherein the bridge includes a third leg connected to the second leg, and a fourth leg connected to the third and-first legs.

22. The sensing system of claim 22, wherein the third leg includes a first resistor connected to the second leg, and the fourth leg includes a second resistor connected to the third and first legs.

24. The sensing system of claim 22, wherein the third leg includes a first capacitor connected to the second leg, and the fourth leg includes a second capacitor connected to the third and first legs.

23. The sensing system of claim 23, wherein at least one of the first or second resistors is a variable resistor.

25. The sensing system of claim 25, wherein at least one of the first or second capacitors is a variable capacitor.

26. A sensing system for sensing user contact with a saw blade, the saw blade being mounted to an arbor shaft that is electrically isolated from a frame of the saw, the sensing system comprising:

means for forming a capacitor in series with the capacitance of the blade to ground to form a first leg of a bridge circuit;

a reference capacitor connected to the first leg to form a second leg of the bridge circuit;

a third leg connected to the second leg of the bridge circuit;

a fourth leg connected to the third and first legs of the bridge circuit; and

means for energizing the bridge circuit;

wherein contact of the blade by a user increases the capacitance of the blade to ground and unbalances the bridge.