BROKEN TOOL DETECTOR

• US 3,728,919 A
• Filed: 11/15/1971
• Issued: 04/24/1973
• Est. Priority Date: 11/15/1971
• Status: Expired due to Term

• Current Assignee: William B. Scott
• Original Assignee: William B. Scott
• Inventors: Scott, William B.
• Primary Examiner(s): Juhasz, Andrew R.
• Application Number:
  US05/198,689
• Time in Patent Office: 526 Days
• Field of Search: 83/62,686 408/6 175/39
• US Class Current: 83/62
• CPC Class Codes: B21D 55/00 Safety devices protecting the machine or the operator, specially adapted for apparatus or machines dealt with in this subclass for presses in general B30B; safety devices in general F16P
• CPC Class Codes: B30B 15/28 Arrangements for preventing distortion of, or damage to, presses or parts thereof
• CPC Class Codes: F16P 5/00 Emergency means for rendering ineffective a coupling conveying reciprocating movement if the motion of the driven part is prematurely resisted
• CPC Class Codes: Y10T 408/14 Responsive to condition of Tool or tool-drive
• CPC Class Codes: Y10T 83/088 Responsive to tool detector or work-feed-means detector
• CPC Class Codes: Y10T 83/9428 Shear-type male tool

Abstract

A portion of a pneumatic circuit for sensing the breakage of a punch is formed by a normally closed passageway in the punch itself. If the punch is broken, the passageway is opened up and pressurized air in the circuit is vented to the atmosphere through the passageway. A pressure differential switch in the circuit senses the resulting pressure change and, in response thereto, produces an electric signal to indicate breakage of the tool.

Claims

1. In a machine tool for performing work on a workpiece, the combination of, a tool carrier reciprocable toward and away from the workpiece, a tool having a first end mountable on the carrier for movement therewith and having a second end for performing work on the workpiece when said carrier is reciprocated, a passageway formed in said tool and terminating adjacent the second end of the tool, means for pressurizing said passageway with air to a preselected pressure, and means responsive to changes in said pressure resulting from breakage of the tool and venting of the terminal end of the passageway to produce a signal indicating the breakage.

2. A punch press having a ram reciprocable upwardly and downwardly relative to an underlying workpiece, a punch carried on the lower end of the ram for punching a hole in said workpiece during the downstroke of the ram, the improvement in said press comprising, a pneumatic circuit having a passage extending axially of said ram and opening out of the lower end thereof, a passageway extending from the upper end of said punch toward the lower end portion thereof and terminating within the punch in said lower end portion, the upper end of said passageway communicating with the lower end of said passage, means for introducing pressurized air into said passage to pressurize said passageway to a preselected pressure, and means for producing a signal in response to changes in said pressure resulting from breakage of the punch and venting of the lower end of said passageway.

3. A punch press as defined by claim 2 wherein said signal producing means includes a pressure sensitive switch responsive to the pressure between said passageway and said pressurization means and operable to produce an electrical signal as an incident to such pressure dropping below a preselected level.

4. A punch press as defined by claim 3 wherein said circuit includes an adjustable restriction located between and communicating with said pressurization means and said passage, said pressure sensitive switch being a pressure differential switch located between and communicating with said pressurization means and said passage and connected in parallel across said restriction so as to be responsive to changes in the differential pressure on opposite sides of the restriction.

5. A punch press having a ram reciprocable upwardly and downwardly in successive automatic cycles relative to an underlying workpiece, a punch carried on the lower end of the ram for punching a hole in the workpiece during the downstroke of the ram, said punch having an elongated body with an upper head and a lower punching surface, the improvement in said press comprising, a pneumatic circuit having a passage extending axially through said ram and opening out the lower end thereof, a small hole drilled through the head of said punch, extending axially within said body and having a closed lower end spaced just upwardly from the lower punching surface of the punch, said hole communicating with said passage forming a portion of said circuit so that the circuit will be vented to the atmosphere when the lower end portion of the punch is broken to open up the lower end of said hole, means for normally pressurizing the circuit to a preselected pressure different than atmospheric pressure so that the pressure in the circuit will change when the circuit is vented to the atmosphere upon breaking of said punch, and means operable in response to such change in the pressure of the circuit to terminate automatic cycling of the ram.