Patent GB-1340680-A (GB)
Title: Broken tool detection
IPC: B23B49/00
Filed: 1970-12-31
Abstract: 1340680 Broken tool detector H E ROHRAFF SNR 31 Dec 1970 [2 Jan 1970 14 Sept 1970] 61991/70 Headings B3B and B3C Means for detecting breakage of a tool 20 in a machine tool comprises a body 21 adapted to be attached to a bush plate 17, a valving member 31 in the body, and a feeler 33 movably supported by and projecting from the block and operatively connected to the valving member, the feeler being biased toward a portion of the tool whereby in the event said portion of the tool is absent due to breakage, said feeler and valving member are movable to a detecting position not otherwise obtainable. In normal operating work cycles, tool 20 reciprocates in guide bush 24 and in an anti-deflection bush 38 carried by an extension 28<SP>1</SP> of top plate 28 of the block. The retracted position of the tool, "X" in Fig. 2, has only the end of the tool overlapping the feeler. If breakage occurs the feeler will be moved upwardly by bias spring 32 so that ports 35, 36 in block 27 are unblocked thus venting the main air supply. Reduction in pressure actuates a pressure switch and causes the machine to stop or at least stop head 13. The valving member 31 and feeler 33 can be reset by pressure applied through port 37. This pressure is removed when the tool has been replaced and is correctly positioned so that normal working can commence. In a modification, Fig. 4 (not shown), cover plate (28A) is attached to body (27A) by means of a long screw (22A), hollow dowel (45) and three short screws (22B). This arrangement enables plate (28A) to be pivoted around screw (22A) after removal of screws (22B), for removal of a broken tool. In a further embodiment, Fig. 7, the feeler tip 60 is normally biased upwardly against the action of spring 70 by resetting air entering via port 69. Fig. 10 (not shown), illustrates a control system for use with this embodiment whereby at the end of each cycle of the tool the resetting air is vented so that the feeler tip is moved toward the tool. If the tool is unbroken then after a predetermined time the resetting air is reintroduced to the mechanism to move the feeler tip upwardly. If the tool is broken then ports 72, 71 are connected due to the movement of valve element 62 and a signal is produced to stop the machine. This may take the form of a piston caused to act on the main stop button of the machine, Figs. 11 and 12 (not shown). The operation of a further embodiment, Figs. 13 and 14 (not shown) is similar to that for the previously described embodiment except that operation of feeler (64B), is controlled by plunger (120) and valve (121). A yet further embodiment, Fig. 15, has feeler tip 60C attached to an ejectable feeler stem 64C which acts as a piston and a blocking valve for the main air line connected to side port 72C. The feeler is normally urged against a tool by spring 70C. When a tool breaks the tip and stem are ejected from the body and the main controlling air line is vented causing the machine to be stopped. The tip and stem may be replaced in the body or treated as expendable and a new one fitted. Stem 64C has a longitudinal slot 145 and a circumferential slot. Thus to fit a stem into the body it is pushed upwardly and turned to assume a position as shown in full line in Fig. 17. Pin 148 maintains the stem in the body. As the newly fitted tool 20C moves forward it turns the stem so that pin 148 is aligned with slot 145. The mechanism may be formed with limited built in air leakage and arranged so that the operating air pressure keeps the parts clean.