Patent GB-505532-A (GB)
Title: Improvements in or relating to electrical apparatus for the supervision of machine tools
IPC: B24B49/18
Filed: 1938-07-19
Abstract: 505,532. Grinding. PATENTVERWERTUNGS-GES. HERMES. July 19, 1938, No. 21460. Convention date, Jan. 26. [Class 60] [Also in Group XXXVIII] The amount of movement of a tool during a machining process is indicated by an indicator connected across a bridge formation of bolometric resistances. The bridge circuit is adjustable to allow for the wear of the tool and the output current may be utilized to control the tool automatically. Fig. 1 shows the indicating apparatus applied to an internal grinding machine having a grinding disc 1 carried on a support 3 which is slidably mounted on a bed plate 4 under the control of a spindle 5. The indicating apparatus comprises a bridge arrangement of heated resistances 11 ... 14 supported on a plate 10 which is provided with nozzles,15, 16 through which pass currents of air from a reservoir mounted behind the plate 10. The plate 10 is supported on a pivoted lever 9 which is oscillated by a rod 24 when an arm 27, mounted on a tool 31 for surfacing the disc 1, is adjusted. A vane 18 movable between the nozzles and the resistances is mounted on a pivoted arm 8 which is oscillated by a rod 23 when the support 3 is moved relatively to a stop 25. The resistances 11 ... 14 are connected to an indicator 21 and a relay 22 which automatically stops the machine when the work-piece is ground to the correct size. In operation, a pattern work-piece is first made with the aid of a gauge, the grinding disc being surfaced by the tool 31 prior to the last cut by the disc. The tool 31 is adjusted by a spindle 30 and the arm 27 simultaneously adjusts the plate 10 to allow for the wear of the disc. Before a fresh work-piece is machined the stop 25 is adjusted by the spindle 26 until zero reading is given by 'the indicator 21. The apparatus is then set ready for accurately machining the next work-piece. This operation is effected by advancing the disc 1 under the control of the spindle 5 until the indicator gives approximately a zero reading. The disc is then resurfaced, allowance for this being made by the adjustment of the plate 10, and the finishing cut is then made by again advancing the disc 1 until zero reading on the indicator is reached. In a modification, two separate vanes operated by the arm 27 and stop 25 co-operate with separate stationary sets of bolometric resistances. This arrangement is used in the system shown in Fig. 4 for automatically controlling the operation of the grinding disc. The disc is driven by a motor 46 which is started up by a looking relay 47 operated by a push button switch 50. Relay 47 also operates a control magnet 53 for the valve of a hydraulic or pneumatic motor which reciprocates the grinder spindle. As the disc is advanced during machining, the vane 33 associated with the resistances 36 ... 39 is operated to decrease the current until when the current passes through its zero value and reverses, relay 22 closes at contacts 56, the circuit of a locking magnet 70 which releases the magnet 53 controlling the reciprocating motion. Surfacing of the disc is then effected the motion of the associated vane 32 being such as to reduce the current and open contacts 56. The finishing cut is then initiated by operation of the button 60 which releases magnet 70 and restarts the reciprocating motion. The disc is then advanced until relay 22 again operates magnet 70 to de-energize the magnet 53 and pull up a magnet 68 which opens a switch 69 to stop the motor 46. The relay 22 may be replaced by a measuring instrument which operates the control circuits through the intermediary of photo-electric or bolometric apparatus.