Patent GB-1066941-A (GB)
Title: Improvements relating to proximity detectors
Inventor: BENCH DAVID EWART
IPC: B23Q15/00
Filed: 1963-03-01
Abstract: 1,066,941. Proximity detector. DONOVAN ELECTRICAL CO. Ltd. June 1, 1964 [March 1, 1963], No. 8213/63. Heading GIN. In a proximity detector for detecting the proximity of magnetic or conductive material comprising a winding energized by alternating current to provide an output signal in response to coupling between the object and the winding, an amplifier, and an indicator or control device, the winding comprises two air coils connected differentially to produce unbalance when magnetic or conductive material is brought into the detection field. Coils (L1) (L2) Fig. 1 (not shown) are connected with resistors (R6) (R7) in an A. C. bridge. Energized by a transistor oscillator (TR1) and the output is applied to operate a relay (RL1) through an A.C. transistor amplifier (TR2), and two D. C. amplifier stages (TR3) (TR4). Potentiometers (VR1) (VR2) provide for coarse and fine adjustment of the bridge balance and the relay operates when the collector current reaches a predetermined value. Feedback through resistor (R14) compensates for temperature changes in the transistors. The two coils may be mounted by a thermo-setting resin on a T-shaped member (12), Fig. 2 (not shown) of insulating material for attachment to apparatus, and they may be a wave or pile winding. A hole (25) is provided for the passage of a drill tap or reamer in an arrangement for detecting tool breakage, and the arrangement is said to be responsive to breakage of radially projecting parts. A modified arrangement comprising two sensing heads and a dummy drill moving in conformity with the axial movement of the operative drill is described with reference to Fig. 4 (not shown), and an arrangement for removing swarf may be included. An elongated coil for extending across a conveyer for the detection of the presence of conveyed objects and having a balancing coil of smaller dimension is described with reference to Figs. 5, 6 (not shown). The developed signals may control means such as shears for operation on the object. A hollow coil for immersion in a fluid medium for the detection of a passing object such as a billet being quenched is described with reference to Figs. 7-9 (not shown), the balancing coil being housed in the bracket supporting the sensor coil. The arrangement is made to shut down rollers conveying billets after predetermined time if a billet is not sensed. Two similar coils aligned axially and having an armature movable within them to serve as a positional transducer is described with reference to Fig. 10 (not shown), and the application of the positional transducer to maintaining the tension in a web or filament by coupling the armature to a tensioning roll is described with reference to Fig. 12 (not shown). The arrangement includes servo loop control of the speed of one of the rollers adjacent the tensioning roll. Detection of the needle position of a meter by means of armatures coupled to the needle and a pair of coils is described with reference to Fig. 13 (not shown). Again control such as acceptance or rejection may be initiated by the device. A limit switch in which a rod carrying collars at each end passes through a pair of coils and in which the presence of a roller in the vicinity of either coil causes unbalance is described with reference to Figs. 14, 15 (not shown).