Patent GB-1102041-A (GB)
Title: Automatic grinding method and apparatus
IPC: B24B49/00
Filed: 1966-02-04
Abstract: 1,102,041. Grinding. P. DRUMMOND (Gillette Co.). 4 Feb., 1966, No. 4980/66. Heading B3D. A method of automatically grinding an edge on a moving metal strip, such as a razor blade strip, comprises the steps of scanning each of two adjacent bevels on the strip and producing a signal from each scan as a function of the width of the bevel, comparing the signals derived from the respective bevels and producing an error signal as a function of the difference in widths of the bevels, producing grinding head control signals from the error signal, and applying the control signals to grinding head positioning means in accordance with a predetermined programme to adjust the position of the grinding heads as required to reduce the error signal. As described, the razor blade strip 10 has its two top bevels 1, 3 scanned by optical scanners 11, 12 and its two lower bevels 2, 4 scanned by optical scanners similar to the scanners 11, 12. The upper and lower halfwidths of the blades are also detected by measuring devices 23, 50, such as differential transformers, which produce signals which are compared with those produced by standards 24. The signals from the optical scanners 11, 12 are fed to amplifiers 13, 14. The raw signal pulses have their widths detected and amplified in units 15, 16 and the outputs therefrom pass to units 17, 18 which clip the signals to precise square form and integrate the signals to produce a D.C. potential which is the average of the width-potential product of a series of signals. The D.C. outputs are fed to amplifiers 19, 20 connected by a cam-operated switch 40 to a meter relay 21 connected to a programmer 32. The top half width of the blade, i.e., the distance between the top edge of the blade and the upper part of the slot in the blade, is continuously measured by the differential transformer 23 which produces an A.C. signal of a sense and magnitude, compared to that produced by the standard 24, according to the deviation of the half width, and this signal passes through an amplifier 26, a phase-sensitive device 27 which produces a D.C. output, and a D.C. amplifier 28, the output of which is connected by a camoperated switch 42 to a meter relay 30 also connected to the programmer. The scanners for the lower bands 2, 4 of the blade, and the lower half width detector 50 are connected through similar circuits to the switches 40, 42. The programmer 32 controls the operation of the switches 40, 42 so that the meter relays 21, 30 respond to the signals from, say, the scanners 11, 12 and differential transformer 23 associated with the top edge of the blade and, according to the deflections of the relays 21, 30, operates the controls 34, 35 for the grinding heads 1, 2 operating on the bevels 1, 3 of the blade strip, and then operates the switches so that the relays respond to the signals detected from the lower edge of the strip, and according to the deflections, operates the controls 36, 37 for the grinding heads 3, 4 for the lower edge of the strip. The bevels are thus ground to the same width and the half-widths of the blades are maintained constant. The scanners for the bevels of the blade are substantially identical, and each scanner comprises a light source 100, Fig. 2, which directs a beam of light on to the ground bevel, the beam covering an area starting below the heel, Fig. 6, where the bevel begins but not extending to the edge of the bevel. A microscope 102 is mounted on a stand 124 so as to view the bevel and is adjustable about a trunnion 128 by a worm- and-wheel arrangement 144, 148, a ratchet mechanism 154, 156 releasably locking the microscope in its adjusted position. The reflected light viewed by the microscope is converted into pulses by a rotating disc 172 which is driven by an induction motor 178 and is formed with slots 180, the pulses of light passing through an aperture 175 in a mask 174 and falling on a photo-multiplier tube 181. The microscopes associated with associated bevels, say microscopes 11, 12, are adjusted initially until the light transmitted through the apertures 175 is equal when a correctly ground blade strip is being viewed. The blades strip is guided in a bracket 185 secured to the base between the pairs of scanners, the bracket having a supporting block, 210, Fig. 7, formed with a wedge 210 carrying blade supporting plates 214, 215. The plates are spaced apart the thickness of the blade strip and the plate 214 is formed with a groove while plate 215 is provided with a channel for a key that extends part-way into the groove and is tapered at both ends so that the parts of the blade strip joining the upper and lower halves of the strip bend round the key but the lower edges of the portions adjacent the slots will rest on the top of the key to maintain the vertical position of the strip as it moves through the guide. The differential transformer 23 for producing a signal proportional to the top half width of the strip is mounted on the bracket 185 and consists of a transformer 203, Fig. 8, having a movable core 203 provided with a pin 200 which is urged by a spring 206 into engagement with a carbide key 194 resting on the top edge of the blade. As the half-width of the blade varies, the movement of the key moves the core 203 to vary the output of the differential transformer. The circuits for converting the electrical signals received by the photo-multipliers of the scanners for the bevels to the D.C. potentials applied to the meter relay 21 and for converting the A.C. signals from the differential transformers for detecting the half-widths of the blades to D.C. potentials applied to the meter relay 30 are described in the Specification, the deflections of the meters determining the number and direction of correction steps necessary for the grinding heads to produce bevels of equal size and maintain the halfwidths constant. The meter relays 21, 30 have pointers 424, 425, Fig. 14, which are moved according to the amplitude and direction of correction to be applied to the grinding heads first according to the upper and then the lower edge of the blade strip. The relays are associated with a multi-bank stepping switch 430 which, together with the relays and a relay circuit connected to the positioning means for the grinding heads, alternately determines the direction and amount of movement of the positioning means for the grinding heads associated with the upper edge, and then the positioning means for the grinding heads for the lower edge of the strip. The grinding heads are arranged side-by-side, and each head comprises a grinding wheel 600, Fig. 20, carried by a slide 602 mounted for movement in ball slides 622. The carriage rotatably supports a nut which engages a fixed screw 612 on the bed 604 and is formed with a gear engaging a helical gear 650 on a shaft 618 connected by gearing 652, 654 to a motor 539 comprising the positioning means, the motor being rotatable in one direction or the other in steps according to the output of the meter relays 21 or 30, each step moving the grinding wheel 0À0001 inch. The blade strip 10 is supported during grinding against a carbide plate (662) having a ledge (663). The grinding wheel may be adjusted manually by rotation of the shaft 618 or by rotation of the lead screw 612. The nut is comprised of two parts 630, 636 adjustable relative to each other to take up backlash between the nut and screw. A nozzle 668 is disposed adjacent the grinding area.