Patent GB-781172-A (GB)
Title: A new or improved high precision indexing mechanism for accurately positioning work-pieces
IPC: B23Q16/06
Filed: 1953-12-30
Abstract: 781,172. Photo-electric control systems. WARNER & SWASEY RESEARCH CORPORATION. Dec. 30, 1953 [Dec. 31, 1952], No. 36122/53. Class 40 (3). [Also in Groups XIX, XXII, XXXVII and XXXVIII] The invention relates to means for angularly positioning a workpiece to any one of a number of selected positions by means of two sets of inter-related stop means. Indexing.-The indexing head 17, Fig. 5, comprises a spur gear 18, a carrier disc 19, a sleeve 20 and a flange 21, as an integral unit freely rotatable on a stationary shaft supported at one end in a bearing 14 and having at the other end a hardened conical centre 16. The head is driven in either direction through the gear 18 and a pinion 50 by a motor RM. The disc 19 has ninety holes 51 into each of which is tightly fitted an axially extending stop pin 52. Axially projecting annular flanges 53 on either side of the disc 19 are pierced by ninety radially extending threaded holes 54 staggered with respect to the pins 52, each hole having a screw 55 locked in its adjusted position by a lock nut 57. A block 66, Fig. 3, is dovetailed on and moves over a fixed block 65 towards and away from the disc 19 and supports a pawl carriage 24. Two locking pawls 22, 23 are provided each comprising an arm 76, 78 extending from a sleeve supported on a pivot pin 70 near the periphery of the disc 19 and a tooth 77, 79 projecting inwardly towards the centre of the disc, the pawls 22, 23 when swung inwardly engaging with the stop pins 52 and the screws 55. Each pawl tooth has a flat side 81 lying at a slight angle with respect to the radius of the disc 19 and the arm of the pawl 22 is shorter than that of the pawl 23 so that their flat faces 81 are angularly separated by two degrees. On the other side each pawl has a bevelled face 80. Each arm 76, 78 forms part of a bell-crank, the other arm of which e.g. in the case of arm 78, the rod 85, is joined by a spring 86 to a rod 87 secured to the block 66, the spring urging its respective pawl into engagement with the indexing stops 52, 55. Lugs 95 on a shaft 90 having a hand knob 93 are rotatable into engagement with the rods 85 to disengage the pawls from the indexing elements. Micro-switches RS1, RS2 are provided having contact buttons 106, 105 operated by the pawls 23, 22 on movement outwards from the disc 19. As shown in Fig. 3, the tooth 79 of the pawl 23 is located between two pins 52a, 52b in engagement with a screw 55 and the tooth 77 of the pawl 22 is cammed outwardly by the pin 52a. On operating the control for the motor RM the disc is driven clockwise by the gears 50, 18 and firstly the pawl 23 is cammed outwardly by the pin 52b and operates switch RS1. The pawl 22 then falls off the pin 52a and swings inwardly until the crown of its tooth 77 strikes the end of a screw 55. At this point the switch RS2 is released. The changed conditions of switches RS1, RS2 reverses the motor RM until the stop pin 52a bears against the flat face 81 of the tooth 77 whereupon the motion of the disc 19 ceases and the motor is stalled under the continuing reversed torque. The next indexing operation is performed by again energizing the motor RM in the forward direction. Each step performed by this " walking " action of the pawls with the pawls alternately locking the disc at the principal indexing stations corresponds to a two-degree angular indexing movement. The stalling of the motor with a pin in contact with a flat face of a pawl tooth prevents backlash. Coarse control.-A lead screw 126, Fig. 5, mounted in threaded bores in a sleeve 120 with its axis parallel to that of the disc 19, is driven through gears 18, 117 and 118, 133, the gear 133 having a coupling rod 132 slidably mounted therein and rigidly secured to the lead screw hub 131 to which it transmits the rotary drive while allowing free axial movement of the screw 126. The lead screw hub 131 carries the coarse control drum 27 which is provided with helically arranged control indicia apertures 145 which can be scanned by a photo-cell 147 co-operating with a lamp 146 mounted in a fixed position internally of the drum. Fine control.-Rotation of a lead screw 158 supported for rotation without axial movement in threaded supports in the lower block 65 and bearing between those supports a nut 156 secured to the upper block 66 enables the pawl carriage 24 to be moved towards and away from the disc 19. In its retracted (or " reset ") position the carriage 24 opens the contacts of a microswitch AB. To set the disc 19 to any desired position intermediate of two principal stations the screw 158 is rotated to retract the carriage 24 to its reset position. The motor RM is then started and the disc 19 driven until the principal station nearest exceeding the desired position is reached whereupon the motor reverses and stalls with a stop pin 52 abutting either pawl 22 or 23. The lead screw 158 is then rotated to move the pawl carriage 24 towards the disc 19, the flat face 81 of the engaged tooth undergoing the same displacement. As the motor is in reverse, the disc 19 follows up counterclockwise this displacement of the engaged tooth until the lead screw is halted at the desired position of the disc leaving the motor RM still stalled in reverse. The pitch of the lead screw 158 is chosen to advance the carriage to rotate the disc 19 through thirty minutes of arc for one revolution of the screw. An unthreaded continuation of the lead screw 158 carries a drive gear 165, a calibration ring 166, a locking ring 167 and a fine control drum 28. The lead screw 158 is driven from a fast align motor AFM and a slow align motor ASM through gears 175, 179, 177, 178, 182, 185 and 165. The calibrating ring 166 has a peripheral graduated scale. The fine control drum is clamped by the locking ring 167 to a mounting flange 191a on the lead screw 158 and bears a series of control indica apertures 192 distributed in a plurality of peripheral lines 193 disposed around the drum, each line 193 being utilized in a separate indexing operation in a preselected sequence of desired positions of the head 17, each aperture 192 representing the desired angular displacement from an imaginary datum 194. The lamp and photo-cell for the fine control drum are supported from a base 207, Fig. 2, mounted by cross blocks 205, 206 for sliding movement parallel to the drum axis along slider rods 203, 204 (not shown). The photo-cell 209 is contained in a housing 208 having a viewing chamber projecting outwardly at right angles therefrom to move over the external surface of the drum. The lamp is supported adjacent the internal surface of the drum by a support structure which includes members 216-219. The scanning base 207 is positioned step-by-step to register in turn with each of the lines 193 by an escapement drum 229 driven from a reversible motor PCM, the drum having two parallel peripheral rows of equally spaced pins 232, the pins of one row being staggered with respect to those of the other. An escapement lever 233 normally restrains the drum 229 from counterclockwise movement with the motor continuously stalled by the engagement of its flat lower surface 238 with one of the pins 232. The lever 233 is pivotable against a spring 245 by means of a rotary solenoid PS acting through a coupling 246, 248. Upon energizing the solenoid the lever 233 is moved from engagement with a tooth in the nearer row as seen in Fig. 2 to register with a tooth in the further row and the drum 229 advances under the motor PCM in the counter clockwise direction. On deenergizing the solenoid PS the lever 233 is returned to engage the next tooth 232 in the nearer row and the drum is again driven counterclockwise. The movement of the escapement drum is conveyed to the scanning base 207 by means of a gear 250 on the escapement drum shaft and a gear 251 on a shaft bearing a pinion in engagement with rack 254 secured to the cross blocks 205, 206, the base 207 being driven away from the disc one full registering movement for each two movements of the drum 229 corresponding to energizing and de-energizing of the solenoid PS. On reaching the end of the scanning movement of the base 207 an adjustable actuator block 265 operates the contact 262 of a limit switch FS carried by the base which reverses the motor PCM and the drum 229. The bevelled upper surface of the escapement lever 233 permits the free reverse movement of the drum to drive the scanning base back towards the disc 19 until the actuator block 264 strikes the contact 261 of a second limit switch B2 when the motor PCM is again reversed to its normal condition and the drum 229 is locked by the flat face 238 of the escapement lever 233 with the cell 209 and the lamp positioned to register with the first peripheral line 193. The gauging assembly.-The pairs of twin probe members 44, 45, Fig. 6, are carried by holders 293, 294 on the horizontal section 292 of a probe bar having also a vertical section 291 and a first horizontal section 290, this latter section being freely rotatable about a pivot pin projecting from a bracket carried by a block 287 slidable vertically in a block 285 secured to the edge of an offset carriage 272 in turn sliding in a perpendicular horizontal direction on a block 270. The sliding movement of base 272 on the block 270 is controlled by a lead screw having a knob 273 and that of the offset carriage 275 on the base 272 by means of a lead screw rotated by a gear train 277 driven by an offset motor 278. The probe bar is rotated about its pivot pin from a position completely clear of the gear teeth being gauged into its gauging position by means of a solenoid secured to the vertical block 287 with its armature coupled to the horizontal section 290 of the probe bar. Gauging commences with the probe bar down and the offset carriage 275 in a central reference position. The probe bar is then lifted upwards so that the probe tips are located opposite but spaced by a sm