Patent GB-945450-A (GB)
Title: Improved grinding machine
IPC: B23Q15/00
Filed: 1962-05-29
Abstract: 945,450. Grinding; trueing grinding wheels. NORTON CO. May 29, 1962 [Sept. 5, 1961], No. 20569/62. Heading B3D. A grinding machine comprises means for feeding a grinding wheel to the workpiece according to a pre-set feed sequence, gauge means operable independently of this sequence for reversing the wheel feed when a workpiece is ground to a desired final size, and means operable when the wheel feed means is reversed to provide full correction for either fore-shortening or protraction of the wheel feed relative to the pre-set sequence so that the next workpiece will reach final size as the sequence is completed. The machine, which is operated under hydroelectric control, comprises a slide 12, Fig. 2, carrying an assembly 16 of grinding wheels driven by a motor 30 and arranged to be advanced on roller units (Fig. 18, not shown) through successive coarse and fine grinding feeds towards the workpiece which is carried between headstock and tailstock assemblies 41, 43, Fig. 1, on a worktable 40 also mounting one or more steady rests 45. The tailstock spindle 412, Fig. 14, is moved into engagement with the workpiece by a spring 414 when pressure fluid is applied to both ends of an hydraulic cylinder 403 so as to balance its piston 404 which has a rack-and-pinion engagement with the spindle 412. Each steady rest comprises upper and lower pivoted shoe-carrying members 353, 357, Fig. 11, urged apart by a spring 367 and so controlled through a lever 361 by two coacting hydraulic cylinders 373, 377 that the shoes are applied rapidly to the workpiece and then at pressures commensurate with the respective coarse and fine increments of feed. Sizing gauges G1 . . . G4, Fig. 1, are provided for manual or automatic application to the workpiece with their contacts arranged in the control circuit of the machine. Movement of the slide 12 is effected by a feed screw 102, Figs. 2 and 17, which for rapid movement is shifted bodily by its connection with a piston 107 in an hydraulic cylinder 108 and for coarse feed grinding is rotated by the movement of a piston 121 in an hydraulic cylinder 122, the piston-rod 123 driving the screw through worm gearing 124, 125 and clutch gears 131, 133; the control circuit provides for fast advance by the piston 107 until a limit switch slows down the feed, and, when this piston reaches the end of its stroke, coarse feed by the piston 121. Intermittent fine feed automatically follows the coarse feed after a brief delay to allow " sparking out " and is effected by the stepped rotation of a rod 164, Fig. 17, acting through worm gearing 165, 166, clutch 167 and spur gearing 172, 173, to rotate the piston-rod 123 and feed screw 102. The rod 164 is actuated by the intermittent operation of an hydraulic cylinder 181 to cause its pawl piston 182 to act upon a ratchet wheel 186 carried by a sleeve 187 keyed for axial movement on the rod. In order to enable the wheel feed to pick up each increment of fine feed the piston-rod 123 is at the same time given a partial rotation by causing the piston-rod 163 of an hydraulic cylinder 162 to give the rod 164 an axial push against the action of a return spring 307. Each normal fine feed action of the ratchet wheel 186 operates, through clutch gears 336, 337 (provided these are engaged) and a gear 335 rotatable on the rod 164, to correspondingly advance in its hydraulic cylinder 331 a rack piston 332 which is subsequently used to reverse and re-set the fine feed for the next grinding cycle. The intermittent fine feed actions are effected as a switch LS8 is actuated by its engagement in successive peripheral recesses 156 in a disc 155 which is rotated during the fine feed cycle by the rack piston 153 of an hydraulic cylinder 151. Included in the control circuit of the machine is a counter which is pre-set to the desired number of fine feed increments to bring the workpiece to the high limit of size and to count out to effect certain control operations after receiving the set number of signals from the switch LS8. The contacts of the gauges G1 . . . G4 are also so included in the circuit that the rack piston 153 is slowed to reduce the rate of actuation of the fine feed ratchet wheel 186 as long as any gauge senses the workpiece to be of greater than a predetermined size and automatic reverse of the slide is effected when a gauge senses that a desired final size has been reached; reverse of the slide is caused by the pistons 107, 121 upon actuation of the cylinders 108, 122 and return of the reset piston 332 (the clutch gears 336, 337 being engaged) to the extent permitted by an end stop upon actuation of the cylinder 331. Should a gauge register attainment of the desired final size before the counter has signalled the preset number of fine feed increments, a compensating fine reverse of the slide is effected under the control of the switch LS8 by the actuation of a cylinder 321 causing its pawl piston 322 to act intermittently upon a reverse ratchet wheel 188 on the sleeve 187, the clutch gears 336, 337 being disengaged by actuation of the cylinder 161 during this operation to uncouple the reset piston 322. Reverse drive is stopped when the counter counts out and the spring 307 then pushes the rod 164 to engage the clutch gears 336, 337, and render the reset piston 332 effective in the return of the slide which will therefore be automatically set so that on the next grinding cycle the workpiece will reach final size as the counter counts out. Should the counter count out before any of the gauge contacts is actuated, the re-set piston is again uncoupled but fine feed by the ratchet wheel 186 continues under the control of the switch LS8 until one of the gauges operates to reverse the wheel slide and render the re-set piston effective in that action so that compensation to achieve correct operation on the next grinding cycle is achieved. A second counter provided in the control circuit and pre-set to the number of fine feed increments to reduce the workpiece to a minimum acceptable size is arranged to count out and return the wheel slide should the gauges not operate first to do so. An indicating dial 230, Fig. 17, has two pointers driven by flexible cables 234, 244 from the clutch gear 133 and rod 164 for recording coarse and fine feeds. The slide 12 is also given an automatic compensating feed when the grinding wheels are being trued as described below by hydraulic cylinders 305, 301, Fig. 17, which are so controlled that an advance of the rod 164 by the piston 306 of the cylinder 305 to provide this feed is followed by temporary disengagement of the clutch 167 by the cylinder 301 to prevent cancellation of the feed when the rod 164 is returned by its spring 307. A modified feed system for the wheel slide (Fig. 19, not shown) employing mainly hydraulic operation omits the counter for pre-setting the fine feed, the cylinder 331 and re-set piston 332 from the system of Fig. 17 and uses the cylinder 305 acting through its piston 306 on the rod 164 to effect the desired compensation in the next grinding cycle. For this purpose, the piston 306 is actuated automatically during the initial fast feed part of a grinding cycle to retract the rod 164, and so the slide, a coarse increment which is equal to the desired number of fine feed increments and is set by an adjustable end stop for the piston ; the clutch 167 is temporarily disengaged on the return of the piston as described above. In this case, feed of the slide is effected as before, but the fine feed by the ratchet wheel 186 continues, irrespective of whether or not the number of feed increments so provided equals that set, until a gauge signalling that the desired final size of the workpiece has been reached operates to return the slide ; the piston 306 has therefore effected a compensation to enable the desired final size of workpiece to be reached at the end of the ensuing pre-set fine grinding sequence which is carried out under electronic control by the ratchet wheel 186. The reverse fine feed by the ratchet wheel 188 is used only for manual adjustment of the slide when desired. The grinding wheel assembly 16, Fig. 17, on the slide is automatically moved axially at the start of an operation to align the grinding wheels correctly with the workpiece mounted between the headstock 41 and tailstock 43 by the rotation of a nut 445 on a stationary screw 446 disposed coaxially with, and at one end of, the assembly, the nut being driven by a rack piston 443 in an hydraulic cylinder 442. Mounted on the worktable 40 is a pivoted probe 431 which is engageable with a locating surface on the workpiece under the control of a spring 427 and hydraulic cylinder 425. At the start of an operation the probe contacts the locating surface and a feeler 433 moving with the probe contacts and closes a switch LS9 on a spring- pressed arm 435 and so energizes the cylinder 442 to move the wheel assembly to the right. During this movement, a flexible cable 452 engaging between the nut 445 and arm 435 is urged by the latter to follow the nut until the switch LS9 leaves the feeler and so de-energizes the cylinder 442. For edge trueing of the grinding wheels, a support 48, Fig. 11, disposed in an opening in the work-table 40 carries for each grinding wheel a tool holder 262 at the end of a rod 261 disposed inside a tube 250; each tube is spring- urged towards the grinding wheel so that a follower 254 on the tube co-operates with a fixed form bar 255 as the support is reciprocated transversely of the grinding wheels by an hydraulic cylinder 291, Fig. 17. Each rod 261 is urged to the left in Fig. 11 by a spring 265 and controlled by a gear screw 269 carrying a worm wheel 270 meshing with a worm 274, Fig. 12, on a shaft 275 which is moved axially against the action of a spring by an hydraulic cylinder 277 so that feed rotation may be applied to the worm by an hydraulic piston 282 having a pawl engaging a gear 284 o