Patent GB-947447-A (GB)
Title: Automatic wheel trueing means for grinders
IPC: B24B47/06
Filed: 1962-03-12
Abstract: 947,447. Trueing grinding wheels. CINCINNATI MILLING MACHINE CO. March 12, 1962 [March 31, 1961], No. 9370/62. Heading B3D. A grinding machine which has means for traversing a trueing tool across the grinding wheel and giving it an increment of advance towards the wheel on each of its traverses, has means for bringing the regulating wheel slide of a centreless machine or the workhead of a centre-type machine mounted on the slide in place of the regulating wheel into phase with the trueing tool after one or more fine incremental advances of the slide independently of the trueing tool, such means comprising selectively-operable means for giving the slide a fine incremental movement to compensate for wear of the grinding wheel during grinding operations, means effective each time the trueing tool is advanced towards the grinding wheel to give the slide a coarse increment of advance equal to the incremental advance of the trueing tool and mechanical sensing means responsive to the amount of fine incremental movement given to the slide by the selectively-operable means for the purpose of reducing by this amount the amount of coarse increment given to the slide and so bringing the slide into phase with the trueing tool. The machine is described as applied to a conventional centreless grinding machine comprising a grinding wheel and a regulating wheel mounted on a slide in which the trueing tool is mounted on the forward end of a bar 30, Fig. 3, which is longitudinally slidable in a tubular housing 31 arranged for longitudinal movement between ball tracks 33 on a carriage 32 movable transversely for operative reciprocation of the tool across the grinding wheel by a feed screw 34, Fig. 5, driven by an hydraulic motor 35. The fluid pressure circuit of the motor comprises a reversing valve 47 under the control of a solenoid valve 48 which is actuated at opposite ends of the traverse of the carriage by limit switches coacting with dogs 64, 69 on the carriage 32. The return line from the motor 35 leads to one end of a pressure reducing valve 74 and thence via an adjustable valve 82 to the opposite end of the valve 74, manual adjustment of the valve 82 providing for variation in the rate of travel. Rapid traverse of the carriage may be effected by actuating a solenoid valve 90 to by-pass the valves 74, 82. Feed of the trueing bar 30 is effected automatically at each end of the traverse of the carriage 32 by a feed screw 36, Fig. 4, which is rotated through a ratchet-and-pawl device 117, 118 from a gear 115 meshing with a rack piston 95 movable in a cylinder 96 by fluid pressure controlled by a solenoid valve 110. With the valve set to supply fluid to the cylinder 96, the piston 95 moves to the left a distance determined by an adjustable stop 103 and thereby advances the ratchet-wheel 117, feed screw 36 and trueing bar 30; the stop 103 can be set in any one of four axial positions providing for advance of the ratchet-wheel through one, two, three and four teeth, respectively. The feed screw may be operated by hand after a knob 123 has been turned to cause a lug 125 to raise the pawl 118 from engagement with the ratchetwheel ; the lug also actuates a switch to disable the automatic trueing circuit. Feed of the regulating wheel slide is carried out by a feed screw 135, Fig. 6, which is bodily movable in the axial direction by walking-beam mechanism 129, 134 for rapid traverse of the slide and rotated through stepped increments to effect its coarse and fine compensating feed. This feed motion is provided through gearing 143, 146 from a shaft 147 which is given stepped rotation when either of two arms 156, 173 is rocked on the shaft so as to act through pawls upon corresponding ratchet-wheels 151, 168 fixed on the shaft. Rocking of the arms 156, 173 is caused by their toothed engagement with pistons 190, 191, Fig. 7, movable in cylinders arranged in a fluid pressure circuit having solenoid valves 214, 215 for controlling the respective pistons. The ratchet-wheel 151, which provides for fine feed, has closely-spaced teeth coacting with two pawls 153, 154 so spaced on the arm 156 that they are effective alternately on successive rocking strokes of the arm to advance the wheel through a half-tooth distance. Whenever, during a grinding operation, the operator finds that the workpieces are tending to become oversize he presses a pushbutton in the control circuit to actuate the solenoid 214 and so advance the wheel 151 to . give the slide a movement of feed. The other ratchet-wheel 168, which coacts with a feed pawl 171 on the arm 173 and is adapted to provide the coarser feed, may have only onefifth the number of teeth of the wheel 151 so that ten intermittent advances of the latter wheel equal one tooth advance of the wheel 168 and it is arranged for this one tooth advance to move the regulating wheel slide a distance equal to the feed advance of the trueing tool by operation of the piston 95, Fig. 4. With the specified relative tooth spacings of the two wheels, the result of, say, four compensating movements by the wheel 151 during a grinding operation is to move the coarse wheel 168 ineffectively a distance so that its drive pawl 171 moves only four-tenths of the way up the inclined face of a tooth face. If at this stage the operator presses a push-button to start an automatic trueing cycle, the control circuit provides that, at the end of the first traverse of the trueing carriage 32 by the motor 35, not only is the feed screw 36 actuated to feed the trueing tool towards the grinding wheel but the correct phase relationship between the trueing tool and regulating wheel slide is restored by causing the valve 215 to advance the ratchet-wheel 168 for a coarse increment of feed of the slide; the actual increment of this advance provided by the pawl 171 in its action upon the wheel 168 corresponds, in the present instance, to six-tenths of a tooth space since the first four-tenths of a tooth space (representing the amount of fine compensation) is taken up by lost motion between the pawl and tooth. In the subsequent trueing cycle, a sensing pawl 179, Fig. 6, co-operating with the wheel 168 actuates a switch whenever it drops into the bottom of a tooth space for the purpose of setting the control circuit for advance of the slide by the wheel 168 a complete coarse increment for each feed of the trueing tool. Should the operator during any one grinding operation attempt to effect a number of fine compensations exceeding the number of steps of the fine wheel 151 per tooth of the wheel 168, it is arranged that the same sensing pawl, when it drops into the bottom of a tooth space in the wheel 168 and actuates the switch, causes advance of the trueing tool by the feed screw 36, but no coarse compensation of the slide. The operative feed advance of the two pistons 190, 191, Fig. 7, is limited by stops 202, 207 which can be set in any of four axial positions, each of the adjustments of the coarse stop 207 being made to correspond with one of the four adjustments of the feed stop 103, Fig. 4, of the trueing tool and necessitating the use of a coarse ratchet-wheel 168 having appropriately space teeth for obtaining the desired advance of this wheel in relation to the fine ratchetwheel 151. A manually-operable pressure release valve 232 may be opened to release pressure in the circuit when it is desired to change the setting of the stops 202, 207. A check valve 226 and resistance 227 in the circuit act to brake the feed advance of the arm 171 and allow its unimpeded return. The control circuit of the machine includes, in addition to the solenoids of the hydraulic valves, timer and other relays, and limit switches for the purpose of providing the grinding and automatic trueing cycles, a pre-settable counter arranged to stop the trueing cycle when the carriage 32 has made the required number of passes. A further counter may be provided for counting the number of workpieces ground between trueing cycles and a signal from this counter may be used to start a trueing cycle. When the invention is applied to centre-type machines, the work is mounted between centres on a head on the slide referred to as the regulating slide above.