Patent GB-1010591-A (GB)
Title: Improvements in or relating to grinding machines
Inventor: GLADSTONE ROBERT
IPC: B24B49/16
Filed: 1960-10-12
Abstract: 1,010,591. Grinding. WIGGINS TEAPE RESEARCH & DEVELOPMENT Ltd. Jan. 12, 1962 [Oct. 12, 1960], No. 35018/60. Heading B3D. [Also in Division G1] A grinding machine comprises a grinding wheel for grinding the circumferential surface of a workpiece of circular cross-section, means for effecting relative traversing movement between the grinding wheel and the workpiece in the direction of the length of the workpiece, means for rotating the workpiece while it is being ground and means for adjusting the rate of grinding of the workpiece by the grinding wheel; a control system comprises gauging means for determining, while the grinding wheel is grinding the workpiece, any difference between a datum value and the diameter of the particular circumference of the workpiece on which the grinding wheel is acting, and means for automatically controlling the rate of grinding so that it decreases as the difference decreases, so that the diameter of the workpiece is progressively brought towards a value determined by the datum value. In one embodiment, Figs. 1-5, a workpiece 12, Fig. 1, rotated about a horizontal axis, is ground by a grinding wheel 13 driven by an A.C. electric motor 14, the wheel and motor being mounted on a cross-slide 15 movable, towards and away from the workpiece, by feed mechanism including a motor 42 driving a cam 16a acting, through a rocking lever 16b, on a saddle 17 traversed on a slideway 20. The output terminal JJ of the input network shown in Fig. 4 is connected to the input terminal J of the amplifier shown in Fig. 3 to constitute a grinding machine control amplifier 33. A pneumatic measuring head 18 is mounted at the top of a rigid frame 19 rigidly connected to the saddle 17. A diameter of the workpiece at that portion in register with the grinding wheel is engaged at one end by an anvil 21 projecting from the frame 19 and at the other end by the feeler 22 of the measuring head. Standard pressure air from a supply unit 23 is delivered through line 24 to the measuring head, and axial movement of the feeler, due to change of workpiece diameter, alters the pressure drop across an orifice in the head 18. The resultant modified air pressure, which is a measure of the difference between the workpiece diameter and a datum diameter determined by the position of the orifice, is transmitted through line 27 to bellows 31, 31a. Standard pressure air from the supply unit 23 is delivered through line 25 to bellows 29, 29a. The bellows 29a, 31a operate a pressure gauge 34 indicating the workpiece diameter error. An A.C. signal of 6 volts at mains frequency is fed in at terminals A-A of the input network. A voltage tapped off across a potentiometer 38 is applied to the primary winding 39 of a differential transformer 36 the armature of which is coupled to the bellows 29, 31 so that an output signal representing the diameter error is obtained. The rate of grinding is measured by measuring the load on the wheel motor 14, the current passing through the primary 35a of a transformer so that the secondary winding 35b provides an alternating voltage signal at mains frequency proportional to the wheel motor current. This signal is fed in at terminals B-B of the input network.  A signal at mains frequency is fed in at terminals C-C of the input network to cancel out that part of the motor load signal which represents the " no-load condition of the grinding wheel so that the resultant signal represents the mechanical load on the grinding wheel. The " no-load " cancelling signal is adjusted by a potentiometer 41 to an experimentally determined value. A signal in opposition to the load signal and representing the velocity with which the grinding wheel is moved towards or away from the workpiece is fed in at terminals D-D of the input network from output terminals DD-DD of the amplifier, the negative feed back thus provided checking any tendency to hunt. The signals derived from inputs at terminals C-C and D-D may both be adjusted by a potentiometer 43 and the feed back to input at D-D may also be adjusted by a potentiometer 41. The potentiometers 38, 41 are provided with calibrated knobs 109, 111 and control respectively the maximum and minimum grinding wheel loads.  An over-riding manual control for controlling the motor 42 to withdraw the grinding wheel from the workpiece is provided. For this purpose a mains frequency of 6À3 volts is applied to terminals H-H and through a potentiometer 45 in such a way that when the resultant voltage at terminal F is applied to the grid of the second stage of the amplifier the latter controls the motor 42 to withdraw the grinding wheel. A self-latching relay 46 is powered by 300 volts D.C. When the button 47 is pushed contacts 49 are held closed connecting point F to point G on the amplifier until button 48 is pushed. The output of the control amplifier 33 drives a motor 51 mechanically coupled to a synchro transmitter 52 which drives the feed motor 42, the controls of the input network and amplifier being set so that when button 48 has been pushed the amplifier controls the motor 42 so that the rate of grinding varies with the error of the workpiece diameter from the datum diameter.  To alter the datum diameter the position of the orifice within the pneumatic measuring head 18 is altered by a zero-set synchro receiver motor 61 driven by a transmitter 62. In parallel with the motor 61 is a zero-set motor 63 which adjusts the zero-position of a pneumatic reference head 64 identically and simultaneously with the zero-position of the measuring head 18. Standard pressure air from the supply unit 23 is delivered through line 26 to the reference head and the modified air pressure, depending on the position of the reference head feeler 65, is transmitted to bellows 68. Standard pressure air from the supply unit 23 is delivered through line 25 to bellows 67. The output terminal JJJ of the input network shown in Fig. 5 is connected to the input terminal J of the amplifier shown in Fig. 3 to constitute a zero-set control amplifier 72. An A.C. signal of 6 volts is fed in at terminals AA-AA of the input network. The bellows 67, 68 are coupled to the armature of a differential transformer 71. A signal representing the rate of rotation of a motor 74 controlled by the amplifier 72, is fed in at terminals DDD-DDD of the input network from output terminals DD-DD to provide negative feed back adjustable by the potentiometers 44, 75. The output of the zero-set control amplifier 72 drives a motor 74 mechanically coupled to the transmitter 62. To grind tapered or cambered workpieces, the datum diameter is varied, by varying the position of the reference head feeler 65, as the grinding wheel traverses the workpiece. The end of the feeler 65 rests on an arm 76 supported at one end by a spring strip 83; the other end of the arm 76 is urged downwardly by a spring 79 and is adjustably supported by a steel tape 81 wound round and attached to a " datum set " spindle 82. An arm 84, supported by a spring 85, has its lower end attached by a spring strip 86 to the arm 76, and has at its upper end a roller 87 which bears against an arm 88 pivoted at 91. The arm 88 has a roller 94 urged by a spring 96 into contact with a cam 95. A spring 89 urges the arm 84 away from the pivot 91. Attached to the arm 84 is a steel tape 92 wound round and attached to a " set percentage camber " spindle 93, so that the distance of the roller 87 from the pivot 91 can be adjusted by rotating the spindle 93 so as to vary from zero upwards the transmission ratio between arms 88, 84. Thus the position of the reference head feeler 65 depends upon (i) the angular position of the " datum set " spindle 82, (ii) the angular position of the " set percentage camber " spindle 93, and (iii) the angular position of the cam 95. The cam 95 is rotated through gearing 102 by a synchro receiver motor 97 driven by a synchro transmitter 98 mounted on the saddle 17, a pinion 99 mounted on the shaft of the transmitter engaging a rack 101 secured on the slideway 20 so that the cam 95 is rotated automatically by an amount proportional to the distance of travel of the grinding wheel 13 along the workpiece. An automatically operated reversing switch 103 is provided to reverse the sense of rotation of the motor 97 with respect to that of the transmitter 98 at the mid-point of the traverse, the cam 95 rotating to its full extent for half the traverse and then rotating in the opposite direction for the remainder of the traverse. A permanent record of the variation of the diameter of the workpiece along its length is provided by a chart recorder 104, the recording pen moving under the control of a diameter error indicator (not shown) similar to the pressure gauge 34 and the rotation of the chart being produced by a motor (not shown) driven by the synchro transmitter 98. An indicator 106 driven by a receiver motor 107 electrically coupled to the transmitter 32 indicates continuously how far the grinding wheel is fed towards the workpiece. An ammeter 108 indicates the current passing through the grinding wheel motor 14. An indicator 112 driven by the zero-set motor 63 of the reference head 64 gives a continuous indication of the instantaneous value of the datum diameter. In another embodiment, Figs. 6-10, a workpiece 212, Fig. 6, rotated about a horizontal axis is ground by a grinding wheel 213 driven by a D.C. electric motor 214, the wheel and motor being mounted on a table 215 mounted on a saddle 216 traversed along a slideway 217. The table 215 is pivotally mounted relative to the saddle 216 about an axis 222 and the grinding wheel is moved towards and away from the workpiece by pivoting the table about the axis 222. This is effected by a motor 223 driving a cam 224 bearing against one end of a lever 225 pivoted on the saddle 216, the other end of the lever gearing against a stop 227 on the table 215. A rigid frame attached to the sadd