GB892862A - Instrumental control of precision grinding - Google Patents

Abstract

892,862. Grinding. JONES & SHIPMAN Ltd., A. A., and HOULDSWORTH, J. Oct. 13, 1959 [July 21, 1958], No. 23319/58. Class 60. [Also in Group XXXVIII] In the grinding of a workpiece to an accurate finish the size of the piece is measured during the operation and a signal is given when it has reached a particular value approaching the desired size, followed by a further signal when the latter has been reached, the first signal stopping the feed and then automatically applying further feed, and the second signal causing the grinding wheel to be removed from the workpiece; alternatively, the first signal may be produced at a fixed time interval from the beginning of the operation. The method of the invention reduces errors due to wear of the grinding wheel and elastic deformation of the machine (see also Specification 730,172). In Fig. 11 the size of the workpiece 33 is measured by a transducer 34 (attached, e.g. as in Specification 810,316) which passe signals to a control box 36 for adjusting th feed by a pawl-and-ratchet 48 and adjustabl stop 50, and actuating the removal solenoid 41 When a particular size has been reached, th transducer sends a signal to the control bo which cuts off the feed at the unit 44 and als starts a timer 39. Grinding continues by virtu of the elastic stresses in the machine, and i these are sufficient to allow the operation to proceed until the final size is reached, the method of the present invention will not be required but a further signal will be passed from th transducer 34 to the control box to actual the withdrawal solenoid 41 and remove the grinding wheel from the work. If on the othe hand grinding ceases before the final size i reached, a signal will be delivered by the time 39 to the control box after a predetermined interval to restart the feed at 44. At the same time, however, the amount of feed is reduced by adjustment of the stop 50 by the unit 46 as a result of the control box sending a signal which may be pre-determined or may be derived fron signals of the transducer 34 and thus dependen on the progress of the operation. This cycle is repeated if necessary until the final size is reached In the alternative method of Fig. 12 the firs signal is delivered at a predetermined time from the commencement of grinding, based on an optimum grinding procedure calculated on the initial size of the workpiece. A main control box 53 is connected as before to a measuring transducer 51 and withdrawal solenoid 78. The feed is controlled by a shaft 56 which is rotated by a pawl-and-ratchet 58 as before or continuously by a hydraulic motor 59. The stop for controlling the amount of feed comprises an abutment 63 on a wheel 64 driven via a worm 66 from a motor 67. The angular positions of the shaft 56 and wheel 64 are signalled by potentiometers or selsyns 68, 69, respectively, to an auxiliary control box 72 which is connected to the main box 53. At the commencement of grinding, contact between the grinding wheel and the work is detected by the increase in power taken by the wheel, or by a vibration transducer 74, and a signal sent via the auxiliary box to the main box. At this point the latter compares the actual size of the work with the desired final size and sends a difference signal to the motor 67 to set the stop 63 accordingly. After a predetermined time (see above) the timer 82 passes a signal to the main box to stop the feed, and some time later the transducer 51 will sense that the final size has been reached and actuate the withdrawal solenoid as before. When the stop 63 is engaged by the attachment on the shaft 56 a signal is sent to the timer 82, which after a predetermined interval passes a signal to the main box 53 which then sends a further signal via box 72 to the motor 67 to move the stop 63 and allow more feed to be applied, as in the previous case. A further modification (Fig. 13, not shown) allows for the possibility that slowness of grinding may be due to excessive strains in the machine rather than wear of the wheel, in which case no extra feed will be necessary. This is sensed by a differentiating circuit attached to the main control box and continuously supplying signals representing the rate of change of size of the workpiece. If the rate of change drops when the feed stops, extra feed is required, but otherwise no feed signal is passed to the motor 67 and grinding continues until the final size is reached. The first of these states can be used to indicate that trueing of the wheel is necessary or to initiate automatic trueing processes. For extra precision near the final size the level of the signal from the size transducer can cause the application of very small amounts of feed, e.g. by the method of Specification 885,062. If desired, the rate of feed can be controlled early in the operation in accordance with signals from the size transducer, to allow initial rapid removal of material. The size values at which the transducer issues its signals can be varied by instructions from another gauge which takes its setting from a bore which is to be matched to the workpiece. The whole of the above procedure is equally applicable to the grinding of cylindrical holes and to the production of surface-ground work.