Patent GB-495818-A (GB)
Title: Improvements in or relating to electric control systems for machine tools and other machines and apparatus
IPC: B23Q5/32
Filed: 1937-04-14
Abstract: 495,818. Control of several motors ; photo-electric control of drilling &c. machines. ASSOCIATED EQUIPMENT CO., Ltd., and JONES, E. J. H. April 14, 1937, No. 25008/38. Divided out of 495,762, [Group XL]. [Class 38 (iii)] [Also in Groups XXII and XL] Travelling to predetermined limits.-Relates to electric control systems for machines or other apparatus, wherein a predetermined succession of movements of a movable member is required, including a variablespeed feed-movement having superimposed thereon at a predetermined stage a reverse movement followed by a return of the member approximately to the position occupied by it immediately before the reversal. The invention is characterized by the use for controlling in the required manner an electrically operated device by which the movements of the movable member are controlled, of movable main and auxiliary circuitcontrol elements, the auxiliary element being adapted to be oscillated during the reverse and return movements of the movable member so as to modify the control effected by the main element. The control of drilling and reaming machines is a particular object of the invention, but it is not restricted to such applications. In the machine described and shown, the main and auxiliary circuit - control elements are shutters controlling the admission of light to photo - electric cells, but they may be replaced by switches such as drums or discs carrying suitably spaced contacts. The Figures show machines particularly intended for drilling and reaming aligned journals of crank-shafts for internalcombustion engines. Two machines are arranged side by side on a common mounting, but each is separately driven and controlled. Each machine comprises a counterbalanced drill-head 15, Fig. 1, movable up and down vertical guideways 14 on a pillar 13 by a screw 16, and carrying an electromotor 23 for rotating the drill spindle. The screw is driven by two motors (not shown) within the pillar, the motors operating through differential gearing. The work to be drilled is suitably supported, e.g. by V-blocks 234 and clamping-plates (not shown). The differential gear, Fig. 6, comprises bevel wheels 169, 178 geared respectively to the spindles 140, 141 of a slow-speed motor and a high-speed motor, these bevel wheels gearing with planetary wheels 170 mounted on stub-shafts on a driven shaft 29. The slow motor operates continuously when the machine is working; the fast motor, which is reversible, and is started, stopped, and reversed as required under automatic control, as subsequently described, has an electromagnetic brake which is automatically applied whenever the motor is de-energized. When the fast motor is at rest, its brake serves to hold the bevel wheel 178 stationary, and the wheel 169 therefore drives the shaft 29 slowly, through the wheels 170. When the fast motor runs, its drive is added to or over-rides that of the slow motor, and the shaft 29 is consequently driven fast in one direction or the other. The shaft 29 is geared to the feed-screw 16, and also to a lateral shaft 36 which drives mechanism for controlling the traverse of the drill-head. The shaft 36, which thus rotates at a speed proportional to that of the screw 16, extends through a side wall of the pillar 13, Fig. 3, and drives at a reduced speed, through epicyclic gearing 50 ... 53 in an oil casing, a hollow shaft 55, in which the reduced end 57 of the shaft 36 is received. The shaft 55 drives two control members consisting of a disc 59 and a quadrant 60 respectively, these members being provided with suitable apertures whereby light is admitted at predetermined periods to photoelectric cells which control the motors in such a way as to produce the required movements of the drill-heads. In drilling aligned journals of a crank-shaft, the following sequence of movements of the drill-head is required: (1) a fast forward feed to bring the drill close to the work ; (2) a slow forward cutting feed (3) a fast reverse movement to clear out swarf; (4) a fast forward movement to return the drill to the work ; and (5) a further slow cutting feed. When the first journal has been fully drilled, with required repetitions of operations (3) to (5), a fast forward movement of the drill between the two journals is needed. During these operations, the main control disc 59 moves forward intermittently, and the auxiliary quadrant 60 performs oscillatory movements during operations (3) and (4). For this purpose, the disc 59 is coupled to the shaft 55 through a one-way pawl-andratchet coupling 66 (means being provided for enabling angular adjustment of the disc about the axis of the driving shaft to be made), while the quadrant 60 is secured to a ring 80 supported by arms 81 from a ring 83 which is driven from the shaft 55 through a slipping clutch 85. This arrangement is such that the quadrant is driven in either direction through the clutch 85, but its forward movement is limited by a stop 79 ; when reverse rotation.of the feed-screw 16 (and consequently of the shaft 55) occurs, the disc 59 is held stationary by a brake 70. As shown in Fig. 5, the disc 59 has two circumferential rows of slots, an outer row comprising a long slot 118 and shorter slots 119, and an inner row of slots 120. In the quadrant 60 there is a single wide slot 121 having a stepped end 122. All these slots co-operate to admit light selectively through windows 111, 112, 114 to photo-electric cells 90, 91, which respectively effect the forward and reverse movements of the drill-head by operating relays, Fig. 10 (not shown), which control the motor circuits. The general operation of the machine is as follows. With the drill-head at the top of its travel, when a push-button switch is operated to start the high-speed motor forwardly the drill head is carried downwardly by the screw 16. The disc 59 turns from the position shown in Fig. 5, until the slot 118 uncovers the window 111 of the cell 90, whereby a switch is closed to maintain the circuit of the fast motor. The push-button switch may then be released, and a second manual switch operated to start the drill-rotating motor and the slow feed motor. Just before the point of the drill touches the work, the slot 118 moves fully past the window 111, and the cell 90 is de-energized, so that the fast motor is stopped, and the drill-head continues to be moved down slowly by the slow motor operating through the differential gear. This proceeds until the first slot 120 reaches the window 114 and allows light to pass to the cell 91. A circuit is thereby closed to operate the fast motor reversely, and the drill-head is moved quickly upwards. The shafts 36, 55 are consequently reversed also the one-way coupling 66 allowing the disc 59 to remain stationary, whilst the quadrant 60 is driven counterclockwise, Fig. 5, through the friction clutch 85. The reverse movement continues for a period determined by a delayed-action relay, which, through the discharge of a condenser, becomes de-energized a predetermined time after the " reverse " cell has operated, and thereby causes the reversing circuit of the fast motor to be broken. Meanwhile the slot 121 in the quadrant 60 has exposed the cell 90 to light, preparing the " forward" circuit through the fast motor, which is completed at the instant when the reverse circuit is broken. The drill head is then again fed quickly forward, and the quadrant, also moving forward, cuts off light from the cell 90 when the point of the drill has almost reached the last cutting point in the work. Thus the fast motor is again stopped, and the feed of the drill-head is effected only by the slow motor, proceeding during the next stage of drilling. The drive of the disc 59 is picked up where it had previously ended. Additional " reverse slots 120 in the disc 59 cause the above-described sequence of reverse and return movements to be repeated at intervals during the drilling of the journals, the slots 119 serving to bring about rapid forward movements of the drill-head whilst the drill is passing through the space between the journals. When the drill-head has reached the bottom of its travel, a lower limit switch 196 is closed, Fig. 1, and effects the completion of the reversing circuit, an upper limit switch 195 being opened, when the drill-head has been returned to the starting position, to stop the motor. Overload switches are associated with the motors, and means are provided for automatically reversing the travel of the drillhead if excessive resistance is encountered. Such means comprise a switch adapted to be operated by endwise movement of a worm in the reduction gear associated with the slow feed motor. The worm-operated switch, co-operating with the delay-action relay, effects repeated timed reversals of the drill-head if an accumulation of swarf is impeding the drill. For reaming operations, control may be effected by the disc 59 alone. Instead of a disc and quadrant as shown, the shutters for the photo-electric cells may be formed as rotatable cylinders, reciprocable slides, endless bands, or the like. Specification 495,762 is referred to.