Patent GB-691771-A (GB)
Title: Driving control means for machine tools
IPC: B23Q5/10
Filed: 1951-05-21
Abstract: 691,771. Operating clutches reversing gearing. WARNER & SWASEY CO. May 21, 1951 [June 30, 1950], No. 11790/51. Class 80 (ii). In a power drive of a lathe or like machine tool an electromagnetically operated friction clutch includes a resistance in its control circuit, which is effective upon initial energisation of the clutch to limit the torque transmitting capacity, and a delayed action means adapted to short circuit automatically this resistance after commencement of rotation of the driven member. The clutch shown in Fig. 3 comprises a driving member 32 in the form of a motor driven pulley which carries an energising coil 35 for an armature 39 secured to a driven shaft 33. The armature 39 is adapted to engage frictionally a plate 40 covering the coil 35 on energisation thereof to transmit the drive. A brake 45 is also adapted to act upon a plate 44 secured to the driven shaft 33 upon energisation of a fixed coil 46. A circuit for controlling the clutch and brake of Fig. 3 is shown in Fig. 6 and includes a 3-phase supply L1, L2, L3 to a driving motor 30, a transformer T, and a rectifier 110 for supplying a direct current for the clutch and brake coils 35, 46. Resistances 120, 121 are provided in series with the clutch coil 35, the resistance 120 being adjustable to determine the maximum torque capacity of the clutch and the resistance 121, also adjustable, being provided to limit the torque capacity upon initial energisation under control of a relay STD of the time delay type. An adjustable resistance 124 is also provided in series with the brake coil 46. The engagement of the clutch is effected by means of a control lever 66, Fig. 5, which also controls through lostmotion a sleeve 72 for operating forward and reverse mechanical clutches, and which in its central stop position shown engages and holds open a switch SS. The switch SS controls the supply of energy to a relay BR and when closed by movement of lever 66 to the left or right, for forward or reverse speed of the machine, operates this relay to energise the clutch coil 35 and de-energise the brake coil 46. The relay BR also operates simultaneously the relay STD which after a predetermined interval of time short-circuits the resistance 121 to allow the maximum torque capacity of the clutch to be transmitted. To stop the machine the lever 66 is returned to its central position and the switch SS opened so that the clutch is disengaged and the brake applied. Owing to the lost-motion between lever 66 and sleeve 72 the mechanical clutch remains engaged so that " inching can be carried out by momentary operations of lever 66 so that a power operated chuck wrench can be utilised. Movement of the lever 66 to the opposite position changes the mechanical clutches over and re-engages the electro-magnetic clutch in the manner as described above. An interlock switch WLS is also provided for this wrench so that while it is operating the clutching circuit cannot be completed. A solenoid WS in the clutching circuit also operates a lock for the power wrench so that the wrench cannot be operated whilst the machine is running. In a modified arrangement instead of the time delay relay STD for short-circuiting the clutch coil resistance 121 a speed responsive switch of the type described in Specification 603,286, [Group XXXVII], on the driven shaft 33 or other shaft of the machine is utilised so that on this shaft reaching a certain speed the low torque-resistance is cut out to allow full torque capacity. In this case the switch SS is replaced by two switches operated by movement of the lever 66 to its forward or reverse position respectively to control the energisation of the clutch coil and de-energisation of the brake coil. In another arrangement the mechanical clutches for forward and reverse selection are dispensed with and separate forward and reverse electromagnetically operated clutches employed, these clutches and the brake being controlled by two switches operated by the lever 66 as before for forward and reverse driving. In this case also a speed responsive switch is used for short-circuiting the initial low torque capacity-clutch resistance at a determined speed of the driven shaft. This last arrangement may be further modified by omitting the electromagnetic brake and energising the opposite clutch to provide a braking effect. In this arrangement two speed responsive switches are provided one acting as before to cut-out the initial torque capacity resistance at a predetermined speed and the other to de-energise the braking clutch when the machine shaft is substantially brought to a stop. In a still further modification separate forward and reverse clutches are employed as above but in conjunction with time delay relays for cutting out the initial low torque resistance for the clutches, the control lever co-operating with forward and reverse switches and a central switch controlling the time relays. The opposite clutch is again used for braking when it is desired to stop and a single speed responsive switch is used to de-energise the braking clutch on the machine shaft coming substantially to a. stop.