Patent GB-702226-A (GB)
Title: Improvements in or relating to electric circuit controlling apparatus particularly for effecting electric cycles of movement of the work tables of machine tools
IPC: G05B19/06
Filed: 1951-05-02
Abstract: 702,226. Milling. VICTORIA MACHINE TOOL CO., Ltd., FRYE, J., and SELBY, J. April 30, 1952 [May 2, 1951], No. 10307/51. Class 83 (3). [Also in Group XXXVII] Relates to electric circuit controlling apparatus for effecting selected cycles of movement of the work tables of milling machines &c. A number of dogs 1 are carried by the work-table 2 and a corresponding number of electric switches 3 are mounted on an adjacent fixed structure. The dogs and their corresponding switches are mounted at different levels so that each dog engages its own switch at a given position of the work-table and cannot engage any other switch. Each dog is capable of yielding pivotably so that it rides past a switch-actuating element 4 when moving in one direction, and only engages and depresses the element when moving oppositely to initiate a given speed and direction of the table or to stop it. As shown, there are five sets of dogs and switches which, when operative, either stop the machine, institute slow feeding movement in either direction, or establish fast travelling movement in either direction. Each of the dogs 1 can be adjusted to a selected horizontal position on the table 2 and can be arranged either way round. The switches 3 are plunger-actuated and are all secured to a fixed circular carrier-block 5, spring-biased balls 4 constituting the actuating elements. Pawls 11 on the dogs 1 turn on a pivot in opposition to a light spring which normally holds the pawl against a fixed stop so that the pawl can only tilt in one direction. The plungers of the switches 3 require only a small movement for operation, the contacts being carried by flat springs which move through a dead-centre position to and from the normal and operation positions. Motors 22, 23 move the table in either direction at feeding speed and quick-travel speed respectively, motor 22 being controlled by contactors FLC, FRC, and motor 23 by contactors TLC, TRC. The switches 3 have contacts such as FL, AFL, in the circuits of relays, e.g. AFLW, which control the windings, such as FLCI, of the self-maintaining contactors FLC ... TRC. If the table is being fed to the left, actuation of an appropriate switch 3 will discontinue that operation and initiate feed-right operation, similar action taking place during quick-travel. Relays TW, FW, allow the transfer from feeding operation to quick travel in the opposite direction. The stop switch has contacts ST for isolating the automatic control circuit. Manual operation is instituted by opening contacts AC and closing contacts HC, hand operation being controlled by four push-buttons FLPB, FRPB, TLPB and TRPB. In the case of the feed push-buttons FLPB, FRPB, momentary depression only is necessary to energize and maintain the corresponding windings FLCI, FRCI. In the case where a feed movement is taking place following depression of a pushbutton, actuation of another push-button will stop said feed movement and will substitute the movement called for. If two bush-buttons are depressed together, however, no action takes place. Closure of contacts AC energizes a relay having contacts CR3 in the automatic control circuit, and one of the consequences of setting the change-over switch for automatic operation is that neither of the feed push-buttons can function to initiate maintained closure of the respective feed contactors. Automatic feeding operation in one direction may be stopped by actuating a push-button to set up feeding operation in the opposite direction, but release of the push-button restores the original condition unless one of the dogs has operated. When feeding the table under automatic conditions, depression of a reverse quick-travel push-button causes both motors 22, 23 to run simultaneously. These motors are coupled to the table through differential gearing so that the motor 23 prevails and the table responds to the quick-travel button. Depression of a quick-travel button when the table is being fed under automatic control in the direction called for by that button has no effect due to interlocking provided by relays FLRI, FRRI. During quick travel in either direction under automatic control, depression of any push-button appertaining to a different movement will supplant the quick-travel by the appropriate movement as long as the push-button is depressed. Interlocks are provided to prevent two feed contactors closing together and two quick-travel contactors closing together. When contacts AC are closed to initiate automatic operation it may be necessary to start the cycle by a quick-travel push-button until one of the dogs actuates its appropriate switch. The spindle of the machine is driven by a motor 29 and a three-position switch S selectively arranges that the machine can run when either the motors 22, 23 are running, only when the motor 22 is running, or not at all. A signal lamp SL is illuminated when no table movement is in operation. A back-lash eliminator as described in Specification 664,824 is provided, a selector switch K putting the eliminator in operation during feed movements only. Hand control is initiated and stopped by pushbuttons PPB, SPB respectively. Limit switches ULP, ULL, are provided. A construction of the push-button switches FLPB ... TRPB is illustrated in Figs. 4 and 5 (not shown). Each switch comprises a reciprocable spring-biased plunger mounting a number of ring contacts which cooperate with fixed contacts in a block of insulating material. The fixed contacts are biased inwardly by leaf springs mounted on the outside of the block. According to the Provisional Specification, each push knob for operating a plunger has a cap marked with insignia, in a similar manner to that described in Specification 665,738.