Patent GB-857030-A (GB)
Title: Duplex driving mechanisms
Inventor: ROYLE JOSEPH KENNETH
IPC: B23Q5/50
Filed: 1958-10-02
Abstract: 857,030. Programmed electric control systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 2, 1959 [Oct. 2, 1958], No. 31482/58. Class 38 (6). [Also in Group XXII] Driving apparatus for causing relative movement along a predetermined path between a first object 1 and a second object 2, comprises a first driving mechanism CI and a second driving mechanism CII, each such mechanism in turn comprising two members between which relative movement takes place to provide driving action of the mechanism, the first of such members being secured to the first object and the second of such members being provided with means for releasably securing it to the second object at different positions along a track parallel to the said predetermined path, means adapted in response to an incoming driving signal to initiate driving action on the part of the driving mechanism, means for positioning the first member relative to the second member when the driving mechanism in question is not executing a driving action and means for indicating the relative positions of the two members at least at a plurality of predetermined relative positions of the two members, the apparatus further comprising means for operating the locking means of the first drive and releasing the locking means of the second drive, means for applying driving signals to the first drive actuating means, means for actuating the second drive positioning means to place the members of the second drive in predetermined relative positions, means under control of the first drive indicating means for operating the second drive locking means and bringing the second drive actuating means under control of the driving signals and means, operable when the locking means of both drives are operated and before either of the driving mechanisms has reached an end of its range of driving action, for releasing the locking means of that one of the two driving mechanisms which is nearest to an end of its driving range which it is at that instant approaching in the course of its driving action and removing the actuating means of that driving mechanism from the control of the driving signals, the first drive and the second drive being interchangeable in respect of the functions of the various means further comprised in the apparatus as aforesaid whereby the two driving mechanisms may operate in turn to produce relative movement between the first object and the second object. The similar driving mechanisms CI, CII each comprise a piston PI (PII) attached to a slide FI (FII) which can be locked to a slideway 2 by applying pressure within a space LC, Fig. 3, which slideway may be that on which the machine tool table 1 slides. Programmed driving signals are supplied in turn to actuators AI, All controlling valves VI, VII of the mechanisms so that one drives while the slide of the other is locked, there being a short overlap when both slides are locked. While, say, mechanism CI is driving the table to the right, the piston PII must be moved to the right-hand end of its cylinder. To achieve this latter movement, the mechanism is cut off from its valve VII and a connection TII is opened to allow fluid to pass from one end of the cylinder CII to the other. The sequence of movements, some of which may occur simultaneously, is then: indicating means indicate the approach of piston PI to the end of its stroke, similar means indicate that PII is positioned, the slide FII is locked, valve VII is connected to receive signals, connection TII is closed, slide FI is released, valve VII is disconnected, and connection TI is made operative. If there is to be a change of direction, however, the change-over from one drive to the other is quickly reversed. Yet again, if a signal to change direction is received while the overlap of both slides being locked occurs, no changeover of drive occurs and the original drive is re-established. Attached to the underside of the table 1 are a cylinder CIII containing a piston PIII and a valve-body VIII having a valve attached to the piston PIII. The piston PIII carries a slide 4 having a pinion 5 engaging racks 6, 7 secured to the slides FI, FII. Whenever the piston PIII moves from its central position, the valve VIII restores it as long as a connection TIII is open to allow fluid to pass from one end of the cylinder CIII to the other. Whenever the piston PIII is locked, relative movement of the piston and cylinder of one drive results in an opposite movement of the other drive unless both slides F are locked in which case TIII is open to allow the piston PIII to move freely. The movements are controlled by limit switches 1S 2S and 3S, 4S co-operating with cams CaI, CaII. Each mechanism is associated with a MoirÚ fringe device having light cells MI, MII to provide a monitoring system in which error signals can be supplied to the actuator of the operative driving mechanism. The monitoring devices are brought into phase before a change-over by applying a correction signal to an electromechanical transducer inserted between the rod of the piston PIII and the valve VIII. In a modification, the cylinders CI, CII are connected in series and a single control valve is provided. In a further modification, the rack- and-pinion devices 5, 6, 7 are replaced by auxiliary piston-cylinder devices connected in parallel with the main drives. In yet another modification, to position the free foot, the command signals are applied in the reversed sense to the valve controlling the corresponding piston-cylinder assembly. The rack-and-pinion devices 5, 6, 7 and the piston assembly PIII are omitted. In this case, the phasing of the monitoring devices may be achieved by spaced plugs LPg, Fig. 6, in each foot F, one of which plugs can be forced by fluid pressure into an adjacent recess LH in the slideway 2. In other modifications, the control circuit is modified to dispense with the connections TI, TII, or to accelerate the positioning of a foot by amplifying the reversed command signals, or a single long MoitrÚ fringe device is used instead of two short ones.