Patent GB-959295-A (GB)
Title: Improvements in and relating to machine tools
Inventor: POLLARD PETER JACK
IPC: G05B19/04
Filed: 1961-03-08
Abstract: 959,295. Grinding; machine tool details. MOLLART ENGINEERING CO. Ltd. March 8, 1962, [March 8, 1961], No. 4700/61. Headings B3B and B3D. A sequence analyser for a fixed-cycle machine tool, such as a high-speed grinding machine, comprises a plurality of switch members adapted to be actuated in a predetermined sequence during each cycle of the machine tool, a plurality of control members associated with said switch members and each adapted to be actuated following actuation of a switch member associated therewith so as sequentially to control the machine tool operations in accordance with the fixed cycle thereof, a first plurality of visual indicators associated one with each sequential step of the cycle and adapted to be illuminated so as to indicate the progress of the machine cycle, a further plurality of visual indicators associated with the control members and a timing device operatively connected to said further plurality of visual indicators and to said switch and control members and arranged to run-down at a predetermined rate and to be reset at the beginning of each step of the cycle whereby whenever a fault occurs, a visual indication thereof is produced after the rundown period of the timing device has expired. A further visual indicator may be associated with each switch member such that a direct indication is given to the operator should any particular switch member not be actuated within the run-down period of the timing device, thereby facilitating the analysis and location of the fault. A high-speed special purpose grinding machine comprises two spaced heads, one of which is provided with a carriage carrying a pair of high-speed grinding spindles, one for fine grinding and the other for coarse grinding, the other head comprising a rotatable turret having four work stations, viz.: (1) receiving a new workpiece, (2) coarse grinding, (3) fine grinding, and (4) automatically ejecting a finished workpiece. The turret is rotatable about a horizontal axis and presents to the grinding spindles a circular vertical face in which are mounted four spindles carrying work-holding fixtures equispaced round a common pitch circle. The turrent is indexed in increments of 90 degrees, a V-shaped plunger locating and locking the turret in each index position. A first microswitch indicates when the plunger is operative, and a second microswitch indicates when it is inoperative so as to allow indexing of the turret. During grinding of a workpiece, when the turret is locked, the spindles and workholding fixtures are slowly rotated through 270 degrees in the same direction as the index rotation of the turret. The 270 degrees rotation of the spindle is effected in one direction only and does not return, but at the end of the grinding operation the turret indexes through 90 degrees to present the work-holding fixture to the next station in the same datum angular position as at the beginning of the partial rotation. Each spindle is geared to a central gear mounted coaxially with the turret and integral with another gear meshing with two parallel racks one on each side of it. The racks are cylindrical and mounted in bushes allowing movement of the racks in opposite directions to effect a partial rotation of the coaxial gear in either direction. One rack is operated by a double-acting air cylinder and the other is connected to an oil dashpot system for controlling the speed of operation. Stops limit the rack movement to give a 90 degrees rotation to the coaxial gear which, through a freewheel ratchet device imparts a 90 degrees index rotation to the turret when its locking plunger is inoperative and the rack is made to travel in a particular direction, the limit of which is controlled by a dead stop and recorded by a further microswitch. When the turret is locked and the rack movement is reversed, the coaxial gear rotates 90 degrees in the opposite direction and is geared to the spindles in such a way as to rotate them all through 270 degrees in the same direction as the index rotation of the turret, the ratchet freewheeling against the locked turret and the dashpot system controlling the speed of the spindle rotation. Another dead stop controls the end of the 270 degrees spindle rotation which is recorded by a further microswitch. The turret is maintained stationary in an indexed position for a sufficient period for coarse and fine grading to be completed. Dressing or trueing diamonds disposed opposite the grinding stations can be moved into operative position or inoperative position, as required, by pneumatic rams controlled by valves. The high speed grinding spindles are mounted with one vertically above the other in a carriage movable on slideways to move the grinding wheels into and out of the bores of the workpieces. Superimposed on this motion is a high speed, short and fixed stroke reciprocation. The carriage reciprocation is effected by the piston of an automatic pneumatic reciprocating cylinder, the latter being moved by an air cylinder with oil dashpot speed control. As the grinding wheels approach the workpieces they pass the trueing diamonds which are swung into position to contact the wheel peripheries. When the wheels have just entered the workpieces, which is recorded by microswitches, the diamonds are swung to inoperative position and the fast reciprocation started, an air interlock valve system preventing the reciprocation starting before diamond removal. The back position of the carriage is recorded by a further microswitch The indicator panel has eight flashing lights 30-37 corresponding to the eight sequential steps of the cycle, viz.: (1) carriage forward (2) loading ram forward, (3) diamond clear, (4) grinding, (5) loading ram back, (6) carriage back, (7) index pin out, and (8) index. Further lights 29, 28 representing " Index pin in " and " Diamond in " are illuminated at the beginning of each cycle and remain so until the index pin and trueing diamonds are withdrawn. Ten lights 10-19 are indicative of the condition of five relays A, C, D, E, F controlling the cycle, illumination of a light indicating failure of the corresponding relay to respond within the allotted timing period. A microswitch analyser comprises a translucent panel adapted to be illuminated so as to project on to the face thereof a numerical representation of the particular microswitch at fault.