GB1378921A - Method of and circuit arrangement for controlling speed ratios in gear tooth generating machines operint by the hobbing method - Google Patents

Abstract

1378921 Hobbing gears; hobbing machine controls WERKZEUGMASCHINENKOMBINAT "FRITZ HECKERT" KABL-MARXSTADT VEB 14 Jan 1972 1858/72 Headings B3K and B3B [Also in Divisions G3 and H2] A control system for a gear tooth generating machine operating by the hobbing method comprises a store 1 to which is fed a mathematically calculated pulse train representative of a desired speed ratio between a master and a follower motor for respectively driving the tool and the workpiece carrier, a measuring system 11 generating pulses in response to rotation of the master drive, which pulses are passed through a gate circuit 12 after a zero mark on a disc of the system 11 has moved past a zero sensing indicator 13, a measuring system 4 generating pulses in response to rotation of the follower drive, which pulses are counted by a counter 5 as soon as the workpiece carrier has reached a predetermined initial position detected by a zero-sensing indicator 14, summators 3, 7 which respectively receive the outputs of members 1, 5 each time a pulse from the system 11 opens gates 2, 6, and a comparator 9 deriving for each such pulse the difference between the outputs of summators 3, 7 and controlling a D/A converter 10 to adjust the speed of the follower motor, whereby the master-follower speed ratio is maintained at the desired value and the workpiece carrier and tool shaft are started at and maintained in a desired angular relationship. Fig. 2 shows the application of the invention to helical milling by the axial method, wherein a master motor M1 is connected through fixed transmission ratio (reduction) gears i n1 and iF to the tool WZ, a follower motor M2 is connected to the workpiece table T through a fixed ratio (reduction) gear i n2 and a tool feed motor M3 is connected through (reduction) gears i n3 , i v to the feed spindle Sp, the latter gears being coupled to the gears i n1 , iF through differential change gear-wheels i DW , a fixed ratio reduction gear i DA and the cage and drive input shaft of a differential gear D. The output shaft of the latter gear drives the measuring system 11 which thus receives the additional movement corresponding to the tooth helix and adjusts a higher speed of the follower drive corresponding to this movement. Various advantages of this arrangement of members 11 and D are discussed, including the provision of a second equivalent measuring system at the gear D and selection of either one according to whether straight or helical tooth systems are to be machined. During helical milling, the system 11 effects more than one revolution per revolution of the tool WZ and hence the desired tool/workpiece table angular relation is no longer obtained. This defect can be overcome by either inserting between members D, 11 an additional gear having a reduction ratio 1/i F or reducing by the factor iF the measurement range of the system, the latter solution making it necessary to count over iF revolutions.