gear 82 of a spiroid gearing 83 whose pinion 84 is eccentrically in engagement with the ring gear 82 received in the tubular piece 75 is a tubular support 85 which is fixed in its position by screws 86 inserted in tubular piece 75 the support 85 consists of a tube 87 a hollow cylinder 88 directly above it and an annular end flange 89 mounted in tube 87 is a shaft 90 which carries at its lower end the pinion 84 and is firmly connected to an annular shoulder 91 which abuts against the lower end of tube 87 in the region of its upper end shaft 90 is embraced by the inner race of a ball bearing 93 pressed into the hollow cylinder 88 the upper end of shaft 90 is coupled rigidly with an output shaft 95 of a step motor 96 whose housing is screwed tight on the end flange 89 a strobe disk 100 is mounted on the main shaft 6 fig1 of the sewing machine which has two pulse tracks each cooperating with a pulse generator 101 102 one track comprises a plurality of pulse markers 103 uniformly distributed on its circumference fig6 while the other track has only two pulse markers 104 one of which passes by the pulse generator 101 as needle 13 emerges from the workpiece while the other does so when needle 13 enters the workpiece the pulse generator 101 is connected to a control unit 105 control unit 105 is connected via a control line 106a to a reversing arrangement 106 and.