DEVICE FOR PRESSING DOWN THE MOVEABLE BLADE OF AN ALTERNATELY MOVING CUTTING TOOL OF GRAIN HARVESTING MACHINES,SUCH AS HARVESTER-TRESHERS,COMBINED MOWERS AND STRAW CUTTERS AND THE LIKEHEM INSTRUMENTE S PEREMENNYM DVIZHENIEM MASHIN DLJA UBORKI ZERNOVYKH KUL'TUR,ZERNOVYKH KOMBAJJNOV,KOSILOK-SILOSOREZOK I T.P.