图示传动系统,已知\( {Z}_{1}={Z}_{2}={Z}_{3}={Z}_{4}\)=20,\( {Z}_{5}\)=40,\( {D}_{1}\)=130mm,\( {D}_{2}\)=260mm,双头蜗杆,蜗轮齿数\( {Z}_{7}\)=80,卷筒直径D=200mm.

求:
(1)若要使重物G上升,则\( {n}_{1}\)转动方向如何(标在图上)?蜗轮的螺旋方向如何(左旋,右旋)?
(2)从齿轮\( {Z}_{1}\)至蜗轮\( {Z}_{7}\)这一传动路线的总传动比\( {{i}_{1}}_{7}\)为多少?
(3)若要使重物G下降6.28m,电动机需运转多少时间(以秒计)?
(4)\( {Z}_{4}\),在系统中起何作用?对系统总传动比有无影响?