JPS6446053A - Belt transmission mechanism - Google Patents

Abstract

PURPOSE:To miniaturize the captioned mechanism even if the number of grooves of either or both of timing-belt pulleys is not a multiple of an integer by providing grooves on the peripheries of the pulleys at a specified pitch when the minimum number of grooves of both of the pulleys is not a multiple of an integer. CONSTITUTION:When the ratio N1:N2 of the number of grooves of two timing-belt pulleys 4, 5 is set in such way that either is not the multiple of integer of a positive number as, 20:81, grooves of 20 (N1), 81 (N2) in numbers are provided on the peripheries of the pulleys 4, 5 respectively at a fraction of integer, e.g., 1/2 of the tooth pitch P of a timing belt 3. In this case, since the number of grooves (20) of the pulley 4 is an even number, the teeth of the belt 3 are engaged with the grooves at every other tooth, actually engaging with only ten (10) grooves. Hence, if ten (10) grooves are provided around the pulley 4 at the same groove pitch as the tooth pitch P of the belt 3, the diameter of the pulley 4 becomes 1/2 the original diameter. On the other hand, the diameter D' of the pulley 5 becomes, D'=P/2X81/pi, which is also 1/2 the original diameter. That is, the outside dimension of the pulley 5 can be made small to 1/2 notwithstanding that the number of grooves is not a multiple of an integer.