Festo Belt Drives 2, Промышленное обслуживание

Страница: 16 / 31

Job Sheet 3 – Variable-Speed Belt Drives
38
© Festo Didactic 54977-3C
Figure 31. Closed and open positions of a variable-pitch pulley.
As seen in Figure 31, the geometric aspects of a variable-pitch pulley can be
defined by the following parameters:
•
The groove angle of the pulley (
𝑎𝑎
)
•
The width (
𝑏𝑏
)
•
The groove height (
ℎ
𝑔𝑔
)
•
The clearance (
𝐶𝐶
𝐿𝐿
)
•
The outside diameter (
𝐷𝐷
𝑜𝑜
)
•
The maximum pitch diameter (
𝐷𝐷
𝑚𝑚𝑚𝑚𝑚𝑚
)
•
The minimum pitch diameter (
𝐷𝐷
𝑚𝑚𝑚𝑚𝑛𝑛
)
Based on the geometry of the variable-pitch pulley, the speed of the driven shaft
can be determined using the following formula:
𝑛𝑛
2
= 𝑛𝑛
1
∙
𝐷𝐷
𝑑𝑑
(3-1)
where
𝑛𝑛
1
is the speed of the driving shaft, in rpm
𝑛𝑛
2
is the speed of the driven shaft, in rpm
𝑑𝑑
is the pitch diameter of the driving pulley
𝐷𝐷
is the pitch diameter of the driven pulley
Since the speed of the driving shaft is fixed, the speed of the driven shaft
depends on the pitch diameters of the pulleys. A basic variable-speed belt drive
has one variable-pitch pulley and one pulley with a fixed-pitch diameter, thus the
speed of the driving shaft depends on only one variable. The diameter of a
variable-pitch pulley will vary between
𝐷𝐷
𝑚𝑚𝑚𝑚𝑛𝑛
and
𝐷𝐷
𝑚𝑚𝑚𝑚𝑚𝑚
, as seen in Figure 31.
𝑎𝑎
𝑐𝑐𝑐𝑐𝑜𝑜𝑐𝑐𝑐𝑐𝑐𝑐
𝑎𝑎
𝑜𝑜𝑜𝑜𝑐𝑐𝑛𝑛
𝑏𝑏
𝑐𝑐𝑐𝑐𝑜𝑜𝑐𝑐𝑐𝑐𝑐𝑐
𝑏𝑏
𝑜𝑜𝑜𝑜𝑐𝑐𝑛𝑛
𝐷𝐷
𝑜𝑜
𝐷𝐷
𝑚𝑚
𝑚𝑚𝑚𝑚
𝐷𝐷
𝑚𝑚
𝑚𝑚𝑛𝑛
𝐶𝐶
𝐿𝐿
ℎ
𝑔𝑔