Page 92 - Electric Drives and Electromechanical Systems

Chapter 3 Power transmission and sizing 85

V L 1 1
u i ¼ ¼ 1000 rev min ¼ 104:7 rad s
L
_ u i ¼ 104:7 rad s 1
and the theoretical input torque to accelerate the system is given by
N L
T m ¼ I tot þ T ext ¼ 0:97 Nm
t
If the lead screw efficiency is included, the continuous torque requirement is 0.88 Nm and the
acceleration torque is 1.14 Nm. In addition, no allowance has been made for the power
transmission and motor’s inertia’s and inefficiencies, including bearing and other sources of
friction.
nnn
3.3 Belt drives

A toothed belt or a chain drive is an effective method of power transmission between the
motor and the load, while still retaining synchronism between the motor and the load
(see Fig. 3.10). The use of belts, manufactured in rubber or plastic, offers a potential cost
saving over other methods of transmission. Typical applications that incorporate belt
drives include printers, ticketing machines, robotics and scanners. In the selection of a
belt drive, careful consideration has to be given to ensuring that positional accuracy is
not compromised by selection of an incorrect component. A belt drive can be used in
one of two ways, either as a linear drive system (for example, positioning a printer head)
or as speed changer.
In a linear drive application, the rotational input speed is given by,
V L
u i ¼ (3.20)
pD in
where D in is the diameter of the driving pulley (in metres), and V L is the required linear
1
speed (in m s ). The inertia of the transmission system, I tot , must include the

FIG. 3.10 A belt drive system, being used as a speed changer. The amount of belt in contact with the pullies is a
function of their diameters and the distance between the centre’s of the pullies.