外文资料翻译
Belt Conveying Systems Development of driving system
Among the methods of material conveying employed
，
belt conveyors play a very important part in the reliable carrying of material over lo
ng distances at competitive cost
．
Conveyor systems have become larger and more co
mplex and drive systems have also been going through a process of evolution and wi
ll continue to do so
．
Nowadaysbigger belts require more power and have brought the
need for larger individual drives, the ability to control drive acceleration torque is cr
itical to belt conveyorsperformance
．
An efficient drive system should be able to prov
ide smoothsoft starts while maintaining belt tensions within the specified safe limits
．
For load sharing on multiple drives
．
torque and speed control are also important co
nsiderations in the drive systems design. Due to the advances in conveyor drive contr
ol technologyat present many more reliable
．
Cost-effective and performance-driven
conveyor drive systems covering a wide range of power are available for choices.
1 Analysis on conveyor drive technologies
1
．
1 Direct drives Full-voltage starters
．
With a full-voltage starter designthe conveyor head shaft is dire ct- co upled to
the mo to r through the ge ar drive
．
Direct full-voltage starters are adequ
ate for relatively low-power, simple-profile conveyors
．
With direct fu11-voltage starters
．
no control is provided for various conveyor loads and
．
depending on the ratio betw
een fu11- and no-1oad power requirementsempty starting times can be three or fou
r times faster than full load
．
The maintenance-free starting system is simplelow-cost
and very reliable
．
However, they cannot control starting torque and ma x i mu m st a l
l torqu e therefore
．
th e y ar e li m i t e d t o th e lo w - p o w e r, si m p l e - p r o f i l e
conveyor belt drives
．
Reduced-voltage starters
．
As conveyor power requirements increasecontrolling the applied motor torque
during the acceleration period becomes increasingly important
．
Because motor torqu
e 1s a function of voltagemotor voltage must be controlled
．
This can be achieved thr
ough reduced-voltage starters by employing a silicon controlled rectifier(SCR)
．
A co
mmon starting method with SCR reduced-voltage starters is to apply low voltage initi
ally to take up conveyor belt slack
．
and then to apply a timed linear ramp up to full v
oltage and belt speed
．
However, this starting method will not produce constant conve
yor belt acceleration
．
When acceleration is complete
．
the SCRs, which control the ap
plied voltage to the electric motor
．
are locked in full conduction, providing fu11-line
voltage to the motor
．
Motors with higher torque and pullup torquecan provide better
