1、 第 1 页 外文翻译 英文原文 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 long distances at competitive cost Conveyor systems have become larger and more complex and driv
2、e systems have also been going through a process of evolution and will continue to do so Nowadays，bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the case for the conveyor drives in Chen
3、gzhuang Mine) The ability to control drive acceleration torque is critical to belt conveyors performance An efficient drive system should be able to provide smooth， soft starts while maintaining belt tensions within the specified safe limits For load sharing on multiple drives torque and speed contr
4、ol are also important considerations in the drive systems design. Due to the advances in conveyor drive control technology， at present many more reliable Cost-effective and performance-driven conveyor drive systems covering a wide range of power are available for customers choices1. 1 Analysis on co
5、nveyor drive technologies 1 1 Direct drives Full-voltage starters With a full-voltage starter design， the conveyor head shaft is direct-coupled to the motor through the gear drive Direct full-voltage starters are adequate for relatively low-power, simple-profile conveyors With direct fu11-voltage st
6、arters no control is provided for various conveyor loads and depending on the ratio between fu11- and no-1oad power requirements， empty starting times can be three or four times faster than full load The maintenance-free starting system is simple， low-cost and very reliable However, they cannot cont
7、rol starting torque and maximum stall torque； therefore they are limited to the low-power, simple-profile conveyor belt drives Reduced-voltage starters As conveyor power requirements increase， controlling the applied 第 2 页 motor torque during the acceleration period becomes increasingly important Be
8、cause motor torque 1s a function of voltage， motor voltage must be controlled This can be achieved through reduced-voltage starters by employing a silicon controlled rectifier(SCR) A common starting method with SCR reduced-voltage starters is to apply low voltage initially to take up conveyor belt s
9、lack and then to apply a timed linear ramp up to full voltage and belt speed However, this starting method will not produce constant conveyor belt acceleration When acceleration is complete the SCRs, which control the applied voltage to the electric motor are locked in full conduction, providing fu1
10、1-line voltage to the motor Motors with higher torque and pullup torque， can provide better starting torque when combined with the SCR starters, which are available in sizes up to 750 KW Wound rotor induction motors Wound rotor induction motors are connected directly to the drive system reducer and
11、are a modified configuration of a standard AC induction motor By inserting resistance in series with the motors rotor windings the modified motor control system controls motor torque For conveyor starting， resistance is placed in series with the rotor for low initial torque As the conveyor accelerat
12、es， the resistance is reduced slowly to maintain a constant acceleration torque On multiple-drive systems an external slip resistor may be left in series with the rotor windings to aid in load sharing The motor systems have a relatively simple design However, the control systems for these can be hig
13、hly complex， because they are based on computer control of the resistance switching Today， the majority of control systems are custom designed to meet a conveyor systems particular specifications Wound rotor motors are appropriate for systems requiring more than 400 kW DC motor DC motors available f
14、rom a fraction of thousands of kW ， are designed to deliver constant torque below base speed and constant kW above base speed to the maximum allowable revolutions per minute(r/min) with the majority of conveyor drives, a DC shunt wound motor is used Wherein the motors rotating armature is connected
15、externally The most common technology for controlling DC drives is a SCR device which allows for continual variable-speed operation The DC drive system is mechanically simple, but can include complex custom-designed electronics to monitor and control the complete system This system option is expensi
16、ve in comparison to other soft-start systems but it is a reliable, cost-effective drive in applications in which torque,1oad sharing and variable speed are primary considerations DC motors generally are used with higher-power conveyors， including complex profile conveyors 第 3 页 with multiple-drive s
17、ystems， booster tripper systems needing belt tension control and conveyors requiring a wide variable-speed range 1 2 Hydrokinetic coupling Hydrokinetic couplings， commonly referred to as fluid couplings are composed of three basic elements； the driven impeller, which acts as a centrifugal pump； the
18、driving hydraulic turbine known as the runner and a casing that encloses the two power components Hydraulic fluid is pumped from the driven impeller to the driving runner, producing torque at the driven shaft Because circulating hydraulic fluid produces the torque and speed， no mechanical connection
19、 is required between the driving and driven shafts The power produced by this coupling is based on the circulated fluids amount and density and the torque in proportion to input speed Because the pumping action within the fluid coupling depends on centrifugal forces the output speed is less than the
20、 input speed Referred to as slip this normally is between l% and 3% Basic hydrokinetic couplings are available in configurations from fractional to several thousand kW Fixed-fill fluid couplings Fixed-fill fluid couplings are the most commonly used soft-start devices for conveyors with simpler belt
21、profiles and limited convex/concave sections They are relatively simple,1ow-cost,reliable,maintenance free devices that provide excellent soft starting results to the majority of belt conveyors in use today Variable-fill drain couplings Drainable-fluid couplings work on the same principle as fixed-f
22、ill couplings The couplings impellers are mounted on the AC motor and the runners on the driven reducer high-speed shaft Housing mounted to the drive base encloses the working circuit The couplings rotating casing contains bleed-off orifices that continually allow fluid to exit the working circuit i
23、nto a separate hydraulic reservoir Oil from the reservoir is pumped through a heat exchanger to a solenoid-operated hydraulic valve that controls the filling of the fluid coupling To control the starting torque of a single-drive conveyor system， the AC motor current must be monitored to provide feed
24、back to the solenoid control valve Variable fill drain couplings are used in medium to high-kW conveyor systems and are available in sizes up to thousands of kW The drives can be mechanically complex and depending on the control parameters the system can be electronically intricate The drive system cost is medium to high, depending upon size specified Hydrokinetic scoop control drive The scoop control fluid coupling consists of the three
