毕业设计电梯外文翻译.docx

毕业设计：PLC应用的电梯设计外文翻译 PAGE \* MERGEFORMAT 9 ELEVATOR SAFETY :GIVE THE MINER ABRAKE ABSTRACT Over a five-year period,there were at least 18 documented cases of ascending elevators striking the overhead.In some cases,the accidents resulted in serious injuries or fatalities.These accidents occurred on counterweighted elevators as a result of electrical,mechanical,and structural failures.Elevator cars are fitted with safeties that grip the guide rails and stop a falling car;however,these devices do not provide protection in the uoward direction. Rules and regulatioins applying to elevator safety have come under review in response to these accidents .Some governing authorities have already revised their regulations to require ascending car overspeed protection. this paper will discuss basic elevaton design ,hazard,regulation,and emergency braking systems designed to provide ascending car overspeed protection.In addition ,a case-study report on a pneumatic rope brake system installed and tested on a mine elevator will be discussed. INTRODUCTION Elevators incorporate several safety features to prevent the car from crashing into the bottom of the shaft .safeties installed on the car can prevent this type of accident form occurring when the machine brake fails or the wire ropes suspending the car break .However,the inherent design of the safeties render them inoperative in the ascending direction. In the upward direction, the machine brake is required to stop the cage when an emergency condition occurs.Under normal operation,the machine brake serves only as a parking braked to hold the cage at rest .However,when an emergency condition is detected,modern elevator control system designs rely solely on the machine brake to stop the car. In theUnited States mining industry,the accident history has proven that this is not the best control strategy [2],[3].These accidents occurred when the retarding effort of the drive motor was defeated when the mechanical brake were inop