外文文献 电梯.doc

1外文文献：LiftsThere are three categories of lifts: passenger lifts are designed primarily for passenger use; goods lifts axe mainly for goods but can on occasion carry passengers; and service lifts are for goods only and are of such a size that passengers cannot get into the car. Lift speeds are determined by the number of floors served and the quality of service required. They vary from 0.5ms to 3.0ms in high office blocks.11In deciding the size of car one can allow 0.2m for each passenger, and when 2determining the load the average weight of a passenger can be taken as 75 kg. It must, however, be remembered that in many buildings the lift will be used for moving in furniture and the car must be big enough for the bulkiest piece of furniture likely to be needed. The author has made measurements of domestic furniture and has concluded that the most awkward item to maneuver is a double bed, which can be up to 1670 mm wide by 1900 long and 360 high. In fiats it is unfortunately also necessary to make sure that stretchers and coffins can be carried in the lift. To accommodate these, a depth of 2.5 m is required. The whole car can be made this depth or it can be shallower but have a collapsible extension which can be opened out at the back when the need arises. The lift well must, of course, be deep enough to allow the extension to be opened. In hospitals some of the lifts must take stretchers on trolleys and also hospital beds and these lifts must be the full depth of a complete bed.Grade of serviceThe quality of service is a measure of the speed with which passengers can be taken to their destination. It is the sum of the time which the average passenger has to wait for a life and of the traveling time once he is in the lift. The maximum time a person may have to wait is called the Waiting Time (W.T.) and is the interval between the arrivals of successive cars. It depends on the Round Trip Time (R.T.T.) of each lift and on the number of lifts.The average time a person has to wait is W.T./2. The average time he is traveling is R.T.T./4 the sum of these, W.T./2+R.T.T./4, is called the grade of service. If there are N lifts, then W.T.=R.T.T./N, and grade of service becomes W.T. (2+N)/4.2It is usual to classify the grade of service as excellent if W.T. (2+N)/4 is less than 45s, good if it is between 45 and 55s, fair if it is between 55 and 65s and casual if it is more than 65s.The best way of showing how all this data is used to assess the grade of service is by means of an example. Let us assume we are dealing with an office block with eight floors. The heaviest traffic will occur in the morning when people are arriving at work, and we shall assume that we know enough about the occupancy of the building to have been able to estimate that 75% of the work force will arrive in one particular half hour. For estimating the probable number of stops traffic to the first floor can be ignored and we can set out the number of people requiring service as follows:The number of people requiring serviceFloor 2 3 4 5 6 7 8 TotalNo.of persons requiring service36 93 160 85 120 105 63 662The figures in the second line are 75% of the floor populations, which we assume we have either been given or can guess. The distance between the ground and eighth floor is 25m.The round trip time can be calculated and hence it is possible to calculate the number of lifts needed to carry 662 people in 30 min. From this, the grade of service can be obtained. If the calculation is set out in tabular form, different combinations can be easily compared. A 10% margin is added to the calculated total time to allow for irregularities in the time interval between different lifts in the bank of lifts.It can be seen that in this example the most satisfactory arrangement is four lifts each taking 10 persons at a speed of 1.5ms . 2.0ms would be unnecessarily extravagant.1It will be found that where the service is not so concentrated lower speeds are sufficient. For this reason, it should not be necessary to use speech of more than 0.75 or 1.0m in blocks of 1fiats.AccommodationThe machine room for the lifting gear is normally at the top of the lift shaft or well. It can be at the bottom or even beside the well, and in the latter case it can be at any height, but from these positions the ropes must pass over more pulleys so that the overall arrangement becomes 3more complicated. It is, therefore, better to provide space for the machine room at the top of the well. Room must also be left for buffers and for inspection at the bottom, or pit, of the well. The sizes of the machine and pit rooms must ultimately be agreed with the lift manufacturers.DriveNearly all lifts use a traction drive. In this, the ropes pass from the lift car round a cast iron or steel grooved sheave and then to the counterweight. The sheave is secured to a steel shaft which is turned by the driving motor. The drive from the motor to the shaft is usually through a worm gear. 。