Home – Elevator World, Inc. - 02-10-1 pg90-98 …...ELEVATOR SAFETY AND GOVERNORS by K. Subramaniam, Johnson Lifts Private Ltd., Chennai, India Drum-type gradual safety gear Pendulum-type

90 Educational Focus Compilation

EDUCATIONAL FOCUS: ELEVATOR SAFETIES AND GOVERNORS

The recent introduction in Europe of the directive 95/16/ECand of the corresponding harmonization standard EN 81,have brought with them numerous changes in the elevatorfield thereby revolutionizing a way of thinking entrenchedafter decades of stagnation. Among the numerous variationsintroduced in the area of safety, one of the more impor-tant ones is, without doubt, the obligation to furnish theelevators with gear designed to prevent uncontrolled move-ments of the cabin when traveling upwards.

The EN 81 standard sanctions the minimum safety criteriaas follows:u mandatory application for elevators with friction; u the capacity to stop or slow the empty cabin to a maxi-mum speed, defined as a function of the nominal speed,and in the presence of a deceleration less than 1gn,where gn signifies the acceleration due to gravity equal to9.81m/sec^2.

Considering that the concepts of braking a cabin travelingupward is new and that it was not taken into considera-tion by the previous standard, I believe that a clarificationof Standard EN 81 is necessary or at least more necessarythan others, as for example Annex M, where diagrams,formulas and examples regarding concepts already knownare shown, such as that of the adhesion of the cables tothe traction sheave. Unfortunately, the standard giveslittle information regarding how to define the technicalcharacteristics or the required performance for thesafety gear. In my opinion, the lack of a suitable expla-nation as well as the general habit of reasoning on thebasis of the old standards has undervalued certain as-pects which have proven to be a source of ambiguityand misinterpretation.

Example:To order a pair of safety gears, it normally would suffice

to provide, in addition to the data regarding the guidesand the velocity, the total mass of the cabin, the nominalcapacity and the weight of the accessories, in practicalterms, the so-called P+Q.

This is now no longer adequate, in so far that thecoming of bi-directional gear devices has imposed anadditional stress. In other words, it’s not necessary to

indicate the sum total of that mass but rather to list indetail the mass of the capacity (Q kg), the mass of thecabin plus the frame complete with accessories (P kg)and the mass of the counterweights (Mcwt kg). Thesefigures are the minimum required to verify the suitabilityof the desired equipment, whether dealing with a safetygear or another device.

In fact, it’s necessary to be able to calculate the forcenecessary to brake the empty cabin traveling upward inorder to then compare it with the characteristics normallydescribed on the type-examination certificate allowed forthat device.

To illustrate, I give a simplified formula for this calculation:FS = Mcwt x (gn + a) - P x (gn + a)FS (N.) = force necessary for brakingMcwt (kg) = mass of the counterweights complete withany sheavesP (kg) = mass of the empty cabin including the framecomponents which it supportsgn (m/sec^2) = acceleration due to gravity = 9.81m/sec^2a (m/sec^2) = expected deceleration which must be <1gn

If the value of the counterweights is not known, yet thebalancing factor is, the following formula may be used:FS = (2 x P + Bil x Q) x a + bil x Q x gn

bil = balancing factor (for example, 50% = 0.5 or also 40% = 0.4)Q (kg) = cabin capacity

These formulas are greatly simplified and do nottake into account potentially crucial factors (for exam-ple: friction, roping mass, sheave inertia, etc.). I never-theless believe that they may be used in the majority of cases.

The selection of the safety components is crucial in thedesign and construction of an elevator system. There aremany other factors that come into play in their selectionand during construction with respect to the past andthese must also be made known to the dealer, in additionto the design engineer or to the manufacturer.

A clearer and more detailed standard could have preventedlack of understanding and ambiguity.

With this article, I hope to help anyone who still hasdoubts on the matter. c

BI-DIRECTIONAL SAFETYGEARS FOR CABIN

by Bertoni Stefano, Technical Director, Montanari Giulio & Co.

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Educational Focus Compilation 91


Elisha Otis standing on a platform with his safety clutchhad the ropes of the platform to be cut to demonstrateand prove the mechanical safety of his innovation. Eversince, it has become an industry norm to have a mechanicalsafety for the lift cabin. Instead of cutting the ropes, a deviceknown as an overspeed governor was introduced to sensethe speed of the lift and, in the event of an overspeed, itactuates the safety clutch of the car to bring the car to astop mechanically.Safety Clutch/Safety Gear or Car Safety – As Known in Elevator Parlance

Generally, two designs of safety gear are in use – theinstantaneous type and the progressive type.

The selection of a safety is made considering the totalinertia in the system. Inertia is a multiplication factor ofload and speed. The selection is normally recommendedin the various standards for typical loads and speeds.u Instantaneous type: There are two types – one with eccen-tric cam grip and the other with roller. Cam is a bulkierdesign when compared to roller.u Gradual/Progressive type: This also has two versions,the older version with drum, screw and wedge and themodern version with disc springs or block springs.

Several shapes and designs of safety gears are availablewith its associated link mechanism. Most of the designshave the linkage system on top of the car and the safetygear located at the bottom. An electrical safety switch isincorporated in the assembly, which, when actuated,will also stop the lift. This switch is provided to make anattempt to stop the lift by removing the power from themotor and thereby applying the brake before the me-chanical gripping takes place.

GovernorsNormally, the pendulum-

type governor is locatedin the machine room. If it islocated elsewhere due tocertain site conditions, itshould be ensured that it iseasily accessible from out-side the hoistway. Thefunction of the governoris to check the overspeed-ing of the car and initiatethe safety gear in case thespeed of the lift exceedsthe predetermined value.The governor is connectedto the lift car by way of arope and is connected tothe car safety. A tensionweight is provided tokeep the rope in tension.Two types of governors arein use. Governors withwheel having weights linkedwith springs, which tryto move outward due tocentrifugal action and actu-ate the pawl. The secondhas a pendulum and anyincrease in the throw of thependulum due to overspeedwill actuate the pawl. Thepawl, in turn, releases thegovernor jaws to grip thegovernor rope, which inturn actuates the safety

gear. In the present-day modern pendulum governors, thegovernor wheel has a deep “V” groove and, in the event ofoverspeed, the wheel is stopped by the pawl. Since it is a“V” groove, the rope also stops along with the wheel creatingsufficient tension to actuate the safety gear on the car.Some Guidelines on Installations

The correct positioning of the safety gear with respectto the guides is very important. After the car sling andcounterweights are roped and suspended, the clearances

ELEVATOR SAFETY AND GOVERNORS

by K. Subramaniam, Johnson Lifts Private Ltd., Chennai, India

Drum-type gradual safety gear

Pendulum-type governor

“V” groove-type governor

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between guide and safety gear roller or cams are to bechecked and gaps must be uniform on either side and onboth ends. By adjusting the guide shoes and the safety,the required clearances can be obtained. In the older camdesign, the rope to the master cam should neither be tootight nor too slack. For such cam designs, normally the ropeis from a spring-loaded arrangement known as “torpedorope release.” This torpedo rope release will avoid actuationof cams due to any jerk in the car. The spring in the torpedorelease must be to the correct pressure. The same procedureis adopted for the gradual safety gears as well.

The rope from the governor to the car anchorage mustbe in plumb from where it is connected to the safety gear.In older designs, the return rope from the tension weightis anchored separately at the bottom of the car. The ropefrom the governor to the tension weight must also be inplumb and adjustments will normally be available in thetension weight brackets to make good any error in theplumb line. Care must be taken to ensure that governorropes are free from any obstruction along the travel of thelift. There are occasions where locating the governor andtension weight becomes a difficult task, especially in crampedlift shafts. The governor rope holes in machine room floorslab to be made good without any undulations and projec-tions, preferably to be finished by inserting a two-inchPVC pipe to the full thickness of the floor slab.

Any mistake in safety gear location with respect to theguides could lead to severe damages to the guides. When-ever safety gear is actuated if gripping is not uniform, theimpact will tend to create a twisting moment that can resultin the bending of the guides.

Nowadays, many governors are made with a test grooveof smaller diameter. Transferring the rope to the test groovewill create overspeed for the governor with lift running atnormal speed and the safety gear can be tested. It is recom-mended having the safety gear test done with a rated loadin the car.Guide Lines on Maintenance and Repairs

Unlike the other components in an elevator, the safetygear and the governor are passive components and donot perform in the normal working of the lift. Even in thegovernor, except the wheel rotating with the movementof the car, other elements are passive. Normally, lessattention is given to the safety gear and governor by themaintenance personnel and is mostly taken for granted.Though much attention need not be given during theroutine maintenance visits, nevertheless it cannot betotally neglected or ignored. It is advisable to check thesafety gear linkages at least once in four months and lookfor problems in pivots and joints and also to check thesystem for free movement.

In older lifts, the gover-nor wheel will have gun-metal or bronze bushingand similar bushings willalso be there in the springguides, weight, pivots, etc.Over a period of usage,these bushings are likely towear out, creating noiseduring lift running and ifleft unattended will startgetting actuated even atnormal speed. This noisewill be one of the promptingfactors to replace the bush-ing. Being calibrated equip-ment, much care is to betaken to recalibrate the

governor after the necessary replacement and repairs ofthe bushings. Preferably, the recalibration should be doneon a regular test bench and not on the installation site. Ingovernors with weights, there are chances that oil withdust can clog the bushings preventing free movementof the weights. This particular aspect is to be checkedperiodically, preferably at every routine service call,especially in installations with dusty atmospheres andvery cold places.

The same could happen even to the safety gear assembly.Over a period of time, governor rope tends to stretch andelongate, especially in very tall buildings. With this stretchof ropes, the tension weight goes down. Once it reaches itslimits, the rope becomes slack, and chances are it can getentangled causing severe damages.

An electrical safety switch is provided for such elongationof the ropes, but many times, you will find it bypassed.This is done at the first instance as a temporary measureand seldom gets rectified on subsequent visits. Mainte-nance personnel should check the switch and the status ofthe tension weight and necessary corrective action beplanned and completed at the earliest. In certain buildings,rodents like rats getting in between rope and wheel canalso lead to such damage as the rope getting entangled.

Torpedo rope releaser

Typical safety gear link mechanism

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Many times, the safety gear comes into action on itsown due to the jerk in the car or due to sudden stoppageof the car. The governor type with a “V” groove is very proneto such nuisance breakdowns. The most tricky situationwill be when the car overshoots the top floor with anabrupt stop as the safety gear comes into action in the topmost travel section. Releasing the safety gear is not easyin such a situation and sometimes maintenance personnelhave to jack up the counterweight and remove its bufferspring to allow enough up travel for the car to release thesafety gear.

The electrical switch that is provided in the safety gearassembly is to be critically adjusted for it to be effective instopping the lift. This critical adjustment can also be anuisance factor for creating unwanted breakdowns bygetting actuated due to jerk or shake during running.After actuation and stopping, the system restores itselfand the lift will continue to work normally. Service peopleattending such callbacks will find nothing amiss with thelift working normally. Such callbacks can be due to thesafety gear linkages getting disturbed – maybe someonejumped inside the cabin when the lift is running for reasonsbest known to him.

There are cases where the counterweight is also to beprovided with a separate governor and safety gear unit,whenever installations have constraints in the pit. Normallythe pit is to withstand the impact of counterweight hittingthe buffer whenever car over travels in the up direction. Thegovernor and safety gear is recommended for the counter-weight whenever the pit floor cannot take the impact loador whenever the area below the pit floor is being put tobeneficial use. Dual-acting governors and safety gears areintroduced to take care of overspeeding in both up anddown directions. In certain countries, this has been mademandatory in the standards.

Governors and safety gears, whether older designs or thenew versions, are all proven designs. The most cumber-some design is the gradual-acting screw wedge type with thedrum. Releasing the safety can be done only by unwindingthe drum from inside the car. So when the safety is actuated,one should enter into the lift cabin through the trap doorprovided in the car roof, which is quite laborious. Improve-ments have been made from time to time to make thingseasier in installation, alignment and releasing the safetygear. With high-speed lifts with high capacities, a consider-able amount of energy is dissipated by way of heat when-ever the safety gear is actuated. The temperature rise in guiderail and safety gear may be so enormous it can deformthe guides and safety gear assembly. Ceramic/powdermetallurgy technology are being experimented with thesafety gear gripping jaws. c

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With the issuing of the LG1 (Guidance notes on thethorough examination of lifts) in the U.K., it has becomenecessary to carry out regular safety gear tests with fullload on all lifts. In certain cases, the guidance notes allowalteration of these tests, provided a risk assessment iscarried out.

One method that has originated in Germany is the useof an accelerometer to obviate the need to use weightsduring the test. This method allows the prediction of the freefall acceleration to check that it is above 0.2g, as requiredby the European Standard.

This method has a number of advantages. The mostimportant of which is that it prevents any damage to thelift system components caused by the large forces generatedduring a full-load application of the safety gear.

This article describes a number of practical tests carriedout to validate the method for heavy duty lifts. The relevantformulae are derived and analyzed. The conditions underwhich the method applies are also discussed. Introduction

One of the most onerous requirements of the LG1 is thecarrying out of a full-load rated speed test on the safetygear. There is always concern about the damage thatcould take place to lifts from such a test. The so-calledTÜV method uses a software tool that allows predictionof the results of the fully loaded test based on measurementsduring a no-load test. LG1 in fact does allow alteration tosome tests, provided a risk assessment is carried out:

“In order to determine which examinations and tests shouldbe carried out and with what frequency, the installationin question should be the subject of a risk assessmentthat includes consideration of design, condition, usage of thelift, relevant component manufacturer’s recommendations.The results of the risk assessment may necessitate variationsto the nature of the examinations and tests described later inthis document and to the frequency with which they areperformed.” (clause 3.1.1 of [6]).This article will set out to explain what the predictive

method is and the theory on which it is based. It will thenoutline the advantages of using no-load tests during theLG1 tests. And finally it discusses results from a numberof site tests, in order to give further confidence in the oper-ation of the predictive method.

Safety Gear Application Equations During the application of a safety gear, a number of

forces are acting on the car (and its load). Figure 1 showsa simplified diagram. When the safety gear applies, thefollowing forces are acting on the car: 1. The weight of the car: This will be referred to as FC, andis equal to the mC xg, where mC is the mass of the car inkilograms, and g is the acceleration due to gravity, 9.81mps2.2. The weight of the passengers/load: This will be referredto as FP/L, and is equal to the mP/Lxg, where mP/L is themass of the passengers/load in kilograms, and g is the acceler-ation due to gravity, 9.81mps2.3. The force of the safety gear: This applies in the upward di-rection, as it is a frictional force resisting the movement of thecar in the down direction. It will be denoted by FSG in Newtons.4. The upward force in the ropes acting on the car: Assumingthat the ropes are still in tension during the application of thesafety gear, then they would apply an upward force. This forceis the resultant of two forces: The weight of the counterweight(denoted as FC/W), and the traction force from the sheave re-sulting from the inertia of the drive (denoted as FT).

The resultant force on the car would be: ResultantForce = FSG -FP/L-FC + FC/W - FT

LIFT SAFETY GEAR TESTING WITHOUT WEIGHTS:

A CRITIQUE AND OVERVIEWby Dr. Lutfi Al-Sharif, BSc, MSc, PhD, CEng, MIEE, DBA,Associate Director, Building Transportation, WSP Group

FcFP/L

FSG

FC/W

Counterweight

Passenger/Load

Car

FT

FC/W -FT

Inertia ofrotating masses

Figure 1: General force diagram for a lift under safety gear application

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The derivation of the general case equation is containedin Appendix B. The derivation of the two special caseequations is contained in Appendix C. These equationsare necessary in order to understand the derivation of theso-called TÜV method, introduced in the next section,and which is pivotal to the argument of this method.The TÜV Method Masses and Its Application

In 1990, the TÜV in Germany developed a system calledthe ADIASYSTEM [1,2,3 & 4], which is basically a computer-aided system for lift testing. Although the core of the systemis the measurement of the deceleration caused by safety gearapplication, it also has some other features. These include,among others, measurement of traction and door pressure.

The method attempts to do away with the use of loadsduring the safety gear test. It carries out a measurementduring no-load application, and infers what the value atfree fall full-load would be. The method was formally approvedby the German Lift Committee in 1992, and is now usedin about six European countries [4] and has been trialed inCanada [7]. Up to June 1999, 650,000 lifts had been testedby ADIASYSTEM in Germany [4]. It is interesting to notethat the main motivation for developing this tool in Ger-many is the existence of a statutory requirement of theGerman Lift Safety Code (TRA), which stipulates a biennialsafety gear full-load test [4]. The method relies on twomajor and two minor assumptions: 1. The progressive safety gear force, which is generatedby friction, is load independent.2. During a no-load application of the safety gear, the ef-fect of the counterweight and the traction force from thedrive sheave can be eliminated, as the rope would beslack. This would be caused by the counterweight “jump-ing” or “bouncing” when the safety gear applies. It is as-sumed that the rope would stay slack during the full dura-tion of the deceleration of the empty car to a full stop. Thisassumption relies on the fact, that at a speed of 1mps, andassuming a deceleration of around 1g caused by the safetygear, the duration of the deceleration is around 100 milli-seconds. The only case where we can be assured that the ropeis slack is if the resultant deceleration is more than 1g. This isbecause the counterweight is decelerating under gravity at 1g.So if the car accelerates at more that 1g, then its speedbecomes slower than that of the counterweight, and the ropethus becomes slack. The problem with the second assumptionis that when we are testing a lift which has a rated speed whichis relatively high (e.g., 4mps), the full duration will be muchmore that 100 milliseconds (in this case 400 millisecondsassuming a deceleration of 1g). What the TÜV method does toovercome this problem is to carry out the no-load test at areduced speed, in order to reduce the duration of the decel-eration phase. As an example, in the British Columbia studydescribed in [7], a 2mps lift is tested at 1mps for these reasons.This leads us to the third assumption.

3. The third assumption, which the method makes whentesting higher speed lifts, is that the safety gear force (fric-tional force) is independent of speed. This is not completelytrue [5]. Although friction is broadly constant, there isnevertheless some dependence on speed. 4. The fourth point is not so much an assumption as much asit is a simplification for measurement purposes. The methodwhen reading off the deceleration from recorded graph, tries to“fit” a best “straight” line to the deceleration curve.

The last point becomes clearer when looking at a samplecurve taken from TÜV literature [2]. The curve in Figure 2shows logged data of the acceleration in the vertical direc-tion, using a data logger. The acceleration is integrated toproduce a speed curve. The operator then has to move twovertical cursors on the computer screen, to identify thestart and the end of the safety gear operation (denoted asthe upper and lower limits respectively in the figure). Thecursors are placed so that they fit the best line of decelera-tion. Once that has happened, the software automaticallycalculates and displays the following: 1. Lower limit (in milliseconds): This represents the startof the deceleration caused by the safety gear.2. Upper limit (in milliseconds): This represents the end ofthe deceleration caused by the safety gear.3. The average acceleration between these two times, in mps2,which is referred to as “a_empty” in the figure. This is basicallya measured value. It represents the average measured decel-eration during the safety gear application with an empty car.4. The predicted (or calculated) deceleration that the carand the full load would undergo in the case of a true freefall (i.e., suspension failure) in mps2. This is denoted as“a_loaded” in the diagram. This value is the most impor-tant result from the safety gear test. The theory behind itis discussed later in this section.

The full derivation of the equation used for this methodis contained in Appendix C. It relies heavily on the firsttwo assumptions mentioned at the beginning of this sec-tion. Using these two assumptions, we see that the forcefrom the safety gear is the same at no-load and full-loadfree-fall conditions and that we can ignore the effect ofthe rope during the no-load safety gear application. This

time (msec)upper limit 294 a_empty [mps2] 40 a_loaded [mps2] 12lower limit 256892

- a

Figure 2: A speed/acceleration curve illustrating the TÜV method (repro-duced from [2])

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gives us the important equation Equation 6 derived inAppendix C):

aNL – g x RmaFFFL = ––––––––––––– (6)

1 + Rm

mP/Lwhere: Rm = –––––

mcmP/L is the mass of the passengers/load in kilograms, mC is the mass of the car in kilograms, aNL is the no load deceleration during a safety gear

application in mps2,aFFFL is the deceleration during a safety gear applica-

tion in free fall conditions in mps2, andg is the acceleration due to gravity (9.81mps2). The interesting point to note is that the formula relies

only on the ratio of the mass of passengers/load to themass of the car, and not on their absolute values.

Accepting the four assumptions given at the beginning ofthis section, we can see that the method gives a very simpleand practical tool to predict the free-fall full-load decelerationunder a safety gear application by just knowing the relativemass of the car and full load, and making one measurement ofacceleration during a safety gear application on an empty car.Motivation and Benefit for Using the TüV Method

There are two main reasons forusing the TÜV method, when doingsafety gear tests and when carrying outLG1 [6] inspections. 1. The first and most obvious reason is thepossible damage that the full-load, full-speed safety gear test could cause to thelift components. It is known that such atest does stress the main components inthe lift system, especially the gearbox. 2. The second main reason is the dif-ference to timescales that the use ofweights has on a program of testing.This is due to the difficulty of carrying and moving theweights, and the lack of storage space in some locations.This is not just an inconvenience, but it also presents arisk to the travelling public in delaying the LG1 tests, dueto a longer program.

In addition to the motivation to use the TÜV methodand eliminate weight, there is actually an extra benefitfrom using the method. It gives an extra result, which thefull-load test does not give. It can predict what the free-fallfull-load deceleration would be. This, in fact, is necessaryto fully comply with the requirements of EN 81-1 clause9.8.4 [8]: “For progressive safety gear, the average retardationin the case of free fall with rated load in the car shall liebetween 0.2g and 1g.”

The important word to note here is free fall. A full-loadtest at rated speed with the suspension intact does not nec-essarily provide the worst case scenario. So there is anextra benefit and further assurance using the TÜV method. Site Test Results

In this section, some practical results are reviewed andcompared to the theoretical expected values predicted bythe TÜV method. The Canadian Study

During the end of 1996, the Safety Engineering ServicesDivision of the Ministry of Municipal Affairs and Housing ofBritish Columbia carried out a study to look into the possi-bility of using the TÜV method to obviate the need to useweights during the safety gear tests. The results have beenpublished in a report issued by TÜV [7]. Most of the testswere carried out with an empty car, and only one test wascarried out in the cases of both empty and fully loaded car.

All the results for the cars with progressive safety gearshave been extracted. The six lifts have been denoted withthe arbitrary letters A to F. All lifts, except lift E, were onlytested in the empty car condition. Lift E, had two tests:One with an empty car and one with a fully loaded car.Nevertheless, for completeness, the results for all six liftshave been tabulated in Table 1.

*The no-load test was carried out at a reduced speed to ensure that the durationwas short enough to justify the assumption of slack rope. **The value of a calculation by the ADIASYSTEM truncates the acceleration value toa whole number. For completeness, I have added the exact value to two decimalplaces in brackets, based on Equation 6 shown earlier, and derived in Appendix C.

As mentioned earlier, only the ratio of the full load andthe car mass are needed in the formula for calculating thepredicted deceleration under free-fall full-load conditions(Equation 6 shown earlier and derived in Appendix C). Sothe ratio of the two values is shown in a dedicated column.A reduced speed test was carried out in the case of E andF, in order to ensure that the counterweight and the tractioneffects could be cancelled.

The only comparison that could be done is the result ofcase E, as that is the only one that had a no-load test in

Table 1: Summary of Results from the British Columbia Study [7].

Lift Rated Car Ratio Speed a_measured_ a_free fall a_measured

Load mass Rm empty calculated** full load

[kg] [mps] [mps2] [mps2] [mps2]

[kg]

A 907 1813 0.50 1.25 8.76 2(2.57) N/A

B 680 1613 0.42 1.25 10.01 4(4.15) N/A

C 816 1804 0.45 1 7.88 2(2.39) N/A

D 1588 3270 0.49 1.5 18.91 9(9.47) N/A

E 1011 2023 0.50 2 (1)* 13.2 5(5.53) 5.36

F 1590 2900 0.55 4 (1.5)* 9.73 2(2.79) N/A

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addition to the full-load test. The numbers compare verywell: 5.53 mps2 calculated, compared to 5.36 mps2 measured.This shows that in this case, the effect of the counter-weight had been completely eliminated by the traction forcein the case of the full-load test. Examining the general caseequation (derived in Appendix B, denoted Equation 1:

FSG -FP/L -Fc +Fc/w -FT = aFL x(mP/L + mc ) . . .(1)As the result for this was identical to the free-fall case,

we conclude that during a full-load safety gear applica-tion: Fc/w = FT . In other words, the effect of the counter-weight is cancelled by the effect of the traction sheave force.

This is obviously a special case, and it is not always thecase in all lifts that the force from the counterweight will beequal to the traction force from the sheave caused by thedrive inertia. Heavy-Duty Lift Results

A no-load and full-load safety gear test was carried outon a heavy-duty lift, during an LG1 test. The results andparameters for the lifts and the test are tabulated Table 2.

*Actual speed against rated speed. The speed in brackets is the figure usedin any calculations. **The TÜV software truncates the number to the lowest whole number. Theexact calculation to two decimal places has been carried out, and that isshown in brackets. ***These deceleration values have been calculated for information and compar-ison purposes. They assume a constant deceleration and are based on the markson the guide rails following the safety gear application. The actual measured dis-tances have been reduced by the width of the safety gear block, which is 180mm.

The deceleration during no load was more that 1g, vali-dating the assumption that the ropes were slack duringthe no-load tests and thus the effect of the counterweightcould be ignored. Looking at the results from the heavy-duty lift test, the following can be noted: 1. The no-load deceleration is 11.16mps2. As this is morethan g (9.81mps2), it gives the confidence that the ropeswere actually slack for most of the time while the safetygear was applying. The duration of the safety gear appli-cation is 118 milliseconds, calculated from these figures andbased on an actual speed of 1.32mps. The fact that the ropewould have been slack validates one of the assumptionsrequired for the TÜV method, to allow the counterweightand traction forces to be ignored during the no-load test.

2. From that figure, the calculated free-fall full-load deceler-ation value is (based on Equation 6 from Appendix C):

aNL – g x Rm 11.16 – 9.81 x 0.57aFFFL = ––––––––––– = ––––––––––––––––––––– = 3.54 mps2

1 + Rm 1.57 Comparing this value with the value measured during

the full-load test, which is 6.62mps2, we note that the full-load test measured value is higher than the free-fall value.This points to the fact that the counterweight is assistingthe safety gear in retarding the fully loaded car, and thatthe counterweight effect has not been eliminated by thetraction force from the sheave, as was the case of lift E inthe British Columbia project. In fact, the predicted figure bythe ADIASYSTEM is the worst case figure and is the figureneeded to comply with the requirements of EN 81-1. Conclusions

The LG1 tests stipulate that a full-load rated speed test is car-ried out on the safety gear, but allows the use of risk assess-ment to alter the tests or their frequency. There are concerns

regarding carrying out these tests for thefollowing reasons:1. The effect these tests could have onthe lift components, in terms of long-term invisible damage. 2. The significant increase in the lengthof the time of an LG1 program that in-cluded the full-load test, due to the logis-tics of moving and storing the weights.

The TÜV method can be used to predictthe full-load free-fall performance safetygear by merely carrying out a measure-ment on the empty car during a safetygear application. Although the methodmakes some assumptions, these assump-

tions only have a small effect on the accuracy of the results.Trials on the British Columbia project and on a heavy-duty

lift have shown that the measurement can give a reliable pre-diction of the free-fall full-load safety gear tests deceleration,in order to comply fully with the requirements EN 81-1.REFERENCES1. “ADIASYSTEM - a computer-Aided elevator DIAgnosis SYSTEM,” TÜV, 10/97. 2. “Computer-Aided Periodic Testing of Lifts with ADIASYSTEM,” TÜV Lift Serv-

ice Seminar, London, March 1999. 3. “Computers and Safety-Related Lift Data,” Alfons Petry, Elevatori, September/

October 1995, pages 33-45. 4. “Adiasystem Technical Dossier,” TÜV Product Services, June 1999, Issue number 01/99.5. “Deceleration During Free Fall, Free Wheel and Emergency Stop,” Johannes de

Jong, Lift Report, January/February 1998. 6. “Guidelines on the Thorough Examination and Testing of Lifts,” Safety Assess-

ment Federation, 1998. 7. “Supplement to the Report: TÜV Adiasystem/British Columbia Project,” TÜV

Building Services Inc., April 22, 1997. 8. “Safety Rules for the Construction and Installation of Lifts - Part 1 Electric

Lifts,” BS EN 81-1, BSI, 1998.

Appendix A: NomenclatureaNL deceleration during a safety gear application under

no loaded car with suspension intact [mps2]aFL deceleration during a safety gear application under

full loaded car with suspension intact [mps2]

Table 2: Summary of Results from Heavy-duty Lift Test

Parameters Rated Load [kg] 3750

Car mass [kg] 6570

Ratio Rm 0.57

Speed [mps] 1.5 (1.32)*

Measured a_measured_empty [mps2] 11.16

a_full_load measured [mps2] 6.62

Stopping distance, no load [mm] 100

Stopping distance, no load [mm] 200

Calculated a_free_fall_full_load [mps2] 3(3.55)**

a_no_load (from stopping distance) [mps2] 8.8***

a_full_load (from stopping distance) [mps2] 4.4***

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aFFF deceleration during a safety gear application ofthe car in full-load free-fall condition [mps2]

Lg acceleration due to gravity [10mps2]mC mass of the car [kg]mP/L mass of the load/passengers in the car [kg] mc/W mass of the counterweight [kg] Rm ratio of the full-rated passenger/load mass to the

mass of the car [ ] FSG force of the safety gear [N] FT traction force from the sheave on the ropes [N] FC/W force due to the weight of the counterweight [N] FC force due to the weight of the car [N] FP/L force due to the weight of the passengers/load in

the car [N] α counterbalance ratio [ ], where mc/w = mc + α x mP/L

Appendix B: Derivation of Safety Gear Application Equations

In this Appendix, the equations for the general case ofsafety gear application, and the equations for two specialcases are derived. The General Case

The general case is derived first. This will then be used forthe two special cases. The general case assumes that none ofthe factors (discussed earlier) can be ignored, and that the sus-pension is still intact (i.e., no suspension failure). Looking at afree force diagram for the car and the passenger/load, we canderive the following (based on Figure 1). The total mass is:

mT =mP/L+mcThe resultant force on the car (assuming a positive

value represents an upward force): Resultant Force=FSG -FP/L -Fc + Fc/w -FTLet us assume that the full-load deceleration under no

load conditions is: aFL (full-load deceleration in mps2). Wethen get the following result:

FSG -FP/L -Fc +Fc/w -FT = aFL x (mP/L +mc ) (1)The difficult item to calculate in this equation is the traction

force. This is dependent on two main groups of data: Data re-lated to the inertia of rotating masses (which depend on inertiaof motor, gearbox, flywheel/handwheel, brake); data relatedto traction parameters (profile of groove, angle of wrap. . . etc.).No-Load Case

The no-load case is a special case of the general case,for two reasons: 1. The load in the car is zero. 2. In general, the stop is relatively fast (in many caseswith a deceleration exceeding g). When that happens, theropes become slack and the effect of the counterweight andthe traction force can be eliminated from the equations. Gen-erally the stop happens within around 100 milliseconds. Thistime is short enough to be able to ignore the effect of the coun-terweight, as it actually “jumps” during that period of time.

Using both of these points, and assuming that: aNL Noload deceleration in mps2. The special case of the generalequation (1), becomes:

FSG -Fc =aNL x (mc)FSG = aNL x(mc )+g x (mc )FSG = (mc)x(aNL +g) (2)

Free Fall Case The second special case is when the suspension of the

car fails completely, and the car goes into free fall underthe acceleration of gravity. We will assume that the car isfully loaded. Let us assume that: aFFFL Free-fall full-loaddeceleration in mps2. The equations then become:

FSG -FP/L - Fc = aFFFL x (mc +mP/L )FSG =aFFFL x(mc +mP/L)+g x(mc +mP/L )FSG =( mc + mP/L )x(aFFFL +g) (3)The importance of these three cases and their corre-

sponding equations will become evident when derivingthe TÜV equation in the next section. Appendix C: The TÜV Method Equation

The calculation for the TÜV method will now be fur-ther explored in order to derive the equation used. Usingassumptions 1 and 2, we see that the force from thesafety gear is the same at no load and full load free fallconditions, coupled with the fact that we can ignore theeffect of the rope during the no load safety gear applica-tion, gives us the following (from Figure 1):

FSG = (mc + mP/L)x(aFFFL +g)= mc x (aNL +g) Þ aFFFL x(mc + mP/L)+g x mc +g x mP/L =g x mc + aNL x mcÞ aFFFL x(mc + mP/L)= (aNL x mc)-(g x mP/L)

(aNL x mc ) – (g x mP/L)Þ aFFFL = (–––––––––––––––––––––––) (4)

(mc + mP/L)

Dividing throughout by mc, gives us the important result:

(5)

And if we denote Rm as the ratio of the passenger/loadmass to the car mass, we can see that the formula only relieson the ratio of two masses and not on the absolute values:

aNL – g x RmaFFFL = ––––––––––––– (6)

1 + RmmP/L

where: Rm = ––––––––mc

mP/L is the mass of the passengers/load in kilograms, mc is the mass of the car in kilograms,aNL is the no load deceleration during a safety gear applica-

tion in mps2,aFFFL is the deceleration during a safety gear application

in free fall conditions in mps2, g is the acceleration due togravity (9.81mps2).Reprinted from Elevator Technology 12, Proceedings of Elevcon 2002.

mp/L (aN/L) – g x –––––mcaFFFL = –––––––––––––––––mp/L

mc1 + –––––––( )

( )(( ))

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