HOW TO GET THE MAXIMUM LIFE OUT OF YOUR ESCALATOR …

Educational Focus Compilation 121

EDUCATIONAL FOCUS: ESCALATORS

HOW TO GET THE MAXIMUMLIFE OUT OF YOUR ESCALATOR HANDRAILSby Field Technical Services, EHC Overview

Escalator handrails are complex – they must be extremelyflexible while remaining dimensionally stable. Handrailsare required to perform a number of functions: bend for-ward and backward as they pass through the drive, main-tain a constant length, be strong enough not to snap andbe absolutely rigid in their profile. All of the componentswithin the handrail that preserve flexibility and rigiditymust be cured together in a way that ensures the compo-nents stay together while in use on the application.

It is essential that you select a product from a trustedsupplier to be sure that the handrail lip dimensions do notgrow to the point where the gap between handrail lip andbalustrade can pinch fingers or be easily pulled from theguides. Neither must the lip dimensions decrease causinginterference with the balustrade, excessive friction, heat,slippage and premature handrail failure. Traditionally, esca-lator handrails have been made from rubber compounds.New technology has allowed for the use of thermoplasticelastomers resulting in a product that excels on escalatorsor walks in many ways that rubber handrails cannot.Installation

The majority of escalator handrails are installed endless inthe factory, however, in some cases it is preferable to orderopen-ended handrails and have them spliced on the jobsite. Itis, in some cases, difficult to accurately calculate the length ofthe handrail that is needed for new construction units. In thiscase, the best solution is to overestimate the length and havethe handrail spliced to fit at the jobsite. Another remarkablebenefit of splicing handrails onsite is that it can save signifi-cant time, reducing the total unit downtime – a handrail canbe spliced onsite in less than five hours, two handrails in lessthan eight hours. Compared to the time required for endlessinstallations, the cost in time and money is substantial.Maintenance

Proper handrail maintenance is critical in prolongingthe life of your handrail. Tensioning Handrails

One of the most common factors that affect handrail life isover-tensioning of the handrail. While some types of escala-tors require tension in order for the handrail to drive, mostmodern units do not. It is very important for the unit to be setup with the appropriate amount of tension for the system, astoo much slack can be as dangerous as too much tension.Handrail Cleaning

Routine cleaning of escalator handrails is perhaps themost important and most neglected handrail maintenanceprocedure. Controlling a rubber handrail’s accumulationof operational grime and residue maximizes the handrail’soperating efficiency and service life, as well as promoting

a more pleasant ride for pedestrians. Due to its proximityto the handrail guide and drive wheels, the handrail under-side requires extra attention and must be carefully cleanedon a regular basis in addition to all the handrail components,such as guides, newel ends and take-ups.

With the introduction of thermoplastic handrails, routinecleaning is simplified and offers superior results over rubberhandrails. If you have customers who insist on pristinehandrails, consider this new type of handrail. At the timeof installation, thermoplastic handrails do not have to becleaned as they are provided with a removable protectivefilm that can be left in place until after installation. The hand-rail won’t get scratched or gather debris while transportingthrough a construction site. Another benefit to thermo-plastic handrails is that polishing is not required following aroutine cleaning. Rubber handrails should be polished aftercleaning to protect the porous surface until the next cleaning.Handrail Storage

Unless stored under ideal conditions, rubber handrailswill age to some degree, but this will be greatly acceleratedif exposed to light (especially sunlight), heat and humidity.During storage, rubber handrails may develop a waxy,protective haze over the rubber cover. This is the normalmigration of a protective wax in the rubber to the surfaceto guard the rubber handrail against aging.

Storage recommendations:u Store in a dark, cool and dry environment, with a lowrelative humidity.u New handrails are best stored in their original packaging.u Used handrails should be coiled up according to handrailmanufacturers’ coiling procedures, avoiding excessivelytight coils or kinks in the handrails.u Avoid storing in penthouses or elevator pits, as bothlocations leave the handrail susceptible to high temperaturesas well as oil and moisture contamination.u After storage, uncoil handrail and let it “relax” in thatstate for at least 24 hours before installing on the escalator.u The surface of a stored handrail will require cleaningbefore installation.Troubleshooting

What to do if your handrail is running at a differentspeed to the unit (slippage)? Handrail slippage is usuallya result of improper handrail set up, but can also be a signthat the handrail slider ply is wearing out. The followingitems can all contribute toward a slippage problem:u Excessive handrail tension;u Improper adjustment of the pressure belt or rollersaround the driver(s);u Rubberized drive surface is hard, shiny or glazed;u Contaminated handrail driver or handrail drive surface,e.g., wax or other lubricants;u Seized idler or newel end rollers;u Sources of excess drag along the handrail’s path (accumulationof dust or debris can sometimes be an indicator of drag area);u Flat spots or excessive wear of handrail drive surface.

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122 Educational Focus Compilation


What Does it Mean if the Handrail is Hot?Unless in direct sunlight, a handrail should run at very close

to room temperature and be cool to the touch. A hot handrailis a symptom of trouble ranging from over tensioning to align-ment or drag problems. Over tensioning is by far the mostcommon cause of excessive heat. To test for over tensioning,stop the escalator and take the bottom six feet (1.8 meters) ofhandrail off of the guide. If you cannot lay it down flat alongthe bottom curve of the escalator, there is not enough slackhandrail on the unit. Over tensioning can cause permanentand fatal damage to the handrail such as lip cracking and sliderwear. While increasing the handrail tension is a common re-sponse to handrail slipping, it often increases slippage andshould not be practiced.New Handrail DevelopmentsAnti-Bacterial Additives

Thermoplastic handrails can be ordered with an op-tional anti-bacterial agent – ideal for keeping handrailsgerm free.Thermoplastic Handrails

Traditionally, escalator handrails have been comprised ofrubber compounds. The latest technology has allowed forthe introduction of thermoplastic handrails. Currently, thereare more than 200,000 meters in operation globally. Thesenew handrails run with less slippage and often require lesspower to drive. An extraordinarily tough cover helps preventvandalism, is easy to clean, and has an extremely glossy ap-pearance. The small diameter pressure rollers opposite thedrive wheels of the typical linear drives put high stresses onthe body of the handrail. The pressure can distort the hand-rail and cause heat buildup, increased rolling resistance andpossible delamination. As a result of many years of intensiveengineering, thermoplastic handrails have been successfullydeveloped to avoid these linear drive vulnerabilities whilealso displaying high performance on reverse bend drives.Exotic and Customized Handrails

Thermoplastic handrail technologies are allowing theintroduction of specialty finishes such as metallic and fluo-rescent colors. Historically, color handrails have been difficultfor building owners to maintain but with thermoplastic hand-rails, whose smooth, glossy surface does not trap dirt or grease,the colors stay vibrant throughout the handrail life. Architectscan specify Pantone colors to match building decors anddepartment stores can purchase handrails that match theircorporate identity. You will also see safety messages, adver-tising and seasonal decorations applied to handrail surfacesin Europe, Asia and North America (patents pending).

The market for escalator handrails will be much differentin years to come, as with the technology available, build-ing owners and designers can demand highly decorativeappearances, that they could only dream of until now. c

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Ideally, to operate satisfactorily, an escalator shouldrun between tracks which lie in parallel vertical planesthroughout their length. Also, a line joining correspondingpoints, for example, track mounting points, on oppositesides of the escalator should be precisely normal tothese planes. If either of these conditions are not met, theescalator steps cannot run smoothly.

In the case of London Transport, before the King’sCross disaster of 1987 (see ELEVATOR WORLD, January-March 1988, March and May 1989, and February 1991),escalator misalignments were largely accommodated bysimply providing sufficient space between the sides ofthe steps and the skirting panels, allowing the steps adegree of lateral movement. However, since thattragedy, and following the Fennel report, much tighterspecifications have been enforced, among which is onerestricting this space to 4mm (.2in.). The imposition ofthis restriction has resulted in skirt and step side wearand production of substantial noise in many escalators.In some cases, they have had to be taken out of service.

Until recently, no satisfactory method existed for suc-cessfully rebuilding London Transport escalators to the toler-ances required by the Fennel report, and many of themcontinued to give trouble even after a rebuild. This arti-cle describes an escalator surveying procedure developedby the author and used over the past three years, enablingescalators to be successfully rebuilt to required spacing tol-erances. The procedure has been applied in 17 cases and iscurrently being used at Wood Green and Notting Hill GateStations as well as Oxford Circus where the No.8 machinewas recently rebuilt by an outside contractor but failed tomeet requirements.

The method has been strikingly successful at Moorgatewhere machine No.3 had never, since first installed,functioned properly because of a sideways bend in theescalator track at the start of the incline. This particularjob, now functioning perfectly, necessitated a completerealignment and reconstruction but, nevertheless,was completed by your author and a team of eightmen in 16 weeks.

ESCALATOR ALIGNMENT TECHNIQUESby Marcus R. Hoffmann de Visme, BSc

The Critical Combination:

Plumb Bob and T-Square

1

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Center Line Alignment Correctly aligning the tracks of an escala-

tor during rebuild would be feasible if a linecould be established running from end toend of the escalator and lying in a verticalplane parallel to the direction of motion ofthe escalator. From this line, one would beable to measure the perpendicular distanceto each track at a number of points alongthe escalator. By equalizing these distances,one could position the tracks parallel to thisline and, therefore, confine them to twoparallel vertical planes throughout theirlength, as required.

If the escalator landings are fairly short,such a line can be established by simplystretching a wire between two framesplaced beyond the extreme ends of theescalator and, by means of plumb lines, useit to align the tracks. Most of the escalatorsin London Transport Underground stations,however, have long landings and low ceil-ings, making this impossible. A wire thelength of the escalator would normally bebent at two “diversion points” (X and Y inFigure 1). There is no guarantee, however,that the points A, X, Y and B shown in Fig-ure 1 all lie in a vertical plane.

This method overcomes this problem,firstly by positioning the wire so that onlyone diversion point is required; secondlyby suspending the wire itself at a pointsome six feet above the diversion point.Figure 2 shows the arrangement, viewedfrom the side. Wire ends P, R and S arefixed to the brackets which can each bemoved along fixed horizontal rods set atright angles to the escalator. The junctionpoint Q is entirely free. X is a plumb linehanging between the tension carriageguide rails, and Y is a plumb line hangingbetween the upper step chain sprocketwheels. By suspending a plumb line froma point on the S bracket to bring the wireSQ exactly into line with it, the planecontaining the points P, Q, R (and S) ismade vertical. The crux of the surveyingmethod is shown in Photo 1. A movableplumb line may now be suspended fromvarious points along PR from which thehorizontal distance between the verticalplane, and the escalator tracks at thesepoints can be measured.

BY

A X

WIRE

ESCALATORTRACK

TUNNEL CEILING

P

X

S

QY R

WIRE

ESCALATOR TRACK

TUNNEL CEILING

-2 0 2 4 6 C L -6 -42 0 -2 -4 -66 4

RH639

LH639

TS1

TS2

TS3

TS4

I1

I2

I3

I4

Figure 1

Figure 2

Figure 3

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The surveying procedure is neces-sarily tedious. Initially, it requires re-peated adjustments of the positions ofthe P, R and S brackets on their respec-tive horizontal supports until theplumb lines at X and Y hang exactlyover the midpoint between the reartension carriage guide rails and themidpoint of the top shaft sprocket axle,respectively, with SQ in line with theplumb line from the S bracket. Oncethis has been achieved, a “center line,”P X Q Y R, has been established, andthe track survey itself can begin.

The survey is normally conductedwith the escalator dismantled, i.e., withthe chains and steps removed. The firststep is to measure and record the hori-zontal distance at a number of points be-tween each track-side flange and thecenter line. This requires the use of amovable plumb line suspended fromsuccessive points along the centerlinewire. The results are plotted as a chart,as shown in Figure 3. The chart thenshows the amount the tracks haveto be moved sideways to make theopposite track flanges parallel andequidistant from the center linethroughout their length. Vertical Adjustment of Track Position

The foregoing procedure ensures thatthe tracks are parallel and straight,

viewed from above. It is then neces-sary to assure that corresponding pointson the opposite tracks are preciselyat the same level. This involves adjust-ing the track position in a verticalplane at each mounting point. Theneeded adjustment is determined usinga very large T-square (Figure 4). ABis a round rod the length of which issome 40mm (1.6in.) less than theaverage distance (typically 1,278mm[50-1/3in.]) between opposite chainwheel guide flanges. The ends ABare laid on the wheel running surfacesand the end C rests on an escalatorcross-member. The edge CD of the T-square axis is made to lie exactlybelow the centerline wire by meansof plumb lines hanging just clear ofthe edge at C and D. The levels of thetwo running surfaces are equalizedusing a highly sensitive spirit levelplaced on the rod AB at S. Any inaccu-racy in the T-square itself is cancelledby repeating the measurements withthe T-square turned over. Sprocket Adjustment

This entails ensuring that the axleconnecting the sprocket wheels isperfectly horizontal and perpendicu-lar to the center line. This can be dif-ficult but involves no new principle.

Conclusion This method of escalator track ad-

justment has been used successfullyon a number of London Transportescalators and accepted as standardprocedure by the Lifts and EscalatorsManagers Division. It can be modifiedto suit any escalator. The surveytechnique is necessarily tedious andtime-consuming but can achieve ex-tremely close accuracy, being limitedonly by the time and care spent con-ducting the survey. It has the advantageof being simple in principle. Typically,dismantling, surveying and reassem-bling an escalator occupies eight menabout 10 weeks.

Marcus Hoffmann de Visme graduatedfrom the North Staffordshire Polytechnic in1984 with an honors degree in MechanicalEngineering. While studying, he was em-ployed as a student engineer by G.E.C.Switchgear Ltd., for whom he worked until1986. In 1988, he joined the Lift and Esca-lator Engineers’ Division of London Under-ground as a graduate trainee, moving aftera year to the Lift and Escalator Managers’Division as a test engineer, dealing mainlywith the mechanical aspects of major esca-lator refurbishment projects.

Reprinted from the September 1993 issue ofELEVATOR WORLD

A

S

B

C

D

Author Hoffmann de Vismeon a London undergroundjobsite. Using the inventor’stechnique, the T-square, incombination with the equallysimple plumb bob, assuresproper escalator alignment.

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E scalatorsessentially consist of twolong sprocket chains runningparallel to each other, with stepspivoted on axles between. Steps arefitted with wheels running on carefullypositioned tracks supporting the chains,steps and passengers. These tracks also con-trol the formation of “steps” on the escalatorincline and “landings” at the top and bottom of theescalator. The chains are driven by a pair of sprocketgears locked in axial alignment and mounted on a shaftat the top of the escalator, usually called the top shaft. Atthe bottom of the escalator, the chains run around a similarpair of sprocket gears mounted on an idler shaft.

In order to maintain the necessary tension in the chains,the idler shaft and its bearings are mounted on a frame,called the tension carriage, which can move horizontallyalong the lower escalator landing in the line of the esca-lator motion. On most large escalators, the tensioncarriage is rectangular in shape and tensioned on eachside by independent mechanisms providing equal tension.These mechanisms consist of either a system of springs,or preferably of a weight and lever arrangement, sinceweights provide a degree of inertial damping.

It is essential that the faces of both pairs of sprocket gearsremain exactly parallel to, and equidistant from, an imaginaryvertical plane through the escalator center line. As far asthe idler shaft is concerned, the tension carriage must notsuffer distortion due to unequal chain tensions and mustbe constrained to move strictly in the desired direction bysome guiding mechanism. This article considers the difficultyof fulfilling the latter requirement using conventional guid-ing mechanisms and proposes an alternative mechanismbased on a well-known mechanical principle. Problems Associated with Escalator Tension Carriages

The usual tension carriage used on the London Under-ground units consists of a rectangular steel frame carry-ing the idler shaft, bearing assembly and all trackwork, overwhich the wheels run on their way around the idler shaft.

The frame is supported on four rollers, two oneach side, running on a pair of level tracks. On

early machines, sideways movement of theframe was restricted by steel strips riv-eted to the side of the roller tracks,which bear against the sides of the

rollers. On later machines, two addi-tional pairs of horizontally mounted side

rollers were provided, which bear against theside rails. To allow movement of the tension

carriage with respect to the main escalator, “half-tracks” are required to enable the step wheels to runsmoothly between carriage and main escalator trackwork.Figure 1 shows the principle of the half-track, of whichthere may be as many as 14 on any one tension carriage.

The main problem arising from the tension carriage occursdue to a difference in length of the two sprocket chains.When first installed, the two chains are approximately equallength, and the escalator steps, as they pass through thecomb on the lower landing, lie square to their direction ofmotion. Equal chain tension is therefore experienced by thetwo sides of the tension carriage, which, in consequence,has no tendency to distort or slew out of line. However, intime, chain lengths increase unequally, particularly at theLondon Underground stations, where escalators are very

A PROPOSED SOLUTION TOESCALATOR

TENSION CARRIAGE

PROBLEMSby Marcus Hoffmann de Visme, BSc

FIXED TO ESCALATORFIXED TO TENSION CARRIAGE

ESCALATOR CENTER LINE

Figure 1 – Left and right half tracks viewed from above

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long, and passengers are encouraged to stand on the right-hand side. Additionally, since the Kings Cross fire in 1987,restrictions on the use of certain types of chain lubricanthave been imposed, resulting in the appearance of kinksin the chains, which effectively reduce their lengths in anunpredictable way.

The effect of chain length difference causes the tensioncarriage to distort and slew. While distortion can be over-come by bracing, current methods of guiding the carriageare unable to prevent slewing. In the early days, this did notmatter much since (a) the tension carriage was long – somesix feet or so – and unable to slew significantly within itsguides, (b) the comb system could tolerate considerablemisalignment and (c) half tracks were capable of resistingthe slewing effect. The Watt’s Link

Your author recently suggested tension carriage slew-ing could be completely eliminated by fitting the tensioncarriage with a pair of Watt’s links instead of the usualguide arrangements. This could be achieved simply andinexpensively by using sealed motor vehicle-type “sealedfor life” track rod and steering components without entailingmajor escalator modification. Servicing would then merelyconsist of unit replacement.

The Watt’s link is a very simple mechanical device forproducing linear motion invented by the famous steamengineer James Watt more than 150 years ago. Figure 2 isa schematic diagram of the link. A and B are fixed points.AP and PQ are arms of equal length (this is not a require-ment of the link but is convenient for this application).The arms pivot freely about A and B, respectively. Ends Pand Q are joined by a third arm, PQ, which pivots freelyabout ends P and Q. R is the midpoint of PQ. AP and BQare the undisplaced positions of AP0 and BQ0, definedwhen AP and BQ are parallel. In this position, the point Roccupies the position O, the origin of axes Ox and Oy, andthe third arm makes an angle ∝ with Oy.

P

y

P

R

Q

A E

Bθ

o

Po

Qo

X

∝

Figure 2 – Schematicdiagram of Watt’s link

For AP and BQ of unit length, the locus of point R(x,y),as the arm BQ is rotated about B, is given by:

cos φ - cos θ sin φ + sin θx = ––––––––––––––––––– , y = ––––––––––––––––––

2 2where LQ0 BQ=θ and LP0AP=φ. This shows that when

θ and φ are both small (i.e., when R is in the neighbor-hood of 0), the locus of R is substantially coincident withthe y-axis. The actual locus can be calculated in terms of θ,for various values of ∝, using the somewhat complicatedformula relating θ and φ:

where a=PQ/AP. This formula holds for θ lying betweenits two values, for which the points A, P and Q arecollinear.

Figure 3 (a, b and c) shows the locus of R with AP =BQ = 30in. and PQ = 18in., for ∝ = 0°, 2.5° and 5.5°. With∝ = 2.5°, we see that the maximum departure from astraight line is ±1-1/2 thousandths of an inch over adistance along the y-axis of 16-1/2in. – an incrediblysmall deviation.

Figure 4 shows the proposed tension carriage installa-tion. Where the four points A, B, A' and B' are accuratelyplaced symmetrically on either side of the escalator’scenter line, the two Watt’s links are lettered A P R Q B andA'P'R'Q'B'.

The advantages of such a system are: 1. Since the links have no free play, the system can be

3 - 4a sin ∝ - 2 cos θ - 2a sin (θ - ∝)φ - cos-1

5 = 4a2 - 8a sin ∝ - 4 cos θ - 4a sin (θ - ∝)√√

tan-1 2a cos ∝ - sin θ

2 - 2a sin ∝ - cos θ

(

10

5

-.5 .5

-5

-10

∝ = 5.5°

XR( 1 ''

100

10

5

-.5 .5

-5

-10

∝ = 2.5°

XR( 1 ''

100

YR (inches)

10

5

-.5 .5

-5

-10

∝ = 0°

XR( 1 ''

1001 1 1( (

YR (inches)YR (inches)

Figure 3 – Watt’s link performance

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used on a short tension carriage frame operating in aconfined space; 2. The carriage cannot slew, as it can only move in a straightline parallel to itself, irrespective of differing tensions onthe idler sprockets. Risk of seizure at the half-tracks islargely removed; 3. Lateral forces applied to the pivots R and R' are evenlydivided between the two sides of the escalator truss structure,thereby halving the stress on each truss; and 4. The system can be fitted to most existing installations,and once correctly set up, is easy to maintain.

Conclusion Many escalator failures on the London Underground result

from half-track seizure and other damage due to slewingof the tension carriage as it moves back and forth betweenits side guides. This article proposes the replacement of theside guides by two accurately positioned Watt’s links attachedto the tension carriage frame. It is suggested that not onlywould such a system entirely eliminate carriage slew, butmaintenance would be considerably simplified.Reprinted from the June 1994 issue of ELEVATOR WORLD

Marcus Hoffmann de Visme graduated from the North Stafford-shire Polytechnic in 1984 with an Honor’s degree in Mechanical

Engineering. While studying, he was employedas a student engineer by G.E.C. SwitchgearLtd., for whom he worked until 1986. In 1988,he joined the Lift and Escalator Engineers’ Di-vision of London Underground as a graduatetrainee, moving after a year to the Lift and Es-calator Managers’ Division as a test engineerdealing with mechanical aspects of major es-calator refurbishment projects.D

eV

ism

e

B

Q R P

A

B

Q P

A

1

1 1 11

1

o Ro

Figure 4 – Proposed tension carriage fitted with two Watt’s links

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HOW TO GET THE MAXIMUM LIFE OUT OF YOUR ESCALATOR …