Elevator Ride Quality

Categories: Issue 1/2007 Date: Jan 2, 2007 Title: Elevator Ride Quality

The Human Ride Experience

Roger E. Howkins (Ove Arup & Partners, UK)

Elevator ride comfort and elevator ride quality are two distinct and separate concepts that are verysubjective but can be very objective depending if you are a passenger, manufacturer, elevator consultant orbuilding owner. This paper will concentrate on the passenger expectations which are very subjective andcan also be classified as imaginary as there are multiple sources of experiences transferred to the elevatorpassenger during a journey, these experiences being both variable or fixed. The variable experiences arechanges in the effect of gravity on the human body caused by acceleration, deceleration, jerk and alsonoise and vibration generated by the elevator systems. The fixed experiences are the architectural designadditions to the elevator cars which include lighting, finishes and car furniture.

All of this is classified as the Human Elevator Ride Experience.

History

When the first elevators were installed in the mid 1800‘s, passengers were probably not overly concernedabout safety until Elisha Otis demonstrated his safety gear in 1852 which heralded the new business of theelevator manufacturer. Milestones in the new business were the use of electric elevators by Siemens in1880 and the Eiffel Tower in 1889 which at 321 meters is still recognised as the symbol of Paris. The firstgeneration of elevators used either water hydraulic or steam as their motive force and the travelling publicwere probably only too glad to move automatically up and down buildings rather than using stairs orramps. Passenger comfort was not thought of as an important item for elevators, if you consider the motorcar industry of that time the modern cars were open, with no heating and were very noisy, very differentfrom today.

The elevator industry, and building owners remained stagnated in this position for over 100 years afterElisha Otis gave his revolutionary demonstration, in that elevator ride quality was not a major concern asit did not have an affect on sales or maintenance revenues.

It was not until the last quarter of the 20th Century did the concept of Elevator ride quality start appearingin specification documents. The Japanese Elevator industry had basic ride quality requirements in placeduring the early 1980‘s due to the cultural demands of the Japanese population. These Japanese conceptsstarted to be incorporated into international building owners and elevator consultants‘ specifications withvarying degrees of success. The ride quality requirements were also being graded into local Standards ofquality without specifying other parameters and requirements essential for enhanced passenger perception.To some elevator suppliers, manufacturers, consultants and installers it was an easy way to increase salesincome without understanding the dynamics of elevator ride quality or what really was good or badelevator ride quality in terms of human perception.

Crucially there was no accepted method of testing for elevator ride quality, at the simplistic end testingwas by placing a coin on its edge in the centre of the car floor and driving the elevator up and down, if thecoin did not fall over it was good ride quality. A more sophisticated approach on the same theme was tobalance the coin on the car handrail.

To overcome these shortfalls some elevator consultants‘ specifications attempted to incorporate very

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detailed testing procedures using highly complex testing and recording instruments which also requiredhighly skilled technicians to operate, keep the instrumentation in calibration and understand the data andresults obtained.

To enable a Worldwide method of standardized elevator testing of ride comfort an ISO Standard for: Lifts(elevators) – Measurement of lift ride quality ISO 18 738 was published in 2003. This went a long way toprovide an International standardised method of testing and recording elevator ride quality, providedstandardised terms and definitions, measuring instrumentation, evaluation of ride quality, procedures formeasuring ride quality and reporting of results. ISO 18 738 crucially does not detail what is poor or goodelevator ride quality.

Technical Specifications

The classification of elevator ride quality is a perception of the passenger, but technical specificationsbeing produced by elevator manufacturers and elevator consultants have only brought confusion, assometimes they are without technical or commercial basis and it is doubtful that they bring added value toa project in terms of base commercial cost, reduced maintenance prices, increased reliability or increasedrentable value of a building.

From an analysis of four international elevator consultants ride comfort specifications for 1600 kg groupof elevators at 4.0 m/sec in a common shaft the basic requirements were as detailed in table 1.

ISO 18 738 classifies noise, lateral quaking, acceleration and jerk as:

Noise – Sound – a weighted sound pressure level in decibels.Lateral Quaking – A sideways acceleration measured in m-g.Acceleration – A rate of acceleration measured on the z-axis velocity and expressed in metres per

second squared (m/s2).Jerk – The rate of change of z-axis acceleration, attribute to lift motion control and expressed in

metres per second cubed (m/sec3).

From Table 1 it can be seen that the variations in the specifications for elevator ride quality areconsiderable, in that two consultants appear to concentrate on noise as the main driving factor for goodelevator ride quality and two consultants appear to demand specific requirements in terms of jerk andacceleration.

Which is the correct method, the simple answer is neither as noise levels are perception as are accelerationand jerk, the human perception of elevator ride quality is a combination of all three acting on thepassengers body.

International elevator companies become more complicated when the marketing departments classify theirproducts into a ride comfort category as can be seen in Table 2 where there are considerable differences inlateral quaking, when considering a good ride quality elevator at 4.0 m/sec.


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Could the elevator passenger really perceive the difference in the acceptable 35+ m-g from Internationalelevator Company “C” or the acceptable 12 – 20 m-g offered by other International elevator companies?As there is no International norm for defining the quality of elevator lateral quaking, this solely becomesan issue of perception of the passenger. Unlike other forms of passenger transport the potential buildingowner will find it very difficult to find an elevator installation which is exactly of the same design herequires for his building as there are too many variables to give an exact replication of the ride qualityexpected.

Noise is complex, what is acceptable? Everyone has a different perception of acceptable noise levels ineveryday applications, the user of an MP3 player may require a noise level of 105-120 dB(A) and amodern air conditioned office environment will have a design target of 50 dB(A).

In table (3) which is a comparison of maximum noise in the elevator car measured in dB(A) there is aconsiderable difference between elevator manufacturers in max sound levels and their later quakingrequirements in m -g.

From the specific requirements of the elevator consultants’ technical requirements the maximum elevatorcar noise and lateral are detailed in Table 4.

When comparing the elevator consultants requirements and elevator companies performance only oneelevator company can totally comply with the elevator consultants’ specifications. The major area of noncompliance is the noise level, which is one of the major areas of perception of the passenger. Does thismean the three elevator consultants requirements are technically unachievable or the elevator companiesdesigns are technically incorrect?


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Perceived Elevator Ride Quality

Each and every elevator passenger is the sole judge of what constitutes accept - able elevator ride quality,they make their subjective assessment on single or multiple journeys in the same or similar elevators in agroup or in a building. This assessment in simple terms is to ride the elevator and consciously or subconsciously analyse the journey, compare using memory and past experiences. Therefore if a group ofindividuals were asked to rate a particular lift journey the majority of responses would be different rangingfrom those who have an inbuilt fear of elevators and because of the physiological differences between menand women the perceived elevator ride classification will be different. Who is to say who is right and whois wrong as it is a subjective analysis?

It has been established and agreed that the basics of elevator ride quality is subdivided into noise,vibration, sensation of speed and elevator car design and all of these are very subjective due to gender,age, culture, well being and perception. A Multi -National Elevator manufacturer will have a differingview of ride quality from a local regional manufacturer and a local elevator consultant will have a differentperception from a International elevator consultant. In simplistic terms the elevator ride experience mustbe a pleasant experience that the passenger wants to have on multiple journeys.

The passengers perception of elevator ride quality is transmitted from the moving elevator to human bodyby means of experiences and signals received, analysed from the cardiovascular and digestive systems,organs and nerves. The capillaries within the inner ear, muscle groups surrounding the spine and nerves inthe soles of the feet are the key receptors which respond to changes in noise, vibrations, acceleration andlevels of jerk. The major internal organs of a human body are responsible for detecting changes in bloodpressure, so the perception of elevator ride quality depends on the quality of information received by thebrain and this will depend on the age, gender and well being of the individual riding in the elevator.

Noise

Some individuals say that we live in a noisy world and it is becoming nosier than ever, for some it is anencouragement, it is a sign of entertainment, industry and a bustling society. For others a serious form ofpollution, annoying, selfishness and the absence of concord and harmony. How this applies to elevators isdifficult to quantify in pure sound levels, does a building owner who has a super fast elevator installationreally want to experience super quiet and vibration free journey without the sense of speed and motion?

Noise is the easiest of all the elevator ride comfort factors to measure and compare with recognised norms,but also the most complex to control as multiple factors are all interacting with each other. Is themeasurement taken with the elevator car stationary/moving, car fan on/off, doors opening/closing, voiceannouncements on/off and the ambient noise level on the lobbies? For comparison purposes Table 5 giveslevels of noise norms in typical environments and suggested classifications. For elevators where the noiselevels are specified below 50 dB(A) this is classified as “faint” and would be the equivalent of living in asemi rural environment. The question is, is this an appropriate design criteria for an elevator in acommercial building?


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Noise is measured in units of decibels (dB). If sound is intensified by 10 dB, it appears to a persons ears asif the sound intensity has doubled, however if it is reduced by 10 dB it would appear as if the intensity hasbeen reduced by half. If the change of noise level is increased or decreased by 3 dB(A) the change wouldbe just perceptible, but if the noise level changes by 5 dB(A) the change is clearly noticeable. This is veryimportant to the perceived noise level within a moving elevator car.

It would be very unusual for an elevator car to have a generated noise level which will have an effect ordestroy a persons hearing. But high elevator noise levels can put stress onto other parts of the bodyincluding the heart. Noise will put undue stress onto the body by quickening the pulse rate, increasedblood pressure. Noise within a travelling elevator car can be both unpleasant and potentially harmful to thepassengers and this would not be classified as an imaginary, but a real concern. It is generally consideredthat continued exposure to a noise level in excess of 85 dB(A) is likely to degrade the hearing of a largepercentage of the population.

In an elevator car the noise generated must be analysed into 3 areas:

1 Will the noise become a nuisance inside and outside the elevator car?

2 Will the noise generated be safe to those passengers in the elevator car?

3 Will the generated elevator noise affect productivity?

It is recognised that people do have perceived levels of noise when it becomes either unpleasant oruncomfortable and this will affect perception of elevator ride quality.

Vibration

Apart from hearing which is the human response to audible sound there are other responses which can bemassed together under the banner of perception or feeling. Within a moving elevator, vibration is causedby surfaces and a component vibrating strongly enough to turn them into a secondary sound source, this


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vibration is generated by an elevator moving through the shaft and will change in intensity during theacceleration, full speed and deceleration elements of each journey.

The effects of vibration on a human body are difficult to quantify as people will accept different criteriafor different situations, a home is totally different to a hospital and a motor vehicle cannot be classified tobe similar as an elevator. There are defined levels of induced vibration which can cause nausea to humans,damage structures or cause equipment to fail or malfunction.

The vibration induced feeling is complex, but it is known that people using transportation systemsincluding elevators will tolerate more induced vibration than in a stationary environment. The humanperception to vibration, is how the body responds to acceleration, velocity and displacement which areeither taken singularly or as a combination.

In any elevator, the travelling passenger will have the perception of vibration acting on their bodies in 3differing axes classified as:

x the horizontal axis – front to back of the elevator car

y the horizontal axis – side to side of the elevator car

z the vertical axis of the elevator car.

Horizontal vibration is also called Lateral Quaking.

Vibration is defined as a variation with time of the magnitude of acceleration, when the magnitude isalternately greater and smaller than a reference level. Acceleration is normally expressed in terms ofmilli-g (m-g) or one thousandth of a “g” (.001 g).

The human body is very sensitive to low frequency horizontal vibration but normally immune to thehigher frequency horizontal vibrations. As most elevator passengers travel by standing up during thejourney, at low levels of frequency the whole body moves but at higher frequencies the feet move but theupper body remains stationary. It is very unusual for an elevator passenger to feel unsafe because ofvibration caused by horizontal vibration, on the x and y axis.

Normally elevator passenger concerns are due to incorrect installation of equipment, most probably causedby the guide rails not being fitted correctly or damaged, also the elevator car if not statically balanced willgenerate high levels of vibrations which will be perceived by most passengers.

Apart from horizontal vibration the elevator passenger is subjected to vertical vibration on the z axis, thisis generally a high frequency vibration generated by a primary source vibration through the rotating drivemachinery which is transmitted into the elevator car by the suspension ropes. The number of elevatorrotating components transmitting vibration are classified as motors, sheaves, rollers, bearings and gearswhich all have differing levels of frequency generation which at high rotating speeds should bedynamically balanced to reduce unwanted vibration. Most of the transmitted vibrations can be isolated bythe car frame assemblies, but an incorrect car design or installation procedures can result in mechanicalshort circuiting between the car body and its sling, inducing high levels of vibration.

The passengers perception of vibration is not normally apparent in an elevator at rest although a recordingof 4 milli-g would not be unusual due to natural vibrations generated within the building and elevatorshafts.

Passengers within an elevator car which is travelling at contract speed would not normally be able toperceive any noticeable difference in horizontal axis vibration between 10 and 20 milli-g or in the verticalaxis between 15 and 25 milli-g. So defining exact vibration levels may not alter a passengers perception ofelevator vibration or ride quality.


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Acceleration

Most people understand that acceleration is the rate of change of velocity. The effects of acceleration areboth physical as well as psychological and will have major variances between people travelling in theelevator. Elevator acceleration is perceived as good when it is constant. If the acceleration is by noticeablesteps it will be perceived as objectionable.

Obviously when slowing down an elevator will produce a negative acceleration curve which should mirrorthe step-less acceleration curve.

The passenger perception of acceleration is that for values below 1.1 m/s2 the majority of passengerswould not have any perception of a difference in overall elevator ride quality. Acceleration and motion is

noticeable if between 1.3 m/s2 and 1.6 m/s2, and in the majority of elevators this would be an optimum

value for acceleration to provide a good quality of elevator ride comfort. Acceleration above 1.8 m/s2

would often be perceived as objectionable.

Jerk

This is the term used for the rate of change in acceleration and is expressed as metres per second cubed or

m/s3. Jerk is probably the most important of the elevator variables and the most difficult to quantify whendefining overall elevator ride quality. The human body responds very quickly to rates of change inacceleration rather than the actual velocity of the elevator car.

With the rate of change of acceleration, the forces upon the human body change and if severe enough theelevator passengers will start to become uncomfortable. However changing the jerk rate of an elevator is avery convenient and cost effective way to improve the overall elevator system performance, but at a costto overall passenger perception of ride quality.

For an elevator with a jerk rate of 6.0 m/s3 this will be perceived to be totally unacceptable to a very high

proportion of passengers, a rate of 2.0 m/s3 would be entirely acceptable for a high proportion ofpassengers. The only exception to this would be where elevators are installed in hospitals where the effects

of a high jerk rate may be harmful to the patients and low jerk rates of 0.7 m/s3 could be required toreduce the possible risk to patients health.

Elevator ride comfort

An elevator ride should be a pleasant experience that the passenger wants to be repeated, they do not wantit to be frightening, to get this they would go to a theme park. The ride in the elevator must be a pleasure,but some passengers will not be satisfied, some may experience discomfort, therefore it is almost certainthat 100 % elevator ride comfort satisfaction will never be achieved.

A survey of actual passenger ride comfort perception was carried out on 367 people and also using anindustry standard Elevator Ride Quality Analyzer (EVA-625) manufactured by Physical MeasurementTechnologies, Inc. The following parameters were recorded, acceleration, jerk and noise inside the car atcontact speed, vibration on x-y axis and vibration of z axis. These have been compared with the passengerperception of ride quality from those passengers surveyed.

Table 6 details the maximum vibration recorded in milli-g on the x-y-z axis and ranks each lift in termsfrom best to worst.


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Table 7 details the maximum acceleration in m/sec2 and jerk in m/sec3 recorded in each lift car and rankseach lift from best to worst.

Table 8 details the overall level of recorded noise within the elevator car taken at full speed and ranks eachelevator from best to worst, the range of recorded noise is 5 dB (A).

Table 9 details the data collection from the elevators and ranks each lift in terms of data averages andgives an overall ranking of the elevator based on a comparison of points scored on data collection.


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Table 10 details the 367 passengers surveyed and their perception of the overall lift ride quality rankingand it is significant that the overall passenger perception of good elevator ride quality is significantlydifferent to that obtained by recording and analysing equipment. This suggests that just basing elevatorride quality on data gathering and specific specification requirements is not the only method ofdetermining good elevator ride quality. Passenger perception of quality is also very important as they arethe people who matter.

Conclusion

Elevator ride quality is a difficult topic to quantify in terms of good, average or bad as it is solely aperceived area of judgement of the individual riding in the elevator. But certainly guidelines can beestablished so that perceived good elevator ride quality can be specified and achieved within the confinesof the elevator shaft.

ISO 18 738 defines how to measure elevator ride quality but does not venture into defining what is good,bad or acceptable elevator ride quality.

Elevator ride quality is being driven by international elevator companies and international elevatorconsultants without reference to passenger perception and what is achievable.

The majority of elevator passengers would be happy with elevator noise levels below 50 dB(A),acceleration levels lower than 1.6 m/sec2 and jerk less than 2.0 m/ sec3.

Technically and commercially there is no justification for super quiet or super low vibration elevators asthe passenger perception would not significantly alter, and the overall elevator performance and reliabilitywould not improve.

References

Earl Abraham (April 1984) Performance Criteria: Car Ride Quality, Elevator World.

Aldia J. M. Aranbura I. Pagalday J. M. (1993) Single Parmater Elevator Comfort Elevation – Procuedureof Elevcon 1993.

Dipl-Ing. Peter Pini (2002) Elevator Diagnostics and More Lift Report – July/August 2002

Safety Line Institute (1998) Human vibration.

League For Hard of Hearing (2003) Hearing Fact Sheet.

ISO 19 738 (2003) Lifts (Elevators) – Measurement of Lift Ride Quality.

ISO 11 205 (2002) Acoustics – Noise Emitted by Machinery and Equipment.

Torsten Wintergerste, Sabine Sulzer (2004) Ascending The Matterhorn in Eight Minutes: Low Noise, High


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End Elevator, Sulzer Technical Review 3/2004.

Australian Government – National Occupational Health and Safety Commission.

Hillel Schwatz (1995) – Noise and Silence: The Soundscape and Spirituality, University of California.

Lyle F. Yerges (1969) Sound, Noise and Vibration Control, Van Nostrand Reinhold Co.


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