Ergonomics for Passenger Cars

Marek, Siebertz: Ergonomics. Chapter 247 of the FISITA Encyclopedia Automotive Engineering, Wiley

Ergonomics for Passenger Cars Clemens Marek, Ford Werke Köln & Karl Siebertz, Ford Forschungszentrum Aachen

Introduction Definition of Ergonomics The term “ergonomics” consists of two parts, both of them with Greek origin. “Ergon” can be interpreted as “the worker who has accomplished something” or simply as “work”. “Nomos” relates to the existing laws and conventions in the context of the human capabilities (Bhise, 2012). In other words: respect the human limits in the working environment. First attempts to regulate working conditions trace back to England in 1802, with the Morals and Health Act to protect children. Similar regulations have been rolled out in Prussia in 1839 and 1853. Schmidtke (1989) mentions fundamental ergonomic studies between 1850 and 1920 by Lavoisier, Lahy and Marey as well as basic research in physiology by Gustav Fechner in 1860. Industrial ergonomics established in the 1920s and 30s. Automotive ergonomics developed in the 1950s onwards. Driving a vehicle is a demanding task, even if it is not done as a profession. Ergonomics therefore plays an important role during the development process. Human limits are manifold, which makes ergonomics a multi-disciplinary task. Capacity and demand need to be considered simultaneously. A task can only be performed if the individual human capacity exceeds the demand of the particular task (Kroemer, 1997). What are the limits? A number of constraints are pure geometrical and caused by the dimension of the human body, which is a science of its own, called “Anthropometry”. Dempster (1955) investigated the space requirements of the seated operator. Internal loads of the human body build the next category of constraints. The operation of the vehicle requires a mechanical interaction. Biomechanics is the dedicated science for that. Human senses are remarkably good, so good that their limits are not always understood. Vision is of course the most important sense in this context, but also hearing and proprioception are relevant for a driver. Human senses are investigated in “Physiology “ (Schmidt, 2005). Even if the driver can reach everything, the operational forces are in the perfect range and the senses can master the situation, there is still the need to understand how the system works and the duty to come up with the right decision in the given time. Cognitive limits are difficult to investigate. Psychology is in the lead of this field, which is interdisciplinary itself. geometrical

Anthropometry

mechanical

Biomechanics

performance limits reception

Physiology

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Figure: Categories of human performance limits and relevant scientific fields. Rev 130531

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The individual capacity depends on a vast number of parameters, but even then it is not constant. Age, training, boundary conditions, fatigue and motivation come into play. For engineers it is sometimes difficult to accept this large spectrum, which causes some uncertainty. However, this is “the nature of the beast”. Decades of scientific work are condensed in ergonomic rules, tables and simplified functions (Salvendy, 2006 and Schmidtke, 1989). Typically these have been generated with test series on a sufficient number of subjects and under very controlled conditions. This is always a very good starting point and sometimes the only tangible instrument at all. Recent studies are more and more CAE driven (Seidl, 1994). Main advantage of this approach is a wider range of validity compared to experiments that only explain the tested conditions. However, the human body is too complex to be squeezed into a single model. Each model therefore has limits, which are not always obvious. A validation of the model is essential and any extrapolation beyond the scope of the model will be misleading.

Figure: RAMSIS model to investigate the package conditions. (Printed with permission from Human Solutions, Kaiserslautern, Germany.) Automotive Context Developing the technical ingredients of a vehicle is easy. Engineering is a straight forward science that follows rules of physics, math and chemistry. The interesting part starts when it comes to fit the human into the machine. Knowing and understanding the human is the real challenge. For this reason a vehicle is most often developed using known and proven technology in known and proven combinations. So, in most cases, there is already something to build on, a structure or platform that must be reconfigured or Rev 130531

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slightly altered. When there is nothing to start with but a clean sheet of paper, then it is good to know all the ingredients, requirements and prerequisites needed to develop a vehicle architecture that meets customers’ expectations. Science As indicated, ergonomics is a science that combines various branches of science into what is the approach to making the work environment fit the user. Here the work environment is not used in the traditional sense but more translated into the inside of a vehicle. Customer Knowing the customer is most important in this context. Here customer knowledge goes beyond personal tastes. Customers are divers in their body dimensions, physical constitution and cognitive abilities. Market Vehicles for personal transportation are being sold in many markets. Most of those share common requirements, but that is not the rule. For various reasons different rules and requirements exist in different markets. In order to be compliant to these rules, it is important to be aware of and to comply with those rules.

Interaction Models It is always helpful to start with a model to get a quick understanding and overview over a system. The operator is the driver who acts in a constant engagement with the machine, here the vehicle. This system is part of the environment in which the driver and the vehicle are interacting.

Figure: A model of the Human Machine Interface or HMI. (Ford Motor Company) The environment constantly sends out signals to the driver which are received and processed via the human senses. Of those five senses, probably sight, hearing and touch are the most relevant for vehicle operation. Also see under ‘Human Physiology’.

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Once the external inputs are received, the brain initiates actions or interactions with the vehicle. The reactions of the vehicle are being monitored and in a feedback loop overlaid with the original intention of the driver.

Figure: The Input/Output Model applied to vehicle control operation (Ford Motor Company) Human capability and performance Human capability is limited. Depending on training, age and physical condition, the driver may encounter his or her own limits sooner or later. This condition is also related to comfort. The driver may feel at ease as long as all external factors do not add up to create an uncomfortable driving situation or unfavorable conditions over an extended time period.

Log S

B‘

Max. Burden

Log T Comfort Threshold Figure: The relationship of sustained stress S over duration T and the subjective burden B’. (Printed with permission from Prof. H. Bubb)

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International Standards Standards help in the definition of vehicle parameters, components and attributes. There are engineering standards that can be used and altered to fit specific needs and requirements of the engineer and there are legal requirements that cannot be altered and must be followed by the engineer. Both have their roots in subject matter expert and peer groups that develop these standards, sometimes over a number of years. These standards are also called and used as recommended practices. SAE standards represent the largest collection of standards defined for vehicle development. The vehicle concept engineer should be familiar with a few that represent the basic set of SAE standard: • • • • • •

J1100 defines common rules for how vehicle dimensions are to be determined J826 describes two representations of the human inside the vehicle J1516 and J1517 position the human inside the vehicle J941 shows the definition of the eyellipse, the theoretical position of the drivers eyes J1052 provides an exclusion zone for the occupants heads J287 allows a determination of the drivers reach zones

These zones have been determined via initial representative anthropometric studies and have been complemented and improved by further data collection over time. The most recent effort resulted in a complete update of the relevant standards. Nevertheless, it is worthwhile to look at and discuss both as these are still being used side by side. SAE J1100 This standard provides a system of a defined nomenclature to describe vehicle dimensions. A combination of letters and numerals helps the engineer to easily identify interior and exterior as well as volume and some surface dimensions. It all starts with the 3-dimensional reference system as shown in figure xxx.

Figure: The three dimensional reference system (Ford Motor Company)

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The vehicle is positioned such that the Y-plane determines the intersection at the exact middle of the vehicle, sometimes called the Y0 section. The origin point is placed in front and below the vehicle for convenience and ensures that X and Z sections always carry a positive station. Length dimensions use the letter L and are being measured along the X-axis. Likewise, W is being used for Width dimensions and measured along the Y-axis. Finally, H is being used for height dimensions and measured along the Z-axis. The second part of this code system is the number, single and double digit numbers identify interior dimensions. Three digit numbers are being used for external dimensions, cargo volumes and glazed surfaces. Figure xxx gives an overview of the possible combinations for unique identifier codes.

ALPHA PREFIXES Meaning

Letter L W H A PL PW PH SL SW SH TL TH PD PV V IV S D F

Length measurements (longitudinal distance), or location of X coordinate Width measurements (cross car distance), or location of Y coordinate Height measurements or location of Z coordinate Angular measurement Lengths associated with pedal and pedal usage Widths associated with pedal and pedal usage Heights associated with pedal and pedal usage Lengths associated with seats Widths associated with seats Heights associated with seats Lengths defining H-point locations/travel Heights defining H-point locations/travel Passenger distribution Passenger volume indices Luggage volume and cargo volume indices Interior volume indices Surface area measurements Diameter measurements Planar area measurments

NUMERIC SCHEME Number range 1 - 99 100 - 199 200 - 299 400 - 599

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Type of dimension Interior dimensions Exterior dimensions Cargo, luggage or rear access compartments Dimensions unique to trucks, vans, sport utility vehicles, etc.

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J1100 has been updated to make the code system even more use friendly. For those codes that are to be used repeatedly, mainly applicable to interior dimensions, a suffix has been introduced to label specific rows. For an example, the code for seat height is H 30 (H for height dimensions, two digit number for interior dimensions), likewise the code for the first row of seats is H30-1, for the third row of seats, it is H30-3. Finally, J1100 provides guidance for determination of critical measurement locations including specific sections and definition of the Daylight Opening (DLO). SAE J826 As J1100 defines technical dimensions, J826 defines the human inside the vehicle. There are two devices. One is the CAD model, either as a 2- or 3-dimensionsonal figure. The second one is a physical device with a defined weight. Both devices share the same dimensions with a separate torso and length adjustable legs. The torso is fixed in its size and represents a 50th percentile torso length. The leg segments can be adjusted to represent 95th, 50th or 10th percentile anthropometric dimensions.

Figure: The 2D and 3D Manikins/HPM I and HPD I. (Printed with permission from SAE)

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The CAD model is called the H-Point Device or HPD and is being used for the basic concept layout. It features important hard points like the hip center H-point, the ball of foot and the heel point. Also, the torso line is defined. Consequently, the H-Point Machine HPM is used to verify actual interior dimensions inside the vehicle. Thus it supports concept verification with prototypes as well as enables benchmarking of existing vehicles. It features two buttons, one on either side of the seat pan to measure the H-point, a headroom probe and landing surfaces to take exact measurements of the torso and thigh angles. SAE J1516 and J1517 The HPD needs to be positioned inside the vehicle in relationship to the accelerator paddle and the seat. At the center of the hip, the HPD features the so-called H-point. This point is defined as the hip center and the torso rotation point. Assuming that a car seat is adjustable to accommodate various sizes of drivers, the H-point moves relative with the seat. The concepts engineer however needs a fixed reference point. Therefore the Seating Reference Point (SgRP) has been established and defined. SAE J1516 establishes the recommended standard SgRP which accommodates the 95th percentile HPD. SAE J1517 goes beyond and defines the so-called accommodation range for a 2.5th to a 97.5th percentile occupant. The formula for the calculation of the 95th percentile SgRP with x95 being the distance between the accelerator actuation point and z being the seat height or H30-1 (according to SAE J1100) is shown here:

ܺଽହ = 913.7 + 0.672316 Z – 0.0019553 ܼ ଶ The formulae for the extended accommodation range according to J1517 are shown here:

ܺଽ଻.ହ= 936.6 + 0.613879 Z – 0.00186247 ܼ ଶ ܺଽହ = 913.7 + 0.672316 Z – 0.0019553 ܼ ଶ ܺଽ଴ = 885.0 + 0.735374 Z – 0.00201650 Z2 ܺହ଴ = 793.7 + 0.903387 Z – 0.00225518 Z2 ܺଵ଴ = 715.9 + 0.968793 Z – 0.00228674 Z2 ܺହ = 692.6 + 0.981427 Z – 0.00226230 Z2 ܺଶ.ହ= 687.1 + 0.895336 Z – 0.00210494 Z2 SAE J941 This recommended practice covers the location of the human eyes. It is not so much a fixed location of eye points but rather a statistical distribution. Therefore a 95th and a 99th percentile eyellipse (eye and ellipse) were defined. Based on initial research of the eye point locations of various statured drivers, these were derived using the so called tangent cutoff method. Using this method, the concept engineer can determine the visibility performance of a concept for a given population. Figure xxx shows how the Rev 130531

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eyellipses have been derived from a distribution of eye points with the 99th percentile eyellipse being the largest, however still not capturing a large amount of eye locations.

Figure: Development of the 99th, 95th, 90th and 80th percentile eyellipse. (Ford Motor Company) Figure xxx demonstrates how the tangent cut off method is being used to determine up-vision for the 95th percentile of the driver population. A tangent is drawn between the top of the eyellipse and the bottom of the roof rail section in front of the driver. 95 % of eye points are now located below the tangent line.

Front header structure

95%ile eyellipse

Figure: Methodology used to determine the 95%ile up vision angle using the tangent cut off method. (Ford Motor Company)

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Figure xxx shows a 3D view of the eyellipses for both eyes. They overlap and are slightly tilted forward.

Figure: Isometric view of the left and right eyellipse. (Printed with permission from SAE) Finally, SAE J941 provides a guide how to position the eyellipse relative to the drivers SgRP. Here the reference or preferred back angle is 25°. The work line of the eyellipse is then positioned 635 mm above the SgRP. With smaller back angles (L40), the eyellipse will move further up and forward, with larger back angles down and rearward.

Figure: Positioning of the SAE eyellipse. (Printed with permission from SAE)

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SAE J1052 SAE J1052 completes the definition of the drivers’ space towards the headlining and roof. It defines a 95th and 99th percentile head contour that is used as a tangent cutoff line. The head contour for fixed seats resembles a half circle, the head contour for moving seats (like the front row seats) is more stretched and traces the shape of the eyellipse. Figure xxx shows the head contour for fixed seats, figure xxx demonstrates the relationship between the head contour for fixed seats and the eyellipse leading to the moving seat contour.

Figure: The 95th percentile SAE head contour for fixed seats. (Printed with permission from SAE)

Figure: The SAE head contour for moving seats, using the 95th percentile eyellipse. (Printed with permission from SAE)

SAE J287 Having defined the drivers’ basic needs for space, it is now useful to look at the boundaries for reach to controls. SAE J287 establishes the method for determination of reach envelopes. Based on a set of

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package dimensions, population gender distribution and the type of restraint, this standard offers the method to calculate drivers’ reach relative to the SgRP. Package factor G is taking certain key dimension like back angle and distance to pedals and steering wheel into consideration. With this factor and the appropriate gender mix, a table is being selected that offers a grid of longitudinal and vertical dimensions relative to the SgRP planes.

Figure: Factor G is calculated using these package parameters. (Printed with permission from SAE)

Figure: Table 25mm is the table of longitudinal, transversal and vertical dimensions for a 50% female/50% male gender distribution and a 3-point safety belt. Factor G was calculated to lie between -1.25 and -0.75. (Printed with permission from SAE)

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The new ASPECT manikin Towards the end of the 1990ies, SAE established a team to replace the HPM and HPD. Over the years it had become apparent that the old devices had some considerable deficiencies with regards to usability and accuracy. The new ASPECT manikin was introduced as HPM II in 2010 and has been specified by SAE J4002 and subsequently in ISO 20176. Some of the HPM II characteristics remained however. It still weighs 75 kg and the shape of the seat cushion and torso shell resembles the old HPM. The biggest difference is exactly there in the torso. It consists of three parts that allow a closer alignment with the actual seat back contour. The lumbar prominence can be determined via the moving lordosis section of the HPM II torso. Two more differences are important: • •

An independent seat cushion pan allows the measurement of the seat cushion angle, an important characteristic for seat comfort definition The foot and shoe device can be used independent of cushion angle and allows for a more meaningful measurement of the pedal position relative to the SgRP

Both, the old HPM and the new HPM II exist in parallel, concepts engineers are free to use either one as the basis for their concept layouts.

Figure: The individual parts of the HPM II with seat cushion pan, back pan and foot/leg apparatus. (Printed with permission from SAE) International Standards Due to the increased globalization, engineering standards have very much interrelated. SAE standards seem to be the source for most national and international standards. DIN and BS often are drawing their definitions from SAE. Finally the ISO organization brings together national and international work groups that develop ISO standards, mostly from already existing rules, refined for international use by global committees. The Rev 130531

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end products are international standards that often are used as the basis for legal requirements like UNECE. Some of the most important standards are defining mirror vision, wiped field and pedal spacing:

Figure: 2003/97/EC defines the area behind a vehicle as a zone that is required to be seen via the exterior mirrors. The zones represent passing or passed vehicles. (Adopted from ECE)

Figure: 78/318/EEC describes the wiped field, Area A on the left hand side is required to be wiped by 98%, Area B needs to be wiped by 80%. (Adopted from ECE)

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Figure: The requirement for distances between pedals is defined in ECE 35. Note that the distance between brake and accelerator pedal is very much limited. Therefore build tolerances need to be taken care of. (Adopted from ECE)

Internal Standards Most automotive manufacturers can draw from a wealth of experience and therefore have their own internal standards. In general, it can be determined that these internal standards oftentimes use national or international standards as a basis and enhance these by certain best practices based on experience and research. It is their nature that these internal standards are more strict and severe as some of the international standards or even legal requirements often just formulate a framework for specific standards. Therefore internal standards lend themselves as unique identifiers for brands. Public Domain Tests These tests are not necessarily related to legal requirements but can serve as customer selection criteria. To name a few, EURO NCAP is a public domain test that looks at the crash performance, hence passenger protection capability of vehicles. The test uses star ratings and points to identify the best performers. Another one is Consumer Reports. This is a magazine that is very popular for purchasing decisions of US customers. Based on a set of criteria, ratings are established and communicated via regular reports. These are only two of many. As a consequence, it is worthwhile understanding the rating criteria and catering to them. A high score will drive purchasing decisions, an opportunity that cannot be disregarded.

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Knowledge about the Human Body Anthropometry As already mentioned, anthropometry is a science of its own. Standardized measurement protocols with clearly defined test codes exist to create a globally usable database of human dimensions. Figure xxx shows an excerpt of an anthropometric database with some of the critical dimensions useful for vehicle occupant definition. These databases usually add the statistical distribution values, here 5th to 95th percentile dimensions.

Figure: Anthropometric data tables: results for buttock-knee length measurements. (From Kantowitz/Sorkin. Printed with permission from Wiley, 1983)

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Figure: Anthropometric measurement devices: fixture to measure functional arm reach. (From Kantowitz/Sorkin. Printed with permission from Wiley, 1983)

Anatomical variation Unique challenges for the concept developer represent the so-called somatotypes. To understand the challenge it is also important to understand that no 95th percentile is like another 95th percentile stature. Looking at the dimensions of certain body parts that make the human, torso, legs and head, there is a large variation between individuals. In other words, comparing two 95th percentile males, one might have very long legs and a short torso whereas the other one might have shorter legs and a long torso. (Please compare with section ‘user collective’) Percentiles and variation in strength Anatomical research has proven that there is a correlation between body dimensions. Thus it is safe to assume that a smaller person has smaller extremities. Using the correlation factors, the concept developer can derive important dimensions for a concept layout by just knowing the size of the stature of a certain percentile. This is however not true for a person’s strength. There is no correlation since strength depends on individual physical characteristics, training, gender and age. Figure xxx shows the relationship between median strength levels and gender. It also demonstrates the effect of age, a steady, proportional decline over the years.

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Maximum Strength in %


Age Figure: The relationship between of age related to % maximum strength for males and females (Adopted by Ford Motor Company after Hettinger, 1960) Populations and their properties Sources of information As implied, it is mandatory to gather a lot of information on the driver population when working on a vehicle concept that is suitable for a large customer group. Sources of information on anthropometric data are those tables that are available in human factors handbooks. Unfortunately, these are often a bit outdated and their usability is limited. Even more useful are those that databases that are attached to human model CAE tool. These are integrated into the tool and deliver representative manikins that offer a high degree of flexibility. Importance of anthropometric information Anthropometric data is needed to define the boundaries of a concept, as will be discussed later, it supports finding the solution to the developers challenge: defining an occupant concept that accommodates a diversity of a number of user populations.

Biomechanics The human body has been optimized for the traditional life, dominated by physical activity. Vehicle operation was not part of the evolutionary plan. Drivers and passengers might therefore have difficulties to perform the required motion tasks or experience discomfort in static seating positions. The same external operational force (e.g. pulling a handbrake) will produce totally different internal loads for each driver, depending on the specific anatomy. A mismatch between individual capacity and the demand of the motion task will causes issues. This is the link between ergonomics and biomechanics.

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Typical ergonomic issues related to the locomotor system are: 1.

2.

3.

4.

1

5.

Muscular effort is too high to perform the task. This could, for instance, apply to lift-gates, luggage handling or mechanical handbrakes. It is more of an issue for elderly people as they often, simultaneously, have limitations of the joint movement range. Kinematics of the motion task is too restricted. Ingress and egress are typical examples, but also the folding of the rear seats or luggage handling can fall into this category. A kinematic restriction might be caused by the vehicle package, but also a limited range of joint motion in the human body (e.g. stiff knee) can create a motion task which is not possible for the individual subject. A suboptimal movement pattern will increase the muscular load and might shift it beyond the personal limit. Muscular efforts are too high to fulfil a task over the required time. This applies for all control tasks such as steering and pedal operation. After just one hour, the maximum muscle force drops down to less than ten percent of the short-term maximum force. Therefore, even low activation levels can become critical. A lack of postural support. The muscles become over-loaded after a certain time (sitting in the seat) and cannot stabilize the body any more. This leads to fatigue and higher loads on the passive locomotor system. Problems with cartilage (e.g. vertebral discs) and ligaments are resulting longterm consequences. Activation levels are too low or have the wrong characteristics in order to fulfil the control task. These issues are a little more complicated because the goal is not simply to reduce the effort. The driver is part of the man-machine control system, at least until auto-pilots become standard in our vehicles. Using the current vehicle layout, the entire control communication (steering, shifting, braking, accelerate) relies on the human locomotor system's input. The control communication is bidirectional: The driver submits commands through mechanical forces or torques and the vehicle gives feedback through the same control elements. Unfortunately, the driver moves during driving (probably the original reason to use the car) resulting in dynamic loads, on the same extremities that are used to operate the controls.

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Figure: Muscle fatigue. The maximum muscle force can only be generated for a short time, due to metabolic constraints. (fatigue model from Ford, validated against data from Niemi et al.)

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Biomechanics offers analytical tools to analyse how difficult a specific driving tasks will be, depending on vehicle parameters and the individual subject. This is a real challenge because the human locomotor system consists of more than 200 bones, connected with various kinds of joints and more than 600 muscles which can be activated independently. Adding all degrees of freedom in the human skeleton, the total number will be significantly smaller than the number of skeletal muscles. In mathematical terms, this means that the equation system is indeterminate. In physiological terms, this means that the human body has several options to recruit the muscles and still fulfil the same movement task. How the muscular loads are distributed within the human body is not just a question of energy expenditure or relative muscle tension (related to the available cross section). Innervation speed and the mechanical loads in bones and ligaments (the passive part) are relevant as well (Pauwels, 1965 and Siebertz, 1994). Many muscles cross two joints, others only one joint. Tendons are in place to optimize the effective lever arms and introduce wrapping points in the line of action, if a simple straight line would not be ideal for the human body. A complex system of ligaments is needed to utilize different bones and allow for the right amount of movement. For instance, the knee joint would almost fall apart without ligaments since the contacting bone surfaces of the femur (long bone of the upper leg) and tibia (long bone of the lower leg) are not congruent (Schünke, 2004).

Figure: AnyBody, a CAE tool to model the human locomotor system. External loads are balanced with internal loads and there are many more muscles than degrees of freedom to move. (Printed with permission from John Rasmussen, University of Aalborg, Denmark.)

Human gait analysis has a long history in Biomechanics (Winter, 2005) and most of the current methods are derived from this field. Over the decades many these tools evolved from undocumented unique applications to affordable and easy to use turnkey solutions. There is a clear trend to include more analytical tools (originating from Biomechanics) in automotive ergonomics to provide guidance earlier in the development process and to quantify benefits of ergonomic improvements. Kinematic motion analysis is helpful to investigate how people perform complex tasks such as ingress/egress. Despite the fact that motion patterns are very individual, there are general mechanisms, e.g. the use of a planning level, guiding level and stabilization level (Cherednichenko, 2008). Depending Rev 130531

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on vehicle design parameters such as door opening height or step over height, many people change their movement pattern completely. Motion analysis also builds the backbone of further biomechanical analysis with CAE models. A multi-segment model of the human body is the underlying assumption to solve the resulting system of equations (Zatsiorsky, 1998). Output is a reproducible description of the kinematics in terms of joint angles or joint centre movement.

Figure: Motion analysis of the vehicle ingress. Based on real 3-D motion capture, the joint motions of a segmented surrogate model can be described and used for further mathematical analysis. (Ford)

Skin movement and loose clothing are critical. A 3D reconstruction requires at least two independent unobstructed views, which can be difficult to obtain inside the vehicle. A robust motion tracking works with a set of four or more synchronized cameras to make sure that at least two views are available at any time. The redundancy also reduces errors due to optical distortion. Video-based systems and infrared-based systems with passive markers are current state of the art. The link between marker trajectories and motion of the kinematic model is one of the key issues in practice. However, new algorithms have been developed for that (Anderson, 2009). Future systems might even utilize pattern recognition and make markers obsolete.

Figure: Typical experimental setup of 3D motion capture. Visual obstructions need to be removed. (Ford)

In general, muscle and joint forces cannot be measured. It would require very difficult invasive methods to implant force transducers into the human body (which has been done in the past, but it will never be relevant for automotive applications). However, the electrical innervation of muscles can be Rev 130531

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traced (De Luca, 1997) using the so called Electromyography (EMG). In this context only a non-invasive surface Electromyography (EMG) makes sense. Small electrodes are attached to the skin and capture electrical signals in the range of millivolts. For medical applications or sport science, there is also the option to reach the deeper layers of muscles with thin needle electrodes. From EMG signals it is possible to judge about the activity of certain muscles and their state of fatigue, but it does not allow conclusions about the absolute muscle force. Biceps

Figure: Sample result from the study mentioned above. Post-processed EMG signal vs. CAE prediction of the biceps force. Both curves are normalized to the individual maximum. Only the shape of the curves can be compared. (Ford)

Test: EMG envelope CAE: muscular power

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External forces can be measured with conventional force transducers. For a full body analysis it is required to measure all external forces acting on the human body, not just the forces acting on the upper or lower extremities. Unlike in a crash event, the voluntary muscular activity plays a dominant role in slow and controlled movements. The CAE method of choice is therefore the so-called “inversedynamics” with experimental input related to kinematics and external forces. Required internal forces from the muscles to fulfil this motion task are then the output of the CAE tool.

Figure: AnyBody Car-Driver-Model by Ford (Siebertz 2007). External loads and human body movement need to be provided via experiment. The CAE model is then able to calculate all required muscle forces for this particular motion task. Rev 130531

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Human Physiology Physiology explains how the human body functions. This is of course relevant knowledge for ergonomics, in particular anything related to the human senses. It would exceed the scope of this chapter to present a comprehensive overview. There are many good books available in all languages and with very explanatory illustrations. Anyone who is seriously interested in ergonomics should take a closer look. Vision is clearly the most important sense for the driver in order to fulfil the driving task. Watching the traffic has always been the duty of the driver. In addition, the largest portion of vehicle related information is presented via the visual channel. There are several analogies between the human eye and a digital camera, starting with the receptors. Red, green and blue receptors (cones) are used for colour vision. Each of the receptor types has a specific spectral sensitivity curve (Schmidt, 2005). Like in a photographic sensor, there is a certain sensitivity and dark noise. As a side effect of these spectral sensitivity curves, the optical performance depends on light intensity and the wavelength. “High Dynamic Range” (HDR) is a lot older than digital photography suggests. The human eye simultaneously works with high sensitivity cells (rods). Their spectral sensitivity curve lies between the curves of the blue cones and the green cones (Kokoschka, 2003). The detected image is always a composition of the signals from all four cell types. The overall level of sensitivity can adjust to the lighting conditions in a certain range, similar to the ISO setting of a digital sensor. However, this adjustment is rather slow. Most of the cones are in the centre. 6 million cones and 120 million rods would deliver more information than a human brain can handle. Signal processing takes place in neurons and basically converts sequences of pictures to contrasts (black-white, red-green, blue-yellow) and changes over time (Haken, 1992, Silbernagl, 2012). Vision is not just the result of static pictures. The human eyes continuously scan the environment in small movements. A spatial picture is composed by the binocular vision through the two eyes. The focal adjustment works via a change of the refraction, which takes some time and degrades significantly after an age of 40. The aperture is in the range of 2.5-12, depending on the light intensity and on age (approx. 4-12). The average focal length is about 22mm. The “sensor diagonal” is approximately 40mm, but only very few cells are on the outside. For an ergonomic design it is important to know and to respect the physiological limits of resolution, acuity, colour vision, sensitivity, focal adjustment, adaptation speed and contrast. Reading is a complex process that starts with the (pattern) recognition of letters. Intensive research has been conducted in the past to optimize fonts for readability, mainly to enable the failsafe recognition of road signs. Needless to say that Typography is a science of its own. Herrmann (2010) investigated several dedicated fonts for road signs around the world and created a new font, called “Wayfinding sans”.

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Figure: Fonts can be optimized for readability. The lowest word is typed in a special font called: Wayfinding Sans. (Printed with permission from Ralf Herrmann, Weimar, Germany)

Hearing and orientation are crucial to survive in nature. Eyes can be closed, but ears are always open, for good reasons. 20-20kHz is the nominal frequency range, but in age the upper limit shifts dramatically (10kHz, or lower). As a result, separation of different voices becomes a lot more difficult. Hearing in general can degrade, as well as the ability to locate the source of the sound. Hearing and acceleration are sensed in the vestibular organ. This “g-sensor” and the visual impression merge to a sense for the absolute orientation of the head. The relative orientation of the body segments to each other are sensed via proprioception, using a large number of natural strain gauges, mainly in the muscle spindles. Proprioception plays a major role in motor control. Most people will know the simple sobriety test: Touch your nose with eyes closed. Alcohol can raise the typical tolerance of 20mm to a much higher value. Precise movement can be trained. There is clear evidence for a significant learning potential, see Goble (2010). However, difficult movements will take more time, even for trained subjects. Bhise (2012) explains the so called Fitt’s law of hand motion. The relevance of non-visual information for the driving task has been investigated by Sainio (2007) in cooperation with Ford. Icy road conditions are very frequent in Finland. It is therefore important to “feel the grip”. The human eyes can only detect the current location, not the acceleration. A significant fraction of the information for the driver is the detection of vehicle acceleration via mechanical coupling to the seat and the human vestibular organ. The human locomotor system utilizes an army of biological strain gauges in the muscles, joint position sensors, accelerometers, force sensors, vision and more via “sensor fusion”. Without such mechanisms it would be completely impossible to walk or perform other movement tasks e.g. play tennis. Driving a car takes advantage of the sophisticated control features that our body offers. In a sense, the driver becomes part of a symbiotic man-machine system. The resulting cognitive workload depends on the information density, the way the information is presented, training, the required precision and other factors. Driving is a chain of perception, signal processing, decision, action and control of the effect. Like in any chain, the weakest link will determine the overall strength. Human Vibrations and Dynamic Seating Comfort Beside ergonomic and static seating aspects is the dynamic seating comfort accepted to be one of the most important properties of a passenger car in terms of customer acceptance. Thereby are vibrations in the focus that act on the occupant in various ways. It is commonly known that vertical accelerations on top of the seat cushion, i.e. between seat and occupant, have the most influence on the occupant’s Rev 130531

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comfort impressions. Accordingly is the seat-transfer-function, defined as the quotient of the vertical vibration at the cushion surface divided by the exposition at the seat rail, the most important quantity to evaluate the seat designs. For determining the seat transfer function in the real or in the virtual domain the occupied seat must be investigated as the dynamic properties of the human body influence the behaviour of the complete system. An accepted value for describing the dynamic behaviour of the human body is the apparent mass which is defined by:

M ( Ω) = F(Ω ) / a(Ω )

Apparent Mass [kg]

The main characteristics are different for the percentiles f05, m50 and m95 which enables a classification of the dynamic behaviour with respect to the anthropometry.

Frequency [Hz] Figure: Measurement results of apparent mass for test persons from percentile f05, m50 and m95. (Printed with permission from Wölfel Beratende Ingenieure, Höchberg, Germany) In the traditional engineering process the dynamic seating comfort is evaluated by measurements with test persons. This provides the benefit of subjective ratings e.g. by questionnaires but includes disadvantages with respect to reproducibility which is important for absolute and relative assessments. Consequently testing procedures by applying hardware dummies have been developed within the last years. Thereby a prerequisite for realistic results is that the dummy must reproduce the dynamic behaviour of the human body defined by the apparent mass. Accordingly rigid mass approaches fail. Possible solutions are the superposition of several single dof oscillators or active systems as the dummy MEMOSIK® (see Mozaffarin, 2008).

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Figure: Hardware dummy MEMOSIK® for investigation of dynamic seating comfort (Printed with permission from Wölfel Beratende Ingenieure, Höchberg, Germany)

An alternative to the hardware testing are investigations using digital prototypes. This transfer to the virtual reality enables the assessment of the dynamic seating comfort in an early stage of the development process. Further design variants differing in material and geometric properties can be compared overnight, while already the production of adequate hardware prototypes would take days or weeks. A challenge within the virtual development is the modelling of the seat and the human body representing the real static and dynamic properties. A possible solution is represented by the application of the FE human body model CASIMIR (see Siefert, 2008) in combination with detailed seat models, where the real behaviour is reflected by nonlinear and frequency dependent properties.

Figure: Human Body Model CASIMIR and detailed seat model of a car passenger seat (Printed with permission from Wölfel Beratende Ingenieure, Höchberg, Germany)

Finally analysis methods must be applied at the end of the real or virtual process to assess physical quantities as the seat transfer function or vibration amplitudes regarding the dynamic seating comfort. Thereby is a basic approach the evaluation of the main characteristics of the seat-transfer-function as: amplitude or frequency of maximum peak, isolation frequency and level of amplitude after isolation. Further methods as the ISO 2631-1 or the determination of the SEAT following the ISO 10326-1 are computing one scalar value out of the RMS results of the vibration acting on the occupant. A more detailed approach was developed by Lennert (2009) and is named ‘Dimension of perception’. Thereby the frequency spectrum is separated in ranges as in real measurements a correlation between them and real vibration phenomena as e.g. high-frequency-shake was identified. This procedure is already established in acoustics and enables nowadays a more detailed assessment for the dynamic seating comfort.

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Layout of the driver’s environment To make a vehicle run it takes two things in a very broad sense: the mechanical package combines the powertrain and all its adjacent components on one hand. On the other hand there is the occupant package made up by the primary and secondary controls. Primary controls are defined as necessary for performing the driving tasks and are steering wheel, pedals, shifter and handbrake. Secondary controls are those that indirectly required for the driving tasks, controls like headlamp switch, steering wheel mounted switches and climate controls. The mechanical package The mechanical package combines front end package and underbody package. As the latter is taking up space underneath the vehicle, only the front end mechanical package is competing with the occupant package for the same space. The target is to minimize the front end package space for the benefit of a larger occupant package on the same given footprint. The mechanical package engineer will try to deliver the most space efficient powertrain by optimizing and ‘nesting’ components.

Figure: An example of ‘nested’ powertrain components. Here the cooling package is ‘nested’ between the engine and the battery and fuse box package. (Ford Motor Company) Also, structural requirements need to be met and observed to meet a certain crash performance. So the target is to minimize the length dimension between the front most point of the front bumper and the separation wall between engine compartment and vehicle interior. For simplification purposes it is advisable to look at the distance to the accelerator heel point. Key Features differences

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Powertrain orientation has a considerable impact on the seating position relative to the front axle. According to figure xxx, the distance A between the axle and the occupant is influenced by the powertrain width. East/west oriented powertrains have the advantage of a relatively small tunnel that enables a seating position closer to the front of the vehicle, thus minimizing the distance between the front bumper and the accelerator heel position. With a north/south orientation, the transmission

Figure: The relationship between powertrain orientation and distance to front axle. Due to the transmission package size requirement, the distance increases. (Ford Motor Company)

requires a lot of space and forces the occupant to be positioned further rearward. The distance between front of vehicle and the occupant is increased. Pedal package There are a few things to be defined around the pedal package. Again it is important to create a pedal package that does not consume too much space, thus moving the occupant further away from the front of the vehicle again. Therefore the pedal travel has to be optimized while maintaining a low level of efforts. This can be achieved by arranging the pedal geometry such that the initial undepressed pedal position is roughly horizontal compared to the end stop position.

Figure: Critical pedal angles relative to maximum force exertion capability. (Printed with permission from Wiley)

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Next the clearances need to be observed as directed by the legal requirements described in ECE 35. These clearance requirements need to be maintained throughout the entire pedal motion range. Finally there typically needs to be a provision for a footrest as this is an important customer posture comfort requirement. Application of SAE J826 and SAE J1516/1517 When this step is completed, the layout can be continued with the application of J826 and J1516/1517. At the beginning of these steps, it is vital to have a good understanding of the target population. As discussed, sources of anthropometric data are very useful to gain the necessary understanding and facts of what to cater for. Figure xxx demonstrates what the challenge might be. When developing concepts for a global customer base, the accommodation range needs to be stretched to cover a larger range of statures with one given layout of the seat adjustment.

Figure: The challenge for the concept developer is the wide spread of anthropometric properties of different populations. (Ford Motor Company)

By starting with the established accelerator heel point AHP and the accelerator actuation point AAP an appropriate seat height H30 needs to be selected according to which kind of vehicle concept is intended to be pursued. Then by use of the formulae out of J1516 and J1517 the concept can be established.

• 190 to 230 mm for coupes • 230 to 300 mm for sedans and wagons • >300 mm for MAV’s/CUV’s

Figure: Layout of the driver position with typical values for the seat height H30. (Ford Motor Company)

To explain the use of the accommodation curves a bit further, it is worthwhile to explain the options. With a higher seat and H30 moving beyond 300 mm, the manikin shifts its position following the Rev 130531

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percentile accommodation curves. As a consequence, the driver moves further forward. This in return enables to achieve additional knee room in the second row while maintaining a given footprint

Figure: Gain of rear leg space while maintaining the targeted footprint. (Ford Motor Company) Use of CAE tools Once the concept has been established based on the SAE standards, it has become standard practice to use CAE tools to verify the base layout and further define the driving environment. Here it is useful to define a user group consisting of all possible anthropometric configurations, so called somatotypes. This collective would address the special needs of drivers with long torsos and short torsos respectively. Here the purpose is to test the established concept for all possible use cases i.e. when a driver with a short torso and long legs still needs to be able to reach the steering wheel. Likewise, a driver with shorter legs has to sit further forward and would have insufficient head clearance to the headlining due to his long torso. Figure xxx displays such a ‘user collective’ generated using the RAMSIS software. Other CAE tools can also be used for this purpose.

Figure: User collective established using RAMSIS. (Ford Motor Company)

Primary and Secondary Controls, Guidelines for the Layout

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•

•

•

Steering wheel Having defined the user group it is now possible to refine the initial concept and verify the accommodation range. o Layout requirements With a representative torso angle selected, the steering wheel position can be determined by exploring the maximum and minimum reach by investigating a 5th percentile female and a 95th percentile male data set . Typically there would be a range of around 100 mm between the capabilities for tall and small persons. In other words, ideally the steering wheel adjustment range should achieve 100 mm. Since this dimension is restricted by technology, adjustable steering columns can achieve a maximum travel of up to 60 mm only, a center point has to be determined based on the 50th percentile reach. o System expectation Steering wheel efforts should be uniform and not exceeding strength capabilities for older customers. Locking efforts for the column adjustment should follow the same strategy. All steering wheel mounted controls should be within reach and usable with hands on the steering wheel. There needs to be sufficient clearance around the steering wheel rim to adjacent components when turning the steering wheel. Sufficient care needs to be taken that the shape of the steering wheel does not obscure vision to components on the instrument panel like the main light switch, stalks and most importantly the cluster. Gear shifter o Layout requirements Based on the preferred seating position that is defined by the selected Seating Reference Point and seat back angle the reach to the gear shifter needs to be established. Note that a full hand grasp is required to determine the reach to the foremost and most distant gear position. o System expectation System expectations for manual transmissions are more crucial than those for automatic transmissions. Due to the higher frequency of use while driving, it is important to ensure low shift efforts and high precision gear engagement together with positive feedback of gears being engaged. The shifter should neither obstruct visibility nor access to other controls. Also, clearance to adjacent controls needs to be maintained. Appropriate clearance envelopes can be established based on the specified user population. Drivers wearing work gloves or gloves to protect from cold weather need more operational clearance then those drivers that drive with bare hands. Pedal Package o Layout requirements The pedal package needs to be arranged to fulfill the legal requirements as defined in ECE 35. As discussed the clearances between pedals are vital to avoid inadvertent actuation. For the same reason, it is important to place the pedals in an expected location relative to the mid-sagittal plane of the driver’s body.

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System expectation Due to the higher frequency of use with manual transmissions, the clutch pedal needs to be treated with extra care. The pedal travel is important for pedal operation. If the clutch pedal travel is too large, drivers will complain about difficulties depressing the pedal too much in conjunction with discomfort of the thigh against the seat cushion. If the pedal travel is too short, then it is hard to control and modulate around the clutch engagement point. Research exists which suggests that drivers position themselves further forward in vehicles with a manual transmission. Accelerator pedal efforts need to be well balanced for actuation and holding cycles. When accelerating, the pedal efforts need to be relatively low for a good performance perception. On the other hand, at steady speeds, pedal holding efforts should not be too low to avoid muscular cramps due to insufficient foot support. Hand brake o Layout requirements Depending on the chosen system (Power park brake, manual hand brake, foot operated park brake) different requirements do apply. All of these systems need to be within reach by hand and foot respectively. Sufficient clearance needs to exist throughout the entire range of application. o System expectation In the last few years the design of power hand brake interfaces has shifted towards the handbrake stereotype. Drivers are more familiar with pulling the manual handbrake upwards, so the expectation to the power handbrake is the same. Pushing a switch is rather not intuitive. Due to the compact space requirement of the park brake switch the positioning is very flexible, therefore a place in the center console area is easily found and in line with the customer expectation. Efforts for manual hand brakes are critical for older customers. The level of force required needs to be rather low so that it is safe to hold the vehicle on mild slopes with only a little application travel. Switches o Layout requirements The layout strategy needs to be based on the importance of the required switches. Those with higher frequency of use should be located around and well within reach of the driver. Good visibility and unobstructed access shall be provided. The switches with higher importance should be located within the 95th percentile reach and forward of the minimum reach to avoid awkward posture when in use. o

•

•

o System expectation There exist a number of prime requirements for switches. The switch interface needs to provide the driver with a sufficiently large interface. In case a number of small switches are required to be placed next to each other it is advisable to add a physical separation between them to avoid inadvertent actuation.

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All switches have to be clearly identified with a meaningful label. A large number of labels is defined by ISO 2575, some are regulated by ECE 121. In some countries, text is preferred over labels. It is self-evident that all switches need to be illuminated, except for those switches where illumination is difficult (stalks, other trim mounted switches). Upon actuation, a switch needs to provide some sort of feedback, either a haptic or a visual feedback. Customer expectation is that within a certain time the desired action is completed. Finally, switches need to be designed so that they function according to human stereotypes. This is described in SAE J1139. Figure xxx shows an example of different variants of power window switches. The stereotype that can be applied here is pushing the switch down to open the window and pulling it up to close the window. Another concept related to stereotyping is coding. The pictures in the lower left hand corner are a demonstration of both, perfect stereotype and coding. The switches mimic the function of the power window and can be attributed to the respective side windows.

Figure: Demonstration of stereotypes using the example of power window switches. (Printed with permission from SAE) o Quality perception Perceived quality can play a major role in the attempt to create a driver environment that is pleasing and easy to use. The work environment is influencing the driver motivation, therefore makes a positive contribution to the drivers well-being and his willingness to perform. It also contributes to the technical demands that lead to enhanced human performance.

Vehicle evaluation Subjective Rating

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Subjective rating is the oldest method to evaluate something and will probably continue to survive. As mentioned earlier, the human body is fully equipped with hundreds of biological sensors. Experienced evaluators essentially use these sensors in order to detect small differences in design, which are not yet measurable or only with excessive effort. Many different evaluation schemes have been reported in the literature and it is beyond the scope of this chapter to come up with a complete review or guideline. However, some basic rules should be mentioned: 1. Clear definition of the evaluation criteria and precise description of the evaluation conditions. Ergonomics is multi-dimensional. This means that several independent criteria need to be defined and separated from each other. For each criterion there should be one critical task or boundary condition where the differences between good and bad design are evident. Many criteria require real driving exercises on the test track. Pure show room evaluation might not be appropriate. 2. Reference design. It is much easier to compare two designs than rate a single construction without any reference. The reference design needs to be in a controlled condition over the time of usage. Paired comparison is even better, but the number of combinations increases quadratic, which will be prohibitive in many cases. 3. Descriptive rating scale. The rating scale should be clearly defined and not too fine. It is important that all evaluators have the same understanding of a particular rating level. For design optimisation it can be helpful to use bi-modal scales instead of one-dimensional scales. For instance, a seat can be too wide or too narrow. Just rating the seat width on a scale from 1 to 10, would not give guidance on how to improve the design. 4. Customer oriented weighting. Complex tasks such as ingress or luggage handling can be split into subtasks to better understand the problem and to give the evaluator a better guidance. In many cases the evaluation will be multidimensional anyway (e.g. seat comfort with posture support, lateral support, vibration damping, climate comfort, etc.). The multi-dimensional rating needs to be combined to one total score for each design proposal. A representative picture can only be obtained if all important aspects are captured and weighted according to the customer preference for the particular vehicle type. 5. Trained evaluators. Subjective vehicle evaluation is like wine tasting. The evaluator needs much experience, the ability to focus on specific aspects and the ability to separate the differences caused by boundary conditions from the difference in performance. 6. Sufficient evaluations. Even trained evaluators do not always come to the same conclusion. However, a smaller number of observations are needed, compared to regular customers. For a proper evaluation, it is necessary to represent a certain range of the population with a number of selected evaluators because the “ergonomic performance” of a design depends on the physical constitution of the evaluator. This “subjective truth” can hardly be debated. An alternative approach is the measurement of the performance. Ergonomic design supports the driver and enables better performance or similar performance with less strain. Physiological measurements such as heart rate or eye movement can be used to monitor the test subjects. Operational time or failure rate are possible measures for the performance. A video analysis should run in parallel, if possible. However, there are several problems connected to this approach, mainly preRev 130531

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conditioning of the test subjects and learning effects. It will therefore be very difficult to evaluate a large number of design proposals. On the other hand, this approach can reveal differences that the subjects themselves could not express in words. Data versus Knowledge “Data driven”, that sounds great in general, but can be totally misleading in the context of ergonomics. Of course, the pressure is high while competing with other attributes in the development process. It is important to provide guidance as early as possible, but unfortunately many ergonomic methods require a prototype or at least a mock-up. Once the human is part of the setup, a vast number of variables are added. Subjective ratings are not as reliable as measurements. The order of the experiments will play a role due to potential bias and precondition of the test subjects. Analytical CAE models need to fit to the problem and the selected response needs to be meaningful. In all cases it will be possible to generate data, but not all data can be condensed to knowledge. Existing knowledge from anthropometry, physiology, biomechanics and psychology should not be neglected. Time and money can be saved, if the specific problem relates to a simple fact, e.g. red numbers on black are more difficult to read than white numbers on black. This is pure physiology and does not need to be revalidated. Remaining questions should be expressed clearly, before starting any activity. What is the desired behaviour of the system (the response)? Where are the boundaries of the investigated system? What are the parameters we would like to vary? Who is the customer? Data calls for explanation whereas knowledge explains something. That is a big difference. Knowledge drives the generation of meaningful data, which subsequently increases the knowledge (see Gauch, 2003). Develop a qualitative sketch of the investigated system, the parameter-diagram. Quantify the effect of multiple design variables on a system response. Reduce the number of tests. Detect interactions. Describe the system behaviour and provide estimates for new input combinations. Optimize the setting of the design variables with in the given constraints. Communicate the results to non-experts in a standardized way. In essence, these are the goals of the DoE method (Siebertz, 2010). DoE has definitely not been invented for ergonomics, but it addresses a number of key problems that arise during “design for ergonomics”. Especially the analytical methods will be difficult to explain to an audience which is not really interested in the approach, but in the results of the design evaluation.

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Method

Pro's

Con's

Knowledge about the human body

Cheap. Quick. Proven.

Needs to fit exactly to the issue, otherwise only background info.

Existing results from ergonomic studies

Cheap. Quick. Mostly proven.

Expert evaluation

Fits to the issue. Cheap. Reasonably quick and accurate

New ergonomic study

Fits to the issue. Very high acceptance of the results within the vehicle development team.

CAE

Precise and predictive. Early available in the development process. Mostly quick in execution. High acceptance if models are validated.

Vast number of potential sources. Needs to fit exactly to the issue. Studies are not always good documented. Useless if statistical significance is not demonstrated. Limited use if the boundary conditions / population are different. Requires prototypes and knowledgeable experts. Relatively low acceptance outside the department. Significance cannot be proven. Expensive. Slow. Requires prototypes. Only useful with proper setup and data processing / statistics. Model generation and validation can be expensive and slow. Requires CAE experts and software. Misleading if the model is used outside of the validated range.

Figure: Methods with their pro’s and con’s. The cheapest ways to obtain results are pure knowledge and literature reviews. However, in many cases these will not answer the specific questions. Expert evaluations are very useful, but also limited. New ergonomic studies and suitable CAE models are most powerful, but also most expensive. In practice, there is always a trade-off between accuracy, speed and expense.

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Niemi, J., Nieminen, H., Takala, E., Viikari-Juntura, E. (1996). A static shoulder model based on a timedependent criterion for load sharing between synergistic muscles. Journal Biomechanics 29, 451-460). Pauwels, F.: Gesammelte Abhandlungen zur funktionellen Anatomie des Bewegungsapparates. Berlin, Heidelberg, New York: Springer-Verlag, 1965. Salvendy, G.: Handbook of Human Factors and Ergonomics. John Wiley & Sons, New York, 2006. Sainio, P.: Non Visual Information in Vehicle Handling. Licenciate of science in technology thesis, Helsinki University of Technology, 2007. Schmidt, R.F., H.G. Schaible: Neuro- und Sinnesphysiologie. Springer-Verlag, Berlin, 2005. Schmidtke, H.: Handbuch der Ergonomie. Bundesamt f. Wehrtechnik und Beschaffung, Koblenz, 1989. Schünke, M., E. Schulte, U. Schumacher: PROMETHEUS, Lernatlas der Anatomie. Allgemeine Anatomie und Bewegungssystem. Thieme-Verlag, Stuttgart, 2004. Seidl, A. : The Man Model RAMSIS: Analysis, Synthesis and Simulation of 3-dimensional Human Body Postures. Dissertation, Technische Universität München, 1994. Siebertz, K.: Biomechanische Belastungsanalysen unter Berücksichtigung der Leichtbauweise des Bewegungsapparates. Dissertation, RWTH Aachen, 1994. Siebertz, K., J. Rausch, J. Rasmussen, S. Tørholm: Simulation des menschlichen Bewegungsapparates zur Innenraumgestaltung von Fahrzeugen. In: DGLR-Bericht 2007-04 „Simulationsgestützte Systemgestaltung“ , Hamburg, 2007. Siebertz, K., D. van Bebber, T. Hochkirchen: Statistische Versuchsplanung: Design of Experiments (DoE). Berlin, Heidelberg, New York: Springer-Verlag, 2010. Siefert, A. et al. Virtual optimisation of car passenger seats: Simulation of static and dynamic effects on drivers’ seating comfort. Int. Journal of Industrial Ergonomics, Vol. 38 410-424, 2008 Silbernagl, S., A. Despopoulos: Taschenatlas Physiologie. Thieme, Stuttgart, 2012. Winter, D.A.: Biomechanics and Motor Control of Human Movement. John Wiley & Sons, New York, 2005. Zatsiorsky, V.: Kinematics of Human Motion. Human Kinetics, Champaign, IL, 1998.

Acknowledgements The authors would like to thank everyone who contributed to this chapter. In particular: Alexander Siefert, the company Human Solutions, John Rasmussen, Ralf Herrmann, Nanxin Wang, . We would also like to thank our wives Magdalena Malicki-Marek / Birgit Siebertz for their patience with us, while we wrote the chapter after work and on weekends.

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