Optimal "Belt-in-Seat"
A study to evaluate the optimal positioning of a Belt in a car’s frontal seats
Elin Bryggman
Industrial Design Engineering, bachelor's level 2020
Luleå University of Technology
Department of Business Administration, Technology and Social Sciences
Optimal “Belt-in-Seat”
A study to evaluate the optimal positioning of a Belt in a car’s frontal seats
Elin Bryggman Industrial Design Engineering 2020 Supervisors:
Lars Eklöf (LTU) Jan Mazanek (CEVT) Tomas Nilsson (CEVT) Examiner:
Åsa Wikberg Nilsson (LTU)
Bachelor of Science, Thesis in Industrial Design Engineering Optimal Belt-in-Seat:
A study to evaluate the optimal positioning of a Belt in a car’s frontal seats
© Elin Bryggman
Licensed by CEVT between 2020 – 20xx
Cover: Illustration from A2mac.1, edited Elin Bryggman
All photos and illustrations belong to the author unless otherwise is stated.
Published and distributed by:
Luleå University of Technology SE-971 87 Luleå, Sweden
Telephone: + 46 (0) 920 49 00 00 Printed in Luleå, Sweden by
Luleå University of Technology Reproservice Luleå
ACKNOWLEDGEMENTS
During my master Thesis have I been in contact with people who both have contributed to and helped me with various parts of the process, and for these people would I like to give a special thanks.
First off, I would like to especially thank my supervisors at CEVT, Tomas Nilsson, Jan Mazanek and Henrik Öhrvall for their unremarkable support and opportunity to develop a proposition for a future Belt-in-Seat. Despite the fact that we’ve been working from different locations have your fast responses and time offered been a really valuable guidance. I’m all so grateful for the material I was allowed to borrow and use for the tests performed, and I earnestly hope that my assignment will be of use in your upcoming projects.
From Autoliv AB would I like to thank Nicole Schaerer, Daniel Artursson and everyone involved who so generously supplied me with the seatbelt components to use in the project.
Although we haven’t spoken directly do I thank you for providing me the opportunity to actually carry out my project.
As for the user experience test would I like to thank all participants who took the time to help me evaluate the systems, for providing feedback and knowledge on new perspectives regarding the seatbelt. Your participation has been a great assessment that statistic data can’t appraise, and your safe to know that your opinions have been of great value when selecting the most optional components and placements.
And even though it could be somewhat of a cliché, would I like to thank my parents, Maria and Anders Bryggman, who have been supporting me at home during the entirety of the project.
It’s been a really great help to have Anders, who is a part of the restraints team at CEVT, to assist me with knowledge I was lacking. Thanks for the patient, encouragement and help you’ve both been offering.
Last, but not least, do I want to thank my supervisor at LTU, Lars Eklöf, who has provided me with guidance to ensure that the project fulfill the requirements set on the Master Thesis in Industrial Design Engineering. Furthermore do I want to thank all involved parties from LTU that have been giving me feedback throughout my progress to guarantee the best possible results.
ABSTRACT
The world is continuously moving, and so are the life on it. As our society is constantly evolving and the width of human needs are rising, do organization need to provide new solutions that can satisfy our needs. Consequently, every designer is going to meet new challenges whenever the situation calls for it. This is the situation that CEVT’s engineers have found themselves in and the reason as to why this engineering project has become relevant for their industrial development and innovation. The seatbelt designers at CEVT’s Restraints department have encountered a situation where it forces them to change their product as it can no longer be installed in the cars’ B-pillars. The company must investigate alternative positionings with regard to the car's new design criteria in order to recreate or improve the functionalities in both safety and comfort of their seatbelt system.
My project objective is to investigate alternative positionings and components that are part of the classic three-point seatbelt system with an aim to ensure good user experience in the area of comfort. By the end of this thesis I ought to have answered the following Mission Statement:
“Determine the most optimal positioning and components of the seatbelt system to reduce inertia for a fontal Belt-in-Seat, where the system’s performance should be comparable to the users’ experience from an installation of a seatbelt in a B-pillar.”
To establish the best component combination out of the parts delivered from Autoliv AB and secure an optimal placement for the involved parts, have I followed the three-stage process described by IDEO (2015). The Inspiration phase has included a Literature study, benchmarking, analytical assessments of user needs as well as prepared and performed of a test on the seatbelt system. The Ideation phase was focusing on establishing a placement for the system's components through a brainstorming so that it could be mounted in a seat prototype prepared for the user experience tests performed. The last phase, Implementation, consisted of an analysis that was focusing on the feedback received from users of different anthropometry. But also concentrated on summarizing
all data collected throughout the project to select the final concept for this assignment.
My process and methods delivered one concept that focuses on the placement of the seatbelt’s components while a conceptual combination of parts I received from Autoliv AB was selected. Considering all 12 possible combinations, the best concept was a retractor with a 0,20mm thin spring cassette paired with a low-friction webbing B and a ∅32mm Loop made out of plastic. The components are places according to Figure 1.
KEYWORDS: Seatbelt * Retractor performance * Belt- in-Seat/Seat-integrated belt * System force * Industrial design engineering * User experience *
Retractor:
0,20mm spring cassette
Webbing B
Loop with ∅32mm
Figure 1: Loop and off-center placement of the retractor beneath the seats cushion
SAMMANFATTNING
Världen och allt liv på jorden är i ständig rörelse. När samhället strävar efter utveckling uppkommer samtidigt nya behov hos människan och dess omgivning, vilket gör att olika organisationer och företag behöver leverera nya lösningar och designa artefakter för att tillfredsställa människans behov. Varje designer kommer att möta nya utmaningar när en situation tvingar dem att ändra sina produkter. Detta är en situation som CEVT:s bilbältesdesigners står inför och anledningen till att detta arbete blivit aktivt för företagets industriella utveckling inom innovation. Situationen som tvingar konstruktörerna att ändra bältessystemets design är att systemet inte längre kan monteras i passagerarbilens B-stolpar.
Därför måste företaget undersöka alternativa positioneringar som överensstämmer med bilens designkriterier för att återskapa bältets funktionalitet som berör både säkerhet och komfort av deras bältessystem.
Arbetets syfte är att undersöka alternativa positioneringar och de inkluderade komponenterna som utgör ett klassiskt tre-punkts bälte med målet att säkerställa en god användarupplevels inom området komfort. I slutet av projektet skall jag ha uppfyllt följande Mission Statement:
“Bestäm den mest optimala positioneringen och komponenter av ett säkerhetsbältes system för att reducera krafterna från ett bältes-integrerat framsäte, en ’Belt-in- Seat’, där systemets prestandard skall vara jämförbart med användarens upplevelse av en installation av bältet i bilens B-stolpe.”
Jag har följt IDEOs (2015) tre-stegs process för att säkerställa den bästa kombinationen av komponenter som har tillhandahållits av Autoliv AB samt fastställa en optimal placering av varje komponent i systemet. Inspirationsfasen har inkluderat en litteraturstudie, benchmarking, analytiska bedömningar av användarens behov samt förberett och genomfört ett test på bältesystemets prestandard. Ideationsfasen fokuserade på att etablera en placering för systemets komponenter genom en brainstorming så att dessa kunde monteras i en sätesprototyp som förberetts inför testerna för att evaluera användarens komfortupplevelse.
Den sista fasen, Implementation, bestod av en analys som fokuserade på feedbacken från testpersonerna som erhöll olika antropometri. Fasen kretsade kring att sammanfatta all data som samlats in genom hela projektet för att välja det slutliga konceptet för uppgiften.
Min process och metoder levererade ett koncept som fokuserar på placeringen av bältets komponenter och en konceptuell kombination valdes av komponenterna jag fick levererat från Autoliv AB. Med tanke på de 12 möjliga kombinationer bestod det bästa konceptet av en 0,20mm tunn fjäderkassett som kompletteras med ett lågfriktionsband jag kallade B och en
∅32mm omlänkare.
CONTENT
1 INTRODUCTION 1
1.1BACKGROUND 1
1.2STAKEHOLDERS 2
1.3PROJECTOBJECTIVES 2 1.3.1MISSION STATEMENT: 2
1.4DELIMITATIONS 2
1.5THESISOUTLINE 3
2 CONTEXT 5
2.1ORIGIN 5
2.2WHOISCEVT? 7
2.3SEATBELTUSAGE 7
3 LITERATURE REVIEW 8
3.1INDUSTRIALDESIGN
ENGINEERING 8
3.1.1USEREXPERIENCEDESIGN 9
3.2ERGONOMICS 10
3.2.1ANTHROPOMETRY 11
3.2.2COMFORT 13
3.3PRACTICALFRAMEWORK 14
3.3.1FUNCTIONALITIES 14
3.3.2MATERIAL 15
3.3.3FORCESANDFRICTION 15 3.3.4STANDARD,LEGAL-ANDPART
REQUIREMENTS 15
4 METHOD 16
4.1PROCESS 16
4.1.1PROJECTPLANNING 17
4.2INSPIRATION 17
4.2.1LITERATURESTUDY 17
4.2.2BENCHMARKING 18
4.2.3USERNEEDS 20
4.2.4EXPERIMENTPREPARATION 20
4.2.5ANALYSIS 22
4.3IDEATION 23
4.3.1BRAINSTORMING 23
4.3.2USEREXPERIENCETESTING 24 4.4IMPLEMENTATION 26
4.4.1TESTANALYSIS 26
4.4.2CONCEPTSELECTION 27
4.5METHODDISCUSSION 27
4.5.1INSPIRATION 28
4.5.2IDEATION 28
4.5.3IMPLEMENTATION 29
5 RESULTS 30
5.1RESULTSOFCONTEXT
IMMERSION 30
5.1.1BENCHMARKING 30
5.1.2USERNEEDS 31
5.1.3SYSTEMEXPERIMENT 31
5.1.4ANALYSOFSYSTEMTESTS 32 5.2RESULTSOFIDEATION 33
5.2.1BRAINSTORMING 33
5.2.2USEREXPERIENCETESTING 33 5.3RESULTSOFIMPLEMENTATION 35
5.3.1TESTANALYSIS 35
5.4FINALSELECTION 35
6 DISCUSSION 37
6.1CONCEPTASSESSMENT 37 6.2PROJECTRELEVANCE 38 6.2.1ECONOMICSUSTAINABILITY 39 6.2.2ECOLOGICALSUSTAINABILITY 39 6.2.3SOCIALSUSTAINABILITY 39
6.3REFLECTION 39
6.4RECOMMENDATIONSFOR
CONTINUATION 40
7 CONCLUSIONS 42
7.1RESEARCHQUESTION1 42 7.2RESEARCHQUESTION2 42 7.3RESEARCHQUESTION3 43 7.4PROJECTOBJECTIVESAND
CONCLUSION 44
8 REFERENCES 45
9. APPENDIXES 48
APPENDIX A 48
ACCEPTABLE FORCES REQ. RETRACTING REQ.
APPENDIX B1BENCHMARKING
APPENDIX B2BENCHMARKING CAR TESTS
APPENDIX CAUTOLIV DATA
CA.RETRACTOR WITH 0,20MM SPRING CASSETTE
CB.RETRACTOR WITH 0,23MM SPRING
CASSETTE
CC.RETRACTOR WITH 0,24MM SPRING CASSETTE
APPENDIX D1EXPERIMENT PLAN
HOW TO MEASURE
APPENDIX D2SYSTEM EXPER.DATA
D2A.RETRACTOR 1 D2B.RETRACTOR 2 D2C.RETRACTOR 3
APPENDIX EUSER TEST PLAN
APPENDIX F1ASQ QUESTIONS
APPENDIX F2ASQANSWERS
LIST OF TABLES
Table 1: Data measurement for all 15 tests on each combination, extraction and retraction for the three distances
Table 2: Chosen concept's components for the user experience testing
Table 3: Comparison of the extraction force between a BIS and B-pillar installations
Table 4: Identified user needs for a BIS Table 5: The concepts that delivered the best and worst forces (average)
Table 6: Difference in forces between the best and worst concepts presented in Table 5 above
Table 7: Comparison of the forces (N) generated from the 0,20mm spring cassette’s retractor and the complete system
Table 8: Comparison of the extraction force between my concept and the existing BIS and B-pillar installations, (the
concept is displayed between 1600mm to 600mm since it’s not certain what the distances where in the cars)
Table 9: Data chart for each combination in room temperature
LIST OF APPENDIXES
Appendix A: Seatbelt system requirements Appendix B1: Benchmarking from A2mac1 Appendix B2: Benchmarking of various cars
Appendix C: Retractor performance data from Autoliv AB in Vårgårda Appendix D1: System experiment planning
Appendix D2: Result from system experiment Appendix E: User experiment planning
Appendix F: After-Scenario Questionnaire questions Appendix G: After-Scenario Questionnaire answers
LIST OF FIGURES
Figure 1: Loop and off-center placement of the retractor beneath the seats cushion
Figure 2: Placement of the three-point belt in a car’s B-pillar (image from A2mac1.com) Figure 3: Difference between the simplified arrangement (right) and the current proposition of an adjustable seat (left)
Figure 4: Components included in the retractor assembly, and the new Loops with different diameters
Figure 5: How the belt falls onto individuals of different height
Figure 6: Included theories to apply in this project
Figure 7: Product development as a combination of Industrial design and Engineering design
Figure 8: A common, iterative process Figure 9: Visualization of a few percentiles’
measurements (Inspired by related images on Google)
Figure 10: The frequency distribution of individual stature. (Inspired by Pheasant &
Haslegrave, 2005)
Figure 11a: Person with tall torso Figure 11b: Person with short torso Figure 12: Project overview
Figure 13: Planning and deadlines for the Inspiration phase
Figure 14: A Belt-in-Seat from a BMW 4- Series 428i Convertible
Figure 15: Extraction force measured on a BMW 420d Cabrio with a dynamometer Figure 16: Set-up for the experiment’s execution
Figure 17: Components and Dynamometer used in the system experiment
Figure 18: Planning and deadlines for the Ideation phase, where the benchmarking is presented in the Inspiration phase
Figure 19: A possible positioning of retractor and Loop in relation to the fixed D-loop (top- view)
Figure 20: Test by a male with a height of 177cm
Figure 21: Planning and deadlines for the Implementation phase
Figure 22: BIS from a BMW 4-Series 428i Convertible, also used in the Cabrio
Figure 23: Evaluating seatbelt installment of a B-pillar
Figure 24: System testing set-up Figure 25: The markings for the three distances determined by CEVT
Figure 26: Loop and off-center placement of the retractor beneath the seats cushion Figure 27: Fastening of the 32mm Loop Figure 28: The users noted experiences of the belts’ fitness on their body
Figure 29: The summarized grade given to both concepts
Figure 31: Components in the final concept selection (also an external webbing 1) Figure 30: Loop and off-center placement of the
Figure 32a: Benchmarked placement of D-loop outlet
Figure 32b: Seat prototype placement of D- loop outlet
Figure 33: Adding Loops to guide the webbing to avoid unnecessary contact
Figure 34: Measuring the force of the driver seatbelt in the BMW 420d Cabrio
Figure 35: The markings for the three distances determined by CEVT
Figure 36: The webbing has been marked with a chalk
Figure 37: The value should be read when the marking is by the frame of the retractor Figure 38: The distance between the dynamometer’s attach point ant the D-loop when a marking (300, 600 or 1600mm) is by the retractor's frame.
1 Introduction
Design is a wide-ranging subject that covers almost everything. However, many years ago was the focus on functionality while an appealing design was of less importance. Today, the market offers many design alternatives for one artifact that fills the same general function, the purpose is more about being appealing to the individual’s experiences of design (Desmet, 2002). An example of artifacts that have the same overall purpose but is designed to have numerous variations is passenger cars. A physical part of the car or its’ systems stimulates various feelings and experiences in different individuals. For example, this can be compared to the definition of "perfection", where Pacht (1984) explains that each person has its unique interpretation and are experiencing things in different ways.
Several cars have noticeable differences that make them unique in comparison to other manufacturer’s car models, or even to other cars within the same branches. One component whose appearance isn’t obvious but is of high value as the primary restraint system – and which is the focus of my Bachelor Exam in Industrial Design Engineering – is the seatbelt. The project is concentrated on the frontal seat row and will emphasize the forces generated from a seat- mounted safety belt system. This thesis will be carried out in collaboration with the company China Euro Vehicle Technology AB (CEVT) in Gothenburg during the second part of the spring semester (covers 15 Swedish university credits) at Luleå University of Technology 2020.
1.1 BACKGROUND
Mounting the belts retractor in the B-pillar – between the front and back door shown in Figure 2 – is the most common placement for the frontal seatbelts in passenger vehicles. Consequently, when a design situation rises, where there’s no longer possible to place the belt systems in the car's B-pillars, it forces designers from different departments (manufacturing, chassis, seats, seatbelt, etc.) to change their products.
This is the situation that CEVT have found themselves in and the reason as to why this project has become relevant for their industrial development. With regard to a car's new design criteria must the company investigate alternative positionings that can recreate or improve the functionalities in both safety and comfort of the seatbelt. The main problem that CEVT’s Restraints department discovered when the seatbelt was mounted in a frontal seat was that the friction added to the system caused the extracting forces to
increase and the retracting force to decrease. Besides Figure 2: Placement of the three-point belt in
1.2 STAKEHOLDERS
The main stakeholders are divided as to the specific phases of a car’s life cycle. The individual is the main stakeholder by the time the car reaches the market and is whom the complete product is intended for. However, the minor stakeholders for my project are whom this study is aimed for, which is a direct concerned for the seatbelt designers. An established location of the seatbelt’s retractor has yet been determined and the result will therefore be of great importance to the designers working to connect the involved components, such as the actual seat and chassis for future installation.
Even though the seatbelt developers at CEVT are the study’s stakeholders, is it the end customer that is the aimed audience for the project. The seatbelt is the main restraint system that a car has to offer, and the one restraint that comes in direct contact with the occupant during a drive. It’s therefore important that the final product is designed with the end customers’ best interest and needs in mind to ensure that the final product is adapted to the intended stakeholder.
1.3 PROJECT OBJECTIVES
The purpose of my project is to investigate alternative positionings and components that are part of the classic three-point seatbelt system with an aim to ensure good user experience in the area of comfort. By the end of this thesis I ought to have answered the following issues:
1. How can alternative components reduce friction and thus the extraction/retraction force to ensure a comfortable user experience?
2. How low resistance force can be achieved in the system and what may the results depend on?
3. What is the most optimal installation with regard to user experience and the forces created when extracting/retracting the seatbelt?
1.3.1 Mission statement:
My goal from CEVT’s point of view is to: “Determine the most optimal positioning and components of the seatbelt system to reduce inertia for a fontal Belt-in-Seat, where the system’s performance should be comparable to the users’ experience from an installation of a seatbelt in a B-pillar.”
1.4 DELIMITATIONS
With regard to the large extent of the project was the decision made to delimited activities to fit the period set for the assignment. Due to CEVT’s role as the design engineers in a car’s development wouldn’t I necessarily need to achieve a new product, but visualize my results through sketches or models. The design process will exclude iterative activities and therefore only deliver a concept in its first stage, since the company wants to further investigate whether the mounting is possible with the seat’s design. Another reason is that the study will use a simplified arrangement of the required components necessary in the system to ensure an adjustable seat. The backrest will remain static and can therefore exclude additional components needed when angling the seat, see Figure 3 below.
In short, the test set-up does partly ignore CEVT’s designers’ current proposal of the seatbelt installation where the durability aspect, number of Loops, and various angles of the retractor and D-loops are included. It was recommended since the experiment examines alternative positioning with different unit combinations. Here, the aspect of comfort (when using the belt) is the main focus rather than the safety aspect, since the positioning has to be determined before safety tests can be initiated. CEVT is responsible for designing this would-be placement as well but works with external suppliers to construct what they design, one of these suppliers is Autoliv AB in Vårgårda, Sweden. This supplier selected and provided the specific components (seatbelt retractors, webbings and D-loops) that are to be used in this study and I will therefore not assess the components’ particular properties through literature research.
1.5 THESIS OUTLINE
If there is any interest in the included activities in each chapter of the report, then you’re free to read the following paragraphs that mention the purpose of every chapter.
Chapter 1 initiates the report by introducing the project and explaining stakeholders, project objectives and delimitations made for the process.
Chapter 2 is a pre-study of the three-point belt that is used in passenger vehicles, the seatbelt’s impact on the user and a short introduction to CEVT, who I’ve been collaborating with in this thesis.
Chapter 3 covers the resulted data gathered from the literature study and includes
Figure 3: Difference between the simplified arrangement (right) and the current proposition of an adjustable seat (left)
chapter is divided into three phases described in IDEO (2015), overall does it include a data collecting procedure, practical experiments, idea integration and analytical activities.
Chapter 5 presents the results given by the methods used in the design process. This chapter excludes the literature study and benchmarking since these results are presented in chapter 2 Context.
Chapter 6 covers a discussion from the results’ relevance and reflections on the process used for this specific assignment. The chapter does also include recommended action on the continuation of the project, and therefore will include a discussion of the delimitations made.
Chapter 7 is the concluding chapter where the project objectives are reflected upon, if it has been fulfilled though the design process used for this assignment. It shall also argue from different perspectives as to why the stated issue have been solved based on the process and relative theory used in the project.
Chapter 8 hold every external reference used in this thesis. They are listed under the same headline in alphabetical order and according to the reference management system APA.
The Appendix chapters holds any additional pictures, documents and results. An Appendix can be used more than once but every Appendix isn’t referenced to in the text.
2 Context
This chapter highlights the importance of seatbelt usage, what the system consists of and why the forces play a significant role in the aspects of comfort. For starters, all vehicles should be equipped with seatbelts, different vehicles use various types that the occupant must use for safety purposes. The type that are mostly recognized in passenger cars is according to Huang, Zhou & Chen (2018) the three-point seatbelt, and will be the one referred to in this project.
2.1 ORIGIN
The first modern three-point seatbelt for the frontal seat was developed for Volvo Cars by the Swedish inventor Nils Bohlin in 1958 and was proclaimed a car standard equipment in 1959 by Volvo (Volvo, 2009). What made this seatbelt such an accomplishment was that Bohlin designed it upon realizing that both the lower and upper body had to be secured in the events of an accident. His goal and biggest challenge were to create a safety solution that was effective and simple to use so that the user should be able to put it on with one hand. Bohlin took patent on his solution, but Volvo immediately made it available for free to other car manufacturers in interest of sharing the new safety equipment (History, 2019. Volvo Cars, 2009. The New York Times, 2002.). The belt’s importance to human lives is well summarized in the following citation from Volvocars.com:
“Since the 1960s, Bohlin's belt has saved many hundreds of thousands of lives and prevented or reduced the severity of injuries among many millions. This makes the three-point safety belt the single most important safety device in the car's 120-year history. And that's not just Volvo's claim.”
– (Volvocars.com, 2009) Nils Bohlin’s solution describes how the positioning of the webbing should be placed over the upper and lower body, and also the D-loop, buckle and ANCH plate. But it was not made clear where the retractor was placed when the new system was introduced in 1958. Huang, Zhou and Chen (2018) explains that the seatbelt safety system consists of three parts: the retractor assembly, the buckle assembly and the shoulder adjuster assembly. Figure 4 below shows the parts included in the retraction assembly where their respective name is also presented as they will be called in this report.
The structure of the retractor assembly includes the webbing that is wrapped around the retractors spindle, and then the webbing is threaded through the D-loop and tongue, and lastly anchored to a fixed point connected to the ANCH plate. What many people might know and what Huang et al. (2018) also mentions is that the retractors usual placement for the front seats is in the cars’ B-pillars. Some manufacturers that doesn’t construct B-pillars in their cars has come up with a solution that attaches the seatbelt system to the car’s chassis (e.g. in the door or along the upper side of the door on a coupe) or in the seat itself according to Tame
Figure 4: Components included in the retractor assembly, and the new Loops with different diameters
By the current proposition of the retractor’s placement under the seat, the engineers at CEVT have discovered that the resulted forces in the system will increase. The issue is due to the number of contact areas that are to be included in the new system placement (Olsson, Åström, De Wit, Gäfvert, & Lischinsky, 1998). There’s only the D-loop on the B-pillar that supplies a friction force but in a BIS, there’s at least one more. To decrease the extraction force but ensure a high retraction force do I need to evaluate the system with the purpose of finding a concept that stabilizes forces comparable to a B-pillar installation. Not only to make the occupant comfortable when using the belt but also secured in events of misfortune.
Retractor and Webbing Loop (s) Tongue D-loop
ANCH-Plate
2.2 WHO IS CEVT?
China Euro Vehicle Technology (CEVT) is an innovative engineering center that works with technology and invention of future cars (Cevt.se, n.d.). They have one office with approximately 2000 employees and is located at Lindholmen in the Swedish city of Gothenburg. The company are collaborating with external suppliers to manufacture the designs that they have created.
What's important to note is that CEVT’s only developing the design of the component and are therefore relying on other suppliers to manufacture and test the specific component. One of their many suppliers is Autoliv AB, whom has facilities in 27 countries and is working with the component’s physical development and testing (Autoliv, n.d.). Among other things are CEVT the creators of the CMA (Compact Modular Architecture) platform, which is used in the Volvo XC40, but also for the new car brand Lynk&Co developed together with the Chinese organization GEELY (Wikipedia.org, 2020).
2.3 SEATBELT USAGE
When considering the relation between the occupant and the seatbelt, I believe people would often point out that the restraints system should offer safety and reduce the impact in case of a collision. The seatbelt system is mounted and usable for the same number of occupants as the total of seats in the vehicle, whether the car has two or seven seats. Whenever someone is traveling in a vehicle (car, bus, or airplane), it’s necessary to use the seatbelt to secure their position in their seat to protect themselves but also the other occupants. The somewhat obvious reason is that the velocity and momentum of the body is not reduced when the car suddenly loses speed drastically or are stopped entirely due to a collision.
In the aspect of comfort does Pheasant (2014) claim that the experience differs between occupants can be a result of a person’s anthropometry, see Figure 5. Another attribute that affects the user’s experience is gender since the male and female body structure is biologically different (Furnham & Radley, 1989). Gender and percentiles will be a major part of the experimental testing of the occupant’s experience of the seatbelts comfort, this is described in chapter 4.3.2 User experience testing. The aim of testing with users of various percentiles is to determine how the user’s experience may differ and investigate if the user’s needs are satisfied.
3 Literature review
The literature review is the resulted data collected from the literature study performed in the Inspiration phase. It includes various theories that are related to the project process and the final result but also highlights how and why each theory is relevant, see Figure 6. This chapter also covers the description of Industrial design engineering, UX-design and Ergonomics such as anthropometry, comfort and safety.
Figure 6: Included theories to apply in this project
3.1 INDUSTRIAL DESIGN ENGINEERING
Products, systems and services that people come across in everyday life are characterized by at least one design. Adam Judge (n.d.) did once say that “...There is no such thing as no design”, by evaluation do I recognize that design has been around since the first artifact was created several million years ago. Though Arvola (2017) explains that the concept of design doesn’t have a specific definition due to its multitude of facilities and extent, it implies different things depending on the context. According to Österlin (2003) is the term widely used, including industrial design, architecture, system design, construction and mechanical design to name a few. Each component in a car can be embodied by different types of design, where some parts need various mechanics to adjust (like an airbag) while some can only remain static (like the chassis) during its entire life cycle.
Krippendorff (1989, p.9) has made the definition that the science of design is about “making sense of things”. His definition is not so far fledged since the foundation of the word design comes from the Latin designare that can be translated to composition or give meaning (dictionary.com, 2020). The desire to make the design more scientific goes, according to Cross (2001), back to the early 1900s. At this time, they realized that a scientific evaluation of what design was is needed in order to know how it could be used in the development of products.
The development of products, also known as product design, is described by Roozenburg &
Eekels (1995) as engineering design and therefore includes the process of designing and integrating elements required for a product's functionality. However, product design can also be referred to as industrial design and is described by Österlin (2003) as the final design of the product and how it should be adapted to the user.
Ulrich & Eppinger (2012) claim that product design is a combination of engineering- and industrial design and is part of a product development process where many participants (employees, suppliers, manufacturers, etc.) are involved. In short, it’s the collaboration between the two areas that govern the process of Industrial Design Engineering, see Figure 7. Hubka and Eder (2012) explain that despite the process of making a product, its main purpose should always emphasize the satisfaction of human needs.
3.1.1 USER EXPERIENCE DESIGN
The term user experience, also called UX-design, was introduced by Don Norman where he portrays it to be a collective of theory covering all of the aspects of what a user experiences when interacting with a product, system or service (Norman, 2013). User experience is a branch within the concept of human-centered design which is about securing a design process where human needs remain in focus (IDEO, 2015). A developing process that focuses on human-centered design can be different depending on the assignment and what the designers aim for in the final stage of the work. What most processes have in common is that they are iterative as shown in Figure 8, starting with researching information about the topic, generating ideas, creating and testing prototypes and so repeating the process after feedback from users (IDEO, 2015).
Figure 8: A common, iterative process
Arvola (2017) points out that user experience is the part about how the artifact acts when the user interacts with it and not the internal work of the artifact itself. Like Arvola (2017) does Rogers, Sharp and Preece (2011) argue that the main purpose behind the concept of user
Figure 7: Product development as a combination of Industrial design and Engineering design
The definition of usability explains how simple an artifact is to use. Rogers et al. (2011) and Jordan (1998) explain that usability is not determined by the properties of the product alone but is also by the user, the surrounding environment and the task which is to be performed. In this user scenario (Interaction Design Foundation, n.d.), the environment is a passenger car.
The task that the user should perform is to put the seatbelt on, so they may reach and grab for the tongue, pull the webbing across their body to lock the tongue in the buckle and then tighten the webbing into a correct placement. How simple this task is to perform in this environment is determined by the user. Past experiences may play a huge part on the users’ perceptions of whenever a seatbelt is to be used, are in use or have been used, especially in the context of mounting the seatbelt system into the seat instead of the B-pillar.
3.1.1.1 USABILITY
Usability is a quality attribute that defines how easily a human can interact with and use a product, a system or an interface. Jakob Nielsen (2003) has stated that usability can be defined by the 5 following quality components:
• Learnability: How easy can a user, who for the first time interacts with a design, perform a basic task?
• Efficiency: When the user is used to a design, how quickly can they perform the same task again?
• Memorability: If the user has been away, how easy can they remember and restore the achieved knowledge?
• Errors: How many errors does the user make during the interaction, how serious are the consequences and how easily can the error be corrected?
• Satisfaction: How satisfied is the user after interacting with a design?
Some of Nielsen’s (2003) quality components that are more relevant to an occupant’s interaction with a seat-integrated belt are learnability, errors and satisfaction, where satisfaction is the most valuable in the case of comfort. Satisfaction has a close connection to user experience and plays a part in the error quality, together with the aspect of safety since an error can lead to an unsafe placement of the belt. Jakobsson & Bohman (2019) claim that one error in the belt usage is its placement over the shoulder which may interfere with the safety before, during and after a collision (more of this is explained in 3.2 Ergonomics). Satisfaction can be described as qualitative data that are obtainable from users and will in this project be retrieved by testing with the actual intended stakeholders in a prototype that represents a Belt- in-Seat.
3.2 ERGONOMICS
Wikberg Nilsson, Ericsson & Törlind (2015) deem that ergonomics is about the principle of modifying an interaction between a user and an artifact to human needs and conditions instead of having the human adapt to the product, system or service. Based on the composition of the Greek words’ ergon [work] + nomos [knowledge, science] can ergonomics be defined as a belief of how humans act in relation to mental and physical work (Wikberg Nilsson et al., 2015.
Burandt & Grandjean, 1963). Pheasant & Haslegrave (2005) define ergonomics as the science of “work”: involving who it concerns, how it’s done, what equipment/tools are used, the surrounding environment and the psychosocial aspects of the situation. In the aspect of design, the ergonomics approach may be summarized in the principle of user-centred design:
“If an object, a system or an environment is intended for human use, then its design should be based upon the physical and mental characteristics of its human users…”
-- Pheasant & Haslegrave (2005, page 5) The objective is to accomplish a design that has the best match between an artifact and its user, in other words, ergonomics is about fitting the product, system or environment to the affected user (Pheasant & Haslegrave, 2005). A few criteria’s that the authors suggest in order to make a successful match in a design is by considering usability, ergonomic comfort, human health and the surrounding environment. Other aspects related to the use of ergonomic devices was made public by Volvo Cars in 2010 with the purpose to share their 40 years of research on the safety department. The documentations hold a collection of crash data and are made accessible worldwide to better understand what happens during a collision, this global campaign is called The E.V.A. Initiative (Equal Vehicles for All).
The E.V.A. Initiative holds various topics and studies related to the safety systems offered in passenger cars and other vehicles. In one of the studies did Jakobsson & Bohman (2019) evaluate the safety belts positioning over the shoulder with 394 participants. The results showed that 4 in 10 participants wore the seatbelt incorrectly and that an adjustment of only a few centimeters could make a difference between a minor and severe injury in a car crash.
Between the men and women in the study did more women place the belt in the position off the shoulder or on the neck, which is claimed by Jakobsson & Bohman (2019) to be less effective in a collision. They direct the attention to the seatbelt’s geometry and its corresponding placement in relation to the participants body size and shape, and claim that their anthropometry may be an aspect that influences the incorrect use.
3.2.1 ANTHROPOMETRY
Anthropometry is an important section of physical ergonomics that include science that deals with the human’s body measurements: such as size, shape and flexibility. This science is an essential subject in the car development industry since the manufacturers aim is for their cars to be adaptable to as many different occupants as possible. This has become an important requirement as the relation between the construction and the user’s body measurement affect the overall experience and safety of the occupant (Pheasant, 2014). It is described in this context that all humans are variable and possesses unique percentiles (see Figure 9 below), which is an aspect of the human body that is necessary for designers to understand in order to achieve a human-centred design (Wikberg Nilsson et al., 2015. Hägg et al., 2015. and Pheasant
& Haslegrave, 2005).
There are two categories when speaking about anthropometry, which is static and dynamic.
Static is the part that focuses on the features and the composition of the body while the dynamic anthropometry refers to measurements of the body’s flexibility and strength (Bohgard et al. 2015). Both categories are important while driving a car since the occupant should be able to move around and adjust their posture to be more comfortable but the bodies are mainly static while driving. Measuring static anthropometry may prove to be easier in regard to the occupants’ body size and other percentiles.
Anthropometry will be used when it’s time to evaluate the chosen component combinations with the user to comprehend how they are experiencing a BIS system, see Figure 9. Because the body’s measurements are of a high importance when designing various parts of the car will it be an essential part to include in order to ensure a human-centred design.
3.2.1.1 PERCENTILES
To create an artefact that is adaptable to every individual’s unique measurements might prove to be impossible. Pheasant & Haslegrave (2005) explains that designers design the product to fit the majority of a country’s population and can be described by the symmetrical chart presented in Figure 10 below. The highest point represents the average person’s height (in a specific population) and since the chart is symmetrical, it transpires that 50% of the population are taller than average and 50% is shorter. This does however not only apply to height, where Wikberg Nilsson et al. (2015) writes that different variables are of interest depending on the targeted stakeholders, a specific situation or task that is to be performed.
Figure 9: Visualization of a few percentiles’ measurements (Inspired by related images on Google)
Figure 10: The frequency distribution of individual stature. (Inspired by Pheasant & Haslegrave, 2005)
It’s common to design products to be adaptable from the 5th percentile (5%ile) to the 95th percentiles (95%ile), which covers 90% of a selected population (Wikberg Nilsson et al., 2015.
and Pheasant & Haslegrave, 2005). The 5%ile includes individuals who are shorter than 95%
of the population while the 95%ile are taller than 95% of the population. This is no exception for the car industry who, nowadays, often uses the 5%ile stature women and the 95%ile stature men when designing and testing the car seats dimensions (Kolich, 2002). For records, the height anthropometry is according to Dreyfuss (2012) and Pheasant & Haslegrave (2005) 154cm (5%ile stature women) and 185cm (95%ile stature men) but may differ depending on the average height of the country’s population. The Crash Test Dummies uses for safety testing are based more on the specific percentiles used in the 5:e, 50:e and 95%ile tests and are specified by the designers at Humanetics (2015).
A comfortable driving position is determined by the occupant’s specific percentiles, but Kyung
& Nussbaum (2009) argues that two individuals with the same exact height experiences different comfort if, per example, their width percentile differs. Kyung & Nussbaum (2009) does like Pheasant & Haslegrave (2005) clarify that a person, whose various body measurements can be placed according to the same percentile, does not exist. They point out that percentiles only apply to a selected measure (torso, hands, thighs, etc.) and that’s why it’s always recommended to evaluate the artifact with the actual stakeholders since excluded individuals may experience the product in different ways from what was intended.
3.2.2 COMFORT
The meaning behind the concept of comfort lack a clear definition but are often used in the context of marketing, especially in the car development industry. Hägg, Ericson & Odenrick (2015) imply that the complexity of comfort involves various factors; perceived relaxation and general well-being are two of them. Further do they mention that the concept is mainly based on a person’s subjective experiences and can also vary depending on physical condition.
Percentiles plays a role in comfort as well.
For instance, if the D-loop outlet is designed to best suite an occupant with a tall torso height then the belt might not have the same fit for a user with a shorter torso, see Figure 11a and 11b. Although, it’s important to consider comfort and safety as two different attributes since a comfortable placement of the seatbelt might not provide safety for the occupant.
To achieve high safety that fully compromise with the aspect of comfort for a user might prove to be difficult. From the safety aspect explained by Jakobsson &
Bohman (2019) should the belt be placed on mid-shoulder or closer to the neck, but having the webbing abrasive on the neck can be perceived to be far from comfortable.
3.3 PRACTICAL FRAMEWORK
This subchapter includes some practical theory regarding the seatbelt system that I’ll refer to in the upcoming chapters. They briefly explain the components functionalities and areas of interest when dealing with this system.
How a belt is used is known to those who use the product, however few people understand how the product itself operates and what factors it requires from its environment to achieve proper functionality. It is described by Hayashi & Matsui (1976) that a seatbelt’s purpose is to act whenever needed to ensure the occupant’s safety when something abrupt happens to the vehicle. Presented below are a couple of headlines that clarifies a few features that the seatbelt system offers.
3.3.1 FUNCTIONALITIES
According to Autoliv (2019) does a retractors sensor activate a mechanism that lock or release the webbing, either when the passengers try to extract the belt too abruptly or in events of an accident. Once a collision occurs does a pair of locking wheels with teeth tighten over the webbing, making it extremely difficult to extract it further and thus the seatbelt catches its occupant and secure their positioning in the seat (Hayashi & Matsui, 1976). To not cause any complications while experimenting on the system, did I request that this sensor was removed since the retractor must be in a specific angle for the belt to be extractable without the mechanism locking.
The retractors possesses something called a spring cassette. A spring cassette is what determines the inertia of the product (personal communication, 7 April 2020). The thicker the spring cassette is, the higher the force for both extraction and retraction. And so when the spring cassette is thinner does the opposite occurs, the belt is easier to extract but the retraction
Figure 11a: Person with tall torso
Figure 11b: Person with short torso
force decreases. When the webbing extracts does the spring cassette become more tense, which results in that the belt is slightly harder to extract, the force increases the more webbing that is extracted.
3.3.2 MATERIAL
The form of the D-loop as well as its possible materials generates quite different friction forces (Huang, et al., 2018). Since the friction coefficient diverges between different metals and plastics (most common materials for the D-loop), it is of high interest to analyze how respective material influences the friction in the seatbelt system. This is also accurate for the Loops that will be used. However, only one D-loop in metal and two Loops of the same plastic materials will be tested according to the experiment that will be performed in this project.
The webbing can be divided by various weaving methods, whereas the weaving can have different kitting methods as well (Huang, et al., 2018). It’s therefore important to mention that unique knitting methods have dissimilar contact areas and therefore presents different friction forces. In the upcoming experiment, two low-friction webbings will be used for each retractor.
3.3.3 FORCES AND FRICTION
Even though the selection of material that is based on the friction force is of high value, it’s also important to consider the weight, cost and quality of each component (CEVT personal communication, 17 April 2020). Now that at least one Loop is to be included in the design of the seatbelt system then the friction is going to increase with yet another contact area, (Olsson et al., 1998). The friction phenomena are highly nonlinear and it’s thus important for designers to early consider and so be able to deal with friction in unwanted areas. In this case, to prevent kinetic friction that arise as the webbing moves along or glides on a surface (the D-loop and Loop). With concern for system design does Olsson et al. (1998) explain that the lack of friction may improve quality, economy and safety of a system, attributes that CEVT is aiming for personal communication, 7 April 2020).
Friction occurs in areas where two surfaces meet and are the resulted force, either kinetic or static, that depends on multiple mechanisms. Huang et al. (2018) does as well as Olsson et al.
(1998) mention physical traits that are valid for friction to arise: i.e. material, geometry and relative velocity, are a few considerable features.
3.3.4 STANDARD, LEGAL- AND PART REQUIREMENTS
As for all products does the seatbelt needs to follow various requirements set on different levels. They follow standards on nuts, markings, length of the webbing etc. and also must fulfill the legal requirements for the component to be approved. Part requirements is the demands that the company puts on their product, these are of less importance than the legal but should still be fulfilled for the company’s standard.
There are a few requirements that I had to apply in my project to ensure that the selected
4 Method
My project followed a process that focuses on a human-centred design but have been modified to better fit the assignment. I have used IDEOs (2015) three stage process to gather information on the topic, test existing systems (performance and with user), generate ideas for potential placements and to test a few combinations of components. This chapter shows the process and what methods has been used to deliver the final result.
4.1 PROCESS
This process focuses on human-centred design and is describe by IDEO (2015) as an iterative process that can be applied differently depending on what’s to be developed. My project was divided in the three phases Inspiration, Ideation and Implementation as shown in Figure 12. But my main focus is to evaluate the positioning of the seatbelt system which makes the Inspiration phase a more extensive part of the process.
The first phase consisted of information-gathering methods. A literature study, benchmarking, test preparations and Pugh’s Matrix was applied to collect theoretical data and an experiment was preformed to gather the practical data. The results were analyzed with the purpose to identify how the BIS impacts the users need, what performance is already achieved by other manufacturers and what component combinations gave the most pleasant values.
The second phase, Ideation, consisted of an idea integration which I choose to use a brainstorming for. The result from this method was used in the user experience testing performed with both male and female participants of different anthropometry. The participants used the method Think Aloud during the test and answered an ASQ thereafter. The data collected was analyzed in the third and last phase.
The last phase was Implementation where the final concepts of placement and component combinations was selected based on the users’ experiences. This phase was mostly used to conclude the project by completing the report and prepare the final presentations to be held for LTU and the Seat and Restraints department at CEVT.
Figure 12: Project overview
4.1.1 PROJECT PLANNING
The second thing I did after the introduction with CEVT to discuss the project, was to construct a project plan that included a temporary description of each design phase as well as a time schedule. Its purpose was to organize the project to get an overview structure of each and every part that was to be carried out. The schedule type I chose to demonstrate my path and deadlines in was a timeline that is divided in three to visualize each phase and involved sections. Figure 12 above visualizes the three phases put together but without dates to simply show all sections, each section will be presented for respective phase where the deadlines are set. More spontaneous meetings and journeys is absent from the timelines as they were reviewed with clients, supervisors and other involved parties during the course of the project. Meetings with supervisors, from CEVT and LTU alike, are planned to be held on a regular basis, whenever needed and after the completion of major activities. The purpose is to validate and receive feedback on my progress.
4.2 INSPIRATION
The first phase consisted of various information-gathering methods, see Figure 13. A literature study, multiple benchmarkings and a Pugh’s Matrix was used to collect theoretical data and an experiment was preformed to gather practical data. The results were analyzed with the purpose to identify how the BIS impacts the users need, what performance is already achieved by other manufacturers and what component combinations gave the most pleasant values.
Figure 13: Planning and deadlines for the Inspiration phase
4.2.1 LITERATURE STUDY
Knowledge is of great importance when creating an understanding for different issues that can occur in or are related to the seatbelt system. By applying a literature study, I will be able to gather intelligence about the significant areas that are relevant to my project specifically. The purpose of this method is to gather information at a larger extent from several scientific sources such as dissertations, articles and books. Milton & Rodgers (2013) clarifies that the information in turn must be critically reviewed to ensure its quality and relevance, low quality sources tend to require multiple references that can both verify but also contradict each other.
The authors also highlights that both qualitative and quantitative data can be of interest in a literature study.
complemented with at least another reference if possible. My sources were collected by using the Google search engine, Google Scholar and old assignments that are based on scientific publications, books and websites.
The aim of my literature study was to establish knowledge as well as gather information regarding user’s needs, design theories and seatbelt structure, functionalities and requirements. Information that was lacking was supplemented later whenever needed. The resulted data collected from this method are presented in chapter 2. Context and chapter 3.
Literature review.
4.2.2 BENCHMARKING
Benchmarking is a method that doesn’t have a concrete, all-embracing definition. Stapenhurst (2009) describes it as a commonly used method where organizations researches the market to get inspired or compare their product with other designers/manufacturers. This process can be applied to any area where the organization wants to compare performance and/or learn from others. Wikberg Nilsson et al. (2015) as well as Johannesson, Persson & Pettersson (2013) adds that one of the methods main purposes is to examine how similar or related problems has been solved through design.
My intention in using this method is divided in two, whereas one is to identify the positioning of the seatbelt from other manufacturers BIS with the use of the service A2mac1.com which offers different ways to evaluate a complete car but also its included components and assemblies. The other examination is to test the belt’s performance in physical cars, both BIS and from seatbelt in the B-pillar. With some valuable input achieved from CEVT regarding car models, did I started off with the component evaluation in A2mac1 with the purpose to find cars with belt-integrated seats.
4.2.2.1 SYSTEM RESEARCH IN A2MAC1
A2mac1.com is a service that sells licenses to companies to simplify activities regarding benchmarking. Thanks to CEVT’s contract and a license from a colleague did I get access to the site to search for cars with frontal BIS. My goal was to find and evaluate the placement of every component in the retractor assembly. The purpose was to see how other manufacturers placed the system so I later would be able to measure their performances in physical cars. However, the issue was that BIS cars where only available in A2mac1’s program AutoVision which shows the market documentation of the complete vehicle, see Appendix B1. My hopes were to access AutoReverse which presents each component and their assembly and also its positioning in their demolished car.
As a work around did I use Google to find reviews that somehow would state where the retractor – or possibly other parts of the system – was located in a BIS. This way, I could also find out if the specific cars’ owners have had any problems with the integrated system, so I analyzed the owners’ complaints and noted if the problematic situations had been a result of a function failure or a simple inconvenience. Problems that had occurred in one or more models where observed to understand why and how the situation had occurred but also to get an input on what BIS car users have experienced with this type of manufacturing. The information
gathered was used to understand the users and note down the users’ needs for the system before trying the BIS myself.
4.2.2.2 PERFORMANCE EVALUATION IN PHYSICAL CARS The second part of the benchmark was to visit various businesses that sell at least one car with BIS. Since the car branch that had the most BIS appeared to be BMW, was it the first I looked for. Unfortunately did I only find one, see Figure 14, so I could only compare the forces to a B-pillar installation. Since the main purpose was to evaluate the force needed to extract/retract the belt without annoyances and test the comfort, see Appendix B2, was it accurate to seek the total force from a traditional mounting in the B-pillar as stated in my mission statement. The new placement should generate the same or similar force to be comfortable, safe and fulfill requirements allied to the component, no matter the placement.
The inertia testing was carried out on a second-hand BMW 420d Cabrio from 2014 and two car models with B-pillar installations where the extraction force was measured with a dynamometer. Since the velocity had to be consistent was an average value calculated based on 20 measurements, these tests were made on both the driver’s and the passenger’s side to evaluate potential differences. The driver’s seatbelt are usually used more than the other front seats (personal communication with Bilia Group Trollhättan, 27 April 2020), so this was a thing to consider as it was a second-hand car.
In addition to the measured data for the benchmarking did I try various car models myself to evaluate the user experience and also to test a retracting requirement that are explained in Appendix A. Try It Yourself is a learning method that is quite self-explained, you’re interacting with a marketing product and check/verify existing faults or potential errors
Figure 15: Extraction force measured on a BMW 420d Cabrio with a dynamometer
Figure 14: A Belt-in-Seat from a BMW 4- Series 428i Convertible
(Image from A2mac1's AutoVision)
From all aspects evaluated in the benchmarking did I get to analyze the user’s needs as well as compare the extraction force generated from a BIS and B-pillar installations. Due to the limited space was measurements of the retraction force with the dynamometer excluded.
4.2.3 USER NEEDS
The costumer is aware of the part of the seatbelt system that they can see and interact with, but also the safety aspect in events of a collision. The other attribute that the seatbelt provides is the concept of comfort. Since a delimitation in this thesis was to only focus on the aspect of comfort, was the crash safety to be temporarily neglected.
The reviews that I analyzed during the benchmarking provided me with information regarding a user’s needs, or more specifically what causes a dissatisfaction of the product. Additional information did I gather from CEVT and by asking a few acquaintances about their experience of different seatbelts. The first thing I wanted to confirm when questioning individuals with a driver’s license was how recent it was that they drove a car, because I wanted to know if they had a recent reference in mind. Other questions that they answered was if, and in case of what and when, they encountered something problematic or inconvenience. The majority of their experiences was something I’ve also noticed or experienced but others gave me a new perspective, mostly how a short or tall person experiences the fitting e.g. around their abdomen and over the shoulder.
Since I’m part of the current and future stakeholders was it relevant for me to apply the method Try It Yourself. Here, I tried to evoke and examine obstacles that in some way may affect the user's experience of using the seatbelt. I documented the attempts by recording a video of each car and the specific features I observed. Josh Brown (n.d.) claim that a recording is an insurance about what took place and are often used with the purpose to focus on the task at hand. I also attempted to Think Aloud in the observations recorded to be able to recall my experiences during the interactions.
4.2.4 EXPERIMENT PREPARATION
This type of experiment does not directly involve stakeholders and serves the purpose of statistically finding the most optimal combination in regard to the measured forces. The nature of these tests is to examine the three forces (extraction, retraction and friction) that originates in the seatbelt systems, whether it’s a BIS or a B-pillar manufacture. A decision that I made together with my colleagues was to construct a plan for the experiments with the purpose of ensuring that each measure and assessment was performed the same way. I structured one to fit my tests since Rosenzweig (2015) explains that an experimental planning can be constructed in many different ways depending on what the designer wants to establish.
The purpose and aim for the tests are to find what combination of components that could create the best user experience. CEVT shares the same vision as Huang et al. (2018, p.788) who explains that the wanted combination is “when the friction coefficient is minimum, the pull- out force is minimum and the retract force is maximum”. The forces from the system can be sampled with a dynamometer. Before delivering the components did Autoliv test each retractors’ performance. The data where retrieved with the rest of the components and will be used as a guide of what results are the best of the system performances, see Appendix C.
I didn’t have access to a professional testing set-up since the BIS is a new concept for CEVT, so I built one myself. I use the measurements from a 3D-modelling drawing that my colleague made, the construction consists of a base where the retractors are mounted and a vertical part that symbolize the backrest where the D-loop and Loop are mounted, Figure 16.
Further agreements were made to potentially perform the tests in a temperature chamber to evaluate the problems that occurs in a cold climate according to system requirements. I got the contact information to a maintenance service center on the outskirts of Gothenburg, the employees at Säve are working with different vehicle tests, cold climate being one of them. Unfortunately, was I never granted access to the cold climate camber and could therefore not perform the tests in a cold environment. And so will this requirement be a continuing work for when my thesis period is over.
4.2.4.1 EXPERIMENT EXECUTION
The room temperature testing proceeded as planed and were performed according to the experimental plan routine in Appendix D1. The equipment uses is presented in Figure 17. Each component where named and a chart was constructed to present every combination’s extraction- and retraction force, see Table 1 below. One obstacle I encountered was the velocity, that I had to be very consistent when pulling in order to get a valid value. The method I used required consistency when pulling, which was very hard, and due to contractual errors did I have to redo the test. For the second testing did I manage to include the retraction force, which was absent in the first testing and I was also more aware of other metrics that affected the value, such as added a weight of the webbing. This weight was due to fact that the hook for the dynamometer was attached on the same position for all three distances. The experimental planning was updated to the new routine and the errors were corrected before the testing resumed.
The second testing was easier to perform because I had assistance to note down the measured data and keep an eye on the marked distances.
What made the experiment valuable was that I could note
Figure 16: Set-up for the experiment’s execution
