Connection between aim and theory

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Theoretical framework

Connection between aim and theory To do relevant conclusions about how to test and evaluate the wheel, this study will refer to three theories. Theory 2.2, EN-1888 Irregular surface test, is a European test standard for strength- and durability test of strollers. Theory 2.3 will describe the connection between the use of a stroller and the European standard test, Irregular surface test. Finally, theory 2.4 will present mathematical formulas used to analyze data. The thesis concept study has been done in help of theory 2.5, product development, by following its different phases. Therefore, it can be good for the reader to get an understanding of what the different phases mean. Further, different material contacted in this study is described under theory 2.6. When it comes to making decisions that have been done in the thesis, a first feeling is often the gut feel, and more of that is described in theory 2.7. EN-1888 Irregular surface test (IrregularST) According to safety standards for strollers, Irregular surface test (IrregularST) must be run. The stroller should be mounted on a treadmill. The treadmill has two different obstacles mounted to it, and they are defined according to the test’s standards (see Figure 3). The speed should be 5±0.1 km/hand the stroller must pass over the obstacle’s configuration (see Figure 4) 72 000 times. The purpose of IrregularST is to expose the stroller for lifetime use. By doing these types of test, the stroller doesn’t need to be used for a lifetime by the owner to see if it last and not breaks.


Connection between aim and method The used methods are adapted to follow the described theory 2.5 Product development. The methods can be divided into two parts, an information-gathering part, and a concept-creation/ evaluation part. From the information-gathering part, methods like experimental analysis and Benchmarking are presented because these are the basis for how Thule Chariot CAB’s front wheel should be evaluated. Quality function deployment, QFD, were used in order to weigh the specification requirements that were set on the product. Further, all concepts were evaluated by Pugh’s matrix. Methods for pilot study Experimental analysis This method is used to see whether something is happening or lacking in any situations. By looking and document the sequence of events, requirements can be obtained. The method may need some test- equipment, measurement instrument, photographing or video- technics that can register what is happening and makes it possible to review afterward. The advantage with the method is that quick or complicated registration of event in real-time can be observed afterward by some of the test- equipment. One disadvantage can be to gain a test situation that doesn’t explain the events you want to study. For example, this method is used when studying manikins when crash testing cars.

Implementation and result

Pilot study A pilot study was executed to gather information about Thule Chariot CAB’s front wheel and how the wheel should be evaluated and compared to other wheels. To determine how the wheel would be evaluated, an experimental analysis was performed, where theory and test standards were included. Furthermore, a benchmarking was performed to map possible competitor wheels and measure those performances. At first, a Gantt-schedule was done to clarify and plan all individual parts in the project. The Gantt-schedule can be seen in (Appendix 1. Gantt). 4.1.1 Experimental analysis Before it was possible to improve the comfort of the front wheel, decisions were made on what possible increased comfort could be throughout an experimental analysis. Because Thule Chariot CAB doesn’t have front fork suspension, an experiment was performed to test the stroller with front suspension. By doing that, possible differences of the stroller’s behavior may occur and be inspected. To ensure that the stroller’s two different setups were tested properly and comparable, the stroller was driven on the IrregularST. Thereby, there was no difference at the test tracks obstacles, speed and how the stroller should have been driven by its user. The experiment can be divided into two different test configurations (see Table 1). – Configuration 1: Thule Chariot CAB with its original front wheel and original rigid front fork. – Configuration 2: Thule Chariot CAB with its original front wheel but with front fork including suspension.


Brainstorming was performed together with one senior concept designer at Thule in Hillerstorp. The person has great experience in work of strollers. To get the most out of the brainstorming session, the time was decided to remain a maximum of 45 minutes. The subject was described, and the brainstorming of the whole wheel was then started. The purpose of the brainstorming was to create a new wheel with the idea of flexible materials and wheel design. Ideas were drawn on the whiteboard (see Appendix 3. Brainstorming) individually by each one the first 15 minutes. After that 15 minutes, the ideas were described by the creator and discussed together. Further, the ideas were divided into four different groups to make it clear and describe in which area some improvements could be done. Then, the ideas were combined to see if it would lead to new improved solutions. Also, some ideas were improved by each other. Based on gut feel, three concepts were chosen to continue working with. These concepts were then built up in CAD-software, so it was possible to do rapid prototyping.

Discussion and conclusions

Implications This thesis work has resulted in an evaluation method, for how Thule Chariot CAB’s front wheel should be evaluated regarding increased comfort. The evaluation method that was done in this study is just one way to evaluate wheels, and was made since there is no existing method. Further, a concept study was performed were several concepts were produced by purpose to improve the comfort of the stroller. Two concepts broke during the evaluation test. It may depend on that the 3D-printed material (PA12) is more brittle at hard impact or that the parts were under-dimensioned. However, one of the concepts that were produced resulted in improved comfort properties since its bounce height was lower than the original wheel when the wheels were evaluated. Because this study didn’t conduct the three latest step in the development phases, see 2.5 Product development, no one knows if Concept 3 will be able to be manufactured or not. Conclusions and recommendations The purpose of the study was to create an evaluation method for how Thule Chariot CAB’s front wheel should be evaluated regarding improved comfort. Further, a concept study was performed, where the goal was to achieve a stroller wheel that could contribute to increased comfort. With respect to the delimitations set in the project, both of the study’s question formulation considered to be fulfilled.

Table of content :

  • 1 Introduction
    • 1.1 Background
    • 1.2 Problem description
    • 1.3 Purpose and aim
    • 1.4 Delimitations
    • 1.5 Outline
  • 2 Theoretical framework
    • 2.1 Connection between aim and theory
    • 2.2 EN-1888 Irregular surface test (IrregularST)
    • 2.3 Connection between Thule’s customers and IrregularST
    • 2.4 Mathematical formulas
    • 2.5 Product development
    • 2.6 Materials
    • 2.7 Feasibility Evaluations (Gut Feel)
  • 3 Method
    • 3.1 Connection between aim and method
    • 3.2 Methods for pilot study
      • 3.2.1 Experimental analysis
      • 3.2.2 Benchmarking
      • Measurement tools, Accelerometer – Science Journal by Google
      • Use of accelerations
      • 3.2.3 Quality Function Deployment – QFD
      • 3.3 Methods for concept generation and elimination
      • 3.3.1 Brainstorming
      • 3.3.2 Idea sketching
      • 3.3.3 Rapid prototyping
      • 3.3.4 Pugh’s matrix
    • 3.4 Validity and reliability
  • 4 Implementation and result
    • 4.1 Pilot study
      • 4.1.1 Experimental analysis
      • 4.1.2 Benchmarking
      • Benchmarking setup
      • Benchmarking result
      • 4.1.3 Quality function deployment (QFD)
    • 4.2 Concept generation and rapid prototyping
      • 4.2.1 Brainstorming
      • 4.2.2 Idea sketching
      • 4.2.3 Concepts
      • Concept
      • Concept
      • Concept
      • Concept
      • 4.2.4 Rapid prototyping
    • 4.3 Concept elimination
      • 4.3.1 Testing the wheels
      • Testing result
      • 4.3.2 Pugh’s matrix

Concept Development of Stroller Wheel

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