Using integrated quality function deployment and theory of innovation problem solving approach for ergonomic product design

Computers & Industrial Engineering 76 (2014) 60–74

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Using integrated quality function deployment and theory of innovation problem solving approach for ergonomic product design Fanglan Zhang a,b,⇑, Minglang Yang a, Weidong Liu a a b

College of Art and Design, Yanshan University, Qinhuangdao 066004, China School of Mechatronics Engineering, Nanchang University, Nanchang 330031, China

a r t i c l e

i n f o

Article history: Received 20 December 2012 Received in revised form 17 July 2014 Accepted 21 July 2014 Available online 1 August 2014 Keywords: Theory of innovation problem solving (TRIZ) House of Quality (HoQ) Quality function deployment (QFD) Ergonomic product innovative design Customer satisfaction needs (CSNs) Fuzzy group decision-making

a b s t r a c t A multidisciplinary approach integrating method of identification of customer satisfaction needs (CSNs), the House of Quality (HoQ) chart of quality function deployment (QFD), theory of innovation problem solving (TRIZ) and fuzzy group decision-making theory for ergonomic product innovative design and evaluation in the early design stages was proposed. An integrated model and the approach procedures consists of four steps. In step 1, identification of CSNs is based on a data source triangulation approach, questionnaire survey, 5-point liner numeric rating scale, factor analysis, and Cronbach’s coefficient alpha statistic are utilized to guarantee that the CSNs are complete and reliable. In step 2, a correlation matrix is built to identify the critical ergonomic design areas and the key problems are established by analysis of the negative relationships obtained from interrelationship half-matrix at the roof of the HoQ. In step 3, to solve the problems, TRIZ main tools and contradiction analysis are utilized. Several innovative alternatives are generated by combining appropriate Inventive Principles of TRIZ, the critical ergonomic design areas and the ergonomic design principles. In step 4, a general and easy fuzzy group decision-making method for evaluating of the best design alternatives is presented. A case study of the integrated kitchen stove innovative design and evaluation is conducted to demonstrate the applicability of the proposed approach. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Product design is a critical factor during the early phase of new product development (Crawford, 1997, Chapter 4). Enhancing customer satisfaction and providing innovative products become crucial strategies for success. Product designers normally focus on functionality, quality and cost, which have long been the most important factor in product design. However, in recent years, research in ergonomics and design aesthetics has illuminated that product functionality, quality and cost may not be the main determinant of customer satisfaction but that other design elements such as safety, comfort (Vink, Overbeeke, & Desmet, 2005, Chapter 4), usability and pleasurable appeal (Jordan, 1998, Chapter 3, 2000), emotion (Nagamachi, 2002), attractiveness and individuation (Liu, 2003) also play an important role. The focus of ergonomics is to study the role of humans in the safe and efficient operation of complex industrial systems and the application of ergonomic principles and anthropometric data to the design of ⇑ Corresponding author at: College of Art and Design, Yanshan University, Qinhuangdao 066004, China. Tel.: +86 018633526082. E-mail address: [email protected] (F. Zhang). http://dx.doi.org/10.1016/j.cie.2014.07.019 0360-8352/Ó 2014 Elsevier Ltd. All rights reserved.

products. An ergonomic product may be expressed through the elements of safety, comfort, easiness, size, etc. With regard to design aesthetics, it may refer to the objective features of a stimulus such as shape, color, tone and texture (Postrel, 2003, Chapter 5; Schifferstein & Hekkert, 2007, Chapter 2) or to the subjective reaction like attractiveness to the specific product features. Customers have been pursuing ergonomically well-designed and aesthetic product. The reason for customers shifts is that ergonomic product design based on anthropometric dimensions and ergonomic principles may prevent the risk of occupational injuries (Sperling et al., 1993) and ergonomically well-designed product also offer comfortable use and high pleasure to the customers (Motamedzade, Choobineh, Mououdi, & Arghamj, 2007). Through experiments, Sonderegger and Sauer (2010), reported that perceived usability was positively influenced by the design aesthetics of the product. Design aesthetics is an important tool to attracts customers and gain their attentions. Product designers should thus provide ergonomic and aesthetic expertise to ergonomic product design problem through innovative methods and tools. With regard to the design mehods for new product development, quality function deployment (QFD) is an important methodological approach to increase customer satisfaction and reduce the

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product costs and development cycle time. Proposed by Akao (1997, Chapter 1), QFD was originally developed at Mitsubishi’s Kobe shipyards in 1972. According to House of Quality (HoQ) chart, the most recognized and widely used form of QFD, voice of customer can be availably and entirely translated into engineering characteristics. QFD has been successfully applied by industries around the world (Bergman, 1994, Chapter 3; Geuma, Kwak, & Yongtae Park, 2012; Vezzetti, Moos, & Kretli, 2011). In addition, originally proposed by Altshuller, the theory of innovation problem solving (TRIZ) solves technical problems and provides innovative product structures by employing a knowledge base built from the analyses of approximately 2.5 million invention patents. The TRIZ approach has applied to numerous design problem-solving such as therapy bike design proposal for cerebral palsy children (Lin & Luh, 2009), vacuum cleaner design (Russo, Regazzoni, & Montecchi, 2011), five cooling device concept solutions to overcome the interface conflicts (Wessel, Tom, & Vaneker, 2011), and Technology Forecasting of washing machine (Solomani, Hua, Shi, & Wang, 2004). In each of these cases TRIZ is used as problem solving tool in order to provide solutions for innovative product design. Besides, designers provided eco-friendly solutions to product design problem through TRIZ methods to help implement eco-friendly designs. Fresner et al. (2010), used TRIZ in cleaner production to minimize industrial waste and emissions by increasing the efficiency of the use of materials and energy. Pelt and Hey (2011), compared the BetaMax by Sony Corporation with the Video Home System (VHS) by Japan Victory Corporation to exemplify technologically superior products failing to become a success. Several TRIZ specialists, as a result, have made efforts to integrate TRIZ with other design methods and tools. Alan Van Pelt addressed the application of TRIZ together with Human-Centered Design (HCD). Others have proposed integration with the Neuro Linguistic Programming to understand customers (Mann, 2002, Chapter 5) or the Kano model (Hashim & Dawal, 2012). Hipple (2006) interprets many consumer products from the perspective of the TRIZ methodology and Mann (2002, Chapter 2) provides an extension of the classical 9-Windows tool to include consideration of behavior, capability, and beliefs, values, and identity. Known as an innovative idea generation tool, TRIZ was prevailed and accepted in worldwide corporations such as Philips, Samsung, Siemens and Motorola. Moreover, several alternatives of ergonomic product innovative design are generated in the early design stages. The method for evaluating of the best design alternatives is critical to success in new product development. Recently, Multi-Criteria Group Decision-Making (MCGDM) method is used in many real-world decision-making situations in various kinds of engineering and management fields (Hatami-Marbini & Tavana, 2011; Mojtahedi, Mousavi, & Makui, 2010; Vahdani, Meysam Mousavi, TavakkoliMoghaddam, & Hashemi, 2013). Selecting of design alternatives is a MCGDM problem which involves many factors of both customer needs and business constraints. In the early design stages, evaluation of design alternatives is difficult to precisely express by crisp data because the information available is usually subjective or imprecise. So, it is more appropriate to present the data by fuzzy numbers instead of crisp numbers (Buyuközkan, Arsenyan, & Ruan, 2012; Geng, Chu, & Zhang, 2010). Despite of many success stories on both QFD and TRIZ applications, all of them implementation are not without problems. QFD is effective to indicate what problems to solve in order to satisfy customer needs, but does not necessarily offer a guide on how to generate solutions for the problem identified. With regard to overcome this challenge, TRIZ is one of the effective tool, However, TRIZ specialists are in doubt whether the problem or contradiction to be solved is the right one. Accordingly, a method of integrated QFD and TRIZ at product design stage for generating innovative

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alternatives is proposed. Besides, evaluating of ergonomic design alternatives is formulated as MCGDM problem and the evaluation criteria of alternatives have subjective perceptions. Therefore, fuzzy group decision-making method is proposed for the ergonomic design alternatives evaluation to ensure a more efficient and rational decision process. In this paper, we put forward a multidisciplinary approach integrating identification of customer satisfaction needs (CSNs), HoQ chart of QFD, TRIZ and fuzzy group decision-making theory for ergonomic product innovative design and evaluation in the early design stages. 2. Theoretical background 2.1. Quality function deployment (QFD) 2.1.1. The House of Quality (HoQ) chart of QFD Quality function deployment (QFD) is a method for developing a design quality aimed at satisfying the customer and then translating the consumer needs into design targets and major quality assurance points to be used throughout the production stage. The primary chart used in QFD is the House of Quality (HoQ). According to the HoQ, customer needs are translated into engineering characteristics, and subsequently into part or component characteristics, the process operations, and production requirements associated with the manufacturing process. Therefore, accuracy of customer needs input is critical for applying the HoQ with success. Toyota halved their design costs and reduced development time by a third after use QFD (Hauser and Clausing, 1988, Chapter 4). Marsot (2005) used the HoQ to design a boning knife. Haapalainen (1999/2000) evaluated pruning shears using the HoQ. Kuijt-evers, Morel, Eikelenberg, and Vink (2009), applied QFD as a design approach to ensure comfort in screwdriver design. Lo, Tseng, and Chu (2010), advanced One-step QFD for concept generation of computer mice design. The SOFRAGRAF Company has used QFD for the design of hand tools, staplers, nailing machines, etc. with success. In each of these cases QFD is successfully used as the tool that illustrates the translation of customer needs into product design characteristics in order to increase customer satisfaction (Lai, Xie, Tan, & Yang, 2008; Raharjo, Brombacher, & Xie, 2008). The procedures of the traditional HoQ chart of QFD are divided into the following six steps (Fig. 1). Step 1: Identifying the customers. Step 2: Determining customer needs.

Fig. 1. QFD procedures model.

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F. Zhang et al. / Computers & Industrial Engineering 76 (2014) 60–74

Step 3: Determining relative importance of the needs. Step 4: Competition benchmarking. Step 5: Translating customer needs into measurable engineering characteristics. Step 6: Setting engineering targets for the design.

matrix and 40 inventive principles. The procedure of the contradiction analysis and elimination is shown in Fig. 3.

2.1.2. Defects of the traditional QFD The HoQ chart of QFD in its traditional form presents many limitations on its implementation. It has 5 defects as follows:

(1) Defects 1: The traditional TRIZ is not involved the method to establish the key problems for innovation. (2) Defects 2: Using TRIZ for solving problems, the implementation process still needs the designers’ knowledge, experience and level. (3) The traditional TRIZ does not provide an objective method for alternatives evaluation.

(1) Defects 1: Matrix size is too large, increasing the computational complexity and time consuming. (2) Defects 2: Completeness and effectiveness of the customer needs cannot be guaranteed. (3) Defects 3: Relying on individual engineers to determine the product engineering characteristics have strong subjectivity. (4) Defects 4: The traditional QFD method is not involved in specific ways and means to solve the innovative problem. (5) Defects 5: The traditional QFD is not involved the method for alternatives evaluation. 2.2. Theory of innovation problem solving (TRIZ) 2.2.1. Main tools The key of TRIZ is the realization that contradictions can be methodically resolved by using innovative solutions, which is contained many useful tools. The main tools of TRIZ include 40 Inventive Principles, the Contradiction Matrix, and the Separation Principles. 40 Inventive Principles (Table 1) are used to guide the TRIZ specialists in developing useful concepts of solution for inventive situation, and they are distributed (up to 4 most likely inventive principles for solving the design problems) among the cells of a 39  39 matrix, called contradiction matrix (Fig. 2) that identifies 39 engineering parameters (Table 2) most frequently involved in design process. The Separation Principle includes 4 types with numbers corresponding to 40 Inventive Principles as shown in Table 3. The main tools of TRIZ are simple and easy to use. Each tool provides effective solutions for product innovation. 2.2.2. Contradiction analysis and elimination Contradiction analysis is a process for identifying, formulating the specific contradictions, which are transformed into the TRIZ genetic contradictions relying on 39 engineering parameters. Moreover, analysis of contradictions type is the key to use appropriate inventive tool. There are two types of contradiction: physical contradiction and technical contradiction. The physical contradiction describes antipodal characteristics requirements for the problem. It can be solved by Separation principles and 40 inventive principles. The technical contradiction is generated when two system parameters oppose each other, an improvement in one leading to a deterioration of the other. It can be solved by contradiction

2.2.3. Defects of TRIZ TRIZ is a knowledge base tools, but it has 3 defects as follows:

2.3. Fuzzy decision theory with linguistic variables 2.3.1. A concept of trapezoidal fuzzy number

e ¼ ða1 ; a2 ; a3 ; a4 Þ, its membership Definition 1. A trapezoidal fuzzy number A function is defined by

8 0; > > > > > > < ðx  a1 Þ=ða2  a1 Þ; leA ðxÞ ¼ 1; > > > ðx  a4 Þ=ða3  a4 Þ; > > > : 0;

x 6 a1 a1 < x < a2 a2 6 x 6 a3

ð1Þ

a3 < x < a4 x P a4

e ¼ ða1 ; a2 ; a3 ; a4 Þ, its defuzzification Definition 2. For a trapezoidal fuzzy number A value is defined to be

b ¼ ða1 þ a2 þ a3 þ a4 Þ=4

ð2Þ

From Fig. 4, if the left area Da1ca2 + Da2cdb is equal to the right area Da3ea4 + Da3edb, then

ð1Þða2  a1 Þ=2 þ ðb  a2 Þð1Þ ¼ ða3  bÞð1Þ þ ð1Þða4  a3Þ=2 ) b ¼ ða1 þ a2 þ a3 þ a4 Þ=4 Therefore, the defuzzification value of the trapezoidal fuzzy number is established by b = (a1 + a2 + a3 + a4)/4. 2.3.2. Linguistic variables and fuzzy number The linguistic weighting variables and the linguistic rating variables are shown in Tables 4 and 5, respectively. 2.3.3. Fuzzy Delphi method The Fuzzy Delphi method includes the following steps. Step 1: Experts Ei, i = 1,   , n, provide the possible realization ðiÞ rating of a certain event: the pessimistic rating a1 ; the most ðiÞ ðiÞ ðiÞ plausible rating (a2 ; a3 ), and the optimistic rating a4 . The

Table 1 40 Inventive principles. 1. Segmentation 2. Taking out 3. Local quality 4. Asymmetry 5. Merging 6. Universality 7. ‘‘Nested doll’’ 8. Anti-weight 9. Preliminary anti-action 10. Preliminary action

11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

Beforehand cushioning Equipotentiality ‘‘The other way round’’ Spheroidality – curvature Dynamics Partial or excessive actions Another dimension Mechanical vibration Periodic action Continuity of useful action

21. 22. 23. 24. 25. 26. 27. 28. 29. 30.

Skipping ‘‘Blessing in disguise’’ or ‘‘Turn Lemons into Lemonade’’ Feedback ‘‘Intermediary’’ Self-service Copying Cheap short-living objects Mechanics substitution Pneumatics and hydraulics Flexible shells and thin films

31. 32. 33. 34. 35. 36. 37. 38. 39. 40.

Porous materials Color changes Homogeneity Discarding and recovering Parameter changes Phase transitions Thermal expansion Strong oxidants Inert atmosphere Composite materials

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Fig. 2. The part of the contradiction matrix.

rating given by each expert Ei are presented in the form of a trapezoidal fuzzy number

e ðiÞ ¼ ðaðiÞ ; aðiÞ ; aðiÞ ; aðiÞ Þ; i ¼ 1;    ; n:; A 1 2 3 4

ð3Þ

e m of all A e ðiÞ is computed. This requires Step 2: First, the mean A ðiÞ ðiÞ ðiÞ ðiÞ computation of the mean of alla1 ; a2 ; a3 ; a4 ; i = 1,   , n. Hence

e m ¼ ðam1 ; am2 ; am3 ; am4 Þ A ¼

n n n n X X X 1X ðiÞ 1 ðiÞ 1 ðiÞ 1 ðiÞ a1 ; a2 ; a3 ; a n i¼1 n i¼1 n i¼1 n i¼1 4

! ð4Þ

Then for each expert Ei the differences

  ðiÞ ðiÞ ðiÞ ðiÞ am1  a1 ; am1  a2 ; am1  a3 ; am1  a4 ¼

n n n n X X X 1X ðiÞ ðiÞ 1 ðiÞ ðiÞ 1 ðiÞ ðiÞ 1 ðiÞ ðiÞ a1  a1 ; a1  a1 ; a1  a1 ; a  a1 n i¼1 n i¼1 n i¼1 n i¼1 1

!

ð5Þ

Table 2 39 Engineering parameters. 1. 2. 3. 4. 5. 6.

Weight of moving object Weight of stationary object Length of moving object Length of stationary object Area of moving object Area of stationary object

7. Volume of moving object 8. Volume of stationary object 9. Speed 10. Force 11. Stress or pressure 12. Shape 13. Stability of the object’s composition 14. Strength 15. Duration of action by a moving object 16. Duration of action by a stationary object 17. Temperature 18. Illumination intensity 19. Use of energy by moving object 20. Use of energy by stationary object

are found and sent back to the expert Ei for reexamination.

21. 22. 23. 24. 25. 26.

Power Loss of Energy Loss of substance Loss of Information Loss of Time Quantity of substance/the matter 27. Reliability 28. Measurement accuracy 29. Manufacturing precision 30. External harm affects the object 31. Object-generated harmful factors 32. Ease of manufacture 33. Ease of operation 34. Ease of repair 35. Adaptability or versatility 36. Device complexity 37. Difficulty of detecting and measuring 38. Extent of automation 39. Productivity

Step 3: Each expert Ei presents a revised trapezoidal fuzzy number

  e ðiÞ ¼ bðiÞ ; bðiÞ ; bðiÞ ; bðiÞ ; i ¼ 1;    ; n: B 1 2 3 4

ð6Þ

e m is calThis process starting with Step 2 is repeated. The average B ðiÞ

ðiÞ

ðiÞ

Step 4: At a later time, the same process may reexamine the ratings, if there is important information available due to new discoveries.

ðiÞ

culated by formula (4) with the differences that now a1 ; a2 ; a3 ; a4 ðiÞ ðiÞ ðiÞ ðiÞ b1 ; b2 ; b3 ; b4 :

are substituted correspondingly by If it still necessary new trapezoidal fuzzy numbers e m is e ðiÞ ¼ ðcðiÞ ; cðiÞ ; cðiÞ ; cðiÞ Þ are presented, and their average C C 1 2 3 4 calculated. The process could be repeated again and again until em; B e m ; . . . become reasonably close (we em; C to successive means A can define the distance of two fuzzy numbers, di 6 0:2).

2.4. Ergonomic product design principles and evaluation 2.4.1. The ergonomic design principles Over the last decades, functionality of a product has long been the most important factor in designing a product. However, once appropriate functionality is satisfied, the user has tendency to need

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F. Zhang et al. / Computers & Industrial Engineering 76 (2014) 60–74 Table 3 Separation Principles corresponding to 40 inventive principles. Types

The number of 40 inventive principles

1. Separation of opposite requirements in space 2. Separation of opposite requirements in time 3. Separation within a whole and its parts 4. Separation upon condition

1, 2, 3, 4, 7, 13, 17, 24, 26, 30 9, 10, 11, 15, 16, 18, 19, 20, 21, 29, 34, 37 12, 28, 31, 32, 35, 36, 38, 39, 40

Table 5 Linguistic variables for the ratings. Linguistic term

Membership function

Very poor (VP) Poor (P) Medium poor (MP) Fair (F) Medium good (MG) Good (G) Very good (VG)

(0, (1, (2, (4, (5, (7, (8, 9,

0, 1, 2) 2, 2, 3) 3, 4, 5) 5, 5, 6) 6, 7, 8) 8, 8, 9) 10, 10)

1, 7, 25, 27, 5, 22, 23, 33, 6, 8, 14, 25, 35, 13

Design Principles (Seva, Gosiaco, Santos, & Pangilinan, 2011), as shown in Table 6. 2.4.2. Ergonomic design alternatives evaluation Identifying accurate criteria and applying logical method are keys to a successful alternatives evaluation process. From the extensive review of ergonomics literature (Dul et al., 2012; Laios & Giannatsis, 2010; Wellings, Williams, & Tennant, 2010), the ergonomic design alternative criteria are established as shown in Table 7. However, these criteria usually cannot concretely quantify and with fuzziness. Therefore, evaluating ergonomic design alternatives by fuzzy group decision-making is considerately. 3. An multidisciplinary approach

Fig. 3. The procedure of the contradiction analysis and elimination.

c

d

1

0

a1

a2 b a3

a4

Fig. 4. The defuzzification value of the trapezoidal fuzzy number.

The HoQ chart of QFD in its traditional form presents many defects (Sections 2.1.2 and 2.2.3) on its implementation. A combination of both can compensate for their defects. Besides, how to identify customer needs accurately and extensively and evaluation design alternatives are not yet mentioned in both of the method. Therefore, we put forward a multidisciplinary approach integrating identification of customer satisfaction needs (CSNs), HoQ chart of QFD, TRIZ and fuzzy group decision-making theory at ergonomic product design stage. An integrated model for ergonomic product innovative design is shown in Fig. 5. The proposed integrated model for ergonomic product design consists of four steps. (1) Identification of customer satisfaction needs (CSNs). (2) Construction of the HoQ chart of QFD for identifying the key problems and the critical areas for innovation. (3) Using the TRIZ main tools and contradiction analysis to generate the innovative design alternatives. (4) Application of fuzzy group decision-making theory for the alternatives evaluation and selecting the best design alternative. These steps are presented in detail as follows:

Table 4 Linguistic variables for the importance weight.

3.1. Identification of the CSNs

Linguistic term

Membership function

Very low (VL) Low (L) Medium low (ML) Medium (M) Medium high (MH) High (H) Very high (VH)

(0, 0, 0.1, 0.2) (0.1, 0.2, 0.2, 0.3) (0.2, 0.3, 0.4, 0.5) (0.4, 0.5, 0.5, 0.6) (0.5, 0.6, 0.7, 0.8) (0.7, 0.8, 0.8, 0.9) (0.8, 0.9, 1, 1)

something more beyond the functionality. In this sense, ergonomic usability recently considered more important than the functionality in the product design. In order to capture the usability, a product must be designed by adapting some or all of the Ergonomic

The first step involves identification of the CSNs. To guarantee the completeness of the CSNs and enhance the validity of the study results, a data source triangulation approach is used, including questionnaire, expert interviews and the extensive review of ergonomics literature. The conceptual model of the data source triangulation approach for collecting initial CSNs descriptors is shown in Fig. 6. With regard to the initial CSNs descriptors, pre-screening including grouping/eliminating/combining procedure is performed by ergonomists based on such criteria as relevancy, dependency, redundancy, and similarity. As a result, the initial CSNs are obtained. To gain reliable CSNs, questionnaire consists of full set of pre-screened list of the initial CSNs are employed. 5-point liner

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Table 6 The ergonomic design principles. Principles 1. Product size fits in with body dimensions and environmental space dimensions 2. Product form fits in with Human physiological structure and curve 3. Product color in accord with human cognitive psychology 4. Product interface correspondence with human cognitive behavior 5. User interacts with the product operating system intelligently Fig. 6. The conceptual model of the data source triangulation approach for collecting initial CSNs descriptors. Table 7 The ergonomic design alternative criteria. Criteria

Item

1. Ergonomic interaction

1.1 1.2 1.3 1.4 1.5

Safety Dimension Comfort Save effort Easy to use

2. Ergonomic emotion

2.1 2.2 2.3 2.4 2.5 2.6

Aesthetics Style Semantics Attraction Easy to learn Maintenance

3. Ergonomic performance

3.1 3.2 3.3 3.4 3.5

Efficiency Effectiveness Function Environmental protection Save energy

numeric rating scale is utilized to measure the relative importance of each CSN as shown in Fig. 7. From the result of questionnaire survey, the initial CSNs were analyzed and classified into meaningful categories to be related to customer satisfaction dimensions

including ergonomic interactive needs, ergonomic affective needs and ergonomic performance needs. Factor Analysis with varimax rotation was utilized for classifying the initial CSNs. To gain reliable data about customer needs with respect to customer satisfaction, a large number of questionnaire survey are employed. Questionnaire consists of full set of pre-screened list of the initial CSNs. 5-point liner numeric rating scale is utilized to measure the relative importance of each CSN as shown in Fig. 7. The internal consistency reliability of CSNs is tested with Cronbach’s coefficient alpha statistic. Analysis of Cronbach’s coefficient alpha was conducted using statistical analysis package (SAS v.9.1). The cutoff thresholds were 0.7 of Cronbach’s coefficient alpha and 0.4 of item-total correlation coefficient. If item-total correlations of CSNs are below the cutoff threshold of 0.4, they are unreliable and therefore would be removed. As a result, according to the mean score, standard deviation and item-total correlations of CSNs, the final CSNs are identified. 3.2. Construction of the HoQ chart of QFD The second step involves construction of the HoQ chart of QFD, as shown in Fig. 8, for identifying the key problems and the critical

Fig. 5. An integrated model for ergonomic product design.

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Fig. 7. Example of questionnaire for CSNs.

Fig. 8. Construction of the HoQ chart of QFD.

design areas for innovation. Information about product design characteristics (PDCs) can be obtained from the final CSNs. CNsPDCs correlation matrix is built. The correlation between the PDCs and CSNs are evaluated by using rating scale (0-1-3-5) which is corresponded to four relationship levels (i.e. no, weak, moderate, and strong relationships). Design priorities of PDCs are represented by the overall importance score of each product design characteristics related to customer needs, which is calculated by the following equation:

Sj ¼

X C i Pij

ð7Þ

i¼1

where Sj is the overall importance score of the jth product design characteristic, Ci is the importance score of ith customer needs, Pij is score of the impact of the jth design characteristics on the ith customer needs of the jth product design characteristic. The roof of the HoQ is used to identify interrelationships in PDCs. The symbol ‘‘+’’, ‘‘’’ represents positive and negative relationships. Improving one PDC and causing deterioration in the other PDC represents negative relationship. Improving one PDC and causing improvement in the other PDC represents positive relationship. As a result, the key innovative problems from the negative relationship of PDCs and the critical design areas from the design priorities of PDCs are established.

Fig. 9. The traditional ceiling rage hood and gas hob.

3.3. Generation of design alternatives using TRIZ The third step involves using the TRIZ main tools and contradiction analysis to generate design alternatives. The contradictions derived from the HOQ are formulated. By contradiction analysis of TRIZ, the type of contradiction is firstly established in this step. Within a PDC itself, where two mutually opposite requirements exist, is defined as a physical contradiction which can be resolved by using separation principles. The negative relationships between the pairs of PDCs which can be translated into two of the 39 engineering parameters are described as technical contradiction which can be resolved by using contradiction matrix. Next, applying separation principles solves physical contradiction and using contradiction matrix solves technical contradiction. As a result, some recommended inventive principles in 40 inventive principles are identified. For specific products and practice problems, the most effective solutions from the recommended inventive principles are selected.

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Fig. 10. The HoQ for rage hood and gas hob innovative design.

According to solution concept proposal, design priority of PDC and ergonomic design principles, the innovative idea of ergonomic product design are generated. Generate innovative product design in terms of solution concept proposal, design priority of PDC and ergonomic design principles. The alternatives are expressed by sketch, and the three-dimensional (3D) model is built by using computeraided design software like Coreldraw, Rhino, 3DS Max and others.

3.4. Alternatives evaluation and selection using fuzzy group decisionmaking theory The fourth step involves application of fuzzy group decisionmaking theory. The algorithm for our proposed method is introduced as follows:

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(2) Calculate the mean of fuzzy rating and weighting, and transfer linguistic terms to trapezoidal fuzzy numbers. (3) Construct fuzzy decision matrix by normalizing the mean of fuzzy rating for all of the alternatives. e i ¼ ½~ ~ j t , (4) Aggregate the fuzzy evaluations by A xij   ½x i = 1,   , m, j = 1,   , n, i.e.,

Table 8 Initial CSNs descriptors related to use rage hood and gas hob. Initial CSNs descriptors 1. 2. 3. 4.

Strong suction Low noise Gas combustion and energy saving Provide the required fire size

5. Be safe 6. Avoid the user’s head inadvertently bumping the hood 7. Easy to clean surface oil 8. Oil box is easy to disassemble 9. Oil box is easy to clean 10. Strong stove fire 11. The key is easy to clean and maintain 12. The ignition switch is easy to use 13. The key is easy to use 14. Save space 15. Provide secure voice alarm 16. Superior quality 17. Strong and durability 18. Beautiful appearance 19. Be advanced 20. Stylish 21. Individuation 22. 23. 24. 25. 26. 27. 28.

Be decorative Color is matching with kitchen style Streamlined appearance Pleasant color Good shape Provide timing Provide play music

29. 30. 31. 32.

Fit for different pots Automatic cleaning Add useful function Reasonable structure of the function system 33. Intelligent control 34. Be silent 35. Suction fumes rate 100% 36. Control panel is easy to use 37. Provide comfort 38. Avoid error use 39. No fatigue 40. Pleasant use 41. The burner is universal 42. Provide leakage protection 43. Provide the only gas imports 44. High thermal efficiency, grater than 50% 45. Provide flameout protection device 46. Provide fine detail 47. Noise is not greater than 74 dB 48. Amount of wind as large as possible 49. Pressure of wind as large as possible 50. Reasonable scale 51. Be unique 52. Be distinct 53. Elegance 54. Operation fun 55. Comfortable height control 56. Keys are comfortable to use

(1) Fuzzy Delphi method to adjust the consensus condition. The linguistic weighting variables are utilized for evaluating the importance of the criteria. The linguistic rating variables are used to assess the rating of alternatives with respect to each criterion. Then, to adjust the fuzzy rating and weighting, the importance weight of the linguistic criteria and the rating of the three decision-makers under linguistic criteria are obtained by using fuzzy Delphi method.

2 3 ~x11 ~x12    ~x1n 3 e1 A 6 ~x 7 6 . 7 6 21 ~x22    ~x2n 7 6 . 7¼6 . .. .. .. 7 7 4 . 5 6 . 4 . . . . 5 em A ~xm1 ~xm2    ~xmn 3 2 3 2 ~1 ~ 1 þ ~x12  x ~ 2 þ    þ ~x1n  x ~n ~x11  x x 7 6 6x ~ 1 þ ~x22  x ~ 2 þ    þ ~x2n  x ~n 7 7 6 ~ 2 7 6 ~x21  x 7 6 . 7¼6 . 7 6 . 7 6 . 5 4 . 5 4 . ~ 1 þ ~xm2  x ~ 2 þ    þ ~xmn  x ~n ~n ~xm1  x x 2

ð8Þ

~ j denote where ~xij denote fuzzy rating of i alternative at j criteria, x fuzzy weighting of j criteria. e i , i = 1,   , m. The defuzzification (1) Ranking fuzzy number A value of the trapezoidal fuzzy number is used to rank the design alternatives orderings. In addition, a committee of three decision-makers including ergonomics expert, industrial designer and engineer (denoted by D1, D2 and D3) has been formed to select the best ergonomic design alternative. 4. Case study The traditional ceiling rage hood and gas hob for household, as shown in Figs. 9 and 10, exist some design deficiencies. For example, it is not completely suck fumes, not safe to use, not save space, etc. Besides, ergonomics studies show that the Chinese women who are exposed to cooking oil fumes (COFs) at home suffer from high risks of lung cancer (Li et al.,1994), respiratory diseases (Svendsen, Sjaastad, & Sivertsen, 2003), cervical intraepithelial neoplasm and bladder cancer (Tai-An et al.,1999). Because of Several mutagenic and carcinogenic compounds have been identified in COFs (Vainiotalo & Matveinen, 1993)which are produced and released into the environment when food is fried, stir-fried, or grilled using cooking oil at high temperatures. To reduce the risk of working in kitchen, two measures are taken into consideration.

Table 9 Pre-screening of CSN. No.

CSNs

Definition

From

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Strong suction Comfort Fire effectiveness Safety Maintenance Easy to use Save space Durability Beautiful appearance Individuation Be streamline Decoration Nice color Time display Play music Universal design Style harmony Multifunction Intelligent operation Uniqueness Meticulous process

The product provides good effect of suction fumes and capabilities The hood noise as low as possible; the product is comfort to use The product has high fire intensity; fire size adjustable; capable of full combustion and save energy The product provides safe operation, safe use and related safety devices The product is easy to maintain/clean/repair The product provides simple operation The product has proper volume; match with the kitchen environment; place in reasonable way; save space The product provide superiority quality and fine detail; Strong materials The product has beautiful appearance The product is different and highlights features The product outline with streamlined curves The product has decorative pattern and material The product has harmonious and nice color The product has auxiliary function of time display The product has auxiliary function of play music The burner fits for different pot; has proper size and form The product style is match with kitchen cabinets and other objects The product has variety of useful functions Intelligent control panels; automation systems The product is outstanding, prominent and unique The materials and process has high degree of detail

1/35/48/49 2/34/37/39/47/55/56 3/4/10/44 5/6/15/38/42/43/45 7/8/911 12/13/36 14/50 16/17 18/26 21 24 22 25/23 27 28 29/41 19/20 31/32 30/33/40/54 51/52 46

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F. Zhang et al. / Computers & Industrial Engineering 76 (2014) 60–74 Table 10 Factor matrix from the result of Factor Analysis (factor loadings >0.4 are shown). Initial CSNs

Factor 1

Beautiful appearance Nice color Style harmony Decoration Individuation Be streamline Uniqueness Universal design Save space Intelligent Operation Easy to use Comfort Maintenance Safety Time display Play music Meticulous process Multifunction Strong suction Durability Fire effectiveness

0.782 0.779 0.773 0.773 0.755 0.713 0.700 0.678 0.653 0.629 0.547 0.542 0.513 0.457

Factor 2

Factor 3

Factor 4

0.426 0.422

0.415

Factor 5

Factor 6

0.651 0.618 0.587 0.535 0.501

0.403

Table 11 Classification of initial CSNs. Dimension

Initial CSNs

Ergonomic interactive needs Ergonomic affective needs Ergonomic performance needs

Universal design, Save space, Intelligent operation, Easy to use, Comfort, Maintenance, Safety Beautiful appearance, Nice color, Style harmony, Decoration, Individuation, Be streamline, Uniqueness, Meticulous process Strong suction, Fire effectiveness, Multifunction, Time display, Play music, Durability

Table 12 Result of test for internal consistency reliability. Dimension

Rank

The initial CSNs

50 participants Mean

SD

Item-Total Correlation

Alpha if Item deleted

Alpha with all items

Ergonomic interactive needs

2 5 6 7 9 10 11

Safety Easy to use Comfort Maintenance Intelligent operation Save space Universal design

4.16 4.04 4.02 3.90 3.18 3.02 2.98

0.49 0.94 1.07 0.58 1.02 0.92 0.97

0.584 0.625 0.553 0.699 0.604 0.530 0.537

0.784 0.805 0.721 0.762 0.801 0.797 0.749

0.807

Ergonomic affective needs

12 13 14 15 16 17 19 21

Beautiful appearance Nice color Meticulous process Style harmony Decoration Individuation Be streamline Uniqueness

2.92 2.70 2.60 4.52 4.30 4.26 3.96 4.16

0.75 0.79 0.94 1.09 0.96 1.02 1.10 1.26

0.382 0.765 0.609 0.512 0.316 0.304 0.257 0.355

0.822 0.764 0.852 0.835 0.891 0.877 0.884 0.895

0.873

Ergonomic performance needs

1 3 4 8 18 20

Strong suction Fire effectiveness Durability Multifunction Time display Play music

4.04 4.02 3.90 3.18 3.02 2.98

0.43 0.64 0.83 1.05 1.06 1.37

0.489 0.482 0.579 0.602 0.217 0.256

0.711 0.737 0.749 0.736 0.794 0.781

0.765

Firstly, changing the Chinese kitchen fried and stir-fried cooking habits can be reduced COFs. Lastly, developing good ergonomic design on rage hood and gas hob which are the core products for cooking in Chinese kitchen can be created the environmental health kitchen. The last one is the aim of our study. Therefore, the traditional rage hood and gas hob are selected for ergonomic innovative design and evaluation to demonstrate the feasibility of the proposed multidisciplinary method.

We use our proposed method to redesign the traditional ceiling rage hood and gas hob and the detailed procedures are addressed as follows: Step 1: Identification of CSNs for using rage hood and gas hob By application of the triangulation approach, including questionnaire, expert interviews and the extensive review of

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ergonomics literature, a total of 56 customer satisfaction descriptors related to customer satisfaction in using rage hood and gas hob were initially collected, as shown in Table 8. Pre-screening procedure including eliminating, combining, and translating 56 descriptors to customer satisfaction attributes was performed by ergonomists in light of Ergonomics knowledge. As a result, a total of 21 CSNs were defined as shown in Table 9. A total of 50 participants volunteered to participate in the questionnaire for evaluating the priority of 21 CSNs. The relative importance ratings of CSNs are obtained by using 5-point liner numeric rating scale. Factor Analysis with varimax rotation was utilized for classifying 21 initial CSNs. As a result, the initial CSNs could be classified into 6 factors with criterion of eigenvalues greater than 1. After Factor Analysis with varimax rotation, the initial CSNs were derived and the factor loadings were shown in Table 10. As a result, 21 initial CSNs were classified into three customer satisfaction dimensions as shown in Table 11. Table 12 shows the mean score and standard deviation of each CSNs and the result of internal consistency reliability test with Cronbach coefficient alpha and item-total correlation coefficient, which were conducted using SAS v.9.1. From the result of item-total correlation coefficient, all CSNs were also above the cutoff threshold of 0.4, except for the CSNs (Decoration, Individuation, Be streamline, Uniqueness, Time display and Play music) which were below the threshold. The result indicated that these CSNs were unreliable and therefore would be removed. Finally, 15 CSNs were identified as shown in Table 13.

Table 13 Final list of CSNs and priority. Dimension

Rank

CSNs

Priority

Ergonomic interactive needs

2 5 6 7 9 10 11

Safety Easy to use Comfort Maintenance Intelligent operation Save space Universal design

4.38 4.16 4.04 4.02 3.90 3.18 3.02

Ergonomic affective needs

12 13 14 15

Beautiful appearance Nice color Meticulous process Style harmony

2.98 2.92 2.70 2.60

Strong suction Fire effectiveness Durability Multifunction

4.52 4.30 4.26 3.96

Ergonomic performance needs

Table 14 Identification of PDCs. CSNs

PDCs

Safety ?

1. Alarm device

Easy to use ?

2. Key structure 3. Key shape

Comfort ?

4. Distance between the rage hood and user’s head 5. Height of worktops 6. Position of the control panel

Maintenance ?

7. Surface smoothness 8. Oil box structure and shape

Intelligent operation ?

9. Intelligent key

Save space ?

10. Volume 11. Structure

Universal design ?

12.Panel material

Beautiful appearance ?

13. Whole shape 14. Whole size

Nice color ?

15. Color

Meticulous process ?

16. Chamfering 17. Seam 18. Connecting piece

Style harmony ?

19. Point and line process

Strong suction ?

20. Distance between the suction outlet and the burner 21. Hood suction outlet structure

Fire effectiveness ?

22.Burner structure

Durability ?

23. Material and Process

Multifunction ?

24. Functional space allocation 25. Function system

Step 2: Construction of the HoQ chart of QFD 15 CSNs were translated into 25 PDCs by designers, as shown in Table 14. The HoQ for rage hood and gas hob innovative design was built as shown in Figs. 9 and 10. In light of the interrelationships between PDCs at the roof of HoQ, we can get three pairs of negative relationships as shown in Table 15. As a result, three specific contradictions, namely, the key innovative problems were established, describing as follows: (1) How to eliminate contradiction between ‘‘20. Distance between the suction outlet and the burner’’ and ‘‘4. Distance between the rage hood and user’s head’’? (2) How to eliminate contradiction between ‘‘25. Function system’’ and ‘‘14. Whole size’’? (3) How to eliminate contradiction between ‘‘24. Functional space allocation’’ and ‘‘11. Structure’’? From the rank of PDCs in Figs. 9 and 10, the design priority should go to ‘‘25. Function system’’, ‘‘24. Functional space allocation’’, ‘‘21. Hood suction outlet structure’’, ‘‘23. Burner structure’’, ‘‘14. Whole size’’, and ‘‘6. Position of the control panel’’, which were identified to be the six critical design area of rage hood and gas hob.

1 3 4 8

Step 3: Generation of the innovative design alternatives using the TRIZ main tools. The three specific contradictions were translated into TRIZ genetic contradictions by using 39 engineering parameters as shown in Table 16. For the first TRIZ genetic contradiction, the length of stationary object should be long to avoid user’s head inadvertently bumping the hood, but it also should be short to ensure strong suction. The length of stationary object should have two mutually exclusive properties: long and short, belonging to physical contradiction. Therefore, the Separation Principles about separation in space was used to solve this physical contradiction. The number of the recommended Inventive Principles are: No.1, No.2, No.3, No.7, No.13, No.17, No.24, No.26, No.30 (Table 3). For the actual problem,

the ‘‘No.13: the other way round’’ was firstly selected. The up exhaust hood structure was changed into the down one. Due to the cabinet is under the gas hob worktop, we proposed to nest the down exhausting hood structure in the cabinet by using the ‘‘No.7: nested doll’’. Then, the ‘‘No.17: another dimension’’ was utilized for moving the position of suction outlet from the horizontal down to the vertical side or ring. As a result, the first pair of TRIZ genetic contradiction was eliminated. For the second TRIZ genetic contradiction, if the reliability (function system) is increased, the Length of stationary object (whole size) would be deteriorated. So it was identified to technical contradiction. For the third TRIZ genetic contradiction, if ease of operation (functional space allocation) is improved, the structure

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F. Zhang et al. / Computers & Industrial Engineering 76 (2014) 60–74 Table 15 The negative relationships of PDCs. The negative relationships The first pair The second pair The third pair

‘‘20. Distance between the suction outlet and the burner’’ and ‘‘4. Distance between the rage hood and user’s head’’ ‘‘25. Function system’’ and ‘‘14. Whole size’’ ‘‘24. Functional space allocation’’ and ‘‘11. Structure’’

Table 16 The specific contradictions were translated into TRIZ genetic contradictions. The specific contradictions

Corresponding to 39 engineering parameters

(1) Solve contradiction between ‘‘20. Distance between the suction outlet and the burner’’ and ‘‘4. Distance between the rage hood and user’s head’’

Distance between the suction outlet and the burner Distance between the rage hood and user’s head

?

?

TRIZ genetic contradictions

4. Length of stationary object 4. Length of stationary object

(1) Solve contradiction in ‘‘4. Length of stationary object’’

(2) Solve contradiction between ‘‘25. Function system’’ and ‘‘14. Whole size’’

Function system Whole size

? ?

27. Reliability 4. Length of stationary object

(2) Solve contradiction between ‘‘27. Reliability’’ and ‘‘4. Length of stationary object’’

(3) Solve contradiction between ‘‘24. Functional space allocation’’ and ‘‘11. Structure’’

Functional space allocation Structure

?

33. Ease of operation 32. Ease of manufacture

(3) Solve contradiction between ‘‘33. Ease of operation’’ and ‘‘32. Ease of manufacture’’

(ease of manufacture) would be deteriorated. So it was also identified to technical contradiction. Therefore, the two pairs of technical contradictions were solved by using the Contradiction Matrix as shown in Fig. 11. In the recommended Inventive Principles: No.15, No.28, No.29, No.11, the ‘‘No.28: mechanics substitution’’ was selected to propose increasing disinfection system and microwave cooking system. In the recommended Inventive Principles: No.2, No.5, No.12, the ‘‘No.5: merging’’ was selected to advise assembling all function systems. As a result, the second and third pairs of TRIZ genetic contradiction were eliminated. In summary, the whole innovative concepts of integrated kitchen stove with gas hob, range hood, cabinet, disinfection system, microwave cooking system and the vertical side or ring suction outlet are generated. In addition, the ergonomic design principles (Section 2.4) and the six critical design area are taken consideration. Finally, by drawing sketch and using the computer-aided design software of Rhino 5.0, four ergonomic design alternatives of the integrated kitchen stove were shown in Fig. 12 (A1), (A2), (A3), (A4). Step 4: Alternatives evaluation and selection using fuzzy decision theory. We use our proposed evaluation method to selected the best alternatives.

?

We use fuzzy Delphi method to adjust the fuzzy rating and weighting by every expert to achieve the consensus condition, which obtain the importance weight of the linguistic criteria and the rating of the three decision-makers under linguistic criteria, it is shown as Tables 17 and 18, respectively. Calculate the mean of fuzzy rating and weighting, and transfer linguistic terms to positive trapezoidal fuzzy numbers; it is listed in the last column of Tables 17 and 18. Construct fuzzy decision matrix by normalizing the mean of fuzzy rating for three alternatives, it is shown in Table 19. e i ¼ ½~ ~ j t , i = 1,   , m, Aggregate the fuzzy evaluations by A xij   ½x j = 1,   , n, i.e., 2

3 2 e1 ð0:66;0:76;0:78:0:88Þ A 6e 7 6 6 A 2 7 6 ð0:64;0:74;0:74;0:84Þ 6 7¼6 6 e 7 4 ð0:68;0:78;0:82;0:90Þ 4 A3 5 e4 ð0:56;0:66;0:70;0:80Þ A

ð0:67;0:77;0:78;0:88Þ ð0:72;0:82;0:90;0:94Þ

0:50;0:60;0:65;0:75Þ 0:56;0:66;0:70;0:80Þ 2 3 3 ð1:39;1:90;2:04;2:35Þ 0:73;0:83;0:87;0:93Þ 6 7 6 7 6 ð1:28;1:70;1:86;2:27Þ 7 7 4 0:53;0:63;0:67;0:77Þ 5 ¼ 6 4 ð1:46;1:91;2:20;2:50Þ 5 0:77;0:87;0:93;0:97Þ ð1:11;1:50;1:70;2:10Þ 2

e1; A e2; A e3; A e 4 for the four Therefore, we get Aggregate fuzzy number A ergonomic design alternatives of the integrated kitchen stove respectively,

e 1 ¼ ½ð1:39; 1:90; 2:04; 2:35Þ; A e 3 ¼ ½ð1:46; 1:91; 2:20; 1:70Þ; A

e 2 ¼ ½ð1:28; 1:70; 1:86; 2:27Þ A e 4 ¼ ½ð1:11; 1:50; 1:70; 2:10Þ A

e 1; A e2; A e3; A e 4 as in the following: Hence, we can defuzzify A

e 1 ¼ ð1:39 þ 1:90 þ 2:04 þ 2:35Þ=4 ¼ 1:90; A e 1 ¼ ð1:28 þ 1:70 þ 1:86 þ 2:27Þ=4 ¼ 1:77; A e 1 ¼ ð1:46 þ 1:91 þ 2:20 þ 1:70Þ=4 ¼ 2:02; A e 1 ¼ ð1:11 þ 1:50 þ 1:70 þ 2:10Þ=4 ¼ 1:60 A Fig. 11. The contradiction matrix.

3

ð0:57;0:67;0:73;0:83Þ ð0:66;0:76;0:78;0:88Þ 7 7 7 ð0:75;0:85;0:90;0:95Þ ð0:74;0:84;0:94;0:96Þ 5

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Fig. 12. Four ergonomic design alternatives of the integrated kitchen stove.

Table 17 The importance weight of the linguistic criteria and its mean. Criteria

D1

D2

D3

Mean

Ergonomic interaction Ergonomic emotion Ergonomic performance

VH H VH

H M VH

H MH VH

(0.73, 0.83, 0.87, 0.93) (0.53, 0.63, 0.67, 0.77) (0.77, 0.87, 0.93, 0.97)

Therefore, the ordering of the four ergonomic design alternatives of e3 > A e1 > A e2 > A e 4 : A3 is the best the integrated kitchen stove is A choice for all of the alternatives. Comparing with the traditional ceiling rage hood and gas hob, the new design A3 has five aspects improvement: (1) the side suction and down exhausting structure is utilized to ensure low noise and high efficiency of sucking fumes. Keeping safe distance between the suction outlet and stove flames avoids the risk of

explosion derived from sucking flames. (2) The open lateral groove suction outlet which is easy to clean is developed. (3) The control panel is located on the table and touch-key is employed for easy to use and maintain. (4) Large capacity oil box design is located in the lower cabinet for easy to disassemble and clean. (5) The lower part of the cabinet adding embedded disinfection cabinet and microwave cooking function module are developed to achieve the versatility of the integrated kitchen stove, saving space in the kitchen. Summarily, the alternative A3 reflects a good ergonomic interaction, ergonomic emotions and ergonomic performance, well matching with the kitchen environment.

5. Discussion The integrated model for combining identification of the CSNs, the HoQ of QFD, TRIZ and fuzzy group decision-making was

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F. Zhang et al. / Computers & Industrial Engineering 76 (2014) 60–74 Table 18 The ratings of criteria item for the four ergonomic design alternatives of the integrated kitchen stove. Criteria

Items

Four ergonomic design alternatives A1

A2

A3

A4

Ergonomic interaction

Safety Dimension Comfort Save effort Easy to use Mean

MG G G G G (6.60, 7.60, 7.80, 8.80)

F G G G G (6.40, 7.40, 7.40, 8.40)

MG G VG VG VG (6.80, 7.80, 8.20, 9.00)

F G MG MG G (5.60, 6.60, 7.00, 8.00)

Ergonomic emotion

Aesthetics Style Semantics Attraction Easy to learn Maintenance Mean

G G G G MG G (6.67, 7.67, 7.83, 8.83)

MG G G MG MG MG (5.67, 6.67, 7.33, 8.33)

G VG G VG G VG (7.50, 8.50, 9.00, 9.50)

F F G MG MG MG (5.00, 6.00, 6.50, 7.50)

Ergonomic performance

Efficiency Effectiveness Function Environmental protection Save energy Mean

VG VG G VG MG (7.20, 8.20, 9.00, 9.40)

MG G G G G (6.60, 7.60, 7.80, 8.80)

VG VG VG VG MG (7.40, 8.40, 9.40, 9.60)

MG MG F G G (5.60, 6.60, 7.00, 8.00)

Table 19 Normalizing the ratings of criteria item for the four ergonomic design alternatives of the integrated kitchen stove. Ergonomic interaction

Ergonomic emotion

Ergonomic performance

A1

(0.66, 0.76, 0.78.0.88)

(0.72, 0.82, 0.90, 0.94)

A2

(0.64, 0.74, 0.74, 0.84) (0.68, 0.78, 0.82, 0.90) (0.56, 0.66, 0.70, 0.80)

(0.67, 0.77, 0.78, 0.88) (0.57, 0.67, 0.73, 0.83) (0.75, 0.85, 0.90, 0.95) (0.50, 0.60, 0.65, 0.75)

A3 A4

(0.66, 0.76, 0.78, 0.88) (0.74, 0.84, 0.94, 0.96)

innovative process and the fuzzy group decision-making method provides scientific decision-making process in order to avoid selecting the wrong alternative and wasting time and costs. Therefore, the proposed methodology can enhance the product’s quality and accelerate the innovative cycle and increase customer satisfaction index. The feasibility of the proposed methodology is demonstrated by the case of the integrated kitchen stove innovative design. Therefore, the method has great significance for product innovation and provides theoretical guidance to other ergonomic product for innovation.

(0.56, 0.66, 0.70, 0.80)

6. Conclusion proposed in ergonomic product design. And the whole process is involved in four steps: (1) Identification of the CSNs by using the data source triangulation approach and statistical analysis. (2) Establishment of the critical ergonomic design areas and the key problems by constructing the HoQ of QFD. (3) Several alternatives are generated by application of TRIZ. (4) Alternatives evaluation for selecting the best one by using the fuzzy group decision-making method. The proposed methodology makes up for deficiencies of QFD and TRIZ and ensures integrity of ergonomic product innovative design and evaluation in design stage. The CSNs are completed and reliable because the method for identification of CSNs is based on a data source triangulation approach and statistical analysis. For ergonomic product innovation, the critical ergonomic design areas and the key problems are obtained by using the HoQ of QFD. In construction of the HoQ, the CSNs are translated into PDCs for constructing CSNs-PDCs correlation matrix, which is used to identify the critical ergonomic design areas for innovation. The key problems for innovative design are obtained by analyzing interrelationship of PDCs in the roof of the HoQ. To solve the problems, the main tools of TRIZ including 40 Inventive Principles, the Contradiction Matrix, and the Separation Principles and contradiction analysis are utilized. The innovative concepts are generated by combining the solution of the recommended Inventive Principles of TRIZ, the critical ergonomic design areas and the ergonomic design principles. As a result, several alternatives of ergonomic innovative design are generated. Then, we have constructed a general and easy fuzzy group decision-making method for choosing the best alternative. The best alternative is based on the CSNs and TRIZ provides objective and specific innovative method for conflicts elimination in

In this paper, we put forward an integrated model and a multidisciplinary approach integrating identification of customer satisfaction needs (CSNs), HoQ chart of QFD, TRIZ and fuzzy group decision-making theory for ergonomic product innovative design and evaluation in the early design stages. The proposed approach comprises of four steps. In step 1, we develop a method of identification of CSNs based on a data source triangulation approach, questionnaire survey, 5-point liner numeric rating scale, factor analysis, and Cronbach’s coefficient alpha statistic for guaranteeing the completeness and reliability of the CSNs. In step 2, we establish the critical ergonomic design areas and the key problems by constructing the HoQ of QFD. In step 3, TRIZ main tools and contradiction analysis are utilized to solve the problems. Several innovative alternatives are generated by combining appropriate Inventive Principles of TRIZ, the critical ergonomic design areas and the ergonomic design principles. In step 4, we present a general and easy fuzzy group decision-making method for evaluating of the best design alternatives. The alternative with the highest score is finally chosen. The strength of our approach is the ability to improve the product design process by integrating a number of methods to give a better product design. The innovative design of an integrated kitchen stove verifies the feasibility and validity of the proposed methodology. Acknowledgements The authors would like to thank all of the anonymous referees for the comments and suggestions, which have helped to improve

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