Scholarly article on topic 'Assistive Products Development: A Framework to Respond to the Value Requirements from Users and Manufacturers Points of View'

Assistive Products Development: A Framework to Respond to the Value Requirements from Users and Manufacturers Points of View Academic research paper on "Materials engineering"

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Procedia CIRP
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{"Design model" / "assistive products" / "disabled people" / "volume and variety" / "lean development" / "mass customization" / "walking aids."}

Abstract of research paper on Materials engineering, author of scientific article — Marcel de Gois Pinto, Guillaume Thomann, François Villeneune

Abstract This article presents an Assistive Product (AP) design model built in order to respond to the requirements of persons with disabilities. This target population is heterogeneous and their needs change over time, which is a great challenge in terms of customers’ satisfaction, operational manufacturing performance, and financial results. The design model proposed is composed of design approach, containing the design principles that guide the process; and the design methodology (stages and their activities). This process was applied in a case study in the context of walking aids such as canes, crutches and walking frames was performed. This case brings insights about how to offer products variety to respond to different users in a suitable manufacturing environment.

Academic research paper on topic "Assistive Products Development: A Framework to Respond to the Value Requirements from Users and Manufacturers Points of View"

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Procedia CIRP 50 (2016) 559 - 564

26th CIRP Design Conference

Assistive products development: a framework to respond to the value requirements from users and manufacturers points of view

Marcel de Gois Pintoa , Guillaume Thomanna,b, François Villeneune

"Univ. Grenoble Alpes, G-SCOP, F-38000 Grenoble, France bCNRS, G-SCOP, F-38000 Grenoble, France

* Corresponding author. Tel.: +33 (0)4 76 57 48 43; fax: + 33 (0)4 76 57 46 95. E-mail address:


This article presents an Assistive Product (AP) design model built in order to respond to the requirements of persons with disabilities. This target population is heterogeneous and their needs change over time, which is a great challenge in terms of customers' satisfaction, operational manufacturing performance, and financial results. The design model proposed is composed of design approach, containing the design principles that guide the process; and the design methodology (stages and their activities). This process was applied in a case study in the context of walking aids such as canes, crutches and walking frames was performed. This case brings insights about how to offer products variety to respond to different users in a suitable manufacturing environment.

© 2016Published byElsevierB.V. This isanopenaccess article under the CC BY-NC-ND license (

Peer-review under responsibility of the organizing committee of the 26th CIRP Design Conference

Keywords: Design model; assistive products; disabled people; volume and variety; lean development; mass customization; walking aids.

1. Introduction

Assistive Products (AP) comprises any device, equipment, instruments and software used by persons with disability in order to protect, support, train, measure or substitute body functions or structures. They are prescribed to prevent impairments and to avoid activity limitations or participation restrictions [1]. AP design is a great challenge because the population of disabled individuals is restricted to a small and heterogeneous group whose requirements change over time.

To develop a product valued by users, firms use strategies ranging from mass produced products to customized devices. However, this decision may consider trade-offs among users' value and effects in operational performance due to the increasing product variety to respond to diverse needs [2]. This is the key aspect of our problematic on AP design given that product features are decided on design, which affect users and manufacture. In this context, the literature points some AP rejection due to poor performance (bad value) and some AP with unaffordable prices justified by their production scale [3].

Therefore, this paper treats the conflict between customer's value and companies' operational performance. Firstly, that duality was analyzed through the literature about AP design

approaches and studies about relations between product design and systems of fabrication. Next, a model of AP development was proposed and applied in a study case related to Walking Aids (WA) for personal mobility. Thus, this research brings insights about how offer products variety to respond to different users in a suitable fabrication environment. Moreover, it enables one to glimpse this model application in other AP.

2. Literature Review

Product development is defined as the conversion of a market opportunity and a set of assumptions about product technology into a product available for sale [4]. This occurs through a design process carried out through plans of action and methods that link and support the working phases [5]. Those supports are the models of design process, which are composed by some different levels of details. In the former layer one can found the design principles which are the process guidelines or the design philosophy (approach level).

In the level below we placed the methodology that contains the design steps (stages and activities) and the strategy about how to perform such steps. A design stage covers a large period of time, being based on the state of the product under design.

2212-8271 © 2016 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of the 26th CIRP Design Conference doi:10.1016/j.procir.2016.04.203

In addition, a design activity is shorter and directly related to the design actions. The model design is influenced by the levels of complexity and innovation of the project. However, as least three stages are usually present: the problem definition, the solution search (conceptual design), and the solution selection in a detailed design [5]. Taking into account those elements, the next subsections present a research that aimed to outline an AP design model composition.

2.1. Assistive products design approaches

The literature has two categories of approaches o AP design: universal and specialized. In the first, designers try to make products to be usable to almost everyone, regardless of age, ability, etc. The results are standard products for mass production [6]. In contrast, in the specialized branch, products are designed for disabled people and produced in small batches. Thus, some AP are unaffordable without funding policies.

Universal approaches are quite similar since they emerge from the barrier-free movement. That initiative intended to remove environmental barriers to mobility and, progressively, its ideas were generalized, founding the universal design (UD). This process was busted by firms that became aware to the viability of elderly and disabled people as customers, and by globalized companies that provide products adjustable to different cultures and environments. A universal designed product must respect some principles such as equitable use and flexibility in use, simple and intuitive use, perceptible information, tolerance for error, low physical effort, and size and space for approach and use [6]. The specialized approaches include adaptable design, rehabilitation design, and assistive technology. The former performs modifications in regular products to make them usable for disabled people. The second focuses on the design of products for people with a new or temporary but severe disabilities. The last designs to medical conditions and the users are patients [7].

Although those categories are presented as separated sides, in the practice approaches may evolve. For instance, the approach Design for disability has evolved and became Inclusive Design. This approach assumes that every decision may exclude people, even in UD. Thus, the source of exclusion must be identified and removed. So, there is a dilemma: designers should design for the mainstream and make products more inclusive, or design for disabled people, making products mainstream-friendly. Fig. 1 permits the analysis of this issue dividing the population into three groups: people with severe disabilities (top of the pyramid), able-bodied people (bottom), and people with reduced strength and mobility (middle) [7].

people are gradually mainstreamed. On the other hand, the universal approaches target the mainstream with more inclusive products. The two approaches meet in the middle, where products and environments intermediate characteristics. In practice, the relevant question is not which is better, a universal or specialized views, but when each branch is most suitable. There are potential benefits of cooperation between both fields, and it is mostly not largely exploited [6], [7].

2.2. Product design and manufacturing systems

The product design processes shall be aware of their impacts on downstream business activities. In this sense, manufacturing deserves a special attention given that in most cases products are introduced on existing facilities [8]. Therefore, there is a parallel between manufacturing systems and products design.

Fig. 1 - The user pyramid and design approaches [7]

The design of specialized products can be understood as a top-down strategy and products are designed for disabled

Fig. 2 - Volume-variety relationship of the manufacturing paradigms [9]

The Fig. 2 shows the volume-variety relations of paradigms of manufacturing. Design and fabrication of AP require volume and variety conciliation in order to respond to the disabled people needs with affordable costs. This indicates that lean manufacturing and mass customization are suitable models to AP context, being more detailed in the subsections below.

2.3. Lean manufacture and lean product design

Lean manufacturing organizes the activities to maximize value and eliminate waste through initiatives such value flow analysis, just-in-time etc. In this context the products are usually designed via lean product design, which is defined as cross-functional design practices governed by lean principles, some of them were used in this work [10], [11]:

• Customer value - it concentrates the process in the reaching of a deep customer understanding, centered in observation and immersion in the user's context;

• Front-loaded the process - it involves to map the design space, to explore solution alternatives and to narrow gradually the alternatives while the details are increased;

• Standardization - It involves to standardize design patterns, to standardize the design process making it predictable, and to balance the people skills to allow scheduling flexibility.

Taken into account this focus on standardization, the challenge is to reduce variation while preserving creativity. Thus, the value definition guides which standardize, which design from new, and direct the process of narrowing solutions. It concentrates the creativity to the added-value activities.

2.4. Mass Customization

Mass customization (MC) is a strategy focused on providing a large variety of personalized products via modular design, flexible processes, and supply chain integration [2]. This personalization may have many levels, as the Table 1 presents.

Table 1 - Mass customization levels. Adapted from [12]

Customization Level Description

Design It refers to collaborative projects according to

individual customer preferences

Fabrication It refers to manufacturing of customer-tailored

products following basic, pre- defined designs

Assembly It refers the arranging of modular components

into structures according to customer orders

Additional custom It refers to adding custom work to standard

work products, often at the point of delivery

Additional services It refers to adding custom services to standard

products, often at the point of delivery

Package and It refers to provide similar products in different

distribution packaging options according to market niche

Usage It refers to products that can be adapted to

different functions or situations (after delivery)

Standardization It refers to a pure standardization

MC focuses on order elicitation, design, manufacturing, and supply chain. The aspects highlighted on design are the postponement and use of platforms. The former aspect is about the customer influence on products, being based on delaying product delivery or product differentiation in downstream processes. The last aspect is the balance between component commonality and variety in order to balance the manufacturing efficiency and users' satisfaction [2].

3. Assistive products design process model

The literature permitted to outline an AP design process model (Fig. 3). The process input is a market opportunity and its outputs are the products' specifications. The process is divided into design principles (section 3.1) applied throughout the process, and the design methodology (stages and activities presented in section 3.2).



Fig. 3 - Process model for the design of assistive products

The design stages are discovery, definition, development and distribution, which are executed in a linear way and are divided into Specific Activities (SA) of design and Generic Activities (GA) of stage transition. The first two stages are divergent (ideas creation) and the last two are convergent (solutions choice). The model is adaptable to the characteristics of the product under development. The project's innovation and complexity levels determine the amount of SA activated.

3.1. Design principles

The former principle, (I) User-Centered Value Process, involves the value creation stream, the disabled person perceived value, and the value appropriation. Value creation is about the products offering, involving the whole supply chain. After, perceived value involves an interaction between the AP and the disabled person, being an assessment comparative, personal and situational. The last aspect is a financial reward to retailers, manufacturers, and suppliers.

The user-perceived value has two variables: self-oriented (own benefit) and other-oriented (benefit of others); and extrinsic (product functions) and intrinsic (product features). Table 2 shows a typology user value with these variables [13].

Table 2 - Types of customer-perceived value [13]

Extrinsic Intrinsic

Self-oriented Economic value Hedonic value

Other-oriented Social Value Altruistic value

The economic value covers product functions efficiency. The social value refers to the status and the esteem related to the product possession. The hedonic value is about the pleasure of using the product and product aesthetic. The altruistic value involves an engaged consumption. The objective is to identify what is value to a disabled user, communicate the value to the design team, and to assess and update it periodically [13].

The second principle (Fig. 4a), (II) Concurrent exploration of Alternatives, is related with how the solutions are created and evaluated. In the concurrent exploration, the idea is to map a region of solutions, to search and expand the overlaps between solutions sets according to the user value. Then, a convergence process takes place and the region of overlaps shrinks since some options are eliminated or merged. Then, ideas are detailed and tested, and a final solution is selected.






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Fig. 4 - (a) Concurrent exploration of alternatives [14]; (b) Standardization of product platform design

The last principle is about (III) Process and Product the Standardization. The design model (Fig. 3) standardizes the process. In turn, the product patterns standardization (Fig. 4b) is about the definition transversal platforms to the product architecture and the use of standard components shared across different products. It initiates with the identification of mainstream, universal and AP with similar functions. After, the products are analyzed in terms of functions and architecture in order to identify specific and transversal functions among them. That leads the design problem to a high level of abstraction, and designers can propose a generic functional structure to fill with modules according to user's profiles.

3.2. Design methodology (stages and activities)

The design process (Fig. 3) is composed of stages that are divided in SA and connected by GA. The SA of the stages are organized in cycles, or spirals when the variable time is added. The spirals overlaps represent the concurrent engineering and GA (1 to 5 in the Fig. 3). The former GA is |1| to analyze the stage results to check if design principles were taken into account. After, the team needs to |2| plan the following phase, what includes forecast about activities and resources. Next, in the end of SA, the team shall |3| document and communicate the stage results and |4| analyze the results to validate decisions and improve then. Finally, the team |5| document lessons learned to support continuous improvement of the process. In turn, the SA of a stage (Fig. 5 ) are performed according to the type of AP under design.

Fig. 5 - Specific activities from each design stage

The Discovery Stage (Fig. 5 a) is responsible for obtaining a deep comprehension of the design context in order to explicit what is value to the person with disabilities. In view of this, the former activity is the Determination of Product Functions. This activity is guided by AP classifications and international taxonomies of disability. Those documents allow the product families identification that responds to similar users profiles.

The following activity is the Characterization of Users, which means to identify medical aspects of disability profiles, to observe situations of AP use, to discuss with users, relatives, and caregivers to understand the needs, aesthetical preferences, and create emotional connections with the user. The positive aspect of disability must be examined, such as remaining skills of a person and skills developed due to the disability status.

In parallel, an Analysis of Related Products may be done in the current solutions proposed to the users. For such, some AP may pass through a teardown process in order to assess features such product morphology, architecture, level and types of customization, etc. It permits the identification of improvement opportunities and the identification of intersection among assistive, universal, and mainstream products.

Finally, a Characterization of the Environment of the AP use should be done because it influences the product performance. It includes the physical aspects but also human relationships, and services and policies concerning people with disabilities.

In the Definition Stage (Fig. 5b) the AP concept is defined through the Discovery outputs (disabled person value). The stage starts with a Functional Modeling to specify the technical functions, i.e. the product purpose. It is divided into operative functions, related to the transformation of energy, and the structural functions that ensure the product stability. The AP modeling is done at the platform level, resulting in a more flexible structure. After, the Ergonomic and Aesthetics functions (interactive functions), are added to those techniques listed before. They cover the interface between the product and the disabled user, enhancing the product use in physiologic, anthropometric and cognitive terms.

The next activity involves a creative process of Solutions Alternatives creation. Techniques of creativity allow the conception of several solutions for the listed functions and that will be developed concurrently. Technical, ergonomic, and aesthetical functions must be considered equally important. If possible, such aspects should be considered concurrently.

Finally, the AP concepts are embodied in a flexible Product Architecture. It is the scheme by which the functional elements of the product are arranged into physical chunks or modules. Some variables must be defined, as the stability of the function allocated to the component, the final product configuration, and the nature of the interface between components.

The process enters in the Development Stage (Fig. 5c). The team defines values for the design parameters, tests and validates the performance of different product concepts. The first activity of development stage is the Systems Description, where designers develop product details such as dimensions, tolerances, materials etc. This activity is related with to the technology of the AP under design. In parallel, the design team proceeds the Suppliers Involvement according to the type of implication of them in the development work and the importance of parts provided.

After, the activity of Product Optimization comprises the test and validation of product features through functional prototypes. It may confirm the design or provokes changes in the systems descriptions (internal or from suppliers). These project updates depend on the accomplishment of three groups of requirements: if the user-defined value is satisfied, if legal or normative requirements are respected, and if product defined features respect the manufacturing system constraints. This prototyping is the last building test to validate the product and its manufacture. Finally, Product Documentation takes place. It comprehends the detailed information to communicate the product features to some process such as manufacturing, certification and patent authorities, marketing and sales etc.

Finally, the Distribution stage (Fig. 5d) in charge of the connection between designers and users. It includes the prediction of customer influence in terms of customization possibilities. The first activity is to develop the processes of assembly and fabrication, their technology and operations. Under the AP design point of view, the designs must define which modules can be assembled or manufactured according to disabled user orders. In the same way, Package and distribution, Sales Approach and After Sales Monitoring processes need to be defined. Those processes must be foreseen in their operational terms, which include the level of influence of the person with disabilities in each process.

4. Walking Aids design

This section presents the study case carried out in the context of WA devices. This family of products comprehend AP such as canes, crutches and walking frames. Differences in the walking patterns leads users to different WA, and the respect to such variability was the focus of this case study.

4.1. Discovery of the walking aids devices

This stage begins with the determination of products functions. For this, the norm ISO 9999: 2011 was used given that it brings a large classification of AP for persons with disability. Additionally, the relations between the norm and the International Classification of Functioning, Disability and Health (ICF) were helpful to indicate aspects of user's profiles and activities and participations allowed by the WA. The class of AP for personal mobility brings 3 subclasses of WA, which are detailed into their categories in Table 3.

Table 3 - Types of walking aids devices



WA manipulated by one arm

Canes, Canes with seat, Canes with three or more legs, Auxiliary crutches, Elbow crutches and Forearm support crutches

WA manipulated by both arms

Lateral support frames, Walking frames, Rollators , Walking chairs, Walking tables

Tips for WA; Products to properly grip WA; Seats for WA; Accessories to help manoeuvre WA; Accessories to adjust height of WA; Tyres and wheels; etc.

Accessories for AP for walking

The analysis of the WA categories (without the accessories) permitted to propose some platforms. The first alternative was to divide the family into three platforms (canes, crutches, and frames). The second option was to design WA in two platforms (canes and crutches, and frames). The last was to design WA as a single platform structured in tubular elements.

Moreover, the ICF body functions concerning the WA users is the same for all the whole family [15]. Thus, all the WA are supposed to be applied in movement patterns associated with walking, running or other whole body movements (ICF code b770). The activities and participation (with their ICF codes) allowed by the WA categories are presented in Table 4.

Table 4 - Activities and participation supported by the WA [15], [16]

Category Activities and participation

d450 d460 d410 d415

Canes x x

Canes with seat x x x

Canes with 3 or more legs x x

Auxiliary crutches x x

Elbow crutches x x

Forearm support crutches x x x

Lateral support frames x x

Walking frames x x

Rollators x x

Walking chairs x x

Walking tables x x x x

The code d450 is about walking along a surface on foot, step by step, so that one foot is always on the ground. The code d460 refers to moving around in different locations and the code d415 treats of the maintaining of a body position such as remaining seated or remaining standing. Finally, the code d410 is about changing the basic body position, such as getting into and out of a body position and moving from one location to another, such as getting up out of a chair to lie down on a bed, and getting into and out of positions of kneeling or squatting [16]. One may verify that d450 and d460 are transversal to all the WA, while d410 and d415 are specific for some categories.

Once determined the global functions of the products, the next activity was to search a deeper knowledge into the users' profiles. Hence, we proceeded discussions with medical staff, observations of patients using WA, and reed some scientific papers on the topic. This research allowed the determination of the main functions of WA devices: compensation of loss of balance and to weight bearing due to weakness in the lower limbs. It may include impairments such as spastic gait, hemiplegic gait, paraplegic gait, limping and stiff gait pattern.

To increase balance and permit the weight bearing the WA provide an extension of the user's base of support. The Fig. 6 was built in a collaborative work with physiotherapists in order to show the differences among the WA devices. In addition, we studied the walking patterns of the people using those devices.

Fig. 6 - Assistance provided by each WA category

Next, we proceeded an analysis of WA present in the market. For this, we selected 200 products and proceeded a teardown analysis of their features. We verified that most WA are not customizable, and those whose permit some customization concentrate it on size setting during usage, and aesthetics choices during the selection and purchase. Mass customization were not found. Moreover, the analysis of products' architecture showed that the whole WA family should be assembled with four systems: structure, handling and support, ground contact and additional elements.

Finally, in the characterization of the environment of WA, we verified that WA are used in internal and external contexts. WA may be used to walk between rooms in a house, within a building, or down the street of a town, to go to work or school, etc. Thus, WA use is affected to several physical barriers that may lead the user to be blocked or fall down. In terms of acceptance, we verified that WA are well-accepted by the user entourage, but they are usually rejected by the user due to stigmatization caused by the appearance of the products.

4.2. Definition of the walking aids devices

4.4. Distribution of the walking aids devices

The technical and interactive functions of WA focused weight bearing allowing and the boss of support increasing. They composed the main technical functions. Next, the ergonomics aspects were focused in adjustment of the product handling, sizing settings, and reduction of WA weight. Finally, the aesthetics sought to remove the medical appearance of WA devices and aspects that may denounce the aging process.

Table 5 - Cross architecture of WA with accessories from ISO 9999

System Subsystem Accessories

Product structure Tubular elements Structure connections Accessories to adjust height

Support for the disabled person Handling elements Additional support Other elements of support Accessories to help manoeuvre; products to properly grip Accessories to provide support for specific parts of body; Seats Pads and cushions to prevent bruising or skin injury

Ground contact Contact elements Additional contact Tips Tyres and wheels

Appendices Safety elements Facilities Lights and safety signalling devices Accessories to hold or carry objects; WA holder (when WA is not in use)

The alternative solutions search streamed in the sense of single platform structured in tubular elements. In this product architecture, the whole products of WA family may be assembled with structural elements and be completed by accessories for WA. This is shown in Table 5. The product concept proposition were sketched in freehand drawings.

4.3. Development of the walking aids devices

This stage started with the systems description, which represents the product embodiment into pieces, subassemblies, and modules that compose a library of product chunks. Such elements were developed in order to allow the assembly of the WA presented in the Fig. 6. Moreover, the design team tried to minimize the number of modules developed, which was achieved through the use of the Table 5 to develop parts shared cross the whole WA family. Then, the product optimization activity was performed through prototyping activities. It allowed parts evolution, in terms of format and assembly simplification. We did not involve suppliers in our case study, because it was developed in academic environment with theoretical purposes. Thus, the stage finished with product documentation. Some developed WA are shown in the Fig. 7.

Fig. 7 - WA developed in the case study

Finally, the last stage of distribution was performed in order to define the processes of assembly and fabrication, package and distribution, sales approach, and after sales monitoring. The former AP design stages were performed with regard to the impact of the product features in the distribution processes. Thus, MC strategy may be used in any of these processes. Moreover, AP design model of the case study allows product variety not only in terms of changes in the same product, but customization of diverse products using the same modules in order to respond to different technical and interactive needs.

5. Concluding remarks

This article aimed to propose a design model for the development of assistive products destined to disabled people. For this, a literature research was performed in order to identify which elements should be provided by this type of framework. As a result, we outlined a generic hierarchical model composed of design principles and design methodology. The proposed framework was tested in a scientific research environment in order to validate it. This was done in the personal mobility area with studies completed in the WA context. This case study allowed the development of a generic platform to assembly canes, crutches and different types of walking frames and improve details of the model in the practice. A second case study focused on the design of non-motorized vehicles is under development in order to validate the model.


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