A multi-criteria ergonomic and performance methodology for evaluating alternatives in “manuable” material handling

International Journal of Industrial Ergonomics 43 (2013) 314e327

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A multi-criteria ergonomic and performance methodology for evaluating alternatives in “manuable” material handling Diana Rossi*, Enrico Bertoloni, Marco Fenaroli, Filippo Marciano, Marco Alberti Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze, 38, 25123 Brescia, Italy

a r t i c l e i n f o

a b s t r a c t

Article history: Received 18 September 2012 Received in revised form 3 April 2013 Accepted 23 April 2013 Available online 19 June 2013

The objectives of this study were: 1) to develop an efficient multi-criteria approach for choosing the optimal alternative for “manuable” material handling, and 2) to apply the multi-criteria approach to a case study. In this paper, the authors use the single-word term “manuable” to refer to the definition “can be performed manually”. The case study results indicated that the use of the manipulator tested in this work may be preferable to manual material handling in situations in which the lifted weight is large (61% vs. 39%) as well as those situations in which the weight of the load could not apparently justify the investment necessary for a manipulator (53% vs. 47%). The case study also validated the selected approach. Furthermore, the applicability of the methodology was confirmed by the CEO of an Italian logistics and supply chain management company (Blu Pegaso S.r.l.). Relevance to industry: This paper provides to the decision manager a structured approach regardless of industry and country for selection of the best alternative for manuable material handling that is able to satisfy the company objectives related to ergonomic criteria and production performance measures. The methodology also supports manufacturers of material handling devices in the optimisation of their products. Ó 2013 Elsevier B.V. All rights reserved.

Keywords: Manual material handling Intelligent assist devices Analytic hierarchy process Human factors Multi-criteria analysis Production performance

1. Introduction Manual material handling (MMH) tasks may expose workers to several risk factors, mainly of the physical type. If performed repeatedly or over long periods of time, these tasks can lead to overwork and injury. The main risk factors or conditions associated with the development of injuries in MMH tasks include:





Awkward postures (e.g. bending, twisting); Repetitive motions (e.g. frequent reaching, lifting, carrying); Forceful exertions (e.g. carrying or lifting heavy loads); Pressure points (e.g. grasping [or contact from] loads, leaning against parts or surfaces that are hard or have sharp edges);
Static postures (e.g. maintaining fixed positions for long periods of time). Repeated or continual exposure to one or more of these factors may initially lead to fatigue and discomfort (Van der Beek et al., 1999). Over time, injury to the back, shoulders, hands, wrists, or other parts of the body may occur. Injuries can include damage to

* Corresponding author. Tel.: þ39 (0) 303715725; fax: þ39 (0) 303715722. E-mail address: [email protected] (D. Rossi). 0169-8141/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ergon.2013.04.009

muscles, tendons, ligaments, nerves, and blood vessels (NIOSH, 2007). Repetitive high-exertion lifting is a major contributor to injuries of the low back (Resnick and Chaffin, 1997), and MMH activities are a significant source of worker absence and high costs due to compensation claims. Numerous investigations have demonstrated the association between unassisted manual material handling and increased risk of musculoskeletal injury occurring particularly in the low back and upper extremities (Nussbaum et al., 2000). The relevance of this issue is also evidenced by the European Council Directive 90/269/EEC of 28 May 1990 (Council of European Communities, 1990), which highlights this problem as a risk factor and calls for the assessment and definition of manual load handling as “transporting or supporting of a load, by one or more workers, including lifting, putting down, pushing, pulling, carrying or moving of a load, which, by reason of its characteristics or of unfavourable ergonomic conditions, involves a risk particularly of back injury to workers”. Specifically, the general provision of the Directive obliges the employer to take appropriate organisational measures or to use the appropriate means (e.g. mechanical equipment) to avoid the need for manual load handling by workers or, at the very least, to reduce the risks involved in manual load handling. Consequently, manufacturing engineers specify the use of material handling devices (MHDs) to eliminate or reduce the lifting requirements in MMH in many industrial facilities. These devices

D. Rossi et al. / International Journal of Industrial Ergonomics 43 (2013) 314e327

are used to assist in such diverse tasks as assembly, racking, palletising and other jobs that may include both vertical and horizontal translation (Resnick and Chaffin, 1997). Among the major MHDs mentioned are chain blocks, cranes, hoists, industrial manipulators, jib cranes and overhead cranes. The authors have focused their attention on industrial manipulators because these devices are better suited to the tasks considered in this study: the handling of moderate loads (manuable material handling). The definition of a manipulator given by the European Committee for Standardization is a “powered machine, where the operator has to be in contact with the load or holding device, in order to guide and/ or control the motion of the load to bring it to a position in space” (EN 14238, 2009). The basic function is simple: to eliminate the magnitude of the static (gravitational) load that the worker must handle, with an expected reduction in musculoskeletal stresses. Even if manipulators exist for this purpose, their use can be ineffective because it requires significant dynamic forces due to large system inertias and forced pace production. Woldstad and Chaffin (1994) state that many MHDs do not always decrease the workload or the workload as perceived by the operator. In addition, a number of informal interviews with workers who use these devices have revealed that, in many cases, the workers find using the devices equally as fatiguing as actually lifting and carrying the load. Indeed, in a situation where the load is only marginally heavy (i.e. 30e50 lbs, approximately 13.6e22.7 kg), it is not unusual to see the assist devices discarded in favour of manual methods. For moderate loads, manipulators are often discarded after installation, and the operators do not always report decreases in perceived workload when using them (Nussbaum et al., 2000). Nussbaum et al. (2000) also claims that a significant time penalty is incurred when using manipulators, especially in jobs with relatively short cycle times. Rossi et al. (2012) defined a methodology to select the best solution to perform a task from an ergonomic point of view. However, the analysed papers rarely propose a comparison of the performance of the different handling solutions as well as a cost-benefit analysis. In any case, the literature presents several articles that address problems of production performance with the support of multicriteria methodologies (e.g. Byun (2001), Vinodh et al. (2012), and DiDomenico and Nussbaum (2011)) but without treatment of the performance of the industrial manipulators. In light of this evidence, the authors have carried out a study to select the best handling solution for short-distance movements of moderate-load objects considering both ergonomic criteria and production performance. The best handling solution is assumed as the alternative that best satisfies the company objectives. The study develops a systematic approach using the analytic hierarchy process (AHP), a decision support methodology for multicriteria analysis that enables the combination of tangible and intangible criteria. Various ergonomic methods are available for the assessment of exposure to workplace risk factors for work-related musculoskeletal disorders (David, 2005). So the purpose is to support the integration of the results of those ergonomic methods, although the standardised methods for the ergonomic evaluation of manual handling (ISO 11228-1, 2003; ISO 11228-2, 2007; ISO 11228-3, 2007) are generally applied separately (Cocca et al., 2008). The authors chose this method because it is suitable for resolving complex multi-criteria decision problems by ranking of decision alternatives followed by selection of the best alternative under multiple objectives (Okur et al., 2009; Lee et al., 2009; Saaty, 2008; Hsu and Chen, 2007). 2. Material and methods The basic problem of decision-making is to choose the best option from a set of competing alternatives that are evaluated

315

under conflicting criteria. The AHP is a multi-criteria decisionmaking tool developed in the 1970s by Saaty (1980) to solve a specific class of problems that involve prioritisation of potential alternative solutions that considers both qualitative and quantitative criteria (Henderson and Dutta, 1992). This technique consists of a systematic approach based on breaking the decision problem into a hierarchy of interrelated elements. Such a structure clarifies the problem and presents the contribution of each of the elements to the final decision. Two features of the AHP differentiate it from other decisionmaking approaches. First, it provides a comprehensive structure that combines the intuitive rational and irrational values during the decision making process. Second, the AHP has the ability to judge the consistency in the decision-making process (Akarte et al., 2001). The advantage of the AHP is its flexibility, ease of use, and the ability to provide a measure of the consistency of the decision maker’s judgment (Park and Lim, 1999). In addition, this method allows the incorporation of tangible and intangible factors that would otherwise be difficult to take into account. The AHP has been used in almost all applications related to decision-making. Vaidya and Kumar (2006) critically analysed a subset of the papers with applications of the AHP published in international journals of high repute and gave a brief summary of many of the referred publications. Subramanian and Ramanathan (2012) reviewed the literature on the applications of the AHP in operations management and suggested possible gaps from the point of view of both researchers and practitioners. They also found that the AHP was predominantly used in the engineering, personal and social sectors. The references were grouped by region and year to track the growth of AHP applications. The AHP has been applied for many purposes (e.g. selection, evaluation, allocation, etc.) and in different areas of applications (e.g. personal, social, manufacturing, political, engineering, education, sports, etc.). Briefly, and according to Saaty (1980), Saaty (1987, 2008), the step-by-step procedure in using AHP is the following. 1. Structuring of the decision problem into a hierarchical model This includes decomposition of the decision problem into factors that are important for the decision. These factors are arranged in a hierarchic structure having various levels: from the top (i.e. the Goal, an overall objective) through intermediate levels (i.e. elements: Strategic Criteria, Criteria, Sub-criteria, .) to the lowest level (i.e. the decision alternatives). 2. Making pairwise comparisons and obtaining the matrices of element evaluation In this step, the elements of each level are compared pairwise, weighting them as a function of their importance for corresponding element of the higher level. The aim is to construct a set of pairwise

Table 1 Scale of relative importance according to Saaty (1980) and Saaty (1987). Intensity of importance

Definition

1 3 5 7 9 2, 4, 6, 8 Rationals Reciprocals

Equal importance between Ai and Aj Weak/moderate importance of Ai over Aj Essential or strong importance of Ai over Aj Demonstrated/very strong importance of Ai over Aj Absolute/extreme importance of Ai over Aj Intermediate Ratios arising from the scale If Ai has one of the above numbers assigned to it when compared with Aj, then Aj has the reciprocal value when compared with Ai

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comparison matrices for each of the lower levels of elements. An element in the higher level governs the elements in the lower level. Following each branch point in the hierarchy, the importance of each element is compared, in turn, with every other element immediately below that branch point. A matrix of element evaluation, denoted as A, will be formed using the comparisons. Each entry aij of the matrix, in the position (i, j), is obtained comparing the row element Ai with the column element Aj:

2

a11 6 a21 6 6 a31 6 A ¼ 6 6 « 6 ai1 6 4 « an1

a12 a22 a32 « ai2 « an2

a13 a23 a33 « ai3 « an3

. . . 1 . « .

. . . « . « .

a1j a2j a3j « aij 1 anj

3 a1n a2n 7 7 a3n 7 7 7 7 ain 7 7 5 ann

where: aij is the relative importance of the element Ai respect to the element Aj. The comparison of any two elements Ai and Aj with respect to the higher level element is made using questions of the type: “How much more is the element Ai preferred over the element Aj under the higher level element?”. Saaty (1980) suggests the use of a 9point linguistic scale to convert the verbal responses into numerical quantities representing the values of aij. The scale is explained in Table 1. The entries aij are governed by the following rules: aij >0; aji ¼ 1/ aij; aii ¼ 1 for i, j ¼ 1, 2, ., n. Because of the above rules, the pairwise comparison matrix A is positive and reciprocal (Saaty, 1987), and it can be rewritten:

2

1 6 1=a12 6 6 1=a13 6 A ¼ 6 6 « 6 1=a1j 6 4 « 1=a1n

a12 1 1=a23 « 1=a2j « 1=a2n

a13 a23 1 « 1=a3j « 1=a3n

. . . 1 . « .

a1j a2j a3j « aij 1 1=ain

. . . « . « .

3 a1n a2n 7 7 a3n 7 7 7 7 ain 7 7 5 1

3. Determining local priorities of elements After the matrices of element evaluation have been developed, the next step is to calculate a vector of local priorities or weights of elements in the matrix A. In terms of matrix algebra, this consists of calculating the principal eigenvector w of the matrix using the following formula, and then normalising it to sum to 1.

A w ¼ lmax w where: lmax is the largest eigenvalue of the matrix A and the corresponding eigenvector w contains only positive entries. When the vector w is normalised, it becomes the vector of local priorities of the elements with respect to the element of the higher level. 4. Verifying the consistency of comparisons Once the local priority vector has been determined, it is then necessary to evaluate the consistency of the pairwise comparison matrix. When a positive reciprocal matrix of order n is consistent, the largest eigenvalue has the value n. When it is inconsistent, the largest eigenvalue exceeds n and its departure from n serves as an indicator of inconsistency by forming a measure called the Consistency Ratio (CR), defined as:

CR ¼ CI=RI where: CI is called the Consistency Index and RI the Random Index. CI is given by:

CI ¼ ðlmax  nÞ=ðn  1Þ where: n is the order of the matrix A. RI is the CI of a randomly generated reciprocal matrix using the 9-point linguistic scale. Saaty (1980) provided average consistencies (RI values) of randomly generated matrices for a sample size of 500. These values are shown in Table 2, for matrices of different orders. If the CR of the matrix is high, it means that the input values are not consistent, and hence are not reliable. In general, a CR of 0.10 or less is considered acceptable. If the CR is higher, the comparisons need to be revised in order to improve their consistency. All positive reciprocal matrices of order 2 are consistent. 5. Making pairwise comparisons, obtaining the matrices of alternative evaluation, determining local priorities of alternatives and verifying the consistency of comparisons In this step, using a very similar procedure (steps 2, 3 and 4), the local priorities of alternatives with respect to each element of the lowest level can be estimated. In particular, the alternatives are compared pairwise, scoring them as a function of their relative preference with respect to each element of the lowest level. The comparison of two alternatives Mi and Mj is made using questions of the type: “How much does the alternative Mi benefit over the alternative Mj under the element?”. The matrices of alternative evaluation are consequently developed; it is possible to calculate a vector of local priorities or scores of alternatives and to verify the consistency of comparisons. 6. Determining global priorities of alternatives In the last step, the local priorities (scores) of an alternative with respect to each element of the lowest level are multiplied by the corresponding local priorities (weights) of element of the lowest level. The sum of these products is the global priority or final score of the alternative. Determining global priorities of all alternatives, it is possible to obtain the rating of the alternatives in achieving the goal of the decision problem. To implement the AHP process and construct the hierarchy presented in this paper, the authors carried out a thorough literature review of the existing guidelines and technical standards in dealing with material handling from ergonomic and production points of view. The information and knowledge provided by the manufacturers allowed the authors to better understand the features and function of the available manipulators. 3. Results and discussion The definition and the construction of the hierarchy required significant time resources, discussions, research and analyses. According to the step 1 of the AHP procedure in Section 2, this activity entailed the formulation of an appropriate hierarchy based on the AHP model consisting of a Goal and three levels of elements (Strategic Criteria, Criteria, and Sub-criteria). The Goal is to satisfy the company objectives with consideration of ergonomic and productive elements. The Strategic Criteria are Ergonomics and safety performance and Production performance. There are 5 Criteria related to Ergonomics and safety performance, namely Anthropometry and biomechanics, Cognitive

D. Rossi et al. / International Journal of Industrial Ergonomics 43 (2013) 314e327 Table 2 Random Index values (Saaty, 1980). n

1

2

3

4

5

6

7

8

9

10

RI

0.00

0.00

0.58

0.90

1.12

1.24

1.32

1.41

1.45

1.49

GOAL

ergonomics, Work environment, Work management, and Safety. The Criteria associated with Production performance are Productivity, Adaptability, Capability, and Flexibility. The last level of the hierarchy is composed of 34 Sub-criteria, which are described in Section 3.1 and grouped with respect to the nine previously mentioned Criteria. The elements have been identified after a detailed study of the scientific literature and technical standards, discussions with experts and visits to companies that produce or use industrial manipulators as well as logistics centres. The main sources of hierarchies relevant to choose the optimal alternative for “manuable” material handling were: Jung and Jung (2001), Chan et al. (2001), and Henderson and Dutta (1992). Jung and Jung (2001) decomposed the focus “Intensity of perceived workload” into a hierarchy of 4 Criteria (physical job demand, environmental factors, postural discomfort, mental job demand) and 13 Sub-criteria: weight, frequency, duration, and distance for physical job demand; working climate, lighting, noise, vibration, and exposure to chemicals for environmental factors; standing, stopping, squatting, and twisting for postural discomfort. The elements concern only ergonomic and safety aspects. To evaluate these elements, their benefit was not stated, the indicators were defined as sets of linguistic values. Chan et al. (2001) developed a hierarchy for “The best commercial AVG model selection” providing 4 Criteria and 15 Subcriteria: performance measures with speed, load capacity,

accuracy, efficiency, and repeatability; technical with maintenance, convenience, compatibility, technological risk, and safety; economic with initial cost, and operating cost; strategic with flexibility, manufacturer, and future plan. The elements concern both production performance and ergonomics and safety performance. However, the latter is represented by one Sub-criterion without further specifications. Henderson and Dutta (1992) used the AHP in analysis of ergonomics guidelines. They focused on manual lifting utilising 9 Criteria that are the main risk factors (ISO 11228-1, 2003): frequency of lifting, distance lifted, height lifted, size of load, design of load, location of load, worker’s size, worker’s gender, worker’s age. Other types of manual material handling (i.e. pushing, pulling, carrying, and moving of a load) and Criteria of production performance were not considered. Other authors focused their attention only on the ergonomic elements, but referring to usability analysis. For example, Park and Lim (1999), and Delice and Güngör (2009) defined hierarchal structures to evaluate the user interfaces, software, and web sites. Also in the context of Cellular Manufacturing Systems (CMS) and Flexible Manufacturing Systems (FMS) the selection criteria are not sufficiently detailed for the construction of the hierarchy of this work. Lashkari et al. (2004), and Sujono and Lashkari (2007) proposed models of operation allocation and material handling system selection. To realise the selection they evaluated the compatibility and the costs for different material handling operations carried out by an equipment or manually. The purpose of the models is to assign the material handling equipment to the operation so as to minimise the total costs and to maximise the compatibility, without explaining the elements analysed.

Satisfaction of company objectives

Strategic Criteria

Criteria Sub-criteria

317

Ergonomics and safety performance

Anthropometry and biomechanics

Cognitiv e ergonomics

Work env ironment

Metabolic activity level

Easy to understand

Thermal environment

Lifting and carrying

Easy to use

Lighting environment

Pushing and pulling

Risk perception

Noise exposure

Repetitive handling at high frequency

Mental stress

Space demands

Work management

Production performance

Saf ety

Productiv ity

Adaptability

Capability

Competence and training

Mechanical hazards

Production capacity

Generality

Efficiency

Work experience

Work clothing and PPE

Investments costs

Elasticity

Effectiveness

Shift work and suitable population

Postures

Motivation and satisfaction

Visual requirement

Training procedures

Operating costs

Accessibility and reach zones Comfort of use

Fig. 1. Schematic representation of the hierarchy.

Customer satisfaction Corporate image

Flexibility

Required space Constraints on the layout

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Some authors suggest other approaches to select material handling equipment. Tuzkaya et al. (2010) proposed a fuzzy multicriteria decision methodology defining 4 Criteria (Operational, Economical, Environmental, and Strategical considerations) in order to determine the most convenient industrial truck alternative. Risks (safety) are considered an indicator of the Strategical considerations. Welgama and Gibson (1995) presented a model to minimise the total handling costs and the total aisle space. Hassan (2010) proposed a framework to compare candidate classes of equipment with the aim of satisfying requirements, objectives and functions. In comparison with the hierarchies present in the literature, e.g. Jung and Jung (2001), the authors have developed the ergonomic Strategic Criterion using a different approach due to the specific application of their hierarchy. For example, some elements, such as Exposure to chemicals, were not included because they were considered not significant in this case. Other elements, however (e.g. Exposure to vibration) are not present because other complementary factors are already included in the hierarchy. Elements considered particularly relevant were detailed and reorganised (e.g. Sub-criteria of Anthropometry and biomechanics). Particular attention was given to international standards since they give the state of art specifications for products, services and good practices. The authors searched in the databases of the International Organisation for Standardisation (ISO), of the European Committee for Standardization (CEN) and of the British Standards Institution (BSI), browsing by the International Classification for Standards (ICS): mainly 53 “Material handling engineering” (in particular 53.020.20 “Cranes”), 13 “Environment. Health protection. Safety” (in particular 13.180 “Ergonomics”, and 13.110 “Safety of machinery”) and 03 “Services. Company organization, management and quality. Administration. Transport. Sociology” (in particular 03.120 “Quality”, 03.100.01 “Company organization and management in general”, and 03.100.50 “Production. Production management”). The relevance of international standards is that they are developed in an open process, reflecting the views of many stakeholders including technical experts, government representatives and consumers. The authors defined the elements of the hierarchy referring to the standards in order to facilitate its application. Companies usually have a greater familiarity with the technical standards than the scientific literature. Furthermore, the decision maker generally can consult and follow the standards regardless of industry and country. In the light of the literature review, the hierarchy proposed by the authors is more complete than other hierarchies. In fact, the set of elements is more numerous and wide considering ergonomics, safety, and production aspects. 3.1. Hierarchy and element evaluation The elements of the hierarchy developed by the authors are grouped according to homogeneity, and a level may consist of one or several homogeneous groups. The elements in each level may be regarded as constraints, refinements or decompositions of the element above. The data thus obtained are summarised to formulate the AHP hierarchy, as shown in Fig. 1. According to the step 2 of the AHP procedure in Section 2, the question of how to evaluate the elements with respect to the element above must be defined; an example application for the pairwise comparison is the following: “How much more is Metabolic activity level preferred over Lifting and carrying under the “Anthropometry and biomechanics” Criterion?”. The syntax used is: Sub-criterion: benefit [indicators (standards)]. An example is “Metabolic activity level: requires less physical effort and therefore has a lower metabolic energy cost [metabolic rate (ISO 8996,

2004)]”, where “Metabolic activity level” is the Sub-criterion, “requires less physical effort and therefore has a lower metabolic energy cost” is the “benefit”, “metabolic rate” is the “indicator” and “ISO 8996, 2004” is the “standard”. Based on this syntax, it is possible to construct the questions for the pairwise comparisons. The value obtained from this comparison is included in the corresponding matrix. The typical method used to phrase a question to fill an entry in the matrix of comparison is: when considering two elements, Ai on the left side of the matrix and Aj on the top, which has more of the property or which one better satisfies the element above, i.e. which one is considered more important under the element above and how much more (using the fundamental scale values)? This value yields aij; the reciprocal value is then automatically entered for the transpose (Saaty, 1987). To make such comparisons and properly formulate the questions, the authors propose the following meanings attributed to the hierarchy Sub-criteria (in alphabetical order):
Accessibility and reach zones: can be used by a larger number of people from a population with the widest range of characteristics to achieve a specified goal in a specified context of use [work area clearance, size of objects, action demand, coordination demand, stability demand (ISO 26800, 2011; ISO 14738, 2002)].
Comfort of use: allows a better physical interaction between specified users and command devices to achieve specified goals in a specified context of use [device characteristics, quality of gripping (ISO 26800, 2011; ISO 11228-3, 2007; EN 1005-5, 2007)].
Competence and training: requires lower training needs associated with its occupational health and safety risks [roles and responsibility, skills and knowledge, awareness, ability, information and training (OHSAS, 18001, 2007)].
Constraints on the layout: puts fewer constraints on the surrounding areas and other workstations if the distribution of space changes [sizes, potential incompatibilities with other activities (EN 15221-4, 2011)].
Corporate image: allows a better sum of impressions and expectations built up in the mind of stakeholders [perceived added value, impact on brand perception (BS 7000-10, 2008)].
Customer satisfaction: allows a greater customer perception of the degree to which the customer’s needs or expectations have been fulfilled [customer satisfaction feedback, gap between the customer’s expectation and perceived experience (ISO 9000, 2005; ISO 10004, 2012)].
Easy to understand: allows better perceptive and cognitive interaction between specified users and information devices to achieve specified goals in a specified context of use [task characteristics, information device characteristics, personal details, skills and knowledge, personal attributes (ISO 26800, 2011; ISO 9241-11, 1998)].
Easy to use: allows better perceptive and cognitive interaction between specified users and command devices to achieve specified goals in a specified context of use [task characteristics, command device characteristics, personal details, skills and knowledge, personal attributes (ISO 26800, 2011; ISO 9241-11, 1998)].
Effectiveness: allows a better quality of results in terms of integrity and accuracy of unit loads [stability during storage, stability during handling, stability during transportation (ISO 9000, 2005; ISO 10531, 1992; ISO 3534-2, 2006)].
Efficiency: requires less time to achieve a unit load [processing time for a unit load, possible use of standard unit load (ISO 9000, 2005; ISO 3676, 2012)].

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Elasticity: allows a greater possibility of changing the volume within limited time and costs [present volume of products/ activities, predictable variability of the volume of products/ activities, need for adaptation of devices or processes (EN 15221-4, 2011)].
Generality: allows a greater possibility of changing the function in terms of range of products/activities with limited time and costs [core products/activities, predictable variability of the type of products/activities, need for adaptation of devices or processes (EN 15221-4, 2011)].
Investment costs: requires a lower initial monetary investment [costs of acquisition or costs of design and implementation, possible incentives (EN 1325-1, 1996)].
Lifting and carrying: requires less force in performing lifting or carrying tasks [mass of object, lifting and carrying frequency, work and object position, quality of gripping, cumulative mass, distance of carrying (ISO 11228-1, 2003; EN 1005-2, 2008)].
Lighting environment: guarantees a greater visual comfort considering the required work tasks [illuminance and its distribution, luminance and glare, directionality, colour aspects, type of visual work tasks (ISO 8995-1, 2002; EN 12464-1, 2011)].
Mechanical hazards: presents less risk of injury in terms of crushing, cutting, trapping, etc. [presence and characteristics of moving and/or rotating elements, angular and/or cutting parts, stored energy, residual risks (ISO 12100, 2010; ISO 31000, 2009)].
Mental stress: reduces the influences upon a human being from external sources and mental effects on the person [task demands, social and organisational factors, physical conditions, individual characteristics (ISO 10075, 1991; ISO 10075-2, 1996)].
Metabolic activity level: requires less physical effort and therefore has a lower metabolic energy cost [metabolic rate (ISO 8996, 2004)].
Motivation and satisfaction: guarantees greater pleasure and gratification in the performance of the work task [perceived quality of working life, perceived mental demand, perceived physical demand, worker expectation (OHSAS, 18002, 2008)].
Noise exposure: guarantees a greater acoustic comfort considering the need to also hear information messages, verbal alerts and danger signals [possible noise emission, ambient noise, properties of the work environment (ISO 9921, 2003; ISO 9612, 2009)].
Operating costs: requires less fixed and variable costs associated with administering the business on a day-to-day basis [costs of operation, user training, support, maintenance (EN 1325-1, 1996)].
Postures: allows position of body segments and joints to be more comfortable while executing work tasks [trunk posture, head posture, upper extremity posture, lower extremity posture (ISO 11226, 2000; EN 1005-4, 2008)].
Production capacity: allows a greater volume of products/activities using the current resources [feasible production rate, Table 3 Example of pairwise comparison matrix (element evaluation). Ergonomics and safety performance

AB

CE

WE

WM

SA

Local priorities

Anthropometry and biomechanics (AB) Cognitive ergonomics (CE) Work environment (WE) Work management (WM) Safety (SA)

1

6

4

3

1/3

0.293

1/6 1/4 1/3 3

1 2 4 5

1/2 1 3 4

1/4 1/3 1 2

1/5 1/4 1/2 1

0.051 0.081 0.181 0.394 CR ¼ 0.066


































319

need for setup or breaks, threshold limit value for manual handling (ISO 9001, 2008)]. Pushing and pulling: requires less initial, sustained and stopping forces to perform push or pull tasks [pushing and pulling force, object position, pushing and pulling frequency (ISO 11228-2, 2007; EN 1005-3, 2008)]. Repetitive handling at high frequency: requires fewer actual technical actions than the reference activity in performing repetitive work tasks involving manual handling of low loads at high frequency [actual technical actions, reference technical actions, force, posture and movement of upper limbs, repetitiveness, recovery time (ISO 11228-3, 2007; EN 1005-5, 2007)]. Required space: is less rigid and has fewer requirements if the distribution of space changes [required areas, required facilities and utilities, special installation requirements (EN 15221-4, 2011)]. Risk perception: provides workers and safety managers with a better view of a risk [needs, issues, knowledge, belief and values (ISO Guide 73, 2009)]. Shift work and suitable population: allows for better job scheduling and a larger population employment [methods time measurement, shift work characteristics, percentage of working population (OHSAS, 18001, 2007)]. Space demands: guarantees a greater freedom of movement for a working area of equal size [clearances, dimensions of devices and objects, action demand, possibility for adopting different posture (ISO 14738, 2002; ISO 12100, 2010)]. Thermal environment: guarantees a greater thermal comfort considering the required physical effort and the thermal load emitted by the equipment [air temperature, mean radiant temperature, air velocity, humidity, clothing, metabolic rate (ISO 7730, 2005)]. Training procedures: allows for easier establishment, implementation and maintenance of a training procedure [competence, training and awareness (OHSAS, 18001, 2007)]. Visual requirement: allows a better view of visual targets [visual field, angles of view, viewing distance, size of the visual target (ISO 9241-5, 1998)]. Work clothing and PPE: requires reduced use of special work clothing and personal protective equipment [required protective clothing, required gloves against mechanical risks, required protective and occupational footwear (EN 388, 2003; ISO/TR, 18690, 2012)]. Work experience: improves the use of acquired knowledge and experience [years experience, roles and responsibility, skills and knowledge (OHSAS, 18001, 2007)].

Based on the attributed meanings, Table 3 shows the pairwise comparison matrix of the elements with respect to the Ergonomics and safety performance Strategic Criterion, local priorities and the Consistent Ratio (CR) of the matrix, calculated in accordance with steps 3 and 4 of the AHP procedure in Section 2. In this matrix, the first nontrivial comparison is (AB, CE). The question is: How much more is AB preferred over CE under Ergonomics and safety performance Criterion? AB is actually preferred 6 times over CE, and thus the value 6 is entered in the (1,2) position. The reciprocal value is automatically entered in the transpose position (2,1) for (CE, AB). All matrices of pairwise comparison (element evaluation matrices) are in Appendix. 3.2. Case study A case study was conducted to test the developed hierarchy. The following subsections describe the participants, the hierarchy, the

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Table 4 Local priorities of elements. Ergonomics and safety performance (0.250)

Anthropometry and biomechanics (0.293)

Cognitive ergonomics (0.051)

Work environment (0.081)

Work management (0.181)

Safety (0.394) Production performance (0.750)

Productivity (0.297)

Adaptability (0.087) Capability (0.563)

Flexibility (0.053)

comparisons performed, the equipment used, the evaluations carried out, the testing conditions, the results obtained from the case study, and the results of a real application of the methodology for validation.

Metabolic activity level Lifting and carrying Pushing and pulling Repetitive handling at high frequency Postures Visual requirement Accessibility and reach zones Comfort of sue Easy to understand Easy to use Risk perception Mental stress Thermal environment Lighting environment Noise exposure Space demands Competence and training Work experience Shift work and suitable population Motivation and satisfaction Training procedures Mechanical hazards Work clothing and PPE Production capacity Investment costs Operating costs Elasticity Generality Efficiency Effectiveness Customer satisfaction Corporate image Required space Constraints on the layout

0.053 0.230 0.182 0.110 0.314 0.045 0.039 0.027 0.089 0.239 0.239 0.433 0.518 0.127 0.061 0.294 0.415 0.049 0.127 0.200 0.209 0.800 0.200 0.123 0.557 0.320 0.500 0.500 0.108 0.255 0.472 0.165 0.200 0.800


gather a decisional group that could realistically reproduce a corporate decision-making system, consisting of CEO and managers;
also contemplate issues of more direct interest to workers, because of the importance of ergonomic factors for handling activities.

3.2.2. Local priorities of elements All of the pairwise comparisons performed to determine the priorities of all elements (Strategic Criteria, Criteria, and Sub-criteria) were carried out by the evaluation team using the 9-point scale suggested by Saaty (1980) and assuming stable market conditions. The local priorities obtained for all of the elements, i.e. the components of the normalised eigenvector of the pairwise comparison matrix (element evaluation), are shown in Table 4, computing the pairwise comparison matrices (element evaluation) in Appendix. The local priorities represent the relative weights of the elements in a group with respect to the element above. The global priorities are obtained by multiplying the local priorities of the elements by the global priority of their above element. For example, the global priority of the Sub-criterion Metabolic activity level (0.0039) is obtained multiplying the local priority of the same Subcriterion (0.053) by the local priority of the Criterion Anthropometry and biomechanics (0.293) by the local priority of the Strategic Criterion Ergonomics and safety performance (0.250). From each set of pairwise comparisons, the element weight and consistency ratio were calculated using Saaty’s eigenvector approach (1980). From the analysis of Table 4, it is observed that the most important Strategic Criterion that affects the satisfaction of company objectives is Production performance, with a weight of 0.750. The Ergonomics and safety performance follows Production performance, with a local priority of 0.250. Among the Criteria referenced to Production performance, the most important item is Capability, with a local weight of 0.563. The most important Criterion referenced to Ergonomics and safety performance is Safety, with a local weight of 0.394.

The evaluations were carried out collectively by the team. The team members participated in the tests, handling loads both manually and by a manipulator, to gain greater awareness.

3.2.3. Material handling device In this paper, the authors analysed a particular type of MHD, the LiftronicÒ EASY E80 INDEVA (Intelligent Devices for Handling),

3.2.1. Subjects The evaluation team was composed of eight researchers (including the authors), six males and two females between the ages of 24 and 38. The participants’ mean height and weight were 174.9 cm (SD ¼ 11.4 cm) and 76.5 kg (SD ¼ 17.1 kg), respectively. No subject reported any musculoskeletal disorders, and all were healthy at time of testing. Subjects were not paid for their participation. The participants were academic and industrial researchers, with expertise in products and workstations design, management and ergonomics, and in production management and handling optimisation. They had interactions with several stakeholders, asking them structured opinions to take account of their different skills, experiences and expectations: CEOs, accounting managers, production managers, safety managers, and workers. The involved companies, mainly SMEs, were manufacturers and users of MHDs. The members of the team and the contacted stakeholders were picked out in order to:

D. Rossi et al. / International Journal of Industrial Ergonomics 43 (2013) 314e327

which is column mounted and includes an articulated arm equipped with a linear pantograph and is designed for simple applications with non-complex and rapid gripping. This model has a high base of 2.43 m, a total arm length of 2.50 m, a gross capacity of 80 kg and a maximum lifting speed of 36 m/min. The linear pantograph allows this device to handle loads of different sizes and configurations by a relatively simple and quick jaw adjustment or replacement. A failsafe mechanical lock is triggered in the case of a power shortage, and a brake limits the lowering speed of the motor. This manipulator, as illustrated in Fig. 2, belongs to the most advanced class of industrial manipulators currently available on the market, known as IADs (Intelligent Assist Devices). IADs are computer-controlled servo-driven tools that enable production workers to lift, move and position objects. IADs can provide a variety of benefits to the users, including:
Strength amplification;
Inertia masking (i.e. reducing the starting, stopping, and turning forces, and ensuring that motions in all directions respond equally to human input);
Interface to auxiliary sensors for special purposes such as weighing of parts and tracking on moving assembly lines;
Auto-weight sense and automatic load balancing;
Quick response to human touch. Factors driving the adoption of IADs include a shift in workforce demographics towards older workers and more women and a decreasing tolerance of dangerous jobs, as evidenced by increasing ergonomics legislation in the US and EU (Colgate et al., 2003). One of the key enabling technologies for IADs is that of servo control. The use of servomotors and high-speed digital controls allows the IADs to respond quickly to human input and other sensory inputs (i.e. line tracking signals).

Fig. 2. LiftronicÒ Easy E80 Indeva.

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The analysed manipulator is equipped with microprocessorbased logic instead of the traditional pneumatic logic. A balancing device automatically and continually detects and compensates for the load weight. A special force-sensing handle provides fine control of up and down speeds, thus drastically reducing the inertia. By grasping the fingertip-sensitive handle and gently applying force in the desired direction, the operator can manipulate loads as if they weighed very little. 3.2.4. Apparatus, configuration and procedure The subjects involved in the case study were first informed of the purpose and procedure of the experiment. Next, a certain amount of practice trials were conducted to allow the subjects to become familiar with the test procedure and the apparatus. The tasks performed in the study included the lifting of low-lying objects. The participants were instructed to repeatedly lift common industrial tote boxes. The boxes were grasped from a pallet placed on the ground and released onto a weighing system located on a table. The system, composed of a digital weight indicator (mod. DINI ARGEO 3590E) and a pair of modular weighing bars (mod. DINI ARGEO BPM150), allowed for an easy count of the boxes moved and the measurement of the force exerted during the release of the load. During the lift process, the boxes were rotated anti-clockwise by 90 around the normal to the ground. Precision placement of the box was not required at the lift destination. The tasks were performed both manually (two-handed) and using the LiftronicÒ EASY E80 INDEVA (assisted lifting), such that the alternatives are Manual Material Handling (manual) and Material Handling with the LiftronicÒ EASY E80 INDEVA (assisted). Each participant carried out four different lifting tasks; a manual 5-kg box, a manual 20-kg box (performed only by males), an assisted 5-kg box, and an assisted 20-kg box. Each task had a duration of 10 min. Lifting frequency was not imposed on subjects. To reduce fatigue and boredom effects, a rest break of at least 10 min was scheduled between successive experimental sessions. The experiment required the help of two assistants; one assistant removed the boxes from the table and the other repositioned the boxes on the pallet. The height of the pallet was 100 mm and the height of the table was 750 mm, and therefore, the absolute value of the difference between the vertical heights at the destination and origin of the lift was 650 mm. The boxes, regardless of weight, had the following dimensions: 280 mm width, 430 mm length and 200 mm depth. Fig. 3 shows the layout of the testing environment. After they completed the test, the impressions of each subject regarding the tasks performed were collected. 3.2.5. Local and global priorities of alternatives The two alternatives (manual and assisted) are compared with respect to each Sub-criterion, according to the step 5 of the AHP procedure in Section 2. To execute the comparisons, the question is “How much does ASSISTED benefit over MANUAL under Element?”. For example, Table 5 represents the pairwise comparison matrix of the alternatives with respect to the Metabolic activity level Subcriterion and the question is “How much does ASSISTED require less physical effort and therefore has a lower metabolic energy cost then MANUAL under Metabolic activity level?”. In Table 5 also the local priorities are stated. With reference to 5 kg-box, because the assisted option was preferred by subjects 5 times over that of manual, the value 5 is entered into the (1,2) position. The reciprocal value 1/5 is automatically entered in the transpose position (2,1) for (manual, assisted). All matrices of pairwise comparison (alternative evaluation matrices) are in Appendix. According to the step 6 of the AHP procedure in Section 2, the final step is to weight the results to obtain the final scores of the

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D. Rossi et al. / International Journal of Industrial Ergonomics 43 (2013) 314e327 Table 6 Final scores of alternatives. Alternatives

5 kg-box

20 kg-box

Manual Assisted

0.47 0.53

0.39 0.61

The company was considering the opportunity of providing workstations that require more physical demanding activities of an IAD. These activities require to pick primary packaging containing food and create grouped packaging at the end of the freezing process (from 10 to 15 kg of weight). The main phases of the collaboration were:
the presentation of the methodology and its steps;
the sharing of the hierarchy, elements (Strategic Criteria, Criteria, and Sub-criteria), benefits, indicators, and standards;
the execution of the pairwise comparisons by the CEO (decision maker);
the discussion of the outcome of the application and validation of the hierarchy. Fig. 3. Layout of the testing environment (measurements in mm).

two alternatives, i.e. the global priorities achieved and summarised in Table 6. The values were calculated computing Table 4 and the pairwise comparison matrices (alternative evaluation) in Appendix. The judgments of the decision makers allowed them to obtain the global priorities of the alternatives for the 5-kg box and the 20kg box. The obtained results confirm the advantages offered by the manipulator in heavy load handling and also demonstrate the potential benefits for moderate load objects. The application of the AHP showed greater satisfaction of the company objectives (the Goal) replacing manual load handling with appropriate equipments, according to the European Council Directive 90/269/EEC (Council of European Communities, 1990). 3.2.6. Validation of the methodology In order to validate the defined methodology and hierarchy the authors submitted them to some companies interested in acquiring industrial manipulators to eliminate or at least reduce the manual handling of loads in some working activities. On the basis of the consent to publication of the obtained results and similarity between simulated case study and real working activities, the authors selected as most significative application the case of the company Blu Pegaso S.r.l. This section summarises the findings of the application of the methodology by the CEO of Blu Pegaso S.r.l., supported by the safety manager. Blu Pegaso S.r.l. is a logistics and supply chain management company operating mainly in Northern Italy and offering services of logistics and transport management, warehouse construction and management, logistics consulting. In 2012 the company had 36 direct employees and more than 200 indirect employees, with a turnover of 12 million Euro.

Table 5 Example of a pairwise comparison matrix (alternative evaluation). Metabolic activity level 5 kg-box

20 kg-box

Manual Assisted Local Manual Assisted Local priorities priorities Manual Assisted

1 5

1/5 1

0.167 0.833

1 7

1/7 1

0.125 0.875

Due to judgments made by the decision maker, the alternative “IAD assisted” was preferred to the alternative “manual” with global priorities equal to approximately 0.56 and 0.44 respectively. The application has confirmed that the use of the methodology avoids to overlook important factors for the selection and allows to consider ex ante the factors related to health and safety of workers. In the light of this application (and also of the other ones), it was noted that:
the understanding of the methodology and its implementation was easy, despite the decision maker did not know the AHP procedure. For the evaluation of ergonomic elements the support of the safety manager was useful;
the time required for the description of the elements and the making of comparisons was approximately 260 min; the calculation of the priorities by the authors lasted about 10 min using a preset spreadsheet;
the global priorities obtained on the basis of the judgements made by the CEO were in line with those obtained by the authors and reported in Table 6. The application showed that the use of the hierarchy is efficient and easy also thanks to the linguistic scale of relative importance, but it is necessary a detailed explanation of the evaluation elements. 4. Conclusions This paper presents an AHP-based methodology to support the resolution of a real-world problem: to select the best manuable material handling solutions evaluating ergonomic criteria and production performance measures. To validate this approach, a case study was carried out that considered manual material handling versus IAD-assisted handling. Chaffin et al. (1999) reported that pneumatic and hydraulic manipulators solve the problem highlighted by Woldstad and Chaffin (1994) regarding tasks performed with manipulators that are considered just as difficult as jobs carried out without them. In addition, according to Chaffin et al. (1999) and downstream of the analyses and experiments conducted, the authors confirm the importance of the use of manipulators by properly trained personnel to prevent the occurrence of musculoskeletal problems

D. Rossi et al. / International Journal of Industrial Ergonomics 43 (2013) 314e327

arising from their improper use. As also reported in literature, and in particular from Granata et al. (1996), it is not easy to learn how to move smoothly and precisely using the new MHDs. Regarding the time of publication of the cited papers, the reported evidence is the result of analysis of manipulators that are very different from those currently available; in the last 15 years, the technology and electronics in this area have progressed immensely. As evidence of this progress, electronic manipulators were introduced with the aim of improving the working conditions for employees and reducing the risk of diseases caused by manual material handling. The results reported in this study were obtained with the use of an IAD (LiftronicÒ EASY E80 INDEVA). In particular, the application of the methodology developed by the authors notes that the use of this IAD may be convenient not only in those situations in which the lifted weight is large, and it is therefore necessary to provide the operator with a suitable aid, but also in situations in which the weight of the load could not apparently justify the investment for the manipulator introduction in the work environment. As may be expected, the use of the IAD is the best alternative in the application of the proposed hierarchy for the case of handling a 20-kg box. However, even for the handling of a 5-kg box, it was observed that the alternative IAD is still preferable to manual handling for the satisfaction of the company objectives. The most significant factors contributing to the choice of the IAD are: Metabolic activity level, Lifting and carrying, Postures, Visual requirement, Thermal environment, Work experience, Shift work and suitable population, Motivation and satisfaction, Effectiveness, Customer satisfaction, and Corporate image. The IAD is penalised by reference to the factors Easy to understand, Easy to use, Mental stress, Noise exposure, Space demands, Training procedures, Investment costs, Operating costs, Generality, and Constraints on the layout. Moreover, in the case study, with reference to the role of frequency of handling, the IAD homogenises the performance of different operators. In fact, the frequency (expressed in number of items handled during the trial) that participants were able to maintain was essentially similar despite the different anthropometric data and strengths that characterised the workers, while these frequencies were rather variable during manual handling. In fact, in 10 min the participants moved a number of 5 kg-boxes between 87 and 175 manually, and between 50 and 61 using the IAD. These considerations allow the authors to highlight the following observations: the use of the IAD may permit handling in a greater percentile range of the worker population as well as for operators with physical limitations; in addition, the levelling of the handling frequency allows for a more constant production rate and additional benefits from the ergonomic point of view. In fact, since the frequency is a risk factor for lower back and upper limb disorders (ISO 11228-1, 2003; ISO 11228-2, 2007; ISO 11228-3, 2007) and the use of the IAD prevents an excessive frequency, it is possible to reduce health risks using a manipulator to support manual handling. The hierarchy provides a support for the decision manager, regardless of industry and country. Compared to the hierarchies in the literature (e.g. Jung and Jung, 2001; Chan et al., 2001; Henderson and Dutta, 1992), the authors have defined a hierarchy more complete because the set of Sub-criteria is numerous and wide since it considers both ergonomics, safety and production aspects. Furthermore, all Sub-criteria have been detailed with the benefit, indicators and reference standards in order to carry out evaluations in a more guided and objective way. The approach allows the use of pairwise comparisons between alternatives to also identify possible changes that may improve the same alternative.

323

For example, from the ergonomic point of view, it is clear that certain features of the IAD could be improved. Consequently, further improvements may be made in the evaluation of currently penalised Sub-criteria, and thus there may be a further shift in preference towards the alternative IAD. For example, it is possible to improve the interface of the manipulator from the anthropometric and cognitive points of view. The validation of the applicability of the methodology and hierarchy was performed by some companies, in particular by the CEO of a logistics and supply chain management company (Blu Pegaso S.r.l.). With reference to manual handling of 10/15 kg-box, the final scores were coherent with the global priorities obtained by the authors: the alternative “assisted” was preferable to the alternative “manual”. Downstream of this work, the authors shared the obtained results with their technological partner, Scaglia Indeva S.p.A. Together they are studying possible changes to further improve the LiftronicÒ EASY E80 INDEVA. The authors aim to repeat the case study presented in this paper using the modified IAD and evaluate the effects of the ameliorative interventions by means of the proposed hierarchy. In conclusion, the authors consider the evaluation methodology and the proposed hierarchy to represent a useful and valid support to decision making for companies that wish to improve their manuable material handling activities as well as for manufacturers of MHDs. Acknowledgements The authors thank Scaglia Indeva S.p.A., C.S.M.T. Gestione S.c.a.r.l., and Blu Pegaso S.r.l. for supporting this research. Appendix A Element evaluation matrices

Focus

ES

PP

Local priorities

Ergonomics and safety performance (ES) Production performance (PP)

1 3

1/3 1

0.250 0.750

Ergonomics and safety performance AB

CE WE WM SA

Local priorities

Anthropometry and biomechanics (AB) Cognitive ergonomics (CE) Work environment (WE) Work management (WM) Safety (SA)

1

6

4

3

1/3 0.293

1/6 1/4 1/3 3

1 2 4 5

1/2 1 3 4

1/4 1/3 1 2

1/5 1/4 1/2 1

0.051 0.081 0.181 0.394 CR ¼ 0.066

Production performance

PR

AD

CA

FL

Local priorities

Productivity (PR) Adaptability (AD) Capability (CA) Flexibility (FL)

1 1/5 3 1/6

5 1 6 1/2

1/3 1/6 1 1/8

6 2 8 1

0.297 0.087 0.563 0.053 CR ¼ 0.045

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Anthropometry and biomechanics

MA LC

Metabolic activity level (MA) Lifting and carrying (LC) Pushing and pulling (PP) Repetitive handling at high frequency (RH) Postures (PO) Visual requirement (VR) Accessibility and reach zones (AR) Comfort of use (CU)

1 5 5 3

PP

1/5 1 1/2 1/3

1/5 2 1 1/3

RH PO VR AR CU Local priorities 1/3 3 3 1

1/6 1/2 1/2 1/4

1 5 4 3

2 6 5 4

3 6 5 5

0.053 0.230 0.182 0.110

6 2 2 4 1 6 1 1/5 1/4 1/3 1/6 1 1/2 1/6 1/5 1/4 1/7 1

7 1 1

8 2 2

0.314 0.045 0.039

1/3 1/6 1/5 1/5 1/8 1/2 1/2 1

0.027 CR ¼ 0.031

Capability

EF

EE

CS

CI

Local priorities

Efficiency (EF) Effectiveness (EE) Customer satisfaction (CS) Corporate image (CI)

1 2 4 2

1/2 1 2 1/2

1/4 1/2 1 1/3

1/2 2 3 1

0.108 0.255 0.472 0.165 CR ¼ 0.017

Flexibility

RS

CL

Local priorities

Required space (RS) Constraints on the layout (CL)

1 4

1/4 1

0.200 0.800

Alternative evaluation matrices Cognitive ergonomics

EA

EU

RP

MS

Local priorities

Easy to understand (EA) Easy to use (EU) Risk perception (RP) Mental stress (MS)

1 3 3 4

1/3 1 1 2

1/3 1 1 2

1/4 1/2 1/2 1

0.089 0.239 0.239 0.433 CR ¼ 0.008

Work environment

TE

LE

NE

SD

Local priorities

Thermal environment (TE) Lighting environment (LE) Noise exposure (NE) Space demands (SD)

1 1/4 1/6 1/3

4 1 1/3 4

6 3 1 5

3 1/4 1/5 1

0.518 0.127 0.061 0.294 CR ¼ 0.079

Work management

CT

WE

SS

MS

TP

Local priorities

Competence and training (CT) Work experience (WE) Shift work and suitable population (SS) Motivation and satisfaction (MS) Training procedures (TP)

1 1/6 1/3

6 1 3

3 1/3 1

4 1/5 1

2 1/4 1/3

0.415 0.048 0.127

1/4 1/2

5 4

1 3

1 1/2

2 1

0.201 0.209 CR ¼ 0.080

Safety

MH

WP

Local priorities

Mechanical hazards (MH) Work clothing and PPE (WP)

1 1/4

4 1

0.800 0.200

Metabolic activity level

5 kg-box Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

Manual Assisted

1 5

1/5 1

0.167 0.833

1 7

1/7 1

0.125 0.875

Lifting and carrying

5 kg-box Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

Manual Assisted

1 6

1/6 1

0.143 0.857

1 9

1/9 1

0.100 0.900

PC

IC

OC

Local priorities

Production capacity (PC) Investment costs (IC) Operating costs (OC)

1 4 3

1/4 1 1/2

1/3 2 1

0.123 0.557 0.320 CR ¼ 0.016

Adaptability

EL

GE

Local priorities

Elasticity (EL) Generality (GE)

1 1

1 1

0.500 0.500

20 kg-box

Pushing and pulling 5 kg-box

20 kg-box

Manual Assisted Local Manual Assisted Local priorities priorities Manual Assisted

1 1/3

3 1

0.750 0.250

1 1/3

3 1

0.750 0.250

Repetitive handling at 5 kg-box 20 kg-box high frequency Manual Assisted Local Manual Assisted Local priorities priorities Manual Assisted

Productivity

20 kg-box

1 1/2

2 1

0.667 0.333

Postures 5 kg-box

1 2

1/2 1

0.333 0.667

20 kg-box

Manual Assisted Local priorities Manual Assisted Local priorities Manual 1 Assisted 2

1/2 1

0.333 0.667

1 4

1/4 1

0.200 0.800

Visual requirement

5 kg-box Manual

Assisted

Local priorities

20 kg-box Manual

Assisted

Local priorities

Manual Assisted

1 3

1/3 1

0.250 0.750

1 3

1/3 1

0.250 0.750

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Accessibility and 5 kg-box 20 kg-box reach zones Manual Assisted Local Manual Assisted Local priorities priorities

Lighting environment 5 kg-box

Manual Assisted

Manual Assisted

1 1

1 1

0.500 0.500

1 1

1 1

0.500 0.500

5 kg-box

Manual Assisted

Assisted

Local priorities

Manual

Assisted

Local priorities

1 1

1 1

0.500 0.500

1 3

1/3 1

0.250 0.750

Easy to understand 5 kg-box

1 1/2

1 1

2 1

0.667 0.333

1 1/2

2 1

0.500 0.500

5 kg-box

1 1

1 1

0.500 0.500

20 kg-box Assisted

Local priorities

Manual

Assisted

Local priorities

Manual Assisted

1 1/3

3 1

0.750 0.250

1 1/3

3 1

0.750 0.250

Space demands

5 kg-box

20 kg-box

Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

1 1/3

3 1

0.750 0.250

1 1/3

3 1

0.750 0.250

20 kg-box

Manual Assisted Local Manual Assisted Local priorities priorities Manual Assisted

1 1

Manual

20 kg-box

Manual

20 kg-box

Manual Assisted Local Manual Assisted Local priorities priorities

Noise exposure Comfort of use

325

Manual Assisted

0.667 0.333 Competence and 5 kg-box 20 kg-box training Manual Assisted Local Manual Assisted Local priorities priorities

EASY to use 5 kg-box

20 kg-box

Manual Assisted Local priorities Manual Assisted Local priorities Manual Assisted

1 1/3

3 1

0.750 0.250

1 1/3

3 1

Manual Assisted

1 1/2

2 1

0.667 0.333

1 1

1 1

0.500 0.500

0.750 0.250 Work experience 5 kg-box

20 kg-box

Manual Assisted Local Manual Assisted Local priorities priorities

Risk perception

Manual Assisted

5 kg-box

Manual Assisted

20 kg-box

Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

1 1/3

3 1

0.750 0.250

1 2

1/2 1

0.333 0.667

1 3

Manual Assisted

5 kg-box Assisted

Local priorities

Manual

Assisted

Local priorities

1 1/3

3 1

0.750 0.250

1 1/3

3 1

0.750 0.250

1/3 1

0.250 0.750

1 7

1/7 1

0.125 0.875

1 9

1/9 1

0.100 0.900

20 kg-box

Motivation and satisfaction

5 kg-box Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

Manual Assisted

1 4

1/4 1

0.200 0.800

1 7

1/7 1

0.125 0.875

1/4 1

0.200 0.800

1 6

1/6 1

20 kg-box

Training procedures 5 kg-box

Manual Assisted Local Manual Assisted Local priorities priorities 1 4

1 3

20 kg-box

Manual

Thermal environment 5 kg-box

Manual Assisted

0.250 0.750

Shift work and 5 kg-box 20 kg-box suitable population Manual Assisted Local Manual Assisted Local priorities priorities Manual Assisted

Mental stress

1/3 1

0.143 0.857

20 kg-box

Manual Assisted Local Manual Assisted Local priorities priorities Manual Assisted

1 1/3

3 1

0.750 0.250

1 1/3

3 1

0.750 0.250

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Mechanical hazards

5 kg-box Manual

Assisted

Local priorities

20 kg-box Manual

Assisted

Local priorities

Efficiency

Manual Assisted

1 1/2

2 1

0.667 0.333

1 2

1/2 1

0.333 0.667

Work clothing and PPE

5 kg-box Manual

Assisted

Local priorities

20 kg-box Manual

Assisted

Local priorities

Manual Assisted

1 1

1 1

0.500 0.500

1 1

1 1

0.500 0.500

Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

Manual Assisted

1 1/3

3 1

0.750 0.250

1 3

1/3 1

0.250 0.750

20 kg-box

Investment costs

5 kg-box Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

Manual Assisted

1 1/3

3 1

0.750 0.250

1 1/3

3 1

0.750 0.250

5 kg-box Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

Manual Assisted

1 1/3

3 1

0.750 0.250

1 1/3

3 1

0.750 0.250

Generality

Manual Assisted

Local priorities

Manual

Assisted

Local priorities

1 1/3

3 1

0.750 0.250

1 3

1/3 1

0.250 0.750

5 kg-box

Manual Assisted

20 kg-box

Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

1 4

1/4 1

0.200 0.800

1 6

1/6 1

0.143 0.857

5 kg-box

20 kg-box

Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

1 4

1/4 1

0.200 0.800

1 5

1/5 1

0.167 0.833

Corporate image

5 kg-box Manual

Assisted

Local priorities

20 kg-box Manual

Assisted

Local priorities

Manual Assisted

1 5

1/5 1

0.167 0.833

1 5

1/5 1

0.167 0.833

20 kg-box

Operating costs

Manual Assisted

Assisted

Manual Assisted

Customer satisfaction

5 kg-box

20 kg-box

Manual

Effectiveness

Production capacity

Elasticity

Manual Assisted

5 kg-box

20 kg-box

5 kg-box

Required space

5 kg-box Manual

Assisted

Local priorities

20 kg-box Manual

Assisted

Local priorities

Manual Assisted

1 2/3

3/2 1

0.600 0.400

1 2/3

3/2 1

0.600 0.400

Constraints on the layout

5 kg-box Manual

Assisted

Local priorities

20 kg-box Manual

Assisted

Local priorities

Manual Assisted

1 1/2

2 1

0.667 0.333

1 1/2

2 1

0.667 0.333

20 kg-box

Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

1 1

1 1

0.500 0.500

1 1

1 1

0.500 0.500

5 kg-box

20 kg-box

Manual

Assisted

Local priorities

Manual

Assisted

Local priorities

1 1/3

3 1

0.750 0.250

1 1/3

3 1

0.750 0.250

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