Introduction Background Factor assessment

Instructions

A more detailed pdf of the instructions, can be found here!

Introduction to the Handbook

The overall purpose of the Cognitive Load Assessment for Manufacturing method (hereafter denoted the CLAM method) is to help identifying and assessing the occurrence of cognitive load in manufacturing personnel, as well as educating and assisting manufacturing companies to reduce cognitive load in the personnel at the shop floor early on. The CLAM method is an inspection method and has primarily been developed as a proactive approach for workstation design and evaluation. It is designed for quick assessment of cognitive load connected to tasks and workstation design. The motivation for this approach, focusing on identification of relevant issues pro-actively, may lead to effective and efficiently changes in the existing manufacturing environment. The overall goal with the CLAM method has been to make it cost efficient, taking a holistic perspective (both work task and workstation as a whole), saving time and resources in assessing assembly workers’ cognitive load in manufacturing.

The CLAM method considers both assembly tasks and workstation layout/design for the assessment. By addressing and identifying cognitive load problems proactively, and designing the workstation and the assembly task properly, one avoids high cognitive load in the personnel. High cognitive load during pro-longed longer time-frames, may lead to inefficient work procedures, bad performance, high error rates, low acceptance as well as ergonomic and mental health symptoms in the personnel.

The developed CLAM method and its assessment tool are designed to be used by non-experts, i.e. it will not require a researcher or anyone with any major knowledge of human cognition, cognitive psychology or human factors. This handbook is intended to make the method usable by different user roles, most usually engineers, production leaders, technicians, and assembly workers.

The CLAM handbook consists of four parts:
It contains a background part, where underlying relevant theories of the human cognitive systems (strengths and limitations) and especially cognitive load are briefly presented. It is also emphasized why it is important to consider these issues within manufacturing.

It consists of an instruction part of how to use the CLAM assessment tool, either individually or pluralistically. It briefly introduces the 11 factors as well as the overall procedure of how to assess the factors. This part also contains the necessary material in order to apply the CLAM assessment tool by providing instructions for how to use it.

It provides a description part that presents in more details how the 11 different factors could be observed and the procedure regarding how to assess them in manufacturing as well as what kinds of cognitive load they could result in. This part provides guidance to the evaluator(s) how to interpret and understand a particular factor and offers suggestions on why a particular score should be assessed at a certain level of cognitive load.

It finally provides a result and recommendation part that concerns how to interpret and use the obtained overall result of the CLAM assessment tool, which is a calculated result of the 11 factors. It also provides some recommendations that can contribute to reducing high cognitive load (when identified) in order to minimize identified problems of high cognitive load, and thereby improving manufacturing.

The CLAM method, the CLAM tool, and the accompanying handbook have been developed in the Sense&React Consortium. This work was financially supported by Sense and React - the context-aware and user-centric information distribution system for manufacturing project. Sense and React is an Integrated Project funded by the European Commission under the 7th Framework Programme by the EU grant FP7-314350. All parts of the CLAM assessment tool (http://www.clam.se) is licensed under the MIT Licence.

The MIT License (MIT)
Copyright (c) 2014 - 2015, British Columbia Institute of Technology

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Developers and designers:
Peter Thorvald, Senior Lecturer at University of Skövde
PhD in Manufacturing Engineering
peter.thorvald@his.se

Jessica Lindblom, Senior Lecturer at University of Skövde
PhD in Cognitive Systems

jessica.lindblom@his.se

 

Background

The human cognitive system and cognitive load

Technology either empowers or frustrates us, but the people designing the technology have the responsibility, and one should credit or blame the designer of the technology and not technology itself. Following the line of arguments put forward by Norman in 1996, our goal is to develop a human-centred view of the technologies of cognition. It is not an anti-technological approach, it is pro human. Taken together, technology should be considered as a resource in the creation of a better working environment, it should complement human abilities, aid those activities for which we are poorly suited cognitively, and enhance and help develop those cognitive skills for which we are ideally suited.

Characteristics of human cognition and cognitive load

Cognition has traditionally been described as mental activities that take place inside the human brain. More recent views emphasize the importance of the environment as well as the body of the cognizer as well as the interaction between these factors and the brain. Cognitive abilities enable the human being to experience the world and act in it. Perception, decision-making, problem solving, memory processes etcetera are all cognitive activities that human beings are engaged in every day. They are also cognitive activities that are depending on the cooperation of the body (e.g. the musculoskeletal system and peripheral nervous system) and sensory inputs from the environment as well as the workings of the brain.

Human cognition is comprehensive, but there are limitations. When exposed to stimuli the cognitive system experiences what is commonly referred to as cognitive load. Briefly stated, cognitive load refers to the mental load that performing a specific task imposes on the human’s cognitive system. Perception, decision-making, problem solving, attention, memory processes et cetera are examples of cognitive activities that enable the human being to experience and act in the world. These cognitive processes are constantly processing information indicating that human beings always experience some level of cognitive load. The level of cognitive load is constantly fluctuating as a response to the stimuli that the situation, the task, and demands are imposing on the human. This is naturally individually and depending on the individual´s experience and previous knowledge. While some situations make it possible for the individual to perceive and interpret the stimuli and the pattern of information and without an apparent effort generate an appropriate response, some other situations demand conscious awareness and reflection. This implies that some cognitive processes of an individual are more demanding than others.

Different modes of cognition

There are many modes of cognition, in which different kinds of thinking occur.  Norman (1996), for example, describes two different types of cognition that are particularly relevant for the CLAM method. He denotes them as experiential and reflective cognition. Roughly speaking, experiential cognition is characterized by an automatic nature and the reactions to the situations appear to flow naturally. This is likely to be due to experience and perhaps years of training are required in order to achieve this. Norman (1996, pp. 23) explain this with the words: “Experiential thought is reactive, automatic thought, driven by the patterns of information arriving at our senses, but dependent upon a large reservoir of experience”.

The reflective mode, on the other hand, is about concepts, planning and reconsideration. Reflective cognition does often require external support (computational tools, writing, instructions et cetera) and also the support of other people. Norman (1996, pp. 25) expresses: “Reflective though requires the ability to store temporary results, to make inferences from stored knowledge, and to follow chains of reasoning backward and forward, sometimes backtracking when a promising line of thought proves to be unfruitful. This process takes time”.

Similarly, Kahneman (2011) differentiates between the automatic operations of System 1 (which he generally refers to as ‘fast thinking’, which is similar to experiential cognition) and the controlled operations of System 2 (which he generally refers to as ‘slow thinking’, which is similar to reflective cognition). The process of demanding and effortful cognitive work is related to system 2 in which the demands of memory, attention and other aspects of performing non-automatic cognitive tasks actually put some constraints on the cognitive processes, resulting in a slower thinking process because of the limited available cognitive capacity, resulting in increased cognitive load. Broadly stated, Kahneman (2011, p. 20-21) describes the two systems as follows:
“System 1 operates automatically and quickly, with little or no effort and no sense of voluntary control.
System 2 allocates attention to the effortful cognitive activities that demand it, including complex computations. The operations of System 2 are often associated with the subjective experience of agency, choice and concentration”.
Kahneman (2011) points out that some of our cognitive activities become fast and automatic because of prolonged practice, although they from the very beginning needed conscious attention, e.g., reading skills which normally runs on our automatic pilot in the skilled reader. The limited human capacity for attention is the central pinnacle for cognitive load, and when acting beyond that limit, failure appears. The division of labour between the two systems is very efficient, it minimises effort and optimises performance, in most of the time. However, System 1 has some biases, and sometimes provides the wrong reaction and it cannot be turned off. This becomes obvious when there is a conflict between the two systems.  One major task of System 2 is to overrule or provide a reflective and conscious “second opinion” of the automatic reactions of System 1. This is for instance common when perceiving so called optical illusions, like the Müller-Lyer illusion (see figure 1).


Figure 1. The Müller-Lyer illusion.

Although consciously knowing via System 2 that the two horizontal lines have the same length, the automatically reaction when visually perceiving the two lines via System 1, offers another answer that is hard to deny, namely that the lines seem to be of different length. Following this line of argument, humans sometimes suffer from cognitive illusions, i.e., illusions of thought, which are quite hard to detect and overcome. The reason is that System 1 operates automatically and cannot be switched off by choice, and biases cannot be avoided since System 2 has not received any hint that there might be an error. A promising way to overcome this bias is learning to recognise particular situations in which mistakes are likely to appear. Continuously questioning our thought processes via System 2 is not a viable approach, however, since it is impractical, too slow and has a limited capacity (Kahneman, 2011).

To sum up, the both modes of cognition; (1) System 1/Experiential cognition and (2) System 2/Reflective cognition are needed and neither is superior to the other, but they differ in requirements and function, as described earlier. It should be pointed out that they are essential for human cognition, although each mode requires different kinds of technical support to function properly. Figure 2 below display the two modes of cognition in the so called “cognitive iceberg” model and visualises that Experiential cognition/ System 1 are the mode that is less demanding, and has the largest capacity, while the Reflective mode/ System 2 requires a higher degree of awareness, has a limited capacity, and is the mode we usually assume is the place in which “thinking” actually occurs.


Figure 2. The cognitive iceberg model, depicting the two different types of cognition – System 1/Experiential and System 2/Reflective cognition.

However, these two modes of cognition do not cover the whole cognitive spectrum, but it makes it possible to highlight and compare certain characteristics of human cognition. In everyday life, we use a mix of these modes simultaneously, and the challenge when designing technology is to avoid forcing the use of technology towards one extreme or the other. That is, there is a need to have a proper balance between reflection and experiencing, so the human cognizer is not forced to use her/his limited conscious capacity to interpret the user interface as such, instead the human cognizer should use the cognitive capacity to solve the problem at hand or make appropriate decisions.

Human beings always experience some level of cognitive load, however this level can change depending on the situation, the tasks and their demands on the individual. For example: an assembly worker performing a manual assembly task is constantly exposed to situations with varying demands. Important aspects to consider concerning the level of cognitive load that the industrial worker can be experiencing is amount of information, time pressure, interruptions, rapid decisions, high variant flora of components and physical layout of workstations. These factors create a mental load primarily in combination with each other, where time pressure is assumed to be the triggering factor. Arguably, problems within most of the above factors can be handled with relative ease as long as there is no time pressure. Dealing with poor information design is for instance not a big problem unless the information has to be dealt with swiftly, as is the case in most industry applications.

Through studies in the industry, an interesting observation was made regarding the use of information [26, 27]. Often the assemblers were provided with too much information rather than the appropriate information, causing information overload for the assembler. Wilson [28] defines information overload as:

“A perception on the part of the individual (or observers of that person) that the flow of information associated with work tasks is greater than can be managed effectively, and a perception that overload in this sense creates a degree of stress for which his or her coping strategies are ineffective”.

In a manual assembly environment, the problem with information overload is usually due to a combination of high demands on work rate and accuracy respectively, especially in the automotive industry. When the assembler is faced with too much information, the information overload turns into a stressful situation, which causes high cognitive load. Information overload is exemplified in figure 3, where the information on the plastic boards instructs the assembly personnel of what component variant to select and assemble.


Figure 3. An example of too much information in one small area.

Both too high cognitive load and information overload increase the risk for humans to err. Certain reasons why people make errors are we sometimes are forced to interact with technology, machines or instructions that are designed in ways that incompatible with our modes of cognition. The limited memory capacity is used for remembering details that make no sense to us or (it is easier to recognize than recall), having to focus our attention on static situations or very similarly appearing displays or rows, and lack of adequate feedback. Thus people make errors, and the overall aim is to design technology etc., in ways that we are cognitively suited to and offer situations that minimize errors and high cognitive load.

How to use the CLAM assessment tool

A brief presentation of the factors USED in CLAM This section briefly presents all the relevant factors that affect cognitive load for the assessment applicable in the interactive CLAM assessment tool. Note that the unit of analysis is on the workstation level (including both the human and his/her working environment in the unit of analysis), including the tasks and the workstation design/layout. Each factor should thus be considered by their impact on each workstation, not individual tasks. These factors are then accompanied by details and motivations of good and poor design according to the cognitive and design literature. The 11 factors identified in the assessment tool include both task- and workstation-related factors are the following ones.
  • Task-based factors are:
  • 1. Saturation
  • 2. Variant flora
  • 3. Level of difficulty
  • 4. Difficulty of tool use
  • 5. Production awareness
  • Workstation factors are:
  • 6. Number of tools available
  • 7. Mapping of workstation
  • 8. Parts identification
  • 9. Information cost
  • 10. Quality of instructions
  • 11. Poke-a-yoke and constraints

In the following, each factor will be described in more detail, as well as presenting examples of good and bad solutions/design of each factor, as a guiding principle for the assessment by the user.

As an outcome of using the CLAM for assessment, a scoring interval of cognitive load is developed, see figure 4, below.

Interval
6 - 8 High cognitive load
4 - 6 Moderate cognitive load
2 - 4 Low cognitive load
0 - 2 Very low cognitive load
Figure 4. The different scoring levels of cognitive load in CLAM.


Procedure – individual or pluralistic assessment

The assessment can be performed either individually or pluralistically. If you want to perform it individually you just jump over the next paragraph and follow the instructions.

If you want to perform it pluralistically, this is how we suggest you should do it. The motivations for doing a pluralistic assessment are the added values of collecting several evaluators’ assessments, their opinions as well as the insights gained in the upcoming discussions. The identified drawbacks of a pluralistic assessment are that it takes more time to perform, extra effort to find additional and relevant evaluators, and that several evaluators need to be present simultaneously at the same time and on the same place. The additional evaluators could be other engineers, production leaders, technicians, but also assembly workers. We suggest that 3-5 evaluators are sufficient (preferably with varying expertise), otherwise the pluralistic assessment will be too time consuming and not beneficial of bringing additional value. The pluralistic assessment is similar to the individual assessment but with the following adjustments. We recommend that one of the evaluators takes field notes or audio record the discussions or that an observer conducts this task. (1)Each evaluator assesses separately how he/she will assess the current factor. This practice is important in order to ensure independent and unbiased assessments from each evaluator. (2) When all evaluators have done their assessments a discussion begins, in which each evaluator starts to verbalize and discuss his/her assessment and opinions. If an assembly worker participates, he/she should begin. When the first evaluator’s comments are exhausted then the next evaluator offers his/her assessment and opinions for the current factor. This will continue until all evaluators have provided their assessments and opinions. (4) After the discussion, you should move on to the next factor and repeat the same procedure. Thus the pluralistic assessment moves to the next step. (5) When the pluralistic assessment is completed (all the 11 factors are assessed and discussed), a general debriefing is conducted in the pluralistic team in order to discuss the obtained result (the overall cognitive load of the workstation) and the insights derived. The debriefing serves as a starting point for future work in order to decrease potentially identified high cognitive load.

The assessment is most easily conducted directly in your lap top computer/smartphone/PDA (available at http://www.clam.se). However, if you are unable to complete the assessment ”online”, away from the unit of assessment (i.e. the workstations at the shop floor), it is possible to print out the factor sheets, bring them to the shop floor for assessment, and then transfer the scores to the computer. The procedure for performing the assessment is based on the computer version of the CLAM tool.

Saturation

The term ‘saturation’ refers to the amount of work that is planned on a workstation. For a simple example; consider a workstation within an assembly flow where the tact time is 100 seconds. If this workstation has an occupancy of 92 seconds then the saturation is 92%.

The saturation of a task or a workstation can and should be measured through time studies. Most industry have normative descriptions of how much time should be spent on each task and the comparison of this value to the balance of the workstation (the time set aside for the whole workstation), reveals a value for the saturation of each workstation.

Assessment

Description:
The saturation of a workstation is related to the particular balance of the assembly tasks. Actual work operations can rarely occupy 100% of the available time and the saturation assessment indicates how much of the available time is occupied by work tasks.

Measurements:
Percentage of planned occupied time.

How to evaluate:
Accurate time studies should be available in most SME's and larger organizations.

Levels:


Level

Description

L0

Not applicable

L1

 

L2

65% saturation or lower

L3

 

L4

65-75% saturation

L5

 

L6

75-85% saturation

L7

 

L8

85% saturation or higher

 

Variant flora

It is a well-documented fact that the variant flora does have significant effect on production efficiency and it can easily be argued that this effect relates to the cognitive workload of the assembly worker (Thorvald, 2011). However, the concept of variant is only relevant in, more or less, one-piece production where there can also be said to be a volume product. In many manufacturing companies, one does not consider variant and volume products but different types of products are instead batched together. This greatly benefits ramp up times and allows for routine work by the assembly worker, but does not, perhaps, comply with lean production, low fill rate through MTO (Make To Order) and other current manufacturing paradigms. However, considering only the cognitive workload of the assembly worker, batching can become a quality risk when batches are small and workers are expected to adjust to new batches relatively often. What would be considered a high variant flora or a small batch size is very dependent on the product and differences between variants or batches and thus this factor would have to be calibrated internally.

Assessment

Description:
The variant flora is relevant to manufacturing organizations running a mixed mode assembly flow, i.e. a flow where volume and variant products are assembled intermixed and not according to a batching strategy. A variant is defined as product or process variation from the most common type of product.

Measurements:          
Percentage of products being considered variants (i.e. non-volume) products.

How to evaluate:
Assessment of what percentage of daily output is made up of variant products.

Levels:


Level

Description

L0

No variant products.

L1

 

L2

Up to 10% variant products.

L3

 

L4

Up to 35% variant products.

L5

 

L6

Up to 50% variant products

L7

 

L8

One piece production. Full variation.


 

Level of difficulty

The level of difficulty is a subjective assessment regarding the estimated difficulty that a workstation entails. To aid the evaluator in assessing this, the factor is heavily tied to the amount of time required to acquire the necessary training and skills needed for independent work. It is also very beneficial to gather opinions from blue-collar workers about the estimated level of difficulty at this workstation. As this factor is quite difficult to assess objectively, subjective opinions from both white and blue-collar workers are required.

Assessment

Description:
The level of difficulty should be assessed on the entire station and is an estimation about the required physical and cognitive effort to perform a task.

Measurements:
Subjective

How to evaluate:
Observation; the assessment is divided into eight categories where the assessment should be based on how long it would take before a recently employed worker is allowed to work alone with the task.

Levels:


Level

Description

L0

Not applicable

L1

 

L2

The task requires little to no training and is recommended for newly employed personnel.

L3

 

L4

The task is quite simple with little training required.

L5

 

L6

The task is slightly complex and requires moderate training and experience.

L7

 

L8

The task is very difficult and requires significant training and experience.

Details

In most manufacturing facilities, the level of difficulty on workstations varies to some degree. The result of evaluating the level of difficulty is highly susceptible to the inclinations of the individual assessor. Thus, the assessment is based on practice in introducing new personnel to a workstation. If a workstation requires very little or no training for new personnel, then the lower levels of assessment should be chosen. If specific training and a small degree of monitoring is required, level two should be selected. For more moderate training and experience, level three should be selected and if the workstation requires significant amounts of expertise and experience is required, then the fourth level is recommended

 

Production awareness

The attention resources of humans are very limited and thus must be considered when designing for cognitive work. This factor is focused on the amount of focused or active attention that is associated with a task through the estimation of variability of work. Note that this is not limited to the presence of variant products but is also dependant on workstation times and the longevity of the tasks performed. Fastening of dozens of bolts within the same task should be considered routine work even though the bolts might not be of the same type.

Assessment

Description:
An assessment on how much focused attention must be applied to the task and the level of "production awareness" that the worker has to muster.

Measurements:
Subjective

How to evaluate:
Observation according to levels.

Levels:


Level

Description

L0

Not applicable

L1

 

L2

The assembly task is done purely out of routine and the sequence seldom changes.

L3

 

L4

The assembly task is mostly done on routine but deviant parts or assemblies do occur.

L5

 

L6

The assembly task is quite variable but still contains much routine work.

L7

 

L8

The assembly task is highly variable and contains little to very little routine work.

Details

Attention is, along with response time and short-time memory, the most limited cognitive capacity that humans have. Specifically, focused or active attention is finite and cannot cope with too much or too similar information. A rule of thumb is that if a task can be done by routine it is not focused but passive and thus is not subject to this limitation.

To understand the concept, consider learning to drive. When you are in the learning process, this task requires very often significantly focused attention resources, but when learned, it is done automatically, on routine. Tasks that do not differ from each other in actual performance are soon automatized and do not require much attention resources whereas tasks that do differ (e.g. due to variant flora or poor information design) require much more attention resources. If large amounts of the work can be done by routine where the same work is repeated, the assessment should be in the lower levels whereas if focused attention is required to find information, identify product variants or find tools and material, the assessment should be in the higher levels.

 

Difficulty of tool use

The difficulty of tool use is assessed station wide based on accessibility and operation of a tool and is also a very subjective assessment, very dependent on the experience of the evaluator. The factor focuses on both the amount of tool use required and also on the estimated complexity of said tool use. Furthermore, the factor includes all tool use, meaning that all work not done by hand or bodily manipulation is considered here. Also, the use of special tools or non-standard tools is highly relevant.

Assessment        

Description:
The difficulty of tool use should be assessed workstation wide based on accessibility and operation of a tool. If several tools are used, the assessment should be a mean of these. All tool and fixture use is included in this factor, i.e. power tools, hand tools, fixtures etc.

Measurements:
Subjective

How to evaluate:
Observation according to levels.

Levels:


Level

Description

L0

No tool use

L1

 

L2

The assembly task is performed mostly by hand and requires little or very simple tool use.

L3

 

L4

The assembly task contains little to moderate tool use

L5

 

L6

The assembly task contains moderate tool use of some complexity

L7

 

L8

The assembly task requires complex tools/tool use and/or special tools to perform

Details

The discrimination between complex and simple tool use might be difficult to assess objectively. For your assistance as an evaluator, consider the following questions:
Does the work require any tool use at all?
What kinds of tools are required? Is the tool use straightforward or does it require any non-standard tools?
Are the tools adapted to the task?
Is the same tool used for several different operations? If so, is it clear in what way the tool should be used for the different operations?
Does the task require complex or non-standard tools where specific training is required?
Finally, try also to consider the training time normally associated with the task as this might give you a valuable clue to the level of difficulty associated with tool use.

 

Number of tools available

A simple metric describing the number of tools used during normal assembly work at a workstation.

Assessment

Description:
The number of tools available and used on the workstation. This factor also includes fixtures and special contraptions that are used for work. If in doubt, include anything that is handled by the worker but that is not part of the product.

Measurements:
Assessment of tool availability.

How to evaluate:
Observation according to levels.

Levels:


Level

Description

L0

No tools used

L1

 

L2

1 to 5 tools and easily identified

L3

 

L4

More than 5 tools and easily identified

L5

 

L6

5-8 tools and not easily identified

L7

 

L8

More than 8 tools

Details

Tools that should be considered include both manual tools as well as power tools.

 

Mapping of workstation

An assessment of how well the workstation design complies with the assembly sequence. For instance, tools and parts that are used together should be placed together and in the correct order.

Assessment

Description:
The mapping of a workstation refers to the correspondence with the workstation layout to the assembly sequence. Are items and tools placed in the order that they are to be used?

Measurements:
Subjective

How to evaluate:
Observation assessment on correspondence between workstation layout and assembly sequence for common products.

Levels:


Level

Description

L0

Not applicable/the worker is free to set up the workstation and all it's components to their own preferences.

L1

 

L2

Workstation layout almost completely corresponds to assembly sequence.

L3

 

L4

Workstation layout heavily corresponds to assembly sequence.

L5

 

L6

Workstation layout somewhat corresponds to assembly sequence.

L7

 

L8

Workstation layout does not correspond to assembly sequence.

Details

The relevant parts of the workstation layout for this factor includes all artefacts, materials, or tools that the assembly worker interacts with. You should consider material racks, tools and the positioning of these, and also secondary items such as packaging materials and recycling bins, if they are regularly used. Bins and equipment that is not regularly used can be omitted. An easy way to start organizing the work regarding tools can be found in the Toyota production systems 5S (Monden, 1995), this methodology can also be used in the assessment of this factor.

There are five primary 5S phases: They can be translated from the Japanese as "sort", "straighten", "shine", "standardize", and "sustain". Other translations are possible. A selection of the factor relevant issues from 5S are:

  • Remove unnecessary items and dispose of them properly.
  • Arrange all necessary items in order so they can be easily picked for use.
  • Make it easy to find and pick up necessary items.
  • Maintain everything in order and according to its standard.
  • Everything in its right place.

In a mixed mode flow, naturally it is impossible for the workstation layout to correspond completely to the assembly sequence. In this case, the assessment should be at L4 or higher.

 

Parts identification

Different types of part identification systems are more or less adapted to human use. The use of article numbers, for instance, has many benefits when used in computer systems as they are easily discriminated from each other and they are infinitely combinable. However, for human workers, they pose many challenges as their information value is limited at best. Lately, other types of parts identification and material supply solutions such as different types of kitting and sequencing of material are used.

Assessment

Description:
Parts identification can be done in several different ways. The traditional way is through article numbers and material racks but other approaches can include kitting and alternate parts identification syntaxes.

Measurements:
Selection

How to evaluate:
Determine type of parts identification system.

Levels:


Level

Description

L0

Not applicable

L1

 

L2

Sequenced kits or kanban is used for most items.

L3

 

L4

Unsequenced kits or kanban is used for most items.

L5

 

L6

Majority of parts identification through symbol syntax or similar.

L7

 

L8

Majority of parts identification through article numbers.

Details

There are different approaches to parts identification and material supply that may not fit into the level explanation provided here. If your strategy cannot be found in the level description, please do your best to translate it into a suitable level. L1 is for tasks where the worker has to do no selection of material but rather just picks the part that is in the next sequenced area. L2 is where there are some prepared kits or trays of material but the different parts for one product are bundled together. For L3, parts identification is done with some syntax that carries semantic content. For instance, using symbols or colours instead of random numbers has been shown to be beneficial to human cognitive processing. Even though the symbols or colours are not connected to the part they are referring to, the mere usage of recognizable syntax that has any meaning to the human is beneficial and easier to recognize and remember. L4 is reserved for cases where parts identification codes are randomly generated, such as in the case of most (but not all) article numbers, in numbers or letters that have no meaning to the worker.

 

Quality of instruction

An assessment of the general quality of the instructions used in order to gather information about the work. There exist a lot of guidelines within the Human-Computer Interaction (HCI) area for instructions, e.g., Clark et al.’s (2006) evidence-based guidelines to manage cognitive load, Black et al.’s (1987) work on minimal instruction manuals, Carroll et al.’s (1988) minimal manuals, Mullet and Sano’s (1995) design of visual interfaces, and Eiriksdottir and Catrambone’s (2011) procedural instructions, principles, and examples, to mention but a few.

Assessment

Description:
The quality of instruction is a subjective measure that can be assessed according to several different factors. Focus on general visibility and readability of the instructions is recommended.

Measurements:
Subjective

How to evaluate:
Observation assessment on quality of instruction. The following points should be considered when assessing the factor:

  • Text to background contrast is adequate
  • Avoid dark on dark or light on light
  • Font size and spacing is adequate
  • If in doubt, larger font sizes are generally preferred. Also, line spacing should not be too small as it tends to make lines hard to discriminate to each other.
  • Only relevant information. Manufacturing workers are often under time pressure and information that is of no use to them only slows them down in search of the relevant information.
  • Reasonable time to find relevant information. This is highly connected to the assembly time and must not be excessive.
    Major tasks are clear and descriptive
  • Critical content is clearly visible
  • Emphasis (bold, colouring etc.) is used only where relevant, not elsewhere.
  • Information is placed “above the fold”. The user should not be required to scroll/turn the page on the interface/instructions.
    Labels and buttons are clear. If the interface is interactive (i.e. the user is supposed to interact with the interface) the labels and buttons must be easily identified.

    Levels:

Level

Description

L0

No instructions required

L1

 

L2

Assembly sequences are clearly separated and contains only relevant information

L3

 

L4

Assembly sequences are separated and contains mostly relevant information

L5

 

L6

Assembly sequences are not clearly separated and visibility OR readability is diminished.

L7

 

L8

Instruction is filled with non-priority information. Visibility AND readability is diminished.

Information cost

The cost of information is described as an assessment of how much physical or cognitive effort that is required to utilize the information (Thorvald, 2011). It has been both argued and empirically confirmed that the cost of gathering information has great impact on the actor’s proneness to do it. Most likely, actors value the information that they believe is to be gathered from experience and make an internal cost-benefit calculation to see if the information should be gathered or if there is room for a “gamble” (i.e. making an experienced assumption on what the information contains). The factors that affect this calculation are the following:
The cost of gathering the information.

    • Physically – is the information located far away from the actor or can it be attended with minimal physical effort?
    • Cognitively – is the information structured so that a mere glance at the information medium is enough for information gathering or is extensive search through the documentation necessary to find the correct information?

The perceived value of the information – largely based on the frequency with which the information varies. The less the information varies, the lower the perceived value is since it is almost always the same and an educated guess is probably enough in a majority of the cases.

Assessment

Description:
The cost of information can be described as an assessment of how much physical or cognitive effort that is required to utilize the information.

Measurements:
Subjective

How to evaluate:
Determine if access to information requires physical or cognitive effort. What constitutes as a significant effort can be quite tricky to define but the general conclusion seems to be that it is less than you would think. If accessing information requires more than just a turn of the head while doing the task, it might be considered significant in certain cases. To assess this factor properly, it is highly recommended that you consult the assembly workers and get their opinions.

Levels:


Level

Description

L0

No instructions required

L1

 

L2

Information is not required for standard operations.

L3

 

L4

Information is no more than one step away and easily found.

L5

 

L6

Information is accessible through some cognitive or physical effort (several steps or visual search).

L7

 

L8

Significant movement or actions are required for information access.

Details

An academic experiment, set up to mimic truck assembly showed as much as a 50% reduction in quality defects when using a mobile, handheld information unit as opposed to a computer terminal situated about 2-3 meters away. Workers were more inclined to attend the information in the mobile unit since it was always at arm’s length. They were also more inclined to go back and look a second and third time to avoid having to keep all information in their short-time memory.

 

Poke-a-yoke and constraints

Poke-a-yoke is a Japanese term that means "mistake-proofing". A poke-a-yoke is any mechanism in a lean manufacturing process that helps an equipment operator avoid (yokeru) mistakes (poka). Its purpose is to eliminate product defects by preventing, correcting, or drawing attention to human errors as they occur.Forcing functions - A forcing function is an aspect of a design that prevents the user from taking an action without consciously considering information relevant to that action. It forces conscious attention upon something ("bringing to consciousness") and thus deliberately disrupts the efficient or automatized performance of a task. Using a forcing function is self-evidently useful in safety-critical work processes. It is however also useful in situations where the behaviour of the user is skilled, as in performing routine or well-known tasks. Execution of this type of tasks is often partly or wholly automatized, requiring few or no attention resources (controlled processes), and it can thus be necessary to "wake the user up" by deliberately disrupting the performance of the task (www.interactiondesign.org).

Assessment          

Description:
Using poke-a-yoke solutions or constraints in assembly is a common way to reduce assembly errors. This includes designing the task and/or the product so that assembly errors cannot be made.

Measurements:
Subjective

How to evaluate:
Determine to what extent constraints or poke-a-yoke solutions exist.


Levels:


Level

Description

L0

Assembly errors cannot be made due to the design and fit of the product.

L1

 

L2

Assembly errors can barely be made due to the design and fit of the product.

L3

 

L4

Assembly constraints are present in most of the assembly sequence.

L5

 

L6

Assembly constraints are present but not throughout the assembly sequence.

L7

 

L8

No poke-a-yoke solutions are implemented in the task.

Details

Some of the most common examples of poke-a-yoke are the use of;

  1. Guide pins – assuring that components can only be assembled in the correct way.
  2. Counters – confirming that the correct number of components or steps have been assembled or carried out.
  3. Checklists – reminding workers to perform specific actions

 

Assessment of results

When all assessments have been made, press the calculate button for your results. For more information about how to value your assessment, please refer to the complete pdf handbook at the top of this page.