article 1- getting a grip

8/9/2019 Article 1- Getting a Grip

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Cutlery design undergoes extensive evaluation of hand-obJect Interaction,

leading to Improved products for people with hand use limitations.

EOPLE USE THEIR HANDS TO CONTROL AND

interact with their environment. Although a

number of studies explain the physical inter-

action between hand and object during a task, they fall

short of describing a simplified model. Guidelines and

performance specifications that can be easily applied by

human factors/ergonomics professionals, industrial

designers, and other members of a product develop-

ment team are vital for an effective outcome. The

model of hand-object interaction described here uses

current clinical and ergonomics measurement tech-niques, such as task analysis, observation, interview,

focus groups, questionnaires, anthropometrics, and

measurement of range of movement and grip strength.

In addition, we undertook further measurements of fin-

ger friction and finger compliance, or finger stiffness.

We employed this user-centered design approach to

elicit information from users about their needs and

aspirations and the physical functionality (effectiveness)

of the tool. This approach validates the research out-

comes to support new product development and a more

holistic and evidence-based approach for designers

BY GEORGE TORRENS, DEANA

McDONAGH-PHilP, & ANNE NEWMAN

(McDonagh-Philp, Lebbon, & Torrens, 1999). We

begin with a detailed description of hand-object inter-

action in this case study and provide criteria for evalu-

ating existing and new cutlery products. This work

resulted in the design of an improved product.

Hand-Object Interaction Model

The following model is based on eight years of

research on hand-object interaction (Brown, Torrens,

& Wright, 1992; Torrens & Gyi, 1999). For the pur-

poses of this study, our focus was on the physical inter-action between the hand and the task object, rather

than the cognitive interaction. The measurements

described here reflect the emphasis on characterizing

the physical attributes of the hand and relating them to

a defined physical interaction with an object during the

performance of a given task. The model is based on

three levels of physical interaction: macro, intermedi-

ate, and micro interaction. Figures I and 2 show the

three levels of interaction and the forces they resist.

Note that micro- and intermediate interaction resist

shear forces in parallel with the palmar surface, whereas

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Bone

Skin surfaceSoft tissue

Product surface

I Shear forces

Interlockingcontactarea-.:=-

I

Figure 1.

Micro interaction is the friction between the skin and prod-

uct surface materials. In intermediate interaction, the soft

tissues underlying the palm face interlock with surface details

of a product to provide a mechanical interlock beyond skin

friction. These two levels of interaction have been found to

work best at less than 20 Newtons force.

Rotational and~

linear forces ••• ;:in shear to hand '\surface

Lateral force perpendicular to

hand surfaceAxial forces acting

~ perpendicular to handsurface

Figure 2.

In macro interaction, the structure of the hand (bone,joints,

and muscles) interlocks with the shape of the product. This

level of interaction has beenfound to work at all levels of

force, but primarily in tasks requiring more than 20

Newtons force.

TABLE 1. OVERVIEW OF HAND-OBJECT INTERACTION AND RELATED TEST METHODS

Hand/body Object

Characteristics Characteristics Equipment Outcome

Micro Skin friction; skin Surface material; Friction meter; Skin performance

interaction moisture; stress; state surface finish; surface thermocouple; blood (friction), related to skin

of physical exertion; ternperature; flow meter; humidity and underlying soft tissue

heart rate; blood contaminants, edge meter (galvanic compliance. Pressure (Pa)

pressure; blood flow; detail (sharp) resistance) at points on the surface of

surface pressure the hand, finger tempera-

ture and surface moisture

Intermediate Skin and soft tissue Surface features; Compliance meter; Compliance characteristics

interaction friction and mechanical surface material; thermocouple; blood of skin and underlying soft

shear/hydraulic surface finish; surface flow meter; humidity tissues that enable mecha-

pressure; temperature; temperature meter nical interlocking to occur

humidity; stress; heart related to finger friction.

rate; blood pressure Excel file; hand and finger

and flow; surface surface pressure, finger

pressure temperature and surface

moisture

Macro Finger and hand joint Object handle/grip CODA, Goniometer; The ability of the hand to

interaction segment position (grip size; shape; surface video; stadiometer; mechanically interlock

pattern); joint capsule temperature; edge anthropometer with an object shape, opti-

integrity; skeletal detail (sharp) mizing soft tissue and skin

integrity; tendon friction. Excel file, x, y, z

integrity; range of coordinates related to time,

movement; muscle force (vector and resultant,

bulk; temperature; torque), hand surface pres-

humidity; stress; heart sure, surface temperature

rate; blood pressure and and surface moisture

flow; surface pressure;

anthropometrics

ERGONOMICS IN DESIGN . SPRING 2001


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TABLE 2. THE HANDS OF EACH PARTICIPANT AND

THEIR MEDICAL CONDITION

macro-interaction resists forces that are perpendicular

to the palmar surface.

Table 1 is a comprehensive overview of hand-object

interaction, showing measurements taken and their out-

comes. Selected individual measurements may be used

in isolation and may be adequate to validate hand char-

acteristics and interaction performance. The choice of

Participant

Case Study

Assistive technology products support an individual

in daily livings tasks, such as opening a can or using

eyeglasses. Many of the available assistive technology

cutlery products have originated from clinical studies or

individual clinicians' expertise. However, in the United

Kingdom and Northern Ireland, such products are

often categorized as wheelchairs, lifting hoists, hear-ing aids, or environmental controllers. Although these

products satisfy utilitarian-functional needs, it is clear that they do not always meet users' cultural and social

aspirations.

Industrial design brings together the physical func-

tionality and social and cultural function (i.e., desir-

ability) through a user-centred design approach.

Nottingham Rehab Supplies Limited commissioned

design research on cutlery for users with limited grip

and dexterity. The cutlery was to be marketed to a large

user group within the UK and Northern Ireland,

Europe, and United States. The cutlery reviewed in the

study reflected the commercially available ranges in the

UK and Northern Ireland; many of these items are alsoavailable in Europe and the United States. The pilot

study involved volunteers from the Loughborough

(Leicestershire, UK) area who had a variety of muscu-

loskeletal and neuromuscular diseases. The samplegroup reflected the larger population that is likely to

require assistive technology cutlery. The contacts were

obtained through national, regional, and branch offices

of special interest groups in the UK (e.g., age concern,

arthritis care, and community groups).

We selected seven individuals for the initial pilot

study whose medical conditions caused a weak grip or

limited dexterity. Table 2 shows these participants'

measurements to be taken may depend on project con-

straints, such as time scales, user group characteristics,

funding, and available resources (e.g., staffing).

The following case study exemplifies the application

of some of the measurements shown in Table 1. The

measurements taken at a given moment during a task

or series of tasks performed by an individual can vary

considerably. This is because the person's physiological

and psychological states are constantly changing, main-

ly caused by external influences such as stress (needing

to complete a job in a hurry, for example), humidity,

temperature, and vibration (including noise).

The physiological changes that affect grip can be

measured through heart rate, blood pressure, skin or

body temperature, and skin humidity. The external

influences, such as pressure to perform a task, environ-

mental temperature, noise/vibration, and humidity can

also be measured to compare the measurements. Such a

comprehensive set of measurements of a given task

enables a more detailed characterization of an individ-ual and the task he or she is performing.

RA in all joints, had disease

for 16 years, restricted fin-

ger and upper limb move-ment.

Skin disease (itching), left

hand index finger fixed in

extension, frail condition.

RA, in most joints, severe

Ulna deviation, contracture

of finger tendons.

Rheumatoid Arthritis (RA),

had disease for 40 years,

affects most joints.

Osteoarthritis of the hands

and upper limb, enlarged

knuckle (MCP) joints, frail

condition.

Spinal infarction (form of stroke) in the spine, injured

in 1987, diabetes, generalloss of upper-limb function,

limited haptic perception.

Description of Medical

Condition

Tetraplaegic C6 Complete.

Injured in 1984, contractureof right hand fingers enables

grip through wrist flexion.

5

1

7

6

4

3

2



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TABLE4. PARTICIPANT2 USINGTHE RANGEOF

CUTLERYEVALUATED

Cutlery

NOTE: From the above details, it can be seen that this person (par-

ticipant 2), when using a knife and fork, approached the plate with

the utensils at a steep vertical angle. This is to maximize the downward

force applied through the hands. Knife, fork, and spoon are balanced

in the hand when not in active use.

t o " ~

Spoon

.~., -7"

,; ~t"I r J '\"":

------ --

C

F

D

E

Knife & fork

TABLE 3. EXSTINGPRODUCTSUSEDFOR PRODUCT

DESIGNAUDITANDBENCHMARKING

Sample Name Supplier

A Queens cutlery Smith & NephewLimited

B AMEFA Nottingham RehabLimited

C Selectagrip Nottingham Rehab

Limited

D Caring cutlery Nottingham Rehab

Limited

E Ultralite Nottingham Rehab

Limited

F Goodgrips Nottingham RehabLimited

hands and an outline of their medical conditions. Ini-

tially, the assessment involved the use of a grip dynamo-

meter and a simple task. Participants were accepted if

they had a grip strength of less than 150 Newtons in

their right hand, if they could not touch one or more of

their fingers to their thumb of the same hand, or if they

could not make a fist. We asked them to present their

own cutlery and used these products as a benchmark for

comparison with seven sets of cutlery (see Table 3) cho-

sen to represent the range of products currently avail-

able for users who have limited dexterity and grip

strength.

The sample group for this pilot study represented a

broad spectrum of medical conditions, age, and socio-

economic backgrounds. Five participants lived in single-

level home (i.e., no stairs or elevator), and two lived in

apartments with care worker support. The mean grip

strength was extremely low, not exceeding 50 Newtons.

Three of our volunteers could not hold the grip

dynamometer, and five could not make a fist with their right hand.

Participants provided a subjective rating (1 = very good,

2 = good, 3 = adequate, 4 = poor,S = very poor) for each set

of cutlery, including their personal use cutlery. The rat-

ings, or scores, covered physical functions (usability, for

example) and design detailing (e.g., color, shape, and

ease of cleaning). As part of the evaluation, we asked

them to demonstrate how they would normally use the

products while simulating the cutting of a piece of rub-

ber that represented a piece of lean meat. During a rat-

ing exercise, the researcher noted any additional

comments relating to social and cultural issues made by

ERGONOMICS IN DESIGN· SPRING 2001


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TABLE 6. FEEDBACK ON CUTLERY SAMPLES

Current Cutlery Deficiencies

Handles too large in diameter to hold (samples A, C, D,

and E were more than 30 mm wide).

Handle surface inadequate in assisting grip through skin

friction.

Handle shapes incorrect for the majority of users inter-

viewed.

Center of gravity of some cutlery incorrectly positioned

(sample E was very utensil head heavy).

Length of the knife blade was found to be as long as

handle, reducing possible leverage applied by the

user through the handle (all knife samples were

around 50/50 handle/blade).

Poor styling.

Poor build quality.

Appear to be difficult to clean.

mm to 36 mm from the distal end of the handle (a

minus value indicates that the point is beyond the dis-

tal end of the handle; see Figure 4, page 11).

Cutlery handles of sample E were found to have the

highest coefficient of friction (2.58), primarily because

they are made of a foam elastomer material. Knife sam-

ples D and F were found to be the most efficient at cut-

ting the meat block. Knife D had a serrated blade, as

did all other knives except knife F. The angle of the

blade may have had a greater effect on performance

than did blade serration. Knives A, B, C, and E had

conventionally shaped blades; the front of knives D and

F were steeply angled (D = 25°, F = 30°).

The values shown in Table 5 and Figure 3 are a

composite value produced by combining the rating

Specification for Design Solution

A handle with a thin section to enable the user to jam

the utensil between fingers.

Handles with a ridge between the utensil head and the

handle and at the base of the handle to stop the hand

slipping onto the blade or off the handle during cutting.

High-friction handle material should be used on the

handle.

The cross-section of the handle should be faceted, with

the main area of grip smooth to avoid high pressure

points.

The knife blade should be angled, if possible.

The handle should to be perceived by the user to be

easy to clean.

The handle should be machine washable and avoid dirt

traps.

given by each of the seven participants for each ques-

tion. A value over 80 indicated a strong dislike of the

product, and a value less than 60 indicated that they

liked the product. The scale provides an indication or a

trend of opinions from within the sample group.

Table 5 indicates a noticeable dislike for samples B,

C, and E; all three had high overall rating values and

individual values. Sample A was well liked for its per-

ceived weight and ease of cleaning. The user group dis-

liked cutlery sets Band C, expressing dissatisfaction

about the defined aspects of all other sample sets. The

cutting forces of between 2 and 4 Newtons involved in

meat cutting using a knife are small compared with the

force required to lift a coffee pot, for example.

Figure 5. Prototype cutlery development (left) and the final preproduction design solution (right).

E RGONOMICS IN DESIGN. SPRING 200 I


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TABLE 7. DETAILS OF NEW CUTLERY PRODUCT

DESIGN SPECIFICATION

• The new cutlery has been designed to be inconspic-

uous when used in public places; it looks like con-

ventional kitchen-grade cutlery.

• The black handle color was chosen to visually reduce

the overall handle size.

• The conventional handle shape and steel utensil head

make it acceptable to other family members and

friends (inclusive design).

• The handles are all the same shape, providing a

strong identity with the set and reducing production

costs.

• The handles are injection molded over the steel uten-

sil head to avoid dirt traps, and all materials used are

dish-washable.

• The flattened hexagonal handle section is large

enough to enable a finger to be comfortably pressed

onto the edge of the knife, or jammed (cleat-like)

into the crotch of the thumb and index finger.

• Ridges and dimples have been avoided because they

cause discomfort to the target users, as they often have

poor skin quality because of their medical condition.

• The high-friction elastomer covering on the handle

provides an effective grip to the skin surface.

• The flared sections to the front and back of the han-

dle length provide more stability against the utensil's

turning in the hand.

• The flared sections also stop the hand's sliding off

the handle front or back.

• The new designs are lightweight for ease of handling.

Points to Consider

Our study participants highlighted a number of

problems when using the commercially available ranges

of cutlery. Table 6 (page 12) illustrates functional and

physical problems they noted, their visual aspirations

for this product, and a cutlery specification we devel-

oped to reverse these deficiencies. Although such asmall-sample survey of opinions and observed abilities

should not be taken as a representation of the UK and

Northern Ireland population as a whole, in the absence

of accessible information, it provides product develop-

ers with some guidance on the points to consider in

improving cutlery design.

Based on the initial findings, we produced concept

designs using the CAD/CAM and injection molding

facilities in our department (see Figure 5). The new

designs incorporated many of the needs and aspirations

expressed by those involved in the cutlery evaluation

(see Table 7).

The same partICipants evaluated the prototypes

pictured in Figure 5 (page 12). A cycle of evaluation,

feedback, reflection, and refinement was undertaken on

two additional occasions and with a larger number of

participants. The final design was then tooled for pro-

duction, and the product is now available through the

Nottingham Rehab Supplies Limited (which has U.S.

distributors).

The evidence-based approach and user-centered

design methods applied in this study are generic, don't

cost a lot of money, and are just good practice. The

extra effort to obtain a closer empathy among manu-

facturer, designer, and client reduces the risk for in-

vestors and provides a product that people actually want

to use and will buy.

ReferencesBobjer, O. (1989). Ergonomic knives. In A. Mital (Ed.), Advances in

industrial ergonomics and safety I (pp. 291-298). London: Taylor &

Francis.

Brown, F. R., Torrens, G. E., & Wright, D. K. (1992). Research intooptimising hand and body function for tasks in everyday living:

The development of a range of "easy use" saucepan handles. In M.

Bracale & F. Denoth (Eds.), Medicon '92, Proceedings of the VI Mediterranean Conference on lVledical and Biological Engineering (pp.

549-553). Naples: Associazione Italiana di Medica e Biologica.

McDonagh-Philp, D. c., Lebbon, c., & Torrens, G. E. (1999). Anevidence based design method within a user-centred design

approach. In Proceedings of The 4th Asian Design Confere1lce Inter-

national Symposium on Design Science. Nagaoka, Japan: The Pro-

gram Committee. [CD-ROM].

Torrens, G. E. (1995). Designing for physical disability: A discussion

of research and development methods through to a commercial

conclusion. In R. Cooper (Ed.), Designing interfaces: Inaugural con-

ference of the European Academy of Design (pp. 13-21). Salford, Eng-

land: University College Salford.

Torrens, G. E. (1997). What is the optimum surface feature? In S. A.

Robertson (Ed.), Contemporary ergonomics (pp. 314-319). London:

Taylor & Francis.

Torrens, G. E., & Gyi, D. E. (1999). Towards the integrated mea-

surement of hand and object interaction. In Proceedings of the 7th

International Conference on Product Safety Research (pp. 217-226).

Washington, DC: U.S. Consumer Product Safety Commission.

George E. Torrens is a lecturer in industrial design in the De-

partment of Design and Technology, Loughborough University,

Loughborough, Leicestershire, LEU 3TU, 1-509-222-664,fax

1-509-223-999, [email protected]. A practicing industri-al designerfor the last 12 years, he is also director of Dexterity

Research Limited, a company specializing in researchand devel-

opment on hand-related products. Deana McDonagh-Philp is an

industrial design lecturer at Loughborough University whose

areas of research include gender and design, focus group tech-

niques, and user-centered design techniques and methods. Anne

Newman is a consumer scientist and ergonomist and manager of

the Loughborough Advanced Technology Initiative, part of the

Loughborough Partnership, where her main role is to advise

high-tech companies on networking, growth, and innovation.

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