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Investigation into the Accessibility of Clasps

Conducted as part of the MediVoice Project (a Co-operative Project, funded by the European Commission under FP6)
by Antoinette Fennell
February 2007

 

The aim of this investigation was to assess the accessibility of six different locking mechanisms (termed "clasps") and, on the basis of the results, provide recommendations for the optimal choice of clasp for the MediVoice device.

A sample of eleven (four women, seven men) blind and partially sighted test subjects were presented with six containers in random order, representing six different types of clasp. The age range of the female participants was 40-79 years (Median = 54.5), and of the male participants was 36-70 years (Median = 58). Three of the test subjects mentioned that they have arthritis.

For each test, only one test subject and the evaluator was present. The test subjects were asked to open the container and close the container. They were also asked for their opinion on the design of the locking mechanism. After they have viewed all six containers, they were asked to compare the containers and identify a favourite and least favourite, focussing only on how the container opens and closes.

Six different plastic containers were chosen to represent different types of clasp and/or different user actions required to open and close the clasp. The containers, clasp-types and required user actions are described beside the accompanying photographs below.

 

Clasp 1: Simple tooth clasp

Container: Calculator case (see Figs. 1 and 2)

General description of clasp: When closing, the two sides of the container are simply pushed together. As this occurs, a tooth (on the inner side of the top of the container) slides over a sloped area and then clicks into a small recess on the other side of the container. When opening, force is required to pull the tooth out of the recess. A noticeable click is heard when the container is both closed and opened. 

Description of this clasp in the sample provided: The top of the case (the lid) overlaps the bottom of the case at one point, so that a tooth on the top slides into a small recess on the bottom.

Required user action: Place thumb of one hand on front of top lid, place thumb of other hand on front of bottom lid, pull thumbs apart to open. Squeeze top and bottom lids together to snap closed.

Figure 1: Photograph of closed calculator, demonstrating a closed tooth clasp.

Photograph of a calculator showing closed tooth clasp

 

Figure 2: Photograph of open calculator, demonstrating an open tooth clasp. The recess can be seen at the bottom centre of the calculator, the tooth is located on the inside centre of the top lid.

Photograph of a calculator showing open tooth clasp

 

Clasp 2: Flip-over clip clasp

Container: Storage container (see Figs. 3 and 4)

General description of clasp: a hinged hooked section of plastic is permanently attached to one side of the container, and it clips over a lip on the second free side of the container, holding the two parts together.

Description of this clasp in the sample provided: The two blue clasps are attached to the bottom part of the container and hook over the lid of the container, holding the bottom and the lid together.

Required user action: To open, tuck a finger or thumb underneath the blue clasp and pull upwards and outwards to unhook. To close, the blue clasp is pushed from the bottom upwards and inwards, clicking the clasp into place around the lid. Repeat for the second clasp.

 

Figure 3: Photograph of closed flip-over clip carton, demonstrating two closed flip-over clips. The blue clips are attached to the bottom of the container and clip around the lid of the container, securing the lid on top.

Photograph of closed flip top carton

Figure 4: Photograph of open flip-over clip carton, demonstrating two open flip-over clips. once the flip over clips are opened the lid just sits loosely on top of the bottom part of the container.

Photograph of open flip top carton

 

Clasp 3: Strong spring clasp

Container: Glasses case (see Figs. 5 and 6)

General description of clasp: A button, attached to a strong internal spring, is pressed, releasing a tooth clasp.

Description of this clasp in the sample provided: A button located on the front centre of the bottom half of the container is pressed, releasing a tooth clasp, and the top half of the container flips open.

Required user action: To open, the user presses a button. The lid flips open and the user uses one or both hands to open it fully. To close the user pushes the top and bottom of the container together until a click is heard.

Figure 5: Photograph of closed glasses case, demonstrating a closed strong spring clasp.

Photograph of closed glasses case, whoeing strong spring clasp

Figure 6: Photograph of open glasses case, demonstrating an open strong spring clasp.

Photograph of glasses case showing open strong spring clasp

 

Clasp 4: Push clasp

Container: Hard plastic geometry set box (see Figs. 7 and 8)

General description of clasp: An indentation in the container is pressed releasing a tooth clasp.

Description of this clasp in the sample provided: An indentation in the centre front of the bottom half of the container is pressed, releasing a tooth clasp.

Required user action: To open the user presses on the indentation with a finger or thumb of one hand, this releases a tooth clasp, and using the other hand the user lifts the lid. To close the user presses both sides of the container together until a click is heard.

Figure 7: Photograph of closed geometry box, demonstrating a closed push clasp.

Photograph of plastic pen box, showing closed push clip

Figure 8: Photograph of open geometry box, demonstrating an open push clasp.

Photograph of plastic pen box, showing open push clasp

 

Clasp 5: Slide-lock clasp

Container: Toolmaster toolbox (see Figs. 9 and 10)

General description of clasp: A bar is slid to one side, releasing a lock.

Description of this clasp in the sample provided: A plastic strip with a tactile arrow on it is slid to one side, releasing the locking mechanism.

Required user action: To open, the user slides the plastic bar across, requiring a pushing or pulling motion, depending on which way the container is facing. The top of the container is then held in one hand, the bottom in the other hand and the two side are pulled apart. To close the top and bottom of the container are pushed together. The plastic lock is then slid across in the opposite direction to before.

Figure 9: Photograph of closed tool box, demonstrating a closed slide-lock clasp.

Photograph of tool box showing closed slide lock clasp

Figure 10: Photograph of open tool box, demonstrating an open slide-lock clasp.

Photograph of tool box showing open slide lock clasp

 

Clasp 6: Friction fit clasp

Container: Small tupperware container (see Fig. 11)

General description of clasp: One half of the container has a double ridge around the perimeter of it. The other half has a single ridge. The single ridge slots in between the two parts of the double ridge forming an air-tight seal.

Description of this clasp in the sample provided: See General Description above.

Required user action: To open, the user pulls the two sides of container away from each other. To close, the user aligns the two sides, and then pushes or squeezes them together.

Figure 11: Photograph of closed tupperware box, demonstrating a closed friction fit clasp.

Photograph of closed tupperware box, demonstrating closed friction fit clasp

 

Statistical Analysis of Results

It should be noted that the statistical analysis of "favourite" and "least favourite" is merely preliminary. No one clasp was unanimously chosen as favourite. But rather, detailed feedback was recorded for each of the six containers. On the basis of this more detailed feedback, examples of good and bad practice (both of which are demonstrated in each of the six containers) are provided in Tables 1 and 2 below.

 

Statistical Analysis of Results - Positive Feedback

There was a significant degree of variation in the number of times each clasp was chosen as favourite (Kruskal-Wallis Test: Chi-Square = 15.8, df = 5, p < 0.01). As a whole, the most popular clasp was the strong spring clasp (glasses case). The glasses case was significantly more popular than the simple tooth clasp (calculator; Mann-Whitney Test: Z = -2.7, n = 22, p < 0.01) and the slide lock clasp (toolbox; Mann-Whitney Test: Z = -2.7, n = 22, p < 0.01).

Although the glasses case was the most popular overall, this container did demonstrate examples of bad practice, as well as good. A more detailed assessment of the accessibility of the clasps is provided in Table 1, where examples of good practice are provided. Examples of bad practice are described in Table 2.

Table 1: Positive feedback and recommendations

Good practice
Further comments (examples)
Audible click when successfully opened
(calculator)
Audible click when successfully closed
(calculator, glasses case)
High colour contrast on clasp/button
(flip-over clip)
Can be opened when sitting on a table
(glasses case)
Sits open on a table
(calculator, geometry box)
Tactile features allow easy identification of clasp
(glasses case)
When button is pressed the wallet pops open slightly
(glasses case)
Protruding lip to grip onto if pulling open
(tupperware)
It is obvious when the clasp is open and closed
The case pops open slightly (glasses case)

 

Statistical Analysis of Results - Negative Feedback

There was a significant degree of variation in the number of times each clasp was chosen as least favourite (Kruskal-Wallis Test: Chi-Square = 12.1, df = 5, p < 0.05). As a whole, the least popular clasp was the friction fit clasp (tupperware). The tupperware container was significantly less popular than the strong spring clasp (glasses case; Mann-Whitney Test: Z = -2.5, n = 22, p < 0.05) and the flip-over clip clasp (flip-over clip carton; Mann-Whitney Test: Z = -2.5, n = 22, p < 0.05).

Although the tupperware container was the least popular overall, this container did demonstrate examples of good practice, as well as bad. A more detailed assessment of the accessibility of the clasps is provided in Table 2, where examples of bad practice are provided. Examples of good practice are described in Table 1 above.

Table 2: Negative feedback and recommendations

Bad practice
Further Comments (example)
Box is distorted when opening. For example, the lid requires excessive effort to open, therefore box is twisted. Not appropriate for people with reduced manual dexterity or the use of only one hand (tupperware)
Two clasps that have to be opened simultaneously Not appropriate for people with low strength, reduced manual dexterity or the use of only one hand (flip-over clip)
Container has to be actively held open to access contents (i.e. it does not sit open when placed on a flat surface) Not appropriate for people with low strength, reduced manual dexterity or the use of only one hand (glasses case)
Fully removable lid The lid could be lost (flip-over clip)
Unsure if wallet is locked or unlocked There is no obvious change from the open to the closed state (toolbox)
More action required than simply pushing shut Not appropriate for people with low strength, reduced manual dexterity or the use of only one hand (toolbox, flip-over clip)
Excessive force required to open Not appropriate for people with low strength, reduced manual dexterity or the use of only one hand (tupperware)
Pops open too forcefully Pills could fall out (tupperware)
Both hands are absolutely necessary to open Not appropriate for people with low strength, reduced manual dexterity or the use of only one hand (tupperware)
Sharp protruding parts Hands could be injured or nails could be broken on clasp (toolbox)
Fingernails are needed to open the container There is nothing to grip onto with fingers to pull apart the two sides of the container (calculator)
Additional tactile features that can be confused with a clasp/button Raised branding on an otherwise smooth container was confused for part of the clasp (calculator)
When held in both hands, one hand impedes the other from opening Size of two sides of container are too small (calculator)

 

Acknowledgements

This project was funded by the European Commission under FP6. The author wishes to thank the anonymous test subjects who took part in this study. Sincere gratitude is extended to the staff of RNIB Bristol, in particular David LePoidevin, for considerable help.

 

 

 



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