Electric Toothbrush Redesign

ED&G 100 Section 7                                Team 1                            Submitted to:  Prof. Sven Bilén                    March 5, 2007

Team Members

Kevin Hom  Email:  kyh5028@psu.edu

Pat McNally  Email:  pkm5007@psu.edu

Matt Ekinci    Email: fme5002@psu.edu

Dennis McHugh  Email:  djm5129@psu.edu

Abstract

Our team was tasked with redesigning the Dollar Tree Toothbrush with Vibrating Action, a very low-end electric toothbrush whose main drawing power was its low cost.    Over the course of our design process, we determined that problems involving the head motion, head design, and battery cover were the most crucial to address.  Our final redesign involves moving the eccentric weight that produces vibration to the neck of the brush, splitting the brush head, incorporating a screw-on battery cover, and varying the height of the bristles.  This will greatly increase the cleaning ability, comfort, and safety of the brush while representing a minimal difference in manufacturing costs.

Introduction

For the past several weeks, our team has been working to redesign the Dollar Tree Toothbrush with Vibrating Action.  This is a low-quality but also extremely low-cost electric toothbrush that is manufactured by Dollar Tree, Inc. for sale in their own chain of dollar and low-end retail stores.  Starting with a customer needs analysis in order to determine problems in the current design that must be addressed as well as gather ideas for potential consumer-pleasing features to incorporate, our team began a lengthy design process.  Aiming to redesign the toothbrush to improve its quality while maintaining its exceptionally low cost, our product was benchmarked against competitors and dissected for part and feature analysis, and then redesigned on the basis of a number of proposed conceptual features and total designs that were whittled down to a select few.  Ultimately, one final design was chosen that we believe achieves our goal of increased performance and overall quality while maintaining a low cost.

Mission Statement

Mission:  Our goal is to redesign the Toothbrush with Vibrating Action into a more effective cleaning device for your teeth while maintaining an especially low cost.

Product Description:  A handheld, battery-operated device to help clean teeth.

Primary Markets:  Dollar store consumers and low income families.

Secondary Market:  Travelers.

Assumptions:  Hand-held; battery operated.

Customer Needs Analysis

At the very beginning of the design process, our team decided that our redesign would continue to focus on the target markets our sample toothbrush would have possibly appealed to; that is, the average dollar-store consumer, low income families, travelers, and other people that would desire a very low-cost electric toothbrush.  In order to determine the features and functions our redesigned electric toothbrush would need in order to appeal to these consumers, a list of possible customer needs was compiled via team brainstorming and straw-polling techniques of people outside of our ED&G class.  Statements made during this process were then interpreted into needs that could be incorporated into our redesign.  The results of this process can be seen in Table 1.

Table 1.  Customer Needs and Rankings

Customer Statement

Interpreted Need

“The batteries fall out when it’s on!”

The battery cover is more secure.

“The bristles hardly move.”

The bristles oscillate more rapidly.

“This feels like it’ll break if I drop it.”

The brush functions normally after dropping.

“It looks cheap and crappy.”

The brush is aesthetically appealing.

“The brush itself shakes too much.”

Vibrations away from the brush head are minimized.

“The noise from electric toothbrushes irritates me, but this one isn't that loud."

Noise is minimized during use.

“I shouldn’t have to change the batteries before I need to change the brush head.”

Power source life span is at least equal to the ADA suggested brush head replacement time (3-4 months).

“Those bristles won’t actually clean anything.”

Bristle design effectively removes plaque and food particles.

"Plastic like that is slippery when it's wet." The brush is non-slick.
"Stiff bristles just hurt your gums." Bristles are soft.

“If I’m looking in a dollar store for a toothbrush, it better actually cost close to a dollar.”

The cost of the brush is roughly $1.00.

External Research

Patent Research

One of the first research steps our team took during our redesign process was to research patent information on features that may be incorporated into an electric toothbrush.  This search served dual purposes.  Firstly, it is often cheaper and more efficient to implement an already thought-off feature design in order to effectively solve a design-related problem, as opposed to engineering an entirely new problem solution from scratch.  Secondly, for legal reasons, it is always wise to see if anyone else has already laid design and patent claim to a potential feature so as to avoid unintentional patent infringement.  Several patents that were of particular interest to our redesign process can be seen below in Table 2.

US Patent Number

Feature Claimed

7,065,821

Conversion of rotational motor energy into oscillatory motion

5,815,875

Bi-positional toothbrush heads

7,117,555

Multi-action brush head motion

6,973,694

Oscillatory brush head motion

7,151,357

Oscillation frequency control

5,862,558

Pulsating in-out head motion

5,274,870

Combination static-oscillatory brush heads

Product Benchmarking

In order to gain an idea as to how our sample toothbrush stood when compared to others on the market, our team compiled databases of both qualitative and quantitative data regarding the sample toothbrushes that had been given to the other teams in Section 7, as seen in Tables 3 and 4.  The information contained in these tables was gathered by the teams themselves.

 

Table 3.  Quantitative Toothbrush Data

Toothbrush Avg. Noise Level  (dB) Oscillation Speed (Hz) Cost (USD) Weight (g) Battery Life (mAh)
Dollar Tree Toothbrush w/ Vibrating Action 70.1625 35.06 $1.00  ~65 5.07
Crest Spinbrush 71.5 51.35 <$6.00 248 5.7
Colgate SpongeBob Square Pants Toothbrush 78.25 116.67 $6.99 120 29.23
GUM Sesame Street Toothbrush 70.74 52.97 $6.99 109 4.5
Zooth Model #455 77.13 37.5 $5.99 N\A 1.98
Greenbrier International, Inc. Toothbrush 92 71.083 $1.00 72 N\A
Crest Spinbrush Pro 72.1 20.25 $6.99 N\A 5.76
Oral B CrossAction 84.575 35.87 $8.99 71 14.79

Table 4.  Qualitative Toothbrush Data

Toothbrush

Aesthetics

Power Switch

Ergonomics

Battery Location

Safety

Dollar Tree Toothbrush w/ Vibrating Action

Three small blue areas only flair to an off-white body; overly large boxy body with really narrow neck unappealing

Obvious and conveniently placed; easy to press

Not actually contoured to hand but still relatively easy to hold; could be better.

Centralized and doesn’t unbalance the brush.  Location marked via packaging and on the brush itself.  Cover too easily removable.

Battery cover shakes self off during operation at times; could cause injury if cover and battery fall.

Crest Spinbrush

Plain, but can be purchased in other colors.

Center of the brush; overly sensitive.

Needs a grip.

Bottom of the body; secure, but difficult to remove.

Safe; well-sealed and waterproof.

Colgate SpongeBob Squarepants Toothbrush

Brightly colored and features a SpongeBob motif.

Separate buttons for on and off; unlabeled which is which.  Easy to use.

Molded to fit a child’s hand; features on handle provide extra grip.

Bottom of the brush; must unscrew cover to access.

Battery cover design prevents children from easily removing; sealed and no sharp edges.

GUM Sesame Street Toothbrush

Colorful design featuring a Sesame Street motif.

Centralized and obvious single on\off button with soft cover.  Easily pressed.

Wide handle, is slippery and lacks a grip.

Bottom of the brush; cover comes off too easily.

Batteries can easily fall out of toothbrush.

Zooth Model 455

Multicolored and themed for children.

Sensitive button located where thumb is when holding brush.

Size makes it difficult for a child’s hand to hold.

Very difficult to access; cover held on with a small screw.

No noticeable dangers.

Greenbrier International Toothbrush

Plain and bland.

Ideally located and easy to use.

Awkward feel to the brush; grip located in an essentially useless location

Good location.

Toothbrush groove design presents chance of easy bacteria growth.

Crest Spinbrush Pro

Shiny; looks expensive and colors make you think of clean.

Conveniently located and easy to use.

Grooves make it easy to hold.

Logical.

Safe.

Oral B CrossAction

Good selection of colors; multicolored brush head indicates when it needs to be replaced

Located where the thumb would be placed while holding; easy to press.

Limited vibration doesn’t disturb brushing; easy to grip.

Bottom of the brush; out of the way of normal handling but still easy to access.

Sturdy and will not break during use.

 

After gathering this data, our team decided to do a more detailed comparison and evaluation between our own sample brush and the two others that were similar.  (Team 2's Crest Spinbrush and Team 4's GUM Sesame Street toothbrush).  This was choosing several possible customer requirements that could be addressed later in our redesign process and assigning them physical metrics that were associated with the need.  The metrics were then given target values that could reasonable be aimed for in a redesign, and our brush was compared and contrasted with the two others on this basis in a House of Quality table.  The results of this comparison can be seen below in Table 5.

Table 5.  House of Quality Evaluation.

Product Dissection

Part of the data gathering process for our redesign involved the breakdown and dissection of our sample toothbrush.  After gathering the benchmarking data that could only be gathered while the brush was still fully functional, we began to take it apart.  At first, only the parts and pieces that were easily removable by hand and could be replaced with no change in functionality were removed and analyzed.  This consisted of four parts:  the main brush body, the brush head, the battery cover, and a small, colored o-ring around the bottom of the brush head, and can be seen here in Figure 1.

Figure 1.  Detachable Brush Parts.

These parts were then measured and analyzed for their purpose in the overall functionality of the brush.  Following this, tools were used to further remove other parts of the brush that were not accessible or could be removed by hand.  These included the motor, battery contacts, motor housing, on\off switches, and a few other smaller parts.

Figure 2.  Exploded View of Toothbrush with Vibrating Action.

  As with the previous parts, these were measured and analyzed for their role in the operation of the brush.  The results of this process and our conclusions were then organized into a Bill of Materials table that can be seen below in Table 5.  One of the key pieces of information to result from this process that is not noted in the table was the discovery that the oscillatory motion of our brush resulted purely from the spinning of an unbalanced weight in the body of the brush, an obviously inefficient method of motion generation that could (and would) be touched upon during the upcoming concept generation process.

Table 6.  Bill of Materials for Dollar Tree Toothbrush with Vibrating Action.

 

Part #

Part Name

Quantity

SOP Effect

Function

Mass (oz)

Material

Dimensions

1

Brush Body

1

Brush Falls Apart

Holds other parts together

0.416

Plastic

4.5” x 1.25” x 1”

2

Brush Head

2

Can’t clean

Brushing surface

.096

Plastic\nylon

2.875” x 0.375” x 0.625”

3

O-ring

2

No effect

Aesthetics

N\A

Rubber

0.4375” diameter

4

Motor

1

No vibration

Causes brush to vibrate

.672

Metals

0.625” x 0.875” x 1.5”

5

Battery Cover

1

Battery falls out

Holds battery into brush

0.256

Plastic

1.75” x 1.25” x 1

6

Motor Housing

1

Motor no longer touches contacts

Stabilizes motor

0.064

Plastic

1.25” x 0.75” x 0.75”

7

Battery Contact

1

Circuit broken; no vibration

Carries current to motor

0.032

Copper

2” x .125” x 0.5”

8

Spring Contact

1

Circuit broken; no vibration

Completes circuit

N\A

Metal

0.625” x 0.4375”

9

On\Off Buttons

1

Harder to turn brush on\off

Pushes Switch Contact

N\A

Rubber

0.375” x 0.625”

10

Switch Contact

1

Breaks battery circuit

Completes circuit when “On” is pushed

N\A

Metal

0.4375” x 1.5”

Miscellaneous Research

Our team also conducted a large amount of miscellaneous external research in order to gain an idea of how certain features are implemented, their complexity, cost of implementation, variations in implementation, and the pros and cons of certain features.  Technical analyses of certain brush designs were considered, and a variety of medical studies regarding the effects of electric toothbrushes as compared to manual toothbrushes were also consulted.  Expanding on the latter, our team also read several studies that independently compared several varieties of electric toothbrushes, then compared and contrasted those against manuals.  Over the course of our research, we discovered that numerous studies supported the idea that electric toothbrushes in general consistently outperformed manuals by a statistically significant margin in cleaning ability, with multi-action and "sonic" brush head motion designs clearly having the best ability.  However, while the cleaning ability of these brush designs is unquestionable, they are also very complex and costly to implement, with some models such as the Oral B 7550 Professional Care multi-action reaching into the $70.00 range for suggested retail price, while the Sonicare Elite 9500 can cost up to $150.00.  Vibrating designs, which work via conducted vibration caused by an eccentric weight, were generally found to be inferior in cleaning ability to the driven-motion designs, but still performed better than manuals.  These designs are much simpler, and hence must easier to implement and less costly to manufacture, with prices ranging as low as the $1.00 of our own sample brush.  In terms of bristle design, it has been unequivocally shown that round-ended nylon bristles are key for toothbrushes, as natural hair brushes tend to not only deteriorate extremely rapidly while also accumulating bacteria faster than synthetic materials, and bristle ends that are any geometry other than rounded lend themselves to gum irritation and excessive enamel abrasion, though they may have superior cleaning ability.  Also, it has been shown in numerous studies that varying-height or "ripple" bristle designs are much more effective than even-trimmed bristles in removing plaque and food particles; however, until recently, it was difficult to produce this design while maintaining the desired bristle-roundness uniformly across the brushing surface.

 

Concept Generation

Following the benchmarking and dissection processes, our team's focus shifted to the actual redesign of the product.  We started with a functional decomposition of an electric toothbrush, analyzing the system as a whole and breaking it down into individual processes that contribute to the final goal of cleaned teeth.  This would enable us to more clearly see what smaller problems involved with the operation of the entire toothbrush could possibly be adjusted, modified, and redesigned. 

Figure 3.  Functional Decomposition of an Electric Toothbrush

Combining our customer needs, gathered benchmarking and dissection data, and functional decomposition while keeping our mission statement in mind, our team decided that for our redesign, our chief areas of focus would be head motion, the battery cover, and brush head design.  A concept tree was then created to address each of these problems, listing a number of possibilities for each.  These can be seen below in Figures 4-7.

Figure 4.  Concept Tree for Brush Head Motion

 

Figure 5.  Concept Tree for Battery Cover

Figure 6.  Concept Tree for Brush Head

Concept Selection

Based on our external research and goals of improvement while maintaining cost-effectiveness, many concepts were immediately eliminated during the selection process.  Some of these concepts included pulsing, sonic, rotary, and combinatory brush head motion, along with driven motion in general while utilizing a split-head design, as our research showed that they were simply far too intricate and expensive to possibly incorporate into our redesign while maintaining our low cost without some absolutely revolutionary manufacturing breakthrough.  Others, such as a permanent head rather than a replaceable one, were eliminated simply because they excessively increased cost to the consumer.  This greatly restricted our possible options for final designs, but our team was adamant in meeting one of our chief goals of maintaining exceptionally low cost even after redesign and were fully aware at the start of the design process of the potential limitations this would create.  The remaining individual concepts were then ranked against each other on 1-10 scale (with 5 being the base values provided by our sample brush) in weighted tables.  These can be seen below in Tables 7-9.

Table 7.  Concept Selection Table for Head Motion.

 

 

A

B

C

Head Motion

 

Base

 

 

 

 

 

 

Eccentric Weight-Body

Eccentric Weight-Neck

Driven Motion-Linear Side to Side

Selection Criteria

Weight

Rating

Weighted Score

Rating

Weighted Score

Rating

Weighted Score

Oscillation Speed

10%

5

0.5

7

0.7

8

0.8

Cost of Manufacture

60%

5

3

5

3

3

1.8

Vibrations Away from Brush Head

5%

5

0.25

8

0.35

7

0.35

Cleaning Motion Effectiveness

10%

5

0.5

5

0.5

8

0.8

Comfort

10%

5

0.5

4

0.4

6

0.6

Noise Produced

5%

5

0.25

3

0.15

5

0.25

Total Weighted Score

 

 

5.0

 

5.15

 

4.60

Rank

 

 

2

 

1

 

3

 

Table 8.  Concept Selection Chart for Battery Cover.

    A B C D E E E
Battery Cover   Base                        
    Loose Pop-Off Cover Sealed Latched Cover Twist-On Cover   Screw-Secured Pin-Push Release Latch Tight Pop-Off Cover
Selection Criteria Weight Rating Weighted Score Rating Weighted Score Rating Weighted Score Rating Weighted Score Rating Weighted Score Rating Weighted Score Rating Weighted Score
Ease of Intended Access 13% 5 0.625 0 0 4 0.5 4 0.5 1 0.125 2 0.375 4 0.5
Secure During Use 25% 5 1.25 10 2.5 7 1.75 8 2 9 2.25 7 1.75 6 1.5
Waterproof 13% 5 0.625 10 1.25 4 0.5 7 0.875 9 1.125 6 0.75 6 0.75
Cost of Manufacture 25% 5 1.25 2 0.5 4 1 5 1.25 3 0.75 4 1 5 1.25
Effect on Related Consumer Costs 25% 5 1.25 1 0.25 5 1.25 5 1.25 3 0.75 4 1 5 1.25
  Total Score 5.00 4.50 5.00 5.88 5.00 4.88 5.25
  Rank 3 7 3 1 3 6 2

Table 9.  Concept Selection Chart for Head Design

    A B C D
Head Design   Base            
    Solid- Even Bristles Solid- Varying Bristles Split- Even Bristles Split- Varying Bristles  
Selection Criteria Weight Rating Weighted Score Rating Weighted Score Rating Weighted Score Rating Weighted Score
Cost of Manufacture 25% 5 1.25 4 1 4 1 3 0.75
Head Durability 25% 5 1.25 5 1.25 4 1 4 1
Bristle Durability 25% 5 1.25 6 1.5 7 1.75 8 2
Effectiveness of Cleaning 25% 5 1.25 6 1.5 6 1.5 7 1.75
  Total Score 5.00 5.25 5.25 5.50
  Rank 4 2 2 1

 

Final Design

Following the concept selection phase, the individual concepts that were judged to be the best were then mixed and matched to create several possible overall designs.  Given the constraints of analysis and time, three of these were then chosen as possible final designs: Model 1, featuring a split head, V-ripple bristles, neck located eccentric weight, and a screw-on battery cover; Model 2, featuring a solid head, V-ripple bristles, body-located eccentric weight, and tight-grip pop-off cover; and Model 3, featuring a split head, even-trimmed bristles, body-located eccentric weight, and latch-on cover.  Diagrams were created of each of these, with the designs themselves run through a final scoring matrix similar to that used for the individual concepts behind them.  The results of these processes can be seen below in Table 10 and Figures 7-9.

Table 10.  Scoring Matrix for Final Designs

    A B C D
Final Designs                
    Sample Brush (Base) Model 1 Model 2 Model 3
Selection Criteria Weight Rating Weighted Score Rating Weighted Score Rating Weighted Score Rating Weighted Score
Cost 28% 5 1.4 4 1.12 5 1.4 5 1.4
Oscillation Speed 13% 5 0.65 7 0.91 5 0.65 6 0.78
Brush Head Cleaning Ability 13% 5 0.65 8 1.04 6 0.78 6 0.78
Safety 10% 5 0.5 8 0.8 7 0.7 6 0.6
Overall Durability 18% 5 0.9 7 1.26 6 1.08 4 0.72
Body Vibration Dampening 9% 5 0.45 7 0.63 5 0.45 4 0.36
Ease of Use 9% 5 0.45 4 0.36 5 0.45 6 0.54
      0   0   0   0
      0   0   0   0
      0   0   0   0
  Total Score 5.00 6.12 5.51 5.18
  Rank 4 1 2 3

 

Figure 7.  Final Design Model 1

Figure 8.  Final Design Model 2

Figure 9.  Final Design Model 3

In the end, Model 1, which features vibration induced by eccentric weight in the neck, a varying height "ripple" bristle style, split brush head, and screw-on battery cover was selected.  This design meets several customer needs by more firmly securing the battery in place, reducing vibrations in the main body of the brush (due to the fact that the part that produces vibrations has been moved out of it), increasing oscillation speed of the bristles (by moving the center of vibration closer to the brushing surface), and introducing both brush head and bristle designs that lend themselves to more efficient and effective teeth cleaning.

 

Conclusions

Our team believes that we have successfully redesigned the Dollar Tree Toothbrush with Vibrating Action into a brush that not only meets a substantial amount of customer requirements, but meets our own goals as well.  The redesigned brush will not only outperform the original in several key areas related to cleaning ability such as bristle oscillation speed and bristle design, but will also improve customer comfort and safety as issues regarding excessive body vibrations and the potential for the battery falling out of the brush have been resolved as well.  At the same time, the difference in manufacturing costs, and hence retail cost to the consumer, will be minimal, resulting in a new product that is clearly superior to the original.

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