SAMSUNG SLIDE PHONE MODEL SGH-T404G. M3 Design Product Teardown

Transcription

1 SAMSUNG SLIDE PHONE MODEL SGH-T404G M3 Design Product Teardown January 2014

2 CONTENTS Introduction Why, and how? Product Teardown Overview External construction Systems Conclusion 2

3 INTRODUCTION M3 product teardown process Why do product teardowns? Part of the product development process is to apply knowledge gained from prior experience during the concept development and design phases. Some experience comes from having directly designed something in the past and other experience is more indirect. It is this indirect product development experience that is gained from product teardowns. This process serves two purposes: 1. It forces the deconstruction team to carefully investigate the product pieces and learn as much as possible about the design details. 2. It provides a detailed record of the process for future reference by other product designers. Teardowns are different from Reverse Engineering Reverse engineering a product is nothing more than figuring out the design and manufacturing methods, typically for copying. M3 Design views product teardowns as ways to gain insight into the design to become better product developers. We focus on "Why" questions. Why did the designer make the choices they did? Why were certain construction techniques chosen? Why were some features included and others left out? Why was the design approach chosen? This serves to gain more in depth understanding into the product's design rather than a superficial once-over. 3

4 INTRODUCTION M3 product teardown process How does M3 Design approach product teardowns? The product teardown process is a rigorous approach to carefully catalog the deconstruction in both pictures and written descriptions. The overall approach is outlined below. When we come across products that claim to be unique, look complex, seem interesting, or no longer work, we want to know the how and why of the product's design. We take apart products to learn valuable lessons from other product developers. By studying how products are designed, constructed, or failed, we expand our knowledge of design solutions. We think critically about the products as we take them apart in order to deduce the design decisions of the original developers. By placing ourselves in their shoes, we expand our experience by imagining hypothetical design constraints to answer the how and why questions. In turn, we learn valuable lessons that we can later apply to our own product development process and share our findings with others. By answering the questions below, we can then apply the learning into future brainstorming, concept exploration, prototype development, detailed design, design for manufacturing (DFM), cost reduction analysis, and maintenance/troubleshooting. Why were specific materials or components chosen? How was the size and shape maintained? Why were certain construction or assembly techniques used? How were specific features or mechanisms executed? 4

5 PRODUCT TEARDOWN Samsung Slide Phone Model SGH-T404G 5

6 OVERVIEW Samsung Slide Phone Model SGH-T404G In our quest for really slick solutions to product challenges, we came across a perplexing feature on a sliding keyboard cell phone. Prior to the rise of touch screen phones this slide-type design was pretty common as a way to get a physical keyboard in a small form-factor: put the keyboard under the main display / phone keypad. The odd thing about the design is that the aspect ratio of the sliding feature is so bad that the phone should easily jam when opened. Since that doesn t happen, the Teardown Team decided to investigate. Sliding keyboard in closed position Sliding keyboard in opened position 6

7 EXTERNAL CONSTRUCTION Construction Overview Though the feature of interest is the keyboard slider, we will briefly mention the phone construction and interesting items we encountered during disassembly. And of course the bearing was buried deep inside the phone so we had to remove virtually everything from the phone in order to access the slider. Keyboard sliding assembly is buried deep inside the phone 7

8 EXTERNAL CONSTRUCTION Construction Overview The phone was largely held together with tiny screws, and a lot of them. There were also a few snaps that secured covers in place. We did a pretty good job of removing those without damage, since the person who supplied the phone asked if we could put it back together after our investigation. Very tiny screws 8

9 SYSTEMS System Interconnect There are many delicate flex cables to remove that provide communication to the QWERTY keypad, phone keypad, earpiece, and display, along with a tiny antenna cable. Most of them came off with a little effort and the team only broke one (well it is called the Teardown Team). Very small ZIF (zero insertion force) connectors terminate all the flex cables. Keypad flex with ZIF connector Very small antenna cable 9

10 SYSTEMS Keypad Design The tiny keypads appear to be silicone molded pieces with a painted front face, either printed or laser-etched digits, and a protective cover coat to prevent the ink from rubbing off. The keys press on small snap domes that complete a circuit path to indicate a button push. This is a pretty typical keypad design, nicely executed. Phone keypad assembly QWERTY keypad assembly 10

11 SYSTEMS Keypad Slider Once we tore through all the outer systems we finally reached the slider mechanism. The system consists of a moving carriage attached to the QWERTY keyboard, and a painted base. The carriage has two molded guides attached to it that act as low-friction elements. The painted base is assembled from two pieces of sheet metal attached to each other. This allows two raised lips to be formed that act as the slide rails for the carriage. The paint appears to be some kind of powder coating, but may also be some type of low friction coating. Plastic guide Sheet metal tab Close-up of slider sheet metal base and molded plastic guide 11

12 SYSTEMS Keypad Slider Also part of the slider system are two spring elements. The springs are a straight length of square cross-section material constrained such that they are forced to bend around a center radius and behave like a torsion spring (without any coils), resulting in a very flat package. They connect the carriage to the base, and are free to pivot at each end attachment point. The attachment point on the base allows the carriage to move between two stable positions. As the carriage moves away from a stable position (keyboard fully open or fully closed), the springs deflect and the user feels a resistance to motion. When the carriage moves past the overcenter position, the carriage snaps to the opposite stable position. Carriage Spring attachment points Torsion spring element Base Spring elements, carriage, and base 12

13 SYSTEMS Keypad Slider 1. Carriage in open stable position 2. Carriage in intermediate (unstable) position 3. Carriage in closed stable position 13

14 SYSTEMS Keypad Slider So the team then knew how the phone snapped between the open and closed positions, but what about the bearing system? As mentioned at the beginning of the teardown, the aspect ratio of the bearing system is very bad. According to Alexander Slocum s book Precision Machine Design, the ratio of the bearing pad spacing should be 2:1 length to width, with an absolute minimum 1:1 ratio. The phone bearing system (L/D) is 15 mm/73 mm = 0.21, which is very poor. By all accounts, this bearing should easily jam. So the teardown team decided to investigate a little further. L D = 73mm L = 15mm D L/D = 2:1 (ideal) ; 1:1 (minimum) Linear bearing pad spacing schematic Bearing pad dimensions for phone slider 14

15 SYSTEMS Keypad Slider Taking a free body diagram approach to the system, friction turns out to be a key element to determining how the system behaves 1. y Equation 1: ΣF Y (acceleration); F 1 > F 4 + F 5 (this condition must be met to allow the carriage to slide) Equation 2: Friction forces; F 4 = F 2 *µ and F 5 = F 3 *µ C L/2 F 5 F 3 x (µ is the coefficient of friction between the molded guides and guide rails) F 2 L = 15mm D = 56mm Equation 3: F 1 > F 2 *µ + F 3 *µ à F 1 > (F 2 + F 3 ) µ Equation 4: ΣM C (reaction forces); F 1 x D - (F 2 x L/2) - (F 3 x L/2) = 0 F 4 F 1 Substituting Equation 3 into Equation 4 at the transition point where forces F 1, F 2, and F 3 balance: (F 2 + F 3 ) x µ x D = (F 2 x L/2) + (F 3 x L/2) Equation 5: Simplifying; (F 2 + F 3 ) x µ x D = (F 2 + F 3 ) x L/2 à µ = L/2D 1 This approach was adapted from the technical whitepaper Demystifying the 2:1 Ratio and the Stick-Slip Phenomenon by PCB Linear ( F 1 = User force F 4, F 5 = Friction force F 2, F 3 = Reaction force Free Body Diagram of bearing system H = 73mm L = Length of molded guides D = Distance between carriage center and end of the phone (half of the phone s overall length) H = Distance between guide rails 15

16 SYSTEMS Keypad Slider Therefore, the phone s bearing arrangement could work, depending on the coefficient of friction. Since the bearing system was now readily accessible, it was straightforward to experimentally determine the coefficient of friction. Measuring the coefficient of friction (µµ) was performed by hanging a mass from the carriage when installed on the rails, and measuring the force (F f ) required to move the carriage. Two masses were used, 1kg and 1.5kg. The results are presented below. Mass (m) Force (F f ) Calculated Friction (µ) 1 kg 0.67 N kg 0.76 N µ = F f m x g Mass applied to bearing Measuring force to move carriage 16

17 SYSTEMS Keypad Slider Using the phone s measurements in Equation 5, we can determine the maximum allowable coefficient of friction to ensure the slider doesn t jam. It is assumed that in the worst case the user would be pushing at one end of the phone to slide it open, hence D equals half of the phone length. µ = L 2D ; D = 56mm; L = 15mm µ = 15mm 2 x 56mm = 0.13 Since the worst measured friction coefficient was 0.068, about half that of the maximum allowable friction coefficient, the phone s slider system is able to work without jamming even at such a low aspect ratio. Mass applied to bearing Measuring force to move carriage 17

18 CONCLUSION Keypad Slider Although the phone slider system broke a common rule-of-thumb with regards to linear bearing design, detailed analysis and careful material selection allowed the phone s development team to create an elegant packaging solution. Phone components 18

19 Product Teardown