Smart Plug – Optimization of design and material regarding environmental aspects

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Smart Plug – Optimization of design and material regarding environmental aspects

Mechanical design of an environmentally friendly Smart Plug

Smart Plug – Optimering av konstruktion och material med avseende på miljöaspekter

Mekanisk konstruktion av en miljövänlig Smart Plug Nadia Samson

Faculty of Health, Science and Technology

Degree Project for Master of Science in Engineering, Mechanical Engineering 30 hp

Supervisor: Mikael Grehk Examiner: Jens Bergström 2020-06-30

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Abstract

A Smart Plug is a remote-controlled power socket that allows the user to, through an app, control any appliances that is plugged into the outlet. Since not all appliances are constructed with a smart function, the usage of a Smart Plug can be beneficial to facilitate the everyday life.

Existing Smart Plug products from various companies are available on today’s market. Sigma Connectivity has therefore initiated this degree project with the ambition of constructing a Smart Plug distinguished from the others by optimizing the design and material selection with regard to environmentally friendly aspects.

The product concept development process generally consists of several different phases. Due to limitations in design and requirements, a traditional product concept development process was not followed. Customer requirements and wishes, as well as a preconstructed PCB assembly was given upon start of the project. The product concept development process consisted of a concept generation and a concept selection phase. The concept generation phase was performed by brainstorming where one product concept solution was determined and alterable parts of that concept was developed. Concept selection was executed on the alterable parts through Pahl and Beitz elimination matrix.

Injection molding was determined to be the optimal manufacturing method and it was determined after the concept selection was performed. The determination of manufacturing process for the Smart Plug was implemented in the early stages so potential design requirements could be applied in the three-dimensional design model. The three-dimensional model was created, where components of the Smart Plug were designed separately and later assembled into one product.

Material selection was performed on the plastic casing of the Smart Plug. The most promising candidate was the biodegradable thermoplastic Polylactic Acid.

Impact simulations were performed on the Smart Plug where the simulations corresponded to 1 meter drop simulations. The impact simulations were performed on both a rigid- and a wooden surface. The simulations resulted in high absorption of stresses for certain designed parts in almost all performed simulations. Design alterations on those parts is therefore necessary to perform.

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Sammanfattning

En Smart Plug är en fjärrströmbrytare som tillåter användaren att styra apparater genom att styra strömuttaget. Då alla apparater inte är konstruerade med en smartfunktion kan användandet av en Smart Plug vara fördelaktigt för att underlätta det vardagliga livet. Andra företag har sedan tidigare konstruerat olika varianter av en Smart Plug. Sigma Connectivity har initierat detta examensarbete med ambitionen att konstruera en Smart Plug som skiljer sig från de befintliga konstruktionerna genom att optimera design och materialval med avseende på miljövänlighet.

Utveckling av produktkoncept består vanligtvis av flera olika faser men på grund av design- och kravbegränsningar på produkten kunde inte en traditionell produktutvecklingsprocess följas. Vid projektarbetets start tilldelades kundkrav och kretskort.

Produktutvecklingsprocessen bestod av en idégenereringsfas och en konceptvalsfas. Under idégenereringsfasen användes idégenereringsmetoden brainstorming där en produktkonceptslösning framtogs med möjliga modifieringsalternativ. Konceptvalsfasen utfördes på modifieringsalternativen genom Pahl och Beitz elimineringsmatris.

Den optimala tillverkningsmetoden fastställdes till formsprutning efter att konceptvalsfasen var avklarad. Val av tillverkningsmetod fastställdes i ett tidigt stadie så att eventuella designkrav som tillverkningsmetoden krävde kunde implementeras direkt i den tredimensionella designmodellen. Den tredimensionella Smart Plug modellens alla delar designades separat och sattes därefter ihop till en produkt.

Ett materialval utfördes på plasthöljet. Den mest lovande materialkandidaten var den biologiskt nedbrytbara termoplasten polylaktid.

Mekaniska struktursimuleringar utfördes på Smart Plugen där simuleringarna motsvarade 1 meters droppsimuleringar. Effektsimuleringarna utfördes mot både en icke deformerbar stel yta och ett träunderlag. För vissa av Smart Plugens designade delar resulterade nästan alla simuleringar i höga spänningsupptagningar vilket innebär att modifieringar i designen för de delarna behöver utföras.

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Acknowledgements

I would like to express my sincere gratitude to my supervisors Pernilla Jonsson and Sara Novak at Sigma Connectivity for their invaluable support during this project. I also want to give special thanks to Henrik Fristedt who has helped me during the construction of the Smart Plug.

Finally, I would like to thank my supervisor at Karlstad University, Mikael Grehk, for his commitment and support during this degree project.

Nadia Samson April 28^th, 2020 Lund, Sweden

“What is now proved was once only imagined” – William Blake

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Abbreviations

ABS Acrylonitrile butadiene styrene CAD Computer aided design

IEC International Electrotechnical Commission IoT Internet of things

IP Ingress protection

PC Polycarbonate

PCB Printed circuit board PLA Polylactic acid PSU Polysulfone

FDM Fused deposition modeling FE Finite element

FEA Finite element analysis FEM Finite element method

FMEA Failure mode and effects analysis FR Flame retardant

UL Underwriters laboratories

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1 Introduction

This section describes the background of this master thesis and the aim, purpose, problem statements and limitations are presented.

Technology is constantly evolving, and it has become the backbone of most people’s everyday life. With most functions of technology being just a click away on a Smart Phone, accessible and comfortable is one way of describing technology’s impact on today’s society [1]. Even if it is to light up your home or to make coffee in the mornings, one thing a great deal of products and appliances have in common is their need of power to operate. The usage of a Smart Plug, which is to be used between the plug of an appliance and the wall socket, makes it is possible to operate any appliances through a Smart Phone, making the everyday life even more accessible and comfortable [2].

1.1 Smart Plug

A Smart Plug is a remote-controlled power socket that gives you control over an outlet. A Smart Plug is plugged in between a plug of an appliance and a socket and is typically operated over Wi-Fi. By using a Smart Plug, the controlment of an appliance is possible through a Smart Phone or by speaking through virtual assistance. This makes it possible to do everything between turning on a pre-prepared coffee machine from bed to turning off lights in a home. It is possible to actively control a Smart plug, or to automate it so it reacts on scheduled times similar to a regular timer [2]. Every Smart Plug has the same basic functionality. Some Smart Plugs have, in addition to the basic functionality, a few extra functions such as zones (groups of plugs) or USB outlets for example to distinguish them from competitors’ products. The design of different Smart Plugs is another thing that distinguishes Smart Plugs from each other, where the size and shape of the Smart Plug is of importance [3], [4]. Figure 1.1 displays two Smart Plugs designed by different companies where the left Smart Plug is manufactured with Acrylonitrile butadiene styrene (ABS) material and the right Smart Plug is manufactured with Polycarbonate (PC) material.

Figure 1.1. Smart Plugs on the left is manufactured by Fasdga while the Smart Plug on the right displaces IKEAs mounted Smart Plug. [3], [4]

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1.2 Sigma Connectivity

Sigma Connectivity is a consulting innovation company that develops beneficial solutions with connectivity. Sigma Connectivity was established in 2013 when Sigma group acquired the company from Sony mobile. Today, Sigma Connectivity has over 500 employees and possesses one of Europe’s most advanced design, test and verification labs [5].

This master thesis is carried out at the IoT Mechanics and Design department at Sigma Connectivity AB in Lund, Sweden.

1.3 Purpose

Since more people are beginning to become more environmentally conscious, products designed and produced from an environmentally friendly perspective are becoming more attractive products to consumers. During this master thesis project, a Smart Plug that is optimized with regard to environmentally friendly aspects is designed. The purpose of this thesis is to develop an environmentally friendly Smart Plug that Sigma Connectivity thereafter can present as a product to their client. Due to today’s competitive market, an environmentally friendly aspect to the Smart Plug could potentially be what makes this Smart Plug stand out from competitors’ corresponding products, making this Smart Plug more attractive on the market.

1.4 Problem statements

To be able to develop an environmentally friendly Smart Plug, following questions are answered:

- How should a Smart Plug casing be mechanically designed to be considered environmentally friendly?

- What material is optimal to use when environmentally friendly aspects are in focus for the Smart Plug?

- What manufacturing method should the Smart Plug be manufactured with?

1.5 Objective

The aim of this master thesis is to develop a sustainable Smart Plug with minimal environmental impact. To ensure that the Smart Plug has minimal environmental impact, the Smart Plug is designed with a thin material thickness and produced with an environmentally friendly material.

By the end of the master thesis, a design of a 3D-modeled Smart Plug with a material optimized for the product while minimizing the environment impact is presented. The potential manufacturing method of the Smart Plug will be analysed, and an optimal manufacturing method is selected.

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1.6 Delimitations

This project is performed as a master thesis by one student for 20 weeks which corresponds to 30 academic credits. The project includes the development a Smart Plug which covers the mechanically designed casing of the Smart Plug as well as a structural simulation analysis, material selection and manufacturing method of the Smart Plug. All parts required to manufacture a fully functional Smart Plug is developed, but only the casing of the Smart Plug is optimized during this project.

The Smart Plug is restricted by following delimitations:

- The design of the Smart Plug is restricted by standard requirements regarding plugs and sockets.

- A predeveloped assembly of printed circuit boards (PCBs) is used, which limits the design of the Smart Plug.

- Due to only accessing Abaqus with a student license, the simulation model may need to be simplified in order to obtain a result.

- The casing of the Smart Plug is the main task to develop and optimize. The ground springs etc. are designed according to required standards in order to develop a fully functional Smart Plug, but no material selection and further analyses on these parts is performed.

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2 Preparatory study

This section describes some fundamentals and requirements needed to construct a Smart Plug in order to aid the reader. The provided PCB and requirement specification are also presented.

Electrical equipment connects to the electrical grid through an electrical outlet, where the electrical grid provides the outlet with alternating current. A connection system consists of a socket and a plug, which can vary in design due to the use of different standards in different countries [6].

According to the international electrotechnical commission (IEC), there are 14 IEC standard types of sockets and plugs which are used in various parts of the world [7]. Figure 2.1 presents the plug and socket type appearances whereas figure 2.2 illustrates where in the world the different types of plugs and sockets are being used.

Figure 2.1. Type A to N sockets with appurtenant plug. [8]

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Figure 2.2. The usage of different socket and plug types in the world. [9]

Depending on factors such as number of pins, shape of pins and whether the plug or socket is grounded, a standard type plug can be compatible with other standard type sockets [7]. Table 2.1 lists relevant information and requirements for all standard socket and plug types.

Table 2.1. Information and requirement of type A to O [7]

Type Number of pins (pcs)

Grounded Ampere (A) Single-Phase Voltage (V)

Socket compatible with plug types

A 2 No 15 100-127 A

B 3 Yes 15 100-127 A, B

C 2 No 2.5 220 - 240 C

D 3 Yes 5 220 - 240 D

E 2 Yes 16 220 - 240 C, E, F

F 2 Yes 16 220 - 240 C, E, F

G 3 Yes 13 220 - 240 G

H 3 Yes 16 220 - 240 H

I 2 or 3 2 pins: No

3 pins: Yes

10 220 - 240 I

J 3 Yes 10 220 - 240 C, J

K 3 Yes 16 220 - 240 C, K

L 3 Yes 10 and 16 220 - 240 10 A socket: C, L

(10 A version) 16 A socket: L (16 A version)

M 3 Yes 15 220 - 240 M

N 3 Yes 10 and 20 100 - 240 C, N

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A connection system can either be polarized or unpolarized. Polarized electrical outlets consist of a smaller hot slot and a larger neutral slot to ensure that the electrical current flows through the correct wires in the circuit, i.e. hot along hot and neutral along neutral. In a unpolarized connection system however, the plug can be inserted into the socket in either direction since line and neutral are connected at random. Polarized systems are commonly used in North America while unpolarized systems are commonly used in Europe [10].

According to the national electrical safety board [11], all wall sockets must be grounded. This requirement regards new constructions, renovations and electrical extension installations, meaning all buildings built or renovated after the requirement emerged consist of grounded wall outlets [11]. While ungrounded connectors only can be assembled in ungrounded sockets, grounded connectors can be assembled in both ungrounded and grounded sockets. Products with ungrounded connectors developed must have double isolation and should thereby have a flat connector, assuring that the product can be used in all sockets [7], [11].

2.1 Printed circuit board

A printed circuit board (PCB) is a board with attached electronical parts. The board has lines and pads electrically connecting various connectors and components to each other. By using a PCB, signals and power can be directed between physical devices where the metal solder makes the electrical connection between the surface of the PCB and the electrical components possible [12].

During the development of the Smart Plug, this master thesis will orbit around a preexisting electrical design created by Sigma Connectivity. The inclusion of a PCB is required in order to design a fully functioning Smart Plug. The predeveloped electrical design used during this degree project consists of four PCBs which are soldered together, see figure 2.3 and 2.4. The four PCBs are;

- Power PCB - Relay PCB - Digital PCB - Antenna PCB

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Figure 2.3. Illustration of the four PCBs assembled.

Figure 2.4. Top respective bottom view of the PCBs.

By using a trace antenna on a PCB, wireless communication is possible. It is due to the trace antenna on one of the PCBs that the Smart Plug will be able to connect and communicate with a Smart Phone from a distance through an app [13]. However, depending on the surrounding of the antenna, the wireless connection might be affected. To avoid degradation of the wireless connection between the soldered PCBs and a Smart Phone, one should [13]:

- Not design any plastic close to the antenna since the dielectric constant (ratio of the permittivity of a substance and the permittivity of free space) is higher for plastic than air. By placing the antenna adjacent to the plastic, the antenna will pick up a higher effective dielectric constant which will result in an increase of the electrical length of the antenna trace and reduce the resonant frequency.

Antenna PCB

Power PCB Relay PCB

Digital PCB

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- Not place any ground directly below the antenna.

- Not cover the antenna completely with a metallic casing. If the developed product has a metallic casing or a shield, the casing must not cover the antenna since no metal is allowed in the antenna near-field. Near-field is the region close to the antenna which allows near-field communication to create a signal between a transmitting device and the receiving NF tag. The tag’s field can communicate back to the transmitter to send information.

- Not use carbon fiber as a casing near the antenna. Carbon fiber is conductive, and the resonant frequency signal will have trouble passing through the carbon fibers.

- Not place any components or mounting screws in the antenna keep-out area. The actual keep-out area depends on the antenna used.

2.2 Standards

To be able to use a product containing electrical components, certain standard requirements must be fulfilled.

DIN 49440:1989-12 and DIN 49441:1972-06

In order to ensure that all plugs fit to an associated socket, certain design and measurement requirements must be fulfilled. Standard DIN 49440:1989-12 contains a technical drawing with required measurements of a type F socket [14]. An extraction from this standard can be seen in appendix A. Standard DIN 49441:1972-06 contains technical drawings with required measurements valid for type F plugs as well as required additions if said plug is supposed to be operable with a socket of type E as well [15]. An extraction of this standard can be seen in appendix B. In order to operate a plug of type C in a socket of type F, no alterations to the design is required [15].

SS-IEC 60884-1 and IEC 60884-2-5

Standard IEC 60884-2-5 and SS-IEC 608874-1 comprises requirements regarding plugs and socket for general use, for example when plugs and socket are used within a household.

Standard IEC 60884-2-5 is an updated version of standard SS-IEC 608874-1 and this master thesis will therefore have its base on the original standard but use the updated version when possible [16], [17].

Section 10 regarding protection against electric shock states in paragraph 1 that a design must guarantee that live parts are not accessible when the product is mounted. This also applies after removal of parts which can be removed without the use of a tool. When a plug is partially or completely inserted in a socket, live parts are required to not be accessible [16], [17].

External parts of plugs must be of insulating material according to paragraph 10.4. This however is with exception of assembly screws, current-carrying and earthing pins, earthing straps and metal rings around pins that fulfills requirements in paragraph 10.2.1 or 10.2.2 [17].

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A shutter can be a person or an object that covers or closes an opening, e.g. a person who opens and closes doors at hotels, or a mechanism on the lens of a camera that opens and closes so the quantity of the light entering the camera can be regulated [18].

According to standard IEC 608874-1, a shutter must be integrated in a socket due to personal safety since it offers increased contact protection for children as well as adults against electric shocks. A shutter must be designed in such way that they can’t without difficult be operated by anything other than a plug according to paragraph 10.5, and the shutter should not be able to be accidentally removed. A commonly used shutter design opens when both opening is pressed simultaneously by the pins of a plug [19]. An example of this type of shutter system is presented in figure 2.5 which displays a shutter system designed in 1928 for a socket of type G.

Figure 2.5. Shutter system designed by MK Electric. [19]

The shutter system presented in figure 2.5 is still in use for certain G type sockets. By inserting the plug, the earthing pin which also is the longest pin, pushes the shutter away and the entire plug can be inserted in the socket. Upon removal of the plug, a spring which is not visible in figure 2.5, pushes the shutter back to its original position [19].

To ensure that the grounded contacts is in contact at all times, paragraph 11.1 requires that the design must be made so the grounded connection is made before current-carrying contact when inserting a pin into a socket. The paragraph further requires that the grounded connection is broken after the current-carrying pins has separated [16].

In paragraph 14.3 the standard also includes the requirements that the pins must be locked against rotation and not be removable without destroying the plug [17].

IEC 62368-1:2018

Standard IEC 62368-1:2018 comprises safety requirements regarding audio and video, information and communication technology equipment [20].

According to standard IEC 62368-1:2018 paragraph 0, there are three kinds of persons that can come in contact with a product; a skilled person, an instructed person and an ordinary person.

A skilled person is a person with training or expertise in the equipment technology, an instructed person is a person who have been instructed and trained by a skilled person, or who is

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supervised by a skilled person and an ordinary person represents everyone else. Depending on what type of persons that will handle a product with energy sources, different safeguards must be met to decrease the risk of pain, injury and, in case of fire, property damage. The most commonly used basic safeguard against an electrical energy source capable of causing pain is electrical insulation. A supplementary safeguard may be additional insulation or a protective earthed conductive barrier. Another factor that will determine the level of safeguard required is the grade of energy source. According to paragraph 0.3, energy sources can be divided into three groups; class 1, class 2 and class 3. The classes are defined according to table 2 [20].

Table 2.2. Division of energy classes [20]

Energy source Effect on the body Effect on combustible materials Class 1 Not painful, but may be detectable Ignition not likely

Class 2 Painful, but not an injury Ignition possible, but limited growth and spread of fire

Class 3 Injury Ignition likely, rapid growth and

spread of fire

An energy source that origins from a wall socket is considered a class 3 energy source. In the event of a proper shock, the rate of the heartbeat can become out of balance and lead to dangerous consequences. If combustible material is used, ignition will probably be inevitable and a rapid growth and spread of fire will occur, especially if other furniture such as curtains etc. is close by [20].

When an ordinary person is intended to operate an electrical product with energy source of class 3, following safeguards must be met according to paragraph 4.3.2.4; there must be an equipment basic safeguard and equipment supplementary safeguard, or a reinforced safeguard [20].

According to paragraph 0.5.8, equipment safeguards is defined as following [20]:

- Basic safeguard: Valid under normal operating conditions

- Supplementary safeguard: Valid in the event of failure of the basic safeguard

- Reinforced safeguard: Valid under normal operating conditions and in the event of a single fault condition elsewhere in the equipment

In part Annex V paragraph U.1, an accessible part of an equipment is a part that can be touched by a body part. All parts that can be touched is regarded as an accessible part if the part of the equipment can be opened without the use of a tool. However, accessible parts do not include parts that have become accessible when floor standing equipment with a mass over 40 kg is tilted. According to part Annex K paragraph K.3 and K.4, safety interlock is not a sufficient safety measure for an ordinary person when handling a product with energy source 2 or 3. The usage of a tool is thereby required to hinder the energy source of being located in an accessible area [20].

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IP-classification

Ingress protection classification (IP-classification) is an international standard (EN 60529) which specifies different levels of safety requirements for electrical products. The European standard EN 60529:1991 applies in Sweden where the official version, written in Swedish, includes standards EN 60529:1991, EN 60529/A1:2000 and EN 60529/A2:2013. Depending on the level of effective sealing, a product’s IP-classification can be high or low. IP- classification normally consists of the letters IP, followed by 2 digits where the first digit indicates the product’s capability to withstand penetration from foreign objects. The second digit indicates the product’s capability of withstanding penetration from liquids. Depending on if an electrical product is intended to be used indoors or outdoors, the level of IP-classification varies [21].

Figure 2.6 below illustrates and describes the different levels of IP classifications an electrical product can have. The figure can be seen in a larger format in appendix C.

Figure 2.6. IP ratings. [22]

When there are no specified requirements of either solid- or water penetration, the respective digit is then denoted by the number zero (0), i.e. IP10 has no water penetration safety requirements while IP01 has no solid penetration safety requirements. The digit is replaced with the letter X if there is a lack of sufficient data to assign a protection level [21].

An indoor Smart Plug should, at minimum, have an IP20 classification.

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2.3 Flame retardant

In order to prevent fire or delay the spread of fire, flame retardant (FR) substances or compounds can be used [23]. Flame retardants are well used in the plastic industry and are used in thermoplastics, thermosets coatings and textiles. It is commonly used in the plastic industry to reduce the risk of fire related accidents since the use of plastics is very widespread, and all carbon-based materials are combustible. If it is not possible to use a polymer that is characteristically flame retardant for a product or application, using a non-flame-retardant polymer and adding a flame retardant to the polymer is a solution [24]. The FR additive can be incorporated into the polymer matrix through chemical reaction, chemical modification of the prepolymer or by a melt processing method. Incorporating FR additives into the polymer matrix through a melt processing method is a simple and efficient method that achieves a higher fire performance at industrial level and allows a wider range of polymers to be processed by extrusion or injection molding [25].

The classification of FRs can be implemented differently depending on which method the FRs is classified by. FRs can be classified by; Organic and Inorganic types, chemical types, being reactive or additive, or whether it contains halogens. When classified by its containment of halogens, FRs are commonly classified as non-halogenic which for example contains Nitrogen FRs or Antimony trioxide, or halogenic, which contains chlorine and/or brominated FRs [26].

Halogen FRs generally act in the gaseous phase and is more efficient, have a wider application and a lower cost. However, halogenated FRs have been linked to health and environmental issues due to its persistence, bioaccumulation and release of toxic and corrosive gases when heated. This makes halogenated FRs dangerous for the environment and human health, making non-halogenated FRs better suited additive for this Smart Plug [25], [27], [28].

UL standards

To ensure a plastic material meets the requirements for flammability safety in devices and appliances, regardless of which FR is being used, the underwriter’s laboratories (UL) standard UL94 is used. There are six main flammability classifications in which polymers can be classified as within the UL94 standard [29]. The standard classifies the polymer by the minimum thickness at which it stops burning when tested in a horizontal or vertical orientation [29]. Table 2.3 presents the flammability classifications and their definition.

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Table 2.3. UL94 classifications used for plastics [29]

Class Orientation of test sample

Definition Time of burn allowed

Particle drop allowed Plaque holes Flaming Non-

flaming

HB Horizontal Slow

burning

Burning rate of less than 76 mm/min for a specimen less than 3 mm thick and burning stops before 100 mm

V-2 Vertical Burning

stops

30 seconds Yes Yes -

stops

30 seconds No Yes -

stops

10 seconds No Yes -

5VB Vertical Burning

stops

60 seconds No No Yes

5VA Vertical Burning

stops

60 seconds No No No

2.3.1.1 Yellow card

When UL testing has been successfully performed on a polymer, the polymer will receive a UL Recognized Component Mark, also known as a Yellow Card [30]. The UL testing consist of electrical, physical and mechanical characteristics, ignition and burning characteristics from thermal and electrical sources and the effect of exposure to elevated temperatures, cold, water, ultraviolet rays etc. Yellow Cards are listed in the UL iQ database and UL’s Prospector database. By selecting a polymeric material that has a certified yellow card, the need for material testing to ensure that the material attains required safety standards is eliminated [30].

2.4 Definition of environmentally friendly plastic materials

There are no standards on which or what criteria a material must fulfill in order to be labeled as environmentally friendly. Two factors that affects the environment, and often are discussed in this type of context, is how much emission is released when the material and/or the product is manufactured, and the product’s impact on the environment after disposal. The decision on what factor to prioritize or finding a material that partially fulfills both factors without being optimized in ether one, can be made freely based on what seems optimal for the specific product and marketing strategies.

This degree project will focus on minimizing released emissions, both when manufacturing the material and the product. However, in order to also be able to dispose of the product in an environmentally friendly way when needed, the Smart Plug should be easy to disassemble so separating plastic from metals is possible.

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2.5 Requirement specification

A hardware requirement specification regarding the development of the Smart Plug was provided in the initial state of the project.

Table 2.4. Provided hardware requirements

Criterion Designation Requirement/requests

BLE / Zigbee as single module R1 Requirement

(110) - 220-230 V 50/60 Hz input & output R2 Requirement Be used in temperature range of 0 to + 40 °C R3 Requirement 3600 VA / 16A Relay (if needed to fit the size 10A) R4 Requirement Standard power socket & plug (F-Schuko) R5 Requirement

Button+ LED R6 Requirement

Smart metering Re1 Request

Requirements:

- R1: BLE / Zigbee as single module

Use Bluetooth Low Energy (BLE) and/or Zigbee as single module.

- R2: (110) - 220-230 V 50/60 Hz input & output

To ensure the Smart Plug is functioning properly, the Smart Plug needs be able to function run on the frequency 50-60 Hz and, depending on which countries the Smart Plug is intended to be used in, able to use Single-Phase voltage in the range between 110 to 230 V.

- R3: Be used in temperature range of 0 to + 40 °C

The Smart Plug needs to be able to operate in indoor temperature. With margin, this temperature range is set at 0 to 40°C.

- R4: 3600 VA / 16A Relay (if needed to fit the size 10A)

Use a 3600 VA/16 A relay (an electrically operated switch, i.e. a circuit breaker).

- R5: Standard power socket & plug (F-Schuko)

The Smart Plug must be designed with a socket and plug of type F, or designed to ensure that a socket and plug of type F can be used with the Smart Plug. Type F refers to the CEE 7/3 outlet and CEE 7/4 plug and is also commonly known as Schuko [31].

- R6: Button+ LED

The Smart Plug must have a button so Factory Reset / Manually switch the relay ON / OFF is possible.

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Request:

- Re1: Smart Meter

A Smart meter measures the usage of gas and electricity and transfers the information to the electricity supplier for monitoring and billing. By implementing a smart meter in the product, the costumer can for instance get a better understanding of how the usage of the product affects their bills [32].

R1, R2, R4 and Re1 are directly related to the setup of the assembled PCB and is therefore not taken into account when designing the Smart Plug during this degree project. This however does not apply to requirement 6 since R6 must be implemented in the PCB as well as adjusted to in the three-dimensional design of the Smart Plug in order to have a functioning button and LED.

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3 Method

This section describes all methods used to develop the Smart Plug.

3.1 Failure Modes and Effects Analysis

A risk assessment in form of a failure modes and effects analysis (FMEA) was constructed in the early stages of the project in effort to identify various risks and failure modes which may rise when developing a product [33]. The purpose of conducting a risk assessment in the early stages of a project is to detect potential risks and deficiencies so they can be kept in mind during the development of the product and therefore potentially be minimized.

3.2 Concept development

In a traditional concept development process, a morphological analysis is generally performed after solution ideas have been generated from both creative methods, such as brainstorming, or through systematic methods, such as literature research. The morphological analysis will generate in several possible solutions, where the acceptable solutions later should be screened out [34].

The selection of concept is performed by a three-step evaluation after acceptable solutions have been screened out [34];

- Pahl and Beitz elimination matrix – eliminates bad ideas - Pughs criteria-based decision matrix – concept screening - Kesselrings weighted criterion matrix – concept scoring

After the three steps have been performed, the best suited concept solution remains.

Concept generation

Generally, this process includes developing as many conceptual product solutions as possible in order to select the best possible solution for the product through a concept selection process [34]. However, due to the standard dimension requirements plugs and sockets have, and the predetermined design of the PCBs, the design of the Smart Plug was limited. Traditional concept generation was therefore not performed. Instead, one product design was developed where alterable parts of that design was evaluated and alternative solutions were developed.

Concept generation for the alterable parts was performed using brainstorming where the main purpose was to shape as many ideas as possible. The aim with brainstorming is quantity over quality regarding the amount of solution-ideas in order to later select the best suited solution [34].

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Concept selection

The concept selection process was executed by only performing concept screening where the screening was performed by using Pahl and Beitz elimination matrix. However, since different concepts of the Smart Plug was not produced in the concept generation process, concepts were not evaluated against each other in the way Pahl and Beitz elimination matrix generally is used.

Instead, the alterable part solutions generated during the concept generation process were evaluated against each other.

The alterable parts were evaluated in regard to:

- Solving the problem - Fulfilling the requirements - Realizable

- Can be considered environmentally friendly - Usable by as many products/appliances as possible

3.3 Manufacturing method

Different manufacturing methods require different design details, making it important to select an optimal manufacturing method for a product before creating the three-dimensional design model. When selecting a manufacturing method, various factors should be taken into consideration in order to select an optimal manufacturing process for a specific product. To select an optimal manufacturing process for a Smart Plug, the following factors (3.3.1 - 3.3.3) were prioritized when determining the manufacturing technique [35].

Manufacturing cost

There are two factors that generally determine the manufacturing cost; tooling cost and part cost. Tooling cost is a non-recurrent cost associated with the start of the production, for example the cost to create a mold. On the contrary, part cost is an acquired cost which occurs every time a part is manufactured. The total amount of products which is to be manufactured usually determines if a high part cost or a high tooling cost is most cost effective [35].

Capability of the manufacturing techniques

Each manufacturing technique has various capabilities of creating a certain type of geometry.

It is therefore important to select a suitable manufacturing technique so desired product shape can be obtained. For example, depending on if the product has a complex geometry or a hollow shape, different manufacturing techniques must be used [35].

Surface finishing of a product

While some manufacturing techniques allows surface finishing, others do not. Therefore, if surface finishing is necessary for the product’s durability, endurance or design, a manufacturing process which allows surface finishing should be selected [35].

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3.4 Detailed design Product design

During product design, a three-dimensional model of the concept was created with selected alterable parts. The concept with selected alterable parts was thereby further developed until both costumer and standard requirements was fulfilled. This was executed by using the computer-aided design (CAD) software program NX. The components of the Smart Plug were designed separately and then assembled into one complete product.

Prototype

Prototypes are commonly used to test the function and performance of a new design before the product is sent to production. Prototypes can also be used to get a better comprehension of a possible design, or to evaluate a created product design. A prototype can be virtual or physical and can be created by hands, with traditional manufacturer or by additive manufacturing. The method of creating a desirable prototype varies on what the purpose of the prototype is for [36].

To evaluate the design of the Smart Plug, a total of two Smart Plug prototypes were created during the product design phase. The second prototype was created after adjustments on the three-dimensional CAD design was performed. The adjustments were performed after evaluating the first prototype. Both prototypes were created by using the additive manufacturing technology fused deposition modeling (FDM), for which ABS material were used. The prototype components were created layer by layer through FDM by melting plastic wire and applying it through a heated nozzle [37].

3.5 Determination of material

The material selection process for the Smart Plug was done in five phases; translation-, screening-, rank-, documentation- and final material selection phase [38].

• Translation phase – States the demands, wishes and limitation of the product according to Ashby’s methodology process [38]:

- Identify what to optimize.

- Select a free variable. It may for example be a geometric variable such as length or thickness which is allowed to be varied when designing the product.

- Define a function that describes the aims, including the free variable.

- Define a function, an active restriction, that describes the desired mechanical property which is desired to be optimized. This function must include the free variable.

- Break out the free variable from the function describing the active restriction and replace the free variable from the function describing the goals with this function.

- Divide the new function of goals into functional-, geometry- and material

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𝑃 = 𝑓(𝐹𝑢𝑛𝑐𝑡𝑖𝑜𝑛) × 𝑓(𝐺𝑒𝑜𝑚𝑒𝑡𝑟𝑦) × 𝑓(𝑀𝑎𝑡𝑒𝑟𝑖𝑎𝑙) (3.1)

- The variables and constants associated with “Material” define a merit value. The material best suited for the application is the material with the maximum credit value if the function is to be minimized, or the material with the minimum credit value if the function is to be maximized.

• Screening phase – Defining passive restrictions that the material must meet. This is a final factor in Ashby’s methodology process.

• Ranking phase – By creating material maps, the best suited materials can be evaluated by ranking.

Ranking of the possible best suited materials was performed by a weight analysis. The weight analysis was performed by calculating the weight (W) of the merit indices values through following equation [38]:

𝑊_𝑖 = ^𝑤^𝑖^∙𝑀^𝑖

𝑀_{𝑖,𝑚𝑖𝑛} (3.2)

Where wi is the weight factor. The value of the weight factor corresponds to how prioritized the multiple aims are. The sum of the weight factors must be equal to one.

Since the merit indices should be minimized, an aim is considered more prioritized if corresponding weight factor consists of a small value. The materials are thereafter ranked by their total weight where the material with the lowest total weight is ranked on top [38].

• Documentation phase – Further evaluate and compare the top ranked materials.

• Final material selection – The best suited material is selected.

3.6 FE-analysis

A widely practiced computational technique, used for solving various engineering and mathematical problem is the finite element method (FEM), also known as finite element analysis (FEA). Using FEA, it is possible to solve problems in numerous departments such as structural analysis, fluid flow, electromagnetic potential etc. This is achieved by solving partial differential equations where a larger system is separated into simpler parts known as finite elements. By developing a mesh of a part, finite elements can be created by converting an initially infinite number of degrees of freedom problem into a limited degree of freedom problem. A system of algebraic equations is created when boundary conditions are entered into the FEA by approximating the unknown function over the domain. These equations form the finite elements, which are assembled into a bigger arrangement of equations that represents the entire problem. FEA then approximates a solution by using these equations [39].

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Model description

To ensure that the designed Smart Plug was able to withstand accidental impacts, simulations were made using the FEA software Abaqus FEA. Dynamic simulations were made in Abaqus/Explicit to analyze the structural behavior of the Smart Plug. The simulations were performed to resemble impact simulations where the Smart Plug was dropped on a rigid- and a wooden surface from a 1 m distance.

All separate parts of the Smart Plug were imported into Abaqus and reassembled into one product. The explicit analysis was performed over a time period of 2 ms by using isotropic linear elasticity as the material model. Mass-scaling was used in order to reduce the computational analyzes time without sacrificing the simulations accuracy. This was implemented by scaling the mass of the elements with a time increment below 2×10^-8. The instantaneous velocity the Smart Plug had at one meter free fall was calculated using following equation [40]:

𝑣_𝑖 = √2𝑔ℎ (3.3)

Where g is the force of gravity and h is the traveled distance during the fall.

The shape of tetrahedral elements was used as the mesh-shape with an explicit element library using a linear geometric order.

Optimization

An optimization process is generally performed to obtain an attractive product. Optimization can, for example, be performed to reduce weight or size for ergonomic and environmentally aspects. An optimization process can be performed using FEA and an iterative process where the construction is simulated until satisfaction is reached [34].

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4 Results

This section presents all produced results, including concept generation and selection, product design, material selection and simulation results. A step-by-step manual is presented that illustrates how to assemble the designed Smart Plug.

4.1 Failure Modes and Effects Analysis

The performed FMEA is presented in table 4.1 and consists of predicted errors and remedies in order to prevent or minimize them before they emerge. A larger format of the FMEA is presented in appendix D.

Table 4.1. Performed FMEA

The concerning conclusions drawn from the FMEA was the user’s risk of getting an electrical shock or burn. Although the minimum requirement of IP-classification for the Smart Plug is IP20, only hindering penetration from objects equal to, or greater than 12.5 mm is an unnecessary risk of potential danger. Therefore, the ability to penetrate foreign objects into the smart Plug should be minimized in the design when it is possible. By minimizing the possibility of penetrating the Smart Plug, fingers and conductive objects ability of coming into contact with current when the Smart Plug is inserted to a socket is minimized. Selecting an insulating material is of great importance, both due to Smart Plugs functionality and personal safety for the use.

23/01/2020 (Rev.): 04/04/2020

Process Step/Input

Potential Failure Mode

Potential Failure Effects

Potential Causes

Current Controls

Action

Recommended Resp. Actions Taken

Child handling the product

Small fingers penetrating the

casing

The person get an electric

shock 10

Childrens fingers smaller than openings in casing

7 Visual

Inspection 5 350

Follow IP 20 (protection against objects ≥ 12.5mm)

Nadia

Minimize openings in casing

15/03

10 6 3 180

Person inserts an object other than a plug into the Smart Plug while the

Smart plug is incerted to a wall

socket

A conductive object comes in

contact with the current

The person get an electric

shock 10

Shutter get stuck

in open position 4 Visual Inspection 4 160

Ensure the shutter follows standard IEC

60884-1

Nadia Shutter designed

22/02 10 2 4 80

Smart Plug incerted in wall

socket

Smart Plug becomes warm

Customer burn fingers 10

Material casing becomes hot due

to hot components on

PCB

10 - 6 600 Select a insulating

material Nadia Material selection

03/04 10 1 5 50

Severity Scale; Effect 10 – Hazardous – Without warning

9 – Hazardous – With warning 8 – Very high

7 – High 6 – Moderate 5 – Low 4 – Very low 3 – Minor 2 – Very minor 1 – None

Occurrence Scale; Probability of faliure

10 – Very high; ≥1 in 2 9 – Very high; 1 in 3 8 – High; 1 in 8 7 – High; 1 in 20 6 – Moderate; 1 in 80 5 – Moderate; 1 in 400 4 – Moderate; 1 in 800 3 – Low; 1 in 1500 2 – Very Low; 1 in 3000 1 – Remote; 1 in 6000

Detection Scale 10 – Almost impossible 9 – Very remote 8 – Remote 7 – Very low 6 – Low 5 – Moderate 4 – Moderately high 3 – High 2 – Very High 1 – Almost Certain

Risk level 1-63 – Acceptable risk 64-342 – Further review 343-1000 – unacceptable risk Responsible: Nadia Samson FMEA Date (Orig.):

FMEA

Process/Product Name: Smart Plug Prepared By: Nadia Samson

DETECTION (1 - 10) RPN What is the process

step, change or feature under investigation?

In what ways could the step, change or feature go wrong?

What is the impact on the customer if this

failure is not prevented or corrected?

What causes the step, change or

feature to go wrong? (how could it occur?)

What controls exist that either prevent or detect the failure?

What are the recommended actions for reducing the occurrence of the

cause or improving detection?

Who is responsible for making sure the actions are completed?

What actions were completed (and when) with respect

to the RPN?

SEVERITY (1 - 10) OCCURRENCE (1 - 10) DETECTION (1 - 10) RPN SEVERITY (1 - 10) OCCURRENCE (1 - 10)

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4.2 Concept development Concept generation

The concept development of the Smart Plug is very limited by the socket design standard DIN 49440:1989-12 and the plug design standard DIN 49441:1972-06, as well as the predeveloped PCB assembly. The Power PCB must be in contact with two terminal pins so the current can flow from a wall socket to the PCBs, see figure 4.1. Due to this, the Power PCB and, at least parts of the Relay PCB, must be submerged in the plug design of the casing. The terminal springs located on the digital PCB, must be penetrated by terminal pins connected to the plug whose appliance we want to give current through. This leads to that the digital PCB should be relatively close to the socket design of the Smart plug since terminal pins are 19±0.5 mm in length according to DIN 49 441:1972-06 [14], [15].

Figure 4.1. Further PCB layout explanation.

Due to the mentioned standards that must be fulfilled, and the layout of the PCBs, the design of the Smart Plug shape became limited. With the diameters of the plug and socket design predetermined by standards, the casing in between the socket and the plug design were designed alongside the shape of the PCBs, creating an as small Smart Plug as possible as material usage and size was minimized, see figure 4.2.

Antenna PCB

Power PCB Relay PCB

Terminal springs

Must be in contact with the terminal pins connected to the Smart Plug

Digital PCB

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Figure 4.2. Sketch of the intended Smart Plug.

Alterable parts of the concept solution were developed. The alterable parts of this concept were the plug-section where the compatible socket types can vary depending on the design, and the mounting of the assembly in order to hinder the Smart Plug from becoming an accessible part.

4.2.1.1 The plug

- Alt 1.1: Plug of type F, see figure 4.3.

Figure 4.3. Sketch of plug type F.

- Alt 1.2: The plug must be compatible with a socket of type F according to requirements.

However, by designing a plug compatible with both type F and E sockets (and type C since they are not grounded), the Smart Plug can be used in more sockets and thereby will be a more useful product in certain countries, see figure 4.4.

Figure 4.4. Sketch of plug type F, compatible with sockets of type E.

4.2.1.2 Mounting of the assembly

- Alt 2.1: The plug and socket are glued together, ensuring that the Smart Plug cannot be mounted apart without harming the Smart Plug.

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- Alt 2.2: The plug and socket are attached together by fitting and screwed together to secure the Smart Plug from being mounted apart without the use of a tool.

Concept selection

The altering parts were evaluated in an elimination matrix that can be seen in table 4.2.

Table 4.2. Elimination matrix

The alterable parts 1.2 and 2.2 passed the screening. The smart plug will therefore be designed so disassembling is a possibility so that separation of plastic and metal can be done before disposal of the product. By making waste separation a possibility, the Smart Plug’s impact on the environment when disposed of can be reduced if conducted correctly. The Smart Plug will also be designed with a plug compatible with both type E and F sockets so the possibility of utilizing the Smart Plug is maximized.

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4.3 Manufacturing method

The Smart Plug is presumed to be produced in large quantities, making it favorable to use a manufacturing technique with high tooling cost rather than a high part cost. The geometry of the Smart plug is assumed to become relatively complex and surface finishing is necessary for the design. Since the Smart Plug is intended to be sold as a consumer product, the company that contracted Sigma Connectivity to design a Smart Plug will have their company’s name displayed on the Smart Plug. However, since this client is not to be disclosed during this degree project, the surface finishing required will not to be visible on the results for detailed design.

The surface finishing is nevertheless still taken into consideration when determining the manufacture method.

Due to above-mentioned factors, injection molding was determined as the optimal manufacturing technique. The total cost for injection molding is mostly determined by the cost of the mold, making the process cost efficient when large number of products are manufactured.

The technique can handle complex geometry but when constructing a 3D-model of the Smart Plug, the geometry should, if possible, be kept as simple as possible to keep the manufacturing cost as low as possible. This since an increase in size and complexity of the mold increases the cost to create the mold.

Injection molding

Due to common complications such as cracking, warping, sinking, shrinking and breaking when manufacturing a product, the manufacturing method must be kept in mind when designing a product in order to avoid such problems. Important parameters and their design guidelines that should be regarded when injection molding is the chosen manufacturing method can be seen below [41].

4.3.1.1 Wall thickness

Minimizing the wall thickness is preferred since thick walls can lead to long cycle times and poor mechanical properties. The wall thickness should be as uniformed as possible to simplify the flow pattern and minimize variations in shrinkage that can lead to warpage. Shrinkage can appear when the thicker wall sections cools, and thereby increasing the stress level between the two thicknesses. When non-uniform walls are required, its beneficial to transition the wall thickness by e.g. gradually adjusting the wall thickness so stress concentrations and other potential issues are reduced [41].

Stress concentration areas that could reduce the part’s impact strength can also be created where there are abrupt changes in wall thickness. This should therefore also be avoided when designing a part [41].

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4.3.1.2 Ribs

By adding ribs to a part, the part’s bending stiffness increases without increasing the wall thickness of the part. To avoid sinking, the maximum thickness of the ribs should be 50-75%

of the nominal wall thickness. Furthermore, to avoid large variation in wall thickness, the height of the ribs should not be greater than three times the nominal thickness. To avoid non-uniform shrinking than can lead to warping, ribs should be designed on both sides of the nominal wall if possible [41].

4.3.1.3 Draft angle

A minimum of 0.5-degree draft angle per side is required in order to easier eject the part from the mold. The draft angle should tilt on all walls parallel to parting directions [41].

4.3.1.4 Radius

Stress concentrations are created where sharp corners are present, and they should therefore be avoided. The inside radius should be designed to be at least 50 % of the nominal wall thickness, making the outside radius 150 % of the nominal wall since uniform walls are desired [41].

4.3.1.5 Bosses

Bosses are generally designed to secure fasteners, aid in assemblies or be used as a detector for a mating pin. To strengthen the structural parts, connecting ribs should if possible be designed with bosses where the connection ribs should be 0.6 times the nominal wall thickness at their base to avoid sink. Bosses that are designed as stand-alone bosses should be designed following the design guidelines for ribs [41].

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4.4 Detailed design 3D-modeling

The final design of the Smart Plug can be seen from different views in figure 4.5 and figure 4.6.

The design was constructed so all requirements were fulfilled, and the Smart Plug can therefore be used safely when manufactured with the right materials.

Figure 4.5. Final design of the Smart Plug displayed in different angles.

Figure 4.6. Top and bottom view of the Smart Plug.

The Smart Plug is in total 70,47 mm high, 52,2 in length and 45,2 mm in width. The casing of the Smart plug is 51,47 mm high. The Smart Plug consists of 14 parts, see figure 4.7 for a full assembly description.

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Figure 4.7. Assembly of the Smart Plug.

1x socket 1x spring

1x shutter casing

1x female ground spring

2x screws M2x8

1x button

1x

light guide

1x PCBs

1x plug

1x male ground spring

2x terminal pins 1x screw 2.5x10 1x shutter

1x isolation

sheet

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Figure 4.8 and 4.9 displays the center of the Smart Plug from different views.

Figure 4.8. Smart Plug viewed by trimming the section by the x-plane.

Figure 4.9. Smart plug viewed by trimming the section by the y-plane.

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4.4.1.1 Shutter assembly

The shutter is mounted on the rear of the socket and consists of three parts; a shutter which can move in both the horizontal and vertical direction, a spring which ensures the shutter regains its original position when a plug is withdrawn, and a shutter casing. The shutter casing was designed so it performs two functions. The casing was designed to ensure that the shutter remains mounted correctly, and the ribbons on the rear side was designed to support the digital PCB. When terminal pins are inserted into the socket, the shutter will rise in the vertical direction while simultaneously slide in the horizontal direction, see figure 4.10.

Figure 4.10. Shutter displayed in different positions.

If an object only presses the shutter through one of the holes, or presses the shutter with dissimilar forces, the shutter will tilt and will therefore not open to let the object penetrate the Smart Plug. See figure 4.11 for clarification.

Figure 4.11. Shutter fail-safe.

Smart Plug – Optimization of design and material regarding environmental aspects