Concept Design Proposal ( file)
Contents
1. margin because it was never penalized for failing to meet a requirement When geared down six times this motor produces a torque that is more than sufficient for the automatic jar and bottle opener The addition of a 6 1 gear train proved to be a key design variable This component allows the DC geared motor to meet the torque requirements for this project While the Globe rotary table geared motor produces an enormous amount of torque for its small size it is still too large to fit within the constraints set in our requirements It exceeds the 5 lb weight requirement by 1 lbs Its diameter is over 5 2 in It is also a little over 5 in tall Furthermore it was the most expensive motor to survive the preliminary rounds of selection All of these factors made the Globe motor an inferior option to the much cheaper Buehler motor The small size and standard cylindrical shape of the Buehler motor do not pose any constraints on the diameter of the base Furthermore the output shaft on the Buehler motor is slightly off center diminishing the effective radius of the motor s body in relation to the base diameter permitting a smaller and lighter base Its length requires the base to be at least three inches tall This constraint was not very demanding and was easily met in the design of the appliance s base Parametric analysis of this technical issue succeeded in selecting a motor well suited to the unique requirements of the automatic jar and lid opene2. more motors means more weight requires high torque and parts fabrication adds weight requires threaded gear requires spill protection height adjustment force transmission difficult to clean if necessary Impractical considerations of mechanics parts interference may be too heavy for consumers difficult to center on container insufficient torque transmission no height adjustment difficult to package expensive worm gears 2 motors 1 per linkage requires fabrication powerful motor The final concept chosen for further study is a combination of many of the above systems It essentially incorporates the systems from Table 3 1 that had the greatest advantages and the least disadvantages Thus the final concept was determined based on considerations for the consumer manufacturing and effectiveness of the product 13 Team Pratham AME470 Ltd The chosen concept hinges on the spiral radial plate assembly of subsystem B It allows for one motor per assembly regardless of the number of grips deemed necessary for proper operation It also allows for the gripping and twisting of the container simply by continuing turning the driving motor The top and bottom assemblies rely on this design the bottom incorporating the twisting aspect of the product The final concept has the round shape of concept 3 although is fundamentally very different Other concepts had influences on the design as well Concept 1
3. outer diameter of the grippers There are a handful of constraints on the design variables one of which is the radius from the center of the container to the outer surface of the grippers This is a maximum of 2 5 in and a minimum of 1 5 The minimum radius is used for evaluation to account for the maximum necessary gripping force Another constraint is the radius from the center of the container to the inner surface of the grippers which is a maximum of 1 75 in and a minimum of 0 5 in Again the minimum radius is used for evaluation for maximum necessary gripping force The coefficient of friction of the pads used to grip the lid is the final constraint The material used is 35 Team Pratham AME470 Ltd a polymer made by 3M called Bumpon Fig 4 9 and the friction coefficient is estimated to be 1 for plastics and slightly higher for metals This lower value of 1 is used as a safety precaution in order to account for both surfaces Figure 4 9 Bumpon ae 4 4 3 State Variables amp Measures of Merit The state variables as a result of the design variables are essential in determining a system s performance based on the defined design variables The state variables for this design issue are the force required to grip the lid without slipping the pressure on the lid at the point of contact space constraints and weight Each of these state variables has a significant effect on the overall layout of the gripping arms and
4. Variables The design variables are the parameters over which we have direct control In regards to the motor selection the design variables are the choice of motor model and the gear ratio applied to the system at the output of the motor Determining a gear ratio and gear assembly to transfer torque from the motor shaft to the twisting plate is more difficult due to the numerous available options For this analysis it was assumed beforehand that it would possible to achieve a gear ratio of 6 1 between two spur gears given the constraints on diameter For example if the larger gear has a diameter of 4 in then the gear attached to the motor shaft would have to have a diameter of 2 3 in to achieve this ratio This arrangement requires an inline motor positioned vertically or a right angle motor laid horizontally For the case of an inline motor the diameter of the motor which will most certainly be greater than the 2 3 in diameter of the spur gear attached to it will require the shape of the base to be oblong extended out in one direction to accommodate the motor Another possible arrangement using bevel gears would allow an inline motor to be laid horizontally but 29 Team Pratham AME470 Ltd bevel gears usually are produced in pairs at a 4 1 ratio and are much more expensive than standard spur gears The limited space of the appliance constrains the choice of gear assemblies considerably The choice of motor is constrained by the torque
5. height should be extendable and its width should be adjustable to meet the jar bottle specifications It must be able to ee a et A be easily cleaned It will be waterproof in case of spills and it must have a convenient power supply for the user whether by ae battery or AC electricity from the user s house The materials od that will be used are rubber aluminum and plastic The rubber will be very useful for the grips and for the opener s base and Sap anne Shonen metal parts should be coated with an anti corrosive material Since safety is a priority all safety risk issues will be identified and dealt with during the completion process The mechanism should not have sharp corners and it should have enclosed gears and motor it should have warning labels where potential hazard may be encountered by the user Also the user will be provided with a user manual with the product s specifications and safety issues Team Pratham AME470 Ltd 2 2 Top Assembly The primary function of the top assembly is to grasp jar lids of varying diameters Every grasping component will be made of rubber to provide a firm grip The device will be able to adjust to lids of the specified range of diameters On the grasping components there will be contact switches which will press against the side of the lid When pressed a signal will be sent to the microprocessor confirming the grasping of the lid The top assembly must also be able to adjust t
6. its resulting plot are shown in Appendix 5 4 2 According to Figure 3 in Appendix 5 4 2 the resisting torque must be close to 0 2 ft lbs at approximately 45 It is best to keep the torque at a lower level so the motor does not have to overcome too many forces in order to twist the body Since all values between 10 and 45 keep the resisting torque well below 1ft lb any of these angles work Since there seems to be a slight increase in the slope in the middle of the graph it is best to keep the angle below 35 Once the angle was calculated the force applied to the body by the graspers needed to be studied In order to accomplish this the grasper was analyzed as it comes into contact with the body A free body diagram was set up with all the forces acting on the grasper pin With an input torque of 14 ft lbs onto the spiral grooved plate it was necessary to create a force of friction greater than that torque to ensure that the grippers will not slip while opening the container The coefficient of friction of the grasping devices on the jar is one Therefore the spiral groove must transmit the torque into a force toward the container equal to the circular force at that radius What made this easy to accomplish was the torque preventing the radial plate from rotating With the torque already placed on the radial plate the spiral grove plate needed a moment to build the torque required to break away from that This does not happen because the t
7. s automatic height adjustment system although a nice feature is unnecessary The disadvantages are large enough to outweigh the advantages in terms of weight savings part count and cost of manufacture Concept 2 has all of the electronics mounted to the bottom assembly The final concept splits its electronics between top and bottom but with the microcontroller and power source in the lower assembly in order to lower the center of gravity The slender arms of concept 2 do not easily transmit a large force to the lid of the container thus eliminating such a design The pages that follow address this final concept and its development They describe its operation and interface with the user They also detail three of the more important issues associated with the development of this product Thus the reader may now turn the page and delve into the Open Aid 14 Team Pratham AME470 Ltd 4 CONCEPT TECHINCAL DESCRIPTION AND VALIDATION This section discusses the operation of the system product and user interface It also discusses three technical design issues components that are central to the operation performance of the Open Aid spiral plate design motor selection and lid gripping arms Engineering justifications for the design of the Open Aid are detailed for each of these key design issues components 4 1 Operation of the system product and user interface 4 1 1 Introduction This section is divided in three main parts user interface p
8. to center the container and divides the force into two surfaces to distribute the pressure on the cap into two points of contact instead of one which divides the force experienced by each point in half The primary source of information used to account for the force necessary to open a container was determined in a simple experiment This experiment determined that the necessary torque to open a container is approximately 6 5 lbein A safety factor of 2 3 was used to account for especially difficult containers This bumps the maximum torque up to a value of approximately 15 lbrin The equations and corresponding figures used to determine the optimal design angles are found in Appendix 5 4 4 4 4 5 Impact on Design The determined angles and number of arms used to grip the container were instrumental in the design of the entire gripping mechanism Determining the allowable angles in the gripping arms 150 and 160 for 0 and y respectively is what allowed for the determination of the number of gripping arms The number of arms deemed necessary three allowed for a less costly motor by putting less stress on it and the gear train This is because the maximum amount of force necessary for to grip the container is 10 3 lbp versus 15 5 lbp for 2 gripping arms 37
9. Team Pratham AME470 Ltd 1 EXECUTIVE SUMMARY 1 1 Product Description The Open Aid is designed to open glass jars and plastic bottles It is a kitchen appliance whose main purpose is to assist anyone but especially older or arthritic consumers in opening containers The product is capable of opening glass jars and plastic bottles of many sizes It is designed to handle round containers It is capable of opening containers of other shapes given that such containers are of a symmetrical design Table 1 1 presents the design requirements decided upon for the Open Aid Issue Requirement Budget 400 100 personal funding Schedule 14 weeks for total project Lightweight Appliance user friendly easily stored Height in 2 10 o Body Diameter in 15 5 Lid Diameter in 1 5 Intelligence microprocessor integrating sensors H Bridges and motors Safety protect electronics oe safe for user operation i e no sharp edges Table 1 1 Design requirements for Open Aid The product has a manually adjustable height over the range specified above It relies on two motors for operation one is in the top assembly and the other in the bottom Both assemblies use a gripping system that relies on a bracket assembly sliding in a slot oriented radially inward with a peg riding in a spirally slotted plate as seen in Figure 1 1 In both instances the motor drives the spiral plate to compress the grippers onto the con
10. Volts necessary to operate the H Bridge are shown This voltage can be obtained from the microcontroller power supply Also the two connections below the 5 Volts represent the PWM and Direction pins In this case an On signal is sent to the PWM pin when the appliance is activated by pressing the start button A change in the value for this pin is not necessary when the appliance is on as we do not need to change the speed of the motor or the pulse modulation The Direction pin will receive either a 1 or 0 signal to control the motor direction Connecting both pins to two of the Mini Max I O ports can do this The motor behavior is dictated by the value of the I O ports given by the microcontroller which are controlled by the status of the hall effect and push button sensors Table 4 1 shows the motor behavior for the different combination of values given to PWM and Direction FUNCTION TABLE PWM DIR OUT1 OUT2 MODE Guiescent supply eurent mode 0 1 LS HS Motor turns clockwise 1 0 HS LS Motor turns counter clockwise 1 1 HS HS Brake both HSDs turned on hard Table 4 1 Function Table that characterizes the behavior of the motor Hall effect sensors Four hall effect sensors are used as explained in the product logistics section Two of them will be in the bottom assembly radial plate and the other two will be in the top assembly spiral plate These sensors tell the microprocessor when to turn off on the motors 21 Team Pratha
11. ded by the housing both out of sight and out of reach of the user Figure 3 4 Concept 2 Figure 3 5 Concept 3 Concept 4 is a handheld device with a similar appearance to the crane arm used in arcade machines to pick up plush toys It is held over the container by the user with the batteries placed in the handle to distribute the weight of the appliance Its crane arms are screw driven with some options of how to do so The upper gripping portion would contain the Figure 3 6 Concept 4 11 Team Pratham AME470 Ltd system found in Concept 1 Figure 3 6 depicts the shape and rough proportions of the concept as well as the proposed arm driving mechanisms Some other subsystems were offered as well Subsystem A shown in Figure 3 7 is a container grasping mechanism It is a type of four bar mechanism driven by a worm gear at one of the base points As the worm gear turns the linkage extends out to the container Subsystem B is a grasping mechanism used for the lid It consists of two plates one with a spiral groove and the other with a radial groove for the gripping mechanism to ride in The entire assembly is driven by a single motor as depicted in Figure 3 8 The concept is similar to that of the grips used to hold a drill bit in place Driven pin Figure 3 7 Subsystem A 4 bar grasping mechanism Figure 3 8 Subsystem B Given such a diverse offering of concepts and subsystems the systems propo
12. e grips are positioned back to the maximum radial outer diameter This is done with the use of another hall effect sensor located at one of the grips on the top assembly Once the grip gets close enough to the 17 Team Pratham AME470 Ltd magnet located in the housing maximum radial outer diameter the magnet sends a signal to stop the motor The same function occurs at the bottom assembly Once the top assembly motor is turned finished the bottom assembly motor reverses and stops until hall effect sensor 1 is detected again This will bring the bottom grips back to their initial position maximum radial outer diameter Another off design issue is if the lid cap of the container is too small for the appliance There are certain specifications for the sizes of bottles the product can open Notice however that when the Open Aid tries to open a smaller bottle out of specification the switch is never pressed as there is not a contact force anymore To solve this problem a hall effect sensor placed at the minimum radial inner diameter for the grips in order to specify when the grips are closest to each other Then when the hall effect sensor is sensed the top assembly motor is turned off There are no major safety concerns with the product All the electronics are covered by the housing Also there are no dangerous or harmless external gaps between components The only safety concerns will occur when adjusting the height of the top assemb
13. enough frictional force to prevent slipping when the radial plate turns This is the most important measure of merit because it affects the primary function of the tool Ifthe spiral shape does not create enough friction the Open Aid opener will be unable to open the jar bottle A third measure of merit was the cost of producing the parts If a smaller angle on the spiral plate creates the best result we still cannot just create the smallest angle piece possible It is also important to remember the cost of the smaller angles The smaller the angle the longer it takes for the slot to cover the necessary 3 5 in This creates longer and more difficult work that should try to be avoided 4 2 4 Method of Analysis The method used to solve this problem was based on static mechanics There were two states in which static mechanics were looked at The first was while the grasping devices were sliding up the radial groove The force that is needed to keep the radial disc in place depends on 25 Team Pratham AME470 Ltd the force needed to move the graspers and the angle of the spiral groove The force needed to move the graspers due to acceleration and friction was calculated at approximately 0 25 Ibp for each grasper The equation relating this value and the angle to the force needed is shown in Appendix 5 4 2 as Equation 1 This equation was then used in a Matlab script in order to simulate the effects of many different values for 8 This program and
14. f in order to avoid overloading 16 Team Pratham AME470 Ltd the motor and potentially destroying the electronics This off design issue will happen when the torque required to open the container is greater than that for which the Open Aid is designed A hall effect sensor is a magnetic sensor consisting of 2 magnets and our product will have two of them on Fig 4 1 located on the radial plate of the bottom assembly and 180 from each other As shown in Figure 4 1 one of the hall effect sensors sensor 1 will be placed so it is sensed when the bottom grips are moving radially inward Then our program will be looking for the presence of the second hall effect sensor sensor 2 If it senses hall effect sensor 2 second hall effect sensor is on the radial plate has rotated enough to open the container and the bottom assembly motor will be turned off If the container opens due to the torque generated before the contact switch is pressed the motor will be on until hall effect sensor 2 is sensed Again the radial plate will rotate 180 enough to open the container Container to open Hall effect sensor 1 Housing Radial plate Hall effect sensor 2 bottom assembly Figure 4 1 Representation of the hall effect sensors to help comprehend the logistics of the product After either of the two scenarios discussed above takes place the container needs to be released First the top assembly motor is reversed This motor turns until th
15. gear mounted onto the housing As the gear spins it rides up and down the threaded shaft automatically adjusting the height of the appliance Sensors are embedded in the upper assembly to sense when it makes contact with the container Top View Front View Side View Figure 3 2 Grasping arms for concept 1 Motor x3 Gear teeth Height Adjustment Turning Assembly Threaded Figure 3 3 Concept 1 upper housing components Concept 2 is a unique device It uses slender arms to grasp the lid of the container and has grips that close in on the body at the bottom The lid gripping arms are manually adjusted 10 Team Pratham AME470 Ltd for height and the driving motors are encased in the base of the product The grips that close in on the bottom of the container s body once held in place are then twisted so that the container is opened by turning the body rather than the lid A rough sketch is shown in Figure 3 4 Concept 3 is a round machine enclosing all of the moving parts in its housing in some manner In doing so it takes the safety of the user into utmost consideration Its shape also suggests the shape of the containers it is designed to open as well as being easy on the eyes Figure 3 5 depicts a rough sketch of concept 3 The concept uses a base twisting on a threaded shaft to serve the dual purpose of height adjustment and twisting the container open The grips on the top are for the lid and are shiel
16. gest of these is the potential for two totally different systems used for gripping the container This is avoided by the product s spiral radial plate assembly containing gripping arms for both the top and bottom grasping functions The similarity of between the assemblies minimizes assembly time and complications The Open Aid is designed to be a robust product appealing to the consumer and selling in mass produced quantities It has the ability to open plastic bottles which is one step ahead of the competition It is user friendly easy to operate and easy to maintain everything a person could ask for in an appliance Team Pratham AME470 Ltd 2 DESIGN REQUIREMENTS AND TARGET SPECIFICATION This section describes the design requirements and provides quantitative targets for given specifications It discusses the product first by specifying the general requirements of the Open Aid and then by describing the top and bottom assemblies separately 2 1 General Requirements Team Pratham is creating an intelligent device to address the problem of opening and re sealing jars and bottles The idea was brought up through discussion with a team member s relative Due to carpal tunnel syndrome the task of opening jars and bottles had become difficult This problem can be extended to elderly and other complications The function of the product is to open sealed glass jars and plastic bottles Team Pratham initially defined general design requ
17. his microcontroller at no cost Mini Max is a general purpose low cost high reliability and highly expandable microcontroller system It has 33 general purpose I O pins which is more than enough ports for the Open Aid Also the Mini Max series board comes with a 6 volt unregulated DC power supply This power is needed for the hall effect sensors and the H bridges to be discussed Motors Two Buehler DC geared motors were selected for our system They are in charge of providing the necessary torque to open the containers The motors operate in a range of 3 to 12 Volts and need a maximum current of 200mA For more information about the motors refer to the Motors Selection section H Bridges 2 NMIH 0030 H bridges are used in the intelligent system They are design specifically for DC motor applications ranging from 6 to 18Volts up to 5A current These devices provide forward reverse and brake modes of operation The PWM input can be driven from a dedicated PWM port while the direction input is driven as a simple low speed toggle Figure 4 4 shows the connection of the microcontroller to the H bridge If the motor is turning oppositely of what is expected simply reversing the connections of the motor will correct it The voltage above the motor in Figure 4 4 represents the voltage supply for the motors 20 Team Pratham AME470 Ltd Figure 4 4 H bridge connection to the motor and microcontroller To the left of the H bridge the 5
18. irements to guide the team through all of the project s phases It has been decided that the design objective must be a stationary mechanism that will be able to open the lid cap on a container The team has 14 weeks to design the product and to build a prototype The team members must conduct individual trade studies order parts revise mechanism designs fabricate parts account for electronics sensors and control logic model parts in CAD construct the product and give an in house demonstration of the product In addition to time constraints the budget assigned by AME470 Ltd to all teams is an important constraint A total of 400 is assigned to each team with the option of increasing the total budget to 500 by member contributions The team members have also set specific target requirements on the containers for the product to be able to open e 2 in lt body height lt 10 in e 1 5 in lt body diameter lt 5 in e 1 in lt lid cap diameter lt 5 in Team Pratham AME470 Ltd e 0 3 in lt lid height lt 1 in e Plastic Glass Containers e Twist off lids no pull off caps The opening device will have to be smart enough to automatically adjust to the different varieties of body cap lid sizes that a container may have A microprocessor will be integrated into the mechanism in order to provide it with the necessary programming to accomplish its required task The product Fig 2 1 should be kept as light as possible Its
19. ld be best to try and keep in closer to the maximum while at the same time keeping a high factor of safety Based on the results of the study and the three measures of merits the appropriate choice should be less than 35 but at the same in a close range The decision was made that the best choice to make the spiral cut would be 30 Without this research the idea of how to design this spiral shape was just a vague idea but after it the numbers are right in front of me The numbers attained from this engineering work definitely justify the decision to make the groove converge toward the center at a 30 angle This decision will then affect the major function of the product which is grasping and opening of the jar bottle 28 Team Pratham AME470 Ltd 4 3 Issue No 2 Motor Selection 4 3 1 Introduction This section of the report will present the scientific method used to choose a motor for the purpose of twisting the base plate This motor must provide the necessary torque to break the seal on the jar lid It is located inside the base of the Open Aid and must transfer torque to the twisting plate through a central shaft The choice between an inline and right angle motor constrains the possible methods of transferring power from the shaft of the motor to the rotating plate A gear train is being used as well since the Open Aid requires a small lightweight motor capable of providing enough torque to open even the tightest lids 4 3 2 Design
20. ly A warning sign will be placed on the housing that warns about pinching one s hands Figures 4 2 and 4 3 show the algorithms that represent the action of opening and releasing the container respectively 18 Team Pratham AME470 Ltd Sense top assembly Stop turning top contact switch assembly motor Start turning bottom assembly motor Sense bottom assembly contact switch Count to ce 1 secon Hall effect econd sensor 2 senses magnet T i Hall effect sensor 1 still senses magnet Turn top assembly motor on Stop bottom assembly motor Figure 4 2 Algorithm representing the opening of the container Reverse top assembly Sense top assembly hall effe Stop top assembly Reverse bottom assembly Hall effect sensor 1 senses Stop bottom assembly Figure 4 3 Algorithm representing the releasing of the container 19 Team Pratham AME470 Ltd 4 1 4 Hardware and Electronics The following electronics are used to create the circuit and intelligent system AC DC adapter The converter plugs into the wall and converts the 120Volts AC source to 500mA 6Volts DC current This is the necessary amount of voltage and current for all the other electronics to work appropriately AME470Ltd provided this adapter at no cost Mini Max PIC Microcontroller This microcontroller utilizes the PICI6F877A microprocessor It demands a minimum of 6Volts and a minimum of 100mA current AME470Ltd also provided t
21. m AME470 Ltd as explained above The hall effect sensors switch the signal sent to the microprocessor when both the magnet and sensor come close together The normal of the faces of these magnets have to be parallel to each other in order to function and send the signal change appropriately Figure 4 5 shows a picture of the magnetic sensor used in our product Figure 4 5 Hall effect sensor Push button sensors Three push button sensors are used Two of them are simple small push button sensors that will be located in both top and bottom assembly grips When the button is pushed a signal is sent to the microprocessors to start a determined action as explained in the Logistics of the Product The other push button sensor is the start button that the user pushes to activate the appliance All of these electronics are incorporated into a circuit shown in Figure 4 6 The Open Aid integrates this circuit However it has an extra motor and extra H bridge connected to the Mini Max since two are used in the product These are not shown in the circuit to avoid messiness Similarly the push button sensors and hall effect sensors are all shown together Another device incorporated in the circuit is a fuse It is a safety device to prevent the motor from drawing too much current 22 Team Pratham AME470 Ltd 120V Start Button Push button Hall effect sensors sensors Figure 4 6 Representation of the electronics circ
22. maximum torque to account for any containers which might be tighter than the salsa lid This is approximately equivalent to 1 400 oz in a standard measurement for motor output torques The constraints were for the motor weight at 5 lbs and the motor diameter at 6 in as mentioned previously The 50 limit was also applied Several online manufacturers produce motors which fulfill the required role of the primary twisting motors but do not give a price for their motors After requesting a quote from one such manufacturer it became obvious that these products were not available in small quantities and were much too expensive All of the potential motors that came from such sources were stricken from the weighted decision matrix Furthermore any motors that produced torques much smaller than the required torque of 1 400 oz in were also removed from the matrix This final list of potential motors was the product of approximately 8 2 hours of searching through catalogues and webpages Appendix 5 4 3 Very few motors came even close to satisfying our requirements for this project because of its unique demands Most hobby sized motors are intended for use in robots or small remote 32 Team Pratham AME470 Ltd control vehicles The Open Aid will subject this motor to large amounts of torque relative to its required size Finding a motor that would fit in a small appliance and still produce large amounts of torque was difficult Eventually it became obvi
23. o the difference in radii of the specified containers 4 2 3 State Variables amp Measures of Merit There were many state variables directly affecting the performance of the Open Aid that resulted from this one design variable The first of these state variables was the speed at which the grasping device moves up the radial groove Based on this a second state variable was the 24 Team Pratham AME470 Ltd torque that must be withstood by the radial plate to prevent it from rotating before the body is securely grasped The next state variable was the ratio of the torque applied by the spiral plate and the frictional force between the graspers and the body of the jar of bottle This state variable was the one that confirmed that there was enough friction to twist the lid without slipping The final state variable was the cost that it will take to create and assemble this unit into one piece There were three measures of merit used to determine the best solution for this design variable The first was the amount of torque needed to be applied to the radial plate in order to resist plate rotation while the graspers are moving toward the body This is important because it is the delay of the radial plate s rotating until the body is grasped that allows the Open Aid to sense that it has begun removing the top The second measure of merit was making sure that enough force was being applied to the body by the graspers This force ensures that there is
24. o various container heights The height adjustment is a purely manual function The top assembly rests at its lowest position for easy storage To accommodate containers it may be lifted by the user with one hand while the user places the jar in the machine with the other hand It was determined that if the user is able to lift a jar or a bottle with one hand he or she is able to lift the top assembly to place in it the jar or bottle to be opened 2 3 Bottom Assembly The bottom assembly must be able to grasp the body of the container It must do so efficiently i e without requiring multiple power sources It also must be able to open a sealed container The design requirement is for a maximum torque of 15 Ibin The design must be able to detect angular displacement so that the motors can be signaled to stop The following section Concept Selection describes the competing offer unique solutions proposed concepts developed to satisfy these requirements They are all very different and offer unique solutions to the proposed problems Team Pratham AME470 Ltd 3 CONCEPT SELECTION This section gives a detailed discussion of several appropriate competing concepts considered for subsystems including sketches and schematic representations It also contains a table that compares strengths and weaknesses of competing designs that justifies the selection of the final concept chosen by Team Pratham 3 1 Competing concepts The Open Aid container
25. ogistics of the product Once the user has placed the jar bottle in the Open Aid it will open the container automatically after pushing a start button that will be found in its housing When the user activates the appliance an automated series of steps will start the opening of the container Notice that every time the product is turned on the grips at the top and bottom assembly will be reset to their initial position at the maximum radial outer diameter First the top assembly motor is started This action will move the top assembly grips radially inward until the lid cap is held secured The motor will then stop when the contact switch located on the grip is pressed due to the contact force between the grips and the lid cap At this same time the bottom assembly motor will be started and the bottom grips will start moving radially inward At this point of the logistics the following two scenarios may occur The first case is fairly similar to the top assembly action A time count will start when a contact switch located at the bottom grip is pressed due to the contact force between the grips and the bottom of the container The function of the count is to account for the amount of torque being applied twisting time in order to open the container If after one second there is no presence of hall effect sensor 2 and hall effect sensor 1 is still sensed the radial plate did not move at all Thus the bottom assembly motor will be turned of
26. opener started out with various concepts for its design and those of its subsystems Eventually those concepts were either eliminated or refined to be part of the product outlined elsewhere in this report The following is a general overview of the proposed concepts and the decisions made to arrive at the final concept The first concept Figure 3 1 is a square looking device in which all of the mechanisms are found in the top assembly A pair of arms driven by one motor grips the body while a set of grips closes in on the lid each grip driven by its own motor Another motor is used to turn the entire gripping assembly to open the container Finally another set of motors is used to automatically adjust the height of the device using a threaded nut riding up and down a threaded shaft A microcontroller drives all these mechanisms Pure dete Concept The visible grasping arms are proposed in Figure 3 2 They are comprised of a single motor driving two arms simultaneously Embedded in the upper portion of the product are a turning assembly lid grasping assembly and vertical height adjustment assembly all seen in Figure 3 3 The turning assembly relies on a single motor mated to a rounded gear to spin the entire grasping assembly The lid grasper relies on 3 motors each attached to its own gripping Team Pratham AME470 Ltd arm Finally the vertical height adjuster relies on 2 to 4 motors at opposing support posts They turn a threaded
27. orque that is being applied by the spiral grove to the grasper pin increases as the force applied to the 26 Team Pratham AME470 Ltd bottle increases This created more and more friction never allowing the graspers to slip The only way for the spiral plate to continue to move was by breaking the seal between the jar and the lid thus allowing freedom to continue the rotation By solving this system it was possible to create a Matlab code to find values for the design variables The Matlab code is shown in Appendix 5 4 2 along with the results of the simulation The graphs represent the angle of convergence vs the force of friction between the body and the graspers at various positions of the graspers These graphs gave us quite a bit of information As expected every chart shows that as the angle of convergence decreases the friction created on the body grows larger and larger The other important data that can be gathered from these charts is that as the graspers move in further they create more and more friction The reason behind the first phenomenon is an idea as simple as a wedge As the wedge is pushed in one direction it transfers force in other directions perpendicular to the surfaces of the wedge The second fact deals with the radius and torque that the particle is experiencing The important idea behind this fact is the ratio of force and torques The torque that the spiral plate has applied to it and in turn applies to other pa
28. ous that only a geared motor or rotary plate motor would produce 1 400 oz in of torque with a low amount of power given the space constraints imposed on both the motors and gears After assigning the scores based on these considerations the relative importance of each category was rated in relation to the others Normally a survey of customers retailers and manufacturers would be used to help determine these weighting factors Instead the weight of each category was determined based the group s judgment The two most important categories were cost and torque since they determine the competitiveness and functionality of the automatic jar and bottle opener If the Open Aid lags in either of these areas it is essentially worthless The weight diameter and power of the motor comprised the categories of middling importance while the length and angular velocity were considered relatively less important 4 3 5 Impact on Design The weighted decision matrix used to evaluate this design problem is located in Appendix 5 4 3 According to the matrix the best option was to use motor No 2 a Buehler 12V DC Geared Motor from Electronic Surplus Inc and a 6 1 gear ratio It is pictured below Fig 4 7 Figure 4 7 Motors used in Open Aid 33 Team Pratham AME470 Ltd The decision to use the Buehler motor was made based on the dimensionless number scale used in the weighted decision matrix This motor outperformed all of the others by a large
29. r Due the high torque requirements and demanding size and weight constraints the selection of this motor was a difficult and important task By setting precise quantitative requirements on the important state variables of the system and implementing a weighted decision matrix to sort through the remaining potential motors this study methodically reduced numerous motor options down to the one most qualified selection 34 Team Pratham AME470 Ltd 4 4 Issue No 3 Lid Gripping Arms 4 4 1 Introduction This section outlines the method used to determine the geometric shape and the number of arms used to grasp the lids of the containers to be opened The grippers are cut to a sharp angle for ease of manufacture and to ensure 2 points of contact per grip on the lid in order to reduce the pressure of the gripper on the lid The following text discusses how that optimal angle was obtained both for an upper and lower part of the gripping arm The results impact the spiral plate geometry and its manufacture 4 4 2 Design Variables This study investigates three independent design variables These variables are number of arms required Inner Diameter N the angle 0 and the angle y Fig 4 8 0 represents the more DE angle between the two faces used to grip the cap on the inner diameter of the grippers while y represents the angle between the two faces used to grip the cap on the Figure 4 8 Gripping arm with indicated angles
30. r is given a constraint of 6 in on the diameter or length depending upon the configuration No requirement was set for the height of 30 Team Pratham AME470 Ltd the base so the length of the motor or diameter depending upon the configuration has no hard constraint However motors that require a taller base were penalized in the Measure of Merit The cost of the motor is a crucial state variable since the customer will not want to pay a high price for the Open Aid regardless of the features it possesses Because of this restriction a hard constraint of 50 was set for the motor price Even though this entire appliance should not sell for much more than 50 developing a prototype is an expensive process Mass production cuts the cost of manufacturing considerably from the cost of prototyping 4 3 4 Methods of Analysis Since this design analysis involves a choice between different product designs a weighted decision matrix was used to quantitatively analyze and compare the strengths and weaknesses of each option The final selection process focused on four models that did not grossly exceed the set requirements To select the best motor each motor option was rated on a scale from 0 to 10 If an option failed to meet the initial requirement for a category it received a 0 for that mark Likewise designs that were completely satisfactory in a particular category in which the overall performance of the product could not be improved with e
31. related systems Minimizing the force required to hold the pads in place minimizes the force required for the motor to sustain This ultimately results in a less costly motor Reducing the force required to grip the lid also reduces the pressure experienced by the lid at each point where the arms meet the lid This avoids denting or crushing the lid Increasing the angle ultimately reduces the size of the arms It also becomes a question of whether or not 3 arms fit in this system The angles determine the size of the arms In order to maximize manufacturing efficiency by using the fewest number of cuts in the arms larger wider angles will decrease the size of the arms used consequently decreasing their weight The design variables detailed above were evaluated through a force analysis conducted on a general form of the geometric design for the grasping arms The equations for these forces 36 Team Pratham AME470 Ltd and geometries are described in detail in Appendix 5 4 4 The results were plotted in Matlab and are fully discussed in Appendix 5 4 4 4 4 4 Method of Analysis The normal force provided by the lid contacting the faces on the arms produces the gripping force necessary for the container lids The material used to do so is the aforementioned 3M Bumpon polymer with a coefficient of friction u approximately equal to 1 The primary concern with the normal force is to distribute it onto two faces at an angle This allows the machine
32. requirement for the system The motor must be able to provide 1 400 oz in of torque This value was determined through experimentation and will be explained in greater detail in the Methods of Analysis section 4 3 3 State Variables amp Measures of Merit The state variables quantitatively describe the performance of the system They are determined entirely by the choice of design variables It is important to formulate a group of state variables that adequately describes all of the aspects of a product For the Open Aid the important state variables are output power output torque angular velocity of the twisting plate weight of the motor size of the motor and cost of the motor While there is no direct constraint on the output power of the motor and gear assembly it must be able to produce an output torque of 1 400 oz in This is the most important constraint since a motor that is incapable of opening a jar is worthless Initial requirements set a target weight of 8 lbs for the Open Aid appliance In light of this goal a hard constraint of 5 lbs was placed on the primary motor Motors above this weight will not be considered and motors nearing the five pound limit will be heavily penalized in the Measure of Merit The size of the motor is constrained by the size requirements for the base of the assembly The Open Aid has been designed to accommodate containers with diameters up to 5 in The width of the base is larger than this so the moto
33. roduct logistics and hardware and electronics First the user interface is explained This brief explanation shows the interaction between the customer and the Open Aid Then the logistics of the product are given This incorporates a detailed description of the different actions required and performed by our appliance in order to open a container It also addresses off design issues and safety concerns It also shows the mode in which the system functions and is operated with means of flow charts Finally the hardware section explains and details the different electronic components that are used in the product This section also includes a complete circuit drawing of the electrical system 4 1 2 User Interface It only takes six simple steps for the customer to use the appliance The rest of the necessary actions required to open the container are done automatically after the customer presses the start button The operation and automation are discussed in the following section The customer will take the following steps in order to use the appliance 1 Connect Open Aid to wall outlet Turn on appliance 15 Team Pratham AME470 Ltd 2 Adjust height of the top assembly to fit container to open 3 Place the container on the bottom plate of the opener 4 Activate appliance by pressing a start button found on the side of the housing 5 Take container out of the container opener 6 Open another container unplug the appliance 4 1 3 L
34. rts is always constant As the graspers move closer to the center the force tangent to the circle grows due to a shorter moment arm This larger force in the tangent direction directly relates to a larger force in the direction normal The goal of this planning was to get a rotation that would not allow slipping to occur All that needed to be done was pick an angle of convergence and make sure the resulting frictional force was greater than the torque needed to detach the lid form the jar approximately 14lbs From the graphs it was easy to see that most of the logical choices for the angle do in fact offer the necessary frictional force The only questionable scenarios result while the graspers are at a 27 Team Pratham AME470 Ltd radius of 6 in or 4 8 in In these situations angles that are over 35 could present some problems and not open all lids It would be nice to have a bit of space between the angle chosen and the failure angle therefore it would be wise to keep the chosen angle under 35 This may be familiar because from the graph with the pin in motion it was determined that the angle should try and be kept under 35 4 2 5 Impact on Design While it would be possible to try and create the smallest possible angle it is important to remember the third measure of merit That was the simplicity of the design The smaller the angle the longer the groove and the harder the work it will be to create this piece That is why it wou
35. sed in each were compared based on their strengths and weaknesses Table 3 1 is a complete listing of such characteristics It shows the different features for the 4 different concepts and 2 subsystems This table was used to compare and ultimately arrive at a final concept agreed upon by the group discussed next 12 Team Pratham AME470 Ltd concept Features Strengths Weaknesses Subsystem 4 A all components in upper assembly 1 motor for container grippers 3 motors for gripping lid 1 motor for twisting lid 2 4 motors for height adjustment all electronics in lower assembly 2 slender arms for gripping the lid bottom twists container open round design all components shielded from view bottom raises and twists container handheld device crane like arms 4 bar linkage for gripping ai i Spiral radial grippers Table 3 1 Strengths and weaknesses of the concepts and their features 3 2 Final Concept all torque transmission occurs on the housing minimizes motor count for system good force application minimizes motor count for system automatically operates for the user bottom heavy aesthetically pleasing requires less torque than the lid aesthetically pleasing safety clean appearance integrates two functions into one unique concept aesthetically pleasing efficient force transmission minimizes motor count allows for multiple grips top heavy crowded assembly
36. ss than the preset spring force the microcontroller does not sense the presence of a container and must continue opening the container However if it senses the container the microcontroller counts for a specific amount of time and if it senses through the magnet sensor that the container is still not opening it reverses to prevent the motors from drawing too much current potentially destroying the product s electronics Figure 1 2 Gripping assembly components Driving these gripping assemblies are gears with a 6 1 ratio to transmit the desired torque The advantage to using gears is the positive contact between the two Finally the gravity dependent height adjustment of the appliance allows it to grasp the lid without resisting vertical displacement while the container twists causing the lid to rise off of the container The Team Pratham AME470 Ltd only disadvantage to this is that the user must manually raise and lower the top portion However it is rationalized that if the user is able to lift the jar or bottle to be opened he or she is able to lift the appliance top 1 3 Design Influences Designing a kitchen appliance requires the consideration of many factors The consumer must see it as a viable and user friendly product The manufacturer must be able to market and sell the product all at a reasonable price The following are the key issues addressed in designing the Open Aid user effort container centering height adju
37. stment cleaning and simplicity of assembly Once plugged into the wall outlet the user has a minimal amount of effort The product rests at its 2 in minimum height allowing for easy storage The user simply raises the upper portion of the product and with the other hand places the container to be opened roughly in the center of the appliance The user then lowers the upper assembly onto the container resting there by gravity and presses the start button The appliance closes first on the lid to center the container then on the body of the container and continues twisting the container open with the bottom assembly Once open the appliance reverses its motors to release the opened container The user lifts the upper assembly off of the container and removes the open container with the lid resting on top Cleaning is addressed in the design of the product by essentially enclosing the electronics and sealing them away from the atmosphere Both the upper and lower assemblies employ plastic shields built into the system that also serve the purpose of supporting the subassemblies used by the product The upper assembly will not need to be cleaned as the spillage will drip down off of the product The bottom assembly shown in Figure 1 3 allows the user to remove Team Pratham AME470 Ltd the gripping assembly in order to clean the tray below Figure 1 3 Bottom plates with coupling and tray Ease of assembly encompasses many issues The lar
38. tainer and its lid The design of these systems is of utmost importance as it only requires two motors to provide three functions grasp the lid grasp the body of the container and twist the container open The entire product was built around these systems of which the rotating plates are approximately 7 inches in diameter The sensors are embedded in the gripping brackets and Team Pratham AME470 Ltd turning plates to ensure consistent operation and the motors and gearing were selected specifically for the gripping systems All of the electronics are managed through a microcontroller powered by the alternating current of the house with an AC DC adapter Figure 1 1 Gripping System 1 2 Concept strengths and weaknesses The number of moving parts requires that the product s systems be evaluated in all aspects of the design Table 1 2 highlights the major issues with the design of the product Component Strength Weakness Importance Spiral unlimited number of potential grippers Carefully selected geometry high the basis of design for the entire product Magnet Sensors only sensors require power magnet does not None low there are no wires to tangle reducing problems Grippers spring loaded for more uniform grasping force reaches contact switch increases part count only a fixed medium ensures that all grippers grip with even force Contact Switches Small
39. uit 23 Team Pratham AME470 Ltd 4 2 Issue No 1 Spiral Plate Design 4 2 1 Introduction The first key technical design issue is the functionality of the bottom assembly of the Open Aid This section will describe the scientific method used to design the spiral plate This assembly must grasp the body of the bottle jar container and rotate it until the seal of the lid has been broken In order to achieve this a two plate system was conceived The top plate contains radial grooves that allow the grasping devices to slide in and out The bottom plate has spiral grooves that push the graspers into the body of the container The basic set up of this device is shown in Appendix 5 4 2 This analysis determined the best way for these parts to interact focusing on the transmission angle between the spiral groove and radial groove 4 2 2 Design Variables The design variable is the parameter that is directly engineered into the Open Aid For this technical issue the only design variable is the shape of the spiral and radial grooves on the two plates This variable had an infinite number of design options The effects of different constant angles of convergence and different variable angles of convergence were compared The major constraint on the design variable the grooves was the ability to hold bodies with a minimum 1 5 in diameter and a maximum of 5 in diameter This gave the constraint of a minimum 3 5 in of movement on the radial grooves due t
40. wires can get twisted if not controlled medium wires twist which must be accounted for in the design Gears Height adjustment positive contact force transmission automatically moves up with lid displacement precision requires user to initially adjust it manually may be loud small pitch requires high gears transmit the torque to the container applied by the motors low automated system not necessary user able to lift top assembly manually Table 1 2 Strengths and weaknesses of the main components of the Open Aid As previously stated the spiral plate assemblies minimize motor count and allow for as many gripping arms as the manufacturer desires The magnetic sensors are optimal for position Team Pratham AME470 Ltd sensing because the sensor is stationary while the magnet rotates Because the magnet itself is not electrically powered it has no wires to get tangled The contact switches however are prone to tangling Thus the design employs the magnetic sensors to prevent unnecessary turning of the mechanism and will not allow the switches wires to tangle The gripping assembly shown in Figure 1 2 consists of a bracket with the embedded contact switch housing a gripping pad and spring One switch is used per assembly to avoid redundancy This allows the product to sense the presence of a container but only for a given spring force If the force required to grip the container is le
41. xtra enhancement of the feature were scored with a 10 For features that met initial constraints but were not optimal a linear scale was made between the maximum and minimum values for that feature from 0 to 10 and points were awarded to each motor option based upon where it performed on this scale For categories without hard constraints a relative score was determined in between 0 and 10 when a motor met the basic requirements but could be improved to raise the overall quality of the product The requirements for these categories were carefully constructed The torque requirement of 1 400 oz in was determined through several experiments in which a Quickgrip 31 Team Pratham AME470 Ltd bar clamp was fastened to a lid Weights were then attached to a lever arm on the clamp until the resulting moment was large enough to open the lid The required torque for breaking the seal of the lid was then calculated by multiplying the force of the weights by the length of the lever arm The required opening torque for the particular containers is summarized below e Glass applesauce jar T 460 oz in e Glass salsa jar lid T 1 013 oz in e Plastic Powerade bottle T 273 oz in e Glass Snapple bottle T 422 oz in The data from these experiments can be found in Appendix 5 4 3 The experiment was initially performed in metric units so that the salsa jar required 6 5 lbein of torque A required torque of 15 Ibr in was selected as a
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