Tire Arm Process Documentation
- 1. Table of Contents Project Scope ……………………………………………………………………………………………. 1 Logbook ………………………………………………………………………………………………….. 1 o Gantt chart for project process ……………………………………………………..3 o Project emails records ………………………………………………………………….. 4 o Project QFD ……………………………………………………………………………………. 11 Literature and Patent survey …………………………………………………………………… 12 Brainstorming/concept generation and free hand sketches ……………………… 13 o Early Lego model ............................................................................... 16 Design Feasibility Analysis ………………………………………………………………………… 16 Final design concept selection ………………………………………………………………….. 17 o Gripper ………………………………………………………………………………...………. 17 o Two degree of freedom …………………………………………………………………. 18 o Differential gear system& worm gears …………………………………………. 19 o Stationary base ………………………………………………………………………………. 20 o Touch sensors and Timing ……………………………………………………………….20 Project QFD ………………………………………………………………………………………………… 2 Lego Mindstorm Program …………………………………………………………………………… 21 Fem Report & Images ………………………………………………………………………………… 22 o Loads ………………………………………………………………………………………………. 22 o Constraints ……………………………………………………………………………………… 23 o Structural results ……………………………………………………………………………..24 o Images …………………………………………………………………………………………….. 25 Maintenance Guide ……………………………………………………………………………………… 26 Safety Factor Calculation ……………………………………………………………………………… 27 Bibliography …………………………………………………………………………………………………. 28
- 2. 1 | P a g e Document scope The project required a device to be built that could grab 3 different sizes of tires one at a time from 1-3 separate input locations, rotate the tire 180 degrees around an axis parallel to the shop floor, then place the tire on a single universal output location. Two tires of same size must be stacked on top of each other, only two motors can be used, and bonus marks are given if the device can service more than one input location. After brainstorming and generating a concept, a design was created using NX Unigraphics, as well as a Lego prototype used to prove functionality. Logbook Task Name Duration Start Finish RobotArm Project 49 days Mon 26/09/11 Thu 01/12/11 FirstMeeting -Gettingtoknowthe group members -Exchangingcontactinformation -Decidingonwhere andwhentomeetnext 1 day Mon 26/09/11 Mon 26/09/11 ProjectOverview -Discussionof the projectrequirements -Assigningthe rolesandsplittingthe partsforcompletion -Decidingwhohasthe neededskill level tocomplete acertaintask 1 day Wed28/09/11 Wed28/09/11 Brain StormingSession -Brief sessionondecidingwhatwillbe done forthe designof the robot arm -Drawingupsome sketchesandsharingideasfor makinga workable deign - Literature review onthe existingrobotdesigns 1 day Mon 03/10/11 Mon 03/10/11 "Drop Box"File SharingInitiated -groupmemberscannowshare the fileswiththe groupmembers online 1 day Wed05/10/11 Wed05/10/11 Preliminary Prototype - Firstprototype made withLEGO - Helpedtoorientthe effortsandgetonthe same page Milestone Fri 21/10/11 Fri 21/10/11 PreliminaryDesign,BasicPrototype,andSkill Gathering - Determiningwhatskillsneedtobe obtainedtocomplete the project - Workingwiththe basicprototype andimprovingitbasedonthe set requirements 1 day Fri 21/10/11 Fri 21/10/11 ProjectClarification 1 day Mon 24/10/11 Mon 24/10/11
- 3. 2 | P a g e -Briefingonwhatneedstobe completedandwhere the team Workingon Prototype -WorkingwithLEGO to make a good design 3 days Sun06/11/11 Tue 08/11/11 Workingon Prototype 1 day Tue 08/11/11 Tue 08/11/11 Workingon Prototype 1 day Sun13/11/11 Sun13/11/11 Functional prototype made - The final prototype isestablished Milestone Mon 14/11/11 Mon 14/11/11 Making partsin CAD -Creatingthe partsfor the real-worldrobotarmbasedonthe prototype 6 days Tue 15/11/11 Tue 22/11/11 CAD partsare finalized -The parts are readyfordrafting Milestone Tue 29/11/11 Tue 29/11/11 Draftingparts inCAD 2 days Tue 29/11/11 Wed30/11/11 CAD DraftingisComplete Milestone Wed30/11/11 Wed30/11/11 FEM Simulationof HoldingJaw 3 days Mon 28/11/11 Wed30/11/11 FEM SimulationisComplete Milestone Wed30/11/11 Wed30/11/11 MotionSimulationof the robotassembly 2 days Tue 29/11/11 Wed30/11/11 MotionSimulationisComplete Milestone Wed30/11/11 Wed30/11/11
- 4. 3 | P a g e Gantt Chart for the Project Progress:
- 5. 4 | P a g e Project QFD
- 6. 5 | P a g e Literature and patent survey The JP 6262699 is a device used to grab tires one by one from a rack, and then move them to a pre-determinedlocation.The handhas4 fingersthat grab the tire from an upright position. This allows the arm to grab a fairlywide varietyof sizesof tirescomparedwithour conceptwhichgrabs tires from a horizontal position using two fingers. The JP 6262699 also has a much wider range of motion due to it having3 jointseachwiththeirownaxisof rotation yieldingsix degreesof freedom, allowing the device to be usedina more diverse range of operations.Ourdesignwouldhave asimilarrange of motion if we had more parts to workwith,andweren’tlimited by only being allowed to use 2 motors. Although the JP 626699 has a wider range of motion, it is only capable of rotating from 0-90 degrees around the Y- axis,meaningit cannot flip tires over 180 degrees as our design must. Both designs only have one arm and one hand,and can onlymove ontire at a time.Bothdesignsmustbe installedin the floor, meaning there is little to no mobility. The CN 101691033 is a robot for handling tires on a catenary coating line. A ball screw drives a moving seat and upper components along moving direction of catenary, a waist rotates with respect to the moving seat, a lower arm swings with respect to the waist, an upper arm swings with respect to the lowerarm,a wristrotatesandswings with respect to the upper arm, and a pneumatic wheel gripper is locatedat the endof the wrist. Thiscreatesa much greaterdegree of freedomthanourdesign,allowing for a widerrange of motionandgreaterdiversityof applications. A fixed camera is used to dynamically locate position of valve holes. This allows tires to be transported to and from unfixed points since the camera is able to gather the information required to determine the orientation of each part of the robot. This means the process can be changed without needing to alter the design or reprogram the
- 7. 6 | P a g e robot.Our designwouldrequirealterationsandreprogrammingif the process were to be changed. The designisreliableandquickingrippingandhandling,andisveryaccurate inpositioning.The designmust be installedto the floor resulting in little to no mobility. Also, the design only has one arm/hand, so it can only move one tire at a time. Brainstorming/Concept Generation & Freehand Sketches The project required a device to be built that could grab 3 different sizes of tires one at a time from1-3 separate inputlocations,rotate the tire 180 degrees around an axis parallel to the shop floor, thenplace the tire on a single universal output location. Two tires of same size must be stacked on top of each other, only two motors can be used, and bonus marks are given if the device can service more than one input location. The group agreed the simplest design of a gripper is simply two fingers that close in on either endof a horizontallyorientedtire.A fourfingered“claw”type approachwasbrieflyconsidered,but was considered infeasible using only the given Lego. Either both fingers could move towards each other
- 8. 7 | P a g e simultaneously, or one mobile finger could move towards the other stationary finger. The decision to have to parallel fingers move towards each other at the same rate would be made further down the road when more constraints and interdependencies were known. In order to flip the tire over 180 degrees, the tire could be flipped by rotating a wrist, or by rotating the entire arm. It was agreed to make the entire arm flip to best comply with the project specifications.Flipping the entire arm requires a great deal more torque than rotating the tire using a wrist.Usinga worm gear assemblywassuggestedthen laterimplementedtocompensate for this, since worm gears are capable of generating relatively large amounts of torque.
- 9. 8 | P a g e The group agreedthat all three inputlocationswould be serviced in order to get the maximum possible bonus marks. This creates the challenge of requiring three distinct types of motion from two motors. In orderto create three types of motion(opening/closinggripper,flipping the tire, and moving tire from input to output location) using only two motors, one of the motors must create two types of motion while the other creates one. The exact route we would take to do this could not be known during the brainstorming stage, but it was agreed that a differential gear system would be used to create two ranges of motion from one motor. The specific mechanics involving the differential gear systemwere workedoutwhilebuilding the model in order to ensure our ideas would comply with the limited supply of parts. The first motor would simply rotate the entire assembly around the Z-axis to move the arm from input locations to output locations, and the second motor would both flip the tire and open/close the grippers.
- 10. 9 | P a g e Early Lego model: Thismodel wasan earlyattemptto use one motorto both open/closethe gripper,andflipthe tire over. Thisconceptwas scrappedbecause itdid notfunctionvery well, was unreliable, and the group wanted to try using a differential gear system. Design Feasibility Analysis The designisverysimple,functional,andcosteffective,making it particularly feasible. The arm has only two degrees of freedom when compared with the usual 6 degrees of freedom of modern industrial robot arms, but it still completes its required tasks without a hitch. Reducing the degrees of freedomtothe minimum number greatly simplifies the design and reduces the total number of parts. These bothdecrease the overall costof the design,andmakestaskssuchas maintenance muchsimpler. The design does not allow for any dynamic changes such as altered location of input/output conveyor, but this is acceptable and feasible within the scope of the project. The technology used in the system is extremely simple and feasible. Input from two seperate touch sensors are sent to a controller, which in turn tells the motors how to move for the given situation. Such a simple system avoids potential complications. From an economicstandpoint,the designisveryfeasible. It is comprised of 17,000 kilograms of aluminum(comparedwithmax tire weightof 50 Kg) and consistsof 39 unique components, resulting in a total cost of around $30,000-$50,000 per production. More complex robot arms used for similar purposestypicallycostinexcessof $100,000, makingthe designparticularly economically feasible. The project required a device to be built that could grab 3 different sizes of tires one at a time from 1-3
- 11. 10 | P a g e separate inputlocations,rotate the tire 180 degreesaroundanaxisparallel tothe shopfloor,then place the tire on a single universaloutput location. The design meets all of these specifications, and is much cheaper than alternatives, which suggests sales would be excellent with proper marketing. Using an estimated sale price of $50,000-$60,000, it would only take 1-2 years for a company to warrant buying the machine when compared with hiring an employee to perform this task. Final design concept selection Roboticarm with2 degreesof motion2-prongparallelgripper,360 degrees of motion in X-Y plane, and 180 degrees of motion in Z-Y plane. Gripper: The 2-prong parallel gripper was chosen for our design over other considered grippers. This option effectivelyaccomplishesourgivenmission,whileremainingrelativelysimple toachieve. Usingthe 4-bar mechanism to keep the two prongs parallel, we achieve the desired movement and sufficient equal pressure on a tire from both prongs. Anotherfeature of the gripperisthe driverthatrotates the gearsof the 4-bar mechanism. A high-torque worm-gearisusedtogive goodgrip strengthonthe tire,while atthe same time back-pressure from the gripper cannot rotate the worm-gear. This is because the angle of the worm is set so that the friction between the gear and the worm is too great for the gear to overcome without massive amounts of torque. Effectively, the worm-gear locks the grippers until the worm-gear itself is driven when prompted.
- 12. 11 | P a g e Two Degrees of Freedom: The requiredtaskforthe roboticarm requiresonlytwodegreesof freedom*; one along the XY- plane rotational around the Z-axis, and one in the YZ-plane rotational around the X-axis. We designed our robotic arm to accomplish this with an optimal/idealrange of motion around both axes.Once the gripperhaspickedupa tire,the roboticarm has the capacityto place the tire inthe same orientation or rotated180 degrees,andalsoallowstiresof identical size to be stacked one on top of each other at the output location *Although the gripper moves in the X or Y direction (depending on which input/output is being serviced) while opening/closing, it can be simply regarded as open or closed. A rotationof 180 degreesispossible inthe YZ-plane aroundthe X-axis in order to flip the tires over 180 degrees A rotationof 360+ degrees ispossiblearoundthe Z-axisinthe XY-planinordertoservice all 3inputand 1 outputlocation(s)
- 13. 12 | P a g e Differential gear system & work gears The use of a differential gear system allows the motion from the motor to not only produce a differential in speed along its axis, but it also provides a secondary rotation when the axial rotation is unable tocontinue. Once the grippers have closed on a tire, the worm gear locks the gripper closed as well as stops rotation of the central shaft. Due to the internal gear structure of the differential, the outer casing of the differential, which acts as a gear, rotates when the central shaft locks. This complicated mechanism makes one motor capable of two functions that require rotation, closing the grippers then rotating the arm about the X-axis. Separate worm-gearsystemsare usedoneitherendof the differentialsystem to drive the gripping and flippingof the tire.Thisisto lockeach submechanisminplace whenthe worm gear is not being driven. The gear interactions can be best viewed below.
- 14. 13 | P a g e Stationary base The base of the robot is fixed in the ground to greatly increase stability and load capacity. This allows full motiontotake place at groundlevel withoutany issues of clearance. Since the base constrains the rest of the robotic arm, it is required that it be stable and not affect the movement of the rest of the arm. For thisreason, we placed the base and the motor controlling the rotation around the Z-axis just below the surface of the ground. This will require a pit to be prepared before installation. Touch Sensors and Timing: The motionof the robotic arm is limited and controlled by timing the voltage applied to the motors as well astouch sensorstodetectthe positionof the arm. When initialized,the roboticarmwill move into position opposite the output conveyor (input 2), which has a touch sensor that signals the motor to stop. The arm will theneitherpickup a tire at this position by closing the grippers, or rotate about the X-axistoflipthe tire over to the output location. The required timing and application of voltage to the motor foreach respective taskhasbeencalculatedandprogrammedintothe controller. Whenthe arm has a tire within the gripper, it then rotates around the Z-axis back to input2 using timed rotation, and then rotates around the X-axis 180 degrees until it contacts a second touch sensor. When the second touch sensor is triggered, the gripper motor is signalled to open and release the tire. This system provides the arm with the ability to adapt to different conveyor positions, different numbers of conveyors, and with the possibility of a different output position.
- 15. 14 | P a g e Lego Mindstorm Program: Legomindstormprogramto pickup the tire twice fromall conveyorbelts,speedof the motorB has beenadjustedaccordingtoangle we need,andtiminghasbeensettopickup the tire fromside conveyorbelts.
- 16. 15 | P a g e FEM Report and Images: Loads Step Name Number of referenced loads Loads Subcase - Static Loads 1 1 Pressure(1) Type Pressure - Normal pressure on2D elementsor3D elementfaces SolverCard Name PLOAD4 Layer 1 Appliedto 18 PolygonFace Description Pressure 9607.73 N/mm^2(MPa) Method Constant
- 17. 16 | P a g e Constraints Step Name Number of referenced constraints Constraints Subcase - StaticLoads 1 2 Fixed(1) Type Fixed- Fixed SolverCardName SPC Layer 1 Appliedto 1 PolygonFace Description Fixed(2) Type Fixed- Fixed SolverCardName SPC Layer 1 Appliedto 1 PolygonFace Description
- 18. 17 | P a g e Structural Results Coordinate System : Absolute Rectangular Number of load cases : 1 Subcase - Static Loads 1 : Number ofIterations = 1 Displacement (mm) Stress (mN/mm^2(kPa)) X Y Z Magnitude Von-Mises Min Principal Max Principal Max Shear Static Step 1 Ma x 1.563e+00 4 5.467e+00 3 4.192e+00 2 1.650e+00 4 6.248e+00 8 1.017e+00 8 7.231e+00 8 3.351e+00 8 Min - 2.317e+00 2 - 9.775e+00 2 - 1.825e+00 3 0.000e+00 0 4.146e+00 3 - 7.714e+00 8 - 1.938e+00 8 2.384e+00 3
- 19. 18 | P a g e Images Stress: Displacement:
- 20. 19 | P a g e Maintenance Guide WARNING:All energysourcesMUST be taggedANDlockedoutbefore anymaintenance. Pre-Production:Before runningthe machine forfull timeproductionforthe firsttime,itisimportantto run the pre-programmedbreakincycle once ortwice.Thisprogramruns a gentle cycle thatlightly worksinthe gearsto avoidthe damagesthat can occur whenrunningthe systematfull capacity immediatelyafterassembly. On a dailybasis,the pre-productiondiagnosticprogramshouldbe run.Thisisa program that assesses the state of the systembymovingthe arm ina varietyof motions.There are alsoa varietyof maintenance functionsthatholdthe assemblyinacertainpositionthenlockinplace.Thisallowsfor easyaccessibilitytoinnercomponents. Once these programshave run,the machine MUST be locked out andtagged. ProductionMaintenance:All gearsandaxlesneedtobe lubricatedevery4-6monthstopreserve longevityof productlife aswell asensure optimal performance. The differential gearsystemwearsfasterthanthe regulargears,andthe wormgears wearevenfaster than that.These parts shouldbe routinelyexpectingbiannually,andwill usuallyneedtobe replacedon a 10 yearmaintenance schedule. Many jointsare underextreme levelsof stressandneedtobe inspecteddailyforstrainandsignsof degradation. Underideal conditions,the jointsinthe jaw assemblyshouldbe placedina2 year maintenance replace cycle,however,diligence isrequireduponinspectiontoreportand/orreplace in case of degradation. The base containsball bearings,whichrequire dailyinspectionandfrequentlubrication. The bearings shouldbe placedona 2 year maintenance replace cycle.
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- 22. 21 | P a g e Bibliography Machine Design;Apr 17, 1997; 69, 8; ProQuest Science Journals. pg. 132 AMSoil.Advertisement. AMSOILSyntheticMotorOilDiesel Motorcycle Engine Transmission.Web.28 Nov.2011. <http://www.1st-in- synthetics.com/change_gear_lube_after_break_in_period_for_long_differential_life.htm>. Explanationof breakinperiodandimportance of lubricationtopreventdifferential wear Espacenet- HomePage.PatentArchive.Web.25 Nov.2011. <http://worldwide.espacenet.com/>. Usedto researchexistingpatentsonsimilarproducts "ArmsE- RoboticsTechnology." ElectronicTutorials,Electronic Kits, Electronic Tutorials,Electronic Hobby Kits, News.Electronicsteacher.com.Web.30Nov.2011. <http://www.electronicsteacher.com/robotics/robotics-technology/arms.php>. Usedto gain informationontypical industrial roboticarms Wilcher, Don. Lego Mindstorms Mechatronics.Google Books.Web. 23 Oct. 2011. <http://books.google.ca/books?id=iTvKboAoT5sC>. Used to learn about programming the controller "EngineeringandApplicationsFactorof SafetyReview." Engineersedge.com.Web.26Nov.2011. "Differential GearSystem." Gears.Web.27 Nov.2011. <http://www.gearinfo.com/Differential-Gear- System.html>. Usedto learnabout howto use differentialgearsystems "SCIENCE :: PHYSICS:MECHANICS :: GEARINGSYSTEMS :: WORM GEAR Image." Visual Dictionary Online. Web. 25 Nov. 2011. <http://visual.merriam-webster.com/science/physics- mechanics/gearing-systems/worm-gear.php>. Information on how to use a worm gear Thibault, Ray. "The Ins and Outs of Worm Gears." Machinerylubrication.com. May-June 2001. Web. 28 Nov. 2011. More information on worm gears "How Industrial Robot Is Made - Material, History, Used,Parts,Components, Industry, Machine, History, Raw Materials, The Manufacturing Process of Industrial Robot, Quality Control, The Future." How Products Are Made. Web. 29 Nov. 2011. <http://www.madehow.com/Volume-2/Industrial- Robot.html>. Details on common industrial robots