Autodesk's VEX Robotics Curriculum. Unit 15: Linkages

Transcription

1 Autodesk's VEX Robotics Curriculum Unit 15: Linkages 1

2 Overview In Unit 15, you learn about linkages: why they are used and how they are designed. You build your own linkage to use with a drivetrain and a gripper from previous units, improving on overall robot design. Design process and findings are also communicated. The concepts behind linkages have countless real-world applications. In STEM Connections, questions are posed regarding a pair of vise grips that make use of an adjustable four-bar linkage system. After completing the Think and Build Phases, you see how those concepts come into play in the real world. Unit Objectives After completing Unit 15: Linkages, you will be able to: Describe the primary use for linkages and determine uses for linkages in a robot design. Use Dynamic Simulation in Autodesk Inventor Professional software to analyze four-bar linkage mechanisms. Apply the knowledge gained in the Unit 15: Linkages > Think Phase to design and build a linkage. Understand the advantages of linkage designs. Prerequisites and Related Resources Related resources for Unit 15: Linkages are: Unit 1: Introduction to VEX and Robotics Unit 2: Introduction to Autodesk Inventor Unit 4: Microcontroller and Transmitter Overview Unit 5: Speed, Power, Torque, and DC Motors Unit 6: Gears, Chains, and Sprockets Unit 12: Object Manipulation Unit 13: Rotating Joints Key Terms and Definitions The following key terms are used in Unit 15: Linkages: 2 Term Definition Four-Bar Linkage Or simply a 4-bar or four-bar, is the simplest movable linkage. It consists of four rigid bodies (called bars or links), each attached to two others by single joints or pivots to form a closed loop. Four-bars are simple mechanisms common in mechanical engineering machine design and fall under the study of kinematics. Joint A link between two rigid components, such as parts or subassemblies. A joint applies force from the first component on the second component. Autodesk's VEX Robotics Unit 15: Linkages

3 Term Definition Linkage Designed to convert some input motion into a different output motion, it typically consists of a series of rigid links. Each link has one or more joints that rotate freely, connecting the links. Typically, one link is fixed and cannot move, and one link is driven in some input motion. Mechanism An assembly with one or more degrees of freedom in specific components. A mechanism is also called a dynamic assembly. Simulation A process by which the mathematical relationships between various parts of mechanisms are used to emulate or predict physical relationships and their effects. Trace A graphical representation of the path followed by a point on a mechanism. Required Supplies and Software The following supplies and software are used in Unit 15: Linkages: Supplies Software VEX Classroom Lab Kit Autodesk Inventor Professional 2011 One of the drivetrains built in Unit 9: Drivetrain Design 1 > Build Phase or Unit 10: Drivetrain Design 2 > Build Phase Gripper built in the Unit 12: Object Manipulation > Build Phase Notebook and pen Work surface Small storage container for loose parts One soda can Overview 3

4 Academic Standards The following national academic standards are supported in Unit 15: Linkages. Phase Standard Think Science (NSES) Unifying Concepts and Processes: Change, Constancy, and Measurement; Form and Function Physical Science: Motions and Forces Science and Technology: Abilities of Technological Design Technology (ITEA) 5.8: The Attributes of Design Mathematics (NCTM) Algebra Standard: Understand patterns, relations, and functions. Measurement Standard: Understand measurable attributes of objects and the units, systems, and processes of measurement. Communication: Communicate mathematical thinking coherently and clearly to peers, teachers, and others. Connections: Recognize and apply mathematics in contexts outside of mathematics. Create Science (NSES) Unifying Concepts and Processes: Form and Function Physical Science: Motions and Forces Science and Technology: Abilities of Technological Design Technology (ITEA) 5.8: The Attributes of Design 5.9: Engineering Design 6.12: Use and Maintain Technological Products and Systems Mathematics (NCTM) Numbers and Operations: Understand numbers, ways of representing numbers, relationships among numbers, and number systems. Algebra Standard: Understand patterns, relations, and functions. Geometry Standard: Use visualization, spatial reasoning, and geometric modeling to solve problems. Measurement Standard: Understand measurable attributes of objects and the units, systems, and processes of measurement. 4 Autodesk's VEX Robotics Unit 15: Linkages

5 Phase Standard Build Science (NSES) Unifying Concepts and Processes: Change, Constancy, and Measurement; Form and Function Physical Science: Motions and Forces Science and Technology: Abilities of Technological Design Technology (ITEA) 5.8: The Attributes of Design 5.9: Engineering Design 6.11: Apply the Design Process Mathematics (NCTM) Algebra Standard: Understand patterns, relations, and functions. Geometry Standard: Use visualization, spatial reasoning, and geometric modeling to solve problems. Numbers and Operations: Compute fluently and make reasonable estimates Measurement: Understand measurable attributes of objects and the units, systems, and processes of measurement. Measurement: Apply appropriate techniques, tools, and formulas to determine measurements. Connections: Recognize and apply mathematics in contexts outside of mathematics. Problem Solving: Solve problems that arise in mathematics and in other contexts. Problem Solving: Apply and adapt a variety of appropriate strategies to solve problems. Overview 5

6 Phase Standard Amaze Science (NSES) Unifying Concepts and Processes: Change, Constancy, and Measurement; Form and Function Physical Science: Motions and Forces Science and Technology: Abilities of Technological Design Technology (ITEA) 5.8: The Attributes of Design 5.9: Engineering Design 6.11: Apply the Design Process Mathematics (NCTM) Algebra Standard: Understand patterns, relations, and functions. Geometry Standard: Use visualization, spatial reasoning, and geometric modeling to solve problems. Numbers and Operations: Compute fluently and make reasonable estimates. Communication: Communicate mathematical thinking coherently and clearly to peers, teachers, and others. Connections: Recognize and apply mathematics in contexts outside of mathematics. Measurement: Understand measurable attributes of objects and the units, systems, and processes of measurement. Measurement: Apply appropriate techniques, tools, and formulas to determine measurements. Problem Solving: Solve problems that arise in mathematics and in other contexts. Problem Solving: Apply and adapt a variety of appropriate strategies to solve problems. 6 Autodesk's VEX Robotics Unit 15: Linkages

7 Think Phase Overview This phase describes characteristics of and common applications for linkages. Phase Objectives After completing this phase, you will be able to: Describe the primary use for linkages. Determine uses for linkages in a robot design. Prerequisites and Related Resources Related phase resources are: Unit 5: Speed, Power, Torque, and DC Motors Unit 6: Gears, Chains, and Sprockets Unit 12: Rotating Joints Unit 13: Object Manipulation Required Supplies and Software The following supplies are used in this phase: Supplies Notebook and pen Work surface Think Phase 7

8 Research and Activity Linkages are designed to convert input motion into a different output motion. A linkage typically consists of a series of rigid links. Each link has one or more joints which rotate freely, connecting the links together. Typically, one link is fixed and cannot move and one link is driven in some input motion. Linkages are a fundamental part of machine design because of their ability to create such a wide variety of output motions and their ability to alter the path, velocity, and acceleration of the input. Very precise and somewhat complicated motions can be designed using a simple linkage design. Linkage motions are extremely repeatable. Linkages are all around us in the world. A simple linkage found on a pair of vice grips is shown here. The second picture shows the linkage at the other end of its motion. This is a linkage with four links; each link has two joints and they are connected in a closed system. This is one of the most common types of linkage system. 8 Autodesk's VEX Robotics Unit 15: Linkages

9 An example of a more complex linkage is shown here: Four-Bar Linkages The simplest and one of the most common linkage types is the four-bar linkage. This is a closed-loop linkage system that can provide a wide variety of motion types. The most basic type of four-bar linkage is one in which the links are equal length and parallel to each other. You focus on this linkage type for the rest of this unit. Think Phase 9

10 An example of a four-bar linkage in which opposing links are parallel and of equal length is shown here: In the above example of a four-bar linkage, the link on the left side is the fixed link. This fixed link is typically attached to the robot structure. One of the diagonal links is the driven link. The output link is the link at the far right. Some sort of object manipulator is mounted on the output link. When the linkage travels through its motion, the output link remains parallel to the fixed link as shown. 10 Autodesk's VEX Robotics Unit 15: Linkages

11 This type of motion is useful for any application in which you want the object manipulator to stay in the same orientation as the robot arm moves. Some examples of this linkage are shown: The above example uses two four-bar linkages; each side of the claw is a four-bar linkage. These are useful because the tip of the claw remains in the same orientation while the claw opens and closes. The above robot utilizes a four-bar linkage to deploy its tools. The tools remain parallel to the floor at all times during their deployment. Think Phase 11

12 This robot uses four-bar linkages for its front suspension. Varying Motion By modifying the lengths of the links in the four-bar linkage, it is possible to create very different motions. This is extremely useful for robot design. Imagine needing a robot that can pick up a cup of water, lift it up without spilling, and then pour it out once it reaches over the height of a bucket. This motion is possible by using a modified four-bar linkage. Try playing with linkage lengths and experiment to find the optimal motion for your application. 12 Autodesk's VEX Robotics Unit 15: Linkages

13 Create Phase Overview In this phase, you review four-bar linkages. Using Dynamic Simulation, you analyze two different mechanisms. The completed exercise Phase Objectives After completing this phase, you will be able to: Use Dynamic Simulation to analyze four-bar linkage mechanisms. Prerequisites Before starting this phase, you must have: A working knowledge of the Windows operating system. Completed Unit 1: Introduction to VEX and Robotics > Getting Started with Autodesk Inventor. Completed Unit 2: Introduction to Autodesk Inventor > Quick Start for Autodesk Inventor. Create Phase 13

14 Technical Overview The following Autodesk Inventor tools are used in this phase: Icon Name Description Construction Mode Is the environment for modifying your model. Output Grapher Displays graphs and numerical values of all the input and output variables during and after a simulation. The Output Grapher contains a toolbar, a browser, a time steps pane, and a graph window. Also, shortcut menus have content based on the location of the cursor when you right-click. Trace Creates a graphical representation of the path followed by a point on a mechanism. Publish to Studio Activates the Studio environment so the current simulation results can be recorded in either a realistic or an illustrative style of animation. Render Animation Uses assembly constraints and parameters as animation input. You can animate the same mechanistic movement you are designing in your product. Required Supplies and Software The following software is used in this phase: Software Autodesk Inventor Professional Autodesk's VEX Robotics Unit 15: Linkages

15 Exercise: Analyze Mechanisms In this exercise, you review four-bar linkages. Using Dynamic Simulation, you analyze two different mechanisms. Start Dynamic Simulation You use Dynamic Simulation to analyze products under real-world conditions without having to build physical prototypes. In this section of the exercise, you determine the motion of the four-bar linkage. 1. On the Environments tab, Begin panel, click Dynamic Simulation If required, click No to close the tutorial dialog box. Review the browser. The assembly constraints are automatically converted into joints. The completed exercise Open the File Make IFI_Unit15.ipj the active project file. Open Drag_Link.iam. It is important to note that the length of is not greater than On the Simulation Player, click Run or Replay the Simulation. No parameters are applied to the mechanism, so there is no motion. On the Simulation Player, click Construction Mode. Drag bar 2 to review the motion of the four-bar linkage. Undo to return the mechanism to its original position. Create Phase 15

16 6. 7. In the browser, under Standard Joints, rightclick Revolution:6. Click Properties. On the dof 1 (R) tab, click Edit Imposed Motion. 8. Select the Enable Imposed Motion check box. 9. Click the arrow beside Input Grapher. Click Constant Value Enter 300 rpm. 11. Click OK. Review the joint axes and direction of rotation. 12. On the Simulation Player, click Run or Replay the Simulation. The mechanism moves for one second. In this example, bars 2, 3, and 4 have continuous motion. 13. In the browser, click Revolution:2. Review the location of the joint. 14. On the Results panel, click Output Grapher. 15. Under Drag_Link > Standard Joints, expand Revolution:2 > Accelerations. Select the A [1] check box. Autodesk's VEX Robotics Unit 15: Linkages

17 16. Review the Output Grapher. The acceleration of the joint is displayed. Create Traces Dynamic Simulation can create a trace of the trajectory path and velocity and/or acceleration vectors in the graphics window by activating the Output Grapher and setting up the traces you want displayed. In this exercise, you trace the path of two joints on the mechanism. 1. On the Output Grapher toolbar, click Add Trace. 2. In the graphics window, select the corner of the joint between bars 2 and In the Output Grapher window, double-click on the graph. A vertical line is displayed and the mechanism moves to the matching position. A sphere is displayed at the location. 18. On the keyboard, press the forward or back arrow keys to cycle the mechanism. Note the position of the mechanism and the position of the line on the graph. 3. Click Apply. The trace is displayed. Create Phase 17

18 4. Repeat this workflow for the joint between bars Analyze a Second Mechanism 3 and 4. In this section of the exercise, you analyze a second mechanism to determine the motion. 1. Open Crank_Rocker.iam. It is important to note that the length of is not greater than Click Cancel. Since you have already run a simulation, the traces are displayed. On the Simulation Player, click Rewind to the Beginning of the Simulation The trace is no longer displayed. On the Simulation Player, click Run or Replay Simulation. You can now see the motion path of the two joints. 2. On the Environments tab, Begin panel, click Dynamic Simulation. 3. If required, click No to close the tutorial dialog box. Review the browser. The assembly constraints are automatically converted into joints Close the Output Grapher. On the Simulation Player, click Construction Mode. 10. Close the file. Do not save changes. 18 Autodesk's VEX Robotics Unit 15: Linkages

19 5. In the browser, under Standard Joints, rightclick Revolution:2. Click Properties. 10. Click OK. Review the joint axes and direction of rotation. 6. On the dof 1 (R) tab, click Edit Imposed Motion. 11. On the Simulation Panel, enter 3 for Final Time. 7. Select the Enable Imposed Motion check box. 12. On the Simulation Player, click Run or Replay the Simulation. The mechanism moves for three seconds. In this example, bar 2 has continuous motion. Bars 3 and 4 have oscillating motion. 13. In the browser, click Revolution:5. Review the location of the joint. 14. On the Results panel, click Output Grapher. 15. Under Standard Joints, expand Revolution:5 > Accelerations. Select the A [1] check box. 16. Review the Output Grapher. The acceleration of the joint is displayed Click the arrow beside Input Grapher. Constant Value should be selected. Enter 60 rpm. You will be creating an animation of this mechanism, so you are setting a low value. 17. In the Output Grapher window, double-click the graph. A vertical line is displayed and the mechanism moves to matching position. Create Phase 19

20 18. On the keyboard, press the forward or back arrow keys to cycle the mechanism. Note the position of the mechanism and the position of the line on the graph. 7. On the Simulation Player, click Run or Replay the Simulation. You can now see the motion path of the two joints Close the Output Grapher. Do not return to the construction environment. You must be in the simulation environment to create the animation. Use Traces 1. On the Output Grapher toolbar, click Add Trace. 2. In the graphics window, select the corner of the joint between bars 2 and 3. A sphere is displayed at the location. Click Apply. The trace is displayed. 3. Create an Animation Repeat this workflow for the joint between bars 3 and On the Animation Timeline, click Animation Options. 3. Under Length, for Seconds, enter Click OK. Click Cancel. On the Simulation Player, click Rewind to the Beginning of the Simulation. The trace is no longer displayed. 20 Dynamic Simulation creates parameters for Inventor Studio that make the creation of an animation much simpler. In this section of the exercise, you create a studio animation. 1. On the Animate panel, click Publish to Studio. Autodesk's VEX Robotics Unit 15: Linkages

21 5. On the Animation Timeline, drag the slider to 4 seconds In the browser, expand Animation Favorites. Right-click Simulation_Timeline. Click Animate Parameters. 20. Close the player when the animation is finished. 21. Close all windows. 22. Close the file. Do not save changes. 8. In the Animate Parameters dialog box, under Action, for End, enter Under Time, click Specify. 10. For Start, enter 1. For End, enter Click OK. 12. On the Render panel, click Render Animation. 13. On the Output tab, under Time Range, click Entire Animation. 14. Select the Launch Player check box. 15. Click Open an Existing Folder For File Name, enter Crank_Rocker. Click Save. Click Render. Click OK. The animation is created. This may take a few minutes. Create Phase 21

22 Build Phase Overview In this phase, you design and build a linkage to lift a soda can without spilling its contents. Phase Objectives After completing this phase, you will be able to: Apply the knowledge gained in the Unit 15: Linkages > Think Phase to design and build a linkage. Use your knowledge of geometry to calculate the shape of the linkage and to plot out the resulting range of motion. Prerequisites and Related Resources Before starting this phase, you must have completed: Unit 15: Linkages > Think Phase. Related phase resources are: Unit 1: Introduction to VEX and Robotics Unit 4: Microcontroller and Transmitter Overview Unit 5: Speed, Power, Torque, and DC Motors Unit 6: Gears, Chains, and Sprockets Unit 12: Object Manipulation Unit 13: Rotating Joints Required Supplies and Software The following supplies are used in this phase: Supplies VEX Classroom Lab Foundation Kit One of the drivetrains built in Unit 9: Drivetrain Design 1 > Build Phase or Unit 10: Drivetrain Design 2 > Build Phase The gripper built in the Unit 12: Object Manipulation > Build Phase Notebook and pen Work surface 22 Autodesk's VEX Robotics Unit 15: Linkages

23 Supplies Small storage container for loose parts One soda can Optional: Autodesk Inventor Professional 2011 Activity Design and Build a Linkage In this activity, you design and build a linkage to lift a soda can without spilling its contents. You use your previously designed gripper to grasp the soda can. You then mount the linkage to a drivetrain of your choice. This robot will then be used in the Amaze Phase to place the soda can on a stack of textbooks. Your goal is to successfully place the can on the highest possible stack of textbooks without spilling it. 1. In your notebook, brainstorm different linkages that could be used to lift the soda can. An example of a four-bar linkage is shown in the following image: When designing your linkage, you will need to consider many factors; some of which include: Build Phase 23

24 What range of motion is needed from the linkage? How far can the soda can tilt before its contents are spilled? What type of gear reduction should be used to make sure it can lift the weight of the gripper and the can? How fast should the linkage rotate? How will the gripper attach to it? How much reach does the arm need? How/where will the linkage attach to the drivetrain? Work as professionals in the engineering and design fields by leveraging the power of Autodesk Inventor software to explore potential solutions through the creation and testing of digital prototypes. Note: Come to class prepared to build and test your best ideas! Team members can download a free version of Autodesk Inventor Professional software to use at home by joining the Autodesk Education Community today at Based on your criteria, choose a design and start building! Attach your gripper to your completed linkage. Once your linkage is complete, hook it up to a Microcontroller and test out the functionality. Make improvements as you see fit. Pay careful attention to the range of motion generated. Mount the entire linkage to the chosen drivetrain. Plug motors and servos into the appropriate ports in the Microcontroller. Test your linkage with a transmitter to make sure everything is functioning correctly. Move on to the Amaze Phase and get ready for your upcoming challenge! Autodesk's VEX Robotics Unit 15: Linkages

25 Amaze Phase Overview In this phase, you use your robot from Unit 15: Linkages > Build Phase to place a soda can on the highest possible stack of textbooks without spilling the contents of the can. Phase Objectives After completing this phase, you will be able to: Explain the advantages of linkage designs. Modify your design on the fly for improved results. Prerequisites and Related Resources Before starting this phase, you must have: Completed Unit 15: Linkages > Think Phase. Completed Unit 15: Linkages > Build Phase. An assembled single-jointed arm from the Unit 13: Rotating Joints > Build Phase attached to the gripper created in the Unit 12: Object Manipulation > Build Phase that is attached to a drivetrain of your choice. Related phase resources are: Unit 1: Introduction to VEX and Robotics Unit 4: Microcontroller and Transmitter Overview Unit 5: Speed, Power, Torque, and DC Motors Unit 6: Gears, Chains, and Sprockets Unit 7: Advanced Gears Unit 8: Friction and Traction Unit 12: Object Manipulation Unit 13: Rotating Joints Required Supplies and Software The following supplies are used in this phase: Supplies VEX Classroom Lab Kit The robot built in the Unit 15: Linkages > Build Phase Amaze Phase 25

26 Supplies Notebook and pen Work surface 3 x 3 of open space Five to fifteen textbooks Evaluation Soda Can Stack Challenge In this phase, you use your robot from Unit 15: Linkages > Build Phase to place a soda can on a stack of textbooks without spilling the contents of the can. The goal is to place the soda can on the highest possible stack of textbooks. 1. Fill a soda can with water. 2. Place your robot from the previous phase on the ground behind the can. 3. Place one textbook in front of the can. 4. Using your robot s gripper, grab the soda can. 5. Using the robot s linkage, slowly lift the soda can. 6. Gently attempt to place the soda can on the textbook without spilling any of the water from the can. 7. Each time you successfully place the soda can on the stack of books without spilling it, add another textbook to the stack and try again. 8. Continue adding textbooks until you ve gone as high as you possibly can! Engineering Notebook In your engineering notebook, calculate the theoretical maximum height that your linkage can reach. Were you able to successfully place a soda can at that height without spilling it? If not, what design factors prevented this from happening?. If you were to redesign your robot to repeat this challenge, what feature(s) would you allow for more reliable placement? What feature(s) would you add to allow for placement on higher stacks? Presentation Present your design and potential improvements to the class. Pick the most unique feature of your design and explain it to the class. How did you come up with this idea? 26 Autodesk's VEX Robotics Unit 15: Linkages

27 STEM Connections Background Vise grips are useful tools because the jaws can be adjusted to close in parallel around different size surfaces. Additionally, adjustments can be made to vary the amount of force exerted on the closing jaws as they grip an object. Science Traditionally, the material used in the manufacture of vise grips is steel. 1. Why do you think steel is a good choice of material? 2. Can you describe any disadvantages of using steel as the primary material for vise grips? 3. Can you think of some new materials that can be incorporated into the design of vise grips to make them more effective, more durable, and easier to use? Technology The surface of the vise grip jaws are serrated. 1. What are the advantages of this surface design? 2. Are there changes that can be made to the design of the jaw to accommodate gripping fragile objects? 3. Can you think of examples from nature where a serrated jaw design is used to improve efficiency? STEM Connections 27

28 Engineering As shown in the image, vise grips are based on a four-bar linkage system. The vise grips depicted have a maximum gripping range of approximately two inches. 1. What engineering changes can you make to increase the distance that the jaws can open and close? 2. What engineering changes can you make to increase the amount of force that can be applied at the jaws? 3. Can you think of engineering changes that would make it easier and more comfortable for a person using the vise grips to maximize the force applied at the jaws? Math A 12-inch wide x 12-inch long x 4-inch deep flat-bottomed wire basket is attached as the moving link on a four-bar linkage system like the one shown in the Build Phase. Each of the two long parallel links is 24 inches long as measured from the center of their pivot points. In a manufacturing plant, assembled vise grips are placed in a basket and moved from a starting position on the right through a 180-degree arc and then unloaded from the basket when they get to the left side. As the parts are moved from right to left, they pass through a spray stream of powder-coating material (similar to spray paint) for final finishing before they are packaged and shipped. 1. Calculate the horizontal distance that the basket travels over the 180-degree arc. 2. If the motor operating this linkage assembly is running at five rpms with a full load, how much time does it take to move through a 180-degree arc to transport the basket from the right side to the left side? 3. If one basket load holds 12 vise grips, how many vise grips can be powder coated in one hour? 28 Autodesk's VEX Robotics Unit 15: Linkages