28 excercise machine mechanism kho tài liệu bách khoa

ME-430 INTRODUCTION TO COMPUTER AIDED DESIGN Exercise Machine Repeated Assembly Analysis Pro/ENGINEER Wildfire 2.0 - MECHANISM Dr Herli Surjanhata Servo Motors Servo motors are used to impose a particular motion on the mechanism model Servo motors behave like motors, by forcing a specific type of motion to occur between two bodies in a single degree of freedom You can add a servo motor to a joint axis or a geometric entity, such as part planes, datum planes, and points You use servo motors to impose a particular motion on a mechanism Servo motors cause a specific type of motion to occur between two bodies in a single degree of freedom You add servo motors to your model to prepare it for analysis Servo motors specify position, velocity, or acceleration as a function of time, and can control either translational or rotational motion For example, a servo motor starts in a specific configuration After one second, another configuration is defined for the model The difference between the two configurations is the motion of the model By specifying your servo motor's function, such as constant or ramp, you can define the motion's profile You can select from several predefined functions, or input your own function You can define as many servo motors on an entity as you like Note: If you select or define a position or velocity function for your servo motor profile that is not continuous, be aware that it will be ignored if you run a kinematics or dynamic analysis However, you can use a discontinuous servo motor profile in a repeated assembly analysis When you graph a discontinuous servo motor, Mechanism Design displays messages indicating the discontinuous points You can place servo motors on joint axes or on geometric entities such as part planes, datum planes, and points You can use the following types of servo motors: • Joint Axis Servo Motors—Use to create a well-defined motion in one direction • Geometric Servo Motors—Use to create complex 3D motions such as a helix or other space curves Force Motors You use force motors to impose a particular load on a mechanism You can create force motors for your mechanism if you have a Mechanism Dynamics Option license Force motors cause a specific type of load to occur between two bodies in a single degree of freedom You add force motors to your model to prepare it for a dynamic analysis Force motors cause motion by applying a force on a translational or rotational joint axis You can place force motors on joint axes You can define as many force motors on a model as you like You can turn force motors on and off within the definition of each dynamic analysis Geometric Servo Motors If you select points or planes to define the servo motor, you are creating a geometric servo motor Use geometric servo motors to create complex 3D motions such as a helix If you select Point or Plane, you must also select a point or plane as a reference If you select a point for the reference entity, you must also select a motion direction You can create the following geometric servo motors: • plane-plane translation servo motor • plane-plane rotation servo motor • point-plane translation servo motor • plane-point translation servo motor • point-point translation servo motor REPEATED ASSEMBLY ANALYSIS Repeated Assembly analysis was called Kinematic analysis in previous releases of Mechanism Design It is a series of assembly analyses driven by servo motors Only joint axis or geometric servo motors can be included for repeated assembly analyses Force motors not appear in the list of possible motor selections when adding a motor for a repeated assembly analysis Note: If you edit an analysis that you created as a Kinematics analysis in a previous release of Mechanism Design, the definition will now specify it as a Repeated Assembly analysis A repeated assembly analysis simulates the mechanism's motion, satisfying the requirements of your servo motors profiles and any joint, cam-follower, slot-follower, or gear-pair connections, and records position data for the mechanism's various components It does not take force and mass into account in doing the analysis Therefore, you not have to specify mass properties for your mechanism Dynamic entities in the model, such as springs, dampers, gravity, forces/torques, and force motors, not affect a repeated assembly analysis Use a repeated assembly analysis to study: • positions of components over time • interference between components • trace curves of the mechanism's motion Force Motors You use force motors to impose a particular load on a mechanism You can create force motors for your mechanism if you have a Mechanism Dynamics Option license Force motors cause a specific type of load to occur between two bodies in a single degree of freedom You add force motors to your model to prepare it for a dynamic analysis Force motors cause motion by applying a force on a translational or rotational joint axis You can place force motors on joint axes You can define as many force motors on a model as you like You can turn force motors on and off within the definition of each dynamic analysis Download the Component Parts for Assembly In a system window, create a new directory and download the zip file exercise_machine.zip Unzip the file, and set the working directory Create A New Subassembly Called raiser_subasm.asm The raiser_subasm.asm is consisted of raiser.prt and raiser_shaft.prt Click on Enter the name raiser_subasm OK Open raiser.prt, and assemble it at default location – click OK Open raiser_shaft.prt, and click on Connect tab Create Pin type connection as the following: Axis alignment: Axis of the raiser_shaft (A_2) is aligned with the axis (A_3) of the hole on the raiser For Translation constraint, pick FRONT datum plane of the raiser_shaft, and then pick FRONT datum plane of the raiser OK Save the raiser_subasm.asm Create A New Subassembly Called pedal_left_subasm.asm The pedal_left_subasm.asm is consisted of pedal_left.prt and roller.prt Click on Enter the name pedal_left_subasm OK Open pedal_left.prt, and assemble it at default location – click OK Open roller.prt, and click on Connect tab Create Pin type connection as the following: Axis alignment: Long axis of the roller (A_1) is aligned with the axis (A_2) of the left cut (half cylinder cut) on the pedal_left For Translation constraint, pick FRONT datum plane of the roller, and then pick FRONT datum plane of the pedal_left OK Save the pedal_left_subasm.asm Create A New Subassembly Called pedal_right_subasm.asm The pedal_right_subasm.asm is consisted of pedal_right.prt and roller.prt Click on Enter the name pedal_right_subasm OK 10 Under Graph, select to plot the motion of the slider with respect to time Note: Magnitude Settings Depending on the type of motion you want to impose on your mechanism, you can define the magnitude of your servo motors or force motors in many ways The following table lists different types of functions that Mechanism Design uses to generate the magnitude You need to enter the values of the coefficients for the functions The value of x in the function expressions is supplied by the simulation time or, for force motors, by either the simulation time or a measure you select Function Type Description Required Settings Constant Use if you want a constant profile q=A where A = Constant Ramp Use if you want a profile that changes linearly over q = A + B*x 39 time where A = Constant B = Slope Cosine Use if you want to assign a cosine wave value to the motor profile q = A*cos(360*x/T + B) +C where A = Amplitude B = Phase C = Offset T = Period SineConstantCosineAcceleratio n (SCCA) Use to simulate a cam profile output SCCA can only be used when Acceleration is chosen This profile is not applicable for force motors Cycloidal Use to simulate a cam profile output q = L*x/T – L*sin (2*Pi*x/T)/2*Pi where L = Total rise T = Period Parabolic Can be used to simulate a trajectory for a motor q = A*x + 1/2 B(x2) where A = Linear coefficient B = Quadratic coefficient Polynomial Use for generic motor profiles q = A + B*x + C*x2 + D*x3 where A = Constant term coefficient 40 B = Linear term coefficient C = Quadratic term coefficient D = Cubic term coefficient Table Use to generate the magnitude with values from a two-column table If you have output measure results to a table, you can use that table here User Defined Use to specify any kind of complex profile defined by multiple expression segments Custom Load This option is only available for the force motor definition Use it to apply a complex, externally-defined set of loads to your model Use a single profile if possible But you can use a combination of profiles to generate certain types of motion For example, a combination of ramp and cosine generates a sinusoidal motion that ramps up over time For more information, see figure shown below which shows different types of motion the motor creates Example: Types of Motor Profiles The following graph depicts different types of motion the motor creates 41 Following are the values from the formulas that were used to generate the profiles in this graphic: Constant Ramp Cosine Cycloidal SCCA Parabolic Polynomial A=8 A= 18 A=6 L = 12 0.4 A=4 A=7 B= –1.2 B= 40 T=8 0.3 B = –0.6 B = –1.5 C=3 C=1 T=5 10 D = –0.1 42 Select OK to complete the servo motor definition The Servo Motor icon is created on the slider joint The zero position for the joint should be defined Select Mechanism ->Joint Axis Settings Then select the slider connection of the raiser and check the Specify References box 43 For the Green Body Reference select the top surface of the base of chassis.prt For the Orange Body Reference select the bottom horizontal surface of raiser.prt Click on OK Now the servo motor for the fly wheel pin connection should be created 44 From Mechanism toolbar, select Define Servo Motors icon The Servo Motors dialogue box appears Select New button to create a new driver Select the pin joint for fly_wheel.prt as the driven entity – see figure below 45 46 Then select the Profile tab to define the driving function In the Profile tab set the specification to Velocity Leave the Initial Angle setting as Current This setting would allow you to adjust the initial position of the component with respect to the zero reference prior to the driver starting The driver being created only needs to spin the fly_wheel.prt and therefore the initial position is of no importance Fill out the Profile tab by entering a Constant angular velocity A of -180.0 (deg/second) This servo motor is now fully defined OK Select Close to exit the Servo Motors dialogue box This model is now ready for a Repeated Assembly analysis 47 Running the Model for a Repeated Assembly Analysis Select the Run an Analysis icon Or select Mechanism -> Analyses The Analyses dialogue box appears Select New button to define a new Repeated Assembly analysis The Analysis Definition dialogue box appears 48 Change the analysis type to Repeated Assembly Keep the default analysis settings and select OK to finish this analysis definition This will return you to the Analyses dialogue box with AnalysisDefinition1 listed Select Run to start the analysis The model display will start moving as the analysis is running 49 Once the model has finished running, select Close to exit Analyses dialogue box Playback the Results of Analysis The Repeated Assembly analysis results are now available for playback Click on - the Relay previously run analyses icon, or select Mechanism -> Playback to bring up the Playback dialogue box In this dialogue box the results set may be selected for playback, results sets may be saved for later use and results sets can be 50 loaded for playback Furthermore, the dialogue box allows for Interference checking in the model during its motion Depending on what type of interference checking is selected it may take Mechanism Design sometime to prepare the results Select Global Interference for the interference mode, check the Include Quilts box and then select the play icon After interference is computed for each step an Animate video tool appears Press the play button to start the animation 51 Click on the Capture button to create MPEG movie of the animation Notice how interferences get highlighted in red on the model display This particular model does not have much interference As an exercise, dimensions on the model may be changed to cause interference and can be seen on the playback Once finished with animating the model, select Close to exit the Animate video tool 52 In the Playbacks dialogue box select save icon results set to save this Accept default name for the playback file Click Save These results will be available again by selecting restore icon from the Playbacks dialogue box without the need to run the motion analysis again Select Close to exit the Results Playback dialogue box 53 ... servo motors: • plane-plane translation servo motor • plane-plane rotation servo motor • point-plane translation servo motor • plane-point translation servo motor • point-point translation servo... requirements of your servo motors profiles and any joint, cam-follower, slot-follower, or gear-pair connections, and records position data for the mechanism' s various components It does not take force... trace curves of the mechanism' s motion Force Motors You use force motors to impose a particular load on a mechanism You can create force motors for your mechanism if you have a Mechanism Dynamics