WORKSHOP 9 LIFT MECHANISM II

Workshop Objective Optional: In this workshop, you will use the model you previously built in (Workshop 8-Lift Mechanism I) and create joints. Optional: If you’d like a challenge, add the following joints and motions without going through the detailed steps presented on the following slides. Rotational motion to the mount-to-base joint. D(t) = 360d*time Rotational motion to the shoulder-to-mount joint. D(t) = STEP(time, 0, 0, 0.10, 30d) Translational motion to the boom-to-shoulder joint. D(t) = STEP(time, 0.8, 0, 1, 5) Rotational motion to the bucket-to-boom joint. D(t) = 45d*(1-cos(360d*time)) Otherwise, continue by following the detailed instructions.

Software Version Files Required Tips before you start ADAMS 2013 Use directory exercise_dir/mod_08_lift_mech_1 Tips before you start Use the figure on slide 3 to find out what type of constraints you need. Simulate the model at regular intervals to check the constraints. Rename joints as soon as you create them. Adjust icon sizes whenever necessary (see Set up the working environment on slide 7 of Workshop 8 - Lift Mechanism I.)

Problem Description Use the diagram below for the placement of the joints. Review the problem statement and quiz the students on what they think needs to be done to complete the workshop. Before they start, ask for questions.

Suggested Steps Import model and construct constraining parts. Verify and simulate. Add joint motion. Run simulation and export. Perform optional tasks.

Step 1. Import Model and Constrain Parts To import model: From the Welcome dialog box, select Existing Model. Set the Working directory to exercise_dir/mod_09_lift_mech_2.and uncheck Use File Directory as Working Directory. Find and select the model file which you completed in the previous workshop from the directory exercise_dir/mod_08_lift_mech_1, If you need a fresh copy of the model, select and opens the command file, lift_mech_I_completed.cmd, from the directory exercise_dir/mod_08_lift_mech_1/completed. In this section, you’ll constrain the parts that you created in the previous workshop. To constrain the parts: Use the Fixed joint tool to fix the base to ground. Constrain mount to base (revolute joint): Use the options 2 Bod-1 Loc and Pick Geometry Feature. Place the joint at the mount’s cm marker. Select the + y-axis as the axis for the rotation. a b

Step 1. Constrain Parts (Cont.) Constrain shoulder to mount (revolute joint): Use the option Normal To Grid. Right-click to select the cylinder’s anchor marker. Constrain the boom to the shoulder (translational Joint): Use the option Pick Feature. Select the x-axis as the axis for the translation. Constrain the bucket to the boom (revolute joint): Select the end point of the cylinder. b a c

Step 2. Verify and Simulate To verify your model: Check model topology by constraints (from the Status bar, right-click the Information tool stack, and then select the Model topology by constraints tool) to ensure that all the parts are constrained as expected. Perform a simulation. Are the visual results of the simulation (the animation), what you expected? a

Step 3. Add Joint Motion B A b a Add joint motions to your model: Build the joint motions using the default expressions in the container and then modify the expressions using the Motion Generators, use Rotational Joint Motion (A) for revolute joint and translational motion (B) for Translational Joint. Follow Modify dialog box (right-click the joint, point to the joint name, and then select Modify). To add joint motions: Use the Rotational Joint Motion tool to add a motion to the mount-to-base joint such that: D(t) = 360d*time b

Step 3. Add Joint Motion (Cont.) Add a motion to the shoulder-to-mount joint such that: D(t) = -STEP(time, 0, 0, 0.10, 30d) Note: By using Normal to Grid, the motion will be opposite the illustration in Problem statement (by the right-hand rule). When a motion is opposite of what you expect, add a negative sign in front of the expression, in the Modify Motion dialog box. We will discuss the specifics of the STEP function in the next module, Lift Mechanism III. Add a translational motion to the boom-to-shoulder joint such that: D(t) = -STEP(time, 0.8, 0, 1, 5) Note: if arm is angled downwards, remove (-). Right hand rule. Add a motion to the bucket-to-boom joint such that: D(t) = 45d*(1-cos(360d*time)) c

Step 4. Run Simulation and Export Run a simulation: Run a simulation such that the mount achieves one full rotation. Save your work: Save the model such that the saved file contains only the model topology and not the results (File > Export).

Step 4. Run Simulation and Export While during simulation module should look like:

Step 5. Optional Tasks If you did not already do so as explained in the Optional tasks for Lift Mechanism I: Add tires to your model using the Torus tool. Constrain the tires to the base using revolute joints.

Workshop 9, Review Workshop Questions What are the markers that a joint refers to called? __________________________________________________________________________________________________________ When motion is applied to a joint, what dictates its direction (positive versus negative)? __________________________________________________________________________________________________________ Are motions considered a constraint? Why? __________________________________________________________________________________________________________ Is it possible to determine the torque required to achieve a prescribed motion imposed on a revolute joint? How? __________________________________________________________________________________________________________