ME 3120: Kinematics of Mechanisms
MIDTERM EXAM
1. Draw kinematic models for the two clamping devices below. Specify the number of links, the number of primary joints, the number of higher order joints, and calculate the mobility for the mechanism. Use numbers to represent links and letters to represent joints in your kinematic diagram. For the first picture, the front and back are points of interest. For the second picture, the end of the handle is a point of interest.
kinematic model (4pts) + links (2pts) + joints (4pts) = 10 pts each
2. For the mechanism below, classify the four-bar mechanism based on its possible motion. The picture is not drawn to scale. Show all work that led to your conclusion.
Answer and work = 5 pts
3. For the vectors shown below, analytically determine the vector, J=B-> A+> C. Show all work using an analytical method. Usage of a CAD software program can only be used to check your work. Your answer should have a magnitude and direction.
Magnitude+direction=8 pts
4. The timing chart below is for a mechanism that lifts, dwells, then returns to its original starting position. Determine the following:
a) Determine the time ratio, cycle time, and motor speed of the mechanism.
b) Determine the peak velocity of the lifting motion.
c) Determine the peak velocity of return motion.
d) Construct an acceleration timing chart. Identify the accelerations achieved and label both axes with the appropriate units. Use the axes provided for convenience.
e) Optimize the motion so the maximum acceleration of any part is less than 0.15g (1g = 386.4 in/s2
). Assume the same dwell time of 1 second. An extra page is provided if all your work doesn’t fit below.
6pts + 2pts + 2pts + 5pts + 5pts = 20 pts
5. Design a slider-crank mechanism with a time ratio of Q = 1.68, stroke of |ΔR4|max = 54 mm and time per cycle of t = 2.4 sec. Specify the link lengths L2, L3, offset distance L1 and the crank speed. Assume the smallest angle (w.r.t. horizontal) the slider makes with the crank pivot point is 15°. A general picture of a slider-crank is shown below.
2pts + 2pts + 2pts + 2pts = 8pts
6. Determine the stroke of the mechanism below. 6 pts
7. For the rear windshield wiper mechanism in the initial position shown, the crank rotates counterclockwise 25°. Determine the angular displacement of the wiper blade. Assume the wiper blade, wiper arm, and follower link are stationary with respect to each other. If you are using the MS Excel spreadsheet, please list the variables you are inputting and state that you are using the spreadsheet in your work. 6 pts
8. If the angular velocity of link 4 is 60 rpm counterclockwise, find the velocity of vB. Write your answer in Cartesian vector notation or magnitude/angle format with units of m/s. (6 points)