Week 8 & 9 - Four Bar Mechanism
AIM :-
To modify the motion curve or BISTOP expression that is applied to the revolute joint of a trunk lid mechanism in such a way that the trunk lid should stop the moment it comes in contact with the body of the car.
FOUR BAR MECHANISM MODEL :-
A four bar mechanism is created to move the trunklid. The schematics of the mechanism is shown below.
The input link controls the movement of the trunk lid.
To create the model first the points are created. 11 points are created and the coordinates are defined as shown below.
Points 3 and 4's coordinates are highlighted in blue because they are created using the "create points along a vector" option.
After the points are created the freebodies are created. 3 bodies are created which are connected to the follower, coupler and the input link. The connectivity of the free bodies are given below.
The cylinders which make up the links are created by using the graphics option. The links for the follower, coupler and input are created and their connectivity and diameters are defined as shown below.
Cylinder 1 is the link for the follower,
Cylinder 2 is the link for the coupler,
Cylinders 3, 4, 5 and 6 comprise of the input link,
After the links are created and defined, joints between the follower, coupler and input links are created. A total of 4 joints are used which are 3 revolute joints and 1 inline joint. The joints are created and defined as shown below.
Revolute joints,
Inline joint,
The complete model is shown below.
IMPORTING THE TRUNK LID AND CAR BODY TO MOTION VIEW :-
After the four bar mechanism is created, the trunk lid is imported into hyperworks. This is done by selecting Tools ---> Import CAD or FE using Hypermesh. Once selected a dialouge box appears as shown below.
Once the file is selected and when applied, a new window opens which displays the Hypermesh model of the trunk lid.
To import this model as a graphic in Motion View, on the left hand side under MV import options select save and quit. This saves the FE model as a motion view graphic and imports it to the motion view window.
Once the trunk lid is imported, it's connectivity is defined by selecting the input body as shown below.
Similarly the car body is also imported to motion view as an FE model from hyperworks.
Finite Element model,
Imported model,
The connectivity of the car body is then defined.
After importing both the models, the simulation is run for collision detection.
SIMULATION :-
Before running the simulation a motion curve is added. This curve depicts the motion of the trunk lid. The motion curve is created by selecting the add curve option. Once the curve is created, it is defined by choosing the file of the curve. The file is in a .csv format which is a spreadsheet. The file is selected and the X and the Y components are defined as shown.
Once defined, the curve can be previewed by selecting show curve.
Once the curve is created and defined a motion is created where the curve is added to it.
After the motion is defined a simulation is run for 4 seconds. After the simulation is completed a graph of the displacement of the trunk lid with respect to time is plotted.
From the Hyper View window, the collision detection option is selected to see at what time interval the trunk lid collides with the car body. This is done by selecting the collision detection option.
A collision set is added, the trunk lid is added to group A and the car body is added to group B. Under animation event, Stop on collision is selected to detect at what time the collision occurs.
After the properties are defined, the simulation is run again where the trunk lid stops moving the moment it touches the car body.
It is shown that the trunk lid stops at 3.11 seconds.