SimMechanics

Configuring the Ground and Joint Blocks

Now configure the Ground blocks with the data from the following table. Grounded coordinate systems (CSs) are automatically created.

Geometry of the Four Bar Base

This table summarizes the geometry of ground points.

Geometric Properties of the Four Bar Grounds 

Property	Value	MAT-File Variable
Ground_1 point (m)	[ 0.434 0 0.04]	gpoint_1
Ground_2 point (m)	[-0.433 0 0.04]	gpoint_2

The base of the mechanism has these measurements:

• The base is horizontal, with length 86.7 cm.
• Ground_1 represents the ground point 43.3 cm to the right of the World CS origin.
• Ground_2 represents the ground point 43.4 cm to the left of the World CS origin.
• The bottom revolutes are 4 cm above the origin (x-z) plane.

Configuring the Ground Blocks

To represent ground points on the immobile base, configure the Ground blocks. Use the variable names if you've loaded fourbar_data.mat into your workspace:

1. Open Ground_1 and enter [ 0.434 0 0.04 ] or gpoint_1 in the Location field.
2. Open Ground_2 and enter [-0.433 0 0.04 ] or gpoint_2 in the Location field.
3. Leave both pull-down menus for units at default m (meters).

   
   
   

Configuring the Revolute Joints

The three nongrounded bars move in the plane of your screen (x-y plane), so you need to make all the Revolute axes the z-axis (out of the screen):

1. Open each Revolute's dialog box in turn. In its Parameters area, note on the Axes pane that the z-axis is the default: Axis of rotation [x y z] is set to [0 0 1] in each, relative to Reference csys WORLD. Leave these defaults.

1. A Revolute block contains only one primitive joint, a single revolute DoF. So the Primitive is automatically Revolute. Its name internal to the block is R1.

2. Leave these Revolute joint block defaults and ignore the Advanced tab.

The Body CS and base-follower joint directionality should be set up as shown in the block diagram of Figure 2-5. In the Connection parameters area, the default Joint directionality for each Revolute automatically follows the right-to-left sequence of Grounded and Body CSs:

• Revolute1: Base to follower: GND@Gound_1 to CS1@Bar1
• Revolute2: Base to follower: CS2@Bar1 to CS1@Bar2
• Revolute3: Base to follower: CS2@Bar2 to CS1@Bar3
• Revolute4: Base to follower: CS2@Bar3 to GND@Ground_2

In this Joint directionality convention:

• At each Joint, the leftward Body moves relative to the rightward Body.
• The rotation axis points in the +z direction (out of the screen).
• Looking at the mechanism from the front in Figure 2-4, the positive rotational sense is counterclockwise. All Joint Sensor and Actuator data are interpreted in this sense.

  
  
  
  
  
  
  

Setting Up the Block Diagram

Configuring the Body Blocks