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Creating a Four Bar Multibody Mechanism in MATLAB

This example constructs a four bar mechanism in MATLAB using Simscape Multibody. It demostrates various classes under simscape.multibody.* package to build a multibody system in MATLAB.

A custom function fourbar constructs the four-bar multibody with user specified link lengths. Each parameter is expected to be a Simscape Value, specifying a scalar length.

openExample('sm/CreateAFourBarMechanismInMATLAB');
[fb, op] = fourBar(simscape.Value(12, 'cm'), simscape.Value(10, 'cm'), simscape.Value(5, 'cm'), simscape.Value(8, 'cm'));

The four-bar is constructed so that the X-Y plane is the plane of motion, with gravity in the -Y direction. Output op is an operating point that sets the bottom left joint angle to a nominal value with high priority.

To visualize the mechanism, run the following :

cmb = compile(fb);
visualize(cmb,computeState(cmb,op),'vizFourBar');

FourBar.PNG

Once the four bar mechanism is created, we can also perform some analysis on it like computing and plotting the trajectory of the top (distal) link of the specified four-bar mechanism. The function fourBarMotionPlot plots the trajectory of the top link over a full 360 deg range of the crank angle (when the left link is a crank of the four bar). This function varies the crank angle over a full 360-deg range in steps of 1 deg. The trajectory of the midpoint of the top link is plotted over these 1-deg steps to form a (typically) smooth curve. The coordinates along this curve are relative to the world frame.

fourBarMotionPlot(fb);

Figure Four Bar Motion Plot contains an axes object. The axes object with title Trajectory of Top Link (cm) contains 53 objects of type line.

See Also