Specify Joint Motion Profile

Model Overview

In this tutorial, you prescribe the time-varying crank angle of a four-bar linkage using a Revolute Joint block. Then, during simulation, you sense the actuation torque at the same joint corresponding to the prescribed motion.

Build Model

1. At the MATLAB^® command prompt, enter smdoc_four_bar. A four-bar model opens. This is the model you create in tutorial Model a Closed-Loop Kinematic Chain.

2. In the dialog box of the Base-Crank Revolute Joint block, specify the following parameters settings.

   Parameter	Setting
   Actuation > Torque	Automatically Computed
   Actuation > Motion	Provided by Input
   Sensing > Actuator Torque	Selected

   The joint block displays two physical signal ports. Input port q accepts the joint angular position. Output port t provides the joint actuation torque required to achieve that angular position.

3. In each of the four Revolute Joint block dialog boxes, set Internal Mechanics > Damping Coefficient to 5e-4 N*m/(deg/s). During simulation, damping forces between the joint frames account for dissipative losses at the joints.

4. Drag the following blocks into the model. These blocks enable you to specify an actuation torque signal and plot the joint position.

   Block	Library
   Simulink-PS Converter	Simscape > Utilities
   PS-Simulink Converter	Simscape > Utilities
   Scope	Simulink > Sinks
   Signal Builder	Simulink > Sources

5. Connect the blocks as shown in the figure.

   

6. In the Input Handling tab of the Simulink-PS Converter block dialog box, specify the following block parameters.

   Parameter	Value
   Filtering and derivatives	Filter input
   Input filtering order	Second-order filtering

7. In the Signal Builder window, specify the joint angular trajectory as shown in the figure.

   

   This signal corresponds to a constant angular speed of 1 rad/s from t = 1s onwards.

Simulate Model

Run the simulation. Mechanics Explorer opens with a dynamic display of the four-bar model.

Open the Scope window. The scope plot shows the joint actuation torque with which you can achieve the motion you prescribed.

Related Topics

• Prescribe Joint Motion in Planar Manipulator Model
• Sense Motion Using a Transform Sensor Block
• Specifying Motion Input Derivatives