Main Content

Specify Joint Motion Profile

This example shows how to specify the motion of a Revolute Joint block and sense the corresponding actuation torque at the joint. The example uses a four-bar linkage mechanism.

Four bar linkage

To drive the linkage, you prescribe a time-varying position signal for the crank angle. Then you use the Revolute Joint block to sense the actuation torque at the joint that corresponds to the prescribed motion.

Build Model

  1. At the MATLAB® command prompt, enter smdoc_four_bar to open the linkage model. To learn how to build the model, see Model a Closed-Loop Kinematic Chain.

  2. Double-click the Base-Crank Revolute Joint block and specify these parameters:

    ParameterSetting
    Actuation > TorqueAutomatically Computed
    Actuation > MotionProvided by Input
    Sensing > Actuator TorqueSelected

    The 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 the prescribed angular positions.

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

  4. Add these blocks to the model. These blocks enable you to specify an actuation position signal and plot the actuation torque for the joint.

    BlockLibrary
    Simulink-PS ConverterSimscape > Utilities
    PS-Simulink ConverterSimscape > Utilities
    ScopeSimulink > Sinks
    Signal EditorSimulink > Sources

  5. Connect the blocks as shown in the figure.smdoc_four_bar model with the new blocks connected to the Base-Crank Revolute Joint block

  6. Double-click the Simulink-PS Converter block and specify these parameters:

    ParameterValue
    Input Heading > Filtering and derivativesFilter input, derivatives calculated
    Input Heading > Input filtering orderSecond-order filtering

  7. Use the Signal Editor block to specify the position signal.

    • Double-click the Signal Editor block to open the dialog box.

    • Under Signal properties, click the Launch Signal Editor button Launch Signal Editor button to open the Signal Editor window.

    • In the Signal Editor window, in the left pane, expand Scenario, select the Plot/Edit check box, and edit data as shown in the image. This signal corresponds to a constant angular speed of 1 rad/s from t = 1s onwards.

      Signal Editor UI showing position data

    • On the Signal Editor tab, click Save to save the data to a MAT-file. Close the Signal Editor window.

    • In the dialog box, under Signal properties, select Interpolation data, click Apply and OK.

Simulate Model

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

3-D Mechanics Explorer animation showing the modeled four-bar mode

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

Actuation torque plot

Related Topics