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Stewart Platform - Simscape Model

Table of Contents

1 Parameters used for the Simscape Model

2 Simulation Configuration - Configuration reference

As multiple simulink files will be used for simulation and tests, it is very useful to determine good simulation configuration that will be shared among all the simulink files.

This is done using something called “Configuration Reference” (documentation).

Basically, the configuration is stored in a mat file conf_simscape.mat and then loaded in the workspace for it to be accessible to all the simulink models. It is automatically loaded when the Simulink project is open. It can be loaded manually with the command: 

load('mat/conf_simscape.mat');

It is however possible to modify specific parameters just for one Simulink file using the set_param command: 

set_param(conf_simscape, 'StopTime', 1);

3 Subsystem Reference

Several Stewart platform models are used, for instance one is use to study the dynamics while the other is used to apply active damping techniques.

However, all the Simscape models share some subsystems using the Subsystem Reference Simulink block (documentation).

These shared subsystems are:

  • Fixed_Based.slx - Fixed base of the Stewart Platform
  • Mobile_Platform.slx - Mobile platform of the Stewart Platform
  • stewart_strut.slx - One strut containing two spherical/universal joints, the actuator as well as the included sensors. A parameter i is initialized to determine what it the “number” of the strut.

These subsystems are referenced from another subsystem called Stewart_Platform.slx, that basically connect them correctly. This subsystem is then referenced in other simulink models for various purposes.

4 Basic configuration for the Fixed base, Mobile Platform and Struts

5 Sensors included in the Struts and on the Mobile Platform

6 Inertial Sensors

6.1 Z-Axis Geophone

This Matlab function is accessible here. 

function [geophone] = initializeZAxisGeophone(args)
    arguments
        args.mass (1,1) double {mustBeNumeric, mustBePositive} = 1e-3 % [kg]
        args.freq (1,1) double {mustBeNumeric, mustBePositive} = 1    % [Hz]
    end

    %%
    geophone.m = args.mass;

    %% The Stiffness is set to have the damping resonance frequency
    geophone.k = geophone.m * (2*pi*args.freq)^2;

    %% We set the damping value to have critical damping
    geophone.c = 2*sqrt(geophone.m * geophone.k);

    %% Save
    save('./mat/geophone_z_axis.mat', 'geophone');
end

6.2 Z-Axis Accelerometer

This Matlab function is accessible here. 

function [accelerometer] = initializeZAxisAccelerometer(args)
    arguments
        args.mass (1,1) double {mustBeNumeric, mustBePositive} = 1e-3 % [kg]
        args.freq (1,1) double {mustBeNumeric, mustBePositive} = 5e3  % [Hz]
    end

    %%
    accelerometer.m = args.mass;

    %% The Stiffness is set to have the damping resonance frequency
    accelerometer.k = accelerometer.m * (2*pi*args.freq)^2;

    %% We set the damping value to have critical damping
    accelerometer.c = 2*sqrt(accelerometer.m * accelerometer.k);

    %% Gain correction of the accelerometer to have a unity gain until the resonance
    accelerometer.gain = -accelerometer.k/accelerometer.m;

    %% Save
    save('./mat/accelerometer_z_axis.mat', 'accelerometer');
end

Author: Dehaeze Thomas

Created: 2020-01-28 mar. 17:37