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Stewart Platform - Dynamics Study

Table of Contents

Some tests

Simscape Model

open('stewart_platform_dynamics.slx')

test

stewart = initializeStewartPlatform();
stewart = initializeFramesPositions(stewart);
stewart = generateGeneralConfiguration(stewart);
stewart = computeJointsPose(stewart);
stewart = initializeStrutDynamics(stewart);
stewart = initializeCylindricalPlatforms(stewart);
stewart = initializeCylindricalStruts(stewart);
stewart = computeJacobian(stewart);
stewart = initializeStewartPose(stewart);

Estimation of the transfer function from \(\mathcal{\bm{F}}\) to \(\mathcal{\bm{X}}\): 

%% Options for Linearized
options = linearizeOptions;
options.SampleTime = 0;

%% Name of the Simulink File
mdl = 'stewart_platform_dynamics';

%% Input/Output definition
clear io; io_i = 1;
io(io_i) = linio([mdl, '/F'], 1, 'openinput');  io_i = io_i + 1;
io(io_i) = linio([mdl, '/X'], 1, 'openoutput'); io_i = io_i + 1;

%% Run the linearization
G = linearize(mdl, io, options);
G.InputName  = {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'};
G.OutputName = {'Edx', 'Edy', 'Edz', 'Erx', 'Ery', 'Erz'};

%% Options for Linearized
options = linearizeOptions;
options.SampleTime = 0;

%% Name of the Simulink File
mdl = 'stewart_platform_dynamics';

%% Input/Output definition
clear io; io_i = 1;
io(io_i) = linio([mdl, '/J-T'], 1, 'openinput');  io_i = io_i + 1;
io(io_i) = linio([mdl, '/X'],   1, 'openoutput'); io_i = io_i + 1;

%% Run the linearization
G = linearize(mdl, io, options);
G.InputName  = {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'};
G.OutputName = {'Edx', 'Edy', 'Edz', 'Erx', 'Ery', 'Erz'};

G_cart = minreal(G*inv(stewart.J'));
G_cart.InputName = {'Fnx', 'Fny', 'Fnz', 'Mnx', 'Mny', 'Mnz'};

figure; bode(G, G_cart)

%% Options for Linearized
options = linearizeOptions;
options.SampleTime = 0;

%% Name of the Simulink File
mdl = 'stewart_platform_dynamics';

%% Input/Output definition
clear io; io_i = 1;
io(io_i) = linio([mdl, '/Fext'], 1, 'openinput');  io_i = io_i + 1;
io(io_i) = linio([mdl, '/X'],    1, 'openoutput'); io_i = io_i + 1;

%% Run the linearization
Gd = linearize(mdl, io, options);
Gd.InputName  = {'Fex', 'Fey', 'Fez', 'Mex', 'Mey', 'Mez'};
Gd.OutputName = {'Edx', 'Edy', 'Edz', 'Erx', 'Ery', 'Erz'};

freqs = logspace(0, 3, 1000);

figure;
bode(Gd, G)

Compare external forces and forces applied by the actuators

Initialization of the Stewart platform. 

stewart = initializeStewartPlatform();
stewart = initializeFramesPositions(stewart);
stewart = generateGeneralConfiguration(stewart);
stewart = computeJointsPose(stewart);
stewart = initializeStrutDynamics(stewart);
stewart = initializeCylindricalPlatforms(stewart);
stewart = initializeCylindricalStruts(stewart);
stewart = computeJacobian(stewart);
stewart = initializeStewartPose(stewart);

Estimation of the transfer function from \(\mathcal{\bm{F}}\) to \(\mathcal{\bm{X}}\): 

%% Options for Linearized
options = linearizeOptions;
options.SampleTime = 0;

%% Name of the Simulink File
mdl = 'stewart_platform_dynamics';

%% Input/Output definition
clear io; io_i = 1;
io(io_i) = linio([mdl, '/F'], 1, 'openinput');  io_i = io_i + 1;
io(io_i) = linio([mdl, '/X'], 1, 'openoutput'); io_i = io_i + 1;

%% Run the linearization
G = linearize(mdl, io, options);
G.InputName  = {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'};
G.OutputName = {'Edx', 'Edy', 'Edz', 'Erx', 'Ery', 'Erz'};

Estimation of the transfer function from \(\mathcal{\bm{F}}_{d}\) to \(\mathcal{\bm{X}}\): 

%% Options for Linearized
options = linearizeOptions;
options.SampleTime = 0;

%% Name of the Simulink File
mdl = 'stewart_platform_dynamics';

%% Input/Output definition
clear io; io_i = 1;
io(io_i) = linio([mdl, '/Fext'], 1, 'openinput');  io_i = io_i + 1;
io(io_i) = linio([mdl, '/X'],    1, 'openoutput'); io_i = io_i + 1;

%% Run the linearization
Gd = linearize(mdl, io, options);
Gd.InputName  = {'Fex', 'Fey', 'Fez', 'Mex', 'Mey', 'Mez'};
Gd.OutputName = {'Edx', 'Edy', 'Edz', 'Erx', 'Ery', 'Erz'};

Comparison of the two transfer function matrices. 

freqs = logspace(0, 4, 1000);

figure;
bode(Gd, G, freqs)

Seems quite similar.

Comparison of the static transfer function and the Compliance matrix

Initialization of the Stewart platform. 

stewart = initializeStewartPlatform();
stewart = initializeFramesPositions(stewart);
stewart = generateGeneralConfiguration(stewart);
stewart = computeJointsPose(stewart);
stewart = initializeStrutDynamics(stewart);
stewart = initializeCylindricalPlatforms(stewart);
stewart = initializeCylindricalStruts(stewart);
stewart = computeJacobian(stewart);
stewart = initializeStewartPose(stewart);

Estimation of the transfer function from \(\mathcal{\bm{F}}\) to \(\mathcal{\bm{X}}\): 

%% Options for Linearized
options = linearizeOptions;
options.SampleTime = 0;

%% Name of the Simulink File
mdl = 'stewart_platform_dynamics';

%% Input/Output definition
clear io; io_i = 1;
io(io_i) = linio([mdl, '/F'], 1, 'openinput');  io_i = io_i + 1;
io(io_i) = linio([mdl, '/X'], 1, 'openoutput'); io_i = io_i + 1;

%% Run the linearization
G = linearize(mdl, io, options);
G.InputName  = {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'};
G.OutputName = {'Edx', 'Edy', 'Edz', 'Erx', 'Ery', 'Erz'};

Let’s first look at the low frequency transfer function matrix from \(\mathcal{\bm{F}}\) to \(\mathcal{\bm{X}}\).

2.0e-06 -9.1e-19 -5.3e-12 7.3e-18 1.7e-05 1.3e-18
-1.7e-18 2.0e-06 8.6e-19 -1.7e-05 -1.5e-17 6.7e-12
3.6e-13 3.2e-19 5.0e-07 -2.5e-18 8.1e-12 -1.5e-19
1.0e-17 -1.7e-05 -5.0e-18 1.9e-04 9.1e-17 -3.5e-11
1.7e-05 -6.9e-19 -5.3e-11 6.9e-18 1.9e-04 4.8e-18
-3.5e-18 -4.5e-12 1.5e-18 7.1e-11 -3.4e-17 4.6e-05

And now at the Compliance matrix.

2.0e-06 2.9e-22 2.8e-22 -3.2e-21 1.7e-05 1.5e-37
-2.1e-22 2.0e-06 -1.8e-23 -1.7e-05 -2.3e-21 1.1e-22
3.1e-22 -1.6e-23 5.0e-07 1.7e-22 2.2e-21 -8.1e-39
2.1e-21 -1.7e-05 2.0e-22 1.9e-04 2.3e-20 -8.7e-21
1.7e-05 2.5e-21 2.0e-21 -2.8e-20 1.9e-04 1.3e-36
3.7e-23 3.1e-22 -6.0e-39 -1.0e-20 3.1e-22 4.6e-05

The low frequency transfer function matrix from \(\mathcal{\bm{F}}\) to \(\mathcal{\bm{X}}\) corresponds to the compliance matrix of the Stewart platform.

Transfer function from forces applied in the legs to the displacement of the legs

Initialization of the Stewart platform. 

stewart = initializeStewartPlatform();
stewart = initializeFramesPositions(stewart);
stewart = generateGeneralConfiguration(stewart);
stewart = computeJointsPose(stewart);
stewart = initializeStrutDynamics(stewart);
stewart = initializeCylindricalPlatforms(stewart);
stewart = initializeCylindricalStruts(stewart);
stewart = computeJacobian(stewart);
stewart = initializeStewartPose(stewart);

Estimation of the transfer function from \(\bm{\tau}\) to \(\bm{L}\): 

%% Options for Linearized
options = linearizeOptions;
options.SampleTime = 0;

%% Name of the Simulink File
mdl = 'stewart_platform_dynamics';

%% Input/Output definition
clear io; io_i = 1;
io(io_i) = linio([mdl, '/J-T'], 1, 'openinput');  io_i = io_i + 1;
io(io_i) = linio([mdl, '/L'], 1, 'openoutput'); io_i = io_i + 1;

%% Run the linearization
G = linearize(mdl, io, options);
G.InputName  = {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'};
G.OutputName = {'L1', 'L2', 'L3', 'L4', 'L5', 'L6'};

freqs = logspace(1, 3, 1000);
figure; bode(G, 2*pi*freqs)

bodeFig({G(1,1), G(1,2)}, freqs, struct('phase', true));

Author: Dehaeze Thomas

Created: 2020-02-11 mar. 15:27