%% Clear Workspace and Close figures clear; close all; clc; %% Intialize Laplace variable s = zpk('s'); simulinkproject('../'); % Cube's center at the Center of Mass of the mobile platform % Let's create a Cubic Stewart Platform where the *Center of Mass of the mobile platform is located at the center of the cube*. % We define the size of the Stewart platform and the position of frames $\{A\}$ and $\{B\}$. H = 200e-3; % height of the Stewart platform [m] MO_B = -10e-3; % Position {B} with respect to {M} [m] % Now, we set the cube's parameters such that the center of the cube is coincident with $\{A\}$ and $\{B\}$. Hc = 2.5*H; % Size of the useful part of the cube [m] FOc = H + MO_B; % Center of the cube with respect to {F} stewart = initializeStewartPlatform(); stewart = initializeFramesPositions(stewart, 'H', H, 'MO_B', MO_B); stewart = generateCubicConfiguration(stewart, 'Hc', Hc, 'FOc', FOc, 'FHa', 25e-3, 'MHb', 25e-3); stewart = computeJointsPose(stewart); stewart = initializeStrutDynamics(stewart, 'K', 1e6*ones(6,1), 'C', 1e1*ones(6,1)); stewart = initializeJointDynamics(stewart, 'type_F', 'universal', 'type_M', 'spherical'); stewart = computeJacobian(stewart); stewart = initializeStewartPose(stewart); % Now we set the geometry and mass of the mobile platform such that its center of mass is coincident with $\{A\}$ and $\{B\}$. stewart = initializeCylindricalPlatforms(stewart, 'Fpr', 1.2*max(vecnorm(stewart.platform_F.Fa)), ... 'Mpm', 10, ... 'Mph', 20e-3, ... 'Mpr', 1.2*max(vecnorm(stewart.platform_M.Mb))); % And we set small mass for the struts. stewart = initializeCylindricalStruts(stewart, 'Fsm', 1e-3, 'Msm', 1e-3); stewart = initializeInertialSensor(stewart); % No flexibility below the Stewart platform and no payload. ground = initializeGround('type', 'none'); payload = initializePayload('type', 'none'); % The obtain geometry is shown in figure [[fig:stewart_cubic_conf_decouple_dynamics]]. displayArchitecture(stewart, 'labels', false, 'view', 'all'); % #+name: fig:stewart_cubic_conf_decouple_dynamics % #+caption: Geometry used for the simulations - The cube's center, the frames $\{A\}$ and $\{B\}$ and the Center of mass of the mobile platform are coincident ([[./figs/stewart_cubic_conf_decouple_dynamics.png][png]], [[./figs/stewart_cubic_conf_decouple_dynamics.pdf][pdf]]) % [[file:figs/stewart_cubic_conf_decouple_dynamics.png]] % We now identify the dynamics from forces applied in each strut $\bm{\tau}$ to the displacement of each strut $d \bm{\mathcal{L}}$. open('stewart_platform_model.slx') %% Options for Linearized options = linearizeOptions; options.SampleTime = 0; %% Name of the Simulink File mdl = 'stewart_platform_model'; %% Input/Output definition clear io; io_i = 1; io(io_i) = linio([mdl, '/Controller'], 1, 'openinput'); io_i = io_i + 1; % Actuator Force Inputs [N] io(io_i) = linio([mdl, '/Stewart Platform'], 1, 'openoutput', [], 'dLm'); io_i = io_i + 1; % Relative Displacement Outputs [m] %% Run the linearization G = linearize(mdl, io, options); G.InputName = {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'}; G.OutputName = {'Dm1', 'Dm2', 'Dm3', 'Dm4', 'Dm5', 'Dm6'}; % Now, thanks to the Jacobian (Figure [[fig:local_to_cartesian_coordinates]]), we compute the transfer function from $\bm{\mathcal{F}}$ to $\bm{\mathcal{X}}$. Gc = inv(stewart.kinematics.J)*G*inv(stewart.kinematics.J'); Gc.InputName = {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'}; Gc.OutputName = {'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'}; % The obtain dynamics $\bm{G}_{c}(s) = \bm{J}^{-T} \bm{G}(s) \bm{J}^{-1}$ is shown in Figure [[fig:stewart_cubic_decoupled_dynamics_cartesian]]. freqs = logspace(1, 3, 500); figure; ax1 = subplot(2, 2, 1); hold on; for i = 1:6 for j = i+1:6 plot(freqs, abs(squeeze(freqresp(Gc(i, j), freqs, 'Hz'))), 'k-'); end end set(gca,'ColorOrderIndex',1); plot(freqs, abs(squeeze(freqresp(Gc(1, 1), freqs, 'Hz')))); plot(freqs, abs(squeeze(freqresp(Gc(2, 2), freqs, 'Hz')))); plot(freqs, abs(squeeze(freqresp(Gc(3, 3), freqs, 'Hz')))); hold off; set(gca, 'XScale', 'log'); set(gca, 'YScale', 'log'); ylabel('Amplitude [m/N]'); set(gca, 'XTickLabel',[]); ax3 = subplot(2, 2, 3); hold on; for i = 1:6 for j = i+1:6 p4 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(i, j), freqs, 'Hz'))), 'k-'); end end set(gca,'ColorOrderIndex',1); p1 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(1, 1), freqs, 'Hz')))); p2 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(2, 2), freqs, 'Hz')))); p3 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(3, 3), freqs, 'Hz')))); hold off; set(gca, 'XScale', 'log'); set(gca, 'YScale', 'lin'); ylabel('Phase [deg]'); xlabel('Frequency [Hz]'); ylim([-180, 180]); yticks([-180, -90, 0, 90, 180]); legend([p1, p2, p3, p4], {'$D_x/F_x$','$D_y/F_y$', '$D_z/F_z$', '$D_i/F_j$'}) ax2 = subplot(2, 2, 2); hold on; for i = 1:6 for j = i+1:6 plot(freqs, abs(squeeze(freqresp(Gc(i, j), freqs, 'Hz'))), 'k-'); end end set(gca,'ColorOrderIndex',1); plot(freqs, abs(squeeze(freqresp(Gc(4, 4), freqs, 'Hz')))); plot(freqs, abs(squeeze(freqresp(Gc(5, 5), freqs, 'Hz')))); plot(freqs, abs(squeeze(freqresp(Gc(6, 6), freqs, 'Hz')))); hold off; set(gca, 'XScale', 'log'); set(gca, 'YScale', 'log'); ylabel('Amplitude [m/N]'); set(gca, 'XTickLabel',[]); ax4 = subplot(2, 2, 4); hold on; for i = 1:6 for j = i+1:6 p4 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(i, j), freqs, 'Hz'))), 'k-'); end end set(gca,'ColorOrderIndex',1); p1 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(4, 4), freqs, 'Hz')))); p2 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(5, 5), freqs, 'Hz')))); p3 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(6, 6), freqs, 'Hz')))); hold off; set(gca, 'XScale', 'log'); set(gca, 'YScale', 'lin'); ylabel('Phase [deg]'); xlabel('Frequency [Hz]'); ylim([-180, 180]); yticks([-180, -90, 0, 90, 180]); legend([p1, p2, p3, p4], {'$R_x/M_x$','$R_y/M_y$', '$R_z/M_z$', '$R_i/M_j$'}) linkaxes([ax1,ax2,ax3,ax4],'x'); % Cube's center not coincident with the Mass of the Mobile platform % Let's create a Stewart platform with a cubic architecture where the cube's center is at the center of the Stewart platform. H = 200e-3; % height of the Stewart platform [m] MO_B = -100e-3; % Position {B} with respect to {M} [m] % Now, we set the cube's parameters such that the center of the cube is coincident with $\{A\}$ and $\{B\}$. Hc = 2.5*H; % Size of the useful part of the cube [m] FOc = H + MO_B; % Center of the cube with respect to {F} stewart = initializeStewartPlatform(); stewart = initializeFramesPositions(stewart, 'H', H, 'MO_B', MO_B); stewart = generateCubicConfiguration(stewart, 'Hc', Hc, 'FOc', FOc, 'FHa', 25e-3, 'MHb', 25e-3); stewart = computeJointsPose(stewart); stewart = initializeStrutDynamics(stewart, 'K', 1e6*ones(6,1), 'C', 1e1*ones(6,1)); stewart = initializeJointDynamics(stewart, 'type_F', 'universal', 'type_M', 'spherical'); stewart = computeJacobian(stewart); stewart = initializeStewartPose(stewart); % However, the Center of Mass of the mobile platform is *not* located at the cube's center. stewart = initializeCylindricalPlatforms(stewart, 'Fpr', 1.2*max(vecnorm(stewart.platform_F.Fa)), ... 'Mpm', 10, ... 'Mph', 20e-3, ... 'Mpr', 1.2*max(vecnorm(stewart.platform_M.Mb))); % And we set small mass for the struts. stewart = initializeCylindricalStruts(stewart, 'Fsm', 1e-3, 'Msm', 1e-3); stewart = initializeInertialSensor(stewart); % No flexibility below the Stewart platform and no payload. ground = initializeGround('type', 'none'); payload = initializePayload('type', 'none'); % The obtain geometry is shown in figure [[fig:stewart_cubic_conf_mass_above]]. displayArchitecture(stewart, 'labels', false, 'view', 'all'); % #+name: fig:stewart_cubic_conf_mass_above % #+caption: Geometry used for the simulations - The cube's center is coincident with the frames $\{A\}$ and $\{B\}$ but not with the Center of mass of the mobile platform ([[./figs/stewart_cubic_conf_mass_above.png][png]], [[./figs/stewart_cubic_conf_mass_above.pdf][pdf]]) % [[file:figs/stewart_cubic_conf_mass_above.png]] % We now identify the dynamics from forces applied in each strut $\bm{\tau}$ to the displacement of each strut $d \bm{\mathcal{L}}$. open('stewart_platform_model.slx') %% Options for Linearized options = linearizeOptions; options.SampleTime = 0; %% Name of the Simulink File mdl = 'stewart_platform_model'; %% Input/Output definition clear io; io_i = 1; io(io_i) = linio([mdl, '/Controller'], 1, 'openinput'); io_i = io_i + 1; % Actuator Force Inputs [N] io(io_i) = linio([mdl, '/Stewart Platform'], 1, 'openoutput', [], 'dLm'); io_i = io_i + 1; % Relative Displacement Outputs [m] %% Run the linearization G = linearize(mdl, io, options); G.InputName = {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'}; G.OutputName = {'Dm1', 'Dm2', 'Dm3', 'Dm4', 'Dm5', 'Dm6'}; % And we use the Jacobian to compute the transfer function from $\bm{\mathcal{F}}$ to $\bm{\mathcal{X}}$. Gc = inv(stewart.kinematics.J)*G*inv(stewart.kinematics.J'); Gc.InputName = {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'}; Gc.OutputName = {'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'}; % The obtain dynamics $\bm{G}_{c}(s) = \bm{J}^{-T} \bm{G}(s) \bm{J}^{-1}$ is shown in Figure [[fig:stewart_conf_coupling_mass_matrix]]. freqs = logspace(1, 3, 500); figure; ax1 = subplot(2, 2, 1); hold on; for i = 1:6 for j = i+1:6 plot(freqs, abs(squeeze(freqresp(Gc(i, j), freqs, 'Hz'))), 'k-'); end end set(gca,'ColorOrderIndex',1); plot(freqs, abs(squeeze(freqresp(Gc(1, 1), freqs, 'Hz')))); plot(freqs, abs(squeeze(freqresp(Gc(2, 2), freqs, 'Hz')))); plot(freqs, abs(squeeze(freqresp(Gc(3, 3), freqs, 'Hz')))); hold off; set(gca, 'XScale', 'log'); set(gca, 'YScale', 'log'); ylabel('Amplitude [m/N]'); set(gca, 'XTickLabel',[]); ax3 = subplot(2, 2, 3); hold on; for i = 1:6 for j = i+1:6 p4 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(i, j), freqs, 'Hz'))), 'k-'); end end set(gca,'ColorOrderIndex',1); p1 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(1, 1), freqs, 'Hz')))); p2 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(2, 2), freqs, 'Hz')))); p3 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(3, 3), freqs, 'Hz')))); hold off; set(gca, 'XScale', 'log'); set(gca, 'YScale', 'lin'); ylabel('Phase [deg]'); xlabel('Frequency [Hz]'); ylim([-180, 180]); yticks([-180, -90, 0, 90, 180]); legend([p1, p2, p3, p4], {'$D_x/F_x$','$D_y/F_y$', '$D_z/F_z$', '$D_i/F_j$'}) ax2 = subplot(2, 2, 2); hold on; for i = 1:6 for j = i+1:6 plot(freqs, abs(squeeze(freqresp(Gc(i, j), freqs, 'Hz'))), 'k-'); end end set(gca,'ColorOrderIndex',1); plot(freqs, abs(squeeze(freqresp(Gc(4, 4), freqs, 'Hz')))); plot(freqs, abs(squeeze(freqresp(Gc(5, 5), freqs, 'Hz')))); plot(freqs, abs(squeeze(freqresp(Gc(6, 6), freqs, 'Hz')))); hold off; set(gca, 'XScale', 'log'); set(gca, 'YScale', 'log'); ylabel('Amplitude [m/N]'); set(gca, 'XTickLabel',[]); ax4 = subplot(2, 2, 4); hold on; for i = 1:6 for j = i+1:6 p4 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(i, j), freqs, 'Hz'))), 'k-'); end end set(gca,'ColorOrderIndex',1); p1 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(4, 4), freqs, 'Hz')))); p2 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(5, 5), freqs, 'Hz')))); p3 = plot(freqs, 180/pi*angle(squeeze(freqresp(Gc(6, 6), freqs, 'Hz')))); hold off; set(gca, 'XScale', 'log'); set(gca, 'YScale', 'lin'); ylabel('Phase [deg]'); xlabel('Frequency [Hz]'); ylim([-180, 180]); yticks([-180, -90, 0, 90, 180]); legend([p1, p2, p3, p4], {'$R_x/M_x$','$R_y/M_y$', '$R_z/M_z$', '$R_i/M_j$'}) linkaxes([ax1,ax2,ax3,ax4],'x');