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Nano-Hexapod

Nano-Hexapod

Nano Hexapod object

The nano-hexapod can be initialized and configured using the initializeNanoHexapodFinal function.

n_hexapod = initializeNanoHexapodFinal('flex_bot_type', '4dof', ...
                                       'flex_top_type', '3dof', ...
                                       'motion_sensor_type', 'struts', ...
                                       'actuator_type', '2dof');

Jacobian from Solidworks Model

Center of joints a_i with respect to {F}:

Fa = [[-86.05,  -74.78, 22.49],
      [86.05,   -74.78, 22.49],
      [107.79,  -37.13, 22.49],
      [21.74,   111.91, 22.49],
      [-21.74,  111.91, 22.49],
      [-107.79, -37.13, 22.49]]'*1e-3;

Center of joints a_i with respect to {M}:

Mb = [[-28.47, -106.25, -22.50],
      [28.47,  -106.25, -22.50],
      [106.25,  28.47,  -22.50],
      [77.78,   77.78,  -22.50],
      [-77.78,  77.78,  -22.50],
      [-106.25, 28.47,  -22.50]]'*1e-3;
Fb = Mb + [0; 0; 95e-3];

si = Fb - Fa;
si = si./vecnorm(si);
ki = ones(1,6);
bi = Fb;
ki.*si*si'
1.8977 2.4659e-17 1.3383e-18
2.4659e-17 1.8977 -2.3143e-05
1.3383e-18 -2.3143e-05 2.2046 
OkX = (ki.*cross(bi, si)*si')/(ki.*si*si');
Ok = [OkX(3,2);OkX(1,3);OkX(2,1)]
-1.7444e-18
2.1511e-06
0.052707

The center of the cube is therefore 52.7mm above the bottom platform {F} frame.

Let's compute the Jacobian at this location:

Jk = [si', cross(bi - Ok, si)'];

And the stiffness matrix:

Jk'*diag(ki)*Jk
1.8977 0 0 0 -3.4694e-18 2.5509e-06
0 1.8977 -2.3143e-05 4.1751e-06 1.3878e-17 0
0 -2.3143e-05 2.2046 -5.0916e-11 -3.4694e-18 0
0 4.1751e-06 -5.0916e-11 0.012594 2.1684e-19 8.6736e-19
-3.2704e-18 0 -4.206e-18 3.9451e-19 0.012594 -9.3183e-08
2.5509e-06 0 0 8.6736e-19 -9.3183e-08 0.043362

Jacobian for encoders on the plates

Goal: Compute the 6-DoF motion of the top platform (relative to the bottom platform) from the 6 encoder measurements.

The main differences with the case where the encoders are parallel with the strut are:

  • the encoder and ruler may not be parallel anymore as the top platform is moving
  • the derivation of the Jacobian (if possible) will not be the same

Compare encoders on the struts and encoders on the platforms 

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

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

%% Input/Output definition
clear io; io_i = 1;
io(io_i) = linio([mdl, '/F'],  1, 'openinput');  io_i = io_i + 1; % Actuator Inputs
io(io_i) = linio([mdl, '/D'],  1, 'openoutput'); io_i = io_i + 1; % Relative Motion Outputs
n_hexapod.motion_sensor = struct();
n_hexapod.motion_sensor.type = 1; % 1: Leg / 2: Plate
Gs = linearize(mdl, io, 0.0, options);
Gs.InputName  = {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'};
Gs.OutputName = {'D1', 'D2', 'D3', 'D4', 'D5', 'D6'};
n_hexapod.motion_sensor = struct();
n_hexapod.motion_sensor.type = 2; % 1: Leg / 2: Plate
Gp = linearize(mdl, io, 0.0, options);
Gp.InputName  = {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'};
Gp.OutputName = {'D1', 'D2', 'D3', 'D4', 'D5', 'D6'};

Nano Hexapod 

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

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

%% Input/Output definition
clear io; io_i = 1;
io(io_i) = linio([mdl, '/F'],  1, 'openinput');  io_i = io_i + 1; % Actuator Inputs
io(io_i) = linio([mdl, '/Fe'], 1, 'openinput');  io_i = io_i + 1; % External Force
io(io_i) = linio([mdl, '/D'],  1, 'openoutput'); io_i = io_i + 1; % Relative Motion Outputs
io(io_i) = linio([mdl, '/Fm'], 1, 'openoutput'); io_i = io_i + 1; % Force Sensors
io(io_i) = linio([mdl, '/X'],  1, 'openoutput'); io_i = io_i + 1; % Absolute Motion of top platform

%% Run the linearization
G = linearize(mdl, io, 0.0, options);
G.InputName  = {'F1', 'F2', 'F3', 'F4', 'F5', 'F6', ...
                'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'};
G.OutputName = {'D1', 'D2', 'D3', 'D4', 'D5', 'D6', ...
                'Fm1', 'Fm2', 'Fm3', 'Fm4', 'Fm5', 'Fm6' ...
                'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'};
size(G)
State-space model with 18 outputs, 12 inputs, and 60 states.

Verify the number of DOF:

Element DoF
Bot Plate 0
Struts 6*4
Top Plate + Sample 12
Total: 36

DVF Plant

The DC gain from actuator to relative motion sensor should be equal to (for the 2dof APA): \[ \frac{1}{k + k_a + kk_a/k_e} \]

1.8732e-08

Which is almost the case:

-1.8676e-08 5.2396e-11 -8.8935e-11 2.6392e-11 9.7629e-11 -1.5609e-10
-1.4754e-11 -1.8725e-08 1.4348e-11 -5.7189e-11 -3.3327e-11 7.0799e-11
-3.4924e-11 -7.7445e-11 -1.8607e-08 -4.6578e-11 -1.9592e-11 4.0299e-11
6.1699e-11 -7.1962e-11 1.3374e-11 -1.8623e-08 -1.7898e-10 5.4541e-11
9.735e-11 -1.0698e-10 -1.6424e-11 2.3718e-11 -1.8826e-08 8.387e-11
-3.94e-11 2.6436e-11 -1.1338e-10 5.0793e-11 1.2358e-10 -1.8792e-08

Other (off-diagonal) elements should be close to zero (probably limited to joint's stiffness). However, when setting joint's axial stiffness to infinity, I obtain better diagonal.

/tdehaeze/nass-simscape/media/commit/ecec6ab19b1c22dd1ce584ea979b539a29369494/org/figs/nano_hexapod_struts_2dof_dvf_plant.png

IFF Plant

IFF Plant

/tdehaeze/nass-simscape/media/commit/ecec6ab19b1c22dd1ce584ea979b539a29369494/org/figs/nano_hexapod_struts_2dof_iff_plant.png

DVF Plant

Decoupling at the CoK 

Gx = inv(Jk)*G({'D1', 'D2', 'D3', 'D4', 'D5', 'D6'}, {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'})*inv(Jk');
Gx.inputname  = {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'};
Gx.outputname = {'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'};
-9.8399e-09 -8.0785e-11 -1.5723e-11 2.6356e-10 -4.9857e-10 5.2177e-11
-8.7554e-11 -9.8585e-09 2.6292e-11 2.0485e-10 2.0385e-10 8.2942e-11
4.3837e-11 -5.5862e-14 -8.4859e-09 -9.0036e-12 2.9325e-10 -3.104e-11
1.901e-09 5.3078e-10 -7.5477e-10 -1.4759e-06 -7.7918e-09 -7.491e-10
-7.1795e-11 -1.6333e-09 -1.8359e-10 5.2707e-09 -1.4794e-06 3.2304e-10
7.0322e-11 1.7713e-12 -5.8019e-11 7.4838e-11 -8.9677e-10 -4.2938e-07

Jacobian

Compute Jacobian 

Ai = [out.b1.Data(1,:)
      out.b2.Data(1,:)
      out.b3.Data(1,:)
      out.b4.Data(1,:)
      out.b5.Data(1,:)
      out.b6.Data(1,:)]';


Bi = [out.a1.Data(1,:)
      out.a2.Data(1,:)
      out.a3.Data(1,:)
      out.a4.Data(1,:)
      out.a5.Data(1,:)
      out.a6.Data(1,:)]';
stewart = initializeStewartPlatform();
stewart = initializeFramesPositions(stewart, 'H', 95e-3, 'MO_B', 150e-3);
stewart = generateGeneralConfiguration(stewart);
stewart.platform_F.Fa = Ai;
stewart.platform_M.Mb = Bi - [0;0;1]*stewart.geometry.H;
stewart = computeJointsPose(stewart);
stewart = initializeStewartPose(stewart, 'AP', [0;0;0], 'ARB', eye(3));
stewart = initializeCylindricalPlatforms(stewart);
stewart = initializeCylindricalStruts(stewart);
stewart = initializeStrutDynamics(stewart, 'K', 1e6*ones(6,1), 'C', 1e2*ones(6,1));
stewart = initializeAmplifiedStrutDynamics(stewart);
stewart = initializeJointDynamics(stewart);
displayArchitecture(stewart, 'views', 'all');
describeStewartPlatform(stewart)
GEOMETRY:
- The height between the fixed based and the top platform is 95 [mm].
- Frame {A} is located 150 [mm] above the top platform.
- The initial length of the struts are:
	 82.8, 82.8, 82.8, 82.8, 82.8, 82.8 [mm]

ACTUATORS:
- The actuators are mechanicaly amplified.
- The vertical stiffness and damping contribution of the piezoelectric stack is:
	 ka = 2e+07 [N/m] 	 ca = 1e+01 [N/(m/s)]
- Vertical stiffness when the piezoelectric stack is removed is:
	 kr = 5e+06 [N/m] 	 cr = 1e+01 [N/(m/s)]

JOINTS:
- The joints on the fixed based are universal joints
- The joints on the mobile based are spherical joints
- The position of the joints on the fixed based with respect to {F} are (in [mm]):
	 -86.2 	 -74.7 	  22.3
	  86.3 	 -74.6 	  22.3
	  108 	 -37.3 	  22.3
	  21.5 	  112 	  22.3
	 -21.5 	  112 	  22.3
	 -108 	 -37.5 	  22.2
- The position of the joints on the mobile based with respect to {M} are (in [mm]):
	 -28.4 	 -106 	 -22.4
	  28.5 	 -106 	 -22.5
	  106 	  28.5 	 -22.5
	  77.8 	  77.8 	 -22.5
	 -77.8 	  77.8 	 -22.5
	 -106 	  28.4 	 -22.5

stewart = computeJacobian(stewart);

Verify Jacobian 

load('./mat/nano_hexapod_object.mat', 'stewart');
J = stewart.kinematics.J;

Transformation of motion:

G1 = -inv(J)*G({'D1', 'D2', 'D3', 'D4', 'D5', 'D6'}, {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'});
G2 = G({'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'}, {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'});

Transformation of Forces and Torques

G1 = G({'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'}, {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'});
G2 = G({'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'}, {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'})*inv(J');

Not working because the forces applied on the APA are not really forces applied on the top platform (reduced by a factor ~ka/ke)

Plant from APA forces to sample's displacement 

Gx = G({'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'}, {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'})*inv(J');
Gx.inputname  = {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'};

Plant in the Cartesian frame

Transfer function from forces/torque to displacement/rotation:

GJ = inv(J)*G({'D1', 'D2', 'D3', 'D4', 'D5', 'D6'}, {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'})*inv(J');
GJ.inputname  = {'Fx', 'Fy', 'Fz', 'Mx', 'My', 'Mz'};
GJ.outputname = {'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'};

Plant in the frame of the legs => Verification of Jacobian for displacements

Transfer Function in the frame of the legs

G1 = -J*G({'Dx', 'Dy', 'Dz', 'Rx', 'Ry', 'Rz'}, {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'});
G1.outputname = {'D1', 'D2', 'D3', 'D4', 'D5', 'D6'};

G2 = G({'D1', 'D2', 'D3', 'D4', 'D5', 'D6'}, {'F1', 'F2', 'F3', 'F4', 'F5', 'F6'});

It is working fine (until internal resonance of strut).

Stiffness matrix

Neglecting stiffness of the joints, we have: \[ K = J^t \mathcal{K} J \] where $\mathcal{K}$ is a diagonal 6x6 matrix with axial stiffness of the struts on the diagonal.

Let's note the axial stiffness of the APA: \[ k_{\text{APA}} = k + \frac{k_e k_a}{k_e + k_a} \]

Them axial stiffness of the struts $k_s$: \[ k_s = \frac{k_z k_{\text{APA}}}{k_z + 2 k_{\text{APA}}} \]

kAPA = k + ke*ka/(ke + ka);
ks = kz*kAPA/(kz + 2*kAPA);
Ks = J'*(ks*eye(6))*J
1.9937e-06 7.7027e-12 -1.5885e-11 -1.6811e-10 8.7902e-06 3.0476e-11
7.7027e-12 1.9937e-06 2.7221e-11 -8.7901e-06 6.5081e-12 2.8619e-11
-1.5885e-11 2.7221e-11 2.6114e-07 -1.3209e-10 -6.1725e-11 4.0402e-11
-1.6811e-10 -8.7901e-06 -1.3209e-10 4.5712e-05 -5.7781e-10 -4.5817e-10
8.7902e-06 6.5081e-12 -6.1725e-11 -5.7781e-10 4.5712e-05 5.1628e-10
3.0476e-11 2.8619e-11 4.0402e-11 -4.5817e-10 5.1628e-10 1.3277e-05
1.9869e-06 2.043e-08 1.6444e-09 -4.094e-08 8.7579e-06 -3.5002e-09
3.746e-09 1.9841e-06 -5.5274e-09 -8.7257e-06 -5.5082e-08 -7.6978e-09
-3.2056e-09 -6.4295e-11 2.6079e-07 3.4103e-10 -9.3873e-09 9.6146e-10
-1.1677e-08 -8.736e-06 2.4322e-08 4.5343e-05 2.52e-07 2.5932e-08
8.7439e-06 8.441e-08 5.9144e-09 -1.6879e-07 4.546e-05 -9.8986e-09
3.3453e-09 4.508e-10 1.8718e-09 -2.7294e-09 2.8776e-08 1.3193e-05

We can see that we have almost the same stiffness:

1.0034 0.00037703 -0.0096597 0.0041063 1.0037 -0.0087071
0.0020562 1.0048 -0.0049247 1.0074 -0.00011815 -0.0037178
0.0049552 -0.42338 1.0013 -0.38734 0.0065754 0.042021
0.014397 1.0062 -0.005431 1.0081 -0.0022929 -0.017668
1.0053 7.7101e-05 -0.010436 0.0034233 1.0055 -0.052157
0.0091102 0.063485 0.021584 0.16786 0.017941 1.0063

Function - Initialize Nano Hexapod

<<sec:initializeNanoHexapodFinal>>

Function description 

  function [nano_hexapod] = initializeNanoHexapodFinal(args)

Optional Parameters 

  arguments
      %% Bottom Flexible Joints
      args.flex_bot_type      char {mustBeMember(args.flex_bot_type,{'2dof', '3dof', '4dof', 'flexible'})} = '4dof'
      args.flex_bot_kRx (6,1) double {mustBeNumeric} = ones(6,1)*5 % X bending stiffness [Nm/rad]
      args.flex_bot_kRy (6,1) double {mustBeNumeric} = ones(6,1)*5 % Y bending stiffness [Nm/rad]
      args.flex_bot_kRz (6,1) double {mustBeNumeric} = ones(6,1)*260 % Torsionnal stiffness [Nm/rad]
      args.flex_bot_kz  (6,1) double {mustBeNumeric} = ones(6,1)*1e8 % Axial Stiffness [N/m]
      args.flex_bot_cRx (6,1) double {mustBeNumeric} = ones(6,1)*0.1 % X bending Damping [Nm/(rad/s)]
      args.flex_bot_cRy (6,1) double {mustBeNumeric} = ones(6,1)*0.1 % Y bending Damping [Nm/(rad/s)]
      args.flex_bot_cRz (6,1) double {mustBeNumeric} = ones(6,1)*0.1 % Torsionnal Damping [Nm/(rad/s)]
      args.flex_bot_cz  (6,1) double {mustBeNumeric} = ones(6,1)*1e2 % Axial Damping [N/(m/s)]
      %% Top Flexible Joints
      args.flex_top_type      char {mustBeMember(args.flex_top_type,{'2dof', '3dof', '4dof', 'flexible'})} = '4dof'
      args.flex_top_kRx (6,1) double {mustBeNumeric} = ones(6,1)*5 % X bending stiffness [Nm/rad]
      args.flex_top_kRy (6,1) double {mustBeNumeric} = ones(6,1)*5 % Y bending stiffness [Nm/rad]
      args.flex_top_kRz (6,1) double {mustBeNumeric} = ones(6,1)*260 % Torsionnal stiffness [Nm/rad]
      args.flex_top_kz  (6,1) double {mustBeNumeric} = ones(6,1)*1e8 % Axial Stiffness [N/m]
      args.flex_top_cRx (6,1) double {mustBeNumeric} = ones(6,1)*0.1 % X bending Damping [Nm/(rad/s)]
      args.flex_top_cRy (6,1) double {mustBeNumeric} = ones(6,1)*0.1 % Y bending Damping [Nm/(rad/s)]
      args.flex_top_cRz (6,1) double {mustBeNumeric} = ones(6,1)*0.1 % Torsionnal Damping [Nm/(rad/s)]
      args.flex_top_cz  (6,1) double {mustBeNumeric} = ones(6,1)*1e2 % Axial Damping [N/(m/s)]
      %% Relative Motion Sensor
      args.motion_sensor_type char {mustBeMember(args.motion_sensor_type,{'struts', 'plates'})} = 'struts'
      %% Actuators
      args.actuator_type char {mustBeMember(args.actuator_type,{'2dof', 'flexible frame', 'flexible'})} = 'flexible'
      args.actuator_Ga  (6,1) double {mustBeNumeric} = ones(6,1)*1 % Actuator gain [N/V]
      args.actuator_Gs  (6,1) double {mustBeNumeric} = ones(6,1)*1 % Sensor gain [V/m]
      % For 2DoF
      args.actuator_k   (6,1) double {mustBeNumeric} = ones(6,1)*0.35e6 % [N/m]
      args.actuator_ke  (6,1) double {mustBeNumeric} = ones(6,1)*1.5e6 % [N/m]
      args.actuator_ka  (6,1) double {mustBeNumeric} = ones(6,1)*43e6 % [N/m]
      args.actuator_c   (6,1) double {mustBeNumeric} = ones(6,1)*3e1 % [N/(m/s)]
      args.actuator_ce  (6,1) double {mustBeNumeric} = ones(6,1)*1e1 % [N/(m/s)]
      args.actuator_ca  (6,1) double {mustBeNumeric} = ones(6,1)*1e1 % [N/(m/s)]
      args.actuator_Leq (6,1) double {mustBeNumeric} = ones(6,1)*0.056 % [m]
      % For Flexible Frame
      args.actuator_ks (6,1) double {mustBeNumeric} = ones(6,1)*235e6 % Stiffness of one stack [N/m]
      args.actuator_cs (6,1) double {mustBeNumeric} = ones(6,1)*1e1 % Stiffness of one stack [N/m]
      % For Flexible
      args.actuator_xi  (1,1) double {mustBeNumeric} = 0.01 % Sensor gain [V/m]
  end

Nano Hexapod Object 

nano_hexapod = struct();

Flexible Joints - Bot 

nano_hexapod.flex_bot = struct();

switch args.flex_bot_type
  case '2dof'
    nano_hexapod.flex_bot.type = 1;
  case '3dof'
    nano_hexapod.flex_bot.type = 2;
  case '4dof'
    nano_hexapod.flex_bot.type = 3;
  case 'flexible'
    nano_hexapod.flex_bot.type = 4;
end

nano_hexapod.flex_bot.kRx = args.flex_bot_kRx; % X bending stiffness [Nm/rad]
nano_hexapod.flex_bot.kRy = args.flex_bot_kRy; % Y bending stiffness [Nm/rad]
nano_hexapod.flex_bot.kRz = args.flex_bot_kRz; % Torsionnal stiffness [Nm/rad]
nano_hexapod.flex_bot.kz  = args.flex_bot_kz;  % Axial stiffness [N/m]

nano_hexapod.flex_bot.cRx = args.flex_bot_cRx; % [Nm/(rad/s)]
nano_hexapod.flex_bot.cRy = args.flex_bot_cRy; % [Nm/(rad/s)]
nano_hexapod.flex_bot.cRz = args.flex_bot_cRz; % [Nm/(rad/s)]
nano_hexapod.flex_bot.cz  = args.flex_bot_cz;  %[N/(m/s)]

Flexible Joints - Top 

nano_hexapod.flex_top = struct();

switch args.flex_top_type
  case '2dof'
    nano_hexapod.flex_top.type = 1;
  case '3dof'
    nano_hexapod.flex_top.type = 2;
  case '4dof'
    nano_hexapod.flex_top.type = 3;
  case 'flexible'
    nano_hexapod.flex_top.type = 4;
end

nano_hexapod.flex_top.kRx = args.flex_top_kRx; % X bending stiffness [Nm/rad]
nano_hexapod.flex_top.kRy = args.flex_top_kRy; % Y bending stiffness [Nm/rad]
nano_hexapod.flex_top.kRz = args.flex_top_kRz; % Torsionnal stiffness [Nm/rad]
nano_hexapod.flex_top.kz  = args.flex_top_kz;  % Axial stiffness [N/m]

nano_hexapod.flex_top.cRx = args.flex_top_cRx; % [Nm/(rad/s)]
nano_hexapod.flex_top.cRy = args.flex_top_cRy; % [Nm/(rad/s)]
nano_hexapod.flex_top.cRz = args.flex_top_cRz; % [Nm/(rad/s)]
nano_hexapod.flex_top.cz  = args.flex_top_cz;  %[N/(m/s)]

Relative Motion Sensor 

nano_hexapod.motion_sensor = struct();

switch args.motion_sensor_type
  case 'struts'
    nano_hexapod.motion_sensor.type = 1;
  case 'plates'
    nano_hexapod.motion_sensor.type = 2;
end

Amplified Piezoelectric Actuator 

nano_hexapod.actuator = struct();

switch args.actuator_type
  case '2dof'
    nano_hexapod.actuator.type = 1;
  case 'flexible frame'
    nano_hexapod.actuator.type = 2;
  case 'flexible'
    nano_hexapod.actuator.type = 3;
end
nano_hexapod.actuator.Ga = args.actuator_Ga; % Actuator gain [N/V]
nano_hexapod.actuator.Gs = args.actuator_Gs; % Sensor gain [V/m]

2dof

nano_hexapod.actuator.k  = args.actuator_k;  % [N/m]
nano_hexapod.actuator.ke = args.actuator_ke; % [N/m]
nano_hexapod.actuator.ka = args.actuator_ka; % [N/m]

nano_hexapod.actuator.c  = args.actuator_c;  % [N/(m/s)]
nano_hexapod.actuator.ce = args.actuator_ce; % [N/(m/s)]
nano_hexapod.actuator.ca = args.actuator_ca; % [N/(m/s)]

nano_hexapod.actuator.Leq = args.actuator_Leq; % [m]

Flexible frame and fully flexible

switch args.actuator_type
  case 'flexible frame'
    nano_hexapod.actuator.K = readmatrix('APA300ML_b_mat_K.CSV'); % Stiffness Matrix
    nano_hexapod.actuator.M = readmatrix('APA300ML_b_mat_M.CSV'); % Mass Matrix
    nano_hexapod.actuator.P = extractNodes('APA300ML_b_out_nodes_3D.txt'); % Node coordinates [m]
  case 'flexible'
    nano_hexapod.actuator.K = readmatrix('APA300ML_full_mat_K.CSV'); % Stiffness Matrix
    nano_hexapod.actuator.M = readmatrix('APA300ML_full_mat_M.CSV'); % Mass Matrix
    nano_hexapod.actuator.P = extractNodes('APA300ML_full_out_nodes_3D.txt'); % Node coordiantes [m]
end

nano_hexapod.actuator.xi = args.actuator_xi; % Damping ratio

nano_hexapod.actuator.ks = args.actuator_ks; % Stiffness of one stack [N/m]
nano_hexapod.actuator.cs = args.actuator_cs; % Damping of one stack [N/m]

Save the Structure 

if nargout == 0
  save('./mat/stages.mat', 'nano_hexapod', '-append');
end