Error when using Matlab Function block in Simechanics (nested functions and parsing of Matlab function both error)

Question

I create a simple simulink model using Matlab Function block to calculate angles of 4 dof robotic arm using Robotic toolbox Matlab while input is x, y and z values. I used forward kinematics to calculate angles. Model and error is shown in below images:

My code is given below (which is put in matlab funcrion block):

function [theta1,theta2,theta3,theta4]=invkin(px,py,pz)
% code to find inverse kinematics solution for 4 dof rootic arm
preach = [px py pz]; % reach point of end-effector
theta1 = 0;  theta2 = 0; theta3 = 0; theta4 = 0;
% create links using D-H parameters
L(1) = Link([ 0 0 0 pi/2 0], 'standard');
L(2) = Link([ 0 .15005 .4318 0 0], 'standard');
L(3) = Link([0 .0203 0 -pi/2 0], 'standard');
L(4) = Link([0 .4318 0 pi/2 0], 'standard');
%define link mass
L(1).m = 4.43;
L(2).m = 10.2;
L(3).m = 4.8;
L(4).m = 1.18;
%define center of gravity
L(1).r = [ 0 0 -0.08];
L(2).r = [ -0.216 0 0.026];
L(3).r = [ 0 0 0.216];
L(4).r = [ 0 0.02 0];
%define link inertial as a 6-element vector
%interpreted in the order of [Ixx Iyy Izz Ixy Iyz Ixz]
L(1).I = [ 0.195 0.195 0.026 0 0 0];
L(2).I = [ 0.588 1.886 1.470 0 0 0];
L(3).I = [ 0.324 0.324 0.017 0 0 0];
L(4).I = [ 3.83e-3 2.5e-3 3.83e-3 0 0 0];
% set limits for joints
 L(1).qlim=[deg2rad(-160) deg2rad(160)];
 L(2).qlim=[deg2rad(-125) deg2rad(125)];
 L(3).qlim=[deg2rad(-270) deg2rad(90)];
 L(4).qlim=[deg2rad(-170) deg2rad(110)];
   %build the robot model
  rob = SerialLink(L, 'name','Puma56');
  qready = [0 -pi/4 pi/4 0]; % initial position of robot
T1= transl(preach); % convert of reach point of 4x4 homogenous matrix
[qreach,err,exitflag] =  rob.ikcon(T1, qready); % find inverse kinematics with error
%rob.fkine(qreach);
theta1 = qreach(1,1);  theta2 = qreach(1,2); theta3 = qreach(1,3); theta4 = qreach(1,4);
end

How to solve these errors.

Thanks.

Answer 1

After looking closer at your code, I'll reiterate my comment - why are you doing this in Simulink? I'll make your code briefer for clarity:

function [theta]=invkin(px,py,pz)
theta = 0;
L = <const>;
preach = <const>;
rob = f(L);
qready = <const>;
T1= f(preach);
qreach = f(rob,T1,qready);
theta = qreach;
end;

So,

1. You aren't using the inputs at all.
2. You're constantly resetting theta to zero at the start of the script, so if you did happen to make the inputs time-varying, I don't think the time-varying output would be what you want because you're not progressing through time. Your script would run a complete simulation at every call.

Imagine plotting this from a Matlab script - plot(time,theta) - again, there's no time dependence here. You just have one value, theta, that describes the joint angles required to achieve the desired end effector position. Your plot would be a horizontal line.

I would imagine this might be contributing to the trouble you're having implementing the fix you were given.

Answer 2

In Simulink the Matlab embedded function block supports only a subset of the available commands in Matlab. If you want to use external functions, you have to declare these using coder.extrinsic().

If the problem is with nested functions and not with declaring the external function, you could try to de-nest the function, by simply deleting the 'value' function from the file it is defined in and create a new, separate file for the function on the same path. Please keep in mind that this is a workaround, not really a fix.