Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

2 views (last 30 days)
AOF on 20 Jun 2020
Answered: Devineni Aslesha on 24 Jul 2020
% DH parameters using symbolic tool box
clear
clc
%%
syms theta1 theta2 theta3
R1 = [ cos(theta1), 0, sin(theta1), 0;
sin(theta1), 0, -cos(theta1), 0;
0, 1, 0, 0;
0, 0, 0, 1];
R2 =[ cos(theta2), -sin(theta2), 0, 0.1*cos(theta2);
sin(theta2), cos(theta2), 0, 0.1*sin(theta2);
0, 0, 1, 0;
0, 0, 0, 1];
R3 =[ cos(theta3), 0, sin(theta3), 0;
sin(theta3), 0, -cos(theta3), 0;
0, 1, 0, 0;
0, 0, 0, 1];
% Total Forward Matrix
A_03 = simplify(R1 * R2 * R3);
A_13 = R2 * R3;
%% inverse kinematic
Px = -0.135;
Py = -0.000;
Pz = -0.128;
A_03_ = A_03;
A_03_(1:3,4) = [Px Py Pz];
A_13_ = simplify(R1 \ A_03_);
A_23_ = simplify(R2 \ A_13_);
I = simplify(R3 \ A_23_);
%%
eq(1) = Px == A_03(1,4);
eq(2) = Py == A_03(2,4);
eq(3) = Pz == A_03(3,4);
eq(4) = A_13_(1,4) - R1(1,4) == 0 ;
eq(5) = A_13_(2,4) - R1(2,4) == 0 ;
eq(6) = A_13_(3,4) - R1(3,4) == 0 ;
eq(7) = A_23_(1,4) - R2(1,4) == 0 ;
eq(8) = A_23_(2,4) - R2(2,4) == 0 ;
eq(9) = A_23_(3,4) - R2(3,4) == 0 ;
eq(10) = I(1,4) == 0;
eq(11) = I(2,4) == 0;
eq(12) = I(3,4) == 0;
sol = solve(eq);
q(1:4,1) = double(sol.theta1);
q(1:4,2) = double(sol.theta2);
q(1:4,3) = double(sol.theta3);
I dont know why it keep sending me an error
Error in Inverse_kinematic (line 58)
q(1:4,1) = double(sol.theta1);
How should i change this:
sol =
struct with fields:
theta1: [0×1 sym]
theta2: [0×1 sym]
theta3: [0×1 sym]

Star Strider on 20 Jun 2020
The reason is that it cannot solve your system:
sol =
struct with fields:
theta1: [0×1 sym]
theta2: [0×1 sym]
theta3: [0×1 sym]
AOF on 20 Jun 2020
how should i change it ?
because in the work space it show me 1x1 sym
i am really confused
How to solve this problem ?

Devineni Aslesha on 24 Jul 2020
The reason for showing 1x1 sym for theta1 is that they are declared as symbolic variables using syms theta1. However, 0x1 sym is for struct sol fields theta1,theta2 and theta3 as it cannot solve your system.