Code for 2R Robotic Arm using MATLAB

Objective

• To write a program to simulate the forward kinematics of a 2R Robotic arm
• To create a video/animation of the plot result.

Theory

• A robotic arm is a mechanical arm with 2 links that move at various angles in order to satisfy the commands of the user.
• The links of such an arm are connected with joints allowing either linear or rotational motions.
• For this challenge, we consider a 2R Robotic arm. The 2R means an arm with 2 rotations. ie, it has 2 links that work over a two-dimensional plane.
• Also, both links are restricted to a 90`degree` of rotation with reference to the axis.

• Let, L1 & L2 be the lengths of link-1 & link-2 Respectively.
• Let, theta1 be the angle formed by link-1 with horizontal.
• Let, theta2 be the angle formed by link-2 with horizontal.
• Let, the starting and end co-ordinates of link-1 be (x₀, y₀) and (x₁, y₁)
• Let, the starting and end co-ordinates of link-2 be (x₁, y₁) and (x₂, y₂)

Code explanation

• The program is executed using the program language Matlab(trial version).
• The program is started by adding comments to explain the program
• The commands close all, clear all, and clc are used.
• the input variables are added and defined like L1 and L2.
• values are provided for theta1 and theta 2 using linspace command for theta=0 to 90 degrees for 10 values.
• using the 'for' command for adding the values for the desired variable
• using the 'for' command again to add movement to the 2nd arm.
• providing the equation for defining the co-ordinates for x,x2,y1,y2.
• plotting all the coordinate values.
• Use the pause command to slow down the video/plot to make the movements more understandable.
• ending the 'for' loop twice.
• using the movie commands to combine all the figures saved to make an animation movie.
• using the video writer command to name the file being saved.
• saving the movie file in a .avi format.

Matlab code

% formula for forward kinematics of a robotic arm manipulator

close all
clear all
clc

%inputs
l1=1
l2=0.5
ct=1

theta1= linspace(0,90,10);
theta2= linspace(0,90,10);

for i=1:length(theta1)
    THETA1=theta1(i);
    for j=1:length(theta2)
        THETA2=theta2(j);
        x0 = 0;
        y0 = 0;

        x1=l1*cosd(THETA1);
        y1=l1*sind(THETA1);

        x2=x1 + l2*cosd(THETA2);
        y2=y1 + l2*sind(THETA2);

        %plotting
        plot([x0 x1],[y0 y1],[x1 x2], [y1 y2],'linewidth',3);
        axis([-0.1 1.5 0 1.5]);
        pause(0.03)
        M(ct)= getframe(gcf);
        ct= ct+1;
    end
end
movie(M)
videofile=VideoWriter('forward_kinematics.avi','uncompressed AVI');
open(videofile);
writeVideo(videofile,M);
close(videofile)

Errors, command window and workspace.

• No errors were found in the command window.
• Use of the semi-colon(;) in the code results in fewer outputs in the command window.

Results

• Thus the simulation for 2R Robotic arm was coded using Matlab and also a movie/animation was obtained from the plots.

Below is the link for the given program output animation posted and uploaded on youtube

https://youtu.be/dxIvlOW1c-8