how to make input to the system time variable?

Question

Min Khant 2023-10-31

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评论： Min Khant 2023-11-3

采纳的回答： Sam Chak

Screenshot 2023-10-31 at 7.26.47 PM.png

I would like to make an input that is time varying.

I have attached a photo that describe the time varying input I want.

Im a beginner. I hope someone can help me with this. Thank you

Im open to all suggestions or references that can help me learn.

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Rik 2023-10-31

I have some difficulty understanding what you actually want to achieve in terms of Matlab code. It seems like there are a few steps missing.

Have a read here and here. It will greatly improve your chances of getting an answer.

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Answer 1

Sam Chak 2023-10-31

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编辑：Sam Chak 2023-10-31

在 MATLAB Online 中打开

Okay @Min Khant, the problem is incomplete. However, you can learn by yourself using this example for tracking the desired trajectory

. Change the tau number as you wish to observe the time response of

.

tspan = linspace(0, 20, 3001); % can set tspan from 0 to π

y0 = [0; 0]; % initial values

[t, y] = ode45(@odefcn, tspan, y0);

yd = pi/2 - pi/4*cos(t); % desired trajectory

% Plots

plot(t, yd), hold on

plot(t, y(:,1)), grid on

title('Time response of \theta(t) in tracking \theta_{d}', 'fontsize', 10)

xlabel('t', 'fontsize', 10), ylabel('\theta', 'fontsize', 10)

legend('\theta_{d}', '\theta(t)', 'location', 'best', 'fontsize', 10)

% Simplified Robt dynamics

function dydt = odefcn(t, y)

dydt = zeros(2, 1);

% parameters

M = 1;

b = 1;

m = 1;

g = 1;

r = 0.16; % true value

rmeas = 0.08; % measured

kp = 1;

kd = 2;

% desired trajectory

yd = pi/2 - pi/4*cos(t);

dyd = 1/4*pi*sin(t);

ddyd = 1/4*pi*cos(t);

% tau input (3 variants)

tau1 = M*ddyd + b*dyd + m*g*rmeas*cos(yd); % so-called feedforward control

tau2 = M*ddyd + M*kd*dyd + M*kp*yd - M*kd*y(2) - M*kp*y(1) + b*y(2) + m*g*r*cos(y(1)); % perfect r

tau3 = M*ddyd + M*kd*dyd + M*kp*yd - M*kd*y(2) - M*kp*y(1) + b*y(2) + m*g*rmeas*cos(y(1)); % imperfect r

dydt(1) = y(2);

dydt(2) = (- b*y(2) - m*g*r*cos(y(1)) + tau3)/M; % <-- change the tau number

end

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Sam Chak 2023-10-31

Hi @Min Khant

Good to hear that you like Simulink. This following approach is generally more accurate than applying the differentiation block twice to get

. If you find the solution helpful, please consider clicking 'Accept' ✔ on the answer and voting 👍 for it.

Min Khant 2023-11-3

May I know how to use derivative block consecutively? sir

as i tried , it does not function properly

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Answer 2

Aquatris 2023-10-31

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You can create your own numeric integration to solve the equation and provide the desired input in each time step.

Here is an example (the accepted answer) which you can modify for your need.

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