Varying weight of a ball with time in a Maglev system

Question

Tyler Mudge 2020-12-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/692025-varying-weight-of-a-ball-with-time-in-a-maglev-system

回答： Kyle Rawding 2021-3-17

Maglev_Model.slx

Hello, I'm trying to vary the weight of a magnetically levitated ball with time. Namely, the balls weight is supposed to suddenly chand at time t=20s by 15%. Here is the code I have so far including the initial mass of the ball (0.06 kg):

clc
clear
%% Define knowns
g = 9.81; % gravity [m/s^2]
k = 1.32435*10^-4; % Magnet force constant, [N/amp]
x_0 = 0.015; % steady state position [m]
m_0 = 0.06; % initial ball's weight [kg]
i_0 = 1; % Steady state amps, assumed from NYU experiment [amp]
%% Define variable parameters
i = 1;
R = 10; % From NYU experiment [Ohm]
L = 0.4125; % Inductance from NYU experiment [Henry]
%% Checking Current System Stability
a = (2*k*i_0)/(m_0*x_0^2); % num of TF
b = (2*k*i_0^2)/(m_0*x_0^3); % part of den for TF
num = [a];
den = [1 0 b];
sys = tf(num,den)
% step(sys,t)
%% Simulate Model
maglev_sim = sim('Maglev_Model.slx');
%% Plotting m = 0.06 kg response
figure(1)
plot(maglev_sim.maglev,'LineWidth',2)
title('Position Response for m = 0.06kg')
ylabel('Position (m)')
xlabel('Time (s)')
%% Changing mass with time

The Simulink model is attached. So far I have been able to achieve the desired output of the ball's position being 0.015 m away with the original mass of 0.06 kg but now I need to change the mass with time and have the system still keep the ball at that position.

Any help is appreciated!

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Answer 1

Kyle Rawding 2021-3-17

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/692025-varying-weight-of-a-ball-with-time-in-a-maglev-system#answer_650642

Hi -

It sounds like you're interested in updating your transfer function as the simulation runs to account for the changing mass, rather than defining static 'a' and 'b' constants.

I'd recommend taking a look at the accepted answer to this question:

https://www.mathworks.com/matlabcentral/answers/10373-dynamic-transfer-function-in-simulink

Hope that helps!

-Kyle