How to include a "time delay" in a simscape custom code [Matlab 2015a]

I created a SimScape custom component that implements an externally commanded brake on my rotational degree of freedom. I modified the rotational friction block to respond to an external signal who applies the friction torque instantaneously.

Now, I would like to apply this braking friction gradually within a certain time. In Matlab2017b, I believe that it is fairly straightforward to do with the new events feature. However we are currently locked-up to 2015a, so I am trying to find a way to do something similar.

Anyone has a tip?

In summary, when A becomes active, I want to ramp the friction from 0 to Max in a specified time TAU.

Thanks

[Birdman]

Can you share your model in R2015a?

Answer 1

[Francois Godin]

Good day!

I found how to do what I wanted! It was a bit of a stretch, but it seems to works well! For the benefit of the community, here is my solution:

component test 
% Delayed Ramp 
  inputs
    A = { 1.0, '1' }; % A:left
  end
  outputs
    B = { 0.0, '1' }; % B:right
  end   
  parameters    
    Ts = {0.05, 's'};                  % delay value
  end
  variables
    x = { 0.0, '1' };
    E = { 0.0, '1' };
  end
  function setup
    if Ts <= 0
        pm_error('simscape:GreaterThanZero','Time Constant Ts' )
    end
  end

    equations
      E == A - delay(A,Ts,History = 0);   % change occured in the past Ts sec
      if E > 0.5                          % A changed from 0 to 1
          x.der == 1/Ts;
      elseif E < -0.5                     % A changed from 1 to 0
          x.der == -1/Ts;
      else    
          x.der == 0;                     % no changes
      end    
      B == x;       %  When A changes, B will ramp up to A within Ts seconds
    end
  end

Answer 2

[Francois Godin]

      _Component rotbrake 
      % Rotational Brake 
      % The block applies friction in the contact between rotating bodies as a 
      % specified torque within a certain time delay.
      % The friction force is simulated as a function of relative velocity and 
      % assumed to be the sum of Coulomb, and viscous components. 
      % Connections R and C are mechanical rotational conserving ports. 
      % The block positive direction is from port R to port C. This means that if 
      % port R velocity is greater than that of port C, the block transmits 
      % torque from port R to port C.
      %
      %  By default, the brake is engaged and requires an external command
      %  to be de-energised.  (based on rotational friction block)
      %
      % Time delay is not yet implemented

      nodes
          R = foundation.mechanical.rotational.rotational; % R:left
          C = foundation.mechanical.rotational.rotational; % C:right
      end

      inputs
          A = { 1.0, '1' }; % A:left
      end

      parameters
          Col_trq = { 20, 'N*m' };            % Brake friction torque
          Ts = {0.002, 's'};                  % Brake delay
          visc_coef = { 0.001, 'N*m*s/rad' }; % Viscous friction coefficient
          vel_thr = { 1e-4, 'rad/s' };        % Linear region velocity threshold
      end

      parameters (Access=private)
          brkwy_trq_th = { 20, 'N*m' };   % Breakaway torque at threshold velocity
      end

      variables
          t_in = { 0, 'N*m' };     % Brake active torque
          t_out = { 0, 'N*m' };    % Brake reacting torque
      end

      function setup
          % Parameter range checking
          if Col_trq <= 0
              pm_error('simscape:GreaterThanZero','Coulomb friction torque' )
          end
          if visc_coef < 0
              pm_error('simscape:GreaterThanOrEqualToZero','Viscous friction coefficient')
          end   
          if vel_thr <= 0
              pm_error('simscape:GreaterThanZero','Linear region velocity threshold')
          end
          if Ts < 0
              pm_error('simscape:GreaterThanZero','Brake (de)energizing delay')
          end   
          % Computing breakaway torque at threshold velocity
          brkwy_trq_th = visc_coef * vel_thr + Col_trq;
      end

      branches
          t_in  : R.t -> *;
          t_out : C.t -> *;
      end

      equations
          if (A >= 0.5)
              if (abs(R.w) <= vel_thr)
                  % Linear region
                  t_in == brkwy_trq_th * R.w / vel_thr;
              elseif R.w > 0
                  t_in == visc_coef * R.w + Col_trq;
              else
                  t_in == visc_coef * R.w - Col_trq;
              end
          else
              t_in == 0;
          end  
          t_out == -t_in;
      end
      end_

---------- Essentially, what I want is that the friction is not applied instantaneously, but linearly ramped in within a specified deltaT. Col_trq*x where range from 0 to 1 within DT sec.

I have external workarounds for this, but I'd like to figure out a clean way of doing this within the block.