How to implement a simscape cam component (variable ratio transmission)?

Hello,

I am trying to make a cam component in simscape. A cam has a fixed relation between the input shaft angle (phi_in) and the output shaft angle (phi_out). It can be regarded as a sort of variable ratio transmission, where the transmission ratio is function of the input angle. phi_out = f(phi_in); w_out = dfdphi_in(phi_in)*w_in t_in = -dfdphi_in(phi_in)*t_out

When I simulate the model, I get "Initial conditions solve failed to converge". What is the reason for this? How can I diagnose the initial conditions? If I put a spring+damper between the cam component and the cam follower inertia, the simulation works.

In the explanation for a variable ratio transmission http://www.mathworks.nl/help/physmod/sdl/ref/variableratiotransmission.html it is mentioned that the transmission ratio cannot be negative. In a cam component, the instantaneous transmission ratio crosses zero. Is this maybe the reason for the numerical problems of my cam component? I don't see how this is a problem physically. Is it a problem numerically?

Thank you!

My component looks as follows: component cam % Cam % The block represents an ideal cam. % Connections S and O are mechanical % rotational conserving ports associated with the cam input and % output shaft, respectively. %

outputs A = {0,'rad'}; % A:right W = {0,'rad/s'}; % W:right end

nodes S = foundation.mechanical.rotational.rotational; % S:left O = foundation.mechanical.rotational.rotational; % O:right end

variables t_in = { 0, 'N*m' }; t_out = { 0, 'N*m' }; phi_in = {0, 'rad'}; phi_out = {0, 'rad'}; end

function setup % Parameter range checking end

branches t_in : S.t -> *; t_out : O.t -> *; end

equations let f = 5*cos(phi_in); dfdphi_in = -5*sin(phi_in); in -dfdphi_in * t_out == t_in; dfdphi_in * S.w == O.w; phi_in.der == S.w; phi_out.der == O.w; A == f; W == dfdphi_in * S.w; end end

end