Hi Anteneh Tadesse Yitbark,

Since you didn't provide sufficient info about your model and the controller, the natural explanation for this is that the sliding mode control system requires persistent excitation through the system input.

here is the output i get when i gave ramp and step input to my ISMC of robot arm respectively.

Hi Anteneh Tadesse Yitbark,

I don't see any 'error' problem with the results. Those are transient nature of the output responses. Try plotting both the step error response and the ramp error response under the same scale, and you should be able to learn something.

here is my ramp input i don't know how to create an equivalent step input. if you can help me please

Hi Anteneh Tadesse Yitbark,

Please plot the step error signal and ramp error signal, NOT the comparison between the input signal and output signal.

i will send the whole model to your email. please help me with that. thanks

Hi Anteneh Tadesse Yitbark,

As mentioned previously, there seemed to be no problem with your results. Please specify the exact parts of your project which you had difficulty in. If you want to compute the error as suggested, then here is the algorithm:

Error, xe(t) = x(t) − xref(t),

where xref is the reference state.