problem of acceleration

I am doing a simulation that  down steps with a wheelchair.
I am using Hyperworks 2017.2.

I would like to change the step and output the acceleration for each step. However, a good waveform is not output and the value is not appropriate.

I think that it is a matter of contact penalty, but I am in trouble because I can not find a suitable penalty.

Please give me advice.
It is also possible to share the file if necessary.