Mechanical assembly mate...pls help

Hi guys...

I have a problem on creating 1 simple mechanism which involve 'mechanical mate' feature as I guess. I tried to put on 'cam mate' to this assembly but it   seems not following the slot. It is such as simple cam rotation.

As I applied a standard mate, the shaft in the slot fixed itself in the slot that can make it as a main reference. But this shaft need to move along the slot that can cause a short movement to the bigger part. Can anybody explain to me, what type of mate I can apply on the assembly?

SolidworksAssemblies