How do you detect a physical collision of a robot arm with an unexpected obstacle?

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I am using ROS kinetic with the moveit cpp interface. I am working on a robot arm motion controller. I want to handle collisions with undetectable obstacles. Does the moveit framework have a way of doing this? Like a tolerance of how much the needed effort deviates from the expected effort? Or even a maximum allowed effort would do the trick. It seems like the only thing causing the plan execution to fail is not reaching the goal in time.