This is a very important battle in the preseason right now. Worilds is MIA with his injured wrist and by his own report was planning on being back within a couple months (that was back the spring). He's still week to week and Tomlin has no updates other than that.
Carter and Robinson are battling it out, each getting regular playing time in place of Harrison. Carter started last week and probably will do so this week. He's got the edge over Robinson right now based on experience and ability. Robinson is raw but is showing flashes of a very nice skill set. If he makes the team he can learn for a year or two and perhaps become a force in the future.
It sucks for Worilds, this man could have put a strangle hold on the OLB position had he been able to be in the offseason workouts and in camp. Keith Bulter has said many times that he needs to get Worilds back on the field. His absence puts a serious depth strain on the outside, just like last year.