If your bird is living alone this behavior could be the result of sexual frustration. If you are able, slowly introduce a partner for your bird. Some folks say a mirror will help but then you have your bird rubbing his beak on the mirror all the time!
On the other hand, you bird needs attention. Toys, although helpful, do no give the attention a hand-raised bird craves. If your pet has learned beak rubbing will make you stop what you are doing and turn to him he is rewarded for his behavior and will continue this behavior to gain attention. Make sure his cage is in a quiet area and if near a window. Provide a place in the cage that will provide him a comfort zone just in case something scary (cat, other bird) appears at the window.
So, what to do? As suggested another bird will help, otherwise you'll have to start spending hands on time with your bird. Don't reward you bird when he's beak rubbing the cage bars. Give your bird attention when he's doing an appropriate behavior. Remember, pet birds are not animals you can simply throw in the back yard when they get on your nerves. They are living creatures evolved to have a close relationship with their kind. They crave attention and even wild-caught parrots can learn to love their human caretaker if that person takes the time to understand their pet's need.
Pet parrots do need attention and if they don't get attention you will see strange/repetitive behaviors such as weaving, beak rubbing, or excessive grooming leading to plucking. You gotta take the time to make your bird happy.
And it is always a good idea to consult with an avian vet to make sure you bird is not suffering from a physical issue.
Good luck and enjoy your Conure!