Question: A patent expired for a device. I improved it drastically. Can I patent my new device and be protected?
I found a basic patent for a device from 1990. I developed a new device with great improvements and updated for technological advances but its utility is identical in purpose to the original device.
Answer: Whether you can patent your new device depends on whether 1) someone else has previously made the same invention or, if not, whether 2) your invention is an obvious design in view of what has been invented before your invention.
Simply because your invention and the old design have the same utility does not necessarily mean you cannot get a patent. However, the more changes and more improvements you have made over the old design improves the likelihood of you getting a patent.