Under the U.S. Copyright
Act, the worker could sue for copyright infringement
to the extent that any of the drawings, models or manufacturing specs are copied. Unfortunately, proving that copies were made could be difficult or impossible until such time as the product is manufactured and distributed -- at which point the marketing, data sheets, installation instructions, etc., may demonstrate that copies were made, and then a copyright infringement action could be possible.
Alternatively, the worker could sue immediately and ask for a preliminary injunction to prohibit any copies from being made.
If the device is unique and nonobvious (i.e., patentable), and not yet being marketed for sale, then the worker could immediately apply for a patent
, and thereby prevent the company from selling the product without paying all profits to the worker. If the device is already being marketed, and thus published, then no patent is possible, which would prevent the use of the patent to protect the worker.
The worker could sue for "quantum meruit," which is the reasonable value of services rendered. This is an arguable point, because the company willa rgue that the worker's time is work at most a few hundred dollars an hour, while the worker will argue that the creation of an entirely new design is worth a small fortune. It would be for a jury to decide. I like the worker's chances here, because a jury would be highly disposed to use an award to send a message to the company. However, the court might "remit" the award, as unreasonable, and only permit hourly fees to the worker.
Those are the basic claims. The patent would be the strongest -- but each has merit.
Hope this helps.