Research is a constant throughout the invention development process.
Obviously, a prototype will be required to prove and develop your invention. You will want to determine what your invention will cost to place in the hands of an end user.
Some of these costs would include materials, labor and packaging. You will have to determine what someone would pay as a purchase price for your product. All of this requires constant research.
Although initial research may indicate that your invention may have the potential to be a profitable commercial success, it's important to realize that invention development can take months, if not years, to complete and that much can change during that period of time.
So while you're focused on your invention, new materials can emerge, new technologies can arise, new patents can be issued, and economic, political or demographic factors could change, which may potentially effect what you're doing with your invention.
Research continues throughout the invention development process because new information may help you, or it could possibly interfere with your success.
Many inventors "believe" they know what the market wants but the reality is often different. Short of having a long list of existing satisfied buying customers, everything is an assumption when it comes to your invention.
But these assumptions can be more plausible if you have conducted consumer surveys, or have polled manufacturers and distributors for information. This can provide details about your pricing, design and development costs.
You may discover a manufacturing method or material that will have a major impact upon your design. Sourcing the cost and availability of workable components can be critical.
You don't want to develop your invention with components that are to be discontinued or subject to escalating costs or long delays in availability.