For something to be patentable, you have to have your application approved by the patent office (USPTO). To do this, you need to use a registered patent attorney or agent. I’m assuming rates are approximately a few thousand dollars; however, maybe if you can find an agent (who is not a lawyer), it might be cheaper. Nobody is going to be out to invalidate your patent now. What you have to do is convince the patent examiner that your application should be allowed (ie approved). The patent examiner will conduct searches and see if your invention is patentable subject matter (35 USC 101), if anything is out there that anticipates your invention (35 USC 102), or if your invention is obvious (35 USC 103). As Homeowner discussed, there are many cases out there that elucidate these standards. For something to be patentable, it has to be patentable subject matter. Since it sounds like you made an appartus (some kind of machine), then you shouldn’t have to worry about it. Anticipation is complicated, but basically you (meaning your patent agent) should conduct a search to make sure there are no patents or publications out there that disclose your invention. There are other things that might disqualify you under teh statute, such as public use, sale, etc. You don’t have to conduct a search before submitting an application, but is a very good idea, as patent applications are expensive. You also will need to make sure it is not obvious. There are also many court decisions on this: including KSR. However, the basic idea is that someone who is ordinary skill in your art (ie inventing simple household inventions) would not think it was obvious based on other inventions. While filing your patent, the main thing you have to do (or your patent agent has to do) is to convince the examiner that these sections do not apply and write up the patent in such as way that it is enabled. The only way companies get involved is if they chose to infringe your patent and then you chose to sue them or if they initiate a reexamination of your patent. Assuming you don’t have an invention worth millions, these scenarios are not likely.
You can probably use the internet to find patent agents/attorneys. You do need one if you chose to pursue a patent.