Great news! You have a patent on your invention, so you are all sorted. Unfortunately that's not quite the case. You may still have to deal with someone else's patent even if you already have a patent on your product. This is because often your innovation will be an improvement on something else, in which case you may have to deal with a dominant patent; the patent on the original innovation.
Balance bike versus pedal bike
Let me explain this using an archetypal Dutch product: the bicycle. Now suppose inventor A invented the very first bicycle on earth and nobody had ever seen one before. One that you go and sit on and propel forward by pushing your feet along the ground; a balance bike. The patent claim would then read something along the lines of a means of transport with two wheels, a handlebar, a brake and a saddle; the balance bike. The patent would remain in force for 20 years.
Next, inventor B felt that pushing your feet along the ground was rather tiring. He came up with the idea of a propulsion mechanism and added pedals and a chain to the bicycle. Needless to say he then applied for a patent on this pedal bike. The patent claim would then probably read something like a means of transport with two wheels, a handlebar, a brake and a saddle and a pedal mechanism. Inventor B's product is then a means of transport with the features of inventor A's patent. In other words, the pedal bike is an improvement on the balance bike and comes under inventor A's patent.
In this case, inventor A has a dominant patent. In theory, inventor A could therefore stop the pedal bike from entering the market. However, inventor A would not be allowed to market the pedal bike themselves. That is because it was invented by inventor B, who can stop pedal bikes with their patent.
Patent holders can end up in stalemate: will their improvements on the original invention be stopped or will the patent holders come to a mutual agreement? In many cases the latter is a win-win situation. If there is market demand for the improved developed variant there is generally also a willingness to pay more. It is therefore not unusual for a holder of a dominant patent and the party that has made the improvement to come to a financial agreement. We refer to these as cross-licences.
When an engineer elaborates on an existing invention it should therefore be clear that there could possibly be a dominant patent. They should then consider what the relationship with any competitors is like and where they operate. It is good to be aware of problems with any other patents at an early stage. Innovations require a lot of investment. So it is good to be thorough and proceed with care.
If you are dealing with innovations and want to know whether you are at risk of infringing or own a dominant patent and want advice, please feel free to contact me. I would be happy to discuss your options with you.