If I apply for an invention patent myself and suddenly feel that there is room for improvement, can I reapply for a patent on the original basis?

First of all, talk about equipment. You should know whether the improvement of your equipment is creative and novel. If so, you can apply for a patent for the improved equipment to protect your improvement. Your previous patent depends on whether it is important to you. If your improvement doesn't work, you can just give up. If the previous patent is more important, you can continue to apply. The former patent does not conflict with the latter patent. If your improvement is not creative enough, but you want to protect it, just ask for domestic priority at present, no problem.

As for the method, first of all, it depends on whether the previous patent protects the invention idea, which is the principle you said. If you protect your principles, if you reapply for a patent, the previous application will constitute a conflict application for your later application, so it is not recommended to reapply at this time, which will waste financial resources. But then again, if the prior application has consciously protected the principle, you don't need to apply for a patent for this method. In fact, whether the scheme to be protected by the inventor ranks properly is one of the methods to identify the agent level. Nowadays, many agents write whatever the inventor gives them, which is irresponsible to the inventor.