When applying for a patent, can I cite an existing patent?

For the published technical scheme, whether it is applied by yourself or by others, just quote the patent number directly and then indicate it. As for the undisclosed part, if the part cited by your whole machine can be a prior patent or other existing ones, a brief explanation is enough. If the designation is a prior application and is not published, it is best to quote it all. One way is to say it briefly in the background, and the specific structure is described in detail in the embodiment, so there is no need to repeat the description.