After I filed the patent application, can I exhibit my invention to the public, even though the 18-month period needed for the publication has not yet passed?
As soon as the patent application has been filed, you can act in the most appropriate manner, including exhibiting the invention in public even if the 18 months have not yet passed. In fact, the “veto” of showing the invention before filing the application, derives from, on the one hand, the fact that by showing it you are making it known to others and therefore it loses the requisite of novelty, and on the other hand, even by revealing it to a restricted circle of friends, there is still a risk of someone filing the patent in his name.
The period of secrecy of 18 months, or 9 depending on the cases, from the time of filing the application, even though it does not forbid showing to the public the invention, it imposes caution as any action to defend the patent can only be taken after publication of it. This means that, should anybody copy the invention during this period, the requestor could not start any legal action, but would have to first notify the whole text of the patent to whoever is copying it, and only afterwards could start a dispute.
Furthermore, for the production of identical objects made during the period of secrecy, no compensation is owed. Practically it is as if the patent does not exist for the others, even though there are sufficient methods to advance the effects of the patent against them, so protecting the inventor who could then present his own idea without the risk of losing the novelty requisite.