Okay, I shall try to rephrase the question. Please do keep in mind that we are talking about robots taking peoples' jobs and, in that light, wealth distribution.
Allow us to assume that a truly excellent 3D printer technology is invented in the not to distant future, such that it becomes the normal means by which most things are produced. Let us further assume that the inventors, not being idiots, patent their work. So, for 20 years, they control all the robots that produce whatever.
This kind of lead time will lead to a market force difficult to overtake. Let's consider that instead of selling the machines, they lease them for a long time (maybe forever) for a percentage of revenue . Among other things, they will own the machines that mass produce stuff, so assume that those machines are not allowed to produce other machines that 3d print stuff.
Now, this may not end up being a single firm, but let's assume that the companies involved are relatively small in number compared to the size of the planet's population.
How long into the future do you think that people will tolerate 1/2 of all the value being produced being taken by those who happened to either invent the machine or inherit from those who did.
I'm willing to grant that these mysterious machines more than double the output of a factory, so it's still better than the status quo without them. But how long until people's baseline expectations reset, and they just start refusing to pay?