The sentence containing the 役に立つ in question: お年寄りや体に障害がある人の介護などの役に立つ新しい機械の展示会が東京ビッグサイトで始まりました。
First, my attempt at translation: "On a Tokyo-big-website(???) the exhibition of a new machine, which is useful for nursing the elderly and physically impeded, has begun."
First, I don't really know what to make of this 東京ビッグサイト. It is not the focus of this question, but unfortunately I couldn't make much sense of it (is this really just a "websiteexhibition"???) and therefore its translation is really botched...
So now, let's turn to the thing that really matters: 役に立つ. At first, when I looked at 介護などの役に立つ I wondered about the の connecting the "verb" 役に立つ and the nominal phrase. Then I thought about the fact that 役に立つ, although usually just translated as some kind of special copula "being useful", is actually a phrase consisting of the noun 役 and the verb 立つ. So, if I literally translated this part in isolation 介護などの役に立つ the result would be => "it stands in service of elderly care".
Does 役に立つ work that way? If it did, it would make perfect sense to me because A it expresses the meaning „being of use“ and B it would perfectly suit the usual function of の to make the preceding noun the attributing of the following noun.