[Tex/LaTex] Adding space between text and footnote rule

Question

How I can change the distance between the text and footnote rule in this example:

\documentclass[11pt]{book}
\RequirePackage{luatex85}
\usepackage[paperwidth=140mm,paperheight=210mm,top=25mm,bottom=20mm,left=20mm,right=20mm,heightrounded]{geometry}
\usepackage{kantlipsum}

\addtolength{\footskip}{22mm}
\makeatletter
\def\footnoterule{\kern-3mm\kern-3\p@
  \hrule \@width 2in \kern 2.6\p@
  \kern 3mm}
\makeatother

\begin{document}

Some text\footnote{Footnote example}
\kant[1-3]
\end{document}

Answer 1

With the option footnotesep, at best (like the default) with a bit shrink and stretch:

\documentclass[11pt]{book}
\RequirePackage{luatex85}
\usepackage[paperwidth=140mm,paperheight=210mm,top=25mm,bottom=20mm,
         left=20mm,right=20mm,heightrounded,
         footnotesep=3cm plus 4pt minus 4pt %<--- change to a suitable value
         ]{geometry}
\usepackage{kantlipsum}

\addtolength{\footskip}{22mm}
\makeatletter
\def\footnoterule{\kern-3mm\kern-3\p@
  \hrule \@width 2in \kern 2.6\p@
  \kern 3mm}
\makeatother

\begin{document}

Some text\footnote{Footnote example}
\kant[1-3]
\end{document}