Translate function

I had the code
test =" not(preceding-sibling::*[self::aaa][bbb]/bbb/ccc/@ddd=$zzz)"
which was working fine. But i wanted to make this case-insensitive.
$zzz is always in lower case. So i used translate to make left-hand side
of expression lower-case.

This was not giving the expected  result
not(translate(preceding-sibling::*[self::aaa][bbb]/bbb/ccc/@ddd,
$uppercaseAlphas, $lowercaseAlphas)=$zzz)

but this is
not(preceding-sibling::*[self::aaa][translate(bbb/ccc/@ddd,
$uppercaseAlphas, $lowercaseAlphas)=$zzz])