powershell mouse move does not prevent idle mode

The solution from the blog Prevent desktop lock or screensaver with PowerShell is working for me. Here is the relevant script, which simply sends a single period to the shell:

param($minutes = 60)

$myshell = New-Object -com "Wscript.Shell"

for ($i = 0; $i -lt $minutes; $i++) {
  Start-Sleep -Seconds 60
  $myshell.sendkeys(".")
}