Intervention\Image 怎么保存多张图片

$img = Image::make($u_img->getRealPath());

$path = $_SERVER['DOCUMENT_ROOT'] .'/Uploads/cms_uploads/'. date('Ymd').'/';
if(! file_exists( $path) && ! $this->file->isWritable($path)) {
    $this->file->makeDirectory($path, 0777, true);
}


$file_name = date('ymdHis').mt_rand(10000, 99999);

$name_thumb = "{$path}{$file_name}_thumb.jpg";
$name_medium = "{$path}{$file_name}_medium.jpg";
$name_large = "{$path}{$file_name}.jpg";

$img_large = $img->encode('jpg');
$img_medium = $img->resize(240, 180)->encode('jpg');
$img_thumb = $img->resize(120, 90)->encode('jpg');

$img_thumb->save($name_thumb);
$img_medium->save($name_medium);
$img_large->save($name_large );

最后保存的三张图片全是120*90 的. 在不用image/cache 的情况下怎么处理