Multiple File zip in CI

I have multiple image in folder,And i get it on Href button so how to zip that file in codeingiter

HERE is MY View Code:

Code:

<a href="<?php echo base_url()."index.php/itr1/download/".$key['pan_card']."/".$key['previous_itr'] ?>" name="images">Downalod All Attachments</a>

Here my Controller:

Code:

public function download()
{
   // File path
   $id =  $this->uri->segment(3);
   $id1 =  $this->uri->segment(4);

   $filepath1 = FCPATH.'upload/'.$id;
   $filepath2 = FCPATH.'upload/'.$id1;

   $filename = "backup.zip";
   $this->zip->download($filename);
}