Codeigniter วนลูปเพื่อสร้าง กราฟ ด้วย jpGraph ครับ ทำไมมันสร้างได้แค่อันเดียวครับ

<?php if( !defined('BASEPATH')) exit('No direc script access allowed');

class Test extends CI_Controller{

	function __construct(){
		parent::__construct();	
		require_once PUBPATH.'jpgraph/jpgraph.php';
		require_once PUBPATH.'jpgraph/jpgraph_pie.php';
		require_once PUBPATH.'jpgraph/jpgraph_pie3d.php';
	}
	
	function index(){
					
			for($i=0; $i<=3;$i++){
				
				@unlink(PUBPATH.'chart/img'.$i.'.jpg');
				
				// Some data
				$data = array(20,27,45,75,90);
				
				// Create the Pie Graph.
				$graph = new PieGraph(800,450);
				$graph->SetShadow();
				
				// Set A title for the plot
				$graph->title->Set("Pie Graph");
				$graph->title->SetFont(FF_VERDANA,FS_BOLD,18); 
				$graph->title->SetColor("darkblue");
				$graph->legend->Pos(0.1,0.2);
				$graph->legend->Pos(0.9,0.9,'left','bottom');
				$graph->legend->SetLayout(LEGEND_VERT);
				
				// Create pie plot
				$p1 = new PiePlot3d($data);
				$p1->SetTheme("earth");
				$p1->SetCenter(0.4);
				$p1->SetAngle(20);
				$p1->value->SetFont(FF_ARIAL,FS_NORMAL,12);
				$p1->SetLegends(array("Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct"));
				
				$graph->Add($p1);
				$graph->Stroke(PUBPATH.'chart/img'.$i.'.jpg');
				
			}			
	}

}