FPDF จะทำ title ของรายงานแต่ละหน้าแต่ติด error ค่ะ : Fatal error: Call to a member function Output() on a non-object

<?php
require('fpdf.php');

class PDF extends FPDF
{


$strSQL = "SELECT i.inventory_id, p.pro_name, b.brand_name, i.qty_available, i.all_income, i.unitCost, (i.all_income*i.unitCost) as total1 FROM inventory i, product p, brand b where p.inventory_id = i.inventory_id and p.brand_id = b.brand_id"; 
$objQuery = mysql_query($strSQL);
$rows = mysql_num_rows($objQuery); 
if(rows>35){ 
$pdf=new PDF();

$header=array('Inventory ID','Product Name','Brand','Available','Income','Cost','Amount');
$pdf->SetMargins(10,2,10);//กำหนด Margin

$strSQL = "SELECT i.inventory_id, p.pro_name, b.brand_name, i.qty_available, i.all_income, i.unitCost, (i.all_income*i.unitCost) as total1 FROM inventory i, product p, brand b where p.inventory_id = i.inventory_id and p.brand_id = b.brand_id Limit 0,35";
$objQuery = mysql_query($strSQL);
$resultData = array();
for ($i=0;$i<mysql_num_rows($objQuery);$i++) {
	$result = mysql_fetch_array($objQuery);
	array_push($resultData,$result);
}
//*** Table 1 ***//
$pdf->AliasNbPages( 'tp' );
$pdf->AddPage();
$pdf->SetFont('Arial','',10);
$pdf->Image('images\header\logo-inventory.png',30,8,150);
$pdf->Ln(35);
$pdf->FancyTable($header,$resultData);


}else if(rows>35 && rows<=85){
   $strSQL1 = "SELECT i.inventory_id, p.pro_name, b.brand_name, i.qty_available, i.all_income, i.unitCost, (i.all_income*i.unitCost) as total1 FROM inventory i, product p, brand b where p.inventory_id = i.inventory_id and p.brand_id = b.brand_id Limit 35,85"; 
$objQuery1 = mysql_query($strSQL1);
$resultData1 = array();
for ($i=0;$i<mysql_num_rows($objQuery1);$i++) {
	$result1 = mysql_fetch_array($objQuery1);
	array_push($resultData1,$result1);
}
//*** Table 2 ***//
$pdf->AliasNbPages( 'tp' );
$pdf->AddPage();
$pdf->SetFont('Arial','',10);
$pdf->Image('images\header\logo-inventory.png',30,8,150);
$pdf->Ln(35);
$pdf->FancyTable($header,$resultData1);
}else if(rows>85 && rows<=135){
$strSQL2 = "SELECT i.inventory_id, p.pro_name, b.brand_name, i.qty_available, i.all_income, i.unitCost, (i.all_income*i.unitCost) as total1 FROM inventory i, product p, brand b where p.inventory_id = i.inventory_id and p.brand_id = b.brand_id Limit 85,135"; 
$objQuery2 = mysql_query($strSQL2);
$resultData2 = array();
for ($i=0;$i<mysql_num_rows($objQuery2);$i++) {
	$result2 = mysql_fetch_array($objQuery2);
	array_push($resultData2,$result2);
}
//*** Table 3 ***//
$pdf->AliasNbPages( 'tp' );
$pdf->AddPage();
$pdf->SetFont('Arial','',10);
$pdf->Image('images\header\logo-inventory.png',30,8,150);
$pdf->Ln(35);
$pdf->FancyTable($header,$resultData2);
}else if(rows>135 && rows<=185){
$strSQL3 = "SELECT i.inventory_id, p.pro_name, b.brand_name, i.qty_available, i.all_income, i.unitCost, (i.all_income*i.unitCost) as total1 FROM inventory i, product p, brand b where p.inventory_id = i.inventory_id and p.brand_id = b.brand_id Limit 135,185"; 
$objQuery3 = mysql_query($strSQL3);
$resultData3 = array();
for ($i=0;$i<mysql_num_rows($objQuery3);$i++) {
	$result2 = mysql_fetch_array($objQuery3);
	array_push($resultData3,$result3);
}
//*** Table 4 ***//
$pdf->AliasNbPages( 'tp' );
$pdf->AddPage();
$pdf->SetFont('Arial','',10);
$pdf->Image('images\header\logo-inventory.png',30,8,150);
$pdf->Ln(35);
$pdf->FancyTable($header,$resultData3);
}


$pdf->Output();
?>