Call to a member function validate() on a non-object using own library

Hi;

Why do I get these error?

1 -

Code:

A PHP Error was encountered

Severity: Notice

Message: Undefined variable: CI

Filename: libraries/Generate_token.php

Line Number: 15  ( Line 15 is $CI->validate($token);)

2 - http://grab.by/E7A2

Main controller:

PHP Code:

$this->load->library('generate_token');
     echo $token = $this->generate_token->generate(); 


Library:

PHP Code:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
//Custom error handling
class Generate_token  
{
    public function __construct()
        {
            $CI =& get_instance();
        }
      
    public function generate()
        {
            $raw_random_bytes = mcrypt_create_iv(6, MCRYPT_DEV_URANDOM);
            $encoded_random_bytes = base64_encode($raw_random_bytes);
            $token = strtr(trim($encoded_random_bytes, '='), array('+' => '-', '/' => '_'));
            if($CI->validate($token)==$token)
                {
                    return true;
                }
        }
    public function validate($token)
        {
            $sql = "SELECT id FROM url_tokens WHERE short_url = ?";
            $query = $CI->db->query($sql, array($token));
            if($query->num_rows==0)
                {
                    return $token;
                }
            else
                {
                    $CI->generate();
                }    
        }    
} 


Cheers