public static function get_instance() {

        if (self::$_entityManager === null) {
            self::initConfig();
            //setando as configurações definidas anteriormente
            $config = Setup::createAnnotationMetadataConfiguration(self::$settings['entidades'], self::$settings['isDevMod']);
            $config->addCustomStringFunction('group_concat', 'Oro\ORM\Query\AST\Functions\String\GroupConcat');
            $config->addCustomNumericFunction('hour', 'Oro\ORM\Query\AST\Functions\SimpleFunction');
            $config->addCustomNumericFunction('timestampdiff', 'Oro\ORM\Query\AST\Functions\Numeric\TimestampDiff');
            $config->addCustomDatetimeFunction('date', 'Oro\ORM\Query\AST\Functions\SimpleFunction');
            //criando o Entity Manager com base nas configurações de dev e banco de dados
            self::$_entityManager = Em::create(self::$settings['dbParams'], $config);
        }

        return self::$_entityManager;
    }