unlink does not work

You see, I have a table Photo with these values:

    Schema::create('fotos', function(Blueprint $table){
        $table->increments('id');
        $table->string('foto')->unique();
        $table->string('nombre')->unique();
        $table->date('fecha');
        $table->unsignedInteger('categoria_id'); // Forarea de Categoria.
        $table->foreign('categoria_id')->references('id')->on('categorias');
        $table->unsignedInteger('user_id'); // Foranea de User.
        $table->foreign('user_id')->references('id')->on('users');
        $table->timestamps();
    });

The variable foto is the one that stores the image, which is in public/archivo , and I access it using this variable:

public function ruta(){
    return asset("archivo/".$this->foto);
}

It turns out that I want that after deleting a photo, the image stored in the folder is also deleted. This is the function:

public function eliminar(Foto $f){
        $f->limpiarImagen();
        $f->delete();
        return back()->with('message',['success',"La foto ha sido eliminada de la base de datos"]);
}

And this is the function that removes the image from the folder:

public function limpiarImagen(){
    if(file_exists($this->ruta()))
        unlink(public_path($this->ruta()));
}

But the image is not deleted. How do I solve it?