En este trabajo se presenta el control automatico de posicion de un brazo mecanico de 3 grados de libertad. Para esto se utilizaron tecnicas de vision por computador que determinan las coordenadas tridimensionales del brazo mecanico y un controlador digital RST que le permite al dispositivo ubicarse, en tiempo real, en las coordenadas enviadas a traves de un PC de forma rapida y con error nulo en estado estable. El brazo esta conformado por 3 servomotores cuyo comportamiento se registra por dos camaras webcam y analiza con un software especializado en procesamiento de video; se advierte la ventaja de utilizar las camaras como sensores: asi se logra medir las variables de posicion con precision sin adicionar carga al sistema. De esta forma se unen tecnicas de procesamiento digital de video y algoritmos de control digital para desarrollar un prototipo mecanico de posicionamiento tridimensional. In this work, it is presented a positional automatic control of a mechanical arm with 3 degrees of freedom. For this, we implemented several techniques of computer vision that determine the three-dimensional coordinates of the mechanical arm and a RST digital controller that allows the device to be located, in real time, in the coordinates sent across a PC quickly and without mistakes and in a stable state. The arm is made of 3 servomotors whose behavior is registered by two webcams and is also examined with the help of a specialized software in video processing. It is important to emphasize the advantage of using these cameras as sensors: they make it possible to measure the positional variables accurately without adding load to the system. This way, different digital video-processing techniques and digital control algorithms are combined in order to develop a mechanical prototype of three-dimensional positioning.