Page - 23 - in Proceedings of the OAGM&ARW Joint Workshop - Vision, Automation and Robotics

III. STATE OF THE ART At the beginning of this project an extensive market and patent review was done to find out, if any similar applica- tions are already on the market. Thereby a few patents for automated organ tuning were found belonging to the German organ builder Voigt ([5], [7] and [6]). Furthermore, a project within the framework of a bachelor thesis by Fachhochschule Kiel [2] was found. But in contrast to the idea of automating the tuning process for reed pipes all these applications are developed to modify the pitch of flue pipes, whereby these projects are primarily concerned with conceptual studies. The company Rieger Orgelbau [1], which was the main cooperation partner for this project, has developed a system, which allows the tuning person to control the organ with a smartphone app. Specifically it is possible to play the keys of the organ via the smartphone, so the second person is no longer needed. This system represented the newest state of technology at the beginning of this project. If an actuator, which should be developed in the course of this project, would be combined with this system, a fully automated tuning application would be established. IV. ACTUATOR RESEARCH Following the analysis of the mentioned system a research on actuators was performed. Thereby the most important criteria were cost efficiency and space requirements. Fur- thermore the components and structure of reed pipes should not be modified, or if it is unavoidable, as little as possible. This would make it feasible to upgrade already existing organs with the tuning system. Before the research took place, force investigations on various tuning springs on three different pipes of different size were conducted to determine, how much force an actuator should be able to apply. The highest value which was measured was 6,0N. Including an appropriate safety surcharge for the following research a minimum guide value of 10N was defined. A. Piezoelectric drives Because of the required precision, piezoelectric drives were examined as a first step. One possible new type of piezo drive is the motor X15G (Fig. 2) from Elliptec [3]. If the piezo crystal inside this actuator is driven by the natural resonant frequency of the whole actuator, the rotor begins to move forward. With a second specific frequency the motor could also be moved backwards. According to the datasheet Fig. 2. Piezo motor X15G; 1...wires, 2...piezo ceramic, 3...resonator, 4...spring, 5...rotor [3] Fig. 3. Piezomike [4] Fig. 4. Piezomike implemented on reed pipe the drive can also be used as a linear actuator, whereby the drive could be attached directly to the tuning spring to move it up or down. Unfortunately, it became apparent that this drive can only raise 1.2N, which is much too little for this application. A second piezoelectric drive, which was investigated, is the Piezomike (Fig. 3) from PI GmbH [4]. With 20N thrust, it would be strong enough for the tuning application. The piezo crystal inside the actuator is expanded slowly because of the controlled increase of voltage, whereby the gripper starts rotating the screw. If the final position is reached, the voltage is switched off and the gripper goes back to the starting position jerkily without moving the screw. Right side of Fig. 4 shows a schematic diagram for a possible implementation on a reed pipe with a spring, whereby the tuning spring is pulled against the Piezomike. A resulting advantage with this kind of drive would be the possibility to tune the pipe manually through rotation of the screw shaft without disassembling the tuning system. Unfortunately the highpriceof500$/pcs. inhibits theapplication in thisproject. B. Stepper motors Because of the possibility of fine positioning of stepper motors, these drives were investigated following the piezo drives. Stepper motors with premounted threaded-spindle shafts were examined in detail. A possible application is illustrated in Fig. 5. The spindle nut in combination with a connected adapter part transforms the rotation into transla- tional movements for the tuning spring. This solution could bring up the required forces, but because of the centric motor shaft and the frame size of a stepper motor this motor type would not fit between the pipes. 23