Seite - 24 - in Proceedings of the OAGM&ARW Joint Workshop - Vision, Automation and Robotics

Fig. 5. Stepper motor with threaded shaft as tuning device C. DC gearbox drives As a smaller and cheaper alternative to stepper motors DC gearbox motors were explored. Thereby the structure with a threaded shaft, as in the last section on stepper motors, should be used. Due to the gear reduction such a motor could be significantly smaller. Also the drive electronics would be simpler to implement. V. PRACTICAL REALIZATION In the following section the implemented solution is described in detail. A. Implemented drive technology Owing to the fact, that the last described drive technology with a gearbox motor seems to be the best one, it was chosen to build a prototype and for further evaluation. An appropriate gearbox motor was available, wherefore this drive was used for a first prototype (Fig. 6). For testing the prototype, software, which will be described in section V- C, was developed in parallel. With the experimental setup, first successes in tuning the pipe were achieved. Nonethe- less searching for alternative gearbox drives was continued, whereby a very compact and cheap gearbox motor was found, which is perfectly suited to the tuning application. This drive already has a threaded metric output flange. Furthermore, there is an alternative ”‘Flip-Type”’ of this Fig. 6. First prototype with gearbox motor Fig. 7. Prototypes with compact gearbox motors motor available. Thereby the input and output shaft are on the same side of the gearbox. This allows a more compact design and the reduction of the distance between the tuning spring and the threaded shaft. In Fig. 7 prototypes with both kinds of motors are pictured. Note that the left prototype contains the same pipe as in Fig. 6 to enable one to see the difference in size. To transform the rotating movement of the spindle into translation for the tuning spring, an adapter component of high-strength plastic was manufactured. In this component the tuning spring is fixed with a grub screw. If this single screw is loosened, the pipe can be tuned manually without disassembling the automatic tuning system. Thus an excellent, mechanical solution for the tuning system was found. Because of the low thread pitch, high precision positioning in micrometre range creates no problems for this actuator system. Additionally, the high gear reduction results in a very low drive torque needed for the motor. Performed force measurements showed, that the solution can generate about 60N, which is 10-times more than required. To move the tuning spring and correct the pitch of the pipes, a control loop is necessary. This loop must contain the final control element or actuator, which executes the calculated move, frequency detection and a logic unit or software, which processes the frequency measurements. In Figure 8 such a control loop is depicted. Fig. 8. Control circuit for automated pipe tuning 24