2011 11th International Conference on Control, Automation and Systems Oct. 26-29, 2011 in KINTEX, Gyeonggi-do, Korea Harmonic modulated feedback in control to lower oscillations in mechatronic systems Peter H¨ auptle 1,2 , Peter Hubinsk ´ y 1 and Gerhard Gruhler 2 1 Faculty of Electrical Engineering and Information Technology, Slovak University of Technology in Bratislava, SK-812-43 Bratislava, Slovakia (E-mail: haeuptle@ieee.org ; peter.hubinsky@stuba.sk) 2 Faculty of Mechanics and Electronics, Heilbronn University, D-74081 Heilbronn, Germany (E-mail: gruhler@hs-heilbronn.de) Abstract: In this contribution we’ll introduce a new control structure for mechatronic drives. Such a drive combines motor, gear-box, electronics as well as control to one module. In light-weight applications like robotics as well as in general automation industry, the end-effector prone to oscillate due to a relatively low system damping. For ”transient”- effects methods like input shaping or posicast-control can reduce or even eliminate an unwanted oscillation. Additionally ”semi-stead-state”-effects can arise an oscillation two. Therefor the relatively new method of harmonic modulation can be applied. We now focus on a control structure where these techniques are joined together. In many applications the set-point generation is done by a host system (e.g. PLC) and transfered to the drive. Hence, we seek a control structure for the mechatronic drive without affecting the set-point generation process. Further, the advantage of this new structure will be shown along measurement results. Keywords: oscillation, harmonic, modulation, control 1. INTRODUCTION The method of harmonic modulation of the set-point signal was introduced here [1]. The method of input- shaping, which leads also to a changed set-point signal given to a system, was applied by [2, 3, et al.]. A similar method is namely the posicast-control where a positive cast is added to the set-point signal which was originally invented from [4]. Here we want to show a way where the harmonic modulation of the set-point signal can be changed to a modulation of a sensor-feedback (velocity sensor) in a cascaded control structure (shown in Fig. 2). Further, the validation with an experimental setup mod- eled and introduced here [5, 6] will be shown. Regarding the control of mechatronic drives (MDs), specially with harmonic drive R ⃝gear-boxes (like we also used in our ex- perimental setup) huge efforts have been made by [7, 8, 9, et al.]. But the advantage of not using an additional sen- sor (e.g. torque-, acceleration-sensors) in standard indus- try drives may show that a harmonic modulator in control can be seen as a further alternative. 1.1 Transient effects First of all, let’s consider a torsional damped spring mass system, which can be stated out to Equ. 1.  () =  1+2 ⋅  ⋅  0 +  2  2 0  =  2 ⋅  ⋅     < 1 (1) And in a more visible way in Fig. 1. Regarding to the used experimental setup the values of the parameters can be seen in Table 1. Where c is the torsional spring constant, d the damp- ing, i the gear-ratio (of the i.e. harmonic drive R ⃝(HD)) Fig. 1 P-T 2 system: Torsional damped spring mass. [6, 5] Table 1 System parameters. [6, 5] PARAMETER: VALUE: UNIT: i 1/121 - c 2409 Nm/rad d 0.54 Ns/m J  0.2132134 kg m 2 D 0.012 - f  16.918 Hz f 0 16.919 Hz f 16.917 Hz and   the overall momentum of inertia. In such a low damped system, the resonance frequency f  , the damped oscillating frequency f  (see add. Fig. 4) and the eigen frequency f 0 differs just slightly. Transient effects occur i.e. during acceleration or deceleration of a movement when having such a lightly damped system [6, 5]. 1.2 Semi-steady-state effects Semi-steady-state effects can occur in a MD when moving with a constant velocity (which means not in transient mode). These effects (e.g. kinematic error, etc.) arise in the gear-box due to friction issues among others [8, 9, 6, 5]. Fig. 3 shows a measurement of acceleration at the end-effector of our experimental setup during semi- steady-state. Where the upper half shows the oscillation by time (t) and the lower half by frequency normed to the motor turn- ing frequency (f/f  ). 273 978-89-93215-03-8 98560/11/$15 ⓒICROS