On Vibration Control Engineering
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Kyoto Univ.- KAIST Joint Workshop On Vibration Control Engineering |
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| August 31 - September 1, 2006 | ||
Akihito Ito (Dept. of Mechanical Eng, Doshisha University)
At present, robots are expected to extend their range of activities to not only industry but also to care and welfare apparatuses, such as care robots that handle advanced tasks. Concurrent with the expansion of robots' application field, the requests for tactile sensors have also been increasing. Though research and development of various tactile sensors have been carried out until now, the practical sensor has not been completed yet. To accomplish practical tactile sensors, it is necessary to acquire forces and moments acting on the fingertips of the robot hand, and in addition, it is necessary to detect the slip. Especially, evaluation of relative movements between the sensor and the contacting object is indispensable when detecting slip. Thus, the force acting on the fingertips of the robot hand needs to be measured as distribution of forces in the direction of three axes. In our previous study, we proposed a distributed-type tactile sensor having 12 sensor elements, each of them able to detect vertical force and shear force, arranged in the 15 mm 20 mm area on the same plane. The prototype sensor, five times larger than those to be used in practice, was developed, and the algorithm for evaluating relative movements between the sensors and the contacting object was completed.
However, the slip is divided into micro slip and macro slip. Micro slip appears in the initial state of slip, and then, by the expansion of micro slip it becomes the macroscopic slip, namely the relative slip between contacting object and sensor. Micro slip and macro slip are the phenomena that occur continuously, and by detecting micro slip, it is possible to predict macro slip.
In this paper, we present a method for detecting micro slip. Micro slip is detectable from the vibration information of output value of strain gauge attached on the surface of sensor elements. From the experiment, we showed that micro slip is detectable using the slip information trained in advance. Since this sensor can detect both of the macro and micro slip, it is possible to construct a sensor system robust to slip.
Joonkeol Song and Chong-Won Lee (Center for Noise and Vibration Control (NOVIC), Dept. of Mechanical Eng., KAIST)
Club fitting is one of best ways to improve your performance without hard time of practice. Many club fitting methods have been suggested and some are employed. However most of them require very expensive equipments and good instinct of clubmakers. This research proposes the cost effective and automatable way. With 6 DoF sensor signals attach to the club, the motion, deflection and torsion can be calculated and it imparts perfect information for this purpose. In this paper, the developing 6 DoF sensor module will be introduced and the basic simulation results for golf club's deflection response for base excitement will be presented.
Tomonao OKUYAMA (Department of Precision Engineering, Kyoto University),
Hiroshi MATSUHISA, Hideo UTSUNO (Department of Mechanical Engineering and Science, Kyoto University)
and PARK Jeong Gyu (LG Electronics Inc.)
When a new high way road is planning, traffic noise will be predicted through the scale model experiment before the construction. In this study, the method to calculate the sound pressure at the evaluation point from the moving source is proposed. The proposed method discusses an interpolation method of measured transfer functions at several points on the road model. There are some paths from the sound source to the evaluation point, and the transfer function is expressed theoretically as the function of each path length and each diffraction and reflection coefficients. The impulse response obtained from measured transfer function consists of superposition of impulse response for each path. Comparing the impulse response with theoretical one, each sound path can be separated and each coefficient of the sound path can be identified. Using the identified coefficients and path lengths, transfer function at an arbitrary point between the measured points can be interpolated. From the digital sampled sound pressure at neighborhood of the moving source and each interpolated transfer function at the position of the moving source at each time, the sound pressure at the evaluation point is obtained in the frequency domain. By Inverse Discrete Fourier Transformation (IDFT), the sound pressure in the time domain can be derived. In this method, only once IDFT is required.
Ok-Hyun Kang , Youn-Sik Park, Young-Jin Park (Korea Advanced Institute of Science and Technology)
Structural Dynamics Modification (SDM) is to improve dynamic characteristics of a structure, more specifically of a base structure, by adding or deleting auxiliary (modifying) structures. In this paper, the focus will be concentrated on the optimal layout of the stiffeners which are attached to the plate to maximize 1st natural frequency. Recently, a new topology method was proposed by yamazaki. He uses growing and branching tree model. In this paper, to overcome limitations of the method, modified tree model will be suggested. To expand the layout of stiffeners, non-matching problem will be considered. The problem is solved by using local lagrange multiplier without the mesh regeneration. Moreover CMS(Component mode synthesis) method is employed to reduce the computing time of eigen reanalysis using reduced component models.
Keisuke YAMADA (JSPS Research Fellow, Department of Precision Engineering, Kyoto University),
Hiroshi MATSUHISA, Hideo UTSUNO (Department of Mechanical Engineering and Science, Kyoto University)
and Jeong Gyu PARK (LG Electronics Inc.)
This paper describes a new precise technique for measuring the electromechanical coupling coefficient of piezoelectric elements. Knowing piezoelectric elements' precise electromechanical coupling coefficient is necessary for estimating their performance and determining the optimum design of active vibration control and the passive vibration suppression systems that use piezoelectric elements. The electromechanical coupling coefficient can be derived using theoretical formulations, however, simulation results using those values usually do not agree well with experimental results. Therefore, it is much more favorable to experimentally measure the electromechanical coupling coefficient. However, the precision of conventional methods is not sufficient for some applications. This is particularly true when the difference between natural frequencies is too small to achieve good precision. For these reasons, a measurement technique that is less sensitive to error in the measuring apparatus is required. In this paper, a new method using resonance frequencies when an inductance is coupled to the piezoelectric element was proposed. By using this method, the difference between resonance frequencies becomes large enough to precisely determine the electromechanical coupling coefficient. The effectiveness of the new method was validated in experiment.
Byungbo Jung , Youn-Sik Park, Young-Jin Park (Korea Advanced Institute of Science and Technology)
We investigated a longitudinal acceleration wave decomposition method in time domain. The proposed method is useful to separate up- and down-stream acceleration waves with an axial strain and axial acceleration measured at a single point on the 1 dimensional transmission paths. The advantages such as low computation load and easy implementation would be accomplished by the extension to time domain under the assumptions; low frequency range, uniform cross sectional area and elastic wave propagation. We confirmed the feasibility and performance of the method through experiment using Split Hopkinson Pressure Bar (SHPB). The method can be effective in several applications, including active vibration power control, where wave separation should be obtained in real time.
Han-Wook Jeon and Chong-Won Lee (Center for Noise and Vibration Control (NOVIC), Dept. of Mechanical Eng., KAIST)
Nowadays, flywheel system is well know for energy storage system, and active magnetic bearings are adopted due to low energy loss and so on. For the efficiency of energy storage, the flywheel system is operated at very high speed and have large polar moment of inertia. Therefore, flexible vibration among the vibration modes and rotational speed dependent dynamic characterstics should be considered to control the system safely. Moreover operation condition of rapid rotational variation during the charge and discharge also should be considered for safe control. FEM model that are used for vibration analysis is not appropriate for the control model because of its large degree-of-freedom. Therefore this study proposes modal approach to reduce the size of the control model instead of FEM model. Morever the study proposes the simple polinomical fitting method to describe the speed-dependent dynamics and modal truncation method via residue value evaluation on the modal equation of motion.
Yanqing LIU (JSPS Research Fellow, Department of Mechanical Engineering and Science, Kyoto University), Hiroshi MATSUHISA, Hideo UTSUNO (Department of Mechanical Engineering and Science, Kyoto University)
Semi-active systems with variable damping and stiffness have demonstrated excellent performance. However, conventional devices for controlling variable stiffness are typically complicated and difficult to implement in most applications. To address this issue, a new configuration that requires two controllable dampers is proposed. A controllable damper and a constant spring comprise a Voigt element. The Voigt element and a spring are in series. This paper presents theoretical and experimental analyses of the proposed system. The stiffness of the net system is changed by controlling the damper in the Voigt element, and the other damper provides variable damping for the system. The proposed system is experimentally implemented using two magnetorheological (MR) fluid dampers. The experimental results agree well with the theoretical analyses. Six different control schemes involving soft spring, low damping, high damping, damping on-off, stiffness on-off, and damping and stiffness on-off control are explored. The responses of the system to sinusoidal and random excitations show that the variable damping and stiffness control can be realized by the proposed system. Moreover, the system with damping and stiffness on-off control provides good vibration isolation.
Bo-Ha Lee and Chong-Won Lee (Korea Advanced Institute of Science and Technology)
As a dynamic actuator for attenuating the engine-induced vibration transmitted to passenger vehicle chassis or investigating the vibration transfer path of the vehicle, an electromagnetic actuator, consisted of a runner, two stators and pairs of electromagnets and permanent magnets, is developed. It features that it is compact to be fit into the limited space and yet, it possesses high efficiency and wide frequency bandwidth for effective control of engine vibrations in standard size passenger cars.
By using the permanent magnets in electromagnetic system, we can increase the actuating force of the electromagnetic system and decrease the total amount of the power consumption of actuator when it operates. In addition to that an electronic circuit device is also developed such that the displacement between the electromagnet pair and the target can be estimated from measurement of flux density of the installed permanent magnet only. It is found that the resolution and frequency bandwidth of the displacement estimator are about 3?m and 0 to 4kHz, respectively.
The designed electromagnetic actuator is capable of attenuating the vibration over the frequency range of 100 to 400Hz, which is satisfactory for applications of interest
Mai Bando and Akira Ichikawa (Graduate School of Engineering, Kyoto University)
In this paper, we consider the output regulation problem for linear time-invariant systems with unknown parameters. First we consider the stabilization problem of time-invariant system with unknown parameters.
We introduce an estimator of the system and adaptive laws which decrease the estimation error of the state and parameters. We then introduce a feedback law based on an algebraic Riccati equation. We give a sufficient condition for the global asymptotic stability of the closed-loop system. We then consider the output regulation problem and give sufficient conditions for solvability in terms of the regulator equation. To relax the condition on the solution of the Riccati equation imposed above, we introduce normalized adaptive laws. Using the solutions of the Riccati equation and regulator equation we show that the some feedback law fulfills the output regulation.
An example is worked out numerically and a simulation result of the tracking of a sine function is presented.
Sang-Hyun Park and Chong-Won Lee (Korea Advanced Institute of Science and Technology)
Recently, design of low-cost miniaturized active magnetic bearings (AMBs) becomes important. For lower power consumption, a novel design of small-sized hybrid type AMB is proposed. The proposed 3- pole's configuration requires fewer number of power amplifiers compared to a conventional 4-pole AMB. But it has heavy nonlinear properties in the magnetic flux between magnetic poles, and exists coupling effect, which leads to non-linearity both states and control inputs. So it is hard to make simple controller in general. In this paper, the redundant coordinates to construct the identical controller are introduced. Also permanent magnets are implemented to provide a constant bias flux, so that stator windings generate only control flux to stabilize the bearing. In addition, instead of extra proximity probes, three Hall diodes are used for the rotor displacement measurement, which reduces the cost. And the experimental results showed the feasibility of the proposed AMB.
Lovely Son (Department of Precision Engineering, Kyoto University),
Hiroshi MATSUHISA, Hideo UTSUNO (Department of Mechanical Engineering and Science, Kyoto University)
and Jeong Gyu PARK (LG Electronics Inc.)
This paper deals with reducing floor impact vibration and sound by using a momentum exchange impact damper. The impact damper consists of a spring supporting a mass that is contact with the floor. When a falling object collides with the floor, the floor interacts with the damper mass and the momentum of the falling object is transferred to the damper. In this works a computational model is formulated to simulate dynamic floor vibration induced by impact. The floor vibration is simulated for various sized damper masses. A proof-of-concept experimental apparatus was fabricated to represent a floor with an impact damper. This example system consists of an acrylic plate, a tennis ball for falling object, and an impact damper. A comparison between simulated and experimental results were in good agreement in suggesting that the proposed impact damper is effective at reducing floor impact vibration and sound by 25% and 63%, respectively