Kazuhiko Oshima

Application of self-sensing actuator to control of a cantilever beam

A self-sensing actuator is a new concept for intelligent material, where a single piece of piezoelectric element simultaneously performs as both a sensor and an actuator. This idea should be advantageous especially for control of flexible structures. The key of this device is an electric bridge circuit that includes a piezoelectric element as a component. This circuit could give significant information about strain in the element if it were well-balanced. Our aim is to design controllers which enable practical self-sensing actuation in the presence of uncertainty that loses the balance of the circuit. In this paper, we proposed two approaches to realize self-sensing actuation which deal with this uncertainty differently. Experimental results proved the effectiveness of self-sensing actuation in both vibration suppression and tracking control of a cantilever.

Modal filtering for simply supported plate using equally segmented piezoelectric film

A method to measure the modal coordinates of a simply supported rectangular plate using an equally segmented piezoelectric film is studied. Modal sensors which can measure specific modal coordinates by shaping distributed piezoelectric sensors were proposed by Lee et al. (1990). However, basically, it can be only applied to one dimensional vibrations and only measure the specific modal coordinates corresponding to the shape of the sensor. In this paper, we propose a method, in which estimated modal coordinates are obtained by the sum of appropriately weighted sensor signals from the segmented piezoelectric film. This method can be easily applied to two dimensional vibrations and can measure arbitrary modal coordinates by selecting the weight. In this paper, the weight is determined to minimize a cost function. The orthogonality of the unit modal sensing signal vectors for a simply supported rectangular plate with an equally segmented piezoelectric film is proven, and the transpose of the unit model sensing signal matrix is chosen as the weight. Effects of aliasing caused by finite segmentation are also discussed. Simulation is shown to prove efficiency.

Parameter identification method for piezoelectric shunt damping

Piezoelectric shunt damping is a method to reduce structural vibration by shunting a piezoelectric element with an electrical circuit. This paper proposes a method to identify the physical parameters that are required to design piezoelectric shunt damping systems. Employing self-sensing actuator methodology, the proposed method requires no additional sensor or actuator other than a simple bridge circuit. The parameters can be identified from a transfer function simply by linear least squares method. To demonstrate the validity of the proposed method, the shunt damping of the steel plate with the piezoelectric ceramic is performed based on the identified parameters.

Cylindrical tactile sensor for a robot hand using position sensitive detectors on a suspension shell

In this paper, we propose a cylindrical tactile sensor for robot hands that can simultaneously detect the contact angle, contact location, and magnitude of the contact force. This sensor consists of an inner frame with light sources and an outer shell to which two position sensitive detectors (PSDs) are fixed; the concentric outer shell and inner frame are separated by two elastic rings. Since each two-dimensional PSD is installed on the same cross section as an elastic ring, the output of a PSD directly corresponds to displacement of an elastic ring. Based on experiments performed on a prototype, we found that values for contact angle, contact location, and magnitude of the contact force could be obtained with good accuracy from simple mathematical expressions. Consequently, this cylindrical tactile sensor is considered to be effective as a tactile sensor for robot hands.

PWM Driving Characteristics with Its Self-Locking of Ultrasonic Motor

A traveling wave-type ultrasonic motor (USM) has a self-locking characteristic due to a static frictional force present when its power supply is turned off, because its rotor is pressed strongly to the stator in the USM. We propose a pulse width modulation (PWM) method in consideration of this self-locking characteristic in order to control the motion of USM. The vibration waveform and the driving characteristics of USM were examined experimentally at different switching frequencies under PWM. When the period of PWM switching pulse is longer than the time constant of the piezoelectric element in USM, the rest duration appears in the vibration waveform of USM. It was confirmed that the rotor speed of USM was approximately proportional to the duty ratio of the applied voltage under the condition of the low switching frequency of PWM, and the large torque was obtained even when the duty ratio was small.

Noise Reduction by a Loud Speaker Based on Self-Sensing Actuation

Abstract A study on noise reduction or noise cancellation has been concerned widely from the enviromnental point of view. Active noise control is very effective in such problem where noise reduction is attained by a canceling speaker driven by the feedback signal from a pick up microphone in the noise field. In this paper, a quite new technique for active noise reduction control is proposed taking notice of electromechanical duality of a loud speaker, that is, selfsensing actuation of a loud speaker. A single loud speaker Wlit is capable concurrently to sense soood radiation and to actuate soood vibration in the control loop with use of a bridge circuit that can distinguish the sensor voltage from the actuation voltage.