Kyihwan Park

Design optimization of a piezoresistive pressure sensor considering the output signal-to-noise ratio

Piezoresistive sensors often suffer from poor signal-to-noise ratios, limiting their use for measuring small pressure differentials. As the pressure range is reduced, and the sensitivity of the sensor increased, the effect of noise on the output signal becomes the limiting factor in the sensor design. In this paper, the optimization of the design to enhance the signal-to-noise ratio of a piezoresistive-type pressure sensor is performed considering different noise components commonly present with these types of sensors. The optimal design for the cases of constant voltage and current is achieved by maximizing the performance index, which is defined as the output signal versus noise. The output voltage and noise are separately analyzed and experimentally tested with respect to the geometric parameters of the piezoresistor and the applied voltage and current. Brownian, Johnson and flicker (1/f) noises are modeled, the latter two of which are dominant for piezoresistive sensors operated at low frequencies to dc. The experimental results show that the optimal design with respect to the resistor length, and number of turns is significantly different when noise is considered. For the special case of the piezoresistive sensor tested, the flicker noise required more turns and longer active elements than if only the effective and non-effective resistances were considered. The optimal Vout/Vnoise was over twice that of the sensor designed maximizing Vout alone.

Modeling eddy currents with boundary conditions by using Coulomb's law and the method of images

Since the eddy-current problem usually depends on the geometry of the moving conductive sheet and the pole shape, there is no general method for solving it analytically. This paper presents a method for analysis of the eddy current in the special case of a rotating disk in a time-invariant field. The analysis uses Coulombs law and the method of images to consider the boundary conditions. First, the surface charge generated in the rotating disk is obtained and Coulombs law is applied to calculate the electric field intensity, assuming an infinite disk radius. Second, the finite disk radius is taken into account by introducing an imaginary electric field intensity to satisfy the boundary condition that the radial component of the eddy current is zero at the edge of the rotating disk. Third, the braking torque is calculated by applying the Lorentz force law. The paper compares the computed braking torque with the experimental results to establish the validity of the model.

Feasibility test of an electromagnetically driven valve actuator for glaucoma treatment

Although conventional glaucoma implants have a capability of pressure regulation, they cannot maintain the intraocular pressure (IOP) desired for different patients. In this paper, we present an analysis of the operation of a conventional implant using a bond graph and show its defects and the limitations of a conventional valve analytically. On the basis of the analysis, the design and fabrication of an active valve actuator is performed considering actuation principles, resistance elements, and control methods. An electromagnetic actuator is used for realizing the active resistance element. A passive resistance element is also included in in order to reduce power consumption. A pulsewidth modulation (PWM) control method is used for enhancing the power consumption saving. Finally, we describe experiments and simulations with the fabricated valve actuator in an in vitro environment, and estimate the in vivo performance from the in vitro experimental results.

In vitro experiment of the pressure regulating valve for a glaucoma implant

Glaucoma is an eye disease which is caused by abnormal high intraocular pressure (IOP) in the eye. If the condition of the patient becomes serious, the use of an implant device is recommended, which decreases the IOP compulsory. Active implants for glaucoma implants are capable of controlling the IOP actively and coping with the personal differences of patients. However, the conventional active valves for the glaucoma implant are not convenient for the patient and feasibility is not shown for the glaucoma treatment. In this paper, we propose, analyze, fabricate and experiment on the pressure regulating valve for the active implant. Based on the analysis, we carry out optimal design of the proposed valve. The in vitro experiments are performed extensively both using and not using a rabbit in open- and closed-loop pressure control. The various experimental results verify the possibility of the proposed valve for a glaucoma implant.

A new torque control method of a switched reluctance motor using a torque-sharing function

A torque sharing function (TSF) method is one of the torque control methods that drives each phase of a switched reluctance motor so that the overall torque becomes a constant torque. The conventional TSF method defined the TSF only at a positive torque production region, which causes a poor torque-speed performance as the speed increases due to the delay of the current rising and falling time. This paper extends the definition region of the TSF to the negative torque region to have enough time to raise or decrease the current at the positive torque region. This extended TSF enables to increase the positive torque even in relatively high speed operation. Optimal determination of the TSF is investigated for various control objectives in mathematical and experimental ways.

Continuous scanning laser Doppler vibrometer for mode shape analysis

The vibration mode shape measurement technique utilizing a continuous scanning laser Doppler vibrometer (SLDV) is addressed. Continuous scanning capability is added to the conventional discrete laser Doppler vibrometer by reflecting the laser beam on the surface of the object using two oscillating mirrors. Bow scanning resulting from the proposed scanning mechanism is compensated by controlling the two mirrors. If a continuous sinusoidal scanning method is used, it can be shown that the velocity output signal from the SLDV is modulated to give the spatial velocity distribution in terms of coefficients that are obtained from the Fourier transformation of the time-dependent velocity signal. Using the Chebyshev series form, the analysis of vibration mode shape techniques for 2-D scanning is presented and discussed. The performance of the proposed SLDV is presented using the experimental results of the vibration mode shape of a plate.

Magnetic levitated high precision positioning system based on antagonistic mechanism

A six degree-of-freedom magnetically levitated high precision micro positioning system is designed to get rid of the friction which is one of the important factors limiting the resolution and accuracy of positioning devices. Since magnetic levitation systems are inherently unstable, most of the emphasis is placed on a magnetic circuit design so as to increase the system dynamic stability. For this, the proposed levitation system is constructed by using an antagonistic structure which permits a simple design and robust stability. From the dynamic equations of motion, it is verified that the proposed magnetic levitation system is internally stable in 5 degree-of-freedom. Experimental results of motion of free vibration are presented to verify the proposed modeling method.

Magnetic force driven six degree-of-freedom active vibration isolation system using a phase compensated velocity sensor

A six-axis active vibration isolation system (AVIS) is developed using voice coil actuators. Point contact configuration is employed to have an easy assembly of eight voice coil actuators to an upper and a base plates. The velocity sensor, using an electromagnetic principle that is commonly used in the vibration control, is investigated since its phase lead characteristic causes an instability problem for a low frequency vibration. The performances of the AVIS are investigated in the frequency domain and finally validated by comparing with the passive isolation system using the atomic force microscope images.

Fuzzy deisign of a switched reluctance motor based on the torque profile optimization

This paper presents a new design method for improving the torque performance of a switched reluctance motor (SRM) for high speed applications. The drawback of the conventional design method based on the overall static average torque maximization is that the torque control performance is degraded at high speed. On the other hand, the proposed method optimizes the torque profile by dividing it into several regions so that it is suitable for high speed operation. This multi-objective optimization problem is solved by using a fuzzy optimization algorithm which incorporates a finite element method. The torque performance of the motor for various speed ranges is investigated and the optimally designed motor shows a better performance at high speed.

Design and control of six degree-of-freedom active vibration isolation table

A six-axis active vibration isolation system (AVIS) is designed by using the direct driven guide and ball contact mechanisms in order to have no cross-coupling between actuators. The point contact configuration gives an advantage of having an easy assembly of eight voice coil actuators to an upper and a base plate. A voice coil actuator is used since it can provide a large displacement and sufficient bandwidth required for vibration control. The AVIS is controlled considering the effect of flexible vibration mode in the upper plate and velocity sensor dynamics. A loop shaping technique and phase margin condition are applied to design a vibration controller. The performances of the AVIS are investigated in the frequency domain and finally validated by comparing with the passive isolation system. The scanning profiles of the specimen are compared together by using the atomic force microscope. The robustness of the AVIS is verified by showing the impulse response.