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The characteristics of a differentially-operated optical displacement sensor developed for wind-tunnel using magnetic suspension are studied both analytically and experimentally. The target sensor measures the three-dimensional displacement of the suspended object (floator) from the variations of the shadow of the floator. It is composed of eight optical systems. First, the output characteristics of the fabricated sensor are measured. As to linearity, it is good in the direction of light (x-axis) but inferior in the other directions (y and z axes). In addition, interferences among the axes are observed. Because the differences in characteristics among the optical systems cause such errors, adjustments by software are carried out. They reduce the nonlinearity and interferences. However, residual errors still remain. To clarify the reasons, the output characteristics are studied analytically by investigating the movement of the shadow of the floator and the variations of the illuminated area on the lenses. The results suggest that nonlinearity and interaxial interferences exist on some extent in the sensor, which was observed in the experiments.

DC magnetic suspension operated by transmitted power is introduced to AC magnetic suspension system using magnetic resonant coupling for dynamic stabilization. The target AC magnetic suspension system has a self-stabilization property. Although restoring force is produced without active control in this system, damping is necessary for dynamic stabilization. To generate damping force, a DC magnetic suspension mechanism, which is operated by the power transmitted to the floator through magnetic resonant coupling, is installed in parallel with the AC magnetic suspension mechanism. The newly developed system has a pair of AC electromagnets and another pair of DC electromagnets. The former pair generates positive stiffness according to the self-stabilization property. The latter pair is expected to produce positive damping by shortening the coil of the electromagnet on the stator. However, it is experimentally shown that negative damping is produced because the latter pair also has the self-stabilization property. Therefore, a bias voltage is applied to the DC electromagnet on the stator to make the stiffness negative. As a result, stable suspension is achieved without active control in the developed system. However, the overall stiffness decreases and the stability range is small because the latter pair has negative stiffness. To solve such a problem, a phase-lead compensation is applied to the latter pair instead of the bias voltage. This method can produce positive damping and positive stiffness at the same time so that the suspension characteristics are improved.

PurposesWe report the experimental use of completely autologous biomaterials (Biosheets) made by “in-body tissue architecture” that could resolve problems in artificial materials and autologous pericardium. Here, Biosheets were implanted into full-thickness right ventricular outflow tract defects in a rat model. Their feasibility as a reparative material for cardiac defects was evaluated.MethodsAs the evaluation of mechanical properties of the biosheets, the elastic moduli of the biosheets and RVOT-free walls of rats were examined using a tensile tester. Biosheets and expanded polytetrafluoroethylene sheet were used to repair transmural defects surgically created in the right ventricular outflow tracts of adult rat hearts (n = 9, each patch group). At 4 and 12 weeks after the operation, the hearts were resected and histologically examined.ResultsThe strength and elastic moduli of the biosheets were 421.3 ± 140.7 g and 2919 ± 728.9 kPa, respectively, which were significantly higher than those of the native RVOT-free walls (93.5 ± 26.2 g and 778.6 ± 137.7 kPa, respectively; P < 0.005 and P < 0.001, respectively). All patches were successfully implanted into the right ventricular outflow tract-free wall of rats. Dense fibrous adhesions to the sternum on the epicardial surface were also observed in 7 of 9 rats with ePTFE grafts, whereas 2 of 9 rats with biosheets. Histologically, the vascular-constructing cells were infiltrated into Biosheets. The luminal surfaces were completely endothelialized in all groups at each time point. There was also no accumulation of inflammatory cells.ConclusionsBiosheets can be formed easily and have sufficient strength and good biocompatibility as a patch for right ventricular outflow tract repair in rats. Therefore, Biosheet may be a suitable material for reconstructive surgery of the right ventricular outflow tract.

An 11-year-old, 12.3-kg, female Miniature Dachshund was presented to our institution with ascites of unknown etiology. The dog had been administered moxidectin for 3 years to treat a heartworm infection. Thoracic radiographs showed enlargement of the right heart. Echocardiography revealed right atrial and ventricular dilatation as well as flattening of the interventricular septum. Heartworm was identified in the main pulmonary artery, which was dilated. Tricuspid regurgitation (TR) was observed using color Doppler ultrasonography, and 2.5 L of ascites were removed. The dog was diagnosed with pulmonary hypertension, severe TR, and right-sided congestive heart failure. Except at the initial site, heartworm was not detected using echocardiography, and the antigen test was negative. However, pharmacological treatment did not improve the right-sided congestive heart failure. Instead, De Vega tricuspid annuloplasty (TAP) was performed on the beating heart under cardiopulmonary bypass with the owner's consent. Sutures terminated between the two commissures in the middle of the annulus and were secured using another pledget. Annular reduction was performed by tying down the plication suture while the cylindrical sizer was inserted into the tricuspid valve orifice. The size of the cylindrical sizer was 16 mm, which was set based on the height and width of the septal leaflet. A 6-month follow-up showed a reduction of TR and right-sided volume overload with no evidence of ascites retention/recurrence or any other complication. Our findings indicate that TAP may be a valid treatment option for dogs with right-sided congestive heart failure caused by secondary TR.

A mass measurement system with a relay feedback of velocity has been developed to achieve measurement without gravity. In this system, mass is estimated from the periods of oscillation in the relay-feedback system. Originally, the velocity of the object was solely fed back, which caused the orbit of the object to drift easily. A restoring force compensation by a spring was introduced to avoid such drift. However, a slight drift still occurs in spite of the restoring force element. A new estimation formula has been derived which can estimate mass regardless of the position of the closed orbit. An analytical study on this formula shows that mass is overestimated when the restoring force is neglected in the estimation. Several experimental results show that the estimated mass is slightly larger than the actual value even though the new formula is used in estimation. In the measurement, the periods of oscillation are measured with a digital oscilloscope. A delay in the period measurement is expected to cause such overestimation. To reduce the error due to delay in measuring periods, a new device for rapid period measurement is developed, which uses the edge detecting function of a micro-computer. It is experimentally demonstrated that the measurement error is reduced by the developed measurement device.

Mass measurement using relay feedback of velocity and restoring force compensation is investigated for determining the mass of an object under weightless conditions. In the measurement system, the velocity of the object is fed back through a relay with hysteresis and the force acting on the object is switched from a positive value to a negative value when the velocity reaches a positive threshold and vice versa. As a result, a limit cycle is induced in the measurement system and the mass is estimated based on the period of the limit cycle. In addition, restoring force compensation with a spring is introduced to avoid the drift of the trajectory. This compensation makes the static equilibrium state unique. However, the trajectory still drifts slightly. It causes some error in measurement when a simple formula of estimating mass is applied. To eliminate such an error, a new formula is derived to estimate the mass independently of the position of the trajectory that is determined by the switching positions in the relay actions. When the switching positions deflect from the origin at which the spring is in the natural length, the trajectory is not at the center and becomes asymmetric. It is analytically shown that the period of the limit cycle is minimum when the switching positions are at the origin. It indicates that mass is overestimated with the simple estimation formula when the trajectory is not at the center. The validity of the modified formula and the analytical results are confirmed experimentally.

A miniaturized force measurement device with zero-compliance mechanism is designed and fabricated using MEMS technology. Zero-compliance mechanism consists of two suspensions connected in series through a detection point. When a force is applied to an object suspended by this mechanism, the position of the object can be kept constant by controlling the detection point. Furthermore, the force can be estimated from the displacement of the detection point because the displacement of the detection point is proportional to the force. The measurement method using zero-compliance mechanism is effective for measuring interatomic force, which is usually a function of the gap between objects. This work focuses on the miniaturization of this mechanism by MEMS technology. An experimental device is designed and fabricated. This device consists of comb-drive actuators, capacitance sensors using comb electrodes and leaf springs. It is experimentally confirmed that zero-compliance can be realized in such a miniature device fabricated using MEMS technology. In addition, measurement performances are improved in the device.

A mass measurement system using relay feedback of velocity was developed. In this system, the velocity of the object was fed back through a relay with hysteresis. Although the efficacy of the proposed method has been already confirmed experimentally, it was subject to a drift mainly because only the velocity was fed back. To prevent such a drift, a spring element was added to produce restoring force. However, smaller drifts still occurred, and the trajectory of the object fluctuated. To eliminate such fluctuations, intermediate control is introduced. It succeeds to eliminate fluctuation of the trajectory in the developed apparatus.

A three-degree-of-freedom AC magnetic suspension system using magnetic resonant coupling was fabricated. The AC magnetic suspension system can produce restoring force without active control. This system is dynamically stabilized by adding indirect damping, which is produced by suspending to the stator with viscoelastic support mechanisms. A non-contact electrical power transmission is achieved simultaneously by magnetic resonant coupling. The structure of magnetic resonant coupling is similar to the structure of the transformer. The magnetic flux path for suspension is combined with that of electrical power transmission. The electric characteristics of the transformer depend on the resistance of a load connecting the secondary circuit. The measured results indicate that the driving frequency needs to be adjusted to achieve stable suspension in relation to the resistance of the load. These characteristics are confirmed experimentally.

An interaction through a negative-stiffness spring is introduced into a dual-mass dynamic vibration absorber (DVA) to lower its resonance frequency. DVA is one of the practical vibration control devices. In principles, it consists of an absorption mass and a spring. It can eliminate vibration at a specified frequency that equals the resonance frequency of the DVA. To eliminate low-frequency vibration, it is necessary to increase the absorption mass or lower the spring constant. The former method increases the size of the device and the latter method may cause difficulty in supporting the absorption mass. Although there are reports on the optimal design and robust optimal design of DVAs, there are few reports that focus on lowering the anti-resonance frequency. In addition, there are few studies on the parallel dual-mass DVA that has interference between the vibration absorption masses. This work focuses on parallel dual-mass DVA and proposes to insert a negative spring between the absorption masses. It is analytically shown that one of the resonance frequencies of the DVA can be set lower than that of the conventional DVA. Such characteristics are confirmed by numerical analyses and experiments.

A first-order-reset element (FORE) controller is modified to adjust the vibration attenuation characteristic of a magnetic suspension system. The proportional-derivative (PD) feedback control is the simplest control method of stabilizing magnetic suspension systems. In the PD-controlled system, restoring force is produced with the proportional element and damping effect is produced with the derivative element. Meanwhile, a feedback control using a FORE has been proposed to stabilize magnetic suspension systems. The FORE replaces a linear integrator built into a first-order low-pass filter by a non-linear integrator. The proposed controller can stabilize a magnetic suspension system with one element. The restoring force and damping effect are generated simultaneously. However, the two effects could not be adjusted separately. To adjust the vibration attenuation characteristic, the FORE controller is modified to adjust the transition value at reset. The characteristics of the modified controller are studied through numerical analysis. Then the effectiveness of the modification is demonstrated by several simulations and experiments.

In the assembly of micro components, a slight impact during assembly affects product performance. This work focuses on the assembly of parts including magnetized components. In the assembly of such parts, the attractive force acting between the parts causes a difficulty of assembly without collision. For this reason, such a work is conducted by skilled workers. However, the lack of successors has become a problem. Therefore, a bilateral operation system is developed for training such successors. A bilateral control is installed using two devices including a voice coil motor, a leaf spring and a sensor. The slave device is controlled to follow the motion of the master device. The force applied to the slave device is estimated with a full order observer to reflect the force on the master device. It is confirmed experimentally that the slave device can follow the master device and that the force applied by the slave device can be presented to the master device. In addition, assembling experiments are conducted using the bilateral operation system. The displacement of each device and the applied external force to slave device are obtained. It is demonstrated that the assembling technique could be evaluated quantitatively.

Force measurement using zero-compliance mechanism is proposed and studied experimentally. A zero-compliance mechanism is composed of two suspensions connected in series; one of them is operated to cancel the deflection of the other so that the total length of the suspension is maintained even if force acts between the ends. In the proposed measurement system, one of the ends becomes the point of force and the point of the connection becomes the detection point. The force is estimated from the displacement of the detection point. An apparatus is fabricated for experimental study to show the validity of the proposed measurement method. Double series magnetic suspension is used to achieve zero compliance. In the apparatus, the motions of two suspended objects (floators) are controlled with a single electromagnet. Each floator is supported by leaf springs to move in the vertical direction translationally. The attractive force of the electromagnet directly acts on the first floator in which a permanent magnet is installed. The motion of the second floator is controlled indirectly through the attractive force of the permanent magnet. To achieve the zero compliance characteristic, PID control is applied to the second floator. It is confirmed experimentally that the deflection of the second suspension, i.e., the distance between the first and second floators, is proportional to external force acting on the second floator. This result indicates that the force can be estimated for the deflection of the second suspension. It is also demonstrated that dynamic force can be measured by the proposed method.

The bellows pneumatic actuator, which is made by folding a non-stretch film, has been proposed for various applications because it is easy to fabricate and is extremely thin and light. However, it has subpar durability performance, especially in the folded part of the film. In this study, we propose an actuator with a pod structure that possesses high design flexibility and is free from folding. A method of molding a pod structure on a polyimide film was established and a pneumatic actuator was successfully fabricated by using PI films. Two types of PI film pneumatic actuators with the same curvature, bellows type, and pod type were fabricated. Both were confirmed to have equivalent output characteristics. The bending angle and generated torque of the pod-structure actuator were 34° and 3.3 mNm, respectively. In addition, the pod structure has approximately twice the durability of the bellows structure. By using the fabrication method proposed in this paper, it is possible to realize an air chamber (i.e., an actuator) that has both high durability and bending motion.

A vibration isolation device with an active dynamic vibration absorber is developed to remove vibration induced by a cryopump. Cryopump is used to make high-vacuum and low-temperature environments for precise measurement. However, it induces vibrations with multiple frequencies, which may deteriorate measurement accuracy. This study focuses on removing the vibration of low frequencies because conventional vibration isolation devices for cryopump can hardly remove them. In the developed vibration isolation device, an active vibration absorber is used to remove the vibration efficiently at low frequencies. The controller is designed based on the internal model principle. The pole assignment is used to tune the controller. The efficacy of the designed and tuned controller is demonstrated in the developed apparatus.

The fundamental characteristics and performances of alternating current (AC) magnetic suspension using magnetic resonant coupling are studied analytically and experimentally. Nowadays, wireless power transfer to the suspended object is required during non-contact suspension in some applications. Therefore, magnetic resonant coupling has been introduced for AC magnetic suspension to achieve self-stabilizing magnetic suspension and energy transfer to the floator simultaneously. The effect of circuit parameters for developing an experimental apparatus and performances are predicted from the solution of the equivalent circuits analytically. First, an equivalent magnetic circuit is derived and analyzed to characterize the self-inductance and mutual inductance with the gap. Second, an equivalent electrical circuit is analyzed to derive the current and force equations including magnetic parameters of the circuit. The derivation of these equations is numerically solved to study the characteristics of the primary current, the secondary current, and the force with respect to the gap and the applied frequency. The comparison between theoretical and experimental results is depicted, and the reason for differences is explained. The experimental and theoretical results show that positive stiffness is possible, which is essential for achieving self-stabilization. The self-stability is confirmed by the frequency response of the suspension system to disturbance experimentally.

A magnetic suspension system with three flux-path control mechanisms are developed to achieve three-dimensional positioning of the suspended object (floator). In the flux-control mechanism, a ferromagnetic control plate is located in the lateral direction of the magnetic source (permanent magnet). It was shown that the attractive force acting on the floator could be varied by moving the control plate in the vertical direction. In addition, the lateral force was generated by using two control plates located on both sides of the floator and moving them differentially. In this work, an apparatus is fabricated which has three flux-path control mechanisms. The configurations of the apparatus are described. Stable suspension is achieved and basic characteristics are studied. In addition, 3-degree-of-freedom (3-DOF) control suspension is achieved by moving three control plates individually. The 3-DOF control is evaluated by moving the floator in circular orbits.

A basic single-degree-of-freedom magnetic suspension system consists of one floator, one electromagnet and one amplifier. For multi-degrees-of-freedom control, multiple electromagnets and multiple amplifiers are necessary, which increases the cost of total system. As a means of overcoming this problem, parallel magnetic suspension has been proposed which controls multiple floators or multi-degree-of-freedom motions with a single power amplifier. In this system, all of the suspended points move simultaneously even when a disturbance acts on one of the suspended points solely because all electromagnet's coils are connected. This paper studies the moving direction of each suspended point with respect to a step disturbance in double parallel magnetic suspension system. The analytical study shows that the response direction is determined by the system parameter that relates the response speed of each subsystem. In the slower subsystem, the suspended point moves in the same direction as the applied force while in the faster subsystem, the suspended point moves in the opposite direction. In other words, the slower subsystem has positive stiffness while the faster system has negative stiffness. To confirm this prediction, step responses are measured in the experimental apparatus.

A novel force measurement instrument is designed and fabricated to validate multi-dimensional force measurement using zero compliance mechanism. In each axis, there is a point of force and a detection point for zero-compliance force measurement. Both the detection point and the point of force are suspended in series and attached with the base frame through leaf springs. When external force is applied at the point of force, it moves from its original position. The motion of the point of force can be regulated by displacing the detection point in the same or opposite direction of the applied force. The control system is designed and implemented to control the movement of the point of force and the detection point in vertical and horizontal direction force measurement. The effect of applied force on the point of force is cancelled to maintain its position by displacing the detection point. The motion of the detection point is controlled in such a way that it displaces proportionally to the applied force. Thus, applied force can be estimated from the displacement of the detection point and zero-compliance is accomplished at the point of force. The effectiveness of the proposed instrument in multi-dimensional force measurement is demonstrated by the experimental results of the horizontal and vertical direction force measurement with good linearity and almost zero interference.

In silicon nanoscale transistors, dopant atoms can significantly affect the transport characteristics, in particular at low temperatures. Investigation of coupling between neighboring dopants in such devices is essential in defining the properties for transport. In this work, we present an overview of different regimes of inter-dopant coupling, controlled by doping concentration and a selective doping process. Tunneling-transport spectroscopy can reveal the fundamental physics of isolated dopants in comparison with strongly-coupled dopants. In addition, observations of surface potential for Si nano-transistors can provide direct access to understanding the behavior of coupled dopants.