A practical approach to the design and control of active endoscopes

Actual endoscopes and boroscopes, widely used in industry and in minimal invasive surgery, have considerable limitations, mainly due to their low number of degrees of freedom and their manual operation. Two different solutions for the electrical actuation of articulated endoscopes are presented in this paper. The technical constraints for this kind of application are very limited space for the actuators and high performance in terms of torque and angular reach. The first solution classically consists in a 2 d.o.f. structure steered by two pairs of antagonist shape memory alloy (SMA) wires. The sizing and preload determination for those actuators follow an original analytical approach. The second solution consists in a multi-d.o.f. structure actuated by thin NiTi springs mounted in an antagonist configuration and directly integrated in the structure of the endoscope. The geometry of the springs is obtained by optimization through genetic algorithms and finite elements method. Experiments show good adequacy between real behaviour and numerical model and also validate the approach.This study is also enhanced by a control scheme specifically developed for SMA actuators in an antagonist configuration. It is based on a first order sliding mode scheme, which has the advantage of a great structural simplicity. The experimental results show that this solution can reach a good compromise between the dynamic behaviour of the actuator, its energy consumption and the structural lifetime of the endoscope.     

A novel mechanical cochlea “Fishbone” with dualsensor/actuator characteristics

Through detailed investigation of the sophisticated functions of the mammalian cochlea, we are aiming to apply its resonator array structure to efficient and smart sensors and actuators. We outline our study on an equivalent mechanical model of the cochlea named the “fishbone structure,” which can be fabricated from a thin Si plate alone. Special emphasis is placed on applications of the structure to both sensors (“artificial cochlea microphone”) and actuators (“giant impulse generator”). The applicability of the “fishbone structure” to both sensors and actuators is an outcome of the passive and loss-free property of it, which is originated from the transmission line model of the cochlea. We fabricated the structure by the Si micro-machining process and examined the soundness of the approach first by finite-element analysis and secondly by experiments using the fabricated devices     

Fault Detection for Nonlinear Networked Control Systems with Markov Data Transmission Pattern

This paper is concerned with the fault-detection problem of nonlinear multiple channels data transmission networked control systems (NCSs). Two irrelevant Markov chains are introduced to describe the data transmission characterization of nonlinear delayed NCSs with data loss in both from sensors to controller and from controller to actuators, and a nonlinear Markovian jump system model is established. Based on this novel model, employing a mode-dependent fault-detection filter as residual generator, a fault-detection filter design of nonlinear NCSs is formulated as a nonlinear H _∞-filtering problem. Then an appropriate Lyapunov functional is chosen to derive the sufficient condition which satisfies the stochastic stability and prescribes the H _∞ attenuation level simultaneously. Especially, the desired mode-dependent fault-detection filters are constructed in terms of certain linear matrix inequalities (LMIs), and explicit parameters are characterized if these LMIs are feasible. The effectiveness of the proposed method is demonstrated by a simulation example.     

Extension of the bond graph causality inversion method for fault detection and isolation

Controlled systems can be subjected to faults that may affect the performance of the system, and unable its objectives to be achieved. Fault detection and isolation algorithms are then used to study these faults. The bond graph tool can be used for modeling purposes and then its structural, and causal properties can be exploited for automatic generation of analytical redundancy relations (ARRs) through a procedure named causality inversion method, which are used for diagnosis applications. These ARRs are mathematical constraints that are used to verify the coherence between the process measurements and the system model. This paper proposes an extension of the causality inversion method by different versions of the same ARR. The goal is to increase the number of isolable faults. Moreover, structural conditions are given in order to avoid the generation of redundant ARRs. To validate the obtained structural procedure, a fault is imposed in a traction of an omnidirectional mobile robot.     

Genetic algorithm-based design of the active damping for an LCL-filter three-phase active rectifier

Active rectifiers/inverters are becoming used more and more often in regenerative systems and distributed power systems. Typically, the interface between the grid and rectifier is either an inductor or an LCL-filter. The use of an LCL-filter mitigates the switching ripple injected in the grid by a three-phase active rectifier. However, stability problems can arise in the current control loop. In order to overcome them, a damping resistor can be inserted, at the price of a reduction of efficiency. The use of active damping by means of control may seem attractive but it is often limited by the use of more sensors compared to the standard control and also by a complex tuning procedure of the controllers. This paper introduces a new active damping method that does not require the use of more sensors. It consists of adding a filter on the reference voltage for the modulator. The tuning process of this filter is easily done, for a wide range of sampling frequencies, with the use of genetic algorithms. This method is used only for the optimum choice of the parameters in the filter and an on-line implementation is not needed. Thus the resulting active damping solution does not need new sensors or complex calculations. Moreover, in the paper particular attention is devoted to the susceptibility of the system in a high polluting environment.     

Improving CNC contouring accuracy by integral sliding mode control

In this paper, an integral sliding mode controller (ISMC), based on input–output models, is proposed as a refinement from a two-degree-of-freedom controller with independent objectives for tracking and regulation. Thus, the knowledge of pole placement can be utilized in ISMC. The robustness is improved by a disturbance estimation, which results in an equivalent control. To eliminate the problem of chattering, two measures adopted are an appropriate choice of the sliding surface and an integral control action. It was found that the choice of a slower natural frequency of the sliding surface dynamics than that of the open loop can ease the problem of chattering. The choice of k_i, the integral control coefficient, is based on the two-degree-of-freedom controller. Root locus is used in assisting in choosing an appropriate value of k_i to ensure the closed-loop stability. The proposed ISMC was implemented and experimentally tested in a mini-CNC machine. The contouring accuracy of the mini-CNC machine was greatly improved by the proposed ISMC. Furthermore, no chattering was observed, which is beneficial to machine actuators.     

电控机械式自动变速器在线故障诊断系统的开发

根据电控机械式自动变速器系统的特点,采用基于模型的设计方法,在MATLAB／SIMUuNK软件环境下,运用Stateflow逻辑系统建模工具建立了AMT系统的在线故障诊断模型,从而有效地对AMT系统中的传感器、执行机构和TCU硬件的主要故障进行在线诊断。大量试验表明,该设计方法是行之有效的且非常实用。     

Vibration control for active seat suspension systems via dynamic output feedback with limited frequency characteristic

This paper investigates the problem of H_∞ control for active seat suspension systems via dynamic output feedback control. A vertical vibration model of human body is introduced in order to make the modeling of seat suspension systems more precise. Meantime, different from the existing H_∞ control methods which conduct disturbance attenuation within the entire frequency domain, this paper addresses the problem of H_∞ control for active seat suspension systems in finite frequency domain to match the characteristics of the human body. By using the generalized Kalman-Yakubovich-Popov (KYP) lemma, the H_∞ norm from the disturbance to the controlled output is decreased over the chosen frequency band between which the human body is extremely sensitive to the vibration, to improve the ride comfort. Considering a practical situation of active seat suspension systems, a dynamic output feedback controller of order equal to the plant is designed, where an effective multiplier expansion is used to convert the controller design to a convex optimization problem. Compared with the entire frequency approach for active seat suspension systems, the finite frequency approach achieves better disturbance attenuation for the concerned frequency range, while the performance constraint is guaranteed in the controller design, which is verified by a practical example with certain and random road disturbances.     

All inkjet-printed piezoelectric polymer actuators: Characterization and applications for micropumps in lab-on-a-chip systems

Digital printing technologies are promising as future manufacturing approaches due to their capabilities of highly flexible and additive material deposition on various substrates. In this contribution, all inkjet-printed piezoelectric polymer actuators are presented based on polyvinylidene fluoride trifluoroethylene (P(VDF-TrFE)) and electrodes printed from silver nanoparticle dispersions. The target application for the actuators described here are membrane pumps for microfluidic lab-on-a-chip (LOC) systems. For the first time, all-inkjet-printed P(VDF-TrFE) actuators are reported and the corresponding piezoelectric d₃₁ coefficient is measured. For manufacturing the actuators, a low-cost procedure is employed that consists of only three inkjet printing and post-processing steps where moderate thermal treatments (T_max = 130 °C) are combined with plasma sintering. The processing is therefore compatible with a wide range of temperature sensitive polymer substrates, completely additive and highly flexible. A sandwich-like structure of a piezoelectric P(VDF-TrFE) layer between two silver electrodes is inkjet-printed onto a polyethylene terephthalate (PET) substrate. When a voltage is applied across the piezoelectric layer, the reverse piezoelectric effect will lead to a bending deflection of this unimorph structure. The piezoelectric d₃₁ coefficients are found to be approximately 7 to 9 pm V⁻¹, which allows the generation of significant actuator deflections. For the application in a micropump, flow rates of several 100 μL min⁻¹ are anticipated, which is promising for LOC applications. Most current micropumps are based on actuator elements that are fabricated separately and mounted on a passive membrane. By using all inkjet-printed actuators, as presented here, the joining step is avoided and the benefits of low-cost printed devices are added to the well-developed processing approaches for microfluidic chips.     

Joint optimization approach to building vibration control via multiple active tuned mass dampers

This paper puts forward a novel optimization approach for Multiple Active Tuned Mass Dampers (MATMDs) system under seismic and wind-induced building vibration. A model of an n-storey building with MATMD system is established and a joint optimization method is used to obtain an optimal state-feedback controller gain and the parameters of the MATMD system. A mixed H₂/H_∞/GH₂ control is employed to attenuate the seismic and wind-induced vibration of the building with the constraints of the actuating forces and strokes of the masses. Genetic algorithm (GA) is used to search for the optimal parameters and obtain the corresponding controller gain. Two illustrative examples are presented in this paper. In the first comparison, the GA-based approach can obtain a better set of parameters and achieve better control performance. When comparing with an Active Tuned Mass Damper (ATMD), an MATMD system can achieve similar control effects with much smaller acting forces.     

Fault diagnosis of active magnetic bearings

Active magnetic bearings (AMBs) are intrinsically unstable systems and require feedback control to ensure stable operation. Further, sensors, actuators, and the rotor need to operate under normal conditions, and a fault detection and diagnostics system is necessary to ensure a safe and reliable operation. Accordingly, several studies have developed methods to detect failures associated with the rotor or the electrical system (i.e., AMB). However, prior identification of the dynamic system parameters or the magnetic forces is usually desired, which can be impractical for real machines. To overcome this problem, this study proposes a failure detection method based on a mathematical model and the correlation between the measured states related to the rotor and the control. Artificial neural networks are used to map the states that cannot be measured, and faults are determined by comparing the output correlations of neural networks. Faults in the AMB/rotor system are identified considering various rotor unbalance configurations (mechanical failures) and failures in the position sensor gain and in the magnetic actuator current (electrical failures). Various fault configurations were explored for each case cited. A comparison of the theoretical and experimental results showed good agreement, which demonstrates the adequacy of the method in detecting mechanical and electrical failures in industrial machines.     

Modeling and control of a 2Dof PM synchronous actuator using Hall effect sensors

At the present time, actuators with several degrees of freedom (Dof) are being used more and more frequently. In order to yield viable devices, it is necessary to ensure high performance, as well as keeping the cost low. This paper deals with the modeling and control of a 2Dof permanent magnet planar actuator. A prototype dedicated to theoretical conclusion validations is presented and its operation explained. A model, based on a permeance network, is introduced. The simulation results are compared to measurements obtained using a manufactured prototype. Three Hall effect sensors are then used to obtain the x–y position of the moving part. From these signals, simulations of a scalar control are obtained using Matlab Simulink^®.     

A compact instrumentation amplifier for MEMS thermal sensor interfacing

A compact CMOS instrumentation amplifier, based on a properly modified second order G _m?CC low pass filter (LPF), is proposed as a possible readout channel for integrated thermal sensors. Low noise and low offset characteristics are obtained by applying chopper modulation to the input transconductor. The high input thermal noise density, typical of low frequency G _m?CC filters, has been significantly reduced by adopting a two-stage topology for the first transconductor. Using this approach, an input noise density adequate for thermal sensor interfacing was obtained with no need of off-chip capacitors. The intrinsic filtering property of the amplifier effectively rejects the modulated offset ripple, allowing direct connection of the amplifier output to a low sampling rate AD converter. An original switching strategy involving swapping of the input and feedback ports is used to improve the gain precision. The effectiveness of the technique is proven by means of analytical arguments and electrical simulations performed on a prototype, designed with the STMicroelectronics BCD6s process.     

H∞ control of a flexible gantry robot arm using smart actuators

This paper presents new feedback actuators to achieve an accurate position control of a flexible gantry robot arm. The translational motion in the plane is generated by two d.c. motors and controlled by electro-rheological (ER) clutch actuators. The generated motion can be continuously controlled by controlling the intensity of electric fields imposed to the ER fluid domains of bi-directional rotating ER clutches. On the other hand, during control action of the translational motion, a flexible arm attached to the moving part produces undesirable oscillations due to its inherent flexibility. The oscillations are actively suppressed by employing feedback voltage to the piezoceramic actuator bonded on the surface of the flexible arm. Consequently, an accurate position control at the end-point of the flexible arm can be achieved. In order to accomplish this control target, the governing equations of the proposed system are derived and rewritten as transfer functions to design a robust H_∞ controller. The control electric fields to be applied to the ER clutch and the control voltage for the piezoceramic actuator are determined via the loop shaping design procedures (LSDP) in the H_∞ control technique. Control results of position regulating and tracking are provided to evaluate the effectiveness of the proposed methodology.     

Robust Adaptive Fault Estimation for a Class of Nonlinear Systems Subject to Multiplicative Faults

In this paper, a fault estimation problem for a class of nonlinear systems subject to multiplicative faults and unknown disturbances is investigated. Multiplicative faults usually mixed with system states and inputs can cause additional complexity in the design of fault estimator due to parameter changes within process. Especially for the nonlinear system corrupted with unknown disturbances, it is not an easy work to distinguish the real fault factor from the mixed term. Under the nonlinear Lipschitz condition, the proposed robust adaptive fault estimation approach not only estimates the multiplicative faults and system states simultaneously, but also extracts the real effect of the faults. Meanwhile, the effect of disturbances is restricted to an L ₂ gain performance criteria which can be formulated into the basic feasibility problem of a linear matrix inequality (LMI). In order to reduce the conservatism of the proposed method, a relaxing Lipschitz matrix is introduced. Finally, an illustrative example is applied to verify the efficiency of the proposed robust adaptive estimation scheme.     

Design and control of a mechanical rotary variable impedance actuator

To realize different tasks in human-robotic interaction, various mechanical variable stiffness actuators are being investigated. A mechanical-rotary impedance actuator (the MeRIA) is presented that is based on the controllable effective length of a mechanical bending bar, which can be implemented into an orthosis for future research on rehabilitation training. The actuator provides joint motion and variable stiffness, simultaneously. The control task can be decoupled to be a decentralized control structure for which the controller of the two motor power sources can be designed respectively. For the movement control-loop, a cascaded impedance controller with position-torque-velocity control-loops are designed to maintain a stable and safe working environment. Using an H_∞ loop-shaping methodology, a robust stabilization torque controller is achieved. The trade-off between the actuators performance and stability is taken into account to obtain a desired shape as a precondition of an H_∞ controller synthesis. The actuator is tested on a test bench using rapid control prototyping. A model reduction algorithm is implemented to simplify the controller, and a prefilter design reduces the control-loop overshoot, thereby improving the robust stability and tracking performance during application. Experiments show that the MeRIA meets all the requirements for a mechanical device attached to the body.     

Experimental modeling of hysteresis in stage systems: A Maxwell–Iwan approach

Dynamic links of high-precision stage systems consist of wires and hoses that are used for example to transport electrical current to the actuators and sensors or cooling liquids to the stages. During stage motion, these dynamic links typically express complex hysteretic behavior due to internal friction and viscoelastic properties. As such, dynamic links give rise to unwanted disturbances acting on the high-precision stage systems. This paper presents a simple but accurate physics-based and experimental modeling procedure. The generalized Maxwell model and a modification of the Iwan model are combined in parallel to capture both frequency dependencies by viscoelastic effects and amplitude dependencies by friction-based effects. The modified and physically meaningful Iwan model is shown to be equivalent to the well-known Bouc–Wen model. A so-called normalized dissipation factor is introduced to quickly recognize frequency and/or amplitude dependent behavior using measured data. Using this information, a well-founded choice for an (initial) model structure to be identified can be made. Subsequently, an identification procedure is proposed to estimate values of the model parameters again using the measured data. A simulated experiment is used to show the use of the normalized dissipation factor and validate the identification procedure. Finally, the validity and usefulness of the Maxwell–Iwan modeling approach is demonstrated by experimental results obtained from an industrial wafer stage system.     

Hybrid fault diagnosis for telerobotics system

Fault detection and isolation (FDI) of a class of networked control systems (NCS), applied for telerobotics system is studied in this paper. The considered NCS application is related to telerobotics system, where it is modelled with a hybrid manner, by including the continuous, discrete, uncertain, and stochastic aspects of all the system components. The main considered components of the NCS namely the network system and controlled system are completely decoupled according to their operation characteristics. The network part is taken as a discrete and stochastic system in presence of non-structured uncertainties and external faults, while the controlled part is considered as a continuous system in presence of input and output faults. Two model based fault diagnosis approaches are proposed in this paper. The first concerns a discrete and stochastic observer applied to the network system in order to detect and isolate system faults in presence of induced delay on the network part. The second is based on the analytical redundancy relations (ARR) allows detecting and isolating the input and output system’ faults. Experimental results applied on telerobotics system, show the performance and the limit of the proposed fault diagnosis approach.     

Deformation Anisotropy of <Emphasis Type="Italic">Y</Emphasis> + 128°-Cut Single Crystalline Bidomain Wafers of Lithium Niobate

Bidomain single crystals of lithium niobate (LiNbO₃) and lithium tantalate (LiTaO₃) are promising materials for use as actuators, mechanoelectrical transducers, and sensors capable of working in a wide temperature range. One need to take into account the anisotropy of the properties of the crystalline material when such devices are designed. In this study we investigated deformations of bidomain round shaped Y + 128°-cut wafers of lithium niobate in an external electric field. The dependences of the piezoelectric coefficients on the rotation angles were calculated for lithium niobate and lithium tantalate and plotted for the crystal cuts which are used for the formation of a bidomain ferroelectric structure. In the experiment, we utilized an external heating method and long-time annealing with the lithium out-diffusion method in order to create round bidomain lithium niobate wafers. Optical microscopy was used to obtain the dependences of the bidomain crystals’ movements on the rotation angle with central fastening and the application of an external electric field. We also modelled the shape of the deformed bidomain wafer with the suggestion that the edge movement depends on the radial distance to the fastening point quadratically. In conclusion, we revealed that the bidomain Y + 128°-cut lithium niobate wafer exhibits a saddle-like deformation when a DC electric field is applied.