Index Terms—Semiactivecontrol; backstepping; Quantitative Feedback Control; Suspensioncontrol; magnetorheological damper. F
1 I NTRODUCTION
Suspension systems are one of the most critical com- ponents of a vehicle. They are designed to provide comfort to the passengers, to protect the chassis and the freight. In the case of aircrafts, the landing gears fulfill these tasks. Not only are they designed to provide com- fort during taxiing but absorb the energy during touch down. Suspension systems are normally provided with dampers that mitigate these harmful and uncomfortable vibrations . In general, these dampers are passive, meaning that they are tuned once during design and construction not allowing for further changes once they are installed. This class of dampers is still in wide usage, but the fact that passive dampers cannot change their dynamics in response to different inputs is a drawback because they may not respond as expected in every single circumstance. This is why active and semiac- tively tuned dampers are being widely studied. As a result, several active and semiactive damping devices are already installed in commercially distributed vehicles and big efforts towards the implementation of active and semiactivedampers in aircraft are being done . Compared with passive dampers, active and semiactive
But this capability increases the sensitivity to high impact disturbances. If the hard mode damping is increased too much, the system cannot damp the sudden impacts. As it can be seen in the Table 5.4, very large hard damping coefficient, makes the comfort response of the system worse. Hence, there is a tradeoff between this sudden impact response and road holding capability. For all values of hard damping mode that are evaluated in the tables that show the response of the ON/OFF system for the step shaped obstacle, the system reaches steady state earlier than passive system. Even when the system gives the same transient response characteristics, the semi active ON/OFF system reaches the steady state earlier. According to all of these results, the semi active ON/OFF system is better than the passive system for smooth road disturbances when compared with their accelerations and suspension deflections. But in transient response of high end impact disturbance, as the damping increases, the comfort drops dramatically for the ON/OFF system.
experimental off-road vehicle which is equipped with suspensionmagnetorheological (MR) dampers. Accelerometers and vehicle progressive velocity sensors are installed in body and underbody parts of the vehicle and are used in control scheme. Furthermore, IMU modules and suspension deflection sensors were used for validation of measurement part of the system. Semiactive Skyhook control algorithm, including on/off and smooth suspension MR damper control, was implemented in order to validate the control system. Quality of measurements is deteriorated by multiple factors including vehicle engine and shape of tires which was examined. Experimental results indicated better vibration suppression of vehicle body part for smooth Skyhook controller compared with passive soft and hard suspension. The presented semiactivesuspensioncontrol system can be applied for complex vehicle dynamics analysis and control schemes dedicated to both the ride comfort and ride safety issues.
max = 0.15 A where a is varied between zero and one. As with the linearized modiﬁed sky- hook system, pure skyhook control (a = 0) provides the most superior response in terms of passenger comfort (Fig. 13(a)). However, with reference to Fig. 13(b), the on/off system is unable to signiﬁcantly suppress the wheel hop vibrations when a is increased. Although some improvement can be observed for a > 0, an analysis of the area under the PSD curves illustrates that there is no improvement in the RMS wheel contact force. Thus it is concluded that pure skyhook control is more suitable than modiﬁed skyhook control, for an on/off system. This result is in agreement with the present authors’ previous ﬁndings in a recent numerical study of a Fig. 12 Damping force-time history for the linearized quarter car MR suspension .
Benjamin B. Stewart, M.S.T.
Western Carolina University (October 2015) Advisor: Dr. Sudhir Kaul
Magnetorheological (MR) fluid is a smart fluid containing ferrous particles that allow it to change its apparent viscosity in the presence of a magnetic field. Dampers consisting of MR fluids provide a means of active damping by using a current input to an electromagnet to control the damping properties. A swing arm suspension system is unique to two-wheeled vehicles, and links the rear wheel to the frame of the vehicle through a pivot. The swing arm also connects the rear suspension system to the frame. The goal of this study is to experimentally analyze the vibration mitigation capabilities of MR dampers in a (rear) swing arm suspension system in a motorcycle. A set of commercially available MR dampers is used in a fixture that has been developed to represent the rear swing arm system. The dampers are characterized and preliminary mathematical models have been developed to investigate the capability of the damping system. Multiple iterations of testing are performed on the shaker table to evaluate the performance of the damping system at different locations of the frame. Accelerometers are used for this evaluation, and the analysis of the acceleration data is performed in time domain as well as frequency domain. Results indicate that the mitigation in root mean square (RMS)
Stability analysis is one of the most essential issues in system and control engineering fields. However, a critical question would often arise; “Should a stability issue be formulated for a semiactivecontrol system design?” The reason to ask this question is that it is generally said that a semiactivecontrol system is inherently stable in bounded input and bounded output (BIBO) sense because a semiactive device does not add mechanical energy into a structural system (Jung et al. 2003). This might be true for open loop systems; however, it is not always necessarily true for feedback control systems because a semiactivecontrol system can be destabilized due to structure- semiactive device interaction, inaccurate plant or actuator modeling, etc. (Kuehn and Stalford 2000; Jin et al. 2005). However, what should be more stressed here is that actually the statement that a semiactivecontrol system is stable in the BIBO sense can not be automatically generalized. Note that the building-MR damper system is a nonlinear time-varying (NTV) dynamic system. Therefore, stability should be necessarily considered for a semiactivecontrol system design. In particular, it might be much more important issue in a semiactive nonlinear control system.
These days road vehicles contain several individual active control mechanisms that solve a large number of control tasks. These components are often highly nonlinear, which are mod- elled as hybrid systems. An example is the semiactive/active suspension system, which can be modelled as a nonlinear dynamics augmented with an actuator that has a bimodal dy- namics, i.e. a closed loop switching system with two modes. Moreover, in traditional control systems the vehicle functions to be controlled are designed and implemented separately. Al- though in the design of the individual control components only a subset of the full vehicle dy- namics is considered these components inﬂuence the entire vehicle. Thus in the operation of these autonomous control systems interactions and conﬂicts may occur that might overwrite the intentions of the designers concerning the individual performance requirements. The aim of the integrated controlmethodologies is to combine and supervise all controllable subsys- tems affecting vehicle dynamic responses in order to ensure the management of resources. The solution might be the integration of the control logic of subsystems.
Consistent attempts have been made in the past to design efficient shock absorbers without compromising the weight of an aircraft. Since the World War II, many revolutionary shock absorber designs were implemented for the fighters as well as for the commercial aircraft. A good shock absorber should absorb most of the impact kinetic energy during landing and taxiing of an aircraft. Currently, Oleo-pneumatic shock absorbers are the most commonly used shock absorbers in aircraft landing gears because of their high efficiency and ability to absorb shocks and dissipate energy effectively. Due to the conflicting damping requirements during taxiing and landing phases, the performance efficiency of the aircraft with the passive Oleo dampers is often limited. The existing dampers are not capable of providing the variable damping depending upon the requirements during each operational phase. In order to improve the landing performance, a soft suspension would be desirable during compression, whereas a stiffer spring would be needed during extension. These variable damping and stiffness requirements cannot be achieved with the existing passive shock absorbers .
Fig. 6. 3D vision of damper force.
IV. C ONCLUSION
Magnetorheological (MR) dampers are devices that can be used for vibration reduction in structures. However, to use these devices in an effective way, a precise modeling is required. In this sense, in this paper we have considered a modified parameter identification method of large scale magnetorheologicaldampers which are represented using the normalized Bouc-Wen model. The main benefit of the proposed identification model is the accuracy of the parame- ter estimation. The validation of the parameter identification method has been carried out using a black-box model of an MR damper in a smart base-isolated benchmark building. Magnetorheological (MR) dampers are used in this numerical platform both as isolation bearings as well as semiactivecontrol devices.
In the past forty years, the concept of controllable vehicle suspension has attracted extensive attention. Since high price of an active suspension system and deficiencies on a passive suspension, researchers pay a lot attention to semi-active suspension. Magneto-rheological fluid (MRF) is always an ideal material of semi-active structure. Thanks to its outstanding features like large yield stress, fast response time, low energy consumption and significant rheological effect. MR damper gradually becomes a preferred component of semi-active suspension for improving the riding performance of vehicle. However, because of the inherent nonlinear nature of MR damper, one of the challenging aspects of utilizing MR dampers to achieve high levels of performance is the development of an appropriate control strategy that can take advantage of the unique characteristics of MR dampers. This is why this project has studied semi-active MR control technology of vehicle suspensions to improve their performance.
to update the MR damper parameters by using sinusoidal excitations with different frequencies and amplitudes being applied at the ground level of the structure. Concretely, three configurations are studied: (1) Two MR dampers installed between the base and the first floor (2) Two MR dampers installed between the first and second floor and (3) two MR dampers on each of the fist two floors of the structure. Forces generated by each MR damper and accelerations induced to each floor are measured in order to identify and optimize the MR damper parameters. The FMINCON optimization function is used to determine the optimal values by taking the values obtained in the step 1 as the initial values. The objective function is defined as the error between the experimental and predicted accelerations at each floor. Predicted responses are calculated by using the optimal M s , C s and K s matrices. As a result, the following optimal MR damper parameters are obtained: δ a = 0.0454;
In recent years, magnetorheological (MR) fluids have attracted researchers’ interest due to their wide range of use as vibration dampers for vehicle suspension systems (Bakar et al., 2011). Their damping capabilities can be adjusted very quickly by applying suitable electric or magnetic fields (Stanway et al., 1996; Bakar et al., 2011). MR fluid dampers enable vibration control of semi active suspension systems with reaction times in the range of milliseconds; in addition, it requires low power consumption. Due to their rather simple mechanical design which involves only few moving parts thus ensure high technical reliability and exhibit almost no wear (Butz and Stryk, 2002). These fluids can vary their viscosity by varying the magnetic field across the fluid. The fluid contains iron particles which are aligned by magnetic field (Spencer et al., 1997) and this alignment makes the oil stiffer and rigid. The fluid responds very quickly and the alignment can be done within 6.1 ms (millisecond) (Symans and Constantinou, 1999). The MR damper is seen as a safe damper, because of its action when power loss occurs; after semi active suspension loss its power it will reverts to a passive damper.
Serving as a semiactivecontrol element, a magnetorheological (MR) damper is a smart damping device that is controlled by a magnetic field . An MR damper with semiactivecontrol integrated with the controllability and flexibility of active dampin g can adjust its damping force in response to load force and structure and is characterized by passive stability and energy conservation. The dynamics of an MR damper under different input voltages  enable the input voltage to pass through a current driver, which generates an electric current. The electric current then passes through a coil to generate a magnetic field; adjusting the input voltage thus changes the magnetic field strength.
The recent advent of commercial magnetorheological (MR) fluid dampers has made it possible to vary the damping force almost instantaneously with very few mechanical parts [14,18]. This reduc- tion in complexity permits high-bandwidth, low-power performance with reduced concerns about durability and maintenance. These semiactivedampers contain MR fluids, which are suspensions of micron-sized, magnetizable particles in an oil-based fluid. In the absence of magnetic fields, these fluids exhibit Newtonian behavior. The application of an external magnetic field causes the particles to become aligned with the field, and dramatically changes the effective viscosity of the fluid. MR dampers are controlled by manipulating a low-power coil current to vary the effective damping coef- ficient [14,18]. Recently, Carerra has introduced MagneShocks TM for semiactive vehicle suspensions
Output feedback control using Magnetorheologicaldampers and Variable Sti ﬀness Tuned Mass Dampers is considered. Firstly, seismic response control of a building with MR dampers is considered. Optimal Static Output Feedback (OSOF) control yields the desired control force. Two laws are proposed to obtain voltage that achieves the desired force. OSOF yields a reduction in responses and CPU time vis-a-vis LQG and Passive-on controllers. Instantaneous Optimal Control is also considered. Next, a sti ﬀ and a ﬂexible building are connected by a MR damper. Input voltage is predicted by a Recurrent Neural Network using desired control force from LQG /OSOF. Both output feedback controllers yield signiﬁcant reduction in response and base shear and require much less control e ﬀort compared to passive-on control. Lateral-torsional seismic response control of plan asymmetric buildings connected by MR dampers is also studied. Finally, control of a wind excited benchmark building using a Variable Sti ﬀness TMD is considered. The nominal sti ﬀness corresponds to the fundamental frequency, resulting in an LTI system for which the desired control force is computed using OSOF /LQG control. A simple control law yields the device conﬁguration. The present control is comparable with active-TMD and better than Short-time-Fourier-Transform control. A variable length pendulum TMD is proposed.
2.2. Experimental Setup. The viscoelastic properties of the
MRE samples were investigated by a system shown in Figure 1(b). In this system, two MREs worked as system springs/dampers, and they were placed between the iron cores of an electromagnet. While the lower core was installed on a base exposed to excitation, the upper core was fixed along with a load sensor. The base was excited by a shaker (EMIC Corp. Model 371-A) whose excitation signal was supplied by a signal generator and a power amplifier (EMIC Corp. Model 371-A). The displacement of the base and upper core’s force were measured by using a laser displacement sen- sor (KEYECE LB-02) and a load sensor (PCB PIEZOTRON- ICS 208C02), respectively. The force-displacement response was processed by a Fast Fourier Transform (FFT) spec- trum analyzer (ONOSOKI CF-5220Z). A direct current (DC) power supply (TAKASANGO ZX-400LA) provided adjustable DC current to a magnetic coil. In dynamic tests, numerous experiments were implemented for various har- monic inputs. The excitation frequency was adjusted from 1 Hz to 30 Hz, excitation amplitude was changed from 0.4 mm to 1.4 mm, and applied current was driven from 0 A to 6 A (magnetic flux density was adjusted from 0 mT to 326 mT).
The proposed nonlinear time-frequency control method evaluated in this research can be successfully applied to MR dampers in vehicle suspension to reduce vibration amplitudes and forces transmitted to the passenger. For every test case presented, the nonlinear time-frequency control outperformed the skyhook control algorithm in terms of minimizing acceleration of the car body. If the priority of the controller is only to reduce the amplitude of vibrations, the skyhook controller should be selected over the proposed nonlinear time-frequency controller. Because nonlinear time-frequency control is a feed-forward controller, it has a better ability to compensate for the time delay of the MR damper compared to a feed-back controller such as skyhook. Another benefit of the nonlinear time-frequency controller is that it is adaptive. This is important so that the controller can account for changes in the physical model. The adaptive algorithm also benefits the system because when the controller is implemented in a physical system, additional nonlinearities not previously accounted for in simulation can be managed. For example, depending on how the vehicle is loaded, the mass values will be different and the controller must be able to adapt to provide an ideal response.
2.2 MR Fluid Dampers
MR dampers typically consist of a piston, magnetic coils, accumulator, bearing, seal, and damper reservoir filled with MR fluid . Figure 2.3 shows a Lord RD-1005-3 MR fluid damper , which is used in this study. In this damper, as the piston rod enters the housing, MR fluid flows from the high pressure chamber to the low pressure chamber through orifices in the piston head. The accumulator contains a compressed gas (usually nitrogen) and its piston provides a slightly moveable barrier between the MR fluid and the gas. The accumulator serves three purposes: (i) it provides a degree of softening by providing an extra allowance for the volume changes that occur when the piston rod enters the housing; (ii) it accommodates thermal expansion of the fluid; (iii) it prevents cavitation in the MR fluid during piston movements. The magnetic field generated in the activation regions by the magnetic coils changes the characteristics of the MR fluid as discussed in the previous section. Consequently, the magnitude of the magnetic coils’ input current determines the physical characteristics of the MR damper. The maximum force that an MR damper can deliver depends on the properties of the MR fluid, its flow pattern, and the size of the damper .
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Magnetorheological (MR) dampers are a promising alternative structural active actua- tors as they provide adjustable damping over a wide range of frequencies without large power requirements. However, the complex dynamics that characterizes these devices makes it di ﬃcult to formulate control laws based on the MR damper model. Instead, many semiactivecontrol strategies proposed in the literature have been based on the idea of ”clipping” the voltage signal so that the MR damper force ”tracks” a desired active control force which is computed on-line. With this idea many algorithms have been proposed using, among others, techniques such as optimal control, H ∞ control, sliding mode control, backstepping and QFT.
A heavily damped suspension will yield good vehicle handling, but also transfers much of the road input to the vehicle body. When the vehicle is traveling at low speed on a rough road or at high speed in a straight line, this will be perceived as a harsh ride. The vehicle operators may find the harsh ride objectionable, or it may damage cargo. A lightly damped suspension will yield a more comfortable ride, but can significantly reduce the stability of the vehicle in turns, lane change maneuvers, or in negotiating an exit ramp. Good design of a passive suspension can to some extent optimize ride and stability, but cannot eliminate this compromise. The need to reduce the effects of this compromise has led to the development of active and semiactive suspensions. Active suspensions use force actuators. Unlike a passive damper, which can only dissipate energy, a force actuator can generate a force in any direction regardless of the relative velocity across it. Using a good control policy (here fuzzy loggy), it can reduce the compromise between comfort and stability. However, the complexity and large power requirements of active suspensions make them too expensive for wide spread commercial use. Semiactivedampers are capable of changing their damping characteristics by using a small amount of external power. Semi active suspensions are less complex, more reliable, and cheaper than active suspensions. They are becoming more and more popular for commercial vehicles.