Magneto-rheological fluids consist of stable suspensions of micro-sized

Magneto-rheological fluids consist of stable suspensions of micro-sized, magnetisable particles dispersed in a carrier medium such as silicon oil or water. When an external magnetic field is applied, the polarization induced in suspended particles results in the MR effect of the MR fluids. The MR effect directly influences the mechanical properties of the MR fluids. The suspended particles in the MR fluids become magnetized and align themselves, like chains, with the direction of the magnetic field. To design the MR fluid brake for a given specification, one must establish the relationship between the torque developed by MR fluids and the parameters of the structure and the magnetic field strength. In this paper the fundamental design method of the cylindrical MR brake is investigated theoretically. A Bingham model is used to characterize the constitutive behaviour of the MR fluids subject to an external magnetic field strength. The theoretical method is developed to analyze the torque transmitted by the MR fluid within the brake. An engineering expression for the torque is derived to provide the theoretical foundation in the design of the brake.
Magneto-static analysis was performed, to understand the dependence of casing thickness on the generation of magnetic flux density in the MR fluid region of a MR brake. Initially, analysis was performed for an electromagnet and the analysis was extended for MR brake. The validation of the magneto-static analysis was performed by comparing the reading obtained from Gauss meter for the developed electromagnet. For MR brake, magneto static analysis was performed by varying the thickness of casing from 0.001m to 0.01m, by a step of 0.001m. It was observed that the magnetic flux density values increased with increase in thickness till 0.007m and remained almost constant thereafter. Based on this results an MR brake was developed with casing thickness of 0.007m.
This study explores the CFD model of a MR fluid, based on the Bingham model whereby the yield stress is dependent on the height of the fluid gap and flux density in the gap. This model may be useful in design of semi-active and passive devices containing MR fluid, which are being investigated by the authors under the current research project.
Experiments results were obtained for a commercially available MR fluid MRF-122EG (manufactured by Lord Corporation), operated in squeeze mode. The relationship was established between the yield stress and the position of the plate. The pro-posed viscosity model agrees well with experimental data.
The analysis of MR fluid’s behavior in squeeze mode is a major challenge for researchers. In the next step the proposed model should be verified under different excitations applied to the plate and for higher values of the magnetic flux density, taking into account other types of fluids and the real MR devices operated in squeeze mode. The current version of the CFD model fails to take into account the extension of fluids. mineral oil and synthetic oil can be used for preparation of MR fluid and also by using ferrous is mixed with vegetable oil. it was also known that addictives are added to the fluid to reduce friction and preventing particle oxidation and wear Approximately 70 years ago, Jacob Rainbow (1948) invented the magnetorheological (MR) fluid at the US National Bureau of Standards. As a classical smart material, MR fluid consists of soft micrometer-sized (0.1–100 mm) magnetic particles, carrier liquid, and stabilizing additives. In principle, a shearing torque can be created and controlled by changing the direct current which applied to the electromagnet as the viscosity of MR fluid changes, that is, in the inactive state, the magnetic particles in the MR fluid maintain a state of free suspension as the fluid behaves a free flowing fluid, while upon activation, MR fluid stiffens in the presence of a magnetic field. Moreover, MR fluid exhibits approximately linear response,that is, the increase in stiffness is directly proportional to the strength of the applied current, and it provides shorter delayed response time, i.e., MR fluid can change from a fluid state to a semi-solid or solid state within milliseconds (200 -300 ms) of exposing a magnetic field (Wiehe and Maas, 2013. At present, two main types of brake are concerned and widely studied, that is, disc-shaped MRB and cylindrical MRB. In general, the disc-shaped MRB is composed of a rotary shaft and braking disc, an electromagnetic coil, MR fluids, and casings, and the MR fluid fills the MR fluid gap between the braking disc and the casings. In the cylindrical MRB, the MR fluid fills the MR fluid gap between the fixed outer cylinders; Northeastern tem is a thin cylinder (Nguyen and Choi, 2010). In the realm of MRB, the theoretical and structural study of MRB has been proposed by scholars. Huang et al. (2002) theoretically investigated the geometric design method of a cylindrical MR fluid brake and derived the engineering design calculations of the volume, thickness, and width of the annular MR fluid within the brake. Li and Du (2003) designed, fabricated, and tested a disc-shaped MRB prototype to address the effects of magnetic field and rotary speed on the transmitted torque. Senkal and Gurocak (2010) developed an experimental setup for a new flux path to obtain higher torque; meanwhile, a low friction sealing technique was used to reduce the off-state braking torque and to prevent the fluid from leaking. And the results showed that due to the serpentine flux path, their smaller MRBs could generate about 2.7 times more torque than a commercial one. While Park et al. (2008) designed a MRB consists of multiple rotating discs, meanwhile, a finite element analysis (FEA) was designed to analyze the resulting magnetic circuit and heat distribution within the brake.. The extremely severe heating of MRBs restricts their application in high power situations, and Wang et al. developed a novel MRB with a water cooling system, the experimental results indicated that the proposed MRB was capable of producing a highly controllable brake torque, and the water cooling method can effectively assist in heat dissipation from the MRB. Shiao and Nguyen (2013) presented a new approach in the design and optimization of a novel multi-pole MRB that employed magnetic flux more effectively on the surface of the rotor. The results indicate that the braking torque of the proposed MRB is higher than that of the MRB operating only under shear. Nguyen et a investigated a new configuration of MRB with coils placed on the side housings of the brake on the side housings, which was much easier for manufacturing, testing, and maintenance than the conventional one. Both rectangular and seven-control point polygon shapes of the brake envelop were considered to minimize the mass of the brake that can provide a required braking torque, and the results showed that the off state torque of the proposed MRB is smaller than that of the conventional one. A smaller gap will be better because it could reduce the magnetic reluctance, and thus increase the magnetic field intensity of the MR fluid gap so as to enlarge the brake torque; however, it would pose many difficulties for manufacture and Therefore, there are few experimental investigations about the braking performances of MRB with small gap. In this article, the concept of a MRB whose gap can be altered freely and precisely is proposed to investigate the effect of a small gap on the braking torque, with detailed adjusting principle. The braking torque of each disc-type MRB is derived based on the Bingham plastic behavior of the MR fluid and a simple braking torque model. In addition, this work considers uneven distribution of magnetic field on the left and right sides of the housing. FEA is employed to evaluate the performance of the proposed MRB, and the prototype of the proposed MRB is built and a series of tests are carried out to verify the effect of a small gap on the braking performance. Theoretically, a smaller gap distance is better because the permeability of the MR fluid in the gap is much less than those of the iron-based bobbin and flux return, and practical gaps typically range from 0.25 to 2 mm for ease of manufacture and assembly. Previously, in order to improve the working efficiency of MR valves, some methods proven effective were employed by scholars to change the MR fluid gap (Similarly, in order to reduce the experiment cost, the structure of the brake with the adjustable fluid gap should be designed to investigate the braking performance of a disc-type MRB in different small gaps with high efficiency, a configuration of the proposed MRB is introduced, which mainly consists of the shell part, the coil, the fluid gap adjusting system, the subsidiary structure, the sealing components, and the MR fluid. The first part is the shell part which is composed of the front shell, the rear shell, the out ring, and the back end cover. The second part is the coil which is located in the shell and the MR fluid is in a freely flowing state when the electrical current is not applied to it, and the off-field viscosity of the MR fluid only produces a small braking
Journals of Intelligent Material Systems and Structures
. However, a magnetic field is generated in the MRB when the coil is energized, and the MR particles gather to form many particle chains in the field direction in this state; in the meantime, the mutual attraction between the adjacent micron-sized particle chains leads to the formation of a columnar or reticular structure, which presents a controllable yield stress. The third part is the fluid gap adjusting system, which is mainly composed of the shaft, the braking disc, the inner and outer sleeve, and the bearing, and this part completes the gap adjustment function of the brake. There is a small MR fluid gap represented by the black area above, which is filled with MR fluid between the braking disc and the housing. The shear friction between the braking disk and the solidified MR fluid provides the main braking torque, and the braking torque could be continuously adjusted by regulating the applied current and the fluid gap size. The fourth part is the subsidiary structure which is comprised of the bracket, the baffle ring, and the magnetic-insulator, and the bracket is used for fixing the brake to complete the experiment, while the magnetism-insulator is placed between the front shell and the rear shell to guarantee the fluency of magnetic flux and to reduce the magnetic flux leakage. The last part is the sealing components, which mainly composed of the skeleton oil seal and the O-ring. The former is mainly used to prevent the MR fluid from leaking to the gap regulating system which is located on the left side of the braking disc, and the latter can effectively prevent the MR fluid from leaking at the contact gap between the back end cover and the rear shell. The fixed sleeve is fastened on the bracket through screws; the front shell and the rear shell are connected into a whole through the out ring, meanwhile, using six screws to fix the position of the back end cover in circumferential direction to prevent the position change of the back end cover caused by vibration produced in the braking process. In this configuration of the proposed MRB, the gap filled with MR fluid is altered by adjusting the distance between the braking disc and the shells in both sides of the brake the adjustment of the gap is transformed into that of the shaft along the horizontal with precise movement.; at this time, the gap between the braking disc and the right side wall is 0 mm. Second, the inner sleeve is rotated for two circles counter clockwise; at this time, the gap between the braking disc and the front shell wall is 2 mm. Third, the back end cover is rotated until it is close to the braking disc; at this time, the gap between the braking disc and the back end cover is 0 mm. Finally, the inner sleeve is rotated for one circle clockwise, the displacement of the braking disc moving toward the front shell wall is 1 mm, and the left and right sides of the fluid gap of 1 mm will be obtained MRB can meet the design targets for obtaining different small fluid gaps. Feasibility and accuracy of the method on the braking torque calculating of irregular structure MRB is verified by the experimental results. The tests results show that the braking performance of the proposed MRB behaves stable for an extended period of time, and the impact of the gap size on the initial torque generated by the off field viscosity can be disregarded because this part is relatively lower than that produced by MR effect; moreover, the fluid gap has a hung influence on the braking performance within the range from 0.25 to 1 mm. Future work may focus on friction and wear tests to assess the longevity of the braking disc and the system, and to ensure that it can effectively replace the existing hydraulic brake technology. The proposed MRB can be further improved in terms of magnetic circuit design and heat dissipation by introducing water cooling system or using other kinds of MR fluid with better temperature properties—Magneto-rheological (MR) fluid is a widely used smart material due to its outstanding properties. This paper presents the design, development, modeling, and prototype testing of a self-energizing and self-powered magnetorheological (MR) brake-by-wire system, whose aforementioned capabilities are enabled by brake energy harvesting. The system is composed mainly of a typical T-shaped drum-type MR brake and a wedge mechanism for self-energizing purpose. Into the system, we also install a generator that harvests regenerative energy during braking; thereby creating a self-power capability that cannot be found in common vehicular brake-by-wire systems. Brake torque analysis is conducted, and the braking process is simulated in a Matlab/Simulink environment. Finite element analysis of the magnetic field, temperature field, and mechanical strength of critical components is carried out. The simulation results are used to optimize design parameters and material selection. Finally, prototypes and a corresponding test rig are established. A MR brake within a specified volume is normally not large enough for the automotive applications. From the previous research works the conclusion can be drawn that there are mainly three ways to increase the brake torque. The first way is modifying the structure of the brake disc, so that the effective working area of the MR fluid could be increased. Multiple-disk MR brakes and clutch were widely tested generating much larger brake torque than single-disk MR brakes Other scholars changed the form of the disc from disk-type into drum-type, including the so-called T-shape MR brake Besides, the change of the edge of a brake disk can also enlarge the brake torque, such as a wave form disc or a disk with circular cuts at the end The second way is altering the layout and size of the coils, through which the magnetic field is generated by applying electric current to them In this way, different numbers of coils with different sizes might be amounted either around the periphery or on both sides of the rotor. In addition, whether the coils are fixed in the rotors or in the stators also make a difference in terms of the intensity of the magnetic field which influences the brake torque. In the last way, the property of the MR fluid was utilized that its shear yield stress will be enlarged under compression As a consequence, the brake torque could be improved by the compression force either from the radial direction or the axial direction However, to achieve this goal, extra components which provide the compression force are necessary MR-brakes create braking torque by changing the viscosity of the MR ?uid between the rotor and the housing of the brake (In the inactive state, the ?uid has a viscosity similar to low viscosity oil. Upon activation with a magnetic ?ux, it changes to a thick consistency similar to peanut butter, creating friction between the rotor and the housing
To design an MR brake with higher torque without increasing the size of the brake, more surface area of the MR ?uid between the rotor and the housing must be activated by the magnetic ?ux. Serpentine magnetic ?ux path weaving through the rotor and the housing (left). The design was optimized based on the magnetic ?ux density computed in the ?uid gap. Number of coil turns, wire thickness, MR ?uid gap, rotor radius and width were the primary design variables. A single cycle in the optimization process consisted of making incremental changes to these variables and using FEM to ?nd the magnetic ?ux density at that design point.
An MR brake exploits the MR fluid property where polar particles in the fluid are aligned in the direction of a magnetic field to provide yield stress perpendicular to the field. Generally, the magnetic field is created by applying current to a coil. The torque of a disk-type MR brake is determined by the yield stress of the MR fluid due to the magnetic force and the diameter of the disk. The maximum yield stress is the unique property of the MR fluid and the maximum braking torque can be estimated from the disk diameter, the MR brake is designed based on the results calculated using the analytic formulation and magnetic analysis. Disposed inside the brake are the shaft for transferring rotational power, the bearing supporting and preventing the shaft from twisting, the oil sealing preventing internal fluid loss, and the disks and stators designed to apply the brake torque. Since the brake torque is determined by the contact surface coming in contact with the stators with the disks rotate, three disks are incorporated to increase torque generated. The coil is positioned inside the stator to apply the magnetic field to the MR fluid, and the housing of the aluminum material encloses the exterior to prevent magnetic field leakage.
The MR brake was constructed based on the determined disk size, inner shape, and material. The magnetic analysis results predict that the maximum yield strength of the MR fluid .The magnetization of each particle depends on the applied ?eld and on the disturbance ?elds emanating from the neighboring magnetized particles The particles then behave as magnetic dipoles which undergo magnetic interaction forces Hence, this mutual interaction amongst the particles causes the formation of chain-like structures or ?brils, aligned roughly parallel to the applied ?eld If the magnetic poles are considered as a potential surface, the interaction between a particle and the pole can be modeled as equivalent to the interaction of the particle and the dipole images of all other particles re?ected about the surface Thus, the particle, when close to the wall, has the same translational velocity. According to Bossis et al the chains are supposed to deform with the strain, thus the distance between two neighboring particles increases according to the motion The chains are subsequently continuously broken and immediately reconstituted due to the ?eld across the poles and due to the pole displacement In the absence of a magnetic ?eld, MR ?uids exhibit a Newtonian behavior. When a ?eld is imposed, the magnetic interaction between particles induces a magnetic force which is proportional to their relative position and orientation to the external ?eld and the magnetic permeability of the carrier ?uid as predicted by electromagnetic theory, there is a quadratic relationship between the applied ?eld strength and the interaction force. The ?uid displays a pre-yield regime characterized by an viscoelastic response and a post yield regime characterized by a viscous behavior The transistion point appears when the shear rate ? ? is zero; this point is called yield point ?z(H). when the ?uid is sheared, by the development of a yield stress which increases with the magnitude of the applied ?eld in a fraction of a millisecond MR-based actuators can be classi?ed as having either a valve mode, a direct shear mode or a squeeze ?lm compression mode On the conception of rotary MR-based brakes the ?uid suspension is typically placed between two magnetic poles which can be relatively displaced by the action of an external force. The chain-like structures then create a resistive force against the pole velocity. The magnetic poles interact hydro dynamically with the particles thus, if an external force induces a displacement between the magnetic poles, the ?brils are stretched according to the motion When the chains are stretched the separation between the particles by the non-magnetic liquid has a large effect on reducing the magnetic environment Thereby, it is possible to detect an external force applied along the braking direction by observing the arrangement of the chain-like structures and measuring the reluctance of the magnetic circuit. Section presents a review of MR ?uids behavior. Subsequently, the reluctance variation hypothesis is developed using an elementary group of ferromagnetic particles placed in a nonmagnetic carrier liquid. The hypothesis has been validated using a test apparatus composed of a miniature rotary MR based brake. Safety brakes are considered an essential part of modern automated robotic systems to avoid any hazardous manipulation during critical situations. A major application of these brakes is in the minimally invasive surgical systems, where the target is to avoid any motion of the end tool that can damage the important organs. Mechanical brake, pneumatic brake and hydraulic brake transmit power using inter-connected friction surfaces. Thus, a huge portion of input power is dissipated during transmission. Electromagnetic-based braking systems operate in two principles: In the first principle, an eddy current is generated in the rotating armature in opposing to the applied magnetic field while in the second principle, attraction force of an electromagnet converts the kinetic energy of rotor into heat energy Commercially available disk type electromagnetic brakes are operated in an on-off fashion, which are hardly controllable In these spring-plate based magnetic brakes, the magnetic forces are utilized to engage the rotating armature against a friction surface whereas the spring restoring force acts to dis-engage the brake. Most of the input power is utilized for overcoming this restoring force and thus the range of adjustable braking force is very limited. Due to the complexity of design parameters and rather conflicting and inter-relating objectives, these brakes require an optimum design. The requirement of wide range of available braking force poses a challenge to input power limitation and size of the brake. In this paper, a new design of Two-layered magnetic brake has been proposed which incorporates two-layer of cores in the electromagnet. In this two-layered design, a wide range of braking force is available to engage the brake even after overcoming the restoring force of the spring. The design also assists in controlling the braking force so that a gradual application of force can be possible.
The commercially available single-core brake design is lacking of the capability of controlling the forces because of their on-off activation. The new design has overcome the problem by utilizing its feature of individual coil state-of-the-art sensors design based on magneto-rheological (MR) fluid. In smart materials, the magneto-rheological fluid is one of the prominent materials, which changes rheological properties on application of magnetic field. The MR fluid is mainly used for designing the dampers clutches and mounts for heavy vehicle systems. However, the MR fluid can also be used for sensor design applications, which has not been much reported in the literature. This review paper summarizes the design of following novel sensors such as resonant, current, magnetic flux and tactile sensors designed using MR fluid. First, this article introduces the design and development of resonant based measurement system used for studying the properties of magneto rheological fluid. Secondly, this paper discusses about the novel electrical current measurement technique using MR fluid in shear mode of operation. This paper discuss on the design of novel variable resistor using the behavioural change of MR fluid in third. Finally, the design of tactile display utilizing magneto rheological fluid is introduced and discussed. Tactile display is used in robotic system in minimally invasive surgery (MIS) to provide a surgeon tactile information of touching remote biological tissues or organs. This review article will motivate the readers to design the novel sensors using magneto-rheological fluid with advanced technology. Inspiration on the increasing applications of magneto rheological fluid leads the researchers to design and develop the novel sensors applicable in the field of electrical, electronic and biomedical engineering. The interesting behavior of MR fluid is the change in apparent viscosity with respect to the change in magnetic field. Some of the innovative products using MR fluids include dampers, clutches, brakes, hydraulic valves and actuators and many of these products are already commercialized Normally, the devices that use MR fluids are classified into two types based on particle shape: i) sphere iron particle and ii) plate iron particle The main aim of this review paper is to provide the reader with a basic understanding of the design techniques of various sensors using MR fluid. Therefore, we have reviewed the available four different MR fluid based sensors implemented in the real time. The magnetic field produced by the coil changes the viscosity of MR fluids and produces an additional stiffness to the resonating cantilever beam. The shift in resonant frequency due to the change in viscosity of the MR fluid is measured and the shift in frequency is analytically related to the yield stress. Resonant frequency due to the change in viscosity of the MR fluid is measured and the shift in frequency is related to the input electrical current to the coil. Another interesting sensor designed using magneto rheological fluid is magnetic flux sensor. Magnetic flux sensors finds wide range of applications in magnetic anomaly detection technology, position tracking of human body movement, magnetic resonance imaging technology for medical / biological applications, detection of machined cracks and mechanical torque measurement Generally, there are two types of magnetic sensors, namely vector and scalar magnetometers based on the method used to measure the magnetic field. An effort has been made to design magnetic flux sensor using a magneto rheological fluid in the change in the magnetic field varies the electrical resistive characteristics of the MR fluid.

x

Hi!
I'm Dora

Would you like to get a custom essay? How about receiving a customized one?

Check it out
x

Hi!
I'm Barry!

Would you like to get a custom essay? How about receiving a customized one?

Check it out