Design, manufacture and experimental characterization of magnetorheological rotary brake based on a peristaltic pump system

In this article, the design and manufacture of an innovative Magnetorheological Fluid(MR) rotary brake based on a peristaltic pump inspired by the concept model of the pliers and the Rochester-Pean forceps are presented. For the calculation and analysis of created structure comprehensive of roller, housing and pliers, simulations concerning stress and strain are conducted to investigate the deformation and possible parts or assembly failure. Experimental assessment, including measurements of compression force and magnetic field were conducted to evaluate the performance of proposed design. MR rotary brake is based on peristaltic pump system constituted by tube containing MR fluid and arms inspired by the concept of the pliers in the Rochester-Pean forceps. The control of peristaltic pump without gear motor is carried out with an internal magnetic field with the goal to work as an a hand that is blocked grabbing the object. The movement of the system is controlled by the viscosity of the MR material inside the tube of rotary system.

. In [5] MR brake is designed to provide high braking torque. The MR fluid brake is more efficient than the conventional braking system in terms of weight reduction, and response time [6,7]. The use of MR fluid has been explored to control the rotary stiffness in the prosthetic knee and to improve its strength, without sacrificing the stability of the fluid. The MR fluids have a high yield-stress, good dispersion stability, and keep a reasonably low off-state viscosity [8,9]. MR actuators are used in the leg exoskeletons as brakes or controlled clutch to provide appropriate assistive torque and adapt to various working conditions or environment [10]. The humanoid robotic and exoskeleton anticipate the behavior and movement alike to the human neuromuscular system, employing MR brakes and variable damping actuators [11]. The MR actuators are fail-safe without additional equipment, unlike traditional active actuators such as motors or passive actuators such as hydraulics.. This article introduces the design and manufacture of MR rotary brake based on the peristaltic pump system (Fig. 1). Its main advantage is that it acts as a rotary brake in the system, eliminating gears, mechanical valves and motors to avoid friction and unwanted elements.
The peristaltic positive displacement pump is selected in rotary brake system. Its great advantages are related to simplicity of construction with real impact on the costs and the number of designed elements, hygienic operation of the system-due to the use of a forcing hose. The system is tightness-the liquid used in the system is transported by a forcing hose. As the current increases, the MR fluid and the systems interacting with it become easier to control.
The proposed device can be used as brakes and for application in Robotic Hand Exoskeleton with the role to grasping the object. The design is inspired by the concept of the pliers in the Rochester-Pean forceps, including the model and the working principle of a peristaltic pump. The rotary brake contains the MR fluid inside the tube of peristaltic pump system. A magnetic field generated by an external coil controls the system. Indeed, when the MR fluid changes its viscosity under the magnetic field, the movement of pliers is blocked. Experiments were carried out to test the implemented system applying pressure force to one arm of pliers and to characterize the behavior of MR fluids at various magnetic field intensities. The designed MR system has been implemented in 3D using the dedicated program Autodesk Inventor Professional 2021. Stress and Strain analysis are conducted to investigate the possible failure of the parts or assembly of prototype and to identify the critical part.
In particular, the modeling components are assembled into a coherent mechanical system that includes moving parts. The proposed rotary brake has been designed, simulated and developed by Autodesk Inventor software. Using the 3D printer, it was realized and tested.
Therefore, detailed force measurements and analysis, magnetic measurements and simulation models are presented as well as experimental measurements which demonstrate suitable performance for future applications in robotic hand exoskeleton including functions such as touching, holding and grasping objects during its manipulation. The forces exerted perpendicular to the mobile arm of the pliers relative to the design specimen were obtained absence of MR fluid and with MR fluid under controlled magnetic field.
The paper is organized as follows: Sect. 2 introduces the design and structure of rotary brake based on peristaltic pump, simulation analysis and properties of MR fluid used in the realized device. Sect. 2.1.2 describes the developed experimental setup, the performed experiments and the obtained experimental results. Sect. 4 closes with the conclusions and future works.

3D design and geometric model of rotary brake based on peristaltic pump
The novel MR rotary brake has been designed and manufactured, requiring an accurate model and simulation. The realized MR rotary brake model has a peristaltic pump characterized by a flexible hose inside it filled with MR fluid, and by an easy control of pumped fluid during the rotation of the impeller. Therefore, pliers, pumps housing and rollers are included in the model. Indeed, the design and manufacture of the innovative rotary brake based on peristaltic pump are inspired by the concept model of the pliers. Based on appearance and functionality inspired by the natural environment, the model shape is designed to resemble the two claws of a crustacean (Fig. 2c) and the Rochester Pean forceps (Fig. 2d) with the pivot point (also known as fulcrum) closer to the center of the pliers (Fig. 2a, b).
The main assumption is to realize peristaltic pump system operating in a closed circuit. The element causing the movement in the experimental model is not a traditional electric motor, but the movement is caused by the external force. For this purpose, the pliers have been designed useful to transfer the linear movement to the rotary movement within the positive displacement pump. The control of peristaltic pump without gear motor is carried out with an internal magnetic field with the goal to work as an a hand that is blocked grabbing the object. The movement of the system is controlled by the viscosity of the MR material inside the tube of rotary brake based on peristaltic pump.
In this model (Fig. 3), the designed pliers are equipped with two arms connected to each other, the roller with the shaft, the housing, forcing hose and fastening elements. The fixed arm of the pliers is designed to grab and keep firm properly as shown in Fig. 4a, c.
The second plier arm of the drive system is a movable arm. The task of this arm is to produce the rotating motion in response to an applied external user force (Fig. 4b, d).When the force is applied to the movable arm, the last one rotates by some angle due to which the roller rotates. The angular displacement cannot overcome 90 • . All elements of the prototype inspired by Rochester-Pean forceps and the two claws of a crustacean were printed using the XYZprinting Da Vinci tubing of diameter 2 mm is made of rigid plastic material (PVC). The compressive force applied by the hand on the pliers is a significant criterion for their construction due to future employment by different users. Simulations were performed to verify the accuracy of the developed prototype and to calculate the resistance to compressive strength. In the simulation, the muscle hand strength of the user affects the mobile arm element of the pliers and doesn't influence their shape. In this simulation, the applied forces of 504N and 310N, selected as maximum values to resist breaking of printed PLA sample in Fig. 5a have caused a deformation of 0.4 mm and 0.15 mm, respectively. Despite the small dimensions, such results guarantee the stiffness of pliers. For the analysis are conducted using Autodesk Inventor software. The stress analysis and test of the housing and pliers including the assembly and all parts of the design such as rollers, housing and grippers also provide structural loads and deformation materials. In addition, the material used for the simulation model developed by Autodesk Inventor software is Polylactic Acid. For housing and the roller model is defined a loading force of 100N, and for the nippers is defined a loading force of 580N.The loading force for housing and roller cannot be greater than 100N in order to prevent the device from being damaged. The loads applied are much higher than those measured during experimentation due to PLA material and to prevent the breaking of sample.
As the results demonstrate, the most important stress exists in the ZZ set for the pliers, because the force is directed in the Z-axis and has the greatest impact on Z-axis as in Fig. 5b that increases the stress level. The maximum stress value reached for this model is of 9.84 MPa. In the housing and roller, the maximum stress values are 1.137 MPa and 0.0188 MPa, respectively, without any negative impact on the functional parts ( Fig. 5c, d).

Peristaltic pump construction and stress analysis
The realized model has been determined and completed considering the design and the working principle of a peristaltic pump. A peristaltic pump is considered a positive displacement pump used for pumping a variety of fluids (Fig.  6a).
Peristaltic pumping systems are widely adopted in the primary mass transport, heat transport and in microfluidics. Each peristaltic pump is equipped with a tube which permits the pumping with high abrasion resistance for easy flow of solids and high viscosity fluids [12]. The pump flow is proportional to the speed, making it suitable for dosing. In peristaltic pumps, the tube is compressed by the rollers during rotation, this compression creates the vacuum needed to aspirate the liquid through the tube. The liquid comes into contact only with the tube, eliminating the risk that the pump contaminates. Others advantages of peristaltic pumps are related to a delicate pumping preventing oxidation, emulsions, crushing of berries and seeds, and contacts between the product and mechanical parts [13][14][15]. Generally the self-priming peristaltic pump is driven directly by stepper motors with 2 or 3-roller rotor or single-phase DC motor that are used to control the direction and speed depending on the flow. The roller system is precisely controlled by motor shaft or via a gearbox between the motor and peristaltic pump head.
The fluid is contained inside the tube of the pump. A rotating roller mounted on a shaft passes along the length of the pipe, creating a temporary seal between the suction and discharge sides of the pump. As the roller moves over the tubing, it expands and creates a vacuum to allow more fluid to enter. Combining these principles of suction and discharge, a powerful self-priming action is obtained. The size of the rollers and shaft ensures the accuracy of the pumps. The manufactured peristaltic pumps offer models with two or more rollers and even twelve rollers for high precision used for medical and laboratory purposes. The number of rollers adopted in peristaltic pumps plays an important role in fluid handling. Two or three rollers lead to higher flow rates. In the design of our model based on peristaltic pump, three rollers have been selected and manufactured as shown in the sketch created using Inventor Professional 2021 (Fig. 6b, d). Stress, displacement and strain analysis can help to find the best design alternatives for a part or assembly. In stress and displacement analysis, structural loading conditions are evaluated. The simulations perform the geometric modeling and determine structural design. Further the analysis of displacement can define the movement of individual points on a structural pump system due to various external loads. In the model, the rollers have been combined with the shaft to form an integral element. The entire element has been 3D printed preserving all the oval contours (Fig. 7a).
The roller size at the end of the drive shaft also affects the performance and efficiency of the pump. The roller presses the flexible tubing causing the liquid displacement inside the hose. A larger roller exerts more force on the tube (Fig. 6b). Due to the small size of housing in which the pump operates, the differences between each variant shaft are small (Fig. 6c).
The simulations have been performed using three different values of forces which act on the roller during the operation. The force is applied to each roller separately. The entire axis of rollers has been retained. Table 1 presents the obtained deformation values that can be observed during the functioning of the pump at various loads with the maximum force value of 100 N.
The deformations caused by the action of the hose on the shaft are very small, even if the shaft has smaller dimensions than them. During the tests, three rollers have been used in the rotary brake system to work correctly. The distinctive     The modeling process for all elements in Autodesk Inventor Professional 2021 has assembled into a consistent set of elements consisting of two plier arms, rollers, case and flexible hose (Fig. 2c).

Properties of MR fluids
Magnetorheological (MR) fluids provide many engineering solutions and braking applications, exhibiting yield stress, and consisting of magnetic particles in a carrier fluid. The suspension of micrometer-sized iron particles changes from liquid to semi-solid state spontaneously under the influence of a magnetic field.
The increase in flow resistance, in particular the apparent viscosity, is proportional to the magnetic field and it is equally proportional to the mechanical energy required to break the forces of interaction between the dipoles.
When the magnetic field is not activated, the fluid has the behavior of the Newtonian fluid and the particles float freely.
As a result, the strength of the material strictly depends on the magnitude of the applied magnetic field, so the direct relationship between the applied field and the yield strength enabling the control and the precision. An energy-efficient arrangement joins the particles together in order to form chains parallel to the magnetic flux lines.
In addition, the rapid response and the controllable yield stress in MR fluids ensure an appropriate interface between the electronic control and the mechanical system. In particular, controllable fluids respond to external excitation such as an electric or magnetic field, in an extraordinary way [16,17].
In this work, the smart fluid MRF is included in the rotary braking system. Under the influence of a magnetic field, the motion of the rotary brake can be controlled according to the changing state of the liquid. Therefore, the effective vibration of rotating components is attenuated or reduced with a very fast reaction of the liquid.

Experimental setup
The aim of this research is to control the rotary brake based on a peristaltic pump system with pipe filled with MR fluid. The each arm has size of 10.5x1.2x0.6 cm. The housing of roller has a diameter of 3.2 cm and the height of roller is of 6.6 cm. All part are made of Polylactic Acid (PLA). Inside the roller is located the flexible tubing of diameter 2 mm made of rigid plastic material (PVC). During this investigation, the commercial MR fluid type Lord MRF-132DG (Lord Corporation, Cary, NC, USA) is contained in an integrated tube inside the casing of the peristaltic pump. The viscosity at room temperature of the MRF-132DG is 0.112 Pa-s. The Shear Stress as a function of Shear Rate with no Magnetic Field applied at 40 o C and the Yield Stress vs. Magnetic Field Strength are reported in [18].
The MR material has been inspected with Keyence VHX-7000 4K High Accuracy digital Microscope capable of capturing high-resolution images (Fig. 8a). Experiments has been carried out to test the implemented system by applying pressure force to an arm of clamps and to investigate the behavior of MR fluids subjected to various magnetic field intensities generated by external coil. This test consists on reproducing repetitive mechanical movements of opening and closing without physical element to grab.
Magnetic stimuli has been provided to evaluate the maximum opening and closing of the arms. In fact, when the MR fluid contained within the system tube changes its viscosity, the movement of the grippers is blocked.
Experiments has been conducted to evaluate the proposed design of RB based on peristaltic pump system. The experimental setup used in this investigation is shown in Fig. 9a consisting of probes for measuring magnetic fields, magnetic sensor, DC Regulated Power Supply, force gauge, cooling fan, electromagnetic coil, and tested MR rotary brake system.
The used Smart magnetic sensor model SMS 102 TEL-Atomic measures the magnetic fields up to 2000 mT with Measurement Probes of 12.5mm long, and it operates on the basis of the Hall effect. This means that it generates an output signal when its sensing area is affected by a magnetic field produced by a magnet. A dynamometer (Model: FG-5000 A LUTRON ELECTRONIC, FORCE GAUGE 5 kgs full scale) is utilized for compressive force measurements. The gauge is equipped with a maximum reading pointer and the gauge has a flat tip with a dial diameter of 1-1/2 inches. In the conducted test, the tip of gauge has been placed perpendicular to the movable arm of the pump system in order to apply compression (push) force and carry out measurements of force.  The magnetic field in the electromagnetic small copper coil EM42/3349 with number of turns N=1400, is generated by the current produced and regulated by DC Regulated Power Supply (GOPHERT CPS-6003 0-60V 0-3A). A Hall probe has been used to measure magnetic field strength accurately. The electromagnetic coil is equipped with part of flexible tube containing MR fluid fitted inside the pump casing and sealed with metal gaskets on top in a closed circuit. The measuring probe is placed inside the system to measure the magnetic field. The fan has been used to cool down the heat of the system during the measurements to avoid also that the temperature influences the behavior of MR fluid.
The tests are conducted, firstly, fixing the rigid arm of the designed system in the bench vise mounted directly to workbench. The force is applied to the movable bar of the MR system. The magnetic field strengths of the coil generated by different currents in the MR system is measured. Specifically, as shown in Fig. 8b one plier arm of realized system kept firm by the bench vise ensuring the angle higher than 90 o between the movable arm and fixed arm of pliers. The tip of the dynamometer has been placed close to the movable arm in order to measure the force necessary to carry out the movement of the arm, in particular, ensuring the movement of the movable arm in the manufactured system parallel to the fixed arm in the bench vise as shown in Fig. 9a and in the described flowchart Fig. 9b.
At the forces applied on the arm of system, the MR device is activated in order to solidify inside the flexible tube under the effects of the magnetic field generated by the electromagnetic coil element, and creates the required mechanical locking action to maintain the system composed by pliers in locked position. As in the case of MR fluid actuators, the locking mechanism strength provided by the MR system design is proportional to the strength of the applied magnetic field. The basic steps of conducted research have included: • Testing of rotary brake based on a peristaltic pump system without MR liquid contained in the flexible tube fitted inside the pump system

First testing campaign
The performance tests are conducted in the absence of magnetic field and without the presence of MR fluid in the RB pump system's tube (Fig. 11). The dynamometer is used to measure the force applied on the movable arm in the realized system. Two rollers of 14mm and 15mm diameters are considered in the MR system (Fig. 10). However, the better results are obtained for roller of 15 mm. The force applied on the movable arm for roller of 15 mm is greater than the roller of 14 mm on equal terms. As a result, the performance tests are conducted to evaluate the force applied to the pliers' movable arm in the implemented system. In this case, the tube was completely filled with MR fluid. External voltages rated using a DC Regulated Power Supply were applied to the coil (Fig. 12). The force value is 1.1N for roller diameter of 15mm and Vcoil of 10V. When the applied voltage increases, the force increases.
External current values rated with a DC Regulated Power Supply are applied to the electromagnetic coil that generates the magnetic B-field. The current varies in the range between 0 and 0.25 A, inducing a magnetic field around the wire coil with linear magnetic field dependence. The magnetic B-field is function of current applied to coil. The recorded values of magnetic B-field and currents values are in accordance with the theory of MR and physics. When an external B-field is carried out, for increasing magnitude of currents, the MR fluid viscosity and yield stress increase considerably, so that the force applied on movable arm increases significantly as shown in Fig. 13. The Force [N] applied to the arms of pump as a function of coil current and after the inserting with MR fluid inside the realized pump system for roller diameters of 14 mm and 15 mm, respectively (Fig. 6c). The force applied to the system with roller diameter of 14 mm is less than the force applied to it with roller diameter of 15mm. The difference in braking force is 12% for roller diameter 14mm and 30% for roller diameter 15mm in Fig. 13. The force is a function of Magnetic B-field as reported in Figs. 14 and 15 for roller diameters, respectively, of 15mm and 14mm of RB based on peristaltic pump system. Thus, the better results are obtained for roller of 15 mm.

Second testing campaign
In the second testing campaign, a small socket is realized within the movable arm of system in order to ensure the easy movement of dynamometer tips on the flat surface of the arm.
However, a Silikon+Teflon smar tf silikon PTFE coating has also been deposited on the arms to eliminate the high friction coefficients. In addition, the tube filled completely with MR liquid is placed part within the coil and part in the rotary system pump. For this reason, higher current levels than 0.7 For high current, the braking force is less than the force obtained in the first campaign with application of current 0.25 A due to the Teflon coating deposited on the arms.
Thus, the cooling fan has been embedded to avoid excessive heating of the system. The force, current and Magnetic B-field values obtained during the tests are linearly dependent on each other. This indicates reliable control of the viscosity of MR fluid and the movement of the arm in the MR rotary brake. As the intensity of Magnetic B-field increases, there is an increase in the force required to move the arm of the system (Fig. 16).

Conclusion and future works
In this article, a novel MR rotary brake based on peristaltic pump is designed and manufactured. The stress and strain analysis of the MR system is computed by numerical method using Autodesk Inventor Professional 2021. A MR fluid has been used as smart material with ability of varying viscosity under magnetic field. By locating this fluid into the tube of the peristaltic pump with an electromagnet coil able to generate magnetic field, a controllable resistance motion can be created. The viscosity has a great role in the movement of the device and in the absence of magnetic field. Experiments were carried out to test the implemented system applying pressure force to movable arm of plier and to characterize the behavior of MR fluids at various magnetic field intensities. The force is applied to the movable arm of MR system. The force, current and Magnetic B-field values obtained during the tests are linearly dependent on each other. This indicates reliably control of the viscosity of MR fluid and the movement of the arm in the MR rotary brake. As the intensity of Magnetic B-field increases, there is an increase in the force required to move the arm of the rotary brake. The percentage increase in braking force in presence of magnetic field with respect to braking force in absence of magnetic field is 12 % for rotary brake comprised of 14 mm roller while its 30% for rotary brake comprised of 15 mm roller. Hence, rotary brake with 15 mm roller yielded better braking performance in terms of resistance to motion of movable arm. This is due to the fact that higher magnetorheological effect occurs when magnetorheological fluid gap subjected to magnetic field is reduced. The design of MR rotary brake works with low power consumption and includes few elements without motor, gear and actuators. The subject of future specific application will be to study the MR rotary brake device based on a peristaltic pump as hand exoskeleton joint with more energy efficient and providing the sensation of holding a virtual object.