Use of Magnetorheological Fluid in a Force Feedback Glove

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IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING, VOL. 15, NO. 1, MARCH 2007

Use of Magnetorheological Fluid in a Force Feedback Glove Scott H. Winter, Member, IEEE, and Mourad Bouzit, Member, IEEE

Abstract—Magnetorheological fluid (MRF) is a smart material that has the property of changing its viscosity when exposed to a magnetic field. By placing this fluid into a sealed cylinder with an electromagnet piston as a core, a controllable resistance motion dampener can be created. A novel exoskeleton mechanical power transmission system was designed, utilizing rapid prototype parts, to transmit these resistive forces to the user’s fingertips. A first iteration force feedback glove was developed and tested on human subjects for overall usability. The eventual goal of the system is to provide an alternative force producing system for exercises and rehabilitation. The entire system is lightweight, low power, and easily portable. Index Terms—Force control, haptics, intelligent materials, user interfaces.

I. INTRODUCTION UMAN computer interfaces and rehabilitation systems are difficult problems with many solutions. The standard interface method is currently based on input from a keyboard and mouse. For enhanced interaction or to provide forces in rehabilitation therapy, a different class of device is needed. In these cases a force feedback system is desirable. Most force feedback devices rely on electric motors, pneumatics, or some other conventional power producing method. In the system presented here, MagnetoRheological fluid (MRF), an intelligent material, was used to create a novel force feedback glove, named the MagnetoRheological actuated glove electronic system (MRAGES). The MRAGES was designed to demonstrate that a MRF based haptic device can be compact, functional and a viable alternative to other methods for providing forces. A pilot human study was designed to confirm this functionality and determine the advantages and drawbacks to the use of MRF based actuators. An additional consideration for the system is a novel exoskeleton developed for power transmission from the MRF based actuators to the fingertips. The exoskeleton was fabricated using a rapid prototype machine and acts as a push/pull control cable.

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Manuscript received September 26, 2006; revised December 10, 2006; accepted December 10, 2006. This work was supported in part by Rutgers University, through the startup funding of the Bio-Robotics laboratory. This paper was presented in part at IWVR 2006, New York City, Aug., 2006. S. H. Winter is with Department of Electrical and Computer Engineering, Rutgers University, Piscataway, NJ 08854 USA (e-mail: [email protected]. edu). M. Bouzit is with Department of Biomedical Engineering, and the Department, Electrical and Computer Engineering, Rutgers University, Piscataway, NJ 08854 USA (e-mail: [email protected]). Digital Object Identifier 10.1109/TNSRE.2007.891401

II. BACKGROUND A. Available Force Feedback Gloves The CyberGrasp [11] from Immersion Corporation, San Jose, CA, is, as of this writing, the only currently available force feedback glove. It is listed as having a working end weight (the part attached to the user’s hand) of 350 g and works using a tendon-based system to oppose the closing of the fingers with up to 12 N of force. An exoskeleton is mounted on the back of the hand to guide the tendons to the fingertips. A specialized PC and umbilical device are used to power and control the CyberGrasp. Optionally, a backpack containing the support components can be worn to make the setup more mobile. Since the CyberGrasp is the only commercially available force feedback glove, there is little option for someone looking to design an interactive system using a force feedback glove. While the glove has a working end weight of about 1 lb, the additional equipment makes transportation difficult since the functional control unit (FCU) has a weight of 44 1bs (20 kg). The CyberGrasp also has no position or flexion sensors and, therefore, requires an additional device, such as the recommended CyberGlove, to provide sensing. A noncommercial haptic force feedback glove is the RMII-ND [5], developed and currently used by the Rutgers Human Machine Interface Laboratory. The RMII-ND has already proven itself to be a useful tool for medical rehabilitation such as in post stroke therapy [10]. By utilizing a graphite-on-glass pneumatics piston for each finger, the static forces are quite low, only 0.014 N of force when the glove is not powered. Pistons are directly attached to the fingers and are located between the palm and the fingertip. The working portion of the device is light and comfortable to wear, weighing only about 100 g. Each finger is equipped with sensors for measuring finger position, flexion, and abduction, along with displacement of the piston. Overall, the glove can produce a force of 16 N per finger, opposing the closing of the hand. Several supporting devices are required when using the RMII, such as compressed air. The air supply can be a dedicated compressor as was the case in the most recent study, or a “house” air supply, as might be found in labs or hospitals. Compressed air is fed into a second required part, the multiplex telarehab interface (MTI), to which each glove is attached while in use. The MTI contains the pneumatics valves for the operation of the Rutgers-Master Haptic glove and the sensor electronics to measure fingertip positions versus the palm. A pressure sensor is also located in the MTI to act as part of the force sensor. The Host PC connects to the MTI, where all commands are processed.

1534-4320/$25.00 © 2007 IEEE

WINTER AND BOUZIT: USE OF MAGNETORHEOLOGICAL FLUID IN A FORCE FEEDBACK GLOVE

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Fig. 1. Basic operational modes for controllable fluid devices. (a) Pressure driven flow mode. (b) Direct shear mode.

Fig. 3. Finished MRF actuator shown with U.S. penny. IEEE 2006. Reprinted by permission.

Fig. 2. Completed MRAGES glove IEEE 2006. Reprinted by permission.

B. MRF Magnetorheological fluid (MRF or MR-fluid) is a smart material with the property of solidifying when exposed to a magnetic field. The type of MRF used for this project is a commercially available product from LORD Corporation, Cary, NC, type MRF-22ED [8], which is a hydrocarbon-based medium with 72% of its weight in solids and 22% solids by volume. The exact composition of the solids is proprietary to LORD Corporation, however most of the weight is from suspended iron particles of varying sizes. In practice, MRF functions by aligning the suspended iron particles’ poles to create a more viscous substance. LORD Corporation provides two models for using MRF [4], [14], the pressure model and the force model, as shown in Fig. 1. For the purposes of this project, the pressure mode is more relevant, although both can be applied. Haptics work using MRF has been done in which the MRF is used to replicate biological tissues [6], [7]. The ability of MRF to replicate tissues is due to its surface tension when energized. Most work with MRF is limited to larger and heavier devices not applicable to haptics, however their concepts remain similar to the ones used in the MRAGES. In particular, the concepts behind motion dampers are the same for large and small devices. Some work has been done in making very small actuators using active fluids such as the work described by Yokota [12], however these are electrorheological fluid (ERF) type which are energized by a high voltage and not MRF, which uses magnetic fields. III. MRAGES GLOVE The completed glove and control circuitry can be seen in Fig. 2. The current generation of the MRAGES requires only

two umbilical cables to the desk, a power cord and USB connection. All other components can be mounted on the upper arm and do not restrict the mobility of the user. The entire system is lightweight with the glove portion weighing only 160 g. Additional components are currently on several solder boards and a COS microcontroller development board. These could be combined into a single unit in future iterations making the processing, sensor and power boards an estimated 20–30 g. This could translate to a total shipping weight of less then one pound or half a kilogram, including program CD and some documentation, for a fully functional system. The light weight, easy control, and portability of the device makes it practical for transporting to patient’s homes, where it can be used with an already existing computer system. A lightweight virtual reality simulation can be developed to run on slower, older computers. This portability is the most significant difference between the MRAGES and the other force feedback gloves mentioned. At the time of writing, no other Magnetorheological fluid haptic device is known to be in use. The MRAGES glove presented here can, therefore, be viewed as an experiment in using MRF as a force producing material. The desired outcome of the MRAGES design is to not only to create a usable haptic device, but also present the possibility of using MRF in other haptic and rehabilitation devices. A. Actuators The MRF actuators, shown in Fig. 3, are the heart of the power system, representing a novel approach to applying forces to the human hand. They have been designed to be powerful, light, use low power, and have a relatively low static force level. Constructed out of both machined and rapid prototype parts, the actuators measure approximately 2 in 0.5 in 0.5 in when fully compressed, and have a weight of roughly 16 grams each. The actuators provide forces up to 6 N; however, simple changes in design can create much higher forces. A total throw of 1.25 in is achieved in this design. The internal wiring is designed to utilize 0.33 A at 5 V.

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Fig. 4. CAD model of MRF actuator.

The main drawback to the actuator design is that the actuator produces a large amount of force, even in the off state. Those used in the final version of the glove had static forces ranging from 1.4 N to 1.9 N. Minor modifications can greatly increase the maximum forces at the cost of increasing these static forces. As discussed later, this high static force creates hand fatigue and may make this type of actuator more suited for stronger, less sensitive portions of the human body. A finished actuator is comprised of several pieces (see Fig. 4): the external retaining shell, 2 O-ring holders retaining a PTFE (generic Teflon) O-ring, a 1.5-in steel (3/8 outer diameter, 11/32 inner diameter) cylinder, a steel spindle, a center stainless steel shaft, and a steel cylinder. The spindle is wrapped with magnet wire, and a pair of wire washers is added to keep the leads and unshielded wire from shorting. The cylinder is filled with MRF fluid before final assembly and sealed using liquid silicon. The center shaft and steel spindle together form the actuator’s piston. To provide the magnetic field, and, therefore, control the forces in the actuator, the steel spindle is wrapped with magnet wire to create an electromagnet. A spindle length of 1/4 in was settled upon as an appropriate size. Taking an unused spindle as an example, the spindle was wrapped, tested, and unwrapped. It was approximated that 350 wraps could be produced using the resistance level of the wire to calculate the total amount of wire. A steel cylinder was added in order to magnify the effects of the electromagnet. To create the steel cylinder, a 3/8 in outer diameter stock tube was machined to have an 11/32 inner diameter. By adding this component, the strength of the magnetic field is increased from approximately 0.06-0.25 T according to the FEMM [13] simulations. It should be noted that the FEMM software can not account for the magnetic properties of the MRF. Since the MRF that is used is approximately 22% iron, it will have a positive effect on the magnetic field, hence a stronger field is created. The nonactive, retaining components, are designed to hold the MRF and electromagnetic components and are not designed to provide any active forces directly. The rapid prototype parts, including the retaining shell, wire washers, and O-ring holders, are a nonmetallic, nonmagnetic material and are thus well suited for the retaining task. The O-ring is the most important portion of the retaining components since it interacts with the center shaft as it moves up and down within it. PTFE (Teflon) -003 O-rings were used for two reasons. First, they have a low friction coefficient, which tend to

Fig. 5. CAD representation of a finger’s mechanical components.

Fig. 6. Single finger bending. IEEE 2006. Reprinted by permission.

produce lower friction forces. Second, they have a hard Durometer (hardness) rating making the O-ring less likely to break or distort. Functionally, the MRF actuator works in the following manner: the piston’s spindle forms two chambers within the actuator; as the piston moves within the actuator, the piston forces MRF to flow from one chamber to the other. A small channel exists between the spindle and the steel cylinder, the only path for the MRF to flow from one chamber to the other. When current running through the magnet wire induces a magnetic field, the MRF’s path is restricted, as shown by the pressure flow model in Fig. 1. The force control method is to use a PWM signal to induce the magnetic field. Varying the duty cycle of the PWM signal will regulate the forces produced by the actuator. MRF actuators have a naturally built-in safety mechanism in that they only apply passive forces. No forces are applied on the hand if the fingers are not moving. FDA approved MRF fluids are also available if there is concern about fluid leaking such as in a situation with possible misuse. B. Exoskeleton and Mechanical Structure Fig. 5 shows the CAD representation of a single finger’s mechanical components, while Fig. 6 shows the finger bending on the completed glove. A control cable is connected to the fingertip on one end and to the actuator on the other by a coupling. This cable runs within the exoskeleton finger spine. When the finger bends, the outside arch length of the finger increases. Therefore, the cable will pull out the piston as the finger bends and conversely, push it inward as the finger straightens. If the actuator is energized, the piston will resist these motions. On the fingertip mount (see Fig. 7), springs are attached to the compression screws and cause the fingertip mount to grasp


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Fig. 7. Fingertip mount. IEEE 2006. Reprinted by permission.

a finger when placed into the mount. The mount will expand to accommodate fingers up to 1/8 in thicker than the nominal size of 1/2 in. The interior of the fingertip mount is curved to allow for the natural shape of the human finger. At the base of the mechanical components of this haptic system is a leather glove with a nylon/spandex back. The exoskeleton finger spine is designed to spread out as the user bends his fingers, which is accomplished through a stretchy fabric on the glove that covers the top of the fingers, where the exoskeleton finger spine is glued. Fabric used for this purpose must, therefore, be strong, flexible, and comfortable to the user. The force gauge sits at the back of the actuator, serving as an intermediary before physically connecting to the glove. In this manner, all forces felt at the back of the actuator are transmitted through the force gauge. The force gauge is constructed from a strain gauge glued onto a sheet metal cutout. Forces are read through an op-amp and analog-to-digital (A/D) channel on a PIC microcontroller. A linear potentiometer is used as the linear sensor in the glove and is glued to the top of the actuator. A small rapid prototype part is connected to the sensor’s moving head. A 1/32-in brass rod is used to connect the sensor head to the control cable via a coupling between the control cable and the piston. An A/D channel on the same PIC microcontroller reads the voltage output of the potentiometer. Most of the exoskeleton and fingertip mount are glued directly to the glove fabric. In order to prevent movement in the actuator’s slider and base of the exoskeleton, these components are glued to an intermediary base plate. An additional curved base plate is used for mounting of the thumb components. The entire configuration can be seen in Fig. 8. C. Control Hardware and Software A microcontroller development board that contains a PIC18F8720 microcontroller and USB interface controls the entire system. This microcontroller, running at 6 MIPS, runs the embedded programming used to control the glove. The embedded software allows for interfacing with the host PC via the USB connection for calibration of the sensors, setting forces, reading sensors and other commands. Calibration is accomplished via a host machine communicating with the PIC over the USB connection. Weights and known forces are used

Fig. 8. Exoskeleton system. IEEE 2006. Reprinted by permission.

TABLE I MAXIMUM SYSTEM POWER REQUIREMENTS (5 V)

to calibrate the force sensor and the actuators’ output forces. No calibration is needed for linear sensing as the maximum and minimum linear distances are a product of the design. Calibration values are stored in the PIC’s onboard EEPROM and loaded at startup. After calibration, forces may be set in two ways: by directly setting the PWM duty cycle (DC) for each actuator manually or by using the force profile established during calibration to determine the appropriate DC value for the desired force. The main control program is constructed as a continuous loop. During this loop, the microcontroller checks the USB for commands and responds accordingly, sensors are read and filtered, and any force adjustments are made if required. Commands may include requests for reading or setting forces, reading sensors, timing requests, or calibration commands. D. Power Requirements Maximum power requirements for the system are low, as seen in Table I. The total power represented in Table I has a large scaling factor since it is unlikely that all actuators will be at 100% power for the majority of the time and the PIC is unlikely to ever reach its maximum power consumption. With a maximum power consumption of 2.2 A at 5 V, the system is an ideal candidate for conversion to battery power. Four rechargeable AA 2500 mA batteries could be used to power the system for well over an hour at full power. Commands and responses are also simple enough that 802.15.4 Zigbee or 802.15.1 Bluetooth wireless connections could be used for communications. By severing the power and communication cables, the system could

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become fully wireless, without the need for a large battery pack or heavy motor pack.

TABLE II RESULTS OF INTENSITY PERCEPTION TEST: BASIC

IV. HUMAN STUDY The goal of the testing process was to determine the viability of the MRF actuators, exoskeleton mechanical power transmission system, and overall glove for use as an interface device. Basic requirements for a usable interface require that a person be able to feel distinctive differences when different force levels are set on the glove, that the glove is comfortable during use and that sensors provide relevant information. The testing suite consisted of four parts and a subjective questionnaire (exit interview). Additionally, the subject was given a description of the glove, its working parts and how it was constructed and programmed, as well as time to ask any questions they might have relating to the glove. The glove was then fitted to the hand and comfort level verified. Each session took approximately half an hour to complete. A total of ten subjects participated with seven subjects completing the study. None of the subjects had any familiarity with the MRAGES system prior to entering into the study; however, all subjects were familiar with computers and able to understand the underlying technology explained. All subjects were healthy individuals, and no testing was performed on any person with abnormal physical or cognitive abilities. Three participants dropped out of the study, due to improper glove fit, during or before the identifying levels stage of the tests. All subjects were male, due to the larger hand size found naturally in males. The glove was constructed to fit a larger hand (approximately 7 3/4 in or slightly larger) with hand size measured from the tip of the index finger to the first wrinkle in the skin on the wrist with the palm side up. It is felt that this hand size had a significant effect on the results of the tests. If hand sizes more closely matched to the glove’s size or more varied sized gloves were used, results are expected to be significantly better. A virtual environment was not developed to accompany the tests performed here. The addition of a simulated environment would certainly have had a positive impact on the results, however given the preliminary nature of the glove and the tests being performed, the additional time requirements seemed unwarranted at this time. The study given here is not a professionally-directed usability study since the MRAGES is a first iteration device. At the time of writing, no other Magnetorheological fluid haptic glove is known of, and, therefore, this trial is a proof of concept trial. An additional test performed, but not described in detail here was the absolute force perception test. This test was an attempt to find the minimum force resolution for the MRAGES glove. Subjects were given a reference force level and then asked to determine when a trial level was different from that reference level. Being that this was the third test, and subjects were already showing signs of fatigue, results proved to be too subjective for meaningful results. Additionally, the loose fit of the glove made this test subjective, in that results were scatted without much syntactical relevance. A more complex objective test should be developed for future studies.

TABLE III RESULTS OF INTENSITY PERCEPTION TEST: STATISTICS

A. Intensity Perception The intensity perception test consists of two parts. In the first part, intensity familiarization, the subject is asked to open and close his hand while the force level of the glove is varied. In 3 s on, 3 s off intervals, the DC for all fingers is varied, from 0 DC (no power or approximately 1.5 N) to 250 DC (about 6 N), by 50 DC (approximately 0.9 N) increments in each cycle, labeled as level 0–6. This process is required to be repeated a minimum of three times; however, the subject may request additional runs. The purpose of the intensity familiarization is to introduce the subject to the glove, its force levels, and to ensure the subject’s comfort level. The subject is informed of the force values felt during the intensity familiarization and is able to see when the values change. Values are given orally and on screen. The second part of the intensity perception testing is the intensity evaluation. After completing the intensity familiarization, the subject is asked to identify the levels that the glove produces. When the subject is ready, a force is administered through the glove for three seconds and then shut off. The subject then identifies the force level, completing the trial. Subjects are given the correct answer after each of the trials. The process is repeated for a total 30 trials in the same order or forces for all subjects. Table II shows the tabulated results for the intensity perception test; the results were mixed but acceptable. Subject SA performed the best, having 73% correct and 97% within one level difference. Subject SP had the worst performance with 23% correct. He was still able to determine 63% of the trials within one level. Averaging the results shows a decision was made within one level of the correct value more than 75% of the time. It is also worth noting that many subjects had a string of incorrect guesses at the start of the test but improved as the test continued. This observation is not expressed in Table II results. The glove’s ability to produce recognizably different and distinctive forces was proved in the intensity perception test. Here, subjects answered the correct level an average of 46.7% of the time. Since a six level system is used, a pure guess would yield the correct answer approximately 17% of the time. Clearly, this result shows that the glove is effective at the basic level of producing a distinctive range of forces. This view is further reinforced when examining Table III, particularly in the


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TABLE IV RELATIVE FORCE PERCEPTION TEST RESULTS

middle levels. The average answer shows a clear progression of people’s answers from the lower levels to the higher ones. Standard deviations, while higher than ideal, still show a good clustering around the correct answer.

TABLE V SUBJECTIVE QUESTIONNAIRE RESULTS

B. Relative Force Perception In the relative force perception test, subjects are asked to identify if there is a difference between a pair of forces. Subjects are given two force levels on a single finger, each one active for three seconds and administered upon request. When the pair is complete, the subject is asked to identify which force level was higher or if they were of equal value. The process was repeated 30 times for all subjects. Pair trial results can be found in Table IV and show mixed results. During these tests, graduations of 25 and 50 DC levels were used. Results are broken down into sets that use 50 level differences and into the high (175–250), mid (75–175), and low (0–75) ranges. Six of the trials differed by 50 levels. The remaining had differences of 25 DC levels or equal values. Given the resolution of a human hand is 0.1 N [3] and the 25 DC level differences is expected to be approximately 0.45 N, the user was expected to perceive a difference. Results of the relative force perception trials were less encouraging than those of the intensity perception. With three choices, a pure guess would produce a correct answer 33% of the time. During the testing, a correct answer was given 45% of the time, as shown in Table IV. Results thus proved to be better than pure guessing, showing that the glove was effective; however, they were not as good as expected. Though better than pure guessing, the result shows a need for an increase in resolution in the glove. It was also expected that the pair trials would produce more correct answers than the intensity perception. This proved not to be true, as seen in Table IV. It is believed that, since most of the trials were either 25 DC levels or the same force level, the decision of the subject was somewhat subjective. The incorrect fit of the glove is most likely the primary cause of the subjectivity. If all the level differences were at 50 DC, it is felt that the results would be more dramatic. Furthermore, by the end of this test most subjects had been using the glove for 20 min or more, so it is expected that some hand fatigue is contributing to the results. Both the weight of the glove and the large forces that the user has experienced would contribute to this fatigue.

C. Subjective Questionnaire Following the tests, a questionnaire was filled out in order to gain a better understanding of how the subject felt about the glove and the tests performed. Other important information, such as the subject’s hand size was also recorded. Results for the Subjective Questionnaire can be seen in Table V. As shown, subjects rated the glove an average of 3.7 out of 5, with 5 being very good. Since all participants wore the glove for at least 20 min and many for 30 min, this rating would be considered only acceptable and not good enough for a commercial product or for long-term use. A similar result was found when asking if the force levels were appropriate with a rating of 3.7 out of 5 with 5 being too much force and 1 not enough. 4.4 out of 5 rated the glove as being usable with 5 indicating very usable. With regard to the yes/no questions, all subjects indicated that the finger workspace was adequate and that arm was not constrained. 71% did feel some finger constraint. Further refinements would be necessary for longer use; however the results of the Subjective Questionnaire are encouraging and support continuing refinement of the MRAGES system. When asked if subjects would like to see any improvements, lower static forces and added padding on top of the fingers was indicated. Both of these were known issues when starting the study but were unable to be rectified before the commencement of the study. The first, lower static forces, is one of the glove’s most dramatic limitations. The need for additional padding is caused by the exoskeleton on the top of the fingers. All exoskeleton parts are made from rapid prototype material, a hard plastic. When the hard plastic compresses through the glove material, it hits the finger and can cause some discomfort, particularly for people with sensitive hands or skin. Several changes to the physical glove could be made to minimize this discomfort; the most intuitive of which would be to add padding, as suggested by several subjects. A redesign of the point where the exoskeleton and glove meet or

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the use of a different material in the exoskeleton, would also help to minimize this problem. V. CONCLUSION AND FUTURE WORK The MRAGES represents a novel type of haptic force feedback glove utilizing MRF and a unique exoskeleton. Human testing provided the proof of concept for the design. Through this testing it was shown that the actuator, exoskeleton, electronics, and overall design were able to function together to make a usable device. Interfacing with the device is easily accomplished by way of sending simple commands over the USB connection from a host PC. Given that a relatively large glove was used, the ability to find subjects with similarly sized hands proved difficult and some subjects with less-than-perfect fits were accepted. The results shown in Table II and Table IV do not show this to be a significant cause of error; however, it is intuitive that a better fitting glove would produce better results, and three subjects were required to drop from the study because of an unacceptable fit. Further studies should include only people with more closely matching hand sizes or the addition of different sized gloves. As a proof-of-concept device, the glove performed admirably. However, it must provide more distinct forces and be more comfortable to use if deployed. The MRF actuator’s limitations of high static forces can be minimized, but not eliminated without a complete redesign, making all fluid completely contained without a seal. While utilizing the current design, it may be more productive for use on a larger, less sensitive portion of the body, such as a leg, arm, or ankle. If a glove setup is desired, then the focus of its use should be for gross strength training and not for fine motor skills. In a rehabilitation environment, the MRAGES glove or similar MRF device, designed for another body part or muscle group, would be linked to a virtual environment. From this setup, a functional exercise and rehabilitation program could be developed to track metrics such as instantaneous forces, work performed, repetitions and time for task completion. Utilizing a virtual environment creates an entertaining atmosphere where patients are more likely to complete exercises as directed by a therapist. The MRAGES glove or other MRF haptic device can provide a low power, highly portable, and inherently safe mechanism for conveying forces in the virtual world. Future improvement to the MRAGES may include integrating wireless and battery connections. Comfort improvements as described by the test subjects should also be implemented. The

force sensor proved to be a temperamental device and needs to be improved. Additionally, a rotational motion dampener using the direct shear model may also be employed as the main force control device and a virtual environment developed. With an extended development cycle the MRAGES glove and MRF shows great promise for use in rehabilitation and haptic devices. ACKNOWLEDGMENT The authors would like to thanks to Dr. G. Burdea and the Rutgers’ Human Machine Interface Laboratory for advice and the use of equipment and laboratory space. REFERENCES [1] S. Winter, “A Haptic force feedback glove,” M.S. thesis, Dept. Electrical Comput. Eng., Rutgers University, Piscataway, NJ, May 2006. [2] S. Winter and M. Bouzit, “Testing and usability evaluation of the MRAGES force feedback glove,” presented at the IWVR 2006, New York, Aug. 2006. [3] G. C. Burdea and P. Coiffet, Virtual Reality Technology. , New Jersey: Wiley-Interscience, 2003. [4] M. R. Jolly, J. W. Bender, and J. D. Carlson, “Properties and applications of commercial magnetorheological fluids,” presented at the SPIE 5th Annu. Int. Symp. Smart Structures Materials, San Diego, CA, Mar. 15, 1998. [5] M. Bouzit, G. Burdea, G. Popescu, and R. Boian, “The Rutgers master II—New design force-feedback glove,” IEEE/ASME Trans. Mechatronics, vol. 7, no. 2, pp. 256–263, Jun. 2002. [6] N. Takesue, J. Furusho, and M. Sakaguchi, “Improvement of response properties of MR-fluid actuator by torque feedback control,” in Proc. IEEE Int. Conf. Robotics Automation, 2001, vol. 4, pp. 3825–3830. [7] E. P. Scilingo, N. Sgambelluri, D. De Rossi, and A. Bicchi, “Haptic displays based on magnetorheological fluids: Design, realization and psychophysical validation,” in HAPTICS 2003 Proc. 11th Symp. Haptic Interfaces Virtual Environ. Teleoperator Syst., Mar. 22–23, 2003, pp. 10–15. [8] LORD , Cary, NC, Rheonetic magnetically responsive technology hydrocarbon-based MR fluid MRF-122-2ED Product Bull.. [9] S. V. Adamovich, A. Merians, R. Boian, M. Tremaine, G. Burdea, M. Recce, and H. Poizner, “A virtual reality based exercise system for hand rehabilitation post-stroke,” in Proc. 2nd Int. Workshop Virtual Rehabil., Sep. 2003, pp. 74–81. [10] R. Boian, A. Sharma, C. Han, A. Merians, G. Burdea, S. Adamovich, M. Recce, M. Tremaine, and H. Poizner, “Virtual reality-based post stroke rehabilitation,” in Proc. Med. Meets Virtual Reality 2002, Newport Beach, CA, Jan. 23–26, 2002, pp. 64–70. [11] “Immersion Corporation Cybergrasp Manual,” ver. 1.2, San Jose, CA. [12] S. Yokota, “Micro actuators using functional fluids,” presented at the 4th Int. Symp. Fluid Power Transmission and Control FPTC03, Wuhan, China, Apr. 8–10, 2003. [13] D. Meeker, Finite element method magnetics (FEMM) Ver. 4.0 [Online]. Available: http://www.femm.foster-miller.net [14] LORD, Materials Division Engineering Note: Designing With MR Fluids Cary, NC.