Hakan Gurocak

Haptic Glove With MR Brakes for Virtual Reality

Haptic gloves open up the world of force feedback by allowing the user to pick up and feel virtual objects in a natural way. In most of the existing gloves, a remote box houses a large number of actuators and sensors. Power to the glove is transmitted via cables. If the haptic gloves were smaller, lighter, and easier to use and control, they could become more common as human-machine interfaces. Recent developments show that actuators based on active fluids, such as the magnetorheological (MR) fluids, can be viable alternatives in haptics. But these devices are desk- or floor-mounted and use relatively large MR brakes. In this research, we developed a compact MR brake that is about 25 mm in diameter, weighs 84 g, and can apply up to 899 Nmiddotmm torque. The compact size was achieved by stacking steel and aluminum rings to create a serpentine flux path through the fluid. Six brakes were used to build a force feedback glove called MR glove. The glove weighs 640 g and does not require any remote actuators. Results of usability experiments showed that the MR glove improved task completion times in grasping virtual objects and could convey stiffness information to the user.

Spherical Brake with MR Fluid as Multi Degree of Freedom Actuator for Haptics

This research explored design of a magnetorheological (MR) spherical brake as a multi-DOF actuator. To the best of our knowledge, our design is the first ever multi-DOF spherical brake using MR fluid. The primary goal was to design a compact but powerful brake using the serpentine flux path approach. An optical position measurement system was also designed to eliminate the gimbal mechanisms that are typically used in spherical joints for position measurement. It was found that the braking torque scales up proportionally to the cube of the brake radius. This enables making much more powerful brakes without increasing the overall size significantly. A prototype spherical brake was built with 76.2 mm diameter and 3.7 Nm braking torque. Experiments were conducted to identify the characteristics of the prototype brake and to test it in virtual wall collision, damping and Coulomb friction simulations for haptics. A joystick was built as a haptic device using the MR spherical brake. Virtual wall collision experiments showed crisp reaction force at initial contact and very high rigidity during the contact.

Weight Sensation in Virtual Environments Using a Haptic Device With Air Jets

The research presented in this paper is the design and implementation of a force feedback hand master called AirGlove. The device uses six ports arranged in a Cartesian coordinate frame setting to apply a point force to the users hand. Compressed air is exhausted through the ports, creating thrust forces. The magnitude and direction of the resultant force are controlled by changing the flow rate of the air jets and by activating different ports. The AirGlove can apply an arbitrary point force to the users hand. However, the main goal of this research is to reflect gravitational forces to the user so that sensation of weight of a virtual object can be created. After introduction of the main concept of the AirGlove, the paper presents design and implementation details of the device. Integration of the AirGlove with a virtual assembly system called VADE is explained next. Finally, details of experiments with the device are presented and discussed. Results indicate that users wearing the AirGlove can feel a minimum mass of about 100 grams (~1N weight) and the device can create a fairly realistic weight sensation.

Compact MR-brake with serpentine flux path for haptics applications

This research explores a new approach to shape the magnetic flux path in a MR brake. Magnetically conductive and non-conductive elements were stacked to weave the magnetic flux through the rotor and the outer shell of the brake. This approach enabled design of a more compact and powerful MR brake. In addition, a ferro-fluidic sealing technique was developed to prevent the fluid from leaking and to reduce off-state friction. Experimental results showed that, when compared to a commercial MR brake, our 33% smaller prototype MR-brake could generate 2.7 times more torque (10.9 Nm). A 1-DOF haptic interface employing the brake enabled crisp virtual wall collision simulations. Significant reduction in the off-state torque was obtained by applying a reverse current pulse to collapse a residual magnetic field in the brake.

Magnetic induction control with embedded sensor for elimination of hysteresis in magnetorheological brakes

This research explored a novel control scheme for magnetorheological brakes to eliminate hysteresis. A Hall-effect sensor is embedded in the flux path to measure the magnetic flux across the magnetorheological fluid. A proportional–integral–derivative controller then controls the magnetic induction directly. To the best of our knowledge, this is the first such design incorporated into a magnetorheological brake. Even though magnetorheological brakes have very desirable characteristics, such as high torque-to-volume ratio and inherent stability, they have a major drawback since they exhibit hysteresis behavior. The hysteresis creates control challenges and significant residual off-state torque, which prevents use of high gear ratios with magnetorheological brakes. The proposed approach is easy to implement and very inexpensive compared to hysteresis modeling techniques or using force/torque sensors. A prototype brake has been experimentally evaluated using three different closed-loop compensation schemes: (a) the Preisach hysteresis model, (b) torque sensor, and (c) the proposed new approach. Results showed that the proposed control scheme could eliminate the hysteretic behavior and reduce the off-state torque in the magnetorheological brake to negligible levels.

Interactive design optimization of magnetorheological-brake actuators using the Taguchi method

This research explored an optimization method that would automate the process of designing a magnetorheological (MR)-brake but still keep the designer in the loop. MR-brakes apply resistive torque by increasing the viscosity of an MR fluid inside the brake. This electronically controllable brake can provide a very large torque-to-volume ratio, which is very desirable for an actuator. However, the design process is quite complex and time consuming due to many parameters. In this paper, we adapted the popular Taguchi method, widely used in manufacturing, to the problem of designing a complex MR-brake. Unlike other existing methods, this approach can automatically identify the dominant parameters of the design, which reduces the search space and the time it takes to find the best possible design. While automating the search for a solution, it also lets the designer see the dominant parameters and make choices to investigate only their interactions with the design output. The new method was applied for re-designing MR-brakes. It reduced the design time from a week or two down to a few minutes. Also, usability experiments indicated significantly better brake designs by novice users.

Haptic glove with mr brakes for distributed finger force feedback

Most existing haptic gloves are complicated user interfaces with remotely located actuators. More compact and simpler haptic gloves would greatly increase our ability to interact with virtual worlds in a more natural way. This research explored the design of a compact force feedback glove using a new finger mechanism and magnetorheological (MR) brakes as passive actuators that oppose human finger motion. The mechanism allowed for a reduction of the number of actuators and application of distributed forces at the bottom surface of users fingers when an object was grasped in a virtual environment. The MR brakes incorporated a serpentine flux path that led to a small brake with high torque output and the elimination of remote actuation. Force analysis of the mechanism, grasping force experiments, and virtual pick-and-place experiments were done. The glove reduced task completion time by 61% and could support up to 17 N fingertip force along with 11.9 N and 18.7 N middle and proximal digit forces.

Linear magnetorheological brake with serpentine flux path as a high force and low off-state friction actuator for haptics

In robotics and haptics, actuators that are capable of high force output with compact size are desired for stable and stiff interfaces. Magnetorheological brakes are viable options for such implementations since they have large force-to-volume ratios. Existing linear magnetorheological brakes have limited strokes, are relatively large, and have high off-state friction forces mainly due to the piston-cylinder internal design. The main contribution of this research is a new alternative internal design for linear magnetorheological brakes. The proposed approach uses the serpentine flux path concept to eliminate the piston-cylinder arrangement. It leads to significantly less off-state friction and infinite stroke. To the best of our knowledge, this is the first such linear magnetorheological brake. Our new brake can produce 173-N force. In comparison, a conventional linear magnetorheological brake with the same size can only produce about 27-N force. Our results showed that the ratio of the off-state friction force to the maximum force output in the prototype linear brake is about 3% compared with more than 10% for most similar devices in the literature and 27% for a commercial brake. At the same time, the compactness was improved as our prototype is about half the size of a commercially available product.

Design of a Haptic Device for Weight Sensation in Virtual Environments

The research presented in this paper is the design and implementation of a force feedback hand master called AirGlove. The device uses six ports arranged in a Cartesian coordinate frame setting to apply a point force to the user’s hand. Compressed air is exhausted through the ports, creating thrust forces. The magnitude and direction of the resultant force are controlled by changing the flow rate of the air jets and by activating different ports. The AirGlove can apply an arbitrary point force to the user’s hand. However, the main goal of this research is to reflect gravitational forces to the user so that sensation of weight of a virtual object can be created. After introduction of the main concept of the AirGlove, the paper presents design and implementation details of the device. Integration of the AirGlove with a virtual assembly system called VADE is explained next. Finally, details of experiments with the device are presented and discussed. Results indicate that users wearing the AirGlove can feel a minimum weight of about 100 grams and the device can create a fairly realistic weight sensation.© 2002 ASME

Fuzzy logic and position sensing for precision assembly

The problem of part mating and assembly with close tolerances has been addressed in the past by active or passive compliance and by force/position control. With ambient sensor and transmission noise and with imprecise measurements it is often difficult to attain high precision in manipulator positioning. In this article, a position-sensing wrist using simple strain gauges is described. A fuzzy logic algorithm to ascertain the positional error during an unsuccessful assembly attempt is explained. The results obtained by using this wrist and the fuzzy logic algorithm to reposition a manipulator for precision assembly are presented and discussed.