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.     

Hybrid control algorithm to improve both stable impedance range and transparency in haptic devices

An ideal haptic device should transmit a wide range of stable impedances with maximum transparency. When using active actuators, transparency improvement algorithms tend to decrease the range of attainable impedances. Passive actuators can transmit high impedances stably, but are not sufficient alone for transparency. In this study, a hybrid force control algorithm employing active and passive actuators was developed to improve the stable impedance range and transparency in haptic devices. A new transparency-Z-width plot is proposed as a way to evaluate the stable impedance range and transparency together. The hybrid control algorithm uses parameters to share the torque demand between two actuators with smooth transition. These parameters were determined and an artificial neural network (ANN) was used to extend them to the entire achievable impedance range. The algorithm was tested experimentally on a 1-DOF haptic device. The transparency experiments employed an excitation motor located at the user side of the device to evaluate various algorithms in time and frequency domains. Results showed that the proposed hybrid control algorithm enables simulation of higher range of impedances with higher transparency than the conventional algorithms.     

Haptic joystick with hybrid actuator using air muscles and spherical MR-brake

In this research, a new 2-DOF hybrid actuator concept is explored as a powerful and compact alternative to conventional haptic actuators. The actuator combines a spherical MR-brake and three air muscles and is integrated into a joystick that can apply forces in two degrees-of-freedom. The air muscles are used to create high active forces in a compact volume and the brake compensates for the “spongy” feeling associated with air muscles. To decrease the overall size of the system an inertial measurement unit has been implemented as a position measurement solution. As high as 16 N of total force output could be achieved at the tip of the joystick. Also, up to 16 times improvement in the stable virtual wall stiffness was obtained when the MR-brake was used to compensate for force errors. Experiments with an impedance-based haptic controller with force-feedback gave satisfactory wall following performance. This device can be employed in applications including computer games, military or medical training applications, rehabilitation and in teleoperation of equipment where high force feedback in 2-DOF in a compact work volume may be desirable while interacting with rigid or elastic virtual objects.     

Design, fabrication, and evaluation of a new haptic device using aparallel mechanism

This paper presents design, fabrication, and evaluation of a new 6-DOF haptic device for interfacing with virtual reality by using a parallel mechanism. The mechanism is composed of three pantograph mechanisms that are driven by ground-fixed servomotors, three spherical joints between the top of the pantograph mechanisms and the connecting bars, and three revolute joints between the connecting bars and a mobile joystick handle. Forward and inverse kinematic analyses are performed and the Jacobian matrix is derived. Performance indexes such as global payload index, global conditioning index, translation and orientation workspaces, and sensitivity are evaluated to find optimal parameters in the design stage. The proposed haptic mechanism has better load capability than those of the pre-existing haptic mechanisms due to the fact that the motors are fixed at the base. It has also a wider orientation workspace mainly due to a RRR-type spherical joint. A control method is presented with gravity compensation and force feedback by a force/torque sensor to compensate for the effects of unmodeled dynamics such as friction and inertia. Also, the dynamic performance is evaluated for force characteristics. Virtual wall simulation with the developed haptic device is demonstrated     

Eddy Current Brakes for Haptic Interfaces: Design, Identification, and Control

We describe the design of an eddy current brake for use as programmable viscous damper for haptic interfaces. Unlike other types of programmable brakes, eddy current brakes can provide linear, programmable physical damping that can be modulated at high frequency. These properties makes them well suited as dissipative actuators for haptic interfaces. We overview the governing physical relationships, and describe design optimization for inertial constraints. A prototype haptic interface is described, and experimental results are shown that illustrate the improvement in stability when simulating a stiff wall that is made possible using programmable eddy current dampers.      

Kinematic and workspace-based dimensional optimization of a 2-DOF mechanism for a novel multipoint device

This paper presents the development of a novel haptic device that allows a user to interact with a computer using force feedback. The mechanism used in this work is expected to interact with a finger without the use of a fixture attached to the body, and by further including multiple identical mechanisms for each finger of the hand; it is possible to interact with virtual objects with gestures such as grabbing or pinching. This work investigates the theoretical workspace of a human index finger and compares it with an experimental workspace, which is obtained using a computer vision system, resulting in a modified theoretical model. Furthermore, the paper uses a two degree-of-freedom 7-bar linkage mechanism, whose dimensions are optimized according to the finger workspace. The paper obtains the mobility of the mechanism by using screw theory and analyzing the constraint screw system of the end-effector. Furthermore, the paper determines the closed-form solutions to the forward and inverse position, velocity and acceleration problems that are of interest in haptic simulations. In addition to this, the singular configurations are obtained by analyzing the Jacobian matrix and screw theory is further used to gain insight into the constraints applied to the end effector in these configurations. Theoretical workspaces are compared with experimental results, where a new finger workspace is proposed in order to account the difference between literature models and experiments. A prototype is built and tested as a proof of concept of the novel device, where the apparatus is comprised by a set of five 2-DOF mechanism; each mechanism sustains the proposed workspace but the dimensions of their components vary in order to fit all the end effectors within the fingers reach. The workspace of the constructed mechanism is compared with their theoretical models for assessing their effectiveness, and the feasibility of the use of accelerometers as position sensing instruments. The paper determines a closed-form solution to the applied force and performs an experiment to determine the force feedback that is experienced by the user. The torque produced by the motors of each mechanism is measured and the results extrapolated to cover the maximum current that can be applied to the motors.     

Development of micromanipulator and haptic interface for networkedmicromanipulation

Telemicromanipulation systems with haptic feedback, which are connected through a network, are proposed. It is based on scaled bilateral teleoperation systems between different structures. These systems are composed of an original 6 degree of freedom (DOF) parallel link manipulator to carry out micromanipulation and a 6-DOF haptic interface with force feedback. A parallel mechanism is adopted as a slave micromanipulator because of its good features of accuracy and stiffness. The system modeling and control of the parallel manipulator system are conducted. Parallel manipulator feasibility as a micromanipulator, positioning accuracy and device control characteristics are investigated. A haptic master interface is developed for micromanipulation systems. System modeling and a model reference adaptive controller are applied to compensate friction force, which spoils free motion performance and force response isotropy of the haptic interface. These systems aim to make the micromanipulation more productive constructing a better human interface through the microenvironment force and scale expansion     

HIFE-haptic interface for finger exercise

A haptic device with two active degrees of freedom and a tendon-driven transmission system was designed, built, and tested. It was constructed as a mechanism with a small workspace that envelops a finger workspace and can generate forces up to 10 N, suitable for finger exercise. Kinematic and dynamic model equations of the haptic device are presented in the paper. The control strategies, the implementation of the application on a PC, the real-time millisecond-class control environment, running under the MS Widows operating system, and safety mechanisms are described. Also, the duration test for the maximum sustained output force, and validations of accuracy of the output force and the consistency of the followed path, were performed. The performance, accuracy, and safety of the device were found to be very good, which makes the device suitable for rehabilitation purposes.     

A General-Purpose 7 DOF Haptic Device: Applications Toward Robot-Assisted Surgery

A 7 DOF haptic device has been designed and developed with applications towards robot-assisted minimally invasive surgery. The device consists of four degrees of force feedback (X, Y, Z, and grasping) capability and seven degrees of position feedback capability. It has a closed kinematic chain with two halves (user interface and spatial mechanism) that connect together via a universal joint. The user interface contains four degrees of position feedback, namely, the roll, pitch, yaw, and linear motion of the hand and forearm. In addition, a grasping mechanism with two thimbles mounted at the end of the user interface provides force feedback to the fingers of the user. The spatial mechanism provides force feedback to the user interface through a universal joint located at the grasping mechanism. This paper presents the design and development of this haptic device. In addition, a kinematic and workspace analysis of the device has been completed to compute the position of the slave robot and end-effector tool. Friction estimation has been presented to enable a higher transparency of the haptic device. Finally, a simulation of needle insertion into soft tissue was developed to test the device.     

Automated Characterization and Compensation for a Compliant Mechanism Haptic Device

Compliant mechanisms and voice coil motors can be used in haptic device designs to eliminate bearings and achieve smooth friction-free motion. The accompanying return-to-center behavior can be compensated using feedforward control if a suitable multidimensional stiffness model is available. In this paper we introduce a method for automatic self-characterization and compensation, and apply it to a planar haptic interface that features a five-bar compliant mechanism. We show how actuators and position sensors already native to typical impedance-type haptic devices can readily accommodate stiffness compensation. Although a portion of the motor torque is consumed in compensation, the device achieves smooth friction-free articulation with simple, low tolerance, and economic components. Empirical models built on self-characterization data are compared to standard empirical and analytical models. We produce a model by self-characterization that requires no inversion and is directly useable for compensation. Although our prototype compliant mechanism, which we fabricated in plastic using fused deposition modeling, exhibited hysteresis (which we did not compensate), the return-to-center behavior was reliably reduced by over 95% with feedforward compensation based on the self-characterized model.     

A control-system architecture for robots used to simulate dynamicforce and moment interaction between humans and virtual objects

Haptic or kinesthetic feedback is essential in many important virtual reality and telepresence applications. Previous research focuses on simulating static forces such as those encountered when interacting with a stiff object such as a wall. Past studies usually employ custom-made devices that are not readily available to other researchers. Consequently, many of the results found in the haptic feedback literature cannot be replicated independently. With experimental results, the paper demonstrates that “off the shelf,” general purpose robotics equipment can be incorporated into an effective haptic/kinesthetic feedback system. Such a system can accommodate a wide variety of virtual reality applications including training and telerobotics. An admittance control scheme is utilized, which enables the simulation of dynamic force and moment interaction as well as contact with stiff objects. The paper shows that the mechanical deficiencies (e.g., friction, inertia, and backlash) often associated with general purpose manipulators can be overcome with a suitable control system architecture     

Virtual environments for medical training: graphical and hapticsimulation of laparoscopic common bile duct exploration

We develop a computer-based training system to simulate laparoscopic procedures in virtual environments for medical training. The major hardware components of our system include a computer monitor to display visual interactions between 3D virtual models of organs and instruments together with a pair of force feedback devices interfaced with laparoscopic instruments to simulate haptic interactions. We simulate a surgical procedure that involves inserting a catheter into the cystic duct using a pair of laparoscopic forceps. This procedure is performed during laparoscopic cholecystectomy to search for gallstones in the common bile duct. Using the proposed system, the user can be trained to grasp and insert a flexible and freely moving catheter into the deformable cystic duct in virtual environments. The associated deformations are displayed on the computer screen and the reaction forces are fed back to the user through the force feedback devices. A hybrid modeling approach was developed to simulate the real-time visual and haptic interactions that take place between the forceps and the catheter, as well as the duct; and between the catheter and the duct     

Development of a six DOF haptic master for teleoperation of a mobile manipulator

An intuitive controller is needed for easier teleoperation of a slave robot. The mobile manipulation task requires three DOFs for planar mobility and six DOFs for 3-D manipulation. Since existing six DOF haptic devices have not been adequately developed for mobile manipulation, they are inefficient for planar three DOF motion. In this paper, a design for a six DOF haptic master suitable for tasks involving mobile manipulation is presented. The proposed device adopts a separable structure composed of lower and upper mechanisms. The lower parallel mechanism offers three DOFs for planar motion, and the upper parallel mechanism mounted on the lower mechanism provides the remaining three DOFs for a total of six DOFs; thus, the workspace can be extended into a full six DOF representation. This separable feature provided efficient actuation and reduced computational burden since only three actuators were involved in the planar task. Moving bodies should have low inertia to improve the back-drivability and transparency; therefore, all actuators were placed at the base, and torques were delivered via wire-driven transmission. A kinematic analysis was performed, and design parameters were determined through workspace analysis. Various experiments demonstrated that the proposed mechanism was efficient for a planar task, and also adequate for a full 3-D task.     

The Rutgers Master II-new design force-feedback glove

The Rutgers Master II-ND glove is a haptic interface designed for dextrous interactions with virtual environments. The glove provides force feedback up to 16 N each to the thumb, index, middle, and ring fingertips. It uses custom pneumatic actuators arranged in a direct-drive configuration in the palm. Unlike commercial haptic gloves, the direct-drive actuators make unnecessary cables and pulleys, resulting in a more compact and lighter structure. The force-feedback structure also serves as position measuring exoskeleton, by integrating noncontact Hall-effect and infrared sensors. The glove is connected to a haptic-control interface that reads its sensors and servos its actuators. The interface has pneumatic servovalves, signal conditioning electronics, A/D/A boards, power supply and an imbedded Pentium PC. This distributed computing assures much faster control bandwidth than would otherwise be possible. Communication with the host PC is done over an RS232 line. Comparative data with the CyberGrasp commercial haptic glove is presented     

Haptic Interaction Stability With Respect to Grasp Force

This paper addresses the contact instability of admittance control of a haptic interface. A high level of rigidity of the grasp of a subject operating the haptic interface will result in unstable behavior of the haptic interaction. Experiments with a system dedicated to measuring grasp force were performed to explore the conditions when grasp force has reached the critical grasp force that destabilizes the haptic interface. The critical grasp force was quantified for various values of virtual environment parameters. The experimental results are compared to simulation results obtained with a model of haptic interaction. To improve stability, two methods were applied: one with virtual coupling, the other with a compensator filter. A model was used to define the structure of the compensator filter and to determine the parameters of the virtual coupling and the compensator filter. Experimental and simulation results confirmed an improvement of stability. Both methods allow higher grasp forces of the human operator, and experiments show that the compensator filter allows higher grasp forces than the virtual coupling.     

On the stability and accuracy of high stiffness rendering in non-backdrivable actuators through series elasticity

This paper addresses the problem of accuracy and coupled stability of stiffness-controlled series elastic actuators, where the motor is modeled as a non-backdrivable velocity source, and the desired value of virtual stiffness is above the physical stiffness of the compliant element. We first demonstrate that, in the mentioned conditions, no linear outer-loop force control action can be applied on the velocity-sourced motor to passify the system. Relaxing the constraint of passivity, we exhaustively search the control design space defined by parametric force and stiffness controllers, expressed in a general lead-lag form, and define a lead-type stiffness compensator that results in acceptable conditions for both coupled stability and accuracy. We also address the effect of a non-ideality in the velocity control loop, such as limited-bandwidth velocity control, and derive relationships between the value of the inner velocity loop time constant and parameters of the stiffness compensator that provide the best performance in terms of both stability and accuracy of haptic display.We show that the parameters of a simple outer-loop stiffness compensator can be optimized to result in a stable and accurate display of virtual environments with stiffness values in a large range, that also comprises values of virtual stiffness higher than the physical stiffness of the compliant element. A requirement for coupled stability is that the actuator is designed such that the minimum value of inertia connected to the compliant actuator load is higher than a control-defined threshold. Finally, we extensively analyze how the minimum value of interaction mass for coupled stability can be minimized through modulation of the stiffness compensator zeros and poles, considering realistic limitations in the velocity control bandwidth of non-backdrivable motors. Our analysis, validated through both numerical simulations and experiments, opens the possibility for alternative approaches to the design of compliant actuators, whereby rendering of high stiffness is possible if the load mass is always higher than a determined threshold.     

Elastomeric Haptic Devices for Virtual and Augmented Reality

Since the modern concepts for virtual and augmented reality are first introduced in the 1960's, the field has strived to develop technologies for immersive user experience in a fully or partially virtual environment. Despite the great progress in visual and auditory technologies, haptics has seen much slower technological advances. The challenge is because skin has densely packed mechanoreceptors distributed over a very large area with complex topography; devising an apparatus as targeted as an audio speaker or television for the localized sensory input of an ear canal or iris is more difficult. Furthermore, the soft and sensitive nature of the skin makes it difficult to apply solid state electronic solutions that can address large areas without causing discomfort. The maturing field of soft robotics offers potential solutions toward this challenge. In this article, the definition and history of virtual (VR) and augmented reality (AR) is first reviewed. Then an overview of haptic output and input technologies is presented, opportunities for soft robotics are identified, and mechanisms of intrinsically soft actuators and sensors are introduced. Finally, soft haptic output and input devices are reviewed with categorization by device forms, and examples of soft haptic devices in VR/AR environments are presented.     

Analysis,modeling, identification and control of pancake DC torque motors: Application to automobile air path actuators

This article is focused on the working, modeling and control of pancake DC torque motors, used in automobile engine air path actuators. These motors, with a limited working angle, provide high torque which makes them suitable for use in actuators without any additional gear reduction. The torque is a nonlinear function of the motor angle. This article provides a modeling scheme, suitable for control purposes, which takes into consideration nonlinearities arising from friction and operating temperature. Comparison between simulation and experiments shows the effectiveness of the proposed model. Second order sliding mode control has been applied to the actuators for robust control under the influence of nonlinearities and uncertainties. The effectiveness of the control algorithm has been proven experimentally.     

Fully 3D-Printed,Stretchable, and Conformable Haptic Interfaces

Integrating rich cutaneous haptic feedback enhances realism and user immersion in virtual and augmented reality settings. One major challenge is providing accurately localized cutaneous stimuli on fingertips without interfering with the user's dexterity. This sub 200 µm thick, fully printed, stretchable Hydraulically Amplified Taxels (HAXELs) enable both static indentation and vibrating haptic stimuli, localized to a 2.5 mm diameter region. The HAXELs are directly bonded to the user's skin, are soft enough to conform to any body part, and can be fabricated in dense arrays with no crosstalk. All functional materials (elastomers, stretchable conductors, and sacrificial layers) are deposited by inkjet printing, which allows rapid prototyping of multi-material, polymer-based structures. The actuators consist of oil-filled stretchable pouches, whose shape is controlled by electrostatic zipping. The 5 mm wide actuators weigh <250 mg and generate cutaneous stimuli well above reported perception thresholds, from DC to 1 kHz. They operate well even when stretched to over 50%, allowing great freedom in placement. The 2 × 2 arrays are tested on the fingers of human volunteers: the actuated quadrant is correctly identified 86% of the time. Printing soft actuators allows tailoring dense and effective cutaneous haptics to the unique shape of each user.     

A Serial-Type Dual Actuator Unit With Planetary Gear Train: Basic Design and Applications

Control of a robot manipulator in contact with the environment is usually conducted by a direct feedback control system using a force–torque sensor or an indirect impedance control scheme. Although these methods have been successfully applied to many applications, simultaneous control of force and position cannot be achieved. To cope with such problems, this paper proposes a novel design of a dual actuator unit (DAU) composed of two actuators and a planetary gear train to provide the capability of simultaneous control of position and stiffness. Since one actuator controls position and the other actuator modulates stiffness, the DAU can control the position and stiffness simultaneously at the same joint. Both the torque exerted on the joint and the stiffness of the environment can be estimated without an expensive force sensor. Various experiments demonstrate that the DAU can provide good performance for position tracking, force estimation, and environment estimation.