Touch screen technology supplies a new approach to interact with virtual environments. For haptic interaction on a touch screen, haptic devices that are capable of simultaneously conveying tactile and force information to users are highly desired for enhancing the sense of reality and immersion. To this end, a prototype haptic interface, called MH-Pen, was developed and fabricated to display the virtual interactive information through multi-mode haptic feedback. The MH-Pen is a self-contained system that provides vibrotactile feedback and precise force feedback by integrating three types of actuators. In this paper, MH-Pen's design, specifications and working principle are described. Subsequently, to accurately display the interaction force, a hybrid actuator was designed by combining a piston-type magnetorheological (MR) actuator and a voice coil motor (VCM), and a closed-loop control scheme was built to manage the hybrid actuator. Finally, we objectively and subjectively evaluated the force feedback performance and the effect of multi-mode haptic display of the MH-Pen through physical measurements and psychophysical experiments of virtual surface stiffness display. The results show that improving the precision of force feedback and using multi-mode haptic display are both useful and necessary to enhance the sense of human-computer interaction realism.
In robotics and haptics, actuators that move at multiple degrees of freedom (DOFs) without the intermediate transmission mechanisms and have high force/torque output with compact size are widely expected to improve the stability and transparency of interactions. For this reason, utilizing the characteristics that the rheological properties of magnetorheological (MR) fluid can be continuously and reversibly changed by an external magnetic field within a few milliseconds, a multidirectional controlled three-DOF spherical MR actuator is proposed in this paper. Through the special design of the stator part, the actuator can implement force feedback control in multiple directions. Then, based on the calculated torque model and analysis of the magnetic circuit, finite-element analysis is used to optimize the geometry and internal magnetic field distribution of the actuator. In order to achieve precise control and positioning of multi-DOF motion, a small inertial measurement unit is integrated in the upper part of the joystick. We built a prototype of this actuator and tested its performance under various control conditions. The results show that the actuator can provide force feedback with reasonable magnitude and direction to users according to the change of interaction conditions, thus overcoming the disadvantage of the existing spherical MR actuators that limit the movement of the user in all directions after being activated.
This paper presents a spherical actuator-based hand-held device that provides lateral force feedback for user interaction with the touch screen. The spherical actuator is built around a ball containing the magnetorheological elastomer (MRE). This design of the actuator not only allows it to move in multiple degrees of freedom but also realizes its direct interaction with the touch screen and enhances its lateral force feedback capability by utilizing the conductive and soft characteristics of the MRE. Meanwhile, using the magnetically conductive properties of the MRE, the lateral force can be controlled by current. In this paper, we introduced the overall structure of the device, described the fabrication of the MRE, and tested the relative permeability and surface friction properties of the MRE. Then, based on the structural parameters obtained by lateral force modeling and finite element analysis, we fabricated a prototype of the actuator and determined the lateral force control method through calibration tests. Finally, through physical measurements and psychophysical experiment, we comprehensively evaluated the lateral force performance of the actuator and its ability in displaying virtual surface friction. The experimental results confirm the effectiveness of the actuator in interacting with the touch screen and displaying the virtual surface friction characteristics. INDEX TERMS Hand-held haptic device, spherical actuator, magnetorheological elastomer, touch screen interaction, friction display, lateral force feedback.
The haptic interface plays an increasingly important role in enhancing the realism and immersion of the user's interaction with the touch screen. Inspired by the wearable haptic system, this paper proposes a finger wearable device called FW-Touch for touch screen interaction. The device provides normal force, lateral force, and vibrotactile feedback for the interaction of the finger and the touch screen through three internally integrated actuators. By displaying the hardness, friction, and roughness of a virtual surface, the device is capable of simulating the active exploration and sensing process of the finger on a real surface. This paper describes the design and specifications of the FW-Touch, and details the design process of a magnetorheological (MR) foam actuator that uses a Hall sensor to correct the output force. Through physical measurements and psychophysical experiments, we comprehensively evaluated the force feedback performance of the FW-Touch and its ability in displaying the stiffness and friction of the virtual surface. The results show that improving the accuracy of force feedback is necessary for virtual stiffness display, and the accuracy and effectiveness of the FW-Touch in displaying virtual surface features can be confirmed from the measured stiffness and friction Weber fractions.
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