SmartSpring: A Low-Cost Wearable Haptic VR Display with Controllable Passive Feedback

With the development of virtual reality, the practical requirements of the wearable haptic interface have been greatly emphasized. While passive haptic devices are commonly used in virtual reality, they lack generality and are difficult to precisely generate continuous force feedback to users. In this work, we present SmartSpring, a new solution for passive haptics, which is inexpensive, lightweight and capable of providing controllable force feedback in virtual reality. We propose a hybrid spring-linkage structure as the proxy and flexibly control the mechanism for adjustable system stiffness. By analyzing the structure and force model, we enable a smart transform of the structure for producing continuous force signals. We quantitatively examine the real-world performance of SmartSpring to verify our model. By asymmetrically moving or actively pressing the end-effector, we show that our design can further support rendering torque and stiffness. Finally, we demonstrate the SmartSpring in a series of scenarios with user studies and a just noticeable difference analysis. Experimental results show the potential of the developed haptic display in virtual reality.

A Tiny Haptic Knob Based on Magnetorheological Fluids

In this paper, we propose a tiny haptic knob that creates torque feedback in consumer electronic devices. To develop the proposed haptic knob, we use a magnetorheological (MR) fluid. When an input current is applied to a solenoid coil, a magnetic field causes a change in the MR fluid’s viscosity. This change allows the proposed haptic knob to generate a resistive torque. We optimize the structure of the haptic knob, in which two operating modes of MR fluids contribute to the actuation simultaneously. We conduct magnetic path simulation and resistive torque simulation using the finite element method and perform experiments to measure the resistive torque and its torque rate according to the rotational speed and applied current. The results show that the proposed haptic knob generates sufficient torque feedback to stimulate users and creates a variety of haptic sensations.

Co-Actuation: A Method for Achieving High Stiffness and Low Inertia for Haptic Devices

Achieving high stiffness and low inertia is a big challenge for current haptic devices. Impedance-based devices are limited in providing high stiffness while, in contrast, admittance-based devices are limited in generating low inertia. Thus, it is difficult to simulate hard contact and small inertia simultaneously in virtual environments. In this paper, we introduce a co-actuation module to overcome this difficulty. The module is a one degree-of-freedom (DOF) revolute joint which consists of a link and a physical constraint with a clearance between the two components. A motor controls the physical constraint moving cooperatively with the link. In free space, the constraint has no contact to the link and thus, users can move the link freely without feeling the inertia of the motor. In constrained space, the constraint comes into contact with the link and thus, users can feel a resistance from the motor. By means of a direct physical contact between the link and the constraint, users can feel a hard virtual surface. This paper describes the principle and the implementation of the proposed co-actuation module. Performance evaluation was conducted using a two-DOF haptic device in a task workspace of 100 mm × 100 mm. The effective inertia of the device is 64-142 g within the task workspace. The device can stably render a virtual wall with stiffness as high as 65 N/mm. The penetration to the virtual wall was 0.02-0.41 mm when tapping the wall with a speed range of 80-320 mm/s. The maximum back driving force was about 0.19 N when moving within 4.5-8.6 mm/s. The experimental results demonstrate that the concept of co-actuation is feasible in achieving high force, high stiffness range and low inertia for haptic devices.

MH-Pen: A Pen-Type Multi-Mode Haptic Interface for Touch Screens Interaction

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.

Note: Hybrid active/passive force feedback actuator using hydrostatic transmission

A hybrid actuator for haptic devices is proposed in this paper. The actuator is composed of a DC motor and a magneto-rheological (MR) brake to realize transparency and stable force control. Two piston cylinders are connected with a flexible tube to lighten the weight of the structures on the endpoint that interacts with an operator. Also, the MR brake is designed to be suitable for hydraulic transmission. For the proposed hybrid actuator, a cooperative force control method using a pressure sensor instead of a force sensor is proposed. To verify the proposed control algorithm, a virtual wall collision experiment was conducted using a developed prototype of the hybrid actuator.

Modeling and test of a kinaesthetic actuator based on MR fluid for haptic applications

Haptic display units have been widely used for conveying button sensations to users, primarily employing vibrotactile actuators. However, the human feeling for pressing buttons mainly relies on kinaesthetic sensations (rather than vibrotactile sensations), and little studies exist on small-scale kinaesthetic haptic units. Thus, the primary goals of this paper are to design a miniature kinaesthetic actuator based on Magneto-Rheological (MR) fluid that can convey various button-clicking sensations and to experimentally evaluate its haptic performance. The design focuses of the proposed actuator were to produce sufficiently large actuation forces (resistive forces) for human users in a given size constraint and to offer a wide range of actuation forces for conveying vivid haptic sensations to users. To this end, this study first performed a series of parametric studies using mathematical force models for multiple operating modes of MR fluid in conjunction with finite element electromagnetism analysis. After selecting design parameters based on parametric studies, a prototype actuator was constructed, and its performance was evaluated using a dynamic mechanical analyzer. It measured the actuator's resistive force with a varying stroke (pressed depth) up to 1 mm and a varying input current from 0 A to 200 mA. The results show that the proposed actuator creates a wide range of resistive forces from around 2 N (off-state) to over 9.5 N at 200 mA. In order to assess the prototype's performance in the terms of the haptic application prospective, a maximum force rate was calculated to determine just noticeable difference in force changes for the 1 mm stoke of the actuator. The results show that the force rate is sufficient to mimic various levels of button sensations, indicating that the proposed kinaesthetic actuator can offer a wide range of resistive force changes that can be conveyed to human operators.