The global deformation model of virtual object by force is a key issue for haptic interaction between human and virtual reality. A discrete globe mass -spring model is proposed for flexible object deformation, and its surface is divided radially along the force center. The mass-spring system is composed of the nodes connected with radial distributed springs. Using the theory of virtual work, the relations between virtual force and nodal displacements are analyzed to get global deformations. Object globe deformation is simulated by measuring the nodal deformations based on a force equation at each node. According to the model, the deformation of the flexible object is simulated, and synchronously the real-time virtual contact force is provided with delta haptic device.
Haptic devices have been applied in interactive operation to perform contact tasks. To explore the haptic perception characteristics of typical push-pull and rotation operation, an experimental system was built by incorporating a three degrees of freedom (3-DOF) haptic device and the virtual environment. In this system, the haptic device is used to provide motion commands to control the avatar in the virtual environment and to exert haptic feedback on the human operator generated by three motors. In order to evaluate the main influential factors of interactive system based on haptic devices, ergonomic assessments are designed and experimentally implemented. Preliminary studies on the factors including restoring force, guidance force, speed of the virtual avatar, and the arm length have been conducted. The results are of great significance for the design of a haptic device and haptic interaction system by analyzing the specific requirements of ergonomics.
For many applications such as tele-operational robots and interactions with virtual environments, it is better to have performance with force feedback than without. Haptic devices are force reflecting interfaces. They can also track human hand positions simultaneously. A new 6 DOF (degree-of-freedom) haptic device was designed and calibrated in this study. It mainly contains a double parallel linkage, a rhombus linkage, a rotating mechanical structure and a grasping interface. Benefited from the unique design, it is a hybrid structure device with a large workspace and high output capability. Therefore, it is capable of multi-finger interactions. Moreover, with an adjustable base, operators can change different postures without interrupting haptic tasks. To investigate the performance regarding position tracking accuracy and static output forces, we conducted experiments on a three-dimensional electric sliding platform and a digital force gauge, respectively. Displacement errors and force errors are calculated and analyzed. To identify the capability and potential of the device, four application examples were programmed.
Unsorted three dimensional (3D) points are commonly acquired from modern tools and they become popular in many virtual reality applications. In order to produce the haptic feedback to enrich the interaction with the captured models, the point clouds are usually converted to structured meshes or implicit representations. The conversion is either time-consuming or not precise, making the haptic rendering with a low fidelity especially for small haptic proxies. We propose to locally reconstruct the points to balance the performance and quality for the haptic rendering of point clouds. We introduce visible patches on the point clouds by noticing that only the points which are visible to the haptic proxy form the candidate contact region. A computational model for the visible patches is introduced and a virtual coupling model is built to update the visible patches online for haptic rendering. The cases with noises and nonuniform samples are also discussed. We demonstrate our method on a set of synthesized and captured 3D point clouds. Various experimental results are collected and show the efficiency of our method.
At present, six-axis force/torque (F/T) sensor has been increasingly used in robot application, and most of the elastic elements of resistance strain type F/T sensors are made of metal materials, such as alloy steel, stainless steel, aluminum alloy, and so on. In this paper, a novel six-axis F/T sensor based on Polyetheretherketone (PEEK) material is presented. Comparison with ordinary F/T sensor purpose was served by building simplified statics model that demonstrates the conclusion of highly sensitivity of the F/T sensor based on PEEK material. The strain mapped on the strain sensitive path was analyzed using finite element analysis (FEA), frequency response curves were depicted by means of harmonic analysis, and the static and dynamic performances analyses of the six-axis F/T sensor based on PEEK material (later called PEEK sensor) were studied. Moreover, the properties of this sensor were compared with a six-axis F/T sensor based on aluminum alloy 2024 material (later called metallic sensor). The results show the properties of linearity (≤1%), hysteresis (≤2%), high sensitivity (force: ≥ 2.37×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> /N; torque (Tx, Ty): 0.19×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> /Nmm), and crosstalk (≤8%) between the dominant F/T component and other components. The dynamic response time of the PEEK sensor was also measured via dynamic calibration experiment, which is much higher than that of the metallic sensor. This study demonstrates that the PEEK sensor has a comparable static performance with the metallic sensor, and even higher sensitivity, but it is only suitable for measurement below 200 Hz.
Background The motor imagery (MI) paradigm is widely used in active brain-computer interfaces (BCIs), but its effectiveness is hindered by accuracy limitations and individual variability. Tactile stimulation has been proposed as a potential method to enhance MI performance; however, integrating such stimulation in real-time MI tasks remains challenging due to the spontaneous nature of MI.
In this paper, we present a new image-based method to display haptic texture information extracted from a static two dimensional image. The three dimensional forces allow the user to feel the contours and textures of the image with sufficient realism using haptic devices. The texture force is decomposed into a normal force component and a tangential force component at the haptic interaction point. The magnitude of the normal force is determined either by the color temperature (i.e. the emotions of warmth/coolness evoked by colors) or the luminance values in images. Warmer/brighter colors determine stronger normal forces to generate bumps, and cooler/darker colors determine weaker normal forces to produce depressions. The tangential force describes the relative color variation between haptic interaction point and its neighbors, thus, can be considered as a descriptor of the local texture feature. Because it is oriented to the pixels with cooler color in the neighborhood, when the user is exploring the bump by a haptic device, tangential resistive forces are sent to the user until the top of the bump is reached and, after the top, the virtual probe is pulled in the other direction. Our force model is by means of simple image processing techniques. The calculation is totally done by local, independent and direct operation. In other words, global operation such as recovering height maps is not necessary.
