Rendering stiffer walls: a hybrid haptic system using continuous and discrete time feedback

Instability in conventional haptic rendering destroys the perception of rigid objects in virtual environments. Inherent limitations in the conventional haptic loop restrict the maximum stiffness that can be rendered. In this paper we present a method to render virtual walls that are much stiffer than those achieved by conventional techniques. By removing the conventional digital haptic loop and replacing it with a part-continuous and part-discrete time hybrid haptic loop, we were able to render stiffer walls. The control loop is implemented as a combinational logic circuit on an field-programmable gate array. We compared the performance of the conventional haptic loop and our hybrid haptic loop on the same haptic device, and present mathematical analysis to show the limit of stability of our device. Our hybrid method removes the computer-intensive haptic loop from the CPU-this can free a significant amount of resources that can be used for other purposes such as graphical rendering and physics modeling. It is our hope that, in the future, similar designs will lead to a haptics processing unit (HPU).

Haptic Feedback for Injecting Biological Cells using Miniature Compliant Mechanisms

We present a real-time haptics-aided injection technique for biological cells using miniature compliant mechanisms. Our system consists of a haptic robot operated by a human hand, an XYZ stage for micro-positioning, a camera for image capture, and a polydimethylsiloxane (PDMS) miniature compliant device that serves the dual purpose of an injecting tool and a force-sensor. In contrast to existing haptics-based micromanipulation techniques where an external force sensor is used, we use visually captured displacements of the compliant mechanism to compute the applied and reaction forces. The human hand can feel the magnified manipulation force through the haptic device in real-time while the motion of the human hand is replicated on the mechanism side. The images are captured using a camera at the rate of 30 frames per second for extracting the displacement data. This is used to compute the forces at the rate of 30 Hz. The force computed in this manner is sent at the rate of 1000 Hz to ensure stable haptic interaction. The haptic cell-manipulation system was tested by injecting into a zebrafish egg cell after validating the technique at a size larger than that of the cell.

Issues in Achievement of Haptic Realism

This paper deals with haptic realism related to Kinematic capabilities of the devices used in manipulation of virtual objects in virtual assembly environments and its effect on achieving haptic realism. Haptic realism implies realistic touch sensation. In virtual world all the operations are to be performed in the same way and with same level of accuracy as in the real world .In order to achieve realism there should be a complete mapping of real and virtual world dimensions. Experiments are conducted to know the kinematic capabilities of the device by comparing the dimensions of the object in the real and virtual world. Registered dimensions in the virtual world are found to be approximately 1.5 times that of the real world. Dimensional variations observed were discrepancy due to exoskeleton and discrepancy due to real and virtual hands. Experiments are conducted to know the discrepancy due to exoskeleton and this discrepancy can be taken care of by either at the hardware or software level. A Mathematical model is proposed to know the discrepancy between real and virtual hands. This could not give a fixed value and can not be taken care of by calibration. Experiments are conducted to figure out how much compensation can be given to achieve haptic realism.