In the above titled paper (ibid., vol. 24, no. 3, pp. 527-536, Jun 08), it is stated in Sec. IV-D3 that the characteristic number of the first variant of the "god object" method applied to texture synthesis is 1. This statement is not always true, and clarification of this issue is presented here.

Advanced, synthetic haptic virtual environments require textured virtual surfaces. We found that texturing smooth surfaces often reduces the system passivity margin of a haptic simulation. As a result, a smooth virtual surface that can be rendered in a passive manner may loose this property once textured. We propose that any texture algorithm is associated with a characteristic number that expresses the relative change in loop gain. We further found that a passive virtual interaction can have severe unwanted artifacts if the synthesized force field is not conservative. The energy characteristics of seven algorithms are analyzed. Finally, a new texture synthesis algorithm, which operates by modulating a friction force during scanning, is shown to have several advantages over previous ones.

We describe the redesign and the performance evaluation of a high-performance haptic device system called the Pantograph. The device is based on a two degree-of-freedom parallel mechanism which was designed for optimized dynamic performance, but which also is well kinematically conditioned. The results show that the system is capable of producing accurate tactile signals in the DC-400 Hz range and can resolve displacements of the order of 10 /spl mu/m. Future improvements are discussed.

This paper describes a new calibration method for robot manipulators using a mobile TV camera and 3D digitizer. This method is motivated by the need of precisely calibrating a large work space without using special instruments or calibration fixtures. The method uses an innovative kinematic model of the robot-camera system, which permits one to combine, without loss of precision, measurements taken from different camera positions of different work volumes. The method includes algorithms for the selection of robot poses and kinematic parameter identification. Results of simulation tests of a surgical robot are presented.