Test bed experiments for various telerobotic system characteristics and configurations

Dexterous manipulation and grasping in telerobotic systems depends on the integration of high-performance sensors, displays, actuators and controls into systems in which careful consideration has been given to human perception and tolerance. Research underway at the Wisconsin Center for Space Automation and Robotics (WCSAR) has the objective of enhancing the performance of these systems and their components, and quantifying the effects of the many electrical, mechanical, control, and human factors that affect their performance. This will lead to a fundamental understanding of performance issues which will in turn allow designers to evaluate sensor, actuator, display, and control technologies with respect to generic measures of dexterous performance. As part of this effort, an experimental test bed was developed which has telerobotic components with exceptionally high fidelity in master/slave operation. A Telerobotic Performance Analysis System has also been developed which allows performance to be determined for various system configurations and electro-mechanical characteristics. Both this performance analysis system and test bed experiments are described

Comparison of force and tactile feedback for grasp force control in telemanipulation

The comparative efficacy of using direct force feedback or a simple vibrotactile display to convey changes in the intensity of remote grasp force relayed from a robotic end effector is examined. The findings show that a simple vibrotactile cue, in the absence of direct force feedback, is effective in signaling abrupt changes in remote grasp force regardless of magnitude, and when changes in force are not too slow or protracted in nature (i.e., ramp time less than 2 s). In cases where the operator must dynamically tract and respond to slow but large variations in grasp force, the comparatively crude vibrotactile display would prove helpful; but would not be as effective as that of a direct contact force display. Immediate applications and utility of current generation and near-term prototype tactile displays are discussed

Impact of inertia, friction, and backlash upon force control in telemanipulation

The mechanical behavior of master controllers of telemanipulators has been a concern of both designers and implementors of telerobotic systems. In general, the literature recommends that telemanipulator systems be constructed that minimize inertia, friction, and backlash in an effort to improve telemanipulative performance. For the most part, these recommendations are founded upon theoretical analysis or simply intuition. Although these recommendations are not challenged on their merit, the material results are measured of building and fielding telemanipulators that possess less than ideal mechanical behaviors. Experiments are described in which forces in a mechanical system with human input are evaluated as a function of mechanical characteristics such as inertia, friction, and backlash. Results indicate that the ability of the human to maintain gripping forces was relatively unaffected by dynamic characteristics in the range studied, suggesting that telemanipulator design in this range should be based on task level force control requirements rather than human factors

Effect of Thermocapillary Flow on the Surface Profile in Pulsed Laser Micro Polishing

The objective of this paper is to understand and predict how surface profiles produced by thermocapillary flow change with material properties and process parameters during pulsed laser micro polishing. Thermocapillary flow is driven by surface tension gradient which is induced by temperature gradient in a melt pool. Experimental work has shown that great reductions in surface roughness can be achieved by manipulating thermocapillary flow (thermocapillary regime). The existing surface prediction model only works for pulsed laser micro polishing through damping of stationary capillary waves (capillary regime) where thermocapillary flow is negligible. It is desirable to develop a predictive capability for the thermocapillary regime to offer guidance for parameter selection and optimization. Analytical heat transfer and fluid flow models are derived for laser induced thermocapillary flow. A dimensionless number, normalized average displacement (NAD) of a liquid particle during thermocapillary flow, is proposed and calculated directly from material properties and laser process parameters. NAD is found to be strongly correlated with the surface profile introduced by thermocapillary flow and successfully used to predict polishing achievable in thermocapillary regime. Combining this model with the existing surface prediction model will enable prediction over a wide range of parameters

Effects of Laser Pulse Duration on Pulse Laser Micro Polishing

Pulsed laser micro polishing (PL?P) has been shown to be an effective method of polishing micro metallic parts whose surface roughness can approach the feature size. This paper will describe the influence of laser pulse duration on surface roughness reduction during PL?P. It will be shown that longer pulse durations attenuate longer wavelength features, with corresponding deeper yet small melt depths and that those pulse durations may result in convective flows, introducing additional short wavelength features, yet significantly reducing the average surface roughness. For this purpose, near-infrared laser pulses have been used to polish Ti6Al4V surfaces produced using the micro end milling process

Irregular, Adaptive Scan Trajectories for Pulsed Laser Micro Polishing

The objective of this work is to generate irregular, smooth, adaptive laser scan trajectories for pulsed laser micro polishing (PL?P). Traditionally PL?P, like other surface finishing processes has used zigzag scan paths. Zigzag trajectories are simple in nature, are comprised of sharp turns, the dynamics of the positioning system are not taken into account, and more importantly are not adaptable because the path generation is independent of surface condition. In this paper, the authors present a scan trajectory generation scheme that can overcome these limitations. These trajectories are based on the artificial potential fields method of path planning that take the surface condition into account. Computer simulations are presented to illustrate the characteristics of the path and guidelines are developed for choosing the trajectory generation parameters. Finally, smooth, irregular scan trajectories are generated for a micro end milled Ti6Al4V surface that has a feature that needs no polishing, thus illustrating the versatility of the trajectory generations scheme

Laser Polishing of Micro-Machined Microfluidic Molds

The objective of this paper is to explore the effective-ness of using a pulsed 1064 nm wavelength Nd:YAG laser to polish micro-machined metal molds. Polishing is desired to reduce the surface roughness of Polydimethylsiloxane (PDMS) devices cast with these molds. Reducing the roughness on polymer microfluidic devices is desirable in order to reduce fluidic resistance, control surface friction, improve optical transparency, and improve the bonding of mating surfaces. This study is focused on modifying the surface roughness of molds in order to improve the finish of cast PDMS devices, thereby enhancing their ability to bond to a glass substrate; standard practice to seal channels when manufacturing a microfluidic device. The results of the laser parameters used in this study showed successful polishing of features with spatial fre-quencies above ~75 mm-1 (i.e., short wavelength features) . Surface features with smaller spatial frequencies (longer wavelength) remained relatively unaffected. Adhesion tests only correlated with the surface roughness metrics that capture the low spatial frequency (<75 mm-1) features. These results demonstrate that adhesion (bond strength) is a function of wavelength (and amplitude) of surface fea-tures. In order to completely describe a bonding interface, roughness metrics need to be obtained across the range of feature sizes; i.e., data collected and analyzed at different magnifications/resolutions. Laser polishing parameters that target longer wavelength features must be applied to the molds in this study in order to enhance the adhesion of the cast PDMS surfaces

Nonlinear dynamics in distributed arrival time control of heterarchical manufacturing systems

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