Regis Hoffman

Terrain mapping for a walking planetary rover

Presents a terrain mapping system for walking robots that constructs quantitative models of surface geometry, The accuracy of the constructed maps enables safe, power-efficient locomotion over the natural, rugged terrain found on planetary surfaces. The mapping system acquires range images with a laser rangefinder, preprocesses and stores the images, and constructs elevation maps from them at arbitrary resolutions, in arbitrary reference frames. To quantify performance in terms of accuracy, timing, and memory utilization, the authors conducted extensive tests in natural, rugged terrain, producing hundreds of millions of map points. The results indicate that the mapping system 1) is one of the few that can handle extremely rugged terrain, and 2) exhibits a high degree of real-world robustness due to its aggressive detection of image-based errors and in its compensation for time-varying errors. >

A system for semi-automatic modeling of complex environments

We present a perception system, called Artisan, that semi-automatically builds 3-D models of a robots workspace. Range images are acquired with a scanning laser rangefinder and then processed, based an a systematic sensor characterization, to remove noise and artifacts. Complex 3-D objects represented as surface meshes are subsequently recognized in the range images and inserted into a virtual workspace. This graphical virtual workspace is then used to by human operators to plan and execute remote robotic operations.

Terrain Roughness Measurement from Elevation Maps

The Autonomous Planetary Rover Project at Carnegie Mellon University is investigating the use of geometric information obtained from terrain elevation maps for mobile robot planning and control. We review how surface geometry has been characterized by surface roughness parameters, and why several of these parameters must be combined to form a vector roughness measurement. Next we propose a technique to localize and extract the intrinsic roughness from terrain elevation maps, and show how this can be used to characterize terrain.

Perception of rugged terrain for a walking robot: true confessions and new directions

The Ambler is an autonomous orthogonal walking robot that operates in rugged environments. The mechanism has two stacks and six circulating legs. On top of the Ambler is mounted a laser scanner to obtain 3D data of the local terrain. It is designed for planetary exploration. During the course of walking experiments unexpected shortcomings in the robots perception system were noted. Unusual perception sensor behavior, random noise sources, and interaction of the perception system with other system components caused both minor errors and large failures in the system. This paper analyzes the sources of the perception system errors, presents solutions to these problems, and proposes a design for a more robust perception system.<<ETX>>

3-D object modeling and recognition for telerobotic manipulation

This paper describes a system that semi-automatically builds a virtual world for remote operations by constructing 3-D models of a robots work environment. With a minimum of human interaction, planar and quadric surface representations of objects typically found in man-made facilities are generated from laser rangefinder data. The surface representations are used to recognize complex models of objects in the scene. These object models are incorporated into a larger world model that can be viewed and analyzed by the operator, accessed by motion planning and robot safeguarding algorithms, and ultimately used by the operator to command the robot through graphical programming and other high level constructs. Limited operator interaction, combined with assumptions about the robots task environment, make the problem of modeling and recognizing objects tractable and yields a solution that can be readily incorporated into many telerobotic control schemes.

CHIMERA: a real-time programming environment for manipulator control

CHIMERA is a real-time computing environment used in the Reconfigurable Modular Manipulator System project. CHIMERA, which is both a hardware and software environment, allows rapid development and implementation of real-time control programs. It provides a C/Unix-flavored concurrent programming environment for a Motorola 68020 multiprocessor hardware configuration connected to a Sun workstation. CHIMERA has been implemented using commercial hardware in conjunction with a sophisticated, locally developed software package, resulting in a reliable, reasonably priced, and easily duplicated system. CHIMERA is currently being ported for real-time control of the CMU Direct Drive Arm II. The authors describe the implementation and capabilities of the CHIMERA environment and illustrate how these features are used in robot control applications.<<ETX>>

Terrain Mapping For Long-duration Autonomous Walking

We describe the perception system for the Ambler, an autonomous, legged mobile robot that operates in rugged environments. The Amblers perception system uses 3-D laser range images to construct elevation maps of the local terrain, processing hundreds of images and thou- sands of elevation points during a walking experiment. This paper presents the design, implementation, and analysis of a perception system to meet the needs of long-duration walking, emphasizing issues of performance, accuracy, and reliability.

Progress towards robotic exploration of extreme terrain

A high degree of mobility, reliability, and efficiency are needed for autonomous exploration of extreme terrain. These requirements have guided the development of the Ambler, a six-legged robot designed for planetary exploration. To address issues of efficiency and mobility, the Ambler is configured with a stacked arrangement of orthogonal legs and exhibits a unique circulating gait, where trailing legs recover directly from rear to front. The Ambler is designed to stably traverse a 30 degree slope while crossing meter sized features. The same three principles have provided many constraints on the design of a software system that autonomously navigates the Ambler through natural terrain using 3-D perception and a combined deliberative/reactive architecture. The software system has required research advances in real-time control, perception of rugged terrain, motion planning, task-level control, and system integration. This paper presents many of the factors that influenced the design of the Ambler and its software system. In particular, important assumptions regarding the mechanism, perception, planning, and control are presented and evaluated in light of experimental and theoretical research of this project.