This article describes a simple control strategy for stable hardon-hard contact of a manipulator with the environment. The strategy is motivated by recognition of the equivalence of proportional gain explicit force control and impedance control. It is shown that negative proportional force gains, or impedance mass ratios less than unity, can equivalently provide excellent impact response without bouncing. This result is indicated by an analysis performed with an experimentally determined arm/sensor/environment model. The results are corroborated by experimental data from implementation of the control algorithms on the CMU DD Arm II system. The results confirm that manipulator impact against a stiff environment without bouncing can be readily handled by this novel control strategy.
This paper presents a complete overview of basic strategies that have been proposed for force control of robot manipulators. First, the model of the plant t o b e c o n trolled is reviewed. Next, the strategies are divided into force-based and position-based categories, according to previously reported implementations. Each of the controller types within these categories are analyzed, and predictions of stability and e cacy are made. Then it is shown that these two categories are actually the same, and this recognition leads to the concept of a novel second order low pass lter controller. Finally, all of the controllers are experimentally tested on the CMU DD Arm II , con rming the theoretical predictions. Among the important results presented is the conclusive demonstration for the rst time that integral gain control is the best basic strategy for force control of manipulators.
Previous work in arti cial potentials has demonstrated the need for an obstacle avoidance p otential that closely models the obstacle, yet does not generate local minima in the workspace of the manipulator. This paper presents a potential function based on superquadrics, which closely models a large class of object shapes. This potential function also prevents the creation of local minima when it is added to spherically symmetric attractive wells. We introduce two compatible forms of the superquadric potential function: one for obstacle avoidance, and another for obstacle approach. We have implemented the avoidance and approach potentials in simulations. In these simulations the end e ector of the manipulator experiences an attractive force f r om a global spherical well, while the end e ector and each of the links experience r epulsive forces from all of the objects. We have also experimentally implemented the avoidance p otentials on the CMU DDARM II. The results demonstrate successful obstacle avoidance and approach, and exhibit an improvement over existing potential schemes.
The current development of applications for sensor-based robotic and automation (R&A) systems is typically a "one-of-a-kind" pmcess, where most software is developed from scratch, even though much of the code is similar to code written for other applications. The cost of these systems can be drastically reduced and the capability of these systems improved by providing a suitable software framework for all R&A system. We describe a novel software framework, based on the notion of dynamically reconfigurable software for sensor-based control systems. Tools to suppon the implementation of this framework have been built into the Chimera 3.0 Real-Time Operating System. The framework provides for the systematic development and predictable execution of flexible R&A applications while maintaining the ability to reuse code from previous applications. It combines object-oriented design of software with port-automaton design of digital control systems. A control module is an instance of a class of port-based objects. A task set is formed by integrating objects from a module library to form a specific configuration. An implementation using global state variables for the automatic integration of port-based objects is presented. A control subsystem is a collection of jobs which are executed one at a time, and can be programmed by a user. Multiple control subsystems can execute in parallel, and operate either independently or cooperatively. One of the fundamental concepts of reconfigurable software design is that modules are developed independent of the target hardware. Our framework defines classes of reconfigurable device driver objects for proving hardware independence to YO devices, sensors, actuators, and special purpose processors. Hardware independent real-time communication mechanisms for inter-subsystem communication are also described. Along with providing a foundation for design of dynamically reconfigurable real-time software, we are. also developing many modules for the control module, device driver, and subroutine libraries. As the libraries continue to grow, they will form the basis of code that can eventually be used by future R&A applications. There will no longer be a need for developing software from scratch for new applications. since many required modules will already be available in one of the libraries.
The Mars Phoenix Lander was equipped with a 2.4 m Robotic Arm (RA) with an Icy Soil Acquisition Device capable of excavating trenches in soil deposits, grooming hard icy soil surfaces with a scraper blade, and acquiring icy soil samples using a rasp tool. A camera capable of imaging the scoop interior and a thermal and electrical conductivity probe were also included on the RA. A dozen trench complexes were excavated at the northern plains landing site and 31 samples (including water‐ice‐bearing soils) were acquired for delivery to instruments on the Lander during the 152 sol mission. Deliveries included sprinkling material from several centimeters height to break up cloddy soils on impact with instrument portals. Excavations were done on the side of the Humpty Dumpty and the top of the Wonderland polygons, and in nearby troughs. Resistive forces encountered during backhoe operations show that soils above the 3–5 cm deep icy soil interfaces are stronger with increasing depth. Further, soils are similar in appearance and properties to the weakly cohesive crusty and cloddy soils imaged and excavated by the Viking Lander 2, which also landed on the northern plains. Adsorbed H2O is inferred to be responsible for the variable nature and cohesive strength of the soils. Backhoe blade chatter marks on excavated icy soil surfaces, combined with rasp motor currents, are consistent with laboratory experiments using grain‐supported icy soil deposits, as is the relatively rapid decrease in icy soil strength over time as the ice sublimated on Mars.
This paper provides a system overview of a new Mars rover prototype, Rocky 7 1. We describe all system aspects: mechanical and electrical design, computer and software infrastructure, algorithms for navigation and manipulation, science data acquisition, and outdoor rover testing. In each area, the improved or added functionality is explained in a context of its path to ight, and within the constraints of desired science missions.
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