Message-Based Evaluation for High-Level Robot Control

In this paper, we present a method for high-level control of robots whose low-level software is based on dynamically reconfigurable, reusable real-time software modules. Our approach is to use an embedded interpreter for a general-purpose programming language to direct the operation of the low-level modules toward meeting the task-level goals of the robot. To this end, we present RSK, a virtual-machine kernel implementing a Scheme interpreter capable of hard real-time operation, and employing a method of code execution we call “message-based evaluation” (MBE). MBE is a novel combination of a traditional code execution model and a message-passing architecture, which simplifies the process of writing code for managing the robot’s reconfigurable subsystem. 1 Dynamically reconfigurable real-time software A major goal of real-time operating systems like Chimera is to enable sensor-based control applications to be built from libraries of reusable software modules. For this purpose, they provide standard interface specifications for implementing reusable real-time software modules, and a library of functions for building and using configurations of these modules [1]. A well-written and debugged library of real-time modules thus facilitates rapid development of reliable sensor-based control systems. In Chimera, these modules or “port-based objects,” typically cycle at some fixed frequency and communicate their inputs and outputs through a global state-variable table. A typical configuration of real-time modules for controlling a robot manipulator arm is shown in Figure 1. A real-time software module is reusable only if it is sufficiently independent of the specific details of the different applications for which it is used. Therefore, an essenSupported by a DOE Fellowship in Integrated Manufacturing generator Trajectory