Instrumented sensor system - practice

technical reportIn previous work, we introduced the notion of Instrumented Logical Sensor Systems (ILSS) that are derived from a modeling and design methodology [4, 2]. The instrumented sensor approach is based on a sensori-computational model which defines the components of the sensor system in terms of their functionality, accuracy, robustness and efficiency. This approach provides a uniform specification language to define sensor systems as a composition of smaller, predefined components. From a software engineering standpoint, this addresses the issues of modularity, reusability, and reliability for building complex multisensor systems. In this report, we demonstrate the practicality of this approach and discuss several design and implementation aspects in the context of mobile robot applications

Adaptive Resource Management in Asynchronous Real-time Distributed Systems Using Feedback Control Functions

Presents feedback control techniques for performing adaptive resource management in asynchronous real-time distributed systems. Such systems are characterized by significant execution time uncertainties in the application environment and system resource state. Thus, such systems require adaptive resource management that dynamically monitor the system for adherence to the desired real-time requirements and perform run-time adaptation of the application to changing workloads when unacceptable timeliness behavior is observed. We propose adaptive resource management techniques that are based on feedback control theory. The controllers solve resource allocation problems that arise during run-time adaptation using the classical proportional-integral-derivative (PID) control functions. We study the performance of the controllers through simulation. The simulation results indicate that the controllers produce low missed deadline ratios and resource utilizations during situations of high workloads

Instrumented sensor system architecture

Journal ArticleSensor systems are becoming ubiquitous throughout society, yet their design, construction and operation are still more of an art than a science. In this paper, we define, develop, and apply a formal semantics for sensor systems that provides a theoretical framework for an integrated software architecture for modeling sensor-based control systems. Our goal is to develop a design framework which allows the user to model, analyze and experiment with different versions of a sensor system. This includes the ability to build and modify multisensor systems and to monitor and debug both the output of the system and the affect of any modification in terms of robustness, efficiency, and error measures. The notion of Instrumented Logical Sensor Systems (ILSS) that are derived from this modeling and design methodology is introduced. The instrumented sensor approach is based on a sensori-computational model which defines the components of the sensor system in terms of their functionality, accuracy, robustness and efficiency. This approach provides a uniform specification language to define sensor systems as a composition of smaller, predefined components. From a software engineering standpoint, this addresses the issues of modularity, reusability, and reliability for building complex systems. An example is given which compares vision and sonar techniques for the recovery of wall pose

State-based Safety of Component-based Medical and Surgical Robot Systems

Safety has not received sufficient attention in the medical robotics community despite a consensus of its paramount importance and the pioneering work in the early 90s. Partly because of its emergent and non-functional characteristics, it is challenging to capture and represent the design of safety features in a consistent, structured manner. In addition, significant engineering efforts are required in practice when designing and developing medical robot systems with safety. Still, academic researchers in medical robotics have to deal with safety to perform clinical studies. This dissertation presents the concept, model and architecture to reformulate safety as a visible, reusable, and verifiable property, rather than an embedded, hard-to-reuse, and hard-to-test property that is tightly coupled with the system. The concept enables reuse and structured understanding of the design of safety features, and the model allows the system designers to explicitly define and capture the run-time status of component-based systems with support for error propagation. The architecture leverages the benefits of the concept and the model by decomposing safety features into reusable mechanisms and configurable specifications. We show the concept and feasibility of the proposed methods by building an open source framework that aims to facilitate research and development of safety systems of medical robots. Using the cisst component-based framework, we empirically evaluate the proposed methods by applying the developed framework to two research systems -- one based on a commercial robot system for orthopedic surgery and another robot soon to be clinically applied for manipulation of flexible endoscopes

Mechanisms for detecting and handling timing errors

Design and analysis of real-time systems is heavily based on knowing worst-case execution times (WCET) of periodic threads and aperiodic servers. Accurately measuring WCET, however, is often difficult and sometimes impossible, for several reasons: •Interrupts in the system, which either execute longer than expected or occur more frequently than anticipated may steal critical execution time from the highest priority threads. •Variations in processing speed due to caching, pipelining, and bus arbitration may alter WCET. •There is no easy way to accurately measure execution times of embedded code. As long as scheduling policies are based on WCET, these difficulties in measuring WCET inevitably lead to timing errors in the system. Many of these errors go undetected until more catastrophic failures occur, and others result in the system failing to meet its specifications, but with non-obvious reasons as to the cause of such failures. We have created low-overhead policy-independent real-time operating system (RTOS) mechanisms, which detect and handle these types of timing errors. The mechanisms can be used with a variety of common scheduling algorithms, and serve as the basis for easily extending these policies to incorporate aperiodic servers, soft real-time threads, imprecise computations, and adaptive real-time scheduling. The mechanisms have been incorporated into the Chimera RTOS[9].</p

Policy-independent real-time operating system mechanisms for timing error detection, handling and monitoring

Abstract: Most research focusing on timing errors deals with scheduling policies that avoid the errors. Since many of the policies are based on estimated worst-case execution times for each task, reliability is a function of the accuracy of the estimates. As a result, many hard real-time systems are implemented with the dangerous assumption that due to correct design and testing, a missed deadline will never occur. We have designed novel policy-independent mechanisms for detecting and handling timing errors, and for monitoring real-time tasks. The detection and handling requires less than 1 microsecond overhead per reschedule operation, and has a latency approximately the length of one context switch for handling an error. The monitoring mechanism uses 6 microsecond per context switch, and requires only 1 Kbyt