Pradeep K. Khosla

Visual tracking of a moving target by a camera mounted on a robot: a combination of control and vision

The authors present algorithms for robotic (eye-in-hand configuration) real-time visual tracking of arbitrary 3D objects traveling at unknown velocities in a 2D space (depth is given as known). Visual tracking is formulated as a problem of combining control with computer vision. A mathematical formulation of the control problem that includes information from a novel feedback vision sensor and represents everything with respect to the camera frame is presented. The sum-of-squared differences (SSD) optical flow is used to compute the vector of discrete displacements each instant of time. These displacements can be fed either directly to a PI (proportional-integral) controller or to a pole assignment controller or discrete steady-state Kalman filter. In the latter case, the Kalman filter calculates the estimated values of the systems states and the exogenous disturbances, and a discrete LQG (linear-quadratic Gaussian) controller computes the desired motion of the robotic system. The outputs of the controllers are sent to the Cartesian robotic controller. Performance results are presented. >

Real-time obstacle avoidance using harmonic potential functions

A novel formulation of the artificial potential approach to the obstacle avoidance problem for a mobile robot or a manipulator in a known environment is presented. Previous formulations of artificial potentials for obstacle avoidance have exhibited local minima in a cluttered environment. To build an artificial potential field, the authors use harmonic functions that completely eliminate local minima even for a cluttered environment. The panel method is used to represent arbitrarily shaped obstacles and to derive the potential over the whole space. Based on this potential function, an elegant control strategy for the real-time control of a robot is proposed. Simulation results are presented for a bar-shaped mobile robot and a three-degree-of-freedom planar redundant manipulator. >

SWATT: softWare-based attestation for embedded devices

We expect a future where we are surrounded by embedded devices, ranging from Java-enabled cell phones to sensor networks and smart appliances. An adversary can compromise our privacy and safety by maliciously modifying the memory contents of these embedded devices. In this paper, we propose a softWare-based attestation technique (SWATT) to verify the memory contents of embedded devices and establish the absence of malicious changes to the memory contents. SWATT does not need physical access to the devices memory, yet provides memory content attestation similar to TCG or NGSCB without requiring secure hardware. SWATT can detect any change in memory contents with high probability, thus detecting viruses, unexpected configuration settings, and Trojan Horses. To circumvent SWATT, we expect that an attacker needs to change the hardware to hide memory content changes. We present an implementation of SWATT in off-the-shelf sensor network devices, which enables us to verify the contents of the program memory even while the sensor node is running.

SORI: a secure and objective reputation-based incentive scheme for ad-hoc networks

In an ad-hoc network, intermediate nodes on a communication path are expected to forward packets of other nodes so that the mobile nodes can communicate beyond their wireless transmission range. However, because wireless mobile nodes are usually constrained by limited power and computation resources, a selfish node may be unwilling to spend its resources in forwarding packets which are not of its direct interest, even though it expects other nodes to forward its packets to the destination. It has been shown that the presence of such selfish nodes degrades the overall performance of a non-cooperative ad hoc network. To address this problem, we propose a secure and objective reputation-based incentive (SORI) scheme to encourage packet forwarding and discipline selfish behavior. Different from the existing schemes, under our approach, the reputation of a node is quantified by objective measures, and the propagation of reputation is efficiently secured by a one-way-hash-chain-based authentication scheme. Armed with the reputation-based mechanism, we design a punishment scheme to penalize selfish nodes. The experimental results show that the proposed scheme can successfully identify selfish nodes and punish them accordingly.

Parameter identification of robot dynamics

This paper presents algorithms for identifying parameters of multi-degrees-of-freedom robotic arm. First, we outline the fundamental properties of the Newton-Euler formulation of robot dynamics from the view point of parameter identification. We then show that the Newton-Euler model which is nonlinear in some of dynamic parameters can be transformed into the equivalent model which is linear in dynamic parameters. We develop both on-line and off-line parameter estimation procedures. To illustrate our approach, we identify the dynamic parameters of the cylindrical robot, and the three degree-of-freedom positioning system of the CMU Direct-Drive Arm II.

Design of dynamically reconfigurable real-time software using port-based objects

The port-based object is a new software abstraction for designing and implementing dynamically reconfigurable real-time software. It forms the basis of a programming model that uses domain-specific elemental units to provide specific, yet flexible, guidelines to control engineers for creating and integrating software components. We use a port-based object abstraction, based on combining the notion of an object with the port-automaton algebraic model of concurrent processes. It is supported by an implementation using domain-specific communication mechanisms and templates that have been incorporated into the Chimera real-time operating system and applied to several robotic applications. This paper describes the port-based object abstraction, provides a detailed analysis of communication and synchronization based on distributed shared memory, and describes a programming paradigm based on a framework process and code templates for quickly implementing applications.

Pioneer: verifying code integrity and enforcing untampered code execution on legacy systems

We propose a primitive, called Pioneer, as a first step towards verifiable code execution on untrusted legacy hosts. Pioneer does not require any hardware support such as secure co-processors or CPU-architecture extensions. We implement Pioneer on an Intel Pentium IV Xeon processor. Pioneer can be used as a basic building block to build security systems. We demonstrate this by building a kernel rootkit detector.

Adaptive robotic visual tracking: theory and experiments

The use of a vision sensor in the feedback loop is addressed within the controlled active vision framework. Algorithms are proposed for the solution of the robotic (eye-in-hand configuration) visual tracking and servoing problem. Visual tracking is stated as a problem of combining control with computer vision. The sum-of-squared differences optical flow is used to compute the vector of discrete displacements. The displacements are fed to an adaptive controller (self-tuning regulator) that creates commands for a robot control system. The procedure is based on the online estimation of the relative distance of the target from the camera, but only partial knowledge of the relative distance is required, obviating the need for offline calibration. Three different adaptive control schemes have been implemented, both in simulation and in experiments. The computational complexity and the experimental results demonstrate that the proposed algorithms can be implemented in real time. >

Survivable information storage systems

As society increasingly relies on digitally stored and accessed information, supporting the availability, integrity and confidentiality of this information is crucial. We need systems in which users can securely store critical information, ensuring that it persists, is continuously accessible, cannot be destroyed and is kept confidential. A survivable storage system would provide these guarantees over time and despite malicious compromises of storage node subsets. The PASIS architecture flexibly and efficiently combines proven technologies (decentralized storage system technologies, data redundancy and encoding, and dynamic self-maintenance) for constructing information storage systems whose availability, confidentiality and integrity policies can survive component failures and malicious attacks.

Feedforward Controller With Inverse Rate-Dependent Model for Piezoelectric Actuators in Trajectory-Tracking Applications

Effective employment of piezoelectric actuators in microscale dynamic trajectory-tracking applications is limited by two factors: 1) the intrinsic hysteretic behavior of piezoelectric ceramic and 2) structural vibration as a result of the actuators own mass, stiffness, and damping properties. While hysteresis is rate-independent, structural vibration increases as the piezoelectric actuator is driven closer to its resonant frequency. Instead of separately modeling the two interacting dynamic effects, this work treats their combined effect phenomenologically and proposes a rate-dependent modified Prandtl-Ishlinskii operator to account for the hysteretic nonlinearity of a piezoelectric actuator at varying actuation frequency. It is shown experimentally that the relationship between the slope of the hysteretic loading curve and the rate of control input can be modeled by a linear function up to a driving frequency of 40 Hz