Dale A. Carnegie

Achieving sub-millimetre precision with a solid-state full-field heterodyning range imaging camera

We have developed a full-field solid-state range imaging system capable of capturing range and intensity data simultaneously for every pixel in a scene with sub-millimetre range precision. The system is based on indirect time-of-flight measurements by heterodyning intensity-modulated illumination with a gain modulation intensified digital video camera. Sub-millimetre precision to beyond 5 m and 2 mm precision out to 12 m has been achieved. In this paper, we describe the new sub-millimetre class range imaging system in detail, and review the important aspects that have been instrumental in achieving high precision ranging. We also present the results of performance characterization experiments and a method of resolving the range ambiguity problem associated with homodyne and heterodyne ranging systems.

Mobile Robot Navigation Modulated by Artificial Emotions

For artificial intelligence research to progress beyond the highly specialized task-dependent implementations achievable today, researchers may need to incorporate aspects of biological behavior that have not traditionally been associated with intelligence. Affective processes such as emotions may be crucial to the generalized intelligence possessed by humans and animals. A number of robots and autonomous agents have been created that can emulate human emotions, but the majority of this research focuses on the social domain. In contrast, we have developed a hybrid reactive/deliberative architecture that incorporates artificial emotions to improve the general adaptive performance of a mobile robot for a navigation task. Emotions are active on multiple architectural levels, modulating the robots decisions and actions to suit the context of its situation. Reactive emotions interact with the robots control system, altering its parameters in response to appraisals from short-term sensor data. Deliberative emotions are learned associations that bias path planning in response to eliciting objects or events. Quantitative results are presented that demonstrate situations in which each artificial emotion can be beneficial to performance.

Analysis of Errors in ToF Range Imaging With Dual-Frequency Modulation

Range imaging is a technology that utilizes an amplitude-modulated light source and gain-modulated image sensor to simultaneously produce distance and intensity data for all pixels of the sensor. The precision of such a system is, in part, dependent on the modulation frequency. There is typically a tradeoff between precision and maximum unambiguous range. Research has shown that, by taking two measurements at different modulation frequencies, the unambiguous range can be extended without compromising distance precision. In this paper, we present an efficient method for combining two distance measurements obtained using different modulation frequencies. The behavior of the method in the presence of noise has been investigated to determine the expected error rate. In addition, we make use of the signal amplitude to improve the precision of the combined distance measurement. Simulated results compare well to actual data obtained using a system based on the PMD19k range image sensor.

Video-rate or high-precision: a flexible range imaging camera

A range imaging camera produces an output similar to a digital photograph, but every pixel in the image contains distance information as well as intensity. This is useful for measuring the shape, size and location of objects in a scene, hence is well suited to certain machine vision applications. Previously we demonstrated a heterodyne range imaging system operating in a relatively high resolution (512-by-512) pixels and high precision (0.4 mm best case) configuration, but with a slow measurement rate (one every 10 s). Although this high precision range imaging is useful for some applications, the low acquisition speed is limiting in many situations. The systems frame rate and length of acquisition is fully configurable in software, which means the measurement rate can be increased by compromising precision and image resolution. In this paper we demonstrate the flexibility of our range imaging system by showing examples of high precision ranging at slow acquisition speeds and video-rate ranging with reduced ranging precision and image resolution. We also show that the heterodyne approach and the use of more than four samples per beat cycle provides better linearity than the traditional homodyne quadrature detection approach. Finally, we comment on practical issues of frame rate and beat signal frequency selection.

Mapping and exploration in a hierarchical heterogeneous multi-robot system using limited capability robots

This paper focusses on the development of a customised mapping and exploration task for a heterogeneous ensemble of mobile robots. Many robots in the team may have limited processing and sensing abilities. This means that each robot may not be able to execute all components of the mapping and exploration task. A hierarchical system is proposed that consists of computationally powerful robots (managers) at the upper level and limited capability robots (workers) at the lower levels. This enables resources (such as processing) to be shared and tasks to be abstracted. The global environment containing scattered obstacles is divided into local environments by the managers for the workers to explore. Worker robots can be assigned planner and/or explorer tasks and are only made aware of information relevant to their assigned tasks.

Improved linearity using harmonic error rejection in a full-field range imaging system

Full field range imaging cameras are used to simultaneously measure the distance for every pixel in a given scene using an intensity modulated illumination source and a gain modulated receiver array. The light is reflected from an object in the scene, and the modulation envelope experiences a phase shift proportional to the target distance. Ideally the waveforms are sinusoidal, allowing the phase, and hence object range, to be determined from four measurements using an arctangent function. In practice these waveforms are often not perfectly sinusoidal, and in some cases square waveforms are instead used to simplify the electronic drive requirements. The waveforms therefore commonly contain odd harmonics which contribute a nonlinear error to the phase determination, and therefore an error in the range measurement. We have developed a unique sampling method to cancel the effect of these harmonics, with the results showing an order of magnitude improvement in the measurement linearity without the need for calibration or lookup tables, while the acquisition time remains unchanged. The technique can be applied to existing range imaging systems without having to change or modify the complex illumination or sensor systems, instead only requiring a change to the signal generation and timing electronics.

Musical Robotics in a Loudspeaker World: Developments in Alternative Approaches to Localization and Spatialization

ABSTRACT Musical robotics is a rapidly growing field, with dozens of new works appearing in the past half decade. This paper explores the foundations of the discipline and how, due to the ability of musical robots to serve as uniquely spatialized musical agents, it experienced a rebirth even in the face of loudspeaker technologys dominance. The growth of musical robotics is traced from its pre-computer roots through its 1970s renaissance and to contemporary installation-oriented sculptures and performance-oriented works. Major figures in the field are examined, including those who in recent years have introduced the world to human/musical robot interaction in a concert setting. The paper closes with a brief speculation on the fields future, with a focus on the increasing ease with which new artists may enter the field.

Prediction of success in engineering study

The New Zealand Government is moving towards restricting access to tertiary education and implementing a managed entry scheme. It is therefore important to be able to predict whether a student has a reasonable likelihood of succeeding in tertiary engineering study. New Zealand secondary schools mostly operate on the National Certificate of Educational Achievement (NCEA) model whereby subjects are assessed on the basis of discrete individual modules. The paper compares the NCEA results to first year grades in tertiary engineering subjects obtained from most New Zealand providers of the BE degree to determine whether these NCEA grades can be used as a predictor of success or failure in tertiary engineering programmes. This is the first nation-wide survey of its kind and has yielded surprising results. For example, predicting success based on whether a student has not achieved is more insightful than basing on achievements, which is counter to the basis of many school league tables worldwide.

Improved measurement linearity and precision for AMCW time-of-flight range imaging cameras

Time-of-flight range imaging systems utilizing the amplitude modulated continuous wave (AMCW) technique often suffer from measurement nonlinearity due to the presence of aliased harmonics within the amplitude modulation signals. Typically a calibration is performed to correct these errors. We demonstrate an alternative phase encoding approach that attenuates the harmonics during the sampling process, thereby improving measurement linearity in the raw measurements. This mitigates the need to measure the systems response or calibrate for environmental changes. In conjunction with improved linearity, we demonstrate that measurement precision can also be increased by reducing the duty cycle of the amplitude modulated illumination source (while maintaining overall illumination power).

The design of a mobile autonomous robot for indoor security applications

Abstract This paper describes the design of a low-cost (below US