Robin Bradbeer

A Novel Actuator for Underwater Robots

Pneumatic muscles have been used for a number of years as actuators in robotic systems, usually for those that mimic human actions. They are most commonly used in systems designed to aid physically handicapped people. This feasibility study reports mechanical testing and modeling results for the Shadowtrade artificial muscle pneumatic actuator working in both air and underwater. The static and dynamic tension-contraction measurements were recorded through both the force and contraction relationship test and the dynamic response and time relationship test. A model of the properties of the muscle working in water was derived from the measurements of the tests that can be considered for its feasibility for use in undersea robotics.

Exploration for novel uses of air muscles as hydraulic muscles for underwater actuator

Since a dextrous robotic arm has been designed for use on land and in space, further development could be its use underwater for performing delicate tasks, just like a human hand, for operations such as picking up small or irregular size objects. Hitherto there has been no report on studies on modelling and control of rubber artificial muscles in hydraulic mode. The feasibility of developing these actuators using water as the articulating medium for underwater robots was therefore investigated by studying the properties of the hydraulic rubber muscle actuator. The rubber muscles used in the present tests were developed by the Shadowtrade Robot Co. Ltd. for installing in dextrous robotic arms. The objectives of this study were, thus, first, to define the kinematics of the hydraulic muscle. A test set up was designed to obtained contraction, force and response time values based on reference of a model defined for the rubber muscle when used in air. Second, to compare the performance of the rubber muscle in air and underwater using the test set up and thus third, to obtain a modelling of the hydraulic rubber muscle which was derived from that of the air rubber muscle.

Application of a real-time underwater surveillance camera in monitoring of fish assemblages on a shallow coral communities in a marine park

An underwater surveillance camera has been designed for monitoring fish species activity on an inshore coral reef in a Marine Park in Hong Kong. The system consisted of a high-resolution camera. It was connected to the shore base station via a fibre-optic cable with power conductors. The camera could record video on a DVD recorder with hard disk in real time. The system was designed to be used for long periods of time up to three months continuously without maintainence. It was used to monitor changes in coral fish abundance with respect to time of day and among months. The present results thus showed two major behavioural patterns of coral fish in Hoi Ha Wan. The first is the diurnal activities as most fish species are active during the daylight rather than at night. Both mean number of species and fish density showed an increase in daylight and a decrease at night. The second was the seasonal migratory pattern. A seasonal variation of fish abundance on a subtropical reef was recorded with water temperature changes from 29degC in summer to 17degC in winter. Mean maximum number of species during daylight in warmer months was ~10-12 while that in colder months decreased to 2-3.

Using multi-frequency modulation in a modem for the transmission of near-realtime video in an underwater environment

The system described in this paper uses multicarrier modulation, and has been successfully tested at a data rate up to 10 kbps over 1 km. The system algorithm generates 48 frequencies for transmitting 48 parallel bits of data in each packet. A long transmitted signal sequence is combined with synchronisation, zero gap and information packets. The long multi-frequency signal packets have been implemented to minimise the effect of multipath fading, which is a particular problem in shallow, open water environments. To acquire the starting point of the transmitting sequence, a linear frequency modulation (LFM) signal is used for synchronisation. In order to reduce noise, adaptive threshold packets are used to set up a suitable signal. Experimental results from sea-trials have shown that the system can cope with multipath fading environments.

Mechatronics and machine vision in practice

Proceedings of 13th Annual Conference on Mechatronics and Machine Vision in Practice, Toowoomba, Australia, 5-7 December 2006.

Real-time monitoring of fish activity on an inshore coral reef

This paper describes an underwater camera and instrumentation system for monitoring fish species activity on an inshore coral reef in a Marine Park in Hong Kong. The system consists of a high-resolution pan, tilt and zoom camera with associated instrumentation package for measuring the local environment, including dissolved oxygen, temperature, pressure, salinity and ambient light conditions. It is connected to the shore base station via a fibre-optic cable with power conductors. The system is designed to be used for long periods of time, continuously. The first period chosen was for 100 days during the coral spawning season from June to August 2004. The system has also been used regularly for 2-3 weeks at a time to monitor changes in fish behaviour in different climatic conditions. Results from the initial experiment show that fish species activity is generally markedly different from that recorded by human divers. There is also some correlation between species, time of day, and climatic and environmental conditions - correlations that have not been reported before. The paper will give details of the results of the observations, as well as technical details of the system. It will also refer to an associated project using an ROV for transect measurements on the reef, data from which has a bearing on the subject of the paper.

An integrated studio approach to teaching basic electronics to first year mechatronics degree students

The introduction of studio teaching at City University of Hong Kong allowed for a comparative study of the benefits of this form of teaching. A four-year longitudinal study was carried out using the Introductory Electronics courses designed for First Year Mechatronic Engineering degree students. A similar group in the same department studying Manufacturing Engineering was used as a control. It has been shown during preliminary analysis of the data that students using the teaching studio approach acquire a deeper understanding of the subject as well as achieving better grades than those students using the more traditional approaches. A typical studio session consists of a mixture of discussions, mini-lectures, demonstrations, computer simulations, problem-solving activities, and computer supported laboratory exercises. It utilises computer based teaching materials that emphasise multimedia and interactive learning.

Underwater acoustic modem using multicarrier modulation

An underwater digital acoustic communications system based on multicarrier modulation technique is presented. This technique is relatively robust in a strong multipath fading environment and has been successfully tested in a shallow water channel at a data rate up to 10 kbps over 1 km. The test system using 48 carrier frequencies for transmitting 48 parallel bits of data in each packet. The data stream is encoded into a sequence of packets. These packets are encapsulated by headers, synchronisation and training signals. In order to reduce the multipath fading problem, an adaptive channel equalisation scheme with a LSM algorithm is used. The multipath fading problem can be further improved by a redundant carrier assignment and wavelet based MFM scheme. The advantage of this scheme is that the fading is reduced without affecting the channel capacity.

An underwater camera for security and recreational use

The objective of this project was to design an underwater camera and instrumentation system that could be used to detect and follow moving objects, and be able to be deployed at a depth of up to 100 m for an extended period of time. This was achieved by using a pan, tilt and zoom high resolution camera connected to a base station via a powered fibre optic cable. The camera was successfully deployed for 100 days continuously, recording video on to a DVD recorder in real time.

A medium resolution intelligent video camera

The most popular method for abstracting visual information from video images is based around image grabbing techniques. This is expensive, bulky and quite often too slow. It also requires the use of large amounts of processing power. There are a number of applications, ranging from intelligent toys to machine vision and security applications which need either low cost video images or ones that can be digitally manipulated. The main criteria for the camera described was its manufactured cost-below