Conclusions

The following main conclusions can be drawn from developing the PGM for IWARD robots:

 Stable human sensing in an unconstructed, busy, crowded public place while relying solely on onboard sensors is a challenging endeavour but stands as a fundamental pre-requisite for the IWARD robots. It is not acceptable to retrofit the whole hospital area with external sensors. Instead, the PGM relies on its own sensor system.

 Speed adaptation is an ambitious task as normal walking speed of people can vary widely. Human motion cannot be modelled as a smooth linear function, as people may stop or change direction abruptly. Moreover, in a hospital environment patients with various physical abilities may require guiding assistance from the robot. Also, a patient may be temporarily hindered from following the robot due to obstacles, people and other robots in the hospital. The developed PGM is able to maintain a pre-defined distance between the robot and the guided person in all guidance scenarios.

 In order to fit into the modular design concept of the IWARD project, all PGM sensors have to be lightweight and small in size to get an easy fit into the rectangular-shaped module box. At the same time, it has to consist of low-cost hardware in order to minimise the cost of the overall system and to make it

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affordable to hospitals. All three sensory systems of the PGM fulfil this requirement.

 ‘Power Save Mode’ had to be incorporated to save battery power of the robot. Furthermore, the power supply specification of each sensor should not exceed more than 12 VDC. Finally, all hardware has to be Linux compatible to integrate with the base robot’s on-board computer. The developed PGM uses two DC power sources only (5 VDC and 12 VDC), and all computing and sensor hardware is Linux compatible.

 A plug-and-play technology is essential so that nurses without any prior knowledge of robotics could easily insert and remove the module from the base robot on demand while the robot is in operation. The developed PGM incorporates plug-and-play features and has proven to be reliable.

 Most of the PGM hardware was shipped with Windows drivers. In contrast, the operating system for the IWARD robots is Linux. As device drivers are hardware-dependent and operating system-specific, separate device drivers had to be developed from scratch and cross-compiled for the Gumstix XScale processor. The Linux-compatible device drivers developed for the PGM are fully functional and operational.

 Following the IWARD software architecture, all software modules had to be developed as orca2 components. The developed interfaces for inter-module communication through Ice have been tested and are functioning properly.

 Research on the development of relative location systems based on infrared and/or radio sensors/emitters is a rather unexplored area. Radio propagation in indoor environments is subject to numerous problems, such as severe multipath, rare line-of sight (LOS) path, absorption, diffraction, and reflection due to the presence of obstacles and people. The wave strength is reduced not only by the distance, but also by the scattering and reflection of the wave. This makes it difficult to measure signals precisely. For these reasons, it is not possible to locate an RFID tag from a single RFID reader, particularly in cluttered or dynamically changing environments. The PGM employs multiple tags for multi- zone speed control. However, it still does not allow precise localisation of the guided person.

 The performance of Stereo-based approaches heavily depends on the lighting conditions, viewing angle, distance to persons, and variability of human’s

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appearance in video streams. Detecting people across multiple image frames as well as robustly identifying them solely with visual features is not reliable enough in a hospital environment.

 The downside of cricket sensors is that they require optical line of sight between the beacon and the receiver. All the existing tests with cricket, found in literature, were carried out in a controlled environment that did not provide enough information about whether it would be feasible for the IWARD project or not. According to the IWARD patient guidance scenario, the robot needs to perform its guidance task in a crowded hospital environment. The line of sight path between the beacon and the listener may not be maintained during guiding. It is unknown how a follower carrying a beacon would orient himself toward the listener (on the robot). Moreover, during obstacle avoidance, cornering etc. the beacon and receiver would certainly disorient from each other which may cause the sound to reach the listener after reflection and/or refraction. All this means that the cricket system alone is not capable of providing reliable guidance information in all guiding scenarios.

 Although none of the individual sensor systems is robust enough to fulfil all requirements of all guiding scenarios, the sensor fusion arrangement provides sufficient data for reliable guidance.

 Having robots working in a hospital, safety and reliability are features of superior importance. This requires that the PGM operates robustly in any condition, which includes the potential breakdown of any device of the system. The built-in self-diagnosis and messaging system of the PGM fulfils the above requirements.