Mid Sweden University

This paper will discuss a wireless control system for a loader crane, where the focus lies on the wireless communication protocol supporting the implementation of the real-time system. To aid the discussion, a system model is included, which together with the control strategy will allow low power consumption for the energy constraint sensor devices. A simple and power aware medium access control protocol is proposed. The protocol together with the specific loader crane requirements make it possible to save valuable sensor resources. Simulations on real world loader crane data show a simplified view of the power requirements for the control model, and the importance of utilizing correct system parameters to achieve low power consumption.

In this paper the use of the IIEEE 802.15.4 standard in a wireless control system is analyzed and discussed. The standard is described and applied on a heavy duty crane application and the discussion focuses on the possibilities and limitations of the standard in the application. A formula is presented which can be used to calculate maximum sample rate according to the number of sensor nodes and the payload the nodes may carry. The discussion reveals that the standard may be utilized in the crane application but that it is not a good solution. Several limitations within the standard, such as network size and system sample rate, will put a stop to future extensions of the wireless control system. As a result, the 802.15.4 standard protocol shall not be employed in the heavy duty crane application.

This paper presents the analysis for joint angle measurement on rigid body that is based on distributed biaxial MEMS accelerometers. It focuses on two methods, one called CMR and another DCMR, and utilizes the property of rigid body kinematics to explain their advantages and weaknesses. Unlike CMR method, DCMR method has no requirement on placing the sensors close to the joint center. This provides greater flexibility for the sensor installation. On the basis of the error model of CMR method, we give an analysis outlining the advantage of theoretically error-free DCMR method. The sensor calibration and alignment is described and both methods are characterized on a rigid body robot arm model. The experiment shows the angular error up to 0.4rad from CMR method whereas just 0.03rad from DCMR method. The noise level from both methods is also compared and analyzed. The result reveals a larger but tunable noise for DCMR method.

A wireless sensor network is always an integrated part of a system. The physical and logical structure of the system, where the sensor network is integrated, are together with other environmental requirements the constraints for the design of the network and the wireless sensor devices. These requirements are very different for different applications and even for one specific system the requirements may be very different on the sensor devices. When developing efficient wireless sensor devices these constraints must be taken into consideration. The diverse constraints we are facing when developing wireless sensor networks and devices for various applications makes it necessary to have a platform-based development approach where as much of the components can be re-used. For the communication, the standard IEEE 802.15.4 provides an excellent platform for developing short range power aware sensor networks. In this paper a hardware platform is presented with its modular structure it provides a highly flexible solution suitable for rapid prototyping of wireless sensors. This platform is a tool for developers of wireless sensor devices as well as system integrators that need to explore different system solutions experimentally