A new type of micro rotary motor with a single piezoelectric stack actuator has been proposed, developed and tested. The conventional principle of elliptical motion is realized by a proposed mechanism which utilizes a Y-shaped stator and a ring rotor, and the biomimetic gait of an inchworm is achieved by integrating one piezoelectric stack actuator into the stator. The performance of the motor is predicted on the basis of computational simulation. An experimental setup was built to validate the working principles and evaluate the performance. Preliminary results have verified the working principle. Differences between the measured and predicted performances of the motor are analyzed.
Random mobility and energy constraint are two main factors affecting system performance in mobile sensor networks, which cause many difficulties to system design. It is necessary to develop high-efficiency algorithms and protocols for mobile sensor networks to adapt to dynamic network environment and energy limitation. In this paper, a new clustering algorithm based on residual energy difference ratio is presented to improve system performance. Firstly, it is an energy-efficient algorithm. The residual energy of sensor nodes and average residual energy of system are considered in the residual energy difference ratio, which effectively avoid the nodes with low residual energy being selected as cluster heads. An energy-optimal scheme is used in cluster formation phase to minimize energy consumption. Secondly, it is a dynamic algorithm. The system dynamically clusters the sensor nodes according to the data transmission delays. It makes the whole system adapt to the random mobility of sensor nodes. The NS2 software is used to simulate the new clustering algorithm. The simulation experiments can verify the validity of the proposed theory.
Deadlock is an undesired situation in multithreaded software since it can lead to the stoppage of software. This paper studies the problem of deadlock control of multithreaded software based on Gadara nets, which are well studied for modelling concurrent programs. In particular, an iterative deadlock prevention policy based on siphons is proposed for a class of ordinary Gadara nets where the initial marking of each idle place is one. At each iteration, we compute emptiable siphons containing the smallest number of resource places. Then, bad markings are computed based on these siphons. On the basis of the bad markings, a constraint is constructed that forbids not only bad markings that empty one of the siphons but also some other bad markings. The algorithm is carried out until no emptiable siphon exists in the net. Compared with the existing methods, the resultant net derived from the proposed method is live and maximally permissive with a simpler supervisor. Finally, two examples are provided to illustrate the proposed deadlock prevention policy.
Fault detection is quite important for discrete event systems. We investigate K-codiagnosability of Petri nets in this paper under the framework that some local sites monitor the operation of the system using their own masks. They exchange information with a coordinator while do not communicate with each other. A fault is detected when there exists a site can diagnose it. We recall the notion of Modified Verifier Nets (MVNs), and prove that K-codiagnosability can be verified looking at some special cycles in the reachability or coverability graph of the MVN. In particular, the proposed approach is available for bounded and unbounded nets. Finally, we give an algorithm to compute the minimum value of K .
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