Sensorless action-reaction-based residual vibration suppression for multi-degree-of-freedom flexible systems

This paper demonstrates the feasibility of controlling motion and vibration of a class of flexible systems with inaccessible or unknown outputs through measurements taken from their actuators which are used as single platforms for measurements, whereas flexible dynamical systems are kept free from any attached sensors. Based on the action reaction law of dynamics, the well-known disturbance observer is used to determine the incident reaction forces from these dynamical systems on the interface planes with their actuators. Reaction forces are considered as feedback-like signals that can be used as alternatives to the inaccessible system outputs. The sensorless action reaction based motion and vibration control technique is implemented on a flexible system with finite modes and all results are verified experimentally

DBKnot: A Transparent and Seamless, Pluggable Tamper Evident Database

Database integrity is crucial to organizations that rely on databases of important data. They suffer from the vulnerability to internal fraud. Database tampering by internal malicious employees with high technical authorization to their infrastructure or even compromised by externals is one of the important attack vectors. This thesis addresses such challenge in a class of problems where data is appended only and is immutable. Examples of operations where data does not change is a) financial institutions (banks, accounting systems, stock market, etc., b) registries and notary systems where important data is kept but is never subject to change, and c) system logs that must be kept intact for performance and forensic inspection if needed. The target of the approach is implementation seamlessness with little-or-no changes required in existing systems. Transaction tracking for tamper detection is done by utilizing a common hashtable that serially and cumulatively hashes transactions together while using an external time-stamper and signer to sign such linkages together. This allows transactions to be tracked without any of the organizations’ data leaving their premises and going to any third-party which also reduces the performance impact of tracking. This is done so by adding a tracking layer and embedding it inside the data workflow while keeping it as un-invasive as possible. DBKnot implements such features a) natively into databases, or b) embedded inside Object Relational Mapping (ORM) frameworks, and finally c) outlines a direction of implementing it as a stand-alone microservice reverse-proxy. A prototype ORM and database layer has been developed and tested for seamlessness of integration and ease of use. Additionally, different models of optimization by implementing pipelining parallelism in the hashing/signing process have been tested in order to check their impact on performance. Stock-market information was used for experimentation with DBKnot and the initial results gave a slightly less than 100% increase in transaction time by using the most basic, sequential, and synchronous version of DBKnot. Signing and hashing overhead does not show significant increase per record with the increased amount of data. A number of different alternate optimizations were done to the design that via testing have resulted in significant increase in performance

Sensorless torque/force control

Motion control systems represent a main subsystem for majority of processing systems that can be found in the industrial sector. These systems are concerned with the actuation of all devices in the manufacturing process such as machines, robots, conveyor systems and pick and place mechanisms such that they satisfy certain motion requirements, e.g., the pre specified reference trajectories are followed along with delivering the proper force or torque to the point of interest at which the process occurs. In general, the aim of force/torque control is to impose the desired force on the environment even if the environment has dynamical motion

Estimation based PID controller-sensorless wave based technique

This paper presents a sensorless estimation algorithm for estimating °exible system parameters, dynamics and externally applied forces or torques due to system interaction with the environment. The proposed algorithm makes it possible to design a chain of observers that require measuring actuator's current and velocity along with performing two off-line experiments that do not require any additional measurement from the flexible system. The output of these observers are estimates of the system parameters, estimates of the system dynamics in con¯guration, motion and acceleration level. Eventually, the estimated positions are used to control the motion and vibration of the °exible lumped system without taking any measurement from the system. Experimental results show the validity of the proposed sensorless estimation algorithm and the possibility of controlling motion and vibration of flexible systems by focusing all the measurements on the actuator side keeping the system free from any attached sensors

Action-reaction based parameters identification and states estimation of flexible systems

This work attempts to identify and estimate flexible system's parameters and states by a simple utilization of the Action-Reaction law of dynamical systems. Attached actuator to a dynamical system or environmental interaction imposes an action that is instantaneously followed by a dynamical system reaction. The dynamical system's reaction carries full information about the dynamical system including system parameters, dynamics and externally applied forces that arise due to system interaction with the environment. This in turn implies that the dynamical system's reaction can be considered as a natural feedback as it carries full coupled information about the dynamical system. The idea is experimentally implemented on a dynamical system with three flexible modes, then it can be extended to more complicated structures with infinite modes

High precision motion control of parallel robots with imperfections and manufacturing tolerances

This work attempts to achieve precise motion control using parallel robots with manufacturing tolerances and inaccuracies by migrating the measurements from their joint space to task space in order to decrease control system’s sensitivity to any kinematical uncertainty rather than calibrating the parallel plant. The problem of dynamical model uncertainties and its effect on the derivation of the control law is also addressed in this work through disturbance estimation and compensation. Eventually, both task space measurement and disturbance estimation are combined to formulate a control framework that is unsensitive to either kinematical and dynamical system uncertainties

An energy-based state observer for dynamical subsystems with inaccessible state variables

This work presents an energy-based state estimation formalism for a class of dynamical systems with inaccessible/ unknown outputs, and systems at which sensor utilization is impractical, or when measurements can not be taken. The power-conserving physical interconnections among most of the dynamical subsystems allow for power exchange through their power ports. Power exchange is conceptually considered as information exchange among the dynamical subsystems and further utilized to develop a natural feedback-like information from a class of dynamical systems with inaccessible/unknown outputs. This information is used in the design of an energybased state observer. Convergence stability of the estimation error for the proposed state observer is proved for systems with linear dynamics. Furthermore, robustness of the convergence stability is analyzed over a range of parameter deviation and model uncertainties. Experiments are conducted on a dynamical system with a single input and multiple inaccessible outputs (Fig. 1) to demonstrate the validity of the proposed energybased state estimation formalism

Assessment of the knowledge of dentists about halitosis at two dental teaching hospitals in Khartoum city

The present study is a descriptive cross-sectional study that was conducted to assess the level of knowledge about halitosis among dental surgeons in Khartoum city.One hundred and six dental surgeons were randomly selected from two dental teaching hospitals: Khartoum Dental Teaching Hospital and Ribat Teaching Hospital in Khartoum city. A fully structured, close ended questionnaire was used. Data collected was assembled and analyzed using the SPSS statistical software. Most of the respondents were general practitioners. The knowledge about the causes and diagnosis of halitosis was generally poor (81%). The awareness about the treatment wasgenerally moderate (37%) and good (38%). No association was found between gender and the level of knowledge about halitosis (p\u3e0.05).A significant association was noted between the level of qualification or the years of clinical experience and the knowledge about the causes and diagnosis of halitosis (p\u3c0.05). The study revealed that dentists lack adequate knowledge regarding causes and diagnosis of halitosis especially for those with lesser years of clinical experience. An increase in knowledge levels could be achieved by emphasizing on this subject during professional training

Sensorless torque estimation in multidegree-of-freedom flexible systems

This paper presents a sensorless torque estimation algorithm for multidegree-of-freedom flexible systems. The proposed algorithm makes it possible to estimate externally applied torques due to flexible system s interaction with the environment without taking any measurement from the system. The algorithm is based on modifying the disturbance observer in order to decouple the reflected torque waves out of the total disturbance on the actuator. Then Reflected torque waves are used along with the actuator s current and velocity to estimate flexible system parameters, dynamics and the external torques or disturbances. Several experimental results are included in order to confirm the validity of the proposed torque estimation algorithm