Joshua Dayan

A biomechanical model of index finger dynamics

A dynamic model of the biomechanics of the index finger for flexion-extension and abduction-adduction motion is introduced. The model takes into account all the tendons in the finger and relates to their varying moment arms during motion. A new set of moment arm coefficients and elongation equations is derived based on experimental measurements of previous studies. Constraint equations using variable coefficients are introduced and an optimization approach used to obtain the tendon forces required for any given motion and external force. The model and optimization approach are tested with data from a rapid pinch experiment as well as a hypothetical disc rotation. Good correlation is obtained with respect to electromyographic data in the literature.

Analysis of the Inverse Problem of Freezing and Thawing of a Binary Solution During Cryosurgical Processes

An integral solution for a one-dimensional inverse Stefan problem is presented. Both the freezing and subsequent thawing processes are considered. The medium depicting biological tissues, is a nonideal binary solution wherein phase change occurs over a range of temperatures rather than at a single one. A constant cooling, or warming, rate is imposed at the lower temperature boundary of the freezing/thawing front. This condition is believed to be essential for maximizing cell destruction rate. The integral solution yields a temperature forcing function which is applied at the surface of the cryoprobe. An average thermal conductivity, on both sides of the freezing front, is used to improve the solution. A two-dimensional, axisymmetric finite element code is used to calculate cooling/warming rates at positions in the medium away from the axis of symmetry of the cryoprobe. It was shown that these cooling/warming rates were always lower than the prescribed rate assumed in the one-dimensional solution. Thus, similar, or even higher, cell destruction rates may be expected in the medium consistent with existing in vitro data. Certain problems associated with the control of the warming rate during the melting stage are discussed.

Simulation and control of ventilation rates in greenhouses

A simple model is presented, which enables the calculation of ventilation in a commercial rose-growing greenhouse (greenhouse). The model represents the greenhouse as three vertically stacked horizontal segments and addresses the energy and vapor transfer among these segments and between them the plant canopy and the external environment. The model equations show how ventilation can be calculated from the heat and vapor balances and how they can describe the internal microclimate. Air exchange rates obtained by the model are similar to published results obtained by tracer experiments and CFD. The model can be updated and calibrated for various conditions and structures, in accordance with online measurements of transpiration, leaf temperature, air temperatures and humidity at several heights above ground level. By making some assumptions, representative plant temperatures (RPTs) can be calculated instead of being measured. The validity of the model assumptions is established by comparing numerical results with experimental data. Good agreement is obtained between the numerical output of the model and the experimental measurements, for most times of the day. The simplified model is used to demonstrate the calculation of representative plant temperatures when forced ventilation is applied to cool the plants. Further study is still necessary to make the model applicable to complete days and throughout the season. Once the model is fully established and proven it will be used for sophisticated greenhouse climate control.

Controlled Freezing of Nonideal Solutions With Application to Cryosurgical Processes

Success of a cryosurgical procedure, i.e., maximal cell destruction, requires that the cooling rate be controlled during the freezing process. Standard cryosurgical devices are not usually designed to perform the required controlled process. In this study, a new cryosurgical device was developed which facilitates the achievement of a specified cooling rate during freezing by accurately controlling the probe temperature variation with time. The new device has been experimentally tested by applying it to an aqueous solution of mashed potatoes. The temperature field in the freezing medium, whose thermal properties are similar to those of biological tissue, was measured. The cryoprobe temperature was controlled according to a desired time varying profile which was assumed to maximize necrosis. The tracking accuracy and the stability of the closed loop control system were investigated. It was found that for most of the time the tracking accuracy was excellent and the error between the measured probe temperature and the desired set point is within +/- 0.4 degrees C. However, noticeable deviations from the set point occurred due to the supercooling phenomenon or due to the instability of the liquid nitrogen boiling regime in the cryoprobe. The experimental results were compared to those obtained by a finite elements program and very good agreement was obtained. The deviation between the two data sets seems to be mainly due to errors in positioning of the thermocouple junctions in the medium.

Contact elimination in mechanical face seals using active control

Wear and failure of mechanical seals may be critical in certain applications and should be avoided. Large relative misalignment between the seal faces is the most likely cause for intermittent contact and the increased friction that eventually brings failure. Adjustment of the seal clearance is probably the most readily implemented method of reducing the relative misalignment and eliminating seal face contact during operation. This method is demonstrated with the aid. of a noncontacting flexibly mounted rotor mechanical face seal test rig employing a cascade control scheme. Eddy current proximity probes measure the seal clearance directly. The inner loop controls the clearance, maintaining a desired gap by adjusting the air pressure in the rotor chamber of the seal. When contact is detected the outer loop adjusts the clearance set point according to variance differences in the probes signals. These differences in variance were found to be a reliable quantitative indication for such contacts. They are complimentary to other more qualitative phenomenological indications, and provide the controlled variable data for the outer loop. Experiments are conducted to test and verify this active control scheme and strategy. The analysis and results both show that contrary to intuition for the seal under investigation, reducing seal clearance can eliminate contact, and the outer cascade loop indeed drives the control toward this solution.

Feasibility of Contact Elimination of a Mechanical Face Seal Through Clearance Adjustment

The feasibility of eliminating contact in a noncontacting flexibly mounted rotor (FMR) mechanical face seal is studied. The approach for contact elimination is based on a parametric study using FMR seal dynamics. Through clearance adjustment it is possible to reduce the maximum normalized relative misalignment between seal faces and, therefore, eliminate seal face contact. Clearance is measured by proximity probes and varied through a pneumatic adjustment mechanism. Contact is determined phenomenologically from pattern recognition of probe signals and their power spectrum densities as well as angular misalignment orbit plots, all calculated and displayed in real-time. The contact elimination strategy is experimentally investigated for various values of stator misalignment and initial rotor misalignment. Contrary to intuition but compliant with the parametric study, the experimental results show that for the seal under consideration contact can be eliminated through clearance reduction.

Odometry and triangulation data fusion for mobile-Robots environment recognition

Abstract Autonomous vehicles usually use more than one positioning system to improve their position estimate. Some positioning systems are advantageous in certain types of environments, while others are more efficient in others. This paper describes a data fusion method, where the differences between measurements are used to identify the type of terrain through which the vehicle is traveling. In this system, position estimate by odometry is compared to that calculated by triangulation , and the differences are fed into a neural network. This neural network, which is pertained by a set of different terrain types, classifies the examined environment by matching it with the most similar environment it can “recognize”.

Dynamic simulation and monitoring of a non-contacting flexibly mounted rotor mechanical face seal

Abstract Mechanical face seal rotor dynamics is investigated through both simulation and real-time monitoring of a non-contacting flexibly mounted rotor (FMR) mechanical face seal in a seal test rig. Dynamic simulation is performed to investigate the seal rotor angular response to the stator misalignment, the stator angle, the initial rotor misalignment and clearance. Rotor angular response orbit is introduced and is able to characterize the rotor dynamic response. A real-time monitoring system is constructed in the test rig to monitor the instantaneous dynamic behaviour of the seal rotor, including its angularresponse, precession angle and angular response orbit. Experimental results agree qualitatively well with those of the dynamic simulation. Potential applications of the monitoring system for detecting seal face contact and for seal control are stated.

Controllability of grasps and manipulations in multi-fingered hands

Manipulation of objects utilizing gravity and using general equilibrium grasps, which are not necessarily force-closure, is discussed. Examining the controllability of the objects dynamics, in the presence of gravity, leads to the conclusion that almost all equilibrium grasps are locally controllable. This fact is used to show that manipulation from any one equilibrium point, to any other, is possible if there is a continuity of equilibrium points between them. In addition, the equilibrium grasps can be used for changing grasps with walking finger manipulation. The system controllability matrix is also used to test grasp quality, depending not only on kinematic values but also on object orientation and dynamic properties.

A probabilistic model for tracer distribution in multiphase spatially inhomogeneous transport systems

A probabilistic model describing tracer transport in multiphase spatially inhomogeneous transport (plug-flow) systems is presented. The properties of the trajectories are completely described by a two-component Markov process with absorbing boundaries. The first component is continuous, the second discrete. Infinitesimal conditions are given. Probabilities associated with the process are derived.