Onset of Mechanical Separation in Bellows-Supported Rotary Face Seals

1965 ◽  
Author(s):  
Franklin D. Hart ◽  
Carl F. Zorowski
Keyword(s):  
Contact Force ◽  
Operating Conditions ◽  
Contact Forces ◽  
Force Distribution ◽  
Continuous Contact ◽  
Dynamic Mechanical ◽  
Face Seals ◽  
Contact Force Distribution ◽  
System Resilience ◽  
Mechanical Separation

The problem of incipient dynamic mechanical separation in bellows-supported rotary face seals is analyzed assuming the bellows to be represented by a series of distributed springs and dampers supporting a rigid seal carrier. An expression is developed for the distribution of contact forces between the seal and mating rings generated by the coupled effects of shaft pulsation and mating-ring wobble. This expression is used to determine the operating conditions which will produce the onset of separation by applying the criterion that the contact force distribution will go to zero at some point on the seal when separation is imminent. Results are presented in the form of equations and graphs which define the minimum initial compression necessary to maintain continuous contact in terms of system resilience and damping, amplitude of mating-ring wobble and shaft pulsation, and operating frequency.

Choosing the Optimal Contact Force Distribution for Multi-Limbed Mobile Robots With Three Feet Contact

2003 ◽  
Author(s):  
Dennis W. Hong ◽  
Raymond J. Cipra
Keyword(s):  
Contact Force ◽  
Dimensional Space ◽  
Contact Point ◽  
Optimal Solution ◽  
Solution Space ◽  
Contact Forces ◽  
Force Distribution ◽  
Normal Vector ◽  
Optimization Criteria ◽  
Contact Force Distribution

One of the inherent problems of multi-limbed mobile robotic systems is the problem of multi-contact force distribution; the contact forces and moments at the feet required to support it and those required by its tasks are indeterminate. A new strategy for choosing an optimal solution for the contact force distribution of multi-limbed robots with three feet in contact with the environment in three-dimensional space is presented. The optimal solution is found using a two-step approach: first finding the description of the entire solution space for the contact force distribution for a statically stable stance under friction constraints, and then choosing an optimal solution in this solution space which maximizes the objectives given by the chosen optimization criteria. An incremental strategy of opening up the friction cones is developed to produce the optimal solution which is defined as the one whose foot contact force vector is closest to the surface normal vector for robustness against slipping. The procedure is aided by using the “force space graph” which indicates where this solution is positioned in the solution space to give insight into the quality of the chosen solution and to provide robustness against disturbances. The “margin against slip with contact point priority” approach is also presented which finds an optimal solution with different priorities given to each foot contact point for the case when one foot is more critical than the other. Examples are presented to illustrate certain aspects of the method and ideas for other optimization criteria are discussed.

Dynamic Coupling Effects in Rotary Face Seal Separation Phenomena

1967 ◽  
Vol 89 (2) ◽  
pp. 296-300 ◽  
Author(s):  
F. D. Hart ◽  
C. F. Zorowski
Keyword(s):  
Surface Friction ◽  
Operating Conditions ◽  
Contact Friction ◽  
Dynamic Coupling ◽  
Continuous Contact ◽  
System Parameters ◽  
Response Characteristics ◽  
Contact Force Distribution ◽  
Mechanical Separation ◽  
System Variables

Dynamic separation phenomena in spring-supported rotary face seals are studied, employing a mathematical model which simulates the dynamic response characteristics of the system. Parameters considered in the model include support resilience, amplitude of shaft pulsation and mating ring wobble, initial preset, operating frequency, and contact surface friction. Inclusion of contact friction necessitates consideration of dynamic coupling in the equations governing the motion of the seal carrier. Combinations of operating conditions and system variables which produce incipient mechanical separation are predicted by examining the behavior of the contact force distribution between the seal and mating ring. Equations and graphs are presented which specify the theoretical preset required to maintain continuous contact as a function of the system parameters considered in the analysis.

Optimal Contact Force Distribution for Multi-Limbed Robots

2005 ◽  
Vol 128 (3) ◽  
pp. 566-573 ◽  
Author(s):  
Dennis W. Hong ◽  
Raymond J. Cipra
Keyword(s):  
Contact Force ◽  
Dimensional Space ◽  
Contact Point ◽  
Three Dimensional ◽  
Optimal Solution ◽  
Solution Space ◽  
Contact Forces ◽  
Force Distribution ◽  
New Strategy ◽  
Contact Force Distribution

One of the inherent problems of multi-limbed mobile robotic systems is the problem of multi-contact force distribution; the contact forces and moments at the feet required to support it and those required by its tasks are indeterminate. A new strategy for choosing an optimal solution for the contact force distribution of multi-limbed robots with three feet in contact with the environment in three-dimensional space is presented. The incremental strategy of opening up the friction cones is aided by using the “force space graph” which indicates where the solution is positioned in the solution space to give insight into the quality of the chosen solution and to provide robustness against disturbances. The “margin against slip with contact point priority” approach is also presented which finds an optimal solution with different priorities given to each foot contact point. Examples are presented to illustrate certain aspects of the method and ideas for other optimization criteria are discussed.

Fast Equilibrium Test and Force Distribution for Multicontact Robotic Systems

2010 ◽  
Vol 2 (2) ◽  
Author(s):  
Yu Zheng ◽  
Chee-Meng Chew
Keyword(s):  
Contact Force ◽  
Time Complexity ◽  
Linear Time ◽  
Optimization Technique ◽  
Contact Forces ◽  
The Other ◽  
Robotic Systems ◽  
Force Distribution ◽  
Contact Force Distribution ◽  
Equilibrium Test

In the research of multicontact robotic systems, the equilibrium test and contact force distribution are two fundamental problems, which need to determine the existence of feasible contact forces subject to the friction constraint, and their optimal values for counterbalancing the other wrenches applied on the system and maintaining the system in equilibrium. All the wrenches, except those generated by the contact forces, can be treated as a whole, called the external wrench. The external wrench is time-varying in a dynamic system and both problems usually must be solved in real time. This paper presents an efficient procedure for solving the two problems. Using the linearized friction model, the resultant wrenches that can be produced by all contacts constitute a polyhedral convex cone in six-dimensional wrench space. Given an external wrench, the procedure computes the minimum distance between the wrench cone and the required equilibrating wrench, which is equal but opposite to the external wrench. The zero distance implies that the equilibrating wrench lies in the wrench cone, and that the external wrench can be resisted by contacts. Then, a set of linearly independent wrench vectors in the wrench cone are also determined, such that the equilibrating wrench can be written as their positive combination. This procedure always terminates in finite iterations and runs very fast, even in six-dimensional wrench space. Based on it, two contact force distribution methods are provided. One combines the procedure with the linear programming technique, yielding optimal contact forces with linear time complexity. The other directly utilizes the procedure without the aid of any general optimization technique, yielding suboptimal contact forces with nearly constant time complexity. Effective strategies are suggested to ensure the solution continuity.

Feasible Contact Forces in Semi-Active Vehicles

1999 ◽  
Author(s):  
S. V. Sreenivasan ◽  
B. J. Choi
Keyword(s):  
Contact Force ◽  
Screw Theory ◽  
Geometric Approach ◽  
Integrated Approach ◽  
Contact Forces ◽  
Force Distribution ◽  
Contact Conditions ◽  
Vehicle System ◽  
Directional Motion ◽  
Contact Force Distribution

Abstract This article provides an integrated approach for identifying the feasible contact force distribution in various classes of semi-active vehicles including (a) vehicles with and without omni-directional motion capability, (b) vehicles with varying levels of actuated, unactuated, and spring joints, and (c) vehicles in singular kinematic configurations. The emphasis is on studying systems that have some level of overactuation which is defined as the number of actuators minus the mobility of the vehicle system. It is well known in the active vehicles and biomechanics literature that such overactuation can be used to optimize contact conditions to enhance locomotion capability. Once appropriate contact forces are computed, the desired actuator efforts can then be obtained. A geometric approach based on screw theory that leads to invariant analytical results has been used.

scholarly journals Dynamics of Multibody Systems With Spherical Clearance Joints

2005 ◽  
Author(s):  
P. Flores ◽  
J. Ambro´sio ◽  
J. C. P. Claro ◽  
H. M. Lankarani
Keyword(s):  
Contact Force ◽  
Multibody Systems ◽  
Contact Forces ◽  
Force Model ◽  
Clearance Joints ◽  
Continuous Contact ◽  
Clearance Joint ◽  
Contact Force Model ◽  
Dynamics Of Multibody Systems ◽  
The Impact

This work deals with a methodology to assess the influence of the spherical clearance joints in spatial multibody systems. The methodology is based on the Cartesian coordinates, being the dynamics of the joint elements modeled as impacting bodies and controlled by contact forces. The impacts and contacts are described by a continuous contact force model that accounts for geometric and mechanical characteristics of the contacting surfaces. The contact force is evaluated as function of the elastic pseudo-penetration between the impacting bodies, coupled with a nonlinear viscous-elastic factor representing the energy dissipation during the impact process. A spatial four bar mechanism is used as an illustrative example and some numerical results are presented, being the efficiency of the developed methodology discussed in the process of their presentation. The results obtained show that the inclusion of clearance joints in the modelization of spatial multibody systems significantly influences the prediction of components’ position and drastically increases the peaks in acceleration and reaction moments at the joints. Moreover, the system’s response clearly tends to be nonperiodic when a clearance joint is included in the simulation.

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