A survey of models, analysis tools and compensation methods for the control of machines with friction

http://cats-fs.rpi.edu/~wenj/ECSE446S06/astrom_friction.pdf

Friction Models and Friction Compensation

The modeling of forces during needle insertion into soft tissue is important for accurate surgical simulation, preoperative planning, and intelligent robotic assistance for percutaneous therapies. We present a force model for needle insertion and experimental procedures for acquiring data from ex vivo tissue to populate that model. Data were collected from bovine livers using a one-degree-of-freedom robot equipped with a load cell and needle attachment. computed tomography imaging was used to segment the needle insertion process into phases identifying different relative velocities between the needle and tissue. The data were measured and modeled in three parts: 1) capsule stiffness, a nonlinear spring model; 2) friction, a modified Karnopp model; and 3) cutting, a constant for a given tissue. In addition, we characterized the effects of needle diameter and tip type on insertion force using a silicone rubber phantom. In comparison to triangular and diamond tips, a bevel tip causes more needle bending and is more easily affected by tissue density variations. Forces for larger diameter needles are higher due to increased cutting and friction forces.

Force modeling for needle insertion into soft tissue

This article presents an overview of the acoustics of friction by covering friction sounds, friction-induced vibrations and waves in solids, and descriptions of other frictional phenomena related to acoustics. Friction, resulting from the sliding contact of solids, often gives rise to diverse forms of waves and oscillations within solids which frequently lead to radiation of sound to the surrounding media. Among the many everyday examples of friction sounds, violin music and brake noise in automobiles represent the two extremes in terms of the sounds they produce and the mechanisms by which they are generated. Of the multiple examples of friction sounds in nature, insect sounds are prominent. Friction also provides a means by which energy dissipation takes place at the interface of solids. Friction damping that develops between surfaces, such as joints and connections, in some cases requires only microscopic motion to dissipate energy. Modeling of friction-induced vibrations and friction damping in mechanical systems requires an accurate description of friction for which only approximations exist. While many of the components that contribute to friction can be modeled, computational requirements become prohibitive for their contemporaneous calculation. Furthermore, quantification of friction at the atomic scale still remains elusive. At the atomic scale, friction becomes a mechanism that converts the kinetic energy associated with the relative motion of surfaces to thermal energy. However, the description of the conversion to thermal energy represented by a disordered state of oscillations of atoms in a solid is still not well understood. At the macroscopic level, friction interacts with the vibrations and waves that it causes. Such interaction sets up a feedback between the friction force and waves at the surfaces, thereby making friction and surface motion interdependent. Such interdependence forms the basis for friction-induced motion as in the case of ultrasonic motors and other examples. Last, when considered phenomenologically, friction and boundary layer turbulence exhibit analogous properties and, when compared, each may provide clues to a better understanding of the other.

/pdf/acoustics-of-friction-o02hi5p86c.pdf

Acoustics of friction.

In this article we first review properties of the LuGre model, including zero-slip displacement, invariance, and passivity. An extension to include velocity-dependent microdamping is also discussed. The resulting model is then used to analyze stick-slip motion. The analysis shows that stick-slip motion modeled by the LuGre model is a stiff system with different behavior in the stick and slip modes as well as dramatic transitions between these modes. The dependence of limit cycles on parameters is discussed along with the notion of rate dependence.

/pdf/revisiting-the-lugre-friction-model-2y1emocrn1.pdf

Revisiting the LuGre friction model

A theory of solid friction damping of mechanical vibrations is presented that is based on a solid friction mathematical model previously proposed by the author. A summary and improved description of the general analytic features of the solid friction model are given as necessary background for the theory. The Coulomb friction damped oscillator is analyzed to establish an approach to the treatment of a simple friction damped oscillator. The approach then is generalized to treat a more general model of friction where the author's model is used to describe friction force primarily as a function of displacement. The solid friction damped oscillator studied is a wire pendulum where solid friction enters via inelastic flexing of the wire at the support. Theoretical results are generalized to be applicable to other types of oscillators and other sources of solid friction. An expression for the decay rate of the oscillation amplitude envelope of an unforced oscillator is derived. The decay rate and an equivalent linear damping ratio are determined for several values of an exponent parameter in the solid friction model.

Solid Friction Damping of Mechanical Vibrations

A method and system for determining three-axis attitude from line-of-sight (LOS) solutions for two or more GPS satellites uses intersections of null cone patterns and LOS vectors to the GPS satellites. In a preferred embodiment, a unified GPS-based sensor also provides navigation information.

Method and system using a GPS-based phased-array scheme for three-axis attitude determination

An off-gimbal pointing system is improved using filtering of resolver and gyro responses respectively applied at the output of the resolvers and gyros for attenuating high frequencies resolver responses and gyro responses that effectively degrades the high frequency responses that are matched and above the control system bandwidth for improving the overall dynamic control of the off-gimbal pointing system for rejecting the affects of base motion disturbances and vibrations.

Philip R. Dahl

Papers

Solid Friction Damping of Mechanical Vibrations

Method and system using a GPS-based phased-array scheme for three-axis attitude determination

Spacecraft off-gimbal IRU precision payload pointing and disturbance rejection system