Craig C. Smith

Development of a parallel wire mechanism for measuring position and orientation of a robot end-effector

Abstract This paper presents a parallel wire mechanism developed for measuring six degrees of freedom of a robot end-effector. The mechanism consists of six parallel wire links. The position and orientation of a robot are obtained from the wire lengths measured in the parallel wire mechanism. The complex nonlinear equations of the forward kinematics are solved by using a Newton–Raphson method, and a unique solution is determined from the geometric configuration of the developed mechanism. The wire length error caused by longitudinal deformation of the wires is compensated by a wire compensation factor. Through the experiment, it is verified that the developed mechanism has an accuracy of ±0.05 mm, ±0.1° in the position and the orientation, respectively. The developed parallel wire mechanism can be used effectively for measuring the position and orientation of a six degree of freedom (DOF) of robot end-effector with low cost and effort.

On Using the ISO Standard To Evaluate the Ride Quality of Broad-Band Vibration Spectra in Transportation Vehicles

Comparisons are made between the ISO standard, the Urban Tracked Air Cushion Vehicle (UTACV) specification, and measured vibrations at the floorboard and seat of an automobile over smooth and rough roads. The data indicate that the ISO standard is less restrictive than the UTACV specification, and generally not restrictive enough to indicate the roughness of an automobile ride on a rough country road.

The Duality of Leakage and Aliasing and Improved Digital Spectral Analysis Techniques

When processing, recording, and analyzing continuous, analog signals or functions with a digital computer, information is lost when the signals are converted to digital form. When signals are sampled in one domain (time or frequency), the loss of information is characterized as aliasing in the other (frequency or time, respectively) domain. When a signal or function is truncated in one domain, the information loss is characterized as leakage in the other domain. It is shown that because of the dual nature of leakage and aliasing, that leakage in one domain reduces aliasing in the other domain and visa-versa. Examples of reducing leakage or aliasing in each domain by the dual in the other domain are given to illustrate. Since current art has not used time aliasing to reduce frequency leakage previously, a time alias processor for this purpose is described. A flat-top window function with spectral lineshape one frequency line in width is used in conjunction with the time alias processor to maintain leakage to within the nearest frequency line.

Robust Tracking Control of a Direct Drive Robot

This paper presents a robust controller for tracking control of a direct-drive robot. The proposed controller consists of two portions: a computed torque method which precompensates for dynamics of the modeled plant and an H∞ controller which postcompensates for residual errors which are not completely removed by the computed torque method. Experimental methods for identifying appropriate model structure and parameters are presented, and three specific controller types are compared. Using the robot designed in our laboratory, the combined controller reduced tracking errors by one half compared to computed torque control alone, and by one sixth compared to conventional independent joint control.

Sound Quality Testing and Analysis of Multiple Brands of Sewing Machines

Sound quality analysis is an invaluable tool for the product designer. This tool is designed to help determine customer preferences, which can help the designer improve product quality, or the consumers’ perception of the product’s quality. Many industries desire to know how the consuming public perceives their product as this affects the product life and viability. This paper will present which of two brands of sewing machines ranging in market segments from entry-level, thru mid-level machines, to high-end computer controlled units, is the most acoustically pleasant. Results across market segments independent of brand will be evaluated and compared, as well. The methods used to determine the sound quality of these machines will be presented. These methods are both jury based listening tests and quantitative sound quality metrics.Copyright

Prediction of impact forces using Hertzian contact theory and measured modal structural data

Abstract A method is presented for predicting the impact force between a mass of known velocity and a structure using measured frequency response functions to characterise the dynamics of the underlying structure and a Hertzian model of the local contact stiffness at the point of impact. The method is applied by obtaining Laplace domain parameters determined by curvefitting the measured frequency response functions and writing linear state equations to characterise the structure. The non-linear contact stiffness is represented by a two parameter Hertzian model, identified by matching a predicted force pulse with a measured force pulse. It is shown that the non-linear dynamic characteristics of an elastomeric pad at the point of contact are modeled very satisfactorily by static Hertz theory during the deformation period and reasonably well during the restitution period of impact.

Combined Braking and Cornering Limits as Related to Automobile Tire Marks

A four-tire quasi-steady state vehicle model is set forth utilizing the well-known friction circle model for each tire, and incorporating vehicle and roadway geometry, weight shift, and brake force distribution. The model equations are nondimensionalized for general applicability. A normalized chart defining limits of braking and cornering for a particular automobile is presented.