Análisis del juego Análisis del juego, repetibilidad , repetibilidad de posicionamiento y precarga de un de posicionamiento y precarga de un mecanismo mecanismo paralelo paralelo

Abstract

Given to the complexity of mathematical models in parallel

mechanisms, a previous analysis of system characteristic errors

is necessary. This paper determines backlash and positioning

repeatability of a two rotary degrees of freedom parallel mechanism

and analyses the needed preload to increase system accuracy. Firstly,

the specialized bibliography in the design and characterization of

mechanisms based on parallel kinematic is reviewed. In the majority

of the analysed studies, errors such as backlash are absorbed by the

kinematic model without characterizing components or analysing

which is the most determining system errors. Subsequently, the

methodology used for the characterization of the positioning

system components is presented. To do this, procedures and

devices used for each measuring system are described, and the

different measurement systems such as optical lineal sensors, laser

interferometer and inductive probes, are presented. Results obtained

show that actuator backlash errors are around 45 µm having an

error deviation of 3 µm. The application of a contraction preload

on the spherical ball joint allows us to obtain a backlash lesser than

3 µm and, therefore, to increase the positioning system accuracy.

Finally, the two degrees of freedom parallel mechanism intended

to be used in metrology applications and machining tool processes,

has been characterized by means of a coordinate measuring

machine. The mechanism characterization developed will allow us

to determine geometric parameters in the mechanism calibration

phase, as well as to develop, subsequently, correction procedures

according to the needed preload to increase system accuracy.