Machine Tool Research

Machine Tool -related research at MTU over the last several years have focused on the following:

Characterization of the role of manufacturing and assembly inaccuracies on slideway errors.

Effect of joint conditions on slideway damping.

Stewart Platform -- dexterity, stiffness, and dynamics.

Micro-actuation

A brief description of efforts in each of these areas follows:

1. The literature describes how machine tools errors are often

characterized. Once a machine is built, a series of measurements are

made to describe the error behavior. This error characterization is most

useful from a control standpoint -- these error maps may also be used for the

purpose of manufacturing planning. These traditional descriptions are

not as useful for the purpose of MT design -- they do not provide a linkage

between the errors and their origin. MTU has spent the last two years

researching the effects of manufacturing and assembly inaccuracies on

the resulting error of a machine tool slideway. For a single-track slideway,

analytical and experimental methods were used to relate form errors to

pitch variation. In addition, clearances were related to yaw errors.

The model that has been established incorporates the effect of contact

mechanics and loading -- the model also has been generalized to a

dual-track slideway.

2. Joints are a major source of damping in MT structures. For nearly 4

years attention at MTU has been directed at understanding how both

fixed and sliding joint conditions influence the energy dissipation

associated with vibration. Experimental evidence indicates that fixed joints

provide little energy dissipation unless an energy absorbing material is

provided between mating surfaces. Sliding joints are primarily responsible for

the damping -- although the joint condiguration influences the degree.

Modal analysis of slideways has been conducted to examine factors effecting

damping potential of slideway joint. Again, clearance appears to be an

important design consideration as far as slideway designed damping is

concerned.

3. Although attention has not been directed to Stewart Platforms as

heavily at MTU as at UIUC for example, some work has been completed. One

student investigated the effects of structural configuration on stiffness and

dynamic response. Another investigated the design and control of multi-stage

platforms.

4. Several Michigan Tech students have examined the use of

magnetostrive actuators in various processes. One student developed an active t

ool holder for use in turning -- he showed how real-time control could be

used to significantly improve the surface finish, effectively attentuating the

effect of process vibrations. Another student examined micro-motions

on the performance of surface grinding. It turned out that transverse

actuation was again able to improve the surface finish.

Continuing (Future) Work

While future work depends of course on our ability to attract interest
(funding) on the topics, the following activities/thrusts are planned:

A. One student is following up the work described in 1 & 2 above. He

will be experimenting with a dual track slideway. The purpose here is to

validate previously established model predictions that relate slideway

errors to manufacturing inaccuracies. He is also looking at the role

that lubrication plays in the dynamic (damping) performance of slideways.

B. The Stewart Platform work will continue with emphasis placed on

multi-stage systems.

C. The partnership with Sandia is allowing us to get involved in

hydrodynamic spindle systems.

This page was created on April 15, 1999 by Marc Greca, magreca@mtu.edu