Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Patent
1994-12-28
1997-07-08
Marmor, Charles A.
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
744248R, 74441, F16H 2522
Patent
active
056449518
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a feed screw aparatus, and a precise positioning and fine feed system widely utilized for apparatus for which fine feeding and positioning are required such as, for example, machine tools, robots, measuring devices and the like.
Recently, as represented in semiconductor technology, it has been required to carry out fine working with high performance, and in accordance with the development of numerical control (NC) technology, the working precision or performance has been remarkably developed through positioning control technology. In order to carry out such positioning control with high precision, in a conventional technique, many power has been shared to increase rigidity of a machine tool.
For example, with respect to a feed screw apparatus used for a linear guide unit of a machine tool, the rigidity is increased by applying a suitable preload to balls disposed between a nut and a feed screw shaft to make zero the gap in the axial direction and to make small an elastic deformation with respect to the axial load, thereby improving the positioning precision.
However, the increasing of the rigidity of the machine tool itself has its limit, and it has become difficult to obtain the working precision required for fine working in these days.
In the meantime, in a machine working, it is necessary to detect a deformed amount of a machine, a tool and a work by measuring a power, to thereby detect a working precision of the work and an abnormality thereof, to consider a disturbance, to avoid an excessive power to be applied to the work or tool and also to consider the working efficiency. The working condition or state can be surely established by monitoring the power.
In these days having improved in automation technology, although unmanned operation and labor saving operation has considerably progressed, there is a rare case where completely unmanned opertion has been actually realized for 24 hours.
This is based on the fact that, in an actual working, when an unexpected breaking of the tool is caused or a set condition is changed due to an environmental change, there is no effective means for detecting these abnormal conditions. Furthermore, a technique for judging the power applied to the tool during the working through the experience of an expert and finely and for safely adjusting the work to carry out the precise working has not been provided for a feed screw apparatus utilized for an existing machine tool.
In this point of view, there has been required the necessity for detecting the force being an important factor for the working lacking for the conventional postioning control and for controlling the machine tool through the feedback of information on the power, and hence, it is required to develop the feed screw apparatus combined with an axial tension detecting sensor for precisely detecting the axial tension. Further, in the conventional technology, a feed screw apparatus having high density and high precision has been required in industrial fields of semiconductors and bio-technology, but the requirement of the high precision such as of micron unit has been raised to the working of general machine tools.
Ball screw devices have been widely utilized for conventional feed screw apparatus performing the precise positioning operation. Namely, a screw shaft is driven to rotate by means of a pulse motor to thereby linearly move a nut screwed with the screw shaft, and accordingly, feeding of a table attached by the nut can be controlled.
However, a resolving power of the conventional ball screw device depends on a lead of the screw shaft and a resolving power (pulse number/revolution number) of a motor rotating the screw shaft, and in order to increase the resolving power of the feed device, it becomes necessary to utilize a ball screw with small lead and a motor having a high resolving power.
However, influence on working error becomes large by reducing the lead of the screw shaft, and accordingly, it is difficult to reduce the lead of the screw shaft. Moreover, in
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patent: 2643845 (1953-06-01), Baker
patent: 3720116 (1973-03-01), Better et al.
patent: 4487087 (1984-12-01), Johnstone
patent: 5129279 (1992-07-01), Rennex
patent: 5263381 (1993-11-01), Shirai
Fenstermacher David
Marmor Charles A.
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