Electricity: motive power systems – Positional servo systems
Patent
1988-02-02
1990-03-20
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
318605, 318651, 33 1M, 33503, G01B 500, G12B 300, B23Q 1100
Patent
active
049104462
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to coordinate positioning apparatus. A typical application of the invention is in three-dimensional measuring machines i.e. in coordinate positioning apparatus adapted for determining the spatial measurement, in three dimensions, of workpieces or other objects.
In such machines, the taking of a measurement involves moving a tool such as a surface-sensing probe into sensing relationship, e.g. into physical engagement, with a surface the position of which is to be determined. Readings of the position in space of the movable parts of the machine relative to the fixed parts are then taken, e.g. from measuring devices such as scales. There are machines where the probe is moved automatically, at desirably high speeds, from one surface to the next of a workpiece to be measured. At each surface the probe has to be decelerated when approaching the surface and accelerated when being withdrawn from the surface to be moved to the next surface. The economy of measuring complex workpieces depends on the speed at which the machine can be operated.
However, in conventional measuring machines the movable components, especially the movable bridges found in such machines, are relatively massive because of the need for stability of measurement. Less massive components would tend to be less stiff, and would suffer dynamic deflections when accelerated and decelerated. Such components require large forces for acceleration and heavy foundations to provide reaction. Therefore, such machines are intrinsically not suitable for high speed operation; there is a conflict between speed and stability of measurement.
SUMMARY OF THE INVENTION
One aspect of the present invention provides coordinate positioning apparatus for positioning a tool comprising:
an output member connected to said tool;
a driving system, including at least one first, drivable carriage; guide means for guiding said first carriage in a first direction; and a first elongate element connected to said output member and extending from the first carriage in a second direction substantially perpendicular to the first direction;
a driven system, including at least one second, driven carriage; guide means for guiding said second carriage in the first direction; and a second elongate element connected to said output member and extending from the second carriage in the second direction;
said tool being subject to positional inaccuracy caused by bending deflection of a said elongate element upon acceleration or deceleration of a said carriage;
the apparatus further comprising means for applying a force between the first and second carriages, in dependence on said acceleration or deceleration, in a sense to reduce said positional inaccuracy.
A second aspect of the present invention provides coordinate positioning apparatus for positioning a tool, comprising:
an output member connected to said tool;
a driving system, including at least one first, drivable carriage; guide means for guiding said first carriage in a first direction; and a first elongate element connected to said output member and extending from the first carriage in a second direction substantially perpendicular to the first direction;
a driven system, including at least one second, driven carriage; guide means for guiding said second carriage in the first direction; and a second elongate element connected to said output member and extending from the second carriage in the second direction; and
closed loop means having driving signal means for driving the first carriage; measuring means for measuring the displacement of the second carriage thereby produced; and feedback signal means for feeding the displacement thus measured back to the driving signal means.
As an example of the present invention, a coordinate measuring machine will now be described with reference to the accompanying drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partly sectioned front elevation of the machine showing a driving and a driven system in operational relationship.
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James Nicholas A.
McMurtry David R.
Renishaw plc
Ro Bentsu
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