METHOD OF CORRECTING THE DETERMINATION OF WORKPIECE AND TOOL POSITIONS IN MACHINE TOOLS

PROCEDE DE CORRECTION DE POSITIONNEMENT DE PIECES ET D'OUTILS DANS DES MACHINES-OUTILS

English Abstract

The invention concerns a method of correcting the determination of positions
of workpieces and tools which can be moved relative to one another in machine
tools, in particular CNC machining centres, by means of measuring systems
internal to the machines. Machining inaccuracies caused by changes in the
positions of the workpiece and/or tool owing to heat in the working region of
the tool can be avoided if the workpiece and tool are moved with associated
measuring points or measuring edges through a stationary optical test barrier,
simultaneously or at short intervals one after the other. If the test barrier
is interrupted, the respective positions of the workpiece and tool are
determined by means of the measuring system internal to the machine. The
positions determined are compared with stored positions determined during a
previous measurement, and the difference between the determined position and
the stored position is used to correct the machine control. The invention
further concerns a machine for carrying out the method.

French Abstract

L'invention concerne un procédé de correction de positionnement de pièces et d'outils pouvant se déplacer les uns par rapport aux autres dans des machines d'usinage, notamment des centres d'usinage à commande numérique par calculateur, à l'aide de systèmes de mesure internes. Des imperfections d'usinage dues à des modifications de position de pièces et/ou d'outils inhérentes à des contraintes d'ordre thermique peuvent être évitées dans la zone de travail de l'outil, si la pièce et l'outil sont déplacés simultanément ou successivement à un court intervalle à travers une barrière de mesure optique fixe. En cas d'interruption de la barrière de mesure, chaque position de la pièce ou de l'outil est détectée à l'aide du système de mesure interne. Les positions détectées sont comparées à des positions mémorisées lors d'une mesure antérieure et les différence entre la position détectée et la position mémorisée sert à corriger la commande de la machine. L'invention concerne en outre une machine d'usinage appropriée pour mettre ledit procédé en oeuvre.

Claims

-6-
Claims
1. Process for correction of position determination of workpieces and tools movable
relatively to each other in processing machines, particularly CNC processing
centres, by the aid of machine-internal measuring systems, characterized in
that the workpiece (4) and the tool with their allocated measuring points or
measuring edges (12,13) are moved simultaneously or within short intervals one
after another though a stationary optical measuring barrier (9), and that on
interruption of the measuring barrier (9) the relevant positions of the workpiece
(4) and/or of the tool are picked-up by the aid of a machine-internal measuring
system, and that the picked-up positions are compared with memorized
positions, and that the difference between the picked-up position and the
memorized position is utilized for correction of the machine control.
2. Process pursuant to Claim 1, characterized by the use of an optical beam (9) as
measuring barrier.
3. Process pursuant to Claim 1 or 2, characterized in that the workpiece (4) andthe tool are moved in the same direction through the measuring barrier (9).
4. Process pursuant to any of Claims 1 to 3, characterized in that the relevant
position picked-up is memorized after formation of a corrective value.

Description

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Process for Correction of Position Determination of Workpieces and Tools in
Processing Machines
5 Description:
The invention relates to a process for correction of position determination of
workpieces and tools movable relatively to each other in processing machines,
particularly CNC processing centres, by the aid of machine-internal measuring
10 systems.
On application of major processing machines and/or in major processing centres,
different heat-conditioned expansion at the machine bed, workpiece carriers and
workpieces as well as at tool carriers and/or tools might be caused especially in the
15 event of changes in ambient temperature. Apart from the changed ambient temperature
the use of coolants may also lead to different expansion. Even an agglomeration of
thermally burdened chips, e.g. in dry processing, may have such effects. Especially
with fast rotating main spindles may a reheating of bearings cause interfering growth in
length. All these thermally conditioned changes take effect in the tool working area on
20 the actual positions of the workpiece and/or tool. The positions of workpiece and tool
are regularly picked-up by the aid of machine-internal measuring systems which
however cannot pick-up thermally conditioned changes in position in the working area
of a tool. Because the design values of workpiece and tool positions predefined in a
machine control are preset by machine-internal measuring systems, inaccuracies in
25 processing might be entailed due to these circumstances.
Known from US PS 4808000 are a device and a process for positioning of tools and/or
workpieces, where they are moved up to an optical measuring barrier and fixed in their
position there.
It is the task of the present invention to avoid processing inaccuracies by thermally-
conditioned position changes of a tool and/or workpiece in the working area of a tool.
REVISED SHEET

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This task is solved by moving the workpiece and/or workpiece carrier and the tool
and/or workpiece carrier with measuring points or measuring edges allocated to each
other simultaneously or in brief intervals one after another through a stationary optical
measuring barrier, and by picking-up the relative positions of the workpiece and/or tool
s on interruption of the measuring barrier by the aid of the machine-internal measuring
system, and by comparing picked-up positions with memorized positions, possibly from
a previous measurement, and by using the difference between picked-up position and
memorized position for correction of the machine control. Preferably each position
picked-up is memorized after formation of a corrective value so that one previous
10 measurement each serves as reference for the next measurement. By application of the
process being the subject of this invention all changes in position of the workpiece and
tool and/or of their carriers in the working area of the tool, no matter which source they
originate from, can be picked-up and be utilized for the formation of a corrective value
for the machine control. In principle the process can be applied to form corrective
15 values for each of the three room axes if suitable optical measuring barriers are
installed.
Preferably an optical beam, e.g. a laser beam is used as measuring barrier. Since a
beam has finite dimensions, it is recommendable to move the workpiece and tool in the
20 same direction through the measuring barrier in order to ensure that the actual
positions of workpiece and tool are picked-up at the same point.
The execution of the process being the subject of this invention is expediently effected
with a processing machine, especially a CNC processing centre, with a workpiece
25 carrier and a tool carrier which are movable relatively to each other, and with a casing
which at least surrounds the working area of a tool connected to the tool carrier,
wherein sender and receiver for an optical beam are arranged at the opposite walls of
the casing, said optical beam crossing the working area of the tool. In particular, the
optical beam should extend orthogonally to the direction of movement of the workpiece
30 carrier and/or tool carrier.
Explained below are the examples for execution shown in the drawing, where:

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Fig. 1 schematically and partly shows a front-end view of a processing machine,
Fig. 2 shows the subject as per Fig. 1 in another function position
Fig. 3 shows another layout of the subject as per Fig. 1
Fig. 4 shows a top view on the subject as per Fig. 3.
Part of the processing machine shown here is a machine bed 1 shown indicative only,
with rails 2, on which a machine table 3 and a workpiece carrier with the workpiece 4
arranged on it is movable. Rails 2 extend in Z-direction as provided for by the
coordinate cross ~ shown indicative at top right on Fig. 1.
The processing machine furthermore includes a spindle 7 resting in a bearing of
spindle carrier 6, with the spindle nose 8 of spindle 7 being equipped to allow for
connection of a tool not shown here. The axis of spindle 7 also extends in Z-direction.
Spindle carrier 6 with spindle 7 is movable in Z-direction.
The working area of the tool not shown here is crossed by an optical beam 9 which in
the layout shown here extends in an X-Y-plane at an angle to the X-direction and thus
orthogonally to the Z-direction. The stationary beam 9 emits from a sender 10 and hits
a receiver 1 1. Sender 10 and receiver 11 are arranged at the opposite sides of a
20 casing not shown here which at least surrounds the working area of the tool.
Fig. 2a shows an enhanced part of workpiece 4 with a measuring edge 12 which
extends in X-direction and points to the Z-direction. The spindle nose 8 uses its front-
end face as measuring edge 13 which extends in X-Y-plane.
Not represented here is that machine-internal measuring systems are allocated to both
the machine table 3 and/or workpiece carrier and to spindle carrier 6, with saidmachine-internal measuring systems being utilized to pick-up the relevant positions of
workpiece carrier 4 and spindle carrier 6 which later-on represent the basis for machine
30 control. These machine-internal measuring systems however cannot pick-up thermally-
conditioned shifts in various components and resultant changes in position of
workpiece and/or tool in the working area of the tool.

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Processing inaccuracies resulting therefrom are avoided as outlined under this
invention by moving the workpiece 4 and the tool with their allocated measuring edges
12 and/or 13 simultaneously or within short intervals one after another through the
laser beam 9 serving as stationary optical measuring barrier, that means preferably in
5 the same direction (Z-direction), and that on interruption of the measuring barrier the
relevant positions of workpiece 4 and/or of the tool are picked-up by the aid of a
machine-internal measuring system, and that the picked-up positions are comparedwith positions memorized from a previous measurement, and that the difference
between the picked-up position and the memorized position is utilized for correction of
10 the machine control. In particular, each picked-up position can be memorized after
formation of a corrective value and thus form the reference value for the next
measurement. It is self-understanding that the picked-up positions are memorizedindependently from the machine-internal measuring system.
15 In the layout shown in Fig. 3 and 4 the same reference symbols designate the same
parts. The machine table 3 is a rotary table with two workpieces 4 arranged on it, which
are also rotatable. Fig. 4 a reflects an enhanced part of workpiece 4 with the allocated
measuring edge 12 which is also open in Z-direction. Sender 10 and receiver 11 for the
stationary beam 9 like the other machines, too, are connected with the machine bed 1.

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List of Reference Symbols
Machine bed
2 Rails
s 3 Machine table
4 Workpiece, workpiece carrier
5 Coordinate cross
6 Spindle carrier
7 Spindle, tool carrier
10 8 Spindle nose
9 Beam, measuring barrier
1 0 Sender
1 1 Receiver
12 Measuring edge at 4
15 13 Measuring edge at 7 and/or 8

Representative Drawing