Geometrical instruments – Distance measuring – Scale reading position sensor
Reexamination Certificate
2002-02-19
2003-09-02
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Distance measuring
Scale reading position sensor
C033S707000, C033S708000, C033S702000, C033S703000
Reexamination Certificate
active
06612047
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a length measuring device.
2. Discussion of Related Art
Length measuring devices for determining the relative position between two objects which can be moved relative to each other are, for example, used for recording the position of linear axes without additional mechanical transfer elements in machine tools or in co-ordinate measuring machines. They include a measurement device and a scanning arrangement, which scans the measurement device as well as a carrier body, which supports the measurement device. Depending upon the conditions of application there is a distinction between open or sealed length measuring devices. Open length measuring devices are used where there is little or no contamination whereas sealed length measuring devices are preferably used on machines and installations with rough conditions of application with regard to contamination wherein an aluminum casing protects the measurement device and the scanning arrangement as well as the guide of the scanning arrangement from filings, dust and spray.
In order to maintain high measurement precision it is necessary for the length measuring device to follow the changes in length of the objects moved relative to each other caused by temperature changes. Furthermore, self-oscillations of the longitudinal measuring device, which can arise in certain circumstances due to oscillations on the objects moved, must be suppressed. If, for example, the length measuring device is used on a machine tool the oscillations occurring on the machine tool are transferred from the machine tool to the length measuring device. If the carrier body of the open or sealed length measuring device is connected at the ends only with one of the objects, as is in particular the case with shorter length measurements, where the middle area is not supported and tends to oscillate with its own resonance frequency when the object's mounting area oscillates. These oscillations are transferred to the measurement device and can amongst other things lead to a situation wherein the scanning arrangement loses contact with the measurement device, which can lead to incorrect measurements.
In the same way, the absence of contact of larger areas of the contact area of the carrier body to be connected to the mounting area of an object leads to poor thermal connection so that temperature-dependent changes in length of the object do not lead to adequate changes in length of the carrier body.
A further problem is that carrier bodies manufactured from an aluminum profile have no preferred orientation for deformation or twisting in such a way that with front fixing of a carrier body on the mounting area of an object the contact area of the carrier body is either pressed against the mounting area, lies plane parallel against it or is directed away from the mounting area. In the latter two cases there is a danger of the carrier body not following the mechanical and thermal changes of the object and showing its own dynamic characteristics with regard to oscillations and thermally dependent changes in length.
From DE 25 05 587 C3, a length measuring device is known wherein a carrier body is fixed at the ends with fixing elements formed in a jointed way on one of the objects which can be moved relative to each other wherein the carrier body lies free between the fixing elements in such a way that oscillations are facilitated which influence the measurement precision in a disadvantageous way.
In order to suppress self-oscillations and to improve the temperature pattern of the carrier body it is known that additional securing devices can be distributed in the middle or over the length of the carrier body and the contact of the support area of the carrier body with the mounting area of the object is thereby strengthened. Screws, fixing clamps or adhesive substances are used as securing devices.
From DE 35 09 390 A1, a length measuring device is known wherein as an addition to the elastic fixing elements at the ends of the measuring device casing further fixing elements are arranged which are however fixed at a distance from the object to be measured in such a way that oscillations can likewise occur which lead to measurement errors. Furthermore, this step for strengthening the contact between the support area of the carrier body and the mounting area of one of the objects requires additional securing devices and therefore higher manufacturing costs as well as greater manufacturing resources in the connection of the length measuring device with the objects which are moved relative to each other. In addition, more space is needed to apply the additional securing device but such space is not available in many applications.
From DE 44 06 798 C2, a position measuring device is known wherein the measurement device is fixed on a carrier body which is fixed rigidly at one point and at least at one further point via elastic elements for translational bearing of the carrier body to one of the objects and is supported at least with a surface area on one of the objects. A highly elastic layer made from an adhesive layer with an anti-friction layer applied thereto is provided in this support area running in the measurement direction between the area of the carrier body and a mounting area of the object running parallel thereto. This step for improving the contact between the contact area of the carrier body and the mounting area of one of the two objects, which can be moved relative to each other does however require increased manufacturing and assembly resources.
Another example of a known length measuring device is shown in FIG.
1
. The length measuring device records the position of two objects which can be moved relative to each other, for example for the measurement of the carriage displacement on a machine tool. The length measuring device has a measurement device
20
in the form of a gauge, which is fixed in a carrier body
22
, which includes, for example, an extruded aluminum profile or aluminum profile produced in a die-casting process. A photo-electric or magnetic sensor arranged in a scanning carriage
24
of a scanning arrangement
26
scans the measurement device
20
. The carrier body
22
and therefore the measurement device
20
are connected with one of the two objects which can be moved relative to each other whereas the scanning arrangement
26
is connected with the other one of the two objects in such a way that a relative change in position of the two objects is recorded.
In the example shown in
FIG. 1
, the carrier body
22
is closed at its front ends
28
,
30
by end pieces
32
which are inserted in a shape-locking way in the profile of the carrier body
22
. In the end pieces
32
, oblong holes
34
or bores
36
perpendicular to the measuring direction, i.e. perpendicular to the length of the measurement device
20
, are arranged. The oblong hole
34
is parallel to the plane of the measurement device
20
or perpendicular hereto as a bore
36
. Fixing screws are put through the oblong hole
34
or the bore
36
and screwed with corresponding threads in the mounting area of one of the two objects in such a way that a secure connection is produced between the carrier body
22
and the mounting area.
FIG. 2
shows a schematic side view of an end-side connection of the carrier body
22
with the mounting area
38
through a force-locking or shape-locking connection of the front ends of the carrier body
22
with the mounting area
38
by end pieces
32
.
With this form of connection,poor contact of the contact area
40
of the carrier body
22
with the mounting area
38
can arise in particular with drawn carrier bodies or carrier bodies produced in the extrusion press process for sealed length measuring devices in such a way that particularly in the middle area of the carrier body
22
the contact area
40
and the mounting area
38
are moved away from each other by the value A. This poor contact leads to the problems explained at the outset with the consequent
Mazgaj Mark
Welker Helmut
Acu-Rite Inc.
Brinks Hafer Gilsonthrone
Gutierrez Diego
Hoolahan Amanda J
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