U.S. patent application number 09/527423 was filed with the patent office on 2002-06-06 for position measuring device.
Invention is credited to Boge, Ludwig, Freitag, Hans-Joachim.
Application Number | 20020066201 09/527423 |
Document ID | / |
Family ID | 7901577 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020066201 |
Kind Code |
A1 |
Boge, Ludwig ; et
al. |
June 6, 2002 |
POSITION MEASURING DEVICE
Abstract
A position measuring device having a graduated scale carrier
member which is secured to a holder is described. The graduated
scale carrier member is secured to the bottom side of the holder,
so as to float over a viscous liquid film. The holder, in turn, is
elastically supported on a mount. The measuring graduation marking
is scanned through the holder, which is preferably made of
transparent glass.
Inventors: |
Boge, Ludwig;
(Jenapriebetanitz, DE) ; Freitag, Hans-Joachim;
(Jena, DE) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
7901577 |
Appl. No.: |
09/527423 |
Filed: |
March 17, 2000 |
Current U.S.
Class: |
33/706 |
Current CPC
Class: |
F16C 41/007 20130101;
G01D 5/34707 20130101; F16C 29/005 20130101 |
Class at
Publication: |
33/706 |
International
Class: |
G01B 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 1999 |
DE |
199 12 310.1 |
Claims
What is claimed is:
1. A position measuring device comprising: a graduated scale
carrier member; a measuring graduation marking disposed on the
graduated scale carrier member; a holder having a first surface,
the graduated scale carrier member being adhesively secured to the
holder by an elastic intermediate film; and a scanning unit for
scanning the measuring graduation marking to produce positionally
dependent signals, the scanning unit being disposed adjacent a
second surface of the holder, opposite the first surface, wherein
the scale carrier member with the measuring graduation marking is
disposed opposite to the scanning unit, and the graduation marking
is scannable by the scanning unit through the holder.
2. The position measuring device as recited in claim 1, wherein the
elastic intermediate film is a viscous liquid.
3. The position measuring device as recited in claim 2, wherein the
viscous liquid is a silicone oil.
4. The position measuring device as recited in claim 1, wherein the
graduated scale carrier member is a thin, flexible steel band.
5. The position measuring device as recited in claim 1, wherein the
measuring graduation marking is a reflecting and photoelectrically
scannable structure.
6. The position measuring device as recited in claim 1, wherein the
holder is a transparent, substantially intrinsically stable and
flexurally stiff glass body.
7. The position measuring device as recited in claim 1, wherein the
intermediate film is a viscous liquid provided homogeneously
between the graduated scale carrier member and the holder.
8. The position measuring device as recited in claim 1, wherein the
intermediate film is a viscous liquid and the position measuring
device further comprises means to form a space between the
graduated scale carrier member and the holder, said space being
free of viscous liquid.
9. The position measuring device as recited in claim 1, wherein the
holder is secured to a mount.
10. The position measuring device as recited in claim 9, wherein
the mount comprises a groove for accommodating the graduated scale
carrier member, and wherein the groove is covered by the
holder.
11. The position measuring device as recited in claim 9, wherein
the holder is secured to the mount via an elastic means that is
elastic in a measuring direction.
12. The position measuring device as recited in claim 11, wherein
the elastic means substantially seals a space between the holder
and the mount.
13. The position measuring device as recited in claim 12, wherein
the elastic means is one of a permanent-elastic adhesive and a
viscous liquid.
14. The position measuring device as recited in claim 10, wherein
the groove is filled with a viscous liquid.
15. The position measuring device as recited in claim 9, wherein
the holder has opposite longitudinal surfaces extending
transversely to the first surface of the holder, said longitudinal
surfaces being parallel to and being rigidly secured to
corresponding stop surfaces of the mount.
16. The position measuring device as recited in claim 9, wherein
the graduated scale carrier member is rigidly secured at one
position directly to the mount.
17. The position measuring device as recited in claim 9, wherein
the graduated scale carrier member is rigidly secured at one
position to the holder, and the holder is rigidly secured at the
one position to the mount.
18. The position measuring device as recited in claim 9, wherein
the mount is a linear guide.
19. The position measuring device as recited in claim 1, wherein
the holder is adapted to guide the scanning unit.
20. The position measuring device as recited in claim 19, wherein
the holder comprises at least one V-shaped groove extending in the
measuring direction, and the scanning unit comprises corresponding
guide elements engaging the at least one V-shaped groove.
21. The position measuring device as recited in claim 1, wherein
the first surface of the holder faces the measuring graduation
marking.
Description
[0001] The present invention relates to a position measuring device
having a graduated scale carrier member which is secured to a
holder.
DESCRIPTION OF RELATED ART
[0002] Position measuring devices of this kind are used, in
particular, on machine tools for measuring the relative position of
a tool with respect to a workpiece. The graduated scale carrier
member is either directly adhesively mounted on an object, such as
a machine part to be measured, or is secured to this object by way
of a holder, for example one that at the same time constitutes a
housing. It has become apparent that the measuring accuracy of a
position measuring device is substantially dependent upon the
mounting attachment of the graduated scale carrier member to the
object to be measured.
[0003] To optimize this attachment, in accordance with German
Patent 196 11 983 C1, a viscous liquid film is used between the
graduated scale carrier member and the holder. The capillary action
of the viscous intermediate layer provides for the coupling between
the graduated scale carrier member and the holder, and it
substantially uncouples the graduated scale carrier member from the
holder with respect to occurring mechanical strains.
[0004] The disadvantage of this arrangement is that the scale
graduation marking of the graduated scale carrier member lies
completely exposed.
[0005] To solve this problem, the European Patent 0 416 391 B1
describes a position measuring device, whose graduated scale
carrier member is made of glass, and which is secured to the holder
by its side bearing on the scale graduation marking by way of a
viscous liquid film. The scale graduation marking is scanned
through the transparent glass carrier.
[0006] In this arrangement, the scale graduation marking is
accommodated in a manner in which it is very well protected from
environmental influences. The drawback of the system, however, is
that the graduated scale carrier member itself is exposed to all
environmental influences. Because of the relatively large distance
of the scale graduation marking from the neutral fiber of the
graduated scale carrier member, the graduation-marking bearing
surface is considerably expanded or compressed under the influence
of external mechanical forces causing an uneven supporting base.
The resulting scale error is relatively significant.
SUMMARY OF THE INVENTION
[0007] The present invention is a position measuring device, whose
graduated scale carrier member is substantially uncoupled from its
holder with respect to mechanical strains, and is also protected in
a simple manner from external mechanical influences.
[0008] In one embodiment, the invention is a position measuring
device comprising a graduated scale carrier member, a measuring
graduation marking disposed on the graduated scale carrier member,
a holder having a first surface facing the measuring graduation
marking, the holder being adhesively secured to the graduated scale
carrier member by an elastic intermediate film, and a scanning unit
for scanning the measuring graduation marking to produce
positionally dependent signals, the scanning unit being disposed
adjacent a second surface of the holder, opposite the first
surface. The measuring graduation marking is disposed opposite to
the scanning unit, and is scannable by the scanning unit through
the holder.
[0009] The present invention provides the benefit that, using
simple means, the scale graduation marking is effectively protected
from impurities and from external mechanical influences, so that
this position measuring device can be used for performing highly
precise measurements.
[0010] Other advantages, which are derived from advantageous
embodiments of the present invention, are delineated in the
following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Exemplary embodiments of the present invention are described
with reference to the drawings. In the drawings:
[0012] FIG. 1 shows a cross-section I-I of a first linear measuring
device;
[0013] FIG. 2 shows a longitudinal cross-section II-II of the
linear measuring device in accordance with FIG. 1;
[0014] FIG. 3 shows a first embodiment of a linear measuring
device, integrated in a guideway;
[0015] FIG. 4 shows a cross-section of a second embodiment of a
linear measuring device;
[0016] FIG. 5 shows a cross-section of a third embodiment of a
linear measuring device;
[0017] FIG. 6 shows a cross-section of a fourth embodiment of a
linear measuring device;
[0018] FIG. 7 shows a cross-section of a fifth embodiment of a
linear measuring device; and
[0019] FIG. 8 shows a cross-section of a further embodiment of a
linear measuring device, including a guideway for the scanning
unit.
DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION
[0020] FIGS. 1 and 2 illustrate a first exemplary embodiment of the
present invention. This position measuring device, in the form of a
linear measuring device to measure length, is made of a graduated
scale carrier member 1 which adheres by adhesive forces via a
viscous liquid film 2 to a holder 3. Holder 3, in turn, is secured
to a mount 4. To accommodate graduated scale carrier member 1 in a
protective manner, a groove 5 is introduced in mount 4. This groove
5 is hermetically covered by holder 3.
[0021] Graduated scale carrier member 1 can be a thin, flexible
strip for example about 0.2 mm thick and 8 mm wide, made of a
polished, commercial high-grade steel band. Applied to surface 3.1
of graduated scale carrier member 1, diametrically opposing holder
3, is a reflecting measuring graduation marking 6 in the form of an
incremental scale graduation marking and/or an absolute coding.
This measuring graduation marking 6 is scanned photoelectrically,
in a generally known way, through transparent holder 3, by a
scanning unit 7. Thus, in response to a relative movement with
respect to measuring graduation marking 6 in measuring direction X,
scanning unit 7 supplies positionally dependent electrical scanning
signals.
[0022] The viscous liquid film 2 can be preferably a transparent
silicone oil having a kinematic viscosity of about 10,000
mm.sup.2/s. Scale graduation carrier member 1 is held adhesively to
bottom side 3.1 of holder 3 solely by the viscosity of liquid film
2. Liquid film 2 ensures that scale graduation carrier member 1 is
secured in a manner that is uncoupled from strain. Film 2 permits a
free linear deformation of graduated scale carrier member 1
relative to holder 3 in response to temperature changes, without
unacceptable strains such as compression and expansion occurring in
graduated scale carrier member 1. This means there are no unwanted
strains being transferred to the holder by graduated scale carrier
member 1 in an unacceptable manner. This linear deformation causes
a partial displacement of graduated scale carrier member 1 in
relation to holder 3 in measuring direction X, with only a small
amount of static friction occurring.
[0023] Due to the small thickness of graduated scale carrier member
1, bending strain influences are likewise negligibly small. Between
graduated scale carrier member 1 and bottom side 3.1 of holder 3,
liquid film 2 is introduced over the entire surface as a thin
intermediate layer that runs homogeneously in measuring direction
X. The viscosity of liquid film 2 induces the thin and flexible
graduated scale carrier member 1, which has a low specific weight,
to cling closely to bottom side 3.1 of holder 3, by the adhesive
forces. This surface 3.1 is used as a reference surface to
determine how straight and even is graduated scale carrier member
1.
[0024] Essentially, graduated scale carrier member 1 floats on
holder 3, without lifting off from it. The advantage of using glass
as a material for holder 3 is that it is available inexpensively in
long lengths, and has a high surface quality and evenness.
Advantageously, the dimensions and material for holder 3 can be
selected to provide a high intrinsic stability and, thus, constant
evenness and straightness along measuring graduation marking X.
Capillary action prevents liquid 2 from flowing out of the gap, and
draws graduated scale carrier member 1 toward bottom side 3.1.
[0025] Holder 3 can be preferably attached to mount 4 in a manner
that is a function of the thermal coefficients of expansion of
holder 3 and mount 4. Given the same coefficients of expansion,
holder 3 could, for example, be rigidly secured over its entire
length to mount 4. In practical use, however, even given the same
coefficients of expansion, different expansions occur because of
temperature gradients. Therefore, it is advantageous to design the
attachment in such a way that holder 3 is also uncoupled from mount
4, viewed in measuring direction X. This can be achieved by
securing holder 3 by a permanent-elastic adhesive 8, which in
particular can be a silicon rubber adhesive layer, to mount 4.
Adhesive 8 between mount 4 and holder 3 ensures a free linear
expansion of mount 4, as well as of holder 3, without unacceptable
strains occurring or being transferred to holder 3.
[0026] To define a fixed reference point 9 of the measuring system,
graduated scale carrier member 1 is rigidly coupled directly to
mount 4 at one place, for example at one single location along
graduated scale carrier member 1. This coupling is shown
schematically in the drawings, as a locally rigid adhesive
connection 9, however, the coupling can also be implemented as a
welded or screw-type connection. In the depicted example, groove 5
is so deep that an adhesive connection 9 between graduated scale
carrier member 1 and mount 4 would be relatively thick, and thus
unstable. For this reason, a spacer plate 10 can be welded onto the
bottom side of graduated scale carrier member 1 to provide leveling
compensation, and the rigid adhesive connection 9 can be formed
between spacer plate 10 and mount 4.
[0027] Instead of on the bottom side of graduated scale carrier
member 1, rigid adhesive connection 9 can also be provided, for
example, on one side edge, on the extremity, or on a front side of
carrier member 1. Alternatively, fixed point 9 can also be defined
by way of holder 3, where graduated scale carrier member 1 is
rigidly fixed at one location (viewed in the X direction) to holder
3. In addition, in this design holder 3 can be rigidly fixed at
this location to mount 4. Preferably, fixed point 9 can be defined
at one end of graduated scale carrier member 1.
[0028] The described configuration provides for an arrangement in
which graduated scale carrier member 1 is protected by holder 3.
The exposed surface of holder 3 can be cleaned quite simply, by
wiping it clean with a wiper 11 mounted on scanning unit 7. Any
forces introduced by cleaning wiper 11 are not transferred to
graduated scale carrier member 1 because of the uncoupled
attachment.
[0029] In one embodiment shown in FIG. 8, scanning unit 7 can be
guided on mount 4. The guidance can also be carried out on holder
3, since scanning unit 7 is only supported on holder 3 by sliding
or roller elements 12. In addition, at least a V-groove 13 running
in measuring direction X is introduced in holder 3, ensuring a
straight guidance of scanning unit 7 transversely to measuring
direction X, thus in the Y direction.
[0030] One especially advantageous application of the length
measuring device shown in FIGS. 1 and 2 is the space-saving
integration in guide units 4, 14, which can be attached as an
independent assembly to the machine base of a machine tool. This
integration is schematically shown in FIG. 3. Graduated scale
carrier member 1 can be housed protectively in a groove 5 of
guideway 4 forming the mount. Scanning unit 7 is secured to guide
block 14. Guide unit 4, 14 can be a recirculating ball guideway, a
recirculating roller guideway, or another commercial guide unit 4,
14. Integration of the measuring device in a linear drive is also
possible.
[0031] The second exemplary embodiment illustrated in FIG. 4
differs from the first exemplary embodiment in that, instead of the
permanent-elastic adhesive 8, a viscous liquid 2 is used to secure
holder 3 to mount 4. For this, a thin gap filled with liquid 2 is
provided between the surfaces of holder 3 and the surfaces of mount
4, so that the viscosity of liquid 2 elastically retains holder 3
on mount 4 in measuring direction X. In addition, the entire groove
space 5 can be filled with liquid 2. However, the gap between the
groove bottom and the bottom side of graduated scale carrier member
1 is substantially larger than the gap between graduated scale
carrier member 1 and holder 3. Thus, the adhesive forces between
graduated scale carrier member 1 and holder 3 should be
substantially greater that the forces between graduated scale
carrier member 1 and the groove bottom of mount 4.
[0032] In this design, groove space 5 can be used as a liquid
repository 4 for forming a homogenous liquid layer 2 between
graduated scale carrier member 1 and holder 3. The required liquid
2 is then drawn by the capillary effect into the gap. Liquid 2 also
provides a sealing action between holder 3 and mount 4. A simple
interchangeability of holder 3 with scale carrier member 1 is also
possible in this refinement.
[0033] In the third exemplary embodiment in accordance with FIG. 5,
holder 3 can be secured to mount 4 exclusively by its longitudinal
sides 3.2 and 3.3 running transversely to surface 3.1. Here, the
advantage is that deformations of mount 4 in the Z direction are
not directly transferred to holder 3. The evenness and straightness
of the intrinsically stable holder 3 is decoupled from mount 4 by
liquid film 2. In place of liquid film 2, a permanent-elastic
adhesive can also be used between holder 3 and mount 4.
[0034] It is also shown in the exemplary embodiment of FIG. 5 that
it is not necessary to provide liquid film 2 over the entire width
of graduated scale carrier member 1, in the Y direction. Thus, when
working with certain specific requirements, one can target specific
areas, for example, of the scanning region of measuring graduation
marking 6 to be kept free of liquid 2. In this case, flow-arrester
edges 15 can be provided on graduated scale carrier member 1 and/or
on holder 3 to prevent liquid 2 from flowing into space 16 that is
to be kept free of liquid.
[0035] FIG. 6 illustrates a fourth exemplary embodiment of the
invention. One important feature of this embodiment is that mount 4
is designed as part of a length measuring device that can be easily
assembled or replaced. In particular, mount 4 can be a rail or bar
section, which the user can easily detachably secure to a machine
tool or measuring machine 18, using known methods. This attachment
can be implemented for example by providing an adhesive layer 17 in
the form of an adhesive film that bonds on both sides. In a
preferred design, only one single fixing point 19 is provided
between mount 4 and attachment surface 18. The fixing point can be,
for example, formed by screws 19. In the remaining area, mount 4
can be allowed to expand in a manner that is free of forces and
strains, in relation to attachment surface 18. It is beneficial to
locate fixing point 19 and fixing point 9 at the same position in
the X direction.
[0036] Mount 4 can also constitute the housing for scanning unit 7
of an encapsulated length measuring device. The guidance for
scanning unit 7 can also be provided on the housing and/or on
holder 3.
[0037] A fifth exemplary embodiment in accordance with FIG. 7
illustrates additional shapes, other than a plate shape, that can
be used in a design for holder 3. The design of holder 3 can also
include the integration of groove 5 to accommodate the graduated
scale carrier member. In this refinement, graduated scale carrier
member 1 is also secured to holder 3 laterally, via liquid layer 2,
and is locked against a lateral displacement or twisting.
[0038] To prevent a lateral displacement in the Y direction or
twisting of graduated scale carrier member 1 in relation to holder
3, in all the exemplary embodiments lateral limit stops can be
provided on holder 3 for graduated scale carrier member 1. Such
displacement or twisting can also be prevented by a crosspiece, to
which graduated scale carrier member 1 is secured via liquid film
2, and whose width corresponds to the width of graduated scale
carrier member 1. A similar system is shown in FIG. 6 of European
Patent 0 416 391 B1.
[0039] In one possible especially advantageous embodiment of the
present invention, a steel band can be used as graduated scale
member 1. Other materials can also be used to form the band of
scale member 1. For example, glass or glass ceramics, and in
particular the Zerodur brand glass ceramic, formed as a thin
bendable band, can be used as the material for scale member 1.
[0040] An especially good result can be achieved when measuring
graduation marking 6 is an optically scannable structure such as a
reflecting phase grating, or alternatively, a section having
reflecting and non-reflecting regions alternating in measuring
direction X. In another embodiment, measuring graduation marking 6
can also be formed by magnetically, inductively, or capacitively
scannable elements.
* * * * *