Geometrical instruments – Distance measuring – Scale reading position sensor
Patent
1990-04-19
1992-02-18
Will, Thomas B.
Geometrical instruments
Distance measuring
Scale reading position sensor
33706, 33493, 33494, 72198, G01B 1102
Patent
active
050882090
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION This invention relates to metrological scales,
e.g. scales for use in opto-electronic scale-reading apparatus.
Such scales are known to comprise an elongate metallic scale member having alternate marks and spaces provided along its length. Our earlier International Patent Specification No. W088/00331,now U.S. Pat. No. 4,926,566, describes such a scale, and a method of producing it by rolling. The scale described in that specification is in the form of a flexible tape having a substrate of spring steel which is relatively inextensible. A softer copper layer is provided on the upper and lower surfaces of the spring steel substrate. The marks and spaces of the scale are embossed in one of the copper layers by an embossing roller having a corresponding profile. The tape is embossed by passing it through a nip between this embossing roller and a support roller, which has a plain cylindrical surface.
Although the structure of the tape with a relatively inextensible substrate and a soft embossing layer allows the embossing to take place while at the same time providing the scale with some stability against longitudinal extension under the roller pressure, nevertheless there are inevitably strains introduced into the tape during the rolling process, however slight, as a result of the stresses caused by the rolling. For example, the embossed surface layer will be strained more than the other surface layer, resulting in bowing of the tape. As the tape emerges from the rollers, the stresses in the tape are relieved and there can be a very slight change in the local pitch of the scale as a result. The resulting errors can be cumulative.
SUMMARY OF THE INVENTION
The present invention has several aspects, each of which seek to reduce this effect.
One aspect of the present invention provides a method of producing a metrological scale wherein the scale comprises an elongate scale member having a reference plane and intended to have a periodic surface profile composed of alternate first and second surface regions which are elongate in a direction transverse to the length of the member and which differ regarding their position relative to the reference plane, the method comprising:
providing a rolling nip comprising two nip members both having profiles extending around their circumferences which consist of alternate raised and lowered portions, the profile of at least one nip member being the counterpart of said surface profile of the scale; and
passing the scale member through the nip of the nip members while applying pressure therebetween thereby to deform opposing surfaces of the scale member in accordance with the respective profiles of the nip members.
In the first aspect of the invention, the two nip members are preferably rollers. The nip members preferably have profiles while cause substantially equal longitudinal strains in the opposing surfaces of the scale member. They may for example have identical profiles, although this is not essential.
Also preferably, the profiles of the nip members are symmetrical.
A second aspect of the invention provides a method of producing a metrological scale wherein the scale comprises an elongate scale member having a reference plane and intended to have a periodic surface profile composed of alternate first and second surface regions which are elongate in a direction transverse to the length of the member and which differ regarding their position relative to the reference plane, the method comprising passing the member between two nip members, at least one of which is a roller having a profile which is the counterpart of the surface profile of the scale, while applying pressure between the nip members, thereby to deform one surface of the scale member in accordance with said profile, characterised in that said roller is freely rotatable.
In the second aspect of the invention, the other nip member may be another roller, and the drive to cause the scale member to pass through the nip of the rollers may be provided by rotatably driving said other rolle
REFERENCES:
patent: 3077131 (1963-02-01), McShane
patent: 3653245 (1972-04-01), Tishken
patent: 4017367 (1977-04-01), Saunders
patent: 4368632 (1983-01-01), Thrash et al.
patent: 4586260 (1986-05-01), Baxter et al.
Patent Abstracts of Japan, Publ. No. 58122103 "Rolling Method of Steel Plate Clad on One Side" Publication Date 7-83.
Henning Brian C. R.
Lummes Stephen E.
Morrison Robert B.
Renishaw plc
Will Thomas B.
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