1. Field of the Invention
The present invention relates generally to a magnetic linear scale unit for precisely measuring a relative motion stroke between relatively displaceable two mechanical components. More specifically, the invention relates to a structure for conveniently and efficiently mounting the magnetic linear scale unit onto the relative displaceable components, which mounting structure allows precise adjustment of the magnetic scale position when the scale is installed between relatively displaceable components.
2. Description of the Background Art
As is well known, a magnetic linear scale unit is used for monitoring displacement of one mechanical component relative to the other mechanical component in precise manner. In general, such magnetic linear scale requires a substantially high accuracy in measurement of the stroke of displacement between two mechanical components in an order of micron or ten microns. This requires strict accuracy in mounting the magnetic linear scale unit between the mechanical components. Especially, in mounting of an elongated magnetic scale in a form of a rod or ribbon, for example, substantial precision is required so that the axis of the magnetic scale is arranged precisely parallel to the axis of movement of the mechanical components.
Conventionally, the magnetic scale is rigidly mounted in a scale channel which serves not only as a support for the magnetic scale but also as a magnetic shield. Both ends of the scale channel are so designed as to be rigidly fixed onto one of the relatively displaceable two mechanical components. This means that, since the magnetic scale is mounted rigidly in the scale channel, the accuracy of mount of the scale channel directly reflects on the mounting accuracy of the magnetic scale. On the other hand, the mounting surface, on which an assembly of the scale channel and the magnetic scale is to be mounted is not always precisely flat and accurately parallel to the axis of the movement of the mechanical component or components. When the mounting surface is not precisely parallel to the axis of the movement of the mechanical component or components, additional difficulty has arisen in assuring holding precise parallelism of the magnetic scale relative to the moving axis. It has been a usual technique to compensate the obliquity of the mounting surface to insert a kind of spacer between one end of the scale channel and the corresponding section of the mounting surface. This requires substantially high skill in mounting the assembly of the scale channel and the magnetic scale. Further to say, even for the skilled engineer, it is still a difficult job for mounting the scale assembly with satisfactorily high accuracy.
In order to solve this problem in the prior art, an improved mounting structure for the magnetic linear scale unit has been proposed in the U.S. Pat. No. 4,649,648, issued on Mar. 17, 1987, to Kazuo NAGAOKA et al, which has been assigned to the common assignee to the present invention. The invention disclosed in the aforementioned United States Patent was also disclosed in the German Patent First Publication (DE-OS) No. 35 30 776. The prior proposed invention, set forth above, is successful in providing satisfactory adjusting ability for the magnetic linear scale unit for providing accuracy of mounting of the magnetic scale precisely parallel to the moving axis of the movable member.