Length measuring apparatus

#The disclosure of Japanese Patent Applications No. 2003-119315 filed Apr. 24, 2003 including specifications, drawings and claims is incorporated herein by references in their entireties.

#1. Field of the Invention

#The invention relates to a length measuring apparatus having a scale held on a frame, and a length measuring apparatus of a type in which the scale is attached directly to an object to be measured. In particular, the invention relates to a length measuring apparatus which is suitably used with a linear displacement measuring instrument, such as a linear scale, a vernier caliper, and an end-measuring unit, as well as a microscope and an image measuring machine. The length measuring apparatus shall have a scale structure by which the material of the scale can be stabilized for a desired coefficient of linear expansion when a printed circuit board or the like having low stability with respect to variations in ambient temperature and humidity is used as the material.

#The above object, features and advantages of the present invention, as well as other objects and advantages thereof, will become more apparent from the description of the invention which follows, taken in conjunction with the accompanying drawings, wherein like reference characters designate the same or similar parts and wherein:

#FIG. 1 is a cross-sectional view showing an entire scale according to a first embodiment of the present invention;

#FIG. 2 is a cross-sectional view showing essential parts of the same embodiment;

#Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

#A first embodiment of the present invention is shown in FIG. 1 (a cross-sectional view of the entire scale), FIG. 2 (a cross-sectional view of essential parts), and FIG. 3 (an enlarged cross-sectional view of the area III in FIG. 2). The present embodiment is a linear scale having a main scale 12 which is held on a frame 10 to be attached to one side of an object to be measured. The main scale 12 is made of a printed circuit board such as a copper-clad laminate of glass fabric based epoxy resin (so-called glass epoxy board). The linear scale comprises a metal tape 14, a powerful adhesive 16, and a two-sided adhesive tape 18. The metal tape 14 has a desired coefficient of linear expansion (for example, the coefficient of linear expansion of iron). The powerful adhesive 16 has a high adhesive force and forms a thin adhesive layer for bonding the main scale 12 to the metal tape 14 firmly. An example thereof is an epoxy type or cement type adhesive. The two-sided adhesive tape 18 fixes the metal tape 14 to the frame 10 so as to be capable of expansion and contraction, forming a thick adhesive layer of high elasticity.

#In the diagram, the reference numeral 20 represents a slider which moves in the longitudinal direction of the main scale 12 (the measuring direction perpendicular to the plane of the diagram) while maintaining a predetermined distance to the surface of the main scale 12, for example, via slide shoes 22. For example, a detector including an index scale, a light source, and a photo detector device is mounted on the slider 20. The reference numeral 24 represents a detection head which is mounted on the other side of the object to be measured and conveys the movement of the same to the slider 20.