Abstract:
A guide assembly to be mounted on a machine-tool or a measuring machine and including a guide rail mountable in the machine-tool or the measuring machine as an independent structural element, and a linear encoder mountable on the guide rail as a separate unit before mounting of the guide rail in the machine-tool or the measuring machine.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to linear or curved guides or guide assemblies; in particular for machine tools or measuring machines, and the rectilinear or arcuate guide rails of which are mounted in the machines as a separate structural element or unit. 
     Such linear or curved guides are represented preferably by anti-friction guideways, which are formed as a hardened and ground rectilinear or arcuate track the matching means of which is formed by either roller or ball elements that support a slide (see publications &#34;Industrie Anzeiger (Report)&#34; 18/92, p.p. 43-45 and &#34;Produktion,&#34; No. 39 of Sep. 29, 1994, p. 23). 
     A linear guide with an integrated linear encoder and mounted in a machine-tool or a measuring machine is disclosed in Japanese Patent Publication JP-OS-3-153915, and in JNA-Technical Product Information TPI 86 of September, 1995 in an article &#34;Integrated Opto-Electronic Measuring Systems CMS.&#34; 
     In the known linear guide assemblies with an integrated linear encoder, which are used in machine-tools or measuring machines, the scale scanning head is displaced directly on the guide rail and at that is fixedly connected with the slide displaceable on the guide rail. This necessitates a special adjustment and may cause, during the mounting of the guide rail or during the operation of the machine, deformations in the encoder which adversely influence the measurement accuracy. Furthermore, in the known linear guides with an integrated linear encoder for machine-tools or measuring machines, the scale is practically rigidly connected with the guide rail, so that, in case of the required maintenance or damage, the entire linear guide should be taken off the machine, which leads to increased operational expenses. 
     Machine-tools or measuring machines, in which a linear encoder is mounted as a separate unit on a machine bed or a machine carriage releasably, either directly with appropriate connection elements or is mounted indirectly by using a mounting rail, are generally known. At that, the mounting rail can have its own connection elements or be fixedly mounted on a machine, with the encoder being releasably connected with the mounting rail by connection elements (see U.S. Pat. No. 3,910,703, European patent No. 3,910,703, European patent No. 0 185 072 and German Utility Model No. 88 08 811). As connection elements, dovetail-shaped elements are used which are provided on the respective structural parts. 
     With the use of pressure cylinders without a piston rod, it is known to secure a sealed linear encoder on a cylinder tube with retaining elements engaging in a longitudinal groove provided in the outer surface of the cylinder tube and extending parallel to the cylinder bore (see European Patent No. 0 214 615). 
     Accordingly an object of the invention is an improved linear or curved guide assembly, in particular for machine-tools or measuring machines, the linear encoder of which can be easily mounted on or dismounted from the machine, while insuring a high measuring accuracy. 
     SUMMARY OF THE INVENTION 
     This and other objects of the invention, which will become apparent hereinafter, are achieved by mounting the linear encoder on the guide rail of the guide assembly as a separate unit before mounting of the guide rail on a machine-tool or a measuring machine. 
     Preliminary mounting of the encoder as a separate unit on the guide rail not only insures separate functioning but also provides for easy assemblage and permits separate maintenance of the guide and the encoder. At that, no weakening of the guide rail takes place, and the measurement precision does not depend on the mounting mode and the loading conditions. For example, the measurement precision would not depend on the tightening torques during screwing of the screws with which the guide rail is secured, or on the manner of attachment of the guide rail. Another advantage of the guide assembly according to the present invention consists in that it is easily adaptable to different guide systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and objects of the present invention will become more apparent, and the invention itself will be best understood from the following detailed description of the preferred embodiments when read with reference to the accompanying drawings, wherein: 
     FIG. 1 shows a first embodiment of a linear guide according to the present invention on a guide rail of which an exposed linear encoder is mounted; 
     FIG. 2 shows a second embodiment of a linear guide according to the present invention on a guide rail of which an exposed linear encoder is mounted; 
     FIG. 3 shows a linear guide according to the present invention on a guide rail of which a sealed linear encoder is mounted; 
     FIG. 4 shows an end view of the linear guide shown in FIG. 3; 
     FIG. 5 shows a linear guide according to the present invention, together with a linear encoder, which is provided with a change-over coupling; 
     FIG. 6 shows a linear guide according to the present invention, together with a linear encoder, which is supported on a mounting rail; 
     FIG. 7 shows another embodiment of a linear guide according to the present invention, together with a linear encoder, which is mounted on a mounting rail; and 
     FIG. 8 shows a sealed incremental linear encoder operable on photoelectrical measuring principle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a bed 2, e.g., of a machine-tool or a measuring machine on which a machine carriage 1 is displaceable in the directions shown by a double arrow. The carriage guide 3 represents a conventional linear guide provided with a guide rail 4 having hardened ground guide surfaces on which a slide 5 is displaceable on non-shown roller or ball elements. The slide 5 of the linear guide 3 is associated with the machine carriage 1 the displacement of which relative to the machine bed 2 should be measured or adjusted. As discussed above, such guides are generally known. In FIGS. 1 and 2, an exposed linear encoder 6 is a separate unit which is mounted on the guide rail 4 before mounting of the linear guide 3 on the machine. The linear encoder 6 has a scale 7, which is supported on carrier 9 and which is scanned with a scanning head 8 which generates appropriate measuring signals. The carrier 9 serves at that as an auxiliary guide for the scanning head 8 displaceable on ball bearings and connected by a coupling 10 with a driver 11 which, in turn, is secured on the slide 5 of the linear guide 3. The coupling 10 consists, in the simplest case, of elements with a curved and a flat surface which are kept in contact by a tension spring. The coupling 10 insures that the scanning head 8 is rigidly coupled to the slide 5 only during the displacement in a measuring direction. In the other directions, the scanning head 8 is pivotable. In FIG. 1, the scanning head 8 is attached to its carrier at the height of the graduation plane of the scale 7, and in FIG. 2--at the height of the neutral axis of the scale 7. Such mounting of the scanning head is shown, e.g., in German Patent No. 2,219,624. 
     The linear encoder in the discussed embodiment represents an incremental measuring device operable according to photo-electrical principle, as shown in FIG. 8. However, the linear encoder 6 mounted on the guide 3 can also be an absolute measuring device operable on a different physical principle, e.g., magnetic, inductive or capacitance principle. 
     FIGS. 3 and 4 show a sealed incremental linear encoder 6 which is mounted on the guide rail 4 as a separate unit before mounting of the guide rail in a machine. The encoder 6, as discussed above, is shown in FIG. 8. The encoder 6 includes a scale (7) having grating ruling which is scanned by the scanning head 8 having corresponding ruling for generating electrical measuring signals. The scale 7 is arranged on a carrier 9 which serves as an auxiliary guide for the scanning head 8, displaceable thereon, and is pivotally connected with a driver 11. The scale 7 and the scanning head 8 are received in a housing 12 sealed by rubber or plastic lip element 13. The driver 11 is fixedly connected with the slide 5 of the guide 3 and extends through the lip element 13. The sealed linear encoder 6 can operate in accordance with different physical principle than that described above with reference to FIGS. 1 and 2. 
     The exposed and sealed linear encoders 6, which, according to the invention, form a separate unit which is provided on the linear guide 3 before mounting the linear guide on a machine, are described in a firm publication &#34;Heidenhain-Lieferubersicht, August 1994, pp. 10-17. 
     FIG. 5 shows a sealed linear encoder 6 which can be easily mounted on the guide rail 4 by means of a change-over coupling 14 and is easily replaceable. The change-over coupling 14 is formed as a dovetail matching pair. The dovetail groove is formed in the guide rail 4, and the dovetail-formed member is provided on the linear encoder 6. 
     FIG. 6 shows a linear guide 3 with which the sealed linear encoder 6 is mounted on the guide rail 4, according to the invention, by means of a mounting rail 15 provided on the guide rail 4. The mounting rail 15 is formed as a punch-in slotter and is secured to the guide rail 4 with a screw 16. It is also contemplated providing a change-over coupling between a mounting rail, which is secured on the guide rail, and the linear encoder. 
     FIG. 7 shows a linear guide 3 which is supported on a mounting rail 15 1 , and on which the linear encoder 6 is replaceably mounted, with the encoder 6 being connected with the slide 5 by a driver 11. 
     The scale and/or its carrier can be connected with the guide or mounting rail, in a manner not shown in the drawings, practically free of reaction or constraining forces by articulated compensation elements provided at the scale ends. The compensation elements at that can be formed as a change-over coupling. 
     Though the present invention was shown and described with reference to the preferred embodiments, various modifications thereof will be apparent to those skilled in the art and, therefore, it is not intended that the invention be limited to the disclosed embodiments or details thereof, and departure can be made therefrom within the spirit and scope of the appended claims.