Method for mounting a length measuring device and corresponding length measuring device

Abstract

A length measuring system that includes a length measuring device and at least one mounting element, which exerts an attractive force between a support and the length measuring device. One or more of the at least one mounting element are of such a size that a frictional force, which is a function of a total attractive force, assures on one hand an adhesion of the length measuring device to the support and, on another hand, also assures displaceablity of the length measuring device along the support during mounting.

Description

[0001] The invention relates to a method for mounting a length measuring device, as well as the corresponding length measuring device itself

[0002] Such length measuring devices are used for example, as linear distance measuring devices in automation technology or for testing devices. Length measuring devices are also used on machine tools in very many cases. It is necessary there to measure the length of the carriage in relation to the machine bed with great accuracy. For this purpose the housing containing the scale graduation is fixedly screwed to the machine bed, for example, and the scanning unit of the length measuring device is connected with the movable carriage of the machine tool.

[0003] Often the length measuring devices are delivered as pre-assembled units, which means that the scale and the scanning unit, which can be moved in the measuring direction, are located together in one housing. Length measuring devices of this type are called closed, or encapsulated length measuring devices. But there are also so-called open length measuring devices, wherein the scanning unit and the scale are delivered separately.

[0004] It is necessary in both cases to align and fasten the housing, or the scale, with the greatest possible parallelism with respect to the measuring direction of the support, for example a machine tool.

[0005] In what follows, length measuring device means a closed, as well as an open length measuring device. It is thus possible by means of the invention to align and mount either only a scale, or a scale with a scanning unit, or a scale in a housing with a scanning unit contained therein.

[0006] Because of the continued improvement of the measuring accuracy of such length measuring devices, a correspondingly matched mounting accuracy with respect to their alignment by means of customary techniques becomes more and more elaborate. Measuring accuracies of ±5 μm or less are quite customary with such length measuring devices. Therefore the time required for the appropriate exact adjustment of the devices in the course of the mounting operations, for example on machine tools, is relatively great. Moreover, the mounting, or adjusting process itself is very difficult for a single assembler, particularly in connection with length measuring devices of some length.

[0007] A method and a device intended for mounting a scale or a scale support on an appropriate machine element are described in DE 199 14 311 A1. So that an undesired adhesive contact prior to the end of the alignment of the scale is prevented, spacers are proposed in this document, so that the scale can be definitely adjusted before it comes into contact with its support.

[0008] In DE 37 15 908 C2, a flexible scale with magnetic holders or suction cups is fastened on a body to be measured. This fastening which can be released relatively easily is also used during the measuring process itself. The disadvantage of this invention is that a permanent precise fixation of the scale is not possible in any way.

[0009] The same applies to published patent application EP 0 922 927 A2, wherein a magnetic fixation on the body to be measured is provided for the measuring process. There, too, the length measuring scale is not permanently brought into contact with the measuring body, and relatively low demands are made on the measuring accuracy.

[0010] The object of the invention is based on disclosing a method for mounting a length measuring device, by means of which a simple and accurate alignment of the length measuring device, or of the scale, on its support becomes possible. It is moreover intended to disclose a length measuring device which is distinguished by easy manipulation and universal employment.

[0011] This object is attained by means of a method in accordance with claim 1 and a device in accordance with claim 10.

[0012] Advantageous embodiments are disclosed in the dependent claims.

[0013] So-called mounting elements, which exert an attractive force between the length measuring device and the support, for example the machine bed of a machine tool, are used for making mounting easier. If the said support surface is perpendicularly arranged, an adhesive friction force results, which corresponds to the product of attractive force and the corresponding coefficient of friction. For the determination of the sum of the normal forces in connection with oblique or horizontal surfaces it is necessary to take into account, besides the total attractive force, also the weight with positive or negative signs in accordance with the respective inclination of the support. In accordance with the invention, the sum of the attractive forces of all mounted elements is of such a size that, on the one hand, the length measuring device adheres to the surface of the support in the installed position but, on the other hand, the displacement of the device for adjusting purposes is still possible. This means that the length measuring device can possibly be manually displaced on the surface of the support and aligned.

[0014] Thereafter it is absolutely necessary for the permanent use of the entire system that the length measuring device be fixedly connected with the support, for example by screw connections. In this state the device cannot be inadvertently, or without being damaged, moved out of adjustment. Alternatively to this it is also possible to provide a permanent adhesive connection, as long as the adhesive permits a linear displacement of the length measuring device in the adjusting phase—in which the length measuring device and the support adhere to each other. In this connection adhesives on the basis of epoxy resins, for example, are advantageous, which have a setting time which is greater than the time required for the exact alignment. The use of adhesives, whose setting phase can be specifically initiated from the outside, is practical. Adhesives can be used in this connection, whose setting is initiated, or significantly accelerated, by heat, UV radiation, moisture or other activators, for example. The length measuring device can be structurally adapted to these adhesives in an advantageous manner. For example, relatively large recesses or bezels can be provided at the end pieces, so that an increased adhesive surface is provided to the means which initiate setting.

[0015] At the end of the setting time, a non-displaceable connection must also be assumed. The adhesive can be applied in spots over the entire contact surface, or over a considerable partial surface. In this case the level application of the adhesive can the be considered as a lineup of many adhesive spots.

[0016] Magnets are particularly suited as mounting elements. The use of permanent magnets is advantageous since, in comparison with electromagnets, it is possible here to dispense with the electrical auxiliary energy. If an embodiment variation is used which does not provide the removal of the mounting magnets at the end of mounting, the electromagnetic solution can also be advantageous, because in this case no magnetic forces are present during the operation of the length measuring device which—for example in connection with machine tools—could trigger the undesired attraction of metal chips. For the same reason an arrangement of the permanent magnets is provided in an embodiment variation of the invention, wherein the magnets are completely surrounded by a steel housing of the length measuring device with the exception of their side facing the support. The size of the magnetic field toward the outside is minimized by the magnetic short circuit between the support and the magnets.

[0017] The use of suction cups as mounting elements for the temporary fastening of the length measuring device on the support is recited as a further embodiment of the invention. These suction cups can become effective either by merely pressing the suction cup on, or also actively, for example by means of appropriate clamping devices or aided by compressed air.

[0018] With shorter length measuring devices the mounting elements are preferably located in the two end areas of the length measuring devices. However, particularly in connection with long length measuring devices, it can be advantageous to arrange several mounting elements over the entire length of the length measuring device, spaced apart in the measuring direction.

[0019] Exemplary embodiments of the invention will be explained in greater detail by means of the drawings.

[0020] Shown are in:

[0021] FIGS. 1 a to 1c, schematically the respective process steps for mounting the length measuring device,

[0022] FIGS. 2A, 2 b , a cross section and a partial view from above on an end element of a length measuring device with permanent magnet units,

[0023] FIGS. 3 a , 3b, a cross section and a partial view from above on an end element of a length measuring device with removable permanent magnet units,

[0024] FIGS. 4 a , 4b, a cross section and a partial view from above on an end element of a length measuring device with magnets in the machine bed,

[0025] FIGS. 5 a , 5b, a cross section and a partial view from above on an end element of a length measuring device with a permanent magnet stuck on it,

[0026] FIGS. 6 a , 6b, a cross section and a partial view from above on an end element of a length measuring device with an inserted magnetic pin,

[0027] FIGS. 7 a , 7b, a cross section and a partial view from above on an end element of a length measuring device with suction cups,

[0028] FIGS. 8 a , 8b, a cross section and a partial view from above on an end element of a length measuring device with an adhesive connection.

[0029] In the drawing figures, elements which are part of a component or have the same function are combined by means of identical first numbers of the reference numeral.

[0030] FIGS. 1 a to 1c are essentially intended to explain the course of the method. The length measuring device 1, consisting of the scanning unit 1.1, the end elements 1.2 and the encapsulated linear scale 1.3, is to be mounted on the support, in this case on the machine bed 2 of a machine tool. It is necessary in the course of this to assure that the alignment Y of the length measuring device 1 is as parallel as possible to the desired direction X. The desired direction X corresponds to the direction of guidance of the movable carriage 3 of the machine tool.

[0031] FIG. 1 a represents the position of the length measuring device 1 during the first mounting step. To make the situation clear, the deviation of the actual alignment Y from the desired direction X is exaggerated. In this first mounting step the length measuring device 1 is put into frictional contact on the perpendicular flat surfaces of the machine bed 2 without use of exact measuring means and in a first approximation parallel with respect to X. Following this mounting phase, the length measuring device 1 adheres to the machine bed 2 without manual support. If the play between the exterior thread of the screws 4 and the interior diameter of the bore 1.5 is of sufficient size, it is already possible to loosely thread the screws 4 through the bores 1.5 during the first mounting step. Means for achieving the required adhesive friction will be described later by means of FIGS. 2a to 8b.

[0032] In the second mounting step, represented in FIG. 1b, it is then easily possible to perform the exact alignment of the length measuring device 1 with the required measuring means. Because the length measuring device 1 adheres to the machine bed 2 without any aid from the assembler, but is nevertheless comparatively easily manually displaceable, a quick and very exact adjustment is possible. No undesired mechanical loads on the measuring device 1 occur in the course of the alignment, because an improper mounting, for example an alignment of the already screw-connected length measuring device 1 by beating on it, can be prevented with this method. It is of course possible to provide a lubricant or sliding additive between the length measuring device 1 and the machine bed 2 in order to ease the displaceability, or to avoid so-called slip-stick effects. The bores 1.5 are used for receiving screws 4 for the final fastening after the exact alignment of the length measuring device 1 on the machine bed 2. It is also necessary in the course of displacing the length measuring device 1 to assure that the bores 1.5 in the length measuring device 1 match the corresponding bores with an interior thread in the machine bed 2. As a rule, the bores 1.5 have a slightly larger interior diameter than the diameter of the exterior thread of the associated screws 4. In this way sufficient play is provided for making the alignment possible without it being necessary to perform drilling during the mounting process.

[0033] The last mounting step is represented in FIG. 1c. After the adjustment is finished, for example with a deviation of the actual direction Y from the desired direction X of less than 0.1 degrees of angle, the length measuring device 1 is solidly and immovably fixed on the machine bed by means of screws 4. In this state the scanning unit 1.1 can be displaced almost parallel in relation to the desired direction X, i.e. the movement direction of the carriage 3.

[0034] An end element 1.2 of a housing of the length measuring device 1 is represented in each of FIGS. 2 to 8. Like the rest of the housing, these end elements 1.2 are often made of aluminum, i.e. of a non-ferromagnetic material.

[0035] FIGS. 2 a and 2b show an arrangement in which the mounting elements are permanent magnets 5.11. In this case the machine bed 2 is made of a ferromagnetic material, for example of steel. If required, the permanent magnets 5.11 can be backed by a rear closure plate 5.12 for increasing the attractive force, in particular if there is an aluminum housing. For example, the magnets can be glued to the rear closure plate 5.12, or the attractive force of the magnets on the rear closure plate 5.12 can be used for fixation. In this case the rear closure plate 5.12 can be inseparably connected with the housing by gluing.

[0036] Basically, it is advantageous for all exemplary embodiments that the mounting elements are designed in such a way that they do not become separated, or fall of, from the length measuring device 1 in the course of the mounting work.

[0037] If magnets are used as mounting elements, they are preferably inserted into the housing of the length measuring device 1 in such a way that their surface is flush with the surface of the length measuring device 1, or is slightly set back. It is achieved by means of this construction that the corresponding surfaces of the length measuring device 1 and of the machine bed 2 are in contact during the entire mounting phase. So that the length measuring device 1 can be mounted by means of the method of the invention on both possible attachment surfaces 1.7, the mounting elements in the exemplary embodiments in accordance with FIGS. 2 to 4, as well as 7 and 8, are arranged, or can be arranged, symmetrical, in particular point-symmetrical, with respect to the center of the cross section of the length measuring device.

[0038] FIGS. 3 a and 3b show a variation, wherein the mounting element is embodied as a removable permanent magnet unit 5.1 with a corresponding rear closure plate 5.12. So that the permanent magnets 5.11 and the rear closure plate 5.12 are sufficiently secure against falling out, undercut recesses 1.4 are provided here in the end elements 1.2 of the length measuring element 1, which are used as guides for the rear closure plate 5.12. To ease the pulling out of the permanent magnet unit 5.1, the rear closure plate 5.12 is appropriately bent at one end (in the partial view from above in FIG. 3b, the rear closure plate 5.12 projects out of the drawing plane at one end). The removed permanent magnet unit 5.1 can be used again with another length measuring device 1 to be mounted.

[0039] FIGS. 4 a and 4b show an embodiment variation, wherein the machine bed 2 consists of a non-ferromagnetic material, such as granite or polymer concrete, for example. A permanent magnet 2.2 can be inserted into the machine bed 2 here, which then interacts with a ferromagnetic insert 5.3 of the length measuring device. It is of course possible to embody the inserts in the length measuring device 1 in the form of permanent magnets, similar to FIGS. 2 and 3, if corresponding magnetically attractive reaction elements, for example strips of steel plate, are then provided in the non-ferromagnetic machine bed 2.

[0040] Alternatively to the embodiments represented so far, an arrangement is represented in FIGS. 5a and 5b, in which a horseshoe-shaped permanent magnet 5.11 extends around the respective end element 1.2. A supporting frictional connection is created by the magnetic attractive force between the machine bed 2 and the permanent magnet 5.11. This frictional connection has a support ability which is sufficiently strong so that the frictional connection is not released even during displacement movement in the course of the adjusting process. The permanent magnets 5.11 can be pulled off in a simple manner after the mounting process.

[0041] A variation is represented in FIGS. 6a and 6b, wherein a magnetic pin 5.2 can be inserted into an auxiliary bore 1.6 in the end element 1.2 of the length measuring device 1. This variation is distinguished by its simple construction. In contrast to the variation in FIG. 5, an interlocking force transfer between the permanent magnet 5.1 and the end element 1.2 is provided here. Here, too, the length measuring device 1 in accordance with the method of the invention can be fastened on both possible attachment surfaces 1.7 of the machine bed 2. The magnetic pin 5.2 should be designed in such a way that it cannot fall out in the course of the mounting operations. The embodiment shown, wherein the pin 5.2 is secured by means of an appropriately tight fit, is particularly advantageous from the viewpoint of production costs.

[0042] Alternatively to this it is also possible for axial securing to provide a plastic element, which is pushed against the wall of the auxiliary bore 1.6 in the course of introducing the pin 5.2, or an appropriate screw thread.

[0043] An embodiment variation is represented in FIGS. 7a and 7b, wherein the adhesive friction is caused by suction cups 5.4 made of a polymer material. Here, too, the application of a lubricant or a sliding additive can be particularly advantageous, for one, to increase the displaceability, and furthermore to prevent the penetration of air into the underpressure area of the suction cup 5.4.

[0044] Finally, an exemplary embodiment is represented in FIGS. 8a and 8b, wherein the adhesive connection is produced by means of a glue connection 5.5. In this case the glue connection 5.5 can be used as a mounting element, as well as a permanent fastening means for the length measuring device 1. In this case the length measuring element 1 is provided with bezels 1.8 of comparatively large size. An adhesive is applied to the attachment surface 1.7, which is distinguished in that its setting process can be triggered by UV radiation. As soon as the length measuring device 1 has been adjusted with sufficient accuracy, the visible glue joints are radiated with UV radiation by the assembler. The polymerization process of the adhesive is started in this way. Setting in the areas of the glue connection 5.5 where no UV radiation penetrates is made possible by an anaerobic secondary system of the glue. Since the glue connection 5.5 shows great strength in the set state, the use of the screws 4 can be dispensed with.

Claims

1. A method for mounting a length measuring device (1) on a support (2), wherein in a first mounting step the length measuring device (1) is placed into frictionally adhesive contact with the support surface, wherein at least one mounting element (5.1, 5.2, 5.3, 5.4, 5.5) exerts an attractive force between the support (2) and the length measuring device (1), and this attractive force is of such a size that the corresponding frictional force assures a displaceability of the length measuring device (1), in a second mounting step the position and direction of the length measuring device (1) is adjusted, so that its orientation, in the sense of the result of the length measurement, has a a tolerably small deviation from the desired direction, in a third mounting step the length measuring device is connected with its support (2) so that it cannot be displaced.

2. The method in accordance with claim 1, characterized in that the length measuring device (1) is an already pre-assembled unit consisting at least of one linear scale (1.3) and at least one scanning unit (1.1).

3. The method in accordance with claim 1, characterized in that at least two spaced apart mounting elements (5.1, 5.2, 5.3, 5.4, 5.5) are arranged on the length measuring device (1), by means of which the length measuring device (1) is connected with its support.

4. The method in accordance with one of claims 1 to 3, characterized in that at least one mounting element (5.1, 5.2, and 5.3) exerts a magnetic attractive force between the support (2) and the length measuring device (1).

5. The method in accordance with one of claims 1 to 3, characterized in that at least one mounting element (5.4) exerts an attractive force, which is caused by underpressure, between the support (2) and the length measuring device (1).

6. The method in accordance with claim 1, characterized in that in the third mounting step the length measuring device (1) is connected in a non-displaceable manner with its support (2) with the aid of screw and/or rivet connections in at least two points.

7. The method in accordance with claim 1, characterized in that in the third mounting step the length measuring device (1) is connected in a non-displaceable manner with its support (2) by means of an adhesive connection (5.5) in at least two points.

8. The method in accordance with claim 7, characterized in that in the second mounting step the adhesive connection (5.5) is in a state which permits a displacement of the length measuring device (1) in relation to the support (2), and thereafter leads to a solid connection between the length measuring device (1) and the support (2).

9. The method in accordance with claim 1, characterized in that all, or only a part, of the mounting elements (5.1, 5.2, 5.3, 5.4, 5.5) are removed in a fourth mounting step.

10. A length measuring device (1), having at least one mounting element (5.1, 5.2, 5.3, 5.4, 5.5), which exerts an attractive force between a support (2) and the length measuring device (1), wherein the mounting element or the mounting elements (5.1, 5.2, 5.3, 5.4, 5.5) are of such a size that the frictional force, which is a function of the total attractive force, assures on the one hand the adhesion of the length measuring device (1) to the support (2) and, on the other hand, also assures the displaceablity of the length measuring device (1) along the support surface during mounting.

11. The length measuring device in accordance with claim 10, characterized in that the length measuring device (1) is an already pre-assembled unit consisting at least of one linear scale (1.3) and at least one scanning unit (1.1).

12. The length measuring device in accordance with claim 10, characterized in that the mounting elements (5.1, 5.2, 5.3, 5.4, 5.5) are or can be arranged in such a way that the length measuring device (1) can be alternatively brought into an adhesive frictional contact with a support (2) on at least two attachment surfaces (1.7).

13. The length measuring device in accordance with one of claims 10 to 12, characterized in that at least two mounting elements (5.1, 5.2, 5.3, 5.4, 5.5) are arranged on the length measuring device (1).

14. The length measuring device in accordance with claim 13, characterized in that the mounting elements (5.1, 5.2, 5.3, 5.4, 5.5) are arranged on the two end sections (1.2) of the length measuring device (1).

15. The length measuring device in accordance with one of claims 10 to 14, characterized in that at least one mounting element (5.1, 5.2, 5.3) exerts a magnetic attractive force between the support (2) and the length measuring device (1).

16. The length measuring device in accordance with claim 15, characterized in that at least one permanent magnet (5.11) is arranged for generating a magnetic attractive force between the support (2) and the length measuring device (1).

17. The length measuring device in accordance with claim 15, characterized in that at least one switchable magnet, in particular an electromagnet, is arranged for generating a magnetic attractive force between the support (2) and the length measuring device (1).

18. The length measuring device in accordance with claim 15, characterized in that on the surfaces facing away from the support (2), the magnets (5.11) are provided with rear closure plates (5.12).

19. The length measuring device in accordance with claim 10, characterized in that the magnets (5.11) are fastened in the length measuring device (1) with the aid of several undercut recesses (1.4), in particular one or several dovetailed recesses.

20. The length measuring device in accordance with claim 15, characterized in that the length measuring device (1) has at least one auxiliary bore (1.6) extending into it, into which cylindrical magnets (5.2) can be inserted.

21. The length measuring device in accordance with claim 15, characterized in that at least one ferromagnetic reaction element (5.3) is attached to the length measuring device (1), which is attracted by one or several magnets (2.2) housed in the support (2).

22. The length measuring device in accordance with one of claims 10 to 14, characterized in that at least one mounting element (5.4) creates an attractive force, which is caused by underpressure, between the support (2) and the length measuring device (1).

23. The length measuring device in accordance with claim 10, characterized in that the length measuring device (1) is designed in such a way that all, or only a part, of the mounting elements (5.1, 5.2, 5.3, 5.4, 5.5) can be removed after mounting has been completed.