DE29807438U1 - Magnetically preloaded linear guide - Google Patents

Description

A 54 456 c Registration number:**!* * *..* »

c-250 K. Jung GmbH

23 April 1998 Jahnstrasse 80 - 82

73037 Goeppingen

Magnetically preloaded linear guide

The present invention relates to a linear guide for a carriage that can be moved relative to a base, with at least two mutually associated, preloadable linear bearing surfaces and with bearing elements arranged between the linear bearing surfaces.

In particular, the invention relates to achieving a preload for such a linear guide for the highest accuracy requirements with regard to parallelism, smooth running and positionability of the moving carriage.

Linear guides can be used to achieve a straight-line, translational movement of a first machine part, hereinafter referred to as the slide or table, relative to a second machine part, hereinafter referred to as the base or frame. In this case, a linear bearing surface is assigned to the slide and the base. The latter can be designed, for example, as separate bearing strips that are mounted on the slide and the base, but it can also be provided that the slide and/or the base itself have a corresponding bearing surface. The running behavior of the slide, i.e. the smoothness, ease of movement and straightness of the movement as well as the uniformity of the friction coefficient depending on the displacement path and the displacement speed of the slide, is essentially

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essentially determined by the type and design of the guidance system used.

If a sliding guide is used, sliding friction occurs when the slide is moved, which depends on the speed. In particular, when the slide changes from rest to movement, the higher static friction must first be overcome before sliding friction sets in. Sensitive, slow and targeted movement of a slide mounted in this way is therefore only possible to a very limited extent.

A considerably improved running behavior can be achieved by inserting bearing elements designed as rolling elements between the at least one linear bearing surface that is operatively connected to the slide and the corresponding linear bearing surface that is operatively connected to the base. This results in very low rolling friction that is largely independent of speed when the slide moves relative to the base. This has the advantage that no increased friction has to be overcome when the slide moves from rest to movement. A slide mounted in this way can therefore be moved more sensitively and precisely.

Comparatively good running characteristics can also be achieved by very fine machining of the linear bearing surfaces and by using bearing elements in the form of special sliding material, for example made of polytetrafluoroethylene, or in the form of pressure oil between the linear bearing surfaces.

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In order to prevent the carriage from being lifted out of its guide, i.e. to prevent the linear bearing surfaces of the linear guide from coming loose, known linear guides usually have a wraparound system with two guide surfaces facing each other. One of the guide surfaces can absorb the weight of the carriage, the other guide surface can absorb any lifting forces acting on the carriage. The flatness and parallelism of the opposing guide surfaces determine the running quality of the carriage. The wraparound system can, for example, be designed in such a way that bearing strips that wrap around each other in a C-shape are used.

By means of a wraparound, the carriage can be reliably prevented from being lifted out of its guide. However, this has the disadvantage that the bearing parts arranged on the carriage must be threaded into the bearing parts located on the base in order to achieve a wraparound in the longitudinal direction, or a relatively complex assembly of the linear guide used is required, and when dismantling, the linear guide must be "opened" by removing the wraparound. This means that such a linear guide must be accessible from all sides for assembly.

Instead of a mechanical grip with bearing parts enclosing each other on all sides, EP 0 418 200 Al proposed holding the slide and base together using a permanent magnet and an associated soft magnetic material in order to prevent the slide from lifting out and to achieve the best possible

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to achieve constant sliding resistance of the slide. The use of a magnet for holding and in combination with an air flow for contact-free displacement of two parts relative to each other is already known from the Swiss patent CH 415 188.

In particular, when the bearing strips engage with each other, there is a risk that they will jam against each other, which will ultimately render the slide unusable. To avoid jamming of this kind, it must be ensured that there is practically no play between the bearing strips that are assigned to each other, so that the slide cannot tilt relative to the base.

A play-free guide must be ensured, especially if the carriage is carrying a variable load. Otherwise there is a risk that the linear guide, which is play-free when it is installed, will spring up under load and become jammed when the carriage moves back and forth.

In order to keep the linear guide free of play even under high, changing operating forces, the linear guide is usually preloaded during assembly, i.e. the associated linear bearing surfaces are subjected to a high preload force during assembly of the linear guide. This ensures that the linear guide remains free of play and yet easily movable even under strongly changing operating forces.

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When using rolling elements as bearing elements, an undersized installation space is usually chosen to achieve a preload for the rolling elements arranged between the associated linear bearing surfaces, so that this is usually too small by 1 to 3 μπα when the rolling elements are inserted. Due to the installation space being too small, the rolling elements are deformed in a defined way when the linear guide is installed, and the associated linear bearing surfaces are thus subjected to a certain preload force.

When using pressure oil as a bearing element, the preload is set by the pressure of the pressed-in oil. If sliding linings or very finely machined, lubricated surfaces are used, the guide is fitted like a roller guide with an undersize. However, preloaded wrap-around guides with sliding elements are very rare.

However, such preloading is highly dependent on the track geometry, i.e. a slight fluctuation in the manufacturing dimensions of the components to be preloaded results in a very strong fluctuation in the preload force. The components of a preloaded linear guide are therefore subject to extremely high demands in terms of straightness and flatness. In addition, very great care is required when assembling such linear guides, because the necessary undersize of the rolling element installation space can often only be determined and created when assembling the slide. The assembly of known preloaded linear guides is therefore usually very time-consuming.

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Another disadvantage of known pre-stressed wraparound guides is that the wraparound must be designed to be very rigid in order to be able to reliably absorb the forces acting during pre-stressing. Such a rigidity requires a considerable material thickness and increased space requirements.

Instead of achieving the required pre-tensioning force through a defined material deformation, it was also considered to increase the weight of the slide so that a sufficiently high pre-tensioning force is provided by its weight alone. However, if the slide is to be reliably prevented from tipping even under high operating forces, a considerable pre-tensioning force is necessary. Achieving such a high pre-tensioning force through a corresponding weight of the slide does not make sense, since such a heavy slide causes very high inertia forces when accelerating and braking, which place a heavy load on the slide's drive, which is usually used.

The object of the present invention is to further develop a linear guide of the generic type in such a way that minor deviations of the components from the ideal path geometry do not lead to a complete loss of preload.

This object is achieved according to the invention in a linear guide of the type mentioned at the outset in that the linear guide comprises at least one magnet which applies a preload force to the associated linear bearing surfaces. To achieve the desired

7» ·

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For pre-tensioning, it is therefore not necessary to provide one of the usual wrap-around solutions, but the pre-tension is achieved by means of magnetic attraction. For this purpose, it is necessary to select the level of the magnetic force in such a way that it corresponds to the desired pre-tensioning force.

Such a design of the linear guide has the advantage that, due to the magnetic preload force, a wraparound to prevent the slide from lifting is no longer necessary. This means that the linear guide does not have to be accessible from all sides during assembly. In addition, the linear guide can be assembled without any adjustment work, so that assembly is less time-consuming. Since the preload force is not achieved by the geometry of the bearing elements, a slight deviation from the ideal guide geometry does not lead to a total loss of the preload force. The straightness and flatness of the linear guide components involved must meet the requirements that are necessary for the straight running of the slide, but by eliminating the wraparound and thus the counter bearing surfaces, the number of surfaces to be manufactured is generally reduced by half. The linear guide according to the invention can therefore be manufactured more cost-effectively. In addition, the machine structure is relieved of internal preload forces by using the magnetic force and can therefore be built much more lightly. This is particularly important when building highly dynamic machine axes.

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To achieve the magnetic preload force, the linear guide can have at least one electromagnet.

In order to adapt the preload force caused by the magnet to the various operating conditions of the linear guide, it can be advantageous if the linear guide includes a control element for adjusting the strength of the preload force. It is particularly advantageous if at least one controllable or adjustable electromagnet is used.

In a preferred embodiment, the linear guide has at least one permanent magnet. Such a design has the advantage that no safety precautions need to be taken in the event of a failure of the magnetic force.

In many cases, the linear guide is used to support a machine-driven slide. If a linear motor is provided to drive the slide, it is particularly advantageous if the permanent magnet of the linear guide forms part of the linear motor that is provided to drive the movable slide. Linear motors are known, for example, from DE 31 23 441 C2. These use a permanent magnet arrangement and a multi-strand winding that can be moved against each other under the effect of a magnetic tensile force. In a particularly preferred embodiment of the invention, the linear motor performs a dual function. On the one hand, it serves, as usual, to move the slide in a defined manner. On the other hand, the

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Linear motor exerts such a preload force on the linear guide that tilting of the bearing strips assigned to one another is reliably prevented even under high operating forces. The permanent magnet of the linear guide forms the electrically passive part of the linear motor, whose electrically active part in the form of coils is located opposite the permanent magnet in a known manner.

When the linear motor is operating, the electrically passive parts are displaced relative to the electrically active parts, whereby one of the two parts, for example the electrically passive part, is held on the carriage, while the other part is held by the base.

It is advantageous if the linear guide comprises at least two magnets, between which at least two mutually assigned linear bearing surfaces are arranged, because this enables a uniform load on the linear bearing surfaces.

In many cases, a linear guide with at least four linear bearing surfaces is used to support a slide that can be moved relative to a base, which form at least two pairs of bearing surfaces aligned parallel to one another. The pairs of bearing surfaces can be designed symmetrically; for example, they can each form a V-shaped guideway. However, different pairs of bearing surfaces can also be used. For example, to compensate for thermal expansion of the slide and/or the base, a V-shaped pair of bearing surfaces can be provided in combination with a flat pair of bearing surfaces. The flat pair of bearing surfaces allows thermal expansion,

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while the V-shaped bearing surface pair forms a guide bearing and can also absorb mechanical loads transverse to the sliding direction of the slide.

In a particularly compact linear guide with at least two pairs of bearing surfaces aligned parallel to one another, it is provided that at least one magnet applying a preload force to the linear bearing surfaces is arranged between the pairs of bearing surfaces.

It is advantageous if the linear bearing surfaces are designed as bearing strips that can be connected to the slide or the base, in particular that can be detachably connected.

The linear guide according to the invention is characterized by particularly good running characteristics. It can therefore preferably be used on a device for machining a
Workpiece with a frame and a movable relative to the frame by means of a drive
The drive of the table can be designed as a linear motor, whose permanent magnet - as explained above - drives the associated linear bearing surfaces of the linear guide
with a preload force. Such a
The device can be used, for example, in the form of a quick lifting table on a profile grinding machine

j come. Using such a quick lifting table,

Small workpieces can be ground with a very high stroke rate and therefore within a short time.

j The linear guide according to the invention enables

a smooth running of the table, which can accommodate a workpiece clamping device for clamping the

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grinding workpieces. Due to the very high number of strokes, high accelerations and speeds occur during grinding, which result in very high and changing operating forces. This requires a strong preload of the linear guide, which is preferably designed as a roller guide. The corresponding preload force is achieved by using the permanent magnet of the linear motor.

The description of a preferred embodiment of the invention serves to explain it in more detail in conjunction with the drawing. They show:

Figure 1: a schematic representation of a

Rapid lifting table with an inventive linear guide in side view;

Figure 2: a sectional view along the line

2-2 in Figure 1 and

Figure 3: a top view of the quick lift table

from Figure 1.

The drawing shows a rapid lifting table, which is designated overall by the reference number 10. As can be seen in particular from Figure 2, the rapid lifting table 10 comprises a substantially U-shaped base plate 14 arranged on a base 12 with a support 16, from which a first leg 18 shown on the left in Figure 2 and a second leg 20 shown on the right in Figure 2 protrude vertically. At their free ends, the two legs 18 and 20 each carry a first and second lower bearing strip 22 and 24, respectively, which

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are screwed to the respective legs and each form a linear bearing surface. The two lower bearing strips 22 and 24 are each assigned a first and second upper bearing strip 26 and 28, respectively, which are fastened by means of screws to a table top 30 that can be moved relative to the base plate 14 in the longitudinal direction of the rapid lifting table 10 and also each form a linear bearing surface. The lower bearing strip 22 thus forms, together with the upper bearing strip 26, just as the lower bearing strip 24 together with the upper bearing strip 28 forms a linear guide for supporting the table top 30 on the base plate 14. The table top 30 thus forms a carriage that can be moved relative to the base plate 14, which represents a base. In order to enable smooth and uniform movement of the table top 30, needle-shaped rolling elements 32 are inserted as bearing elements between the associated bearing strips 22 and 24 or 26 and 28, so that the upper bearing strips 26 and 28 can roll over the rolling elements 32 on the corresponding lower bearing strips 22 and 24.

The second bearing strips 24 and 28 shown on the right in Figure 2 are V-shaped, i.e. the lower bearing strip 24 forms a V-shaped guide groove into which the upper bearing strip 28 engages with a corresponding V-shaped projection. This means that the second bearing strips 24 and 28 can not only absorb forces that point vertically downwards from the table top 30 in the direction of the base plate 14, but can also absorb transverse forces in addition to this load. The second bearing strips

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24 and 28 thus form a guide bearing for the table top 30.

In contrast, the facing linear bearing surfaces of the first bearing strips 22 and 26 shown on the left in Figure 2 are flat. The bearing strips 22 and 26 can therefore only absorb forces that are aligned perpendicular to their facing bearing surfaces on which the needle-shaped rolling elements 32 roll. This allows the table plate 30 and the base plate 14 to thermally expand independently of one another without affecting the running behavior of the linear guide. In addition, this compensates for manufacturing tolerances.

The legs 18 and 20 of the base plate 14, which are aligned parallel to one another, accommodate between them an electrically active part 34 of a linear motor 36, which is only shown schematically in the drawing, for driving the table top 30. The electrically active part 34 is held immovably on the support 16 of the base plate 14 by means of fastening screws 38 and locking pins 40.

In a corresponding manner, opposite the electrically active part 34 and at a short distance from it, a permanent magnet 42 is screwed and pinned to the table top 30 using fastening screws 44 and locking pins 46. The permanent magnet 42 is thus held between the two upper bearing strips 26 and 28 on the table top 30 and exerts a magnetic force on the bearing strips 22, 24, 26, 28 arranged on both sides of the permanent magnet 42.

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Preload force. The permanent magnet 42 is plate-shaped and has a thermal insulation 48 in the area of the fastening screws 44 and the locking pins 46 in order to keep heat transfer from the permanent magnet 42 to the table top 30 as low as possible.

The permanent magnet 42, together with the thermal insulation, forms the electrically passive part of the linear motor 36. With its help, a driving force acting in the longitudinal direction of the high-speed lifting table 10 can be exerted on the table top 30 in a known manner. At the same time, due to the high attraction force of the permanent magnet 42, which is 4.6 kN in the embodiment shown, a sufficiently high preload force is exerted on the bearing strip pairs 22, 26 and 24, 28 and thus on the associated linear bearing surfaces of the linear guide, so that despite the high acceleration forces that occur, tilting or lifting of the table top 30 can be reliably prevented.

During operation of the high-speed lifting table 10, frictional heat occurs due to the rolling friction in the bearing strips 22 to 28. This can be dissipated via a cooling pipe 50 that runs between the upper bearing strips 22 and 28 and the table top 30 as well as between the permanent magnet 42 and the table top 30. This cooling pipe 50 also dissipates the heat from the permanent magnet 42 of the linear motor 36. Another cooling pipe 52 is provided between the lower bearing strips 22 and 24 and the legs 18 and 20.

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The linear motor 36 is controlled by means of a known and therefore in the drawing
control unit (not shown), wherein an electrical measuring system 54 is additionally provided on the side of the leg 18 of the base plate 14 facing away from the electrically active part 34 for determining the respective

• ■ ' .

position of the table top 30. By means of the measuring system 54, both the control of the linear motor 36
as well as the control of a device for processing a workpiece held on the table top 30, in the
drawing of a workpiece not shown. So
For example, it can be provided that the measuring system
54 controls a profile grinding machine known per se, not shown in the drawing, as an additional device
the Sehnell lifting table 10 is used
The fastening of the workpiece to be ground
This can be done using a standard and therefore in the
Drawing also not shown workpiece clamping device, for the attachment of which the table top
30 on its side facing away from the base plate 14
Top side has a T-shaped retaining groove 56.

Claims (11)

A 54 456 c 23 April 1998 C-250 CLAIMS 1. Linear guide for a carriage that can be displaced relative to a base, with at least two mutually assigned, preloadable linear bearing surfaces and with bearing elements arranged between the linear bearing surfaces, characterized in that the linear guide (24, 28, 32; 22, 26, 32) comprises at least one magnet (42) that applies a magnetic preload force to the mutually assigned linear bearing surfaces (22, 26 or 24, 28). 2. Linear guide according to claim 1, characterized in that the linear guide comprises at least one electromagnet. 3. Linear guide according to claim 1 or 2, characterized in that the linear guide comprises a control element for adjusting the strength of the magnetic preload force. 4. Linear guide according to one of the preceding claims, characterized in that the linear guide comprises at least one controllable or adjustable electromagnet. 5. Linear guide according to one of the preceding claims, characterized in that the linear guide (22, 26, 32; 24, 28, 32) comprises at least one permanent magnet (42). · — 17··- · ·· · ·· ·· A 54 456 c
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C-250 6. Linear guide according to claim 5, characterized in that the permanent magnet (42) forms part of a linear motor (36) for driving the displaceable carriage (30). 7. Linear guide according to one of the preceding claims, characterized in that the linear guide comprises at least two magnets, between which at least two mutually associated linear bearing surfaces are arranged. 8. Linear guide according to one of the preceding claims, characterized in that the linear bearing surfaces are designed as mutually associated bearing strips (22, 26; 24, 28) that can be connected to the carriage (30) or the base (14). 9. Linear guide according to one of the preceding claims, characterized in that the linear guide has at least four linear bearing surfaces (22, 26, 24, 28) which form two pairs of bearing surfaces (22, 26; 24, 28) aligned parallel to one another, and in that at least one magnet (42) is arranged between the pairs of bearing surfaces (22, 26; 24, 28). 10. Device for machining a workpiece with a frame, a table that can be moved back and forth relative to the frame by means of a drive and with a linear guide according to one of the preceding claims, characterized in that the drive comprises a linear motor (36) with a ■ ····■ ..■■■- &igr;&dgr;.- : A 54 456 c
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c-250 Permanent magnet (42) which applies a magnetic preload force to the associated linear bearing surfaces (22, 26; 24, 28). 11. Device according to claim 9, characterized in that the device is designed as a quick lifting table (10) for a profile grinding machine.