(19)
(11)EP 4 036 429 A1

(12)EUROPEAN PATENT APPLICATION

(43)Date of publication:
03.08.2022 Bulletin 2022/31

(21)Application number: 21154471.3

(22)Date of filing:  31.01.2021
(51)International Patent Classification (IPC): 
F16C 29/00(2006.01)
F16C 29/12(2006.01)
(52)Cooperative Patent Classification (CPC):
F16C 29/002; F16C 29/004; F16C 29/008; F16C 29/123; F16C 2361/00
(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
Designated Extension States:
BA ME
Designated Validation States:
KH MA MD TN

(71)Applicant: SNR Wälzlager GmbH
33719 Bielefeld (DE)

(72)Inventor:
  • Grote, Detlef
    D-33818 Leopoldshöhe (DE)

(74)Representative: Alatis 
3 rue Paul Escudier
75009 Paris
75009 Paris (FR)

  


(54)DEVIATION COMPENSATION INTEGRATED IN THE CARRIAGE OF A LINEAR AXIS


(57) The invention relates to a linear guiding system (1) comprising a carriage (4) mechanically connected by a deviation compensating device to at least one slider (7) slidably mounted on linear guiding means (10). The deviation compensating device comprises resilient attaching means for connecting a slider upper part (9) to a carriage lower part (5) opposite to said slider upper part (9). The resilient attaching means comprise a first set of elastic fastening means (8, 14) vertically biasing said carriage lower part (5) against said slider upper part (9) with bearing means (18, 18a) located between said carriage lower part (5) and said slider upper part (9). Thereby, said carriage (4) can pivot relatively to said slider (7) at least around a longitudinal axis (X) of said linear guiding means (1). The resilient attaching means comprise further a second set of elastic fastening means (23, 24, 25) horizontally biasing said carriage lower part (5) against said slider (7). Thereby, said carriage (1) can move relatively to said slider (7) at least along a horizontal transversal axis (Y) substantially perpendicular to said longitudinal axis (X). Said carriage lower part (5) is integrally formed with the carriage (4) or mechanically fixed to said carriage (4).




Description

TECHNICAL FIELD OF THE INVENTION



[0001] The invention relates generally to the field of linear guiding systems also known as a linear axis.

[0002] More specifically, the invention relates to a carriage slidably guided along a longitudinal axis of one or more guiding rails via sliders.

[0003] The invention can be used, in particular, for machine tools manufacturing, packaging and printing machines, aircraft construction, automation and assembly lines, wood and paper industry, semiconductor industry and medical engineering.

[0004] In the following, when it is referred to vertical, horizontal, front and rear, or top and bottom, this must be construed by reference to a linear guiding system in regular operating position. It is meant by a longitudinal and transversal axis respectively the sliding direction of the linear guiding system and the horizontal axis perpendicular to the sliding direction.

BACKGROUND ART



[0005] Linear guiding systems are known where a working platform is slidably mounted on a pair of parallel guiding rails through four sliders located underneath the working platform. Usually, a pair of longitudinally spaced apart sliders are slidably mounted on each guiding rail. In such assembly, it is crucial that the guiding rails are accurately parallel and at the same height because conventional linear guiding systems accept only small mounting tolerances. Guiding rails misalignment lead to suboptimal operation of the linear guiding system and generate operational constraints between the sliders and the rails which can damage the guiding system, increase hardware wear and degrade the guiding accuracy.

[0006] Therefore, an accurate positioning of the guiding rails is essential when assembling the linear guiding system. However, such accurate positioning costs time and effort for assembling the system and requires an expensive accurate substructure for supporting the rails.

[0007] Linear guiding systems are used in different working environment where the ambient temperature can vary significantly. Moreover, the driving devices used for shifting the working platform along the guiding rails generate heat. This induces thermal expansion of the substructure and of the gantry formed by the working platform and the sliders. Thermal expansion is not homogenous for all components of the substructure and of the gantry due to different materials or temporary different component temperatures. Therefore, despite costly accurate original positioning of the rails, misalignment can occur during operation of the linear guiding system due to thermal expansion which generates, in addition to the mechanical issues mentioned above, critical tangential load on both the sliders and the rails.

SUMMARY OF THE INVENTION



[0008] Accordingly, an object of the present invention is to provide a cost-effective and easy-to-implement solution to the problem of guiding means misalignment and thermal expansion for linear guiding systems.

[0009] For this purpose, it is proposed according to a first aspect of the invention a deviation compensating device for mechanically connecting a carriage to at least one slider slidably mounted on linear guiding means, and comprising resilient attaching means for connecting a slider upper part to a carriage lower part opposite to said slider upper part. The resilient attaching means comprise a first set of elastic fastening means vertically biasing said carriage lower part against said slider upper part with bearing means located between said carriage lower part and said slider upper part so that said carriage can pivot relatively to said slider at least around a longitudinal axis of said linear guiding means. The resilient attaching means comprise further a second set of elastic fastening means horizontally biasing said carriage lower part against said slider so that said carriage can move relatively to said slider at least along a horizontal transversal axis substantially perpendicular to said longitudinal axis.

[0010] Advantageously, the bearing means establish a linear contact or a point contact between said carriage lower part and said slider upper part.

[0011] Preferably, the bearing means comprise a cylinder located within a blind groove formed into either the carriage lower part or the slider upper part, or a ball located within a blind hole formed into either the carriage lower part or the slider upper part.

[0012] Alternatively, the bearing means comprise a cylindrical part or a spherical part protruding from either the carriage lower part or the slider upper part and in contact with the other one. The cylindrical part or spherical part is integral or mechanically attached to either the carriage lower part or the slider upper part.

[0013] Preferably, the first set of elastic fastening means comprises first attaching means mechanically attaching said slider upper part to said carriage lower part, wherein said carriage can move relatively to said slider within a delimited displacement range at least along a vertical axis perpendicular to a plan formed by said horizontal transversal axis and said longitudinal axis. The first set of elastic fastening means comprises further first spring means cooperating with said first attaching means for pressing the carriage lower part against said slider upper part.

[0014] Preferably, the first attaching means are at least one screw and said first spring means are at least one spring washer compressed by the at least one screw.

[0015] Advantageously, the second set of elastic fastening means comprises a carriage shoulder formed on the carriage lower part and extending substantially parallel to the longitudinal axis along a first side of the slider upper part, and second spring means pressing said slider against said shoulder.

[0016] Preferably, said second set of elastic fastening means comprise further a slider bracket attached to the carriage lower part and extending substantially parallel to the longitudinal axis along a second side of the slider upper part opposite to said first side of the slider upper part.

[0017] Preferably, the second spring means are at least one compression spring located between said slider bracket and said slider.

[0018] Advantageously, the first attaching means pass through at least one hole formed in said carriage lower part or in said slider upper part which is shaped for enabling the carriage to move respectively to the slider at least in the horizontal transversal direction.

[0019] Advantageously, the carriage lower part is integrally formed with the carriage or mechanically fixed to said carriage.

[0020] According to a second aspect of the invention, it is proposed a linear guiding system along a longitudinal axis comprising linear guiding means arranged parallel to the longitudinal axis, and a carriage slidably connected to said linear guiding means for moving along said longitudinal axis. The carriage is mechanically connected to at least one slider by one deviation compensating device as defined above wherein said slider slides along said linear guiding means.

[0021] Advantageously, the carriage is mechanically slidably connected to said linear guiding means by two sliders spaced apart from each other along said longitudinal axis.

[0022] Preferably, the linear guiding means are formed by a guiding rail, and the slider is a recirculating ball bearing slider interacting with said guiding rail.

[0023] Advantageously, the linear guiding system as defined above comprises a worktable attached to two carriages slidably connected to one pair of substantially parallel linear guiding means.

BRIEF DESCRIPTION OF THE FIGURES



[0024] Other features and advantages of the present invention will emerge from the following description of embodiments of the invention provided as non-limiting examples for achieving various aspects of the invention. The description refers to the attached figures which illustrate, also by way of example, embodiments of the different invention aspects:
  • Figure 1 illustrates a perspective view of a carriage of a linear guiding system;
  • Figure 2 shows a cross section view of the carriage of the linear guiding system at the level of a slider;
  • Figures 3a illustrates the compensation of parallelism deviation between the working platform and the substructure;
  • Figure 3b illustrates the compensation of height deviation between the guiding rails; and
  • Figures 4a and 4b illustrate the compensation of horizontal deviation between the guiding rails.


[0025] For the reader's convenience, identical or similar elements bear the same reference over the whole figures set.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT



[0026] Figure 1 shows part of a linear guiding system 1, also known as a linear axis, comprising a carriage 4 presenting bracketing grooves 3 for securing a worktable 2 on the carriage 4 as shown in figures 3b and 4b. In general the worktable 2 is secured to two carriages 4 arranged parallel as explained below in relation with figures 3b and 4b.

[0027] A carriage lower part 5 extends downwardly the carriage 4 and has the shape of reversed T. The carriage lower part 5 presents a mounting flange 6 facing down for attaching at least one slider 7, here two sliders 7, to the carriage 4. Each slider 7 presents a slider upper part 9 secured to the mounting flange 6 of the carriage 4 by four mounting screws 8 arranged vertically. Said mounting screws 8 can be screwed either into said slider upper part 9 (as shown in figures 1 and 2), or screwed into said carriage lower part 5 (not shown). Alternatively, a linear guiding system can comprise two carriages 4 each attached to one slider 7 and arranged one behind the other along a longitudinal axis X (embodiment not shown).

[0028] Each slider 7 is slidably mounted on a linear guiding rail 10 (shown in figure 2) which is attached to a substructure 11 as shown in figure 2. The slider 7 and linear guiding rail 10 present complementary guiding surfaces so that the carriage 4 can only slide along the guiding rail 10 in the direction of the longitudinal axis X. An electric motor, for example a servo motor (not shown), drives the carriage 4 along the longitudinal axis X through a mechanical transmission such as a screw-nut system, a belt transmission, or a rack-and-pinion transmission (not shown). Said at least one slider 7 aims at reducing significantly friction on the guiding rail 10. Therefore, said at least one slider 7 can be for example a recirculating ball bearing slider .

[0029] As shown in the detail view in figure 2, the mounting screws 8 are screwed into vertical threaded blind holes 12 formed in the slider upper part 9. Said mounting screws 8 go through vertical holes 13 formed in the mounting flange 6. The head of the mounting screws 8 compress at least one spring washer 14 against the upper face of the carriage lower part 5. This arrangement enables said carriage 4 to move along a vertical axis Z within a displacement range delimited by the head of the mounting screws 8. Said vertical axis Z is perpendicular to a plan formed by said longitudinal axis X and a horizontal transversal axis Y. Figure 2 shows sets of two opposed spring washers 14 compressed by the mounting screws 8. However, according to the technical context, there could be only one or more than two spring washers for each mounting screw 8. In addition a regular washer 15 is inserted between the mounting flange 6 and the lowest spring washer 14. The mounting screw 8 comprises a cylindrical portion 16 passing through the vertical hole 13 and separated from the threaded part of the mounting screw 8 by a screw shoulder 17 pressing on the slider upper part 9 when the mounting screw 8 is tight. The inner diameter of the vertical hole 13 is larger than the outed diameter of the cylindrical portion 16 so that the carriage 4 can move in a limited displacement range with respect to the slider 7. Moreover, a cylindrical bearing 18 is located within a blind groove 19 formed through the mounting flange 6 of the carriage lower part 5. The cylindrical bearing 18 is arranged horizontally and parallel to the longitudinal axis X. When the carriage 4 is attached to the slider 7, the cylindrical bearing 18 is pinched between the carriage 4 and the slider 7 so that the flange 6 is spaced apart from the slider upper part 9. In addition, a friction pad 20 can be inserted between the cylindrical bearing 18 and the bottom of the blind groove 19.

[0030] As shown in figure 3a, the cylindrical bearing 18 can be replaced by a cylindrical protrusion 18a protruding from the mounting flange 6 and resting on the slider upper part 9. Here, the cylindrical protrusion 18a is integral to the carriage lower part 5. Alternatively, it can be formed as a separated element secured to the mounting flange 6. The combination of the spring washers 14 (or the vertical compression springs 14a) and the gaps between, on one hand, the vertical holes 13 and the cylindrical portion 16, and, on the other hand, the mounting flange 6 and the slider upper part 9 enables the carriage to pivot around the cylindrical protrusion 18a (or cylindrical bearing 18) with respect to slider 7 as shown by pivoting arrow 22.

[0031] Besides, the cylindrical bearing 18 can be replaced by a ball bearing (not shown) located in a blind hole formed into the carriage lower part so that, if required, the carriage 4 can pivot more or less in all directions around a ball joint with respect to the slider 7.

[0032] As shown in figure 3b, when the worktable 2 is secured on two parallel linear guiding systems 1, a height deviation 21 can occur between the substructures 11 on which the linear guiding rails 10 of the linear guiding systems 1 are mounted. The pivoting of the carriage 4 with respect slider 7 around the longitudinal axis X of each linear guiding systems 1 avoids that mechanical constraints are induced in the linear guiding systems 1 by the torque around longitudinal axis X resulting from the height deviation 21.

[0033] As shown in figures 2 and 4a, the slider 7 is horizontally clamped with respect to the carriage lower part 5 between a carriage shoulder 23 and a slider bracket 24. The shoulder 23 extends on one side of the slider 7 vertically downwardly from the mounting flange 6 and horizontally along the side of the carriage upper part 6 parallel to the longitudinal axis X. The slider bracket 24 extends along the other side of the slider 7 opposite to the side facing the carriage shoulder 23, and parallel to the longitudinal axis X. Horizontal compression springs 25 are located in a lateral groove 26 formed in the slider bracket 24 (see figure 2). The lateral groove 26 extends horizontally and faces the slider 7 so that the horizontal compression springs 25 are compressed between the bottom of said lateral groove 26 and the side of the slider 7 by bracketing screws 27 (shown in figure 1) securing the bracket 24 on the carriage lower part 5.

[0034] The spacing between the linear guiding rail can vary along their length resulting in transversal strengths acting along said horizontal transversal axis Y and shown by transversal arrow 28 in figure 4a. These transversal strengths generate transversal shifts of the carriage 4 with respect to the slider 7 by compressing the horizontal compression springs 25 of one or the other linear guiding systems 1 as shown in figure 4a and generating a transversal gap 29 between the carriage shoulder 23 and the side of the slider 7.

[0035] In general, significant amount of heat is generated in the operational environment of the linear guiding systems 1, in particular heat emitted by the electric motor driving the carriages 4. This heat generates thermal expansion also inducing transversal strengths between the carriage 4 and the slider 7.

[0036] Therefore, the transversal effort generated by both the thermal expansion and the lateral rail misalignment causes the carriages 4 of the two linear guiding systems 1 either to move away one from another as shown in the upper part of figure 4b, or to come closer one to another as shown in the lower part of figure 4b.

[0037] As shown in the upper part of figure 4b, when the carriages 4 tend to move away one from another, the carriage shoulder 23 of the right linear guiding system 1 is pressed against the respective side of the slider 7, while the carriage shoulder 23 of the left linear guiding system 1 is separated from the respective side of the slider 7 by transversal gap 29. On the contrary, when the carriages 4 tend to come closer one to another, as shown in the lower part of figure 4b, the carriage shoulder 23 of the left linear guiding system 1 is pressed against the respective side of the slider 7, while the carriage shoulder 23 of the right linear guiding system 1 is separated from the respective side of the slider 7 by transversal gap 29.

[0038] The ability of the carriage 4 of the linear guiding systems 1 to shift laterally in the direction of said horizontal transversal axis Y avoids that shear strengths are exerted on the linear guiding systems 1 between the carriage 4 and the slider 7.

[0039] The above description and the figures show different embodiments of the specific aspects of the invention, in particular the carriage 4 is slidably connected to the linear guiding rail 10 by two sliders 7 and one worktable 2 secured to two carriages 4, they could be configured and implemented in other ways and in different contexts such as, for example, a combination of linear guiding systems where the carriages are slidable along different axes such as longitudinal axis X, horizontal transversal axis Y and vertical axis Z. Besides, the carriage 4 of the linear guiding system 1 could be slidably connected to the linear guiding rail by only one slider or more than two. The carriage lower part 5 could be split two separated pieces, one per slider 7. The spring washers 14 could be inserted between the mounting flange 6 of the carriage 4 and the slider upper part 9. Furthermore, said at least one slider 7 can use different ball bearing arrangement than the recirculating ball bearing, or even gliding pads made of PTFE.


Claims

1. Deviation compensating device for mechanically connecting a carriage (4) to at least one slider (7) slidably mounted on linear guiding means (10), and comprising:

- resilient attaching means for connecting a slider upper part (9) to a carriage lower part (5) opposite to said slider upper part (9);

characterised in that said resilient attaching means comprise:

- a first set of elastic fastening means (8, 14) vertically biasing said carriage lower part (5) against said slider upper part (9) with bearing means (18, 18a) located between said carriage lower part (5) and said slider upper part (9) so that said carriage (4) can pivot relatively to said slider (7) at least around a longitudinal axis (X) of said linear guiding means (1); and

- a second set of elastic fastening means (23, 24, 25) horizontally biasing said carriage lower part (5) against said slider (7) so that said carriage (1) can move relatively to said slider (3) at least along a horizontal transversal axis (Y) substantially perpendicular to said longitudinal axis (X).


 
2. Deviation compensating device according to claim 1, wherein:

- said bearing means (18, 18a) establish a linear contact or a point contact between said carriage lower part (5) and said slider upper part (9).


 
3. Deviation compensating device according to claim 2, characterised in that said bearing means (18, 18a) comprise:

- a cylinder (18) located within a blind groove (19) formed into either the carriage lower part (5) or the slider upper part (9); or

- a ball located within a blind hole formed into either the carriage lower part (5) or the slider upper part (9).


 
4. Deviation compensating device according to claim 2, wherein:

- said bearing means comprise a cylindrical part (18a) or a spherical part protruding from either the carriage lower part (5) or the slider upper part (9) and in contact with the other one; and

- said cylindrical part (18a) or spherical part is integral or mechanically attached to either the carriage lower part (5) or the slider upper part (9).


 
5. Deviation compensating device according to any one of the preceding claims, wherein said first set of elastic fastening means (8, 14) comprise

- first attaching means (8) mechanically attaching said slider upper part (9) to said carriage lower part (5), wherein said carriage (1) can move relatively to said slider (3) within a delimited displacement range at least along a vertical axis (Z) perpendicular to a plan formed by said horizontal transversal axis (Y) and said longitudinal axis (X); and

- first spring means (14, 14a) cooperating with said first attaching means (8) for pressing the carriage lower part (5) against said slider upper part (9).


 
6. Deviation compensating device according to claim 5, wherein said first attaching means are at least one screw (8) and said first spring means are at least one spring washer (14) compressed by the at least one screw (8).
 
7. Deviation compensating device according to any one of the preceding claims, wherein said second set of elastic fastening means comprise

- a carriage shoulder (23) formed on the carriage lower part (5) and extending substantially parallel to the longitudinal axis (X) along a first side of the slider upper part (9) ; and

- second spring means (25) pressing said slider (7) against said shoulder (23).


 
8. Deviation compensating device according to claim 7, wherein said second set of elastic fastening means comprises further:

- a slider bracket (24) attached to the carriage lower part (5) and extending substantially parallel to the longitudinal axis (X) along a second side of the slider upper part (9) opposite to said first side of the slider upper part (9).


 
9. Deviation compensating device according to claim 8, wherein said second spring means are at least one compression spring (25) located between said slider bracket (24) and said slider (7).
 
10. Deviation compensating device according to any one of the claims 5 to 9, wherein said first attaching means (8) pass through at least one hole (13) formed in said carriage lower part (5) or in said slider upper part (9) which is shaped for enabling the carriage (4) to move respectively to the slider (7) at least in the horizontal transversal direction (Y).
 
11. Deviation compensating device according to any one of the preceding claims, wherein said carriage lower part (5) is integrally formed with the carriage (4) or mechanically fixed to said carriage (4).
 
12. Linear guiding system along a longitudinal axis (X) comprising:

- linear guiding means (10) arranged parallel to the longitudinal axis (X); and

- a carriage (4) slidably connected to said linear guiding means (10) for moving along said longitudinal axis (X);

- characterised in that said carriage (4) is mechanically connected to at least one slider (7) by one deviation compensating device as defined in any one of the preceding claims; wherein said slider (7) slides along said linear guiding means (10).


 
13. Linear guiding system according to claim 12, wherein:

- said carriage (4) is mechanically slidably connected to said linear guiding means (10) by two sliders (7) spaced apart from each other along said longitudinal axis (X).


 
14. Linear guiding system according to claim 12 or 13, wherein:

- said linear guiding means are formed by a guiding rail (10); and

- said slider (7) is a recirculating ball bearing slider interacting with said guiding rail (10).


 
15. Linear guiding system according to any one of the claims 12 to 14, comprising:

- a worktable (2) attached to two carriages (4) slidably connected to one pair of substantially parallel linear guiding means (10).


 




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