TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to linear guide way arrangement for use e.g. in a linear module powered by a belt, a pair of cables or a drive screw.

BACKGROUND ART

[0002] Prior art document US 3,998,497 discloses a linear guideway arrangement for guiding a carriage along a linear path defined by first and second horizontal parallel guide rods. First and second roller assemblies are fixed to the carriage and rollingly connect the carriage to the first guide rod. A third roller assembly fixed to the other side of the carriage rollingly connects the carriage to the second guide rod. The third roller assembly comprises a shaft fixed to the carriage and a roller carried by the shaft, which rollingly rides on the top of the second guide rod. The first and second roller assemblies each comprise a shaft fixed to the carriage carrying first and second rollers spaced from each other along the shaft. The first and second rollers straddle the top of the first guide rod and rollingly ride on the upper surface thereof. The apparatus further comprises a shaft fixed to the carriage and which carries a roller, the top of which rollingly engages with the lower surface of the first guide rod. In order to avoid undesired play between the rollers and guide rods, the carriage has to be mounted on the guide rods with some interference, which results in excessive and uncontrolled friction and wear between the rollers and the guide rods.

[0003] US 6,648,508 discloses a linear guide comprises a travelling carriage having track rollers for support and for rolling along a guide rail, said track rollers, each of which rolls on the guide rail, being mounted in pairs for rotation on a first support that is arranged on a first carriage plate of the travelling carriage. The travelling carriage comprises a further carriage plate with a second support arranged thereon, and track rollers rotatably mounted on said second support for rolling on a further guide rail, the two guide rails being parallel to each other and fixed on two longitudinal sides of a central rail support. This system makes it possible to adjust tolerances in one direction transverse to the translation direction, but not in other directions. Moreover, it cannot guarantee equal load capacity in all directions due to tolerances and adjustment problems during assembling.

SUMMARY OF THE INVENTION

[0004] The invention aims at solving the above-described problems. [0005] According to a first aspect of the invention, there is provided a linear guideway arrangement comprising:

- two pairs of guide rods, each one of the pairs of guide rods comprising a first and a second guide rod parallel to a translation axis of the linear guideway arrangement and spaced apart from the first and second guide rods of the other one of the two pairs of guide rods in a first transverse direction perpendicular to the translation axis;

- a carriage comprising central part and at least two legs spaced apart from one another in the first transverse direction, each of the two legs corresponding to one of the two pairs of guide rods, each of the two legs comprising at least one set of first rollers rolling on the first guide rod of the corresponding pair of guide rods, the set of first rollers comprising at least one first roller rotating about a first rotation axis fixed relative to the carriage and perpendicular to the translation axis, each of the two legs being provided with at least one rolling shoe comprising with at least one set of second rollers rolling on the second rod of the corresponding pair of rods, the set of second rollers comprising at least one second roller rotating about a second rotation axis fixed relative to the rolling shoe and perpendicular to the translation axis, the rolling shoe of each of the two legs being moveable with respect to the carriage in a protruding direction perpendicular to the translation axis towards the second guide rod of the corresponding pair of guide rods between a retracted and a protruding positions, the arrangement being further provided with releasable fastening means for releasably fastening the rolling shoe of each of the two legs relative to the carriage in any intermediate position between the retracted and protruding positions.

[0006] Thanks to the screws, it is possible to adjust the position of the rolling shoe with respect to the carriage so that a controlled contact pressure is ensured between the rollers and guide rods.

[0007] According to one embodiment, the releasable fastening means include screws.

[0008] According to a preferred embodiment, each rolling shoe is provided with biasing means for biasing the rolling shoed towards the second guide rod in the protruding direction.

[0009] According to one embodiment, the biasing means include springs.

[0010] For each of the two legs, the first rotation axis is preferably parallel to the second rotation axis.

[0011] Each of the two pairs of guide rods defines a corresponding reference plane, each reference plane containing the guide rods of the corresponding pair of guide rods. This reference plane is preferably perpendicular to the rotation axes of the leg rollers and of the shoe roller rolling on the guide rods of the corresponding pair of guide rods.

[0012] According to a preferred embodiment, the reference planes of the two pairs of guide rods are an angle relative to one another. In particular, the reference planes of the two pairs of guide rods can be perpendicular to one another.

[0013] According to a preferred embodiment, the first guide rods of the two pairs of guide rods are closer to one another than the second guide rods of the two pairs of guide rods. [0014] According to a preferred embodiment, the two pairs of guide rods define a plane of symmetry parallel to the translation axis, the first rods of the two pairs of rods being on each side of and at equal distance from the plane of symmetry, the second rods of the two pairs of rods being on each side of and at equal distance from the plane of symmetry. According to a preferred embodiment, the plane of symmetry is a vertical plane and the first rods of the two pairs of guide rods are above the second guide rods of the two pairs of guide rods. [0015] According to a preferred embodiment, each set of first rollers comprises at least two first rollers rotating about two first rotation axes fixed relative to the carriage, perpendicular to the translation axis and spaced apart from one another along the translation axis.

[0016] According to a preferred embodiment, each set of second rollers comprises two second rollers rotating about two second rotation axes fixed relative to the rolling shoe, perpendicular to the translation axis and spaced apart from one another along the translation axis.

DESCRIPTION OF THE DRAWINGS

[0017] Other advantages and features of the invention will then become more clearly apparent from the following description of a specific embodiment of the invention given as a non-restrictive example only and represented in the accompanying drawings in which:

- figure 1 is a diagrammatic illustration of a guideway arrangement according to an embodiment of the invention; - figure 2 is a cross-section of the guideway arrangement of figure 1;

- figure 3 is a detail of a leg and a shoe of the guideway arrangement of figure 1;

- figure 4 is a side view of a leg of the guideway arrangement of figure 1;

- figure 5 is a section along the line V-V of figure 4. [0018] Throughout the description and drawings, identical reference numbers will be used to indicate identical or similar elements.

DETAILED DESCRIPTION OF A PREFERED EMBODIMENT [0019] With reference to Figure 1, a linear guideway arrangement 10 comprises a frame 12 made of an extruded aluminium profile. The frame 12 is provided with a central track 14 for receiving e.g. a drive screw or a drive belt and two lateral tracks 16 on each side of the central track 14. Each lateral track 16 is provided with a pair of guide rods 18, 20. The guide rods 18, 20 are parallel to a translation axis 22 of the linear guideway arrangement. Each pair of guide rods includes a first, upper guide rod 18 and a second, lower guide rod 20. A plane of symmetry 24 can be defined, which is at mid distance between the two pairs of guide rods 18, 20. The first guide rods 18 of the two tracks 16 are spaced apart from one another on each side of and at equal distance from the plane of symmetry. Similarly, the second guide rods 20 are spaced apart from one another on each side of and at equal distance from the plane of symmetry. For each track 16, a reference plane 26 can be defined, which is parallel to the translation axis 22 and contains a centre line of the respective first and second guide rods 18, 20. The two planes 26 are at an angle relative to one another, preferably between 60° and 120°, e.g. a right angle.

[0020] A carriage 28 is mounted on the guideway frame 12 for moving fore and aft parallel to the translation axis 22. The carriage 28 includes a central plate 30 and two legs 32 on each side of the central plate 30. The central plate 30 and the two legs 32 form a rigid, i.e. non-deformable structure. Each of the two legs 32 is received in a corresponding one of the two tracks 16 as will be explained hereinafter.

[0021] Each leg 32 comprises a set 34 of first rollers, in the present case a set of two first rollers 34.1, 34.2, rolling on the first guide rod 18 of the corresponding track 16. The first rollers of each leg 32 have rotation axes 36.1, 36.2 that are fixed relative to the respective leg 32, spaced apart from one another and perpendicular to the reference plane 26 of the respective leg 32.

[0022] Each leg 32 comprises a cavity 38 for receiving a guide shoe 40 provided with a set 42 of second rollers, in the present case of two second rollers 42.1, 42.2, rolling on the second guide rod 20 of the corresponding track 16. The second rollers 42.1, 42.2 of each leg 32 have rotation axes 44.1, 44.2 that are fixed relative to the respective leg 32, spaced apart from one another and perpendicular to the reference plane 26 of the respective leg 32. [0023] The cavity 38 of each leg has side walls 38.1 for guiding the guide shoe 40 in a protruding direction perpendicular to the first and second guide rods 18, 20 and to the first and second rotation axes 36.1, 36.2, 44.1, 44.2. A compression spring 46 is loaded in the cavity 38 for pressing the second rollers 42.1, 42.2 of the guide shoe 40 against the second guide rod 20 and away from the first rollers 34.1, 34.2 and first guide rod 18.

[0024] A set of axial clamping screws 48 is provided for fastening each guide shoe 40 in the cavity 38 of the associated leg 32. Each screw 48 is received in through hole 50, 52 having a slightly larger diameter than the associated screw 48, so as to allow a limited freedom of motion of the guide shoe 40 in the cavity 38 as long as the screws 48 are not tightened. Hence, when the screws are loosened, each of the guide shoes 40 is free to move at least in the protruding direction parallel to the reference plane 26 of the associated leg 32 and perpendicular to the rotation axes 36.1, 36.2, 44.1, 44.2 between a fully retracted position close to the first rollers 34.1, 34.2 and a protruding position away from the first rollers 34.1, 34.2.

[0025] Before assembly of the guideway arrangement, each guide leg 32 forms a preassembled subunit with its guide shoe 40 retained in the cavity 38 by the axial clamping screws and the loaded spring. The guide shoe 40 is pushed in its retracted position against the biasing force of the spring 46 and the screws 48 are tightened to keep this position. The carriage 28 is easy to insert into the frame. Once the legs 32 are in place into the respective lateral tracks 16, the screws 48 are loosened. The springs 46 automatically push the roller shoes 40 towards the protruding position in the protruding direction, until the second rollers 42., 42.2 engage with the second rods 20 at the appropriate contact pressure defined by the spring 46. The screws 48 are then tightened once again, to secure the position of each rolling shoe 40 relative to the associated leg 32. At the end of this step, the assembly of the guideway arrangement 10 is complete.

[0026] Various modifications are possible without departing from the scope of the appended claims. [0027] The guide rods illustrated in the drawings have a circular cross-section. However, other cross-sectional shapes are possible. The shape of the rollers, which in the drawings include a central groove, may be changed accordingly.

[0028] While the carriage has been described with two legs 32, each provided with one rolling shoe 40, it is to be understood that the number of legs 32 and rolling shoes may vary.

[0029] The intersecting reference planes 26 of the two legs are preferred in all situations in which loads or vibrations in several directions perpendicular to the fore and aft direction of the rods is to be expected. The two pairs of guide rods 18, 20 may be coplanar, i.e. on one and the same reference plane 26. Such an embodiment will be preferred if no load is expected on the carriage perpendicular to the reference plane 26. According to another embodiment, the reference planes 26 of the two legs can be parallel to one another, if no lateral load perpendicular to the reference planes is expected. [0030] Each set 34, 42 of rollers may have one or more rollers.

[0031] The screws can be replaced with other fastening means, e.g. a rotating key.

[0032] The same principle may be used with three guide rods.