Arrangement for Limiting Rotation, and Robot

Abstract

An arrangement for limiting rotation, the arrangement including a base structure; a drive member rotatable relative to the base structure and having a drive feature; a stopping member having at least one driven feature, wherein the stopping member is arranged to be intermittently driven relative to the base structure between a plurality of discrete positions by a continuous rotation of the drive member and by cooperation between the drive feature and at least one driven feature, wherein the stopping member in a first end discrete position is arranged to limit rotation of the drive member in a first end position of a rotation range of the drive member; and a holding mechanism arranged to hold the stopping member in each discrete position, the holding mechanism being at least partly provided in the base structure.

Claims

1. An arrangement for limiting rotation, comprising: a base structure; a drive member rotatable relative to the base structure about a drive axis, the drive member having a drive feature offset from the drive axis; a stopping member having at least one driven feature, wherein the stopping member is arranged to be intermittently driven relative to the base structure between a plurality of discrete positions by a continuous rotation of the drive member and by cooperation between the drive feature and at least one driven feature, wherein the stopping member in a first end discrete position a is arranged to limit rotation of the drive member in a first end position of a rotation range of the drive member and in a second end discrete position is arranged to limit rotation of the drive member in a second end position, of the rotation range; and a holding mechanism arranged to hold the stopping member in each discrete position the holding mechanism being at least partly provided in the base structure.

2. The arrangement according to claim 1, wherein the holding mechanism includes at least one magnet arranged to hold the stopping member in each discrete position by magnetic force.

3. The arrangement according to claim 1, wherein the stopping member is rotatable about a stopping axis.

4. The arrangement according to claim 3, further comprising a plain bearing, wherein the stopping member is rotatably supported about the stopping axis by the plain bearing.

5. The arrangement according to claim 3, wherein the stopping member includes a stopping feature, wherein the stopping feature and the stopping axis are substantially positioned on a line deviating at most 30, such as at most 20 or at most 10, from a tangential line at the drive feature with respect to the drive axis when the stopping member is in the first end discrete position and the drive member is in the first end position.

6. The arrangement according to claim 1, wherein the drive feature is positioned on a drive member surface of the drive member, and wherein a distance from the drive axis to the drive feature is at least 80% of a distance from the drive axis to a radially outermost position of the drive member surface with respect to the drive axis.

7. The arrangement according to claim 1, wherein the drive feature includes a drive pin.

8. The arrangement, according to claim 1, wherein the stopping member is made of plastic.

9. The arrangement according to claim 1, further comprising a cable fixed with respect to each of the base structure and the drive member.

10. The arrangement according to claim 9, further comprising a driven motor fixed with respect to the drive member, wherein the cable is fixedly connected to the driven motor.

11. The arrangement a according to claim 1, further comprising a drive motor arranged to drive the drive member about the drive axis, wherein the drive motor is positioned radially inside the drive feature with respect to the drive axis.

12. A robot comprising an arrangement for limiting rotation, including: a base structure: a drive member rotatable relative to the base structure about a drive axis, the drive member having a drive feature offset from the drive axis; a stopping member having at least one driven feature, wherein the stopping member is arranged to be intermittently driven relative to the base structure between a plurality of discrete positions by a continuous rotation of the drive member and by cooperation between the drive feature and at least one driven feature, wherein the slopping member in a first end discrete position is arranged to limit rotation of the drive member in a first end position of a rotation range of the drive member, and in a second end discrete position is arranged to limit rotation of the drive member in a second end position of the rotation range; and a holding mechanism arranged to hold the stopping member in each discrete position, the holding mechanism being at least partly provided in the base structure.

13. The robot according to claim 12, wherein the robot is an automated guided vehicle, AGV, having at least one wheel unit including a traction wheel rotatable about the drive axis and about a wheel axis perpendicular to the drive axis.

14. The arrangement according to claim 2, wherein the stopping member is rotatable about a stopping axis.

15. The arrangement according to claim 2, wherein the drive feature is positioned on a drive member surface of the drive member, and wherein a distance from the drive axis to the drive feature is at least 80% of a distance from the drive axis to a radially outermost position of the drive member surface with respect to the drive axis.

16. The arrangement according to claim 2, wherein the drive feature includes a drive pin.

17. The arrangement according to claim 2, wherein the stopping member is made of plastic.

18. The arrangement according to claim 2, further comprising a cable fixed with respect to each of the base structure and the drive member.

19. The arrangement according to claim 2, further comprising a drive motor arranged to drive the drive member about the drive axis, wherein the drive motor is positioned radially inside the drive feature with respect to the drive axis.

20. The arrangement according to claim 4, wherein the stopping member includes a stopping feature, wherein the stopping feature and the stopping axis are substantially positioned on a line deviating at most 30, such as at most 20 or at most 10, from a tangential line at the drive feature with respect to the drive axis when the stopping member is in the first end discrete position and the drive member is in the first end position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Further details, advantages and aspects of the present disclosure will become apparent from the following description taken in conjunction with the drawings, wherein:

[0026] FIG. 1: schematically represents a perspective view of a robot comprising a plurality of wheel units each having an arrangement for limiting rotation;

[0027] FIG. 2: schematically represents a perspective view of one of the wheel units;

[0028] FIG. 3: schematically represents a perspective view of the arrangement;

[0029] FIG. 4: schematically represents a top view of the arrangement when a drive member is in a first end position and a stopping member is in a first end discrete position;

[0030] FIG. 5: schematically represents a top view of the arrangement when the drive member has rotated from the first end position;

[0031] FIG. 6: schematically represents a top view of the arrangement when the drive member has rotated further and the stopping member has moved to an intermediate discrete position;

[0032] FIG. 7: schematically represents a top view of the arrangement when the drive member has rotated further;

[0033] FIG. 8: schematically represents a top view of the arrangement when the drive member has rotated further and the stopping member has moved to a second end discrete position;

[0034] FIG. 9: schematically represents a top view of the arrangement when the drive member has rotated further to a second end position;

[0035] FIG. 10: schematically represents a top view of a further example of an arrangement for limiting rotation when a drive member is in a first end position and a stopping member is in a first end discrete position;

[0036] FIG. 11: schematically represents a top view of the arrangement in FIG. 10 when the drive member has rotated from the first end position;

[0037] FIG. 12: schematically represents a top view of the arrangement in FIGS. 10 and 11 when the drive member has rotated further and the stopping member has moved to a first intermediate discrete position;

[0038] FIG. 13: schematically represents a top view of the arrangement in FIGS. 10 to 12 when the drive member has rotated further;

[0039] FIG. 14: schematically represents a top view of the arrangement in FIGS. 10 and 13 when the drive member has rotated further and the stopping member has moved to a second intermediate discrete position;

[0040] FIG. 15: schematically represents a top view of the arrangement in FIGS. 10 to 14 when the drive member has rotated further;

[0041] FIG. 16: schematically represents a top view of the arrangement in FIGS. 10 to 15 when the drive member has rotated further and the stopping member has moved to a second end discrete position;

[0042] FIG. 17: schematically represents a top view of the arrangement in FIGS. 10 to 16 when the drive member has rotated further to a second end position;

[0043] FIG. 18: schematically represents a top view of a joint having limited rotation according to the prior art;

[0044] FIG. 19: schematically represents a top view of a further example of a joint having limited rotation according to the prior art; and

[0045] FIG. 20: schematically represents a top view of a Geneva stopwork according to the prior art.

DETAILED DESCRIPTION

[0046] In the following, an arrangement for limiting rotation, and a robot comprising such arrangement, will be described. The same or similar reference numerals will be used to denote the same or similar structural features.

[0047] FIG. 1 schematically represents a perspective view of a robot, here exemplified as an automated guided vehicle, AGV, 46. The AGV 46 comprises a plurality of wheel units 48a-48d, here four wheel units 48a-48d. Each wheel unit 48a-48d comprises an arrangement for limiting rotation. In FIG. 1, only one such arrangement 50a for the first wheel unit 48a is denoted.

[0048] The first wheel unit 48a comprises a first traction wheel 52a, the second wheel unit 48b comprises a second traction wheel 52b, the third wheel unit 48c comprises a third traction wheel 52c, and the fourth wheel unit 48d comprises a fourth traction wheel 52d. Although the AGV 46 in FIG. 1 comprises four wheel units 48a-48d, the AGV 46 may alternatively comprise less than four wheel units or more than four wheel units. The traction wheels 52a-52d are configured to drive the AGV 46 on a surface, such as a horizontal floor. FIG. 1 further shows a Cartesian coordinate system X, Y, Z for referencing purposes. The horizontal surface may lie in the XY-plane.

[0049] The AGV 46 further comprises a platform 54. The platform 54 is one example of a base structure according to the present disclosure. The platform 54 is rigid. The platform 54 provides a support surface on its upper side for carrying a load, such as a robotic manipulator.

[0050] The AGV 46 further comprises a control system 56. The control system 56 comprises a data processing device 58 and a memory 60 having a computer program stored thereon. The control system 56 is configured to control movements of the traction wheels 52a-52d. In this example, the control system 56 is provided in the platform 54. The control system 56 is in signal communication with each wheel unit 48a-48d. The control system 56 may also comprise a battery (not shown) for powering each wheel unit 48a-48d.

[0051] FIG. 2 schematically represents a perspective view of the first wheel unit 48a. In this example, all wheel units 48a-48d are of the same design. In addition to the first traction wheel 52a, the first wheel unit 48a comprises a drive member 62a. The first wheel unit 48a of this example further comprises a steering member 64 fixed to the drive member 62a. The first traction wheel 52a is rotatable relative to the steering member 64 about a wheel axis 66. The drive member 62a is rotatable about a drive axis 68, here exemplified as a steering axis. The wheel axis 66 is perpendicular to the drive axis 68. Moreover, the wheel axis 66 intersects the drive axis 68. In FIG. 2, the wheel axis 66 is horizontal and the drive axis 68 is vertical.

[0052] The first wheel unit 48a further comprises an electric drive motor 70a. The drive motor 70a is arranged to rotationally drive the drive member 62a, and consequently also the first traction wheel 52a, about the drive axis 68. The drive motor 70a of this example is fixed to the platform 54.

[0053] The first wheel unit 48a further comprises an electric driven motor 70b. The driven motor 70b is arranged to rotationally drive the first traction wheel 52a about the wheel axis 66. The driven motor 70b of this example is fixed to the steering member 64.

[0054] The wheel axis 66 and the drive axis 68 provide two degrees of freedom for the first wheel unit 48a. As a result, the AGV 46 is configured to perform omni directional movements, i.e. it can move in any direction along a floor and can rotate in a controlled manner and independently from its translation along its path.

[0055] The arrangement 50a of this example further comprises a block 72. The block 72 is a further example of a base structure according to the present disclosure. The block 72 is fixed to the platform 54.

[0056] The arrangement 50a further comprises a stopping member 74a. In FIG. 2, the stopping member 74a is in an intermediate discrete position 76a.

[0057] The stopping member 74a is rotatable relative to the block 72 about a stopping axis 78. The stopping axis 78 is here parallel with the drive axis 68. The block 72 is positioned next to the stopping member 74a along the stopping axis 78.

[0058] The drive member 62a comprises a drive pin 80. The drive pin 80 is one example of a drive feature according to the present disclosure. The drive pin 80 is eccentric with respect to the drive axis 68. The drive pin 80 of this example protrudes from a drive member surface 82 on the drive member 62a in parallel with the drive axis 68 (upwards in FIG. 2). The drive member surface 82 is here transverse to the drive axis 68. As shown in FIG. 2, the drive motor 70a is positioned radially inside the drive pin 80 with respect to the drive axis 68.

[0059] As schematically illustrated in FIG. 2, cables 84 are routed from the control system 56, through the drive member 62a, and to the driven motor 70b in the steering member 64. First ends of the cables 84 are fixedly connected to the control system 56 and second ends of the cables 84 are fixedly connected to the driven motor 70b. In this way, slip rings can be avoided. The cables 84 may for example be signal cables and/or power cables. When the first traction wheel 52a rotates about the drive axis 68, the cables 84 are twisted. The arrangement 50a is configured to limit rotation of the drive member 62a about the drive axis 68 relative to the platform 54 to a predefined rotation range. The rotation range is set to limit the twisting of the cables 84 to a tolerable level.

[0060] The rotation range defined by the arrangement 50a may be determined based on the specific application, but should not exceed a critical range of twisting of the cables 84. A larger rotation range reduces the need for the AGV 46 of this example to stop and reorient the traction wheels 52a-52d.

[0061] In this implementation, the center of the drive member 62a is not accessible for cabling. As shown in FIG. 2, the cables 84 are routed through the drive member 62a offset from the drive axis 68.

[0062] FIG. 3 schematically represents a perspective view of the arrangement 50a. In FIG. 3, the block 72 is removed to improve visibility. The arrangement 50a comprises a holding mechanism 86. The holding mechanism 86 is configured to hold the stopping member 74a in each of a plurality of discrete positions, such as in the illustrated intermediate discrete position 76a.

[0063] The holding mechanism 86 of this specific example comprises three base magnets 88a-88c fixed to the block 72 and one stopping magnet 90 fixed to the stopping member 74a. The holding mechanism 86 is thereby partly arranged in the block 72 and decoupled from the drive member 62a. This enables a large area to be provided for the drive motor 70a radially inside of the drive pin 80. Moreover, since the stopping member 74a does not have to contact the drive member 62a to be held in its discrete positions, tolerances can be relaxed and friction can be reduced.

[0064] Each of the block 72 and the stopping member 74a may be a 3D printed plastic component. Optionally, the base magnets 88a-88c and the stopping magnet 90 may be embedded inside the block 72 and the stopping member 74a, respectively. As can be gathered from FIGS. 2 and 3, the stopping magnet 90 and base magnets 88a-88c are not visible from the exterior of the first wheel unit 48a.

[0065] In the intermediate discrete position 76a, the stopping magnet 90 is aligned with and attracted to the second base magnet 88b. In this way, the holding mechanism 86 holds the stopping member 74a in the intermediate discrete position 76a by magnetic force.

[0066] The stopping member 74a of this example further comprises two driven features 92a and 92b. The stopping member 74a may however comprise only one driven feature or more than two driven features. The driven features 92a and 92b are here exemplified as recesses, each configured to receive the drive pin 80.

[0067] The stopping member 74a of this example further comprises two stopping features 94a and 94b. The stopping member 74a may alternatively comprise only one stopping feature. The stopping features 94a and 94b are here exemplified as recesses, each configured to receive the drive pin 80. A damping layer (not shown) may be provided in each of the stopping features 94a and 94b and the driven features 92a and 92b to more smoothly receive the drive pin 80.

[0068] The arrangement 50a of this example comprises a plain bearing 96. The stopping member 74a is rotatable about the stopping axis 78 by means of the plain bearing 96.

[0069] FIG. 4 schematically represents a top view of the arrangement 50a. In FIG. 4, the drive member 62a is in a first end position 98a of the rotation range. The stopping member 74a is in a first end discrete position 100a. In the first end discrete position 100a, the stopping magnet 90 is aligned with and attracted to the first base magnet 88a. In this way, the holding mechanism 86 holds the stopping member 74a in the first end discrete position 100a by magnetic force. When the stopping member 74a is in the first end discrete position 100a and the drive member 62a is in the first end position 98a, the drive pin 80 is seated in the first stopping feature 94a, and the first stopping feature 94a, the stopping axis 78 and the drive pin 80 are positioned on a line 102a. The line 102a is angled less than 30 from a tangential line 103a at the drive pin 80 with respect to the drive axis 68. In FIG. 4, the line 102a is angled approximately 10 from the tangential line 103a. In this way, rotation of the drive member 62a (counterclockwise in FIG. 4) is stopped without generating any substantial torque on the stopping member 74a and without the stopping member 74a having to contact the drive member 62a (except the drive pin 80 thereof). FIG. 4 further shows that a radial distance from the drive axis 68 to the drive pin 80 is approximately 87% of a radial distance from the drive axis 68 to a radially outermost position of the drive member surface 82.

[0070] FIG. 5 schematically represents a top view of the arrangement 50a when the drive member 62a has rotated from the first end position 98a (clockwise in FIG. 5) as illustrated with arrow 104. The drive pin 80 moves along a circular drive path concentric with the drive axis 68.

[0071] When the drive member 62a has rotated almost a full turn about the drive axis 68, the drive pin 80 engages the first driven feature 92a. The rotation of the drive member 62a and the engagement between the drive pin 80 and the first driven feature 92a overcomes the magnetic holding force between the stopping magnet 90 and the first base magnet 88a, and causes the stopping member 74a to rotate (counterclockwise in FIG. 5) as illustrated with arrow 106.

[0072] FIG. 6 schematically represents a top view of the arrangement 50a when the drive member 62a has rotated further. The stopping member 74a has now been rotated to the intermediate discrete position 76a where the stopping magnet 90 is aligned with and attracted to the second base magnet 88b. The arrangement 50a is thus configured to transmit a continuous rotation of the drive member 62a to an intermittent rotation of the stopping member 74a.

[0073] FIG. 7 schematically represents a top view of the arrangement 50a when the drive member 62a has rotated further. In FIG. 7, the drive pin 80 now engages the second driven feature 92b. The rotation of the drive member 62a and the engagement between the drive pin 80 and the second driven feature 92b overcomes the magnetic holding force between the stopping magnet 90 and the second base magnet 88b, and causes the stopping member 74a to again rotate (counterclockwise in FIG. 7) as illustrated with arrow 106.

[0074] FIG. 8 schematically represents a top view of the arrangement 50a when the drive member 62a has rotated further. The stopping member 74a has now been rotated to a second end discrete position 100b. In the second end discrete position 100b, the stopping magnet 90 is aligned with and attracted to the third base magnet 88c.

[0075] FIG. 9 schematically represents a top view of the arrangement 50a when the drive member 62a has rotated further to a second end position 98b of the rotation range. When the stopping member 74a is in the second end discrete position 100b and the drive member 62a is in the second end position 98b, the drive pin 80 is seated in the second stopping feature 94b, and the second stopping feature 94b, the stopping axis 78 and the drive pin 80 are positioned on a line 102b. The line 102b is angled less than 30 from a tangential line 103b at the drive pin 80 with respect to the drive axis 68. In FIG. 9, the line 102b is angled approximately 10 from the tangential line 103b. In this way, rotation of the drive member 62a (clockwise in FIG. 9) is stopped without generating any substantial torque on the stopping member 74a and without the stopping member 74a having to contact the drive member 62a (except the drive pin 80 thereof). The rotation range of the specific arrangement 50a is approximately 1024 degrees.

[0076] The arrangement 50a limits rotation of the drive member 62a regardless of whether the drive motor 70a is powered. Due to the arrangement 50a, bulky and error-prone slip rings for the cables 84 can be avoided.

[0077] Since the drive member 62a is relatively seldom in contact with the stopping member 74a (only when the drive pin 80 contacts the stopping member 74a), the manufacturing tolerances and the assembly tolerances can be relaxed. For example, the drive axis 68 does not have to be perfectly parallel with the stopping axis 78. This enables a more cost-efficient design.

[0078] FIG. 10 schematically represents a top view of a further example of an arrangement 50b for limiting rotation. Mainly differences with respect to the arrangement 50a will be described. Details of the holding mechanism 86 are omitted in FIG. 10. The holding mechanism 86 of the arrangement 50b may be of the same or similar type as the holding mechanism 86 of the arrangement 50a.

[0079] The arrangement 50b comprises a drive member 62b and a stopping member 74b. As shown in FIG. 10, the shapes of the drive member 62b and the stopping member 74b differ from the drive member 62a and the stopping member 74a, respectively, but the principles of operation are the same.

[0080] The stopping member 74b comprises only one stopping feature 94c. Moreover, the stopping member 74b comprises three driven features 92a-92c. In FIG. 10, the drive member 62b is in a first end position 98a and the stopping member 74b is in a first end discrete position 100a. The stopping member 74b is held in the first end discrete position 100a by the holding mechanism 86. The drive pin 80 is seated in the stopping feature 94c.

[0081] FIG. 11 schematically represents a top view of the arrangement 50b when the drive member 62b has rotated from the first end position 98a (clockwise in FIG. 11) as illustrated with arrow 104. When the drive member 62b has rotated almost a full turn about the drive axis 68, the drive pin 80 engages the first driven feature 92a. The rotation of the drive member 62b and the engagement between the drive pin 80 and the first driven feature 92a overcomes the magnetic holding force of the holding mechanism 86 and causes the stopping member 74b to rotate (counterclockwise in FIG. 11) as illustrated with arrow 106.

[0082] FIG. 12 schematically represents a top view of the arrangement 50b when the drive member 62b has rotated further and the stopping member 74b has been rotated to a first intermediate discrete position 76a.

[0083] FIG. 13 schematically represents a top view of the arrangement 50b when the drive member 62b has rotated further. In FIG. 13, the drive pin 80 now engages the second driven feature 92b. The rotation of the drive member 62b and the engagement between the drive pin 80 and the second driven feature 92b overcomes the magnetic holding force of the holding mechanism 86, and causes the stopping member 74b to again rotate (counterclockwise in FIG. 13) as illustrated with arrow 106.

[0084] FIG. 14 schematically represents a top view of the arrangement 50b when the drive member 62b has rotated further and the stopping member 74b has rotated to a second intermediate discrete position 76b.

[0085] FIG. 15 schematically represents a top view of the arrangement 50b when the drive member 62b has rotated further. In FIG. 15, the drive pin 80 now engages the third driven feature 92c. The rotation of the drive member 62b and the engagement between the drive pin 80 and the third driven feature 92c overcomes the magnetic holding force of the holding mechanism 86, and causes the stopping member 74b to again rotate (counterclockwise in FIG. 15) as illustrated with arrow 106.

[0086] FIG. 16 schematically represents a top view of the arrangement 50b when the drive member 62b has rotated further and the stopping member 74b has rotated to a second end discrete position 100b. The holding mechanism 86 holds the stopping member 74b in the second end discrete position 100b. FIG. 17 schematically represents a top view of the arrangement 50b when the drive member 62b has rotated further to a second end position 98b of the rotation range. The rotation range of the specific arrangement 50b is approximately 1410 degrees. When the stopping member 74b is in the second end discrete position 100b and the drive member 62b is in the second end position 98b, the drive pin 80 is again seated in the stopping feature 94c.

[0087] Although the arrangements 50a and 50b have been described in connection with a wheel unit 48a, the arrangements 50a and 50b may very well be used in other implementations where it is desired to limit rotation.

[0088] While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed. Accordingly, it is intended that the present invention may be limited only by the scope of the claims appended hereto.