Devices and robots with limited rotation

Abstract

A device (50a; 50b) for limiting rotation, the device comprising a base structure (54, 72); a drive member (62a; 62b) rotatable relative to the base structure and having a drive feature (80); a stop member (74a; 74b) having at least one driven feature (923-920), wherein the stop member is arranged to be intermittently driven relative to the base structure between a plurality of discrete positions (76a, 76b, 100a, 100b) by continuous rotation of the drive member and by cooperation between the drive feature and at least one driven feature, wherein the stop member is arranged in a first end discrete position (100a) to limit rotation of the drive member in a first end position (98a) of the rotation range of the drive member; and a retaining mechanism (86) arranged to retain the stop member in each discrete position, the retaining mechanism being at least partially disposed in the base structure.

Description

Technical Field

[0001] The present disclosure generally relates to a device for limiting rotation. In particular, a device for limiting rotation and a robot including such a device are provided, the device including a holding mechanism at least partially disposed in a base structure. Background Art

[0002] In some mechanical configurations, such as joints, it is desirable to limit the range of relative rotation between a first member and a second member. One reason for limiting relative rotation is to protect cables passing through the joint. Fig.18 A joint 10 is shown which includes a first member 12 and a second member 14 rotatable relative to the first member 12. By providing a first tab 16 on the first member 12 and a second tab 18 on the second member 14 for engaging the first tab 16 from two directions, the range of rotation may be limited to slightly less than 360 degrees.

[0003] like Fig.18 The concept of limiting relative rotation shown can be extended to provide Fig.19 The joint 20 shown. The joint 20 additionally includes an intermediate member 22 located between the first member 12 and the second member 14. The intermediate member 22 includes a first intermediate tab 24 for engaging the first tab 16 and a second intermediate tab 26 for engaging the second tab 18. For the joint 20, the rotation range can be limited to slightly less than 720 degrees. Additional intermediate members 22 can be added to the joint 20 to increase the relative rotation range. However, each intermediate member 22 increases the size and friction of the joint 20.

[0004] Fig. 20 A Geneva stop 28 is shown, which can be used to limit the rotation between two members. The Geneva stop 28 includes a drive wheel 30 and a driven wheel 32. The drive wheel 30 includes a pin 34 and a blocking disc 36. The driven wheel 32 of this example includes three arms 38a-38c. Each of the first arm 38a and the second arm 38b includes a slot for receiving the pin 34. The third arm 38c does not include a slot and is therefore closed. The concave recess 40 in the blocking disc 36 allows the first arm 38a and the second arm 38b to pass. The continuous rotation of the drive wheel 30 is transmitted to the intermittent rotation of the driven wheel 32. The third arm 38c blocks the pin 34 at each of the two end positions of the drive wheel 30. The rotation range of the drive wheel 30 is here about 1016 degrees. When the pin 34 has left the slot, the driven wheel 32 is prevented from rotating by one of the three curved portions 42 a - 42 c between the arms 38 a - 38 c which tightly abuts against the circular stop surface 44 of the blocking disk 36 .

[0005] although Fig. 20The Geneva stop 28 in FIG. 1 can be designed to be relatively flat and can achieve a rotation range of more than 360 degrees, but it has several disadvantages. Due to the cooperation between the curved portions 42a-42c and the stop surface 44, the Geneva stop 28 must be produced and assembled with narrow tolerances. In addition, even if these tolerances are narrow, contact will occur between the curved portions 42a-42c and the stop surface 44. The Geneva stop 28 therefore has the general problem of friction between the curved portions 42a-42c and the stop surface 44. In implementations where it is desired to provide a large central space on the drive wheel 30 and therefore provide a large blocking disc 36, the friction between the curved portions 42a-42c and the stop surface 44 will act away from the rotation axis of the drive wheel 30 and thereby generate a high torque around the rotation axis, potentially even stopping the rotation of the drive wheel 30. Summary of the invention

[0006] It is an object of the present invention to provide an improved device for limiting rotation. This object is achieved by a device according to the attached claim 1.

[0007] The present invention is based on the realisation that by providing a retaining mechanism arranged to retain a stop member in each of a plurality of discrete positions, and with the retaining mechanism decoupled from the drive member, a large area can be provided in the drive member, tolerances can be relaxed and friction can be reduced.

[0008] According to a first aspect, a device for limiting rotation is provided, which includes a base structure; a drive member rotatable around a drive axis relative to the base structure, the drive member having a drive feature deviating from the drive axis; a stop member having at least one driven feature, wherein the stop member is arranged to be intermittently driven relative to the base structure between multiple discrete positions by continuous rotation of the drive member and by cooperation between the drive feature and at least one driven feature, wherein the stop member is arranged in a first end discrete position to limit the rotation of the drive member in a first end position of the rotation range of the drive member, and the stop member is arranged in a second end discrete position to limit the rotation of the drive member in a second end position of the rotation range; and a retaining mechanism arranged to retain the stop member in each discrete position, the retaining mechanism being at least partially disposed in the base structure.

[0009] Since the retaining mechanism is at least partially arranged in the base structure, the stop member can be held in each discrete position (one at a time) without interacting with the drive member. Therefore, the function of the stop member is more independent of the function of the drive member, for example compared to a Geneva stop (in which the driven wheel is held in place by a stop surface on a brake disc on the drive wheel). This independence has great advantages for several reasons. The manufacturing tolerances and assembly tolerances of both the drive member and the stop member can be made larger, i.e. less precise. The stop member can be, for example, a 3D printed plastic component. In addition, even for large drive members, friction losses in the device are greatly reduced.

[0010] When the driving feature cooperates with the driven feature to intermittently drive the stop member, the driving force from the driving member overcomes the retaining force of the retaining mechanism and moves the stop member. In addition to the retaining mechanism, the device can be used as a Geneva stop. The range of rotation can be at least 360 degrees around the drive axis, such as at least 540 degrees around the drive axis.

[0011] The drive feature may contact each driven feature to cooperate therewith.As a possible alternative, the drive feature may cooperate magnetically with each driven feature.

[0012] The stop member may also include at least one stop feature. In this case, when the stop member is in the first end discrete position, the drive feature of the drive member may cooperate with one of the at least one stop features in each of the first end positions, and when the stop member is in the second end discrete position, the drive feature of the drive member may cooperate with one of the at least one stop features in the second end position. The drive feature may or may not be the same drive feature that cooperates with the at least one driven feature.

[0013] The retaining mechanism may comprise at least one magnet arranged to retain the stop member in each discrete position by magnetic force. The use of at least one magnet enables very reliable operation and a simpler design. For example, at least one magnet may be molded inside the stop member.

[0014] According to one example, at least one magnet includes one stop magnet fixed to the stop member and multiple base magnets fixed to the base structure, wherein the number of base magnets corresponds to the number of discrete positions. According to another example, at least one magnet includes one base magnet fixed to the base structure and multiple stop magnets fixed to the stop member, wherein the number of stop magnets corresponds to the number of discrete positions. One or more stop magnets can be configured to magnetically attract each base magnet. One or more stop magnets or one or more base magnets can be replaced with one or more ferromagnetic metal parts.

[0015] As a possible alternative, the retaining mechanism may include a spring biased pin (eg, on a stop member) that may be seated in one of several recesses (eg, in a base structure), wherein each recess corresponds to a unique discrete position.

[0016] The stop member may be rotatable about a stop axis. In this case, the base structure may be positioned beside the stop member along the stop axis. The stop axis may be substantially parallel to or parallel to the drive axis. However, the device may also be implemented with a linearly translatable stop member.

[0017] The device may also include a sliding bearing, and the stop member may be rotatably supported by the sliding bearing about the stop axis. This makes the device more cost-effective. The use of sliding bearings is in turn enabled by the loose tolerances of the device.

[0018] In the case where the stop member includes a stop feature, when the stop member is in the first end discrete position and the drive member is in the first end position, the stop feature and the stop axis can be substantially positioned on a line that deviates from a tangent at the drive feature by up to 30°, such as up to 20° or up to 10° relative to the drive axis. In this way, the torque acting on the stop member at the first end discrete position can be kept close to zero or zero. Therefore, the mechanical strength of the stop member can be low. Therefore, for example, by using plastic or other cheap, lightweight and easy to form materials, the device can be cost-effective. The stop feature can cooperate with the drive feature of the drive member (for example, by contact) to limit the rotation of the drive member at the first end position. The drive feature may or may not be the same drive feature that cooperates with at least one driven feature. Alternatively or additionally, when the stop member is in the second end discrete position and the drive member is in the second end position, the stop feature and the stop axis can be substantially positioned on or positioned on a line that deviates from a tangent at the drive feature by up to 30°, such as up to 20° or up to 10° relative to the drive axis.

[0019] The drive feature may be located on a drive member surface of the drive member. In this case, the distance from the drive axis to the drive feature may be at least 80% of the distance from the drive axis to the radially outermost position of the drive member surface relative to the drive axis.

[0020] The drive feature may comprise a drive pin. In this case, each driven feature (and optionally each stop feature) may be a recess. The drive pin may protrude parallel to the drive axis.

[0021] The stop member may be made of plastic. The stop member may be made by molding or by 3D printing.

[0022] The device may also include a cable fixed relative to each of the base structure and the drive member. The device may also include a driven motor fixed relative to the drive member. In this case, the cable can be fixedly connected to the driven motor. This fixed connection is different from a connection through a slip ring, which is prone to wear. For example, a first end of the cable can be fixed to the base structure and the other end of the cable can be fixed to the driven motor. The cable can be twisted between the base structure and the driven motor (reaching an extension defined by the device).

[0023] The device may further comprise a drive motor arranged to drive the drive member around the drive axis. In this case, the drive motor may be positioned radially inside the drive feature relative to the drive axis.

[0024] According to another aspect, a robot is provided, the robot comprising the apparatus according to the first aspect. The robot may be an automatic guided vehicle AGV, the AGV comprising at least one wheel unit comprising a traction wheel rotatable about a drive axis and a wheel axis perpendicular to the drive axis. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] Figure 1 : schematically represents a perspective view of a robot, the robot comprising a plurality of wheel units, each wheel unit having a device for limiting rotation;

[0027] Figure 2 : A perspective view schematically showing one of the wheel units;

[0028] Figure 3 : A perspective view schematically showing the device;

[0029] Figure 4 : schematically shows a top view of the device when the drive member is in a first end position and the stop member is in a first end discrete position;

[0030] Figure 5 : schematically shows a top view of the device when the drive member has been rotated from the first end position;

[0031] Figure 6 : schematically shows a top view of the device when the drive member has been further rotated and the stop member has moved to an intermediate discrete position;

[0032] Figure 7 : schematically shows a top view of the device when the drive member has been further rotated;

[0033] Figure 8 : schematically represents a top view of the device when the drive member has been further rotated and the stop member has been moved to the second end discrete position;

[0034] Fig. 9 : schematically shows a top view of the device when the drive member has been further rotated to the second end position;

[0035] Fig.10 : schematically showing a top view of another example of a device for limiting rotation when the drive member is in a first end position and the stop member is in a first end discrete position;

[0036] Fig.11 : Schematically represents when the drive member has been rotated from the first end position Fig.10 A top view of the device in FIG.

[0037] Fig.12 : Schematically represents when the drive member has been further rotated and the stop member has moved to the first intermediate discrete position Fig.10 and Fig.11 A top view of the device in FIG.

[0038] Fig.13 : Schematically represents when the drive member has rotated further Figures 10 to 12 A top view of the device in FIG.

[0039] Fig.14 : schematically represents when the drive member has been further rotated and the stop member has moved to the second intermediate discrete position Fig.10 and Fig.13 A top view of the device in FIG.

[0040] Fig.15 : Schematically represents when the drive member has rotated further Figures 10 to 14 A top view of the device in FIG.

[0041] Fig.16 : schematically represents when the drive member has been further rotated and the stop member has moved to the second end discrete position Figures 10 to 15 A top view of the device in FIG.

[0042] Fig.17 : Schematically represents when the drive member has been further rotated to the second end position Figures 10 to 16 A top view of the device in FIG.

[0043] Fig.18 : schematically shows a top view of a joint with limited rotation according to the prior art;

[0044] Fig.19: A top view schematically showing another example of a joint with limited rotation according to the prior art; and

[0045] Fig. 20 : Schematically shows a top view of a Geneva stopper according to the prior art. DETAILED DESCRIPTION

[0046] Hereinafter, a device for limiting rotation and a robot including such a device will be described. The same or similar reference numerals will be used to denote the same or similar structural features.

[0047] Figure 1 Schematically showing a perspective view of a robot, here illustrated 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 means for limiting rotation. Figure 1 In FIG. 4 , only one such device 50a is shown for the first wheel unit 48a.

[0048] The first wheel unit 48a includes a first traction wheel 52a, the second wheel unit 48b includes a second traction wheel 52b, the third wheel unit 48c includes a third traction wheel 52c, and the fourth wheel unit 48d includes a fourth traction wheel 52d. Figure 1 The AGV 46 in FIG. 4 includes four wheel units 48a-48d, but the AGV 46 may alternatively include 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. Figure 1 Further shown for reference purposes is a Cartesian coordinate system X, Y, Z. The horizontal surface may lie in the XY plane.

[0049] The AGV 46 also includes a platform 54. The platform 54 is an 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 also includes a control system 56. The control system 56 includes a data processing device 58 and a memory 60 on which a computer program is stored. The control system 56 is configured to control the movement of the traction wheels 52a-52d. In this example, the control system 56 is disposed in the platform 54. The control system 56 communicates signals with each wheel unit 48a-48d. The control system 56 may also include a battery (not shown) for powering each wheel unit 48a-48d.

[0051] Figure 2A perspective view of a first wheel unit 48a is schematically shown. In this example, all wheel units 48a-48d have the same design. In addition to the first traction wheel 52a, the first wheel unit 48a also includes a drive member 62a. The first wheel unit 48a of this example also includes a steering member 64 fixed to the drive member 62a. The first traction wheel 52a is rotatable about a wheel axis 66 relative to the steering member 64. The drive member 62a is rotatable about a drive axis 68, which is illustrated here as a steering axis. The wheel axis 66 is perpendicular to the drive axis 68. Furthermore, the wheel axis 66 intersects the drive axis 68. In Figure 2 In FIG. 6 , 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 about the drive axis 68 and thus also the first traction wheel 52a. 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. Thus, the AGV 46 is configured to perform omnidirectional movement, i.e., it can move in any direction along the floor and can rotate in a controlled manner independently of its translation along its path.

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

[0056] The device 50a also includes a stop member 74a. Figure 2 , the stop member 74a is in the intermediate discrete position 76a.

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

[0058] The drive member 62a includes a drive pin 80. The drive pin 80 is an 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 is parallel to the drive axis 68 ( Figure 2 The drive member surface 82 here is transverse to the drive axis 68. Figure 2As shown, the drive motor 70 a is positioned radially inwardly of the drive pin 80 relative to the drive axis 68 .

[0059] like Figure 2 As shown, a cable 84 is routed from the control system 56 through the drive member 62a to the driven motor 70b in the steering member 64. A first end of the cable 84 is fixedly connected to the control system 56, and the other end of the cable 84 is fixedly connected to the driven motor 70b. In this way, slip rings can be avoided. The cable 84 can be, for example, a signal cable and / or a power cable. When the first traction wheel 52a rotates around the drive axis 68, the cable 84 is twisted. The device 50a is configured to limit the rotation of the drive member 62a around the drive axis 68 relative to the platform 54 within a predefined rotation range. The rotation range is set to limit the twisting of the cable 84 to a tolerable level.

[0060] The rotation range defined by the device 50a can be determined based on the specific application, but should not exceed the critical range of twisting of the cable 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 available for wiring. Figure 2 As shown, the cable 84 is routed offset from the drive axis 68 through the drive member 62a.

[0062] Figure 3 A perspective view of the device 50a is schematically shown. Figure 3 , the block 72 is removed to improve visibility. The device 50a includes a retaining mechanism 86. The retaining mechanism 86 is configured to retain the stop member 74a in each of a plurality of discrete positions, such as in the intermediate discrete position 76a shown.

[0063] The retaining mechanism 86 of this particular example includes three base magnets 88a-88c fixed to the block 72 and one stop magnet 90 fixed to the stop member 74a. The retaining mechanism 86 is thereby partially 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 inwardly of the drive pin 80. In addition, since the stop member 74a does not have to contact the drive member 62a to be held in its discrete position, tolerances can be relaxed and friction can be reduced.

[0064] Each of the block 72 and the stop member 74a can be a 3D printed plastic component. Optionally, the base magnets 88a-88c and the stop magnet 90 can be embedded in the block 72 and the stop member 74a, respectively. Figure 2 and Figure 3As shown, the stop magnet 90 and the base magnets 88a - 88c are not visible from the outside of the first wheel unit 48a .

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

[0066] The stop member 74a of this example also includes two driven features 92a and 92b. However, the stop member 74a can include only one driven feature or more than two driven features. The driven features 92a and 92b are illustrated here as recesses, each of which is configured to receive the drive pin 80.

[0067] The stop member 74a of this example also includes two stop features 94a and 94b. Alternatively, the stop member 74a may include only one stop feature. The stop features 94a and 94b are illustrated here as recesses, each of which is configured to receive the drive pin 80. A damping layer (not shown) may be provided in each of the stop features 94a and 94b and the driven features 92a and 92b to receive the drive pin 80 more smoothly.

[0068] The device 50a of this example includes a sliding bearing 96. The stop member 74a can rotate about the stop axis 78 via the sliding bearing 96.

[0069] Figure 4 A top view of the device 50a is schematically shown. Figure 4 , the drive member 62a is in the first end position 98a of the rotation range. The stop member 74a is in the first end discrete position 100a. In the first end discrete position 100a, the stop magnet 90 is aligned with the first base magnet 88a and is attracted to the first base magnet 88. In this way, the retaining mechanism 86 retains the stop member 74a in the first end discrete position 100a by magnetic force. When the stop 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 disposed in the first stop feature 94a, and the first stop feature 94a, the stop axis 78 and the drive pin 80 are positioned on the line 102a. The line 102a is at an angle of less than 30° relative to the drive axis 68 and the tangent 103a at the drive pin 80. Figure 4 In this way, the rotation of the driving member 62a ( Figure 4 , counterclockwise in the direction of rotation) is stopped without generating any substantial torque on the stop member 74a, and the stop member 74a does not have to contact the drive member 62b (except for its drive pin 80). Figure 4As further shown, the radial distance from the drive axis 68 to the drive pin 80 is approximately 87% of the radial distance from the drive axis 68 to the radially outermost location of the drive member surface 82 .

[0070] Figure 5 Schematically showing when the drive member 62a is moved from the first end position 98a ( Figure 5 A top view of the device 50a when rotating (clockwise in FIG. 1 ), as shown by 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 revolution 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 overcome the magnetic holding force between the stop magnet 90 and the first base magnet 88a and cause the stop member 74a to rotate as indicated by arrow 106 ( Figure 5 counterclockwise in the ).

[0072] Figure 6 Schematically shows a top view of the device 50a when the drive member 62a has been further rotated. The stop member 74a has now been rotated to an intermediate discrete position 76a, at which the stop magnet 90 is aligned with and attracted to the second base magnet 88b. Thus, the device 50a is configured to transfer continuous rotation of the drive member 62a to intermittent rotation of the stop member 74a.

[0073] Figure 7 Schematically shows a top view of the device 50a when the drive member 62a has been rotated further. Figure 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 stop magnet 90 and the second base magnet 88b and causes the stop member 74a to rotate again as indicated by arrow 106 ( Figure 7 counterclockwise in the ).

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

[0075] Fig. 9Schematically showing a top view of the device 50a when the drive member 62a has been further rotated to the second end position 98b of the rotation range. When the stop 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 stop feature 94b, and the second stop feature 94b, the stop axis 78 and the drive pin 80 are positioned on the line 102b. The line 102b is at an angle of less than 30° relative to the drive axis 68 and the tangent line 103b at the drive pin 80. Fig. 9 In this way, the rotation of the driving member 62a ( Fig. 9 The rotational range of the particular device 50a is approximately 1024 degrees.

[0076] The device 50a limits the rotation of the drive member 62a, regardless of whether the drive motor 70a is powered or not. Thanks to the device 50a, bulky and error-prone slip rings for the cable 84 can be avoided.

[0077] Since the drive member 62a contacts the stop member 74a relatively infrequently (only when the drive pin 80 contacts the stop member 74a), manufacturing tolerances and assembly tolerances can be relaxed. For example, the drive axis 68 does not have to be completely parallel to the stop axis 78. This makes the design more cost-effective.

[0078] Fig.10 A top view schematically showing another example of a device 50b for limiting rotation. The differences will mainly be described with respect to the device 50a. Fig.10 Details of the retaining mechanism 86 are omitted. The retaining mechanism 86 of the device 50b may be of the same or similar type as the retaining mechanism 86 of the device 50a.

[0079] The device 50b includes a drive member 62b and a stop member 74b. Fig.10 As shown, the shapes of the drive member 62b and the stop member 74b are different from the drive member 62a and the stop member 74a, respectively, but the operating principles are the same.

[0080] The stop member 74b includes only one stop feature 94c. In addition, the stop member 74b includes three follower features 92a-92c. Fig.10 , the drive member 62b is in the first end position 98a and the stop member 74b is in the first end discrete position 100a. The stop member 74b is retained in the first end discrete position 100a by the retaining mechanism 86. The drive pin 80 is disposed in the stop feature 94c.

[0081] Fig.11 Schematically showing that when the drive member 62b has moved from the first end position 98a ( Fig.11 6 (clockwise in FIG. 6 ). When the drive member 62b has rotated almost a full revolution 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 overcome the magnetic retention force of the retention mechanism 86 and cause the stop member 74b to rotate as indicated by arrow 106 ( Fig.11 counterclockwise in the ).

[0082] Fig.12 A top view of the device 50b is schematically shown when the drive member 62b has been rotated further and the stop member 74b is rotated to the first intermediate discrete position 76a.

[0083] Fig.13 Schematically shows a top view of the device 50b when the drive member 62b has been rotated further. 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 overcome the magnetic holding force of the holding mechanism 86 and cause the stop member 74b to rotate again as indicated by arrow 106 ( Fig.13 counterclockwise in the ).

[0084] Fig.14 A top view of the device 50b is schematically shown when the drive member 62b has been rotated further and the stop member 74b is rotated to the second intermediate discrete position 76b.

[0085] Fig.15 Schematically shows a top view of the device 50b when the drive member 62b has been rotated further. 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 overcome the magnetic holding force of the holding mechanism 86 and cause the stop member 74b to rotate again as indicated by arrow 106 ( Fig.15 counterclockwise in the ).

[0086] Fig.16 Schematically represents a top view of the device 50b when the drive member 62b has been rotated further and the stop member 74b is rotated to the second end discrete position 100b. The retaining mechanism 86 retains the stop member 74b in the second end discrete position 100b.

[0087] Fig.17Schematically shows a top view of the device 50b when the drive member 62b has been further rotated to the second end position 98b of the rotation range. The rotation range of the particular device 50b is about 1410 degrees. When the stop 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 stop feature 94c.

[0088] Although devices 50a and 50b have been described in conjunction with wheel unit 48a, devices 50a and 50b may be used equally well with other implementations where limited rotation is desired.

[0089] Although the present disclosure has been described with reference to exemplary embodiments, it should be understood that the present invention is not limited to the contents described above. For example, it should be understood that the size of the components can be changed as needed. Therefore, the present invention can only be limited by the scope of the attached claims.

Claims

1. A device for limiting rotation (50a ； 50b), the device (50a; 50b) includes: - a base structure (54, 72); a drive member (62a; 62b) rotatable relative to the base structure (54, 72) about a drive axis (68), the drive member (62a; 62b) having a drive feature (80) offset from the drive axis (68); a stop member (74a; 74b) having at least one driven feature (92a-92c), wherein the stop member (74a; 74b) is arranged to be intermittently driven relative to the base structure (54, 72) between a plurality of discrete positions (76a, 76b, 100a, 100b) by continuous rotation of the drive member (62a; 62b) and by cooperation between the drive feature (80) and at least one driven feature (92a-92c), wherein The stop member (74a; 74b) is arranged in a first end discrete position (100a) to limit the rotation of the drive member (62a; 62b) in a first end position (98a) of the rotation range of the drive members (62a, 62b), and the stop member (74a; 74b) is arranged in a second end discrete position (100b) to limit the rotation of the drive member (62a; 62b) in a second end position (98b) of the rotation range; and - a retaining mechanism (86) arranged to retain the stop member (74a; 74b) in each discrete position (76a, 76b, 100a, 100b), the retaining mechanism (86) being at least partially disposed in the base structure (54, 72).

2. A device (50a; 50b) according to claim 1, wherein the retaining mechanism (86) includes at least one magnet (88a-88c, 90), and the at least one magnet (88a-88c, 90) is arranged to retain the stop member (74a; 74b) in each discrete position (76a, 76b, 100a, 100b) by magnetic force.

3. The device (50a; 50b) according to claim 1, wherein the stop member (74a; 74b) is rotatable about a stop axis (78).

4. The device (50a; 50b) according to claim 3, further comprising a sliding bearing (96), wherein the stop member (74a; 74b) is rotatably supported by the sliding bearing (96) about the stop axis (78).

5. A device (50a) according to claim 3 or 4, wherein the stop member (74a; 74b) includes a stop feature (94a-94c), wherein when the stop member (74a; 74b) is in the first end discrete position (100a) and the drive member (62a; 62b) is in the first end position (98a), the stop feature (94a-94c) and the stop axis (78) are substantially positioned on a line (102a) that deviates by at most 30° from a tangent (103a) at the drive feature (80) relative to the drive axis (68).

6. A device (50a) according to claim 5, wherein when the stop member (74a; 74b) is in the first end discrete position (100a) and the drive member (62a; 62b) is in the first end position (98a), the stop feature (94a-94c) and the stop axis (78) are substantially positioned on a line (102a) that deviates by at most 20° from a tangent (103a) at the drive feature (80) relative to the drive axis (68).

7. A device (50a) according to claim 6, wherein when the stop member (74a; 74b) is in the first end discrete position (100a) and the drive member (62a; 62b) is in the first end position (98a), the stop feature (94a-94c) and the stop axis (78) are substantially positioned on a line (102a) that deviates by at most 10° from a tangent (103a) at the drive feature (80) relative to the drive axis (68).

8. A device (50a; 50b) according to any one of claims 1-4, wherein the drive feature (80) is positioned on a drive member surface (82) of the drive member (62a; 62b), and wherein the distance from the drive axis (68) to the drive feature (80) is at least 80% of the distance from the drive axis (68) to the radially outermost position of the drive member surface (82) relative to the drive axis (68).

9. The device (50a; 50b) according to any one of claims 1-4, wherein the drive feature (80) comprises a drive pin.

10. The device (50a; 50b) according to any one of claims 1 to 4, wherein the stop member (74a; 74b) is made of plastic.

11. The device (50a; 50b) according to any one of claims 1 to 4, further comprising a cable (84) fixed relative to each of the base structure (54, 72) and the drive member (62a; 62b).

12. The device (50a; 50b) according to claim 11, further comprising a driven motor (70b) fixed relative to the drive member (62a; 62b), wherein the cable (84) is fixedly connected to the driven motor (70b).

13. The device (50a; 50b) according to any one of claims 1-4, further comprising a drive motor (70a) arranged to drive the drive member (62a; 62b) around the drive axis (68), wherein the drive motor (70a) is radially positioned inside the drive feature (80) relative to the drive axis (68).

14. A robot (46) comprising a device (50a; 50b) according to any one of claims 1 to 13.

15. The robot (46) according to claim 14, wherein the robot (46) is an automatic guided vehicle AGV, the AGV comprising at least one wheel unit (48a-48d), the at least one wheel unit (48a-48d) comprising a traction wheel (52a-52d) capable of rotating around the drive axis (68) and a wheel axis (66) perpendicular to the drive axis (68).

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