Patent Application
20230175554
The present disclosure generally relates to a joint arrangement. In particular, a joint arrangement comprising a drive member and a driven member, an electric motor comprising a joint arrangement, and an industrial actuator comprising a joint arrangement, are provided.
An industrial robot may comprise a manipulator programmable in three or more axes. Some known industrial robots comprise an electric motor having a drive member and a pinion connected to the drive member to form a joint. The electric motor may be connected to a first link and the pinion may be used to drive a second link relative to the first link via a gearbox. Today, safety critical joints typically comprise either a press fit or a shape lock. A press fit may alternatively be referred to as an interference fit.
When the pinion is connected to the drive member by means of a press fit, such as a cylindrical press fit, safety against slippage between the drive member and the pinion can be provided by setting a press fit force high enough. Moreover, the press fit eliminates backlash between the drive member and the pinion, which is typically desired in the joints of an industrial robot. A special and calibrated press fit machine is however required to provide and control the press fit force. The press fit machine monitors the press fit force to ensure that a sufficient safety margin against slippage is provided. The press fit is performed at an assembly site remote from a work site of the industrial robot.
In case the pinion is connected to the drive member by means of a shape lock, safety against slippage between the drive member and the pinion is provided.
Examples of shape locks are keyways and splines. A shape lock however has performance issues due to the inherent backlash. Moreover, measures need to be taken in order to avoid fretting problems, for example the provision of grease and seals to keep the grease in the joint. Keyway joints or spline joints are also relatively expensive to produce. Keyway joints also need to be relatively bulky due to the disruptions of the shapes of the drive member and the pinion that introduce weaknesses. The shape lock may alternatively be referred to as a form lock.
EP 0845614 A2 discloses a polygonal coupling using a bore formed in a hub and a contoured section at the end of a shaft having the same polygonal cross-section, so that they fit together without play. The polygonal cross-section is cylindrical or has a slight conical taper, so that a play-free pressure seat is provided upon application of axial pressure.
In order to obtain a high enough press fit force to achieve a press fit between a drive member and a pinion that in practice cannot fail, a press fit machine is required. It is however not feasible to perform press fitting of a pinion to a drive member by means of a press fit machine when the drive member is already mounted to an industrial robot delivered to a customer. The field installation possibilities are in many cases limited or non-existing. Moreover, the remote press fitting of pinions to drive members leads to a requirement of a larger amount of spare parts.
One object of the present disclosure is to provide a joint arrangement that enables a driven member to be connected to a drive member in a simple manner.
A further object of the present disclosure is to provide a joint arrangement that is field attachable.
A still further object of the present disclosure is to provide a joint arrangement that eliminates backlash.
A still further object of the present disclosure is to provide a joint arrangement that prevents relative movement between a drive member and a driven member in case a press fit fails.
A still further object of the present disclosure is to provide a joint arrangement that enables a driven member to be disconnected from a drive member in a simple manner.
A still further object of the present disclosure is to provide a joint arrangement that is field detachable.
A still further object of the present disclosure is to provide a joint arrangement that provides a reliable operation.
A still further object of the present disclosure is to provide a joint arrangement that facilitates replacement of a part of a joint.
A still further object of the present disclosure is to provide a joint arrangement that provides a safe operation.
A still further object of the present disclosure is to provide a joint arrangement that has a compact design.
A still further object of the present disclosure is to provide a joint arrangement that has a cost-effective design.
A still further object of the present disclosure is to provide a joint arrangement that enables a number of spare parts to be reduced.
A still further object of the present disclosure is to provide a joint arrangement solving several or all of the foregoing objects in combination. In particular, one object is to provide a joint arrangement that is field attachable, that eliminates backlash and that prevents relative movement between a drive member and a driven member in case a press fit fails.
A still further object of the present disclosure is to provide an electric motor comprising a joint arrangement, which electric motor solves one, several or all of the foregoing objects.
A still further object of the present disclosure is to provide an industrial actuator comprising a joint arrangement or an electric motor, which industrial actuator solves one, several or all of the foregoing objects.
According to one aspect, there is provided a joint arrangement comprising a drive member rotatable about a rotation axis, the drive member comprising a drive member press fit surface and a drive member shape lock structure; an attachment portion having an attachment thread; and a driven member comprising a driven member press fit surface, a driven member shape lock structure and a through hole; wherein the joint arrangement is configured such that the driven member can be rigidly connected to the drive member by means of a press fit between the drive member press fit surface and the driven member press fit surface by threadingly engaging the attachment thread with an attachment member passing through the through hole; and wherein the joint arrangement is configured such that a shape lock is provided between the drive member shape lock structure and the driven member shape lock structure when the driven member is connected to the drive member.
When the driven member is connected to the drive member, the drive member and the driven member form a joint for transmitting rotation. The joint comprises a press fit and a shape lock. The joint constitutes a field attachable non-backlash safety joint. The drive member and the driven member may be coaxial with the rotation axis when the driven member is connected to the drive member.
The drive member may be a female part and the driven member may be a male part. Alternatively, or in addition, the drive member may be a drive member shaft and the driven member may be a driven member shaft.
The shape lock is relatively loose. For example, the shape lock may not resist the establishment of the press fit. The shape lock prevents slipping between the drive member and the driven member should the press fit fail. The shape lock may thus be referred to as a secondary joint lock or a backup joint lock. One reason for such failure of the press fit may be the execution of an emergency stop. Execution of an emergency stop may cause an uncontrolled acceleration of the joint.
Since the driven member is connected to the drive member by means of the press fit, backlash in the joint is eliminated. The force of the press fit may be just sufficient to withstand maximal acceleration during controlled movement of the joint. For example, the press fit may be set to withstand up to 120% of a maximum controlled acceleration force in the joint. The press fit may be referred to as a primary joint lock. The press fit force may be reduced with at least 20%, such as at least 40%, in comparison with a press fit force for a corresponding press fit without a shape lock, i.e. as pressed in a press fit machine.
Due to the provision of the shape lock that secures against slippage, the press fit force can be reduced. That is, the shape lock enables a reduction of a safety margin of the press fit. Moreover, the press fit force does not have to be carefully monitored in a press fit machine in order to secure against slippage in the joint. This in turn enables the drive member press fit surface and the driven member press fit surface to be made shorter along the rotation axis. Moreover, the press fit distance, i.e. the distance moved by the driven member relative to the drive member to establish the press fit, is reduced. This enables simple connection of the driven member to the drive member, e.g. simpler means of providing the press fit force can be used (like using a screw). With the joint arrangement according to the present disclosure, the driven member can be connected to the drive member with manual force only.
The attachment portion may comprise an attachment hole provided with the attachment thread. The attachment hole may be a blind hole.
After engagement of the press fit, the attachment member may be removed. In this case, forces from the drive member are transmitted to the driven member through the press fit. As an alternative, the attachment member may be left threadingly engaging the attachment thread. In this case, forces from the drive member are transmitted to the driven member through the press fit and through the threaded engagement.
The joint arrangement may be configured such that the press fit can be established by rotating the attachment member when threadingly engaging the attachment thread. To this end, the attachment member may comprise an attachment member thread for threadingly engaging the attachment thread, and an attachment head. By threadingly engaging the attachment thread with the attachment member thread and rotating the attachment member, the attachment head will push the driven member to establish the press fit between the driven member press fit surface and the drive member press fit surface. The attachment member may for example be manually rotated with a torque wrench.
As an alternative, the joint arrangement may be configured such that the press fit can be established by pushing the driven member away from the attachment head when the attachment member threadingly engages the attachment thread. In this case, the drive member does not have to be rotationally locked when establishing the press fit since no significant torsional loads are introduced by pushing the driven member away from the attachment head. Moreover, the attachment member does not have to be threaded the entire way through the attachment thread. The driven member may be manually pushed away from the attachment head by means of reverse pliers or some other expansion tool.
In both cases, the establishment of the press fit between the drive member press fit surface and the driven member press fit surface comprises the threading engagement of the attachment thread with an attachment member passing through the through hole. The joint arrangement thus enables attachment of the driven member to the drive member in a simple manner.
The driven member can thereby be connected to the drive member in the field, for example when the drive member is already mounted to an industrial actuator and/or to an electric motor.
The joint arrangement may further comprise the attachment member. The attachment member may be a bolt or screw. The attachment member may be coaxial with the rotation axis when threadingly engaging the attachment thread.
The driven member may further comprise a detachment thread. In this case, the joint arrangement may be configured such that the press fit can be released by threadingly engaging the detachment thread with a detachment member. The joint arrangement thus enables also detachment of the driven member from the drive member in the field in a simple manner, for example using a simple tool such as a torque wrench. The field attachable and field detachable characteristics of the joint arrangement enables a reduction of spare parts.
The joint arrangement may be configured such that the press fit can be released by rotating the detachment member when threadingly engaging the detachment thread. To this end, the detachment member may comprise a detachment head, an end portion and a detachment member thread between the detachment head and the end portion. The end portion may be cylindrical and have an external diameter so as not to interfere with the attachment thread. The detachment member thread may be configured to threadingly engage the detachment thread. By providing the attachment hole as a blind hole, threadingly engaging the detachment thread with the detachment member thread and rotating the detachment member, the end portion will initially be brought into contact with a bottom of the attachment hole. Further rotation of the detachment member will cause the driven member to separate from the drive member.
As an alternative, the detachment member may be hollow and comprise a detachment member thread. In this case, the detachment member thread may be threadingly engaged with the detachment thread and a detachment pin may be inserted through the detachment member to the bottom of the attachment hole. By pulling the detachment member proximally and pushing the detachment pin distally, the press fit can be released without needing to rotationally lock the joint.
As a further possible alternative, the detachment member may be a nipple comprising the detachment member thread. By threadingly engaging the detachment member thread with the detachment thread and by introducing fluid pressure into the through hole through the nipple, the press fit can be released by fluid pressure. Also in this case, the press fit can be released without needing to rotationally lock the joint.
The detachment thread may be provided in the through hole. The detachment thread may be provided along a major length of the through hole, such as along the entire through hole.
The detachment thread may be larger than the attachment thread. The detachment thread may be larger than the attachment member thread such that the attachment member thread does not interfere with the detachment thread. The detachment thread and the attachment thread may thus be referred to as a large thread and a small thread, respectively.
The joint arrangement may further comprise the detachment member. The detachment member may be coaxial with the rotation axis when threadingly engaging the detachment thread.
The driven member may be a pinion.
The through hole may be substantially concentric with, or concentric with, the rotation axis when the driven member is connected to the drive member.
This contributes to a compact design of the joint.
Each of the drive member press fit surface and the driven member press fit surface may be tapered, such as conical. Each taper may be at least 0.5 degrees with respect to the rotation axis.
Each of the drive member shape lock structure and the driven member shape lock structure may be polygonal. For example, each of the drive member shape lock structure and the driven member shape lock structure may be triangular, or substantially triangular. By providing a polygonal driven member shape lock structure, the driven member can be produced in a near cylindrical shape. This improves the strength of the driven member.
Each of the drive member press fit surface and the driven member press fit surface may be polygonal. For example, each of the drive member press fit surface and the driven member press fit surface may be triangular, or substantially triangular.
The drive member shape lock structure may be a continuous surface. With continuous surface is meant a surface that is not interrupted by sharp edges. Alternatively, or in addition, the drive member shape lock structure may be constituted by the drive member press fit surface.
The driven member shape lock structure may be a continuous surface. Alternatively, or in addition, the driven member shape lock structure may be constituted by the driven member press fit surface.
The drive member may comprise one or more exterior flat surfaces. By means of the one or more exterior flat surfaces, the drive member can be held rotationally still when attaching and/or detaching the driven member, for example by means of pliers.
The attachment portion may be provided in the drive member. As a possible alternative, the attachment portion may be constituted by a nut for being threadingly engaged by the attachment member. In this case, the drive member may be provided between the nut and the driven member.
The attachment thread may be an interior thread. Alternatively, or in addition, the detachment thread may be an interior thread.
According to a further aspect, there is provided an electric motor comprising a joint arrangement according to the present disclosure. The drive member may be an output shaft of the electric motor.
According to a further aspect, there is provided an industrial actuator comprising a joint arrangement according to the present disclosure or an electric motor according to the present disclosure. The industrial actuator may be an industrial robot. Alternative examples of industrial actuators are conveyors, positioners, such as workpiece positioners, and track motion platforms.
Further details, advantages and aspects of the present disclosure will become apparent from the following embodiments taken in conjunction with the drawings, wherein:
In the following, a joint arrangement comprising a drive member and a driven member, an electric motor comprising a joint arrangement, and an industrial actuator comprising a joint arrangement, will be described. The same or similar reference numerals will be used to denote the same or similar structural features.
The industrial robot 10 comprises a plurality of electric motors for driving the axes.
The joint arrangement 20 of this example further comprises an attachment screw 28. The attachment screw 28 is one example of an attachment member.
The attachment screw 28 comprises an attachment head 30 at a proximal end (to the right in
The joint arrangement 20 of this example further comprises a detachment screw 34. The detachment screw 34 is one example of a detachment member. The detachment screw 34 comprises a detachment head 36 at a proximal end, an end portion 38 at a distal end, and a detachment member thread 40 between the detachment head 36 and the end portion 38. The end portion 38 of this example is cylindrical.
The drive shaft 22 comprises a drive shaft press fit surface 42. The drive shaft press fit surface 42 is one example of a drive member press fit surface. The drive shaft press fit surface 42 forms a hole.
The pinion 24 comprises a pinion press fit surface 44. The pinion press fit surface 44 is one example of a driven member press fit surface.
The drive shaft press fit surface 42 and the pinion press fit surface 44 are configured to form a press fit to connect the pinion 24 to the drive shaft 22. Each of the drive shaft press fit surface 42 and the pinion press fit surface 44 is continuous.
The drive shaft 22 further comprises a drive shaft shape lock structure 46. In this example, the drive shaft shape lock structure 46 is constituted by the drive shaft press fit surface 42. The drive shaft shape lock structure 46 is one example of a drive member shape lock structure.
The pinion 24 further comprises a pinion shape lock structure 48. In this example, the pinion shape lock structure 48 is constituted by the pinion press fit surface 44. The pinion shape lock structure 48 is one example of a driven member shape lock structure. The drive shaft shape lock structure 46 and the pinion shape lock structure 48 are configured to form a shape lock when the pinion 24 is connected to the drive shaft 22. Each of the drive shaft shape lock structure 46 and the pinion shape lock structure 48 has a polygonal cross section.
The pinion 24 further comprises a through hole 50. The through hole 50 is concentric with the rotation axis 26 when the pinion 24 is connected to the drive shaft 22.
The drive shaft 22 of this example further comprises an attachment hole 52. The attachment hole 52 is provided in an attachment portion 54 of the drive shaft 22. The attachment hole 52 is substantially centered along a length of the drive shaft 22. The attachment hole 52 is a blind hole that opens into the hole provided by the drive shaft press fit surface 42. The attachment hole 52 comprises an attachment thread 56. The attachment thread 56 is an interior thread.
The through hole 50 comprises a detachment thread 58. The detachment thread 58 is thus an interior thread. The detachment thread 58 extends through the entire through hole 50. The detachment thread 58 is larger than the attachment thread 56.
In order to rigidly connect the pinion 24 to the drive shaft 22, a user may first rotationally align the pinion shape lock structure 48 and the drive shaft shape lock structure 46 and push the pinion 24 slightly into the drive shaft 22. The user may then insert the attachment screw 28 through the through hole 50 and thread the attachment member thread 32 into the attachment thread 56. When moving the attachment member thread 32 through the through hole 50, the attachment member thread 32 does not interfere with the detachment thread 58. As shown in
Once the attachment head 30 abuts the proximal end of the pinion 24, further rotation of the attachment screw 28, e.g. by means of a torque wrench, will cause a press fit to be established between the pinion press fit surface 44 and the drive shaft press fit surface 42 since the attachment head 30 pushes the pinion 24 into the drive shaft 22. In this way, the pinion 24 becomes rigidly press fitted to the drive shaft 22 by threadingly engaging the attachment thread 56 with the attachment member thread 32 and by rotating the attachment screw 28. At the same time, i.e. when the triangular pinion shape lock structure 48 enters into the triangular drive shaft shape lock structure 46, a shape lock is established between the pinion 24 and the drive shaft 22.
When screwing the attachment screw 28 into the attachment thread 56, the user may apply a counter torque to the drive shaft 22, for example by holding the drive shaft 22 by hand or with a tool. Alternatively, or in addition, a brake in the electric motor 18 may be applied to provide a counter torque.
The attachment screw 28 may be left in engagement with the attachment thread 56. In this case, forces from the drive shaft 22 may be transmitted to the pinion 24 also via the threaded engagement between the attachment screw 28 and the attachment thread 56. Alternatively, the attachment screw 28 may be removed by screwing the attachment screw 28 in an opposite direction out from the attachment thread 56.
The joint comprising the pinion 24 connected to the drive shaft 22 is backlash free due to the press fit between the pinion press fit surface 44 and the drive shaft press fit surface 42. Should the press fit fail, the shape lock formed by the drive shaft shape lock structure 46 and the pinion shape lock structure 48 prevents relative rotational movements between the drive shaft 22 and the pinion 24. The shape lock enables the press fit force to be lower in comparison with a joint not comprising a shape lock. That is, a smaller safety margin may be provided for the press fit of the joint. This also enables a length of the drive shaft press fit surface 42 and the pinion press fit surface 44 to be made relatively short along the rotation axis 26, thus contributing to a compact design of the joint. As shown in
The field attachable joint also provides a “cleaner” motor module. That is, since the customer can attach the pinion 24 to the drive shaft 22 in the field, a design interface can be provided between the pinion 24 and the drive shaft 22 of the electric motor 18, instead of an interface provided between the pinion 24 and the gearbox. This contributes to an improved modular design. The design interface may for example specify a torque to be transmitted.
In order to disconnect the pinion 24 from the drive shaft 22, the user may disconnect the attachment screw 28 from the attachment thread 56 (if this has not been done previously). The user may then insert the detachment screw 34 into the through hole 50 and thread the detachment member thread 40 into the detachment thread 58. As shown in Fig. ii, the detachment screw 34 is coaxial with the rotation axis 26 when the detachment member thread 40 engages the detachment thread 58. The end portion 38 does not interfere with the attachment thread 56 when entering the attachment hole 52.
Once the end portion 38 abuts the bottom of the attachment hole 52, further rotation of the detachment screw 34, e.g. by means of a torque wrench, will cause the press fit between the pinion press fit surface 44 and the drive shaft press fit surface 42 to be released. In this way, the pinion 24 can be released from the drive shaft 22 by threadingly engaging the detachment thread 58 with the detachment member thread 40 and by rotating the detachment screw 34.
When screwing the detachment screw 34 into the detachment thread 58, the user may apply a counter torque to the drive shaft 22, for example by holding the drive shaft 22 by hand or with a tool. Alternatively, or in addition, a brake in the electric motor 18 may be applied to provide a counter torque.
A user can thus mount and dismount the pinion 24 to and from the drive shaft 22 in the field in a simple and safe manner by only carrying a torque wrench, the attachment screw 28 and the detachment screw 34. The pinion 24 of this example is thus both field attachable and field detachable. This enables a reduction of spare parts. For example, instead of ordering a particular combination of a pinion 24 and a drive shaft 22, or a particular combination of a pinion 24 and an electric motor 18 comprising the drive shaft 22, only the pinion 24 or only the drive shaft 22 may be ordered by a customer.
In
The drive shaft shape lock structure 46 of this example comprises two flat surfaces, each parallel with the rotation axis 26. Correspondingly, the pinion shape lock structure 48 of this example comprises two flat surfaces, each parallel with the rotation axis 26.
The drive shaft 22 comprises two exterior flat surfaces 60 (only one is visible in
The pinion 24 of this example also comprises a step 62 in the through hole 50. The detachment thread 58 is provided distally of the step 62. The through hole 50 is larger proximal of the step 62 than distal of the step 62.
The pinion 24 may be disconnected from the drive shaft 22 by means of the detachment screw 34 in the same way as described in connection with
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.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/063481 | 5/14/2020 | WO |
