Patent Description:
Harmonic reducers are widely used for driving various devices or machines, such as industrial robots, electric tools, automobiles and the like, due to small size, light weight and high precision thereof. A conventional harmonic reducer includes three basic components, i.e., a flexible spline, a circular spline, and a wave generator. During operation of the harmonic reducer, the wave generator may be rotated so as to cause the flexible spline to produce controllable elastic deformation and mesh with the circular spline. In this way, the harmonic reducer may achieve the transferring of motion and power.

Lubricant is typically provided inside the harmonic reducer so as to reduce the friction between various components of the harmonic reducer. During operation of the harmonic reducer, a high pressure may be built up in an internal space of the harmonic reducer due to various causes, such as temperature rising and vaporization of the lubricant caused by the temperature rising. The internal pressure buildup may cause the lubricant to leak out of the harmonic reducer through oil seals of the harmonic reducer. For example, in case that the harmonic reducer is utilized to drive a joint of an industrial robot, the leakage of the lubricant would degrade the lubricating performance of the harmonic reducer and contaminate the robot and work objects processed by the robot.

Conventionally, to prevent such an internal pressure buildup, a gas release hole closed by a plug may be provided on the harmonic reducer. With such an arrangement, an operator may open the plug to release the gas inside the harmonic reducer when the internal pressure of the harmonic reducer is increased. For example, the operator may open the plug to release the gas after the harmonic reducer has been preheated. However, during operation of a device including the harmonic reducer, such as the industrial robot, the operator would not be able to open the plug on the harmonic reducer to release the gas with high pressure. Moreover, the manual operation of the operator on the harmonic reducer may bring injury to the operator.

Thus, there is a need for a solution for preventing the internal pressure buildup and the lubricant leakage of the harmonic reducer.

Documents <CIT> and <CIT> show such type of reducers.

In view of the foregoing problems, various example embodiments of the present disclosure provide a harmonic reducer that can prevent both internal pressure buildup and lubricant leakage.

In a first aspect of the present invention, example embodiments of the present disclosure provide a harmonic reducer. The harmonic reducer comprises a shaft comprising a first through hole extending from a first end to a second end of the shaft in an axial direction of the shaft; a wave generator arranged on the shaft and being rotatable along with the shaft; a flexible spline arranged around the wave generator; a circular spline arranged around the flexible spline; a first flange coupled to the shaft via a first bearing and coupled to the flexible spline; and a second flange coupled to the shaft via a second bearing and coupled to the circular spline, wherein one of the first and second flanges is arranged near to the first end of the shaft, and wherein a cavity is provided between the one of the first and second flanges and the first end of the shaft, and is in fluid communication with an external environment via the first through hole.

In some embodiments, the harmonic reducer further comprises a porous material arranged in the first through hole.

In some embodiments, the harmonic reducer further comprises a sealing mechanism configured to selectively allow the cavity to be in fluid communication with the external environment via the first through hole in accordance with an internal pressure of the cavity.

In some embodiments, the sealing mechanism comprises: a base element coupled to the first end of the shaft and comprising a second through hole in fluid communication with the first through hole; a first sealing element arranged on the base element and comprising one or more openings and a sealing surface surrounding the one or more openings, the one or more openings being configured to communicate the cavity with the second through hole; and a second sealing element arranged between the first sealing element and the base element, and comprising an elastic sealing lip configured to contact the sealing surface of the first sealing element to block the communication between the cavity and the second through hole when the internal pressure of the cavity is below a pressure threshold and configured to be pushed away from the sealing surface of the first sealing element to communicate the cavity with the second through hole when the internal pressure of the cavity is above the pressure threshold.

In some embodiments, the base element comprises: a mounting part inserted into the first through hole at the first end of the shaft, the second through hole being provided on the mounting part; and a receiving part comprising a first receiving space, a second receiving space, and a step between the first receiving space and the second receiving space, the second receiving space being closer to the mounting part than the first receiving space.

In some embodiments, the first sealing element further comprises: a sealing part arranged in the first receiving space and supported by the step, the one or more openings and the sealing surface being provided on the sealing part; and a mounting pillar coupled to the sealing part and configured to mount the second sealing element.

In some embodiments, the second sealing element further comprises: a supporting part configured to support the elastic sealing lip and comprising a mounting hole into which the mounting pillar of the first sealing element is inserted.

In some embodiments, the base element further comprises a groove at its outer surface.

In some embodiments, the sealing mechanism comprises: a second sealing element arranged at the second end of the shaft and comprising an elastic sealing lip configured to contact the second end of the shaft to block the communication between the first through hole and the external environment when the internal pressure of the cavity is below a pressure threshold and configured to be pushed away from the second end of the shaft to communicate the first through hole with the external environment when the internal pressure of the cavity is above the pressure threshold.

In some embodiments, the second sealing element further comprises: a supporting part configured to support the elastic sealing lip and comprising a mounting hole.

In some embodiments, the harmonic reducer further comprises a pulley arranged on the shaft near to the second end of the shaft and being rotatable together with the shaft, wherein the sealing mechanism further comprises a second base element configured to support the second sealing element and comprising: a pair of mounting parts coupled to the pulley; and a second mounting pillar inserted into the mounting hole of the second sealing element to fix the supporting part of the second sealing element.

In some embodiments, the harmonic reducer further comprises one or more channels arranged between the one of the first and second flanges and corresponding one of the first and second bearings.

In some embodiments, the harmonic reducer further comprises a bearing sleeve arranged around the corresponding one of the first and second bearings.

In some embodiments, the harmonic reducer further comprises a cross roller bearing comprising an outer ring coupled to the flexible spline and an inner ring coupled to the circular spline.

In a second aspect of the present invention, example embodiments of the present disclosure provide an industrial robot comprising a harmonic reducer according to the first aspect of the present disclosure.

According to various embodiments of the present disclosure, the cavity inside the harmonic reducer may be in fluid communication with the external environment via the first through hole in the shaft. When the temperature of the harmonic reducer is increased, the gas inside the harmonic reducer may be released into the external environment via the first through hole, such that the internal pressure of the harmonic reducer could be maintained at a low level. In this way, the lubricant leakage via the oil seals of the harmonic reducer could be prevented effectively.

Moreover, during operation of the harmonic reducer, the rotation of the shaft would cause the lubricant (if any) adhered on the shaft to be subjected to a centrifugal force. Under the centrifugal force, the lubricant would fly away from the shaft during the high speed rotation of the shaft. In this way, the lubricant could be prevented from leaking out of the harmonic reducer via the first through hole in the shaft to a large extent.

Furthermore, according to some embodiments of the present disclosure, a sealing mechanism is provided in the harmonic reducer so as to selectively allow the cavity to be in fluid communication with the external environment via the first through hole. When the internal pressure of the cavity is below the pressure threshold, the sealing mechanism would block the communication between the cavity and the external environment. When the internal pressure of the cavity is above the pressure threshold, the sealing mechanism would allow the cavity to be in communication with the external environment. In this way, the internal pressure of the harmonic reducer could be maintained at a low level. Moreover, the lubricant may be further prevented from leaking out of the harmonic reducer via the first through hole of the shaft. Furthermore, the sealing mechanism could prevent debris in the external environment from entering the harmonic reducer via the first through hole.

Through the following detailed descriptions with reference to the accompanying drawings, the above and other objectives, features and advantages of the example embodiments disclosed herein will become more comprehensible. In the drawings, several example embodiments disclosed herein will be illustrated in an example and in a non-limiting manner, wherein:.

Principles of the present disclosure will now be described with reference to several example embodiments shown in the drawings. Though example embodiments of the present disclosure are illustrated in the drawings, it is to be understood that the embodiments are described only to facilitate those skilled in the art in better understanding and thereby achieving the present disclosure, rather than to limit the scope of the disclosure in any manner.

The term "comprises" or "includes" and its variants are to be read as open terms that mean "includes, but is not limited to. " The term "or" is to be read as "and/or" unless the context clearly indicates otherwise. The term "based on" is to be read as "based at least in part on. " The term "being operable to" is to mean a function, an action, a motion or a state can be achieved by an operation induced by a user or an external mechanism. The term "one embodiment" and "an embodiment" are to be read as "at least one embodiment. " The term "another embodiment" is to be read as "at least one other embodiment. " The terms "first," "second," and the like may refer to different or same objects. A definition of a term is consistent throughout the description unless the context clearly indicates otherwise.

Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Furthermore, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings. In the description below, like reference numerals and labels are used to describe the same, similar or corresponding parts in the figures.

As discussed above, the internal pressure buildup of the harmonic reducer may cause the lubricant to leak out of the harmonic reducer through the oil seals. According to embodiments of the present disclosure, to prevent both internal pressure buildup and lubricant leakage of the harmonic reducer, a through hole is provided in the shaft of the harmonic reducer such that the cavity in the harmonic reducer may be in fluid communication with the external environment. The above idea may be implemented in various manners, as will be described in detail in the following paragraphs.

Hereinafter, the principles of the present disclosure will be described in detail with reference to <FIG>. Referring to <FIG> first, <FIG> illustrates a cross-sectional view of a harmonic reducer in accordance with a first embodiment of the present disclosure. As shown in <FIG>, the harmonic reducer <NUM> generally includes a shaft <NUM>, a wave generator <NUM>, a flexible spline <NUM>, a circular spline <NUM>, a first flange <NUM>, and a second flange <NUM>.

The shaft <NUM> is an input shaft of the harmonic reducer <NUM> and is adapted to receive a drive power (torque) input from a driver, such as a motor. As shown in <FIG>, the shaft <NUM> includes a first end <NUM> and a second end <NUM> opposite to the first end <NUM>. The first end <NUM> is arranged inside the harmonic reducer <NUM> and the second end <NUM> is arranged outside the harmonic reducer <NUM>. The shaft <NUM> is provided with a first through hole <NUM> extending from the first end <NUM> to the second end <NUM> of the shaft <NUM> in an axial direction X of the shaft <NUM>.

The wave generator <NUM> is arranged on the shaft <NUM> and is rotatable along with the shaft <NUM>. That is, the wave generator <NUM> may rotate in synchronization with the shaft <NUM>. The flexible spline <NUM> is arranged around the wave generator <NUM>. The circular spline <NUM> is arranged around the flexible spline <NUM>. During operation of the harmonic reducer <NUM>, the wave generator <NUM> may be rotated so as to cause the flexible spline <NUM> to produce controllable elastic deformation and mesh with the circular spline <NUM>. The number of teeth of the circular spline <NUM> is more than the number of teeth of the flexible spline <NUM> by two. With such an arrangement, the harmonic reducer <NUM> may achieve the transferring of motion and power. It is noted that the constructions and operating principles of the wave generator <NUM>, the flexible spline <NUM>, and the circular spline <NUM> are known in the art, and will not be described in detail any more herein.

The first flange <NUM> is coupled to the shaft <NUM> via a first bearing <NUM>. The second flange <NUM> is coupled to the shaft <NUM> via a second bearing <NUM>. With such an arrangement, the shaft <NUM> may be supported by the first flange <NUM> and the second flange <NUM>. In addition, the first flange <NUM> is further coupled to the flexible spline <NUM> and the second flange <NUM> is further coupled to the circular spline <NUM>. During operation of the harmonic reducer <NUM>, the flexible spline <NUM> may rotate in synchronization with the first flange <NUM> at a low speed, and the circular spline <NUM> and the second flange <NUM> would not rotate.

In the first embodiment, as shown in <FIG>, the first end <NUM> of the shaft <NUM> is arranged inside the harmonic reducer <NUM> and near to the first flange <NUM>. A cavity <NUM> is provided between the first flange <NUM> and the first end <NUM> of the shaft <NUM>. The cavity <NUM> is in fluid communication with internal spaces <NUM> of the harmonic reducer <NUM> via for example gaps on the first bearing <NUM>. Thus, the cavity <NUM> and the internal spaces <NUM> of the harmonic reducer <NUM> may be at substantially the same pressure. Further, the cavity <NUM> is in fluid communication with the external environment via the first through hole <NUM>. If the pressure inside the harmonic reducer <NUM> is increased due to for example the temperature rising, the gas inside the harmonic reducer <NUM> may be released into the external environment via the first through hole <NUM>.

To reduce the friction between various components of the harmonic reducer <NUM>, lubricant is typically provided in the internal spaces <NUM> of the harmonic reducer <NUM>. During operation of the harmonic reducer <NUM>, if the temperature of the harmonic reducer <NUM> rises, the gas in the internal spaces <NUM> may be released into the cavity <NUM> and then into the external environment via the first through hole <NUM>, such that the pressure of the internal spaces <NUM> could be maintained at a low level. In this way, the lubricant leakage via oil seals <NUM> of the harmonic reducer <NUM> could be prevented effectively.

Moreover, during operation of the harmonic reducer <NUM>, the rotation of the shaft <NUM> would cause the lubricant (if any) adhered on the shaft <NUM> to be subjected to a centrifugal force. Under the centrifugal force, the lubricant would fly away from the shaft <NUM> during the high speed rotation of the shaft <NUM>. In this way, the lubricant could be prevented from leaking out of the harmonic reducer <NUM> via the first through hole <NUM> to a large extent.

In the first embodiment, as shown in <FIG>, the harmonic reducer <NUM> further includes a cross roller bearing <NUM>. The cross roller bearing <NUM> includes an outer ring <NUM> coupled to the flexible spline <NUM> and an inner ring <NUM> coupled to the circular spline <NUM>. In other embodiments, the cross roller bearing <NUM> may be replaced by other types of bearings. The scope of the present invention is not intended to be limited in this respect.

<FIG> illustrates a cross-sectional view of a harmonic reducer in accordance with a second embodiment of the present disclosure. The construction of the harmonic reducer <NUM> as shown in <FIG> is similar to that of the harmonic reducer <NUM> as shown in <FIG>, except that the harmonic reducer <NUM> as shown in <FIG> further includes a porous material <NUM> arranged in the first through hole <NUM>. The porous material <NUM> is permeable to the gas and non-permeable to the lubricant. Hence, the porous material <NUM> may adsorb the lubricant mixed in the gas from the cavity <NUM> on one hand, and may prevent debris in the external environment from entering the cavity <NUM> via the first through hole <NUM> on the other hand.

<FIG> illustrates a cross-sectional view of a harmonic reducer in accordance with a third embodiment of the present disclosure. The construction of the harmonic reducer <NUM> as shown in <FIG> is similar to that of the harmonic reducer <NUM> as shown in <FIG>, except that the harmonic reducer <NUM> as shown in <FIG> further includes a sealing mechanism <NUM>. The sealing mechanism <NUM> is configured to selectively allow the cavity <NUM> to be in fluid communication with the external environment in accordance with an internal pressure of the cavity <NUM>. When the internal pressure of the cavity <NUM> is increased due to the temperature rising of the harmonic reducer <NUM>, the sealing mechanism <NUM> may allow the cavity <NUM> to be in communication with the external environment. On the contrary, when the internal pressure of the cavity <NUM> is substantially identical to the environment pressure, the sealing mechanism <NUM> may block the communication between the cavity <NUM> and the external environment.

The sealing mechanism <NUM> may have various constructions. <FIG> illustrate an example construction and arrangement of the sealing mechanism <NUM>. As shown in <FIG>, the sealing mechanism <NUM> includes a base element <NUM>, a first sealing element <NUM>, and a second sealing element <NUM>.

As shown in <FIG>, the base element <NUM> is arranged at the first end <NUM> of the shaft <NUM> and adapted to support the first and second sealing elements <NUM>, <NUM>. In some cases, the base element <NUM> may be detachably mounted onto the shaft <NUM>, for example through screws or in other manners. In other cases, the base element <NUM> may be soldered on the first end <NUM> of the shaft <NUM> or even formed as a part of the shaft <NUM>.

In some embodiments, as shown in <FIG> and <FIG>, the base element <NUM> includes a mounting part <NUM> adapted to be mounted onto the shaft <NUM> and a receiving part <NUM> adapted to receive the first and second sealing elements <NUM>, <NUM>. The mounting part <NUM> is provided with a second through hole <NUM> in fluid communication with the first through hole <NUM>. The mounting part <NUM> may be inserted into the first through hole <NUM> of the shaft <NUM>, and coupled to the shaft <NUM> through screws or interference fit, or in various other manners. The receiving part <NUM> includes a first receiving space <NUM>, a second receiving space <NUM>, and a step <NUM> between the first receiving space <NUM> and the second receiving space <NUM>. The second receiving space <NUM> is in fluid communication with the second through hole <NUM>, and in turn, in fluid communication with the first through hole <NUM>. The second receiving space <NUM> is closer to the mounting part <NUM> than the first receiving space <NUM>. That is, the second receiving space <NUM> is disposed at a lower portion of the receiving part <NUM>, and the first receiving space <NUM> is disposed at an upper portion of the receiving part <NUM>. The first and second sealing elements <NUM>, <NUM> are arranged in the first and second receiving spaces <NUM>, <NUM>, as will be described in detail hereinafter.

As shown in <FIG>, the first sealing element <NUM> is arranged on the base element <NUM> and includes one or more openings <NUM> and a sealing surface <NUM> surrounding the one or more openings <NUM>. The one or more openings <NUM> are configured to communicate the cavity <NUM> with the second through hole <NUM>. The sealing surface <NUM> is configured to cooperate with the second sealing element <NUM>. When the sealing surface <NUM> is in contact with the second sealing element <NUM>, the one or more openings <NUM> would be closed, and when the sealing surface <NUM> is not in contact with the second sealing element <NUM>, the one or more openings <NUM> would be opened.

In some embodiments, as shown in <FIG>, the first sealing element <NUM> includes a sealing part <NUM> and a mounting pillar <NUM>. The sealing part <NUM> is arranged in the first receiving space <NUM> and supported by the step <NUM>. The sealing part <NUM> may be adhered onto the receiving part <NUM> or fixed in the first receiving space <NUM> through interference fit. The one or more openings <NUM> and the sealing surface <NUM> are provided on the sealing part <NUM>. The sealing surface <NUM> is a part of a bottom surface of the sealing part <NUM>. The mounting pillar <NUM> is adapted to mount the second sealing element <NUM>.

As shown in <FIG>, the second sealing element <NUM> is arranged between the first sealing element <NUM> and the base element <NUM> so as to selectively allow or block the fluid communication between the cavity <NUM> and the first through hole <NUM> of the shaft <NUM>. The second sealing element <NUM> is generally located in the second receiving space <NUM>. To cooperate with the sealing surface <NUM> of the first sealing element <NUM>, the second sealing element <NUM> includes an elastic sealing lip <NUM>. The elastic sealing lip <NUM> is configured to contact the sealing surface <NUM> of the first sealing element <NUM> to block the communication between the cavity <NUM> and the second through hole <NUM> when the internal pressure of the cavity <NUM> is below a pressure threshold and configured to be pushed away from the sealing surface <NUM> of the first sealing element <NUM> to communicate the cavity <NUM> with the second through hole <NUM> when the internal pressure of the cavity <NUM> is above the pressure threshold.

In some embodiments, as shown in <FIG>, the elastic sealing lip <NUM> is formed on a supporting part <NUM>. The supporting part <NUM> is configured to support the elastic sealing lip <NUM> and includes a mounting hole <NUM> into which the mounting pillar <NUM> of the first sealing element <NUM> is inserted. Through the cooperation between the mounting pillar <NUM> and the mounting hole <NUM>, the second sealing element <NUM> may be coupled onto the first sealing element <NUM> easily and reliably.

In some embodiments, the second sealing element <NUM> may be made of rubber material or other elastic materials as a whole. In some other embodiments, only the elastic sealing lip <NUM> is made of rubber material or other elastic materials, and the elastic sealing lip <NUM> is coupled to the supporting part <NUM> of a different material.

According to embodiments of the present disclosure, the sealing mechanism <NUM> may provide additional advantages. On one hand, the internal pressure of the harmonic reducer <NUM> could be maintained at a low level. On the other hand, through the cooperation between the sealing surface <NUM> of the first sealing element <NUM> and the elastic sealing lip <NUM> of the second sealing element <NUM>, the openings <NUM> on the first sealing element <NUM> may be blocked most of the time. Thus, the lubricant may be further prevented from leaking out of the harmonic reducer <NUM> via the first through hole <NUM> of the shaft <NUM>, and the sealing mechanism <NUM> could prevent debris in the external environment from entering the harmonic reducer <NUM> via the first through hole <NUM>.

<FIG> illustrates a cross-sectional view of a harmonic reducer in accordance with a fourth embodiment of the present disclosure. The construction of the harmonic reducer <NUM> as shown in <FIG> is similar to that of the harmonic reducer <NUM> as shown in <FIG>, except that the base element <NUM> further includes a groove <NUM> at its outer surface. <FIG> and <FIG> illustrate details of the groove <NUM>. As shown, the groove <NUM> is arranged at an outer surface of the receiving part <NUM> of the base element <NUM>. The groove <NUM> includes a bottom surface and two oblique sidewalls. The oblique sidewalls of the groove <NUM> would cause the lubricant adhered on the base element <NUM> to fly away from the base element <NUM> more easily.

<FIG> illustrates a cross-sectional view of a harmonic reducer in accordance with a fifth embodiment of the present disclosure. The construction of the harmonic reducer <NUM> as shown in <FIG> is similar to that of the harmonic reducer <NUM> as shown in <FIG>, except that the harmonic reducer <NUM> as shown in <FIG> further includes a pulley <NUM> arranged on the shaft <NUM>. The pulley <NUM> is positioned near to the second end <NUM> of the shaft <NUM> and rotatable together with the shaft <NUM>. Through the pulley <NUM>, the shaft <NUM> of the harmonic reducer <NUM> may be driven by a driver via a belt.

In some cases, a large amount of lubricant would probably accumulate in the cavity <NUM>. In order to remove the lubricant in the cavity <NUM>, one or more channels may be provided between the cavity <NUM> and the internal spaces <NUM>. <FIG> illustrate an example approach for removing the lubricant in the cavity <NUM>.

<FIG> illustrates a cross-sectional view of a harmonic reducer in accordance with a sixth embodiment of the present disclosure, <FIG> is a perspective view of the first flange of the harmonic reducer as shown in <FIG>, and <FIG> illustrates a relative arrangement between the first flange and the first bearing of the harmonic reducer as shown in <FIG>. The construction of the harmonic reducer <NUM> as shown in <FIG> is similar to that of the harmonic reducer <NUM> as shown in <FIG>, except that the harmonic reducer <NUM> further includes one or more channels <NUM> arranged between the first flange <NUM> and the first bearing <NUM>. Through the channels <NUM>, the lubricant in the cavity <NUM> may flow back into the internal spaces <NUM>.

In some embodiments, as shown in <FIG>, the harmonic reducer <NUM> further includes a bearing sleeve <NUM> arranged around the first bearing <NUM>. The bearing sleeve <NUM> may protect the first bearing <NUM> from being worn by the first flange <NUM>.

<FIG> illustrates a cross-sectional view of a harmonic reducer in accordance with a seventh embodiment of the present disclosure, <FIG> is a partially enlarged view of the harmonic reducer as shown in <FIG>, and <FIG> is a perspective view of a second base element of the harmonic reducer as shown in <FIG>. The construction of the harmonic reducer <NUM> as shown in <FIG> is similar to that of the harmonic reducer <NUM> as shown in <FIG>, except that the sealing mechanism <NUM> as shown in <FIG> is of a different structure and is arranged at a different position.

As shown in <FIG> and <FIG>, the sealing mechanism <NUM> includes a second sealing element <NUM>. The construction of the second sealing element <NUM> as shown in <FIG> and <FIG> is similar to that of the second sealing element <NUM> as shown in <FIG>. For example, the second sealing element <NUM> includes an elastic sealing lip <NUM> and a supporting part <NUM> adapted to support the elastic sealing lip <NUM>. The elastic sealing lip <NUM> is configured to contact the second end <NUM> of the shaft <NUM> to block the communication between the first through hole <NUM> and the external environment when the internal pressure of the cavity <NUM> is below the pressure threshold and configured to be pushed away from the second end <NUM> of the shaft <NUM> to communicate the first through hole <NUM> with the external environment when the internal pressure of the cavity <NUM> is above the pressure threshold.

In some embodiments, to fix the second sealing element <NUM> at the second end <NUM> of the shaft <NUM>, the sealing mechanism <NUM> further includes a second base element <NUM> configured to support the second sealing element <NUM>. As shown in <FIG> and <FIG>, the second base element <NUM> includes a second mounting pillar <NUM> and a pair of mounting parts <NUM>. The mounting parts <NUM> are coupled to the pulley <NUM>. The second mounting pillar <NUM> is inserted into the mounting hole <NUM> of the second sealing element <NUM> to fix the supporting part <NUM> of the second sealing element <NUM>, such that the second sealing element <NUM> is positioned at the second end <NUM> of the shaft <NUM>.

In an embodiment, as shown in <FIG>, the harmonic reducer <NUM> further includes a third base element <NUM> arranged at the first end <NUM> of the shaft <NUM>. The construction of the third base element <NUM> is similar to that of the base element <NUM> as shown in <FIG>. It is to be understood that in other embodiments, the third base element <NUM> may be removed, as that shown in <FIG> and <FIG>.

In embodiments described above with reference to <FIG>, the first end <NUM> of the shaft <NUM> is arranged near to the first flange <NUM> and the cavity <NUM> is provided between the first flange <NUM> and the first end <NUM> of the shaft <NUM>. However, it is to be understood that in other embodiments, the first end <NUM> of the shaft <NUM> may be arranged inside the harmonic reducer <NUM> near to the second flange <NUM>, and the cavity <NUM> is provided between the second flange <NUM> and the first end <NUM> of the shaft <NUM>. In these cases, the sealing mechanism <NUM> and other arrangements as described above is also applicable. For example, the sealing mechanism <NUM> as described above with reference to <FIG> may be arranged in the cavity <NUM> near to the second flange <NUM>, and the sealing mechanism <NUM> as described above with reference to <FIG> may be arranged at the second end <NUM> of the shaft <NUM> near to the first flange <NUM>. Moreover, the pulley <NUM> may be arranged at the second end <NUM> of the shaft <NUM> near to the first flange <NUM>.

According to embodiments of the present disclosure, the harmonic reducer <NUM> may be used in various devices or machines, such as industrial robots, electric tools, and automobiles. For example, the harmonic reducer <NUM> may be used for driving a joint of an industrial robot.

Claim 1:
A harmonic reducer (<NUM>) comprising:
a shaft (<NUM>) comprising a first through hole (<NUM>) extending from a first end (<NUM>) to a second end (<NUM>) of the shaft (<NUM>) in an axial direction (X) of the shaft (<NUM>);
a wave generator (<NUM>) arranged on the shaft (<NUM>) and being rotatable along with the shaft (<NUM>);
a flexible spline (<NUM>) arranged around the wave generator (<NUM>);
a circular spline (<NUM>) arranged around the flexible spline (<NUM>); characterized in that
a first flange (<NUM>) is coupled to the shaft (<NUM>) via a first bearing (<NUM>) and coupled to the flexible spline (<NUM>); and
a second flange (<NUM>) is coupled to the shaft (<NUM>) via a second bearing (<NUM>) and coupled to the circular spline (<NUM>),
wherein one of the first and second flanges (<NUM>, <NUM>) is arranged near to the first end (<NUM>) of the shaft (<NUM>), and
wherein a cavity (<NUM>) is provided between the one of the first and second flanges (<NUM>, <NUM>) and the first end (<NUM>) of the shaft (<NUM>), and is in fluid communication with an external environment via the first through hole (<NUM>).