Parallel link mechanism and industrial robot

A parallel link mechanism includes a first arm, a second arm, a first auxiliary link, a second auxiliary link, and a drive motor. A cylindrical connection shaft having a first rotational axis is provided near the proximal portion of the first arm. The proximal portion of the first arm is rotatably connected to a fixed base through the connection shaft. The distal portion of the second arm is rotatably connected to a movable base. The proximal portion of the second arm is rotatably connected to the distal portion of the first arm through a connecting portion connected to a transmission mechanism. The first auxiliary link forms a first parallel link together with the first arm, the connecting portion, and the fixed base. The second auxiliary link forms a second parallel link together with the second arm, the connecting portion, and the movable base. The drive motor drives the transmission mechanism to pivot the first arm and the second arm. The drive motor includes a motor shaft having a second rotational axis. The drive motor is fixed to either the first arm or the connection shaft with the second rotational axis being offset from the first rotational axis in a radial direction of the connection shaft in such a manner that, when the first arm rotates about the first rotational axis, the drive motor is allowed to rotate about the first rotational axis together with the first arm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-304824, filed on Oct. 19, 2005 and Japanese Patent Application No. 2006-170734, filed on Jun. 20, 2006, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a parallel link mechanism and an industrial robot.

2. Related Art

General requirements for industrial robots include increased operation speed, improved operation accuracy, and, in certain operation sites, enhanced cleanliness. Particularly, there are demands that the industrial robots be used under particular circumstance involving use of specific gases or chemicals. One known vertical movement shaft mechanism of a SCARA robot includes a ball screw provided in a vertical movement shaft. The mechanism has a bellows as a protecting member for preventing generation of dust and leakage of grease from the interior of an arm. Through contraction of the bellows, the vertical movement shaft mechanism ensures improved cleanliness while maintaining operation speed and operation accuracy at relatively high levels.

However, when the bellows contracts, the pressure in the vertical movement shaft mechanism changes, inducing the dust generation and the grease leakage. It is thus difficult to maintain the increased cleanliness of the vertical movement shaft mechanism having the bellows. Further, to sufficiently prolong mechanical life of the bellows of the vertical movement shaft mechanism, the bellows must be formed of material selected from a limited range. This makes it difficult to operate the vertical movement shaft mechanism having the bellows under the aforementioned particular circumstances.

To solve the problem, a vertical movement shaft mechanism of an industrial robot including a parallel link mechanism, but not a bellows, has been proposed. Specifically, as described in JP-A-2002-326181, first arm is connected to a fixed base and a connection base while second arm is connected to the connection base and a movable base. A drive motor is provided in the fixed base. A spur gear is arranged in the interior of the connection base. The drive motor rotates the spur gear through a reducer. The spur gear thus transmits rotational force to the two arms, selectively raising and lowering the movable base.

However, in this mechanism, the drive motor, or a drive source, is fixed to the fixed base. Therefore, when assembling the industrial robot, the rotational axis of the drive motor must coincide with the rotational axis of the arms. This complicates assembly of the industrial robot.

To maintain relatively high cleanliness of the industrial robot, cables are arranged in the fixed base or the arms. For enabling such internal wiring, the industrial robot employs a hollow motor as a drive motor. This enlarges the sizes of devices provided in the industrial robot.

SUMMARY

An advantage of some aspects of the invention is to provide an easy-to-install parallel link mechanism and an easy-to-assemble industrial robot that enable easy internal wiring without employing a hollow motor as a drive motor.

According to an aspect of the invention, a parallel link mechanism including a first arm, a second arm, a first auxiliary link, a second auxiliary link, and a drive motor is provided. The first arm has a proximal portion and a distal portion. A cylindrical connection shaft having a first rotational axis is provided near the proximal portion of the first arm. The proximal portion of the first arm is rotatably connected to a fixed base through the connection shaft. The second arm has a proximal portion and a distal portion. The distal portion of the second arm is rotatably connected to a movable base. The proximal portion of the second arm is rotatably connected to the distal portion of the first arm through a connecting portion connected to a transmission mechanism. The first auxiliary link forms a first parallel link together with the first arm, the connecting portion, and the fixed base. The second auxiliary link forms a second parallel link together with the second arm, the connecting portion, and the movable base. The drive motor drives the transmission mechanism to pivot the first arm and the second arm. The drive motor includes a motor shaft having a second rotational axis. The drive motor is fixed to either the first arm or the connection shaft with the second rotational axis being offset from the first rotational axis in a radial direction of the connection shaft in such a manner that, when the first arm rotates about the first rotational axis, the drive motor is allowed to rotate about the first rotational axis together with the first arm.

According to another aspect of the invention, an industrial robot including a first parallel link, a second parallel link, a first output shaft, a second output shaft, a cylindrical connection shaft, and a fixing portion. The first parallel link has a fixed base, a connection base, a first arm, and a first auxiliary link. The first arm includes a proximal portion rotatably connected to the fixed base and a distal portion rotatably connected to the connection base. The first auxiliary link has a proximal portion rotatably connected to the fixed base and a distal portion rotatably connected to the connection base. The first auxiliary link is arranged parallel with the first arm. The second parallel link has the connection base, a movable base, a second arm, and a second auxiliary link. The second arm includes a proximal portion rotatably connected to the connection base and a distal portion rotatably connected to the movable base. The second auxiliary link has a proximal portion rotatably connected to the connection base and a distal portion rotatably connected to the movable base. The first output shaft is provided near the distal portion of the first arm. The first output shaft converts drive force of a drive motor and outputs the drive force to the connection base. The second output shaft is provided near the distal portion of the first arm. The second output shaft converts the drive force of the drive motor and outputs the drive force to the second arm. The cylindrical connection shaft is provided near the proximal portion of the first arm. The connection shaft rotatably connects the first arm to the fixed base. The first arm rotates about a first rotational axis. The drive motor has a motor shaft rotating about a second rotational axis. The fixing portion fixes the drive motor to either the first arm or the connection shaft with the second rotational axis being offset from the first rotational axis in a radial direction of the connection shaft.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

As shown inFIG. 1, an industrial robot1has a substantially parallelepiped fixed base2fixed to a floor surface B. As shown inFIG. 2, the fixed base2has a cylindrical first connection shaft5that is rotatably supported by a bearing4. The proximal portion of a first arm3is connected to the first connection shaft5. In other words, a first connection shaft5is provided near the proximal portion of the first arm3, which is connected to the fixed base2through the first connection shaft5. Specifically, a through hole3H is defined in the proximal portion of the first arm3and extends through the first arm3, allowing communication between the interior and the exterior of the first arm3. The first connection shaft5is secured to an outer wall portion of the through hole3H through securing bolts B1. The connecting portion between the first connection shaft5and the first arm3is sealed by an O ring (not shown). The first arm3has a first arm cover3a, which defines a sealed space in the first arm3.

The first arm3rotates about the axis L1(a first rotational axis) of the first connection shaft5(the through hole3H). When the first arm3rotates about the axis L1, the space in the fixed base2and the space in the first arm3are maintained in a sealed state.

As shown inFIG. 3, a disk-like flange6is fixedly connected to an inner wall portion of the through hole3H. The outer diameter of the flange6is smaller than the inner diameter of the through hole3H (the inner diameter of the first connection shaft5) of the first arm3. A bearing hole6ais defined at the center of the flange6and receives a bearing7.

An upper side of the flange6as viewed inFIG. 3is secured to an upper inner wall portion of the through hole3H as viewed in the drawing through a securing bolt B2. The axis M1of the bearing hole6a(a second rotational axis) thus becomes offset from the axis L1of the first connection shaft5(the first rotational axis) in an upward direction as viewed inFIG. 3. Therefore, the flange6blocks a restricted portion of the through hole3H (a restricted portion of the hollow portion of the first connection shaft5) in correspondence with the offset amount of the axis M1, thus defining a space S that permits communication between the space in the fixed base2and the space in the first arm3. When the first arm3pivots about the axis L1, the flange6pivots about the axis L1together with the first arm3. This maintains the space S in the through hole3H and the hollow portion of the first connection shaft5.

A support member8is formed integrally with the side of the flange6corresponding to the fixed base2. The support member8extends through the inside of the first connection shaft5into the space in the fixed base2. A fixing portion9is formed integrally with the side of the support member8corresponding to the fixed base2. A drive motor10is fixed to the fixing portion9. A motor shaft11of the drive motor10extends through the bearing hole6aof the flange6into the space in the first arm3. A pulley P1, or a part of a connection-drive member, is connected to the distal end of the motor shaft11.

The motor shaft11is rotatably supported by a bearing7. The axis of the motor shaft11coincides with the axis M1of the bearing hole6a. The motor shaft11of the drive motor10thus becomes offset from the axis L1of the first connection shaft5in an upward direction as viewed inFIG. 3. Therefore, the drive motor10blocks a restricted portion of the through hole3H (a restricted portion of the hollow portion of the first connection shaft5) in correspondence with the offset amount of the motor shaft11, thus defining the space S that permits communication between the space in the fixed base2and the space in the first arm3. When the first arm3pivots about the axis L1, the drive motor10pivots about the axis L1together with the first arm3. This maintains the space S in the through hole3H and the hollow portion of the first connection shaft5.

Accordingly, a relatively large hollow passage is maintained along a path extending from the fixed base2to the first arm3. This permits arrangement of lines or tubes in the space extending from the fixed base2to the first arm3, without employing a hollow motor as the drive motor10.

The position of the drive motor10is determined solely in correspondence with the position of the first arm3. This makes it unnecessary to arrange the motor shaft11on the axis L1. That is, arrangement of the motor shaft11of the drive motor10does not have to be adjusted in such a manner that the motor shaft11coincides with the pivotal axis of the first arm3. Assembly of the industrial robot1is thus facilitated.

The drive motor10is secured to the first connection shaft5through the motor shaft11, which extends through the hollow portion of the first connection shaft5. Accordingly, compared to a case in which the motor shaft11is provided in the space in the fixed base2or the space in the first arm3, the dimension of the industrial robot1in the direction defined by the axis L1decreases by an amount corresponding to the length of the motor shaft11.

As shown inFIGS. 2 and 4, a harmonic drive gear reducer20, or a transmission mechanism, is arranged at an upper end of the first arm3. A body cover K of the harmonic drive gear reducer20is fixedly connected to the first arm3through connection bolts B3. Referring toFIG. 4, the harmonic drive gear reducer20has a cylindrical input shaft21. A pulley P2, another part of the connection-drive member, is connected to the input shaft21. The pulley P2is operably connected to the pulley P1, which is connected to the motor shaft11, through a non-illustrated belt. The rotational force generated by the drive motor10is thus transmitted to the pulley P2.

The input shaft21has a wave generator22. The wave generator22has an oval cam portion22a, a first ball bearing22b, and a second ball bearing22c. The cam portion22ais secured to the input shaft21. The first and second ball bearings22b,22care arranged along the outer circumference of the cam portion22aas opposed to each other. When the input shaft21rotates about the axis L2, the inner rings of the first and second ball bearings22b,22crotate about the axis L2integrally with the cam portion22a.

A first flexspline24is formed around the outer ring of the first ball bearing22b. The first flexspline24has a substantially cup-like shape. The opening of the first flexspline24is formed of an elastic metal body. The inner wall of the opening of the first flexspline24is held in contact with the outer ring of the first ball bearing22b. When the input shaft21(the cam portion22a) rotates about the axis L2, the portion of the first flexspline24corresponding to the opening elastically deforms in an oval shape along the outer peripheral surface of the cam portion22a. Teeth (not shown) are formed on the outer peripheral surface of the portion of the first flexspline24corresponding to the opening. A first output shaft27is secured to a proximal portion24aof the first flexspline24through non-illustrated connection bolts. The first output shaft27is rotatably supported by the input shaft21and rotates about the axis L2.

A second flexspline25is formed around the outer ring of the second ball bearing22c. The second flexspline25has a substantially silk-hat-like shape. The cylindrical portion of the second flexspline25is formed of an elastic metal body. The inner peripheral surface of the cylindrical portion of the second flexspline25is held in contact with the outer ring of the second ball bearing22c. When the input shaft21(the cam portion22a) rotates about the axis L2, the cylindrical portion of the second flexspline25elastically deforms in an oval shape along the outer peripheral surface of the cam portion22a. Teeth (not shown) are formed on the outer peripheral surface of the cylindrical portion of the second flexspline25. The second flexspline25has a flange25asecured to the cover K through securing bolts B4.

A cylindrical circular spline26is arranged at outer sides of the first and second flexsplines24,25. A second output shaft28is connected to an outer side of the circular spline26through non-illustrated connection bolts. The second output shaft28is rotatably supported by the first output shaft27through a bearing29arranged at an outer side of the first output shaft27. When the circular spline26rotates, the second output shaft28rotates about the axis L2.

A left gear portion26aand a right gear portion26bare formed at the inner circumference of the circular spline26and engaged with the first flexspline24and the second flexspline25, respectively. The left gear portion26ahas a greater number of teeth than the first flexspline24. The left gear portion26abecomes engaged with the first flexspline24solely in a direction defined by the longitudinal axis of the cam portion22a. The right gear portion26bhas a greater number of teeth than the second flexspline25. The right gear portion26bbecomes engaged with the second flexspline25solely in a direction defined by the longitudinal axis of the cam portion22a.

Since the left gear portion26ahas more teeth than the first flexspline24, each of the teeth of the left gear portion26arotates the engaged one of the teeth of the first flexspline24in a counterclockwise direction in a single cycle of clockwise rotation of the input shaft21. In other words, when the input shaft21rotates, the circular spline26rotates the first output shaft27relative to the first flexspline24in the direction opposite to the rotational direction of the input shaft21. The circular spline26rotates the first output shaft27in accordance with the reduction ratio corresponding to the difference between the number of the teeth of the left gear portion26aand the number of the teeth of the first flexspline24.

Since the right gear portion26bhas more teeth than the second flexspline25, each of the teeth of the right gear portion26brotates the engaged one of the teeth of the second flexspline25in a counterclockwise direction in a single cycle of clockwise rotation of the input shaft21. In other words, when the input shaft21rotates, the circular spline26rotates the second output shaft28relative to the second flexspline25(the first arm3) in the direction opposite to the rotational direction of the input shaft21. The circular spline26rotates the second output shaft28in accordance with the reduction ratio corresponding to the difference between the number of the teeth of the right gear portion26band the number of the teeth of the second flexspline25.

That is, the first output shaft27receives rotation of the input shaft21that has been converted into rotation in the opposite direction and reduced by the first flexspline24and the left gear portion26aof the circular spline26. Similarly, the second output shaft28receives rotation of the input shaft21that has been converted into rotation in the opposite direction and reduced by the second flexspline25and the right gear portion26bof the circular spline26.

The ratio of the reduction ratio of the first output shaft27to the input shaft21and the reduction ratio of the second output shaft28to the input shaft21can be varied by changing the number of the teeth of the first flexspline24, the number of the teeth of the second flexspline25, the number of the teeth of the left gear portion26a, and the number of the teeth of the right gear portion26b. In the illustrated embodiment, the number of the teeth of each of these components is selected so that the ratio of the reduction ratio of the first output shaft27to the input shaft21and the reduction ratio of the second output shaft28to the input shaft21become 2:1. In other words, the second output shaft28of the illustrated embodiment rotates in the same direction as that of the first output shaft27at a rotational angle twice as large as that of the first output shaft27.

The lower end of the second arm30is connected to the second output shaft28. Specifically, the second arm30is secured to the second output shaft28through connection bolts B5in such a manner that a cylindrical portion30b, which is provided at a lower end of the second arm30, encompasses the outer circumference of the second output shaft28.

Referring toFIG. 2, the upper end of the second arm30is connected to a movable base40having a substantially box-like shape. The movable base40has a cylindrical second connection shaft43rotatably supported by a bearing42. A through hole30H is defined in the upper end of the second arm30. The second connection shaft43is secured to an outer wall portion of the through hole30H through securing bolts B6. The second arm30is rotatably connected to the movable base40and rotates about the axis L3of the second connection shaft43. The second connection shaft43and the second arm30are hollow. The second arm30is sealed by a second arm cover30a. The connecting portion between the second connection shaft43and the second arm30is sealed by a non-illustrated O-ring.

As shown inFIG. 4, a connection base50, which is arranged at a position outer than the second arm30(at the left-hand side as viewed inFIG. 2), is secured to the first output shaft27of the harmonic drive gear reducer20. The connection base50has a cup-like connecting portion51and an extended portion52secured to the connecting portion51. The connecting portion51is fixedly connected to the first output shaft27through connection bolts B7. A through hole51H is defined at the center of the connecting portion51and communicates with the space in the input shaft21of the harmonic drive gear reducer20. The connecting portion51has a communicating portion50athat extends from the through hole51H to the second arm30. The communicating portion50aallows communication between the space in the input shaft21and the space in the second arm30. The connecting portion51has a communicating portion cover51a, which seals the space between the input shaft21and the second arm30.

In other words, the industrial robot1has the space (the passage) extending from the interior of the fixed base2to the interior of the movable base40along the path including the interiors of the first connection shaft5, the first arm3, the harmonic drive gear reducer20, the communicating portion50a, the second arm30, and the second connection shaft43. Referring toFIG. 2, a wiring tube60extends from the fixed base2to the movable base40while passing through these components throughout the space (the passage). The proximal end of the wiring tube60is connected to a wiring substrate W or a valve (not shown) provided in the fixed base2.

As shown inFIG. 1, a lower extended piece52aand an upper extended piece52bextend from an extended portion52of the connection base50.

The upper end of a first auxiliary link55is rotatably connected to the lower extended piece52a. The lower end of the first auxiliary link55is rotatably connected to an extended frame portion2aof the fixed base2. The line extending from the lower connection point of the first arm3to the lower connection point of the first auxiliary link55is referred to as a first parallel line R1. The line extending from the upper connection point of the first arm3to the upper connection point of the first auxiliary link55is referred to as a second parallel line R2. The first arm3, the first auxiliary link55, the first parallel line R1, and the second parallel line R2each correspond to one of the sides of a parallelogram. Further, the first arm3, the first auxiliary link55, the fixed base2, and the connection base50form a first parallel link mechanism R10in which the first parallel line R1is constant.

The lower end of a second auxiliary link56is rotatably connected to the upper extended piece52b. The upper end of the second auxiliary link56is rotatably connected to the movable base40. The line extending from the lower connection point of the second arm30to the lower connection point of the second auxiliary link56is referred to as a third parallel line R3. The line extending from the upper connection point of the second arm30to the upper connection point of the second auxiliary link56is referred to as a fourth parallel line R4. The second arm30, the second auxiliary link56, the third parallel line R3, and the fourth parallel line R4each correspond to one of the sides of a parallelogram. Further, the second arm30, the second auxiliary link56, the connection base50, and the movable base40form a second parallel link mechanism R20.

A robot arm mechanism61is provided on the movable base40. The robot arm mechanism61has a first horizontal arm62and a first joint shaft63. The first horizontal arm62rotates about the first joint shaft63. A second joint shaft64and a second horizontal arm65are provided at the distal end of the first horizontal arm62. The second horizontal arm65rotates about the second joint shaft64, which is provided at the proximal end of the second horizontal arm65. An operation shaft66is rotatably supported by the distal end of the second horizontal arm65. An end effecter such as a hand device (not shown) is secured to the operation shaft66.

Operation of the industrial robot1will hereafter be explained.

Specifically, operation of the industrial robot1when the movable base40moves from the position indicated by the sold lines ofFIG. 5to the position indicated by the chain double-dashed lines of the drawing will be described.

To pivot the first arm3and the second arm30, the drive motor10is actuated to rotate the input shaft21of the harmonic drive gear reducer20through the pulleys P1, P2in a counterclockwise direction. This causes the first output shaft27to rotate in a clockwise direction, the opposite direction of the rotational direction of the input shaft21, through the first flexspline24and the left gear portion26aof the circular spline26. The first output shaft27adjusts the angle θa through rotation.

The second output shaft28rotates in the clockwise direction, or the opposite direction of the rotational direction of the input shaft21, through the second flexspline25and the right gear portion26bof the circular spline26. The second output shaft28adjusts the angle θb through rotation.

When the first output shaft27rotates in the clockwise direction, the first parallel link mechanism R10maintains the second parallel line R2in a state parallel with the first parallel line R1. In other words, the first parallel link mechanism R10pivots the first arm3and the first auxiliary link55while maintaining the horizontal line D1of the connection base50parallel with the floor surface B. In this manner, the connection base50is moved from the position indicated by the solid lines ofFIG. 5to the position indicated by the chain double-dashed lines of the drawing (leftward and upward as viewed inFIG. 5).

When the first output shaft27rotates in the clockwise direction, the second output shaft28rotates in the clockwise direction (the same direction as the rotational direction of the first output shaft27) at a rotational angle twice as large as that of the first output shaft27. Specifically, if the angle θa increases by an amount corresponding to the rotational angle θ, the second output shaft28operates to increase the angle θb and the angle θc by an amount corresponding to the rotational angle2θ and an amount corresponding to the rotational angle θ, respectively. That is, the second output shaft28always causes the angle θa and the angle θc to be equal to each other.

When the first output shaft27rotates in the clockwise direction, the second parallel link mechanism R20maintains the fourth parallel line R4in a state parallel with the third parallel line R3. Specifically, the second parallel link mechanism R20pivots the second arm30and the second auxiliary link56while holding the movable base40in a horizontal state. In this manner, the movable base40is raised along the vertical line C1and from the position indicated by the solid lines ofFIG. 5to the position indicted by the chain double-dashed lines of the drawing.

Contrastingly, to lower the movable base40from the position indicated by the chain double-dashed lines to the position indicated by the solid lines, the input shaft21of the harmonic drive gear reducer20is rotated in the clockwise direction.

The illustrated embodiment has the following advantages.

(1) In the illustrated embodiment, the first arm3, the first connection shaft5, the communicating portion50aof the connection base50, the second arm30, the second connection shaft43, and the movable base40are all hollow. The motor shaft11of the drive motor10is offset from the axis L1of the first connection shaft5in a radial direction of the first connection shaft5.

The drive motor10thus defines a space (the space S) with volume increased by an amount corresponding to the offset amount of the motor shaft11in the radial direction of the first connection shaft5in the first connection shaft5, which has a relatively large inner diameter. That is, a hollow passage with increased volume is provided from the fixed base2to the movable base40. The wiring tube60of the robot arm mechanism61and wires of the drive motor10are arranged along the hollow passage.

It is thus unnecessary to employ a hollow motor as the drive motor10, making it also unnecessary to provide a sleeve or the like. This decreases the number of the components, reducing the industrial robot1in size. Further, it is unnecessary to arrange the motor shaft11of the drive motor10and the rotational axis of the first arm3in such a manner that the axes coincide with each other, when assembling the industrial robot1. This facilitates assembly of the industrial robot1.

(2) Since the wiring tube60is arranged inside the industrial robot1, an auxiliary arm for cable wiring does not have to be provided. The number of the components thus decreases, reducing the weight of the industrial robot1. Further, since the wiring tube60is not exposed to the exterior, operation of the parallel link mechanisms (the first parallel link mechanism R10and the second parallel link mechanism R20) or that of the robot arm mechanism61are not interfered by the wiring tube60. Also, in operation of the industrial robot1, noise generation by the wiring tube60is suppressed.

(3) In the illustrated embodiment, the flange6is secured to the outer wall portion of the through hole3H for supporting the drive motor10. The drive motor10is arranged in the fixed base2. Therefore, compared to a case where the drive motor10is secured directly to the harmonic drive gear reducer20, influence on pivoting of the arms by the weight of the drive motor10can be decreased. This reduces the load acting on the drive motor10.

(4) In the illustrated embodiment, the harmonic drive gear reducer20, which has the single input shaft21and the two output shafts (the first and second output shafts27,28), is employed as the transmission mechanism. Thus, by actuating the drive motor10to rotate the input shaft21, the first output shaft27and the second output shaft28are rotated to pivot the first arm3and the second arm30, respectively. In other words, pivoting of the first arm3and pivoting of the second arm30are enabled simply by securing the connection base50and the second arm30to the first output shaft27and the second output shaft28, respectively, of the harmonic drive gear reducer20. The assembly of the industrial robot1is thus further facilitated. Further, the harmonic drive gear reducer20has a hollow portion with a relatively large diameter. The wiring tube60is thus easily installed in the hollow portion.

(5) In the illustrated embodiment, the distal end of the first arm3, the axis of the first output shaft27, the axis of the second output shaft28, and the proximal end of the second arm30are aligned along a common straight line. In other words, the first output shaft27and the second output shaft28are arranged coaxially. This arrangement reduces the axial dimension of the harmonic drive gear reducer20. Thus, compared to a case employing a spur gear, the transmission mechanism becomes smaller.

(6) In the illustrated embodiment, the connection base50is arranged at an outermost position of the first arm3and the second arm30(at the left-hand side ofFIG. 2). This arrangement allows accurate transmission of the output of the harmonic drive gear reducer20to the connection base50and the second arm30. This widens the range from which the output of the harmonic drive gear reducer20(the reduction ratio) is selected.

(7) In the illustrated embodiment, the first arm3and the second arm30are sealed by the first arm cover3aand the second arm cover30a, respectively. The connecting portion between the first arm3and the first connection shaft5, the connecting portion between the second arm30and the second connection shaft43, the connecting portion between the connection base50and the second arm30are sealed by the O-ring or the seal member57. This increases seal performance of the industrial robot1, further reliably suppressing dust generation or grease leakage from the interiors of the first and second arms3,30. Accordingly, the industrial robot1can operate under various specific circumstances including clean rooms.

The illustrated embodiment may be modified as follows.

Although the drive motor10is secured to the first arm3in the illustrated embodiment, the drive motor10may be secured to, for example, the first connection shaft5.

In the illustrated embodiment, the first connection shaft5is rotatably connected to the fixed base2and the first arm3is secured to the first connection shaft5. However, the first arm3and the first connection shaft5may be formed as an integral body that forms the first arm3.

In the illustrated embodiment, the first output shaft27corresponds to the inner output shaft of the harmonic drive gear reducer20. The second output shaft28corresponds to the outer output shaft of the harmonic drive gear reducer20. However, the inner output shaft may function as the second output shaft28and the outer output shaft may function as the first output shaft27. In this case, the lower end of the second arm30is connected to the first output shaft27, and the connection base50is connected to the second output shaft28. The connection base50is arranged between the upper end of the first arm3and the lower end of the second arm30. The communicating portion50aof the connection base50thus can be omitted. This further simplifies the structure of the connection base50. In this case, it is preferred that the ratio of the reduction ratio of the first output shaft27to the input shaft21of the harmonic drive gear reducer20and the reduction ratio of the second output shaft28to the input shaft21is set to 1:2. This allows the movable base40to move linearly along the vertical line C1.

In the illustrated embodiment, the ratio of the reduction ratio of the first output shaft27to the input shaft21and the reduction ratio of the second output shaft28to the input shaft21is set to 2:1. However, such ratio is not restricted to this value.

Although the first output shaft27and the second output shaft28are arranged coaxially in the illustrated embodiment, arrangement of the first and second output shaft27,28may be modified in any other suitable manner.

In the illustrated embodiment, the harmonic drive gear reducer20is secured to the upper end of the first arm3. However, the harmonic drive gear reducer20may be secured to, for example, the lower end of the second arm30in a reversed installation state. In this case, the connection base50is connected to the first output shaft27of the harmonic drive gear reducer20. The upper end of the first arm3is connected to the second output shaft28.

In the illustrated embodiment, the harmonic drive gear reducer20, which is a 1-input 2-output type, is employed as the transmission mechanism. However, a bevel gear, for example, may be employed and arranged in such a manner as to allow internal arrangement of the wiring tube60.

In the illustrated embodiment, the parallel link mechanism (the first arm3, the second arm30, the first auxiliary link55, the second auxiliary link56, the connection base50, and the harmonic drive gear reducer20) is arranged in a manner extending on the vertical line C1. However, the parallel link mechanism may be arranged, for example, horizontally.