FIELD OF THE INVENTION

The present invention relates to an industrial robot including a manipulator for movement of an object in space, where the manipulator is a parallel kinematic manipulator.

A parallel kinematic manipulator includes a movable platform arranged for carrying the object, a first arm arranged for influ- encing the platform in a first direction and including a first inner arm part, a first outer arm part pivotally connected to the first inner arm part and to the platform, and a first actuator having a first drive shaft for actuating the first arm, a second arm arranged for influencing the platform in a second direction and in- eluding a second inner arm part, a second outer arm part pivotally connected to the second inner arm part and to the platform, and a second actuator having a second drive shaft for actuating the second arm, a third arm arranged for influencing the platform in a third direction and including a third inner arm part, a third outer arm part pivotally connected to the third inner arm part and to the platform, and a third actuator having a third drive shaft for actuating the third arm.

PRIOR ART

An industrial robot includes a manipulator and a control unit having means for automatically operating the manipulator. There are different types of manipulators, such as a serial kinematic manipulator and a parallel kinematic manipulator. Today fast han- dling and assembly of components on a flat surface, such as the surface of a conveyor is typically performed by paral lel kinematic manipulators.

A paral lel kinematic manipulator (PKM) is defined as a manipul a- tor comprising at least one stationary element, a movable el ement, denoted a platform , and usually three arms. Each arm comprises a link arrangement connected to the movable platform . Each arm is actuated by an actuator preferably arranged on the stationary element to reduce the moving mass. The link arrangements transfer forces to the movable platform . For a fully bui lt-up parallel ki nematic manipulator for movement of the platform with th ree degrees of freedom , three parallel-working arms are required. To obtain a stiff arm system with a large loading capacity and a low weight, the arms connected to the movable platform of the parallel kinematic manipulator should have a total of six li nks.

There exist different types of manipulators for fast material handling , pick and place , and assembly, such as the Scara manipu- lator, the Gantry manipulator, and the Delta PKM manipulator. The Delta PKM manipulators are taking market shares from especially the Scara manipulators, because of its lightweig ht arm structure, which provides hig her dynamic performance in relation to manipulator manufacturing cost. However, the Scara ma- nipulator has some features that cannot be achieved by the De lta manipulator, as for example small footprint, possibility to mount the man ipu lator beside the work space, possibil ities to obtai n a larger vertical stroke and the possibilities to make i nstallations with a hig her man ipulator density. Looking at the ki n- ematics, increasing the horizontal work space size means only that the arms of the Scara manipulator need to be resized wh ile for the Delta manipulator the whole framework and the manipulator m ust be resized, which means that the manipu lator wi ll need to be located higher above the work space . In order to combine the advantages of the traditional Scara ki nematics with the performance potential of the Delta PKM man ipulator, a Scara Tau PKM concept was developed . This concept is disclosed in WO 03/066289. The prior art Scara Tau manipu- lator has three inner arm parts mounted on three bearings, which are in turn mounted on a vertical column , which also holds the motors with its gear boxes. The output s haft from the gear box is connected to a gear wheel , which engages a gear ring mounted on the arm side of the arm bearing . Because the motor and gear box must be mounted with thei r shafts parallel with the rotation axes of the arms, a lot of space is needed between the arm beari ngs i n order to get the space needed for the actuation system . This means that even if the robot obtains a smal l footprint it wil l need a lot of space in the vertical direction . This is especially a problem if the robot is used to serve for example a conveyor, especial ly if the robot must be mounted over the co nveyor. Beside the need of a large space in the z-direction , the prior art robot will also be heavy because of the mounting co lumn supporti ng the arms and the actuation system .

OBJ ECTS AN D SU MMARY OF TH E INVENTION

The object of the present invention is to provide a parallel kinematic robot, which is compact, less expensive than the disclosed Scara Tau man ipulator, and has a large work space compared to the space it occupies, i .e. has a small footpri nt.

This object is achieved by an industrial robot as defined in claim 1 .

The robot includes a manipulator for movement of an object in space, where the manipulator comprises: a movable platform arranged for carrying the object, a first arm arranged for infl uencing the platform in a first direction and including a first i n ner arm part rotatable about a first axis, a first outer arm part pivot- ally connected to the first i nner arm part and to the platform , and a first actuator for actuati ng the first arm , a second arm arranged for i nfluencing the platform i n a second direction and i ncludi ng a second i nner arm part rotatable about a second axis, a second outer arm part pivotally connected to the second inner arm part and to the platform , and a second actuator for actuating the second arm , a th ird arm arranged for influencing the platform in a third direction and includi ng a third inner arm part rotatable about a third axis, a third outer arm part pivotally connected to the third inner arm part and to the platform , and a third actuator for actuating the third arm , wherein the rotation axes of the in ner arm parts are parallel . The robot is characterized in that the manipu lator comprises a hollow part con nected to the third inner arm part, and a support member extending through said hollow part and arranged to rigidly support at least one of the first and second actuators, and the third inner arm part is arranged rotatable about the su pport member. Preferably, the support member is vertically mounted in the work shop.

With the term "the support member is arranged to rigidly support at least one of the actuators" is meant that the support member is arranged to support the actuator in such a way that the mechanical stiffness of the mounting of the two components relative each other is high , which means that the stiffness of the support member and the mounting interfaces between the su p- port member and the actuators are desig ned to be stiff . The support member may be arranged to support the actuator alone or as a part of a support structure supporting the actuator. It should be noticed that the support member can either be a specific mechanical member or be part of the encapsulation of the actuator. For example, the support member is mechanically rigidly connected to at least one of the first and second actu ators, which means that the support structure and the actuator are mounted either i n direct contact with each other or via one or more other components i n such a way that the mechanical stiff- ness of the mounting of the two components relative each other is hig h . The invention provides a possibility to make installations with a high manipulator density and is favorable when the robot is worki ng from the side of, for example, a conveyor . This mount- ing also makes it easy to install and exchange the robot and the robot wi ll be easily accessible for service and maintenance. Since it is possible to move the robot arms and platform outside the work space, cleaning and washing of the robot wi ll be easier since it is not necessary to do this above, for example, a con- veyor.

According to an embodiment of the invention , the hollow part is mounted on a bearing su rrou nding the support member. This will give the third inner arm part free rotation using high stiffness bearings as for example roller bearings.

According to an embodiment of the i nvention , a transmission unit is mechanically connected to the hollow part to rotatably drive the hol low part with the third actuator.

According to an embodiment of the invention , the transmission unit comprises a gear ri ng con nected by at least one pi nion gear to the drive shaft of the third actuator. This is a si mple way to obtai n a h ig h gear ratio because of the relatively large diameter of the gear ring .

According to an embodiment of the invention , the thi rd actuator is mechanical ly connected to the support member. This wil l g ive a compact design for the actuator, which will not need to output as m uch torque as the other actuators because of the gear ratio possible to obtain with the large diameter ri ng gear.

According to an embodiment of the invention , the centre line of the support member is parallel to the rotation axes of all the in- ner arm parts. When no angle tears are used this also means that the support member is parallel to al l the drive shafts of the actuators. This gives the lowest influence of the gravity on the actuator torques.

According to an embodiment of the invention, at least two of the arms have an outer arm part including at least two links pivotally connected to the respective inner arm part and to the platform.

According to an embodiment of the invention, all of the three arms have an outer arm part including at least two links pivotally connected to the respective inner arm part and to the platform. This gives a symmetric link structure for the whole robot.

According to an embodiment of the invention, one of the arms has an outer arm part including three links pivotally connected to the respective inner arm part and to the platform. This will make it possible to obtain less variations of the stiffness of the robot.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained more closely by the description of different embodiments of the invention and with reference to the appended figures. Fig. 1 shows a manipulator according to a first embodiment of the invention.

Fig. 2 shows a cross section through the manipulator shown in figure 1 along a line A-A.

Fig.3 shows a manipulator according to a second embodiment of the invention.

Fig.4 shows a manipulator according to a third embodiment of the invention. Fig.5 shows a manipulator according to a fourth embodiment of the invention.

Fig. 6 shows a manipulator according to a fifth embodiment of the invention.

Fig.7 illustrates the work areas covered by a plurality of closely packed manipulators according to the embodiments of the invention shown in the previous figures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Like or corresponding parts in the following figures are indicated with like numerals.

Figure 1 shows an example of a manipulator of an industrial robot according to the invention. The industrial robot also includes a control system (not shown in the figure) for controlling the movements of the manipulator. The manipulator comprises a movable platform 4 arranged for carrying a wrist and/or an object, such as a tool or a work piece. The manipulator includes three arms 1 - 3. The first arm 1 is arranged for influencing the platform 4 in mainly a vertical direction and includes a first inner arm part 1a rotatable about a first axis A1, a first outer arm part including two links 1b, 1c pivotally connected to the first inner arm part 1a and to the platform 4, and a first actuator 5 for actuating the first arm 1. The second arm 2 is arranged for influencing the platform in a first mainly horizontal direction and in- eludes a second inner arm part 2a rotatable about a second axis A2, a second outer arm part including two links 2b, 2c pivotally connected to the second inner arm part 2a and to the platform 4, and a second actuator 6 for actuating the second arm 2. The two links 2b, 2c are arranged in parallel and have the same length. The third arm 3 is arranged for influencing the platform 4 in a second mainly horizontal direction. The third arm 3 includes a third inner arm part 3a rotatable about a third axis A3 and a third outer arm part including two links 3b, 3c pivotally connect- ed to the third inner arm part 3a and to the platform 4, and a third actuator 7 for actuating the third arm. Each of the actuators 5 - 7 includes a drive shaft 10, 11, 12. In the embodiment shown in figure 1, all three drive shafts are arranged vertically and in parallel. The drive shaft 12 is actually just a shaft with a pinion gear to transmit torque to a gear ring 20 and using angle gear design. The shaft 12 does not have to be parallel with the actuator shafts 10 and 11. However, the rotation axis of the ring gear 20 and thus the third rotation axis of the third inner arm part 3a must always be parallel with the actuator shafts 10 and 11, or in the general case, the rotation axes of all the inner arm parts 1a, 2a and 3a must be parallel. The drive shafts 10 and 11 and the drive transmission 12, 20 are arranged to support the inner arm parts at three different levels in the vertical direction. The first and second drive shafts are arranged coaxial, but they could also be mounted with an offset in the horizontal direction. The first actuator is arranged above the second actuator. The third shaft is arranged displaced in a horizontal direction from the first and second drive shafts. All of the three arms have an outer arm part including two links pivotally connected to the re- spective inner arm part and to the platform.

The second inner arm part 2a is displaced relative the third inner arm part 3a in the direction of the drive shafts 10 and 11 to allow the third inner arm part 3a to pass below the second inner arm part 2a, as shown in the figure, and accordingly to increase the work space of the robot.

Each of the actuators 5, 6, 7 comprises a motor and a gear box including an output drive shaft. It should be noted that the gear ration of the third actuator 7 does not need to be as high as for the other actuators 5 and 6 since the gear ring 20 is used to ob- tain a gear with high gear ratio. The first and second inner arm parts 1a, 2a are mounted directly on the output shafts of the actuators 5, 6 with gear boxes driven by motors. The first inner arm part 1a is attached to a part of the first output shaft 10, which extends above the motor and gear of the first actuator 5. The second inner arm part 2a is attached to a part of the second output shaft 11, which extends below the motor and gear of the second actuator 6. The third inner arm part 3a is attached to a hollow part 14, which is operatively connected to the third output shaft 12 via a small diameter pinion gear and a large diameter gear ring 20, and which is arranged rotatable about a support member 16 by means of a bearing 15. The third output shaft 12 supports the pinion gear driving the gear ring and extending above the third actuator 7. If actuator 7 is mounted inside the support member 16 and there is a hole in the support member through which the gear on the motor shaft can meet a gear ring with the gear teeth on the inside of the ring, the actuator 7 can have its shaft 7 pointing either upwards or downwards. Figure 2 shows a cross section through the manipulator shown in figure 1 along a line A-A where the hollow part 14 for the third inner arm part 3a is situated. One end of the third inner arm part 3a is connected to the hollow part 14 and the other end of the third inner arm part 3a is connected to the third outer arm part 3b-c. The manipulator includes a cylindrical support member 16 extending through the hollow part 14. The hollow part 14 is designed to allow the support member 16 to extend through the hollow part. In this embodiment the hollow part 14 is ring shaped. The first and second actuators 5,6 are rigidly connected to the support member 16 via an attachment 18. The third actuator 7 is rigidly connected to the support member 16 but could also be placed on a separate stand directly on the floor. The centre line 22 of the support member 16 is parallel to the rotation axes of all the inner arm parts 1a, 2a and 3a. The third in- ner arm part 3a is arranged rotatable about the support member 16 by means of a bearing 15. This bearing can either be located inside the hollow part 14 between the hollow part and the support member 16 as in the figure 2, or being arranged above or below the hollow part. It is also possible to have one bearing below and one bearing above the hollow part. When the bearing is not mounted inside the hollow part the diameter of the hollow part can be reduced.

A transmission including a ring gear 20 and a pinion gear on the shaft 12 rotatably connects the hollow part 14 to the third actua- tor 7. In Figure 1 the gears on the gear ring are pointing outwards, but it is also possible to have the gears pointing inwards or having an angled ring gear. The pinion gear will then be adapted to the solution used. In the embodiment of the invention according to figures 1 and 2, the cylindrical pillar 16 is standing on the floor by means of a mounting plate 24. The pillar 16 is hollow to contain cabling and hoses, and an attachment 18 is used to mount the servo actuators 5,6 on the pillar while the attachment 18 connects the servo actuators 5,6 to each other. Of course, the mounting of the servo actuators 5,6 on the pillar 18 can be made in different ways.

The third inner arm part 3a is mounted in such a way that it can pass under the second inner arm part 2a. The second arm 2 can rotate free until it hits the part of the pillar 16 which is between the hollow part 14 and the mounting arrangement 18. To increase the work space the pillar 16 can be made narrower where the second inner arm part 2a collides with the pillar. In Figure 1 it is also shown how the upper joints of links 1b-c are mounted close to each other to reduce the rotations of the platform when it is moved in a radial direction in relation to the centre of the work space. This actuator mounting can also be used when the link 1c is moved from the first inner arm part 1a to the second inner arm part 2a, see Figure 3. Figure 3 shows a manipulator according to a second embod iment of the invention . This manipulator differs from the manipulator shown in figure 1 i n that the first outer arm part includes only one link 1 b pivotal ly con nected by joints to the first inner arm part 1 a and to the platform 4 , and in that the second outer arm part incl udes three links 2b-d pivotally con nected to the second i nner arm part 2a and to the platform 4. The yaw ang le of the platform 4 is here constrained by the link 2d. In Fig ure 1 it is the pair of links 1 b and 1 c that constrains the yaw angle. Also here the platform rotations when the platform moves in a radial direction can be reduced by mounting the joint 2g close to a line between the joints 2e-f connecting the li nks 2b-c with the second inner arm part 2a. Seen both from above and from the side, the link 2d is not parallel with the paral lel links 2b-c. This will reduce the yaw variations of the platform when it is moved in the work space.

Figure 4 shows a manipulator according to a third embodiment of the invention . The manipulator shown in figure 4 differs from the manipulator shown i n figure 1 in that the third arm 3 is arranged for influencing the platform 4 in main ly a vertical direction , and the first arm 1 is arranged for influencing the platform 4 in a mai nly horizontal direction . Further, the first and second actuators 5, 6 are arranged displaced in a horizontal direction . The support member 1 6 is connected to a roof beam 28. The first and second actuators 5, 6 are rigidly connected to the support member 1 6 via supporting elements 30. The third actuator 7 is rigidly connected to the support member 1 6. The third inner arm part 3a is mounted on the hollow part 14 driven by the third actuator 7 having a drive shaft 1 2 engaging the gear teeth of the gear ring 20 in the same way as in Figure 1 . In this way the same robot structu re mounted on the floor as in Figures 1 and 3 can also be mou nted in the roof above the work space, which is necessary in some applications where al l the space around the work space must be accessible. Figure 5 shows a manipulator according to a fourth embod iment of the invention . It can be used to increase the work space when the actuators are mounted directly on a vertical appl ication dependent support structure. The support structu re of the embod i- ment shown i n figure 5 comprises a vertically arranged support beam 40, a fi rst holding device 42 on which the second actuator 6 is mounted , a second holdi ng device 44 on which the first actuator 5 is mounted, and a distance piece 45 arranged to displace the third i nner arm part 3a from the second inner arm part 2a in the direction of the shaft 1 2. The th ird actuator 7 is rigidly connected to the distance piece 45. The support structu re fu rther comprises a support member 48 arranged to rigidly su pport the first actuator 5. One end of the support member 48 is attached to the first holding device 42 and the other end is at- tached to the second holding device 44. The fi rst actuator 5 is rigidly connected to the support member 48 via the second holding device 44. The centre li ne of the support member 48 is parallel to the rotation axes of the i nner arm parts 1 a, 2a and 3a. The thi rd inner arm part 3a is mechanically con nected to a ho I- low part 46 includi ng a thoug h hole to receive the support member 48. The support member extends th rough the hollow part 46.

The arrangement for actuating the th ird i nner arm part 3a shown in figures 1 - 4 is now used to get a support member for only actuator 5. Th us the support member 48 corresponds to the support member 1 6 in Fig ures 1 - 4. Below the gear ri ng 58 , the support member 48 has a larger diam eter. The thi rd inner arm part 3a is mounted on the hollow part 46 corresponding to the hollow part 1 4 in Figure 2. However, here the bearing 57 is mounted below the hol low part 46. As for figures 1 - 4, an actuator 7 drives the hollow part 46 via the gear ring 58 and a pi n ion gear on the shaft 1 2. The actuator is mounted on the distance piece 45 below the gear ri ng 58. Figure 6 shows a manipulator according to a sixth embodiment of the invention . It is here shown that it is also possible to use a band transmission between the third actuator 7 and the hollow part, which will be a cheaper solution , but with less transmission stiffness. The manipulator comprises a holding device 54 and a pillar 52 for positioni ng the holding device 54. The manipu lator comprises a first actuator 5, a second actuator 6, and a th ird actuator 7, which are mounted on the holding device 54. The first actuator 5 includes a first drive shaft 1 0, the second actuator 6 includes a second drive shaft 1 1 , and the third actuator 7 includes a third drive shaft 1 2, which is operatively connected to a hollow shaft 62 by means of a belt 61 . The first actuator 5 is mounted i nside the hollow shaft 62.

The hollow shaft 62 is concentrically mou nted on a belt wheel 63, which in turn is mounted concentrically on a bearing 64 mak- ing it possible to rotate the thi rd inner arm part 3a i n relation to the holding device 54. The output shaft of the actuator has a smaller belt wheel and the belt 61 is mounted between the two belt wheels 60 and 63. The arrangement with a belt driven ho llow part for the thi rd arm 3 can also be implemented in the m a- nipulator configurations shown in Fig ures 1 - 5. Specific for this implementation is that the support member inside the hollow part is the encapsulation of the first actuator 5. This solution is difficult to apply i n the man ipulator config urations shown in Fi gures 1 , 3 and 4. The advantage to have the first actuator 5 i n- side the hollow shaft 62 is that the actuator assembly wil l be more compact, compared with Figure 5.

Figure 7 shows the work area covered by a plurality of closely packed manipulators of any of the embodiments shown in fig- ures 1 - 6. In Figu re 7 only the actuators 1 00 of the manip ulator are shown . The manipu lators are intended to perform pick- and place operations on a conveyor 1 02. As can be seen from figure 7, the work spaces 1 01 of the manipulators are overlapping , which achieves high capacity. Moreover it can be seen that the work space extends far outside the conveyor thereby facilitating clean ing , maintenance and tool exchange.