FIELD OF THE INVENTION AND PRIOR ART

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.

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 handling and assembly of components on a flat surface, such as the surface of a conveyor is typically performed by parallel kinematic manipulators.

A parallel kinematic manipulator (PKM) is defined as a manipulator comprising at least one stationary element, a movable element, denoted a platform , and usually three arms. Each arm comprises a link arrangement connected to the movable plat- form. 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 built-up parallel kinematic manipulator for movement of the platform with three 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 links.

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 lightweight arm structure, which provides higher dynamic performance in rela- tion to manipulator manufacturing cost. However, the Scara manipulator has some features that cannot be achieved by the Delta manipulator, as for example small footprint, possibility to mount the manipulator beside the work space, possibilities to obtain a larger vertical stroke and the possibilities to make in- stallations with a h igher manipulator density. Looking at the kinematics, increasing the horizontal work space size means only that the arms of the Scara manipulator need to be resized while for the Delta manipulator the whole framework and the manipulator must be resized, which means that the manipulator will need to be located higher above the work space.

In order to combine the advantages of the traditional Scara kinematics with the performance potential of the Delta PKM manipulator, a Scara Tau PKM concept was developed. This con- cept is disclosed in WO 03/066289. The prior art Scara Tau manipulator has 3 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 shaft 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 their shafts parallel with the rotation axes of the arms, a lot of space is needed between the arm bearings in order to get the space needed for the actuation system. This means that even if the robot obtains a small foot- print it will 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, especially if the robot must be mounted over the conveyor. Beside the need of a large space in the z-direction the prior art robot will also be heavy because of the mounting col- umn supporting the arms and the actuation system. OBJECTS AND SUMMARY OF THE INVENTION

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

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 influencing the platform in a first direction and including a first inner arm part, an outer arm part pivotally connected to the inner arm part and to the platform, and a first actuator for actuating the arm parts, a second arm arranged for influencing the platform in a second direction and including a second inner arm part, an outer arm part including at least two links pivotally connected to the inner arm part and to the platform, and a second actuator having a second drive shaft for actuating the arm parts, a third arm arranged for influencing the platform in a third direction and including a third inner arm part, an outer arm part including at least two links pivotally connected to the inner arm part and to the platform, and a third actuator having a third drive shaft for actuating the arm parts. According to the invention, at least two of the actuators are arranged side by side, mechanically connected to each other, and with the drive shafts arranged in parallel, and said inner arm parts are directly mounted on the drive shafts of the respective actuator.

With side by side is meant that the actuators are arranged with at least a part of their envelope surfaces facing each other and with the driver shafts spaced apart. The actuators can be slightly displaced in a vertical direction, and can be arranged with a distance between them. By arranging at least two actua- tor side by side, a compact manipulator with small footprint and low height is achieved. A further advantage is that a large scalability is achieved since increasing the works space is easily made with the same actuator mounting just by increasing the lengths of the arms. Further, as the arm parts are attached to the drive shafts, it is possible to use simple, compact and less expensive drive units. This innovation shows how a modification of the mounting of the actuators of the original Scara Tau manipulator according to WO 03/066289 will make it possible to ob- tain compact actuator housing for the Scara Tau arm structure and still preserve most of the useful work space of the manipulator.

According to an embodiment of the invention , the inner arm parts of two of said actuators which are arranged side by side are mounted to be displaced in the direction of drive shafts of said two actuators arranged side by side to allow the one of the inner arm parts to pass by the other inner arm part. This makes it possible to obtain almost 360 degrees working range around the centre of the robot. This is, for example obtained by extending one of the drive shafts of said two actuators above or below the drive shaft of the drive shaft of the other of said two actuators. Th is makes it possible to have all tree actuators on the same level to achieve a very compact actuation system. Another possibility is to d isplace one of the two actuators relative the other in the direction of their drive shafts. Th is opens up for other possible mounting configurations.

According to an embodiment of the invention , two of the actua- tors are mounted with their drive shafts pointing in the same direction , and the other actuator is mounted with its drive shaft pointing in another direction. Preferably, the other actuator is mounted with its drive shaft pointing in an opposite direction in order to achieve an optimal work space. According to an embodiment of the invention, at least one of the actuators comprises a motor integrated with a compact gear as for example a Harmonic Drive gear. This embodiment reduces the complexity of the drive system compared to PKM concepts used today, and accordingly reduces the costs of the dive system. A compact gear is defined as a gear with high gear ratio obtained by interacting components needing smaii space as for example in gears of the types Harmonic Drive, Cycio and RV. According to an embodiment of the invention, the first actuator has a first drive shaft for actuating the arm parts, the first inner arm is attached to the first drive shaft, and the first actuator is rigidly connected to the second and third actuators. Th is embodiment provides a manipulator that is compact in a vertical direction and reduces the power need of the manipulator.

According to an embodiment of the invention, first drive shaft is arranged in parallel with the second and third drive shafts. This embodiment contributes to provide a small footprint.

According to an embodiment of the invention, each of the actuators comprises a motor and a gear, the first inner arm is attached to a part of the first drive shaft , which extends above the motor and gear of the first actuator, the second inner arm is at- tached to a part of the second drive shaft, which extends below the motor and gear of the second actuator, and the third inner arm is attached to a part of the third drive shaft, which extends below the motor and gear of the third actuator. I n th is way a simple mounting of all the three actuators can be obtained.

According to an embodiment of the invention, each of the actuators comprises a motor and a gear, the first inner arm is attached to a part of the first drive shaft, which extends above the motor and gear of the first actuator, and the third inner arm is attached to a part of the third drive shaft, which extends in the opposite direction of the motor and gear of the second actuator. This opens up for other possible mounting configurations.

According to an embodiment of the invention , the robot com- prises a su pporting structure to sustain the actuators, which supporting structure comprises a holding device on which the actuators are mounted , and a support member for positioning the holding device, which support member extends in a direction essentially perpendicular to the direction of the second and third drive shafts. This embodiment makes the mounting of the actuators even simpler. Preferably, the support member is horizontally arranged. This makes it possible to place the manipulator above for example a conveyor for optimal use of the work space of the robot.

According to an embodiment of the invention, the length of the support member is larger than the length of any of the second and third arms inner arms. This embodiment makes it possible for the second and third inner arms to pass beneath the support member, which leads to an increased work space.

According to an embodiment of the invention , the supporting structure includes a horizontal holding device, and the second and third actuators are attached to one side of the holding de- vice, and the first actuator is attached to an opposite side of the holding device. This embodiment makes it possible to design a compact actuator housing.

According to an embodiment of the invention , the supporting structure comprises a support member, such as a beam, extending in a d irection essentially parallel to the second and third drive shafts. Preferably, the support member is vertically arranged. This design makes it possible for the robot to work from the side of for example a conveyor. According to an embodiment of the invention, the first actuator is mounted on top of one of the second and third actuators. This embodiment provides a possibility to make installations with a high manipulator density and is favorable when the robot is working from the side of for example a conveyor.

According to an embodiment of the invention , the robot comprises a distance piece fixedly arranged between the second or third actuator and the supporting structure so as to displace the inner arm parts of the second and third arms relative each other in the direction of the shafts. An advantage with this embodiment is that a large work space is achieved.

Accord ing to an embodiment of the invention the robot com- prises a su pporting structure to sustain the actuators, which supporting structure comprises a holding device on which the actuators are mounted , and a support member for positioning the holding device, which support member extends in a direction essentially parallel to the second and third drive shafts and the drive shaft of one of the second and third actuators is hollow to allow the first actuator to be mechanically connected to the holding device. For example, the support structure comprises a pillar arranged through the hollow shaft, to support the first actuator. Alternatively, the first actuator is mounted inside the hollow shaft. This embodiment provides a possibility to make installations with a high manipulator density and is favorable when the robot is working from the side of for example a conveyor.

According to an embodiment of the invention, one of the second and third actuators includes a gear of a hollow shaft type. The hollow shaft is a part of a gear of the actuator. This will reduce the cost of the large work space side mounted robot.

According to an embodiment of the invention, the robot accord- ing to any of the previous claims, wherein one of the second and third outer arm parts includes three links pivotally connected to the inner arm part and to the platform.

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 the manipulator of figure 1 in a position where the inner arm of the second arm is below the inner arm of the third arm. shows a cross section through an example of an actuator suitable to be used in a manipulator according to the invention. shows a manipulator according to a second embodiment of the invention.

Fig. 5 shows the work space of the manipulator shown in figure

4. illustrates the work areas covered by a plurality of closely packed manipulators of the embodiment shown in figure 4.

Figs. 7a-b show scaling of a manipulator according to the invention compared to a traditional Scara manipulator.

Fig. 8 shows a manipulator according to a third embodiment of the invention. Fig. 9 shows the work area covered by a plurality of closely packed manipulators of the embodiment shown in figure 8. Fig. 10 shows a manipulator according to a fourth embodiment of the invention.

Fig. 1 1 shows a manipulator according to a fifth embodiment of the invention.

Fig. 12 shows a manipulator according to a sixth embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Figures 1 and 2 show 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 control- ling 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 a vertical direction and includes a first inner arm part 1 a, an outer arm part 1 b pivotally connected to inner arm part 1 a and to the platform 4, and a first actuator 5 for actuating the first arm. The second arm 2 is arranged for influencing the platform in a first horizontal direction and includes a second inner arm part 2a, a second outer arm part 2b including two links 2c, 2d pivotally connected to the inner arm part 2a and to the platform 4, and a second actuator 6 for actuating the second arm.

The third arm 3 is arranged for influencing the platform 4 in a second horizontal direction. The third arm 3 includes a third inner arm part 3a and a third outer arm part 3b including three links 3c - e pivotaliy connected to the 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, 1 1 , 12. In the embodiment shown in figure 1 , all three drive shafts are ar- ranged vertically and in parallel. The second and third d rive shafts are arranged to support the inner arm parts at different levels in the vertical direction. All three actuators are arranged rigidly connected to each other by means of a holding structure 14 surrounding the three actuators. Each inner arm part 1 a, 2a, 3a are attached to the corresponding drive shaft 10, 1 1 , 12. The second and third actuators 6, 7 are arranged side by side so that the first and second drive shafts are arranged in parallel and spaced apart from each other. The first actuator 5 is rigidly connected to the second and third actuators 6,7.

Each of the actuators comprises a motor and a gear box including an output drive shaft. The inner arm parts are mounted directly on the output shafts of the gear boxes driven by the motors. The first inner arm 1 a is attached to a part of the first out- put shaft 10, which extends above the motor and gear of the first actuator 5. The second inner arm 2a is attached to a part of the second output shaft 1 1 , which extends below the motor and gear of the second actuator 6, The third inner arm 3a is attached to a part of the third output shaft 12, which extends below the motor and gear of the third actuator 7. The second inner arm part 2a is displaced relative the third inner arm part 3a in the direction of the drive shafts 1 1 and 12 to allow the second inner arm part 2a to pass be!ow the third inner arm part 3a, as shown in figure 2, and accordingly to increase the work space of the robot. In this embodiment the displacement is achieved since the actuator of the second arm is mounted further down than the actuator of the th ird arm. An alternative is to have d ifferent lengths of the shafts of the second and third actuators. 3. The second and third actuators 6,7 are mounted with their drive shafts pointing in the same direction, and the first actuator 5 is mounted with its drive shaft pointing in an opposite direction . The manipulator includes a supporting structure to sustain the arms and the actuators. The supporting structure includes the holding device 14 and a support member 16 in the form of a beam extending in a horizontal direction. The holding device 14 is mounted on the horizontal beam 16. One end of the support member 16 is attached to the holding device 14 and the other end is designed to be operatively attached to the building housing the manipulator, for example via a vertical pillar. The length of the support member 16 is larger than the length of the second and third inner arms 2a, 3a in order to allow the second and third inner arms to pass beneath the support member to achieve an increased work space. Figure 3 shows a cross section of an example of an actuator suitable to be used to manipulate the arms in a manipulator according to the invention. This type of actuator is compact and has a low weight because of densely integrated lightweight drive components. The actuator includes an actuator housing 20, a shaft bearing 22, a shaft 24 for mounting of the inner arm , a gear 26 of a harmonic drive type, which is integrated with the rotor 28 of the motor, a brake 30, and an encoder 32.

Figure 4 shows a manipulator according to a second embodi- ment of the invention. This embodiment differs from the embodiment disclosed in figure 1 in that the supporting structure includes a holding device 34 in the form of a horizontal beam attached to the support member 16, and the second and third actuators 6, 7 are mounted on one side of the holding device 34 and the first actuator 5 is mounted on an opposite side of the holding device 34. The manipulator comprises a distance piece 36 fixedly arranged between the second actuator 6 and the holding device 34 so as to distance the inner arm part 2a of the second arm from the inner arm part 3a of the third arm relative each other in the direction of the shafts. This embodiment represents a less densely packed actuator arrangement than in figures 1 and 2, which is needed in cases where the cooling of the actuators must be considered in the design. The housing of the actuators may in this case contain a fan for forced cooling and the beams 34 and 16 may be used for leading heat out from the housing. The actuators as well as the beam 16 may also be equipped with heat sinks.

Figure 5 shows the work space of the manipulator shown in figures 1 , 2 and 4. The holding device 34, on which the actuators 5, 6, 7 are mounted and the actuators are outlines in the middle of the figure. The second 2 and the third 3 arms of the lower actuators 6, 7 are shown in two situations when the third arm 3 in figure 4 is close to collide with the actuator 6 of the second arm. It can be seen that in comparison with the Scara Tau according to WO 03/066289, this embodiment loses a work space segment 40. However, this part of the work space is not critical since the outer arm part 1 b can anyhow not pass the beam 16 in Figure 15 and by mounting the beam in the direction where the space segment 40 is located, no more loss of work space is obtained. This is illustrated in Figure 6.

Figure 6 shows the work area covered by a plurality of closely packed manipulators of the embodiment shown in figure 4. The figure shows how a plurality of manipulators according to the invention can be mounted along a line for tending a conveyor. In this example a support member 42 is shown, which is suitable when the robot is supposed to work above a conveyor. In the figure it is shown how a part of the work space is lost because the single link 1 a of the first arm will be hindered by the support member 42. This work space part coincides with the lost work space segment 40 in Figure 5. However, this part of the work space is not critical since the installation will mainly use the upper part of the work space areas, which is evident from the layout of robot placements in the figure. This figure shows that it is possible to install the manipulators with higher density than what is possible with for example Delta PKM robots. One advantage with a traditional Scara robot is its scaling properties. The same advantage is found for the manipulators shown in figure 1 , 2 and 4, which is exemplified in figure 7a and 7b. Here the horizontal work space area is doubled between figures 7a and 7b. The frame work for the Delta robot has not been included in the figures, but the volume of this will increase with the cube of the radius increase of the work space. Figure 8 shows a third embodiment of a manipulator according to the invention, in which the first actuator 5 is arranged with the drive shaft directed perpendicular to the drive shafts of the actuators 6, 7. In this embodiment, the shafts 1 1 , 12 are vertically arranged and the shaft 10 is horizontally arranged. The support structure includes a holding device 34 on which the actuators are mounted and a vertically arranged support member 52 in the form of a vertical beam. The upper end of the support member 52 is attached to the holding device 34 and the lower end is, for example, attached to the ground.

Thus, instead of having three motors geared with circular gear trains above each other on a common centre pillar as shown in WO 03/066289, one actuator 5 is mounted on top of a holding device 34 while the other two actuators 6, 7 are mounted side by side on the bottom of the holding device 34. The upper actuator 5 is mounted to have its outgoing shaft 10 directed either upwards as shown in figure 1 , 2 and 4 or sideways as shown in figure 8, while both of the lower actuators 6, 7 have their outgoing shafts 1 1 , 12 directed downwards. Moreover, the lower actua- tors 6, 7 are mounted in such a way that the arm connected to one of the actuators, the second arm 2 in figure 4, can pass below the arm mounted on the other actuator, the third arm 3 in figure 4. For the largest obtainable work space the holding device 34 is mounted on the horizontal beam 16 which is slightly longer than the longer of the two inner arms 2a, 3a mounted on the lower actuators 6, 7. Figure 9 shows the robot density possibility for the manipulator shown in figure 8. Since the most interesting work space wii! be in front of the manipulator and thus restricted sideways it is also realistic to have the upper arm 1 mounted on a horizontal shaft as shown in figure 8. This will give the work space reduction according to figure 9. The work space limits are caused by too small angles between the link 1 b of the upper arm 1 and the links of either the lower arms 2, 3. However, this work space is useful in applications with side mounted manipulators on pillars placed on both sides of a conveyor, as shown in figure 9. Further, it is possible to introduce a redundant actuator, which rotates the upper actuator 5 in such a way that the upper arm 1 will always be in the middle between the lower arms 2, 3. This will increase the stiffness of the manipulator because of more favourable angles between the links.

Figures 10 and 1 1 show a somewhat different mounting principle used to in crease th e wo rk space wh en the actuators are mounted directly on a vertical pillar. In these cases, the lower actuators 6, 7 are mounted with their shafts 1 1 , 12 pointing upwards and a second holding device 44a-b is mounted either on both of the shafts 1 1 , 12 of the actuators as shown in figure 10, on only one of the shafts 1 1 , 12 of one of the actuators or on a shaft 46 fixedly mounted on a pillar 48 and going through a hollow gear or servo actuator 50 as shown in figure 1 1 . In the embodiment disclosed in figure 1 1 , the inner arm 2b of the second actuators is mounted to be able to pass over the inner arm 3b of the third actuator.

The support structure of the embodiment shown in figure 1 1 comprises a vertically arranged support member 52 in the form of a vertical beam, a first holding device 54 on which the second 7 and third 50 actuators are mounted, and a third holding device 44b on which the first actuator 5 is mounted. The support structure comprises a pillar 48 arranged through the hollow shaft 46, to support the first actuator. The first actuator 5 is mounted above the second actuator 50. The drive shafts 10,46 of the first and second actuators have the same direction and may be aligned as in the figure. The embodiment includes a distance piece 56 arranged between the second actuator 50 and the first holding device 54 so as to displace the inner arm part 2b of the second arm from the inner arm part 3b of the third arm in the direction of the shafts. However, in another embodiment the distance piece 56 could be mounted on the third actuator instead.

The second actuator 50 includes a motor 51 , a gear 57 provided with a gear ring 58, and a drive shaft 46. The drive shaft 46 of the second actuator is hollow. The manipulator comprises a pillar 48 arranged through the hollow shaft 46. One end of the pil- lar 48 is attached to the first holding device 54 and the other end is attached to the second holding device 44b. The hollow drive shaft 46 is a part of the gear 57, which is a hollow compact gear or only a bearing for the gear ring 58. It is also possible to use a band transmission between the motor 51 and the actuator 50, which will be a cheaper solution but with less transmission stiffness. Such an arrangement is exemplified in Fig ure 1 2 , which also shows the case when the actuator shafts 12 and 46 in figure 1 1 point in different directions.

Figure 12 shows a manipulator according to a sixth embodiment of the invention. The manipulator comprises a supporting structure to sustain the actuators, which supporting structure comprises a holding device 54 on which a first actuator 5, a second ac- tuator 50, and a third actuator 7 are mounted. The manipulator comprises a support member 52 for positioning the holding device 54. The first actuator 5 includes a first drive shaft 10, the second actuator 50 includes a second drive shaft 46, and the third actuator 7 includes a third drive shaft 12. The support member 52 extends in a direction essentially parallel to the drive shafts, The drive shaft 46 is hollow, and the first actuator 5 is mounted inside the hollow shaft.

The first inner arm 1 a is attached to a part of the first drive shaft 10, which extends above the motor and gear of the first actuator 5, and the third inner arm 3a is attached to a part of the third drive shaft 12, which extends in the opposite direction of the motor and gear of the second actuator 50. The holding device 54 is used for the mounting of the three actuators. Actuator 5 is placed inside the hollow shaft 46 mounted on the belt wheel 63, which in turn is mounted on the holding device 54 by means of a bearing 64. The belt whee l 63 is driven by the motor 51 by means of the belt wheel 60 on the motor shaft and the transmission belt 61 . As can be seen from figure 12 this arrangement of the actuators will give an even more compact actuation unit than the one in Figure 1 1 . In order to increase the work space of the pillar mounted robot in Figure 8, the holding device in figure 4 can be mounted on the shafts of the lower actuators 6, 7. In figure 10, the second holding device 44a is mounted on both shafts of the lower actuators 6, 7 using bearings. However, the second holding device can also be mounted on only one shaft. The second actuator 50 includes a gear of a hollow shaft type as exemplified in figure 3. The new actuation concept, exemplified in figures 1 ,2,4,8, and 1 1 -12 solves the problems with the prior art Scara tau robot by a different arrangement of the actuation system:

- The inner arm parts are mounted d irectly on the output shafts of the gear boxes driven by the motors.

- At least two of the gear boxes together with the motors are placed side by side.

- At least two of the gear boxes have their shafts pointing in the same direction and for these gear boxes the arms are mounted on the shafts in such a way that one of the arms can pass over or under the other arm. This is made by ei- ther having the gear boxes mounted at different levels or by using different shaft lengths,

- In the case the robot is mounted above the work space it is moreover an advantage to mount the robot on a horizontal beam which is longer than the longest inner arm part.

- In the case the robot is mounted beside its work space it is moreover an advantage to use a hollow transmission for one of the arms. The present invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the following claims. For example the horizontal beam in figure 6 can be arranged to be parallel with the conveyor at the side of the conveyor or between 2 conveyors. Moreover, the robot can be used in applications like window cleaning where the mounting wiii usually be vertical instead of horizontal. This means that in the descriptions vertical will be replaced with horizontal and vice versa. It should also be mentioned that the extremely low weight of the robot makes it well suited for mobile robots and in appli- cations where a robot needs to be moved around by another robot or manipulator. Using a wrist with more than 1 degree of freedom the robot can be used for high speed processes like laser cutting, measurements, plasma cutting, water jet cutting, assembly and high speed machine.

For simple mounting of the actuator type shown in Figure 3, a housing box can be used with three holes, two holes beside each other in the bottom and one hole in the top. In these holes the three actuators are then mounted. In an even simpler solu- tion a plate can be used with three holes and in these holes two actuators are mounted in one direction and the other actuator in the other direction. By using different shaft lengths the three actuators can all be mounted side by side giving the smallest possible vertical length of the actuation system.