Abstract:
An industrial robot includes first and second kinematic chains configured to transmit the movements of corresponding first and second actuators to respective movements of an end effector. The first kinematic chain includes a first rod which is stiff. The second kinematic chain includes elements between the second actuator and the first rod such that the actuation of the second actuator causes bending forces on the first rod. The first and second kinematic chains thereby have the first rod as a common element, which improves compactness and accessibility of the robot. This improvement assumes that the robot is provided with one or more stiff rods that can bear the bending forces resulting from the actuation of the corresponding actuators.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an industrial robot comprising a plurality of actuators working in parallel to manipulate an end effector. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional parallel kinematics robots comprise a plurality of drive arms each connected, directly or via a gearbox, to a respective shaft of a servo motor at one end. At the opposite end the drive arms are attached to a proximate end of rods via ball joints having three degrees of freedom (DOF). The rods transmit the rotating movement of the drive arms to a respective movement of an end effector that is attached to a distal end of the rods via ball joints. The servo motors and the respective drive arms are thereby working in parallel in the sense that manipulation of one drive arm does not affect the position of the remaining drive arms. 
         [0003]    A delta robot is one well known type of parallel kinematics robot that can comprise three drive arms. Each drive arm is connected to an end effector with two rods having a ball joint at each end. The drive arms rotate about respective servo motor axes, the servo motors being arranged symmetrically such that their axes intersect at 60 degrees angles. Because the drive arms of a delta robot are relatively long and point in different directions the robot construction needs a lot of space. U.S. Pat. No. 7,188,544 discloses one type of a delta robot comprising three drive arms. Delta robots can also comprise four or more drive arms. 
         [0004]    WO200366289 discloses other and less well known types of parallel kinematics robots comprising three or more drive arms. The robots according to WO200366289 differ from delta robots in that the rotational axes of the drive arms are parallel, and in many embodiments the drive arms even have one common rotational axis. The number of rods between the drive arms and the end effector vary from one to three depending on a drive arm and a robot embodiment. Also the drive arms of the robots according to WO200366289 need to be relatively long and well spread, and consequently need a lot of space. 
         [0005]    Common for the both aforementioned parallel kinematics robot types is that the rods between the drive arms and the end effector are designed to be exposed to axial forces only. The necessary stiffness of the robots is obtained by spreading out the rods. As a consequence the conventional parallel kinematics robots cannot compete with SCARA robots in many applications because of their relatively poor accessibility and large space requirement. 
       SUMMARY OF THE INVENTION 
       [0006]    One object of the invention is to provide an improved parallel kinematics robot which is compact and has a high accessibility. 
         [0007]    This object is achieved by the device according to the claimed invention. 
         [0008]    The invention is based on the realization that by providing a parallel kinematics robot with one or more stiff rods all the remaining rods do not need to be connected directly to an end effector. Instead, some rods can be connected to the end effector via the stiff rod or rods that are able to bear the resulting bending forces and transmit the corresponding movements to the end effector. 
         [0009]    According to a first aspect of the invention, there is provided an industrial robot comprising: a first actuator configured to rotate a first drive arm about a first axis, a second actuator, and a first kinematic chain configured to transmit the rotation of the first drive arm to a respective movement of an end effector. The first kinematic chain comprises a first rod, a first joint between the first drive arm and the first rod, the first joint having at least two degrees of freedom, and a second joint between the first rod and the end effector. The industrial robot comprises a second kinematic chain configured to transmit a movement of the second actuator to a respective movement of the end effector. The second kinematic chain comprises a fourth joint between the second actuator and the first rod, the first rod, and the second joint. By arranging the first and the second kinematic chains to share a rod and a joint, the number of rods and joints directly connected to the end effector can be correspondingly decreased. As a result, the accessibility of the robot is improved. 
         [0010]    According to one embodiment of the invention the second kinematic chain is configured to expose the first rod to a bending force. A bending force implicitly implies that the first and the second kinematic chains are designed to cause movements in different directions. 
         [0011]    According to one embodiment of the invention the second kinematic chain is configured to cause a rotation of the first rod about the first joint. 
         [0012]    According to one embodiment of the invention the second kinematic chain further comprises a second rod, and a third joint between the second actuator and the second rod. A rod is a simple means for transmitting the movement of the second actuator to a respective movement of the end effector. 
         [0013]    According to one embodiment of the invention the second actuator is configured to rotate a second drive arm about a second axis, the first drive arm and the second drive arm working in parallel. The present invention is particularly well adapted to be applied on parallel kinematics robot. 
         [0014]    According to one embodiment of the invention the first kinematic chain further comprises a third rod, a fifth joint between the first drive arm and the third rod, and a sixth joint between the third rod and the end effector. By providing the first kinematic chain with two rods working in parallel the movements of the end effector are further constrained. 
         [0015]    According to one embodiment of the invention the first rod and the third rod are geometrically parallel. By providing the first kinematic chain with two rods being geometrically parallel the movements of the end effector are further constrained. 
         [0016]    According to one embodiment of the invention the first rod is stiffer than the third rod. The first rod needs to be relatively stiff in order to be able to bear the bending force it is exposed to. The remaining rods do not have the same requirement and consequently the remaining rods can be made less stiff to keep the weight of the moving parts as low as possible. 
         [0017]    According to one embodiment of the invention the first kinematic chain further comprises a fourth rod, a seventh joint between the first drive arm and the fourth rod, and an eighth joint between the fourth rod and the end effector. By providing the first kinematic chain with three rods working in parallel the movements of the end effector are further constrained. 
         [0018]    According to one embodiment of the invention the first rod, the third rod and the fourth rod are geometrically parallel. By providing the first kinematic chain with three rods being geometrically parallel the movements of the end effector are further constrained. 
         [0019]    According to one embodiment of the invention the first joint, the fifth joint and the seventh joint have a rotational degree of freedom about a common axis. By arranging the first joint, the fifth joint and the seventh joint on a common axis, the movements of the end effector are further constrained even when all the three joints have three DOF. 
         [0020]    According to one embodiment of the invention the industrial robot further comprises: a third kinematic chain configured to transmit a movement of a third actuator to a respective movement of the end effector, the third kinematic chain comprising a fifth rod, a ninth joint between the third drive arm and the fifth rod, a tenth joint between the fifth rod and the first rod, the first rod, and the second joint. By arranging the first, the second and the third kinematic chains to share a rod and a joint, the number of rods and joints directly connected to the end effector can be correspondingly decreased. As a result, the accessibility of the robot is further improved. 
         [0021]    According to one embodiment of the invention the third actuator is configured to rotate a third drive arm about a third axis, the first drive arm, the second drive arm and the third drive arm working in parallel. The present invention is particularly well adapted to be applied in parallel kinematics robot. 
         [0022]    According to one embodiment of the invention the first axis, the second axis and the third axis are geometrically parallel. 
         [0023]    According to one embodiment of the invention the first axis, the second axis and the third axis coincide. By this measure the robot can be arranged to be able to rotate a full circle. 
         [0024]    According to one embodiment of the invention the first axis can rotate a full circle. By this measure the work area of the robot is improved. 
         [0025]    According to one embodiment of the invention all the rods directly connected to the end effector are geometrically parallel. By this measure the accessibility of the robot is further improved. 
         [0026]    According to one embodiment of the invention the fourth and the second joints are located on opposite sides of the first joint when considering the direction of the longitudinal axis of the first rod. By this measure the accessibility of the robot is further improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The invention will be explained in greater detail with reference to the accompanying drawings, wherein 
           [0028]      FIG. 1  shows an embodiment of the invention with one stiff rod being part of two separate kinematic chains, 
           [0029]      FIG. 2  shows an embodiment of the invention with one stiff rod being part of three separate kinematic chains, 
           [0030]      FIG. 3  shows an embodiment of the invention with two rods connected to an extension of a stiff rod, 
           [0031]      FIG. 4  shows an embodiment of the invention with two stiff rods being part of two separate kinematic chains, 
           [0032]      FIG. 5  shows an embodiment of the invention with a kinematic chain comprising a belt mechanism, 
           [0033]      FIG. 6  shows an embodiment of the invention with a kinematic chain comprising a lever mechanism integrated on a drive arm, 
           [0034]      FIG. 7  shows an embodiment of the invention with a kinematic chain comprising a gear mechanism, and 
           [0035]      FIG. 8  shows an embodiment of the invention with a drive arm divided into two sections. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    Referring to  FIG. 1 , an industrial robot  10  according to one embodiment of the invention comprises a robot frame having a foot  20  via which the robot  10  can be attached to a floor, a fundament, a wall, a ceiling or another steady structure. The robot frame further comprises a pillar  30  fixedly attached to the foot  20 , and a beam  40  fixedly attached to the pillar  30 . Three servo motors  50 ,  60 ,  70  are attached to a base  80  which can be fixedly or movably attached in relation to the beam  40 . Each servo motor  50 ,  60 ,  70  has a shaft  90 ,  100 ,  110  to which a drive arm  120 ,  130 ,  140  is fixedly attached. The first, second and third servo motors  50 ,  60 ,  70  thereby function as actuators for the respective drive arms  120 ,  130 ,  140  that are rotatable about the respective servo motor axes. Each drive arm  120 ,  130 ,  140  is connected to an end effector  150  by means of a respective kinematic chain that is configured to transmit the rotation of the drive arm  120 ,  130 ,  140  to a respective movement of the end effector  150 . 
         [0037]    A first drive arm  120  is fixedly attached to the first servo motor shaft  90 , and is thereby rotatable about a first axis. The first drive arm  120  is connected to the end effector  150  by means of a first kinematic chain consisting of a first rod  160 , a first joint  170  between the first drive arm  120  and the first rod  160 , a second joint  180  between the first rod  160  and the end effector  150 , a third rod  190 , a fifth joint  200  between the first drive arm  120  and the third rod  190 , a sixth joint  210  between the third rod  190  and the end effector  150 , a fourth rod  220 , a seventh joint  230  between the first drive arm  120  and the fourth rod  220 , and an eighth joint  240  between the fourth rod  220  and the end effector  150 . The first kinematic chain thereby comprises three rods and six joints. The three rods are geometrically parallel i.e. the longitudinal axes of the rods are and remain parallel in direction. Consequently, the orientation of the end effector  150  in relation to the first drive arm  120  remains constant. The three rods also work in parallel in the meaning that each of them affects the position of the end effector  150  directly and not via another of the three rods. The six joints can comprise joints with two or three DOF. 
         [0038]    A second drive arm  130  is fixedly attached to the second servo motor shaft  100 , and is thereby rotatable about a second axis. The second drive arm  130  is connected to the end effector  150  by means of a second kinematic chain comprising a second rod  250 , a third joint  260  between the second drive arm  130  and the second rod  250 , a fourth joint  270  between the second rod  250  and the first rod  160 , the first rod  160 , and the second joint  180  between the first rod  160  and the end effector  150 . The second kinematic chain further comprises an elbow  280 , a first hinge  290  between the elbow  280  and a first drive arm offset beam  300 , a first serial rod  310 , an thirteenth joint  320  between the elbow  280  and the first serial rod  310 , and a fourteenth joint  330  between the first serial rod  310  and a first rod offset beam  340 . 
         [0039]    It is to be understood that the elbow  280 , the first hinge  290 , the first serial rod  310 , the thirteenth joint  320  and the fourteenth joint  330  are not essential elements for the invention. The main principle of the invention, i.e. letting a rod be part of at least two separate kinematic chains, would be achieved even if the fourth joint  270  was connected to the first rod offset beam  340  directly i.e. without the aforementioned elements in between. However, these elements and other corresponding elements in the remaining robot embodiments of this disclosure are optional elements the purposes of which include among other things: decreasing the transmission forces, improving the accessibility of the robot  10 , and optimizing the dynamics of the kinematic chains. It is also to be understood that, in the context of the present disclosure, when it is stated that element A is connected to element B, it does not necessarily mean that elements A and B have a direct connection between them. In other words, it is not excluded that there are additional elements between elements A and B via which the element A is connected to the element B. It is furthermore to be understood that rigid extensions of an element are considered to be part of that element. For example, the first drive arm offset beam  300  is part of the first drive arm  120 , and the first rod offset beam  340  is part of the first rod  160 . It is furthermore to be understood that, in the context of the present disclosure, when at least one rigid part of an element is necessary for completing a kinematic chain, the whole elements shall be considered to be comprised in that kinematic chain. 
         [0040]    Further referring to  FIG. 1 , a third drive arm  140  is fixedly attached to the third servo motor shaft  110 , and is thereby rotatable about a third axis. The third drive arm  140  is connected to the end effector  150  by means of a third kinematic chain consisting of a fifth rod  350 , a ninth joint  360  between the third drive arm  140  and the fifth rod  350 , a tenth joint  370  between the fifth rod  350  and the end effector  150 , a sixth rod  380 , an eleventh joint  390  between the third drive arm  140  and the sixth rod  380 , and a twelfth joint  400  between the sixth rod  380  and the end effector  150 . The third kinematic chain thereby comprises two rods and four joints. The two rods are geometrically parallel and they also work in parallel. The four joints can comprise joints with two or three DOF. 
         [0041]    The first rod  160  is stiff such that it can bear the bending force resulting from the actuation of the servo motors  50 ,  60 ,  70 , especially of the second servo motor  60 . In particular, the first rod  160  is stiffer than the second, third, fourth, fifth and sixth rods  250 ,  190 ,  220 ,  350 ,  380  that are designed to be exposed to axial forces only. 
         [0042]    Referring to  FIG. 2 , in contrast to the robot  10  of  FIG. 1  the drive arms  120 ,  130 ,  140  are no longer fixedly attached to the servo motor shafts  90 ,  100 ,  110 . Instead, the servo motors  50 ,  60 ,  70  are arranged to actuate the drive arms  120 ,  130 ,  140  via gear boxes, and the drive arms  120 ,  130 ,  140  are fixedly attached to respective first, second and third output shafts  410 ,  420 ,  430  which are arranged to be coaxial about a fourth axis  440 . The drive arms  120 ,  130 ,  140  thereby have a common rotational axis, which enables the rotation of the drive arms  120 ,  130 ,  140  over a full circle. 
         [0043]    The first and second kinematic chains of  FIG. 2  are similar to those of  FIG. 1 , but the third kinematic chain is very different. Instead of being connected directly (by the tenth joint  370 ) to the end effector  150 , the fifth rod  350  is connected to the end effector  150  via the first rod  160 . Furthermore, in contrast to the robot  10  of  FIG. 1  the sixth rod  380  is omitted. In order to compensate for the missing sixth rod  380  and to constrain all the six DOF of the end effector  150 , the first and second joints  170 ,  180  can be chosen to be cardan joints with two DOF. When comparing the embodiments of  FIGS. 1 and 2 , it can be established that the accessibility of the robot  10  of  FIG. 2  is greatly improved as all the rods  160 ,  190 ,  220  directly connected to the end effector  150  are geometrically parallel i.e. extend in a single direction. 
         [0044]    Referring to  FIG. 3 , all the three kinematic chains are similar to those of  FIG. 2 , the most important difference being that the first rod  160  comprises an extension  450  to which the second and fifth rods  250 ,  350  are connected. As a consequence, the fourth and the tenth joints  270 ,  370 , and the second joint  180 , respectively, are located on opposite sides of the first joint  170  when considering the direction of the longitudinal axis of the first rod  160 . When comparing the embodiments of  FIGS. 2 and 3 , it can be established that the accessibility of the robot  10  of  FIG. 3  is further improved as all the rods  160 ,  190 ,  220  directly connected to the end effector  150  are free from any additional connections between the end effector  150  and the first drive arm  120 . 
         [0045]    Referring to  FIG. 4 , according to an alternative embodiment of the robot  10  the first, fifth and seventh joints  170 ,  200 ,  230  are arranged on a fifth axis  460  which is a common rotational axis for the three joints. This embodiment enables all the three joints having three DOF. This embodiment also enables the second, sixth and eighth joints  180 ,  210 ,  240  to have only one DOF. 
         [0046]    Referring to  FIGS. 5-7 , the respective second kinematic chains are partially integrated with the first drive arm  120 . According to  FIG. 5  the second kinematic chain comprises a belt mechanism with a primary pulley  470 , a belt  480  and a secondary pulley  490 . The secondary pulley  490  is fixedly attached to a second drive arm offset beam  500  which in its turn is attached in a rotatable manner in relation to the first drive arm  120  by means of a first bearing  510 . According to  FIG. 6  the second kinematic chain comprises a lever mechanism with a primary lever  520 , a lever shaft  530  and a secondary lever  540 . The lever shaft  530  is attached in a rotatable manner in relation to the first drive arm  120  by means of second bearings  550 . According to  FIG. 7  the second kinematic chain comprises a gear mechanism with a primary gear  560 , a secondary gear  570  and a gear shaft  580 . The gear shaft  580  is attached in a rotatable manner in relation to the first drive arm  120  by means of the second bearings  550 . The primary pulley  470 , the primary lever  520  and the primary gear  560 , respectively, are fixedly attached to the second output shaft  420  driven by the second servo motor  60 . 
         [0047]    Referring to  FIG. 8 , the orientation of the end effector  150  in relation to the robot frame (not shown) can be kept constant by dividing the first drive arm  120  into two sections; a first drive arm section  590  and a second drive arm section  600 . The second drive arm section  600  is attached in a rotatable manner in relation to the first drive arm section  590  by means of a third bearing  610  rotatable about a sixth axis  620  which is parallel with the fourth axis  440 . The second drive arm section  600  comprises a third drive arm offset beam  630  which is connected to a fixed point at the robot frame via a link  640  with a node  650  at each end of it. Each of the nodes  650  has at least one rotational DOF, and together with the fourth and the sixth axes  440 ,  620  the rotational axes of the nodes  650  form corner points of a parallelogram. 
         [0048]    The invention is not limited to the embodiments shown above, but the person skilled in the art may modify them in a plurality of ways within the scope of the invention as defined by the claims.