Parallel kinematics robot with rotational degrees of freedom

A parallel kinematics robot includes a base and an end effector movable in relation to the base. A first actuator is attached to the base and connected to the end effector via a first kinematic chain including a first drive arm, a first rod, a first joint between the first drive arm and the first rod, and a second joint between the first rod and the end effector. A second actuator is attached to the base and connected to the end effector via a second kinematic chain including a second drive arm, a second rod, a third joint between the second drive arm and the second rod, and a fourth joint between the second rod and the end effector. A third actuator is attached to the base or to the first drive arm, and connected to the end effector via a third kinematic chain including a first gear wheel and a second gear wheel, the first and second gear wheels being journalled in bearings to the end effector and intermeshing with each other. One element of the third kinematic chain constitutes a kinematic pair with at least one element of the first kinematic chain. A kinematic chain responsible for a translational movement of the end effector is utilized as a support structure for a kinematic chain responsible for a rotational movement of the end effector.

TECHNICAL FIELD

The present invention relates to a parallel kinematics robot wherein rotational degrees of freedom are transmitted from a base to an end effector.

BACKGROUND

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 each drive arm is connected to one or more rods, and the rods are further connected to an end effector. Between the drive arms and the rods, and between the rods and the end effector, respectively, there are joints with one to three degrees of freedom. The drive arms together with the rods and the joints form kinematic chains from the servo motors to the end effector for transmitting the rotating movement of the servo motors to a respective movement of an end effector. The servo motors and the respective drive arms work in parallel in the sense that manipulation of one drive arm does not affect the position of the remaining drive arms.

Each kinematic chain of a parallel kinematics robot provides the respective end effector with a degree of freedom. A delta robot is one well known type of parallel kinematics robot that typically comprises three drive arms and has three translational degrees of freedom. Each drive arm is connected to an end effector via 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. 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.

In many applications it is desirable to provide the end effector also with rotational degrees of freedom such that the end effector can change its orientation. US2014/0060234A1 discloses a parallel kinematics robot where the end effector has one rotational degree of freedom, and US2012/0060637A1 discloses a parallel kinematics robot where the end effector has three rotational degrees of freedom. In US2014/0060234A1 an additional actuator (which can be a servo motor) is arranged between two rods that are a part of a kinematic chain between a servo motor and the end effector. In US2012/0060637A1 three additional servo motors are arranged at a base of the robot such that they are immobile in relation to the three servo motors responsible for the translational movements of the end effector.

A drawback with the solution of US2014/0060234A1 is that the additional actuator adds to the weight of the kinematic chain it is attached to, and consequently the servo motor responsible for the movements of that kinematic chain needs to be dimensioned bigger or cannot move as fast as the case would be without the additional weight. A drawback with the solution of US2012/0060637A1 is that the work area of the robot is strongly limited by the largest allowed inclination of the transmission members transmitting the driving force from the additional servo motors to the end effector. Between the transmission members and the end effector there are namely cardan type universal joints that stop working properly as the bend angles of the joints become too large.

There is a desire to provide a parallel kinematics robot where the aforementioned drawbacks are mitigated.

SUMMARY

One object of the invention is to provide a parallel kinematics robot with an alternative way of transmitting rotational degrees of freedom from the base to the end effector.

The invention is based on the realization that kinematic chains responsible for translational movements of the end effector can be utilized as support structures for kinematic chains responsible for rotational movements of the end effector.

According to a first aspect of the invention, there is provided a parallel kinematics robot comprising a base, and an end effector movable in relation to the base. A first actuator is attached to the base and connected to the end effector via a first kinematic chain comprising a first drive arm, a first rod, a first joint between the first drive arm and the first rod, and a second joint between the first rod and the end effector. A second actuator is attached to the base and connected to the end effector via a second kinematic chain comprising a second drive arm, a second rod, a third joint between the second drive arm and the second rod, and a fourth joint between the second rod and the end effector. A third actuator is attached to the base or to the first drive arm, and connected to the end effector via a third kinematic chain comprising a first gear wheel and a second gear wheel, the first and second gear wheels being journalled in bearings to the end effector and intermeshing with each other. At least one element of the third kinematic chain constitutes a kinematic pair with at least one element of the first kinematic chain. The first kinematic chain can thereby be utilized as a support structure for the third kinematic chain such that the third kinematic chain does not limit the movements of the first kinematic chain, and consequently does not negatively affect the robot's work area.

According to one embodiment of the invention, the kinematic pair is a revolute pair. A revolute pair is simple to accomplish with means of a journalled shaft or a hinge.

According to one embodiment of the invention, the first gear wheel is turned with means of a lever. This solution enables the third kinematic chain to consist of simple elements such as levers, rods and joints.

According to one embodiment of the invention, the first gear wheel is turned with means of a cardan shaft. This solution enables the first gear wheel to be turned over an indefinite angle.

According to one embodiment of the invention, the first gear wheel is closer to the third actuator in the third kinematic chain than the second gear wheel, and the first gear wheel has a larger diameter than the second gear wheel. This solution causes a relatively small angular rotation of the first gear wheel to result in a relatively large angular rotation of the second gear wheel, which is advantageous especially when the first gear wheel is turned with means of a lever and an angle over which the first gear wheel can be turned is limited.

According to one embodiment of the invention, the third kinematic chain comprises a rotating shaft parallel with the first drive arm.

According to one embodiment of the invention, the third kinematic chain comprises a belt parallel with the first drive arm.

According to one embodiment of the invention, the robot further comprises a fourth actuator attached to the base or to the second drive arm, and connected to the end effector via a fourth kinematic chain comprising a ninth gear wheel and a tenth gear wheel, the ninth and tenth gear wheels being journalled in bearings to the end effector and intermeshing with each other. At least one element of the fourth kinematic chain constitutes a kinematic pair with at least one element of the second kinematic chain. The second kinematic chain can thereby be utilized as a support structure for the fourth kinematic chain such that the fourth kinematic chain does not limit the movements of the second kinematic chain, and consequently does not negatively affect the robot's work area.

According to one embodiment of the invention, at least one element of the third kinematic chain is identical with an element of the fourth kinematic chain. The total number of differing parts for accomplishing the third and fourth kinematic chains can be reduced when at least one element is identical in both kinematic chains. Preferably as many elements as possible are identical.

DETAILED DESCRIPTION

Referring toFIG. 1, a parallel kinematics robot10according to one embodiment of the invention comprises a base20and an end effector30movable in relation to the base20. A first actuator40in the form of a servo motor is attached to the base20and connected to the end effector30via a first kinematic chain comprising a first drive arm50, a first rod60, a first joint70between the first drive arm50and the first rod60, and a second joint80between the first rod60and the end effector30. A second actuator90is attached to the base20and connected to the end effector30via a second kinematic chain comprising a second drive arm100, a second rod110, a third joint120between the second drive arm100and the second rod110, and a fourth joint130between the second rod110and the end effector30.

A third actuator140is attached to the base20or to the first drive arm50although for the sake of clarity of the figure the third actuator140is illustrated to be separate from the base20and the first drive arm50. The third actuator140is connected to the end effector30via a third kinematic chain comprising a first gear wheel150and a second gear wheel160. The third kinematic chain further comprises three levers170, two bars180and four nodes190(joints with one to three degrees of freedom) for transforming a rotational movement of the third actuator140into a rotational movement of the intermeshing first and second gear wheels150,160. The first gear wheel150is closer to the third actuator140in the third kinematic chain than the second gear wheel160, and the first and second gear wheels150,160are journalled in bearings to the end effector30although for the sake of clarity of the figure the first and second gear wheels150,160are illustrated to be separate from the end effector30. A tool200is attached to a first shaft210rotating along with the second gear wheel160, and an actuation of the third actuator140thereby causes the tool200to rotate about a first rotational axis220at the end effector30. The first gear wheel150has a larger diameter than the second gear wheel160such that a relatively small angular rotation of the first gear wheel150causes a relatively large angular rotation of the second gear wheel160.

One of the levers170is hinged by means of a hinge230to the first drive arm50and thereby constitutes a revolute pair with the same. The first drive arm50of the first kinematic chain is thereby utilized as a support structure for one of the levers170of the third kinematic chain. As the third kinematic chain is in this way integrated to the first kinematic chain, it does not limit the movements of the first kinematic chain, and consequently does not negatively affect the robot's10work area. The third kinematic chain does also not add much inertia to the first kinematic chain because all its elements are relatively light, and because the relatively heavy third actuator140is either attached to the base20or to the first drive arm50. If the third actuator140is to be attached to the first drive arm50, it is preferably attached close to the axis about which the first drive arm50rotates in order to minimize an increase in the inertia of the first kinematic chain.

A fourth actuator240is attached to the base20or to the second drive arm100, and is further connected to the end effector30via a fourth kinematic chain corresponding to the third kinematic chain described hereinbefore. Also here, if the fourth actuator240is to be attached to the second drive arm100, it is preferably attached close to the axis about which the second drive arm100rotates in order to minimize an increase in the inertia of the first kinematic chain. An actuation of the fourth actuator240causes the tool200to rotate about a second rotational axis250at the end effector30, the second rotational axis250being perpendicular to the first rotational axis220.

Referring toFIG. 2, a parallel kinematics robot10according to one embodiment of the invention is shown. The first actuator40, the first drive arm50, the second actuator90and the second drive arm100correspond to the equivalent elements ofFIG. 1. The remaining elements of the first and second kinematic chains are omitted fromFIG. 2since they are not relevant for the illustrated third and fourth kinematic chains. The third actuator140is attached to the base20(not shown), and is further connected to the end effector30via a third kinematic chain comprising a first pulley260, a belt280transmitting the rotation of the first pulley260to a second pulley270, a third gear wheel290, a fourth gear wheel300intermeshing with the third gear wheel290, a first cardan shaft310transmitting the rotation of the fourth gear wheel300to the first gear wheel150, and the second gear wheel160intermeshing with the first gear wheel150. The second pulley270and the third gear wheel290are rotating along with a second shaft320journalled to the first drive arm50, and they thereby constitute a revolute pair with the same. The first drive arm50of the first kinematic chain is thereby utilized as a support structure for the second pulley270and the third gear wheel290of the third kinematic chain.

The fourth actuator240is also attached to the base20, and is further connected to the end effector30via a fourth kinematic chain comprising a fifth gear wheel330, a sixth gear wheel340, a third shaft350transmitting the rotation of the sixth gear wheel340to a seventh gear wheel360, an eighth gear wheel370intermeshing with the seventh gear wheel360, a second cardan shaft380transmitting the rotation of the eighth gear wheel370to a ninth gear wheel390, and a tenth gear wheel400intermeshing with the ninth gear wheel390. The third shaft350is journalled in relation to the second drive arm100to rotate parallel with the same, and the third shaft350thereby constitutes a revolute pair with the second drive arm100. The second drive arm100of the second kinematic chain is thereby utilized as a support structure for the third shaft350of the fourth kinematic chain. It is to be understood that the third and fourth kinematic chains ofFIG. 2are alternative embodiments and consequently interchangeable. The elements of the third kinematic chain can thereby be used to form the fourth kinematic chain and vice versa.

Referring toFIG. 3, the end effector30ofFIG. 2is shown in more detail. The first, second, ninth and tenth gear wheels150,160,390,400are journalled in bearings to the end effector30. The tool200is attached to the first shaft210rotating along with the second gear wheel160, and an actuation of the third actuator140thereby causes the tool200to rotate about the first rotational axis220at the end effector30. The tool200is furthermore connected to a fourth shaft410rotating along with the tenth gear wheel400, and an actuation of the fourth actuator240thereby causes the tool200to rotate about the second rotational axis250at the end effector30, the second rotational axis250being perpendicular to the first rotational axis220.

Referring toFIG. 4, an end effector30with three rotational degrees of freedom is shown. In addition to the elements ofFIG. 3the end effector30ofFIG. 4comprises a third cardan shaft420configured to rotate an eleventh gear wheel430, a twelfth gear wheel440intermeshing with the eleventh gear wheel430, a thirteenth gear wheel450intermeshing with the twelfth gear wheel440, and a fourteenth gear wheel460intermeshing with the thirteenth gear wheel450. The aforementioned elements from the third cardan shaft420to the fourteenth gear wheel460are parts of a fifth kinematic chain actuated by a fifth actuator (not shown) attached to the base20(not shown). The tool200(not shown) is attached to the fourteenth gear wheel460and rotates along with it about a third rotational axis470when the fifth actuator is actuated. The third rotational axis470is perpendicular to the first and second rotational axes220,250, and thereby also perpendicular to the drawing plane ofFIG. 4. The end effector30ofFIG. 4thereby has three rotational degrees of freedom about three perpendicular axes.

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.