Method And Control System For Controlling An Industrial Actuator

Abstract

A method for controlling an industrial actuator (26), the method comprising defining a movement path (10) as a sequence of a plurality of consecutive movement segments (14), where each movement segment (14) is defined between two points (16); defining at least one blending zone (12, 50, 52) associated with one of the points (16) between two consecutive movement segments (14), wherein the blending zone (12, 50, 52) is defined independently in relation to each of the two consecutive movement segments (14); and executing the movement path (10) comprising the blending zone (12, 50, 52) by the industrial actuator (26). A control system (30) for controlling an industrial actuator (26) and an actuator system (24) comprising an industrial actuator (26), are also provided.

Claims

1. A method for controlling an industrial actuator, the method comprising: defining a movement path as a sequence of a plurality of consecutive movement segments, where each movement segment is defined between two points; defining at least one blending zone associated with one of the points between two consecutive movement segments, wherein the blending zone is defined independently in relation to each of the two consecutive movement segments; and executing the movement path comprising the blending zone by the industrial actuator.

2. The method according to claim 1, wherein the blending zone is defined by means of two zone borders, and wherein each zone border is defined in relation to a respective one of the two consecutive movement segments.

3. The method according to claim 1, wherein the blending zone is defined with a factor from 0 to 1 in relation to each of the two consecutive movement segments.

4. The method according to claim 3, wherein the blending zone is defined with a different factor in relation to each of the two consecutive movement segments.

5. The method according to claim 1, wherein the at least one blending zone comprises a first blending zone associated with a first point, and wherein the method further comprises: defining at least one second blending zone associated with a second point, consecutive with the first point; and determining if there is an overlap between the first blending zone and the second blending zone.

6. The method according to claim 5, further comprising modifying the definitions of the first blending zone and the second blending zone, in relation to the movement segment between the first point and the second point, to an average value in relation to the movement segment between the first point and the second point, if it is determined that there is an overlap between the first blending zone and the second blending zone.

7. The method according to claim 5, further comprising reducing the largest of the first blending zone and the second blending zone, by modifying the definition in relation to the movement segment between the first point and the second point until the overlap is eliminated, if it is determined that there is an overlap between the first blending zone, and the second blending zone.

8. The method according to claim 5, further comprising reducing the blending zone of the first blending zone and the second blending zone that has the lowest priority, by modifying the definition in relation to the movement segment between the first point and the second point until the overlap is eliminated, if it is determined that there is an overlap between the first blending zone and the second blending zone.

9. The method according to claim 1, wherein the defining of at least one blending zone associated with one of the points comprises defining at least two blending zones and wherein each blending zone is defined independently in relation to each of the two consecutive movement segments.

10. The method according to claim 1, wherein the method further comprises simultaneously executing two consecutive movement segments within one of the at least one blending zone.

11. The method according to claim 1, wherein the method further comprises initiating a reorientation of a tool of the industrial actuator towards an orientation of the tool associated with one of the points, when the industrial actuator reaches one of the at least one blending zone associated with that point.

12. The method according to claim 1, wherein the method further comprises initiating an operation of an external device associated with one of the points of the movement path, when the industrial actuator reaches one of the at least one blending zone associated with that point.

13. The method according to claim 1, wherein the industrial actuator is an industrial robot.

14. A control system for controlling an industrial actuator, the control system comprising a data processing device and a memory having a computer program stored thereon, the computer program comprising program code which, when executed by the data processing device, causes the data processing device to perform the steps of: defining a movement path as a sequence of a plurality of consecutive movement segments, where each movement segment is defined between two points; defining at least one blending zone associated with one of the points between two consecutive movement segments wherein the blending zone is defined independently in relation to each of the two consecutive movement segments; and commanding the industrial actuator to execute the movement path comprising the blending zone.

15. An actuator system comprising a control system and an industrial actuator, the control system including a data processing device and a memory having a computer program stored thereon, the computer program having program code which when executed by the data processing device, causes the data processing device to perform the steps of: defining a movement path as a sequence of a plurality of consecutive movement segments, where each movement segment is defined between two points; defining at least, one blending zone associated with one of the points between two consecutive movement segments, wherein the blending zone is defined independently in relation to each of the two consecutive movement segments; and commanding the industrial actuator to execute the movement path comprising the blending zone.

16. The method according to claim 2, wherein the blending zone is defined with a factor from 0 to 1 in relation to each of the two consecutive movement segments.

17. The method according to claim 2, wherein the at least one blending zone comprises a first blending zone associated with a first point, and wherein the method further comprises: defining at least one second blending zone associated with a second point, consecutive with the first point; and determining if there is an overlap between the first blending zone and the second blending zone.

18. The method according to claim 2, wherein the defining of at least one blending zone associated with one of the points comprises defining at least two blending zones, and wherein each blending zone is defined independently in relation to each of the two consecutive movement segments.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Further details, advantages and aspects of the present disclosure will become apparent from the following embodiments taken in conjunction with the drawings, wherein:

[0039] FIG. 1: schematically represents a movement path and blending zones according to the prior art;

[0040] FIG. 2: schematically represents a movement path and blending zones according to one embodiment of the present invention;

[0041] FIG. 3: schematically represents blending of movement segments within the blending zones of the movement path in FIG. 2;

[0042] FIG. 4: schematically represents a side view of an actuator system comprising an industrial actuator, an external device and a control system according to one embodiment of the present invention;

[0043] FIG. 5: schematically represents a movement path and three blending zones associated with a point according to one embodiment of the present invention; and

[0044] FIGS. 6a-6f: schematically represents various phases of execution of the movement path in FIG. 5.

DETAILED DESCRIPTION

[0045] In the following, a method and a control system for controlling an industrial actuator to execute a movement path comprising at least one blending zone, will be described. The same reference numerals will be used to denote the same or similar structural features.

[0046] FIG. 2 schematically represents a movement path 10 and blending zones 12b, 12c according to one embodiment of the present invention. The movement path 10 in FIG. 2 comprises the same points 16, the same consecutive movement segments 14 between the points 16, and the same programmed blending zones 18b, 18c, as the movement path 10 in FIG. 1. However, the blending zones 12 are defined differently in FIG. 2.

[0047] The movement path 10 in FIG. 2 is two-dimensional but may alternatively be three-dimensional. In FIG. 2, two consecutive movement segments 14 are executed simultaneously in each blending zone 12 associated with the point 16 between the two consecutive movement segments 14. The movement path 10 may for example be followed by the TCP of the industrial actuator. For this reason, the blending zones 12b, 12c in FIG. 2 may be referred to as TCP blending zones or as Cartesian position blending zones.

[0048] The first point 16a and the fourth point 16d are fine points (stop points). Therefore, no blending zones are defined in association with these points.

[0049] The second blending zone 12b is defined independently in relation to each of the two consecutive movement segments 14a, 14b and the third blending zone 12c is defined independently in relation to each of the two consecutive movement segments 14b, 14c. As a consequence, the blending zones 12b, 12c are not limited by symmetry.

[0050] The blending zones 12 may be defined in various ways. According to one example, the blending zones 12 are defined by means of zone borders. In FIG. 2, the definition of the second blending zone 12b in relation to the first movement segment 14a and the second movement segment 14b may be made by means of two second zone borders 20b1, 20b2, respectively, and the definition of the third blending zone 12c in relation to the second movement segment 14b and the third movement segment 14c may be made by means of two third zone borders 20c1, 20c2, respectively (the zone borders 20b1, 20b2, 20c1, 20c2 may also be referred to with reference numeral “20”).

[0051] The maximum allowable size for a blending zone 12 may be exceeded for several reasons, including for example lack of skill or care by the programmer, changes made to the movement path 10, e.g. a reduced length of a movement segment 14, and automatic generation of the movement path lo based on sensor input, from e.g. a vision system, where the lengths of the movement segments 14 are not known beforehand. The method according to the present invention may comprise a limitation on the maximum size of each blending zone 12. One example of such limitation is that each blending zone 12 should be defined with a factor between 0 and 1 (i.e. between 0% and 100%) in relation to each of the two consecutive movement segments 14 with which the blending zone 12 is associated. In the example in FIG. 2, the definition of the second programmed blending zone 18b in relation to the first movement segment ma is approximately 75% and the definition of the second programmed blending zone 18b in relation to the second movement segment 14b is approximately 50%. Thus, the second programmed blending zone 18b does not need to be reduced due to exceeding a maximum size. The second blending zone 12b may therefore be defined as the second programmed blending zone 18b.

[0052] Furthermore, the definition of the third programmed blending zone 18c in relation to the second movement segment 14b is approximately 75%, which is well within this limitation. However, the definition of the third programmed blending zone 18c in relation to the third movement segment 14c is approximately 200%. Therefore, the definition of the third blending zone 12c is reduced to 100% in relation to the third movement segment 14c. The third blending zone 12c is thereby allowed to extend all the way to the fine point 16d.

[0053] In FIG. 2, there is an overlap between the second programmed blending zone 18b and the third programmed blending zone 18c. Various reasons for such overlap exist, including for example lack of skill or care by the programmer and changes made to the movement path 10, e.g. a reduced length of the second movement segment 14b. The method according to the present invention may comprise determining if there is an overlap between two consecutive blending zones 12. Instead of setting each defined blending zone 12b, 12c to a circle having a radius corresponding to 50% of the length of the shortest of the two consecutive movement segments 14 with which the blending zone 12 is associated according to the prior art, the present invention provides for alternative ways of handling such overlaps.

[0054] One measure of handling overlaps includes modifying the definitions of the second blending zone 12b and the third blending zone 12c to an average value in relation to the second movement segment 14b, if it is determined that there is an overlap between the second blending zone 12b and the third blending zone 12c. In FIG. 2, the definition of the second programmed blending zone 18b in relation to the second movement segment 14b is already 50% of the length of the second movement segment 14b. Thus, the second programmed blending zone 18b remains unchanged and also constitutes the defined second blending zone 12b. However, since the definition of the third programmed blending zone 18c in relation to the second movement segment 14b is beyond 50% (approximately 75%) in FIG. 2, the definition of the third blending zone 12c in relation to the second movement segment 14b (but not in relation to the third movement segment 14c) is reduced to the average value of 50%.

[0055] An alternative measure of handling overlap includes reducing the largest of the second programmed blending zone 18b and the third programmed blending zone 18c. In FIG. 2, the third programmed blending zone 18c is larger than the second programmed blending zone 18b. Therefore, the definition of the second programmed blending zone 18b in relation to the second movement segment 14b is unchanged and the definition of the third programmed blending zone 18c in relation to the second movement segment 14b is reduced until the overlap is eliminated.

[0056] As an alternative measure of handling overlap, one or more programmed blending zones 18 may be prioritized. If for example the second programmed blending zone 18b is prioritized, the second programmed blending zone 18b remains unchanged (given that the second programmed blending zone 18b is defined with a factor from 0 to 1 in relation to each of the two consecutive movement segments 14a, 14b) and thereby constitutes the defined second blending zone 12b. In this case, the third programmed blending zone 18c, which has a lower priority than the second programmed blending zone 18b, is reduced by reducing the definition in relation to the second movement segment 14b until the overlap is eliminated.

[0057] In each of the above three examples, the blending zones 12b, 12c will be defined as illustrated in FIG. 2. As can be seen in FIG. 2, the definition of the second blending zone 12b in relation to the first movement segment ma is larger than 50% and the third blending zone 12c is defined as an ellipse.

[0058] Except for an optional limitation in maximum size of the blending zones 12, the blending zones 12 are only limited by the size of one or two adjacent blending zones 12 and eventually by distances to closest points. By defining the zone borders 20 of each blending zone 12 independently, the blending zones 12 can be made much larger.

[0059] FIG. 3 schematically represents blending of movement segments 14 within the blending zones 12 of the movement path 10 in FIG. 2. In the example of FIG. 3, the two consecutive movement segments 14a, 14b are executed simultaneously in the second blending zone 12b and the two consecutive movement segments 14b, 14c are executed simultaneously in the third blending zone 12c, when executing the movement path 10 by the industrial actuator. Due to this simultaneous execution of consecutive movement segments 14, the industrial actuator follows a defined curve 22b in the second blending zone 12b and a defined curve 22c in the third blending zone 12c (the curves 22b, 22c may also be referred to with reference numeral “22”). In the example in FIG. 3, the curves 22b, 22b are linearly blended between the respective pairs of associated movement segments 14.

[0060] The curves 22b, 22c define the movement path 10 within the respective blending zones 12b, 12c. This defined movement path 10 is the same regardless of speeds and accelerations of the industrial actuator along the movement path 10. The geometry of the movement path 10 is defined independently of the dynamics of the industrial actuator. A dynamic coupling, e.g. speeds and accelerations of the industrial actuator along the movement path 10, may be generated in a second step to define a movement trajectory. The movement path 10 within the blending zones 12 may however be blended in various ways. Instead of curves 22, the movement path 10 may for example adopt various polynomial shapes within the blending zones 12. The movement path 10 within each blending zone 12 may alternatively be referred to as a corner path.

[0061] As illustrated in FIG. 3, when executing the movement path 10 by the lo industrial actuator, the movement path 10 starts in the first point 16a and ends in the fourth point 16d, or vice versa. Since the first point 16a and the fourth point 16d are stop points, the industrial actuator makes a full stop at these points. However, due to the blending zone 12b and the blending zone 12c, the industrial actuator is allowed to fly-by the second point 16a and the third point 16c. The movement path 10 is thereby made more smooth and acceleration and deceleration phases along the movement path 10 can be reduced or eliminated. As a consequence, the speed of the industrial actuator can be increased and the wear on mechanical components of the industrial actuator can be reduced.

[0062] FIG. 4 schematically represents a side view of an actuator system 24 comprising an industrial actuator 26, an external device 28 and a control system 30 according to one embodiment of the present invention. In the example of FIG. 4, the industrial actuator 26 is exemplified as an industrial robot. The external device 28 is exemplified as an external actuator comprising a reorientable table 32. The external device 28 may however, for example, alternatively be constituted by an additional industrial robot.

[0063] The external device 28 is configured to rotate the table 32 around an axis perpendicular to the plane of FIG. 4, as illustrated with arrow 34. The table 32 may however be moved in two or more axes, such as up to six axes. An object 36 is secured to the table 32. The industrial actuator 26 comprises a tool 38, for example a welding tool, for performing a handling operation on the object 36.

[0064] The control system 30 is configured to control the industrial actuator 26 and optionally the external device 28 according to the present invention. The control system 30 comprises a data processing device 40 (e.g. a central processing unit, CPU) and a memory 42. A computer program is stored in the memory 42. The computer program comprises program code which, when executed by the data processing device 40, causes the data processing device 40 to perform the steps of defining a movement path 10 as a sequence of a plurality of consecutive movement segments 14, where each movement segment 14 is defined between two points 16; defining at least one blending zone 12 associated with one of the points 16 between two consecutive movement segments 14 of the movement path 10, wherein the blending zone 12 is defined independently in relation to each of the two consecutive movement segments 14 associated with the point 16; and commanding the industrial actuator 26 to execute the movement path 10 comprising the Cartesian position blending zone 12, an external device blending zone and/or an orientation blending zone. In the example of FIG. 4, the control system 30 is in communication with the industrial actuator 26 and the external device 28 by means of signal lines 44.

[0065] FIG. 4 further denotes a vertical axis 46 and a first horizontal axis 48 of a Cartesian coordinate system for referencing purposes. The industrial actuator 26 and the external device 28 may however be oriented arbitrarily in space.

[0066] FIG. 5 schematically represents a movement path 10 and three blending zones 12b, 50b, 52b associated with a point 1613 according to one embodiment of the present invention. In addition to a Cartesian position blending zone 12b as described in connection with FIGS. 2 and 3, the movement path 10 of the example in FIG. 5 comprises two additional blending zones 50b, 52b. The additional blending zone 50b is constituted by an external device blending zone (which may also be referred to with reference numeral “50”) and the additional blending zone 52b is constituted by an orientation blending zone (which may also be referred to with reference numeral “52”). Each of the three blending zones 12b, 50b, 52b may be defined independently in relation to each of the two consecutive movement segments 14a, 14b associated with the point 16b, as described in connection with the blending zone 12 in FIGS. 2 and 3. Thus, each of the three blending zones 12b, 50b, 52b may be handled in parallel. FIG. 5 further shows that the object 36 of this example comprises a curved profile 54 between its top surface 56 and its perpendicular side surface 58. The programming of the movement path 10 may be made in a coordinate system (not shown) of the table 32.

[0067] During execution of the movement path 10 by the industrial actuator 26, an operation of the external device 28 associated with the point 16b is initiated when the industrial actuator 26 reaches the external device blending zone 50b associated with the point 16b, e.g. when the industrial actuator 26 reaches the one of two zone borders 60b1, 60b2 of the external device blending zone 50b (the zone borders 60b1, 60b2 may also be referred to with reference numeral “60”). Furthermore, during execution of the movement path 10 by the industrial actuator 26, a reorientation of the tool 38 towards an orientation of the tool 38 associated with the point 16b is initiated when the industrial actuator 26 reaches the orientation blending zone 52b associated with the point 16b, e.g. when the industrial actuator 26 reaches one of two zone borders 62b1, 62b2 of the orientation blending zone 52b (the zone borders 62b1, 62b2 may also be referred to with reference numeral “62”).

[0068] In the example of FIG. 5 the external device blending zone 50b is an outermost blending zone, the orientation blending zone 52b is a middle blending zone and the Cartesian position blending zone 12b is an inner blending zone. However, the order of the blending zones 12b, 50b, 52b may be set differently and two or more of the blending zones 12b, 50b, 52b may partly or fully overlap. In particular, the Cartesian position blending zone 12b may be defined as an inner blending zone and the external device blending zone 50b and the orientation blending zone 52b may be defined as a common outer blending zone.

[0069] FIGS. 6a-6f schematically represents various phases of execution of the movement path 10 in FIG. 5. The execution of the movement path 10 is made in connection with a handling operation of the tool 38 on the object 36. The handling operation may be constituted by a welding operation where it may desired to maintain the surface at the welding point substantially horizontal and/or the tool 38 substantially perpendicular to the surfaces of the object 36. However, in order to clearly demonstrate the properties of the blending zones 12, 50, 52, the surface at the welding point of the object 36 is not maintained perfectly horizontal at all times and the tool 38 is not maintained perfectly perpendicular to the surfaces of the object 36 at all times in FIGS. 6a-6f.

[0070] In FIG. 6a, the tool 38 moves along the movement segment 14a. The top surface 56 of the object 36 is oriented horizontally. The first movement segment ma partly follows the top surface 56 of the object 36 (until the zone border 20b1 of the Cartesian position blending zone 12b). The tool 38 is oriented perpendicular to the top surface 56 of the object 36.

[0071] As shown in FIG. 6b, when the tool 38 has passed the zone border 60b1 of the external device blending zone 50b, the external device 28 initiates a rotation of the table 32 towards a 90° rotation associated with the point 16b. The tool 38 still follows the top surface 56 of the object 36 and the tool 38 is maintained in an orientation perpendicular to the top surface 56.

[0072] As shown in FIG. 6c, when the tool 38 has passed the zone border 62b1 of the orientation blending zone 52b, the industrial actuator 26 initiates a reorientation of the tool 38, as indicated by arrow 64, towards a 90° orientation of the tool 38 associated with the point 1613 (in the coordinate system of the table 32). As can be seen in FIG. 6c, the orientation of the tool 38 starts to deviate slightly from the previous perpendicular orientation with respect to the top surface 56 of the object 36.

[0073] As shown in FIG. 6d, the tool 38 follows the curve 22b of the Cartesian position blending zone 12b, which conforms to the curved profile 54 of the object 36 between the top surface 56 and the side surface 58. Furthermore, in FIG. 6d, the rotation of the table 32 towards the 90° rotation associated with the point 16b has come halfway (i.e. 45°) and the reorientation of the tool 38 towards the 90° orientation of the tool 38 associated with the point 16b has come halfway (i.e. 45°).

[0074] As shown in FIG. 6e, at the same time as the tool 38 reaches the zone border 62b2 of the orientation blending zone 52b, the orientation of the tool 38 reaches the 90° orientation of the tool 38 associated with the point 16b.

[0075] As shown in FIG. 6f, at the same time as the tool 38 reaches the zone border 60b2 of the external device blending zone 50b, the rotation of the table 32 reaches the 90° orientation of the table 32 associated with the point 16b.

[0076] The flexible definitions of the blending zones 12, 50, 52 according to the example in FIGS. 6a-6f may thereby contribute to a reduced cycle time (e.g. if the reorientation of the tool 38 and/or the operation of the external device 28 is comparatively slow) for operations involving the industrial actuator 26.

[0077] The definitions of the blending zones 12, 50, 52 may also contribute to an improved performance of a handling operation, e.g. by maintaining a surface horizontal and/or by maintaining the tool 38 perpendicular.

[0078] While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed.