METHOD OF OPERATING A TRANSPORT SYSTEM AND TRANSPORT SYSTEM

Abstract

A method of operating a transport system, in particular a multi-carrier system, which comprises a plurality of linear motors, which are arranged in a row and have a guide track, and a plurality of transport elements that are movable along the guide track by means of the linear motors, has the following steps: generating a travel job for a first one of the transport elements for travelling along at least a part section of the guide track, generating a first movement profile of the first transport element for the travel job based on predetermined movement characteristic values, matching the first movement profile with a second movement profile of a second transport element directly in front of the first transport element and determining whether a predetermined minimum distance between the first transport element and the second transport element is fallen below during the execution of the travel job, updating the first movement profile to maintain the minimum distance if it has been determined that the minimum distance is fallen below, and controlling the linear motors to move the first transport element in accordance with the first movement profile.

Claims

1. A method of operating a transport system that comprises a plurality of linear motors, which are arranged in a row and have a guide track, and a plurality of transport elements that are movable along the guide track by means of the linear motors, wherein the method comprises: generating a travel job for a first one of the transport elements for travelling along at least a part section of the guide track, generating a first movement profile of the first transport element for the travel job based on predetermined movement characteristic values, matching the first movement profile with a second movement profile of a second transport element directly in front of the first transport element and determining whether a predetermined minimum distance between the first transport element and the second transport element is fallen below during the execution of the travel job, updating the first movement profile to maintain the minimum distance if it has been determined that the minimum distance is fallen below, and controlling the linear motors to move the first transport element in accordance with the first movement profile.

2. The method in accordance with claim 1, wherein the first movement profile is newly generated when it is determined that a generation event has occurred.

3. The method in accordance with claim 2, wherein the generation event is a change in the jerk of the second transport element.

4. The method in accordance with claim 2, wherein, when the generation event occurs, a third movement profile of a third transport element directly behind the first transport element is furthermore updated.

5. The method in accordance with any one of the preceding claim 1, wherein the matching of the first movement profile with the second movement profile comprises calculating a distance trajectory of a distance between the first transport element and the second transport element.

6. The method in accordance with claim 1, wherein the speed of the first transport element is reduced to the speed of the second transport element or less when the first movement profile is being updated.

7. The method in accordance with claim 1, wherein the movement characteristic values comprise a maximum speed, a maximum acceleration, and/or an amount of the jerk.

8. The method in accordance with claim 1, wherein the generation and/or the updating of the movement profile comprises determining time sections with a constant jerk and calculating a maximum actual acceleration and a maximum actual speed.

9. A transport system that comprises a plurality of linear motors, which are arranged in a row and have a guide track, and a plurality of transport elements that can be moved along the guide track by means of the linear motors, further comprising a control unit that is configured to carry out a method of operating a transport system that comprises a plurality of linear motors, which are arranged in a row and have a guide track, and a plurality of transport elements that are movable along the guide track by means of the linear motors, wherein the method comprises: generating a travel job for a first one of the transport elements for travelling along at least a part section of the guide track, generating a first movement profile of the first transport element for the travel job based on predetermined movement characteristic values, matching the first movement profile with a second movement profile of a second transport element directly in front of the first transport element and determining whether a predetermined minimum distance between the first transport element and the second transport element is fallen below during the execution of the travel job, updating the first movement profile to maintain the minimum distance if it has been determined that the minimum distance is fallen below, and controlling the linear motors to move the first transport element in accordance with the first movement profile.

10. The method in accordance with claim 1, wherein the transport system is a multi-carrier system.

11. The transport system in accordance with claim 9 wherein the transport system is a multi-carrier system.

Description

[0035] In the following, the invention will be described schematically and by way of example with reference to the drawings. It is shown therein:

[0036] FIG. 1 a plan view of a transport system configured as a multi-carrier system in accordance with an embodiment;

[0037] FIG. 2 a schematic representation of an exemplary movement development for a transport element;

[0038] FIG. 3 a representation of two superposed movement developments of two consecutive transport elements and an associated distance trajectory; and

[0039] FIG. 4 a representation in accordance with FIG. 3, wherein the movement profile of the subsequent transport element has been updated.

[0040] FIG. 1 schematically shows a transport system 10 in a plan view that is configured as a multi-carrier system and that has a plurality of linear motors 11 that, in the present embodiment, are arranged in a closed row and form a closed guide track 13 for transport elements 15, 17, 19. For an illustrative description, only three transport elements 15, 17, 19 are shown in FIG. 1, namely a first transport element 15, a second transport element 17 that is located directly in front of the first transport element 15 in the direction of movement x, and a third transport element 19 that is located directly behind the first transport element 15 in the direction of movement x. “Directly” in this context is not to be understood as referring to a specific distance between the respective transport elements 15, 17, 19, but rather means that there is no further transport element between directly consecutive transport elements 15, 17, 19.

[0041] The transport elements 15, 17, 19 are magnetically driven by the linear motors 11. For this purpose, the transport elements 15, 17, 19 have one or more permanent magnets, not shown, that are acted on by a driving force by means of a changing and/or wandering magnetic field that is generated by the linear motors 11. The driving force leads to a movement of the transport elements 15, 17, 19 along the guide track 13. The transport elements 15, 17, 19 can in particular be moved independently and separately from one another. The linear motors 11 are controlled by a control unit, not shown, to drive the respective transport elements 15, 17, 19.

[0042] As can be seen from FIG. 1, a plurality of, in particular virtual, stations S.sub.1, S.sub.2, S.sub.3 can be arranged along the guide track 13 and can, for example, be defined by their position in the direction of movement x along the guide track 13. At the stations, transport elements 15, 17, 19 can, for example, be combined or isolated again or can pick up a product for transport or deliver it again. For example, the transport elements 15, 17, 19 can receive an instruction from the control unit that causes the respective transport element to move from station S.sub.1 to station S.sub.2. Such instructions are also designated as a travel job.

[0043] As FIG. 1 shows, the first transport element 15 and the second transport element 17 move between station S.sub.1 and station S.sub.2, with the second transport element 17 moving ahead.

[0044] FIG. 2 shows a representation of an exemplary movement development for the first transport element 15 in which a movement from a starting position, for example a station, to a target position x.sub.t, which may also be a station, is considered. The position development x.sub.15 of the first transport element 15 is shown therein over a time axis, starts at the coordinate origin, and ends at the target position x.sub.t. This movement is first divided into an acceleration phase in which the speed v.sub.15 is increased up to a maximum actual speed v.sub.max,act; a subsequent phase of constant speed; and a deceleration phase in which the speed v.sub.15 is reduced up to a standstill in the target position x.sub.t. The acceleration phase comprises a section with linearly increasing acceleration a.sub.15, a subsequent section with constant positive acceleration a.sub.15, wherein the constant acceleration a.sub.15 in this section corresponds to a maximum actual acceleration a.sub.max,act, and a part section with linearly decreasing acceleration a.sub.15 until the acceleration a.sub.15 is reduced to zero, i.e. the speed v.sub.15 is kept constant. Accordingly, the deceleration phase comprises a section with linearly increasing deceleration a.sub.15, a subsequent section with constant negative acceleration a.sub.15 (deceleration), and a section with linearly decreasing deceleration a.sub.15.

[0045] The development of the jerk j.sub.15 as a time derivative of the acceleration a.sub.15 is also shown in FIG. 2. As FIG. 2 shows, the jerk changes abruptly multiple times, namely at points at which the development of the acceleration a.sub.15 is discontinuous, and then remains constant until the next discontinuity of the acceleration a.sub.15. As shown, the acceleration phase is divided into three time sections T11, T12, T13 of constant jerk j.sub.15 in each case. Similarly, the deceleration phase is divided into three time sections T31, T32, T33 of constant jerk j.sub.15 in each case. The phase of constant speed therebetween corresponds to a time section T2 in which the jerk j.sub.15 remains unchanged.

[0046] A maximum speed v.sub.max,set, a maximum acceleration a.sub.max,set, and an amount of the jerk j.sub.set are furthermore shown in FIG. 2. In the present embodiment, these values are predetermined movement characteristic values that can be predefined by the operator or user of the transport system. It is also conceivable that they are not predefined uniformly for an entire path, but rather for specific sections of the path. For example, it may be necessary to reduce the speed of a transport element in a curved region of the guide track to prevent the transport element from leaving the guide track or losing the transported load.

[0047] When a travel job is created for the first transport element 15, the method first provides generating a movement profile of the first transport element 15 for the travel job. In the present embodiment, this takes place based on the maximum speed v.sub.max,set, the maximum acceleration a.sub.max,set, the amount of the jerk j.sub.set, and the target position x.sub.t as predetermined movement characteristic values. In particular, the development of the position x.sub.15 over time is part of the movement profile. As FIG. 2 shows, the maximum actually achieved speed v.sub.max,act in the present example is smaller than the corresponding predefined maximum value, which can, for instance, occur if the distance to be covered is not sufficient to accelerate the maximum speed v.sub.max,set. In this example, the maximum actually achieved acceleration a.sub.max,act is equal to the maximum predefined acceleration a.sub.max,set.

[0048] Furthermore, the previously described time sections T11, T12, . . . , T33 with a constant jerk are determined from the predetermined movement characteristic values and, if necessary, a maximum actual acceleration a.sub.max,act and a maximum actual speed v.sub.max,act are calculated.

[0049] FIG. 3 shows in the lower diagram that two movement developments of two consecutive transport elements 15, 17 are superposed, wherein the speed v.sub.15, v.sub.17, the acceleration a.sub.15, a.sub.17, and the jerk j.sub.15, j.sub.17 of the two transport elements 15, 17 are shown as a development over the time axis in each case. The positions of the two transport elements 15, 17 are not shown separately, but the upper diagram in FIG. 3 rather shows a distance trajectory d(t) that corresponds to the time development of the distance between the two transport elements 15, 17, i.e. the difference of the position developments.

[0050] FIG. 3 illustrates an example in which the second transport element 17 first starts with the traveling of a travel job at a point in time T.sub.0,17. At a point in time T.sub.0,15, the first transport element 15 is also to start with the traveling of a travel job along the same part section of a guide track 13. Accordingly, the two movement developments are shown offset on the time axis, i.e. adapted with respect to the time axis, to be able to compare them. Since the second transport element 17 sets off first, while the first transport element 15 is not yet moving on the part section, a distance d(t) is initially built up between the transport elements 15, 17 that is in each case calculated at the points in time T.sub.0,15 . . . T.sub.5,15, wherein a linear development of the distance d(t) is taken as a basis between consecutive points in time. FIG. 3 shows, however, that the speed v.sub.15 of the subsequent transport element 15 is higher than the speed v.sub.17 of the preceding transport element 17 so that the distance d(t) is successively reduced and would fall below a minimum distance d.sub.min, for example predetermined by an operator or user of the transport system 10, between the points in time T.sub.2,15 and T.sub.3,15 that each mark a point in time with a changed jerk j.sub.15 of the first transport element 15. Based on this comparison, it is thus determined that the predetermined minimum distance d.sub.min between the transport elements 15, 17 would be fallen below during the execution of the travel job of the first transport element 15.

[0051] Accordingly, the movement profile of the first transport element 15 for the travel job first has to be adapted. For this purpose, the movement profile is updated such that the minimum distance d.sub.min is maintained during the travel job of the first transport element 15. In the present example, this takes place by reducing the speed v.sub.15 of the first transport element 15 to the speed v.sub.17 of the second transport element 17, as FIG. 4 clearly shows. As stated above, in the movement development in accordance with FIG. 3, the minimum distance d.sub.min would be fallen below between the points in time T.sub.2,15 and T.sub.3,15. Accordingly, the movement sequence of the subsequent first transport element 15 in FIG. 4 remains unchanged from FIG. 3 from the point in time T.sub.0,15 of the setting off up to the point in time T.sub.2,15. The point in time T.sub.3,15 at which the first transport element 15 decelerates and the jerk j.sub.15 changes accordingly is advanced in FIG. 4 compared to FIG. 3, i.e. the movement of the first transport element 15 is decelerated earlier. Furthermore, FIG. 4 shows that after a deceleration phase between T.sub.3,15 and T.sub.5,15, the speed v.sub.15 of the first transport element 15 corresponds to the speed v.sub.17 of the second transport element 17 so that the minimum distance d.sub.min is not fallen below.

[0052] After a falling below of the minimum distance d.sub.min is avoided based on the updated movement profile, the linear motors 11 are controlled by the control unit to move the first transport element 15 in accordance with the updated first movement profile.

[0053] Thus, a possible falling below of the minimum distance d.sub.min is already recognized before the start of the travel job and the movement profile of the first transport element 15 is adapted to avoid the falling below. The distance from the preceding transport element 17 is thereby controlled predictively rather than adaptively. Delays due to response times are thereby in particular also avoided. Rather, consecutive transport elements can accelerate or decelerate simultaneously and to the same degree so that an accordion effect is avoided. An additional collision prevention, for example in the sense of a switching off of all the transport elements, is obsolete.

[0054] In addition, the movement profile of the first transport element 15 can be newly generated or updated in the same manner as described above when it is determined that a generation event has occurred. For example, it is possible to detect a change in the jerk j.sub.17 of the second transport element 17 as a generation event. This change can, for instance, indicate a deceleration of the second transport element 17. Furthermore, when the generation event occurs, a movement profile of the third transport element 19 directly behind the first transport element 15 can likewise be updated.

Reference Numeral List

[0055] 10 transport system

[0056] 11 linear motor

[0057] 13 guide track

[0058] 15 first transport element

[0059] 17 second transport element

[0060] 19 third transport element

[0061] a.sub.15 acceleration of the first transport element

[0062] a.sub.17 acceleration of the second transport element

[0063] a.sub.max,act maximum actual acceleration

[0064] a.sub.max,set maximum acceleration

[0065] d(t) distance trajectory

[0066] d.sub.min minimum distance

[0067] j.sub.15 jerk of the first transport element

[0068] j.sub.17 jerk of the second transport element

[0069] j.sub.set amount of the jerk

[0070] S.sub.1 station

[0071] S.sub.2 station

[0072] S.sub.3 station

[0073] T time section

[0074] v.sub.15 speed of the first transport element

[0075] v.sub.17 speed of the second transport element

[0076] V.sub.max,act maximum actual speed

[0077] V.sub.max,set maximum speed

[0078] x direction of movement

[0079] x.sub.15 position of the first transport element

[0080] x.sub.t target position