DISTRIBUTION SYSTEM AND METHOD FOR DISTRIBUTING A PLURALITY OF CARRIERS

Abstract

A distribution system for distributing carriers has a transport plane with logical positions. The carriers transport objects and a drive system moves the carriers on the transport plane between the logical positions. A controller moves the carriers on a planned route from a start position to a final destination on the transport plane. The planned route is made up of partial routes, and a routing system calculates routing plans for carriers on the transport plane by modeling the transport plane with graphs of nodes. The routing plans are calculated considering moving time periods and waiting time periods. The waiting time periods are assigned based on a reservation of logical positions of the partial routes of other carriers. Thus, if a carrier experiences a time delay during execution of a move, the routing system shifts the experienced time delay to an upcoming waiting time period of a carrier.

Claims

1. A distribution system, comprising: a transport plane comprising logical positions; a plurality of carriers for transporting objects; a drive system for moving the carriers on the transport plane between the logical positions; and a control system configured for controlling the carriers to move on a planned route from a start position to a final destination position on the transport plane, wherein the planned route comprises partial routes, wherein the control system comprises a routing system configured for calculating routing plans for carriers on the transport plane by modeling the transport plane with graphs of nodes, wherein the routing system is configured for calculating the routing plans considering moving time periods and waiting time periods, wherein the routing system is configured for assigning waiting time periods for carriers depending on a reservation of logical positions of the partial routes of other carriers, wherein, if a carrier experiences a time delay during execution of a move, the routing system is configured for shifting the experienced time delay to at least one upcoming waiting time period of a carrier.

2. The distribution system according to claim 1, wherein the routing system is configured for determining if the delay of the carrier affects at least one further carrier, wherein the routing system is configured for shifting the time delay to at least one waiting time of the at least one further affected carrier.

3. The distribution system according to claim 1, wherein the routing system is configured for recursively resolving the routing plans of carriers which are directly and/or indirectly affected by the delay of the carrier.

4. The distribution system according to claim 1, wherein the routing system is configured for compensating the time delay at least partially by shortening the at least one upcoming waiting time period of a carrier depending on the time delay.

5. The distribution system according to claim 4, wherein, in case of a residual time delay, the routing system is configured for at least partially shifting the residual time delay to second upcoming waiting time period.

6. The distribution system according to claim 5, wherein the first upcoming waiting time period is followed in time by the second upcoming waiting time period.

7. The distribution system according to claim 1, wherein the routing system is configured for calculating routing plans considering a constraint of a maximal number of simultaneous moves per transport plane or per area of the transport plane, wherein the moves allowed to be performed simultaneously form a simultaneous moves group, wherein the total transport surface is divided into one or multiple areas and an allowed maximum number of simultaneous moves is different per area.

8. The distribution system according to claim 7, wherein the routing system is configured for adapting originally planned routing plans of the carriers that would violate the constraint of maximal number of simultaneous moves.

9. The distribution system according to claim 1, wherein the control system comprises at least one executing unit configured for executing the routing plans for transporting the carriers from their respective start position to their respective final position.

10. The distribution system according to claim 1, the routing system is configured for using a cooperative path finding algorithm for calculating the routing plans, specifically a Windowed Hierarchical Cooperative A*-algorithm (WHCA*).

11. A method for distributing a plurality of carriers using a distribution system according to claim 1, wherein the method comprises moving the plurality of carriers on the transport plane of the distribution system between the logical positions by using the drive system, wherein the method comprises controlling the carriers to move on a planned route from the start position to the final destination position on the transport plane by using the control system, wherein the planned route comprises partial routes, wherein the method comprises calculating routing plans for carriers on the transport plane by modeling the transport plane with graphs of nodes by using the routing system, wherein the calculated routing plans comprise moving time periods and waiting time periods, wherein the calculating comprises assigning waiting time periods for carriers depending on a reservation of logical positions of the partial routes of other carriers, wherein the calculating comprises, if a carrier experiences a time delay during execution of a move, shifting the experienced time delay to at least one upcoming waiting time period of a carrier.

12. The method according to claim 11, wherein the method further comprises determining if the delay of the carrier affects at least one further carrier and shifting the time delay to at least one waiting time of the at least one further affected carrier.

13. The method according to claim 11, wherein the method further comprises recursively resolving the routing plans of carriers which are directly and/or indirectly affected by the delay of the carrier.

14. The method according to claim 11, wherein the method comprises compensating the time delay at least partially by shortening the at least one upcoming waiting time period of a carrier depending on the time delay.

15. The method according to claim 14, wherein, in case of a residual time delay, the method comprises at least partially shifting the residual time delay to at least one second upcoming waiting time period, wherein the first upcoming waiting time period is followed in time by the second upcoming waiting time period.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0101] The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0102] Further optional features and embodiments will be disclosed in more detail in the subsequent description of embodiments, preferably in conjunction with the dependent claims. Therein, the respective optional features may be realized in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. The scope of the disclosure is not restricted by the preferred embodiments. The embodiments are schematically depicted in the Figures. Therein, identical reference numbers in these Figures refer to identical or functionally comparable elements.

[0103] FIG. 1 shows an embodiment of a distribution system in perspective view;

[0104] FIGS. 2, 3 and 4 show examples of routings plans;

[0105] FIG. 5 shows a flow chart of an embodiment of a method for distributing a plurality of carriers; and

[0106] FIGS. 6A, 6B, 6C, 6D, 7A, 7B, 7C and 7D show dependency of plans of carriers, consequences of delays and resolving this.

DESCRIPTION

[0107] The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.

[0108] FIG. 1 shows an exemplary embodiment of a distribution system 110 in perspective view. The distribution system 110 may be an element of a laboratory automation system 112 allowing to distribute carriers 114 to a target destination within the laboratory automation system 112. Distribution systems 110 may be used in laboratory automation systems 112 comprising a number of laboratory stations 116, for example, pre-analytical, analytical and/or post-analytical stations.

[0109] The distribution system 110 comprises at least one transport plane 118 comprising logical positions 120 and a plurality of carriers 114 for transporting objects 122. In the example of FIG. 1, the object 122 may be or may comprise at least one sample container 124, such as laboratory diagnostic containers or vessels.

[0110] Further, the distribution system 110 comprises at least one drive system 126 for moving the carriers 114 on the transport plane 118 between the logical positions 120. The drive system 126 may be at least partially implemented in the carriers 114. For example, the carriers 114 may be passive carriers. For instance, a magnetic device may be fixed in the carrier 114 and a magnetic force provided by magnetically active and drivable elements, such as electro-magnetic coils (not shown in FIG. 1), enforce the carriers 114 to move by generated electro-magnetic fields. The coils can be installed under, above, besides or in the transport plane 118. For instance, an arrangement of magnetic coils underneath the transport plane 118 is described, e.g., in EP 2 566 787 or WO 2013/098202. In this example, the logical position 120 may be defined on the transport plane 118 as a position at which the carrier 114 can stop, start and/or change direction. In systems such as described in EP 2 566 787 or WO 2013/098202, the drive system 126 may define these logical positions 120 by its hardware limitations. Logical positions 120 may be defined above an electro-magnetic coil. At these positions 120, it may be possible to stop the carrier 114 and to change its direction with the next move.

[0111] The distribution system 110 further comprises at least one control system 128 configured for controlling the carriers 114 to move on a planned route from a start position to a final destination position on the transport plane 118. The planned route comprises partial routes. The control system 128 comprises at least one routing system 130 configured for calculating routing plans for carriers 114 on the transport plane 118 by modeling the transport plane 118 with graph of nodes 132. The routing system 130 is configured for calculating the routing plans considering moving time periods and waiting time periods. The routing system 130 is configured for assigning waiting time periods for carriers 114 depending on a reservation of logical positions 120 of the partial routes of other carriers 114. If a carrier 114 experiences a time delay during execution of a move, the routing system 130 is configured for shifting the experienced time delay to at least one upcoming waiting time period of a carrier 114.

[0112] As shown in FIG. 1, the distribution system 110 may further comprise an identification and registration system 134. In this example, the identification and registration systems 134 may be a camera system 136. However, other systems such as optical sensors and scanners identifying any optical signature on the carrier 114 or object 122, such as its size, its type, or a bar code, are also feasible. Alternatively or in addition, a RFID-reader system reading a unique RFID of the carrier 114 or object 122 on the carrier 114 or sensors inside the transport plane 118 can be used to identify logical positions 128 and to localize the carriers 114. A further option can be high precision GPS, in particular enhanced with Wi-Fi and/or GSM signals.

[0113] The distribution system 110 may comprise a position determination system 138 configured for determining positions of the carriers 114 on the transport plane 118. The position determination system 138 may send at least one position update message to the control system 128. The update message may trigger releasing of reserved logical positions 128 which were already passed by the carrier 114 on its current movement. The update message may inform the control system 128 about delayed carriers 114.

[0114] The control system 128 may comprise, besides the routing system 130, at least one executing unit 140 for execution of movements of the carriers 114 according to the planned routing plans. The control system 128 may control the drive system 126 to distribute carriers 114 from the initial position to the target destination. Specifically, controlling may comprise controlling the distribution of carriers 114 and, further, monitoring the distribution of carriers 114 and, if necessary, adapting or changing the distribution of carriers 114. The executing unit 140 may be configured for executing the planned routing plans for transporting the carriers 114 from their respective start position to their respective final position.

[0115] The calculating of the routing plans may comprise determining shortest paths for the carriers 114 across the transport plane 118 from the start position to the final destination position. The routing algorithm may be used for determining shortest paths for the carriers 114 across the transport plane 118. For example, a WHCA* search algorithm may be used for calculating the routing plans. With respect to WHCA* algorithm reference is made, e.g., to Silver, D., 2005, Cooperative pathfinding, Young, R. M., and Laird, J. E., eds., AIIDE, 117-122. AAA I Press. The WHCA* search algorithm may be an informed search algorithm such as A* or D* searching algorithm. For each carrier 114 with a final destination the search algorithm calculates a routing plan from the start position to an intermediate destination position on nodes within the cooperative search window of time length T towards their respective final destination position. The search is cooperative because the route can only pass on free time windows of logical positions 120. For the logical positions 120 with free time windows needed the required duration of the free time window will change from free to reserved for the required time slot of the respective logical positions 120. So the free time window will be split into a reserved time window and one or two further free time windows. The search is hence cooperative for the cooperative time window T by respecting the reserved time windows for other carriers 114 of the logical positions 120. The WHCA* algorithm may be designed for planning a route for each carrier 114 individually, wherein cooperation may be obtained using a reservation table. The routing system 130 may be configured for reserving the planned partial route for the carrier 114 until the carriers 114 reaches its intermediate or final destination. This means that no other carrier 114 can use the reserved route while the respective carrier 114 is moving. If the logical position 120 is set to reserved for a finite duration, the position 120 is not available for the other carriers 114 during the finite duration and will be available again for a move once the temporary reservation is over.

[0116] An example of a routing plan 142 is shown in FIG. 2. Specifically, in the example of FIG. 2, a transport plane 118 comprising logical positions 120 no. 1 to 5 and carriers 114 no. 1 to 3, illustrated in FIG. 2 by filled circles, moving on the transport plane 118 via partial routes 144 are shown together with an original routing plan 146 and a new routing plan 148 for the logical positions 120 no. 1 to 5. The routing plan 142 may comprise for each logical position 120 a free time window 150, a reserved time window, specifically a reserved time window 152 being reserved for moving carrier 114 no. n, n=1, 2, . . . 5, and a reserved time window being 154 reserved for waiting carrier 114 no. n, and/or an increased reservation time window 156 for waiting carrier 114 no. n. As can be seen from the partial routes 144 shown on the transport plane 118 and from the original routing plan 146, carriers 114 no. 2 and 3 may have to wait with their partial routes 144 until carrier 114 no. 1 has completed the corresponding partial route 144 over logical positions 120 no. 1 and 2. If carrier 114 no. 1 experiences a time delay 158 during execution of the move over logical positions 120 no. 1 and 2, logical positions 120 no. 1 and 2 may have to be reserved for carrier 114 no. 1 for a longer duration of time in the new routing plan 146. Consequently, logical positions 120 no. 3 and 4 may have to be reserved for a longer duration of time for carriers 114 no. 2 and 3, respectively.

[0117] The reservation for the late carrier 114 no. 1 may need to be adapted, specifically extended. However, in known approaches the extension of the reservation for the late carrier 114 no. 1 would influence and/or cross the reservations for other carriers 114. The present disclosure proposes that the routing system 130 is configured for extending the reservation for the late carrier 114 no. 1 without shifting or recalculating all plans 142, e.g., specifically without shifting or recalculating plans 142 of carriers 114 that are not affected. The present disclosure proposes resolving the delay 158 by using waiting times to compensate for the lost times. If the carrier 114 no. 1 experiences the time delay 158 during a move, the routing system 130 is configured for shifting the experienced time delay 158 to at least one upcoming waiting time period of a carrier 114, e.g., of the delayed carrier 114 no. 1. This is illustrated in FIG. 3. Specifically, FIG. 3 shows the original routing plan 146 and the new routing plan 148 for the delayed carrier 114 no. 1 of FIG. 2. The routing plan 142 for the carrier 114 may comprise a moving time period 160, a waiting time period 162 and/or an increased waiting time period 164, specifically a waiting time period which was increased due to a time delay 158.

[0118] As outlined above, the routing system 130 is configured for shifting the experienced time delay 158 to the at least one upcoming waiting time period 166 of a carrier 114, e.g., of the delayed carrier 114. The routing system 130 may be configured for compensating the time delay 158 by shortening the at least one upcoming waiting time period 166 of a carrier 114, e.g., of the delayed carrier 114, depending on the time delay 158. As can be seen in FIG. 3, the upcoming waiting time period 166 may be at least one waiting time period 162 subsequent to the delay 158. The routing system 130 may be configured for compensating the time delay 158 by shortening the next, also denoted as first, upcoming waiting time period 166 of the delayed carrier 114, e.g., by the amount of the time delay 158 (denoted by reference number 168). However, if the time delay 158 is longer than the upcoming waiting time period 166, the time delay 158 cannot be fully compensated by said upcoming waiting time period 166. Thus, the routing system 130 may be configured for compensating the time delay 158 at least partially by shortening the upcoming waiting time period 166. In case of a residual time delay, i.e., if the time delay 158 cannot be fully compensated by a first upcoming waiting time period 166, the routing system 130 may be configured for at least partially shifting the time delay to at least second upcoming waiting time period, e.g., of at least one affected carrier. The routing system 130 may be configured 158 for shifting a non-compensated part of the time delay 158 to the at least one second upcoming waiting time period. The first upcoming waiting time period 166 may be followed in time by the second upcoming waiting time period. If the time delay 158 still cannot be fully compensated by the next waiting time of a carrier 114, its subsequent waiting time may be used to compensate for the remaining delay, and so on until the delay 158 is completely resolved.

[0119] In this example, one carrier 114 of a plurality of carriers 114 may be delayed in time. Thus, the original plan 146 is failed. The delay 158 may occur at a first moving time period 160. The routing system 130 may be configured for compensating the time delay 158 by shortening the upcoming waiting time period 166. In most cases where only occasionally a short delay 158 occurs, as illustrated in FIG. 3, the upcoming waiting time period 166 may already be long enough to be used for compensation. Hence, a solution can be quickly found without affecting many carriers 114 and without computation-intensive re-planning. If the time delay 158 cannot be fully compensated for the upcoming waiting time period 166, e.g., in case the upcoming waiting time period 166 is too short, all waiting time of the upcoming waiting time period 166 may be consumed and the subsequent upcoming waiting time period may be used partially or completely as well, and so on. Hence, the method is recursively executed into the planning future until all delays 158 have been compensated for.

[0120] FIG. 4 shows another example of routing plan 142. Specifically, FIG. 4 shows an original routing plan 146 for a first carrier 114, a new routing plan 148 for said first carrier 114 and a routing plan 170 of a second carrier 114. The first carrier 114 may be delayed and, thus, may experience a time delay 158. The second carrier 114 may be an additional carrier 114 without time delay 158.

[0121] In the distribution system 110, a maximal number of simultaneous moves may be fixed for the whole transport plane 118 or be defined per area. The moves allowed to be performed simultaneously may form a so-called simultaneous moves group. For example, maximum eight carriers 114 may be allowed to move simultaneously per transport module 172 or software-defined area. The transport module 172 may be a separated constructional unit and/or sub-unit of the transport plane 118 comprising at least one logical position 120, as indicated in FIG. 1 by the dotted lines. In this example, the transport modules 172 comprise a plurality of logical positions 120. The number of maximum allowed simultaneous moves can also be related to the number of logical positions 120 in that area. For instance, the maximum allowed simultaneous moves in an area, e.g., can be in the range of 1% to 70% or 5% to 50% or 10% to 30% or 15% to 25% of the number of available logical positions 120 in the area. This may limit the maximum power draw peaks for that area, such that less or smaller power supplies can be used or to protect electronic circuitry against fast aging or damage.

[0122] As can be seen in FIG. 4, by using the at least one upcoming waiting time period 166 for compensating for the time delay 158 of the first carrier 114, a problem might happen that the maximum simultaneous moves constraint is violated as plans are shifted out of the original time window of the original simultaneous moves group. In this example, the first and the second carrier 114 may violate the maximum simultaneous moves constraint (denoted by reference number 174). The original simultaneous moves group may comprise the moves originally planned to be performed simultaneously, i.e., according to the original plans 146 of the routing system 130 without delays 158. Thus, in case only a maximum number of simultaneous moves is allowed, this rule may be violated if no measures are taken. The routing system 130 may be configured for adapting originally planned move times of the carriers 114 that would violate the constraint of maximal number of simultaneous moves. The plans 142, 170 for the affected additional carriers 114, that would violate the maximum simultaneous moves constraint, in this example the routing plan 170 of the second carrier 114, may be shifted as well and similar to the plans 148 of the delayed carriers 114. Their waiting times may be used to try to compensate for the delays 158.

[0123] FIG. 5 shows a flow chart of an embodiment of a method for distributing a plurality of carriers 114 using the distribution system 110 according to the present disclosure is disclosed. The method comprises using the distribution system 110 as described above, such as according to the embodiment described in FIG. 1 and/or according to any embodiment given in further detail below. The method may comprise the following steps, which may be performed in the given order or may be performed in a different order. Further, one or more additional method steps may be present which are not listed. Further, one, more than one or even all of the method steps may be performed repeatedly.

[0124] The method comprises moving the plurality of carriers 114 on the at least one transport plane 118 of the distribution system 110 between the logical positions 120 by using the at least one drive system 126 (denoted by reference number 176). The method comprises controlling the carriers 114 to move on a planned route from the start position to the final destination position on the transport plane 118 by using the control system 128 (denoted by reference number 178). The planned route comprises partial routes 144. The method comprises calculating routing plans for carriers 114 on the transport plane 118 by modeling the transport plane 118 with graphs of nodes 132 by using the routing system 130 (denoted by reference number 180). The calculated routing plans comprise moving time periods 160 and waiting time periods 162. The calculating comprises assigning waiting time periods 162 for carriers 114 depending on a reservation of logical positions 120 of the partial routes 140 of other carriers 114 (denoted by reference number 182). The calculating comprises, if a carrier 114 experiences a time delay 158 during execution of a move, shifting the experienced time delay 158 to at least one upcoming waiting time period 166 of the delayed carrier 114 (denoted by reference number 184).

[0125] The method may comprise compensating the time delay 158 at least partially by shortening the at least one upcoming waiting time period 166 of the delayed carrier 114 depending on the time delay 158 (denoted by reference number 186). In case of a residual time delay, the method may comprise at least partially shifting the residual time delay to at least one second upcoming waiting time period (denoted by reference number 188), e.g., of at least one affected carrier. The first upcoming waiting time period may be followed in time by the second upcoming waiting time period.

[0126] The method may comprise calculating routing plans, in particular move times, considering a constraint of a maximal number of simultaneous moves per transport plane 118 or per area of the transport plane 118 (denoted by reference number 190), wherein the moves allowed to be performed simultaneously form a simultaneous moves group. The total transport surface may be divided into one or multiple areas and an allowed maximum number of simultaneous moves may be different per area The plans of original routes of the carriers 114 that would violate the constraint of maximal number of simultaneous moves may be adapted.

[0127] FIGS. 6A to 6D and 7A to 7D show dependency of plans of carriers 114, consequences of delays and resolving these. The number in the circles represent the carriers i, with i running from 1 to 7 in this example.

[0128] FIG. 6A shows an example of a partial plan of planned moves. It shows all the moves to be made during the whole partial plan. The carriers 114 may start moving at different times and reserving fields that will also be used for other moves. Because of this, dependencies may exist between the time plans of some of the moves of carriers 114.

[0129] FIGS. 6B to 6D show some of the moves made during certain time periods of the partial plan. The order in which the moves are planned in time are shown by the number of the arrows. A move with a lower number is carried out before a move with a higher number.

[0130] FIG. 7B shows that if carrier 4 wants to move, it can only do so after carrier 1 has passed and released the reservation of the required positions. Likewise with carrier 3. Hence, there is a dependency of the plan of carrier 4 on the plans of carrier 1 and 3. The move plan of carrier 6 depends on carrier 4 and therefore indirectly on 1 and 3 etc. Not all carriers may be planned to move yet, so at this early time, carriers 5 and 7 have no arrows yet. Also at this time, some carriers' moves may not have a dependency (yet), like 5 and 7. The dependencies can be indicated by the directed graphs in FIGS. 7A to 7C. For this first phase, see FIG. 6B, the occurred dependencies are shown by FIG. 7B. An arrow from carrier 1 to carrier 4 indicates that the plan of carrier 4 depends on the plan of carrier 1.

[0131] FIG. 6C shows a later moment in time where new moves, see FIG. 6C, and therefore also dependencies, see FIG. 7C occur. If summing up all dependencies occurring during the full partial plan, the graph as shown in FIG. 7A is obtained. Here it can be observed that the dependency arrows between carriers can be in both directions. Examples are carriers 1 and 4. Initially the move of carrier 4 depends on the move of carrier 1, but later on, it is the other way around. FIG. 6D shows the end result of all moves.

[0132] If the execution of a planned move of a carrier 114 is delayed, this delay may be resolved by using a planned waiting time of a carrier 114. For example, if carrier 1 is delayed, the waiting time of this carrier is used. If the waiting time is too short to completely resolve the delay, the plans of the affected, thus dependent carriers, may be shifted and their waiting times may be used. In this case carrier 4. If this would not affect the plan of carrier 6 the problem is solved, otherwise also carrier 6 has to delay and so on. These time shifts will not affect non-dependent carriers.

[0133] If the initial delay and its causing delays cannot be fully solved by the first moves, the remaining delays may be pushed to the subsequent moves. This may allow solving the delay here and so on. As seen in the dependency graphs (FIG. 7B versus 7A), the deeper in time the method has to find ways for using waiting times to resolve the delay of carrier 1, the more carriers may be involved to donate their waiting times partially or completely.

[0134] While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

LIST OF REFERENCE NUMBERS

[0135] 110 distribution system [0136] 112 laboratory automation system [0137] 114 carrier [0138] 116 laboratory station [0139] 118 transport plane [0140] 120 logical position [0141] 122 object [0142] 124 sample container [0143] 126 drive system [0144] 128 control system [0145] 130 routing system [0146] 132 graph of nodes [0147] 134 identification and registration system [0148] 136 camera system [0149] 138 position determination system [0150] 140 executing unit [0151] 142 routing plan [0152] 144 partial routes [0153] 146 original routing plan [0154] 148 new routing plan [0155] 150 free time window [0156] 152 reserved time window being reserved for moving carrier no. n [0157] 154 reserved time window being reserved for waiting carriers no. n [0158] 156 increased reservation time window for waiting carrier no. n [0159] 158 time delay [0160] 160 moving time period [0161] 162 waiting time period [0162] 164 increased waiting time period [0163] 166 upcoming waiting time period [0164] 168 shortening the upcoming waiting time period [0165] 170 routing plan of a second carrier [0166] 172 transport module [0167] 174 violation of the maximum simultaneous moves constraint [0168] 176 moving the plurality of carriers [0169] 178 controlling the carriers [0170] 180 calculating a routing plan [0171] 182 assigning waiting time periods [0172] 184 shifting the experienced time delay [0173] 186 compensating the time delay [0174] 188 shifting the residual time delay [0175] 190 considering a constraint of a maximal number of simultaneous moves