Method for lifting a stack from a conveyor belt using a robot arm

Abstract

Method for lifting a stack from a conveyor line with a robot arm, wherein the robot arm (22) comprises a fork (23) with at least two prongs (24) for lifting the stack (10) and the conveyor line (1) comprises a plurality of conveyor rollers (3) for conveying the stack (10) in a conveying direction (2), wherein the stack (10) has a stack length (L) in the conveying direction (2) and wherein the prongs (24) are moved into gaps (4) between the conveyor rollers (3) before lifting, characterized in that the stack (10) is stopped at a stop (7) of the conveyor line (1), and that the prongs (24) are moved into gaps (4) which are selected computationally depending on the position of the stop (7) and the stack length (L) such that the center of gravity (S) of the stack (10) lies over an area (B) spanned by the prongs (24).

Description

invention

[0001] The invention relates to a method for lifting a stack from a conveyor line with a robot arm having the features of the preamble of claim 1. field of technology

[0002] The invention DE 20 2019 106 975 U1 lies in the technical field of the graphic arts industry and there in particular in the area of ​​handling (e.g. gripping, holding, moving, turning, flipping and / or setting down) stacks of superimposed, flexible and preferably printed and folded flat products such as folded sheets, preferably made of paper, cardboard, corrugated board, plastic or composite material, with a manipulator, in particular an articulated robot with robot arm and gripper device for the stacks. State of the art

[0003] It is already known in the field of print finishing (postpress) to transport stacks of flat products on a (e.g. roller) conveyor, to grasp the stacks by means of a gripper arranged on a robot arm, to lift them from the conveyor, to move them to a pallet and to place them there, e.g. from DE 10 2020 103 398 A1 or from DE 20 2019 106 975 U1.

[0004] This reveals a conveyor system for stacks of printed products and a so-called collaborative robot system with a robot arm and gripper for picking up the stacks from the conveyor and placing them onto pallets. The robot is positioned at the end of the conveyor. It does not have a fork with tines.

[0005] DE 10 2020 103 398 A1 also discloses a conveyor system for stacks of printed products placed on top of each other and a robot with a robot arm and gripper for picking up the stacks from the conveyor system and placing them onto pallets. The robot can be designed as an industrial articulated robot. The robot is also positioned at the end of the conveyor system and does not have a fork with tines.

[0006] US Patent 4,573,863 A discloses a method for lifting a stack of stacks from a conveyor belt using a robot arm. The robot arm comprises a fork with upper and lower prongs for lifting the stack, and the conveyor belt includes a plurality of conveyor rollers for conveying the stack in a conveying direction. The stack has a stack length in the conveying direction, and the prongs are moved into gaps between the conveyor rollers before lifting. The method is used to lift the stack, turn it over, and place it back onto the conveyor belt. Lifting always occurs at the same point on the conveyor belt. No stop for the stacks is provided.

[0007] DE 40 38 133 C2 discloses a palletizing machine for the automatic stacking or palletizing of flat elements with a lifting table and an intermediate storage table arranged above it and formed by fork tines.

[0008] DE 202 03 818 U1 discloses a gripper for a robot for gripping pressure-sensitive objects, which in particular comprises prongs as support elements.

[0009] On the other hand, it is already known to stop stacks at a stop on a conveyor belt before lifting them off. If stacks of varying lengths are transported depending on the order, the stop would need to be adjustable if lifting is always to occur at the same point on the conveyor belt. However, adjusting the stop, for example when changing orders, can be time-consuming and lead to errors. Technical task

[0010] It is therefore an object of the present invention to provide an improvement over the prior art which in particular makes it possible to lift a stack from a conveyor line even with changing orders with different stack lengths; time-consuming and error-prone adjustment processes should be avoided. Inventive solution to the problem

[0011] This problem is solved according to the invention by a method according to claim 1.

[0012] Advantageous and therefore preferred embodiments of the invention are evident from the dependent claims as well as from the description and the drawings.

[0013] A method according to the invention for lifting a stack from a conveyor line with a robot arm, wherein the robot arm comprises a fork with at least two tines for lifting the stack and the conveyor line comprises a plurality of conveyor rollers for conveying the stack in a conveying direction, wherein the stack has a stack length in the conveying direction and wherein the tines are moved into gaps between the conveyor rollers before lifting, is characterized in that the stack is stopped at a stop of the conveyor line, and that the tines are moved into gaps which are selected computationally depending on the position of the stop and the stack length such that the center of gravity of the stack lies over an area spanned by the tines. Advantageous forms and effects of the invention

[0014] The invention advantageously enables the lifting of a stack from a conveyor line to be carried out even with changing orders and different stack lengths; time-consuming and error-prone adjustment processes are thereby avoided.

[0015] According to the invention, a computational selection, preferably using a digital computer, is made of the gaps between the transport rollers (from the set of available gaps) to be used for lifting; the fork tines are moved into these selected gaps, preferably one tine into each gap and preferably from the side (transverse to the transport direction). The existing stop can then advantageously be fixed in place or at least immovable in the conveying direction, i.e., it does not need to be adjusted for changing orders with different stack lengths. According to the invention, the "adjustment," i.e., the adaptation, is carried out by the already movable robot arm.

[0016] The selection of the gaps into which the tines are moved is calculated and preferably uses the following values: position of the stop, stack length, and positions of the gaps (or spacing of the gap grid). The calculation itself is simple and takes the given geometric conditions into account.

[0017] It can also be provided that, knowing the minimum and maximum processable formats (i.e., the minimum and maximum expected stack lengths), the possible gaps are calculated in advance and their positions are provided. A simple example for a two-pronged fork: minimum format, tines in gaps 1 and 2 (viewed from the direction of the stop); medium format, tines in gaps 2 and 3; large format, tines in gaps 3 and 4.

[0018] The stop can be a physical component, for example a metal surface. Alternatively, the stop can be optical, for example in the form of a light barrier, which interrupts the transport of the stacks and thus stops them. Further developments of the invention

[0019] Preferred embodiments of the invention (hereinafter referred to as embodiments) are described below. These can also be combined with one another, unless technically precluded.

[0020] Further development can be characterized by the fact that the tines are moved in gaps which are selected depending on the position of the stop and the stack length, such that the distance of the center of gravity from the center of the area in the conveying direction is minimal. In this way, it can be ensured that the stack can be easily lifted, moved and set down.

[0021] Further training can be characterized by the fact that the position of the focus in the funding direction is provided or calculated computationally.

[0022] A further development process can be characterized by measuring the stack length in the conveying direction. A further development process can be characterized by measuring the stack length using at least one sensor. A further development process can be characterized by measuring the stack length using two sensors. The sensor(s) can be designed as a light barrier. If a single sensor is used, the stack length can be measured (given a known conveying speed) by the sensor detecting the beginning and end of the stack as it passes by. If two sensors are used, the conveying speed (given a known distance between the two sensors) and thus also the stack length (as with a single sensor) can be measured.

[0023] Further training can be characterized by the fact that the tines are moved between the conveyor rollers from below and / or from the side.

[0024] A further training system can be characterized by the fact that the stop is fixed in the conveying direction. It may be designed so that the stop is movable, for example vertically, to transport individual stacks further and remove them manually for inspection.

[0025] The features and combinations of features disclosed in the above sections Technical Field, Invention and Further Developments, as well as in the following section Exemplary Embodiments, represent – ​​in any combination with one another – further advantageous developments of the invention. Exemplary embodiments of the invention and figures

[0026] The Fig. Figures 1 to 3c show preferred embodiments of the invention and its further developments. Corresponding features are identified in the figures by the same reference numerals. For clarity, some reference numerals that are repeated in the figures have been omitted.

[0027] Fig. Figure 1 shows a schematic top view of a device during the execution of a preferred embodiment of the method according to the invention. A conveyor line 1, preferably divided into three sections, is shown for conveying stacks 10 of printed products stacked on top of each other. The stacks 10 are taken from an upstream machine 30 of the graphic arts industry, for example, a folding machine, and transported horizontally in a transport direction 2, for which the conveyor line preferably includes a drive 1a. In the middle section 5, the stacks are gripped by a fork 23 of a robot 20 and lifted from the conveyor line 1. For this purpose, the robot 20 is positioned on the floor next to the conveyor line 1 with its robot base 21. The lifted stacks 10 are moved by a robot arm 22 to placement positions 6 next to the conveyor line 1 and placed there, for example, on pallets.If a stack 10 is to be inspected by an operator 31, this stack 10 is not lifted, but transported straight ahead to the end of the conveyor line 1. The operator is located outside a danger zone 25, which is defined by the maximum movement of the robot arm 22.

[0028] Fig. Figure 2 shows an excerpt from Fig. 1. The robot 20 with its robot base 21 and robot arm 22 is shown, wherein a fork 23 with several tines 24 is arranged on the robot arm 22. The stack 10 is transported along the transport path 1 to a stop 7 and stopped there. The tines 24 each grasp or engage a stack 10 in the receiving area 5 (the tines 24 under the stack 10 are therefore shown with dashed lines). The stop 7 is preferably fixed in the transport direction 1. However, it can preferably be moved vertically (e.g., to remove stacks to be inspected), for which a motor drive 7a can be provided. One or two sensors 8 can be provided on the transport path 1. The stack length L, i.e., the extent of the stack 10 in the transport direction 1, can be determined by means of these sensors 8.

[0029] The Fig. 3a, Fig. 3b and Fig. Figure 3c is intended to illustrate the process of a preferred embodiment of the method according to the invention. Fig. Figure 3a shows a schematic side view of the conveyor section 1 with the conveyor rollers 3 and the stop 7 in the receiving area 5. A stack 10 has been transported on the conveyor rollers 1 to the stop 7 and stopped there. The stack 10 has a stack length L and a center of gravity S. The position of the stop 7 and the position of the center of gravity are shown on a horizontal coordinate axis (antiparallel to the transport direction 2), with the zero point set at the position of the stop 7 for illustrative purposes. The conveyor rollers 3 can, for example, have a diameter of 50 mm, and the distance between the conveyor rollers can, for example, be 60 mm.

[0030] In Fig. Figure 3a also shows two tines 24 of a fork 23, which engage the stopped stack 10. For this purpose, the tines 24 are positioned in or moved into gaps 4 between the transport rollers 3. The tines 24 span a region with length B (in the transport direction 2). According to the invention, the position of the center of gravity S lies within this region B. The distance A of the position of the center of gravity S from the center M of the region B is preferably chosen to be minimal. Fig. 3a also shows the R spacing of the gap grid.

[0031] In Fig. 3b is similar to in Fig. 3a is shown, however the stack length L has increased. It can be seen that the two prongs 24 grip the stack 10 in the same gaps 4 as in Fig. 3a. The center of gravity S of the stack is still in area B, and the distance A is again preferably chosen to be minimal. In this situation, the stack 10 is not symmetrically gripped by the prongs 24.

[0032] In Fig. Figure 3c depicts a situation in which a stack 10 with an even greater stack length L has been stopped. The two tines 24 of the fork 23 are now positioned in gaps 4 between the transport rollers 3, which are separated from the gaps 4 of the two situations according to the Fig. 3a and Fig. 3b differs, i.e., a different selection of gaps 4 was made. However, it is again ensured that the center of gravity S lies in area B and that the distance A is preferably minimal.

[0033] According to an alternative embodiment (not shown), a sensor or camera (not shown) can be arranged on the robot arm, the fork, or at least one of the tines. This allows the stack length to be detected as the fork approaches the stack, and the gaps to be selected accordingly. Reference symbol list 1 Conveyor line 1a Drive of the conveyor line 2 Direction of conveyance 3 conveyor rollers 4 gaps or their positions 5 Recording area 6 Drop-off area 7. Stop or its position 7a Drive for the stop 8 Sensor(s) 10 stacks 20 robots 21 robot base 22 robot arm 23 Fork 24 prongs 25 Danger area 30 Machine, in particular folding machine 31 operators A distance B area or its extent L stacking length M middle of the area or its position R spacing of the gap grid S center of gravity or its position

Claims

[1] Method for lifting a stack from a conveyor line with a robot arm, wherein the robot arm (22) comprises a fork (23) with at least two prongs (24) for lifting the stack (10) and the conveyor line (1) comprises a plurality of conveyor rollers (3) for conveying the stack (10) in a conveying direction (2), wherein the stack (10) has a stack length (L) in the conveying direction (2) and wherein the prongs (24) are moved into gaps (4) between the conveyor rollers (3) before lifting, characterized by , that the stack (10) is stopped at a stop (7) of the conveyor (1), and that the tines (24) are moved into gaps (4) which are selected computationally depending on the position of the stop (7) and the stack length (L) such that the center of gravity (S) of the stack (10) lies over an area (B) spanned by the tines (24). [2] Method according to claim 1, characterized by, that the tines (24) are moved in gaps (4) which are selected depending on the position of the stop (7) and the stack length (L) such that the distance (A) of the center of gravity (S) from the center (M) of the area (B) in the conveying direction (2) is minimal. [3] Method according to any one of the preceding claims, characterized by that the position of the center of gravity (S) in the direction of conveyance (2) is provided or calculated computationally. [4] Method according to any one of the preceding claims, characterized by , that the stack length (L) is measured in the conveying direction (2). [5] Method according to claim 4, characterized by , that the stack length (L) is measured using at least one sensor (8). [6] Method according to claim 4, characterized by , that the stack length (L) is measured using two sensors (8). [7] Method according to any one of the preceding claims, characterized by, that the tines (24) are moved between the conveyor rollers (3) from below and / or from the side. [8] Method according to any one of the preceding claims, characterized by , that the stop (7) is fixed in position in the conveying direction (2).

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