Method for lifting stack from conveying section by means of robot arm

Abstract

The invention relates to a method for lifting a stack from a conveying section by means of a robot arm (22), the robot arm (22) comprising a fork (23) having at least two teeth (24), the conveying section (1) comprising a plurality of conveying rollers (3) for conveying the stack (10) in a conveying direction (2), the stack (10) having a stack length (L) in the conveying direction (2), the teeth (24) being moved into interspaces (4) between the conveying rollers (3) before lifting, according to the invention, the stack (10) stops at a stop (7) of the conveying section (1), the teeth (24) move into the recess (4), the recess is computationally selected as a function of the position of the stop (7) and the stack length (L), and the center of gravity (S) of the stack (10) lies above the area (B) in which the teeth (24) expand. According to the invention, the stacks can be lifted from the conveying section even under the condition of changing orders with different stack lengths, a time-consuming and error-prone adjustment process is avoided, and the stacks can be used together with a folding machine for post-press processing.

Description

Technical Field

[0001] The invention relates to a method for lifting a stack from a conveying section by means of a robot arm, the method having the features of the preamble of claim 1 .

[0002] The invention belongs to the technical field of the graphics industry and in particular to the field of handling (e.g. gripping, holding, moving, rotating, turning and / or unloading) stacks of flexible (and preferably printed and folded) flat products (preferably made of paper, cardboard, paperboard, plastic or composite materials, such as leaflets) stacked one on top of the other by means of a manipulator (in particular an articulated arm robot with a robot arm and a gripping device for stacking). Background Art

[0003] In the postpress field, it is known that stacks of flat products are transported on a conveyor section (e.g. a roller conveyor section), the stacks are gripped by a gripper arranged on a robot arm, lifted from the conveyor section, moved to a carrier and unloaded there, for example, as known from DE102020103398A1 or DE202019106975U1.

[0004] DE202019106975U1 discloses a conveying section for stacks of printed products stacked one above the other, and a so-called collaborative robot system having a robot arm with a gripper for receiving the stack from the conveying section and unloading the stack on a carrier. The robot is arranged at the end of the conveying section. The robot does not have a toothed fork.

[0005] DE 10 20 20 10 3 398 A1 also discloses a conveying section for stacks of printed products stacked one above the other and a robot with a mechanical arm and a gripper for receiving the stack from the conveying section and for unloading the stack on a carrier. Here, the robot can be designed as an industrial articulated arm robot. Here, the robot is also arranged at the end of the conveying section and also does not have a toothed fork.

[0006] US4573863 discloses a method for lifting a stack from a conveyor section by means of a mechanical arm, wherein the mechanical arm comprises a fork with upper and lower teeth for lifting the stack, and the conveyor section 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 teeth are moved into the gaps between the conveyor rollers before lifting. The method is used to lift the stack, turn the stack over and place the stack back on the conveyor section. The lifting always takes place at the same location of the conveyor section. No stop is provided for the stack.

[0007] On the other hand, it is known that the stack stops at a stop on the conveying path before being lifted. If stacks of different lengths are transported depending on the order, the stop must be adjustable if the lifting is always to take place at the same point on the conveying path. However, adjusting the stop (for example, when changing orders) can be time-consuming and lead to errors. Summary of the invention

[0008] The object of the present invention is therefore to provide a technical solution that is improved compared to the prior art and which in particular allows lifting of the stack from the conveying section even when changing orders with different stack lengths; time-consuming and error-prone adjustment processes are to be avoided.

[0009] The technical solution to solve the task according to the present invention is:

[0010] This object is achieved according to the invention by a method according to claim 1 .

[0011] Advantageous and therefore preferred developments of the invention emerge from the dependent claims as well as from the description and the drawings.

[0012] The method according to the invention for lifting a stack from a conveying section by means of a robot, wherein the robot has a fork with at least two teeth for lifting the stack, and the conveying section has a plurality of conveying rollers for conveying the stack in a conveying direction, wherein the stack has a stack length in the conveying direction, and wherein the teeth move into gaps between the conveying rollers before lifting, characterised in that the stack stops at a stop on the conveying section and the teeth move into gaps which are selected in a computationally technical manner as a function of the position of the stop and the stack length such that the centre of gravity of the stack is located above the area opened up by the teeth.

[0013] Advantageous configuration and effects of the present invention:

[0014] The invention advantageously makes it possible to carry out lifting of a stack from a conveying section even when changing orders with different stack lengths; time-consuming and error-prone adjustment processes are to be avoided.

[0015] According to the invention, the gaps between the conveyor rollers for lifting are selected by computational means (from the number of gaps available) (preferably using a digital computer); the teeth of the fork are moved into these selected gaps, preferably each tooth into one gap, and preferably from the side (transversely to the conveying direction). The existing stops can then be advantageously arranged in a fixed position or at least immovable in the conveying direction, i.e., when changing orders with different stack lengths, it is not necessary to adjust the stops. This "adjustment" (i.e., adaptation) is carried out according to the invention by the already movable robot arm.

[0016] The selection of the gaps into which the teeth move is carried out by calculation and preferably uses the following values: the position of the stop, the stack length and the position of the gaps (or the spacing of the gap grid). The calculation itself is simple and takes into account the given geometric conditions.

[0017] It can also be provided that, knowing the smallest and largest processable formats (i.e. the expected smallest and largest stacking lengths), the possible gaps can already be calculated in advance and their positions provided. A simple example for a fork with two teeth: for the smallest format (Format), the teeth are placed in gaps 1 and 2 (as seen in the direction of the stop); for a medium format, the teeth are placed in gaps 2 and 3; for a large format, the teeth are placed in gaps 3 and 4.

[0018] The stop can be designed as a component, for example a metal surface. Alternatively, the stop can also be designed optically, for example in the form of a light barrier, which interrupts the transport of the stack and thus stops the stack.

[0019] Improvement scheme of the present invention:

[0020] Preferred developments of the invention (developments for short) are described below. These developments can be combined with one another, provided they are not technically mutually exclusive.

[0021] A further development can be characterized in that the teeth move into gaps which are selected according to the position of the stop and the stack length so that the distance between the center of gravity and the center of the region in the conveying direction is minimal. In this way, it can be ensured that the stack can be lifted, moved and unloaded without any problems.

[0022] One development can be characterized in that the position of the center of gravity in the conveying direction is provided or calculated in a computing manner.

[0023] One refinement can be characterized in that the stack length in the conveying direction is measured. One refinement can be characterized in that the stack length is measured using at least one sensor. One refinement can be characterized in that two sensors are used to measure the stack length. One or more sensors can be designed as one or more light barriers. If a single sensor is used, the stack length can be measured by the sensor by detecting the beginning and end of the stack as the stack moves past (given a known conveying speed). If two sensors are used, the conveying speed can be measured (given a known distance between the two sensors) and therefore also the stack length can be measured (as if only one sensor were used for the measurement).

[0024] A development can be characterized in that the teeth are moved from below and / or from the side between the conveyor rollers.

[0025] A feature of an improved solution can be that the stop is arranged in a fixed position in the conveying direction. It can be provided that the stop is movable, for example, in the vertical direction, in order to further convey the individual stacks and allow manual removal for inspection.

[0026] The features and feature combinations disclosed in the above technical fields, the summary of the invention and the developments as well as in the following exemplary embodiments—in any combination of features and feature combinations with one another—constitute further advantageous developments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 , Figure 2 , Figure 3a , Figure 3b and Figure 3c The preferred embodiments of the present invention and the improved solutions are shown. Corresponding features in the drawings are indicated by the same reference numerals. For the sake of clarity, the parts of the reference numerals that appear repeatedly in the drawings are omitted. DETAILED DESCRIPTION

[0028] Figure 1A schematic top view of a device when performing a preferred embodiment of the method according to the invention is shown. A conveying section 1 for conveying stacks 10 consisting of printed products stacked one above the other is shown, which is preferably divided into three sections. In this case, these stacks 10 are taken over from an upstream machine 30 (e.g., a folding machine) of the graphics industry and conveyed horizontally along a conveying direction 2, for which purpose the conveying section 1 preferably comprises a drive 1a. In the middle section 5, the stack 10 is gripped from below by the fork 23 of the robot 20 and lifted from the conveying section 1. For this purpose, the robot 20 is positioned on the ground next to the conveying section 1 with its robot base 21. The robot arm 22 moves the lifted stack 10 to a discharge position 6 next to the conveying section 1 and discharges it at the discharge position 6 (e.g., on a bracket). If the operator 31 wants to check the stack 10, the stack 10 is not lifted, but is conveyed directly forward to the end of the conveying section 1. During this process, the operator 31 is located outside the danger zone 25 which is defined by the maximum movement of the robot arm 22 .

[0029] Figure 2 Shows Figure 1 . A robot 20 is shown here together with its robot base 21 and a robot arm 22, wherein a fork 23 with a plurality of teeth 24 is arranged on the robot arm 22. The stack 10 is transported on the conveying section 1 to the stop 7 and stops at the stop 7. These teeth 24 respectively grab (or grab from below) the stack 10 in the receiving area 5 (the teeth 24 below the stack 10 are therefore represented by dotted lines). The stop 7 is preferably arranged in a fixed position in the conveying direction 1. However, the stop 7 is preferably movable in the vertical direction (for example, for discharging the stack to be checked), for which purpose an electric drive 7a can be provided. One sensor 8 or two sensors 8 can be arranged on the conveying section 1. With the help of the sensor 8, the stack length L, that is, the extension (Ausdehnung) of the stack 10 in the conveying direction 1, can be determined.

[0030] Figure 3a , Figure 3b and Figure 3c It is intended to illustrate the process of a preferred embodiment of the method according to the present invention. Figure 3a A schematic side view of a conveying section 1 with conveying rollers 3 and a stop 7 in a receiving area 5 is shown. A stack 10 has been conveyed on the conveying rollers 1 as far as the stop 7 and stops at the stop 7. 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 S are shown on a horizontal coordinate axis (antiparallel to the conveying direction 2), wherein the origin is arranged, for example, at the position of the stop 7. The conveying rollers 3 can have a diameter of 50 mm, for example, and the distance between the conveying rollers 3 can be 60 mm, for example.

[0031] Figure 3a Also shown are two teeth 24 of the fork 23, which grip the stopped stack 10 from below. To this end, the teeth 24 are positioned or moved into the gap 4 between the conveyor rollers 3. The teeth 24 span an area (in the conveying direction 2) having a length B. According to the invention, the position of the center of gravity S is located in this area B. The distance A between the position of the center of gravity S and the center M of the area B is preferably selected to be minimal. Figure 3a Also shown in FIG. 1 is the spacing R of the cavity grid.

[0032] Figure 3b Shown with Figure 3a Similar content, but the stacking length L is increased. It can be seen that the two teeth 24 are in contact with Figure 3a The stack 10 is grabbed in the same gap 4 in the middle. In the process, the center of gravity S of the stack 10 is always still in the area B, and the spacing A is preferably selected to be minimum again. In this case, these teeth 24 grab the stack 10 from below asymmetrically.

[0033] Figure 3c The stack 10 with a greater stack length L is shown having stopped. The two teeth 24 of the fork 23 are now positioned between the conveyor rollers 3 and according to Figure 3a and Figure 3b The two cases shown have different gaps 4, ie, the gaps 4 are chosen differently. However, it is ensured that the center of gravity S lies in the region B and that the spacing A is preferably minimal.

[0034] 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 tooth. By this, when the fork approaches the stack, the stack length can be detected and the gap can be selected accordingly.

[0035] Reference numerals list

[0036] 1Transportation section

[0037] 1a Drive of the conveying section

[0038] 2 conveying direction

[0039] 3 conveyor rollers

[0040] 4. Gap (or location of gap)

[0041] 5 Receiving area

[0042] 6 Unloading area

[0043] 7. Stopper (or position of stopper)

[0044] 7a Driver for stopper

[0045] 8One or more sensors

[0046] 10 Stacking

[0047] 20 Robots

[0048] 21Robot base

[0049] 22 Robotic Arm

[0050] 23 fork pieces

[0051] 24 teeth

[0052] 25 Danger Zone

[0053] 30Machinery, especially folding machines

[0054] 31 Operator

[0055] A Spacing

[0056] B area (or extension of area)

[0057] L Stacking length

[0058] The center of the M region (or the location of the region center)

[0059] R Spacing of the gap grid

[0060] S Center of gravity (or location of center of gravity)

Claims

1. A method for lifting a stack from a conveying section by means of a robot arm, in, The robot arm (22) comprises a fork (23) having at least two teeth (24) for lifting the stack (10), and The conveying section (1) comprises a plurality of conveying rollers (3) for conveying the stack (10) along a conveying direction (2). The stack (10) has a stack length (L) in the conveying direction (2), and wherein the teeth (24) move into the gaps (4) between the conveying rollers (3) before being lifted. It is characterized in that The stack (10) stops at a stop (7) of the conveying section (1), and The tooth (24) moves into the recess (4), which is selected in a computationally intensive manner as a function of the position of the stop (7) and the stack length (L) so that the center of gravity (S) of the stack (10) lies above the region (B) opened by the tooth (24).

2. The method according to claim 1, It is characterized in that The tooth (24) moves into the gap (4), which is selected according to the position of the stop (7) and the stack length (L) so that the distance (A) between the center of gravity (S) and the center (M) of the area (B) in the conveying direction (2) is minimized.

3. The method according to claim 1, It is characterized in that The position of the center of gravity (S) in the conveying direction (2) is provided or calculated in a computationally technical manner.

4. The method according to claim 1, It is characterized in that Measure the stack length (L) in the conveying direction (2).

5. The method according to claim 4, It is characterized in that The stack length (L) is measured using at least one sensor (8).

6. The method according to claim 4, It is characterized in that The stack length (L) is measured using two sensors (8).

7. The method according to any one of the preceding claims, It is characterized in that The teeth (24) are moved from below and / or from the side between the conveyor rollers (3).

8. The method according to any one of the preceding claims, It is characterized in that The stop (7) is arranged in a fixed position in the conveying direction (2).

Images