Automated Assembly Line

An assembly line is a manufacturing system devoted to the assembly of a set of part. In this system, several work stations are linked together in the sequence of operations required to execute the assembly process. In the present use case we address the modelling of an automated assembly line, i.e., a systems where proper automatic equipment is used to execute the operations in an automatic way, i.e., withouth the need of the intervention of a human operator.

In this use case we consider a single product assembly line, i.e., a system designed to process a single part type, namely a hinge for furniture.

In the following sections the fundamental aspects of the assembly system are modelled: the product to be assembled, the process to be executed and the system operating it.

Modelling the product to be assembled

An assembled product can be described in terms of a product structure, i.e., the way in which a product or assembly is hirarchically structured. In the figure below, the final product is represented in terms of the components it is composed of.

The modelling of the product to be assembled entails the definition of its components and how they are connected together. Specifically, the hinge is composed by two main blocks.

The first block features a Hinge Arm as the main component. That is the part that usually gets fixed to the internal wall of the furniture piece through the Clip, that is the component that allows placing an external screw (not included in this assembly) for this purpose. The Clip is kept into place onto the Hinge Arm by means of a Grub Screw. The second block, called Box Assembly comes pre-assembled downstream, further along the process. This is the subassembly that gets fixed by means of two screws to the door leaf. Its main component is obtained from a stamped metal sheet and houses the lower part of the Hinge Arm when the object is in a closed position. The two blocks are connected by two metal bodies (Connector 1 and Connector 2) through a U-Bolt, to constrain the rotation of the Hinge Arm around the relative pins. In order to improve dampening, a spiral Spring is also inserted in this area.

To carry out this step, all the components must be modelled in terms of their 3D representation as well as their relative position in the final assembly product. Specific details on this phase can be found in a dedicated section.

Modelling of the production process

The assembly process is defined in terms of an assembly plan, i.e., the sequence of operations to be performed in order to assemble a product or subassembly.

Each operation is described in terms of its class, processing time and precedence relations.

Specific details on this phase can be found in a dedicated section.

The product and process can be modeled as an ontology (VFLibProduct). This ontology can be generated using OntoGui-SystemDesign or OntoGui-Utilities which imports a .json file generated from a spreadsheet table.

Modelling of the workstations

The workstation types are modeled as an ontology (VFLibStations), specifying geometric and functional characteristics. The definition of the workstation types can also be found in a spreadsheet table.

In addition, predefined animations can be prepared for common movements of the workstations.

It is possible to develop 3D models of the workstations, also specifically focusing on Virtual Reality applications.

The whole set of 3D models defined according to the GLTF format is available in two versions:

Modelling of the assembly system

The assembly line under study is composed of 19 stations and 4 buffers linked together by a conveyor belt.

The process of the hinge assembly considers the assembly of some sub-assemblies and some components in different workstations of an assembly line.

The assembly line is composed of a linear conveyor capable of handling pallets, and a set of assembly stations adding components to the hinge.

The overall assembly line configuration and the relations between workstations and operations are modeled in the ontology VFLab, making use also of the ontology defining the building (VFLibBuilding). The spreadsheet tables of the assembly line and the building are available as well.

The following table reports the list of operations and the corresponding input component. Each operation is assigned to a workstation.

Oper. n.Oper. typeInput comp.Workstation IDDescription
1

pick&place

Wing

PPW1

Wing is picked from the upstream buffer and placed on the rotating table.

2

tightening

WingScrew

T1

WingScrew is aligned to the corresponding hole on the Wing and screwed.

3

pick&place

PPH1

The wip hinge is taken from the rotating table and placed on a conveyor.

4

pick&place

RPP1

A 6-dof robot picks the wip hinge from a conveyor and places it on a pallet.

5

pick&place

Clip

PP1

Clip is assembled on Wing, hooking to the WingScrew.

6

pin insertion

Pin1-1

PI1

Pin1-1 is inserted to fix Clip on Wing.

7

riveting

R1

Pin1-1 is riveted.

8

pick&place

Connector1

PP2

Connector1 is assembled on Wing.

9

pick&place

Spring

PP3

Spring is assembled on Wing.

10

pin insertion

Pin1-2

PI2

Pin1-2 is inserted to fix Connector1 and Spring on Wing.

11

riveting

R2

Pin1-2 is riveted.

12

pick&place

Connector2

PP4

Connector2 is assembled on Wing.

13

pin insertion

Pin1-3

PI3

Pin1-3 is inserted to fix Connector2 on Wing.

14

riveting

R3

Pin1-3 is riveted.

15

pick&place

Box

PP5

Box is assembled on Wing.

16

pin insertion

Hook

PI4

Hook is inserted to fix Box on Wing.

17

riveting

R4

Hook is riveted.

18

inspection

C1

The finished hinge is visually inspected by a camera.

19

pick&place

CB1

The finished hinge is picked from the pallet and placed in a box.

Performance Evaluation

The candidate solution generated in the modelling stage is evaluated using Discrete Event Simulation (DES). The jsimIO Python module is used to generate a simulation model and simulate the production process, based on the Jsim (JMT) simulation engine.

pagejsimIO Assembly

Detailed Layout

After the formal modeling of the assembly line and the performance evaluation, the detailed layout of the assembly line can be dynamically visualized in a VR environment using the VEB.js application:

The .json file defining the scene and animation are available on an online repository.

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