The boss of a local cardboard factory called me, in 2006, to obtain a technical opinion on an old manual cardboard stapler machine. The machine was a really old project born in 1982 with an electro-mechanical control system. It was necessary to have not only the stapling functionality but glueing also. So I propose immediately, after the initial inspection, to implement a Siemens S7-300 automation cardboard factory glueing machine system.
The physical structure of the machine’s body was perfect and was completely reused. A drum-conveyor was responsible to transport the cardboard during the process, a metallic head applied a series of metal staples depending on the number the operator sets-up as set-point. But no more regulations were available.
The boss asked me a solution to implement an automation extremely flexible and with a different type of possibilities.
The key features of the project were:
- staples in term of number of them to be applied and the distance between subsequent points, head quote where the application process must starts – this because different cardboard are destined to a different purpose and there were specific needs to start the staple application in a different position and not to the head directly;
- the process must be able to be executed with cold glue also and not only with metallic staples;
- manage the finalized product accumulation in the output zone of the machine (never existed before);
- increase the overall versatility of the machine.
So, during the second inspection, I had the possibility to saw the machine during its working process and I took into account the opinion of the operators. I wrote down a list of points on what operators expected the machine to do for them.
After that, I decided to completely shut down the old automation cabinet and to build a new one, to cut off the electrical part of the machine and leave only the mechanical part. A few maintenances were necessary for some ball-bearings and transport chains.
The system has been revamped to the following standards:
- a new Simatic S7-300 PLC with Profibus-DP master embedded – the brain;
- a human-machine interface touchscreen operator panel, a full-colour HAKKO 7″ configured to be connected to the PLC via RS485 port and using Profibus protocol – the eyes;
- a high precision LIKA Encoder multiturn with 4096 pulses per round with 4096 rollover rounds driven in Profibus – the heart
- a variable speed drive to control the speed of the main asynchronous tri-phase motor was selected because the staples distance was mechanically determined and to permit distance variations there was the need to manage another parameter that in that case was the transit speed of the cardboard – the leg to run
The main electrical cabinet was built by a specialized electrical external company that delivered the assembly on the machine also.
On the desk, I tested the communication link between the Simatic S7-300 PLC, the encoder and the operator touchscreen panel.
I could start the test phase when the main cabinet was completely assembled on the border of the machine. A K factor, that correlates the speed of the machine with the speed of the stapler head, was determined.
A glueing head was installed on the machine driven by an electro-valve for enabling the glue.
All the basic working parameters of the machine were determined.
The software for the Simatic S7-300 PLC was developed in a couple of days and tested.
It was capable of:
- select the cardboard working cycle:
- only glue;
- only staples;
- glue and staples combined together;
- if the glue cycle was selected, the operator can specify the following parameters:
- glueing starting point in millimetres;
- total glue length in millimetres;
- if the staples cycle was selected, there are the following parameters to be specified:
- the staples applications starting point in millimetres;
- total numbers of staples to be applied;
- the distance between staples in millimetres;
- how many cardboard must be accumulated in the output store before the machine releases them;
- through the HMI (touchscreen operator panel) all the machine status are displayed in real-time, parameters, events, status and alarms also.
All the operators, the boss and I included are happy to see the machine work fine as we aspected.
It is actually under production without any stop.