Students: Gerben van Dijk, Mike van Amsterdam, Tiemen Markerink & Arian Duine (Spring 2017)
Introduction
Hooymans Products is a company that invents and produces new products and ideas. It’s located in Roelofarendsveen and is a small company with circa 40 employees. They want to invest in new ideas and new technologies. That’s why they give us the chance to do a project at their company.
The objective
Hooymans needs to deliver for the end of the year approximately 16000 sub frames. This is lot of work to do by hand, so we got the assignment to automate this process. Within ten weeks Hooymans Products needs a fully automated TIG welding system to weld little subframes together. A sub frame consist of 2 metal square tubes of 15×15mm and a length of 628mm. And one cylindrical tube of Ø12 with a length of 292mm.
The result
After 8 weeks we can weld the sub frames full automatically. We used two robots, one to weld the frame and one to pick up the welded frames and place the new parts of a frame. We used an indextable to rotate our welding mould and several sensors to detect of the frame is in the welding mould. The whole process is controlled by a PLC.
Welding Robot
The main goal of our project was welding frames together which then could be used to build a frame for some stores. It was quite hard to achieve a perfect weld with the robot beca
use everything had to been done by hand. With this I mean that scripting and coding had to been done on the teach pendant. This was frustrating sometimes because the movements of the robot were hard to make sometimes. Eventually we found a solution on how to do this. We changed the position of the welding torch holder to an easier position so we could make a 270 degree weld around the tubes. Both sides had to be welded so there was another challenge in moving the robot to the other side without hitting our welding mould or anything else. Also, the movement itself needs to be fast because you don’t want to lose time anywhere and want everything as fast as possible. So we optimized the movement of the welding robot and it runs very smooth at the moment. Also the welding itself is almost perfect. By hand these welds couldn’t be made in the way the robot does.
Indextable
The motor of the indextable must turn to the right and left alternately.
With two relays one of the phases is changed so that the motor turns the other way. The indextable is controlled by the plc. The plc gives a start signal to turn the indextable to the right. To turn left it gives two signals a start signal and a signal to turn left. Also there is a stop on the indextable this stop signal is connected to the emergency button.
Weld Mould
On the index table there is a weld mould being placed.
This weld mould hold
s the square tubes and the round tubes in place with magnets and pneumatic cilinders. The weld mould is necessary for the frame to be welded well. The system controls with induction sensors if the round tubes are present. With Limit switches that are mounted on the cylinder blocks, the system controls if the square tubes are present. When one component is missing, the system know there is something wrong and will not continue with the process and gives an error. The error needs to be solved before the system will continue.
Pick and Place robot
We had to find a way to fill the welding mould without the help of human hands, eventually we decided to do this with a second robot, so we had to find a robot ourself. After a long search we found a fanuc M6 which is capable of the tasks we had in mind for this robot. During the programming of the robot we had some problem with picking up the material because the position where to robot needs to pick up the material changes every cyclus. After some help we learned about the position registers in the fanuc robot. In the position register there is to possibility to give the dimensions of the material, so the robot calculates where the next tube is.
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PLC
For this project we used the plc as main controller. So everything what happened in the process is controlled through the plc. The main program consists out of two function blocks. One for turning the indextable to the left and one for turning it to the right. When the FB for turning to the left is finished, it activates the FB for turning to the right. These Function Blocks operate almost the same. But by a turning to the left the opposite components are activated than when turning to the right. How the program operates. First it pulls back the cylinders on the pick and place side. Then it sends an output to the pick and place robot. When the pick and placerobot is finished it gives an output to the plc. Then the cylinders are pushed against the frame and the sensors are checked. When all sensors are activated, so every component of the frame is in the welding mould. The pick and place side is finished.
At the same time on the other side of the table, the frame is already being clamped by the cylinders. So when the indextable is turned it gives a signal to the welding robot. And the welding robot welds the two sides of the frame. When the welding robot is finished it gives a signal to the plc and then is the welding side also finished. When those two sides are finished it means the indextable can turn. This is done by giving two pulses. Because the indextable can turn 90 degree by one pulse. When the indextable is turned the other Function block is activated and the indextable turns to the other side. There are also some other components connected to the plc. A start button to start and stop the process. An emergency button when things go wrong, the whole process can be stopped. When the emergency button has been activated, the operator can reset the process with the reset button, that lights up. Two buttons to turn the indextable left and right manually.
Dispensers
For this project we needed two dispensers. These dispensers have to be made by ourselves. One for the square tubes and one for the round tubes. Originally they were designed to be exchanged with another series, so the process would not be idle for a while, while filling the dispensers. But in the end we found out that it would be easier to refill them in the production area, due to the weight and i would not be so much faster.
For the square tube we were searching solutions, that the square tubes would always be delivered in the same position, so the Pick&Place robot only needed one position. We found out that these solutions were to difficult to realise in this project. So we made this storage for square tubes. The square tubes are being put in in the length direction. With the EOAT, (End Of Arm Tool), we are going to pick these up with two pins. When the left pin is in the position to pick up a tube in the left part of the box. The right pin is in the same position in the right part of the box. With the hooks under The EOAT we want to pick up the round tubes. They are stored in a small cassette that deposits round tubes with the help of gravity.
The round tubes are being stored in a cassette that can hold 50 round tubes at a time, when this cassette is empty, it can be exchanged with a full one or it can be refilled when it is in the production position. When a refill is taking place, the robots and the PLC will wait until the operator gives a start signal again with the start button. When the operator forgets to press the stop button and just walks in, the system will also stop, due to the light screen where the operator passes by.
Conclusion
After eight weeks of hard work, we finally managed to get the whole process working together. This means that both robots work together with the index table. When both robots finished their jobs the index table rotates 180 degrees and the robots go to work again.
The goal of this project was to make a system which is able to automatically weld frames together and to store the welded frames somewhere. SO we came up with a solution where a pick and place robot fills the welding mould, the index table rotates the frame to the welding robot, the welding robot welds the frame together, the table turns back and the pick and place robot picks up the welded frame and hangs it on a frame cart.
During this project we encountered a lot problems. Especially in the last week. Luckily we managed to fix everything and made the system almost production ready.