DAF Trucks is the biggest manufacturer of trucks in the Netherlands. DAF trucks is located in Eindhoven with a work area of 900.000 m2. In the year 2016 they sold over 56.000 trucks worldwide. They employ circa 9.000 people worldwide, with factories in Eindhoven, Westerlo, Leyland and Ponta Grossa.
As part of the differential for the trucks a spiral bevel gear is used as shown in Figure 1. These gears are placed in the truck via a machine. When placed in the trucks they are manually turned to make them fit. This is done by an operator. Due to the process of making such a gear the edges of the tooth are still sharp. Even though the operators wear gloves, it is still possible to cut your fingers with it. Because of this DAF asked 3M to find a solution for this. 3M has passed this assignment to the SMR minor. DAF eventually wants to implement the deburring on all their gears as the one in Figure 1 is their smallest. The deburring has to be done in 5 minutes or less.
The gear is a 40-kg steel crown gear. It has a hardness of 62 HRC which makes it more difficult to deburr. The gear consists of 43 teeth and has an inner diameter of 25 cm and an outer diameter of 45 cm. An example of a sharp edge is shown in Figure 2. The sharp edge is reflecting the light which makes it detectable. Personal cuts have confirmed that the edges are sharp enough to cut through flesh and gloves.
To check if a tooth is properly deburred a vision program is used based on OpenCV. The program measures the area of the edge and compares that to a predetermined area value. If the area value is to low, the edge is not enough deburred. The program takes a picture of the edges and puts a threshold of that picture. Everything below a certain light level becomes black. With that threshold the program finds all the areas and picks the biggest one as the edge. This progress is shown in Figure 3, Figure 4, Figure 5 and Figure 6.
PLC and robotcommunication
Normally, the PLC, the robot and the HMI communicate together without the input or connection with another device. Due to the struggles with the Kawasaki robot, the decision has been made to connect everything via a laptop as shown in Figure 7. This makes for a much smoother communication with the plc and the Kawasaki.
For the end of arm tool(EOAT) a pneumatic dremel was used, as shown in Figure 8, proudly sponsored by Kemet Europe. This piece of machinery rotates at 52000 rpm and has a accessory which can be used to deburr hard metals like the gear. The EOAT is connected to the robot. In the top part of the EOAT a torsion spring is mounted. By using this spring, the EOAT has a bit of leeway and is not a stiff.
To rotate the gear so the robot can deburr the teeth a turntable has been made. To rotate the turntable a stepper motor has been used. This motor is mounted on a wooden plank. This plank is mounted on a frame so it cannot move. On this plank a thrust ball bearing is mounted. On the other side of the bearing another wooden plank is mounted. Due to the bearing this plank can rotate. The stepper motor rotates this plank. In the plank the gear is placed. Rotating the plank will also rotate the gear.
Solution and conclusion
An operator places the gear on the table and presses the start button. The robot deburrs a tooth. After that the gear gets rotated to the next teeth. The robot repeats this until the gear is deburred. When done the operator removes the gear and places it in the truck.