Collaboration model - STIHL opens up new avenues with FANUC’s Collaborative Robot

Hundreds of robots are already in use at the motor saw manufacturer STIHL, based in Waiblingen, near Stuttgart. Now the first Collaborative Robot has been added. STIHL has taken a clear step forward in the development of technology using the FANUC CR-35iA. The robot relieves the burden on employees on the cut-off saw packaging line.

The start-up of production only took three days. By then, the specified piece numbers had already been achieved. This was due to the good preparation behind the first deployment of a Collaborative Robot at STIHL. The company's in-house Production Engineering team spent a whole year developing the technical requirements and preparing the workplace for the CR-35iA. All that intensive preparation has paid off. Even on the first night shift, the robot ran without a single hitch. This is where the team of Group Leader, André Lange, who is responsible for service and hardware planning, benefited from the close familiarity with FANUC robot technology that they have developed over many applications:

Before introduction of robot handling at this workstation, the handling and shake test were performed manually by the operator.

Basically, the shake test is an acoustic test, whereby the cut-off saw is shaken - but it is an important step in quality assurance and final inspection. If a “clicking” sound can be heard when shaking, then the suction head is installed correctly and the cut-off saw can be packed. As a single cut-off saw weighs around 10 kg, this amounts to a total lifted weight of around eight tonnes per shift, per employee. Therefore, the robot provides considerably relief for the employee.
The packing line staff were involved from the outset in the project. Not only were they able to give an expert assessment of the test set-up, they also influenced the design and ergonomics. Markus Wahl, from the Production Engineering department at STIHL and responsible for building the assembly systems, was involved with the robots on a daily basis during the development period: “The packing line employees have introduced many good ideas that we have implemented.” As the suggestions came directly from practical experience, this made both engineering sense and increased the acceptance amongst the workforce from the very beginning.

The suspended conveyor has some 80 workpiece mounts. But as the duration of adjustment work on each cut-off saw, during the end-of-line testing, can vary, not all of the workpiece mounts on the continuous conveyor are occupied. On occasions several positions, one after the other, are unoccupied. A loaded hook on the suspended conveyor, on which a cut-off saw is hanging, is recognised by several camera systems along the conveyor track and this information is transmitted to the master controller and the data management. The robot synchronises its speed with the conveyor, via the FANUC "Line Tracking" software, and then grips at the right moment. As Markus Wahl explains: “The goal is to utilise the robot as continuously as possible in order that it has no idle time.” One of many small tricks used is the hanger speed: It has been designed to be variable.
So that the robot can be utilised to the fullest extent, there is also an intermediate storage after the hanging conveyor. This buffer is used, for example, when more cut-off saws arrive at the packing station than the employee can inspect, or if he goes for a break. Then the robot works fully automatically. The aim in all situations is to keep the suspension conveyor empty. If the “replenishment” from the assembly is less, the robot works to empty the buffer. A variable at this position is the employee. The times for the individual testing can vary.

And as Markus Wahl comments: “We had to get a fix on this with the control engineering”

If the robot misses a workpiece, there are different demolition scenarios. The robot grips the cut-off saw by the two handles, one after the other. Only when both handles are gripped, can the robot remove the cut-off saw from the suspended conveyor. If this does not occur, it waits for the next part.

The effort involved in systems integration, not just in respect of the gripper, raises the question as to why STIHL did not rely on any external system integrator, rather than undertake development in-house. For Markus Wahl, the answer does not require a lot of thought: “We know our products, our processes and our employees at the production centre. And because we talked to the people in production, at an early stage, we also know about the various situations that can occur.” Furthermore, dealing with the relevant product and assembly databases, and gaining knowledge of the production system structure would require considerable time for an external integrator. As André Lange points out: “We would not have been able to define our requirement specifications in advance.”

The ability to use the Collaborative Robot CR-35iA with the normal FANUC control system, just like its yellow “colleagues”, proved to be one of the major advantages: The control technology and user interface are all the same. The system components used, like the FANUC “Line Tracking” software, which is particularly useful for synchronisation with the suspended conveyor system, the integration of camera systems or the proven “Collision Guard” software option, are already well-known and appreciated by STIHL. 
And this is where STIHL has a great deal of experience. Since the first introduction of robotics in the mid-nineties, a great deal of know-how has been accumulated in robotics engineering, particularly with the hundreds of FANUC robots operating in all of the STIHL plants worldwide. André Lange emphasises that: “We adopt and follow relatively uniform production concepts at all locations. Production equipment, which is utilised worldwide, such as FANUC robots, makes life easier for us at various levels, from engineering and programming, right through to service.”

The arguments that André Lange makes in favour of MRC, might more or less equally apply to conventional robotics. However, he clearly points out wherein the key step forward lies for STIHL: “We already have a high degree of automation, but from now on we must seek out and close the existing gaps. This technology opens up new scope for designing production plant.”

Safety takes priority

The CR-35iA has been in daily operation for more than half a year, and satisfaction with the robot is not just amongst the project managers, André Lange and Markus Wahl. It has also been fully accepted by the workforce. Affectionately referred to internally as the Hulk, the Collaborative Robot is something that none of STIHL employees wants to miss.