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Economic cooperation between man and machine on a joint work task. © Phoenix Contact

Robots have long since found their way into industry and have become indispensable. This is because they perform indispensable work, particularly in heavy-duty tasks. For some years now, specialists have been trying to realize cooperation between humans and robots in such a way that both the number of cycles and the diversity remain highly dynamic.

The common work areas are defined and evaluated in the risk assessment. © Phoenix Contact

Back to the project: The individual components from the various manufacturers contain residual risks in accordance with the respective operating instructions, which have been largely minimized as part of the further design of the HRC application. Correctly, the incomplete machine is then delivered with a declaration of incorporation and assembly instructions for the complete system. The necessary safety functions are integrated on the basis of the risk assessment - not the hazard assessment, by the way - and with the help of a normative aid. At the same time, the necessary operating instructions - and not the operating manual - are created. This is followed by the planning of the HRC measurement, which is carried out in combination with the tool and the final product. To carry out a force measurement, the robot application must be fully set up. The travel paths must be programmed and the peripherals - such as storage devices - must be permanently installed.

Grippers need to be redesigned

A pointed, fork-shaped gripper is required so that the blanks can be gripped from the conveyor belt. The concept was to use the same grippers that are used inside the milling machine to place the blanks. However, this poses the challenge that piercing hazards cannot be detected with an HRC measurement. Due to the small contact surface, the measured pressure would inevitably exceed the limit values.

Preparing a measurement also involves planning all joints and clamping points. © Phoenix Contact

Placing the blanks in the appropriate containers also requires sensitive evaluation. The thinnest blanks are less than one millimeter thick. Consequently, the risk of cuts cannot be ruled out if employees reach into the deposit container during the movement. After closer inspection, the grippers are redesigned so that there is an area of at least one square centimeter plus a radius of two millimeters on three edges during the lowering movement. The gripper edge remains sharp-edged. The measurement will show whether the described redesign is sufficient.

How do the sharp-edged blanks behave during movement? The solution is that the grippers move to a set position when picking up the blank and the force is switched off when the position is reached. The blank is then held by positive locking and residual tension. The blank therefore falls out of the grippers immediately if a collision occurs. However, the strength of the collision must also be verified with the load cell. The challenge arises from the fact that the transient force must not be exceeded. The board must therefore fall out of the gripper position before the limit value is reached.

Pressures and forces can be visualized

All in all, the solution is already proving to be a success, as the contact rate of employees gripping the circuit board with their fingers has fallen from 100% to less than 5%. This leaves a residual risk that needs to be evaluated as part of the risk assessment. And what did the measurements reveal? In fact, there is no longer a risk of stinging. In the event of a collision, the surface area and the programmed movement force in the lowering direction show values that are in the middle of the normal range. The specialists have also successfully mastered the second challenge: the PCB falls out of the grippers in the event of a collision. The gripping force is just sufficient to reliably place the blank from the conveyor belt into the storage container. For the lowering movement within the container, the approach has been programmed to implement a diagonal lowering movement from the center. The pressure and force measurement allows the pressures and forces that occur to be visualized and evaluated accordingly.

Filigree work steps can be realized by collapsing robots © Phoenix Contact

Once the measurement has been completed and all documents have been compiled, the risk assessment has been approved and the necessary conformity assessment has been carried out. The latter confirms compliance with the legal requirements. The project is completed by issuing the declaration of conformity and affixing the CE marking. The machine is then transferred to the operator's area of responsibility.

Henrik Vandieken, B.SC, and Benjamin Peters, both Competence Center Services, Phoenix Contact Germany, Blomberg

Control integration should be reviewed

In order for HRC robots to be used safely, they must be tested. However, this statement is only part of the truth: Rather, the correct integration into the control system must be checked. The safety specialists at Phoenix Contact have found that it is worth taking a look at this aspect. They usually do this as part of a supplementary test or machine inspections, which they see as an extension of the risk assessment.

As part of such an inspection, the implementation of the safety functions, the state of the art of the safety devices and their correct installation, including the safety distances, are checked. The electrical, pneumatic, hydraulic and other equipment is also checked. As already described, the HRC measurement can be part of the inspection. The Competence Center Services team provides support in the specific implementation of the detected and defined steps. Further reading can be found in the book "Betreiberpflichten für Alt- und Gebrauchtmaschinen" from Reguvis Verlag.