Effective workplace safety measures are especially important in manufacturing environments when machines carry out fast movements with large forces. Physical barriers, such as fences that spatially separate people from machinery, are common and easy-to-integrate solutions. However, if mechanical systems cannot be installed or if the work process is influenced by them, contact-free safety concepts such as a light grid or a light curtain can be used. A light curtain forms a close-meshed protective field and, therefore, secures the access to the danger zone.
Hexapod robots are multi-axis positioning systems with a limited workspace that can often be safely integrated into industrial setups. However, if people can move into the workspace of the hexapod or of the setup on the hexapod platform then a safety measure must be set in place.
This blog explains:
- when it is useful and necessary to use a safety device;
- how a safety light barrier (or light curtain) works;
- how the risk assessment for hexapods is carried out;
- how the safety device can quickly be integrated in the controller environment.
1.1 Parallel-Kinematic Hexapods Compared to Serial-Kinematic Systems
Serial-kinematic systems consist of individual axes or actuators that build on one another, which means that they are mechanically connected in series. For example, a platform-bearing Z axis can be mounted on a Y axis, which in turn can be mounted on an X axis (Fig. 1) and so on.
In hexapods, all six actuators act directly on a single platform. This allows a considerably more compact setup than is the case with serially stacked multi-axis systems.
Since only a single platform is moved, which is also often equipped with a large aperture, the mass to be moved is considerably smaller. This results in considerably improved dynamics.
In addition, hexapods exhibit higher accuracy since they usually do not contain guides with corresponding guide errors and the errors from the individual drives do not compound. Since the cables are not moved with the platform, the precision is not influenced by corresponding friction or torques. In addition, the parallel structure increases the stiffness and thus the natural frequencies of the overall system as well.
In stacked systems, however, the lower drives not only have to move the mass of the payload, but also the mass of the drives that follow, along with their cables. This reduces the dynamic properties. Guiding errors that accumulate on the individual axes also impair accuracy and repeatability.