The essential guide
When all the equipment is integrated into a working facility, it is called a system. When configuring a system some important guide lines need to be observed.
A cell must comply to all relevant Health & Safety Requirements and must be CE marked, which includes a risk assessment to ensure all aspects of safety are considered in relation to people who will be working with the system. Factors that are taken into account are the stopping distances of the equipment and this determines how close the operator is allowed to work to the robot or positioner.
Solid or steel panels or mesh panels with protective film infill enclose the entire system and access to the cell is provided by means of an interlocked safety gate. These panels should be high enough to prevent the operator being exposed to arc flash. Operator load areas must be protected by means of light guards or physical barriers such as hatches or roller shutter doors. The guard line should extend to the extreme reach of the robot plus its tool, which is the case of a welding robot is the welding gun. If the cell is to be kept as small as possible the robot must be equipped with zone limitations to ensure that it will not be able to reach beyond a certain point. Soft limits can be set in the software, but these do not fulfil safety requirements.
All safety devices such as light guards, interlocks, zone limitations switches and operator functions must be interfaced to the electrical safety system of the cell. These must be dual channel. In recent years robot suppliers have developed a safety controller that is fitted to the robot controller. This allows the user to limit the working range of the robot and there is no need for limitation switches or hard stop as the safety controller offers category 3 safety.
A fume hood above the welding area is connected to an extraction system. Sometimes it is not practical to have a fume hood, e.g. when the welded assembly needs be unloaded by crane or where the robot is suspended from a gantry. In this case electrostatic filter units can be used. The fume extraction system must comply with COSHH regulations.
With so many robots on the market, it is no surprise that there is a good second hand market for robots and robot cells. Whilst it is true that these represent a lower level of investment, it is almost certain that the life cycle cost of such a system is much higher. Apart from the fact that the robot will become less reliable with age, there is the issue of spares availability. Typically robot suppliers will support their product between 7 to 10 years after it has been discontinued. This means that no spares are available. Companies with unsupported equipment find themselves with long periods of downtime, trying to locate a spare. If you production is relying on consistent output, the second had robot route, hardly ever seems attractive.