Collaborative application for the production of safety valves
08. October 2018
The division of labour between plastics processors and their customers is changing. Rather than injection-moulded parts, customers are frequently asking for complete, ready-to-install components. That applies not only to the automotive industry, but also to other sectors, e.g. the household appliance and mechanical engineering industries.
For this reason, the assembly sector at Weiss Kunststoffverarbeitung GmbH & Co. KG has been constantly expanding over the past few years. As an engineering-oriented enterprise, Weiss is striving to meet the latest trends in this sector.
The robot cell that was recently put into operation at the Illertissen plant is a good example. A safety valve with a height of only 15 mm is being assembled in the cell where, in addition to injection-moulded parts, filigree metallic bought-in parts such as springs, washers, valve tappets and balls are also used.
In doing so, the company’s assembly specialists implemented the principle of division of labour between humans and robots in practice. Dipl.-Ing. Robert Heller, responsible among other things for the construction of production and automation technology at Weiss: “The robot works extremely accurately and reliably, while the worker – although he may make mistakes – is more flexible.”
The cell is designed so that each ‘colleague’ can leverage his respective strengths. In the first step the worker, standing in front of the cell, places the key components into an assembly fixture. The robot, situated in the cell, takes over by inserting further small parts, e.g. a tiny ball. The worker then gives the signal to compress the parts, and this takes place pneumatically by means of a cylinder.
Now it is the turn of the robot. It removes the assembled valve from the fixture and inserts it into a testing device, where it is subjected to two pressure tests at 0.9 and 2 bar. Following this 100% test (by which the valve remains closed for the 0.9 bar test and must open when a pressure of 2 bar is applied) a certification stamp is applied with a marking system, and the valve is ready for shipping.
The principle of human-robot-collaboration was put into practice by Weiss in a simple yet elegant way: human and robot each have access to the common workspace. They dispensed with a safety guard or other form of spatial separation of worker and robot. Instead, the workspace is secured on both sides by a photoelectric cell. The two photoelectric cells are interconnected for control and safety purposes, so that the robot does not reach into the joint workspace when the operator is inserting or removing parts. Conversely, the robot is stopped if the worker reaches into the workspace while it is operating there.
It goes without saying that the control of the robot is also integrated into this quite simple and practical safety concept. Robert Heller: “We took advantage of the robot manufacturer’s ‘Function Safety Unit’ that is now available as an option: a slot-in card with which, for example, safety zones can also be programmed.”
With the collaborative robot cell, the engineers at Weiss have once again demonstrated that innovative and highly efficient production solutions can be developed in-house – not only in plastics processing or tool and mould making, but also in the downstream processes of assembly and testing technology.