Plastic injection moulding specialist Theo Hillers from Kall, Germany, was exploring other means to handle plastic mesh filters for the pharmaceutical industry without damaging them. The previous method of transferring them from injection moulding machines to the next production stage was to grip the parts by their sprue (the plastic waste left in the hole through which the mould was filled) and snap it off, dropping the filters onto a conveyor belt. This caused some filters to be damaged, resulting in an unacceptable level of wastage.
For cost reasons, the existing 3-axis sprue picking equipment had to be used, so the robotic hands had to fit around it in order to place the filters gently onto the conveyor. Other design constraints included a maximum gripper weight of 500 grams and a requirement for eight or 12 suction cups in a limited space. In addition, there was a need to reduce overall complexity and so maximise reliability, as well as to ensure that the units were robust and would remain free from fatigue fractures.
The task was taken on by ASS Maschinenbau, Overath, which develops diverse solutions for the automation and robotics sector. Grippers for automated handling are usually made from modular aluminium components, so when it came to using lightweight polyamide for their construction, there was little practical experience to fall back on. For a solution, ASS turned to additive manufacturing using equipment from another German firm, EOS, whose UK subsidiary is in Warwick.
The robotic grippers were required to apply suction to eight or 12 cavities, depending on the application, and release the vacuum to place the parts on the conveyor. Tests showed that the 12-cavity gripper required four air circuits for every three filters, while the eight-cavity version needed four air circuits for every two.
Internal air ducts were integrated into the CAD design so that no additional weight was incurred for air hoses. It also means that the robotic hand is tidier and less complex, saving time during installation and maintenance. To save further weight, the connections for the vacuum suction pads were also incorporated directly into the device, instead of using brass adapters as previously. Additionally, this simplifies changing the pads when they are worn.
Production of the grippers took place overnight in an EOSINT P 390 system from EOS. After the CAD data had been transferred to the machine's control, the components were produced by melting and fusing successive layers of black polyamide powder using laser power.
Following extraction and cleaning away of excess powder, the lightweight grippers complete with connections for the suction cups and air supply and a jaw to recover the sprue were ready for use. The heavier of the two designs with twelve suction cups is 250 mm in diameter by 110 mm high and weighs less than 400 grams.
