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Designing hygienic robots to suit the food industry

21 May 2017

Fast orientation, or fast picking, of raw materials is a complicated operation frequently undertaken using non-hygienic equipment. A state-of-the-art robot designed to meet European Hygienic Engineering & Design Group (EHEDG) guidelines allows complete hygienic control of the process line, says Arnaud Derrien

Robots are increasingly being adopted by the food industry to help increase productivity and efficiency. Three types of robots are, typically specified. Delta, 4-axis and 6-axis. Staubli set out to determine which technology is best suited, from a microbiological standpoint, for bacteria control and to show how EHEDG hygienic guidelines can be used to improve the engineering of these technologies. The resulting Humid Environment (HE) project was a cooperative study between EHEDG, ECOLAB and Stäubli Robotics.

EHEDG design principles refer to both open and closed equipment so can be employed when designing easy-to-clean robots. The EHEDG guidelines – specifically Documents 2, 7, 8 and 10 – have been used to assess robots from a microbiologically hygienic standpoint. Retention zones, corrosion-free components and non-washable parts can be checked for evidence of the presence and spread of bacteria. The findings showed a huge increase in the presence of microorganisms on the equipment, because these robots were originally designed for non-sensitive end-of-line environments. As today’s robotic applications move further up the production line towards the food process area, adapting these technologies by integrating the EHEDG approach to cleanability and hygienic design is more important than ever before.

The primary goal of the project was to remove the oil, motors and condensation buildup from being sited above the product. During operation a robot can heat up to 70°C, when connected to fast-moving equipment. In sensitive environments operating in temperatures between 4°C and 10°C, condensation, oil expansion and cooling off occur within a few minutes. The hotspot created by the robot is most apparent when the robot reaches the end of the production cycle.

Bacterial growth
The ideal conditions for bacterial growth inside the robot include medium temperatures between 15°C and 40°C; water presence and activity; vapour condensation drawn from the environment directly inside the robot; neutral pH; and most significantly, lack of access for cleaning the inner parts of the equipment.

The problem is the same for electrical control boxes: With uncontrolled air pressurisation, bacteria and corrosion can develop within a few weeks. Pressurisation of the arm and electrical boxes is the best solution during and after production periods.

The team studied a number of issues to help advance the hygienic design and suitability of robots in food production environments. Challenges which needed to be overcome included hidden retention zones, the quantity of equipment components involved, and unsuitable materials.

A retention zone is the cumulative area of the robot plus the skeleton frame that holds the robot in place. A water retention area is a place on the equipment where water can stay for extended time periods.  Water retention areas can be external surfaces of the equipment itself, and ‘hidden water retention areas’. The external areas are easy to remove in the conception of the equipment itself. Hidden water retention zones, however, need a specific focus to ensure that the complete mechanical installation does not create dead ends which give bacteria a chance to grow and spread.

The number of peripheral stainless steel pieces of equipment connected to a Delta-style robot also has an impact on hygienic design. The fewer pieces of production equipment attached to the robot will make it easier to clean and there will be less retention areas to harbour bacteria. 

Delta robots were not designed for the routing of flexible pipes and so these are almost always attached ad hoc to the moving arms. Cable ties, even detectable ones, could fall onto the food product and the friction between the moving carbon arms and cable ties can cause particle emission above the food.

The problem is the same for dielectric exchanges between foaming solutions; for example, water and the various metals used in the arm construction. Corrosion honeycombing – the creation of small niches and crevices where bacteria easily grow and survive – will appear as soon as detergents are used on equipment composed of at least two different metals, due to electrolysis action.

Surface cleaning treatments
While the main mechanical benefit of stainless steel is its resistance to rust, it can presents challenges for machining and drilling, as well as being trickier to assemble. Tests were made with robots designed from stainless steel, but they were not successful and the conclusion was that stainless steel is not a suitable material for a dynamic robot. The best compromise is a specific aluminum (light, rigid and mechanically approved for robotics).

But even specific aluminum designed for salt-saturated ambiance can quickly corrode in a raw food production environment, which is why it is important to design the robot such that retention zones and extra components for grippers are avoided.

The HE Project led to the development of a specific surface treatment and a 6-axis robot – A mix of specific aluminum, metal treatment and co-development of a surface that is resistant to detergents and sterilisation solutions. 

This treatment has now been in use for many years and, in many cases, allows the robot to be washed with the same chemical solution as the rest of the line. Some applications allow the robot to clean itself by manipulating the detergent foaming spray nozzle around the gripper, robot and ancillary equipment.

A CIP robot?
To eliminate human mistakes and ensure the cleaning of difficult-to-reach parts a cleaning solution was developed to allow for self-washing, which is used more frequently in sensitive industries such as dairy and meat processing.

One of the main concerns of the study was the structure of the equipment itself:  Common sense dictates that mounting the robot on the
side of the production line will remove the main problems – oil, condensation, and other contaminants – from above the sensitive handling area. Secondly, a vertical frame, fixed on a single mount and sometimes onto the conveyor itself, eliminates the need for a stainless steel structure to affix the robot. 

Ultimately, the cooperative study showed that ‘HE grade’ can be considered a general definition and shape used in the design and engineering of both 4-axis and 6-axis robots.  To achieve enhanced hygienic features a HE robot should be used. Delta architecture robot design is not recommended and any delta robots used in sensitive food production areas need to be covered to prevent possible contamination.

Arnaud Derrin is key account manager for the food industry at Stäubli Robotics in France.

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