Linear motors reduce antibiotics in fish farms
From a global perspective, fish is the most important source of protein for human consumption. Demand could as much as double within one or two decades. Without aquaculture, this hunger for fish cannot be satisfied.
The negative side effects of industrial aquaculture, such as high levels of pollution from medications, have scared off consumers in Europe – in particular – causing sales to collapse a few years ago.
Aquaculture fish are bred for maximum production, and for economic reasons have significantly less living space than their cousins in the wild. This makes them especially susceptible to illness and parasites.
The damage caused by an infestation can quickly threaten the livelihood of the farmer. The epidemic of infectious salmon anaemia (ISA) that broke out in 2007, for example, caused salmon production in Chile to plummet from 400,000 tonnes to just 250,000 tonnes within two years. There are many other diseases besides ISA, such as furunculous, that threaten fish stocks.
Many breeders use large amounts of prophylactic medications, especially antibiotics. Growing criticism of these side effects has led to the use of medications being restricted in Europe.
Norway in particular has long endeavoured to solve the problems faced by those in aquaculture. The country, where fish is the third most important export, has almost eliminated its use of antibiotics in fish farms.
At their peak in 1987, Norwegian fisheries used about 50 tonnes of antibiotics a year – more than were prescribed for the entire population of Norway in the same time period. Their use in fish farms is now less than 100kg a year. Ninety-eight percent of all salmon farmed in there have no exposure to antibiotics. This was made possible by vaccinating the fish.
Typically, several vaccines are injection at once. The metabolic rate of fish depends on the temperature, so the injection contains an agent that heats up the immune system.
This procedure is difficult, because up until now, each fish has had to be manually injected with the vaccine using a syringe. Considering the number of fish bread annually – 1.4 million tonnes of salmon in aquaculture worldwide in 2010 – this procedure has reached its limits.
Machine builder Maskon has turned to automation of the vaccination process. A system developed by the company, that can automatically anaesthetise, sort, single out, and vaccinate up to 20,000 fish an hour, depending on the machine used.
This would have previously required four to six experienced ‘fish injectors’. The machine also ensures a significantly higher level of quality of vaccination than humans can provide.
The core of the system consists of one ( VX-4) or two ( VX-8) vaccination modules each equipped with four vaccination stations. An image processing system by the Oslo company Tordivel first measures each fish and provides information to calculate the point of injection.
The entire vaccination station is then positioned accordingly by a linear motor from LinMot. This makes it possible to hit the optimal injection site for each fish with a precision of more than 98 per cent. The length of the fish, as determined by the image processing system, is also used to calculate the depth of the injection for each individual fish.
A sensor on the needle then monitors the injection process and the vaccine dosage for each fish. As a result, the mortality rate is less than 0.02 percent.
The requirements for the injection station drives are high for this application. In particular, they need to comply with the hygiene requirements of the food products industry.
The stainless steel motors in the P01-
37x120F-HP-SSC series from LinMot optimally meet this requirement. They are made entirely of stainless steel (1.4404/316) and are characterized by their high protection class of IP69K. Gaskets were eliminated from the motor design, and all connections are welded. The motors are also fully potted to prevent condensation forming.
Thanks to these features and the closed, easy-to-clean stainless steel surface, the INOX motors are ideal for use in machinery and equipment that processes food products or pharmaceutical goods.
The compact form factor of the linear motors, which have no protruding parts or gearboxes, appealed to the designers at Maskon.
An evaluation by Maskon of linear motors on the market determined that only the stainless steel ones from LinMot could provide the dynamics, precision, the protection class, and compact form factor required by the vaccination machine.
This applies as well to the LinMot stator model PS0137x120F-HP-SSC-R used in the vaccination unit, with an outer diameter of 48mm and length of 296mm. When used together with the appropriate slider, it is able to apply a constant force of up to 210N over the entire range of its stroke. In the standard product line, LinMot sliders are available for strokes from 75 to 680mm.
A high-clearance variant, PL01-19x350/260, with a stroke of 120mm was selected for the vaccination unit. The motor is controlled by a B1100-VFHC servo inverter, also from LinMot, that is designed for integrating the linear motors into systems with a master axis controller.
The force or speed of the motors is set by the master position controller via an analogue differential signal of ±10V. Either the internal LinMot measurement system or a high-precision external measurement system can be used for feedback.
Simple positioning controls can actuate the E1100-VF controller with stepper motor or directional pulse signals. For testing and commissioning, the VF controller can also be operated in point-to-point mode, with four freely programmable end positions.
In addition to the INOX motors the LinMot range also includes variants with maximum force ratings of up to 496 (maximum stroke of 980mm) or 888N (maximum stroke of 860mm). All stainless steel motors are also available with ATEX certification. Different bearing types for various operating modes (different stroke lengths) round out the offerings.
Automation using LinMot motors enables aquacultured fish to be vaccinated across the board for the first time, eliminating the prophylactic use of antibiotics. Undesirable side effects, such as pollution of the oceans with medication residues, the development of resistances, and reservations against the use aquaculture can be reduced to an absolute minimum.
The VX-8 from Maskon that vaccinates up to 20,000 young fish an hour.