Pacepacker proves its pet food pedigree with case loading cell

The company, a leading UK-based manufacturer of dried and wet pet food, supplies both domestic and international markets. Whilst canned pet food is still a major chunk of the market, in recent years, alternative formats, such as pouches and sealed trays, have grown in popularity due to re-sealable lids that are easier to open and the avoidance of cuts from metal edges.

In line with this trend, the company took the decision to move some of its canned production into plastic trays. However, the system it was using to load cans into autoclave baskets was not compatible with the new tray format.

A director from the pet food company explains: "We needed a machine that could place the individual trays in layers into baskets, transport the baskets into the trolley system that takes them into the autoclaves, and unload the baskets of cooked product afterwards. We needed to do all of this at speeds of 220 trays per minute."

Pacepacker Services conceived a bespoke robotic pick and place cell for this complex application.

Upturned trays of uncooked pet food are counted into the system via a photo-electric sensor mounted on a modular belt conveyor. When a complete row has been counted, the trays are indexed across onto another conveyor. Once the required layer configuration has been reached, for example, 10 rows of 10, and the trays are assembled neatly on the conveyor, a robotic arm equipped with suction cups picks up the trays and places then onto a layer pad, within the autoclave basket.

Richard Gladwin, Pacepacker's technical director explains: "You can't just pile the trays on top of one another as they will stick together during cooking, which is why each layer of trays is separated by a layer pad."

Pacepacker custom designed the layer pads, which comprise a stainless steel mesh supported on spigots in the corners.

Gladwin explains: "We had to come up with a design that was rigid enough to support the trays but without wasting too much space in the basket."

This process is repeated until the basket is full, and the next empty basket is presented to the pick and place system.

Basket transport system

Pacepacker's brief also included designing a system for transporting the empty autoclave baskets into the cell in groups of six, and transporting the full baskets into the trolley car system that services the ovens.

Gladwin says: "Moving the baskets on and off the machine in groups of six was a challenging job in its own right. We did this by using sensors and building different sections of drive into the conveyor to bring the baskets close together."

Once the empty basket is in place in the machine, a hydraulic scissor lift raises the loose stainless steel base plate to the top of the basket ready to accept the first layer of trays. The robot transfers the first layer onto the plate and the lift lowers it down into the base of the basket, ready for subsequent layers.

Besides feeding the trays into the autoclave baskets, the system also handles product post cooking, effectively performing the same pick-and-place process in reverse. The same vacuum gripper picks the cooked product from the basket and loads it onto a conveyor for transfer to a packing area.

Gladwin comments: "The beauty of the system is that it can simultaneously be unloading one basket whilst loading another."

One of the challenges with the design of the outfeed system is that trays exiting the autoclave are very wet. To stop water from collecting in the bases of the upturned trays, Pacepacker incorporated an industrial air knife into the system. Every time a layer of trays is removed by the robot arm, this sweeps across the next layer to remove excess water.

The robot specified by Pacepacker was the M-410iB 300, FANUC's latest generation four-axis, servo-driven industrial robot. Pacepacker has been a strategic automation integrator for FANUC for nearly 20 years, and chose this particular arm for its large working envelope and fast cycle times, but above all, its best in class 300kg payload.

Gladwin says: "We knew that the robot would have to be fitted with pretty heavy tooling due to the technology that went into the vacuum head."

Explaining the vacuum head technology, he says: "The robot needed the capability to pick up not just complete layers but also half layers of product. In order to do this, the head had to be designed so that only the suction cups in contact with a tray apply a vacuum. This was achieved by locating a tiny valve beneath each suction cup and calibrating the valves to stay open if the suction cup is blocked."

The ability to pick up part layers means that whatever the length of the production run, the precise number of trays will be placed into the basket. This design also enables the system to deal with variations in tray sizes and shapes.

Gladwin says: "There might be 42 rectangular trays on a layer one run and 100 round pots the next. This head can cope with any configuration that is thrown at it."

The wet environment in which the system would be operating added to the complexity of the project.

Gladwin says: "This made component sourcing challenging, as everything had to be food grade stainless steel for full washdown, and all the electrics had to be sealed to IP67. It also influenced the type of vacuum system used; we couldn't have specified an electric pump, as it would have broken down as a result of water getting sucked into it. Instead, the vacuum is generated by compressed air."

The entire cell is controlled by two HMIs with colour touchscreens, making it very user-friendly - operators simply have to select the "recipe' or layer configuration they require. In the event of new pot sizes or shapes being introduced, new recipes can easily be created.

For more information about bespoke pick and place systems, please visit www.pacepacker.com.