Robotic cells for Food handling, packaging, and palletizing applications all have one thing in common; your robot is only as good as its End-of-Arm Tool (EOAT) or Gripper. Robotic cells for food handling cover a broad spectrum due to the wide variety of food products and the requirements for each product. There are, however, some considerations that are applicable to food handling EOAT of all types.
The food EOAT
• must be designed to reduce food build up areas
• must be designed and manufactured to withstand various cleaning techniques
• must be robust enough to handle the cycle load and yet light weight to prolong the life of the robot
• cannot damage or mar the food or food package
• must perform the necessary functions to package the food
For food handling EOAT it is preferred to reduce areas that can accumulate debris which will make the EOAT easier to clean and more sanitary. It is preferred for some types of EOAT to have welded tube frames which are very rigid and light weight. When using welded tube frames ensure that the ends are capped. Reducing machined features such as slots and pockets are recommended. Choosing the correct hardware is also important. Using Hex head screws in place of socket head cap screws will eliminate a pocket where debris can collect.
Cleaning techniques for food handling EOAT vary greatly. Components can be cleaned with a soap and water rinse or caustic solution. High pressure, high temperature wash downs are also possible. Electronic elements and enclosures may need IP ratings from 66-69. It is imperative to know what type of cleaning will be performed on the EOAT before you design it. This will determine to which IP specification you use for enclosures and electrical components. It will also determine which material you use for custom details and mounting elements. Wherever you can use aluminum instead of stainless steel you will reduce the overall weight of the EOAT.
Frequently robotic cells for food handling are high cycle 24/7
applications. In order to withstand that type of cycling the EOAT needs to have a robust design. This starts out with a rigid frame. Typically a base frame made of welded aluminum or stainless steel is ideal. This will give a rigid structure upon which to add components. If designed correctly it will give a good strength to weight ratio. The old adage “keep it simple” truly applies to high cycle applications. Reduce moving parts will reduce wear and increase life cycle of your componentry.
Direct contact food grade materials must not only be food safe, they also must withstand wash down. Many types of plastic, rubber, and stainless steel are considered food grade or FDA compliant. They can contact the food
directly in the handling process. This can be accomplished by vacuum cups, gripper jaws, scoops, needles, etc…
Knowing which type to use for a specific type of food depends on the attributes of the food. Bottom line is that the food has to be handled without being deformed. This will determine which type of gripping method is preferred.
Many times food EOAT are required to do more than just pick and place. This usually is the case when the EOAT is required to pick up the food or packaged food and place it into another type of packaging. This typically means adjusting the center to center spacing between the food items and placing it into a retail or wholesale package or corrugated case. It can also mean changing the orientation of each of the products picked which can be very complex for multiple items.
Case 1: Muffin, Cupcake, Brownie and Layer Cake Robotic Depanning
Robotic depanning in the baking industry is typically done with vacuum cups or needle grippers. Using food grade vacuum cups and an adjustable de-centralized vacuum source, the baked good can be removed from the pan and placed onto a conveyor. The quantity
handled per cycle is dependent upon oven throughput per product and the packaging container. This will determine whether a partial pan, whole pan, or multiple pans need to be picked per robot cycle. This will also determine the size and functionality of the EOAT and the size of robot needed.
When the type of baked good does not lend itself to be secured by vacuum usually needle grippers are used. 2-4 Stainless steel needles can be used to penetrate the baked good at an angle to create a means to mechanically lift the baked good out of the pan. The holes that are left behind are barely noticeable to the naked eye and the hole shrinks upon further cooling.
Either of these methods can be used in conjunction with a mechanical system of components and actuators designed to reduce the center to center spacing of the baked good so the robot can place them into a retail or wholesale container. Food grade actuators, bushings, and rods, can be used to create the pitch adjustment.
Case 2: Bag Grippers (palletizing 5-50kg bags of potatoes, grains, etc…)
Palletizing bags of food product is the last step in a fully automated bag fill process. To palletize bags effectively the gripper must secure the bag rigidly without damaging the product and place it with consistency and accuracy onto the pallet. Depending on the type of bag (plastic, woven cloth, paper bags, etc…) and content of the bag, the bag can be loosely packed and flexible to rigid. A universal bag gripper must have the flexibility to handle the various types of bags and products.
Bags are typically picked from a roller conveyor, allowing fingers to access the bottom of the bag through the space between the rollers. This allows the EOAT to lift the product without damaging it. The number of fingers depends on the length, weight, and rigidity of the bag.
As well as lifting from below the bags needs to be secured from the sides and top to eliminate movement as the robot traverses to the pallet location. Plates that rotate in from the side along with the fingers act to secure the bag as well as guide the bag onto the pallet as the fingers release from below. A clamp plate that actuates down from the top gives the final support needed to accurately locate the bag and pack a tight pallet.
To be universal the bag gripper must be able to adjust for different widths and bag sizes. If one bag size is run on the line for days a simple mechanical adjustment may suffice as an inexpensive solution to change the width of the bag gripper. If the robot is servicing more than 1 bag on the same line or 2 different lines with bags of different widths than the bag gripper will need an on-the-fly width adjustment. This can be done with an electric motor that is controlled by the robot controller.
Additional options for the bag gripper could include slip sheet or pallet placement. Slip sheets can be placed on top of the pallet and in between layers as needed with vacuum cup assemblies mounted directly to the bag gripper. As well pallet hooks can be added to the bag gripper to swing down to secure and place pallets into the build area.
Case 3: Fork Style Grippers (palletizing open-top fruit and vegetable cases)
Fork style grippers are used to palletize many types of open-top corrugated cases but work especially well with open-top fruit and vegetable cases. Similar to a bag gripper the fork style gripper typically pick the cases from a roller conveyor, allowing forks to access the bottom of the case through the space between the rollers. The frame of the conveyor may need to be modified to add cut outs to give the forks access to the bottom of the case.
After the robot positions the forks under the cases a rubber coated clamp plate actuates down from the top to secure the case for transit. The force on this plate can be regulated to secure the product without damaging the contents. To place the case on a pallet the forks are retracted from below the case. A static stripper plate keeps the case in place as the forks retract. Multiple cases can be handled in a similar manner and placed on the pallet all at the same time or placed individually if the gripper has independent zones. If independent zones are needed each case that is placed would need independently functioning forks and clamps.
Pallets can also be secured by the forks as an option. As well slip sheets or tier sheets can be secured as an option.
Case 4: Mechanical Case Grippers (closed-top corrugated cases)
Mechanical side clamp grippers work particularly well for closed-top corrugated cases when the food products are durable enough to take the clamping force. The amount of clamp force can be regulated but there still needs to be a certain amount of force to pick and place the case. Being strictly a friction grip, the jaws can have rubber or abrasive anti-slip tape bonded to the face to increase the friction coefficient. This will help to reduce the required force.
The jaw design can be 1 static, 1 moving, or both linked together to move at the same time. Like the fork style gripper, multiple cases can be handled in a similar manner and placed on the pallet all at the
same time, or placed individually if the gripper has independent zones. Similar to other grippers, slip sheet and pallet options are available.
In all of the cases above the grippers can be outfitted with control options as needed, The position and part verification sensors can
be PNP or NPN logic. The control interface can be discrete I/O, DeviceNet, Ethernet, etc… depending on the robot and dress
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