So they tend to underestimate the difficulty of fielding equipment in freezers.
So says Kuka Robotics Corp., Clinton Township, Mich., a developer of robots and automation able to work reliably in severe cold. At least 30% or more of all frozen-food processing takes place in a freezer. Frozen foods must stay at 12°C and quick frozen foods at 18°C for handling. Such temperatures tend to make automation equipment wear out more quickly, says Kuka. One work-around approach has been to shuffle the frozen product in and out of the freezer for packaging or palletizing. Problem is, the product may begin to melt while it's out waiting for the pallet to complete. A similar approach is to stage the product in the freezer before sending it out for palletizing, then immediately rout the full pallet back to the freezer.
In cases where this compromise won't work, processors often adapt robots to work inside the freezer. One method: Enclose the robot in a flexible bag and blow heated air to maintain working temperature. Another tack has been to insert a heater in the base of the robot.
Kuka says a few guidelines help when deploying automation in freezers. For one thing, gear trains that target these temperatures need different tolerances, clearances, and in some cases different materials. Integrators should also plan on dry low-temperature lubricants so viscosity isn't a problem. Similarly, low-temperature seals are a must for joints. Dress packages — the routing system for hoses, power and signal cabling — must likewise allow for extreme temperatures while maintaining flexibility and operating life. The routing of dress packages demands extra care because friction and flex points have greater impact on the material at low temperature. Electronics that goes inside freezers also needs special attention. Ordinary printed-circuit boards will fail at higher than normal rates because of cracked solder joints. Cable connectors need different housings and closures. Teach pendants are especially prone to failure if their keyboards, touchscreens, and electronics aren't designed for low temperatures. Plastic enclosures can become brittle in extreme cold and thus susceptible to breakage.
Kuka also advises use of vacuum actuators for end-of-arm tools. Compressed air is expensive to dry and can cause condensation and water crystals that foul lines, actuators and valves. Positive-displacement dual-action solenoid valves are advisable to ensure proper actuation and to avoid problems from sluggish springs and bellows.
Gripper design depends greatly on the product being handled. Vacuum is still the first choice, but designers should confirm the operating range and life cycle of suction cups at low temperature. And developers should verify the actual performance of the EOA tool early in the design cycle to ensure the cell performs as expected. Mechanics and technicians will maintain and changeover equipment while wearing gloves. So cell design should allow for easy access in gloved hands, and connectors should be selected accordingly.
Cleanliness is an issue. Refrigerated environments mean wash-down ready; freezer environments are wipe-down only. Peripheral devices must also meet the design specs for freezers. Developers should check that conveyors, motors, controls, transmissions, gearboxes can perform in the cold. In the same vein, everything operates more slowly when cold, so plans should reflect this. For example, both friction and vacuum-style grippers take longer to actuate. In packaging applications, it is typical to activate grippers on part-approach to reduce cycle time. But this usually isn't possible in freezers as most packaging operations want to limit the amount of cold air sucked out of freezers through pumps and valves. Though a well-designed system won't need to warm up before production, the initial cycles of the day will be slower than when the system has been fully active. Cycle timing will change, necessitating use of hard sensor logic.
Finally, the physical mounting of robots can trip up the uninitiated. Freezers typically have insulated floors consisting of a layer of urethane insulation sandwiched between two layers of concrete. The top layer of concrete is often thin and unreinforced. It is generally too thin to anchor a large robot. The best approach, says Kuka, is to install lag bolts through all layers to reach reinforced concrete beneath the insulation.
Kuka last year developed the first robot designed specifically for applications in hard freeze environments, the KR 180 PA Arctic Palletizing Robot.
Kuka Robotics Corp., (866) 873-5852, www.kukarobotics.com