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Robotic Palletizing – #4 of the 5 Most Commonly Asked Questions by New and Prospective Buyers

casepacking10If you are new to robotic palletizing and other robotic work cell for manufacturing and warehousing, this series of five articles/questions may help you to prepare for the wave of robotic automation coming to manufacturing and warehousing, and help you decide whether you want to participate in the wave.

Question #4 – How long will the robot in our new robotic palletizer last?

The simple answer to this question, at least for robots manufactured by FANUC – the leading supplier of robots throughout the world – is that the newest robots are running from 80,000 to 1000,000 hours mean time between failures.  A typical work shift in North America is about 2,000 hours, so you can expect a new robot to run anywhere from 10 to nearly 20 years in a three shift operation.

“But…,” you may protest, “…nothing runs that long.  How can a new robotic palletizer run that long?”

Just as advanced computer design tools and sheer experience have allowed automobile manufacturers to lengthen service intervals on automobiles, and automobile reliability has improved after many years of refinements, robot manufacturers have used these tools to develop and refine motor designs, servo motor controls, and mechanical assemblies of robots. 

Robot motions have been optimized to reduce instantaneous loads on motors and reducers.  Robot arms/castings have been optimized to reduce mass and increase strength. 

As long as a robot is used within its design parameters and basic preventive maintenance is performed, there is little to fail on a robot and there is a very good chance your robot will run for 10 to 20 years without a failure.

Three important parameters determine the life of a robot in a palletizing, case packing or material handling application; product weight, product inertia, or shape, and robot duty cycle.

2Product Weight – If you are smart, you wouldn’t bring a ½ ton pickup to a gravel pit to pick up 4000 pounds of gravel (though some have tried…).  Likewise, you don’t want to undersize a robot for an application.  Palletizing 80 pound bags of concrete will require a different robot/robot speed solution than palletizing 20 pound cases of plastic cup lids.

Product Inertia – this is a frequently overlooked element of robot applications;  long, wide, or deep loads place larger moment loads on a robot arm than small, compact loads.  Moving large loads that are well within the weight capacity of a robot but outside its inertia limits can result in oscillation in the robot’s motors that at best will reduce the robot’s life cycle, and at worst can result in out of control motion of the robot.  Make sure your robot integrator takes into account the inertia of both the end of arm tool and product(s) when sizing your robot and selecting its operating speed.

Duty CycleThroughput is a key determinant of robot cell uptime and reliability.  FANUC now quotes case and bag palletizing rates of 20 + moves per minute, or less than three seconds per move.  Tall pallet loads require longer moves than shorter pallet loads on average, so pallet height will in part drive robot cycle time as well.  In addition, if you need to run a robot flat out for its entire life, you will end up with far more wear and tear than if you have intermittent peak demand on the robot.

Here are some simple things that can be done to reduce the robot’s duty cycle in a typical palletizing, case packing or general material handling application; some that the robot integrator can do for you, others you can do for yourself.

  1. Optimize location of the input and exit conveyors to reduce robot arm travel distance between pick and drop locations.  A few inches may not seem like a lot, but a robot running 4 second cycles at 90% utilization, 24 x 6 days per week will run 6,065,280 cycles – in one year.  And 60 million+ cycles in ten years.  A few inches per move in each direction (between pick and drop) will amount to about 1.5 million feet of robot motion (without getting too specific about axis motions, etc.) over a ten year period – a lot of motion for a set of gears and electric motors and drives!
  2. Use smart programming to limit robot motion and make it as smooth as reasonably possible.
  3. PM your robot(s) regularly – fresh grease every 3 to 6 months depending on duty cycle, per the robot manufacturer’s specifications, can significantly reduce robot wear and tear and increase the robot’s life.  And don’t be penny wise and pound foolish by putting cheap substitute grease in your palletizing robot.

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Other elements of the robotic palletizing cell that willimpact its overall uptime and reliability include end of arm tool design and supporting conveyor and material handling equipment such as pallet dispensers.    The end of arm tool will likely require service of some type within a seven to ten year window.  Incoming case or bag conveyor can run for many years of operation with minimal service if you size it properly for the application, purchase it from a reputable company like Motion Controls Robotics’ conveyor partner, Omni Metal Craft , keep photocells clean and limit switches adjusted, and perform routine maintenance like greasing and chain tensioning.  The same goes for full pallet exit conveyor and empty pallet rack or dispenser.

So there you have it – a short and long answer to the question “How long will the robot in our new robotic palletizer last?” along with some tips on improving the life of your new robotic palletizing cell.  Please contact your Sales Engineer at Motion Controls Robotics, Inc in Fremont, OH at 419.334.5886 for support on your potential robotic palletizing operation. 

See question #5 – Why is the safety system laid out the way it is? in the series of Robotic Palletizing Questions