The word ‘cobots’ is a contraction of ‘collaborative robots’, coined in the nineties to describe robots designed specifically to be used by and with human input. These augment human capabilities by taking over repetitive tasks, without requiring extreme safety measures and complex programming.
The key property of cobots is that they can be easily reprogrammed by the operator for a new job. And this suits them for other tasks which stop short of mass production: assembling or welding a batch of identical items, for instance.
Andrew Mason is sales manager at RARUK Automation, which supplies cobot systems to a wide variety of customers. As he describes it: “The food industry, cosmetics, anybody who wants to put something in a box.”
A leading producer of cobots is Danish firm Universal Robots, but third parties develop the software and integration needed for a complete palletising system. “Our palletising solution is from Robotiq, a strategic partner with UR,” says Mason. “They developed their products and software for UR only, so they talk seamlessly.”
Mason describes three aims for cobots: “One is a robot you can effectively move around the factory – if you don’t have a job for it in one corner, you can move it somewhere else.” A consequence of inherent safety (see sidebar) is that cobots are relatively light – to minimise impact force – so can be repositioned easily. “At exhibitions we set them up within a few hours,” Mason says.
“Secondly, it is designed to be safe: there are force sensors built in, so you can run alongside humans without fences and guards. But you’ve got to consider the application. If you’re picking up big, heavy things and swinging them at head height, or if they’ve got sharp edges, you do need to guard it.
“But the third point, the best thing, is that the programming is designed to be done by somebody who’s not a programmer. And that’s where they’ve really opened up the market.” The operator typically uses a movable touchscreen or teach pendant to set the unit up, and may also manually guide the robot into position.
To load a pallet, the operator enters the dimensions of the boxes and the pallet itself, and the software determines a suitable pattern of boxes for each layer: “The operator enters whether there’s a label on one end,” says Mason, “so the robot knows to put the boxes with the label outwards.” The robot can also insert cards between layers, and store multiple block patterns per setup: alternate (A-B-A-B-A-B) layers or an A-A-A-B-B-B pattern, for instance.
“If the palletiser stops halfway through a sequence for some reason – say a box rips because it wasn’t sealed properly – they may have to take a box off the pallet. The screen shows the situation, and you can remove or delete boxes and carry on with the sequence.”
TRAINING IN HOURS
“There’s a difference between a programmer and an operator: full Universal Robots programming is a two-day course, but for palletising only, we can offer a one-day programmer training course. For an operator, it’s a few hours.”
Most suppliers offer simulators to test whether a palletising station might work: “The configurator asks exactly the same questions as when you’re programming the robot: box size, pallet size, pattern etc,” says Mason.
Cobots typically go up to a realistic 10 or 11 cycles per minute, but a multi-pick setup to load two or more boxes at once gives better throughput – and of course they can operate 24 hours a day.
End-of-arm-tooling (EOAT) is typically a vacuum gripper which lifts a box from the top. Air-operated paddle grippers grasp objects from the sides, but these need clearance to operate – less useful for box-stacking. Shrink-wrapped trays of cans may be better handled with an electromagnetic gripper. Grippers generally need an external compressed air supply, although for lighter loads there are self-contained units. The Robotiq AX with ‘PowerPick’ system can lift two boxes at once. EOATs typically weigh 1-2kg, so for instance the UR10e (nominally rated at 12.5kg) can take a payload of 10-11kg.
The other main dimension to consider is reach: how large a volume can the robot cover? Not all palletisers can handle a full-sized Europallet.
Most cobots are ‘six-axis’ machines, having six degrees of freedom: rotating base, ‘shoulder’ and ‘elbow’ joints, and an end tool rotating in pitch, roll and yaw. Seven-axis machines differ: the Robotiq AX Series has a motorised pedestal to raise the whole assembly, giving coverage for taller pallets. Conversely, the Kassow KR810 has an extra ‘wrist’ joint which adds extra flexibility to the EOAT.
Safety sensors include volumetric laser scanners to measure the position and speed of items near the robot, light curtains and contact detectors. “You can set virtual walls or planes,” says Mason, “so the robot could run fast in a safe area, then as it approaches an area where it could come into contact with a human, it sets a lower speed, or a combination of speed and force.” He adds that many customers still want fences to protect the robot from site traffic, such as forklifts.
The cost is obviously variable, but a 10kg payload palletiser might cost £50,000 plus: “It depends on payload and stack height,” says Mason, suggesting that a full installation including risk assessment, training and certification should come in at ‘under £100,000.’
In a case study from Dutch manufacturer Smart Robotics, its palletiser was installed in just two hours, and was claimed to do the job of two employees, giving it a return on investment of less than three years.
Of course, there are some limitations: Mason points out that some robots are “only IP54 rated – we wouldn’t want them in a wet area. And ATEX [explosive atmosphere legislation] is sometimes an issue.” A further limitation is absolute payload: loads above about 18kg are beyond the scope of a typical force-limited robot for safety reasons.
BOS: SAFETY AND ISO/TS 15066
Robots and humans in close proximity are an obvious safety hazard, and the standards for industrial robots (for example, ISO 10218) generally demand that they be kept within interlocked enclosures. But technical standard ISO/TS 15066:2016 (‘Robots and robotic devices – Collaborative robots’) takes a different approach, defining power and force limits to reduce the risk of injury. These were developed after detailed studies of human pain thresholds. The standard defines four acceptable types of operation:
Safety monitored stop: pausing motion while an operator is in a defined workspace, resuming once the workspace is clear. Hand guiding: the robot only moves through direct input (once the operator has overridden a safety stop) either to teach the robot a task, or to assist the operator Speed and separation monitoring: sensors (such as below) detect the relative position and speed of robot and operator to maintain a safe distance, even if the person directly approaches the machine Power and force limiting: sensors limit the inputs given to the robot, allowing operators to remain in the vicinity, even if somebody walks into the machine. Sharp edges and protrusions must be minimised.