At the recent PACK EXPO tradeshow held in Las Vegas, industry observers commented on the proliferation of robotics in packaging machinery compared to just a year or two ago. These new machines are no longer large, articulated arm robots originally designed for the automotive industry and then adapted for end-of-line applications, such as palletizing and case packing. Increasingly, 2-axis and 3-axis Delta robots are operating in both primary packaging systems for product pick-and-place, and secondary operations like cartoning and case packing.
Another difference from old-school packaging machinery: These weren't your typical standalone robots designed by traditional robot manufacturers. Many of today's packaging-system providers are developing their own robot mechanics integral to their other machinery. In so doing, they're also increasing performance, better synchronizing robot motion with the rest of the machine, and reducing componentry and footprint. These designers have recognized that their packaging knowledge allows them to more effectively integrate the flexibility of robotics into the process — and car ve out a new profit center for themselves.
As of this writing, the key U.S. patent on 3-axis Delta robots — those familiar spiderlike arms mounted over a workspace and primarily used for pick-and-place of light objects — has expired. With the end of patent protection, industry observers can expect to see more of these Delta designs enter the packaging marketplace. Already, 2 and 3-axis Delta arms are being offered as “kits,” giving machine builders the option of outsourcing in addition to designing their own. The trend toward machines with integral robotic capability also represents a business strategy for OEMs unwilling to consign themselves to being mere integrators of third party robots with proprietary control systems. These OEMs want to preserve their engineering capabilities, stimulate innovation, and market their own intellectual property.
ARC Advisory Group recently published a research report titled Integral Robotics Raises Agility and Flexibility of Packaging Machinery: Modular Design Techniques Facilitate the Integration of Robotics. In the report, senior analyst Sal Spada explains, “The challenge that packaging machine builders face is that robotic motion is generally out of their domain of expertise.” This refers to kinematics, which “utilizes highly specialized path planning algorithms, blending, and resolving for multiple trajectories to the same point.”
This is why robot manufacturers have for so long been able to market their own control systems together with their robots, and why they are generally guaranteed residual control upgrade business as control technology advances faster than the mechanical arms wear out. But robot control options are changing, as open architecture solutions become available that let OEMs design their own arms or outsource the mechanics. These control solutions are not only meant to replace multiple robot controllers, but the packaging machine's motion controller and PLC as well.
Handling and packaging strategies fulfilled by robotics include adapting to different batches on the fly, varying the grouping patterns of products, and handling vastly different products on the same line by exchanging grippers. What's more, robots are ideal for processing irregularly shaped objects — as when a vision-equipped robot applies seasoning to steaks, for example.
Adaptability means reusability. Robots save engineering costs and time because they are reusable or reprogrammable modules. This applies to software as well as mechanics. Robots are also scaleable, meaning that adding robot modules can increase throughput.
What are some considerations for developing the freedom of movement required for efficient robotic packing? First is to select the right arm for the job. Note that 2 and 3-axis Deltas refer to their fundamental arm configurations; additional servo axes are often applied.
- 3-axis Delta arms are useful for high speeds and light loads. We'll see more of these in coming months as the design became public domain in Europe a year ago, and in the U.S. in late 2007.
- 2-axis Delta arms are for heavier payloads, deeper reach into cases, and collating. Their use is sure to spread with the current trend toward robotics in secondary packaging.
- Articulated arms were traditionally used for case packing and palletizing, but now, smaller versions are useful for carton erecting, filling, and sealing.
- Gantry and portal arms are typically used for palletizing, and to handle heavy payloads and lower speeds.
Motion control considerations
Advanced mathematical algorithms are the key to smoothly coordinating the robot arm's multiple joints, wrist actions, and linear travel. While some simple gantries use point-to-point positioning, the real efficiencies come when motions are fluid, fast, and focused on the Tool Center Point (TCP). Different degrees of freedom are possible, depending on the control software and the manipulator, with a given envelope or workspace. Cartesian movements are inherent to the control system. Both the motion and mechanics are very flexible.
TCP represents a fundamental distinction between machine and robotic motion design. In mechatronic packaging machines, motions are defined as a set of trajectories for each servo axis. These trajectories are individually calculated and synchronized by a virtual camshaft. The various mechanical components operate in unison and can be adjusted dynamically. But compared to robots, only simple kinematics are available.
In robots, on the other hand, motions are related to the TCP and not to individual axes. Every action is defined by the target position and type of robot-arm movement it will require. Then at runtime, the controller calculates required trajectories for each motor, which means the path can easily be changed at runtime.
To overcome the need for the specialized kinematic skills noted in the ARC report, motion control toolkits have been introduced in the past three years that offer robotics libraries. It's possible for engineers to program Cartesian motion, just as they would for a conventional machine, into an IEC 61131-3 function block from this library, and then apply a transformation function block that performs all the necessary kinematics.
This is the software breakthrough that has permitted so many packaging systems designers to implement robotics, allowing them to focus on their core mechanical engineering competencies to optimize arm designs and materials, and to apply their expertise to the packing function and package characteristics. When all the machine functions are embedded in function blocks, it's possible for programs to be developed in a modular structure, which improves diagnostics, reusability, and response to inputs.
Robotic systems can then be designed as modules that link concatenable function blocks to perform the transformation (a.k.a. trafo) necessary, for example, for a familiar 6-axis articulated robot, plus a trafo for the wrist movement and one for the end-of-arm tool actuation. As the ARC report states, “Machine modularity is allowing machine builders to configure a packaging machine based on functional subsystems such as bottle carousels, labelers, and wrappers. Integration of a robotic manipulator further leverages the concept of modularity.”
Robots are capable of developing some g forces, and too much can overcome the gripper's holding force on the product. Therefore, intelligent acceleration monitoring is a useful feature of the development environment, to limit accelerations and velocities and contain the resulting centrifugal forces.
Motion commands should include point-to-point, linear or circular interpolation, and splines. Spline curve algorithms map a continuous path between start and target points. Look for geometrical blending capabilities to reduce cycle times, because “blending” paths optimizes speed and distance traveled to the target point. Programs should let users define criteria for target point, velocity, acceleration, and jerk.
The program should also be able to keep forward and backward movements on the same path. (This is harder than it sounds; it's like being able to back up your car at 60 mph.) Likewise, the program should stay on path during an emergency stop, and be able to precisely trigger peripheral motions, such as indexers, wrappers, and sealing mechanisms.
It's much simpler to integrate robotics with packaging machine operations when control is centralized in a single controller. Response time is faster, too. However, the controller must be powerful enough to manage one or more robot arms plus all related functions, such as belt tracking.
Many controls vendors claim robotic control among their bag of tricks. But ease of development and operation, integration with the rest of the packaging machine, response time (to adjust an ongoing motion such as changing belt velocity), and just plain speed can vary greatly. Be sure to put each supplier through the paces, especially when it comes to checking out the performance of robotic packaging machines developed using their technology.
International gallery of robotic packaging systems
Case packer • Nuspark Engineering, Canada
This compact case packer from Nuspark Engineering can be equipped with one (shown) or two side-by-side 2-axis Delta robot arms depending on throughput requirements. The company also synchronizes infeed systems to transport, collate, orient, and buffer products, as well as provide positive control of case opening. The additional arm has no impact on footprint. The design uses servo modules, and is therefore scalable without increasing the size of the electrical cabinet.
Adabot R700 case packer • Fallas Automation, USA
Fallas Automation calls its design the Adabot because it lets you easily add a ‘bot — actually up to four case-packing robots — and run them all off the original unit's controller. Fallas uses the 2-axis Delta design for its higher payload capacity and deeper reach into cases as compared to 3-axis Deltas. Stiff, lightweight carbon fiber maximizes payload and speed to move loads up to 2 lb at 80 cpm, and 5-lb payloads as fast as 40 cpm. Robotic flexibility, including wrist rotation, allows the Adabot to produce different pack patterns that would typically require two conventional machines. The operator can build these patterns from the HMI and save them as recipes for reuse.
Cartesio G35EFC Cartoner • Cavanna, Italy
The Cavanna Cartesio Model G35EFC robotic cartoning system integrates three articulated robotic arms to form, fill, and seal cartons in a single unit whose footprint is about 16 × 6 × 6 ft. Each articulated robotic arm uses three servomotors; seven other servos are responsible for tightly synchronizing an infeed belt, oscillator device, dual-belt racetrack collator, and a flighted carton infeed conveyor. All of these are synchronized not only with each other, but also with the motions of the three robotic arms, resulting in smooth and precise positioning accuracy.
pac robot 3 orienter and infeed system • Pester Pac Automation, Germany
Pester Pac Automation's pac robot 3 is yet another 2-axis Delta design. It's shown here with their PEWO-pack 450 Compact bottle wrapper for the health and beauty care industry. Continuous product guidance allows gentle handling of up to 300 unstable bottles per minute. As bottles are discharged from the labeler, they enter the collating unit where the pac robot 3 picks two sets of six bottles, indexes them at 90°, and places them on the wrapper's infeed belt. Bottles are then inserted into the servo-controlled, single-lane sealing unit at up to 50 cpm, wrapped and sealed in PE film, and sent down a PEWO-therm shrink tunnel.