Motion Control Resources
Smart Conveyors Move Ahead
by Kristin Lewotsky, Contributing Editor
Motion Control & Motor Association Posted 11/28/2018
Conveyors are the workhorses of industry. Forget about continuous belts run by fixed-speed AC induction motors. Modern conveyors can position components with surprising levels of speed and complexity. Options include short, direct-drive conveyor segments, omnidirectional conveyors, and automated systems that send individual carts whizzing around powered tracks. From manufacturing to meatpacking, from parcel handling to palletizing, conveyors get the job done.
It begins with manufacturing. The old business model of stocking warehouses with vast volumes of a single item has given way to the processing of ever smaller lots as manufacturers pursue the elusive batch of one. What is built needs to be shipped, of course, whether to another factory for additional processing, to resellers, or to the ultimate consumer. Here, the numbers are frankly staggering. Amazon, for example, shipped more than 5 billion items in 2017 through its Amazon Prime program, alone. Conveyor technology is central to making the magic happen.
Analysts project that the global conveyor market will reach $12.3 billion by 2022, up from $8.2 billion in 2016. That corresponds to a compound annual growth rate of nearly 7.5%, which is 2 ½ times the global economic growth projected for 2018. The report lists Asia-Pacific as the region of fastest expansion, with a focus on retail and shipping. And the fastest growing technology sector within that geographical region? Automated conveyors, which apply motion control to deliver programmable positioning at millimeter-scale resolutions.
Direct drive technology
Conveyors capable of precision motion play key roles in manufacturing. A part might need to be stopped in front of an image sensor for inspection, for example, or presented to a robotic arm as part of a pick-and-place operation. Motion control systems can position parts accurately, rapidly, and repeatably.
Although conventional gearmotors operating closed loop can deliver the fast, precise motion required for industrial applications, they aren’t necessarily the optimal solution. Footprint is always critical in the industrial environment, whether on the factory and warehouse floor or within the machine itself. The combination of motor, gearhead, coupling, and feedback consumes a significant amount of space while adding cost, maintenance, and points of failure. The approach can also impact performance. Gearheads can introduce backlash. The coupling that connects the motor shaft with the load can introduce compliance and wind up, decreasing responsiveness and accuracy. Direct-drive motors provide an alternative.
In a direct-drive motor, the motor itself is part of the system. Instead of the motor shaft interfacing with the drive wheel of the conveyor via a coupling, the motor shaft is the axle of the drive wheel (see figure 1). The approach eliminates compliance while maximizing torque. It also supports greater degrees of design freedom, particularly in the case of frameless direct-drive motors. Frameless motors arrive as unhoused rotor and stators. “The principal benefit of frameless torque motors is the fact that they can be built into the conveyor, either at the ends of rollers or inside the roller,” says Ken Wyman, vice president of marketing at Allied Motion Technologies (Amherst, New York). “With or without added gearing stages, this approach often leads to the most compact design.”
Video 1: Frameless motors can be built into the rollers of a conveyor to provide high torque and accurate control in a compact custom package.
Frameless motors do require more expertise than housed versions in the design and installation phases, but users can work with their vendors to streamline the process.
Active conveyor belts
Conventional conveyor systems use long, complex architectures in order to perform common tasks like sortation, palletizing, and depalletizing. Given concerns of floor space and time, modern industrial organizations need more compact, economical, and efficient positioning methods. An approach known as Active Roller Belt (ARB) technology applies relatively simple motion components to innovative conveyors to rapidly and reliably perform even sophisticated positioning.
The technology is based on the roller belt, a belt that is embedded with an array of free-spinning rollers mounted at an angle to direction of travel. The product being conveyed rides on the rollers. Actuators underneath the carryway turn the rollers, enabling the rollers to position the load in the local coordinate system even as it is traveling in the global coordinate system of the belt. Components riding on the conveyor can be rapidly positioned linearly and rotationally, including redirection through a number of angles from 30° to 90°. When combined with machine vision sensors, the technology can be used to sort a stream of products with a significantly simpler and more compact system that would be possible with conventional conveyor technology (see video 2).
Video 2: Merge system combines servo-driven conveyors and ARB technology to sort incoming product at a rate of 42 cases per minute.
Each actuator consists of a rack-and-pinion actuator driven by an integrated stepper drive unit. The stepper motor drives the rack, which turns the pinion. The pinion, in turn, spins the belt rollers to move the package. The number of actuators in a given segment is a function of the complexity and granularity of the motion required. Depending on the width of the belt and the number of actuators, the system can move multiple objects on very sophisticated paths (see video 3).
Video 3: With Ethernet/IP communications, the system controls the actuators to coordinate motion among multiple objects, such as in this pallet layer forming conveyor.
Smart conveyor technology
For more than a century, automation meant developing a machine or production line to perform the same steps repeatedly. The equipment was expensive but long product lifecycles meant that the equipment had a long lifetime after the company had achieved ROI. Today, the paradigm has changed. Consumers want variety, which means that manufacturers need automation and transport solutions that let them respond. “Particularly in consumer packaged goods, the demand for mass customization and personalization is really driving a lot of specifications from end users for equipment that is faster and more flexible,” says Oliver Hyatt, iTrak product manager at MagneMotion (Devens, Massachusetts). “They need to accomplish this in the factories they have today because they're not expanding their footprints very much.”
Smart conveyors, courtesy of motion control, provide a solution. These systems consist of carts individually and asynchronously routed along tracks. High-speed connectivity makes it possible to change programming in real time. The result is a highly responsive transport system effective for applications as varied as assembly, packaging, laboratory services, and even heavy industry.
The smart conveyor concept is based around what is essentially a frameless linear motor. The tracks, which are lined with coils, act as the stator. The carts, which are permanent magnets, act as the rotors/forcers. The stators are broken into zones and controlled either via a centralized or peer-to-peer distributed architecture. The result is a system that can command individual carts to go to a certain point at a certain speed (see video 4). It offers both speed and flexibility to address the modern manufacturing environment.
“The [smart conveyor approach] allows you to dynamically scale your production,” says Nuzha Yakoob, senior product manager at Festo (Islandia, New York). “It also allows you to dynamically change the batch sizes and the number of variations within the batch.
Video 4: Cheese packaging line uses smart conveyor technology to pack filled pouches of product. Note the variable spacing and speed of the individual carts.
One classic application is multi-item packaging for products as varied as snack kits and holiday gift packs of cosmetics. Switching from populating a four-pack of cookies to an eight-pack, for example, is a simple programming step. Carts can be routed differently through the stations in order to optimize throughput.
Traceability is another key advantage. A traditional conveyor system registers the position of a product when it is at a specific station. While the product is in motion, however, the system cannot monitor location without additional sensors such as bar-code readers installed at multiple points on the conveyor. That approach adds complexity, cost, points of failure, and processing burden. More to the point, it is still fundamentally a discrete system.
In smart conveyors, the stator segments incorporate linear encoders, enabling the system to monitor the location of each cart at all times. That level of granularity makes the technology useful for more than just manufacturing. Associated Regional and University Pathologists, a national reference laboratory that offers roughly 3000 different tests of tissues and fluids, has applied smart conveyor technology to handle samples at a rate of thousands per hour (see video 5).
Video 5: Smart conveyor system improves throughput of this test laboratory while enabling it to more effectively respond to process variables.
Traceability is essential to this type of testing. Mislabeling or losing samples could have catastrophic results. The smart conveyor approach makes it possible to trace each sample throughout the process so that there is no risk of mixing up results. “For any unique sample, they have a history of where that sample traveled on the laboratory floor,” says Neil Bentley, product manager for MagneMotion products at MagneMotion. “For their business, it’s very important to have a quality record so that they can confirm they gave the right results to the right patient. The technology applies well to these types of processes where track and trace is valuable.”
The ability for the carts to be routed independently and asynchronously also makes it possible to optimize the efficiency of the laboratory as a whole. Pathology tests have different sample preparation procedures. The test protocols and durations lead to variations in terms of which testing station is available at any given time. The smart conveyor can be used to route any given sample to the next available testing station that offers the appropriate test.
Balancing the benefits
The technology also brings benefits for manufacturing. Stopping products on a conventional conveyor requires stopping every product on the belt. As a result, the slowest process on the line gates the overall speed. The asynchronous operation of smart conveyors makes it possible for some carts to be stationary while others are moving.
Taking advantage of the technology requires a redesign in the process. Manufacturers need to find a way to modularize tasks like clamping, clipping, and gluing, then use the smart conveyor to link the automation cells in the most appropriate way for a specific product, including stopping and starting as required.
Starting and stopping isn’t unique to smart conveyors. As we discussed above, direct-drive or even fixed-speed conveyors can be made in short segments to execute this kind of variable motion. Determining which solution is most appropriate for the application can be nuanced. Certainly, adding more conveyor segments requires additional motors and drives with the usual trade-offs of cost, complexity, maintenance, and points of failure. On the other hand, smart conveyors feature coils and encoders throughout the length of the tracks, making them infrastructure intensive, as well.
Depending on the system, the cost of acquisition may be higher than for a standard conveyor. Total cost of ownership, on the other hand, can be lower. Because the carts are essentially payload-carrying magnets, they are completely passive with no communications or power cables. This increases reliability and reduces maintenance requirements and downtime.
It’s important to consider other aspects of the application. “More and more, when we talk about smart manufacturing with Industry 4.0, they are talking about being able to produce a lot size of one,” says Yakoob. “To reduce the batch count, you need a system that is able to handle it. So, not only do your automation cells need to be more modular, but you also have to look at the transport system that connects these automation systems.”
Consider contract manufacturers, who juggle multiple orders from multiple customers at one time. A job might involve 20 units or 20,000. New orders might come in at a moment’s notice, and the manufacturer needs to respond. In this case, the ERP system can be connected to the smart conveyor so that operations can be dynamically reallocated. “If a change is made to one of the orders, the manufacturer can make that change effective in the system almost immediately,” says Yakoob. It’s an approach that applies to any schedule-intensive operation, from batch-manufacturing in the automotive food chain to medical-device assembly. “The technology allows them to scale production very dynamically and efficiently.”
Conveyors play an increasingly important role in our automation-based economy. Thanks to motion control, OEMs can choose from a variety of automated conveyors to find one the best suits their application. From direct-drive conveyors to ARB conveyors to smart conveyors, motion technology delivers the load to the right place.