A leadscrew-and-nut design fashioned by the company was used to create the new case packer for RPT Motion.
In today’s fast-paced society, speed is a way of life. Such is the case in the industrial automation market, where an increase in speed results in an increase in production rates. Increased production rates, in turn, lead to increased profit, and higher profit margins are something that every company strives to achieve. In the instance of case-packing machines, which move a product down a conveyor to be packaged, it is important for manufacturers to move a large volume of products in a short amount of time. The case packer must not only be fast, but also cost-efficient and durable enough to ensure a long lifespan. Over the last few years, RPT Motion, a provider of custom modular linear motion systems, has experienced an increasing demand for case packers and other linear motion solutions from manufacturing customers across the board.
“So much of our business is driven by speed,” says Peter Ratcliffe, president of RPT Motion. Based in Quebec, Canada, RPT has been providing solutions for industrial automation applications since 1984. “Our customers have always looked to us for ways to speed automation, but in light of the recent globalization, we have observed an intense pressure to provide solutions that reduce downtime and thus increase overall productivity,” said Ratcliffe.
A key segment of RPT’s business is based upon updating existing machinery subsystems with higher-performance linear motion to increase production rates and reliability.
Although speed is a critical component of linear motion applications, size plays a significant role as well—that is, increasing speed without affecting a machine’s or sub-assembly’s dimensions. This is because changes in dimension necessitate redesign, and redesign costs money.
Recently, RPT Motion teamed up with Kerk Motion Products, one of the world’s premier manufacturers of non-ball leadscrews, for a challenging retrofit project involving a major tissue manufacturer whose operation was getting bottlenecked at the case-packing stage. The manufacturer was looking to add a second case packer to its process in order to increase the speed and prevent the slowdown of its current production. However, the process required more than just dropping in the new case packer. The first obstacle lay in the fact that the existing system, which had a two-position lane changer powered by a pneumatic cylinder, wouldn’t provide the four required positions or the higher speeds needed. In order to service the four lanes, a stroke in excess of 40 inches was required, and the lane changer needed to index on average every 10 seconds or less while maximizing time available for product flow.
“We couldn’t fit the ball screw and nut into our existing design with a fast enough pitch to suit the higher speeds,” said Ratcliffe. “It would hit its limits and not allow us to reach the high linear speeds we needed. We could have found a ball screw with a fast lead, but it would not have fit into the current assembly, forcing us to redesign the entire slide system for a bigger, heavier screw.”
To tackle this formidable motion control challenge, RPT teamed with Kerk to design and provide a motion system to feed the required four lanes (two lanes in each of two case packers). The two companies collaborated to include a Kerk screw and nut in the RPT modular slide system, creating a smooth-running, high-speed, servo-powered system with an anti-backlash leadscrew assembly.
The new system featured Kerk’s VHD series of leadscrews, which come in a variety of different leads in the same-size physical package. Components to mount the nut, as well as to support and drive the screw, remained the same over a huge choice of feeds and speeds, and, therefore, of potential uses. In order to meet the high speeds required in this lane changer application, RPT chose a 2.400-in. travel-per-revolution screw of 3¼4-in. nominal diameter, which proved to have approximately the same efficiency as a ball-nut configuration.
“The physical size of the Kerk VHD high-lead-screw-and-nut package was also much smaller than available ball screws of similar leads,” said Ratcliffe, “and contributed significantly to the overall success of the project.”
An up-close view of the case packer machine that RPT was looking to upgrade to solve its productivity, speed, and product flow problems
Kerk is always looking for ways to satisfy the desires of its customers. According to Dave Arguin, sales manager at Kerk, “Kerk is always pushing the limits for its customers. At the time we worked with RPT Motion, the 2.400-in. lead was the longest we produced. We currently offer a much higher 92-mm (3.625-in.) lead on the same-diameter screw.”
The servo-powered system achieved the speeds necessary to accommodate the second case sorter and subsequently eliminate the manufacturer’s bottleneck—within the confines of the system’s original dimensions.
“The lane changer initially functioned without failure or even noticeable backlash for three years, which is typically unheard of in most linear motion applications,” said Ratcliffe.
The use of the self-lubricating Kerk VHD series was also instrumental in combating environmental challenges. Since airborne tissue-paper dust is regularly generated in the cartoning and case-packing area, almost everything eventually gets covered in a light layer of dust. Grease, which captures this dust and creates a harmful, abrasive paste, is eliminated in this process, since the VHD screw does not require grease to operate. Additionally, there are no greasy ball circuits to be damaged by the dusty paste formed on the ballscrew.
According to Ratcliffe, the anti-backlash properties of the VHD screws have proven to be a particularly valuable feature in the system.
“Any wear that does eventually occur in the screw or nut is compensated by the patented Kerk mechanism, which adjusts automatically to maintain a zero backlash over a very long service life,” he said.
Noise reduction was another key benefit of the VHD screws. Because Kerk’s leadscrews do not rely on balls or ball returns that generate noise, the new system runs silently, making for a much more pleasant and safer working environment.
The RPT/Kerk relationship has spawned other notable technical innovations. One such innovation was an ink-jet printer movement system created by RPT using the Kerk VHD series that moves the print head on a linear slide. It is an extremely high-speed application in which the anti-backlash properties translate to excellent print quality. Another application involved gantry robotics for packaging.
“The Kerk VHD system has become the first choice of RPT Motion when addressing linear motion systems,” said Ratcliffe. “It has proven significantly lower cost in most systems than either ball screw or timing-belt drives. The Kerk VHD is more predictable and easier to tune than a timing-belt-powered system and has similar performance at lower initial cost than a ball screw.
Because of the Kerk leadscrew design solution, RPT Motion was able to deliver a fast, high-quality case packer machine at a competitive price.
There is no doubt that the success of this project has presented new opportunities for the two companies to collaborate on future projects. RPT Motion’s relationship with Kerk has allowed the company to become a competitive force in the industry. One can only guess what cutting-edge technology the two companies will collaborate on next.
For more information, contact Tom Solon,applications engineer for Kerk Motion Products, Inc. Prior to joining the company in 1998, Solon worked extensively in the semiconductor manufacturing and injection molding industries. He received degrees in mechanical engineering and economics from Brown University in Providence, RI. A regular contributor to Design News magazine, Solon is also a licensed professional engineer. He can be reached at 603-465-7227, 603-265-3598 (fax), or firstname.lastname@example.org.
About Kerk Motion Products
Established in 1976, Kerk Motion Products, Inc., is one of the world’s largest exclusive manufacturers of non-ball leadscrews. The company, headquartered in Hollis, NH, develops internationally patented anti-backlash designs and materials that provide high accuracy, good repeatability, and long life in a full range of motion control applications.
The company’s production facilities include its own injection molding and moldmaking, CNC machine tools, and a quality control department utilizing real-time SPC. For more information about Kerk Motion Products and its lines of leadscrews, screw rails, and linear rails, contact Kerk Motion Products, Inc., 1 Kerk Drive, Hollis, NH 03049, 603-465-7227, or 603-465-3598 (fax). More information is available at www.kerkmotion.com.