Servo Technology Amps Up Production Output

By Peter Zafiro, General Manager, LinMot USA, Inc.

While some companies put innovation on the backburner and “hunkered down” during the COVID-19 pandemic, Central Machines instead focused on converting its traditional mechanical capping machines to all-electric technology to better serve customer needs. Based in Lincolnshire, Illinois, the firm designs and constructs custom, high-speed assembly machines for the food and beverage, consumer packaged goods and pharmaceutical industries. 

Mechanical capping machines are designed to screw the cap onto all types of containers at high speeds — from small glass vials in pharmaceuticals to large caps for gallon jugs — using a specified amount of torque. Central Machine’s unit topped out at 300 caps/min., with typical running time maxed at 275 caps/min. to avoid any unscheduled downtime.

In addition, the mechanical version meant having to manually calculate when to adjust the machine, lubricate parts and schedule periodic replacements. And its rigid design presented other challenges.

“One of the main drawbacks of the mechanical capping machines is their fixed design,” says Peter Kendler, president and CEO, Central Machines. “As a machine builder, we have to be very careful. Once we get too far along the machine design, we do not have the ability to make any changes. As the machine build progresses and the customer requires changes to the design, are we now stuck with a boat anchor? For instance, what if the tightening torque has to change or there is a new requirement for thread capture prior to cap engagement?”

Such mechanical machine designs become a point-of-no-return, where the system is fixed and no changes are possible, he adds.

So, when Central Machine’s customers needed a capping machine with higher production rates compared to the mechanical machines, the company got to work on an all-electric model for increased speed and flexibility.

Servo Technology Steps In

The new unit needed to feed three plastic parts into the machine for assembly using bowl feeders and air conveyor inline systems, and produce 400 assembled units per minute. To meet these requirements, Central Machine used servo technology from LinMot USA Inc., a Technology Partner in the Rockwell Automation PartnerNetwork™ program.

“To produce this many parts per minute, the machine must be able to screw down the part at 2,500 rpm, stop, reduce torque to 1 inch pound, and rotate at 300 rpm until the plastic screw is completely installed without breaking, and then snap the parts together — all in 550 ms!” says Paul Riportella, technical sales representative for LinMot.

By using servo technology, combined with an Allen-Bradley^® CompactLogix™ programmable logic controller (PLC) and human-machine interface (HMI) from Rockwell Automation, Central Machines was able to increase the production rate significantly. The technology also allows users to make changes for speed, torque and force during the assembly process via the integrated HMI.

Mounted on a rotating dial, 30 LinMot all-electric linear rotary servos and 60 servo drives control the varying speeds. The Ethernet communication, motor and control power, fed through a slip ring, provide power and communication to the 60 drives. The drives communicate with the PLC to control each linear and rotary axis. High-speed EtherNet/IP™ communication allows fast, on-the-fly changeovers.

The servo-driven solution provides greater control and consistency. Each servo commands a specific linear height, and then the amount of downward force is controlled on each screw.

“With the LinMot linear rotary servo motor, we are able to control the downward force when screwing the plastic parts together, the speed of the rotary motion, and the amount of torque applied at the final position,” says Riportella. This provides complete control of every aspect of the assembly process.

“All of these adjustments are made possible thanks to the Rockwell Automation HMI and PLC talking over EtherNet/IP™ to the LinMot servo drives,” he notes. “In fact, the customer is able to capture the final cap installation height for each part and use this as one of the real-time quality control checks made on the machine.”

Consistent Results

With the all-electric technology, one benefit is being able to measure the capping torque for each cap closure, allowing for 100% correct rejects, says Riportella. “Consistency of the screw installation is so critical that vision systems are used in real time on the machine to ensure the quality of each and every part,” he adds.

Kendler of Central Machines points out that having instant data from each cap closure to make quick adjustments isn’t the only benefit. “We are also able to inspect flash and other quality control problems and eliminate these issues downstream. Having in-process validation is very nice,” he says.

“Several other capabilities are detecting bent screws — really impossible to do on a mechanical machine without significant additional cost. Even performing color checks is now easy as each part is presented nearly perfect due to the higher precision capping process,” Kendler adds.

With the conversion, the machine now runs at a consistent 400 caps/min. In addition, the maintenance schedule on the new machine “without a doubt, is much easier and more predictable.”

The customer now is able to monitor multiple points. “The spindle (refers to each linear-rotary station) is tracking each cap and able to determine: Is the part fed correctly? In the correct position? Proper torque applied? All done at 400 parts per minute,” remarks Riportella.

In addition, the flexibility the servo technology provides allowed Central Machines to make design changes more efficiently. “We had to change the capping sequence as the design change from our customer required us to come up with a better capping profile,” explains Kendler.

The servo technology and the improved profile means the machine can now rotate caps backwards to determine the beginning of the thread on the screw, prior to rotating forward to screw the parts together. This can help to prevent cross threading, where the cap doesn’t get put on straight, leading to an incorrect sealing. “In addition to being able to prevent this, our linear rotary is able to detect this problem by providing the finished position linear height of the cap to the PLC. This lets the PLC know if the cap was put on correctly or not,” explains Riportella.

All of this isn’t adjustable on the fly or even possible to measure on a mechanical machine.

“Our customer is very happy and expanding their production capabilities,” concludes Kendler. “We are now building more machines with additional capacity and higher flexibility. Each time, we add to our knowledge, and we get to apply additional production process improvements.” 

Based in Lake Geneva, Wisconsin, LinMot USA Inc. is a Technology Partner in the Rockwell Automation PartnerNetwork™ program. Their motors perform highly dynamic linear and linear-rotary motions to increase productivity and minimize downtime.

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