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Do the linear motion

March 3, 2005
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Little Eva would be impressed by the evolutionary changes in sanitary, linear-motion conveyors.

P. Blake Svejkovsky, product manager-product handling systems, Heat and Control Inc., Carrollton, TX
Around the Texas home of the Svejkovsky family, the running joke is that horizontal motion conveyors aren't rocket science, but having a NASA engineer around to conceptualize the design doesn't hurt.

P. Blake Svejkovsky has been around snack-food conveyors all of his professional life. After graduating from Texas A&M University in 1985 with a degree in mechanical engineering, he worked for Frito-Lay and then Triple/S Dynamics, specialists in dry bulk material separation and conveying for process industries.



In the 1980s, high-speed, multihead weighers brought new packaging precision but also exposed the limitations of belt conveyors, setting off a wave of innovation in linear motion. Vibratory conveyors with simple mechanical drives were the first solution, though product damage and dusting issues posed problems for coated products and precluded their use entirely for delicate goods. Horizontal motion conveyors with inertia drives followed, but they created almost as many problems as they solved. Long-run units couldn't feed packaging machines at an optimum rate, flexibility was an issue and product breakage was sometimes aggravated because of the gate configurations. A more modular approach was ushered in with the introduction of electromagnetic drives, followed by direct drives and servos. Svejkovsky and his father, Paul, have been innovators in direct drive and servo applications, with much of their work on behalf of Hayward, CA-based Heat and Control Inc.

Also a mechanical engineer, Paul Svejkovsky is a former staff member at the National Aeronautics and Space Administration and at Lockheed. His name appears on 19 US patents, nine of which list his son Blake, as well. Those joint patents primarily involve refinements and advances in the field of horizontal motion conveying.

FE: Wouldn't a slow-moving belt conveyor outfitted with a variable frequency drive be just as effective in feeding product to weigh scales as a linear motion conveyor?

Svejkovsky: The problem with a belt conveyor is sanitation. Some materials stick to the belt, and ingredients tend to become trapped in the metal or plastic mesh. If it isn't removed, it comes back after traveling the length of the underside, creating a possible cross-contamination issue.



Offset pulleys in an eccentric drive provide the slow-forward, fast-backward motion that significantly improves conveying speed in the newest generation of horizontal motion conveyors. Source: Heat and Control Inc.
FE: How was sanitation addressed?

Svejkovsky: Aluminum or stainless steel pans on vibratory conveyors with simple mechanical drives were the first solution. Sanitation was improved, and the efficiency of the feed to vertical form/fill/seal machines was greatly improved, though feed rates could be uneven. Unfortunately, product damage increased dramatically, and expensive seasonings and coatings often were knocked off and would build up on the pans. They also are very noisy.

Inertia drives for horizontal motion started to take off in the late 1980s. Great reductions in product breakage and seasoning losses made them popular in many manufacturing segments. By the mid ‘90s, most pretzel manufacturers were using inertial drive horizontal motion. But long runs and slow travel rates were a problem, and the long pans tended to crack. They also couldn't convey product uphill at a respectable rate, and the overall feed rate to packaging machines resulted in line productivity declines of as much as 4 percent.

FE: What was the solution?

Svejkovsky: Two technologies came along-electromagnetic drives and direct drive, which we named the FastBack conveyor. With electromagnetic systems, vibration is created by a spring with a magnet that creates a forward and up motion to cause product to skip. Vibration occurs at up to 1,800 RPMs, which is almost imperceptible to the eye. Travel rates are faster than with inertia drive, and the drive requires less maintenance. The modular approach used also improved throughput on packaging lines. Unfortunately, the short amplitude, high-frequency vibration of the electromagnetic drive creates maintenance issues, and product breakage can be a problem.

With direct drive, the rotation of the motor shaft is transferred by a universal joint to an output shaft that alternately rotates at a slow and a fast speed. A crank connects the output shaft to the conveyor tray, pushing it slowly forward and then quickly back. The trays have a modular design, and the flexible drive platform accommodates multiple pan sizes for future flexibility. Travel rates are higher, and the gate system helps keep product breakage to a minimum.

FE: How did the design of the direct drive come about?

Svejkovsky: After Thanksgiving dinner in 1992, I was sitting around with my father and uncle, eating turkey sandwiches, when my uncle asked me what I was up to at work. I was working at Triple/S, and explained the basics of inertia drives and the problems we had with scale feeding. As engineers tend to do after Thanksgiving dinner, we got the napkins out and started doodling various design solutions. I knew the market requirements, and my father had the concept. Two weeks after Thanksgiving, he showed me a plywood prototype he had built.

My father filed and received a patent for the drive mechanism in 1994, and we literally built the conveyors in our garage. By 1995, when Heat and Control approached us, there were only a handful of FastBacks in operation in the world. Paul and Blake Svejkovsky weren't going to change the world, but Heat and Control could, so we went to work for them.

FE: Why didn't you apply a servo drive instead?

Svejkovsky: We actually patented a servo drive with a pair of counterweights on opposing sides of the drive shaft in 2002. The problem with a servo is that, when the drive tells the pan to go back, the pan still wants to go forward, and servos don't handle that well. You don't get anything for nothing. For every action, there is an equal and opposite reaction, and to prevent premature wear, you have to slowly reverse direction, which means product travel rate is reduced, maybe as little as 10 to 20 feet per minute. Counterweights help, but we weren't satisfied with the results.

FE: Now that you're part of a larger organization, how has the R&D effort changed?

Svejkovsky: We're now part of a group that has been issued 12 patents since 1995. Some of them relate to gate mechanisms for the linear motion conveyor, and we've contributed to a seasoning system for coating food products. We also developed a second generation FastBack based on an eccentric drive. It was a four-year development project, from mathematical models to prototypes to beta testing. A lot of people were involved, including Tom Knodell, the lead development engineer, and Ken Petri, the engineering manager. Both of those engineers played significant roles, but the total package reflects a team effort involving eight to ten people.

FE: How does the eccentric drive work?

Svejkovsky: It's a little like the gears on a bicycle: one cycle on the front gear results in three revolutions on the back gear. It's the same with this drive, except there are two offset pulleys and a timing belt. When the pulley is on the long side of the belt, the opposing gear turns very slowly. When it's on the short side, the opposing gear has to move very fast.

It's more robust than the original direct drive. The universal joint has been eliminated, and product can be moved at up to 40 feet a minute. It's easier and safer to suspend the units from a ceiling: a 12-ft. conveyor weighs 600 to 1,000 lbs., depending on the width of the pan, compared to 1,500 to 1,800 lbs. for a comparable vibratory conveyor. The same drive can be used with a variety of pan widths and lengths of up to 35-ft. long. As a result, there shouldn't be a bone yard of conveyors that don't fit the process anymore in the back of the plant.

FE: Given your group's innovations and patentable concepts, it seems inventiveness may be genetic.

Svejkovsky: Of course, my father's work has been much broader than material handling. He developed a hydraulic valve for prosthetic arms and was one of six engineers whose names are on the patent for the rotary blood pump for heart patients. He also was involved with the miniaturized ventricular assist device, which applies shuttle technology developed to pump liquid hydrogen to space shuttle engines. The device is the size of two AA batteries. It boosts blood pressure without damaging the blood. Researchers from Baylor University's College of Medicine were involved with the project. When NASA honored my father, I had the opportunity to meet heart surgeon Michael DeBakey, who provided much of the project's medical expertise.

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