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Tube & Pipe

A premium on precision

By Lisa Rummler

March 2009 - In the kitchen, people strive for deliciousness, even if it comes at the expense of accuracy. If a teaspoon of cinnamon tastes better than a tablespoon, for example, both amateur and professional cooks will likely sacrifice the excess to create the best-tasting dishes.

On the job shop floor, manufacturers and engineers don’t have this luxury--with forming and fabricating, accuracy matters. And when the particular application involves measuring velocity, position, pressure or any combination thereof, it’s crucial to be as exact as possible.

To ensure precision when measuring these sorts of things, it’s important to have the right tools. One such device is an electro-hydraulic motion controller, such as the RMC75E from Delta Computer Systems Inc., Vancouver, Wash.

"The key to making a hydraulic system move smoothly and precisely is doing closed-loop motion control," says Bill Savela, motion products marketing manager at Delta. "That means that we’re looking at a sensor or a series of sensors. Those sensors feed back into our motion controller, and then the controller determines what kind of signal to send back to the actuator, which is typically a proportional or a servo valve."

This valve often controls a linear motion device, such as a hydraulic cylinder. Taken together, the motion controller, the valve controlling the cylinder and the sensor, which is looking at the absolute position of the cylinder, become the closed loop, says Savela.

The base module for the DIN rail-mounted RMC75E is about 3.5 in. wide and 4 in. tall, but by adding expansion modules, the product’s size--and what it can do--increases. In doing so, users can build motion controllers specific to various applications, allowing them to have precision while they build a product.

"You might be pressing a metal into a shape, you might be cutting a log into different-sized wood products, you might be lifting a heavy piece of equipment on an oil-drilling platform or extruding plastic onto a mold," says Savela. "There are applications in a whole variety of industries where it’s important to have precision of motion for positioning or speed or applying pressure to reshape something."

All the right connections
The RMC75 series of motion controllers is available with three means of communicating to other computers or devices on the factory floor, determined by the letter at the end of the product name: E, P or S. These stand for Ethernet, Profibus and serial communications, respectively.

"These options specify the highway or communication method that allows us to ‘talk’ to other devices," says Savela. "The typical system needs to have some sort of human-machine interface, or HMI, which allows a machine operator to give commands to make the machine work or to monitor the machine’s progress. And there may be other things going on in the application that require a programmable logic controller, or a PLC, as well. PLCs can be used to provide overall supervisory control of a factory system, sometimes providing detailed lists of motions to be performed to the motion controller."

Drilling it
For two recent projects involving tube and pipe, industrial system integrator Advanced Machine Automation, Birmingham, Ala., went the Ethernet route, using the RMC75E.

One project started about a year ago, according to Keith DeMonia, general manager. It involved thermal drilling of thin-wall copper tubes that ranged from 3/4 in. to 5 in. in diameter. The tubes were used to make heating, ventilation and air conditioning units used in dairy cases at a major retailer.

"The HVAC units have a big tube that goes across the top and smaller tubes, called down tubes, that tap off of it," says DeMonia. "Coolant liquid comes in at the top, and then it flows down through the down tubes as air is blown across them by a fan to get the cooling. In the old days, it was customary in making the tube assemblies to simply drill holes in the tubes and solder them together. But this was an imprecise process that often created a lot of leaks."

The copper company that supplies the HVAC units asked Advanced Machine Automation to develop a machine that would make the joint between the down tube and the top tube more rigid and reduce leaks. In response to the request, Advanced Machine Automation developed a special drilling machine that used a process called thermal drilling, using a special thermal drill bit from Flowdrill Inc., St. Louis.

Rather than removing metal during the drilling process, as a conventional drill bit does, thermal drilling makes holes by melting the material being drilled because of friction. The molten metal builds up around the edges of the hole and makes a more substantial surface for soldering or tapping.

"The company was working with copper that had really thin walls," says DeMonia. "It was easy to ding, and they didn’t want it distorted so we had to move the thermal drilling bit very carefully. Initially, we used the motion controller to move the bit in until it just barely touched the product. Once we touched it, we set our drilling measurement to zero. Then we started the bit to rotating, and we drilled the hole to a predetermined depth. Our controls engineer, Jason Woyak, did all this by programming the motion controller to use pressure and positioning information from sensors attached to the drilling mechanism."

Because of the improved tubing assemblies made possible by the drilling system, the number of leaks went down dramatically, according to DeMonia. And in addition to enabling better quality control, efficiency also increased.

"The manufacturing process is a lot quicker now because the precision of the thermal drilling process enables the use of an automatic soldering machine," says DeMonia. "So rather than requiring a whole line of people to do manual soldering of the tubes, the company has just a few people pre-assembling the tube assemblies and setting up the soldering machines."

Hands down
In March, Advanced Machine Automation completed a project involving aluminum handrails using another RMC75E. Specifically, the customer wanted holes flow-drilled all the way down the length of a 24-ft. pipe. "The thing that made that project unique was that our customer wanted to maintain an accuracy of ±0.007 in. in positioning the holes," says DeMonia. "The only way we could take measurements on a pipe that long was to use a long linear transducer, which doesn’t have that kind of accuracy, but does have repeatability, meaning that once the desired hole position is matched with a feedback value from the transducer, it’s possible to repeatedly drill holes in precisely the same position from pipe to pipe by referring to feedback from the transducer. Using the data that we got off the test of the linear transducer, we built a matrix inside the motion controller."

The matrix told DeMonia and his team how much positioning error to compensate for to precisely put the drill bit in the correct position for each hole, based on the historical data.

"Every time the drill bit was moved, the motion controller would look at the position, and it would take the error value out of the file," says DeMonia. "It would add that to the measurement from the transducer and use the result to move the drill bit to the proper position. In this way, we were able to maintain a ±0.007-in. positioning accuracy over the full length of that 24-ft. part."

Automating the drilling process using a motion controller allowed the handrail company to increase production 150 percent, according to DeMonia.

Emphasis on education
Savela says Delta Computer Systems prides itself on training customers on how to use the company’s motion controllers. Delta delivers this information using classroom instruction, face-to-face training and live webinars.

Beyond educating individuals about the functions, features and capabilities of Delta Computer Systems’ products, the company strives to make its customers comfortable with using the products.

DeMonia says he and others at Advanced Machine Automation have participated in Delta’s training sessions and that the knowledge they gained enabled them to better teach other employees how to use the devices.

Specifically, DeMonia attended a local training course when he first came to Advanced Machine Automation, and later, he and one of his electrical engineers traveled to Vancouver, Wash., for an advanced training course at Delta’s headquarters. He says this allowed them to offer more extensive service and technical support to both other companies and nearby college students.

"The programming for the Delta motion controller is easy," says DeMonia. "When I hire new people, it only takes me three or four hours to train them to program it, and then they can do all the programming. In fact, we offer classes on Delta programming to the local college, Jacksonville State University." By providing one credit hour to students, DeMonia says Advanced Machine Automation seeks to do what PLC companies have done to help sell their products.

"They went in and started training young adults in colleges so that when they came out of college, they would be familiar with their products," says DeMonia. "The graduates would go to their employers and say, ‘This is the brand I want because I’ve had training in it so I know it better than anything. That’s an investment we love to make because it provides the industry with loyal and experienced resources that we can tap over the long term." FFJ

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