Small wonder: How one ultra-compact servo motor helped solve one big problem

Monday June 02, 2008
Written by
Timing is everything. That's certainly how Dave Hinder feels. Hinder, a technical consultant with Bosch Rexroth, had dropped by ABB's press automation division in Brampton, Ont., to help the ABB controls group with a little problem. The group was looking for a variable frequency drive (VFD) to go in an aluminum fanning nozzle positioning machine for its client, Charleston Stamping and Manufacturing (CSM).

CSM, a metal stamping and manufacturing plant in West Virginia, has a robotic press line where robots pick up pieces of aluminum blanks and place them, one at a time, in the stamping equipment. The blanks sit one on top of the other, and generally have oil on them, which can bind them together. The blanks must be fanned to remove all the oil and ensure that when the robot comes to pick up one blank, it doesn't grab three or four at once.

It may not sound like a big deal if the robot picks up more than one blank, but for CSM, it's a very big deal. If the robot tries to place more than one blank in a press, it may damage the die - costing the company thousands of dollars in repair costs and days of downtime.

ABB supplied CSM with the machine that positioned the aluminum fanning nozzles. Traditionally, this application uses large hydraulic lift tables to bring the aluminum blanks up to the fanning nozzles, which wasn't the most practical solution. ABB created a machine that brought the fanning nozzles to the blanks instead of the other way around.

It was a great idea - with one small problem. The fanning nozzles needed a drive to control them, and the current configuration ABB was using was causing a lot of headaches. The configuration had an excessive amount of wiring for the motor, the switches and the resolver. Since the arm had to stretch out over the product, the cables and cords would get wrapped up around each other. That made for a lot of wire that was costly and difficult to troubleshoot, not to mention a program that had to work in position loops, slowing down communication.

"With all the wire and cable, it looked like spaghetti," says Larry Montag, an electrical project coordinator with the ABB controls group. "As time wore on, the cables and hoses would start to hang and then drop and fall. Then it would get tangled up and replacing it was a nightmare."

The ABB controls group figured the answer was a VFD. When Hinder dropped in that day with a selection of VFDs, he worked up a quote to give the team the drives they wanted.

"For this application, I didn't think servo motors were the right thing, just because of the cost implications," Hinder says. "Servos cost more, so I thought they wouldn't want it."

Toward the end of the visit, Hinder remembered he had a new product to show his clients. Bosch Rexroth had just launched a brand-new compact servo motor, and Hinder thought the controls group might have some use for it in the future.

The timing was perfect. As soon as the team saw the device, they knew they had their answer.

Cutting out the cable
The drive Hinder showed the team at ABB that day was Bosch Rexroth's IndraDrive Mi. A servo motor with an integrated servo amplifier, the tiny drive is designed to use 50 per cent less control cabinet space than traditional drives, and reduce installation effort by 85 per cent.

But what really sold the ABB controls group was the cable. A conventional drive system connects each servo motor back to a different drive in the cabinet (see Figure 1). Add to that cable to power the devices, and there is a whole lot of cable to try and install and troubleshoot.

The IndraDrive Mi, however, uses only one cable for both power and communication. Multiple units can be daisy-chained, with only one cable going back to the power supply and connector box in the cabinet (see Figure 2). The drives have more than 100 technology functions, including integrated motion logic conforming to IEC 61131-3. Suddenly, ABB had seen a whole new range possibilities for decentralized automation.

The ABB controls group decided to give the new drive a shot - if for no other reason than the very simplicity of the drive.

"Usually, when you do any kind of motion control, it's very complex," says Montag. "This one was so simple. And our biggest sell was the way it was cabled."

The ABB team installed the part in machine and shipped it down to CSM. But the real question remained: would it do the job?

The benefits realized
According to ABB's Montag, not only did the drive work in this application, it was the answer to all of the team's problems.

"We could have gone with a VFD, but there's no way we could have the control that we have. It's so flexible for the customer," Montag says. "If they run into problems and they want to program it differently, they could easily do that. They couldn't do it with a VFD."

Since implementing the positioning machine with the drive, CSM has realized a number of benefits, including:
• Increased flexibility: The drive offers CSM unique integration flexibility. It is fully IEC 61131-1 compliant, allowing the company to get it up and running quickly.
• Lower component costs: With less cabling and fewer parts, the system is much easier to install and troubleshoot. There is also a reduced cost of cabling and connection.
• Reduced assembly and installation time: Montag estimates that installing the new drive and getting the machine up and running only took a weekend. The team is planning to implement more in the future at CSM, and Montag estimates a greatly reduced assembly and installation time.
• Reduced control cabinet size: The installation drastically reduced cabinet space for the application, with only one drive per cart. With no need for a big panel, the system fit into the limited space CSM had available.
• Increased performance: One of the keys to the installation was that the main program doesn't have to work in position loops. The local sensors connect directly to the motor/drive, and the system uses fast, independent SERCOS communications to the drives.

In the end, Montag and his team were thrilled with the simplicity of the tiny drive. "We were really surprised at how simple it was. It went very smoothly," he says. "And now it has opened up doors to other applications."

Alison Dunn is the acting editor of Manufacturing AUTOMATION.

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