What to look for in today's robots.

General-purpose parts-removal robots are pretty consistent in speed, payload, and price range. The buyer's key choices come down to drive type, programming, and basic mechanical design.

Vendors of injection molding parts removers may bombard you with speed and accuracy specifications, but don't be too surprised if you find a great deal of overall similarity among general-purpose robots in the same size range. In fact, many general-purpose robots share similar, and even identical, components. Vendors are quick to point out that those similarities disappear when you start shopping for high-performance robots and those dedicated to a specific task.

"Right now, every vendor has an acceptable general-purpose robot," says Norton Kaplan, sales manager at Automated Assemblies Corp. "General-purpose" encompasses three- to five-axis beam or traversing-type robots designed to serve molding machines in the 150- to 400-ton range and capable of pick-and-place operations with take-out times of roughly 1-2 sec. Robots from a wide variety of vendors can handle basic parts-removal chores, with the possible exception of some packaging or other high-speed applications.

Prices of typical robots are also fairly consistent across the marketplace. For most vendors, this class of robots spans a price range between $15,000 and $45,000, depending on what kind of drives you pick.

Only when you delve into the finer points of robots' performance and look at the details of their mechanical design, drive packages, and controls do differences begin to emerge. Bear in mind that some of these differences become more important as you ask the robot to do more than just pull parts off the machine.

WHAT KIND OF DRIVE?

Just a few years ago, general-purpose robots generally employed pneumatic drives on all three axes. Nowadays, however, this versatile class of robots has expanded to include a wide variety of drive types. Molders today demand more flexible automation systems that can handle assembly, packaging, decorating, and all the other value-added work beyond simply picking a part from the tool. That's because processors today are looking beyond their immediate needs when buying a robot. "Molders are thinking more about what they could run in the future," says John Vandenbergh, commercial v.p. for automation at Conair. As a result, even general-purpose robots increasingly have an electric drive - whether AC frequency type or true servo - on one or more axes.

Yushin America president John Mallon notes that servo robots already make up half of Yushin's sales volume and their sales are growing by nearly 10% each year. "In five years, you won't find pneumatic robots except in high-volume dedicated uses," he predicts. Other vendors report similar rates of growth for entry-level electric robots.

When choosing from among robots having one or more electric drives, the fundamental distinction is between a true servo robot or one with frequency drives. Not all vendors offer frequency drives, but those that sell both kinds of electric drives report a roughly $6000 price premium for the servo type. According to David Preusse, general sales manager of Wittmann Automation, servos' chief benefits are the ability to program curvilinear motions, which can provide cycle-time savings and enable more complex automation tasks such as some types of assembly operations or insert placement. Frequency-drive robots can do much of what the servos can, including stacking and palletizing. "Unless you need the curvilinear motion, you could be better off with frequency drives," says Preusse.

IS IT EASY TO USE?

Aside from performance specs, robot vendors also like to talk about ease of use. This emphasis isn't surprising, given uncertain skill levels on some shop floors. Explains Kaplan of Automated Assemblies, "There has been a big culture change. Five years ago you would call in an engineer for what the average support person must do today."

Ease-of-use can be a slippery concept, especially when it comes to controls. Many vendors have recently sought to make robot programming easier by moving to a graphical programming environment - Yushin and Automated Assemblies are two examples. Others, like AEC, Sterltech, and Conair, have tackled the problem by devising plain-English programming languages. Your best bet with controls, however, is to try out several types to make sure you and your technicians can work with the robot's on- and off-line programming language.

Also, if you do opt for a robot with servo drives, make sure it's freely programmable so you can create entire sequences, not just teach points. "Just teaching points is not real programming," says Mallon. "You need to be able to create unique sequences too."

Also, don't forget to check on the availability and quality of aftermarket training. With general-purpose robots having so many features in common today, support can make all the difference, says Kaplan.

PICKING THE RIGHT DRIVE

Application Needs                       Drive choices

Sprue or runner removal for 100%        Sprue Picker, Pneumatic
part and runner separation.

Simple part removal with limited        3-Axis Pneumatic
flexibility, such as removing a part
and placing it on a conveyor.

Place parts in a row on conveyor,       1-Axis Electric (horizontal)
with multiple mold changes. Remove
parts and place in several positions
on conveyor requiring multiple stops
along the horizontal axis.

Palletizing parts at the press.         2-Axis Electric
                                        1-Axis Servo (for long
                                        cycle)
                                        3-Axis CNC/Servo (for short
                                        cycle)

Boxing parts at the press with          3-Axis CNC
multiple positions and layers.

Automation cell where secondary         3-Axis CNC
equipment can be simplified or          2-Axis CNC
eliminated with the use of
programmable robot.

Insert molding.                         3-Axis CNC/Servo
                                        2-Axis CNC
                                        1-Axis Asynchronous

(Source: Conair)

HOW IS IT BUILT?

General-purpose robots should have features that keep downtime to a minimum. You will find differences in mechanical design between robots that come from different suppliers, but there appears to be no easy way to assess the manufacturers' claims for reliability.

Some makers use belt drives, some have ball-and-screw systems, others rack-and pinion, and still others use combinations of all three. Linear bearings come in all sorts of proprietary and off-the-shelf designs, and vendors tout the advantages of their particular system. The best advice, says Conair's Vandenbergh, is to check references from other robot users and "try before you buy."