There are two kinds of systems that are easy to use: Inherently simple equipment, and more highly engineered “total solution” systems. Here, we'll discuss the latter — and how to make sense of the myriad of options and features available to machine builders.

Let's say an engineer has the luxury of abstracting motors into simple devices that create motion from a voltage signal. Well, brush motors, despite their wearing parts, are certainly the easiest to setup and control. “Applying sufficient voltage to the terminals causes the shaft of the motor to rotate for simpler control schemes,” says Patrick Dell, applications engineer at MicroMo Electronics, Inc., Clearwater, Fla. Indeed, open-loop speed control requires little equipment — sometimes just a battery is enough. “Small brushed motors run in many applications requiring little more in the way of control,” says Dell. To control motor torque, however, more complex circuitry is required to regulate the current in the motor windings.

“Now, sometimes ac inverters have open-loop vector modes that works better pushing simpler constant-torque loads such as conveyors — in addition to adjustable voltage/frequency output that works well with variable torque loads, such as centrifugal pumps and fans,” says John Malinowski, Baldor Electric Co., Fort Smith, Ark. Increasingly, there is a push towards these “smart” components that incorporate multiple logic functions. And with designers today being asked to absorb more engineering responsibilities from their customers, these systems can be very helpful. “OEMs can't save money by acting as integrator. With the algorithms in many devices today, software can automatically program setup at a cost of $200 or less,” says Rich Mintz, U.S. products manager at SEW-Eurodrive, Lyman, S.C. He argues that no OEM could engineer a setup for so little. Integrated, preengineered systems can save weeks of programming and debugging complicated machine control applications. When designers purchase separate motors, encoders, reducers, and brakes, OEMs must act as integrators and are tasked with the sometimes-difficult job of making everything work together. “When, for example, gearmotor and control are a matched package, with self-tuning algorithms and application routines, then it can take as little as two minutes to set up a system,” says Mintz.

In any case, it doesn't make sense to look at any system apart from the mechanical or electrical perspective. “Just as one can never describe an elephant by looking only at an ear or a leg, looking at a motor in isolation never gives you the right solution. You have to look at the entire system and what you're trying to achieve,” explains Mintz. “When you stop seeing standalone components, then you can achieve the greatest precision and efficiency in performance,” he adds. “The motor is only a tool to make something happen; what you're really trying to control are parts to which it's connected.

If a PLC, motion controller, I/O, motion network, drive, and motor each require significant custom programming and record keeping, the control architecture is less easy to use. “On the other hand, advanced auto-tuning algorithms are invaluable to commissioning the axis as quickly as possible,” says Adam Shively, product manager at Rockwell Automation, Eden Prairie, Minn.

Some controls operate right out of the box; simply plugging in motor parameters allows these controls to autotune. “New guys don't realize that setting up a control was once difficult and painstaking, sometimes taking three or four hours,” says Jeff Lovelace of Baldor Electric Co. The software provided with controllers today greatly influences how easy a system is to setup, control, and troubleshoot. “Good setup wizards allow users to configure systems without digesting a PDF treatise,” says Dell.

After setup, if load changes, adaptive tuning continually adjusts and optimizes control loops. Some servomotors utilize feedback devices to provide automatic identification of correct motor-to-drive connectivity, reducing commissioning time and simplifying maintenance. “High-resolution encoders offer higher-bandwidth performance and smoother motion, with multi-turn options available to eliminate homing routines and associated sensors,” explains Shively.

Diagnostic tools allow quick resolution to simple wiring and even some logical issues. Real-time graphs — capable of plotting position, velocity, and other key variables — make writing effective programs much easier,” adds Dell. And any control algorithm that improves the controllability or observability of the overall motor/drive/controller system makes that system inherently easier to use. “Algorithms such as field oriented control, state space observers, and auto tuning fit this bill,” explains Rick Dye, development engineering specialist, Ormec Systems Corp., Rochester, N.Y. Auto commissioning software that can detect and adjust for offsets and phasing errors between motor and feedback cabling greatly simplifies connecting a motor to a drive. “This type of software can also be used to measure motor parameters such as pole count, feedback resolution, resistance, and inductance. This can greatly reduce the time it takes to get a motor spinning under control,” adds Dye. Diagnostics can come from sensors, too. “Some sensors also integrate diagnostics, visual LEDs, and even serial or wireless communication for local or central plant control diagnostics,” says Bo Watson, applications and field service engineer at MTS Systems Corp., Cary, N.C.

All this said, controls can be overspecified: “Their expensive bells and whistles (that can even confuse end users) leads to extras that often don't fit needs — and frustration and down time,” warns Chris H. Medinger, stock product manager at LEESON Electric Corp., Grafton, Wis. Complex routines may require a greater degree of understanding of the controller and the routine than is necessary or warranted. “And sometimes, motion control is the same whether you're moving bottles or cars. So in these situations, canned application routines developed by suppliers already familiar with these operations can be useful,” says Mintz. In fact, common applications such as turntables, winders, and indexing act similarly from application to application; simple precanned routines allow use of limited, non-realtime CPUs here. “But users shouldn't be forced to make applications fit software or hardware constraints. Otherwise, savings from a less sophisticated controller are quickly lost on creative workarounds,” warns Dell.

Down with potentiometers

Analog sensors are the original plug-and-play devices, but always require some adjustment. This used to involve tedious physical tuning or trimming via potentiometers — turned by a screwdriver — or switches,” Watson says. Other sensors with more functions have a series of small DIP switches, usually inside the sensor, that the user flips. But newer sensors can be configured remotely, so control engineers don't need access to the sensor itself: “This is particularly useful in hard-to-reach areas. “The controller stays in an accessible location, attached by wire to a sensing head located at the difficult inspection site,” says Lee Kielblock, senior applications engineer, Banner Engineering Corp., Plymouth, Minn.

Microprocessor-based units do offer more programming flexibility. “However, confusing programming and communication options can blur sensor-to-system functionality and compatibility, often leading to painstaking electrical diagnosis,” explains Watson. Sensors that incorporate analog feedback can be less complicated during the design and installation process. “Digital and fieldbus sensors require more setup time and a more intimate knowledge of the communication platform.

What sensor feature boosts ease of use most? Configuration. “Some single-function sensors have push buttons that users simply press to initialize or teach sensors — teach being an industry buzzword,” says Kielblock.