There is a variety of motion controllers on the market, but which is the right one for your machine? What should you look for? Should you use a stepper or servomotor? To answer these and other questions, let's walk through two applications and select a motion system for each. The first is an X-Y materials deposition system and the second, a multi-axis high speed material handling and labeling machine.

X-Y requirements

The material-deposition machine needs a motion controller that can accurately position a tool head in an X-Y grid and activate a variety of tools using 24Vdc I/O. Tool heads can be suction tubes for liquids or a pneumatically activated pick hand.

A PC will be used on this machine for system setup and data collection. The PC will send and receive high level parametric data, letting the controller handle the low level, fast motion, and I/O functions. The motion controller should be able to store and run several application programs. A Visual Basic or LabView program will be developed as the HMI.

Which controller should we use? Based on these requirements a PCI board-level controller such as the PCI 208 would be best, and for these reasons. For one, it allows fast data transfer from the PC to the motion card which is ideal for data capture, logging, and high speed transfer. A PC-mounted controller uses little panel space. The PCI 208 card has 24Vdc logic I/O ready for interfacing directly with pneumatics, switches, and sensors. It can also control stepper or servomotors scalable to as many axes as needed, up to eight. On the software side, the PCI 208 can have up to seven resident programs that multi-task, while being controlled by an OCX or LabView driver in the PC.

Should we use steppers or servos in the X-Y deposition machine? Technically either would work. But examining a few factors will help determine which is best.

For example, characterize the required machine speed. Move speeds and times are modest and not demanding because of the type of operations the X-Y machine performs.

Define the loads. The load from the tool heads are lightweight and fixed. How much of a factor is cost? The design specs indicate some cost sensitivity.

Is the precision of a closed-loop system needed? Closed-loop control is not a requirement. Hence, these criteria point to a stepper motor running X and Y axes.

Controlling high speed

Our second machine is a high speed material handler and labeler. It needs a motion controller that can operate multiple axes as a standalone system. A small touch screen HMI will be used for operator setup. It must communicate to the motion controller using a simple serial comms such as Modbus. The motion controller must execute resident programs and coordinate multiple machine function at high speed. The motion controller must handle high-speed position capture and make correction moves on-the-fly. Positioning accuracy is critical despite varying product weights. The controller must be easy to program and debug. The controller must handle 24Vdc I/O from sensors and limit switches. Which controller should we use?

Based on the requirements, a stand-alone motion controller such as the MC206X would meet the needs. The MC206X can execute several programs in a multi-tasking fashion to handle the HMI, motion, and I/O functions. The controller has 24Vdc logic I/O ready for interfacing directly with switches and sensors. It can also control stepper or servomotors scalable to more axes as needed. The high level Basic programming makes it easy to perform complex motion.

Should we use steppers or servos for the material handling and labeler? As with our previous machine, look at a few factors to determine which is best. The move times are demanding (less than 50ms) and require high acceleration. The load can vary based on product so the motor must be able to cope. Performance rather than cost is most important. Closed-loop control is a requirement.

We choose servomotors for our material handling and labeling machine. A servomotor has high acceleration and reserve power to best handle the demands of this application.