IEN: Please describe the pros and cons of the PROFIBUS and SERCOS specs.
Zenner: Right now the PROFIBUS profile is widely accepted in most parts of the world. SERCOS, which has its greatest application in North America, runs on fiber optics and can be a better choice in some machining applications where synchronization is required.
When LinMot, Inc started out in Europe, we used for communications modes serial (RS232/485) and PROFIBUS. We next added CANopen profile because of its acceptance in micro processing manufacturing. Next came DEVICENET (Allen-Bradley/Rockwell) when we entered the U.S. market.
Though we are looking closely at SERCOS, we are leaning toward Ethernet as our market becomes increasingly more globalized. Consequently, Ethernet is becoming the accepted BUS.
IEN: What are the R & D hotspots, and which R & D areas are closest to market?
Zenner: The packaging and material handling applications we are working with -- and responding to -- are looking for more speed and reliability along with greater ease of application.
Technology LinMot is working with and developing to meet these missions include:
- Low-cost tubular linear motors with acceleration of 45 g''s. The LinMot P01-48 family of linear motors (an example is shown here) is a totally different design, having both magnets and coils in the stator. Along with high acceleration, these motors generate up to 135 lb of force and can reach speeds of 175 in./sec.
- In principle, LinMot linear direct drives are not subject to wear and tear, unlike air cylinders. When properly applied, these linear motors are capable of an operating life of over 1 billion cycles. Air cylinder systems involve piping systems that can invite trouble and take up space in the setup. Furthermore, the linear motor is comprised of just two parts -- the stator and the slider -- with no seals to wear out. Additionally, there is no mechanical connection between the slider and the stator and linear movement is produced directly by electromagnetic forces.
- The recently introduced E-1100 servo controller line offers simple configuration for linear motor operation through a Windows environment. The user can set up the controller to tell the linear motor how far and how fast it can operate; and how much force it can generate. The user makes the settings and the controller does all the necessary calculations. During operation the controller monitors a wide array of parameters, including current, heat, send voltage, and following error. Should the motor exceed preset limits, the controller will either issue a warning or shut down operation.
IEN: How can users implement preventive or predictive monitoring in motion solutions?
Zenner: Because of the high speed involved with linear motors, these parameters are hard to follow with the eye. Many of our controllers include an oscilloscope, which can capture the event to determine what is happening.
The key to trouble-free operation is accurate, up-front specification for the application. LinMot offers their specially designed Sizing Software as the means for linear motor selection. Using this program, the user can plug in a number of operating variables including motor type, number of motors, and the type of servo to be used.
The software will tell the user the limits to the products you are trying to size, and if those limits are being exceeded. If so, rest assured, the motor choice will not work. Fall within those limits and it will work. It''s just that simple.
For an application, the Sizing Software will indicate the heat generated and if a fan is needed to dissipate it. Turning to the question of power, say the program indicates each motor in a 4-motor system requires 32 watts, indicating a 150 watt motor needs to run the operation.
IEN: Please discuss the benefits and drawbacks of centralized and distributed architectures.
Zenner: Each has its place, depending upon the application. The user has to consider communication speed, complexity of wiring, and troubleshooting. With a very large machine or system, it may be desirable to have all the troubleshooting at one central point, making centralized architecture preferable. But if the machine is made up of a collection of components, it might be best to decentralize so control is right where the event is occurring. For example, decentralized architecture would be the choice for an application where product is being stacked in one area.
Distance and workflow can also be considerations. Say a machine or system is rather large. Technicians would want to have the ability to do troubleshooting right at the location where the function is being performed, rather than having to track it from a central location.
If the operation involves a continuous flow of product such as on a printing press, the diagnostics should be fed to the central controller. In case a problem happens at any point in the run, the whole operation has to be shut down to prevent backups and additional trouble at other points in the line.
On the other hand, in a case where the process involves accumulators at various points, the system can be decentralized.
LinMot, Inc is a manufacturer of linear motors, guided actuators, servo controllers, and MagSpring constant force springs. LinMot motors provide extremely long life, high dynamics, and high repeatability at a moderate cost. Designed for washdown applications, these motors are widely used in packaging, material handling, and the health care industry. Multiposition controllers are available for single or multiaxis control, in a variety of field buses, and are easily programmable for even very complex motion profiles and multiple programs.