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Servo Pneumatic Control System
The Servo Pneumatic Control System provides closed-loop pneumatic proportional control for all Bimba position feedback actuators, including rodless cylinders with external transducers.

Actuator Options for Machine Designers

Positioning systems are a critical component of any manufacturing process to ensure that operational procedures continue without interruption.

Positioning systems are a necessity in material-handling operations for feeding, orientating, loading, and unloading—as well as for shifting objects for handling, machining, storage and transport. Automated positioning enhances material handling operations by:

  • Eliminating human error
  • Improving product quality
  • Lowering injury rates
  • Preventing contamination with hazardous materials
  • Allowing movement in places inaccessible to workers
  • Moving heavy and awkward equipment more quickly and easily

However, positioning systems are more than a matter of convenience. Positioning malfunctions could shut down an entire assembly line, possibly resulting in thousands of dollars in downtime or changeover costs—hidden expenses that consume time and labor. In fact, the hourly cost of downtime in the food and beverage industry is nearly $8,000. For the rubber industry, the loss is three times higher. For electronics, it’s more than 20 times greater ($500,000/hr) than it is for rubber. And in the pharmaceutical, automotive, and oil and gas industries, the cost can rise as high as $1.1 million to $3.0 million/hr.

In short, the type of positioning system one chooses could make the difference between costing or saving a company thousands of dollars in the long run. And yet, only 80% of the market uses positioning solutions, perhaps because not all design engineers are fully knowledgeable about available options.

Types of Positioning Systems

Any of several systems that can be used to achieve the positioning goals of particular manufacturing processes. They include:

Multi-position pneumatic cylinders provide hard stops, although they offer very little adjustability once strokes are set. Pneumatic positioning solutions are employed by approximately 70% of the market. They are the least costly option, but stroke lengths typically cannot be changed, making them less flexible than the electromechanical and electropneumatic actuators.

Electromechanical actuators are highly precise but more expensive than multiple-position pneumatic cylinders. They currently serve about 20% of the market because design engineers value the ability to program different stroke lengths for different jobs. This shortens changeover time when one production line must make different-size products. But while electric actuators make up that deficit, they require motors, drives, controllers, and someone to program the different devices.

Electropneumatic actuators, an intermediate solution that add electric-like features to existing position feedback-capable pneumatic cylinders, provide more control than pneumatics, but without the expense or complexity of electric actuators.

Comparing Pneumatic Actuators to Electric

Multiple-position pneumatic cylinders provide the most basic and repeatable mode of achieving multiple stops within the total stroke length. Here, each stopping point consists of a hard stop, meaning, further travel of the piston rod is prevented because the piston impacts the end cap at the stopping point.

Electric actuators employ electrical signals to control the travel of the piston to achieve multiple stopping points within the stroke length. This can lead to less-than-perfect repeatability, depending on the electronics used.

Multiple-position cylinders, on the other hand, stop the piston on the end cap in the same place every time without the risk of interrupted electrical signals. Consequently, this positioning system is an excellent choice for applications where the discrete stop positions are predetermined and unchanging. Their design offers the highest level of repeatability at a relatively low cost.

However, multiple position pneumatic cylinders do not allow for stroke adjustment and, therefore, may not be best suited for applications requiring different stroke lengths for different tasks. For those situations, electric actuators can offer the best positioning solution—but the cost of the system can be quite high. Therefore, in cases where cost may be a concern, an electro-pneumatic system might be a more viable alternative.

Merging Technologies for Closed-Loop Control

Today’s automated intelligent machines often require a high degree of configurability to perform multiple tasks. Accordingly, pneumatic positioning systems have now been designed to employ the latest integrated sensors and controls to generate motion patterns that mimic the electric actuators needed to regulate signaling—but at a significantly lower cost.

By merging pneumatics with electronics, one can greatly expand the use of pneumatics to provide flexible, nimble, positioning control systems. This leads to better utilization of equipment, less downtime when changing applications, and lower changeover costs (which, as already mentioned, can be staggering). What’s more, reducing changeovers increases production throughput, so resources and labor can be reallocated for other tasks.

And, finally, electropneumatic systems are easy to retrofit into existing pneumatic systems and offer higher load and speed capacities than electromechanical actuators do. They also provide hard stops and accuracy approaching electric levels.

However, electropneumatic systems require electric power, and their software must be programmed for each new application. They also cost more due to their higher technology and expanded flow rates, but again, they cost less than electromechanical actuators do.

The SPCS Alternative

A significant advancement in this field is the Servo Pneumatic Control System (SPCS)—a high-flow pneumatic motion control valve that, when combined with a position feedback actuator, provides a closed-loop positioning control system to quickly and accurately place a payload. These systems have been specifically designed to obtain the best possible uses of equipment. The features and benefits of SPCS include:

  • Continuous closed-loop system with easy-to-configure software
  • On-the-fly adjustments with software controls
  • Horizontal and vertical loads cycled accurately and repeatedly
  • Wide operating range (0 to 150 psi) accommodates higher and lower forces than other electropneumatic controls
  • Compatible with most pneumatic cylinders, up to a 3-in. bore, for additional application flexibility

Conclusion

Clearly, there is a wide range of options available to achieve positioning functionality with pneumatic and electric actuators—from pneumatic multi-position cylinders to electro-pneumatic systems, to electric actuators with either stepper or servo motors. The best positioning solution is always dependent on the individual application and the level of positioning accuracy and repeatability one is attempting to accomplish. Other considerations include cost, complexity, load, speed, precision, location, and similar variables.

Some applications can perform and thrive using multi-position cylinders. Others require the feedback and robustness of the electro-pneumatic system, while still others require the enhanced position, programmability, and repeatability found in electric actuators.

No matter which positioning application may be appropriate for the task at hand, the first step in selecting a positioning cylinder solution is to identify a reputable cylinder manufacturer that understands and makes available all the various positioning technologies, and is able to recommend a solution that best meets the overall needs of the application.

Molly Lynch is regional sales manager at IMI Precision Engineering, Bimba Mfg. Co., University Park, Ill. For more information, visit www.bimba.com.

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