The simplest way to upgrade an existing machine is to use a servo/stepper drive with discrete inputs for commands. The existing control wires for the solenoids can be wired to the servo/stepper drives. Such discrete wiring would make sense in scenarios where the axis count is low.

For a typical double-acting cylinder, the PLC outputs a 24 VDC signal to a solenoid valve to tell the cylinder to move to extend. Once fully extended, the sensor will give an input back to the PLC that it has reached the target position. A second signal from the PLC will tell the cylinder to retract, with another signal from a sensor confirming the movement is complete.

This could all be done with a servo actuator as well. The servo/stepper drives can be configured so that when an input 1 comes on, the actuator moves to position 1, and then when input 2 comes on, it will move to position 2, and so on. When the actuator reaches the desired position, the servo/stepper drives can signal to the PLC it has reached the position. All the motion profiles will all be stored in the servo/stepper drives. With the introduction of a few handshaking signal and the existing valve signals, the PLC would be able to easily control the actuator with minor programming changes.

Whether the incremental improvement is worth the effort will depend a lot on what the user is trying to accomplish. For instance, if the machine is going to have to run products of various sizes and configurations, adding flexibility that servo/stepper drives could bring would be highly desirable. If there was a desire to reduce air consumption or even eliminate the need for a compressor this again could be well worth the effort.

Using servo control in a packaging line can have significant benefits. One can be eliminating or reducing the amount of compressed air used on the machine or in the plant. Capital equipment cost savings can be achieved due to the reduction of compressor capacity required (use smaller compressor) or by eliminating it in total.

Servo control also permits finer control, as the servo actuators are able to be controlled more accurately than a simple two-position pneumatic actuator. What this does in a filling application is that it can result in more accurate fills, thereby reducing costs by eliminating wasted materials.

In a packaging application, this means reduced changeover time and more accurate movements during, say, case packing and palletizing. The reduced changeover time brings added flexibility to the machine, maximizing the machine’s productivity.

As with all solutions depending on the application needs there can be disadvantages by going to an all-servo-controlled system. A servo-controlled system will have a higher initial cost than a simple two-position pneumatic type system. If there is no air for the machine and vacuum is required–for picking up slip sheets or grabbing case flaps, for example–then the initial and operating costs of a vacuum pump must now be considered, as opposed to a low-cost vacuum generator.

Another disadvantage to a servo system specific to a juice line is the environment. A juice line is a food environment and tends to be sticky. Electric actuators are not as well suited for food-grade and/or washdown environments as a pneumatic system, which can have the electronics put into a nearby cabinet. The electric actuators may also need to be food grade, and there is not that large of a supplier base for these actuators, limiting the number of choices.

As compressed air is one of the most expensive sources of energy in a plant, optimum sizing and selection of air preparation equipment is critical to minimize waste and operating cost. Reducing the cost of compressed air pays off handsomely and therefore education is key to selecting the most suitable components for the correct places and sizing them.

The correct sizing of compressed air preparation equipment should generally be carried out on the basis of the following criteria: Quality, Quantity and Pressure.

Also consider these fundamentals:

- Air quality should only be as good as necessary.

- Lubricate the air only when absolutely needed (that is, air motors or very fast cycling and/or long stroke cylinders) and then as close as possible to the load device.

- When possible, use module joiners to match units of different sizes in air prep component families to save space and cost of these and to increase productivity

- The pressure dew point of the compressed air must be at least 3-deg C lower than the ambient air to prevent the formation of ice in the expanding air.

Quality:
Consult the ISO 8573-1:2010 standard to determine what quality levels you need for the accurate selection of filtration and/or drying components. It is especially important to define air quality classes in cases involving requirements for finely filtered or/and low dew points.

Quantity:
To define an adequate flow rate of the air prep components, consider the type and number of load devices and their necessary working pressure requirements. After summing up the total required flow and allowing for possible leakage and a certain safety factor, you can now select the required components based on the flow values provided by the equipment manufacturer.

Note:
- When using air dryers, pay particular attention that flow rates also depend on the dew point to be achieved.
- Consider the use of flow sensors; blocked filters are costly and are often remain unnoticed for some time.

Pressure:
Over/under pressurization is expensive and can quickly damage a system and it’s components. Pressure regulators must be set only to the level required, regardless of flow variations, for the proper functioning of the load devices. In order to ensure the correct pressure is present at the load devices, allowance must be made for pressure drops in long airlines, their routing and the dimensioning of the fittings and tubing in addition to the various air preparation devices used, especially filters.

Consider using dual pressures for larger air actuators to save on air consumption and pressure boosters close to a specific load device instead of oversizing an entire system to accomodate only one or two operations.

As a result of fieldbus implementation, we can reduce the amount of wiring and the need for junction boxes leading to a more modular physical architecture.

Additionally, fieldbus implementation can enhance the modularity and flexibility of a machine by allowing for a design that can be expanded without having to add much to the machine for additional infrastructure. The key point being that the I/O can be offset from a central location, and placed remotely, especially with an IP65 fieldbus product.

For example, if we look at a machine that is designed to sort eight lanes of product, it may have one valve manifold with eight valves and 16 digital inputs all connected to a PLC. If we need to upgrade the machine to handle 32 lanes, depending on the valve manifold design with a fieldbus system, this could be a simple matter of expanding the current manifold to include the new number of required valves and I/O points. In this case, the fieldbus itself would remain unchanged. In the worst case, three additional valve manifolds with the appropriate I/O would need to be added to the machine. Each valve manifold would have an additional power connection along with a fieldbus connection, still keeping the changes to the machine architecture at a minimum.

If we were to take a conventional machine with discrete control via a PLC, the changes would be of a much greater impact. For instance, by adding 24 valves, we would have to consider the conduit system that we are routing the wires in. Can we accommodate the additional wires or do we need an additional cable tray? Do we need to expand the PLC chassis as a result of additional I/O cards? If we expand the PLC chassis, do we still have room in the existing control cabinet of do we need a new cabinet? All of this leads to extra size and installation costs.

In this example, we can see how — with a fieldbus concept — it is much easier to design a modular concept machine and add functionality later on and avoid major design and production costs down the road.