Authored by:
Frank Latino
Product Manager – Valve Terminals & Electronics
Festo Corp.
Hauppauge, N.Y.

Edited by Kenneth J. Korane
ken.korane@penton.com

Key points:
• Valve terminals have evolved into integrated automation platforms.
• Capabilities include control of pneumatic and electric drives, sensing, and motion control.
Resources:
Festo Corp., www.festo.com/usa

Today, OEMs of all stripes strive to supply equipment that is reliable, efficient, and safe to operate — and ultimately cuts operating costs and boosts productivity. But this is nothing new. Valve terminals — modular platforms that combine pneumatic valves with electronic interfaces — were invented two decades ago to help meet these same needs.

Their success speaks for itself. Festo, Hauppauge, N. Y., for instance, has installed more than 100,000 units worldwide, and acceptance continues at a brisk pace. But the latest versions bear little resemblance to original designs. Capabilities now include not only pneumatics and I/O, but also electric drives, motion control, safety functions, and built-in diagnostics. Here’s a closer look.

Valve-terminal basics
When first introduced by Festo in 1989, “fieldbus-valve manifolds” offered several advantages over pneumatic systems built of stand-alone valves. In traditional systems, each individual valve needed a separate electrical connection and each solenoid coil had to be separately wired to the controller. Every valve also needed its own tubing and pneumatic connectors. This made installation expensive and presented plenty of opportunities for miswiring. More connections also meant lower reliability.

In contrast, the modular, “building-block” make-up of valve terminals requires substantially less wiring and tubing than an equal number of stand-alone valves. This lowers installation costs. Also, valve terminals often have IP65 or IP67 ratings, which can reduce or eliminate the need for protective enclosures. And because valve terminals can be mounted close to actuators, rather than near the controller, shorter lengths of I/O wiring and pneumatic tubing can be used. Shorter tubing pressurizes faster and actuators therefore respond quicker.

The first valve terminals typically had standard valves simply mounted on a manifold and wired to a fieldbus node, with individual solenoids controlled over the network. The node also provided I/O, but the main benefit was the capability to connect discrete solenoids to the fieldbus. However, in terms of troubleshooting, one shortcoming of these devices was the entire valve terminal appeared as a single block of data to the controller. This limited the ability to pinpoint a fault.

In addition, procedures to set up and configure a fieldbus system usually varied among PLC vendors — and even among different PLCs from the same vendor — so it often required multivendor support.

Fortunately, valve terminals have kept pace with advances in programming and control. A major breakthrough was the implementation of a dedicated, high-speed bus embedded within the valve terminal. This lets users plug in various pneumatic and nonpneumatic modules and configure the precise system needed for a particular application. Today, capabilities include:
• Control of pneumatic and electromechanical drives.
• Transmission of digital and analog I/O.
• Measurement of temperature, pressure, and position.
• Proportional pressure regulation.
• Safety functions.
• Motion control with servopneumatic and electric drives.

The internal bus ties the modules together, increasing data capacity and communication speed compared with discretely wired versions. An ASIC on every module coordinates the internal bus traffic at the optimum speed and capacity. The modular approach also makes it simple to revise or expand the system, saving setup and commissioning time.

The design conforms to modular configuration schemes dictated by advanced control and fieldbus systems. Engineers can configure valve terminals by individual modules and take advantage of the latest visual-configuration software tools, such as those for DeviceNet and Profibus. Valves and other devices can be set up block by block, on-screen. This approach differentiates between solenoids, digital and analog inputs and outputs, and other data types, making for straightforward setup and troubleshooting.

The integrated bus can also control power distribution throughout the manifold to each module, and isolate solenoids from control electronics. Solenoids require a certain amount of current to initiate movement but substantially less to hold them open or closed. Controlling power in this manner can slash operating costs and extend solenoid life.

Functional modules
A significant benefit from a machine builder’s point-of-view is the ability to build an automation platform exactly tailored to an application’s requirement. Here’s a look at a few of the modules and capabilities of Festo’s CPX and companion valve terminals.

Valves. Depending on the pneumatic interface and configuration, engineers can control up to 128 valve solenoids, up to four different valve sizes, with flow rates to 3,000 lpm/valve. Decentralized systems can increase the number of controlled valves into the thousands. Types include 3/2, 4/2, 5/2, 5/3, and 5/2-way double solenoid, as well as specials such as “clean-design” valves for wash-down applications, 10-mm miniature valves, and pilot valves with flows as little as 10 lpm.

Adding modular proportional valves, such as the VPPM, into a valve terminal permits pressure, force, and speed control of pneumatic drives — as required for demanding applications such as automatic winding and roll cutting in the packaging industry.

Communications protocols. The CPX is compatible with all common fieldbus standards, including Profibus-DP, Interbus, CANopen, DeviceNet, and CC-Link, as well as Ethernet/IP, EtherCat, Modbus/TCP, and Profinet IO.

I/O. The CPX can function as an autonomous I/O system with integrated control. It supports up to 512 I/Os, including digital and analog, as well as temperature, pressure, and displacement measurements.

Controller. An IEC 61131 (CoDeSys) embedded controller, called the CEC, expands the remote I/O valve terminal into a modular PLC with IP65/67 rating. Direct machine mounting reduces installation costs and permits preprocessing or stand-alone control. Units support autonomous control of individual machines or can be networked to higher-level plant control systems.

Functions include control of valves, electric drives, and proportional and servopneumatics. The CEC also preprocesses diagnostic data directly on the valve terminal. This significantly reduces the volume of data traffic on the fieldbus. The CPX-CEC relays aggregated diagnostic messages, for instance describing pressure, flow rate, and cycle times, to the master controller. The data can also be integrated seamlessly into existing systems, for example via OPC servers.

In addition, the controller includes comprehensive diagnostics and a condition-monitoring library for pneumatic elements. Compatible touchscreens let users display and change programs and machine sequences.

Motion control. Motion-control capabilities for electric drives include up to eight axes synchronously; point-to-point asynchronous for up to 31 axes; and 2.5D contour interpolation for demanding positioning tasks, for instance in handling equipment.

Motion control also includes servopneumatic positioning of up to eight axes. Intelligent positioning modules combined with linear or rotary actuators with built-in encoders can control force or position with an accuracy of ±0.2 mm. And an electronic end-position-cushioning (“smart” soft-stop) option can make cycle times up to 30% faster while ensuring shock and vibration-free travel between two hard stops.

Pressure and temperature control. In addition to controlling pneumatic and electrical motion, CPX terminals also can handle open and closed-loop control of pressure and temperature. Measuring modules can upgrade pneumatic cylinders into space-saving sensors. Pressure-measuring modules contain up to four pressure sensors and temperature modules handle four thermocouples or resistive thermal devices (RTDs). These units take up less space than conventional sensing hardware and reduce installation time.

Vision. Festo’s Compact Vision System can operate in combination with the I/O module and a fieldbus node. Here, the camera functions like a binary module with 16 inputs and 16 outputs. Units are designed for on-machine operation. For instance, the SBOC-Q camera measures only about 1.8 × 1.8 × 3.3 in., has resolution to 1,280 × 1,024 pixels, exposure time as short as 0.039 msec, and frame rates up to 150 frames/sec. It can capture and store up to 256 images, and handles tasks such as detecting the position and rotary orientation of workpieces, 2D quality inspection, fine positioning of axes, and sorting applications.

Safety. Machine-safety functions can be built into valve terminals. For instance, soft-start VABF valves ensure a slow, controlled build-up of system output pressure, which means downstream cylinders and working devices travel slowly to their initial positions. Users set the switchover to standard operating pressure and flow. This helps ensure that installations start up safely and reduce workers’ exposure to potential hazards.

Diagnostics. Because the embedded bus makes all system data instantly available to the controller, this lets the CPX integrate internal diagnostics and condition monitoring. For instance, it spots errors such as wire breaks and short circuits, and when devices exceed upper or lower limits for voltage, current, temperature, and pressure. Other diagnostic functions include counting, timing (such as travel times and switching times of actuators), and wear and leak detection.

The system time stamps and stores in memory the last 40 error messages and recognizes sporadic faults. And it records errors by module and, in most cases, via channels within modules for single-point diagnostics. Thus, it increases uptime by immediately localizing faults, saving troubleshooting time and speeding repair.

For preventive and predictive maintenance, software monitors setpoint specifications for each valve as well as downstream processes and mechanical systems, including pressure, flow, cylinder run time, and air consumption.

Alerts are sent in a number of ways, from activating basic LEDs on the valves and permitting data access via handheld terminals, to e-mail and text messages or alarms to a Web-based monitor.

Tangible benefits
The range of control and monitoring functions built into a single valve terminal provides many economic benefits for machine builders and users alike. These include:
• Installation times are cut by up to 60%. Prepackaged units eliminate wiring and setup errors and speed commissioning and time to market. Units come fully preassembled and tested with matching electrical and pneumatic components.
• Higher sensor density can reduce I/O channel costs by 50%.
• Shorter tubes slash air consumption by 50%.
• Condition monitoring reduces downtime by 35%. Channel-specific diagnostics for both electrical and pneumatic systems speeds repair, and integrated condition monitoring means higher process reliability.
• Decentralization and enhanced machine performance can reduce cycle times by up to 30%.
• Servopneumatic soft-stop actuator control also reduces air consumption by up to 30%.

All told, experience shows that lower engineering, hardware, and setup costs can cut total system costs by 20%.

The substantial savings and overall design flexibility of valve terminals makes them suitable for many industries. These include food and beverage; packaging; cement, glass, and raw materials; electronics and semiconductor; process industries; and wood and textile.

© 2010 Penton Media, Inc.