Air leakage is an accepted challenge in pneumatics applications. It is considered unintentional and requires maintenance and continuous monitoring. However, pneumatic systems are also designed for frequent intentional air releases as part of regular operation, which exhausts usable energy and wastes money.

“A pneumatic actuator is pretty much a set of air tanks on either side of a movable piston within a cylinder,” said Matt Williams, the innovation, technology, and commercialization lead at PHD. “After compressed air is introduced into the cylinder to move the piston, the volume behind that piston still contains energy. If we exhaust the air on the next cycle to move the piston in the opposite direction, all that energy is removed from the system.”

PHD is commonly known as a fluid power actuator manufacturer and solution provider. Yet, its customers grew concerned about energy usage and reducing associated operating costs and carbon footprints and began requesting electrically driven actuators. Though pneumatic actuators typically have higher power density, actuate faster, and produce more force than electrically driven counterparts, energy losses result in sunk costs and increase the system’s carbon footprint.

“We needed to figure out a way to remove the energy in the otherwise exhausted air as the key to gaining energy efficiency in a pneumatic system,” said Williams. “So, we asked ourselves, as engineers and solution providers, how can we maintain the benefits of a fluid power actuator system while reducing those energy losses?”

If PHD decided to convert its technologies and substitute electrical components for pneumatics, it would have to redesign almost all its products. This would incur significant investments for the company and its customers, who would have to requalify the products for their applications.

To solve the problem on all fronts, Williams’ team developed the PHD ERDP Remote Drive as an electrified option and point-of-use alternative. The ERDP forms a closed system to recycle energy in the exhaust air. It comprises two opposing cylinders with pistons, each connected to one actuator port. When the remote drive cycles, it compresses air on one side and expands it on the other without exhausting any air.

“If you think about an actuator, we inject compressed air on one side of the piston, and on the other side, we exhaust. Now, traditionally, we exhaust back to the ambient environment, and then we lose all the energy from the previous cycle’s compressed air,” said Williams. “Instead, we bring the compressed air into the exhaust side of the remote drive and extract that energy. The pressure it has provides a force that acts against a piston, and that force is transferred over to the side doing the air compression. If you want to reverse the direction of the actuator, we just reverse the direction of the remote drive.”

The remote drive uses atmospheric air and seals when it begins to operate. However, it will automatically “take a breath” if it ever needs more air.

“We know air leaks out sometimes, regardless of how well the actuator or system seal is,” said Williams. “So, at the end of each cycle, for a brief period, we breach the piston and open the cavity to ambient air. If we’ve lost any air on the prior cycle, a partial vacuum forms when we return the piston back to its original position. And that partial vacuum, if it exists, if the leak has occurred, pulls in whatever quantity of air from the atmosphere it needs to replace the amount of air lost. If there’s no lost air, if you have a well-sealed system, the system remains completely closed, and we never add any air. But if you leak a little air, we add only a little air to compensate. If you leak a lot of air, we add a lot of air to compensate. And that’s all done automatically by the physics within the system.”

The assembly consists of the drive, controller, motor power supply, and regeneration clamp. Machine builders add their own power supply, PLC cables, air lines, fittings, and actuators. Though the ERDP has one set of actuator ports, machine builders can drive multiple actuators in parallel so that they move in the same direction simultaneously. Alternatively, they can add valves between the remote drive and multiple actuators to drive them sequentially.

Not knowing what the market would demand from this new technology, the company selected a starting point based on customer inquiries. It offers a standard ERDP 54 customizable unit based on the application’s actuators, displacement, and desired pressure.

“We’ve targeted the range of actuators predominantly used for end-of-arm tooling applications, but we can scale that technology and make bigger or smaller units,” said Williams. “For instance, we’re working on a very large unit for a major automotive manufacturer that is driving a robot about the size of a piece of Earth-moving equipment and driving multiple actuators at the end of about a 20-ft robotic arm. In this case, the unit becomes big and is about 75 lb worth of weight. So, we can tailor the technology for the load.”

The technology can also be used in industrial and medical applications, food processing, and nearly any picking operation that uses pneumatic actuation. Mobile robots with grippers are just one of many candidates that can benefit.

“Typically, the only piece of pneumatic equipment on mobile robots is the end effector, and they need that for force and speed. So, they’re stuck having an air compressor on the unit solely to drive that particular actuator. Everything else is electrified already,” said Williams. “If we can replace that air compressor with the remote drive and gain some energy efficiency, we can obviate their need for compressed air.”

Williams also noted that when comparing pneumatic and electric actuators, electric ones are typically heavy and have their mechanisms exposed, whereas pneumatic actuators save significant capacity in size and weight. Plus, the ERDP generates equal force and increases longevity at much less cost than an electric actuator.

“If you think about an end-of-arm application, if I add more weight to the end effector, I’m subtracting that weight from the payload capacity of the robot,” he said. “So, we take the motor, which is the heaviest part of the whole system, both for the remote drive, but also for a typical fully electrified actuator, we offboard that, remove it from the actuator, and we place it somewhere not on the end of the robot arm.”

The ERDP can also function as a vacuum to create suction. For instance, instead of using a venturi pump, which is typically regarded as energy-inefficient, engineers can add check valves to the remote drive to create pressure and generate a vacuum.

Overall, the remote drive is positioned to save energy, costs, and carbon footprint while creating more flexible design options for engineers and machine builders. PHD has plans to continuously advance and optimize this new product to enable more lightweight, energy-efficient design options.

PHD

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Contributed by By Frank Langro, Director of Product Market Management, ���ϳԹ� Automation, Festo

���ϳԹ� linear actuators are fundamental for automation because of their low cost, ease of installation and operation, high yet compliant force, speed, compactness, safety in hazardous areas, and long service life in harsh environments. Advancing technology in valves, valve terminals, and remote and decentralized I/O is opening new application solutions for this tried-and-true technology.

This article discusses pneumatics, servo pneumatics, and controlled pneumatics to answer the questions of where, when, and why to apply each form of this automated linear motion technology. First, a review of the basics.

���ϳԹ� actuators for linear motion
The key component in all linear motion pneumatic actuators is the internal piston. By applying compressed air supply into a cylinder’s two inlet ports the piston driving a piston rod can be made to move forward and backward between two points – fully extended and fully retracted. To regulate the speed of the piston, design engineers specify a flow control valve. Opening the flow controller’s orifice allows more flow and the piston moves faster, while closing it reduces flow and slows travel between two points.

To ascertain the location of the piston at either start or end point, proximity sensors are attached to the body of the cylinder. The sensors provide closed loop feedback that the extreme positions have been reached. Measuring the time between positions allows the controller to ascertain speed. To lessen the shock of impact as the piston reaches its start and end points and to reduce vibration and wear, actuators include cushions, throttling screws, or self-adjusting cushioning systems.

Compressed air-based motion is found in most production equipment. Often pneumatic actuators are used for picking and placing in packaging applications. It is also common to use pneumatics for clamping, stamping, and positioning. ���ϳԹ�s also suit applications in hazardous areas, food and beverage, and robotics, due to limited electrical signals, which are well suited to being in washdown areas. Additionally, pneumatics technologies are light weight — a benefit in end of arm tooling.

Servo pneumatics enables multiple positioning and force control
While traditional pneumatic technology is simple with just two positions, servo pneumatics delivers infinite positioning. PLCs, proportional control valves, and actuators with linear displacement encoders attached along their lengths can position the piston anywhere along its route of travel. (The linear displacement encoder gives closed loop feedback of the actual position of that piston.) With this set up, the PLC can select a defined position and the proportional valve will change the pressure and the flow rate to ports 2 and 4 to hunt for that position. Pressure will be equalized at that point, holding the piston in place. Defined acceleration, motion profile, and deceleration are achieved through proportional control.

Along with position control, servo pneumatics also provides force control. By increasing pressure proportionally, the force on the piston is increased, and by reducing pressure, the force is decreased. In gripping applications, force control allows grasping of soft delicate objects or heavy rugged workpieces within the same set up.

Servo pneumatics’ ability to control position and force can be applied in any situation where holding an intermediate position improves cycle time. Visualize a labeling application where multiple sized boxes are coming down a conveyor. Utilizing a two-position pneumatic cylinder to apply the label would require the cylinder to completely extend and retract for every label applied. A servo pneumatic actuator could be positioned at an intermediate distance, speeding up the cycle.

In a hypothetical palletizing scenario, various sizes and weights of shipping cases are traveling down a conveyor. The cases need to be centralized before they are gripped and lifted off the conveyor. A servo pneumatic actuator would be ideal as a centralizer because it can be set at an intermediate position, boosting cycle rate. Furthermore, it offers force control to accommodate the various masses of shipping cases. In pick-and-place applications or positioning, servo pneumatics can be soft stopped with air pressure introduced against the oncoming piston. Soft stop is a key component in pick-and-place applications to control the momentum of the load.

In sawmills, operations staff benefit by recording the contour of the log during milling. An actuator pressing a guide along the log as it is sawed will extend and retract as the log passes underneath. The control system can record the position of the piston via the linear encoder. This provides an accurate record of each log’s circumference. In summary, servo pneumatics provides positioning and force control for linear motion, but not the type of interpolated motion found in servo motors.

Controlled pneumatics
Directional valves control the flow of compressed air to an actuator — either on or off for two position pneumatics or proportionally in servo pneumatics. Controlled pneumatics replaces traditional directional solenoid operated valves with proportional based valves.

One advancement in proportional valve technology has been the development of fast, quiet, accurate, and energy efficient piezoelectric-based valves.

A piezo ceramic element has capacitive properties: meaning it needs voltage to change its shape but does not require a continuous voltage to hold its position, very different from a solenoid that requires continuous voltage to remain activated. This means that a piezo valve generates virtually no heat, requires little energy input, has low wear, and operates silently.

Piezoelectric valves arranged to pilot a higher flowing 2/2-way valve are able to magnify the compact piezo valve’s functionality. For example, four 2/2-way valves in a bridge circuit, when controlled by eight proportionally controlled 2/2-way valves, can act as a standard directional control valve, a flow control valve, a pressure regulator, even so much as to replicate the functionality of a shock absorber on the motion of a cylinder. This is due to the software that controls the response of the proportional piezo pilot valves. The pilot valves can perform exceptionally fast and accurate flow control thereby managing the response of the main valves in the bridge circuit to achieve the desired pneumatic output to the cylinder or system.

A controlled pneumatic valve for linear motion consists of four 2/2-way diaphragm poppet valves that are connected in a bridge. Each diaphragm poppet valve is proportionally piloted and controlled by a pair of piezo valves. The system features embedded temperature, pressure, and position sensors.

Controlled pneumatics offers many capabilities in linear motion. Imagine, for example, an application that calls for one second travel time between position A and position B. If there is a leak in the system, the controlled pneumatics valve terminal can detect the loss and the controller can increase the flow rate to meet the one second travel time and preserve the output of the machine. With pressure detection, the system can trace leakage down to an individual cylinder for better understanding of the condition of the machine and its output. Controlled pneumatics can reduce energy consumption by applying high force to start the piston moving and then reducing pressure once it is in motion.

Controlled pneumatics are ideal for ensuring uniform web tension with high dynamics and precision. The extremely sensitive pressure control compensates for fluctuations and takes kinetic energies into account. Controlled pneumatics is applied for dynamic and flexible surface pressure over the entire machining process when grinding, brushing, or polishing. The solution can eliminate the need for gripper changes, as pre-sets ensure fast commissioning and pre-positioning.

Controlled pneumatics capabilities:

• Flow control
• Selectable pressure level
• Positioning over the entire stroke of the cylinder
• Preset travel time
• Operating actuators with minimum pressure
• Leakage diagnostics
• Soft stop
• Model-based proportional pressure regulation
• Proportional-pressure regulation

Summary
���ϳԹ� actuators are compact, rugged, easy to apply, and suitable for the most harsh or hazardous environments. ���ϳԹ�s is ideal for end position travel. Servo pneumatics provides gentle movements, positioning, and fast switching between position and force control. Controlled pneumatics offer high flexibility, multiple functionalities, controlled movements with more than one axis, force and stroke control, condition and process monitoring, and energy reduction. The real excitement comes when machine and process designers understand how much flexibility these three offer when fluid power is absolutely the best option for automated linear motion.

Festo

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Originally designed as a vibration and impact absorption tool, designers quickly concluded these suspension systems make robust and reliable linear actuators. The air spring offers a few unique benefits to separate them from traditional rod and barrel cylinder actuators. Whereas axial alignment is critical to an air cylinder’s reliability, air springs permit a surprising amount of axial and angular movement.

The air spring’s construction elucidates the reason for its unique advantage over misalignment. Consisting of a top and bottom plate where pressure acts upon to create force, these plates are joined by rubber bellows, which contain the air pressure required to operate. Because of the inherent elastomeric nature of the reinforced rubber bellows, they can move out of axial and angular alignment to a degree while still operating effectively.

The bellows, made of reinforced neoprene or rubber, are as durable as car tires. This robust construction ensures that you can rely on them for many years and cycles of operation before they show signs of wear. The convoluted style uses a rubber or metal ring to help stabilize the bellow, while the rolling lobe air spring folds upon itself in its retracted position, further enhancing its longevity.

Because the entire “body” of these air springs is flexible, they can stroke at an angle or experience movement between the top and bottom mounting locations within the allowances of their dimensions. For example, a lift and tilt table gets by with a single actuator rather than one for lift and one for tilt using traditional actuators.

The air spring actuator comes in large diameter options capable of up to 100,000 lb of force, although the majority of these applications are smaller sizes. Air springs make the perfect contributing actuator to vehicle or aircraft simulators, where the Z-axis (up and down) requires a wide, stable platform with low installed height, leaving the X- and Y-axis to traditional hydraulic cylinders. Essentially, the Y-axis cylinders control the fore/aft tilt of the machine while the X-axis cylinders control the side-to-side motion, making for an inexpensive motion control application.

Air springs make great unconventional options for pressing applications, such as pressing oils, bonding and laminating or stamping and embossing. The air spring is especially suitable for sensitive products, such as wine grapes. The press platen doesn’t have to remain perpendicular as it presses, so any spots with larger bunches of grapes will allow the air spring to provide even force on the uneven product.

With their simple construction and competitive price, you can expect to see more air springs used for industrial applications. Their simple and forgiving nature combined with easy repairability provides an option outside standard fixed-barrel linear actuators.

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