Best pneumatic cylinder for automation applications

Introduction

Industrial automation involves the automatic movement of goods across the production line, within equipment and machines. It is present in control valve operations, elevators, forklifts, and pneumatic tools (for example, in assembly and production lines of various industries like automotive, electronic manufacturing, etc.) A pneumatic system uses cylinders as a critical component, which uses compressed air to perform the desired task. This article is a brief primer on pneumatic cylinders and their associated components. It also lists the types of cylinders along with some standards and applications, serving as valuable reference content for engineers who want to select the right pneumatic cylinder for their applications.

Critical components of a pneumatic system

Figure 1: Key components of a pneumatic system (self-created)

A pneumatic system typically comprises several essential components that work together to harness and control the power of compressed air. The critical components of a pneumatic system are:

• Compressor: This component compresses air to the desired pressure, making it the power source for the entire system.


• Air tank: It stores compressed air, acting as a reservoir for immediate use, and helps to stabilize the system's pressure fluctuations.


• Filter regulator lubricator (FRL): This is a combination unit. FRL filters the compressed air, regulates pressure, and adds lubrication to ensure smooth operation and protect downstream components.


• Directional control valve: This valve controls the airflow direction, determining the movement or operation of pneumatic actuators and other devices.


• Pneumatic actuators: They produce the linear or rotary movement and force necessary to propel a piston, driving the final operation, such as pushing, lifting, gripping, punching, or engaging a vacuum device. Actuator accessories, such as spool assemblies and piston seal kits, are also part of this system.


• Control valves: These valves regulate the airflow to pneumatic actuators, allowing for precise control over the speed, force, and direction of movement.


• Air lines and connectors: These are the network of pipes, hoses, and fittings that transport compressed air between components, ensuring a reliable and efficient flow throughout the system.

Apart from the above, a few other components of pneumatic systems are:

• Vacuum Generators and Ejectors: These work according to the Venturi principle and generate the vacuum to handle objects. They are generally used with vacuum accessories, including vacuum pad assemblies.


• Silencers: release pressurized air into the atmosphere to mitigate the excessive noise produced when pneumatic air exits through an exhaust.

Types of pneumatic cylinder

Pneumatic cylinders are classified into:

• Single-acting cylinders: These cylinders have a single air-entry port and push the piston in a single direction. A spring returns the piston to its original position. Single-acting pneumatic actuators have limited stroke length, which makes them ideally suited for slower-moving operations.


• Double-acting cylinders: A double-acting cylinder can exert force in both directions. These cylinders have two air-entry ports that push and pull the piston without a spring. This makes them versatile for applications requiring both extension and retraction forces.


• Rodless cylinders: A rodless cylinder is a type of pneumatic cylinder that operates without a traditional rod extending from one end. These cylinders have a piston connected to an internal carriage or a guided mechanism inside a tubular housing. Applications that require extended travel distances, such as fundamental drive-in multi-axis gantries, use rodless cylinders. They also facilitate feeding tasks.


• Tie-rod cylinders: Rods or bolts extend from one end cap to the other in tie-rod cylinders, providing structural support to the cylinder barrel. These tie rods help to maintain the alignment and integrity of the cylinder components, preventing the cylinder from distorting or coming apart under pressure. Tie-rod cylinders are a popular pneumatic actuator design extensively employed in robust, high-temperature industrial automation applications.


• Tandem cylinders: In this configuration, two or more cylinders, connected in series, share a common rod or piston. This setup allows the cylinders to work together to achieve a combined output force or extend the stroke beyond what a single cylinder could achieve.


• Magnetic cylinders: These cylinders have magnetic pistons, and sensors in the cylinder can detect these pistons. Designated sensor slots ensure secure installation without the need for additional accessories. The adjustable pneumatic cushioning provides consistent energy absorption.


• Rotary actuators: Rotary actuators generate reciprocating angular or turning motion, facilitating an oscillating stroke through a defined angle. These pneumatic actuators come in rack and pinion, rotary vane, and helical designs. They feature simple, durable designs that reduce maintenance requirements while providing substantial torque relative to their size. Being compact and self-contained, rotary vane actuators occupy less space than rack and pinion counterparts but deliver lower torque. Rack and pinion actuators, on the other hand, offer higher torque but necessitate a larger footprint to achieve specific angular motions.


• Multi-position cylinder: A multi-position pneumatic cylinder is designed to stop at and hold multiple discrete positions along its stroke. This enables the cylinder to perform various tasks or movements precisely and flexibly. These cylinders typically have multiple ports and internal mechanisms that allow the piston to be securely held at different positions. Pneumatic multi-position cylinders are available with two different functional principles. According to the first principle, pneumatic multi-position drives consist of two cylinders connected using a kit and piston rods extending in opposite directions. Depending on the actuation and stroke configuration, this type of cylinder can assume up to four positions. According to the second principle, multi-position cylinders consist of two to five cylinders connected in series with different stroke lengths. With this cylinder type, only one piston rod is visible, which moves to different positions in one direction.

Figure 2: Different types of pneumatic cylinders

ISO standards for pneumatic cylinders

Pneumatic cylinder configurations conform to ISO standards, guaranteeing compatibility, interchangeability, and quality consistency among various manufacturers. Consequently, the specifications for mounting dimensions, cylinder bore, stroke, piston rod characteristics, and airports are contingent upon the specific type, standard, and intended application. The relevant ISO standards for pneumatic cylinders include:

• ISO 6432: These cylinders are round-bodied pneumatic cylinders commonly known as mini air cylinders or round cylinders. ISO 6432 applies to cylinders with bores ranging from 8 mm to 25 mm for use at a maximum working pressure of 10 bar or 1000 kPA. These cylinders lack manual damping adjustment. ISO 6432 cylinders, characterized by a round design for the cylinder body, are widely used for simple handling, holding, and lifting. Moreover, ISO 6432 applies to cylinders with and without magnetic functions for cylinder position sensing.


• ISO 15552: It establishes the standards for pneumatic cylinders for single or double-rod, with or without provisions for magnetic sensors. This standard is designed for a maximum working pressure of up to 10 bar or 1000 kPa and encompasses bore sizes ranging from 32 mm to 320 mm. The ISO 15552 pneumatic cylinder series is equipped with adjustable cushioning, which facilitates precise dampening control and applies to cylinders with detachable mountings. Therefore, these cylinders are well-suited for efficiently handling substantial loads.


• ISO 21287: This standard pertains to compact or short-stroke single-rod pneumatic cylinders featuring a maximum working pressure of up to 10 bar or 1000 kPa and bore sizes ranging from 20 mm to 100 mm. This pneumatic cylinder series lacks adjustable cushioning; instead, it incorporates rubber bumpers at both ends to provide cushioning. The ISO 21287 cylinders are characterized by their compact and lightweight design, making them particularly suitable for applications with space constraints, such as stoppers on conveyor systems.

Criteria for selection of a pneumatic cylinder

When selecting a pneumatic cylinder, consider the following criteria:

• Force requirements: The force or thrust needed to perform the desired task is determined by considering load weight, friction, and acceleration factors. The general thumb rule is that the required force should be twice the load to be moved for vertical and high-friction applications. In some cases, additional force is deemed necessary to compensate for friction. Designers can calculate the cylinder force by multiplying the effective piston area by the working pressure. The effective area for push force is defined as the cylinder bore, while for pull force, it is the bore area, less the cross-sectional area of the piston rod.


• Stroke length: The stroke length represents the piston's linear distance during activation through compressed air. The cylinder's stroke length should be at least one meter to raise a load by one meter, effectively transporting the load from its initial to the final position. Precise estimation of the stroke length is crucial, considering that costs for the cylinder tend to rise with increasing stroke lengths. A cylinder with an insufficiently short stroke length will fail to move the load to the desired position. Conversely, an excessively long stroke length may overshoot the target position, risking piston stress and bending when dealing with a heavy load at the fully extended piston end.


• Bore size: Choosing the correct bore size is critical to ensure the cylinder can provide enough force for the application. The cylinder bore determines the effective area for push force, while for pull force, it's the bore area minus the cross-sectional area of the piston rod. The bore size should be 1.5 to 2 times the diameter of the load being moved. Although larger bore sizes typically increase force output, they may impact the cylinder speed.


• Operating pressure: The operating pressure determines the force the cylinder exerts and affects its overall performance. Higher operating pressures generally result in greater force output, while lower pressures may limit the cylinder's performance. To determine the available pressure for your system, consult the system's specifications or consider the maximum pressure supplied by your air compressor. Common pressure ratings include 10 bar (1000 kPa) or 17 bar (1700 kPa).


• Speed of operation: The speed of a pneumatic cylinder determines how fast the cylinder will complete its stroke. The following equation gives the speed of a pneumatic cylinder:
  Speed = [Flow Rate (liters per minute) / Cylinder Area(cm^2)] * 60
  Selecting a cylinder equipped with adjustable end-of-stroke cushioning at elevated speeds enables faster operations than those without this feature. The speed of a pneumatic cylinder can be controlled by adjusting the air supply pressure, installing a flow control valve, and using an electronic controller or a pressure regulator.


• Mounting options: Pneumatic cylinders are offered with various mounting options, such as flange, foot, or trunnion mounting, for different applications and configurations. Each mounting style has its advantages and considerations when it comes to sizing. Choosing the right mounting option is crucial for proper sizing and ensuring the cylinder integrates seamlessly within your system. Factors such as space limitations, load requirements, desired actuation direction, and range of motion play a role in selecting the appropriate mounting style. Choosing the right mounting style ensures the cylinder fits seamlessly into your system and delivers optimal performance.


• Cushioning: Higher velocities impact the piston against the end covers in pneumatic cylinders. The impacts often occur at both endpoints of the cylinder and generate destructive shocks among the structural members of the machines or equipment. Some form of cushioning is usually needed to reduce the cylinder's travel rate before the piston strikes the end cover to prevent shock. Cushioning is of three types: mechanical and elastic damping, pneumatic and servo-pneumatic damping, and hydraulic damping.


• Operating environment: The environment in which the cylinder will operate plays a significant role in its selection. Factors such as temperature, humidity, corrosive substances, or exposure to dust and debris should be considered. Several manufacturers offer pneumatic.

Innovative applications of pneumatics

• Frugal bottle manufacturing: Frugal Bottle is the world's pioneer paper wine and spirits bottle. The company uses the Festo CPX-E-CEC Controller for precise soft motion interpolation. This controller effectively manages multiple axes simultaneously, enabling the creation of intricate curves on the glue paths during the manufacturing process. The procedure involves an operator placing blanks for the front and back of the bottles at the beginning of the process. The machine then undertakes tasks such as picking, loading, transferring, gluing, repeating transfers, wetting, and conveying the prepared blanks. Festo's core pneumatics products, including valve terminals and process valves, are also used in executing these operations. Finally, the treated blanks are conveyed to the bottle-forming machine.


• Filling and packaging process: Doypack® pouches, prevalent in most FMCG industries, use a filling and sealing machine (SF102) from Thimonnier. In this machine, the stand-up pouch is initially fed in, and then a compact Festo ADNGF cylinder conveys it to the filling station. Based on specific requirements, the accurate filling quantity is determined through electromagnetic or mass flow measurement or a dosing pump. Subsequently, at the next station, screw caps are securely fastened onto the stand-up pouches. The Festo swivel module DSM-B efficiently transports the filled and sealed pouches to a conveyor. The pneumatic functions of the SF102 are seamlessly controlled by the valve manifold VTUG, known for its compact design, high flow rate, and integration of IO-Link® technology. This technological feature facilitates the transition of packaging machines to embrace Industry 4.0 standards.


• Picking, packing, and palletizing machines: Transnova Ruf machines based on pneumatic automation technology from Festo are a tailored solution for packaging, palletizing, and handling. The gripping module of this machine uses vacuum technology, pneumatic drives, grippers, valve manifolds, and an integrated proportional pressure regulator within the valve manifold. The proportional pressure regulator VPPM specifically controls the contact pressure of the parallel gripper, ensuring precise and repeatable gripping pressure regulation. These regulators, incorporated into the CPX/MPA valve manifold, allow online access via the Internet for diagnostic data retrieval.


• Low-cost molecular diagnostic machine: Fast MDx represents a groundbreaking advancement as the first fully automated, high-throughput near-patient testing system. This innovative and affordable platform, capable of rapidly detecting numerous pathogens, relies on Festo's automation technology for pipetting and dispensing. The core of Fast MDx's functionality lies in Festo's EXCM planar surface gantry, operating seamlessly in the X and Y planes to meticulously prepare samples. The automated pipetting system, featuring the Festo DHOE pipetting head and the DHAO disposable syringe ejector, is mounted on the planar surface gantry in the Z direction. The pipetting head demonstrates remarkable precision, dispensing volumes within the 10 µl range, and its adjustable pipetting speed can reach up to 10 ml/s.The operational process involves preparing the master mix, depositing it in the microtiter plate, and adding samples. Drilling the Fast MDx's Pathtube® cap, the disposable tip aspirates and pipettes each patient sample into designated microtiter plate wells. A dedicated Festo handling system utilizes an EHPS-16 electric gripper to lift the filled microtiter plate and position it in the heat sealer. The sealed plate is then introduced into the RT block, initiating the conversion of RNA, if present, into complementary DNA (cDNA). Finally, the NGX2 qPCR thermal cycler amplifies the cDNA, utilizing an ultrafast fluorescence detection system to determine the presence of the pathogen's cDNA sequence in patient samples. Notably, the Fast MDx test platform incorporates Festo's PGVA pressure and vacuum generator to eliminate the need for an external pneumatic supply. This self-contained solution, powered by a 24-volt supply, produces a pressure or vacuum of +/-0.5 bar and integrates a mini compressor, air filter unit, reservoir, and electronic pressure and vacuum control in a compact space, catering to liquid handling in laboratory automation.

Product offerings in the field of industrial pneumatics

Farnell offers an extensive portfolio of pneumatic and fluid control products from industry-leading suppliers. Some of the essential products are as follows:

Conclusion

A proper selection of pneumatic cylinders and associated accessories is essential for optimal industrial process performance, efficiency, and longevity. You can select the correct cylinder for a particular application by performing accurate calculations and considering factors such as force requirements, bore size, stroke length, etc. Farnell offers various pneumatic cylinders and associated accessories suitable for industrial automation applications. This will also yield long-term benefits, ensuring reliable operation and reducing maintenance costs.