Pneumatic cylinders

There’s a bit of a joke in some circles that there’s nothing much new in standard fluid power components — cylinders, valves, pumps. But although these products have been around for many decades, that doesn’t mean that there aren’t new aspects to these workhorses of the industry.

Take pneumatic cylinders. Two recent product releases show some creative updates to these actuators. Emerson’s new Aventics TM5 TaskMaster aluminum cylinder reduces cost, energy consumption, equipment wear and downtime. And Bimba’s Position Feedback Cylinder (PFC) provides continuous position sensing in a lightweight, small bore air cylinder.

It’s all in the cushioning

With its rugged aluminum body construction and a steel piston rod, the TM5 TaskMaster features Emerson’s state-of-the-art pneumatic cushioning technology. This allows an ideal cushion adjustment to slow down the piston to a stop by the time it reaches the endcap. Ideal cushioning reduces the time it takes the cylinder to complete a stroke, allowing an improvement in efficiency that significantly boosts machine speed and lowers endcap hammer. Ideal cushioning also reduces cycle time and enables these cylinders to carry higher loads without sacrificing performance.

The cylinder incurs less stress and there is no end-of-stroke bounce or endcap slamming, which is a main source of cylinder wear, slowness and noise. Ideal cushioning thus lengthens cylinder operating life and reduces downtime related to cylinder failure. Additionally, it reduces machine noise and vibration while reducing energy consumption.

Image courtesy of Emerson

“The all-new TM5 TaskMaster gives machine builders and end-user manufacturers the tools to make their machines faster and more reliable,” said James Ward, VP engineering, machine automation, Americas, at Emerson. “It’s the highest performing and most reliable TaskMaster cylinder ever produced, so it gives them an opportunity to build a competitive advantage.”

The NPFA-compliant TM5 is the latest addition to the TaskMaster line of aluminum cylinders, an industry standard for 50 years. Emerson’s online configurator provides a product part number, pricing and 2D and 3D CAD drawings in one convenient place. In addition, all product information and spare parts can be found in the Aventics Pneumatics Shop.

TaskMaster TM5 provides a high-quality and readily available interchange cylinder to meet OEM and machine requirements. In combination with the online tools, a fast-delivery program allows for quick turnaround of orders, reducing lead times for customers. From configuration to production, Emerson´s process is completely automated.

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Bimba Manufacturing’s PFC provides continuous position sensing in a lightweight, small bore air cylinder. The PFC contains an internal linear resistive transducer (LRT) mounted in the cylinder rear head. The LRT probe, which has a resistive element on one side and a collector strip on the other, sits inside the cylinder rod. A wiper assembly is installed in the piston. Moving the piston creates an electrical circuit between the resistive element and collector strip. Resistance in the circuit is proportional to piston position, which is used to produce an analog signal that the controller uses to determine a precise position.

Three factors — resolution, linearity and repeatability — determine the LRT’s accuracy. Resolution is stroke sensitive: the longer the stroke, the less the resolution. It’s typically around 0.002 to 0.003 in. Linearity, the maximum deviation of the output voltage to a straight line, is ±1% of stroke. And mechanical repeatability is ±0.001 in. Thus, overall accuracy is on the order of a few hundredths of an inch.

The Position Feedback Cylinder Non-Contact (PFCN) is similar to the PFC, except it uses a magnetostrictive sensor instead of an LRT. In basic terms, magnetostriction involves a fixed sensing element, called a waveguide, made of ferromagnetic material that runs the length of the cylinder. A magnet mounted on the piston creates a magnetic field.

Short current pulses generated by the sensor electronics travel along a conductor attached to the waveguide. When the magnetic fields induced by the current and magnet interact, it generates a torsional strain in the waveguide. This mechanical wave travels back to a signal converter in the electronics and is used to determine position — all in a few µsec. It is calibrated to produce exactly 0 V fully retracted and 10 V fully extended.

Image courtesy of Bimba

In practice, the unit senses position as the piston moves back and forth. And it provides absolute position information. Accuracy — the combined effects of non-linearity, repeatability and hysteresis — is ± 0.016 in. maximum anywhere along the stroke.

Non-contact operation provides many advantages. The technology is suitable for applications that involve dirty or moist environments, rapid oscillation over a small increment of stroke, and vibration. In addition, it is relatively immune to airline contamination.

Both of these cylinders can operate with controllers like Bimba’s Pneumatic Control System, Digital Panel Meter Model, or Electronic Controller, as well as similar units. And for rotating applications, Bimba’s Pneu-Turn rotary actuator with position feedback is a rotary rack-and-pinion actuator that has a rotary potentiometric feedback transducer attached to the output shaft. It provides continuous shaft position sensing within ±0.5°.