FEATURE u Hydraulics & Pneumatics


Switching Ireland on to pneumatics innovation


Mark AcArdle, MD of Festo Ireland, explains how a recent pneumatics innovation can improve precision and control without additional cost.


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ylinder sensor switches are mounted on the majority of pneumatic cylinders and provide sensor feedback. They follow a tried and tested design – but there is room for improvement. Cylinder switches are commonly used when the cylinder reaches its advance or retract end- positions and, less frequently, in mid-position: for example when a cylinder movement has cleared an overlap position. These devices are triggered by a ring magnet or magnetic strip contained within the piston inside the cylinder barrel. The magnetic flux reaches beyond the non-magnetic cylinder barrel and indicates its close proximity. Clever design and CAE simulations enable the flux strength and shape to be optimised to match a manufacturer’s cylinders and sensors for reliable operation. This matching minimises the potential influence of adjacent actuators’ magnetic fields, mounted in close proximity to one another, triggering or blocking the reliable sensing of adjacent sensors. However, setting these devices accurately ‘in the field’ has always been problematic.


DIFFICULT POSITION


Mounting a cylinder sensor on the bench is simple enough. You slide the sensor switch into place from the end cap or drop it into the sensor slot from above and then adjust its position to reflect the switching point required. This involves bringing the piston-rod/piston into the end position and then, with a battery or power supply connected to the sensor, moving it until the LED position indicator shows it is in the correct output position. For reliable repeatability, the optimum switching position is mid-way within the sensing position hysteresis. However, once the actuator is installed into the machine it’s impossible to tell precisely where the magnet within the piston is in relation to the external barrel, and often you don’t know the end final positions of the actuator. This results either in the elastomer cushioning being compressed beyond the ambient pressure position at the end of stroke, or the cylinder not reaching its end- position due to external stops. Consequences include wear and tear on the cylinder, noise and vibration. So, what was easy on the bench can be much harder in practice: particularly in difficult to reach


34 October 2022 Irish Manufacturing


Faster assembly times and more reliable cylinder switching are two advantages of the latest pneumatic innovation from Festo


The SDBT-MSX programmable cylinder switch from Festo learns the required switching position simply by cycling the machine four times during set-up


locations. It becomes even more time-consuming on machines with multiple cylinders: yet precise cylinder positioning is crucial to long-term reliability and operating lifetime. A couple of years ago, Festo introduced its patented self-adjusting, end of stroke air cushioning system [PPS], which addressed part of this issue and reduced build times. Now the introduction of our latest cylinder sensor switch, the Festo SDBT-MSX, is set to create a corresponding saving for all users.


LINING UP THE BENEFITS The unique SDBT-MSX is the first auto-teach cylinder switch that learns the required switching position simply by cycling the machine four times during set-up. No in-situ adjustment is required. The switch is simply dropped into place in the


approximate required position, which is made even easier on the latest generation of Festo cylinders with an indicative sensor mark. The fitter then sets the sensor up by aligning the cylinder and sensor marks, either on the bench or in situ. When the cylinder is fitted into position on the machine and the sensor is wired in, it’s LEDs will indicate that the switching point is not yet saved. Cycling the machine, including this actuator, four times enables the self-teach function and the optimum switching position is learnt by the sensor and saved. This technology has several other benefits if users want to go beyond the basic, standard operation. These include the ability to manually teach-in a position using the integrated capacitive teach button and the ability to re-assign the switching operation from PNP to NPN, and from Normally Open to Normally Closed operation. Even the switching window can be adjusted from the pre-set 2mm to any length up to 15mm if the application requires it.


The potential to use one cylinder sensor for


all applications could deliver savings in inventory, warehousing and cost. What’s more, the SDBT- MSX can be manufactured by Festo at virtually the same cost as standard sensors. It demonstrates that, even in a mature technology, innovation is still possible.


Festo www.festo.co.uk www.irish-manufacturing.com


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