SDBT Proximity switch

Innovation in pneumatics

New product innovations will make a real difference to the way you build and commission your machines. Steve Sands, Head of Product Management at Festo GB, looks at how recent developments are driving the pneumatics sector.

Pneumatics can be considered a mature technology having started to become mainstream in the automation sector from the 1960s onward. It has continuously evolved with components becoming smaller, higher performance and lower cost. In the 1970s solenoid valves driven by the early generations of PLCs became state of the art. Today, we see the ongoing integration of electronics creating smart devices integrating software apps, data collection, network communications and embedded machine learning diagnostics for predictive maintenance, improved quality and energy reduction.

However, innovation isn't restricted to technical features. Human factors like usability, convenience and safety are tangible areas for development and improvement. Finance perspectives such as purchasing efficiency, inventory and SKA reduction impact overall costs. Machine assembly and build times, time on the shop-floor, or on-site commissioning costs and maintenance times are also interesting areas beyond the size, performance and cost arguments previously mentioned.

Making the switch

An interesting new introduction that addresses many of these areas comes in a product as lowly as a cylinder sensor switch. These devices are mounted on the majority of pneumatic cylinders and provide sensor feedback. They are most frequently 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.

Cylinder switches 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 constructive/destructive influence of adjacent actuators' magnetic fields, mounted in close proximity to one another, triggering or blocking the reliable sensing of adjacent sensors.

Cylinder switches may appear to be an automation commodity beyond advancement – but there is room for improvement.

Installation challenges

Mounting a cylinder sensor on the bench is straightforward 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 requires bringing the piston-rod/piston into the end position and then, with a battery or power supply connected to the sensor, moving it until you see the LED position indicator show it is in the correct output position. For reliable repeatability, the optimum switching position is mid-way within the sensing position hysteresis. Setting at the edges of the switching window should be avoided as it can give rise to problems later.

On a workbench this is simple, quick and easy to do. However, once the actuator is installed into the machine it is impossible to know precisely where the magnet inside the piston is physically located in relation to the external barrel and you often don’t know the end final positions of the actuator. Commonly, either the air pressure compresses the elastomer cushioning at the end of stroke beyond the ambient pressure position or the cylinder doesn't quite get to its end-position due to external stops. Consequences of poor cushion setting include wear and tear on the cylinder, noise and vibration.

An experienced fitter will set up the switch approximately on the bench and then make the final setting by cycling the cylinder in-situ on the machine. What is an easy job on the bench, can be much harder when access is required inside the machine guarding, at height or in difficult to reach locations. In these circumstances, accessing the sensor Allen key position, adjusting, and observing the indicator LED can require dexterity and suppleness that not all of us possess!

This final setting and adjustment of cylinder sensors, along with speed adjusting flow controls and cylinder end-of-stroke adjustable air cushioning, takes a considerable amount of time on machines with multiple cylinders and yet it can make a big difference to long-term reliability and operating lifetime. The introduction by Festo a couple of years ago of the patented self-adjusting end of stroke air cushioning system [PPS] addressed part of this issue, cutting build times accordingly.

Now the introduction of the 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 suitable for all compatible T-slot cylinder grooves. It 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: instead the switch is dropped into place in the approximate required position. This is made even easier on all of the latest generation of Festo cylinders with an indicative sensor mark. The fitter simply sets the sensor up by aligning the cylinder and sensor marks. This can be done on the bench. When the cylinder is fitted into position on the machine and the sensor is wired in, it’s LEDs will indicate 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.

The technology within the sensor doesn't need to be considered by the user: however, for those that want to know, it utilises a 20mm long hall sensor array and integrated electronics. 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 also 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. This is where purchasing, stores and maintenance can gain – one cylinder sensor for all applications.

Summing up

It is reassuring to know that even in what may be considered the most mundane areas of automation, innovation is still thriving and will have a real positive impact on users. Faster assembly times, more reliable switching, plus less time stretching, going up ladders or lying under machines have got to be welcome improvements.

And there is more good news: due to the planned quantities, the SDBT-MSX can be manufactured in-house by Festo at virtually the same cost as standard sensors. So, most users can buy them at virtually the same price they are currently paying for their standard reed switches or solid-state magneto-inductive cylinder switches. Innovation doesn’t always come at a cost.