Know your pneumatics – Continuous Position Sensing

26 February, 2018

Modern factories are increasingly using industrial networks to make their sensors and actuators more intelligent and the deployment of smart sensors, such as Continuous Position Sensors (CPS), is certainly the pathway to achieving smart motion control in pneumatic systems. These intelligent devices offer more sophisticated, flexible, effective and efficient factory automation, and ultimately, with two-way data flow, help facilitate what can be defined as a true Industry 4.0 environment.

As one of the three principal building blocks of ‘smart pneumatics’ (along with processors and communications protocols), the latest smart sensors are being developed to bring intelligence to pneumatic motion control and provide the necessary continuous data in what are often challenging or harsh operating conditions.

Smart factories

Most manufacturers have their own ideas and interpretations of ‘smart factories’ and what they can offer. However, a common theme is the need for embedded components to have additional intelligence, thereby enabling machine-to-machine communication and response. All of these ideas eventually come down to more practical aspects such as system architectures and how the multitude of new sensors will communicate via the network.

To appreciate the potential of continuous position sensing, it is best to first consider how they function. CPS use contactless technology to continuously detect the linear position of a piston in its cylinder. The data communicated by the sensor allows monitoring and, when information flows in both directions and actuators are employed, control. The result is the transformation of pneumatically actuated processes from ‘dumb’ to intelligent; meaning that positional data is available, which can enhance monitoring and control, allowing for fast detection of any issues that might cause downtime or potential loss of productivity. The intelligent functionality of smart sensors includes the ability to acquire information and communicate with upper level controllers and/or local networks. Importantly, the quick, precise and high-resolution sensing of the piston magnet is achieved without the need for separate position encoders or additional mechanics, therefore minimising the cost of implementation.

Easy mounting

For cylinders, linear slides and grippers with common T-slot or C-slot dimensions, the latest sensors can be mounted without the need for extra accessories, while mounting on other cylinder types, such as round body, tie-rod and profile cylinders (and cylinders with a dovetail groove), is possible using a simple adaptor. Sensors that can be externally mounted on the cylinder body in this way avoid complicated integration requirements or any drilling of the piston rod itself. This design also facilitates quick and simple sensor maintenance or replacement.

Application benefits

Among the principal benefits of continuous position sensing is the ability to monitor quality and provide process control and support optimisation, especially in tensioning applications such as paper or film processing where quality, repeatability and speed are paramount to profitable operations. Here, the remote reading of data from position sensors allows process deviations to be seen quickly and acted upon, thus keeping processes optimised and supporting predictive maintenance strategies.

Many other types of applications will also benefit, including materials handling, consumer packaging, small component assembly, machine building, and even tasks in the renewable energy industry, such as the positional control of solar panels as they track the sun. With the appropriate shock, vibration, moisture, chemical and water ingress resistance, continuous position sensing can be used in challenging environments reliably over very long periods of time.

Two-way data flow

The monitoring of sensor data via traditional discrete or analogue signals is one-way communication; this is sufficient to allow the remote monitoring of automated processes, for example. However, in order to implement Industry 4.0 strategies, two-way communications are required meaning a connection to a network such as Profinet or IO-Link. In terms of CPS implementation with pneumatics, it would include not only monitoring, but also automatic configuration at start up and/or during maintenance replacement.

Among many industry trends, the smart factory concept is moving from a reactive to a proactive mode of maintenance. If smart sensors can tell the end user what is wrong before failure, then maintenance personnel will be able to schedule repairs and avoid downtime. In many cases, the early sensor notification of issues allows system operators to investigate, consider, plan and schedule the required corrective maintenance for a time when production throughput is either low or can be stopped. This could be overnight, or during a larger planned plant maintenance shutdown.

Smart manufacturing plants can only implement a predictive maintenance approach by collecting significant amounts of sensor data; and that data ideally needs to be in real time. Furthermore, production line versatility, which is a key benefit of smart manufacturing for companies making a number of different products, needs data to support decisions and then adjust and re-balance lines. In both cases, a key factor is being vendor agnostic, which frees users to deploy and combine the optimum system components for their particular process.

Leveraging IO-Link

Another critical part in the success of Industry 4.0 manufacturing strategies is choosing the right protocol to connect sensors with controllers and actuators. Here, IO-Link provides the ideal solution, allowing two-way communications to receive data and then download a parameter to the device/actuator. As a result, processes can be adjusted remotely.

IO-Link is a relatively new open communications protocols that was introduced in 2008 by Siemens. The protocol is the first IO technology for communication with sensors and actuators to be adopted as an international standard (IEC 61131-9), meaning that devices can be integrated in the same way in all commonly used fieldbus systems and automation systems, right up to enterprise resource planning (ERP) level. However, it should be noted that IO-Link is not a fieldbus; it enables point-to-point communication between field devices and the automation system. Whereas integrating a fieldbus interface all the way down to the lowest field-level device was typically expensive, IO-Link is a simple, more economical system.

The advantages of IO-Link include the automatic detection and parameterisation of the IO-Link device, device monitoring and diagnostics, changes on the fly, and reduced spare part costs.

Ultimately, the key to unlocking the power of smart sensors is in making diagnostic information easy to access. IO-Link allows for cyclic data exchange capabilities so that programmers can easily send the information directly to where it is required; either to an HMI screen, a signal light or a maintenance request. If sensor or actuator parameters need to be changed or calibrated, this can be done remotely, even while the production line is still running, ensuring that shutdowns, stoppages and unnecessary costs are avoided.

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