Precision Pneumatic Pressure Monitoring for Robotics and Industrial Applications

Precision pressure monitoring using pneumatic sensors is crucial in various robotics and industrial control applications. To ensure reliable operation, pressure monitors must have excellent overpressure and vacuum resistance and should include a measuring cell that’s insensitive to liquids or deposits.

In addition to precise and robust operation, application flexibility is a key feature that can expedite initial installation and support configuration changes, enabling mass customization in Industry 4.0.

The monitor should include an easy-to-read display for quick status checks, programmable outputs for alarms, and local setup and operation using integrated pushbuttons. IO-Link is required for digital data transfer for remote process monitoring and configuration. In some installations, having an analog output is beneficial.

Support for multiple mounting configurations can ensure compatibility with a wide range of system designs.

This article presents the PQ series of precision pressure monitors from ifm Efector (ifm) and details how they cater to diverse needs for pneumatic and compressed air systems in a wide range of industrial and robotics applications.

User interface

The visual interface is a key feature of the PQ series. It includes a 1” color TFT display, switch point LEDS, and switches for changing the display and setting parameters. The primary process value measured is pressure, and it can be displayed in various units, including bar, psi, or kPa. The vacuum level can also be represented as a percentage of the set point.

The display can show the configuration set point (SP) and reset point (rP) for the digital outputs. Switch points are signaled using LEDs. For models with an analog output, the display can be used to set and show the analog start point (e.g., 4 mA) and end point (e.g., 20 mA) for scaling the signal. The user interface includes several elements (Figure 1):

1. Switching status LED lights if output 1 is active
2. Switching status LED lights if output 2 is active
3. TFT display elements:
   1. Device status
   2. Process value. The display can switch from a standard color (green) to an alternative color (red), making it visually clear when the process value moves into or out of an acceptable range.
   3. Diagnostic and performance information, such as the number of switching cycles and the lowest or highest pressure recorded. In Figure 2, Hi.P indicates the highest measured value for pressure.
4. Keys for display configuration and parameter setting

Figure 1: Layout of the PQ series user interface. (Image source: ifm)

The PQ series is available with and without a configurable analog output. PQS models, such as the PQS812, have two digital outputs, while PQC models, like the PQC812, feature a configurable analog output in addition to the two digital outputs. The analog output on the PQC models can be used to send a proportional signal.

Machine and automation designers can select devices with specific measurement ranges. The PQS812 and PQC812 have measurement ranges of -1 bar to 10 bar (-100 kPa to 1,000 kPa, -14.5 psi to 145 psi). Models PQS816 and PQC816 are designed for lower-pressure and vacuum applications, with measurement ranges of -1 to 1 bar (-100 to 100 kPa, -14.5 to 14.5 psi). Applications that require only vacuum measurement can utilize the PQS819 and PQC819, which feature measurement ranges of -1 bar to 0 bar (-100 kPa to 0 kPa, -14.5 psi to 0 psi).

Compressed air treatment is a common operation in pneumatic systems. It’s the process of removing contaminants, such as moisture, oil, and dirt, from the compressed air to protect pneumatic equipment, ensure system reliability, and maintain product quality.

The PQ series is especially suited for compressed air treatment systems since the coated and sealed silicon measuring cell maintains its performance in the presence of air contaminated with water, dust, or oil.

Vacuum gripping applications are a common use of PQ series pressure sensors. These applications can include multiple pick-up effectors. The red/green color change of the display provides operators with an at-a-glance visualization of the process values of each pick-up (Figure 2).

Figure 2: Diagram of PQ series pressure monitors used in a vacuum gripping application, showing one gripper with too low a vacuum (red display). (Image source: ifm)

Application versatility

The PQ Cube pressure sensors are suited for a variety of pneumatic applications, including food and beverage packaging, industrial palletizing machines, consumer white goods manufacturing, and more.

In food and beverage operations, package seals are positioned using a vacuum gripper. In these packaging machines, the IP65 rating is an important feature. It indicates that the sensor is protected against low-pressure water jets from any direction.

To achieve optimal performance, the sensors in food and beverage packaging machines should be positioned as close as possible to the vacuum gripper, utilizing short hose lengths. That places the sensor within the cleaning area of the machine, subjecting it to sprays of water and cleaning chemicals that the PQ Cube easily handles with no loss of performance or reliability.

Vacuum gripper technology is also a key element of robot palletizing machines. PQ Cube pneumatic sensors accurately and quickly determine if sufficient vacuum is available to grip a box. Only when the box is correctly gripped will the machine move it into position on the palletizer (Figure 3).

Figure 3: Palletizing machine showing the position of the PQ Cube sensors (middle frame). The sensor on the left has a red display indicating an out-of-specification condition. (Image source: ifm)

White goods, such as dishwashers, can have dozens or even thousands of model variations in terms of size, shape, color, and technological features. With such a wide variety of components, the use of vacuum grippers is necessary to ensure efficient and smooth production.

The gripper must be actuated with a specific process pressure to secure delicate components without damaging them, and then quickly place and release them during assembly. The 6 ms response time and high precision of PQ Cube sensors are important features in these robotic applications.

These machines often use two PQ Cubes. One for the placement of components and another for a maintenance unit that monitors the overall pneumatic system pressure and supplies two robotic assembly stations.

Custom build the machine

The application flexibility of PQ sensors extends to machine construction. The device can be installed in panels using the E30574 mounting kit. The E30576 wall mounting adapter is another option, and so is the E30575 DIN rail mounting kit.

The sensor can also be mounted to a panel without a mounting kit using two cylindrical screws. For this purpose, the cylindrical screws are first screwed into the panel, then the device is placed on top and locked downwards.

That’s not all. Connecting both process connections to pipes enables PQ sensors to be used as a pneumatic distributor without the need for additional adapters. In other applications, using one of the two connections on the sensor allows for flexible installation on a pipe, enabling precision pressure monitoring with the unused connection closed by a sealing plug.

As machines with PQ sensors are installed, technicians can utilize the installation wizard to expedite the process. The wizard can be implemented on the device using the integrated buttons. It’s available in nine languages and steps through the setup and installation process by asking a series of questions. Installation can also be accomplished using IO-Link.

IO-Link boosts productivity

IO-Link enables digital connectivity beyond the machine to higher-level field buses, speeds up the installation and commissioning of new machines or replacement PQ sensors, and supports configuration changes in existing machines, as well as centralized performance monitoring and diagnostics.

A standard 3-wire sensor/actuator cable is used with IO-Link connections. The PQ Cube connects with an IO-Link master, which provides higher-level connectivity, typically via an industrial Ethernet protocol, to devices such as programmable logic controllers (PLCs) and human-machine interfaces (HMIs), including flat-panel monitors.

IO-Link enhances the performance of PQ series devices by enabling robust digital communication, providing high-resolution data, and supporting more advanced diagnostics. Instead of relying on traditional analog signals or the standard I/O (SIO) interface, IO-Link provides greater accuracy and reliability (Figure 4). SIO is the basic ability to operate as a binary switching sensor.

Figure 4: Example of SIO and IO-Link communication on pin 4. (Image source: ifm)

The onboard memory in these sensors can store operating hours and up to 20 events, such as pressure spikes that exceed a user-defined threshold. Additionally, the system temperature can be transmitted along with the pressure and process values, enabling predictive maintenance.

Using ifm’s moneo software supports remote configuration and adjustments of sensor settings. In the rare event of a device failure, the moneo software can automatically transfer the necessary configuration to the replacement sensor, minimizing downtime.

Conclusion

PQ Cube sensors from ifm feature robust construction, user-friendly operation, versatile communication options, and flexible installation, making them ideal for a range of pneumatic applications. They have fast response times, high precision, and advanced features needed in Industry 4.0 automation and robotics systems.

Recommended reading:

1. How to Make Smart Factory Actuators More Productive Using IO-Link
2. Working Through the Complexities of Selecting the Right Safety Controller
3. Sorting Through Proximity and Distance Sensor Technology Choices
4. Optimizing Industry 4.0 Communication Architectures using Multi-Protocol I/O Hubs and Converters
5. Using Cybersecure PLCs with Integrated Safety for High-Speed Industrial Automation