How Digitising Vacuum Generation Enables Predictive Maintenance and Saves Energy
Published on : Friday 01-10-2021
Piab has upgraded its flagship product – the piCOMPACT® vacuum ejector series – to support Industry 4.0 functionality.
Predictive maintenance is usually defined as monitoring performance and condition of equipment during normal operations. This implies that simply providing a highly efficient, reliable, and small enough to integrate vacuum ejector is no longer enough. Vacuum ejectors powering robotic gripping systems such as suction cups, foam grippers, etc., for pick and place applications common for example, in automotive press-shops are the interconnection between the gripping unit and the robot and can provide insights into both sides to ensure a smooth-running system.
When digitising their flagship product to a smart version, the Piab R&D team therefore put a lot of emphasis on supporting the requirements of predictive maintenance to increase their customers’ competitiveness. The piCOMPACT®23 SMART ejector combines state-of-the-art technology to keep systems up and running at the maximal possible level while minimising energy consumption.
Connectivity allowing communication between devices and the cloud are at the centre stage of any Industry 4.0 set-up. It is a prerequisite for all other Industry 4.0 functions as it allows the interchange and collection of data. This enables among others real-time adjustments of single or multiple settings without the need for a reset of the entire system. Thereby, it simplifies, e.g., maintenance or exchange of parts, which in turn reduces downtimes and increases productivity.
However, in an industrial landscape built with a plethora of different fieldbus protocols, i.e., network systems for real-time distributed control, and with no standardisation in sight, it is difficult for suppliers to know where to start. With different countries and industry segments presenting different preferences, the challenge is often to find solutions that suit as many as possible. Therefore Piab decided to realise connectivity of its piCOMPACT®23 SMART ejector with other devices through an IO-Link.
IO-Link works with any fieldbus
IO-Link by-passes this problem as it is not a fieldbus, but a generic communication technology that will fit any type of fieldbus. IO-Link is the first worldwide standard (IEC 61131-9) for IO technology used for sensor and actuator communication. The powerful point-to-point communication is based on the long established 3-wire sensor and actuator connection and places no additional requirements on the cable material.
Offering fieldbus-independence, IO-Link is a further development of existing, tried-and tested connection technology for sensors and actuators. It offers automated parameter setting and enables operators to read and write parameters for various features even during operation. Such a degree of process overview in real-time means that many potential issues can be dealt with before they have any real impact on the production. The opportunity for system diagnosis allows problems to be identified and corrected more easily and quickly. This has the potential to lead to greatly improved productivity.
One of the key factors behind this diagnostic ability is that contrary to conventional technology, IO-Link offers a data storage function. This enables operators to quickly establish if and why a device or operation might have failed during, for instance, an over-night run. It makes it possible to identify the cause of a failure; perhaps a faulty device needs to be replaced, or the culprit might simply be an incorrect electrical connection. Additionally, if a new, identical substitution device is connected, the parameters of the previous device are automatically transferred saving on precious installation time.
Big data analysis requires measurements of various characteristics to generate the information that can be analysed and used for system optimisation. Sensors enable the collection of information that can be used to improve productivity and reduce downtime, facilitating condition monitoring and predictive maintenance. This led to several sensors being added to the system measuring direct operation characteristics of the vacuum ejector for quick detection of potential operational issues such as leakage in the system, the ejector not running well for enabling predictive maintenance. Users can set trigger points and when data deviates and passes such a trigger point, it is an indication that maintenance will be needed soon. This allows preparation, the exchange of only few parts and avoids unforeseen production line shutdowns.
Therefore, Piab’s R&D team decided to equip piCOMPACT®23 SMART directly with several diagnostic sensors that support predictive maintenance measuring system temperature current, system voltage, acceleration, cycle counter and system self-check features. Changes in these can indicate that something else is broken in the robot cell or plant. Hence, piCOMPACT®23 SMART helps to monitor the whole automation systems and prevents any issues with connected or surrounding equipment in addition to increasing understanding of how the ejector itself is running.
A sensor shows the real operating temperature to ensure fast information in case it moves out of this range, which may indicate problems in the closer environment of the ejector. This feature was integrated on the one hand to increase the ejector’s lifetime and ensure its optimal operation but also as an easy to detect warning signal that there may be issues with other system devices that causes temperatures to rise. A voltage sensor controls the power input and determines the operational status. This feature was added to support users in avoiding damages to the system due to low power and increase the overall systems lifetime. Low power “voltage” in function and warnings are given.
An important parameter to predict maintenance of vacuum-based robotic gripping systems is to keep them clean. Especially in dusty applications where vacuum filters will contaminate over time, which leads to unwanted vacuum pressure drops that slows down the process or even starts to give false signals. A way to monitor this is to keep control of the vacuum system’s built-in pressure drop level, or as it is named in the piCOMPACT®23 SMART; the Free-running Vacuum Level (FVL). When and if the FVL starts to drift from its initial status, the Fresh Free-running Vacuum Level (FFVL) of the system is starting to clog.
Another way to predict maintenance from the beginning to a leak in a vacuum system, e.g., damaged tubing, fittings or a broken suction cup, is to track the time to evacuate to a certain vacuum level. The piCOMPACT®23 SMART refers to its function First Time To Hit (FTTH) in a fully functioning vacuum system which measures the fastest evacuation time from the Fresh Free-running Vacuum Level (FFVL) and further down -15 kPa deeper in vacuum. When and if later cycles use longer time to evacuate to the same level (-15 kPa), monitored and logged as Time To Hit (TTH), the system most likely suffers from leakage and needs service.
Improved safety features
With an eye on the automotive industry with its high degree on automation and handling of large and heavy parts, safety of operations plays an important role when the machines are running as well as when maintenance takes place.
This led to the development of separate power domains for actuators and sensors. The sensor power is also used as main power for the unit. The separation is done by optocouplers. Such systems allow activation of the sensor power separately by the operator for maintenance or trouble shooting in the robot cell while leaving actuators disconnected from power supply, so operators are not endangered by moving parts in case, e.g., of a short circuit. The advantage of the separate power domains is that it allows the use of compact style ejectors without separate valve stations. This reduces the cost of installation – as does the fact that usually expensive workarounds or add-on modules to compact ejectors are not required.
A second safety feature developed is a complementary bit or PDO (process data output). This needs to be enabled to activate vacuum or blow, in addition to the ordinary vacuum or blow signal. It also avoids a “too quick” vacuum on signal creating a risky situation if the rest of the program is not yet fully up and running or communicating. When the complementary bit is enabled it needs to be the opposite of the vacuum signal to get vacuum on and off to function.
Reasons for using multistage vacuum ejectors
Vane pumps are the most common type of mechanical vacuum pumps. These pumps have individual rotors that spin at high velocities. The rotary motion traps air entering the intake port and sweeps it through, creating a vacuum behind the port.
The piston pump, another mechanical pump type, uses a rocking motion to displace air from one side of the system to another. The regenerative or centrifugal blower is a type of mechanical pump that works much like a fan in reverse. Blowers typically produce large amounts of vacuum flow at low levels of vacuum pressure.
A feature common to all mechanical vacuum pumps is that they need to be individually powered either by electric motors or internal combustion engines.
In a compressed-air-driven vacuum pump, compressed air is forced through a small orifice or ejector nozzle at very high speed, resulting in negative pressure building up inside the system. From the outside of the system, atmospheric pressure attempts to balance this negative pressure and reinstate equilibrium. This creates the vacuum flow or induced air flow. The way this works is known as Bernoulli’s principle, after the 18th century scientist Daniel Bernoulli, who discovered that an increase in the speed of flow occurs simultaneously with a decrease in pressure. This means that fast-moving air results in a lower pressure than slow-moving air. Bernoulli presented his findings in the book Hydrodynamica in 1738, and his principle, which can be derived from the principle of the conservation of energy, is of critical use in aerodynamics.
The simplest type of compressed-air-driven vacuum generator is known as a single-stage ejector. In this, as indeed in any air-propelled vacuum generator, the vacuum level produced depends on the diameter of the ejector nozzle. The air stream will reach its highest velocity at the narrowest part of the ejector nozzle, which is also where the deepest vacuum level is created. The compressed air used to generate the low pressure, and the vacuum flow that is created to balance it, mix, and exit through an exhaust.
For a single-stage ejector, the ratio of air consumption to generated vacuum flow is never better than 1:1, but most commonly it is 2:1 or 3:1. In other words, for every 3 cfm of compressed air, only 1 cfm of vacuum flow is generated. This is quite inefficient.
By combining several ejector nozzles and chambers in series, a more efficient multi-stage-ejector pump can be achieved. In the multi-stage-ejector pump, compressed air enters the pump and is led through a system of ejector nozzles and chambers of varying sizes that act as a “pressure amplifier”.
Different vacuum pressures are created at each chamber opening, due to different ejector nozzle diameters. There is also a common chamber in which the vacuum pressure is greater because of the combination of vacuum pressures in all other chambers. Atmospheric pressure outside the system rushes inward attempting to create equilibrium, generating an efficient vacuum flow.
The higher level of vacuum pressure in the common chamber causes rubber diaphragms or flap valves to close over the chamber openings. The only chamber not sealed is the first vacuum chambers where the deepest vacuum levels are attained. The mix of compressed air used to generate the low pressure and the vacuum flow exits through the exhaust. This process is completed in milliseconds and repeats continually as the vacuum level rises and falls.
Multi-stage-ejectors make optimum use of the energy stored in the compressed air through specially designed air nozzles and a series of progressively larger ejectors that allow the compressed airflow to expand in controlled stages. As a result, typical ratios for compressed air to vacuum flow are 1:3, i.e., every 1 cfm of compressed air results in 3 cfm of vacuum flow.
Hence, multistage-ejector vacuum pumps are considerably more efficient than single-stage ejector pumps, and offer many benefits over mechanical vacuum pumps, such as quiet and virtually maintenance-free operation, few moving parts, no heat generation, no vibration, and no oil mist. Additionally, they are usually smaller and lighter in weight an important characteristic for robot and particularly cobot integrated applications. When designing a system, multi-stage ejectors can simply be added in the same system to achieve higher power.
Saving energy by using it in a smart way
One of the major requirements is the reduction of energy consumption as much as possible as this does not only lower operation costs but also environmental impact.
Hence, one of the focus areas during the development of the piCOMPACT® SMART was to realise an ejector that constantly adapts to the environment and thereby minimises energy input required to ensure safe operations of the vacuum gripping device.
This was achieved by bundling several features under an energy saving header. The base energy savings function in a piCOMPACT® SMART ejector will automatically shut off the energy supply when vacuum is no longer needed in a sealed or semi-sealed system. The shut-off level and hysteresis (how much the vacuum level can drop before restart) is fully adjustable. The function can save up to 90–95% of compressed air usage in a lifting cycle.
The Energy Saving System (ES) is combined with Automatic Level Determination (ALD). This feature will automatically set optimized ES shut-off and restart levels in every cycle based on actual conditions.
The Automatic Condition Monitoring (ACM) will turn off the ES function in case of significant leakage in the system to protect the valves from going on/off rapidly and to prolong valve lifetime. A leakage warning output signal is available when ACM is triggered. The leakage warning is an important aid for preventive maintenance and increased uptime. If semi porous material such as cardboard or slightly surface leaking materials such as a bag of crisps is handled more leakage in the system may be necessary to suite the application. In this case the ACM recover cycle can be modified accordingly.
Finally, the Adaptive Pulse Width Modulation (A-PWM) reduces the power to the valves when they are in holding position and allows for full power when switching the valves to achieve as quick a response as possible.
The adaptive part allows for fluctuating voltage without impacting functionality. A-PWM will significantly reduce power consumption, generate a lower temperature, increase robustness of the installation and thereby extend lifetime of the gripping unit.
Digitising vacuum generation for pick and place applications particularly but not limited to the automotive industry is an important factor to truly realise the Industry 4.0 promises of more efficient equipment, systems and processes.
Making predictive maintenance feasible the piCOMPACT®23 SMART ensures high machine up-times not only for the vacuum system itself but for the whole automation system as it monitors a wide a range of environmental conditions that influence the systems performance.
With an eye on the automotive industry with its high degree on automation and handling of large and heavy parts the safety features not only increase operator’s safety but for the first time allow the deployment of compact style ejectors without additional expensive supporting equipment or workarounds.
Taking into consideration the continuously growing trend towards collaboration between robots and humans, Piab is now working on minimising the system size to fit ejectors that can be integrated into specific vacuum cobot gripping solution. Here the IO-Link plays an important role, while sensors can be included in the gripping unit directly. Safety functions as necessary for handling whole car parts are not as necessary due to the nature and weight limitations of cobots themselves.
To support customer requests for Industry 4.0 ready solutions, Piab set up a project to transform its main vacuum ejector, the piCOMPACT®, into a smart solution. The development was based on five pillars:
1. Connectivity to enable communication with other devices and the cloud through an IO-link
2. Sensors to enable collection of information that can be used to improve productivity and reduce downtime, facilitating condition monitoring and predictive maintenance
3. Intelligence to enable products to adapt performance based on information from sensors and the cloud
4. Increasing user safety led to the development of separate power domains for actuators and sensors, and
5. Broadening the scope of the smart energy usage concept to further increase energy savings.
Andrea Bodenhagen, Global Ownership Content Manager, Piab Vakuum GmbH
Tel: +49 (0) 6033 7960 0. Email: Andrea.firstname.lastname@example.org