System-integrated measurement technology simplifies individual condition monitoring
Significantly increased vibration on machines can result in many forms of negative impacts such as reduced system performance or damage to the machine and foundation. Condition monitoring systems (CMSs) are able to detect harmful vibrations at an early stage and optimise maintenance intervals. Using the example of retrofitting a forging press with a maximum press force of 2000 tons, Wölfel Engineering explains how efficiently the process was tailored and implemented with PC-based control and measurement technology from Beckhoff.
Based in Bavaria, Wölfel Engineering has been an expert in all fields related to vibration, structural mechanics, and acoustics for more than 50 years. “Our services range from individual consultations with engineers to delivering turnkey solutions for vibration problems,” explains Dr Marcus Ries, head of Vibration Measurement and Reduction. As a prime example of PC-based condition monitoring, he cites the customised condition monitoring of a large forging press weighing 150 tons, which was put into operation back in 1989 and modernised several times in the following years.
Reliable plant operation through condition monitoring
The first 15 years of operating the press were marked with clearly increased vibration levels, which damaged both the machine and the foundation. While renovating the foundation in 2004, engineers completely overhauled the way in which the press was installed and coupled to its foundation. Although this initially reduced the increased vibration tendency, the dynamic application forces continued to cause issues in the mechanical connections, for example, expansion screws were torn off. This resulted in increased vibrations in 2018, prompting fears of a production shutdown. To ensure that the press continued to operate reliably until the planned overhaul in the same year, the company provisionally revised the installation, while monitoring the effects with a temporary CMS based on a standard measuring system.
Ries explains why this intermediate step was successful: “Based on a renewed increase in the vibration level, combined with a further drop in the natural frequency, the CMS detected that the makeshift measures were failing. This enabled operators to directly implement countermeasures such as retightening or replacing broken connections. This prevented further damage to the concrete base as a result of insufficient pretensioning. More importantly, the machine continued to operate around the clock for several months until the scheduled repair. As the parts were being pre-produced during this time, our customer was able to build up a buffer for the imminent downtime, thereby ensuring their ability to supply.”
After repairing the press and foundation, technicians installed a permanent CMS tailored to the vibration problem in question. This was based on findings of the dynamic vibration behaviour, and also on results of the temporary CMS.” In addition our customer received training on site on how to use the system, and was assisted in defining the alarm thresholds,” says Ries. “Thanks to a specific sensor selection, and the CMS based on PC-based control from Beckhoff, our customer can now detect a change in the force pretensioning and vibration behaviour even earlier than before. They can then forward this information to the plant monitoring system in an automated and integrated manner.”
Decentralised system simplifies CMS retrofit
According to Ries, there was a prerequisite for implementing predictive maintenance. The permanent CMS had to be implemented as a retrofit solution without modifying the press design, and the monitored variables had to be fed into the existing press monitoring system via Modbus. This was supported by the open nature of the PC-based control system with regard to interfaces and communication systems. Wölfel Engineering considers this to be a great advantage because it enables the end user to obtain initial condition assessments easily.
In addition, the decentralised sensor connection, which forwards data via EtherCAT, minimises the cable routing paths and greatly increases the system reliability. In fact, Wölfel Engineering can rely on proven industrial standard components with PC-based control, which is reflected, among other things, in its exceptional reliability and failure-free operation since 2019. This also includes the EtherCAT Box modules for data acquisition, which enable on-site digitisation when installed directly on the plant, and prevents long analogue signal paths.
With the selection of the right sensors, which are placed directly on the critical force-transmitting components, the new CMS provides direct insight into the state of the press installation and foundation. EL3114 analogue input terminals, for example, collect data from position sensors. This allows the pre-tension (tie rod) to be measured to detect a bolt crack as primary damage. It also concludes that a displacement at the disc spring unit represents crack formation, i.e., secondary damage to the foundation. The EP3752-0000 EtherCAT Box modules are each equipped with two integrated three-axis accelerometers. They provide the raw data for calculating the natural frequency of the entire plant as an early indicator for renewing the foundation. They also detect any possible tilting of the head plate. The following infrastructure components are used: an EK1122 2-port EtherCAT junction for connection to the ACC press head, and an EK1100-0008 (M8) EtherCAT Coupler for connection to a further control cabinet.
Ries describes the advantages of the PC- and EtherCAT-based CMS as follows: “An approach involving PC-based control and distributed sensor technology simplifies monitoring and data processing in order to define alarm limits. Although other disturbance variables are present, their influence is minimised. The system would also have enabled complex data processing using models, advanced feature extraction, and machine learning if necessary. However, these options were not required in this case. Since commissioning, the customer has successfully used the system for predictive maintenance tasks such as planning maintenance and procuring spare parts based on demand.”
Powerful embedded PC and the future potential
The data is collected and processed centrally, and the specified alarm thresholds are monitored using a CX5140 Embedded PC with TwinCAT software (TwinCAT 3 PLC and TwinCAT 3 Modbus TCP). The CX5140 can automatically transmit warnings, alarms and information regarding the detection of faulty sensors by email. To track trends, Modbus can be used to store and transmit statistical values of the measurement data (interval data) to the customer’s in-house monitoring system. When alarm limits are exceeded, the raw signals are temporarily stored for later error analysis. “The process of defining limit values for vibrations and temperatures is quite complicated. These parameters differ from one workpiece to another, even in the case of good parts,” adds Ries. “However, when using a PC-based control platform where machine control and measurement technology are integrated into one system, the CMS always detects which workpiece is currently being processed. This means that the limit values can be precisely defined for the workpiece in question. The CX5140 Embedded PC also provides sufficient computing power, even for extensive condition monitoring applications. EtherCAT Terminals can be attached directly to the DIN rail-mountable IPC, which enables extremely compact CMS solutions.”
For future projects, Wölfel Engineering is currently examining the efficiency potential of the EtherCAT P single-cable solution, which combines EtherCAT communication and power on a four-core standard Ethernet cable. In this case, the corresponding CMS could be implemented with the EPP3174-0002 or EPP3752-0000 EtherCAT P Box modules, the EK1322 EtherCAT P junction, or the EK1310 EtherCAT P supply.
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| www: | www.beckhoff.com |
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