Description of Functions
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8.24.3 Predictive Maintenance (PM)
Overview of Predictive Maintenance (PM)
In order to allow early detection of wear and other impairments to the vacuum gripping system, the ejec-
tor provides functions for recognizing trends in the quality and performance of the system. This is accom-
plished using the measured values for leakage and dynamic pressure.
The measurement value for the leakage rate and the related quality assessment in percent are reset at the
start of every suction cycle and constantly updated during the cycle as moving averages. The values there-
fore remain stable until after the suction cycle is complete.
Measurement of Leakage
The control function interrupts suction as soon as it reaches the limit value SP1. Then the leakage is mea-
sured as the vacuum decrease over time (in mbar/s).
Dynamic Pressure Measurement
This measures the system vacuum achieved during unobstructed suction. The measurement length is ap-
prox. 1 s. Thus evaluation of a valid dynamic pressure value requires at least one second of unobstructed
suction after the suction cycle has commenced. The suction point must not be occupied by a component
at this time.
Measured values below 5 mbar or above the limit value SP1 are not regarded as valid dynamic pressure
measurements and are discarded. The result of the last valid measurement is retained.
Measured values that are below the limit value SP1 but simultaneously above the limit value SP2 – rP2 re-
sult in a condition monitoring event.
The dynamic pressure and the percentage performance value based on it are initially unknown when the
ejector is switched on. As soon as a dynamic pressure measurement can be performed, the dynamic pres-
sure and the performance evaluation are updated and retain their values until the next dynamic pressure
measurement.
Quality Assessment [0x00A2]
In order to evaluate the entire gripping system, the ejector calculates a quality rating based on the mea-
sured system leakage.
The greater the leakage in the system, the worse the quality rating of the gripping system. Conversely,
low leakage results in a high quality rating.
Performance Calculation [0x00A3]
The performance calculation helps in evaluating the system status. The performance of the gripping sys-
tem can be assessed based on the measurement of the dynamic pressure.
Optimal configuration of gripping systems leads to low dynamic pressure and thus to high performance.
Conversely, badly configured systems achieve low performance.
Dynamic pressure events that exceed the limit value (SP2 – rP2) always result in a performance rating of
zero percent. A dynamic pressure value of 0 mbar (which indicates that no valid measurement value could
be obtained) also results in a performance rating of zero percent.
8.24.4 Reading the EPC Values
The results of the condition monitoring function are also available in the ejector's process input data.
However, to ensure that the different pairs of values can be read using a controller program, the EPC-Se-
lect acknowledged bit is provided in the process input data.
Proceed as follows to read the EPC values:
1. Start with EPC-Select = 00.
2. Create the selection for the next value pair you require, e.g. EPC-Select = 01.
