Germany – Machine to machine, or M2M for short, is the magic spell for the factory of tomorrow. Only when machines can communicate with other machines without any problems will the vision of Industry 4.0 come true. But for this to work, inline metrology, integrated into the production process, is essential. Experts from the academic community and the industrial sector will be showcasing the current state of the art at the Metav in Düsseldorf from 23 to 27 February 2016.
The metrological units involved include bar, Hz, µm, kW, m/min, kN, rad or rpm. That’s just a small excerpt from the list of measured variables that describe the ongoing process status of a production operation. Only when these data are continuously available in real-time can a stable production process be implemented. The focus here is on achieving full coverage with the as-yet-incomplete control circuits. One important technical tool for this purpose is inline metrology, integrated into the production process. “Production metrology provides the foundations for imaging the real factory world,” explains Walter Kimmelmann, who heads the Model-Based Systems Department at the Faculty for Production Metrology and Quality Management of the Machine Tool Laboratory at RWTH in Aachen University. “With the data thus acquired and evaluated, the ideal operating points can be determined and optimised in a model world, and then serve as manipulated variables for controlling the real production world,” to quote the expert.
Metrology: ten times better than the tolerance
For this job profile, very sturdy and durable sensor technology is needed, which can always be relied upon to function dependably round the clock in a machine tool even under what are sometimes very harsh environmental conditions. “The golden rule of metrology applies here,” emphasises Kimmelmann. “It has to be better than the anticipated tolerance by a factor of 10.” After all, the production staff can only intervene sensibly in the process if they’re getting soundly based, dependable measured data.
But how can a thoroughbred machine tool be transformed into a valid measuring system? “The advantage of using a classical three- or five-axis system for measuring purposes is that it has the same kinematics as a coordinate measuring machine,” Machine Tool Laboratory Group Leader Martin Peterek comments. “This means that similar procedures and guidelines can be used. The aim is to determine a measuring uncertainty for the measuring process, because it’s only by specifying a measuring uncertainty that the measurements will supply a usable statement.” However, it must be remembered that the machine tool and in particular the workplace environment possess some characteristics that are metrologically disadvantageous. Requirements include precise knowledge of the geometrical errors and behaviours encountered during machining and measuring, so as to compensate for disturbance variables with fit-for-purpose metrological equipment and software. To quote Peterek: “Anyone planning to upgrade to a measuring machine should accordingly involve us at a very early stage. This is essential in order to obtain a machine that provides feedback featuring a significantly reduced degree of measuring uncertainty. The requisite steps involved, from mapping out the measuring strategy to determining the measuring uncertainty, are supported by a software package developed in-house. This enables the user to give other machines a measuring capability as well. The acquisition, processing and forwarding of the data concerned are accordingly crucial to the success of the metrological operations integrated into the process. Only when the measured data and thus the information on the product and the process are available can they be utilised for purposes of process control.”
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