Case study: KUKA robot automates calibration procedure for measuring instruments

by David Fleschen

In measuring technology, maximum precision is the only thing that counts. This provides ideal conditions for the use of robots. For efficient use, however, they must be able to grip various large objects without damaging them. At measuring technology specialist Perschmann Calibration GmbH, the sensitive KUKA LBR iiwa robot performs the loading of a coordinate measuring machine and thus automates the calibration process. In addition to this, the measuring instruments are equipped with codes which inform the system of the measurements to be carried out.

“A human hair is roughly 50 µm thick and the silk threads of a spider are approx. 5 µm. The precision with which we at Perschmann Calibration calibrate measuring instruments is approx. 0.5 µm,” explains Dr. Detlef Rübesame, Head of Technology at Perschmann Calibration GmbH. The calibration service provider from Braunschweig specializes in the calibration of manual measuring instruments. Among other things, it performs the high-precision inspection of gauges such as measuring pins and setting rings. The measuring instruments must be calibrated at regular intervals. The company’s customer base consists primarily of customers from conventional mechanical engineering, the automotive industry or the aerospace sector. The customers use the measuring instruments for quality assurance in their production processes.

Measuring instruments must be regularly calibrated in accordance with Standard ISO 9001 in order to fulfill international quality standards. Exact values are thus measured during the calibration process so that not even small dust particles can influence the measurement. Besides dust particles, the temperature also has an impact on the measurement result. For this reason, the temperature is continuously maintained and the measuring instruments themselves are also subject to a controlled climate for a defined period of time so that no measurement variation can occur.

Creating added value for the customer

Medium-sized enterprises such as Perschmann Calibration GmbH are constantly searching for future-oriented solutions to remain competitive in their business segment. “In collaboration with KUKA, the company Hexagon –which also produces the coordinate measuring machine – introduced us to a concept for the automation of our calibration process and, as a result, to an even more customer-friendly option for the quick calibration of many different measuring instruments. We adopted the idea right away,” recalls Detlef Rübesame.

Since December 2017, the KUKA flexFELLOW solution upon which the sensitive KUKA LBR iiwa (intelligent industrial work assistant) robot is installed has been used at Perschmann Calibration. It is able to sensitively pick up various measuring instruments from a material provision carriage and feed these to the Hexagon coordinate measuring machine for calibration. The robot – which is also suitable for human-robot collaboration (HRC) – works in three-shift operation.

Fully automated calibration procedure thanks to Industrie 4.0 elements

“The ultra-high precision Leitz PMM-C is ideally suited for challenging measuring tasks. Due to the increased precision down to the lower sub-micrometer range, the various measuring instruments are calibrated reliably,” notes Felix Balzer, Manager of R&D Sensors and Machines at Hexagon Manufacturing Intelligence.

Perschmann enjoys numerous advantages from the robot-based application. The procedure is shortened and the calibration process can become more customer-oriented since the collective processing of various measuring instruments is no longer a problem with the KUKA lightweight robot. “Automation makes sense since we deal with very large quantities. At the same time, the system is coordinated in a way that allows it to work autonomously for a long period of time,” explains Detlef Rübesame. An important question while planning the production changeover was how the coordinate measuring machine and the LBR iiwa could detect and assign the various different geometries of the measuring instruments. The measuring instrument itself meets this challenge by controlling the measuring process. Equipped with a data matrix code, it forwards all important information (such as the type of measuring equipment or the diameter) on to the coordinate measuring machine. Using this special data matrix code (DMC), the coordinate measuring machine can independently initiate the measurement. Intervention by an employee is no longer necessary.

The second advantage of the system is that the robot detects if the compartment is empty and reacts by independently moving to the next full one. This is real added value since the robot can therefore continue working autonomously during the night shift. The next morning, the employee finds a fully-calibrated unloading system.

Handling various measuring instruments using a sensitive robot

“The Leitz PMM-C stands out with its unique moving table technology. Here, the coordinate measuring machine gantry is fixed and the measuring table is moved. This ensures a high degree of stiffness and long-term stability – the basis for ultra-high precision measurements,” says Felix Balzer.

In addition to the PMM-C coordinate measuring machine from Hexagon, the system is equipped with a KUKA flexFELLOW solution. The KUKA flexFELLOW is a complete solution, consisting of a robot platform on which the HRC-capable LBR iiwa robot is installed. Two transport units with fork slots are provided for this. In the first work step, the LBR iiwa moves to the first transport unit and checks whether there are measuring instruments in the individual slides. It then removes these instruments and moves them into the correct position for the scanner. Besides scanning, the measuring instrument has air blown on it to eliminate any dust and prevent incorrect measurement. Once the system has identified the type of measuring instrument, the LBR iiwa clamps it in the clamping device. The coordinate measuring machine then starts the calibration procedure. Once the process is completed, the robot grips the measuring instrument again and places it in the second transport unit. Meanwhile, the information about the calibration procedure is transferred to a computer where the certificate is issued for each part.

Robot works autonomously during the night shift

With the KUKA LBR iiwa, Perschmann Calibration can now calibrate around the clock – and do so in two different modes. Whereas production during the day runs in the safer, slower HRC mode, a switch to into full automation mode can be made at night when no people are in the robot’s working range. The KUKA LBR iiwa then works ten times as fast. This is possible because other safety regulations apply to operation without humans. Thanks to the additional, fully-automated calibration during the night shift, Perschmann Calibration GmbH gains additional inspection capacity.

Detlef Rübesame is very pleased with the new process and believes that the investment in the system will soon have paid for itself.  “The task of management is to ensure that we continue to be proactive and are not forced to react by the actions of others. With the full automation of the calibration process, we have taken a further step in this direction.”

Source and photo: Kuka

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