> Overview

„The dual-encoder measurement system“

Bihler’s NC units (NCA) ensure that tool movements are executed with outstanding speed and precision. The integrated dual-encoder measurement system contributes greatly to this task. The system, which was developed exclusively by Bihler, compensates for the forces and external influences that occur during production and in this way ensures the greatest possible process consistency, with a positioning and repeat accuracy of +-0.01 millimeter.

Otto Bihler Maschinenfabrik introduced its NC technology and, with it, the first servo-controlled NC units some 20 years ago. A few years later, the company developed its exclusive dual-encoder measurement system which ensures outstanding precision at the servo-controlled units. Among the components that make up these solutions, there is a servo motor together with an initial encoder, as well as a stationary measuring head acting as the second encoder and a moving measurement gage. The gage is located at the mandrel, that is to say on the working part of the NC unit. The measuring head is located in the front third of the housing. Thanks to these installation positions, measurements are taken very close to the running process and all the factors at work are optimally recorded. In practice, the actual position of the mandrel is transmitted to the regulator in the control cabinet in real time. The regulator controls the motor and continuously compensates for any deviations in position.

1 Servo motor together with first encoder 2 Stationary measuring head acting as the second encoder 3 Moving measurement gage

Automatic compensation

The positioning of NC units is therefore always absolutely accurate, both in the presence of changing forming forces acting externally and in the case of gradual changes, such as changes in temperature due to the heating of the machine during operation or fluctuations in the material. The dual-encoder measurement system reacts automatically and can therefore compensate ideally for such influences. This results in exceptional process consistency and manufacturing precision, with excellent positioning and repeat accuracy of ±0.01 millimeters. Another advantage: Thanks to the exact positioning of the NC units, no travel limit stops are needed because the overshoot that occurs with mechanical slide units is completely eliminated.

No more reference runs

Another highlight of the dual-encoder measurement system lies in the fact that it is an absolute measurement system. This means that the exact position of the mandrel is known at all times and all the axes always know exactly where they are currently located. As a result, for example, there is no need to perform a reference run if there is an occasional power outage, the machine is shut down unexpectedly or even after the NC units have been manually adjusted. In practice, this reduces potential stoppage times and ensures that production is resumed extremely quickly after a shutdown. The NC units are programmed via the Bihler VC 1 controller. Easy-to-use input screens permit the simple, fast parameterization of the units, which Otto Bihler Maschinenfabrik has always developed, manufactured and assembled inhouse.

The NC unit continuously compares the position by means of the dual-encoder measurement system.

Practical value added

The dual-encoder measurement system is present in many NCA units and is used, for example, in the Bihler GRM-NC and RM-NC servo-controlled stamping and bending machines just as it is in the Bihler BIMERIC servo production and assembly system. In these systems, the individually programmable NC units permit outstanding precision, speed and flexibility. In this way, they permit the fast, precise execution of tool movements, with process speeds of up to 1,000 rpm coupled with freely programmable stroke movements and movement profiles. Maximum force is also available across the entire operating range and, last but not least, there is no need to change any mechanical components at setup time.

In the diagram, the nominal and actual curves are perfectly superimposed and are displayed here as a turquoise line.

Andreas Möst
MB engineering design/
NC development

Tel.: +49(0)8368/18-9508


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