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New facility for the combined generation of force and torque

  • Metrology for Economy

After a complex planning phase, the implementation of a machine allowing both longitudinal force and torque to be generated simultaneously is entering into its final phase. The measurement facility extends PTB's measuring capabilities for the calibration of so-called "multi-component sensors".

Sensors allowing the clamping force and the friction coefficients of screw joints to be measured have been available for several years. The clamping force attained is a decisive parameter to characterize the quality of a screw fitting. It is significantly influenced by friction and by the applied torque. For this reason, industry is greatly interested in improving these joints in order to obtain greater clamping forces with smaller screws and, thus, smaller tools, machines and facilities. An indispensable step towards such a goal is a uniform measurement procedure allowing various friction coefficient sensors to be compared with each other.

The novel additional facility does exactly this. After its full start of operation, it will be possible to generate axial compression forces in the range from 20 kN to 1 MN as well as torques ranging from 20 N · m to 2 kN · m. Besides the fact that the components can be introduced separately, a sensor may also be loaded with any combination of force and torque. This allows unwanted disturbing reaction such as, e.g., cross-talk from one component to the measurement channel of the other component to be investigated accurately.

The basic idea is to generate a pure torque with the aid of a force couple. In three dimensions, a force can be considered as being a vector with a fixed value and a given direction. In this case, a force couple consists of two parallel force vectors of the same value but of exactly opposite directions.

To generate such a couple, a lever-mass system in double construction was selected, as shown in the right part of Fig. 1. Weights with different masses are attached onto metallic bands, so their gravitational force acting vertically to the Earth's surface. In order to give these forces a horizontal direction, the bands are guided by a low-friction air bearing rotors and their direction is diverted. The ends of the bands are fixed to the ends of a lever of 2 meter in diameter.

Figure 1: Schematic representation of the lever-mass system (right) for the 1 MN force standard machine (left), and the combination of both systems (centre).

In order to ensure the greatest possible accuracy, distance and tilt sensors are integrated into the facility. These sensors permanently check the system for changes in orientation, and thus detect movements. Over the total duration of a measurement several stepping motors allow a constant and perfect orientation.

Other additional facilities, which allow also bending moments to be generated, are being set up. With these facilities, more effects can be investigated, with regard to special multi-component calibrations which increase the PTB's supply of calibration services.

Contact person:

Sebastian Baumgarten, Dept. 1.2, WG 1.22, e-mail: sebastian.baumgarten@ptb.de


Head of Press and Information Office

Dr. Dr. Jens Simon

Phone: +49 531 592-3005


Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig