10.10.2006
Precision force transducers measure the force as a scalar quantity on an axis given by the transducer design. In a research project, transducers shall now be developed which allow the spatial force vector to be measured. PTB develops calibration procedures for this novel measuring technique.
State of the art are uniaxial force and torque transducers with best relative measurement uncertainties of 10-4. When high-precision methods of measurement are used, up to 2·10-5 can be achieved. For many applications, however, precise information about several force components is required. This is why novel transducers have been developed by a manufacturer, which allow all force and torque components to be determined with a very small measurement uncertainty and which can be linked up with the national standards of PTB. Within the scope of a project performed in cooperation with the manufacturer, different calibration procedures as well as calibration auxiliary artefacts are investigated with the aim of optimizing the new transducers.
First of all, the transducer was installed in a loading mechanism with the aid of special mounting facilities and a force or a torque was applied to it. This, however, always allows only one load component to be generated. For the realization of force directions which can be changed by two axes of rotation, a special calibration artefact has been developed in the centre of which the transducer is installed. As no different mechanical adaptations are required for this calibration artefact, no corresponding uncertainty components must be taken into account (Figure 1). This artefact was conceived in two designs which differ in the degree of the possible rotation. This allows different transducer geometries and measuring ranges to be investigated and calibrated.
In addition, the transducer shall be investigated in the 100 kN force standard machine by precise introduction of transverse forces and bending torques. For this purpose, an adequate load frame has been manufactured for this machine. In addition, the force vector sensor will be investigated in the multi-component reference measuring device. It is the aim to quantify individual contributions to the uncertainty budget on the basis of the comparing measurements. The investigation of the calibration procedures and the mathematical description of the uncertainty model are performed in interaction with the development of the sensor as such by the manufacturer. The results constantly enter into the development of new prototypes. The objective is to make an efficient sensor available to the user by the end of 2008 which can be calibrated at PTB as a transfer standard.
Figure 1: Computer image of the spherical calibration artefact with the force vector sensor for the realization of different force directions in an uniaxial loading mechanism
Contact person:
Falk Tegtmeier, FB 1.2, AG 1.21, E-mail: Falk.Tegtmeier@ptb.de