Calibration interferometers for measuring of straightness, angle and position
Two calibration interferometers were developed for measuring lengths up to 6 m especially for narrow spaces. The high-precision straightness measurement makes them also suitable for the alignment of machine components.
Calibration interferometers are used, wherever highly accurate detection of rotational and translational guidance deviations of linear positioning axes, machine tools and coordinate measuring machines is required. In addition to the high measurement resolution and linearity achievable, the traceability to the metre specification is a decisive advantage of the interferometric measurement method. This is ensured by the frequency connection of the laser source used as a benchmark.
The high-precision requirements of a system can only be achieved if the existing deviations are known. These can be documented, for example, in the form of acceptance reports. Nevertheless, what is much more important is the fact that the accuracy can be increased by a compensation of the existing deviations – be it linear axis, coordinate measuring machine or machine tool.
As with all interferometers of SIOS Messtechnik GmbH, the basic concept of the calibration interferometers presented here is the use of a fibre-coupled sensor that avoids any heat generation at the measurement site. The measuring reflectors are completely passive, which means they are electrically and magnetically neutral. Another important advantage is the simultaneous acquisition of several measured variables, a principle that SIOS has been following for more than 10 years, since multicomponent measurements allow a mutual assignment (also random proportions) of guidance deviations and also drastically reduce the required measuring times.
The SP 15000 C5 laser Interferometer has already proven itself on the market as a system that records the linear position up to a distance of 50 m, the pitch and yaw angle as well as a straightness component by laser interferometry in a single measurement process. Special advantages of the system are the long range in the high angular resolution as well as the large measuring ranges for the angle and straightness measurement. This and the integrated alignment aids make system alignment child’s play.
However, in a number of applications, the space available in the machine is limited, or the permissible mass of the measuring reflector is limited due to the system design or measurement task (dynamic analysis). In addition, the attachment of the components of the measuring system can be difficult especially in machine tools.
Since the required measuring range is less than 6 m in many cases, two new calibration interferometers with a compact sensor head and a compact measuring reflector for measuring lengths up to 6 m have been developed on the basis of the tried-and-tested SP 15000 C5.
The position resolution and the resolution of the interferometric straightness measurement remain the same as with the SP 15000 C5, the angular resolution is very high at 0.001 arc seconds. Since the systems are to be used even in narrow spaces, focus was on easy handling of the compact system components. Thus, appropriate alignment aids are also included here.
Calibration interferometer with interferometric straightness measurement
With the new SP 5000 C5 calibration interferometers, all measured variables are recorded by interferometric method. The set-up and functioning are analogous to the large SP 15000 C5. The significantly more compact sensor head detects the position, the pitch and yaw angles as well as the horizontal and vertical straightness.
With dimensions of 50 mm x 50 mm x 50 mm and a weight of 240 g, the measuring reflector used is small and light.
The straightness components are measured in two passes without realignment of the system. The measurement resolution of the interferometric length measurement is 5 pm over a measuring range of up to 6 m. The system is characterised by very high angular and straightness measuring ranges and accuracies.
Calibration interferometer with 2D straightness measurement
The SP 5000 C5 2D calibration interferometers (Figure 2) are designed to further simplify handling and reduce measuring times. The straightness mirror is eliminated, so that the calibration is made easier and functionality is significantly improved. The compact, fully passive measuring reflector allows simultaneous measurement of position, pitch and yaw angle as well as straightness components in a single pass. Due to the absolute, micrometre-accurate straightness measurement, the SP 5000 C5 2D is also ideal for the alignment of machine components.
High-performance software solutions for standardised machine acceptance, volumetric correction of machine tools for all common machine control systems, dynamic component analysis and measuring system-supported alignment of machine components exist for all measuring systems.
Use of C5 and C5 2D series multicomponent interferometers significantly reduces the time required for acceptance inspections, calibrations, system analyses and correction range adjustments. This allows cost reduction, while increasing accuracy.