CHOTEST SJ6000

As the manufacturing industry continues to evolve, it is essential that both the measurements themselves and the interpretation of their results follow generally recognized standards.

With this requirement in mind, Chotest has designed its laser interferometer so that data acquisition and analysis can be performed in accordance with both national and international standards.

Keep in mind that individual measurements, such as a diagonal measurement, can provide important information about changes in the accuracy of your equipment, but only measuring each parameter and thoroughly checking each axis will let you fully understand the nature of the changes and their cause.

The new system is built around a compact laser head (SJ6000) and a standalone compensation unit.

SJ6000 laser head

The small size of the SJ6000 laser and the compensation unit means the entire system (excluding the tripod) can now be packed into a portable wheeled case. The complete linear measurement system in its case weighs about 15 kg.

Compensation unit and sensors

The compensation unit is the key component that ensures the measurement accuracy of the SJ6000 system. It incorporates smart sensors that process absolute readings, allowing very precise measurement of air temperature, pressure and relative humidity.

The compensation unit then recalculates the wavelength to obtain its actual value for use in calculations, which eliminates virtually all measurement errors caused by fluctuations in these parameters. This procedure can run automatically every 7 seconds, as shown by the status LEDs on the unit.

Each sensor effectively switches off between readings to minimize heat dissipation.

Like the SJ6000 laser, the compensation unit connects directly to the computer via USB, which also powers the unit (no additional power supply is required).

The unit weighs only 550 g, and together with the SJ6000 the weight is just over 3 kg (including connecting cables, the SJ6000 power supply and the sensors).

The air and material temperature sensors are smart devices. Built-in microprocessors analyze and process the sensor output signal and then send the digitized temperature values to the compensation unit. This improves measurement reliability and is also essential for keeping the unit compact.

Up to three material temperature sensors can be connected to the compensation unit, allowing linear measurement results to be normalized to the standard material temperature of 20 °C.

The sensor cables are detachable, making them easy to replace if damaged. For long machines, the cables can be extended by joining them together.

SJ6000 series laser measurement systems are designed to measure linear and angular displacements and, on that basis, to determine the geometric and dynamic parameters of machine and machine tool components.

The systems operate on the interferometric displacement measurement principle, using a frequency-stabilized helium-neon laser with circularly polarized output. The laser beam is split into two orthogonal linearly polarized components which, after passing through the interference-forming optics, reach polarization analyzers and photodetectors. The photodetector signals are used to determine the magnitude and direction of the measured displacement. The measurement data is processed by a personal computer running dedicated software.

• The most accurate system in its class of measuring instruments: system accuracy is ±0.5 ppm across the entire operating temperature range of 0 – 40 °C.
• Interferometric systems ensure measurement consistency: all measurements made with the Chotest laser measurement system, including angular and straightness measurements, are interferometric in nature, so their results are based on a known laser wavelength that is verified against the international length standard.
• Fast and safe optical alignment with the tripod-mounted laser: the operator performs all interferometer alignment steps from outside the machine's working area. Measurements do not restrict movement along the machine axes, and loads caused by cable movement do not affect the results.
• The interferometer optics are designed specifically for shop-floor use: all optical elements are housed in hard anodized aluminum casings, which makes them durable and lightweight and lets them reach thermal equilibrium with the environment 10 times faster than optics in steel housings.
• Measurements over a long travel range: linear measurements can be made along axes up to 40 m long, and measurements along the parallel axes of dual-drive machines can be made simultaneously.
• Rotary axis calibration: using the SJ6000 laser interferometer in combination with a rotary device makes it possible to automatically calibrate the rotary axes of machine tools and coordinate measuring machines.
• Innovative software for automatic machine error compensation: software packages are available for automatic compensation of linear positioning errors along an axis, compatible with most CNC controllers.
• Dynamic analysis: analysis of vibration and of the velocity and acceleration of a moving element over time gives a complete picture of the equipment's real dynamic performance.

• The SJ6000 laser produces an exceptionally stable beam whose wavelength is verified to provide traceability to national (British) and international standards
• Laser frequency stability is ±0.05 ppm. This outstanding performance is achieved by thermally controlling the length of the laser tube to within a few nanometers
• Guaranteed linear measurement accuracy is ±0.5 ppm across the entire range of environmental conditions: 0 - 40 °C and 650 – 1150 mbar. Data is captured at 50 kHz with a maximum linear measurement speed of 4 m/s and a linear resolution of 1 nm
• Because the system uses an interferometric scheme as the basis for all measurement functions (not just linear ones), you can be completely confident in the accuracy of every measurement taken
• The built-in USB port eliminates the need for a separate laser-to-PC interface
• LED indicators showing laser status and signal strength provide backup signaling in addition to the on-screen indicators generated by the dedicated software
• Combined with a switchable extended range (20-40 m) and a warm-up time of under 6 minutes, these features make the SJ6000 fast and convenient to use
• The external power supply operates with an input voltage of 100 to 240 V.

Rotary axis positioning verification device

(requires the angular measurement optics kit)

Off-center axis measurement kit (magnetic mounts, 90° bracket, software module for measuring a machine's off-center axis)

(requires the angular measurement optics kit and the rotary axis positioning verification device)

Additional accessories for straightness / 90° squareness measurement: reflective prism, fixed turning mirror (90°), holder, M8 threaded connector (requires the straightness / squareness measurement optics kit)

Squareness measurement optics kit

(requires the straightness measurement optics kit)