Precision Measurement

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1. Multi-degree-of-freedom motion error measurement
High precision multi-degree-of-freedom (DOF) motion measurement technology is important for industrial equipment such as manufacturing and inspection because physical quantities such as linear and angular displacements are key parameters for keeping and improving quality control of products. The key parameters of motion errors along the direction of travel of a linear translation stage are three angular errors, pitch, roll and yaw, and translational errors, ΔX, ΔY and ΔZ. These three angular errors of a linear stage result in Abbe errors, and can often be measured by using angle sensors. To measure these errors, a laser interferometer, an autocollimator or an optical encoder have often been used in the industry. The laser interferometer calibration system is the most famous instrument for the displacement measurement. Also, the laser autocollimation system can measure pitch and yaw errors, but cannot detect roll error, which is defined as the angular rotation about the direction of motion. However, they are so expensive that the optical encoder is preferable for industrial applications. An optical encoder is an opto-mechanicalelectronical device that transforms a light intensity distribution into two sinusoidal electrical signals with a phase shift of 90◦. They are often installed in machine tools, coordinate measuring machines, pick and place machines, semiconductor manufacturing equipment and so on.
The proposed optical sensor is capable of measuring six-DOF motion error along the traverse direction in a simple way. Its configuration is shown in Fig. 1, and consists of a scale grating (groove density 1200 lines/mm), a corner cube, four separate PSDs, four PDs, and auxiliary optics components. A stabilized He-Ne laser (λ= 632.8nm) is adopted for an optical source, and a polarizer is placed after the laser for linear polarization (45°). Through BS1, the reflected beam is projected onto the scale grating and diffracted into PSD1, PSD2, and PSD3, and the transmitted beam is incident upon PSD4 from the corner cube. The 0-th diffracted beam returns to BS1 and is incident upon PSD1, and the ±1st diffracted beams are divided into two beams by BS2 and BS3 and projected onto PSD2 and PSD3, respectively. The reflected beams from BS2 and BS3 are incident onto PBS1, which consists of the grating interferometry loop.
6 DOF Motion Error Measurement using a single unit of optical encoder <6 DOF Motion Error Measurement using a single unit of optical encoder>
2. Thermal mode based thermal error modeling
Thermal displacement has been big issue in the machine tool system. During the last decades, through thermal error compensation technology, thermal distortion errors reduction has been successfully achieved. The most significant step of the thermal error compensation is to create a thermal error model that should be precise and robust. To accomplish thermal error modeling correctly, temperature sensor placement should be determined with great care. The advantage of the thermal error model is to provide instant compensation to the control variables.
Our research group focuses on the thermal mode-based thermal error prediction such as temperature sensor placement using thermal modal analysis, thermal error modeling in transient state and evaluation and comparison.
It can be seen that the temperature sensor placements of suggested method are still effective regardless of multi-heat sources. Also, the thermal error models by using suggested method predict well at any time. Using the suggest method, the time and cost for making thermal error model are significantly reduced.
Thermal error modeling process <Thermal error modeling process> Thermal error modeling process <Temperature sensor position on the slide guide: (a) Using thermal
modal analysis, (b) Conventional method>
Dominant thermal mode shape of the slide guide: (a) mode 1, (b) mode 2 <Dominant thermal mode shape of the slide guide: (a) mode 1, (b) mode 2 > Thermal error prediction: (a) Using thermal modal analysis model, (b) Conventional experience-based method model <Thermal error prediction: (a) Using thermal modal analysis model, (b) Conventional experience-based method model>
3. Development of heat flux sensor
Thermal displacement has been big issue in the machine tool system. During the last decades, through thermal error compensation technology, thermal distortion errors reduction has been successfully achieved. The most significant step of the thermal error compensation is to create a thermal error model that should be precise and robust. To accomplish thermal error modeling correctly, temperature sensor placement should be determined with great care. The advantage of the thermal error model is to provide instant compensation to the control variables.
Our research group focuses on the thermal mode-based thermal error prediction such as temperature sensor placement using thermal modal analysis, thermal error modeling in transient state and evaluation and comparison.
It can be seen that the temperature sensor placements of suggested method are still effective regardless of multi-heat sources. Also, the thermal error models by using suggested method predict well at any time. Using the suggest method, the time and cost for making thermal error model are significantly reduced.

Schematic design of heat flux sensor <Schematic design of heat flux sensor>

Contact noise of thermocouple junctions <Contact noise of thermocouple junctions>

Microscopic image of heat flux sensor <Microscopic image of heat flux sensor>

Heat signal resolution test <Heat signal resolution test >