Precise Angle Measurement For Piezo Driven Tilting Stage

With the developing biotechnology and medical technology, microscopy with higher resolution is required. A minute manipulation tool is desired for biological samples in case objective structures are in a deep part of the object. The development of a manipulation tool for the scanning electron microscopy(SEM:Scanning Electron microscope) is necessary.This paper presents a miniature hemispherical stage which has been proposed for microscopic observation and manipulation. The miniature hemispherical stage can be rotated in omni-direction under the scanning electron microscope. It is composed of a hemisphere and three drive units. Here the drive unite is composed of a hold ball and two piezoelectric actuators AE0203D04. The hold ball is moved by two piezoelectric actuators, which are orthogonally arranged, in a plane. The movable plane of each hold ball is same as the tangent plane between stick-slip motion of each hold ball. The rotational direction of the stage can be controlled by the movable directions of hold balls. The rotational directions of the stage are evaluated using a laser autocollimator.In this paper, we explore to measure the angle of a minute manipulation stage desired for biological samples in case objective structures are in a deep part of the microscope by using photodiode S5981. When manipulating the sample on the stage, it needs to check every side of the target as the stage rotating. Thus to measure and illustrate the angle of the stage can get the position of the side of the target. The stage is driven by the generate waveform from Lab VIEW. The system also employs a AlGa InP red LED as the light source at the bottom of the stage. Then by putting the four current outputs of the quadrant photodiode into operational amplifiers, we can get the displacements in the X direction and Y direction on the photodiode. Thus we can use the trigonometric functions to calculate the angle. In this research, it is also confirmed that applying an autocollimator as a feedback into the computer. So the angles, θ will be evaluated by the software Lab VIEW to turn back from measured value of the angle sensor, also it will improve the standard deviation and linearity. Finally we can check the actions of hold balls by using SolidWorks. The hemispherical stage can be rotated in any direction with the resolution of 0.0012 degree. Then the standard deviation of rotational-direction errors is checked within 0.723 degree. In addition, the linearity of rotational direction is demonstrated within 0.011 degree.