Design and Control of a Compact 6-Degree-of-Freedom Precision Positioner with Linux- Based Real-Time Control

摘要

This dissertation presents the design, control, and implementation of a compact highprecisionmultidimensional positioner. This precision-positioning system consists of anovel concentrated-field magnet matrix and a triangular single-moving part that carriesthree 3-phase permanent-magnet planar-levitation-motor armatures. Since only a singlelevitated moving part, namely the platen, generates all required fine and coarse motions,this positioning system is reliable and potentially cost-effective. The three planarlevitation motors based on the Lorentz-force law not only produce the vertical force tolevitate the triangular platen but also control the platen's position and orientation in thehorizontal plane. Three laser distance sensors are used to measure vertical, x-, and yrotationmotions. Three 2-axis Hall-effect sensors are used to determine lateral motionsand rotation motion about the z-axis by measuring the magnetic flux density generated bythe magnet matrix.This positioning system has a total mass of 1.52 kg, which is the minimized mass toproduce better dynamic performance. In order to reduce the mass of the moving platen, it is made of Delrin with a mass density of 1.54 g/cm3 by Computer Numerical Controlled(CNC) machining. The platen can be regarded a pure mass, and the spring and dampingeffects are neglected except for the vertical dynamic. Single-input single-output (SISO)digital lead-lag controllers and a multivariable Linear Quadratic Gaussian (LQG)controller were designed and implemented. Real-time control was performed with theLinux-Ubuntu operating system OS. Real Time Application Interface (RTAI) for Linuxworks with Comedi and Comedi libraries and enables closed-loop real-time control.One of the key advantages of this positioning stage with Hall-effect sensors is theextended travel range and rotation angle in the horizontal mode. The maximum travelranges of 220 mm in x and 200 mm in y were achieved experimentally. Since the magnetmatrix generates periodical sinusoidal flux densities in the x-y plane, the travel range canbe extended by increasing the number of magnet pitches. The rotation angle of 12 degrees wasachieved in rotation around z. The angular velocities of 0.2094 rad/s and 4.74 rad/s wereproduced by a 200-mm-diameter circular motion and a 30-mm-diameter spiral motion,respectively. The maximum velocity of 16.25 mm/s was acquired from over one pitchmotion. The maximum velocity of 17.5 mm/s in a 8-mm scanning motion was achievedwith the acceleration of 72.4 m/s2. Step responses demonstrated a 10-um resolution and6-um rms position noise in the translational mode. For the vertical mode, step responsesof 5 um in z, 0.001 degrees in roation around x, and 0.001 degrees in rotation around y were achieved.This compact single-moving-part positioner has potential applications for precisionpositioningsystems in semiconductor- manufacturing.