Kinematic Modeling of a 6-Degree of Freedom Tri Stage Micro-Positioner

Abstract

The 6-Degree of Freedom Tri-Stage Micro Positioner (6DFTSMP) can generate high accuracy, small displacement, and high-resolution motions. The moving platform of the device has six degrees (6-D) of freedom motions (translation and rotation about three orthogonal axes, X-Y-Z). The 6DFTSMP is unique because it derives its input motion from a monolithic tri-stage base plate and has struts that may have specially designed flexures. The 6DFTSMP capitalizes on the availability of inexpensive high quality planar micro-positioning stages for the control of its moving platform. Because the struts, which connect the planar micro positioning stages with the moving platform are oriented in a parallel mechanism fashion the in plane motion of the stages is converted into a translation and rotation about three orthogonal axes. Two experimental prototypes of the 6DFTSMP have been built and various mathematical models have been developed. A micro-position and orientation measurement sensor nest has been developed, which will be used to test various calibration and performance testing methods for this type of micro-positioners. Introduction Opto-Electronic Manufacturing and Assembly is quickly becoming part of the critical path in advancing the manufacturing practices of many photonic manufacturers. Without reliable and inexpensive solutions to their manufacturing needs, many of their advanced photonic designs and products will be impractical for production and consumer applications. Usually manufacturing has been overlooked and is an after thought in the development of advances in industry. A critical component of Opto-Electronic Manufacturing and Assembly is the micro-positioner. A reliable, easy to calibrate, five to six degrees of freedom micro-positioner can significantly enhance the alignment and assembly of Opto-Electronic devices. The focus of the work we report in this paper is the development of sensors, calibration and performance testing techniques for parallel mechanism micro-positioners, like the 6DFTSMP. Figure 1 shows a schematic drawing of the 6DFTSMP with struts, which have flexures at both attachment points. The device consists of a base plate, six struts and a moving platform. The base plate is equipped with three X-Y micro positioning stages. Each of these stages is capable of generating motion in two orthogonal directions. The range of these motions depends on the design and size of these stages. The moving plate of each X-Y stage supports two struts, which are firmly attached to the plate on one end and the moving platform on the other and allow motion to take place through elastic deformation of the struts and their flexures thus eliminating backlash and stiction. The moving platform is the load carrying part of the device. Figure 2. Steel wire 6DFTSMP prototype Figure 3. Steel rod 6DFTSMP prototype The coordinates of the base plate support points of the struts form the base of the 6DFTSMP. The size and shape of the 6DFTSMP base changes, the struts deform, and the position and orientation of the moving platform changes when the moving plate of each X-Y stage moves. With proper calibration and sensors it is possible to control the position and orientation of the moving platform by commanding appropriate displacements of each X-Y stage moving plate. The three X-Y micro positioning stages are machined on the monolithic base [1]. This simplifies the design and makes the 6DFTSMP more compact. Also the use of a monolithic actuating base and a deformable three dimensional parallel mechanism structure eliminates backlash and stiction during motion. Because the actuation of motion takes place at the base there is no inherent limit to the size of the micro positioning stages, thus permitting a wider range of motion of the moving platform. Experimental Prototypes Two functioning experimental prototypes have been constructed. Figure 2 shows a prototype that uses six Steel wire struts. The base plate X-Y micro positioning stages are s