Movement precision is a crucial parameter for a micromanipulation of microrobot. An omni-directional mobile microrobot for microassembly in a microfactory is presented. The microrobot size is less than one cubic centimeter and is driven by four electromagnetic micromotors with 3 mm diameter. As two important aspects for the microrobot precision

the structure design and control are analyzed. The structure analysis includes the transmission system and the wheels fabrication. The virtues and drawbacks of the microrobot structure for the movement precision are also analyzed. For eliminating the influences of the drawbacks of the microrobot structure

some novel control methods and ideas which include the path planning and micromotors control are introduced. In the path planning control

the whole workspace is divided into four areas in which the moving distances of the microrobot are different. This path planning method is designed to solve the non-linear problem of the microrobot during translational movement. According the structure constrains of the electromagnetic micromotor

the vector synthesis control of the torque is devised and the torque self-balance characteristic is utilized to improve the microrobot precision. Presently

the microrobot can be achieve 0.07mm/step during translation

and 0.83°/setp during steering

which is three times compared with common control method. The microrobot can do simple microassembly micromanipulation supervised by a computer vision system. The microassembly experiment result demonstrates the validity of these microrobot control methods and concepts based on the actual characteristics of the microrobot structure.