Development Of Automatic Assembly Equipment For Magnet Of Component Miniature Accelerometer

As a typical micro electromechanical product, accelerometer is a core component of the inertial navigation system, so its performance directly affects the accuracy of navigation. The assembly quality of the magnet component in accelerometer will affect non-linear errors of accelerometer. It will influence the performance of accelerometer. Now, assembly task of accelerometer magnet component is mainly accomplished through manual operation, which results in low assembly efficiency, poor accuracy, and high skill requirements for the assembly staff and poor product consistency. It is urgent to solve this problem by the way of developing automated assembly equipment and applying high precision automatic assembly technology.In this paper, automatic assembly equipment based on vision measurement technology is developed, which aimed at magnet component assembly task of a certain type of micro acceleration. By using the modular design idea, the equipment is divided into four modules:the vision measurement module, the assembly operation module, the work platform module and the assembly control module. The vision measurement module can get the information of parts position and posture; the assembly operation module can pick, move and assembly the parts: the work platform module offers space for assembly task and the fixture in module can clamp the part; the assembly control module makes other modules work orderly and provide user interface. Part operation device and fixture are designed according to the characteristic of shell and magnet part, which makes the assembly process stability, high assembly precision and assembly force detected and controlled real time.As a kind of non-contact measurement method, vision measurement has advantages of fast speed and no damage to the parts. In order to improve the vision measurement precision and efficiency, an autofocus method based on image gray value is developed which selects the coarse-fine combination strategy. Variance function and gradient variance function are used as image definition evaluation function in the two steps respectively. Optimum solution will be found with the hill-climbing method and two times interpolation method by searching the curves of evaluation function. Reasonable lighting environment will be set according to. the feature of shell and magnet part, which ensures the image acquisition quality of upper surface of two parts. Accuracy of image recognition is improved by manipulating images with the methods of median filter and linear gray enhancement. The acquisition range of high magnification camera is enlarged by using the image mosaic technology. Finally, extract edge points from image and fitted circle by the way of least squares to complete the measurement task and get the position information of the parts.The paper analysis the main factors which affect the assembly error and establishes error compensation model based on the homogeneous coordinate transformation. Then, calibrate angles among image coordinate system, vision measurement coordinate system and assembly work coordinate system. And orthogonal errors between the stages of 3D motion platform are compensated at the same time. Through assembly experiments, the assembly precision can reach 10?m, which can meet the design requirements, stability and consistency of the assembly process all meet the expectations well.