Research on non-contact length measurement of elongated pins at processing worksites

Abstract

Currently, measurement of long and thin objects is done by the contact method. However, some problems such as long measurement time including fixing the gauge and the object to be measured and the effects of buckling and other problems caused by contact loading. Therefore, there is a need for length measurement of long and slender objects in a short time with high accuracy. In this study, we deem that the non-contact spatial frequency filtering method, which has been studied and developed in our laboratory, can satisfy the requirements given in this study. This method adopts the optical configuration of the traditional projection optical system, but removes the transmitted ray and only allows the high-order diffracted rays generated by the edge of the object to be measured to enter the camera under the condition of parallel ray irradiation. At this time, the diffracted ray generated by the edge of the object to be measured will appear as a bright-dark-bright line segment on the camera. And the position with the lowest brightness value in the dark part will be the specific position of the edge of the object to be measured that is illuminated by parallel light. The standard deviation of the results in 30 repeated placement experiments was around 1 micrometer.

Keywords

• nano/micro measurement and intelligent instruments
• spatial frequency filtering
• profile projection
• parts projection edge detection
• on-machine measurement