INTRODUCTION
Piston is widely used in both fluid and air pressure drive system. The size and structure of its diameter have great influence on the piston’s effective work area, the slide fit between the cylinder and the piston, the minimum star-up pressure and the mechanical efficiency. Therefore, it is a key and important technology to measure the external diameter of the piston exactly.
There are many ways to measure the external diameter. Inductive transducer is not suitable for online detection because of its low automation level. Laser scanning method cannot reach the demand for its accuracy is affected by vibration, scanning speed and many other factors. In this paper we will introduce the parallel light projection method, which is to project the workpiece on the photosensitive units using parallel light through illumination path. In order to make it convenient for photoelectricconversionand circuit processing, charge-coupled device (CCD)is chosen forsignal acquisition. CCD is favorable for high-speed online automatic measurement, position and industrial control, for the benefits of its low power consumption, fine frequency response, wide dynamic range, high resolution, and fine reproducibility.
The specific design on the optical paths, the signal processing circuits, the mechanical structure and the software for the measuring system will be introduced in detail.
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