Scan device with elastic reserve type and its scan method

A scan device with elastic reserve comprising:

• at least a guide means installed on a scan body of the said scan device;
• a chassis perpendicular to the guide means for mounting a gear structure, which includes at least one gear, and the gear structure mounted on the chassis to work with the guide means for transmission;
• an elastic module positioned on the chassis to work with the gear structure and guide means, wherein the chassis moves to reserving a suitable amount of elastic potential energy of the elastic module when turning the gear structure;
• a fastening structure which includes a flexible fastener and a fixed fastener, the flexible fastener provided on the scan body and the fixed fastener provided on the chassis, wherein the flexible fastener is designed to move when the fixed fastener meets or touches the flexible fastener, and the flexible fastener returns to an original position to buckle with the fixed fastener;
• a sensor device which includes a first sensor, a second sensor and an object, wherein the object is provided on the chassis so that when the elastic module reserves a suitable amount of elastic potential energy, the buckling of the fixed fastener and elastic fastener is released, and the chassis moves toward a reverse direction of reserving energy, so that the object meets the first sensor on the scan body after the chassis moves a predetermined distance, then the object meets the second sensor on the scan body after the chassis moves a distance further than the predetermined distance.